Bump to v1.3.8

Previous fixes for "transaction rollback: serialization failure" when updating trim heights
in commits 16397852 and 58ed7205 had the right idea but were broken due to being synchronized
on different objects.

this.repository.trimHeightsLock would be a new Object() for each repository connection/session
and so not actually synchronize concurrent updates.

Implicit saveChanges()/COMMIT is still needed.

Fix is to use a repository-wide object for synchronization - in this case the repositoryFactory
object as held by RepositoryManager.

Added test to cover.

Also reduced DB trim height read to one call at start of thread for both trimming threads.

WindowsInstaller/Install Files/AppData/settings.json

@@ -0,0 +1,3 @@
+{
+  "apiDocumentationEnabled": true
+}

WindowsInstaller/Install Files/log4j2.properties

@@ -0,0 +1,70 @@
+rootLogger.level = info
+# On Windows, uncomment next line to set dirname:
+# property.dirname = ${sys:user.home}\\AppData\\Local\\qortal\\
+property.filename = ${sys:log4j2.filenameTemplate:-log.txt}
+
+rootLogger.appenderRef.console.ref = stdout
+rootLogger.appenderRef.rolling.ref = FILE
+
+# Suppress extraneous bitcoinj library output
+logger.bitcoinj.name = org.bitcoinj
+logger.bitcoinj.level = error
+
+# Override HSQLDB logging level to "warn" as too much is logged at "info"
+logger.hsqldb.name = hsqldb.db
+logger.hsqldb.level = warn
+
+# Support optional, per-session HSQLDB debugging
+logger.hsqldbRepository.name = org.qortal.repository.hsqldb
+logger.hsqldbRepository.level = debug
+
+# Suppress extraneous Jersey warning
+logger.jerseyInject.name = org.glassfish.jersey.internal.inject.Providers
+logger.jerseyInject.level = off
+
+# Suppress extraneous Jersey EOF 'errors' (actually remote peers disconnecting early)
+logger.jerseyEOF.name = org.glassfish.jersey.server.internal
+logger.jerseyEOF.level = off
+
+# Suppress extraneous Jetty entries
+# 2019-02-14 11:46:27 INFO  ContextHandler:851 - Started o.e.j.s.ServletContextHandler@6949e948{/,null,AVAILABLE}
+# 2019-02-14 11:46:27 INFO  AbstractConnector:289 - Started ServerConnector@50ad322b{HTTP/1.1,[http/1.1]}{0.0.0.0:9085}
+# 2019-02-14 11:46:27 INFO  Server:374 - jetty-9.4.11.v20180605; built: 2018-06-05T18:24:03.829Z; git: d5fc0523cfa96bfebfbda19606cad384d772f04c; jvm 1.8.0_181-b13
+# 2019-02-14 11:46:27 INFO  Server:411 - Started @2539ms
+logger.jetty.name = org.eclipse.jetty
+logger.jetty.level = warn
+# Even more extraneous Jetty output
+# 2019-01-26 02:18:10 WARN  ResourceService:718 - java.util.concurrent.TimeoutException: Idle timeout expired: 30000/30000 ms
+logger.jettyRS.name = org.eclipse.jetty.server.ResourceService
+logger.jettyRS.level = error
+
+# Suppress extraneous slf4j entries
+# 2019-02-14 11:46:27 INFO  log:193 - Logging initialized @1636ms to org.eclipse.jetty.util.log.Slf4jLog
+logger.slf4j.name = org.slf4j
+logger.slf4j.level = warn
+
+# Suppress extraneous Reflections entry
+# 2019-02-27 10:45:25 WARN  Reflections:179 - given scan urls are empty. set urls in the configuration
+logger.orgReflections.name = org.reflections.Reflections
+logger.orgReflections.level = off
+logger.sunReflections.name = sun.reflect.Reflection
+logger.sunReflections.level = off
+
+appender.console.type = Console
+appender.console.name = stdout
+appender.console.layout.type = PatternLayout
+appender.console.layout.pattern = %d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n
+appender.console.filter.threshold.type = ThresholdFilter
+appender.console.filter.threshold.level = error
+
+appender.rolling.type = RollingFile
+appender.rolling.name = FILE
+appender.rolling.layout.type = PatternLayout
+appender.rolling.layout.pattern = %d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n
+appender.rolling.filePattern = ${dirname:-}${filename}.%i
+appender.rolling.policy.type = SizeBasedTriggeringPolicy
+appender.rolling.policy.size = 4MB
+# Set the immediate flush to true (default)
+# appender.rolling.immediateFlush = true
+# Set the append to true (default), should not overwrite
+# appender.rolling.append=true

WindowsInstaller/Install Files/ntpcfg.bat

@@ -0,0 +1,33 @@
+@echo off
+
+:: BatchGotAdmin
+:-------------------------------------
+REM  --> Check for permissions
+>nul 2>&1 "%SYSTEMROOT%\system32\cacls.exe" "%SYSTEMROOT%\system32\config\system"
+
+REM --> If error flag set, we do not have admin.
+if '%errorlevel%' NEQ '0' (
+    echo Requesting administrative privileges...
+    goto UACPrompt
+) else ( goto gotAdmin )
+
+:UACPrompt
+    echo Set UAC = CreateObject^("Shell.Application"^) > "%temp%\getadmin.vbs"
+    echo UAC.ShellExecute "%~s0", "", "", "runas", 1 >> "%temp%\getadmin.vbs"
+
+    "%temp%\getadmin.vbs"
+    exit /B
+
+:gotAdmin
+    if exist "%temp%\getadmin.vbs" ( del "%temp%\getadmin.vbs" )
+    pushd "%CD%"
+    CD /D "%~dp0"
+:--------------------------------------
+
+net stop "Windows Time"
+
+w32tm /config "/manualpeerlist:pool.ntp.org 0.pool.ntp.org 1.pool.ntp.org 2.pool.ntp.org 3.pool.ntp.org cn.pool.ntp.org 0.cn.pool.ntp.org 1.cn.pool.ntp.org 2.cn.pool.ntp.org 3.cn.pool.ntp.org"
+
+net start "Windows Time"
+
+sc config w32time start= auto

WindowsInstaller/README.md

@@ -0,0 +1,26 @@
+# Windows installer
+
+## Prerequisites
+
+* AdvancedInstaller v16 or better, and enterprise licence if translations are required
+* Installed AdoptOpenJDK v11 64bit, full JDK *not* JRE
+
+## General build instructions
+
+If this is your first time opening the `qortal.aip` file then you might need to adjust
+configured paths, or create a dummy `D:` drive with the expected layout.
+
+Typical build procedure:
+
+* Overwrite the `qortal.jar` file in `Install-Files\`
+* Open AdvancedInstaller with qortal.aip file
+* If releasing a new version, change version number in:
+	+ "Product Information" side menu
+	+ "Product Details" side menu entry
+	+ "Product Details" tab in "Product Details" pane
+	+ "Product Version" entry box
+* Click away to a different side menu entry, e.g. "Resources" -> "Files and Folders"
+* You should be prompted whether to generate a new product key, click "Generate New"
+* Click "Build" button
+* New EXE should be generated in `Qortal-SetupFiles\` folder with correct version number
+

WindowsInstaller/dictionary.ail

@@ -0,0 +1,117 @@
+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<DICTIONARY type="multilanguage">
+  <!-- Control table -->
+  <ENTRY id="Control.Text.CustomizeDataPathDlg#Description">
+    <STRING lang="en" value="Do you want to store the blockchain, and other data, in a specific folder?"/>
+	<STRING lang="ru" value="Вы можете выбрать место хранения блокчейна и других данных."/>
+    <STRING lang="zh" value="你想把区块链数据存放在一个特定的文件夹吗？"/>
+    <STRING lang="zh_TW" value="你想把区块链数据存放在一个特定的文件夹吗？"/>
+  </ENTRY>
+  <ENTRY id="Control.Text.CustomizeDataPathDlg#Text">
+    <STRING lang="en" value="Select one of the options below, then click &quot;Next&quot;."/>
+	<STRING lang="ru" value="Выберите один из вариантов ниже, затем нажмите Далее"/>
+    <STRING lang="zh" value="请选择，然后“下一步”"/>
+    <STRING lang="zh_TW" value="请选择，然后“下一步”"/>
+  </ENTRY>
+  <ENTRY id="Control.Text.CustomizeDataPathDlg#Title">
+    <STRING lang="en" value="Choose Custom Data Storage Folder?"/>
+	<STRING lang="ru" value="Выберите место хранения данных."/>
+    <STRING lang="zh" value="选择数据保存的文件夹?"/>
+    <STRING lang="zh_TW" value="选择数据保存的文件夹?"/>
+  </ENTRY>
+  <ENTRY id="Control.Text.CustomizeDbDlg#Description">
+    <STRING lang="en" value="Do you want to store the blockchain, and other data, in a specific folder?"/>
+	<STRING lang="ru" value="Вы можете выбрать место хранения блокчейна и других данных."/>
+    <STRING lang="zh" value="Do you want to store the blockchain, and other data, in a specific folder?"/>
+    <STRING lang="zh_TW" value="Do you want to store the blockchain, and other data, in a specific folder?"/>
+  </ENTRY>
+  <ENTRY id="Control.Text.CustomizeDbDlg#Title">
+    <STRING lang="en" value="Choose Custom Data Storage Folder?"/>
+	<STRING lang="ru" value="Выберите место хранения данных."/>
+    <STRING lang="zh" value="Choose Custom Data Storage Folder?"/>
+    <STRING lang="zh_TW" value="Choose Custom Data Storage Folder?"/>
+  </ENTRY>
+  <ENTRY id="Control.Text.DataFolderDlg#Description">
+    <STRING lang="en" value="This is the folder where the blockchain, and other data, will be stored."/>
+	<STRING lang="ru" value="Это папка, в которой будет храниться блокчейн и другие данные."/>
+    <STRING lang="zh" value="这里是区块链及其它数据存放的文件夹"/>
+    <STRING lang="zh_TW" value="这里是区块链及其它数据存放的文件夹"/>
+  </ENTRY>
+  <ENTRY id="Control.Text.DataFolderDlg#Text">
+    <STRING lang="en" value="To store data in this folder, click &quot;[Text_Next]&quot;. To store data in a different folder, enter it below or click &quot;Browse&quot;."/>
+	<STRING lang="ru" value="Чтобы сохранить данные в этой папке, нажмите &quot;[Text_Next]&quot;. Чтобы сохранить данные в другой папке, введите ее ниже или нажмите &quot;Обзор&quot;."/>
+    <STRING lang="zh" value="如果存放在这个文件夹，点 “下一步”。如果存放在其它位置，请选择“浏览”。"/>
+    <STRING lang="zh_TW" value="如果存放在这个文件夹，点 “下一步”。如果存放在其它位置，请选择“浏览”。"/>
+  </ENTRY>
+  <ENTRY id="Control.Text.DataFolderDlg#Title">
+    <STRING lang="en" value="Select Data Storage Folder"/>
+	<STRING lang="ru" value="Выберите папку для хранения данных"/>
+    <STRING lang="zh" value="请选择文件存储地方"/>
+    <STRING lang="zh_TW" value="请选择文件存储地方"/>
+  </ENTRY>
+  <ENTRY id="Control.Text.DbFolderDlg#Description">
+    <STRING lang="en" value="This is the folder where the blockchain, and other data, will be stored."/>
+	<STRING lang="ru" value="Это папка, в которой будет храниться блокчейн и другие данные."/>
+    <STRING lang="zh" value="This is the folder where the blockchain, and other data, will be stored."/>
+    <STRING lang="zh_TW" value="This is the folder where the blockchain, and other data, will be stored."/>
+  </ENTRY>
+  <ENTRY id="Control.Text.DbFolderDlg#Title">
+    <STRING lang="en" value="Select Data Storage Folder"/>
+	<STRING lang="ru" value="Выберите папку для хранения данных"/>
+    <STRING lang="zh" value="请选择文件存储地方"/>
+    <STRING lang="zh_TW" value="请选择文件存储地方"/>
+  </ENTRY>
+  <ENTRY id="Control.Text.NTPDialog#Description">
+    <STRING lang="en" value="Reconfigure Windows for more accurate time?"/>
+	<STRING lang="ru" value="Настроить синхронизацию времени системы Windows?"/>
+    <STRING lang="zh" value="重新配置Windows以获得更准确的时间？"/>
+  </ENTRY>
+  <ENTRY id="Control.Text.NTPDialog#Text_1">
+    <STRING lang="en" value="An accurate Windows clock is required to connect to the [ProductName] network and make transactions."/>
+	<STRING lang="ru" value="Для подключения к сети Qortal и совершения транзакций требуется точная настройка времени Windows"/>
+    <STRING lang="zh" value="需要准确的Windows时钟才能连接到[ProductName]网络并进行交易。"/>
+  </ENTRY>
+  <ENTRY id="Control.Text.NTPDialog#Text_2">
+    <STRING lang="en" value="Select one of the options below, then click &quot;Next&quot;."/>
+	<STRING lang="ru" value="Выберите один из вариантов ниже, затем нажмите"/>
+    <STRING lang="zh" value="请选择，然后“下一步”"/>
+  </ENTRY>
+  <ENTRY id="Control.Text.NTPDialog#Text_3">
+    <STRING lang="en" value="Your computer&apos;s clock needs to be accurate to within 0.5 seconds."/>
+	<STRING lang="ru" value="Точность времени вашего компьютера должна составлять 0.5 секунд."/>
+    <STRING lang="zh" value="您的计算机时钟需要准确到0.5秒内。"/>
+  </ENTRY>
+  <ENTRY id="Control.Text.NTPDialog#Title">
+    <STRING lang="en" value="Windows clock accuracy"/>
+	<STRING lang="ru" value="Настройка времени системы Windows"/>
+    <STRING lang="zh" value="Windows 时钟精度"/>
+  </ENTRY>
+  <ENTRY id="Control.Text.VerifyRemoveDlg#RemoveBlockchainCheckbox">
+    <STRING lang="en" value="Remove downloaded blockchain and other data"/>
+	<STRING lang="ru" value="Удалить загруженный блокчейн и другие данные"/>
+    <STRING lang="zh" value="删除您下载的区块链"/>
+  </ENTRY>
+  <!-- RadioButton table -->
+  <ENTRY id="RadioButton.Text.CUSTOM_DB_BOOL#choose">
+    <STRING lang="en" value="Choose custom data storage folder..."/>
+	<STRING lang="ru" value="Выбрать папку для хранения данных..."/>
+    <STRING lang="zh" value="选择特定的文件夹存储"/>
+    <STRING lang="zh_TW" value="选择特定的文件夹存储"/>
+  </ENTRY>
+  <ENTRY id="RadioButton.Text.CUSTOM_DB_BOOL#default">
+    <STRING lang="en" value="Use default location "/>
+	<STRING lang="ru" value="Использовать папку по умолчанию"/>
+    <STRING lang="zh" value="使用默认存储地点"/>
+    <STRING lang="zh_TW" value="使用默认存储地点"/>
+  </ENTRY>
+  <ENTRY id="RadioButton.Text.RECONFIG_NTP#1">
+    <STRING lang="en" value="Yes, configure Windows to use internet time servers (Recommended)"/>
+	<STRING lang="ru" value="Да, настроить синхронизацию времени Windows (Рекомендуется)"/>
+    <STRING lang="zh" value="是，将Windows配置为使用多个Internet时间服务器 (推荐的)"/>
+  </ENTRY>
+  <ENTRY id="RadioButton.Text.RECONFIG_NTP#2">
+    <STRING lang="en" value="No, I will manage clock accuracy myself"/>
+	<STRING lang="ru" value="Нет, я сам буду управлять настройками часов"/>
+    <STRING lang="zh" value="不，我会自己管理时钟精度。"/>
+  </ENTRY>
+</DICTIONARY>

lib/org/ciyam/AT/1.3.7/AT-1.3.7.pom

@@ -4,6 +4,6 @@
   <modelVersion>4.0.0</modelVersion>
   <groupId>org.ciyam</groupId>
   <artifactId>AT</artifactId>
-  <version>1.3.4</version>
+  <version>1.3.7</version>
   <description>POM was created from install:install-file</description>
 </project>

lib/org/ciyam/AT/1.3.8/AT-1.3.8.pom

@@ -0,0 +1,9 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns="http://maven.apache.org/POM/4.0.0"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
+  <modelVersion>4.0.0</modelVersion>
+  <groupId>org.ciyam</groupId>
+  <artifactId>AT</artifactId>
+  <version>1.3.8</version>
+  <description>POM was created from install:install-file</description>
+</project>

lib/org/ciyam/AT/maven-metadata-local.xml

@@ -3,10 +3,14 @@
   <groupId>org.ciyam</groupId>
   <artifactId>AT</artifactId>
   <versioning>
-    <release>1.3.4</release>
+    <release>1.3.8</release>
     <versions>
       <version>1.3.4</version>
+      <version>1.3.5</version>
+      <version>1.3.6</version>
+      <version>1.3.7</version>
+      <version>1.3.8</version>
     </versions>
-    <lastUpdated>20200414162728</lastUpdated>
+    <lastUpdated>20200925114415</lastUpdated>
   </versioning>
 </metadata>

pom.xml

@@ -3,21 +3,21 @@
 	<modelVersion>4.0.0</modelVersion>
 	<groupId>org.qortal</groupId>
 	<artifactId>qortal</artifactId>
-	<version>1.2.0</version>
+	<version>1.3.8</version>
 	<packaging>jar</packaging>
 	<properties>
+		<skipTests>true</skipTests>
 		<bitcoinj.version>0.15.5</bitcoinj.version>
 		<bouncycastle.version>1.64</bouncycastle.version>
 		<build.timestamp>${maven.build.timestamp}</build.timestamp>
-		<ciyam-at.version>1.3.4</ciyam-at.version>
+		<ciyam-at.version>1.3.8</ciyam-at.version>
 		<commons-net.version>3.6</commons-net.version>
 		<commons-text.version>1.8</commons-text.version>
 		<dagger.version>1.2.2</dagger.version>
 		<guava.version>28.1-jre</guava.version>
-		<hsqldb.version>2.5.0-fixed</hsqldb.version>
-		<hsqldb-sqltool.version>2.5.0</hsqldb-sqltool.version>
+		<hsqldb.version>2.5.1</hsqldb.version>
 		<jersey.version>2.29.1</jersey.version>
-		<jetty.version>9.4.22.v20191022</jetty.version>
+		<jetty.version>9.4.29.v20200521</jetty.version>
 		<log4j.version>2.12.1</log4j.version>
 		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
 		<slf4j.version>1.7.12</slf4j.version>
@@ -313,6 +313,14 @@
 					</execution>
 				</executions>
 			</plugin>
+			<plugin>
+				<groupId>org.apache.maven.plugins</groupId>
+				<artifactId>maven-surefire-plugin</artifactId>
+				<version>2.22.2</version>
+				<configuration>
+					<skipTests>${skipTests}</skipTests>
+				</configuration>
+			</plugin>
 		</plugins>
 		<pluginManagement>
 			<plugins>
@@ -397,12 +405,6 @@
 			<artifactId>hsqldb</artifactId>
 			<version>${hsqldb.version}</version>
 		</dependency>
-		<dependency>
-			<groupId>org.hsqldb</groupId>
-			<artifactId>sqltool</artifactId>
-			<version>${hsqldb-sqltool.version}</version>
-			<scope>test</scope>
-		</dependency>
 		<!-- CIYAM AT (automated transactions) -->
 		<dependency>
 			<groupId>org.ciyam</groupId>

run.sh

@@ -1,51 +0,0 @@
-#!/bin/sh
-
-# There's no need to run as root, so don't allow it, for security reasons
-if [ "$USER" = "root" ]; then
-	echo "Please su to non-root user before running"
-	exit
-fi
-
-# Validate Java is installed and the minimum version is available
-MIN_JAVA_VER='11'
-
-if command -v java > /dev/null 2>&1; then
-    version=$(java -version 2>&1 | awk -F '"' '/version/ {print $2}')
-    version=$(echo $version | cut -d'.' -f1,2)
-    if [ `echo "${version}>=${MIN_JAVA_VER}" | bc` -eq 1 ]; then
-        echo 'Passed Java version check'
-    else
-        echo 'Please upgrade your Java to version 11 or greater'
-        exit 1
-    fi
-else
-  echo 'Java is not available, please install Java 11 or greater'
-  exit 1
-fi
-
-# No qortal.jar but we have a Maven built one?
-# Be helpful and copy across to correct location
-if [ ! -e qortal.jar -a -f target/qortal*.jar ]; then
-	echo "Copying Maven-built Qortal JAR to correct pathname"
-	cp target/qortal*.jar qortal.jar
-fi
-
-# Limits Java JVM stack size and maximum heap usage.
-# Comment out for bigger systems, e.g. non-routers
-# or when API documentation is enabled
-# JVM_MEMORY_ARGS="-Xss256k -Xmx128m"
-
-# Although java.net.preferIPv4Stack is supposed to be false
-# by default in Java 11, on some platforms (e.g. FreeBSD 12),
-# it is overriden to be true by default. Hence we explicitly
-# set it to true to obtain desired behaviour.
-nohup nice -n 20 java \
-	-Djava.net.preferIPv4Stack=false \
-	-XX:NativeMemoryTracking=summary \
-	${JVM_MEMORY_ARGS} \
-	-jar qortal.jar \
-	1>run.log 2>&1 &
-
-# Save backgrounded process's PID
-echo $! > run.pid
-echo qortal running as pid $!

run.sh

@@ -0,0 +1 @@
+start.sh

src/main/java/org/qortal/ApplyUpdate.java

@@ -35,6 +35,8 @@ public class ApplyUpdate {
 	private static final String JAR_FILENAME = AutoUpdate.JAR_FILENAME;
 	private static final String NEW_JAR_FILENAME = AutoUpdate.NEW_JAR_FILENAME;
 	private static final String WINDOWS_EXE_LAUNCHER = "qortal.exe";
+	private static final String JAVA_TOOL_OPTIONS_NAME = "JAVA_TOOL_OPTIONS";
+	private static final String JAVA_TOOL_OPTIONS_VALUE = "-XX:MaxRAMFraction=4";
 
 	private static final long CHECK_INTERVAL = 10 * 1000L; // ms
 	private static final int MAX_ATTEMPTS = 12;
@@ -65,17 +67,19 @@ public class ApplyUpdate {
 	}
 
 	private static boolean shutdownNode() {
-		String BASE_URI = "http://localhost:" + Settings.getInstance().getApiPort() + "/";
-		LOGGER.info(String.format("Shutting down node using API via %s", BASE_URI));
+		String baseUri = "http://localhost:" + Settings.getInstance().getApiPort() + "/";
+		LOGGER.info(() -> String.format("Shutting down node using API via %s", baseUri));
 
 		int attempt;
 		for (attempt = 0; attempt < MAX_ATTEMPTS; ++attempt) {
-			LOGGER.info(String.format("Attempt #%d out of %d to shutdown node", attempt + 1, MAX_ATTEMPTS));
-			String response = ApiRequest.perform(BASE_URI + "admin/stop", null);
+			final int attemptForLogging = attempt;
+			LOGGER.info(() -> String.format("Attempt #%d out of %d to shutdown node", attemptForLogging + 1, MAX_ATTEMPTS));
+			String response = ApiRequest.perform(baseUri + "admin/stop", null);
 			if (response == null)
-				break;
+				// No response - consider node shut down
+				return true;
 
-			LOGGER.info(String.format("Response from API: %s", response));
+			LOGGER.info(() -> String.format("Response from API: %s", response));
 
 			try {
 				Thread.sleep(CHECK_INTERVAL);
@@ -99,19 +103,20 @@ public class ApplyUpdate {
 		Path newJar = Paths.get(NEW_JAR_FILENAME);
 
 		if (!Files.exists(newJar)) {
-			LOGGER.warn(String.format("Replacement JAR '%s' not found?", newJar));
+			LOGGER.warn(() -> String.format("Replacement JAR '%s' not found?", newJar));
 			return;
 		}
 
 		int attempt;
 		for (attempt = 0; attempt < MAX_ATTEMPTS; ++attempt) {
-			LOGGER.info(String.format("Attempt #%d out of %d to replace JAR", attempt + 1, MAX_ATTEMPTS));
+			final int attemptForLogging = attempt;
+			LOGGER.info(() -> String.format("Attempt #%d out of %d to replace JAR", attemptForLogging + 1, MAX_ATTEMPTS));
 
 			try {
 				Files.copy(newJar, realJar, StandardCopyOption.REPLACE_EXISTING);
 				break;
 			} catch (IOException e) {
-				LOGGER.info(String.format("Unable to replace JAR: %s", e.getMessage()));
+				LOGGER.info(() -> String.format("Unable to replace JAR: %s", e.getMessage()));
 
 				// Try again
 			}
@@ -119,6 +124,7 @@ public class ApplyUpdate {
 			try {
 				Thread.sleep(CHECK_INTERVAL);
 			} catch (InterruptedException e) {
+				LOGGER.warn("Ignoring interrupt...");
 				// Doggedly retry
 			}
 		}
@@ -129,13 +135,13 @@ public class ApplyUpdate {
 
 	private static void restartNode(String[] args) {
 		String javaHome = System.getProperty("java.home");
-		LOGGER.info(String.format("Java home: %s", javaHome));
+		LOGGER.info(() -> String.format("Java home: %s", javaHome));
 
 		Path javaBinary = Paths.get(javaHome, "bin", "java");
-		LOGGER.info(String.format("Java binary: %s", javaBinary));
+		LOGGER.info(() -> String.format("Java binary: %s", javaBinary));
 
 		Path exeLauncher = Paths.get(WINDOWS_EXE_LAUNCHER);
-		LOGGER.info(String.format("Windows EXE launcher: %s", exeLauncher));
+		LOGGER.info(() -> String.format("Windows EXE launcher: %s", exeLauncher));
 
 		List<String> javaCmd;
 		if (Files.exists(exeLauncher)) {
@@ -156,9 +162,16 @@ public class ApplyUpdate {
 		}
 
 		try {
-			LOGGER.info(String.format("Restarting node with: %s", String.join(" ", javaCmd)));
+			LOGGER.info(() -> String.format("Restarting node with: %s", String.join(" ", javaCmd)));
 
-			new ProcessBuilder(javaCmd).start();
+			ProcessBuilder processBuilder = new ProcessBuilder(javaCmd);
+
+			if (Files.exists(exeLauncher)) {
+				LOGGER.info(() -> String.format("Setting env %s to %s", JAVA_TOOL_OPTIONS_NAME, JAVA_TOOL_OPTIONS_VALUE));
+				processBuilder.environment().put(JAVA_TOOL_OPTIONS_NAME, JAVA_TOOL_OPTIONS_VALUE);
+			}
+
+			processBuilder.start();
 		} catch (IOException e) {
 			LOGGER.error(String.format("Failed to restart node (BAD): %s", e.getMessage()));
 		}

src/main/java/org/qortal/RepositoryMaintenance.java

@@ -0,0 +1,75 @@
+package org.qortal;
+
+import java.security.Security;
+
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
+import org.bouncycastle.jce.provider.BouncyCastleProvider;
+import org.bouncycastle.jsse.provider.BouncyCastleJsseProvider;
+import org.qortal.controller.Controller;
+import org.qortal.repository.DataException;
+import org.qortal.repository.Repository;
+import org.qortal.repository.RepositoryFactory;
+import org.qortal.repository.RepositoryManager;
+import org.qortal.repository.hsqldb.HSQLDBRepositoryFactory;
+import org.qortal.settings.Settings;
+
+public class RepositoryMaintenance {
+
+	static {
+		// This must go before any calls to LogManager/Logger
+		System.setProperty("java.util.logging.manager", "org.apache.logging.log4j.jul.LogManager");
+	}
+
+	private static final Logger LOGGER = LogManager.getLogger(RepositoryMaintenance.class);
+
+	public static void main(String[] args) {
+		LOGGER.info("Repository maintenance starting up...");
+
+		Security.insertProviderAt(new BouncyCastleProvider(), 0);
+		Security.insertProviderAt(new BouncyCastleJsseProvider(), 1);
+
+		// Load/check settings, which potentially sets up blockchain config, etc.
+		try {
+			if (args.length > 0)
+				Settings.fileInstance(args[0]);
+			else
+				Settings.getInstance();
+		} catch (Throwable t) {
+			LOGGER.error("Settings file error: " + t.getMessage());
+			System.exit(2);
+		}
+
+		LOGGER.info("Opening repository");
+		try {
+			RepositoryFactory repositoryFactory = new HSQLDBRepositoryFactory(Controller.getRepositoryUrl());
+			RepositoryManager.setRepositoryFactory(repositoryFactory);
+		} catch (DataException e) {
+			// If exception has no cause then repository is in use by some other process.
+			if (e.getCause() == null) {
+				LOGGER.info("Repository in use by another process?");
+			} else {
+				LOGGER.error("Unable to start repository", e);
+			}
+
+			System.exit(1);
+		}
+
+		LOGGER.info("Starting repository periodic maintenance. This can take a while...");
+		try (final Repository repository = RepositoryManager.getRepository()) {
+			repository.performPeriodicMaintenance();
+
+			LOGGER.info("Repository periodic maintenance completed");
+		} catch (DataException e) {
+			LOGGER.error("Repository periodic maintenance failed", e);
+		}
+
+		try {
+			LOGGER.info("Shutting down repository");
+			RepositoryManager.closeRepositoryFactory();
+		} catch (DataException e) {
+			LOGGER.error("Error occurred while shutting down repository", e);
+		}
+	}
+
+}

src/main/java/org/qortal/api/ApiError.java

@@ -128,8 +128,8 @@ public enum ApiError {
 
 	// Bitcoin
 	BTC_NETWORK_ISSUE(1201, 500),
-	BTC_BALANCE_ISSUE(1202, 422),
-	BTC_TOO_SOON(1203, 422);
+	BTC_BALANCE_ISSUE(1202, 402),
+	BTC_TOO_SOON(1203, 408);
 
 	private static final Map<Integer, ApiError> map = stream(ApiError.values()).collect(toMap(apiError -> apiError.code, apiError -> apiError));
 

src/main/java/org/qortal/api/ApiErrorHandler.java

@@ -3,6 +3,7 @@ package org.qortal.api;
 import java.io.IOException;
 
 import javax.servlet.RequestDispatcher;
+import javax.servlet.ServletException;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
 
@@ -17,7 +18,7 @@ public class ApiErrorHandler extends ErrorHandler {
 	private static final Logger LOGGER = LogManager.getLogger(ApiErrorHandler.class);
 
 	@Override
-	public void handle(String target, Request baseRequest, HttpServletRequest request, HttpServletResponse response) throws IOException {
+	public void handle(String target, Request baseRequest, HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException {
 		if (Settings.getInstance().isApiLoggingEnabled()) {
 			String requestURI = request.getRequestURI();
 

src/main/java/org/qortal/api/ApiService.java

@@ -18,9 +18,9 @@ import org.eclipse.jetty.http.HttpVersion;
 import org.eclipse.jetty.rewrite.handler.RedirectPatternRule;
 import org.eclipse.jetty.rewrite.handler.RewriteHandler;
 import org.eclipse.jetty.server.CustomRequestLog;
+import org.eclipse.jetty.server.DetectorConnectionFactory;
 import org.eclipse.jetty.server.HttpConfiguration;
 import org.eclipse.jetty.server.HttpConnectionFactory;
-import org.eclipse.jetty.server.OptionalSslConnectionFactory;
 import org.eclipse.jetty.server.RequestLog;
 import org.eclipse.jetty.server.RequestLogWriter;
 import org.eclipse.jetty.server.SecureRequestCustomizer;
@@ -43,6 +43,8 @@ import org.qortal.api.websocket.ActiveChatsWebSocket;
 import org.qortal.api.websocket.AdminStatusWebSocket;
 import org.qortal.api.websocket.BlocksWebSocket;
 import org.qortal.api.websocket.ChatMessagesWebSocket;
+import org.qortal.api.websocket.TradeBotWebSocket;
+import org.qortal.api.websocket.TradeOffersWebSocket;
 import org.qortal.settings.Settings;
 
 public class ApiService {
@@ -113,8 +115,7 @@ public class ApiService {
 				SslConnectionFactory sslConnectionFactory = new SslConnectionFactory(sslContextFactory, HttpVersion.HTTP_1_1.asString());
 
 				ServerConnector portUnifiedConnector = new ServerConnector(this.server,
-						new OptionalSslConnectionFactory(sslConnectionFactory, HttpVersion.HTTP_1_1.asString()),
-						sslConnectionFactory,
+						new DetectorConnectionFactory(sslConnectionFactory),
 						httpConnectionFactory);
 				portUnifiedConnector.setHost(Settings.getInstance().getBindAddress());
 				portUnifiedConnector.setPort(Settings.getInstance().getApiPort());
@@ -197,6 +198,8 @@ public class ApiService {
 			context.addServlet(BlocksWebSocket.class, "/websockets/blocks");
 			context.addServlet(ActiveChatsWebSocket.class, "/websockets/chat/active/*");
 			context.addServlet(ChatMessagesWebSocket.class, "/websockets/chat/messages");
+			context.addServlet(TradeOffersWebSocket.class, "/websockets/crosschain/tradeoffers");
+			context.addServlet(TradeBotWebSocket.class, "/websockets/crosschain/tradebot");
 
 			// Start server
 			this.server.start();

src/main/java/org/qortal/api/Security.java

@@ -5,10 +5,20 @@ import java.net.UnknownHostException;
 
 import javax.servlet.http.HttpServletRequest;
 
-public class Security {
+import org.qortal.settings.Settings;
+
+public abstract class Security {
+
+	public static final String API_KEY_HEADER = "X-API-KEY";
 
-	// TODO: replace with proper authentication
 	public static void checkApiCallAllowed(HttpServletRequest request) {
+		String expectedApiKey = Settings.getInstance().getApiKey();
+		String passedApiKey = request.getHeader(API_KEY_HEADER);
+
+		if ((expectedApiKey != null && !expectedApiKey.equals(passedApiKey)) ||
+				(passedApiKey != null && !passedApiKey.equals(expectedApiKey)))
+			throw ApiExceptionFactory.INSTANCE.createException(request, ApiError.UNAUTHORIZED);
+
 		InetAddress remoteAddr;
 		try {
 			remoteAddr = InetAddress.getByName(request.getRemoteAddr());
@@ -19,4 +29,5 @@ public class Security {
 		if (!remoteAddr.isLoopbackAddress())
 			throw ApiExceptionFactory.INSTANCE.createException(request, ApiError.UNAUTHORIZED);
 	}
+
 }

src/main/java/org/qortal/api/model/ActivitySummary.java

@@ -1,5 +1,6 @@
 package org.qortal.api.model;
 
+import java.util.Collections;
 import java.util.EnumMap;
 import java.util.Map;
 
@@ -13,17 +14,61 @@ import org.qortal.transaction.Transaction.TransactionType;
 @XmlAccessorType(XmlAccessType.FIELD)
 public class ActivitySummary {
 
-	public int blockCount;
-	public int transactionCount;
-	public int assetsIssued;
-	public int namesRegistered;
+	private int blockCount;
+	private int assetsIssued;
+	private int namesRegistered;
 
 	// Assuming TransactionType values are contiguous so 'length' equals count
 	@XmlJavaTypeAdapter(TransactionCountMapXmlAdapter.class)
-	public Map<TransactionType, Integer> transactionCountByType = new EnumMap<>(TransactionType.class);
+	private Map<TransactionType, Integer> transactionCountByType = new EnumMap<>(TransactionType.class);
+	private int totalTransactionCount = 0;
 
 	public ActivitySummary() {
 		// Needed for JAXB
 	}
 
+	public int getBlockCount() {
+		return this.blockCount;
+	}
+
+	public void setBlockCount(int blockCount) {
+		this.blockCount = blockCount;
+	}
+
+	public int getTotalTransactionCount() {
+		return this.totalTransactionCount;
+	}
+
+	public int getAssetsIssued() {
+		return this.assetsIssued;
+	}
+
+	public void setAssetsIssued(int assetsIssued) {
+		this.assetsIssued = assetsIssued;
+	}
+
+	public int getNamesRegistered() {
+		return this.namesRegistered;
+	}
+
+	public void setNamesRegistered(int namesRegistered) {
+		this.namesRegistered = namesRegistered;
+	}
+
+	public Map<TransactionType, Integer> getTransactionCountByType() {
+		return Collections.unmodifiableMap(this.transactionCountByType);
+	}
+
+	public void setTransactionCountByType(TransactionType transactionType, int transactionCount) {
+		this.transactionCountByType.put(transactionType, transactionCount);
+
+		this.totalTransactionCount = this.transactionCountByType.values().stream().mapToInt(Integer::intValue).sum();
+	}
+
+	public void setTransactionCountByType(Map<TransactionType, Integer> transactionCountByType) {
+		this.transactionCountByType = new EnumMap<>(transactionCountByType);
+
+		this.totalTransactionCount = this.transactionCountByType.values().stream().mapToInt(Integer::intValue).sum();
+	}
+
 }

src/main/java/org/qortal/api/model/BitcoinSendRequest.java

@@ -0,0 +1,25 @@
+package org.qortal.api.model;
+
+import javax.xml.bind.annotation.XmlAccessType;
+import javax.xml.bind.annotation.XmlAccessorType;
+import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;
+
+import io.swagger.v3.oas.annotations.media.Schema;
+
+@XmlAccessorType(XmlAccessType.FIELD)
+public class BitcoinSendRequest {
+
+	@Schema(description = "Bitcoin BIP32 extended private key", example = "tprv8ZgxMBicQKsPdahhFSrCdvC1bsWyzHHZfTneTVqUXN6s1wEtZLwAkZXzFP6TbTVGajEB55L1HYLg2aQMecZLXLre5YJcawpdFG66STVAWPJ")
+	public String xprv58;
+
+	@Schema(description = "Recipient's Bitcoin address ('legacy' P2PKH only)", example = "1BitcoinEaterAddressDontSendf59kuE")
+	public String receivingAddress;
+
+	@Schema(description = "Amount of BTC to send")
+	@XmlJavaTypeAdapter(value = org.qortal.api.AmountTypeAdapter.class)
+	public long bitcoinAmount;
+
+	public BitcoinSendRequest() {
+	}
+
+}

src/main/java/org/qortal/api/model/CrossChainBitcoinRedeemRequest.java

@@ -25,6 +25,9 @@ public class CrossChainBitcoinRedeemRequest {
 	@Schema(description = "32-byte secret", example = "6gVbAXCVzJXAWwtAVGAfgAkkXpeXvPUwSciPmCfSfXJG")
 	public byte[] secret;
 
+	@Schema(description = "Bitcoin HASH160(public key) for receiving funds, or omit to derive from private key", example = "u17kBVKkKSp12oUzaxFwNnq1JZf")
+	public byte[] receivingAccountInfo;
+
 	public CrossChainBitcoinRedeemRequest() {
 	}
 

src/main/java/org/qortal/api/model/CrossChainBitcoinRefundRequest.java

@@ -22,6 +22,9 @@ public class CrossChainBitcoinRefundRequest {
 	@Schema(description = "Bitcoin miner fee", example = "0.00001000")
 	public BigDecimal bitcoinMinerFee;
 
+	@Schema(description = "Bitcoin HASH160(public key) for receiving funds, or omit to derive from private key", example = "u17kBVKkKSp12oUzaxFwNnq1JZf")
+	public byte[] receivingAccountInfo;
+
 	public CrossChainBitcoinRefundRequest() {
 	}
 

src/main/java/org/qortal/api/model/CrossChainBuildRequest.java

@@ -12,20 +12,19 @@ public class CrossChainBuildRequest {
 	@Schema(description = "AT creator's public key", example = "C6wuddsBV3HzRrXUtezE7P5MoRXp5m3mEDokRDGZB6ry")
 	public byte[] creatorPublicKey;
 
-	@Schema(description = "Initial QORT amount paid when trade agreed", example = "0.00100000")
-	@XmlJavaTypeAdapter(value = org.qortal.api.AmountTypeAdapter.class)
-	public long initialQortAmount;
-
 	@Schema(description = "Final QORT amount paid out on successful trade", example = "80.40200000")
 	@XmlJavaTypeAdapter(value = org.qortal.api.AmountTypeAdapter.class)
-	public long finalQortAmount;
+	public long qortAmount;
 
 	@Schema(description = "QORT amount funding AT, including covering AT execution fees", example = "123.45670000")
 	@XmlJavaTypeAdapter(value = org.qortal.api.AmountTypeAdapter.class)
 	public long fundingQortAmount;
 
+	@Schema(description = "HASH160 of creator's Bitcoin public key", example = "2daMveGc5pdjRyFacbxBzMksCbyC")
+	public byte[] bitcoinPublicKeyHash;
+
 	@Schema(description = "HASH160 of secret", example = "43vnftqkjxrhb5kJdkU1ZFQLEnWV")
-	public byte[] secretHash;
+	public byte[] hashOfSecretB;
 
 	@Schema(description = "Bitcoin P2SH BTC balance for release of secret", example = "0.00864200")
 	@XmlJavaTypeAdapter(value = org.qortal.api.AmountTypeAdapter.class)

src/main/java/org/qortal/api/model/CrossChainCancelRequest.java

@@ -8,10 +8,10 @@ import io.swagger.v3.oas.annotations.media.Schema;
 @XmlAccessorType(XmlAccessType.FIELD)
 public class CrossChainCancelRequest {
 
-	@Schema(description = "AT creator's public key", example = "C6wuddsBV3HzRrXUtezE7P5MoRXp5m3mEDokRDGZB6ry")
+	@Schema(description = "AT creator's public key", example = "K6wuddsBV3HzRrXFFezE7P5MoRXp5m3mEDokRDGZB6ry")
 	public byte[] creatorPublicKey;
 
-	@Schema(description = "Qortal AT address")
+	@Schema(description = "Qortal trade AT address")
 	public String atAddress;
 
 	public CrossChainCancelRequest() {

src/main/java/org/qortal/api/model/CrossChainOfferSummary.java

@@ -0,0 +1,92 @@
+package org.qortal.api.model;
+
+import javax.xml.bind.annotation.XmlAccessType;
+import javax.xml.bind.annotation.XmlAccessorType;
+import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;
+
+import org.qortal.crosschain.BTCACCT;
+import org.qortal.data.crosschain.CrossChainTradeData;
+
+import io.swagger.v3.oas.annotations.media.Schema;
+
+// All properties to be converted to JSON via JAXB
+@XmlAccessorType(XmlAccessType.FIELD)
+public class CrossChainOfferSummary {
+
+	// Properties
+
+	@Schema(description = "AT's Qortal address")
+	public String qortalAtAddress;
+
+	@Schema(description = "AT creator's Qortal address")
+	public String qortalCreator;
+
+	@XmlJavaTypeAdapter(value = org.qortal.api.AmountTypeAdapter.class)
+	private long qortAmount;
+
+	@XmlJavaTypeAdapter(value = org.qortal.api.AmountTypeAdapter.class)
+	private long btcAmount;
+
+	@Schema(description = "Suggested trade timeout (minutes)", example = "10080")
+	private int tradeTimeout;
+
+	private BTCACCT.Mode mode;
+
+	private long timestamp;
+
+	private String partnerQortalReceivingAddress;
+
+	protected CrossChainOfferSummary() {
+		/* For JAXB */
+	}
+
+	public CrossChainOfferSummary(CrossChainTradeData crossChainTradeData, long timestamp) {
+		this.qortalAtAddress = crossChainTradeData.qortalAtAddress;
+		this.qortalCreator = crossChainTradeData.qortalCreator;
+		this.qortAmount = crossChainTradeData.qortAmount;
+		this.btcAmount = crossChainTradeData.expectedBitcoin;
+		this.tradeTimeout = crossChainTradeData.tradeTimeout;
+		this.mode = crossChainTradeData.mode;
+		this.timestamp = timestamp;
+		this.partnerQortalReceivingAddress = crossChainTradeData.qortalPartnerReceivingAddress;
+	}
+
+	public String getQortalAtAddress() {
+		return this.qortalAtAddress;
+	}
+
+	public String getQortalCreator() {
+		return this.qortalCreator;
+	}
+
+	public long getQortAmount() {
+		return this.qortAmount;
+	}
+
+	public long getBtcAmount() {
+		return this.btcAmount;
+	}
+
+	public int getTradeTimeout() {
+		return this.tradeTimeout;
+	}
+
+	public BTCACCT.Mode getMode() {
+		return this.mode;
+	}
+
+	public long getTimestamp() {
+		return this.timestamp;
+	}
+
+	public String getPartnerQortalReceivingAddress() {
+		return this.partnerQortalReceivingAddress;
+	}
+
+	// For debugging mostly
+
+	public String toString() {
+		return String.format("%s: %s", this.qortalAtAddress, this.mode.name());
+	}
+
+}

src/main/java/org/qortal/api/model/CrossChainSecretRequest.java

@@ -8,14 +8,20 @@ import io.swagger.v3.oas.annotations.media.Schema;
 @XmlAccessorType(XmlAccessType.FIELD)
 public class CrossChainSecretRequest {
 
-	@Schema(description = "Public key to match AT's 'recipient'", example = "C6wuddsBV3HzRrXUtezE7P5MoRXp5m3mEDokRDGZB6ry")
-	public byte[] recipientPublicKey;
+	@Schema(description = "Public key to match AT's trade 'partner'", example = "C6wuddsBV3HzRrXUtezE7P5MoRXp5m3mEDokRDGZB6ry")
+	public byte[] partnerPublicKey;
 
 	@Schema(description = "Qortal AT address")
 	public String atAddress;
 
-	@Schema(description = "32-byte secret", example = "6gVbAXCVzJXAWwtAVGAfgAkkXpeXvPUwSciPmCfSfXJG")
-	public byte[] secret;
+	@Schema(description = "secret-A (32 bytes)", example = "FHMzten4he9jZ4HGb4297Utj6F5g2w7serjq2EnAg2s1")
+	public byte[] secretA;
+
+	@Schema(description = "secret-B (32 bytes)", example = "EN2Bgx3BcEMtxFCewmCVSMkfZjVKYhx3KEXC5A21KBGx")
+	public byte[] secretB;
+
+	@Schema(description = "Qortal address for receiving QORT from AT")
+	public String receivingAddress;
 
 	public CrossChainSecretRequest() {
 	}

src/main/java/org/qortal/api/model/CrossChainTradeRequest.java

@@ -8,14 +8,14 @@ import io.swagger.v3.oas.annotations.media.Schema;
 @XmlAccessorType(XmlAccessType.FIELD)
 public class CrossChainTradeRequest {
 
-	@Schema(description = "AT creator's public key", example = "C6wuddsBV3HzRrXUtezE7P5MoRXp5m3mEDokRDGZB6ry")
-	public byte[] creatorPublicKey;
+	@Schema(description = "AT creator's 'trade' public key", example = "C6wuddsBV3HzRrXUtezE7P5MoRXp5m3mEDokRDGZB6ry")
+	public byte[] tradePublicKey;
 
 	@Schema(description = "Qortal AT address")
 	public String atAddress;
 
-	@Schema(description = "Qortal address for trade partner/recipient")
-	public String recipient;
+	@Schema(description = "Signature of trading partner's 'offer' MESSAGE transaction")
+	public byte[] messageTransactionSignature;
 
 	public CrossChainTradeRequest() {
 	}

src/main/java/org/qortal/api/model/CrossChainTradeSummary.java

@@ -0,0 +1,43 @@
+package org.qortal.api.model;
+
+import javax.xml.bind.annotation.XmlAccessType;
+import javax.xml.bind.annotation.XmlAccessorType;
+import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;
+
+import org.qortal.data.crosschain.CrossChainTradeData;
+
+// All properties to be converted to JSON via JAXB
+@XmlAccessorType(XmlAccessType.FIELD)
+public class CrossChainTradeSummary {
+
+	private long tradeTimestamp;
+
+	@XmlJavaTypeAdapter(value = org.qortal.api.AmountTypeAdapter.class)
+	private long qortAmount;
+
+	@XmlJavaTypeAdapter(value = org.qortal.api.AmountTypeAdapter.class)
+	private long btcAmount;
+
+	protected CrossChainTradeSummary() {
+		/* For JAXB */
+	}
+
+	public CrossChainTradeSummary(CrossChainTradeData crossChainTradeData, long timestamp) {
+		this.tradeTimestamp = timestamp;
+		this.qortAmount = crossChainTradeData.qortAmount;
+		this.btcAmount = crossChainTradeData.expectedBitcoin;
+	}
+
+	public long getTradeTimestamp() {
+		return this.tradeTimestamp;
+	}
+
+	public long getQortAmount() {
+		return this.qortAmount;
+	}
+
+	public long getBtcAmount() {
+		return this.btcAmount;
+	}
+
+}

src/main/java/org/qortal/api/model/NodeInfo.java

@@ -11,6 +11,7 @@ public class NodeInfo {
 	public String buildVersion;
 	public long buildTimestamp;
 	public String nodeId;
+	public boolean isTestNet;
 
 	public NodeInfo() {
 	}

src/main/java/org/qortal/api/model/NodeStatus.java

@@ -20,17 +20,14 @@ public class NodeStatus {
 	public final int height;
 
 	public NodeStatus() {
-		isMintingPossible = Controller.getInstance().isMintingPossible();
-		isSynchronizing = Controller.getInstance().isSynchronizing();
+		this.isMintingPossible = Controller.getInstance().isMintingPossible();
 
-		if (isSynchronizing)
-			syncPercent = Controller.getInstance().getSyncPercent();
-		else
-			syncPercent = null;
+		this.syncPercent = Controller.getInstance().getSyncPercent();
+		this.isSynchronizing = this.syncPercent != null;
 
-		numberOfConnections = Network.getInstance().getHandshakedPeers().size();
+		this.numberOfConnections = Network.getInstance().getHandshakedPeers().size();
 
-		height = Controller.getInstance().getChainHeight();
+		this.height = Controller.getInstance().getChainHeight();
 	}
 
 }

src/main/java/org/qortal/api/model/TradeBotCreateRequest.java

@@ -0,0 +1,36 @@
+package org.qortal.api.model;
+
+import javax.xml.bind.annotation.XmlAccessType;
+import javax.xml.bind.annotation.XmlAccessorType;
+import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;
+
+import io.swagger.v3.oas.annotations.media.Schema;
+
+@XmlAccessorType(XmlAccessType.FIELD)
+public class TradeBotCreateRequest {
+
+	@Schema(description = "Trade creator's public key", example = "2zR1WFsbM7akHghqSCYKBPk6LDP8aKiQSRS1FrwoLvoB")
+	public byte[] creatorPublicKey;
+
+	@Schema(description = "QORT amount paid out on successful trade", example = "80.40200000")
+	@XmlJavaTypeAdapter(value = org.qortal.api.AmountTypeAdapter.class)
+	public long qortAmount;
+
+	@Schema(description = "QORT amount funding AT, including covering AT execution fees", example = "81")
+	@XmlJavaTypeAdapter(value = org.qortal.api.AmountTypeAdapter.class)
+	public long fundingQortAmount;
+
+	@Schema(description = "Bitcoin amount wanted in return", example = "0.00864200")
+	@XmlJavaTypeAdapter(value = org.qortal.api.AmountTypeAdapter.class)
+	public long bitcoinAmount;
+
+	@Schema(description = "Suggested trade timeout (minutes)", example = "10080")
+	public int tradeTimeout;
+
+	@Schema(description = "Bitcoin address for receiving", example = "1BitcoinEaterAddressDontSendf59kuE")
+	public String receivingAddress;
+
+	public TradeBotCreateRequest() {
+	}
+
+}

src/main/java/org/qortal/api/model/TradeBotRespondRequest.java

@@ -0,0 +1,23 @@
+package org.qortal.api.model;
+
+import javax.xml.bind.annotation.XmlAccessType;
+import javax.xml.bind.annotation.XmlAccessorType;
+
+import io.swagger.v3.oas.annotations.media.Schema;
+
+@XmlAccessorType(XmlAccessType.FIELD)
+public class TradeBotRespondRequest {
+
+	@Schema(description = "Qortal AT address", example = "Aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa")
+	public String atAddress;
+
+	@Schema(description = "Bitcoin BIP32 extended private key", example = "xprv___________________________________________________________________________________________________________")
+	public String xprv58;
+
+	@Schema(description = "Qortal address for receiving QORT from AT", example = "Qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq")
+	public String receivingAddress;
+
+	public TradeBotRespondRequest() {
+	}
+
+}

src/main/java/org/qortal/api/resource/AddressesResource.java

@@ -7,6 +7,7 @@ import io.swagger.v3.oas.annotations.media.Content;
 import io.swagger.v3.oas.annotations.media.Schema;
 import io.swagger.v3.oas.annotations.parameters.RequestBody;
 import io.swagger.v3.oas.annotations.responses.ApiResponse;
+import io.swagger.v3.oas.annotations.security.SecurityRequirement;
 import io.swagger.v3.oas.annotations.tags.Tag;
 
 import java.math.BigDecimal;
@@ -473,6 +474,7 @@ public class AddressesResource {
 		}
 	)
 	@ApiErrors({ApiError.TRANSACTION_INVALID, ApiError.INVALID_DATA, ApiError.TRANSFORMATION_ERROR, ApiError.REPOSITORY_ISSUE})
+	@SecurityRequirement(name = "apiKey")
 	public String computePublicize(String rawBytes58) {
 		Security.checkApiCallAllowed(request);
 

src/main/java/org/qortal/api/resource/AdminResource.java

@@ -8,6 +8,7 @@ import io.swagger.v3.oas.annotations.media.Content;
 import io.swagger.v3.oas.annotations.media.Schema;
 import io.swagger.v3.oas.annotations.parameters.RequestBody;
 import io.swagger.v3.oas.annotations.responses.ApiResponse;
+import io.swagger.v3.oas.annotations.security.SecurityRequirement;
 import io.swagger.v3.oas.annotations.tags.Tag;
 
 import java.io.IOException;
@@ -40,7 +41,6 @@ import org.qortal.account.Account;
 import org.qortal.account.PrivateKeyAccount;
 import org.qortal.api.ApiError;
 import org.qortal.api.ApiErrors;
-import org.qortal.api.ApiException;
 import org.qortal.api.ApiExceptionFactory;
 import org.qortal.api.Security;
 import org.qortal.api.model.ActivitySummary;
@@ -57,6 +57,7 @@ import org.qortal.network.PeerAddress;
 import org.qortal.repository.DataException;
 import org.qortal.repository.Repository;
 import org.qortal.repository.RepositoryManager;
+import org.qortal.settings.Settings;
 import org.qortal.utils.Base58;
 import org.qortal.utils.NTP;
 
@@ -118,6 +119,7 @@ public class AdminResource {
 		nodeInfo.buildVersion = Controller.getInstance().getVersionString();
 		nodeInfo.buildTimestamp = Controller.getInstance().getBuildTimestamp();
 		nodeInfo.nodeId = Network.getInstance().getOurNodeId();
+		nodeInfo.isTestNet = Settings.getInstance().isTestNet();
 
 		return nodeInfo;
 	}
@@ -132,6 +134,7 @@ public class AdminResource {
 			)
 		}
 	)
+	@SecurityRequirement(name = "apiKey")
 	public NodeStatus status() {
 		Security.checkApiCallAllowed(request);
 
@@ -152,6 +155,7 @@ public class AdminResource {
 			)
 		}
 	)
+	@SecurityRequirement(name = "apiKey")
 	public String shutdown() {
 		Security.checkApiCallAllowed(request);
 
@@ -180,7 +184,10 @@ public class AdminResource {
 		}
 	)
 	@ApiErrors({ApiError.REPOSITORY_ISSUE})
+	@SecurityRequirement(name = "apiKey")
 	public ActivitySummary summary() {
+		Security.checkApiCallAllowed(request);
+
 		ActivitySummary summary = new ActivitySummary();
 
 		LocalDate date = LocalDate.now();
@@ -192,16 +199,13 @@ public class AdminResource {
 			int startHeight = repository.getBlockRepository().getHeightFromTimestamp(start);
 			int endHeight = repository.getBlockRepository().getBlockchainHeight();
 
-			summary.blockCount = endHeight - startHeight;
+			summary.setBlockCount(endHeight - startHeight);
 
-			summary.transactionCountByType = repository.getTransactionRepository().getTransactionSummary(startHeight + 1, endHeight);
+			summary.setTransactionCountByType(repository.getTransactionRepository().getTransactionSummary(startHeight + 1, endHeight));
 
-			for (Integer count : summary.transactionCountByType.values())
-				summary.transactionCount += count;
+			summary.setAssetsIssued(repository.getAssetRepository().getRecentAssetIds(start).size());
 
-			summary.assetsIssued = repository.getAssetRepository().getRecentAssetIds(start).size();
-
-			summary.namesRegistered = repository.getNameRepository().getRecentNames(start).size();
+			summary.setNamesRegistered (repository.getNameRepository().getRecentNames(start).size());
 
 			return summary;
 		} catch (DataException e) {
@@ -209,6 +213,30 @@ public class AdminResource {
 		}
 	}
 
+	@GET
+	@Path("/enginestats")
+	@Operation(
+		summary = "Fetch statistics snapshot for core engine",
+		responses = {
+			@ApiResponse(
+				content = @Content(
+					mediaType = MediaType.APPLICATION_JSON,
+					array = @ArraySchema(
+						schema = @Schema(
+							implementation = Controller.StatsSnapshot.class
+						)
+					)
+				)
+			)
+		}
+	)
+	@SecurityRequirement(name = "apiKey")
+	public Controller.StatsSnapshot getEngineStats() {
+		Security.checkApiCallAllowed(request);
+
+		return Controller.getInstance().getStatsSnapshot();
+	}
+
 	@GET
 	@Path("/mintingaccounts")
 	@Operation(
@@ -221,6 +249,7 @@ public class AdminResource {
 		}
 	)
 	@ApiErrors({ApiError.REPOSITORY_ISSUE})
+	@SecurityRequirement(name = "apiKey")
 	public List<MintingAccountData> getMintingAccounts() {
 		Security.checkApiCallAllowed(request);
 
@@ -267,6 +296,7 @@ public class AdminResource {
 		}
 	)
 	@ApiErrors({ApiError.INVALID_PRIVATE_KEY, ApiError.REPOSITORY_ISSUE, ApiError.CANNOT_MINT})
+	@SecurityRequirement(name = "apiKey")
 	public String addMintingAccount(String seed58) {
 		Security.checkApiCallAllowed(request);
 
@@ -302,13 +332,13 @@ public class AdminResource {
 	@DELETE
 	@Path("/mintingaccounts")
 	@Operation(
-		summary = "Remove account/reward-share from use by BlockMinter, using private key",
+		summary = "Remove account/reward-share from use by BlockMinter, using public or private key",
 		requestBody = @RequestBody(
 			required = true,
 			content = @Content(
 				mediaType = MediaType.TEXT_PLAIN,
 				schema = @Schema(
-					type = "string", example = "private key"
+					type = "string", example = "public or private key"
 				)
 			)
 		),
@@ -319,13 +349,14 @@ public class AdminResource {
 		}
 	)
 	@ApiErrors({ApiError.INVALID_PRIVATE_KEY, ApiError.REPOSITORY_ISSUE})
-	public String deleteMintingAccount(String seed58) {
+	@SecurityRequirement(name = "apiKey")
+	public String deleteMintingAccount(String key58) {
 		Security.checkApiCallAllowed(request);
 
 		try (final Repository repository = RepositoryManager.getRepository()) {
-			byte[] seed = Base58.decode(seed58.trim());
+			byte[] key = Base58.decode(key58.trim());
 
-			if (repository.getAccountRepository().delete(seed) == 0)
+			if (repository.getAccountRepository().delete(key) == 0)
 				return "false";
 
 			repository.saveChanges();
@@ -418,6 +449,7 @@ public class AdminResource {
 		}
 	)
 	@ApiErrors({ApiError.INVALID_HEIGHT, ApiError.REPOSITORY_ISSUE})
+	@SecurityRequirement(name = "apiKey")
 	public String orphan(String targetHeightString) {
 		Security.checkApiCallAllowed(request);
 
@@ -435,8 +467,6 @@ public class AdminResource {
 			throw ApiExceptionFactory.INSTANCE.createException(request, ApiError.REPOSITORY_ISSUE, e);
 		} catch (NumberFormatException e) {
 			throw ApiExceptionFactory.INSTANCE.createException(request, ApiError.INVALID_HEIGHT);
-		} catch (ApiException e) {
-			throw e;
 		}
 	}
 
@@ -461,6 +491,7 @@ public class AdminResource {
 		}
 	)
 	@ApiErrors({ApiError.INVALID_DATA, ApiError.REPOSITORY_ISSUE})
+	@SecurityRequirement(name = "apiKey")
 	public String forceSync(String targetPeerAddress) {
 		Security.checkApiCallAllowed(request);
 
@@ -492,8 +523,6 @@ public class AdminResource {
 			return syncResult.name();
 		} catch (IllegalArgumentException e) {
 			throw ApiExceptionFactory.INSTANCE.createException(request, ApiError.INVALID_DATA);
-		} catch (ApiException e) {
-			throw e;
 		} catch (UnknownHostException e) {
 			throw ApiExceptionFactory.INSTANCE.createException(request, ApiError.INVALID_DATA);
 		} catch (InterruptedException e) {
@@ -501,4 +530,188 @@ public class AdminResource {
 		}
 	}
 
+	@GET
+	@Path("/repository/data")
+	@Operation(
+		summary = "Export sensitive/node-local data from repository.",
+		description = "Exports data to .script files on local machine"
+	)
+	@ApiErrors({ApiError.INVALID_DATA, ApiError.REPOSITORY_ISSUE})
+	@SecurityRequirement(name = "apiKey")
+	public String exportRepository() {
+		Security.checkApiCallAllowed(request);
+
+		try (final Repository repository = RepositoryManager.getRepository()) {
+			ReentrantLock blockchainLock = Controller.getInstance().getBlockchainLock();
+
+			blockchainLock.lockInterruptibly();
+
+			try {
+				repository.exportNodeLocalData();
+				return "true";
+			} finally {
+				blockchainLock.unlock();
+			}
+		} catch (InterruptedException e) {
+			// We couldn't lock blockchain to perform export
+			return "false";
+		} catch (DataException e) {
+			throw ApiExceptionFactory.INSTANCE.createException(request, ApiError.REPOSITORY_ISSUE, e);
+		}
+	}
+
+	@POST
+	@Path("/repository/data")
+	@Operation(
+		summary = "Import data into repository.",
+		description = "Imports data from file on local machine. Filename is forced to 'import.script' if apiKey is not set.",
+		requestBody = @RequestBody(
+			required = true,
+			content = @Content(
+				mediaType = MediaType.TEXT_PLAIN,
+				schema = @Schema(
+					type = "string", example = "MintingAccounts.script"
+				)
+			)
+		),
+		responses = {
+			@ApiResponse(
+				description = "\"true\"",
+				content = @Content(mediaType = MediaType.TEXT_PLAIN, schema = @Schema(type = "string"))
+			)
+		}
+	)
+	@ApiErrors({ApiError.REPOSITORY_ISSUE})
+	@SecurityRequirement(name = "apiKey")
+	public String importRepository(String filename) {
+		Security.checkApiCallAllowed(request);
+
+		// Hard-coded because it's too dangerous to allow user-supplied filenames in weaker security contexts
+		if (Settings.getInstance().getApiKey() == null)
+			filename = "import.script";
+
+		try (final Repository repository = RepositoryManager.getRepository()) {
+			ReentrantLock blockchainLock = Controller.getInstance().getBlockchainLock();
+
+			blockchainLock.lockInterruptibly();
+
+			try {
+				repository.importDataFromFile(filename);
+				repository.saveChanges();
+
+				return "true";
+			} finally {
+				blockchainLock.unlock();
+			}
+		} catch (InterruptedException e) {
+			// We couldn't lock blockchain to perform import
+			return "false";
+		} catch (DataException e) {
+			throw ApiExceptionFactory.INSTANCE.createException(request, ApiError.REPOSITORY_ISSUE, e);
+		}
+	}
+
+	@POST
+	@Path("/repository/checkpoint")
+	@Operation(
+		summary = "Checkpoint data in repository.",
+		description = "Forces repository to checkpoint uncommitted writes.",
+		responses = {
+			@ApiResponse(
+				description = "\"true\"",
+				content = @Content(mediaType = MediaType.TEXT_PLAIN, schema = @Schema(type = "string"))
+			)
+		}
+	)
+	@ApiErrors({ApiError.REPOSITORY_ISSUE})
+	@SecurityRequirement(name = "apiKey")
+	public String checkpointRepository() {
+		Security.checkApiCallAllowed(request);
+
+		try (final Repository repository = RepositoryManager.getRepository()) {
+			ReentrantLock blockchainLock = Controller.getInstance().getBlockchainLock();
+
+			blockchainLock.lockInterruptibly();
+
+			try {
+				repository.checkpoint(true);
+				repository.saveChanges();
+
+				return "true";
+			} finally {
+				blockchainLock.unlock();
+			}
+		} catch (InterruptedException e) {
+			// We couldn't lock blockchain to perform checkpoint
+			return "false";
+		} catch (DataException e) {
+			throw ApiExceptionFactory.INSTANCE.createException(request, ApiError.REPOSITORY_ISSUE, e);
+		}
+	}
+
+	@POST
+	@Path("/repository/backup")
+	@Operation(
+		summary = "Perform online backup of repository.",
+		responses = {
+			@ApiResponse(
+				description = "\"true\"",
+				content = @Content(mediaType = MediaType.TEXT_PLAIN, schema = @Schema(type = "string"))
+			)
+		}
+	)
+	@ApiErrors({ApiError.REPOSITORY_ISSUE})
+	@SecurityRequirement(name = "apiKey")
+	public String backupRepository() {
+		Security.checkApiCallAllowed(request);
+
+		try (final Repository repository = RepositoryManager.getRepository()) {
+			ReentrantLock blockchainLock = Controller.getInstance().getBlockchainLock();
+
+			blockchainLock.lockInterruptibly();
+
+			try {
+				repository.backup(true);
+				repository.saveChanges();
+
+				return "true";
+			} finally {
+				blockchainLock.unlock();
+			}
+		} catch (InterruptedException e) {
+			// We couldn't lock blockchain to perform backup
+			return "false";
+		} catch (DataException e) {
+			throw ApiExceptionFactory.INSTANCE.createException(request, ApiError.REPOSITORY_ISSUE, e);
+		}
+	}
+
+	@DELETE
+	@Path("/repository")
+	@Operation(
+		summary = "Perform maintenance on repository.",
+		description = "Requires enough free space to rebuild repository. This will pause your node for a while."
+	)
+	@ApiErrors({ApiError.REPOSITORY_ISSUE})
+	@SecurityRequirement(name = "apiKey")
+	public void performRepositoryMaintenance() {
+		Security.checkApiCallAllowed(request);
+
+		try (final Repository repository = RepositoryManager.getRepository()) {
+			ReentrantLock blockchainLock = Controller.getInstance().getBlockchainLock();
+
+			blockchainLock.lockInterruptibly();
+
+			try {
+				repository.performPeriodicMaintenance();
+			} finally {
+				blockchainLock.unlock();
+			}
+		} catch (InterruptedException e) {
+			// No big deal
+		} catch (DataException e) {
+			throw ApiExceptionFactory.INSTANCE.createException(request, ApiError.REPOSITORY_ISSUE, e);
+		}
+	}
+
 }

src/main/java/org/qortal/api/resource/ApiDefinition.java

@@ -1,11 +1,17 @@
 package org.qortal.api.resource;
 
 import io.swagger.v3.oas.annotations.OpenAPIDefinition;
+import io.swagger.v3.oas.annotations.enums.SecuritySchemeIn;
+import io.swagger.v3.oas.annotations.enums.SecuritySchemeType;
 import io.swagger.v3.oas.annotations.extensions.Extension;
 import io.swagger.v3.oas.annotations.extensions.ExtensionProperty;
 import io.swagger.v3.oas.annotations.info.Info;
+import io.swagger.v3.oas.annotations.security.SecurityScheme;
+import io.swagger.v3.oas.annotations.security.SecuritySchemes;
 import io.swagger.v3.oas.annotations.tags.Tag;
 
+import org.qortal.api.Security;
+
 @OpenAPIDefinition(
 		info = @Info( title = "Qortal API", description = "NOTE: byte-arrays are encoded in Base58" ),
 		tags = {
@@ -30,5 +36,9 @@ import io.swagger.v3.oas.annotations.tags.Tag;
 			})
 		}
 )
+@SecuritySchemes({
+	@SecurityScheme(name = "basicAuth", type = SecuritySchemeType.HTTP, scheme = "basic"),
+	@SecurityScheme(name = "apiKey", type = SecuritySchemeType.APIKEY, in = SecuritySchemeIn.HEADER, paramName = Security.API_KEY_HEADER)
+})
 public class ApiDefinition {
 }

src/main/java/org/qortal/api/resource/AtResource.java

@@ -25,7 +25,6 @@ import org.qortal.api.ApiError;
 import org.qortal.api.ApiErrors;
 import org.qortal.api.ApiException;
 import org.qortal.api.ApiExceptionFactory;
-import org.qortal.at.QortalAtLoggerFactory;
 import org.qortal.data.at.ATData;
 import org.qortal.data.at.ATStateData;
 import org.qortal.data.transaction.DeployAtTransactionData;
@@ -147,8 +146,7 @@ public class AtResource {
 			ATStateData atStateData = repository.getATRepository().getLatestATState(atAddress);
 			byte[] stateData = atStateData.getStateData();
 
-			QortalAtLoggerFactory loggerFactory = QortalAtLoggerFactory.getInstance();
-			byte[] dataBytes = MachineState.extractDataBytes(loggerFactory, stateData);
+			byte[] dataBytes = MachineState.extractDataBytes(stateData);
 
 			return dataBytes;
 		} catch (ApiException e) {

src/main/java/org/qortal/api/resource/BlocksResource.java

@@ -480,4 +480,44 @@ public class BlocksResource {
 		}
 	}
 
+	@GET
+	@Path("/summaries")
+	@Operation(
+		summary = "Fetch only summary info about a range of blocks",
+		description = "Specify up to 2 out 3 of: start, end and count. If neither start nor end are specified, then end is assumed to be latest block. Where necessary, count is assumed to be 50.",
+		responses = {
+			@ApiResponse(
+				description = "blocks",
+				content = @Content(
+					array = @ArraySchema(
+						schema = @Schema(
+							implementation = BlockSummaryData.class
+						)
+					)
+				)
+			)
+		}
+	)
+	@ApiErrors({
+		ApiError.REPOSITORY_ISSUE
+	})
+	public List<BlockSummaryData> getBlockSummaries(
+			@QueryParam("start") Integer startHeight,
+			@QueryParam("end") Integer endHeight,
+			@Parameter(ref = "count") @QueryParam("count") Integer count) {
+		// Check up to 2 out of 3 params
+		if (startHeight != null && endHeight != null && count != null)
+			throw ApiExceptionFactory.INSTANCE.createException(request, ApiError.INVALID_CRITERIA);
+
+		// Check values
+		if ((startHeight != null && startHeight < 1) || (endHeight != null && endHeight < 1) || (count != null && count < 1))
+			throw ApiExceptionFactory.INSTANCE.createException(request, ApiError.INVALID_CRITERIA);
+
+		try (final Repository repository = RepositoryManager.getRepository()) {
+			return repository.getBlockRepository().getBlockSummaries(startHeight, endHeight, count);
+		} catch (DataException e) {
+			throw ApiExceptionFactory.INSTANCE.createException(request, ApiError.REPOSITORY_ISSUE, e);
+		}
+	}
+
 }

src/main/java/org/qortal/api/resource/ChatResource.java

@@ -7,6 +7,7 @@ import io.swagger.v3.oas.annotations.media.Content;
 import io.swagger.v3.oas.annotations.media.Schema;
 import io.swagger.v3.oas.annotations.parameters.RequestBody;
 import io.swagger.v3.oas.annotations.responses.ApiResponse;
+import io.swagger.v3.oas.annotations.security.SecurityRequirement;
 import io.swagger.v3.oas.annotations.tags.Tag;
 
 import java.util.List;
@@ -156,6 +157,7 @@ public class ChatResource {
 		}
 	)
 	@ApiErrors({ApiError.TRANSACTION_INVALID, ApiError.TRANSFORMATION_ERROR, ApiError.REPOSITORY_ISSUE})
+	@SecurityRequirement(name = "apiKey")
 	public String buildChat(ChatTransactionData transactionData) {
 		Security.checkApiCallAllowed(request);
 
@@ -203,6 +205,7 @@ public class ChatResource {
 		}
 	)
 	@ApiErrors({ApiError.TRANSACTION_INVALID, ApiError.INVALID_DATA, ApiError.TRANSFORMATION_ERROR, ApiError.REPOSITORY_ISSUE})
+	@SecurityRequirement(name = "apiKey")
 	public String buildChat(String rawBytes58) {
 		Security.checkApiCallAllowed(request);
 

src/main/java/org/qortal/api/resource/PeersResource.java

@@ -6,8 +6,11 @@ import io.swagger.v3.oas.annotations.media.Content;
 import io.swagger.v3.oas.annotations.media.Schema;
 import io.swagger.v3.oas.annotations.parameters.RequestBody;
 import io.swagger.v3.oas.annotations.responses.ApiResponse;
+import io.swagger.v3.oas.annotations.security.SecurityRequirement;
 import io.swagger.v3.oas.annotations.tags.Tag;
 
+import java.net.InetSocketAddress;
+import java.net.UnknownHostException;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.stream.Collectors;
@@ -26,10 +29,17 @@ import org.qortal.api.ApiException;
 import org.qortal.api.ApiExceptionFactory;
 import org.qortal.api.Security;
 import org.qortal.api.model.ConnectedPeer;
+import org.qortal.controller.Controller;
+import org.qortal.controller.Synchronizer;
+import org.qortal.controller.Synchronizer.SynchronizationResult;
+import org.qortal.data.block.BlockSummaryData;
 import org.qortal.data.network.PeerData;
 import org.qortal.network.Network;
+import org.qortal.network.Peer;
 import org.qortal.network.PeerAddress;
 import org.qortal.repository.DataException;
+import org.qortal.repository.Repository;
+import org.qortal.repository.RepositoryManager;
 import org.qortal.utils.ExecuteProduceConsume;
 import org.qortal.utils.NTP;
 
@@ -122,6 +132,7 @@ public class PeersResource {
 			)
 		}
 	)
+	@SecurityRequirement(name = "apiKey")
 	public ExecuteProduceConsume.StatsSnapshot getEngineStats() {
 		Security.checkApiCallAllowed(request);
 
@@ -159,6 +170,7 @@ public class PeersResource {
 	@ApiErrors({
 		ApiError.INVALID_NETWORK_ADDRESS, ApiError.REPOSITORY_ISSUE
 	})
+	@SecurityRequirement(name = "apiKey")
 	public String addPeer(String address) {
 		Security.checkApiCallAllowed(request);
 
@@ -213,6 +225,7 @@ public class PeersResource {
 	@ApiErrors({
 		ApiError.INVALID_NETWORK_ADDRESS, ApiError.REPOSITORY_ISSUE
 	})
+	@SecurityRequirement(name = "apiKey")
 	public String removePeer(String address) {
 		Security.checkApiCallAllowed(request);
 
@@ -248,6 +261,7 @@ public class PeersResource {
 	@ApiErrors({
 		ApiError.REPOSITORY_ISSUE
 	})
+	@SecurityRequirement(name = "apiKey")
 	public String removeKnownPeers(String address) {
 		Security.checkApiCallAllowed(request);
 
@@ -260,4 +274,68 @@ public class PeersResource {
 		}
 	}
 
+	@POST
+	@Path("/commonblock")
+	@Operation(
+		summary = "Report common block with given peer.",
+		requestBody = @RequestBody(
+			required = true,
+			content = @Content(
+				mediaType = MediaType.TEXT_PLAIN,
+				schema = @Schema(
+					type = "string", example = "node2.qortal.org"
+				)
+			)
+		),
+		responses = {
+			@ApiResponse(
+				description = "the block",
+				content = @Content(
+					array = @ArraySchema(
+						schema = @Schema(
+							implementation = BlockSummaryData.class
+						)
+					)
+				)
+			)
+		}
+	)
+	@ApiErrors({ApiError.INVALID_DATA, ApiError.REPOSITORY_ISSUE})
+	@SecurityRequirement(name = "apiKey")
+	public List<BlockSummaryData> commonBlock(String targetPeerAddress) {
+		Security.checkApiCallAllowed(request);
+
+		try {
+			// Try to resolve passed address to make things easier
+			PeerAddress peerAddress = PeerAddress.fromString(targetPeerAddress);
+			InetSocketAddress resolvedAddress = peerAddress.toSocketAddress();
+
+			List<Peer> peers = Network.getInstance().getHandshakedPeers();
+			Peer targetPeer = peers.stream().filter(peer -> peer.getResolvedAddress().equals(resolvedAddress)).findFirst().orElse(null);
+
+			if (targetPeer == null)
+				throw ApiExceptionFactory.INSTANCE.createException(request, ApiError.INVALID_DATA);
+
+			try (final Repository repository = RepositoryManager.getRepository()) {
+				int ourInitialHeight = Controller.getInstance().getChainHeight();
+				boolean force = true;
+				List<BlockSummaryData> peerBlockSummaries = new ArrayList<>();
+
+				SynchronizationResult findCommonBlockResult = Synchronizer.getInstance().fetchSummariesFromCommonBlock(repository, targetPeer, ourInitialHeight, force, peerBlockSummaries);
+				if (findCommonBlockResult != SynchronizationResult.OK)
+					return null;
+
+				return peerBlockSummaries;
+			}
+		} catch (IllegalArgumentException e) {
+			throw ApiExceptionFactory.INSTANCE.createException(request, ApiError.INVALID_DATA);
+		} catch (UnknownHostException e) {
+			throw ApiExceptionFactory.INSTANCE.createException(request, ApiError.INVALID_DATA);
+		} catch (DataException e) {
+			throw ApiExceptionFactory.INSTANCE.createException(request, ApiError.REPOSITORY_ISSUE, e);
+		} catch (InterruptedException e) {
+			return null;
+		}
+	}
+
 }

src/main/java/org/qortal/api/websocket/ActiveChatsWebSocket.java

@@ -6,11 +6,12 @@ import java.util.Map;
 import java.util.concurrent.atomic.AtomicReference;
 
 import org.eclipse.jetty.websocket.api.Session;
+import org.eclipse.jetty.websocket.api.WebSocketException;
 import org.eclipse.jetty.websocket.api.annotations.OnWebSocketClose;
 import org.eclipse.jetty.websocket.api.annotations.OnWebSocketConnect;
+import org.eclipse.jetty.websocket.api.annotations.OnWebSocketError;
 import org.eclipse.jetty.websocket.api.annotations.OnWebSocketMessage;
 import org.eclipse.jetty.websocket.api.annotations.WebSocket;
-import org.eclipse.jetty.websocket.servlet.WebSocketServlet;
 import org.eclipse.jetty.websocket.servlet.WebSocketServletFactory;
 import org.qortal.controller.ChatNotifier;
 import org.qortal.crypto.Crypto;
@@ -22,7 +23,7 @@ import org.qortal.repository.RepositoryManager;
 
 @WebSocket
 @SuppressWarnings("serial")
-public class ActiveChatsWebSocket extends WebSocketServlet implements ApiWebSocket {
+public class ActiveChatsWebSocket extends ApiWebSocket {
 
 	@Override
 	public void configure(WebSocketServletFactory factory) {
@@ -30,8 +31,9 @@ public class ActiveChatsWebSocket extends WebSocketServlet implements ApiWebSock
 	}
 
 	@OnWebSocketConnect
+	@Override
 	public void onWebSocketConnect(Session session) {
-		Map<String, String> pathParams = this.getPathParams(session, "/{address}");
+		Map<String, String> pathParams = getPathParams(session, "/{address}");
 
 		String address = pathParams.get("address");
 		if (address == null || !Crypto.isValidAddress(address)) {
@@ -48,12 +50,19 @@ public class ActiveChatsWebSocket extends WebSocketServlet implements ApiWebSock
 	}
 
 	@OnWebSocketClose
+	@Override
 	public void onWebSocketClose(Session session, int statusCode, String reason) {
 		ChatNotifier.getInstance().deregister(session);
 	}
 
+	@OnWebSocketError
+	public void onWebSocketError(Session session, Throwable throwable) {
+		/* ignored */
+	}
+
 	@OnWebSocketMessage
 	public void onWebSocketMessage(Session session, String message) {
+		/* ignored */
 	}
 
 	private void onNotify(Session session, ChatTransactionData chatTransactionData, String ourAddress, AtomicReference<String> previousOutput) {
@@ -70,7 +79,7 @@ public class ActiveChatsWebSocket extends WebSocketServlet implements ApiWebSock
 
 			StringWriter stringWriter = new StringWriter();
 
-			this.marshall(stringWriter, activeChats);
+			marshall(stringWriter, activeChats);
 
 			// Only output if something has changed
 			String output = stringWriter.toString();
@@ -78,8 +87,8 @@ public class ActiveChatsWebSocket extends WebSocketServlet implements ApiWebSock
 				return;
 
 			previousOutput.set(output);
-			session.getRemote().sendString(output);
-		} catch (DataException | IOException e) {
+			session.getRemote().sendStringByFuture(output);
+		} catch (DataException | IOException | WebSocketException e) {
 			// No output this time?
 		}
 	}

src/main/java/org/qortal/api/websocket/AdminStatusWebSocket.java

@@ -5,62 +5,95 @@ import java.io.StringWriter;
 import java.util.concurrent.atomic.AtomicReference;
 
 import org.eclipse.jetty.websocket.api.Session;
+import org.eclipse.jetty.websocket.api.WebSocketException;
 import org.eclipse.jetty.websocket.api.annotations.OnWebSocketClose;
 import org.eclipse.jetty.websocket.api.annotations.OnWebSocketConnect;
+import org.eclipse.jetty.websocket.api.annotations.OnWebSocketError;
 import org.eclipse.jetty.websocket.api.annotations.OnWebSocketMessage;
 import org.eclipse.jetty.websocket.api.annotations.WebSocket;
-import org.eclipse.jetty.websocket.servlet.WebSocketServlet;
 import org.eclipse.jetty.websocket.servlet.WebSocketServletFactory;
 import org.qortal.api.model.NodeStatus;
-import org.qortal.controller.StatusNotifier;
-import org.qortal.repository.DataException;
-import org.qortal.repository.Repository;
-import org.qortal.repository.RepositoryManager;
+import org.qortal.controller.Controller;
+import org.qortal.event.Event;
+import org.qortal.event.EventBus;
+import org.qortal.event.Listener;
 
 @WebSocket
 @SuppressWarnings("serial")
-public class AdminStatusWebSocket extends WebSocketServlet implements ApiWebSocket {
+public class AdminStatusWebSocket extends ApiWebSocket implements Listener {
+
+	private static final AtomicReference<String> previousOutput = new AtomicReference<>(null);
 
 	@Override
 	public void configure(WebSocketServletFactory factory) {
 		factory.register(AdminStatusWebSocket.class);
+
+		try {
+			previousOutput.set(buildStatusString());
+		} catch (IOException e) {
+			// How to fail properly?
+			return;
+		}
+
+		EventBus.INSTANCE.addListener(this::listen);
+	}
+
+	@Override
+	public void listen(Event event) {
+		if (!(event instanceof Controller.StatusChangeEvent))
+			return;
+
+		String newOutput;
+		try {
+			newOutput = buildStatusString();
+		} catch (IOException e) {
+			// Ignore this time?
+			return;
+		}
+
+		if (previousOutput.getAndUpdate(currentValue -> newOutput).equals(newOutput))
+			// Output hasn't changed, so don't send anything
+			return;
+
+		for (Session session : getSessions())
+			this.sendStatus(session, newOutput);
 	}
 
 	@OnWebSocketConnect
+	@Override
 	public void onWebSocketConnect(Session session) {
-		AtomicReference<String> previousOutput = new AtomicReference<>(null);
+		this.sendStatus(session, previousOutput.get());
 
-		StatusNotifier.Listener listener = timestamp -> onNotify(session, previousOutput);
-		StatusNotifier.getInstance().register(session, listener);
-
-		this.onNotify(session, previousOutput);
+		super.onWebSocketConnect(session);
 	}
 
 	@OnWebSocketClose
+	@Override
 	public void onWebSocketClose(Session session, int statusCode, String reason) {
-		StatusNotifier.getInstance().deregister(session);
+		super.onWebSocketClose(session, statusCode, reason);
+	}
+
+	@OnWebSocketError
+	public void onWebSocketError(Session session, Throwable throwable) {
+		/* We ignore errors for now, but method here to silence log spam */
 	}
 
 	@OnWebSocketMessage
 	public void onWebSocketMessage(Session session, String message) {
+		/* ignored */
 	}
 
-	private void onNotify(Session session,AtomicReference<String> previousOutput) {
-		try (final Repository repository = RepositoryManager.getRepository()) {
-			NodeStatus nodeStatus = new NodeStatus();
+	private static String buildStatusString() throws IOException {
+		NodeStatus nodeStatus = new NodeStatus();
+		StringWriter stringWriter = new StringWriter();
+		marshall(stringWriter, nodeStatus);
+		return stringWriter.toString();
+	}
 
-			StringWriter stringWriter = new StringWriter();
-
-			this.marshall(stringWriter, nodeStatus);
-
-			// Only output if something has changed
-			String output = stringWriter.toString();
-			if (output.equals(previousOutput.get()))
-				return;
-
-			previousOutput.set(output);
-			session.getRemote().sendString(output);
-		} catch (DataException | IOException e) {
+	private void sendStatus(Session session, String status) {
+		try {
+			session.getRemote().sendStringByFuture(status);
+		} catch (WebSocketException e) {
 			// No output this time?
 		}
 	}

src/main/java/org/qortal/api/websocket/ApiWebSocket.java

@@ -3,7 +3,10 @@ package org.qortal.api.websocket;
 import java.io.IOException;
 import java.io.StringWriter;
 import java.io.Writer;
+import java.util.ArrayList;
 import java.util.Collection;
+import java.util.HashMap;
+import java.util.List;
 import java.util.Map;
 
 import javax.xml.bind.JAXBContext;
@@ -13,24 +16,28 @@ import javax.xml.bind.Marshaller;
 import org.eclipse.jetty.http.pathmap.UriTemplatePathSpec;
 import org.eclipse.jetty.websocket.api.Session;
 import org.eclipse.jetty.websocket.servlet.ServletUpgradeRequest;
+import org.eclipse.jetty.websocket.servlet.WebSocketServlet;
 import org.eclipse.persistence.jaxb.JAXBContextFactory;
 import org.eclipse.persistence.jaxb.MarshallerProperties;
 import org.qortal.api.ApiError;
 import org.qortal.api.ApiErrorRoot;
 
-interface ApiWebSocket {
+@SuppressWarnings("serial")
+abstract class ApiWebSocket extends WebSocketServlet {
 
-	default String getPathInfo(Session session) {
+	private static final Map<Class<? extends ApiWebSocket>, List<Session>> SESSIONS_BY_CLASS = new HashMap<>();
+
+	protected static String getPathInfo(Session session) {
 		ServletUpgradeRequest upgradeRequest = (ServletUpgradeRequest) session.getUpgradeRequest();
 		return upgradeRequest.getHttpServletRequest().getPathInfo();
 	}
 
-	default Map<String, String> getPathParams(Session session, String pathSpec) {
+	protected static Map<String, String> getPathParams(Session session, String pathSpec) {
 		UriTemplatePathSpec uriTemplatePathSpec = new UriTemplatePathSpec(pathSpec);
-		return uriTemplatePathSpec.getPathParams(this.getPathInfo(session));
+		return uriTemplatePathSpec.getPathParams(getPathInfo(session));
 	}
 
-	default void sendError(Session session, ApiError apiError) {
+	protected static void sendError(Session session, ApiError apiError) {
 		ApiErrorRoot apiErrorRoot = new ApiErrorRoot();
 		apiErrorRoot.setApiError(apiError);
 
@@ -43,7 +50,7 @@ interface ApiWebSocket {
 		}
 	}
 
-	default void marshall(Writer writer, Object object) throws IOException {
+	protected static void marshall(Writer writer, Object object) throws IOException {
 		Marshaller marshaller = createMarshaller(object.getClass());
 
 		try {
@@ -53,7 +60,7 @@ interface ApiWebSocket {
 		}
 	}
 
-	default void marshall(Writer writer, Collection<?> collection) throws IOException {
+	protected static void marshall(Writer writer, Collection<?> collection) throws IOException {
 		// If collection is empty then we're returning "[]" anyway
 		if (collection.isEmpty()) {
 			writer.append("[]");
@@ -92,4 +99,22 @@ interface ApiWebSocket {
 		}
 	}
 
+	public void onWebSocketConnect(Session session) {
+		synchronized (SESSIONS_BY_CLASS) {
+			SESSIONS_BY_CLASS.computeIfAbsent(this.getClass(), clazz -> new ArrayList<>()).add(session);
+		}
+	}
+
+	public void onWebSocketClose(Session session, int statusCode, String reason) {
+		synchronized (SESSIONS_BY_CLASS) {
+			SESSIONS_BY_CLASS.get(this.getClass()).remove(session);
+		}
+	}
+
+	protected List<Session> getSessions() {
+		synchronized (SESSIONS_BY_CLASS) {
+			return new ArrayList<>(SESSIONS_BY_CLASS.get(this.getClass()));
+		}
+	}
+
 }

src/main/java/org/qortal/api/websocket/BlocksWebSocket.java

@@ -2,17 +2,23 @@ package org.qortal.api.websocket;
 
 import java.io.IOException;
 import java.io.StringWriter;
+import java.util.List;
 
 import org.eclipse.jetty.websocket.api.Session;
+import org.eclipse.jetty.websocket.api.WebSocketException;
 import org.eclipse.jetty.websocket.api.annotations.OnWebSocketClose;
 import org.eclipse.jetty.websocket.api.annotations.OnWebSocketConnect;
+import org.eclipse.jetty.websocket.api.annotations.OnWebSocketError;
 import org.eclipse.jetty.websocket.api.annotations.OnWebSocketMessage;
 import org.eclipse.jetty.websocket.api.annotations.WebSocket;
-import org.eclipse.jetty.websocket.servlet.WebSocketServlet;
 import org.eclipse.jetty.websocket.servlet.WebSocketServletFactory;
 import org.qortal.api.ApiError;
-import org.qortal.controller.BlockNotifier;
+import org.qortal.controller.Controller;
 import org.qortal.data.block.BlockData;
+import org.qortal.data.block.BlockSummaryData;
+import org.qortal.event.Event;
+import org.qortal.event.EventBus;
+import org.qortal.event.Listener;
 import org.qortal.repository.DataException;
 import org.qortal.repository.Repository;
 import org.qortal.repository.RepositoryManager;
@@ -20,22 +26,42 @@ import org.qortal.utils.Base58;
 
 @WebSocket
 @SuppressWarnings("serial")
-public class BlocksWebSocket extends WebSocketServlet implements ApiWebSocket {
+public class BlocksWebSocket extends ApiWebSocket implements Listener {
 
 	@Override
 	public void configure(WebSocketServletFactory factory) {
 		factory.register(BlocksWebSocket.class);
+
+		EventBus.INSTANCE.addListener(this::listen);
+	}
+
+	@Override
+	public void listen(Event event) {
+		if (!(event instanceof Controller.NewBlockEvent))
+			return;
+
+		BlockData blockData = ((Controller.NewBlockEvent) event).getBlockData();
+		BlockSummaryData blockSummary = new BlockSummaryData(blockData);
+
+		for (Session session : getSessions())
+			sendBlockSummary(session, blockSummary);
 	}
 
 	@OnWebSocketConnect
+	@Override
 	public void onWebSocketConnect(Session session) {
-		BlockNotifier.Listener listener = blockData -> onNotify(session, blockData);
-		BlockNotifier.getInstance().register(session, listener);
+		super.onWebSocketConnect(session);
 	}
 
 	@OnWebSocketClose
+	@Override
 	public void onWebSocketClose(Session session, int statusCode, String reason) {
-		BlockNotifier.getInstance().deregister(session);
+		super.onWebSocketClose(session, statusCode, reason);
+	}
+
+	@OnWebSocketError
+	public void onWebSocketError(Session session, Throwable throwable) {
+		/* We ignore errors for now, but method here to silence log spam */
 	}
 
 	@OnWebSocketMessage
@@ -53,13 +79,19 @@ public class BlocksWebSocket extends WebSocketServlet implements ApiWebSocket {
 			}
 
 			try (final Repository repository = RepositoryManager.getRepository()) {
-				BlockData blockData = repository.getBlockRepository().fromSignature(signature);
-				if (blockData == null) {
+				int height = repository.getBlockRepository().getHeightFromSignature(signature);
+				if (height == 0) {
 					sendError(session, ApiError.BLOCK_UNKNOWN);
 					return;
 				}
 
-				onNotify(session, blockData);
+				List<BlockSummaryData> blockSummaries = repository.getBlockRepository().getBlockSummaries(height, height);
+				if (blockSummaries == null || blockSummaries.isEmpty()) {
+					sendError(session, ApiError.BLOCK_UNKNOWN);
+					return;
+				}
+
+				sendBlockSummary(session, blockSummaries.get(0));
 			} catch (DataException e) {
 				sendError(session, ApiError.REPOSITORY_ISSUE);
 			}
@@ -82,26 +114,26 @@ public class BlocksWebSocket extends WebSocketServlet implements ApiWebSocket {
 		}
 
 		try (final Repository repository = RepositoryManager.getRepository()) {
-			BlockData blockData = repository.getBlockRepository().fromHeight(height);
-			if (blockData == null) {
+			List<BlockSummaryData> blockSummaries = repository.getBlockRepository().getBlockSummaries(height, height);
+			if (blockSummaries == null || blockSummaries.isEmpty()) {
 				sendError(session, ApiError.BLOCK_UNKNOWN);
 				return;
 			}
 
-			onNotify(session, blockData);
+			sendBlockSummary(session, blockSummaries.get(0));
 		} catch (DataException e) {
 			sendError(session, ApiError.REPOSITORY_ISSUE);
 		}
 	}
 
-	private void onNotify(Session session, BlockData blockData) {
+	private void sendBlockSummary(Session session, BlockSummaryData blockSummary) {
 		StringWriter stringWriter = new StringWriter();
 
 		try {
-			this.marshall(stringWriter, blockData);
+			marshall(stringWriter, blockSummary);
 
-			session.getRemote().sendString(stringWriter.toString());
-		} catch (IOException e) {
+			session.getRemote().sendStringByFuture(stringWriter.toString());
+		} catch (IOException | WebSocketException e) {
 			// No output this time
 		}
 	}

src/main/java/org/qortal/api/websocket/ChatMessagesWebSocket.java

@@ -8,11 +8,12 @@ import java.util.List;
 import java.util.Map;
 
 import org.eclipse.jetty.websocket.api.Session;
+import org.eclipse.jetty.websocket.api.WebSocketException;
 import org.eclipse.jetty.websocket.api.annotations.OnWebSocketClose;
 import org.eclipse.jetty.websocket.api.annotations.OnWebSocketConnect;
+import org.eclipse.jetty.websocket.api.annotations.OnWebSocketError;
 import org.eclipse.jetty.websocket.api.annotations.OnWebSocketMessage;
 import org.eclipse.jetty.websocket.api.annotations.WebSocket;
-import org.eclipse.jetty.websocket.servlet.WebSocketServlet;
 import org.eclipse.jetty.websocket.servlet.WebSocketServletFactory;
 import org.qortal.controller.ChatNotifier;
 import org.qortal.data.chat.ChatMessage;
@@ -23,7 +24,7 @@ import org.qortal.repository.RepositoryManager;
 
 @WebSocket
 @SuppressWarnings("serial")
-public class ChatMessagesWebSocket extends WebSocketServlet implements ApiWebSocket {
+public class ChatMessagesWebSocket extends ApiWebSocket {
 
 	@Override
 	public void configure(WebSocketServletFactory factory) {
@@ -31,6 +32,7 @@ public class ChatMessagesWebSocket extends WebSocketServlet implements ApiWebSoc
 	}
 
 	@OnWebSocketConnect
+	@Override
 	public void onWebSocketConnect(Session session) {
 		Map<String, List<String>> queryParams = session.getUpgradeRequest().getParameterMap();
 
@@ -85,12 +87,19 @@ public class ChatMessagesWebSocket extends WebSocketServlet implements ApiWebSoc
 	}
 
 	@OnWebSocketClose
+	@Override
 	public void onWebSocketClose(Session session, int statusCode, String reason) {
 		ChatNotifier.getInstance().deregister(session);
 	}
 
+	@OnWebSocketError
+	public void onWebSocketError(Session session, Throwable throwable) {
+		/* ignored */
+	}
+
 	@OnWebSocketMessage
 	public void onWebSocketMessage(Session session, String message) {
+		/* ignored */
 	}
 
 	private void onNotify(Session session, ChatTransactionData chatTransactionData, int txGroupId) {
@@ -123,10 +132,10 @@ public class ChatMessagesWebSocket extends WebSocketServlet implements ApiWebSoc
 		StringWriter stringWriter = new StringWriter();
 
 		try {
-			this.marshall(stringWriter, chatMessages);
+			marshall(stringWriter, chatMessages);
 
-			session.getRemote().sendString(stringWriter.toString());
-		} catch (IOException e) {
+			session.getRemote().sendStringByFuture(stringWriter.toString());
+		} catch (IOException | WebSocketException e) {
 			// No output this time?
 		}
 	}

src/main/java/org/qortal/api/websocket/TradeBotWebSocket.java

@@ -0,0 +1,127 @@
+package org.qortal.api.websocket;
+
+import java.io.IOException;
+import java.io.StringWriter;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.stream.Collectors;
+
+import org.eclipse.jetty.websocket.api.Session;
+import org.eclipse.jetty.websocket.api.annotations.OnWebSocketClose;
+import org.eclipse.jetty.websocket.api.annotations.OnWebSocketConnect;
+import org.eclipse.jetty.websocket.api.annotations.OnWebSocketError;
+import org.eclipse.jetty.websocket.api.annotations.OnWebSocketMessage;
+import org.eclipse.jetty.websocket.api.annotations.WebSocket;
+import org.eclipse.jetty.websocket.servlet.WebSocketServletFactory;
+import org.qortal.controller.TradeBot;
+import org.qortal.data.crosschain.TradeBotData;
+import org.qortal.event.Event;
+import org.qortal.event.EventBus;
+import org.qortal.event.Listener;
+import org.qortal.repository.DataException;
+import org.qortal.repository.Repository;
+import org.qortal.repository.RepositoryManager;
+import org.qortal.utils.Base58;
+
+@WebSocket
+@SuppressWarnings("serial")
+public class TradeBotWebSocket extends ApiWebSocket implements Listener {
+
+	/** Cache of trade-bot entry states, keyed by trade-bot entry's "trade private key" (base58) */
+	private static final Map<String, TradeBotData.State> PREVIOUS_STATES = new HashMap<>();
+
+	@Override
+	public void configure(WebSocketServletFactory factory) {
+		factory.register(TradeBotWebSocket.class);
+
+		try (final Repository repository = RepositoryManager.getRepository()) {
+			List<TradeBotData> tradeBotEntries = repository.getCrossChainRepository().getAllTradeBotData();
+			if (tradeBotEntries == null)
+				// How do we properly fail here?
+				return;
+
+			PREVIOUS_STATES.putAll(tradeBotEntries.stream().collect(Collectors.toMap(entry -> Base58.encode(entry.getTradePrivateKey()), TradeBotData::getState)));
+		} catch (DataException e) {
+			// No output this time
+		}
+
+		EventBus.INSTANCE.addListener(this::listen);
+	}
+
+	@Override
+	public void listen(Event event) {
+		if (!(event instanceof TradeBot.StateChangeEvent))
+			return;
+
+		TradeBotData tradeBotData = ((TradeBot.StateChangeEvent) event).getTradeBotData();
+		String tradePrivateKey58 = Base58.encode(tradeBotData.getTradePrivateKey());
+
+		synchronized (PREVIOUS_STATES) {
+			if (PREVIOUS_STATES.get(tradePrivateKey58) == tradeBotData.getState())
+				// Not changed
+				return;
+
+			PREVIOUS_STATES.put(tradePrivateKey58, tradeBotData.getState());
+		}
+
+		List<TradeBotData> tradeBotEntries = Collections.singletonList(tradeBotData);
+		for (Session session : getSessions())
+			sendEntries(session, tradeBotEntries);
+	}
+
+	@OnWebSocketConnect
+	@Override
+	public void onWebSocketConnect(Session session) {
+		// Send all known trade-bot entries
+		try (final Repository repository = RepositoryManager.getRepository()) {
+			List<TradeBotData> tradeBotEntries = repository.getCrossChainRepository().getAllTradeBotData();
+			if (tradeBotEntries == null) {
+				session.close(4001, "repository issue fetching trade-bot entries");
+				return;
+			}
+
+			if (!sendEntries(session, tradeBotEntries)) {
+				session.close(4002, "websocket issue");
+				return;
+			}
+		} catch (DataException e) {
+			// No output this time
+		}
+
+		super.onWebSocketConnect(session);
+	}
+
+	@OnWebSocketClose
+	@Override
+	public void onWebSocketClose(Session session, int statusCode, String reason) {
+		super.onWebSocketClose(session, statusCode, reason);
+	}
+
+	@OnWebSocketError
+	public void onWebSocketError(Session session, Throwable throwable) {
+		/* ignored */
+	}
+
+	@OnWebSocketMessage
+	public void onWebSocketMessage(Session session, String message) {
+		/* ignored */
+	}
+
+	private boolean sendEntries(Session session, List<TradeBotData> tradeBotEntries) {
+		try {
+			StringWriter stringWriter = new StringWriter();
+			marshall(stringWriter, tradeBotEntries);
+
+			String output = stringWriter.toString();
+			session.getRemote().sendStringByFuture(output);
+		} catch (IOException e) {
+			// No output this time?
+			return false;
+		}
+
+		return true;
+	}
+
+}

src/main/java/org/qortal/api/websocket/TradeOffersWebSocket.java

@@ -0,0 +1,275 @@
+package org.qortal.api.websocket;
+
+import java.io.IOException;
+import java.io.StringWriter;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.function.Predicate;
+import java.util.stream.Collectors;
+
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
+import org.eclipse.jetty.websocket.api.Session;
+import org.eclipse.jetty.websocket.api.annotations.OnWebSocketClose;
+import org.eclipse.jetty.websocket.api.annotations.OnWebSocketConnect;
+import org.eclipse.jetty.websocket.api.annotations.OnWebSocketError;
+import org.eclipse.jetty.websocket.api.annotations.OnWebSocketMessage;
+import org.eclipse.jetty.websocket.api.annotations.WebSocket;
+import org.eclipse.jetty.websocket.servlet.WebSocketServletFactory;
+import org.qortal.api.model.CrossChainOfferSummary;
+import org.qortal.controller.Controller;
+import org.qortal.crosschain.BTCACCT;
+import org.qortal.data.at.ATStateData;
+import org.qortal.data.block.BlockData;
+import org.qortal.data.crosschain.CrossChainTradeData;
+import org.qortal.event.Event;
+import org.qortal.event.EventBus;
+import org.qortal.event.Listener;
+import org.qortal.repository.DataException;
+import org.qortal.repository.Repository;
+import org.qortal.repository.RepositoryManager;
+import org.qortal.utils.NTP;
+
+@WebSocket
+@SuppressWarnings("serial")
+public class TradeOffersWebSocket extends ApiWebSocket implements Listener {
+
+	private static final Logger LOGGER = LogManager.getLogger(TradeOffersWebSocket.class);
+
+	private static final Map<String, BTCACCT.Mode> previousAtModes = new HashMap<>();
+
+	// OFFERING
+	private static final Map<String, CrossChainOfferSummary> currentSummaries = new HashMap<>();
+	// REDEEMED/REFUNDED/CANCELLED
+	private static final Map<String, CrossChainOfferSummary> historicSummaries = new HashMap<>();
+
+	private static final Predicate<CrossChainOfferSummary> isHistoric = offerSummary
+			-> offerSummary.getMode() == BTCACCT.Mode.REDEEMED
+			|| offerSummary.getMode() == BTCACCT.Mode.REFUNDED
+			|| offerSummary.getMode() == BTCACCT.Mode.CANCELLED;
+
+
+	@Override
+	public void configure(WebSocketServletFactory factory) {
+		factory.register(TradeOffersWebSocket.class);
+
+		try (final Repository repository = RepositoryManager.getRepository()) {
+			populateCurrentSummaries(repository);
+
+			populateHistoricSummaries(repository);
+		} catch (DataException e) {
+			// How to fail properly?
+			return;
+		}
+
+		EventBus.INSTANCE.addListener(this::listen);
+	}
+
+	@Override
+	public void listen(Event event) {
+		if (!(event instanceof Controller.NewBlockEvent))
+			return;
+
+		BlockData blockData = ((Controller.NewBlockEvent) event).getBlockData();
+
+		// Process any new info
+		List<CrossChainOfferSummary> crossChainOfferSummaries;
+
+		try (final Repository repository = RepositoryManager.getRepository()) {
+			// Find any new/changed trade ATs since this block
+			final Boolean isFinished = null;
+			final Integer dataByteOffset = null;
+			final Long expectedValue = null;
+			final Integer minimumFinalHeight = blockData.getHeight();
+
+			List<ATStateData> atStates = repository.getATRepository().getMatchingFinalATStates(BTCACCT.CODE_BYTES_HASH,
+					isFinished, dataByteOffset, expectedValue, minimumFinalHeight,
+					null, null, null);
+
+			if (atStates == null)
+				return;
+
+			crossChainOfferSummaries = produceSummaries(repository, atStates, blockData.getTimestamp());
+		} catch (DataException e) {
+			// No output this time
+			return;
+		}
+
+		synchronized (previousAtModes) {
+			// Remove any entries unchanged from last time
+			crossChainOfferSummaries.removeIf(offerSummary -> previousAtModes.get(offerSummary.getQortalAtAddress()) == offerSummary.getMode());
+
+			// Don't send anything if no results
+			if (crossChainOfferSummaries.isEmpty())
+				return;
+
+			// Update
+			for (CrossChainOfferSummary offerSummary : crossChainOfferSummaries) {
+				previousAtModes.put(offerSummary.qortalAtAddress, offerSummary.getMode());
+				LOGGER.trace(() -> String.format("Block height: %d, AT: %s, mode: %s", blockData.getHeight(), offerSummary.qortalAtAddress, offerSummary.getMode().name()));
+
+				switch (offerSummary.getMode()) {
+					case OFFERING:
+						currentSummaries.put(offerSummary.qortalAtAddress, offerSummary);
+						historicSummaries.remove(offerSummary.qortalAtAddress);
+						break;
+
+					case REDEEMED:
+					case REFUNDED:
+					case CANCELLED:
+						currentSummaries.remove(offerSummary.qortalAtAddress);
+						historicSummaries.put(offerSummary.qortalAtAddress, offerSummary);
+						break;
+
+					case TRADING:
+						currentSummaries.remove(offerSummary.qortalAtAddress);
+						historicSummaries.remove(offerSummary.qortalAtAddress);
+						break;
+				}
+			}
+
+			// Remove any historic offers that are over 24 hours old
+			final long tooOldTimestamp = NTP.getTime() - 24 * 60 * 60 * 1000L;
+			historicSummaries.values().removeIf(historicSummary -> historicSummary.getTimestamp() < tooOldTimestamp);
+		}
+
+		// Notify sessions
+		for (Session session : getSessions())
+			sendOfferSummaries(session, crossChainOfferSummaries);
+	}
+
+	@OnWebSocketConnect
+	@Override
+	public void onWebSocketConnect(Session session) {
+		Map<String, List<String>> queryParams = session.getUpgradeRequest().getParameterMap();
+		final boolean includeHistoric = queryParams.get("includeHistoric") != null;
+
+		List<CrossChainOfferSummary> crossChainOfferSummaries = new ArrayList<>();
+
+		synchronized (previousAtModes) {
+			crossChainOfferSummaries.addAll(currentSummaries.values());
+
+			if (includeHistoric)
+				crossChainOfferSummaries.addAll(historicSummaries.values());
+		}
+
+		if (!sendOfferSummaries(session, crossChainOfferSummaries)) {
+			session.close(4002, "websocket issue");
+			return;
+		}
+
+		super.onWebSocketConnect(session);
+	}
+
+	@OnWebSocketClose
+	@Override
+	public void onWebSocketClose(Session session, int statusCode, String reason) {
+		super.onWebSocketClose(session, statusCode, reason);
+	}
+
+	@OnWebSocketError
+	public void onWebSocketError(Session session, Throwable throwable) {
+		/* ignored */
+	}
+
+	@OnWebSocketMessage
+	public void onWebSocketMessage(Session session, String message) {
+		/* ignored */
+	}
+
+	private boolean sendOfferSummaries(Session session, List<CrossChainOfferSummary> crossChainOfferSummaries) {
+		try {
+			StringWriter stringWriter = new StringWriter();
+			marshall(stringWriter, crossChainOfferSummaries);
+
+			String output = stringWriter.toString();
+			session.getRemote().sendStringByFuture(output);
+		} catch (IOException e) {
+			// No output this time?
+			return false;
+		}
+
+		return true;
+	}
+
+	private static void populateCurrentSummaries(Repository repository) throws DataException {
+		// We want ALL OFFERING trades
+		Boolean isFinished = Boolean.FALSE;
+		Integer dataByteOffset = BTCACCT.MODE_BYTE_OFFSET;
+		Long expectedValue = (long) BTCACCT.Mode.OFFERING.value;
+		Integer minimumFinalHeight = null;
+
+		List<ATStateData> initialAtStates = repository.getATRepository().getMatchingFinalATStates(BTCACCT.CODE_BYTES_HASH,
+				isFinished, dataByteOffset, expectedValue, minimumFinalHeight,
+				null, null, null);
+
+		if (initialAtStates == null)
+			throw new DataException("Couldn't fetch current trades from repository");
+
+		// Save initial AT modes
+		previousAtModes.putAll(initialAtStates.stream().collect(Collectors.toMap(ATStateData::getATAddress, atState -> BTCACCT.Mode.OFFERING)));
+
+		// Convert to offer summaries
+		currentSummaries.putAll(produceSummaries(repository, initialAtStates, null).stream().collect(Collectors.toMap(CrossChainOfferSummary::getQortalAtAddress, offerSummary -> offerSummary)));
+	}
+
+	private static void populateHistoricSummaries(Repository repository) throws DataException {
+		// We want REDEEMED/REFUNDED/CANCELLED trades over the last 24 hours
+		long timestamp = System.currentTimeMillis() - 24 * 60 * 60 * 1000L;
+		int minimumFinalHeight = repository.getBlockRepository().getHeightFromTimestamp(timestamp);
+
+		if (minimumFinalHeight == 0)
+			throw new DataException("Couldn't fetch block timestamp from repository");
+
+		Boolean isFinished = Boolean.TRUE;
+		Integer dataByteOffset = null;
+		Long expectedValue = null;
+		++minimumFinalHeight; // because height is just *before* timestamp
+
+		List<ATStateData> historicAtStates = repository.getATRepository().getMatchingFinalATStates(BTCACCT.CODE_BYTES_HASH,
+				isFinished, dataByteOffset, expectedValue, minimumFinalHeight,
+				null, null, null);
+
+		if (historicAtStates == null)
+			throw new DataException("Couldn't fetch historic trades from repository");
+
+		for (ATStateData historicAtState : historicAtStates) {
+			CrossChainOfferSummary historicOfferSummary = produceSummary(repository, historicAtState, null);
+
+			if (!isHistoric.test(historicOfferSummary))
+				continue;
+
+			// Add summary to initial burst
+			historicSummaries.put(historicOfferSummary.getQortalAtAddress(), historicOfferSummary);
+
+			// Save initial AT mode
+			previousAtModes.put(historicOfferSummary.getQortalAtAddress(), historicOfferSummary.getMode());
+		}
+	}
+
+	private static CrossChainOfferSummary produceSummary(Repository repository, ATStateData atState, Long timestamp) throws DataException {
+		CrossChainTradeData crossChainTradeData = BTCACCT.populateTradeData(repository, atState);
+
+		long atStateTimestamp;
+
+		if (crossChainTradeData.mode == BTCACCT.Mode.OFFERING)
+			// We want when trade was created, not when it was last updated
+			atStateTimestamp = crossChainTradeData.creationTimestamp;
+		else
+			atStateTimestamp = timestamp != null ? timestamp : repository.getBlockRepository().getTimestampFromHeight(atState.getHeight());
+
+		return new CrossChainOfferSummary(crossChainTradeData, atStateTimestamp);
+	}
+
+	private static List<CrossChainOfferSummary> produceSummaries(Repository repository, List<ATStateData> atStates, Long timestamp) throws DataException {
+		List<CrossChainOfferSummary> offerSummaries = new ArrayList<>();
+
+		for (ATStateData atState : atStates)
+			offerSummaries.add(produceSummary(repository, atState, timestamp));
+
+		return offerSummaries;
+	}
+
+}

src/main/java/org/qortal/at/AT.java

@@ -51,16 +51,17 @@ public class AT {
 
 		MachineState machineState = new MachineState(api, loggerFactory, deployATTransactionData.getCreationBytes());
 
-		byte[] codeHash = Crypto.digest(machineState.getCodeBytes());
+		byte[] codeBytes = machineState.getCodeBytes();
+		byte[] codeHash = Crypto.digest(codeBytes);
 
-		this.atData = new ATData(atAddress, creatorPublicKey, creation, machineState.version, assetId, machineState.getCodeBytes(), codeHash,
+		this.atData = new ATData(atAddress, creatorPublicKey, creation, machineState.version, assetId, codeBytes, codeHash,
 				machineState.isSleeping(), machineState.getSleepUntilHeight(), machineState.isFinished(), machineState.hadFatalError(),
 				machineState.isFrozen(), machineState.getFrozenBalance());
 
 		byte[] stateData = machineState.toBytes();
 		byte[] stateHash = Crypto.digest(stateData);
 
-		this.atStateData = new ATStateData(atAddress, height, creation, stateData, stateHash, 0L, true);
+		this.atStateData = new ATStateData(atAddress, height, stateData, stateHash, 0L, true);
 	}
 
 	// Getters / setters
@@ -106,23 +107,18 @@ public class AT {
 			throw new DataException(String.format("Uncaught exception while running AT '%s'", atAddress), e);
 		}
 
-		long creation = this.atData.getCreation();
 		byte[] stateData = state.toBytes();
 		byte[] stateHash = Crypto.digest(stateData);
 		long atFees = api.calcFinalFees(state);
 
-		this.atStateData = new ATStateData(atAddress, blockHeight, creation, stateData, stateHash, atFees, false);
+		this.atStateData = new ATStateData(atAddress, blockHeight, stateData, stateHash, atFees, false);
 
 		return api.getTransactions();
 	}
 
 	public void update(int blockHeight, long blockTimestamp) throws DataException {
-		// [Re]create AT machine state using AT state data or from scratch as applicable
-		QortalATAPI api = new QortalATAPI(repository, this.atData, blockTimestamp);
-		QortalAtLoggerFactory loggerFactory = QortalAtLoggerFactory.getInstance();
-
-		byte[] codeBytes = this.atData.getCodeBytes();
-		MachineState state = MachineState.fromBytes(api, loggerFactory, this.atStateData.getStateData(), codeBytes);
+		// Extract minimal/flags-only AT machine state using AT state data
+		MachineState state = MachineState.flagsOnlyfromBytes(this.atStateData.getStateData());
 
 		// Save latest AT state data
 		this.repository.getATRepository().save(this.atStateData);
@@ -151,12 +147,8 @@ public class AT {
 		if (previousStateData == null)
 			throw new DataException("Can't find previous AT state data for " + atAddress);
 
-		// [Re]create AT machine state using AT state data or from scratch as applicable
-		QortalATAPI api = new QortalATAPI(repository, this.atData, blockTimestamp);
-		QortalAtLoggerFactory loggerFactory = QortalAtLoggerFactory.getInstance();
-
-		byte[] codeBytes = this.atData.getCodeBytes();
-		MachineState state = MachineState.fromBytes(api, loggerFactory, previousStateData.getStateData(), codeBytes);
+		// Extract minimal/flags-only AT machine state using AT state data
+		MachineState state = MachineState.flagsOnlyfromBytes(previousStateData.getStateData());
 
 		// Update AT info in repository
 		this.atData.setIsSleeping(state.isSleeping());

src/main/java/org/qortal/at/QortalATAPI.java

@@ -17,7 +17,6 @@ import org.qortal.account.Account;
 import org.qortal.account.NullAccount;
 import org.qortal.account.PublicKeyAccount;
 import org.qortal.asset.Asset;
-import org.qortal.block.Block;
 import org.qortal.block.BlockChain;
 import org.qortal.block.BlockChain.CiyamAtSettings;
 import org.qortal.crypto.Crypto;
@@ -30,13 +29,13 @@ import org.qortal.data.transaction.MessageTransactionData;
 import org.qortal.data.transaction.PaymentTransactionData;
 import org.qortal.data.transaction.TransactionData;
 import org.qortal.group.Group;
-import org.qortal.repository.BlockRepository;
+import org.qortal.repository.ATRepository;
 import org.qortal.repository.DataException;
 import org.qortal.repository.Repository;
 import org.qortal.transaction.AtTransaction;
-import org.qortal.transaction.Transaction;
 import org.qortal.transaction.Transaction.TransactionType;
 import org.qortal.utils.Base58;
+import org.qortal.utils.BitTwiddling;
 
 import com.google.common.primitives.Bytes;
 
@@ -133,9 +132,9 @@ public class QortalATAPI extends API {
 
 			byte[] signature = blockSummaries.get(0).getSignature();
 			// Save some of minter's signature and transactions signature, so middle 24 bytes of the full 128 byte signature.
-			this.setA2(state, fromBytes(signature, 52));
-			this.setA3(state, fromBytes(signature, 60));
-			this.setA4(state, fromBytes(signature, 68));
+			this.setA2(state, BitTwiddling.longFromBEBytes(signature, 52));
+			this.setA3(state, BitTwiddling.longFromBEBytes(signature, 60));
+			this.setA4(state, BitTwiddling.longFromBEBytes(signature, 68));
 		} catch (DataException e) {
 			throw new RuntimeException("AT API unable to fetch previous block?", e);
 		}
@@ -149,59 +148,27 @@ public class QortalATAPI extends API {
 		int height = timestamp.blockHeight;
 		int sequence = timestamp.transactionSequence + 1;
 
-		BlockRepository blockRepository = this.getRepository().getBlockRepository();
-
+		ATRepository.NextTransactionInfo nextTransactionInfo;
 		try {
-			int currentHeight = blockRepository.getBlockchainHeight();
-			List<Transaction> blockTransactions = null;
-
-			while (height <= currentHeight) {
-				if (blockTransactions == null) {
-					BlockData blockData = blockRepository.fromHeight(height);
-
-					if (blockData == null)
-						throw new DataException("Unable to fetch block " + height + " from repository?");
-
-					Block block = new Block(this.getRepository(), blockData);
-
-					blockTransactions = block.getTransactions();
-				}
-
-				// No more transactions in this block? Try next block
-				if (sequence >= blockTransactions.size()) {
-					++height;
-					sequence = 0;
-					blockTransactions = null;
-					continue;
-				}
-
-				Transaction transaction = blockTransactions.get(sequence);
-
-				// Transaction needs to be sent to specified recipient
-				List<String> recipientAddresses = transaction.getRecipientAddresses();
-				if (recipientAddresses.contains(atAddress)) {
-					// Found a transaction
-
-					this.setA1(state, new Timestamp(height, timestamp.blockchainId, sequence).longValue());
-
-					// Copy transaction's partial signature into the other three A fields for future verification that it's the same transaction
-					byte[] signature = transaction.getTransactionData().getSignature();
-					this.setA2(state, fromBytes(signature, 8));
-					this.setA3(state, fromBytes(signature, 16));
-					this.setA4(state, fromBytes(signature, 24));
-
-					return;
-				}
-
-				// Transaction wasn't for us - keep going
-				++sequence;
-			}
-
-			// No more transactions - zero A and exit
-			this.zeroA(state);
+			nextTransactionInfo = this.getRepository().getATRepository().findNextTransaction(atAddress, height, sequence);
 		} catch (DataException e) {
 			throw new RuntimeException("AT API unable to fetch next transaction?", e);
 		}
+
+		if (nextTransactionInfo == null) {
+			// No more transactions for AT at this time - zero A and exit
+			this.zeroA(state);
+			return;
+		}
+
+		// Found a transaction
+
+		this.setA1(state, new Timestamp(nextTransactionInfo.height, timestamp.blockchainId, nextTransactionInfo.sequence).longValue());
+
+		// Copy transaction's partial signature into the other three A fields for future verification that it's the same transaction
+		this.setA2(state, BitTwiddling.longFromBEBytes(nextTransactionInfo.signature, 8));
+		this.setA3(state, BitTwiddling.longFromBEBytes(nextTransactionInfo.signature, 16));
+		this.setA4(state, BitTwiddling.longFromBEBytes(nextTransactionInfo.signature, 24));
 	}
 
 	@Override
@@ -282,7 +249,7 @@ public class QortalATAPI extends API {
 
 				byte[] hash = Crypto.digest(input);
 
-				return fromBytes(hash, 0);
+				return BitTwiddling.longFromBEBytes(hash, 0);
 			} catch (DataException e) {
 				throw new RuntimeException("AT API unable to fetch latest block from repository?", e);
 			}
@@ -296,30 +263,14 @@ public class QortalATAPI extends API {
 
 		TransactionData transactionData = this.getTransactionFromA(state);
 
-		byte[] messageData = null;
-
-		switch (transactionData.getType()) {
-			case MESSAGE:
-				messageData = ((MessageTransactionData) transactionData).getData();
-				break;
-
-			case AT:
-				messageData = ((ATTransactionData) transactionData).getMessage();
-				break;
-
-			default:
-				return;
-		}
-
-		// Check data length is appropriate, i.e. not larger than B
-		if (messageData.length > 4 * 8)
-			return;
+		byte[] messageData = this.getMessageFromTransaction(transactionData);
 
 		// Pad messageData to fit B
-		byte[] paddedMessageData = Bytes.ensureCapacity(messageData, 4 * 8, 0);
+		if (messageData.length < 4 * 8)
+			messageData = Bytes.ensureCapacity(messageData, 4 * 8, 0);
 
 		// Endian must be correct here so that (for example) a SHA256 message can be compared to one generated locally
-		this.setB(state, paddedMessageData);
+		this.setB(state, messageData);
 	}
 
 	@Override
@@ -457,12 +408,6 @@ public class QortalATAPI extends API {
 
 	// Utility methods
 
-	/** Convert part of little-endian byte[] to long */
-	/* package */ static long fromBytes(byte[] bytes, int start) {
-		return (bytes[start] & 0xffL) | (bytes[start + 1] & 0xffL) << 8 | (bytes[start + 2] & 0xffL) << 16 | (bytes[start + 3] & 0xffL) << 24
-				| (bytes[start + 4] & 0xffL) << 32 | (bytes[start + 5] & 0xffL) << 40 | (bytes[start + 6] & 0xffL) << 48 | (bytes[start + 7] & 0xffL) << 56;
-	}
-
 	/** Returns partial transaction signature, used to verify we're operating on the same transaction and not naively using block height & sequence. */
 	public static byte[] partialSignature(byte[] fullSignature) {
 		return Arrays.copyOfRange(fullSignature, 8, 32);
@@ -473,7 +418,7 @@ public class QortalATAPI extends API {
 		// Compare end of transaction's signature against A2 thru A4
 		byte[] sig = transactionData.getSignature();
 
-		if (this.getA2(state) != fromBytes(sig, 8) || this.getA3(state) != fromBytes(sig, 16) || this.getA4(state) != fromBytes(sig, 24))
+		if (this.getA2(state) != BitTwiddling.longFromBEBytes(sig, 8) || this.getA3(state) != BitTwiddling.longFromBEBytes(sig, 16) || this.getA4(state) != BitTwiddling.longFromBEBytes(sig, 24))
 			throw new IllegalStateException("Transaction signature in A no longer matches signature from repository");
 	}
 
@@ -497,6 +442,20 @@ public class QortalATAPI extends API {
 		}
 	}
 
+	/** Returns message data from transaction. */
+	/*package*/ byte[] getMessageFromTransaction(TransactionData transactionData) {
+		switch (transactionData.getType()) {
+			case MESSAGE:
+				return ((MessageTransactionData) transactionData).getData();
+
+			case AT:
+				return ((ATTransactionData) transactionData).getMessage();
+
+			default:
+				return null;
+		}
+	}
+
 	/** Returns AT's account */
 	/* package */ Account getATAccount() {
 		return new Account(this.repository, this.atData.getATAddress());
@@ -563,4 +522,8 @@ public class QortalATAPI extends API {
 		super.setB(state, bBytes);
 	}
 
+	protected void zeroB(MachineState state) {
+		super.zeroB(state);
+	}
+
 }

src/main/java/org/qortal/at/QortalAtLogger.java

@@ -691,6 +691,11 @@ public final class QortalAtLogger extends ExtendedLoggerWrapper implements org.c
         logger.logIfEnabled(FQCN, ERROR, null, msgSupplier, (Throwable) null);
     }
 
+    /** Java 8 version */
+    public void error(final java.util.function.Supplier<String> msgSupplier) {
+        logger.logIfEnabled(FQCN, ERROR, null, () -> msgSupplier.get(), (Throwable) null);
+    }
+
     /**
      * Logs a message (only to be constructed if the logging level is the {@code ERROR}
      * level) including the stack trace of the {@link Throwable} <code>t</code> passed as parameter.
@@ -1375,6 +1380,11 @@ public final class QortalAtLogger extends ExtendedLoggerWrapper implements org.c
         logger.logIfEnabled(FQCN, DEBUG, null, msgSupplier, (Throwable) null);
     }
 
+    /** Java 8 version */
+    public void debug(final java.util.function.Supplier<String> msgSupplier) {
+        logger.logIfEnabled(FQCN, DEBUG, null, () -> msgSupplier.get(), (Throwable) null);
+    }
+
     /**
      * Logs a message (only to be constructed if the logging level is the {@code DEBUG}
      * level) including the stack trace of the {@link Throwable} <code>t</code> passed as parameter.
@@ -2059,6 +2069,11 @@ public final class QortalAtLogger extends ExtendedLoggerWrapper implements org.c
         logger.logIfEnabled(FQCN, ECHO, null, msgSupplier, (Throwable) null);
     }
 
+    /** Java 8 version */
+    public void echo(final java.util.function.Supplier<String> msgSupplier) {
+        logger.logIfEnabled(FQCN, ECHO, null, () -> msgSupplier.get(), (Throwable) null);
+    }
+
     /**
      * Logs a message (only to be constructed if the logging level is the {@code ECHO}
      * level) including the stack trace of the {@link Throwable} <code>t</code> passed as parameter.

src/main/java/org/qortal/at/QortalFunctionCode.java

@@ -12,6 +12,7 @@ import org.ciyam.at.IllegalFunctionCodeException;
 import org.ciyam.at.MachineState;
 import org.qortal.crosschain.BTC;
 import org.qortal.crypto.Crypto;
+import org.qortal.data.transaction.TransactionData;
 import org.qortal.settings.Settings;
 
 /**
@@ -22,8 +23,70 @@ import org.qortal.settings.Settings;
  */
 public enum QortalFunctionCode {
 	/**
-	 * <tt>0x0510</tt><br>
-	 * Convert address in B to 20-byte value in LSB of B1, and all of B2 & B3.
+	 * Returns length of message data from transaction in A.<br>
+	 * <tt>0x0501</tt><br>
+	 * If transaction has no 'message', returns -1.
+	 */
+	GET_MESSAGE_LENGTH_FROM_TX_IN_A(0x0501, 0, true) {
+		@Override
+		protected void postCheckExecute(FunctionData functionData, MachineState state, short rawFunctionCode) throws ExecutionException {
+			QortalATAPI api = (QortalATAPI) state.getAPI();
+
+			TransactionData transactionData = api.getTransactionFromA(state);
+
+			byte[] messageData = api.getMessageFromTransaction(transactionData);
+
+			if (messageData == null)
+				functionData.returnValue = -1L;
+			else
+				functionData.returnValue = (long) messageData.length;
+		}
+	},
+	/**
+	 * Put offset 'message' from transaction in A into B<br>
+	 * <tt>0x0502 start-offset</tt><br>
+	 * Copies up to 32 bytes of message data, starting at <tt>start-offset</tt> into B.<br>
+	 * If transaction has no 'message', or <tt>start-offset</tt> out of bounds, then zero B<br>
+	 * Example 'message' could be 256-bit shared secret
+	 */
+	PUT_PARTIAL_MESSAGE_FROM_TX_IN_A_INTO_B(0x0502, 1, false) {
+		@Override
+		protected void postCheckExecute(FunctionData functionData, MachineState state, short rawFunctionCode) throws ExecutionException {
+			QortalATAPI api = (QortalATAPI) state.getAPI();
+
+			// In case something goes wrong, or we don't have enough message data.
+			api.zeroB(state);
+
+			if (functionData.value1 < 0 || functionData.value1 > Integer.MAX_VALUE)
+				return;
+
+			int startOffset = functionData.value1.intValue();
+
+			TransactionData transactionData = api.getTransactionFromA(state);
+
+			byte[] messageData = api.getMessageFromTransaction(transactionData);
+
+			if (messageData == null || startOffset > messageData.length)
+				return;
+
+			/*
+			 * Copy up to 32 bytes of message data into B,
+			 * retain order but pad with zeros in lower bytes.
+			 * 
+			 * So a 4-byte message "a b c d" would copy thusly:
+			 * a b c d 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
+			 */
+			int byteCount = Math.min(32, messageData.length - startOffset);
+			byte[] bBytes = new byte[32];
+
+			System.arraycopy(messageData, startOffset, bBytes, 0, byteCount);
+
+			api.setB(state, bBytes);
+		}
+	},
+	/**
+	 * Convert address in B to 20-byte value in LSB of B1, and all of B2 & B3.<br>
+	 * <tt>0x0510</tt>
 	 */
 	CONVERT_B_TO_PKH(0x0510, 0, false) {
 		@Override
@@ -38,8 +101,8 @@ public enum QortalFunctionCode {
 		}
 	},
 	/**
-	 * <tt>0x0511</tt><br>
 	 * Convert 20-byte value in LSB of B1, and all of B2 & B3 to P2SH.<br>
+	 * <tt>0x0511</tt><br>
 	 * P2SH stored in lower 25 bytes of B.
 	 */
 	CONVERT_B_TO_P2SH(0x0511, 0, false) {
@@ -51,8 +114,8 @@ public enum QortalFunctionCode {
 		}
 	},
 	/**
-	 * <tt>0x0512</tt><br>
 	 * Convert 20-byte value in LSB of B1, and all of B2 & B3 to Qortal address.<br>
+	 * <tt>0x0512</tt><br>
 	 * Qortal address stored in lower 25 bytes of B.
 	 */
 	CONVERT_B_TO_QORTAL(0x0512, 0, false) {

src/main/java/org/qortal/block/Block.java

@@ -6,6 +6,8 @@ import static java.util.stream.Collectors.toMap;
 import java.math.BigDecimal;
 import java.math.BigInteger;
 import java.math.RoundingMode;
+import java.text.DecimalFormat;
+import java.text.NumberFormat;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.HashMap;
@@ -15,6 +17,7 @@ import java.util.Map;
 import java.util.Set;
 import java.util.stream.Collectors;
 
+import org.apache.logging.log4j.Level;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 import org.qortal.account.Account;
@@ -29,6 +32,7 @@ import org.qortal.controller.Controller;
 import org.qortal.crypto.Crypto;
 import org.qortal.data.account.AccountBalanceData;
 import org.qortal.data.account.AccountData;
+import org.qortal.data.account.EligibleQoraHolderData;
 import org.qortal.data.account.QortFromQoraData;
 import org.qortal.data.account.RewardShareData;
 import org.qortal.data.at.ATData;
@@ -53,7 +57,6 @@ import org.qortal.transform.transaction.TransactionTransformer;
 import org.qortal.utils.Amounts;
 import org.qortal.utils.Base58;
 import org.qortal.utils.NTP;
-import org.roaringbitmap.IntIterator;
 
 import com.google.common.primitives.Bytes;
 import com.google.common.primitives.Longs;
@@ -128,7 +131,7 @@ public class Block {
 
 	@FunctionalInterface
 	private interface BlockRewardDistributor {
-		long distribute(long amount, Map<Account, Long> balanceChanges) throws DataException;
+		long distribute(long amount, Map<String, Long> balanceChanges) throws DataException;
 	}
 
 	/** Lazy-instantiated expanded info on block's online accounts. */
@@ -144,8 +147,8 @@ public class Block {
 		private final Account recipientAccount;
 		private final AccountData recipientAccountData;
 
-		ExpandedAccount(Repository repository, int accountIndex) throws DataException {
-			this.rewardShareData = repository.getAccountRepository().getRewardShareByIndex(accountIndex);
+		ExpandedAccount(Repository repository, RewardShareData rewardShareData) throws DataException {
+			this.rewardShareData = rewardShareData;
 			this.sharePercent = this.rewardShareData.getSharePercent();
 
 			this.mintingAccount = new Account(repository, this.rewardShareData.getMinter());
@@ -188,12 +191,12 @@ public class Block {
 			return shareBinsByLevel[accountLevel];
 		}
 
-		public long distribute(long accountAmount, Map<Account, Long> balanceChanges) {
+		public long distribute(long accountAmount, Map<String, Long> balanceChanges) {
 			if (this.isRecipientAlsoMinter) {
 				// minter & recipient the same - simpler case
 				LOGGER.trace(() -> String.format("Minter/recipient account %s share: %s", this.mintingAccount.getAddress(), Amounts.prettyAmount(accountAmount)));
 				if (accountAmount != 0)
-					balanceChanges.merge(this.mintingAccount, accountAmount, Long::sum);
+					balanceChanges.merge(this.mintingAccount.getAddress(), accountAmount, Long::sum);
 			} else {
 				// minter & recipient different - extra work needed
 				long recipientAmount = (accountAmount * this.sharePercent) / 100L / 100L; // because scaled by 2dp and 'percent' means "per 100"
@@ -201,11 +204,11 @@ public class Block {
 
 				LOGGER.trace(() -> String.format("Minter account %s share: %s", this.mintingAccount.getAddress(), Amounts.prettyAmount(minterAmount)));
 				if (minterAmount != 0)
-					balanceChanges.merge(this.mintingAccount, minterAmount, Long::sum);
+					balanceChanges.merge(this.mintingAccount.getAddress(), minterAmount, Long::sum);
 
 				LOGGER.trace(() -> String.format("Recipient account %s share: %s", this.recipientAccount.getAddress(), Amounts.prettyAmount(recipientAmount)));
 				if (recipientAmount != 0)
-					balanceChanges.merge(this.recipientAccount, recipientAmount, Long::sum);
+					balanceChanges.merge(this.recipientAccount.getAddress(), recipientAmount, Long::sum);
 			}
 
 			// We always distribute all of the amount
@@ -215,6 +218,11 @@ public class Block {
 	/** Always use getExpandedAccounts() to access this, as it's lazy-instantiated. */
 	private List<ExpandedAccount> cachedExpandedAccounts = null;
 
+	/** Opportunistic cache of this block's valid online accounts. Only created by call to isValid(). */
+	private List<OnlineAccountData> cachedValidOnlineAccounts = null;
+	/** Opportunistic cache of this block's valid online reward-shares. Only created by call to isValid(). */
+	private List<RewardShareData> cachedOnlineRewardShares = null;
+
 	// Other useful constants
 
 	private static final BigInteger MAX_DISTANCE;
@@ -349,12 +357,8 @@ public class Block {
 			System.arraycopy(onlineAccountData.getSignature(), 0, onlineAccountsSignatures, i * Transformer.SIGNATURE_LENGTH, Transformer.SIGNATURE_LENGTH);
 		}
 
-		byte[] minterSignature;
-		try {
-			minterSignature = minter.sign(BlockTransformer.getBytesForMinterSignature(parentBlockData.getMinterSignature(), minter, encodedOnlineAccounts));
-		} catch (TransformationException e) {
-			throw new DataException("Unable to calculate next block minter signature", e);
-		}
+		byte[] minterSignature = minter.sign(BlockTransformer.getBytesForMinterSignature(parentBlockData.getMinterSignature(),
+				minter.getPublicKey(), encodedOnlineAccounts));
 
 		// Qortal: minter is always a reward-share, so find actual minter and get their effective minting level
 		int minterLevel = Account.getRewardShareEffectiveMintingLevel(repository, minter.getPublicKey());
@@ -420,12 +424,8 @@ public class Block {
 		int version = this.blockData.getVersion();
 		byte[] reference = this.blockData.getReference();
 
-		byte[] minterSignature;
-		try {
-			minterSignature = minter.sign(BlockTransformer.getBytesForMinterSignature(parentBlockData.getMinterSignature(), minter, this.blockData.getEncodedOnlineAccounts()));
-		} catch (TransformationException e) {
-			throw new DataException("Unable to calculate next block's minter signature", e);
-		}
+		byte[] minterSignature = minter.sign(BlockTransformer.getBytesForMinterSignature(parentBlockData.getMinterSignature(),
+				minter.getPublicKey(), this.blockData.getEncodedOnlineAccounts()));
 
 		// Qortal: minter is always a reward-share, so find actual minter and get their effective minting level
 		int minterLevel = Account.getRewardShareEffectiveMintingLevel(repository, minter.getPublicKey());
@@ -564,22 +564,28 @@ public class Block {
 	/**
 	 * Return expanded info on block's online accounts.
 	 * <p>
+	 * Typically called as part of Block.process() or Block.orphan()
+	 * so ideally after any calls to Block.isValid().
+	 * 
 	 * @throws DataException
 	 */
 	public List<ExpandedAccount> getExpandedAccounts() throws DataException {
 		if (this.cachedExpandedAccounts != null)
 			return this.cachedExpandedAccounts;
 
-		ConciseSet accountIndexes = BlockTransformer.decodeOnlineAccounts(this.blockData.getEncodedOnlineAccounts());
+		// We might already have a cache of online, reward-shares thanks to isValid()
+		if (this.cachedOnlineRewardShares == null) {
+			ConciseSet accountIndexes = BlockTransformer.decodeOnlineAccounts(this.blockData.getEncodedOnlineAccounts());
+			this.cachedOnlineRewardShares = repository.getAccountRepository().getRewardSharesByIndexes(accountIndexes.toArray());
+
+			if (this.cachedOnlineRewardShares == null)
+				throw new DataException("Online accounts invalid?");
+		}
+
 		List<ExpandedAccount> expandedAccounts = new ArrayList<>();
 
-		IntIterator iterator = accountIndexes.iterator();
-		while (iterator.hasNext()) {
-			int accountIndex = iterator.next();
-
-			ExpandedAccount accountInfo = new ExpandedAccount(repository, accountIndex);
-			expandedAccounts.add(accountInfo);
-		}
+		for (RewardShareData rewardShare : this.cachedOnlineRewardShares)
+			expandedAccounts.add(new ExpandedAccount(repository, rewardShare));
 
 		this.cachedExpandedAccounts = expandedAccounts;
 
@@ -780,15 +786,46 @@ public class Block {
 		return BigInteger.valueOf(blockSummaryData.getOnlineAccountsCount()).shiftLeft(ACCOUNTS_COUNT_SHIFT).add(keyDistance);
 	}
 
-	public static BigInteger calcChainWeight(int commonBlockHeight, byte[] commonBlockSignature, List<BlockSummaryData> blockSummaries) {
+	public static BigInteger calcChainWeight(int commonBlockHeight, byte[] commonBlockSignature, List<BlockSummaryData> blockSummaries, int maxHeight) {
 		BigInteger cumulativeWeight = BigInteger.ZERO;
 		int parentHeight = commonBlockHeight;
 		byte[] parentBlockSignature = commonBlockSignature;
+		NumberFormat formatter = new DecimalFormat("0.###E0");
+		boolean isLogging = LOGGER.getLevel().isLessSpecificThan(Level.TRACE);
 
 		for (BlockSummaryData blockSummaryData : blockSummaries) {
-			cumulativeWeight = cumulativeWeight.shiftLeft(CHAIN_WEIGHT_SHIFT).add(calcBlockWeight(parentHeight, parentBlockSignature, blockSummaryData));
+			StringBuilder stringBuilder = isLogging ? new StringBuilder(512) : null;
+
+			if (isLogging)
+				stringBuilder.append(formatter.format(cumulativeWeight)).append(" -> ");
+
+			cumulativeWeight = cumulativeWeight.shiftLeft(CHAIN_WEIGHT_SHIFT);
+			if (isLogging)
+				stringBuilder.append(formatter.format(cumulativeWeight)).append(" + ");
+
+			BigInteger blockWeight = calcBlockWeight(parentHeight, parentBlockSignature, blockSummaryData);
+			if (isLogging)
+				stringBuilder.append("(height: ")
+						.append(parentHeight + 1)
+						.append(", online: ")
+						.append(blockSummaryData.getOnlineAccountsCount())
+						.append(") ")
+						.append(formatter.format(blockWeight));
+
+			cumulativeWeight = cumulativeWeight.add(blockWeight);
+			if (isLogging)
+				stringBuilder.append(" -> ").append(formatter.format(cumulativeWeight));
+
+			if (isLogging && blockSummaries.size() > 1)
+				LOGGER.debug(() -> stringBuilder.toString()); //NOSONAR S1612 (false positive?)
+
 			parentHeight = blockSummaryData.getHeight();
 			parentBlockSignature = blockSummaryData.getSignature();
+
+			/* Potential future consensus change: only comparing the same number of blocks.
+			if (parentHeight >= maxHeight)
+				break;
+			*/
 		}
 
 		return cumulativeWeight;
@@ -914,19 +951,9 @@ public class Block {
 		if (accountIndexes.size() != this.blockData.getOnlineAccountsCount())
 			return ValidationResult.ONLINE_ACCOUNTS_INVALID;
 
-		List<RewardShareData> expandedAccounts = new ArrayList<>();
-
-		IntIterator iterator = accountIndexes.iterator();
-		while (iterator.hasNext()) {
-			int accountIndex = iterator.next();
-			RewardShareData rewardShareData = repository.getAccountRepository().getRewardShareByIndex(accountIndex);
-
-			// Check that claimed online account actually exists
-			if (rewardShareData == null)
-				return ValidationResult.ONLINE_ACCOUNT_UNKNOWN;
-
-			expandedAccounts.add(rewardShareData);
-		}
+		List<RewardShareData> onlineRewardShares = repository.getAccountRepository().getRewardSharesByIndexes(accountIndexes.toArray());
+		if (onlineRewardShares == null)
+			return ValidationResult.ONLINE_ACCOUNT_UNKNOWN;
 
 		// If block is past a certain age then we simply assume the signatures were correct
 		long signatureRequirementThreshold = NTP.getTime() - BlockChain.getInstance().getOnlineAccountSignaturesMinLifetime();
@@ -936,28 +963,51 @@ public class Block {
 		if (this.blockData.getOnlineAccountsSignatures() == null || this.blockData.getOnlineAccountsSignatures().length == 0)
 			return ValidationResult.ONLINE_ACCOUNT_SIGNATURES_MISSING;
 
-		if (this.blockData.getOnlineAccountsSignatures().length != expandedAccounts.size() * Transformer.SIGNATURE_LENGTH)
+		if (this.blockData.getOnlineAccountsSignatures().length != onlineRewardShares.size() * Transformer.SIGNATURE_LENGTH)
 			return ValidationResult.ONLINE_ACCOUNT_SIGNATURES_MALFORMED;
 
 		// Check signatures
-		List<byte[]> onlineAccountsSignatures = BlockTransformer.decodeTimestampSignatures(this.blockData.getOnlineAccountsSignatures());
 		long onlineTimestamp = this.blockData.getOnlineAccountsTimestamp();
 		byte[] onlineTimestampBytes = Longs.toByteArray(onlineTimestamp);
-		List<OnlineAccountData> onlineAccounts = Controller.getInstance().getOnlineAccounts();
+
+		// If this block is much older than current online timestamp, then there's no point checking current online accounts
+		List<OnlineAccountData> currentOnlineAccounts = onlineTimestamp < NTP.getTime() - Controller.ONLINE_TIMESTAMP_MODULUS
+				? null
+				: Controller.getInstance().getOnlineAccounts();
+		List<OnlineAccountData> latestBlocksOnlineAccounts = Controller.getInstance().getLatestBlocksOnlineAccounts();
+
+		// Extract online accounts' timestamp signatures from block data
+		List<byte[]> onlineAccountsSignatures = BlockTransformer.decodeTimestampSignatures(this.blockData.getOnlineAccountsSignatures());
+
+		// We'll build up a list of online accounts to hand over to Controller if block is added to chain
+		// and this will become latestBlocksOnlineAccounts (above) to reduce CPU load when we process next block...
+		List<OnlineAccountData> ourOnlineAccounts = new ArrayList<>();
 
 		for (int i = 0; i < onlineAccountsSignatures.size(); ++i) {
 			byte[] signature = onlineAccountsSignatures.get(i);
-			byte[] publicKey = expandedAccounts.get(i).getRewardSharePublicKey();
+			byte[] publicKey = onlineRewardShares.get(i).getRewardSharePublicKey();
+
+			OnlineAccountData onlineAccountData = new OnlineAccountData(onlineTimestamp, signature, publicKey);
+			ourOnlineAccounts.add(onlineAccountData);
 
 			// If signature is still current then no need to perform Ed25519 verify
-			OnlineAccountData onlineAccountData = new OnlineAccountData(onlineTimestamp, signature, publicKey);
-			if (onlineAccounts.remove(onlineAccountData)) // remove() is like contains() but also reduces the number to check next time
+			if (currentOnlineAccounts != null && currentOnlineAccounts.remove(onlineAccountData))
+				// remove() returned true, so online account still current
+				// and one less entry in currentOnlineAccounts to check next time
+				continue;
+
+			// If signature was okay in latest block then no need to perform Ed25519 verify
+			if (latestBlocksOnlineAccounts != null && latestBlocksOnlineAccounts.contains(onlineAccountData))
 				continue;
 
 			if (!Crypto.verify(publicKey, signature, onlineTimestampBytes))
 				return ValidationResult.ONLINE_ACCOUNT_SIGNATURE_INCORRECT;
 		}
 
+		// All online accounts valid, so save our list of online accounts for potential later use
+		this.cachedValidOnlineAccounts = ourOnlineAccounts;
+		this.cachedOnlineRewardShares = onlineRewardShares;
+
 		return ValidationResult.OK;
 	}
 
@@ -1037,6 +1087,10 @@ public class Block {
 			// Create repository savepoint here so we can rollback to it after testing transactions
 			repository.setSavepoint();
 
+			if (this.blockData.getHeight() == 212937)
+				// Apply fix for block 212937 but fix will be rolled back before we exit method
+				Block212937.processFix(this);
+
 			for (Transaction transaction : this.getTransactions()) {
 				TransactionData transactionData = transaction.getTransactionData();
 
@@ -1240,6 +1294,10 @@ public class Block {
 
 			// Distribute block rewards, including transaction fees, before transactions processed
 			processBlockRewards();
+
+			if (this.blockData.getHeight() == 212937)
+				// Apply fix for block 212937
+				Block212937.processFix(this);
 		}
 
 		// We're about to (test-)process a batch of transactions,
@@ -1271,6 +1329,9 @@ public class Block {
 		linkTransactionsToBlock();
 
 		postBlockTidy();
+
+		// Give Controller our cached, valid online accounts data (if any) to help reduce CPU load for next block
+		Controller.getInstance().pushLatestBlocksOnlineAccounts(this.cachedValidOnlineAccounts);
 	}
 
 	protected void increaseAccountLevels() throws DataException {
@@ -1288,13 +1349,16 @@ public class Block {
 				allUniqueExpandedAccounts.add(expandedAccount.recipientAccountData);
 		}
 
-		// Decrease blocks minted count for all accounts
+		// Increase blocks minted count for all accounts
+
+		// Batch update in repository
+		repository.getAccountRepository().modifyMintedBlockCounts(allUniqueExpandedAccounts.stream().map(AccountData::getAddress).collect(Collectors.toList()), +1);
+
+		// Local changes and also checks for level bump
 		for (AccountData accountData : allUniqueExpandedAccounts) {
 			// Adjust count locally (in Java)
 			accountData.setBlocksMinted(accountData.getBlocksMinted() + 1);
-
-			int rowCount = repository.getAccountRepository().modifyMintedBlockCount(accountData.getAddress(), +1);
-			LOGGER.trace(() -> String.format("Block minter %s up to %d minted block%s (rowCount: %d)", accountData.getAddress(), accountData.getBlocksMinted(), (accountData.getBlocksMinted() != 1 ? "s" : ""), rowCount));
+			LOGGER.trace(() -> String.format("Block minter %s up to %d minted block%s", accountData.getAddress(), accountData.getBlocksMinted(), (accountData.getBlocksMinted() != 1 ? "s" : "")));
 
 			final int effectiveBlocksMinted = accountData.getBlocksMinted() + accountData.getBlocksMintedAdjustment();
 
@@ -1462,6 +1526,10 @@ public class Block {
 			// Invalidate expandedAccounts as they may have changed due to orphaning TRANSFER_PRIVS transactions, etc.
 			this.cachedExpandedAccounts = null;
 
+			if (this.blockData.getHeight() == 212937)
+				// Revert fix for block 212937
+				Block212937.orphanFix(this);
+
 			// Block rewards, including transaction fees, removed after transactions undone
 			orphanBlockRewards();
 
@@ -1474,6 +1542,9 @@ public class Block {
 		this.blockData.setHeight(null);
 
 		postBlockTidy();
+
+		// Remove any cached, valid online accounts data from Controller
+		Controller.getInstance().popLatestBlocksOnlineAccounts();
 	}
 
 	protected void orphanTransactionsFromBlock() throws DataException {
@@ -1581,12 +1652,14 @@ public class Block {
 		}
 
 		// Decrease blocks minted count for all accounts
+
+		// Batch update in repository
+		repository.getAccountRepository().modifyMintedBlockCounts(allUniqueExpandedAccounts.stream().map(AccountData::getAddress).collect(Collectors.toList()), -1);
+
 		for (AccountData accountData : allUniqueExpandedAccounts) {
 			// Adjust count locally (in Java)
 			accountData.setBlocksMinted(accountData.getBlocksMinted() - 1);
-
-			int rowCount = repository.getAccountRepository().modifyMintedBlockCount(accountData.getAddress(), -1);
-			LOGGER.trace(() -> String.format("Block minter %s down to %d minted block%s (rowCount: %d)", accountData.getAddress(), accountData.getBlocksMinted(), (accountData.getBlocksMinted() != 1 ? "s" : ""), rowCount));
+			LOGGER.trace(() -> String.format("Block minter %s down to %d minted block%s", accountData.getAddress(), accountData.getBlocksMinted(), (accountData.getBlocksMinted() != 1 ? "s" : "")));
 
 			final int effectiveBlocksMinted = accountData.getBlocksMinted() + accountData.getBlocksMintedAdjustment();
 
@@ -1615,7 +1688,7 @@ public class Block {
 			this.distributionMethod = distributionMethod;
 		}
 
-		public long distribute(long distibutionAmount, Map<Account, Long> balanceChanges) throws DataException {
+		public long distribute(long distibutionAmount, Map<String, Long> balanceChanges) throws DataException {
 			return this.distributionMethod.distribute(distibutionAmount, balanceChanges);
 		}
 	}
@@ -1632,7 +1705,7 @@ public class Block {
 		// Now distribute to candidates
 
 		// Collate all balance changes and then apply in one final step
-		Map<Account, Long> balanceChanges = new HashMap<>();
+		Map<String, Long> balanceChanges = new HashMap<>();
 
 		long remainingAmount = totalAmount;
 		for (int r = 0; r < rewardCandidates.size(); ++r) {
@@ -1657,8 +1730,10 @@ public class Block {
 		}
 
 		// Apply balance changes
-		for (Map.Entry<Account, Long> balanceChange : balanceChanges.entrySet())
-			balanceChange.getKey().modifyAssetBalance(Asset.QORT, balanceChange.getValue());
+		List<AccountBalanceData> accountBalanceDeltas = balanceChanges.entrySet().stream()
+				.map(entry -> new AccountBalanceData(entry.getKey(), Asset.QORT, entry.getValue()))
+				.collect(Collectors.toList());
+		this.repository.getAccountRepository().modifyAssetBalances(accountBalanceDeltas);
 	}
 
 	protected List<BlockRewardCandidate> determineBlockRewardCandidates(boolean isProcessingNotOrphaning) throws DataException {
@@ -1728,7 +1803,7 @@ public class Block {
 		}
 
 		// Fetch list of legacy QORA holders who haven't reached their cap of QORT reward.
-		List<AccountBalanceData> qoraHolders = this.repository.getAccountRepository().getEligibleLegacyQoraHolders(isProcessingNotOrphaning ? null : this.blockData.getHeight());
+		List<EligibleQoraHolderData> qoraHolders = this.repository.getAccountRepository().getEligibleLegacyQoraHolders(isProcessingNotOrphaning ? null : this.blockData.getHeight());
 		final boolean haveQoraHolders = !qoraHolders.isEmpty();
 		final long qoraHoldersShare = BlockChain.getInstance().getQoraHoldersShare();
 
@@ -1781,7 +1856,7 @@ public class Block {
 		return rewardCandidates;
 	}
 
-	private static long distributeBlockRewardShare(long distributionAmount, List<ExpandedAccount> accounts, Map<Account, Long> balanceChanges) {
+	private static long distributeBlockRewardShare(long distributionAmount, List<ExpandedAccount> accounts, Map<String, Long> balanceChanges) {
 		// Collate all expanded accounts by minting account
 		Map<String, List<ExpandedAccount>> accountsByMinter = new HashMap<>();
 
@@ -1810,7 +1885,7 @@ public class Block {
 		return sharedAmount;
 	}
 
-	private static long distributeBlockRewardToQoraHolders(long qoraHoldersAmount, List<AccountBalanceData> qoraHolders, Map<Account, Long> balanceChanges, Block block) throws DataException {
+	private static long distributeBlockRewardToQoraHolders(long qoraHoldersAmount, List<EligibleQoraHolderData> qoraHolders, Map<String, Long> balanceChanges, Block block) throws DataException {
 		final boolean isProcessingNotOrphaning = qoraHoldersAmount >= 0;
 
 		long qoraPerQortReward = BlockChain.getInstance().getQoraPerQortReward();
@@ -1818,7 +1893,7 @@ public class Block {
 
 		long totalQoraHeld = 0;
 		for (int i = 0; i < qoraHolders.size(); ++i)
-			totalQoraHeld += qoraHolders.get(i).getBalance();
+			totalQoraHeld += qoraHolders.get(i).getQoraBalance();
 
 		long finalTotalQoraHeld = totalQoraHeld;
 		LOGGER.trace(() -> String.format("Total legacy QORA held: %s", Amounts.prettyAmount(finalTotalQoraHeld)));
@@ -1831,9 +1906,13 @@ public class Block {
 		BigInteger totalQoraHeldBI = BigInteger.valueOf(totalQoraHeld);
 
 		long sharedAmount = 0;
+		// For batched update of QORT_FROM_QORA balances
+		List<AccountBalanceData> newQortFromQoraBalances = new ArrayList<>();
+
 		for (int h = 0; h < qoraHolders.size(); ++h) {
-			AccountBalanceData qoraHolder = qoraHolders.get(h);
-			BigInteger qoraHolderBalanceBI = BigInteger.valueOf(qoraHolder.getBalance());
+			EligibleQoraHolderData qoraHolder = qoraHolders.get(h);
+			BigInteger qoraHolderBalanceBI = BigInteger.valueOf(qoraHolder.getQoraBalance());
+			String qoraHolderAddress = qoraHolder.getAddress();
 
 			// This is where a 128bit integer library could help:
 			// long holderReward = (qoraHoldersAmount * qoraHolder.getBalance()) / totalQoraHeld;
@@ -1841,15 +1920,13 @@ public class Block {
 
 			final long holderRewardForLogging = holderReward;
 			LOGGER.trace(() -> String.format("QORA holder %s has %s / %s QORA so share: %s",
-					qoraHolder.getAddress(), Amounts.prettyAmount(qoraHolder.getBalance()), finalTotalQoraHeld, Amounts.prettyAmount(holderRewardForLogging)));
+					qoraHolderAddress, Amounts.prettyAmount(qoraHolder.getQoraBalance()), finalTotalQoraHeld, Amounts.prettyAmount(holderRewardForLogging)));
 
 			// Too small to register this time?
 			if (holderReward == 0)
 				continue;
 
-			Account qoraHolderAccount = new Account(block.repository, qoraHolder.getAddress());
-
-			long newQortFromQoraBalance = qoraHolderAccount.getConfirmedBalance(Asset.QORT_FROM_QORA) + holderReward;
+			long newQortFromQoraBalance = qoraHolder.getQortFromQoraBalance() + holderReward;
 
 			// If processing, make sure we don't overpay
 			if (isProcessingNotOrphaning) {
@@ -1863,44 +1940,43 @@ public class Block {
 					newQortFromQoraBalance -= adjustment;
 
 					// This is also the QORA holder's final QORT-from-QORA block
-					QortFromQoraData qortFromQoraData = new QortFromQoraData(qoraHolder.getAddress(), holderReward, block.blockData.getHeight());
+					QortFromQoraData qortFromQoraData = new QortFromQoraData(qoraHolderAddress, holderReward, block.blockData.getHeight());
 					block.repository.getAccountRepository().save(qortFromQoraData);
 
 					long finalAdjustedHolderReward = holderReward;
 					LOGGER.trace(() -> String.format("QORA holder %s final share %s at height %d",
-							qoraHolder.getAddress(), Amounts.prettyAmount(finalAdjustedHolderReward), block.blockData.getHeight()));
+							qoraHolderAddress, Amounts.prettyAmount(finalAdjustedHolderReward), block.blockData.getHeight()));
 				}
 			} else {
 				// Orphaning
-				QortFromQoraData qortFromQoraData = block.repository.getAccountRepository().getQortFromQoraInfo(qoraHolder.getAddress());
-				if (qortFromQoraData != null) {
+				if (qoraHolder.getFinalBlockHeight() != null) {
 					// Final QORT-from-QORA amount from repository was stored during processing, and hence positive.
 					// So we use + here as qortFromQora is negative during orphaning.
 					// More efficient than "holderReward - (0 - final-qort-from-qora)"
-					long adjustment = holderReward + qortFromQoraData.getFinalQortFromQora();
+					long adjustment = holderReward + qoraHolder.getFinalQortFromQora();
 
 					holderReward -= adjustment;
 					newQortFromQoraBalance -= adjustment;
 
-					block.repository.getAccountRepository().deleteQortFromQoraInfo(qoraHolder.getAddress());
+					block.repository.getAccountRepository().deleteQortFromQoraInfo(qoraHolderAddress);
 
 					long finalAdjustedHolderReward = holderReward;
 					LOGGER.trace(() -> String.format("QORA holder %s final share %s was at height %d",
-							qoraHolder.getAddress(), Amounts.prettyAmount(finalAdjustedHolderReward), block.blockData.getHeight()));
+							qoraHolderAddress, Amounts.prettyAmount(finalAdjustedHolderReward), block.blockData.getHeight()));
 				}
 			}
 
-			balanceChanges.merge(qoraHolderAccount, holderReward, Long::sum);
+			balanceChanges.merge(qoraHolderAddress, holderReward, Long::sum);
 
-			if (newQortFromQoraBalance > 0)
-				qoraHolderAccount.setConfirmedBalance(Asset.QORT_FROM_QORA, newQortFromQoraBalance);
-			else
-				// Remove QORT_FROM_QORA balance as it's zero
-				qoraHolderAccount.deleteBalance(Asset.QORT_FROM_QORA);
+			// Add to batched QORT_FROM_QORA balance update list
+			newQortFromQoraBalances.add(new AccountBalanceData(qoraHolderAddress, Asset.QORT_FROM_QORA, newQortFromQoraBalance));
 
 			sharedAmount += holderReward;
 		}
 
+		// Perform batched update of QORT_FROM_QORA balances
+		block.repository.getAccountRepository().setAssetBalances(newQortFromQoraBalances);
+
 		return sharedAmount;
 	}
 

src/main/java/org/qortal/block/Block212937.java

@@ -0,0 +1,153 @@
+package org.qortal.block;
+
+import java.io.InputStream;
+import java.util.List;
+import java.util.stream.Collectors;
+
+import javax.xml.bind.JAXBContext;
+import javax.xml.bind.JAXBException;
+import javax.xml.bind.UnmarshalException;
+import javax.xml.bind.Unmarshaller;
+import javax.xml.transform.stream.StreamSource;
+
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
+import org.eclipse.persistence.jaxb.JAXBContextFactory;
+import org.eclipse.persistence.jaxb.UnmarshallerProperties;
+import org.qortal.data.account.AccountBalanceData;
+import org.qortal.repository.DataException;
+
+/**
+ * Block 212937
+ * <p>
+ * Somehow a node minted a version of block 212937 that contained one transaction:
+ * a PAYMENT transaction that attempted to spend more QORT than that account had as QORT balance.
+ * <p>
+ * This invalid transaction made block 212937 (rightly) invalid to several nodes,
+ * which refused to use that block.
+ * However, it seems there were no other nodes minting an alternative, valid block at that time
+ * and so the chain stalled for several nodes in the network.
+ * <p>
+ * Additionally, the invalid block 212937 affected all new installations, regardless of whether
+ * they synchronized from scratch (block 1) or used an 'official release' bootstrap.
+ * <p>
+ * After lengthy diagnosis, it was discovered that
+ * the invalid transaction seemed to rely on incorrect balances in a corrupted database.
+ * Copies of DB files containing the broken chain were also shared around, exacerbating the problem.
+ * <p>
+ * There were three options:
+ * <ol>
+ * <li>roll back the chain to last known valid block 212936 and re-mint empty blocks to current height</li>
+ * <li>keep existing chain, but apply database edits at block 212937 to allow current chain to be valid</li>
+ * <li>attempt to mint an alternative chain, retaining as many valid transactions as possible</li>
+ * </ol>
+ * <p>
+ * Option 1 was highly undesirable due to knock-on effects from wiping 700+ transactions, some of which
+ * might have affect cross-chain trades, although there were no cross-chain trade completed during
+ * the decision period.
+ * <p>
+ * Option 3 was essentially a slightly better version of option 1 and rejected for similar reasons.
+ * Attempts at option 3 also rapidly hit cumulative problems with every replacement block due to
+ * differing block timestamps making some transactions, and then even some blocks themselves, invalid.
+ * <p>
+ * This class is the implementation of option 2.
+ * <p>
+ * The change in account balances are relatively small, see <tt>block-212937-deltas.json</tt> resource
+ * for actual values. These values were obtained by exporting the <tt>AccountBalances</tt> table from
+ * both versions of the database with chain at block 212936, and then comparing. The values were also
+ * tested by syncing both databases up to block 225500, re-exporting and re-comparing.
+ * <p>
+ * The invalid block 212937 signature is: <tt>2J3GVJjv...qavh6KkQ</tt>.
+ * <p>
+ * The invalid transaction in block 212937 is:
+ * <p>
+ * <code><pre>
+   {
+      "amount" : "0.10788294",
+      "approvalStatus" : "NOT_REQUIRED",
+      "blockHeight" : 212937,
+      "creatorAddress" : "QLdw5uabviLJgRGkRiydAFmAtZzxHfNXSs",
+      "fee" : "0.00100000",
+      "recipient" : "QZi1mNHDbiLvsytxTgxDr9nhJe4pNZaWpw",
+      "reference" : "J6JukdTVuXZ3JYbHatfZzwxG2vSiZwVCPDzW5K7PsVQKRj8XZeDtqnkGCGGjaSQZ9bQMtV44ky88NnGM4YBQKU6",
+      "senderPublicKey" : "DBFfbD2M3uh4jPE5PaUcZVvNPfrrJzVB7seeEtBn5SPs",
+      "signature" : "qkitxdCEEnKt8w6wRfFixtErbXsxWE6zG2ESNhpqBdScikV1WxeA6WZTTMJVV4tCeZdBFXw3V1X5NVztv6LirWK",
+      "timestamp" : 1607863074904,
+      "txGroupId" : 0,
+      "type" : "PAYMENT"
+   }
+   </pre></code>
+ * <p>
+ * Account <tt>QLdw5uabviLJgRGkRiydAFmAtZzxHfNXSs</tt> attempted to spend <tt>0.10888294</tt> (including fees)
+ * when their QORT balance was really only <tt>0.10886665</tt>.
+ * <p>
+ * However, on the broken DB nodes, their balance
+ * seemed to be <tt>0.10890293</tt> which was sufficient to make the transaction valid.
+ */
+public final class Block212937 {
+
+	private static final Logger LOGGER = LogManager.getLogger(Block212937.class);
+	private static final String ACCOUNT_DELTAS_SOURCE = "block-212937-deltas.json";
+
+	private static final List<AccountBalanceData> accountDeltas = readAccountDeltas();
+
+	private Block212937() {
+		/* Do not instantiate */
+	}
+
+	@SuppressWarnings("unchecked")
+	private static List<AccountBalanceData> readAccountDeltas() {
+		Unmarshaller unmarshaller;
+
+		try {
+			// Create JAXB context aware of classes we need to unmarshal
+			JAXBContext jc = JAXBContextFactory.createContext(new Class[] {
+				AccountBalanceData.class
+			}, null);
+
+			// Create unmarshaller
+			unmarshaller = jc.createUnmarshaller();
+
+			// Set the unmarshaller media type to JSON
+			unmarshaller.setProperty(UnmarshallerProperties.MEDIA_TYPE, "application/json");
+
+			// Tell unmarshaller that there's no JSON root element in the JSON input
+			unmarshaller.setProperty(UnmarshallerProperties.JSON_INCLUDE_ROOT, false);
+		} catch (JAXBException e) {
+			String message = "Failed to setup unmarshaller to read block 212937 deltas";
+			LOGGER.error(message, e);
+			throw new RuntimeException(message, e);
+		}
+
+		ClassLoader classLoader = BlockChain.class.getClassLoader();
+		InputStream in = classLoader.getResourceAsStream(ACCOUNT_DELTAS_SOURCE);
+		StreamSource jsonSource = new StreamSource(in);
+
+		try  {
+			// Attempt to unmarshal JSON stream to BlockChain config
+			return (List<AccountBalanceData>) unmarshaller.unmarshal(jsonSource, AccountBalanceData.class).getValue();
+		} catch (UnmarshalException e) {
+			String message = "Failed to parse block 212937 deltas";
+			LOGGER.error(message, e);
+			throw new RuntimeException(message, e);
+		} catch (JAXBException e) {
+			String message = "Unexpected JAXB issue while processing block 212937 deltas";
+			LOGGER.error(message, e);
+			throw new RuntimeException(message, e);
+		}
+	}
+
+	public static void processFix(Block block) throws DataException {
+		block.repository.getAccountRepository().modifyAssetBalances(accountDeltas);
+	}
+
+	public static void orphanFix(Block block) throws DataException {
+		// Create inverse deltas
+		List<AccountBalanceData> inverseDeltas = accountDeltas.stream()
+				.map(delta -> new AccountBalanceData(delta.getAddress(), delta.getAssetId(), 0 - delta.getBalance()))
+				.collect(Collectors.toList());
+
+		block.repository.getAccountRepository().modifyAssetBalances(inverseDeltas);
+	}
+
+}

src/main/java/org/qortal/block/BlockChain.java

@@ -32,7 +32,6 @@ import org.qortal.repository.DataException;
 import org.qortal.repository.Repository;
 import org.qortal.repository.RepositoryManager;
 import org.qortal.settings.Settings;
-import org.qortal.utils.NTP;
 import org.qortal.utils.StringLongMapXmlAdapter;
 
 /**
@@ -482,7 +481,7 @@ public class BlockChain {
 	}
 
 	/**
-	 * Some sort start-up/initialization/checking method.
+	 * Some sort of start-up/initialization/checking method.
 	 * 
 	 * @throws SQLException
 	 */
@@ -492,7 +491,9 @@ public class BlockChain {
 			rebuildBlockchain();
 
 		try (final Repository repository = RepositoryManager.getRepository()) {
-			BlockData detachedBlockData = repository.getBlockRepository().getDetachedBlockSignature();
+			int startHeight = Math.max(repository.getBlockRepository().getBlockchainHeight() - 1440, 1);
+
+			BlockData detachedBlockData = repository.getBlockRepository().getDetachedBlockSignature(startHeight);
 
 			if (detachedBlockData != null) {
 				LOGGER.error(String.format("Block %d's reference does not match any block's signature", detachedBlockData.getHeight()));
@@ -530,7 +531,8 @@ public class BlockChain {
 
 	private static void rebuildBlockchain() throws DataException {
 		// (Re)build repository
-		RepositoryManager.rebuild();
+		if (!RepositoryManager.wasPristineAtOpen())
+			RepositoryManager.rebuild();
 
 		try (final Repository repository = RepositoryManager.getRepository()) {
 			GenesisBlock genesisBlock = GenesisBlock.getInstance(repository);
@@ -552,17 +554,23 @@ public class BlockChain {
 
 		try {
 			try (final Repository repository = RepositoryManager.getRepository()) {
-				for (int height = repository.getBlockRepository().getBlockchainHeight(); height > targetHeight; --height) {
+				int height = repository.getBlockRepository().getBlockchainHeight();
+				BlockData orphanBlockData = repository.getBlockRepository().fromHeight(height);
+
+				while (height > targetHeight) {
 					LOGGER.info(String.format("Forcably orphaning block %d", height));
 
-					BlockData blockData = repository.getBlockRepository().fromHeight(height);
-					Block block = new Block(repository, blockData);
+					Block block = new Block(repository, orphanBlockData);
 					block.orphan();
-					repository.saveChanges();
-				}
 
-				BlockData lastBlockData = repository.getBlockRepository().getLastBlock();
-				Controller.getInstance().setChainTip(lastBlockData);
+					repository.saveChanges();
+
+					--height;
+					orphanBlockData = repository.getBlockRepository().fromHeight(height);
+
+					repository.discardChanges(); // clear transaction status to prevent deadlocks
+					Controller.getInstance().onOrphanedBlock(orphanBlockData);
+				}
 
 				return true;
 			}
@@ -571,33 +579,4 @@ public class BlockChain {
 		}
 	}
 
-	public static void trimOldOnlineAccountsSignatures() {
-		final Long now = NTP.getTime();
-		if (now == null)
-			return;
-
-		ReentrantLock blockchainLock = Controller.getInstance().getBlockchainLock();
-		if (!blockchainLock.tryLock())
-			// Too busy to trim right now, try again later
-			return;
-
-		try {
-			try (final Repository repository = RepositoryManager.tryRepository()) {
-				if (repository == null)
-					return;
-
-				int numBlocksTrimmed = repository.getBlockRepository().trimOldOnlineAccountsSignatures(now - BlockChain.getInstance().getOnlineAccountSignaturesMaxLifetime());
-
-				if (numBlocksTrimmed > 0)
-					LOGGER.debug(String.format("Trimmed old online accounts signatures from %d block%s", numBlocksTrimmed, (numBlocksTrimmed != 1 ? "s" : "")));
-
-				repository.saveChanges();
-			} catch (DataException e) {
-				LOGGER.warn(String.format("Repository issue trying to trim old online accounts signatures: %s", e.getMessage()));
-			}
-		} finally {
-			blockchainLock.unlock();
-		}
-	}
-
 }

src/main/java/org/qortal/controller/AtStatesTrimmer.java

@@ -0,0 +1,80 @@
+package org.qortal.controller;
+
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
+import org.qortal.data.block.BlockData;
+import org.qortal.repository.DataException;
+import org.qortal.repository.Repository;
+import org.qortal.repository.RepositoryManager;
+import org.qortal.settings.Settings;
+import org.qortal.utils.NTP;
+
+public class AtStatesTrimmer implements Runnable {
+
+	private static final Logger LOGGER = LogManager.getLogger(AtStatesTrimmer.class);
+
+	@Override
+	public void run() {
+		Thread.currentThread().setName("AT States trimmer");
+
+		try (final Repository repository = RepositoryManager.getRepository()) {
+			int trimStartHeight = repository.getATRepository().getAtTrimHeight();
+
+			repository.getATRepository().prepareForAtStateTrimming();
+			repository.saveChanges();
+
+			while (!Controller.isStopping()) {
+				repository.discardChanges();
+
+				Thread.sleep(Settings.getInstance().getAtStatesTrimInterval());
+
+				BlockData chainTip = Controller.getInstance().getChainTip();
+				if (chainTip == null || NTP.getTime() == null)
+					continue;
+
+				// Don't even attempt if we're mid-sync as our repository requests will be delayed for ages
+				if (Controller.getInstance().isSynchronizing())
+					continue;
+
+				long currentTrimmableTimestamp = NTP.getTime() - Settings.getInstance().getAtStatesMaxLifetime();
+				// We want to keep AT states near the tip of our copy of blockchain so we can process/orphan nearby blocks
+				long chainTrimmableTimestamp = chainTip.getTimestamp() - Settings.getInstance().getAtStatesMaxLifetime();
+
+				long upperTrimmableTimestamp = Math.min(currentTrimmableTimestamp, chainTrimmableTimestamp);
+				int upperTrimmableHeight = repository.getBlockRepository().getHeightFromTimestamp(upperTrimmableTimestamp);
+
+				int upperBatchHeight = trimStartHeight + Settings.getInstance().getAtStatesTrimBatchSize();
+				int upperTrimHeight = Math.min(upperBatchHeight, upperTrimmableHeight);
+
+				if (trimStartHeight >= upperTrimHeight)
+					continue;
+
+				int numAtStatesTrimmed = repository.getATRepository().trimAtStates(trimStartHeight, upperTrimHeight, Settings.getInstance().getAtStatesTrimLimit());
+				repository.saveChanges();
+
+				if (numAtStatesTrimmed > 0) {
+					final int finalTrimStartHeight = trimStartHeight;
+					LOGGER.debug(() -> String.format("Trimmed %d AT state%s between blocks %d and %d",
+							numAtStatesTrimmed, (numAtStatesTrimmed != 1 ? "s" : ""),
+							finalTrimStartHeight, upperTrimHeight));
+				} else {
+					// Can we move onto next batch?
+					if (upperTrimmableHeight > upperBatchHeight) {
+						trimStartHeight = upperBatchHeight;
+						repository.getATRepository().setAtTrimHeight(trimStartHeight);
+						repository.getATRepository().prepareForAtStateTrimming();
+						repository.saveChanges();
+
+						final int finalTrimStartHeight = trimStartHeight;
+						LOGGER.debug(() -> String.format("Bumping AT state base trim height to %d", finalTrimStartHeight));
+					}
+				}
+			}
+		} catch (DataException e) {
+			LOGGER.warn(String.format("Repository issue trying to trim AT states: %s", e.getMessage()));
+		} catch (InterruptedException e) {
+			// Time to exit
+		}
+	}
+
+}

src/main/java/org/qortal/controller/AutoUpdate.java

@@ -214,8 +214,9 @@ public class AutoUpdate extends Thread {
 			return false; // failed - try another repo
 		}
 
-		// Give repository a chance to backup in case things go badly wrong
-		RepositoryManager.backup(true);
+		// Give repository a chance to backup in case things go badly wrong (if enabled)
+		if (Settings.getInstance().getRepositoryBackupInterval() > 0)
+			RepositoryManager.backup(true);
 
 		// Call ApplyUpdate to end this process (unlocking current JAR so it can be replaced)
 		String javaHome = System.getProperty("java.home");

src/main/java/org/qortal/controller/BlockMinter.java

@@ -1,4 +1,4 @@
-package org.qortal.block;
+package org.qortal.controller;
 
 import java.math.BigInteger;
 import java.util.ArrayList;
@@ -13,8 +13,9 @@ import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 import org.qortal.account.Account;
 import org.qortal.account.PrivateKeyAccount;
+import org.qortal.block.Block;
 import org.qortal.block.Block.ValidationResult;
-import org.qortal.controller.Controller;
+import org.qortal.block.BlockChain;
 import org.qortal.data.account.MintingAccountData;
 import org.qortal.data.account.RewardShareData;
 import org.qortal.data.block.BlockData;
@@ -60,7 +61,7 @@ public class BlockMinter extends Thread {
 				List<TransactionData> unconfirmedTransactions = repository.getTransactionRepository().getUnconfirmedTransactions();
 
 				for (TransactionData transactionData : unconfirmedTransactions) {
-					LOGGER.trace(String.format("Deleting unconfirmed transaction %s", Base58.encode(transactionData.getSignature())));
+					LOGGER.trace(() -> String.format("Deleting unconfirmed transaction %s", Base58.encode(transactionData.getSignature())));
 					repository.getTransactionRepository().delete(transactionData);
 				}
 
@@ -69,7 +70,7 @@ public class BlockMinter extends Thread {
 
 			// Going to need this a lot...
 			BlockRepository blockRepository = repository.getBlockRepository();
-			Block previousBlock = null;
+			BlockData previousBlockData = null;
 
 			List<Block> newBlocks = new ArrayList<>();
 
@@ -115,7 +116,7 @@ public class BlockMinter extends Thread {
 
 					RewardShareData rewardShareData = repository.getAccountRepository().getRewardShare(mintingAccountData.getPublicKey());
 					if (rewardShareData == null) {
-						// Reward-share doesn't even exist - probably not a good sign
+						// Reward-share doesn't exist - probably cancelled but not yet removed from node's list of minting accounts
 						madi.remove();
 						continue;
 					}
@@ -150,8 +151,8 @@ public class BlockMinter extends Thread {
 				isMintingPossible = true;
 
 				// Check blockchain hasn't changed
-				if (previousBlock == null || !Arrays.equals(previousBlock.getSignature(), lastBlockData.getSignature())) {
-					previousBlock = new Block(repository, lastBlockData);
+				if (previousBlockData == null || !Arrays.equals(previousBlockData.getSignature(), lastBlockData.getSignature())) {
+					previousBlockData = lastBlockData;
 					newBlocks.clear();
 
 					// Reduce log timeout
@@ -162,12 +163,12 @@ public class BlockMinter extends Thread {
 				mintingAccountsData.removeIf(mintingAccountData -> newBlocks.stream().anyMatch(newBlock -> Arrays.equals(newBlock.getBlockData().getMinterPublicKey(), mintingAccountData.getPublicKey())));
 
 				// Do we need to build any potential new blocks?
-				List<PrivateKeyAccount> mintingAccounts = mintingAccountsData.stream().map(accountData -> new PrivateKeyAccount(repository, accountData.getPrivateKey())).collect(Collectors.toList());
+				List<PrivateKeyAccount> newBlocksMintingAccounts = mintingAccountsData.stream().map(accountData -> new PrivateKeyAccount(repository, accountData.getPrivateKey())).collect(Collectors.toList());
 
-				for (PrivateKeyAccount mintingAccount : mintingAccounts) {
+				for (PrivateKeyAccount mintingAccount : newBlocksMintingAccounts) {
 					// First block does the AT heavy-lifting
 					if (newBlocks.isEmpty()) {
-						Block newBlock = Block.mint(repository, previousBlock.getBlockData(), mintingAccount);
+						Block newBlock = Block.mint(repository, previousBlockData, mintingAccount);
 						if (newBlock == null) {
 							// For some reason we can't mint right now
 							moderatedLog(() -> LOGGER.error("Couldn't build a to-be-minted block"));
@@ -195,7 +196,7 @@ public class BlockMinter extends Thread {
 				// Make sure we're the only thread modifying the blockchain
 				ReentrantLock blockchainLock = Controller.getInstance().getBlockchainLock();
 				if (!blockchainLock.tryLock(30, TimeUnit.SECONDS)) {
-					LOGGER.warn("Couldn't acquire blockchain lock even after waiting 30 seconds");
+					LOGGER.debug("Couldn't acquire blockchain lock even after waiting 30 seconds");
 					continue;
 				}
 
@@ -233,8 +234,8 @@ public class BlockMinter extends Thread {
 						continue;
 
 					// Pick best block
-					final int parentHeight = previousBlock.getBlockData().getHeight();
-					final byte[] parentBlockSignature = previousBlock.getSignature();
+					final int parentHeight = previousBlockData.getHeight();
+					final byte[] parentBlockSignature = previousBlockData.getSignature();
 
 					BigInteger bestWeight = null;
 
@@ -274,9 +275,10 @@ public class BlockMinter extends Thread {
 					try {
 						newBlock.process();
 
-						LOGGER.info(String.format("Minted new block: %d", newBlock.getBlockData().getHeight()));
 						repository.saveChanges();
 
+						LOGGER.info(String.format("Minted new block: %d", newBlock.getBlockData().getHeight()));
+
 						RewardShareData rewardShareData = repository.getAccountRepository().getRewardShare(newBlock.getBlockData().getMinterPublicKey());
 
 						if (rewardShareData != null) {
@@ -292,9 +294,7 @@ public class BlockMinter extends Thread {
 									newBlock.getMinter().getAddress()));
 						}
 
-						repository.saveChanges();
-
-						// Notify controller
+						// Notify controller after we're released blockchain lock
 						newBlockMinted = true;
 					} catch (DataException e) {
 						// Unable to process block - report and discard
@@ -305,8 +305,16 @@ public class BlockMinter extends Thread {
 					blockchainLock.unlock();
 				}
 
-				if (newBlockMinted)
-					Controller.getInstance().onNewBlock(newBlock.getBlockData());
+				if (newBlockMinted) {
+					// Notify Controller and broadcast our new chain to network
+					BlockData newBlockData = newBlock.getBlockData();
+
+					repository.discardChanges(); // clear transaction status to prevent deadlocks
+					Controller.getInstance().onNewBlock(newBlockData);
+
+					Network network = Network.getInstance();
+					network.broadcast(broadcastPeer -> network.buildHeightMessage(broadcastPeer, newBlockData));
+				}
 			}
 		} catch (DataException e) {
 			LOGGER.warn("Repository issue while running block minter", e);

src/main/java/org/qortal/controller/BlockNotifier.java

@@ -1,43 +0,0 @@
-package org.qortal.controller;
-
-import java.util.HashMap;
-import java.util.Map;
-
-import org.eclipse.jetty.websocket.api.Session;
-import org.qortal.data.block.BlockData;
-
-public class BlockNotifier {
-
-	private static BlockNotifier instance;
-
-	@FunctionalInterface
-	public interface Listener {
-		void notify(BlockData blockData);
-	}
-
-	private Map<Session, Listener> listenersBySession = new HashMap<>();
-
-	private BlockNotifier() {
-	}
-
-	public static synchronized BlockNotifier getInstance() {
-		if (instance == null)
-			instance = new BlockNotifier();
-
-		return instance;
-	}
-
-	public synchronized void register(Session session, Listener listener) {
-		this.listenersBySession.put(session, listener);
-	}
-
-	public synchronized void deregister(Session session) {
-		this.listenersBySession.remove(session);
-	}
-
-	public synchronized void onNewBlock(BlockData blockData) {
-		for (Listener listener : this.listenersBySession.values())
-			listener.notify(blockData);
-	}
-
-}

src/main/java/org/qortal/controller/ChatNotifier.java

@@ -1,5 +1,7 @@
 package org.qortal.controller;
 
+import java.util.ArrayList;
+import java.util.Collection;
 import java.util.HashMap;
 import java.util.Map;
 
@@ -27,22 +29,34 @@ public class ChatNotifier {
 		return instance;
 	}
 
-	public synchronized void register(Session session, Listener listener) {
-		this.listenersBySession.put(session, listener);
+	public void register(Session session, Listener listener) {
+		synchronized (this.listenersBySession) {
+			this.listenersBySession.put(session, listener);
+		}
 	}
 
-	public synchronized void deregister(Session session) {
-		this.listenersBySession.remove(session);
+	public void deregister(Session session) {
+		synchronized (this.listenersBySession) {
+			this.listenersBySession.remove(session);
+		}
 	}
 
-	public synchronized void onNewChatTransaction(ChatTransactionData chatTransactionData) {
-		for (Listener listener : this.listenersBySession.values())
+	public void onNewChatTransaction(ChatTransactionData chatTransactionData) {
+		for (Listener listener : getAllListeners())
 			listener.notify(chatTransactionData);
 	}
 
-	public synchronized void onGroupMembershipChange() {
-		for (Listener listener : this.listenersBySession.values())
+	public void onGroupMembershipChange() {
+		for (Listener listener : getAllListeners())
 			listener.notify(null);
 	}
 
+	private Collection<Listener> getAllListeners() {
+		// Make a copy of listeners to both avoid concurrent modification
+		// and reduce synchronization time
+		synchronized (this.listenersBySession) {
+			return new ArrayList<>(this.listenersBySession.values());
+		}
+	}
+
 }

src/main/java/org/qortal/controller/Controller.java

@@ -9,21 +9,31 @@ import java.security.Security;
 import java.time.LocalDateTime;
 import java.time.ZoneOffset;
 import java.time.format.DateTimeFormatter;
+import java.util.ArrayDeque;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
+import java.util.Deque;
 import java.util.HashMap;
 import java.util.Iterator;
+import java.util.LinkedHashMap;
+import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
 import java.util.Properties;
 import java.util.Random;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicLong;
 import java.util.concurrent.locks.ReentrantLock;
+import java.util.function.Function;
 import java.util.function.Predicate;
 import java.util.stream.Collectors;
 
+import javax.xml.bind.annotation.XmlAccessType;
+import javax.xml.bind.annotation.XmlAccessorType;
+
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 import org.bouncycastle.jce.provider.BouncyCastleProvider;
@@ -34,7 +44,6 @@ import org.qortal.account.PublicKeyAccount;
 import org.qortal.api.ApiService;
 import org.qortal.block.Block;
 import org.qortal.block.BlockChain;
-import org.qortal.block.BlockMinter;
 import org.qortal.block.BlockChain.BlockTimingByHeight;
 import org.qortal.controller.Synchronizer.SynchronizationResult;
 import org.qortal.crypto.Crypto;
@@ -48,6 +57,8 @@ import org.qortal.data.network.PeerData;
 import org.qortal.data.transaction.ArbitraryTransactionData;
 import org.qortal.data.transaction.TransactionData;
 import org.qortal.data.transaction.ArbitraryTransactionData.DataType;
+import org.qortal.event.Event;
+import org.qortal.event.EventBus;
 import org.qortal.data.transaction.ChatTransactionData;
 import org.qortal.globalization.Translator;
 import org.qortal.gui.Gui;
@@ -83,6 +94,7 @@ import org.qortal.transaction.Transaction.TransactionType;
 import org.qortal.transaction.Transaction.ValidationResult;
 import org.qortal.utils.Base58;
 import org.qortal.utils.ByteArray;
+import org.qortal.utils.DaemonThreadFactory;
 import org.qortal.utils.NTP;
 import org.qortal.utils.Triple;
 
@@ -112,8 +124,10 @@ public class Controller extends Thread {
 	// To do with online accounts list
 	private static final long ONLINE_ACCOUNTS_TASKS_INTERVAL = 10 * 1000L; // ms
 	private static final long ONLINE_ACCOUNTS_BROADCAST_INTERVAL = 1 * 60 * 1000L; // ms
-	private static final long ONLINE_TIMESTAMP_MODULUS = 5 * 60 * 1000L;
+	public static final long ONLINE_TIMESTAMP_MODULUS = 5 * 60 * 1000L;
 	private static final long LAST_SEEN_EXPIRY_PERIOD = (ONLINE_TIMESTAMP_MODULUS * 2) + (1 * 60 * 1000L);
+	/** How many (latest) blocks' worth of online accounts we cache */
+	private static final int MAX_BLOCKS_CACHED_ONLINE_ACCOUNTS = 2;
 
 	private static volatile boolean isStopping = false;
 	private static BlockMinter blockMinter = null;
@@ -128,16 +142,31 @@ public class Controller extends Thread {
 	private ExecutorService callbackExecutor = Executors.newFixedThreadPool(3);
 	private volatile boolean notifyGroupMembershipChange = false;
 
-	private volatile BlockData chainTip = null;
+	private static final int BLOCK_CACHE_SIZE = 10; // To cover typical Synchronizer request + a few spare
+	/** Latest blocks on our chain. Note: tail/last is the latest block. */
+	private final Deque<BlockData> latestBlocks = new LinkedList<>();
+
+	/** Cache of BlockMessages, indexed by block signature */
+	@SuppressWarnings("serial")
+	private final LinkedHashMap<ByteArray, BlockMessage> blockMessageCache = new LinkedHashMap<>() {
+		@Override
+		protected boolean removeEldestEntry(Map.Entry<ByteArray, BlockMessage> eldest) {
+			return this.size() > BLOCK_CACHE_SIZE;
+		}
+	};
 
 	private long repositoryBackupTimestamp = startTime; // ms
+	private long repositoryCheckpointTimestamp = startTime; // ms
 	private long ntpCheckTimestamp = startTime; // ms
 	private long deleteExpiredTimestamp = startTime + DELETE_EXPIRED_INTERVAL; // ms
+
 	private long onlineAccountsTasksTimestamp = startTime + ONLINE_ACCOUNTS_TASKS_INTERVAL; // ms
 
 	/** Whether we can mint new blocks, as reported by BlockMinter. */
 	private volatile boolean isMintingPossible = false;
 
+	/** Synchronization object for sync variables below */
+	private final Object syncLock = new Object();
 	/** Whether we are attempting to synchronize. */
 	private volatile boolean isSynchronizing = false;
 	/** Temporary estimate of synchronization progress for SysTray use. */
@@ -168,8 +197,51 @@ public class Controller extends Thread {
 	/** Lock for only allowing one blockchain-modifying codepath at a time. e.g. synchronization or newly minted block. */
 	private final ReentrantLock blockchainLock = new ReentrantLock();
 
-	/** Cache of 'online accounts' */
+	/** Cache of current 'online accounts' */
 	List<OnlineAccountData> onlineAccounts = new ArrayList<>();
+	/** Cache of latest blocks' online accounts */
+	Deque<List<OnlineAccountData>> latestBlocksOnlineAccounts = new ArrayDeque<>(MAX_BLOCKS_CACHED_ONLINE_ACCOUNTS);
+
+	// Stats
+	@XmlAccessorType(XmlAccessType.FIELD)
+	public static class StatsSnapshot {
+		public static class GetBlockMessageStats {
+			public AtomicLong requests = new AtomicLong();
+			public AtomicLong cacheHits = new AtomicLong();
+			public AtomicLong unknownBlocks = new AtomicLong();
+			public AtomicLong cacheFills = new AtomicLong();
+
+			public GetBlockMessageStats() {
+			}
+		}
+		public GetBlockMessageStats getBlockMessageStats = new GetBlockMessageStats();
+
+		public static class GetBlockSummariesStats {
+			public AtomicLong requests = new AtomicLong();
+			public AtomicLong cacheHits = new AtomicLong();
+			public AtomicLong fullyFromCache = new AtomicLong();
+
+			public GetBlockSummariesStats() {
+			}
+		}
+		public GetBlockSummariesStats getBlockSummariesStats = new GetBlockSummariesStats();
+
+		public static class GetBlockSignaturesV2Stats {
+			public AtomicLong requests = new AtomicLong();
+			public AtomicLong cacheHits = new AtomicLong();
+			public AtomicLong fullyFromCache = new AtomicLong();
+
+			public GetBlockSignaturesV2Stats() {
+			}
+		}
+		public GetBlockSignaturesV2Stats getBlockSignaturesV2Stats = new GetBlockSignaturesV2Stats();
+
+		public AtomicLong latestBlocksCacheRefills = new AtomicLong();
+
+		public StatsSnapshot() {
+		}
+	}
+	private final StatsSnapshot stats = new StatsSnapshot();
 
 	// Constructors
 
@@ -226,21 +298,36 @@ public class Controller extends Thread {
 
 	/** Returns current blockchain height, or 0 if it's not available. */
 	public int getChainHeight() {
-		BlockData blockData = this.chainTip;
-		if (blockData == null)
-			return 0;
+		synchronized (this.latestBlocks) {
+			BlockData blockData = this.latestBlocks.peekLast();
+			if (blockData == null)
+				return 0;
 
-		return blockData.getHeight();
+			return blockData.getHeight();
+		}
 	}
 
 	/** Returns highest block, or null if it's not available. */
 	public BlockData getChainTip() {
-		return this.chainTip;
+		synchronized (this.latestBlocks) {
+			return this.latestBlocks.peekLast();
+		}
 	}
 
-	/** Cache new blockchain tip. */
-	public void setChainTip(BlockData blockData) {
-		this.chainTip = blockData;
+	public void refillLatestBlocksCache() throws DataException {
+		// Set initial chain height/tip
+		try (final Repository repository = RepositoryManager.getRepository()) {
+			BlockData blockData = repository.getBlockRepository().getLastBlock();
+
+			synchronized (this.latestBlocks) {
+				this.latestBlocks.clear();
+
+				for (int i = 0; i < BLOCK_CACHE_SIZE && blockData != null; ++i) {
+					this.latestBlocks.addFirst(blockData);
+					blockData = repository.getBlockRepository().fromHeight(blockData.getHeight() - 1);
+				}
+			}
+		}
 	}
 
 	public ReentrantLock getBlockchainLock() {
@@ -265,7 +352,9 @@ public class Controller extends Thread {
 	}
 
 	public Integer getSyncPercent() {
-		return this.isSynchronizing ? this.syncPercent : null;
+		synchronized (this.syncLock) {
+			return this.isSynchronizing ? this.syncPercent : null;
+		}
 	}
 
 	// Entry point
@@ -320,13 +409,8 @@ public class Controller extends Thread {
 		try {
 			BlockChain.validate();
 
-			// Set initial chain height/tip
-			try (final Repository repository = RepositoryManager.getRepository()) {
-				BlockData blockData = repository.getBlockRepository().getLastBlock();
-
-				Controller.getInstance().setChainTip(blockData);
-				LOGGER.info(String.format("Our chain height at start-up: %d", blockData.getHeight()));
-			}
+			Controller.getInstance().refillLatestBlocksCache();
+			LOGGER.info(String.format("Our chain height at start-up: %d", Controller.getInstance().getChainHeight()));
 		} catch (DataException e) {
 			LOGGER.error("Couldn't validate blockchain", e);
 			Gui.getInstance().fatalError("Blockchain validation issue", e);
@@ -360,6 +444,9 @@ public class Controller extends Thread {
 		blockMinter = new BlockMinter();
 		blockMinter.start();
 
+		LOGGER.info("Starting trade-bot");
+		TradeBot.getInstance();
+
 		// Arbitrary transaction data manager
 		// LOGGER.info("Starting arbitrary-transaction data manager");
 		// ArbitraryDataManager.getInstance().start();
@@ -398,6 +485,11 @@ public class Controller extends Thread {
 		Thread.currentThread().setName("Controller");
 
 		final long repositoryBackupInterval = Settings.getInstance().getRepositoryBackupInterval();
+		final long repositoryCheckpointInterval = Settings.getInstance().getRepositoryCheckpointInterval();
+
+		ExecutorService trimExecutor = Executors.newCachedThreadPool(new DaemonThreadFactory());
+		trimExecutor.execute(new AtStatesTrimmer());
+		trimExecutor.execute(new OnlineAccountsSignaturesTrimmer());
 
 		try {
 			while (!isStopping) {
@@ -439,6 +531,18 @@ public class Controller extends Thread {
 				final long requestMinimumTimestamp = now - ARBITRARY_REQUEST_TIMEOUT;
 				arbitraryDataRequests.entrySet().removeIf(entry -> entry.getValue().getC() < requestMinimumTimestamp);
 
+				// Time to 'checkpoint' uncommitted repository writes?
+				if (now >= repositoryCheckpointTimestamp + repositoryCheckpointInterval) {
+					repositoryCheckpointTimestamp = now + repositoryCheckpointInterval;
+
+					if (Settings.getInstance().getShowCheckpointNotification())
+						SysTray.getInstance().showMessage(Translator.INSTANCE.translate("SysTray", "DB_CHECKPOINT"),
+								Translator.INSTANCE.translate("SysTray", "PERFORMING_DB_CHECKPOINT"),
+								MessageType.INFO);
+
+					RepositoryManager.checkpoint(true);
+				}
+
 				// Give repository a chance to backup (if enabled)
 				if (repositoryBackupInterval > 0 && now >= repositoryBackupTimestamp + repositoryBackupInterval) {
 					repositoryBackupTimestamp = now + repositoryBackupInterval;
@@ -471,7 +575,17 @@ public class Controller extends Thread {
 				}
 			}
 		} catch (InterruptedException e) {
+			// Clear interrupted flag so we can shutdown trim threads
+			Thread.interrupted();
 			// Fall-through to exit
+		} finally {
+			trimExecutor.shutdownNow();
+
+			try {
+				trimExecutor.awaitTermination(2L, TimeUnit.SECONDS);
+			} catch (InterruptedException e) {
+				// We tried...
+			}
 		}
 	}
 
@@ -504,6 +618,10 @@ public class Controller extends Thread {
 	};
 
 	private void potentiallySynchronize() throws InterruptedException {
+		// Already synchronizing via another thread?
+		if (this.isSynchronizing)
+			return;
+
 		List<Peer> peers = Network.getInstance().getHandshakedPeers();
 
 		// Disregard peers that have "misbehaved" recently
@@ -536,11 +654,21 @@ public class Controller extends Thread {
 	}
 
 	public SynchronizationResult actuallySynchronize(Peer peer, boolean force) throws InterruptedException {
-		syncPercent = (this.chainTip.getHeight() * 100) / peer.getChainTipData().getLastHeight();
-		isSynchronizing = true;
-		updateSysTray();
+		boolean hasStatusChanged = false;
+		BlockData priorChainTip = this.getChainTip();
 
-		BlockData priorChainTip = this.chainTip;
+		synchronized (this.syncLock) {
+			this.syncPercent = (priorChainTip.getHeight() * 100) / peer.getChainTipData().getLastHeight();
+
+			// Only update SysTray if we're potentially changing height
+			if (this.syncPercent < 100) {
+				this.isSynchronizing = true;
+				hasStatusChanged = true;
+			}
+		}
+
+		if (hasStatusChanged)
+			updateSysTray();
 
 		try {
 			SynchronizationResult syncResult = Synchronizer.getInstance().synchronize(peer, force);
@@ -584,7 +712,6 @@ public class Controller extends Thread {
 					break;
 
 				case OK:
-					requestSysTrayUpdate = true;
 					// fall-through...
 				case NOTHING_TO_DO: {
 					// Update our list of inferior chain tips
@@ -611,14 +738,18 @@ public class Controller extends Thread {
 				// Reset our cache of inferior chains
 				inferiorChainSignatures.clear();
 
-				// Update chain-tip, notify peers, websockets, etc.
-				this.onNewBlock(newChainTip);
+				Network network = Network.getInstance();
+				network.broadcast(broadcastPeer -> network.buildHeightMessage(broadcastPeer, newChainTip));
 			}
 
 			return syncResult;
 		} finally {
 			isSynchronizing = false;
-			requestSysTrayUpdate = true;
+		}
+	}
+
+	public static class StatusChangeEvent implements Event {
+		public StatusChangeEvent() {
 		}
 	}
 
@@ -636,20 +767,23 @@ public class Controller extends Thread {
 		String heightText = Translator.INSTANCE.translate("SysTray", "BLOCK_HEIGHT");
 
 		String actionText;
-		if (isMintingPossible)
-			actionText = Translator.INSTANCE.translate("SysTray", "MINTING_ENABLED");
-		else if (isSynchronizing)
-			actionText = String.format("%s - %d%%", Translator.INSTANCE.translate("SysTray", "SYNCHRONIZING_BLOCKCHAIN"), syncPercent);
-		else if (numberOfPeers < Settings.getInstance().getMinBlockchainPeers())
-			actionText = Translator.INSTANCE.translate("SysTray", "CONNECTING");
-		else
-			actionText = Translator.INSTANCE.translate("SysTray", "MINTING_DISABLED");
+
+		synchronized (this.syncLock) {
+			if (this.isMintingPossible)
+				actionText = Translator.INSTANCE.translate("SysTray", "MINTING_ENABLED");
+			else if (this.isSynchronizing)
+				actionText = String.format("%s - %d%%", Translator.INSTANCE.translate("SysTray", "SYNCHRONIZING_BLOCKCHAIN"), this.syncPercent);
+			else if (numberOfPeers < Settings.getInstance().getMinBlockchainPeers())
+				actionText = Translator.INSTANCE.translate("SysTray", "CONNECTING");
+			else
+				actionText = Translator.INSTANCE.translate("SysTray", "MINTING_DISABLED");
+		}
 
 		String tooltip = String.format("%s - %d %s - %s %d", actionText, numberOfPeers, connectionsText, heightText, height);
 		SysTray.getInstance().setToolTipText(tooltip);
 
 		this.callbackExecutor.execute(() -> {
-			StatusNotifier.getInstance().onStatusChange(NTP.getTime());
+			EventBus.INSTANCE.notify(new StatusChangeEvent());
 		});
 	}
 
@@ -765,8 +899,10 @@ public class Controller extends Thread {
 		BlockData latestBlockData = getChainTip();
 		network.broadcast(peer -> network.buildHeightMessage(peer, latestBlockData));
 
-		// Send (if outbound) / Request unconfirmed transaction signatures
-		network.broadcast(network::buildGetUnconfirmedTransactionsMessage);
+		// Request unconfirmed transaction signatures, but only if we're up-to-date.
+		// If we're NOT up-to-date then priority is synchronizing first
+		if (isUpToDate())
+			network.broadcast(network::buildGetUnconfirmedTransactionsMessage);
 	}
 
 	public void onMintingPossibleChange(boolean isMintingPossible) {
@@ -774,22 +910,126 @@ public class Controller extends Thread {
 		requestSysTrayUpdate = true;
 	}
 
+	public static class NewBlockEvent implements Event {
+		private final BlockData blockData;
+
+		public NewBlockEvent(BlockData blockData) {
+			this.blockData = blockData;
+		}
+
+		public BlockData getBlockData() {
+			return this.blockData;
+		}
+	}
+
+	/**
+	 * Callback for when we've received a new block.
+	 * <p>
+	 * See <b>WARNING</b> for {@link EventBus#notify(Event)}
+	 * to prevent deadlocks.
+	 */
 	public void onNewBlock(BlockData latestBlockData) {
-		this.setChainTip(latestBlockData);
+		// Protective copy
+		BlockData blockDataCopy = new BlockData(latestBlockData);
+
+		synchronized (this.latestBlocks) {
+			BlockData cachedChainTip = this.latestBlocks.peekLast();
+
+			if (cachedChainTip != null && Arrays.equals(cachedChainTip.getSignature(), blockDataCopy.getReference())) {
+				// Chain tip is parent for new latest block, so we can safely add new latest block
+				this.latestBlocks.addLast(latestBlockData);
+
+				// Trim if necessary
+				if (this.latestBlocks.size() >= BLOCK_CACHE_SIZE)
+					this.latestBlocks.pollFirst();
+			} else {
+				if (cachedChainTip != null)
+					// Chain tip didn't match - potentially abnormal behaviour?
+					LOGGER.debug(() -> String.format("Cached chain tip %.8s not parent for new latest block %.8s (reference %.8s)",
+							Base58.encode(cachedChainTip.getSignature()),
+							Base58.encode(blockDataCopy.getSignature()),
+							Base58.encode(blockDataCopy.getReference())));
+
+				// Defensively rebuild cache
+				try {
+					this.stats.latestBlocksCacheRefills.incrementAndGet();
+
+					this.refillLatestBlocksCache();
+				} catch (DataException e) {
+					LOGGER.warn(() -> "Couldn't refill latest blocks cache?", e);
+				}
+			}
+		}
+
+		this.onNewOrOrphanedBlock(blockDataCopy, NewBlockEvent::new);
+	}
+
+	public static class OrphanedBlockEvent implements Event {
+		private final BlockData blockData;
+
+		public OrphanedBlockEvent(BlockData blockData) {
+			this.blockData = blockData;
+		}
+
+		public BlockData getBlockData() {
+			return this.blockData;
+		}
+	}
+
+	/**
+	 * Callback for when we've orphaned a block.
+	 * <p>
+	 * See <b>WARNING</b> for {@link EventBus#notify(Event)}
+	 * to prevent deadlocks.
+	 */
+	public void onOrphanedBlock(BlockData latestBlockData) {
+		// Protective copy
+		BlockData blockDataCopy = new BlockData(latestBlockData);
+
+		synchronized (this.latestBlocks) {
+			BlockData cachedChainTip = this.latestBlocks.pollLast();
+			boolean refillNeeded = false;
+
+			if (cachedChainTip != null && Arrays.equals(cachedChainTip.getReference(), blockDataCopy.getSignature())) {
+				// Chain tip was parent for new latest block that has been orphaned, so we're good
+
+				// However, if we've emptied the cache then we will need to refill it
+				refillNeeded = this.latestBlocks.isEmpty();
+			} else {
+				if (cachedChainTip != null)
+					// Chain tip didn't match - potentially abnormal behaviour?
+					LOGGER.debug(() -> String.format("Cached chain tip %.8s (reference %.8s) was not parent for new latest block %.8s",
+							Base58.encode(cachedChainTip.getSignature()),
+							Base58.encode(cachedChainTip.getReference()),
+							Base58.encode(blockDataCopy.getSignature())));
+
+				// Defensively rebuild cache
+				refillNeeded = true;
+			}
+
+			if (refillNeeded)
+				try {
+					this.stats.latestBlocksCacheRefills.incrementAndGet();
+
+					this.refillLatestBlocksCache();
+				} catch (DataException e) {
+					LOGGER.warn(() -> "Couldn't refill latest blocks cache?", e);
+				}
+		}
+
+		this.onNewOrOrphanedBlock(blockDataCopy, OrphanedBlockEvent::new);
+	}
+
+	private void onNewOrOrphanedBlock(BlockData blockDataCopy, Function<BlockData, Event> eventConstructor) {
 		requestSysTrayUpdate = true;
 
-		// Broadcast our new height info and notify websocket listeners
-		this.callbackExecutor.execute(() -> {
-			Network network = Network.getInstance();
-			network.broadcast(peer -> network.buildHeightMessage(peer, latestBlockData));
+		// Notify listeners, trade-bot, etc.
+		EventBus.INSTANCE.notify(eventConstructor.apply(blockDataCopy));
 
-			BlockNotifier.getInstance().onNewBlock(latestBlockData);
-
-			if (this.notifyGroupMembershipChange) {
-				this.notifyGroupMembershipChange = false;
-				ChatNotifier.getInstance().onGroupMembershipChange();
-			}
-		});
+		if (this.notifyGroupMembershipChange) {
+			this.notifyGroupMembershipChange = false;
+			ChatNotifier.getInstance().onGroupMembershipChange();
+		}
 	}
 
 	/** Callback for when we've received a new transaction via API or peer. */
@@ -884,21 +1124,58 @@ public class Controller extends Thread {
 	private void onNetworkGetBlockMessage(Peer peer, Message message) {
 		GetBlockMessage getBlockMessage = (GetBlockMessage) message;
 		byte[] signature = getBlockMessage.getSignature();
+		this.stats.getBlockMessageStats.requests.incrementAndGet();
+
+		ByteArray signatureAsByteArray = new ByteArray(signature);
+
+		BlockMessage cachedBlockMessage = this.blockMessageCache.get(signatureAsByteArray);
+
+		// Check cached latest block message
+		if (cachedBlockMessage != null) {
+			this.stats.getBlockMessageStats.cacheHits.incrementAndGet();
+
+			// We need to duplicate it to prevent multiple threads setting ID on the same message
+			BlockMessage clonedBlockMessage = cachedBlockMessage.cloneWithNewId(message.getId());
+
+			if (!peer.sendMessage(clonedBlockMessage))
+				peer.disconnect("failed to send block");
+
+			return;
+		}
 
 		try (final Repository repository = RepositoryManager.getRepository()) {
 			BlockData blockData = repository.getBlockRepository().fromSignature(signature);
+
 			if (blockData == null) {
-				LOGGER.debug(() -> String.format("Ignoring GET_BLOCK request from peer %s for unknown block %s", peer, Base58.encode(signature)));
-				// Send no response at all???
+				// We don't have this block
+				this.stats.getBlockMessageStats.unknownBlocks.getAndIncrement();
+
+				// Send valid, yet unexpected message type in response, so peer's synchronizer doesn't have to wait for timeout
+				LOGGER.debug(() -> String.format("Sending 'block unknown' response to peer %s for GET_BLOCK request for unknown block %s", peer, Base58.encode(signature)));
+
+				// We'll send empty block summaries message as it's very short
+				Message blockUnknownMessage = new BlockSummariesMessage(Collections.emptyList());
+				blockUnknownMessage.setId(message.getId());
+				if (!peer.sendMessage(blockUnknownMessage))
+					peer.disconnect("failed to send block-unknown response");
 				return;
 			}
 
 			Block block = new Block(repository, blockData);
 
-			Message blockMessage = new BlockMessage(block);
+			BlockMessage blockMessage = new BlockMessage(block);
 			blockMessage.setId(message.getId());
+
+			// This call also causes the other needed data to be pulled in from repository
 			if (!peer.sendMessage(blockMessage))
 				peer.disconnect("failed to send block");
+
+			// If request is for a recent block, cache it
+			if (getChainHeight() - blockData.getHeight() <= BLOCK_CACHE_SIZE) {
+				this.stats.getBlockMessageStats.cacheFills.incrementAndGet();
+
+				this.blockMessageCache.put(new ByteArray(blockData.getSignature()), blockMessage);
+			}
 		} catch (DataException e) {
 			LOGGER.error(String.format("Repository issue while send block %s to peer %s", Base58.encode(signature), peer), e);
 		}
@@ -945,59 +1222,110 @@ public class Controller extends Thread {
 
 	private void onNetworkGetBlockSummariesMessage(Peer peer, Message message) {
 		GetBlockSummariesMessage getBlockSummariesMessage = (GetBlockSummariesMessage) message;
-		byte[] parentSignature = getBlockSummariesMessage.getParentSignature();
+		final byte[] parentSignature = getBlockSummariesMessage.getParentSignature();
+		this.stats.getBlockSummariesStats.requests.incrementAndGet();
 
-		try (final Repository repository = RepositoryManager.getRepository()) {
-			List<BlockSummaryData> blockSummaries = new ArrayList<>();
-
-			int numberRequested = Math.min(Network.MAX_BLOCK_SUMMARIES_PER_REPLY, getBlockSummariesMessage.getNumberRequested());
-
-			do {
-				BlockData blockData = repository.getBlockRepository().fromReference(parentSignature);
-
-				if (blockData == null)
-					// No more blocks to send to peer
-					break;
-
-				BlockSummaryData blockSummary = new BlockSummaryData(blockData);
-				blockSummaries.add(blockSummary);
-				parentSignature = blockData.getSignature();
-			} while (blockSummaries.size() < numberRequested);
-
-			Message blockSummariesMessage = new BlockSummariesMessage(blockSummaries);
+		// If peer's parent signature matches our latest block signature
+		// then we can short-circuit with an empty response
+		BlockData chainTip = getChainTip();
+		if (chainTip != null && Arrays.equals(parentSignature, chainTip.getSignature())) {
+			Message blockSummariesMessage = new BlockSummariesMessage(Collections.emptyList());
 			blockSummariesMessage.setId(message.getId());
 			if (!peer.sendMessage(blockSummariesMessage))
 				peer.disconnect("failed to send block summaries");
-		} catch (DataException e) {
-			LOGGER.error(String.format("Repository issue while sending block summaries after %s to peer %s", Base58.encode(parentSignature), peer), e);
+
+			return;
 		}
+
+		List<BlockSummaryData> blockSummaries = new ArrayList<>();
+
+		// Attempt to serve from our cache of latest blocks
+		synchronized (this.latestBlocks) {
+			blockSummaries = this.latestBlocks.stream()
+					.dropWhile(cachedBlockData -> !Arrays.equals(cachedBlockData.getReference(), parentSignature))
+					.map(BlockSummaryData::new)
+					.collect(Collectors.toList());
+		}
+
+		if (blockSummaries.isEmpty()) {
+			try (final Repository repository = RepositoryManager.getRepository()) {
+				int numberRequested = Math.min(Network.MAX_BLOCK_SUMMARIES_PER_REPLY, getBlockSummariesMessage.getNumberRequested());
+
+				BlockData blockData = repository.getBlockRepository().fromReference(parentSignature);
+
+				while (blockData != null && blockSummaries.size() < numberRequested) {
+					BlockSummaryData blockSummary = new BlockSummaryData(blockData);
+					blockSummaries.add(blockSummary);
+
+					blockData = repository.getBlockRepository().fromReference(blockData.getSignature());
+				}
+			} catch (DataException e) {
+				LOGGER.error(String.format("Repository issue while sending block summaries after %s to peer %s", Base58.encode(parentSignature), peer), e);
+			}
+		} else {
+			this.stats.getBlockSummariesStats.cacheHits.incrementAndGet();
+
+			if (blockSummaries.size() >= getBlockSummariesMessage.getNumberRequested())
+				this.stats.getBlockSummariesStats.fullyFromCache.incrementAndGet();
+		}
+
+		Message blockSummariesMessage = new BlockSummariesMessage(blockSummaries);
+		blockSummariesMessage.setId(message.getId());
+		if (!peer.sendMessage(blockSummariesMessage))
+			peer.disconnect("failed to send block summaries");
 	}
 
 	private void onNetworkGetSignaturesV2Message(Peer peer, Message message) {
 		GetSignaturesV2Message getSignaturesMessage = (GetSignaturesV2Message) message;
-		byte[] parentSignature = getSignaturesMessage.getParentSignature();
+		final byte[] parentSignature = getSignaturesMessage.getParentSignature();
+		this.stats.getBlockSignaturesV2Stats.requests.incrementAndGet();
 
-		try (final Repository repository = RepositoryManager.getRepository()) {
-			List<byte[]> signatures = new ArrayList<>();
-
-			do {
-				BlockData blockData = repository.getBlockRepository().fromReference(parentSignature);
-
-				if (blockData == null)
-					// No more signatures to send to peer
-					break;
-
-				parentSignature = blockData.getSignature();
-				signatures.add(parentSignature);
-			} while (signatures.size() < getSignaturesMessage.getNumberRequested());
-
-			Message signaturesMessage = new SignaturesMessage(signatures);
+		// If peer's parent signature matches our latest block signature
+		// then we can short-circuit with an empty response
+		BlockData chainTip = getChainTip();
+		if (chainTip != null && Arrays.equals(parentSignature, chainTip.getSignature())) {
+			Message signaturesMessage = new SignaturesMessage(Collections.emptyList());
 			signaturesMessage.setId(message.getId());
 			if (!peer.sendMessage(signaturesMessage))
 				peer.disconnect("failed to send signatures (v2)");
-		} catch (DataException e) {
-			LOGGER.error(String.format("Repository issue while sending V2 signatures after %s to peer %s", Base58.encode(parentSignature), peer), e);
+
+			return;
 		}
+
+		List<byte[]> signatures = new ArrayList<>();
+
+		// Attempt to serve from our cache of latest blocks
+		synchronized (this.latestBlocks) {
+			signatures = this.latestBlocks.stream()
+					.dropWhile(cachedBlockData -> !Arrays.equals(cachedBlockData.getReference(), parentSignature))
+					.map(BlockData::getSignature)
+					.collect(Collectors.toList());
+		}
+
+		if (signatures.isEmpty()) {
+			try (final Repository repository = RepositoryManager.getRepository()) {
+				int numberRequested = getSignaturesMessage.getNumberRequested();
+				BlockData blockData = repository.getBlockRepository().fromReference(parentSignature);
+
+				while (blockData != null && signatures.size() < numberRequested) {
+					signatures.add(blockData.getSignature());
+
+					blockData = repository.getBlockRepository().fromReference(blockData.getSignature());
+				}
+			} catch (DataException e) {
+				LOGGER.error(String.format("Repository issue while sending V2 signatures after %s to peer %s", Base58.encode(parentSignature), peer), e);
+			}
+		} else {
+			this.stats.getBlockSignaturesV2Stats.cacheHits.incrementAndGet();
+
+			if (signatures.size() >= getSignaturesMessage.getNumberRequested())
+				this.stats.getBlockSignaturesV2Stats.fullyFromCache.incrementAndGet();
+		}
+
+		Message signaturesMessage = new SignaturesMessage(signatures);
+		signaturesMessage.setId(message.getId());
+		if (!peer.sendMessage(signaturesMessage))
+			peer.disconnect("failed to send signatures (v2)");
 	}
 
 	private void onNetworkHeightV2Message(Peer peer, Message message) {
@@ -1040,7 +1368,12 @@ public class Controller extends Thread {
 
 	private void onNetworkGetUnconfirmedTransactionsMessage(Peer peer, Message message) {
 		try (final Repository repository = RepositoryManager.getRepository()) {
-			List<byte[]> signatures = repository.getTransactionRepository().getUnconfirmedTransactionSignatures();
+			List<byte[]> signatures = Collections.emptyList();
+
+			// If we're NOT up-to-date then don't send out unconfirmed transactions
+			// as it's possible they are already included in a later block that we don't have.
+			if (isUpToDate())
+				signatures = repository.getTransactionRepository().getUnconfirmedTransactionSignatures();
 
 			Message transactionSignaturesMessage = new TransactionSignaturesMessage(signatures);
 			if (!peer.sendMessage(transactionSignaturesMessage))
@@ -1342,9 +1675,6 @@ public class Controller extends Thread {
 
 		// Refresh our online accounts signatures?
 		sendOurOnlineAccountsInfo();
-
-		// Trim blockchain by removing 'old' online accounts signatures
-		BlockChain.trimOldOnlineAccountsSignatures();
 	}
 
 	private void sendOurOnlineAccountsInfo() {
@@ -1446,6 +1776,32 @@ public class Controller extends Thread {
 		}
 	}
 
+	/** Returns cached, unmodifiable list of latest block's online accounts. */
+	public List<OnlineAccountData> getLatestBlocksOnlineAccounts() {
+		synchronized (this.latestBlocksOnlineAccounts) {
+			return this.latestBlocksOnlineAccounts.peekFirst();
+		}
+	}
+
+	/** Caches list of latest block's online accounts. Typically called by Block.process() */
+	public void pushLatestBlocksOnlineAccounts(List<OnlineAccountData> latestBlocksOnlineAccounts) {
+		synchronized (this.latestBlocksOnlineAccounts) {
+			if (this.latestBlocksOnlineAccounts.size() == MAX_BLOCKS_CACHED_ONLINE_ACCOUNTS)
+				this.latestBlocksOnlineAccounts.pollLast();
+
+			this.latestBlocksOnlineAccounts.addFirst(latestBlocksOnlineAccounts == null
+					? Collections.emptyList()
+					: Collections.unmodifiableList(latestBlocksOnlineAccounts));
+		}
+	}
+
+	/** Reverts list of latest block's online accounts. Typically called by Block.orphan() */
+	public void popLatestBlocksOnlineAccounts() {
+		synchronized (this.latestBlocksOnlineAccounts) {
+			this.latestBlocksOnlineAccounts.pollFirst();
+		}
+	}
+
 	public byte[] fetchArbitraryData(byte[] signature) throws InterruptedException {
 		// Build request
 		Message getArbitraryDataMessage = new GetArbitraryDataMessage(signature);
@@ -1580,4 +1936,8 @@ public class Controller extends Thread {
 		return now - offset;
 	}
 
+	public StatsSnapshot getStatsSnapshot() {
+		return this.stats;
+	}
+
 }

src/main/java/org/qortal/controller/OnlineAccountsSignaturesTrimmer.java

@@ -0,0 +1,79 @@
+package org.qortal.controller;
+
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
+import org.qortal.block.BlockChain;
+import org.qortal.data.block.BlockData;
+import org.qortal.repository.DataException;
+import org.qortal.repository.Repository;
+import org.qortal.repository.RepositoryManager;
+import org.qortal.settings.Settings;
+import org.qortal.utils.NTP;
+
+public class OnlineAccountsSignaturesTrimmer implements Runnable {
+
+	private static final Logger LOGGER = LogManager.getLogger(OnlineAccountsSignaturesTrimmer.class);
+
+	private static final long INITIAL_SLEEP_PERIOD = 5 * 60 * 1000L + 1234L; // ms
+
+	public void run() {
+		Thread.currentThread().setName("Online Accounts trimmer");
+
+		try (final Repository repository = RepositoryManager.getRepository()) {
+			// Don't even start trimming until initial rush has ended
+			Thread.sleep(INITIAL_SLEEP_PERIOD);
+
+			int trimStartHeight = repository.getBlockRepository().getOnlineAccountsSignaturesTrimHeight();
+
+			while (!Controller.isStopping()) {
+				repository.discardChanges();
+
+				Thread.sleep(Settings.getInstance().getOnlineSignaturesTrimInterval());
+
+				BlockData chainTip = Controller.getInstance().getChainTip();
+				if (chainTip == null || NTP.getTime() == null)
+					continue;
+
+				// Don't even attempt if we're mid-sync as our repository requests will be delayed for ages
+				if (Controller.getInstance().isSynchronizing())
+					continue;
+
+				// Trim blockchain by removing 'old' online accounts signatures
+				long upperTrimmableTimestamp = NTP.getTime() - BlockChain.getInstance().getOnlineAccountSignaturesMaxLifetime();
+				int upperTrimmableHeight = repository.getBlockRepository().getHeightFromTimestamp(upperTrimmableTimestamp);
+
+				int upperBatchHeight = trimStartHeight + Settings.getInstance().getOnlineSignaturesTrimBatchSize();
+				int upperTrimHeight = Math.min(upperBatchHeight, upperTrimmableHeight);
+
+				if (trimStartHeight >= upperTrimHeight)
+					continue;
+
+				int numSigsTrimmed = repository.getBlockRepository().trimOldOnlineAccountsSignatures(trimStartHeight, upperTrimHeight);
+				repository.saveChanges();
+
+				if (numSigsTrimmed > 0) {
+					final int finalTrimStartHeight = trimStartHeight;
+					LOGGER.debug(() -> String.format("Trimmed %d online accounts signature%s between blocks %d and %d",
+							numSigsTrimmed, (numSigsTrimmed != 1 ? "s" : ""),
+							finalTrimStartHeight, upperTrimHeight));
+				} else {
+					// Can we move onto next batch?
+					if (upperTrimmableHeight > upperBatchHeight) {
+						trimStartHeight = upperBatchHeight;
+
+						repository.getBlockRepository().setOnlineAccountsSignaturesTrimHeight(trimStartHeight);
+						repository.saveChanges();
+
+						final int finalTrimStartHeight = trimStartHeight;
+						LOGGER.debug(() -> String.format("Bumping online accounts signatures base trim height to %d", finalTrimStartHeight));
+					}
+				}
+			}
+		} catch (DataException e) {
+			LOGGER.warn(String.format("Repository issue trying to trim online accounts signatures: %s", e.getMessage()));
+		} catch (InterruptedException e) {
+			// Time to exit
+		}
+	}
+
+}

src/main/java/org/qortal/controller/StatusNotifier.java

@@ -1,42 +0,0 @@
-package org.qortal.controller;
-
-import java.util.HashMap;
-import java.util.Map;
-
-import org.eclipse.jetty.websocket.api.Session;
-
-public class StatusNotifier {
-
-	private static StatusNotifier instance;
-
-	@FunctionalInterface
-	public interface Listener {
-		void notify(long timestamp);
-	}
-
-	private Map<Session, Listener> listenersBySession = new HashMap<>();
-
-	private StatusNotifier() {
-	}
-
-	public static synchronized StatusNotifier getInstance() {
-		if (instance == null)
-			instance = new StatusNotifier();
-
-		return instance;
-	}
-
-	public synchronized void register(Session session, Listener listener) {
-		this.listenersBySession.put(session, listener);
-	}
-
-	public synchronized void deregister(Session session) {
-		this.listenersBySession.remove(session);
-	}
-
-	public synchronized void onStatusChange(long now) {
-		for (Listener listener : this.listenersBySession.values())
-			listener.notify(now);
-	}
-
-}

src/main/java/org/qortal/controller/Synchronizer.java

@@ -4,6 +4,7 @@ import java.math.BigInteger;
 import java.text.DecimalFormat;
 import java.text.NumberFormat;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.List;
 import java.util.concurrent.locks.ReentrantLock;
 import java.util.stream.Collectors;
@@ -11,11 +12,13 @@ import java.util.stream.Collectors;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 import org.qortal.account.Account;
+import org.qortal.account.PublicKeyAccount;
 import org.qortal.block.Block;
 import org.qortal.block.Block.ValidationResult;
 import org.qortal.data.block.BlockData;
 import org.qortal.data.block.BlockSummaryData;
 import org.qortal.data.network.PeerChainTipData;
+import org.qortal.data.transaction.RewardShareTransactionData;
 import org.qortal.data.transaction.TransactionData;
 import org.qortal.network.Peer;
 import org.qortal.network.message.BlockMessage;
@@ -126,167 +129,22 @@ public class Synchronizer {
 
 					// Unless we're doing a forced sync, we might need to compare blocks after common block
 					if (!force && ourInitialHeight > commonBlockHeight) {
-						// If our latest block is very old, we're very behind and should ditch our fork.
-						final Long minLatestBlockTimestamp = Controller.getMinimumLatestBlockTimestamp();
-						if (minLatestBlockTimestamp == null)
-							return SynchronizationResult.REPOSITORY_ISSUE;
-
-						if (ourLatestBlockData.getTimestamp() < minLatestBlockTimestamp) {
-							LOGGER.info(String.format("Ditching our chain after height %d as our latest block is very old", commonBlockHeight));
-						} else {
-							// Compare chain weights
-
-							LOGGER.debug(String.format("Comparing chains from block %d with peer %s", commonBlockHeight + 1, peer));
-
-							// Fetch remaining peer's block summaries (which we also use to fill signatures list)
-							int peerBlockCount = peerHeight - commonBlockHeight;
-
-							while (peerBlockSummaries.size() < peerBlockCount) {
-								if (Controller.isStopping())
-									return SynchronizationResult.SHUTTING_DOWN;
-
-								int lastSummaryHeight = commonBlockHeight + peerBlockSummaries.size();
-								byte[] previousSignature;
-								if (peerBlockSummaries.isEmpty())
-									previousSignature = commonBlockSig;
-								else
-									previousSignature = peerBlockSummaries.get(peerBlockSummaries.size() - 1).getSignature();
-
-								List<BlockSummaryData> moreBlockSummaries = this.getBlockSummaries(peer, previousSignature, peerBlockCount - peerBlockSummaries.size());
-
-								if (moreBlockSummaries == null || moreBlockSummaries.isEmpty()) {
-									LOGGER.info(String.format("Peer %s failed to respond with block summaries after height %d, sig %.8s", peer,
-											lastSummaryHeight, Base58.encode(previousSignature)));
-									return SynchronizationResult.NO_REPLY;
-								}
-
-								// Check peer sent valid heights
-								for (int i = 0; i < moreBlockSummaries.size(); ++i) {
-									++lastSummaryHeight;
-
-									BlockSummaryData blockSummary = moreBlockSummaries.get(i);
-
-									if (blockSummary.getHeight() != lastSummaryHeight) {
-										LOGGER.info(String.format("Peer %s responded with invalid block summary for height %d, sig %.8s", peer,
-												lastSummaryHeight, Base58.encode(blockSummary.getSignature())));
-										return SynchronizationResult.NO_REPLY;
-									}
-								}
-
-								peerBlockSummaries.addAll(moreBlockSummaries);
-							}
-
-							// Fetch our corresponding block summaries
-							List<BlockSummaryData> ourBlockSummaries = repository.getBlockRepository().getBlockSummaries(commonBlockHeight + 1, ourInitialHeight);
-
-							// Populate minter account levels for both lists of block summaries
-							populateBlockSummariesMinterLevels(repository, peerBlockSummaries);
-							populateBlockSummariesMinterLevels(repository, ourBlockSummaries);
-
-							// Calculate cumulative chain weights of both blockchain subsets, from common block to highest mutual block.
-							BigInteger ourChainWeight = Block.calcChainWeight(commonBlockHeight, commonBlockSig, ourBlockSummaries);
-							BigInteger peerChainWeight = Block.calcChainWeight(commonBlockHeight, commonBlockSig, peerBlockSummaries);
-
-							// If our blockchain has greater weight then don't synchronize with peer
-							if (ourChainWeight.compareTo(peerChainWeight) >= 0) {
-								LOGGER.debug(String.format("Not synchronizing with peer %s as we have better blockchain", peer));
-								NumberFormat formatter = new DecimalFormat("0.###E0");
-								LOGGER.debug(String.format("Our chain weight: %s, peer's chain weight: %s (higher is better)", formatter.format(ourChainWeight), formatter.format(peerChainWeight)));
-								return SynchronizationResult.INFERIOR_CHAIN;
-							}
-						}
+						SynchronizationResult chainCompareResult = compareChains(repository, commonBlockData, ourLatestBlockData, peer, peerHeight, peerBlockSummaries);
+						if (chainCompareResult != SynchronizationResult.OK)
+							return chainCompareResult;
 					}
 
-					int ourHeight = ourInitialHeight;
-					if (ourHeight > commonBlockHeight) {
-						// Unwind to common block (unless common block is our latest block)
-						LOGGER.debug(String.format("Orphaning blocks back to common block height %d, sig %.8s", commonBlockHeight, commonBlockSig58));
-
-						while (ourHeight > commonBlockHeight) {
-							if (Controller.isStopping())
-								return SynchronizationResult.SHUTTING_DOWN;
-
-							BlockData blockData = repository.getBlockRepository().fromHeight(ourHeight);
-							Block block = new Block(repository, blockData);
-							block.orphan();
-
-							--ourHeight;
-						}
-
-						LOGGER.debug(String.format("Orphaned blocks back to height %d, sig %.8s - fetching blocks from peer %s", commonBlockHeight, commonBlockSig58, peer));
+					SynchronizationResult syncResult = null;
+					if (commonBlockHeight < ourInitialHeight) {
+						// Peer's chain is better, sync to that one
+						syncResult = syncToPeerChain(repository, commonBlockData, ourInitialHeight, peer, peerHeight, peerBlockSummaries);
 					} else {
-						LOGGER.debug(String.format("Fetching new blocks from peer %s", peer));
+						// Simply fetch and apply blocks as they arrive
+						syncResult = applyNewBlocks(repository, commonBlockData, ourInitialHeight, peer, peerHeight, peerBlockSummaries);
 					}
 
-					// Fetch, and apply, blocks from peer
-					byte[] latestPeerSignature = commonBlockSig;
-					int maxBatchHeight = commonBlockHeight + SYNC_BATCH_SIZE;
-
-					// Convert any block summaries from above into signatures to request from peer
-					List<byte[]> peerBlockSignatures = peerBlockSummaries.stream().map(BlockSummaryData::getSignature).collect(Collectors.toList());
-
-					while (ourHeight < peerHeight && ourHeight < maxBatchHeight) {
-						if (Controller.isStopping())
-							return SynchronizationResult.SHUTTING_DOWN;
-
-						// Do we need more signatures?
-						if (peerBlockSignatures.isEmpty()) {
-							int numberRequested = maxBatchHeight - ourHeight;
-							LOGGER.trace(String.format("Requesting %d signature%s after height %d, sig %.8s",
-									numberRequested, (numberRequested != 1 ? "s": ""), ourHeight, Base58.encode(latestPeerSignature)));
-
-							peerBlockSignatures = this.getBlockSignatures(peer, latestPeerSignature, numberRequested);
-
-							if (peerBlockSignatures == null || peerBlockSignatures.isEmpty()) {
-								LOGGER.info(String.format("Peer %s failed to respond with more block signatures after height %d, sig %.8s", peer,
-										ourHeight, Base58.encode(latestPeerSignature)));
-								return SynchronizationResult.NO_REPLY;
-							}
-
-							LOGGER.trace(String.format("Received %s signature%s", peerBlockSignatures.size(), (peerBlockSignatures.size() != 1 ? "s" : "")));
-						}
-
-						latestPeerSignature = peerBlockSignatures.get(0);
-						peerBlockSignatures.remove(0);
-						++ourHeight;
-
-						Block newBlock = this.fetchBlock(repository, peer, latestPeerSignature);
-
-						if (newBlock == null) {
-							LOGGER.info(String.format("Peer %s failed to respond with block for height %d, sig %.8s", peer,
-									ourHeight, Base58.encode(latestPeerSignature)));
-							return SynchronizationResult.NO_REPLY;
-						}
-
-						if (!newBlock.isSignatureValid()) {
-							LOGGER.info(String.format("Peer %s sent block with invalid signature for height %d, sig %.8s", peer,
-									ourHeight, Base58.encode(latestPeerSignature)));
-							return SynchronizationResult.INVALID_DATA;
-						}
-
-						// Transactions are transmitted without approval status so determine that now
-						for (Transaction transaction : newBlock.getTransactions())
-							transaction.setInitialApprovalStatus();
-
-						ValidationResult blockResult = newBlock.isValid();
-						if (blockResult != ValidationResult.OK) {
-							LOGGER.info(String.format("Peer %s sent invalid block for height %d, sig %.8s: %s", peer,
-									ourHeight, Base58.encode(latestPeerSignature), blockResult.name()));
-							return SynchronizationResult.INVALID_DATA;
-						}
-
-						// Save transactions attached to this block
-						for (Transaction transaction : newBlock.getTransactions()) {
-							TransactionData transactionData = transaction.getTransactionData();
-							repository.getTransactionRepository().save(transactionData);
-						}
-
-						newBlock.process();
-
-						// If we've grown our blockchain then at least save progress so far
-						if (ourHeight > ourInitialHeight)
-							repository.saveChanges();
-					}
+					if (syncResult != SynchronizationResult.OK)
+						return syncResult;
 
 					// Commit
 					repository.saveChanges();
@@ -317,7 +175,7 @@ public class Synchronizer {
 	 * @throws DataException
 	 * @throws InterruptedException
 	 */
-	private SynchronizationResult fetchSummariesFromCommonBlock(Repository repository, Peer peer, int ourHeight, boolean force, List<BlockSummaryData> blockSummariesFromCommon) throws DataException, InterruptedException {
+	public SynchronizationResult fetchSummariesFromCommonBlock(Repository repository, Peer peer, int ourHeight, boolean force, List<BlockSummaryData> blockSummariesFromCommon) throws DataException, InterruptedException {
 		// Start by asking for a few recent block hashes as this will cover a majority of reorgs
 		// Failing that, back off exponentially
 		int step = INITIAL_BLOCK_STEP;
@@ -383,14 +241,291 @@ public class Synchronizer {
 		blockSummariesFromCommon.addAll(blockSummariesBatch);
 
 		// Trim summaries so that first summary is common block.
-		// Currently we work back from the end until we hit a block we also have.
+		// Currently we work forward from common block until we hit a block we don't have
 		// TODO: rewrite as modified binary search!
-		for (int i = blockSummariesFromCommon.size() - 1; i > 0; --i) {
-			if (repository.getBlockRepository().exists(blockSummariesFromCommon.get(i).getSignature())) {
-				// Note: index i isn't cleared: List.subList is fromIndex inclusive to toIndex exclusive
-				blockSummariesFromCommon.subList(0, i).clear();
+		int i;
+		for (i = 1; i < blockSummariesFromCommon.size(); ++i)
+			if (!repository.getBlockRepository().exists(blockSummariesFromCommon.get(i).getSignature()))
 				break;
+
+		// Note: index i - 1 isn't cleared: List.subList is fromIndex inclusive to toIndex exclusive
+		blockSummariesFromCommon.subList(0, i - 1).clear();
+
+		return SynchronizationResult.OK;
+	}
+
+	private SynchronizationResult compareChains(Repository repository, BlockData commonBlockData, BlockData ourLatestBlockData,
+			Peer peer, int peerHeight, List<BlockSummaryData> peerBlockSummaries) throws DataException, InterruptedException {
+		final int commonBlockHeight = commonBlockData.getHeight();
+		final byte[] commonBlockSig = commonBlockData.getSignature();
+
+		// If our latest block is very old, we're very behind and should ditch our fork.
+		final Long minLatestBlockTimestamp = Controller.getMinimumLatestBlockTimestamp();
+		if (minLatestBlockTimestamp == null)
+			return SynchronizationResult.REPOSITORY_ISSUE;
+
+		if (ourLatestBlockData.getTimestamp() < minLatestBlockTimestamp) {
+			LOGGER.info(String.format("Ditching our chain after height %d as our latest block is very old", commonBlockHeight));
+		} else {
+			// Compare chain weights
+
+			LOGGER.debug(String.format("Comparing chains from block %d with peer %s", commonBlockHeight + 1, peer));
+
+			// Fetch remaining peer's block summaries (which we also use to fill signatures list)
+			int peerBlockCount = peerHeight - commonBlockHeight;
+
+			while (peerBlockSummaries.size() < peerBlockCount) {
+				if (Controller.isStopping())
+					return SynchronizationResult.SHUTTING_DOWN;
+
+				int lastSummaryHeight = commonBlockHeight + peerBlockSummaries.size();
+				byte[] previousSignature;
+				if (peerBlockSummaries.isEmpty())
+					previousSignature = commonBlockSig;
+				else
+					previousSignature = peerBlockSummaries.get(peerBlockSummaries.size() - 1).getSignature();
+
+				List<BlockSummaryData> moreBlockSummaries = this.getBlockSummaries(peer, previousSignature, peerBlockCount - peerBlockSummaries.size());
+
+				if (moreBlockSummaries == null || moreBlockSummaries.isEmpty()) {
+					LOGGER.info(String.format("Peer %s failed to respond with block summaries after height %d, sig %.8s", peer,
+							lastSummaryHeight, Base58.encode(previousSignature)));
+					return SynchronizationResult.NO_REPLY;
+				}
+
+				// Check peer sent valid heights
+				for (int i = 0; i < moreBlockSummaries.size(); ++i) {
+					++lastSummaryHeight;
+
+					BlockSummaryData blockSummary = moreBlockSummaries.get(i);
+
+					if (blockSummary.getHeight() != lastSummaryHeight) {
+						LOGGER.info(String.format("Peer %s responded with invalid block summary for height %d, sig %.8s", peer,
+								lastSummaryHeight, Base58.encode(blockSummary.getSignature())));
+						return SynchronizationResult.NO_REPLY;
+					}
+				}
+
+				peerBlockSummaries.addAll(moreBlockSummaries);
 			}
+
+			// Fetch our corresponding block summaries
+			List<BlockSummaryData> ourBlockSummaries = repository.getBlockRepository().getBlockSummaries(commonBlockHeight + 1, ourLatestBlockData.getHeight());
+
+			// Populate minter account levels for both lists of block summaries
+			populateBlockSummariesMinterLevels(repository, ourBlockSummaries);
+			populateBlockSummariesMinterLevels(repository, peerBlockSummaries);
+
+			final int mutualHeight = commonBlockHeight - 1 + Math.min(ourBlockSummaries.size(), peerBlockSummaries.size());
+
+			// Calculate cumulative chain weights of both blockchain subsets, from common block to highest mutual block.
+			BigInteger ourChainWeight = Block.calcChainWeight(commonBlockHeight, commonBlockSig, ourBlockSummaries, mutualHeight);
+			BigInteger peerChainWeight = Block.calcChainWeight(commonBlockHeight, commonBlockSig, peerBlockSummaries, mutualHeight);
+
+			NumberFormat formatter = new DecimalFormat("0.###E0");
+			LOGGER.debug(String.format("Our chain weight: %s, peer's chain weight: %s (higher is better)", formatter.format(ourChainWeight), formatter.format(peerChainWeight)));
+
+			// If our blockchain has greater weight then don't synchronize with peer
+			if (ourChainWeight.compareTo(peerChainWeight) >= 0) {
+				LOGGER.debug(String.format("Not synchronizing with peer %s as we have better blockchain", peer));
+				return SynchronizationResult.INFERIOR_CHAIN;
+			}
+		}
+
+		return SynchronizationResult.OK;
+	}
+
+	private SynchronizationResult syncToPeerChain(Repository repository, BlockData commonBlockData, int ourInitialHeight,
+			Peer peer, final int peerHeight, List<BlockSummaryData> peerBlockSummaries) throws DataException, InterruptedException {
+		final int commonBlockHeight = commonBlockData.getHeight();
+		final byte[] commonBlockSig = commonBlockData.getSignature();
+		String commonBlockSig58 = Base58.encode(commonBlockSig);
+
+		LOGGER.debug(() -> String.format("Fetching peer %s chain from height %d, sig %.8s", peer, commonBlockHeight, commonBlockSig58));
+
+		int ourHeight = ourInitialHeight;
+
+		// Overall plan: fetch peer's blocks first, then orphan, then apply
+
+		// Convert any leftover (post-common) block summaries into signatures to request from peer
+		List<byte[]> peerBlockSignatures = peerBlockSummaries.stream().map(BlockSummaryData::getSignature).collect(Collectors.toList());
+
+		// Fetch remaining block signatures, if needed
+		int numberSignaturesRequired = peerBlockSignatures.size() - (peerHeight - commonBlockHeight);
+		if (numberSignaturesRequired > 0) {
+			byte[] latestPeerSignature = peerBlockSignatures.isEmpty() ? commonBlockSig : peerBlockSignatures.get(peerBlockSignatures.size() - 1);
+
+			LOGGER.trace(String.format("Requesting %d signature%s after height %d, sig %.8s",
+					numberSignaturesRequired, (numberSignaturesRequired != 1 ? "s": ""), ourHeight, Base58.encode(latestPeerSignature)));
+
+			List<byte[]> moreBlockSignatures = this.getBlockSignatures(peer, latestPeerSignature, numberSignaturesRequired);
+
+			if (moreBlockSignatures == null || moreBlockSignatures.isEmpty()) {
+				LOGGER.info(String.format("Peer %s failed to respond with more block signatures after height %d, sig %.8s", peer,
+						ourHeight, Base58.encode(latestPeerSignature)));
+				return SynchronizationResult.NO_REPLY;
+			}
+
+			LOGGER.trace(String.format("Received %s signature%s", peerBlockSignatures.size(), (peerBlockSignatures.size() != 1 ? "s" : "")));
+
+			peerBlockSignatures.addAll(moreBlockSignatures);
+		}
+
+		// Fetch blocks using signatures
+		LOGGER.debug(String.format("Fetching new blocks from peer %s", peer));
+		List<Block> peerBlocks = new ArrayList<>();
+
+		for (byte[] blockSignature : peerBlockSignatures) {
+			Block newBlock = this.fetchBlock(repository, peer, blockSignature);
+
+			if (newBlock == null) {
+				LOGGER.info(String.format("Peer %s failed to respond with block for height %d, sig %.8s", peer,
+						ourHeight, Base58.encode(blockSignature)));
+				return SynchronizationResult.NO_REPLY;
+			}
+
+			if (!newBlock.isSignatureValid()) {
+				LOGGER.info(String.format("Peer %s sent block with invalid signature for height %d, sig %.8s", peer,
+						ourHeight, Base58.encode(blockSignature)));
+				return SynchronizationResult.INVALID_DATA;
+			}
+
+			// Transactions are transmitted without approval status so determine that now
+			for (Transaction transaction : newBlock.getTransactions())
+				transaction.setInitialApprovalStatus();
+
+			peerBlocks.add(newBlock);
+		}
+
+		// Unwind to common block (unless common block is our latest block)
+		LOGGER.debug(String.format("Orphaning blocks back to common block height %d, sig %.8s", commonBlockHeight, commonBlockSig58));
+
+		BlockData orphanBlockData = repository.getBlockRepository().fromHeight(ourHeight);
+		while (ourHeight > commonBlockHeight) {
+			if (Controller.isStopping())
+				return SynchronizationResult.SHUTTING_DOWN;
+
+			Block block = new Block(repository, orphanBlockData);
+			block.orphan();
+
+			LOGGER.trace(String.format("Orphaned block height %d, sig %.8s", ourHeight, Base58.encode(orphanBlockData.getSignature())));
+
+			repository.saveChanges();
+
+			--ourHeight;
+			orphanBlockData = repository.getBlockRepository().fromHeight(ourHeight);
+
+			repository.discardChanges(); // clear transaction status to prevent deadlocks
+			Controller.getInstance().onOrphanedBlock(orphanBlockData);
+		}
+
+		LOGGER.debug(String.format("Orphaned blocks back to height %d, sig %.8s - applying new blocks from peer %s", commonBlockHeight, commonBlockSig58, peer));
+
+		for (Block newBlock : peerBlocks) {
+			ValidationResult blockResult = newBlock.isValid();
+			if (blockResult != ValidationResult.OK) {
+				LOGGER.info(String.format("Peer %s sent invalid block for height %d, sig %.8s: %s", peer,
+						ourHeight, Base58.encode(newBlock.getSignature()), blockResult.name()));
+				return SynchronizationResult.INVALID_DATA;
+			}
+
+			// Save transactions attached to this block
+			for (Transaction transaction : newBlock.getTransactions()) {
+				TransactionData transactionData = transaction.getTransactionData();
+				repository.getTransactionRepository().save(transactionData);
+			}
+
+			newBlock.process();
+
+			LOGGER.trace(String.format("Processed block height %d, sig %.8s", newBlock.getBlockData().getHeight(), Base58.encode(newBlock.getBlockData().getSignature())));
+
+			repository.saveChanges();
+
+			Controller.getInstance().onNewBlock(newBlock.getBlockData());
+		}
+
+		return SynchronizationResult.OK;
+	}
+
+	private SynchronizationResult applyNewBlocks(Repository repository, BlockData commonBlockData, int ourInitialHeight,
+			Peer peer, int peerHeight, List<BlockSummaryData> peerBlockSummaries) throws InterruptedException, DataException {
+		LOGGER.debug(String.format("Fetching new blocks from peer %s", peer));
+
+		final int commonBlockHeight = commonBlockData.getHeight();
+		final byte[] commonBlockSig = commonBlockData.getSignature();
+
+		int ourHeight = ourInitialHeight;
+
+		// Fetch, and apply, blocks from peer
+		byte[] latestPeerSignature = commonBlockSig;
+		int maxBatchHeight = commonBlockHeight + SYNC_BATCH_SIZE;
+
+		// Convert any block summaries from above into signatures to request from peer
+		List<byte[]> peerBlockSignatures = peerBlockSummaries.stream().map(BlockSummaryData::getSignature).collect(Collectors.toList());
+
+		while (ourHeight < peerHeight && ourHeight < maxBatchHeight) {
+			if (Controller.isStopping())
+				return SynchronizationResult.SHUTTING_DOWN;
+
+			// Do we need more signatures?
+			if (peerBlockSignatures.isEmpty()) {
+				int numberRequested = maxBatchHeight - ourHeight;
+				LOGGER.trace(String.format("Requesting %d signature%s after height %d, sig %.8s",
+						numberRequested, (numberRequested != 1 ? "s": ""), ourHeight, Base58.encode(latestPeerSignature)));
+
+				peerBlockSignatures = this.getBlockSignatures(peer, latestPeerSignature, numberRequested);
+
+				if (peerBlockSignatures == null || peerBlockSignatures.isEmpty()) {
+					LOGGER.info(String.format("Peer %s failed to respond with more block signatures after height %d, sig %.8s", peer,
+							ourHeight, Base58.encode(latestPeerSignature)));
+					return SynchronizationResult.NO_REPLY;
+				}
+
+				LOGGER.trace(String.format("Received %s signature%s", peerBlockSignatures.size(), (peerBlockSignatures.size() != 1 ? "s" : "")));
+			}
+
+			latestPeerSignature = peerBlockSignatures.get(0);
+			peerBlockSignatures.remove(0);
+			++ourHeight;
+
+			Block newBlock = this.fetchBlock(repository, peer, latestPeerSignature);
+
+			if (newBlock == null) {
+				LOGGER.info(String.format("Peer %s failed to respond with block for height %d, sig %.8s", peer,
+						ourHeight, Base58.encode(latestPeerSignature)));
+				return SynchronizationResult.NO_REPLY;
+			}
+
+			if (!newBlock.isSignatureValid()) {
+				LOGGER.info(String.format("Peer %s sent block with invalid signature for height %d, sig %.8s", peer,
+						ourHeight, Base58.encode(latestPeerSignature)));
+				return SynchronizationResult.INVALID_DATA;
+			}
+
+			// Transactions are transmitted without approval status so determine that now
+			for (Transaction transaction : newBlock.getTransactions())
+				transaction.setInitialApprovalStatus();
+
+			ValidationResult blockResult = newBlock.isValid();
+			if (blockResult != ValidationResult.OK) {
+				LOGGER.info(String.format("Peer %s sent invalid block for height %d, sig %.8s: %s", peer,
+						ourHeight, Base58.encode(latestPeerSignature), blockResult.name()));
+				return SynchronizationResult.INVALID_DATA;
+			}
+
+			// Save transactions attached to this block
+			for (Transaction transaction : newBlock.getTransactions()) {
+				TransactionData transactionData = transaction.getTransactionData();
+				repository.getTransactionRepository().save(transactionData);
+			}
+
+			newBlock.process();
+
+			LOGGER.trace(String.format("Processed block height %d, sig %.8s", newBlock.getBlockData().getHeight(), Base58.encode(newBlock.getBlockData().getSignature())));
+
+			repository.saveChanges();
+
+			Controller.getInstance().onNewBlock(newBlock.getBlockData());
 		}
 
 		return SynchronizationResult.OK;
@@ -433,16 +568,34 @@ public class Synchronizer {
 	}
 
 	private void populateBlockSummariesMinterLevels(Repository repository, List<BlockSummaryData> blockSummaries) throws DataException {
+		final int firstBlockHeight = blockSummaries.get(0).getHeight();
+
 		for (int i = 0; i < blockSummaries.size(); ++i) {
 			BlockSummaryData blockSummary = blockSummaries.get(i);
 
 			// Qortal: minter is always a reward-share, so find actual minter and get their effective minting level
 			int minterLevel = Account.getRewardShareEffectiveMintingLevel(repository, blockSummary.getMinterPublicKey());
 			if (minterLevel == 0) {
-				// We don't want to throw, or use zero, as this will kill Controller thread and make client unstable.
-				// So we log this but use 1 instead
-				LOGGER.warn(String.format("Unexpected zero effective minter level for reward-share %s - using 1 instead!", Base58.encode(blockSummary.getMinterPublicKey())));
-				minterLevel = 1;
+				// It looks like this block's minter's reward-share has been cancelled.
+				// So search for REWARD_SHARE transactions since common block to find missing minter info
+				List<byte[]> transactionSignatures = repository.getTransactionRepository().getSignaturesMatchingCriteria(Transaction.TransactionType.REWARD_SHARE, null, firstBlockHeight, null);
+
+				for (byte[] transactionSignature : transactionSignatures) {
+					RewardShareTransactionData transactionData = (RewardShareTransactionData) repository.getTransactionRepository().fromSignature(transactionSignature);
+
+					if (transactionData != null && Arrays.equals(transactionData.getRewardSharePublicKey(), blockSummary.getMinterPublicKey())) {
+						Account rewardShareMinter = new PublicKeyAccount(repository, transactionData.getMinterPublicKey());
+						minterLevel = rewardShareMinter.getEffectiveMintingLevel();
+						break;
+					}
+				}
+
+				if (minterLevel == 0) {
+					// We don't want to throw, or use zero, as this will kill Controller thread and make client unstable.
+					// So we log this but use 1 instead
+					LOGGER.debug(() -> String.format("Unexpected zero effective minter level for reward-share %s - using 1 instead!", Base58.encode(blockSummary.getMinterPublicKey())));
+					minterLevel = 1;
+				}
 			}
 
 			blockSummary.setMinterLevel(minterLevel);

src/main/java/org/qortal/crosschain/BTC.java

@@ -1,35 +1,63 @@
 package org.qortal.crosschain;
 
 import java.util.ArrayList;
+import java.util.HashSet;
 import java.util.List;
+import java.util.Set;
 import java.util.stream.Collectors;
 
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 import org.bitcoinj.core.Address;
 import org.bitcoinj.core.Coin;
+import org.bitcoinj.core.Context;
+import org.bitcoinj.core.ECKey;
+import org.bitcoinj.core.InsufficientMoneyException;
+import org.bitcoinj.core.LegacyAddress;
 import org.bitcoinj.core.NetworkParameters;
+import org.bitcoinj.core.Sha256Hash;
 import org.bitcoinj.core.Transaction;
 import org.bitcoinj.core.TransactionOutput;
+import org.bitcoinj.core.UTXO;
+import org.bitcoinj.core.UTXOProvider;
+import org.bitcoinj.core.UTXOProviderException;
+import org.bitcoinj.crypto.ChildNumber;
+import org.bitcoinj.crypto.DeterministicHierarchy;
+import org.bitcoinj.crypto.DeterministicKey;
 import org.bitcoinj.params.MainNetParams;
 import org.bitcoinj.params.RegTestParams;
 import org.bitcoinj.params.TestNet3Params;
+import org.bitcoinj.script.Script.ScriptType;
 import org.bitcoinj.script.ScriptBuilder;
 import org.bitcoinj.utils.MonetaryFormat;
+import org.bitcoinj.wallet.DeterministicKeyChain;
+import org.bitcoinj.wallet.SendRequest;
+import org.bitcoinj.wallet.Wallet;
+import org.qortal.crypto.Crypto;
 import org.qortal.settings.Settings;
 import org.qortal.utils.BitTwiddling;
-import org.qortal.utils.Pair;
+
+import com.google.common.hash.HashCode;
 
 public class BTC {
 
-	public static final MonetaryFormat FORMAT = new MonetaryFormat().minDecimals(8).postfixCode();
 	public static final long NO_LOCKTIME_NO_RBF_SEQUENCE = 0xFFFFFFFFL;
 	public static final long LOCKTIME_NO_RBF_SEQUENCE = NO_LOCKTIME_NO_RBF_SEQUENCE - 1;
 	public static final int HASH160_LENGTH = 20;
 
+	public static final boolean INCLUDE_UNCONFIRMED = true;
+	public static final boolean EXCLUDE_UNCONFIRMED = false;
+
 	protected static final Logger LOGGER = LogManager.getLogger(BTC.class);
 
+	// Temporary values until a dynamic fee system is written.
+	private static final long OLD_FEE_AMOUNT = 4_000L; // Not 5000 so that existing P2SH-B can output 1000, avoiding dust issue, leaving 4000 for fees.
+	private static final long NEW_FEE_TIMESTAMP = 1598280000000L; // milliseconds since epoch
+	private static final long NEW_FEE_AMOUNT = 10_000L;
+	private static final long NON_MAINNET_FEE = 1000L; // enough for TESTNET3 and should be OK for REGTEST
+
 	private static final int TIMESTAMP_OFFSET = 4 + 32 + 32;
+	private static final MonetaryFormat FORMAT = new MonetaryFormat().minDecimals(8).postfixCode();
 
 	public enum BitcoinNet {
 		MAIN {
@@ -57,6 +85,10 @@ public class BTC {
 	private static BTC instance;
 	private final NetworkParameters params;
 	private final ElectrumX electrumX;
+	private final Context bitcoinjContext;
+
+	// Let ECKey.equals() do the hard work
+	private final Set<ECKey> spentKeys = new HashSet<>();
 
 	// Constructors and instance
 
@@ -67,6 +99,7 @@ public class BTC {
 		LOGGER.info(() -> String.format("Starting Bitcoin support using %s", bitcoinNet.name()));
 
 		this.electrumX = ElectrumX.getInstance(bitcoinNet.name());
+		this.bitcoinjContext = new Context(this.params);
 	}
 
 	public static synchronized BTC getInstance() {
@@ -88,70 +121,437 @@ public class BTC {
 
 	// Actual useful methods for use by other classes
 
-	/** Returns median timestamp from latest 11 blocks, in seconds. */
-	public Integer getMedianBlockTime() {
-		Integer height = this.electrumX.getCurrentHeight();
-		if (height == null)
-			return null;
+	public static String format(Coin amount) {
+		return BTC.FORMAT.format(amount).toString();
+	}
+
+	public static String format(long amount) {
+		return format(Coin.valueOf(amount));
+	}
+
+	public boolean isValidXprv(String xprv58) {
+		try {
+			Context.propagate(bitcoinjContext);
+			DeterministicKey.deserializeB58(null, xprv58, this.params);
+			return true;
+		} catch (IllegalArgumentException e) {
+			return false;
+		}
+	}
+
+	/** Returns P2PKH Bitcoin address using passed public key hash. */
+	public String pkhToAddress(byte[] publicKeyHash) {
+		Context.propagate(bitcoinjContext);
+		return LegacyAddress.fromPubKeyHash(this.params, publicKeyHash).toString();
+	}
+
+	public String deriveP2shAddress(byte[] redeemScriptBytes) {
+		byte[] redeemScriptHash = Crypto.hash160(redeemScriptBytes);
+		Context.propagate(bitcoinjContext);
+		Address p2shAddress = LegacyAddress.fromScriptHash(params, redeemScriptHash);
+		return p2shAddress.toString();
+	}
+
+	/**
+	 * Returns median timestamp from latest 11 blocks, in seconds.
+	 * <p>
+	 * @throws BitcoinException if error occurs
+	 */
+	public Integer getMedianBlockTime() throws BitcoinException {
+		int height = this.electrumX.getCurrentHeight();
 
 		// Grab latest 11 blocks
 		List<byte[]> blockHeaders = this.electrumX.getBlockHeaders(height - 11, 11);
-		if (blockHeaders == null || blockHeaders.size() < 11)
-			return null;
+		if (blockHeaders.size() < 11)
+			throw new BitcoinException("Not enough blocks to determine median block time");
 
-		List<Integer> blockTimestamps = blockHeaders.stream().map(blockHeader -> BitTwiddling.fromLEBytes(blockHeader, TIMESTAMP_OFFSET)).collect(Collectors.toList());
+		List<Integer> blockTimestamps = blockHeaders.stream().map(blockHeader -> BitTwiddling.intFromLEBytes(blockHeader, TIMESTAMP_OFFSET)).collect(Collectors.toList());
 
-		// Descending, but order shouldn't matter as we're picking median...
+		// Descending order
 		blockTimestamps.sort((a, b) -> Integer.compare(b, a));
 
+		// Pick median
 		return blockTimestamps.get(5);
 	}
 
-	public Coin getBalance(String base58Address) {
-		Long balance = this.electrumX.getBalance(addressToScript(base58Address));
-		if (balance == null)
-			return null;
+	/**
+	 * Returns estimated BTC fee, in sats per 1000bytes, optionally for historic timestamp.
+	 * 
+	 * @param timestamp optional milliseconds since epoch, or null for 'now'
+	 * @return sats per 1000bytes, or throws BitcoinException if something went wrong
+	 */
+	public long estimateFee(Long timestamp) throws BitcoinException {
+		if (!this.params.getId().equals(NetworkParameters.ID_MAINNET))
+			return NON_MAINNET_FEE;
 
-		return Coin.valueOf(balance);
+		// TODO: This will need to be replaced with something better in the near future!
+		if (timestamp != null && timestamp < NEW_FEE_TIMESTAMP)
+			return OLD_FEE_AMOUNT;
+
+		return NEW_FEE_AMOUNT;
 	}
 
-	public List<TransactionOutput> getUnspentOutputs(String base58Address) {
-		List<Pair<byte[], Integer>> unspentOutputs = this.electrumX.getUnspentOutputs(addressToScript(base58Address));
-		if (unspentOutputs == null)
-			return null;
+	/**
+	 * Returns confirmed balance, based on passed payment script.
+	 * <p>
+	 * @return confirmed balance, or zero if script unknown
+	 * @throws BitcoinException if there was an error
+	 */
+	public long getConfirmedBalance(String base58Address) throws BitcoinException {
+		return this.electrumX.getConfirmedBalance(addressToScript(base58Address));
+	}
+
+	/**
+	 * Returns list of unspent outputs pertaining to passed address.
+	 * <p>
+	 * @return list of unspent outputs, or empty list if address unknown
+	 * @throws BitcoinException if there was an error.
+	 */
+	public List<TransactionOutput> getUnspentOutputs(String base58Address) throws BitcoinException {
+		List<UnspentOutput> unspentOutputs = this.electrumX.getUnspentOutputs(addressToScript(base58Address), false);
 
 		List<TransactionOutput> unspentTransactionOutputs = new ArrayList<>();
-		for (Pair<byte[], Integer> unspentOutput : unspentOutputs) {
-			List<TransactionOutput> transactionOutputs = getOutputs(unspentOutput.getA());
-			if (transactionOutputs == null)
-				return null;
+		for (UnspentOutput unspentOutput : unspentOutputs) {
+			List<TransactionOutput> transactionOutputs = this.getOutputs(unspentOutput.hash);
 
-			unspentTransactionOutputs.add(transactionOutputs.get(unspentOutput.getB()));
+			unspentTransactionOutputs.add(transactionOutputs.get(unspentOutput.index));
 		}
 
 		return unspentTransactionOutputs;
 	}
 
-	public List<TransactionOutput> getOutputs(byte[] txHash) {
+	/**
+	 * Returns list of outputs pertaining to passed transaction hash.
+	 * <p>
+	 * @return list of outputs, or empty list if transaction unknown
+	 * @throws BitcoinException if there was an error.
+	 */
+	public List<TransactionOutput> getOutputs(byte[] txHash) throws BitcoinException {
 		byte[] rawTransactionBytes = this.electrumX.getRawTransaction(txHash);
-		if (rawTransactionBytes == null)
-			return null;
 
+		// XXX bitcoinj: replace with getTransaction() below
+		Context.propagate(bitcoinjContext);
 		Transaction transaction = new Transaction(this.params, rawTransactionBytes);
 		return transaction.getOutputs();
 	}
 
-	public List<byte[]> getAddressTransactions(String base58Address) {
-		return this.electrumX.getAddressTransactions(addressToScript(base58Address));
+	/**
+	 * Returns list of transaction hashes pertaining to passed address.
+	 * <p>
+	 * @return list of unspent outputs, or empty list if script unknown
+	 * @throws BitcoinException if there was an error.
+	 */
+	public List<TransactionHash> getAddressTransactions(String base58Address, boolean includeUnconfirmed) throws BitcoinException {
+		return this.electrumX.getAddressTransactions(addressToScript(base58Address), includeUnconfirmed);
 	}
 
-	public boolean broadcastTransaction(Transaction transaction) {
-		return this.electrumX.broadcastTransaction(transaction.bitcoinSerialize());
+	/**
+	 * Returns list of raw, confirmed transactions involving given address.
+	 * <p>
+	 * @throws BitcoinException if there was an error
+	 */
+	public List<byte[]> getAddressTransactions(String base58Address) throws BitcoinException {
+		List<TransactionHash> transactionHashes = this.electrumX.getAddressTransactions(addressToScript(base58Address), false);
+
+		List<byte[]> rawTransactions = new ArrayList<>();
+		for (TransactionHash transactionInfo : transactionHashes) {
+			byte[] rawTransaction = this.electrumX.getRawTransaction(HashCode.fromString(transactionInfo.txHash).asBytes());
+			rawTransactions.add(rawTransaction);
+		}
+
+		return rawTransactions;
+	}
+
+	/**
+	 * Returns transaction info for passed transaction hash.
+	 * <p>
+	 * @throws BitcoinException.NotFoundException if transaction unknown
+	 * @throws BitcoinException if error occurs
+	 */
+	public BitcoinTransaction getTransaction(String txHash) throws BitcoinException {
+		return this.electrumX.getTransaction(txHash);
+	}
+
+	/**
+	 * Broadcasts raw transaction to Bitcoin network.
+	 * <p>
+	 * @throws BitcoinException if error occurs
+	 */
+	public void broadcastTransaction(Transaction transaction) throws BitcoinException {
+		this.electrumX.broadcastTransaction(transaction.bitcoinSerialize());
+	}
+
+	/**
+	 * Returns bitcoinj transaction sending <tt>amount</tt> to <tt>recipient</tt>.
+	 * 
+	 * @param xprv58 BIP32 extended Bitcoin private key
+	 * @param recipient P2PKH address
+	 * @param amount unscaled amount
+	 * @return transaction, or null if insufficient funds
+	 */
+	public Transaction buildSpend(String xprv58, String recipient, long amount) {
+		Context.propagate(bitcoinjContext);
+		Wallet wallet = Wallet.fromSpendingKeyB58(this.params, xprv58, DeterministicHierarchy.BIP32_STANDARDISATION_TIME_SECS);
+		wallet.setUTXOProvider(new WalletAwareUTXOProvider(this, wallet, WalletAwareUTXOProvider.KeySearchMode.REQUEST_MORE_IF_ANY_SPENT));
+
+		Address destination = Address.fromString(this.params, recipient);
+		SendRequest sendRequest = SendRequest.to(destination, Coin.valueOf(amount));
+
+		if (this.params == TestNet3Params.get())
+			// Much smaller fee for TestNet3
+			sendRequest.feePerKb = Coin.valueOf(2000L);
+
+		try {
+			wallet.completeTx(sendRequest);
+			return sendRequest.tx;
+		} catch (InsufficientMoneyException e) {
+			return null;
+		}
+	}
+
+	/**
+	 * Returns unspent Bitcoin balance given 'm' BIP32 key.
+	 *
+	 * @param xprv58 BIP32 extended Bitcoin private key
+	 * @return unspent BTC balance, or null if unable to determine balance
+	 */
+	public Long getWalletBalance(String xprv58) {
+		Context.propagate(bitcoinjContext);
+		Wallet wallet = Wallet.fromSpendingKeyB58(this.params, xprv58, DeterministicHierarchy.BIP32_STANDARDISATION_TIME_SECS);
+		wallet.setUTXOProvider(new WalletAwareUTXOProvider(this, wallet, WalletAwareUTXOProvider.KeySearchMode.REQUEST_MORE_IF_ANY_SPENT));
+
+		Coin balance = wallet.getBalance();
+		if (balance == null)
+			return null;
+
+		return balance.value;
+	}
+
+	/**
+	 * Returns first unused receive address given 'm' BIP32 key.
+	 *
+	 * @param xprv58 BIP32 extended Bitcoin private key
+	 * @return Bitcoin P2PKH address
+	 * @throws BitcoinException if something went wrong
+	 */
+	public String getUnusedReceiveAddress(String xprv58) throws BitcoinException {
+		Context.propagate(bitcoinjContext);
+		Wallet wallet = Wallet.fromSpendingKeyB58(this.params, xprv58, DeterministicHierarchy.BIP32_STANDARDISATION_TIME_SECS);
+		DeterministicKeyChain keyChain = wallet.getActiveKeyChain();
+
+		keyChain.setLookaheadSize(WalletAwareUTXOProvider.LOOKAHEAD_INCREMENT);
+		keyChain.maybeLookAhead();
+
+		final int keyChainPathSize = keyChain.getAccountPath().size();
+		List<DeterministicKey> keys = new ArrayList<>(keyChain.getLeafKeys());
+
+		int ki = 0;
+		do {
+			for (; ki < keys.size(); ++ki) {
+				DeterministicKey dKey = keys.get(ki);
+				List<ChildNumber> dKeyPath = dKey.getPath();
+
+				// If keyChain is based on 'm', then make sure dKey is m/0/ki
+				if (dKeyPath.size() != keyChainPathSize + 2 || dKeyPath.get(dKeyPath.size() - 2) != ChildNumber.ZERO)
+					continue;
+
+				// Check unspent
+				Address address = Address.fromKey(this.params, dKey, ScriptType.P2PKH);
+				byte[] script = ScriptBuilder.createOutputScript(address).getProgram();
+
+				List<UnspentOutput> unspentOutputs = this.electrumX.getUnspentOutputs(script, false);
+
+				/*
+				 * If there are no unspent outputs then either:
+				 * a) all the outputs have been spent
+				 * b) address has never been used
+				 * 
+				 * For case (a) we want to remember not to check this address (key) again.
+				 */
+
+				if (unspentOutputs.isEmpty()) {
+					// If this is a known key that has been spent before, then we can skip asking for transaction history
+					if (this.spentKeys.contains(dKey)) {
+						wallet.getActiveKeyChain().markKeyAsUsed((DeterministicKey) dKey);
+						continue;
+					}
+
+					// Ask for transaction history - if it's empty then key has never been used
+					List<TransactionHash> historicTransactionHashes = this.electrumX.getAddressTransactions(script, false);
+
+					if (!historicTransactionHashes.isEmpty()) {
+						// Fully spent key - case (a)
+						this.spentKeys.add(dKey);
+						wallet.getActiveKeyChain().markKeyAsUsed(dKey);
+					} else {
+						// Key never been used - case (b)
+						return address.toString();
+					}
+				}
+
+				// Key has unspent outputs, hence used, so no good to us
+				this.spentKeys.remove(dKey);
+			}
+
+			// Generate some more keys
+			keyChain.setLookaheadSize(keyChain.getLookaheadSize() + WalletAwareUTXOProvider.LOOKAHEAD_INCREMENT);
+			keyChain.maybeLookAhead();
+
+			// This returns all keys, including those already in 'keys'
+			List<DeterministicKey> allLeafKeys = keyChain.getLeafKeys();
+			// Add only new keys onto our list of keys to search
+			List<DeterministicKey> newKeys = allLeafKeys.subList(ki, allLeafKeys.size());
+			keys.addAll(newKeys);
+			// Fall-through to checking more keys as now 'ki' is smaller than 'keys.size()' again
+
+			// Process new keys
+		} while (true);
+	}
+
+	// UTXOProvider support
+
+	static class WalletAwareUTXOProvider implements UTXOProvider {
+		private static final int LOOKAHEAD_INCREMENT = 3;
+
+		private final BTC btc;
+		private final Wallet wallet;
+
+		enum KeySearchMode {
+			REQUEST_MORE_IF_ALL_SPENT, REQUEST_MORE_IF_ANY_SPENT;
+		}
+		private final KeySearchMode keySearchMode;
+		private final DeterministicKeyChain keyChain;
+
+		public WalletAwareUTXOProvider(BTC btc, Wallet wallet, KeySearchMode keySearchMode) {
+			this.btc = btc;
+			this.wallet = wallet;
+			this.keySearchMode = keySearchMode;
+			this.keyChain = this.wallet.getActiveKeyChain();
+
+			// Set up wallet's key chain
+			this.keyChain.setLookaheadSize(LOOKAHEAD_INCREMENT);
+			this.keyChain.maybeLookAhead();
+		}
+
+		public List<UTXO> getOpenTransactionOutputs(List<ECKey> keys) throws UTXOProviderException {
+			List<UTXO> allUnspentOutputs = new ArrayList<>();
+			final boolean coinbase = false;
+
+			int ki = 0;
+			do {
+				boolean areAllKeysUnspent = true;
+				boolean areAllKeysSpent = true;
+
+				for (; ki < keys.size(); ++ki) {
+					ECKey key = keys.get(ki);
+
+					Address address = Address.fromKey(btc.params, key, ScriptType.P2PKH);
+					byte[] script = ScriptBuilder.createOutputScript(address).getProgram();
+
+					List<UnspentOutput> unspentOutputs;
+					try {
+						unspentOutputs = btc.electrumX.getUnspentOutputs(script, false);
+					} catch (BitcoinException e) {
+						throw new UTXOProviderException(String.format("Unable to fetch unspent outputs for %s", address));
+					}
+
+					/*
+					 * If there are no unspent outputs then either:
+					 * a) all the outputs have been spent
+					 * b) address has never been used
+					 * 
+					 * For case (a) we want to remember not to check this address (key) again.
+					 */
+
+					if (unspentOutputs.isEmpty()) {
+						// If this is a known key that has been spent before, then we can skip asking for transaction history
+						if (btc.spentKeys.contains(key)) {
+							wallet.getActiveKeyChain().markKeyAsUsed((DeterministicKey) key);
+							areAllKeysUnspent = false;
+							continue;
+						}
+
+						// Ask for transaction history - if it's empty then key has never been used
+						List<TransactionHash> historicTransactionHashes;
+						try {
+							historicTransactionHashes = btc.electrumX.getAddressTransactions(script, false);
+						} catch (BitcoinException e) {
+							throw new UTXOProviderException(String.format("Unable to fetch transaction history for %s", address));
+						}
+
+						if (!historicTransactionHashes.isEmpty()) {
+							// Fully spent key - case (a)
+							btc.spentKeys.add(key);
+							wallet.getActiveKeyChain().markKeyAsUsed((DeterministicKey) key);
+							areAllKeysUnspent = false;
+						} else {
+							// Key never been used - case (b)
+							areAllKeysSpent = false;
+						}
+
+						continue;
+					}
+
+					// If we reach here, then there's definitely at least one unspent key
+					btc.spentKeys.remove(key);
+					areAllKeysSpent = false;
+
+					for (UnspentOutput unspentOutput : unspentOutputs) {
+						List<TransactionOutput> transactionOutputs;
+						try {
+							transactionOutputs = btc.getOutputs(unspentOutput.hash);
+						} catch (BitcoinException e) {
+							throw new UTXOProviderException(String.format("Unable to fetch outputs for TX %s",
+									HashCode.fromBytes(unspentOutput.hash)));
+						}
+
+						TransactionOutput transactionOutput = transactionOutputs.get(unspentOutput.index);
+
+						UTXO utxo = new UTXO(Sha256Hash.wrap(unspentOutput.hash), unspentOutput.index,
+								Coin.valueOf(unspentOutput.value), unspentOutput.height, coinbase,
+								transactionOutput.getScriptPubKey());
+
+						allUnspentOutputs.add(utxo);
+					}
+				}
+
+				if ((this.keySearchMode == KeySearchMode.REQUEST_MORE_IF_ALL_SPENT && areAllKeysSpent)
+						|| (this.keySearchMode == KeySearchMode.REQUEST_MORE_IF_ANY_SPENT && !areAllKeysUnspent)) {
+					// Generate some more keys
+					this.keyChain.setLookaheadSize(this.keyChain.getLookaheadSize() + LOOKAHEAD_INCREMENT);
+					this.keyChain.maybeLookAhead();
+
+					// This returns all keys, including those already in 'keys'
+					List<DeterministicKey> allLeafKeys = this.keyChain.getLeafKeys();
+					// Add only new keys onto our list of keys to search
+					List<DeterministicKey> newKeys = allLeafKeys.subList(ki, allLeafKeys.size());
+					keys.addAll(newKeys);
+					// Fall-through to checking more keys as now 'ki' is smaller than 'keys.size()' again
+				}
+
+				// If we have processed all keys, then we're done
+			} while (ki < keys.size());
+
+			return allUnspentOutputs;
+		}
+
+		public int getChainHeadHeight() throws UTXOProviderException {
+			try {
+				return btc.electrumX.getCurrentHeight();
+			} catch (BitcoinException e) {
+				throw new UTXOProviderException("Unable to determine Bitcoin chain height");
+			}
+		}
+
+		public NetworkParameters getParams() {
+			return btc.params;
+		}
 	}
 
 	// Utility methods for us
 
 	private byte[] addressToScript(String base58Address) {
+		Context.propagate(bitcoinjContext);
 		Address address = Address.fromString(this.params, base58Address);
 		return ScriptBuilder.createOutputScript(address).getProgram();
 	}

src/main/java/org/qortal/crosschain/BTCP2SH.java

@@ -0,0 +1,372 @@
+package org.qortal.crosschain;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.function.Function;
+
+import org.bitcoinj.core.Address;
+import org.bitcoinj.core.Base58;
+import org.bitcoinj.core.Coin;
+import org.bitcoinj.core.ECKey;
+import org.bitcoinj.core.LegacyAddress;
+import org.bitcoinj.core.NetworkParameters;
+import org.bitcoinj.core.Transaction;
+import org.bitcoinj.core.Transaction.SigHash;
+import org.bitcoinj.core.TransactionInput;
+import org.bitcoinj.core.TransactionOutput;
+import org.bitcoinj.crypto.TransactionSignature;
+import org.bitcoinj.script.Script;
+import org.bitcoinj.script.ScriptBuilder;
+import org.bitcoinj.script.ScriptChunk;
+import org.bitcoinj.script.ScriptOpCodes;
+import org.qortal.crypto.Crypto;
+import org.qortal.utils.BitTwiddling;
+
+import com.google.common.hash.HashCode;
+import com.google.common.primitives.Bytes;
+
+public class BTCP2SH {
+
+	public enum Status {
+		UNFUNDED, FUNDING_IN_PROGRESS, FUNDED, REDEEM_IN_PROGRESS, REDEEMED, REFUND_IN_PROGRESS, REFUNDED
+	}
+
+	public static final int SECRET_LENGTH = 32;
+	public static final int MIN_LOCKTIME = 1500000000;
+
+	/*
+	 * OP_TUCK (to copy public key to before signature)
+	 * OP_CHECKSIGVERIFY (sig & pubkey must verify or script fails)
+	 * OP_HASH160 (convert public key to PKH)
+	 * OP_DUP (duplicate PKH)
+	 * <push 20 bytes> <refund PKH> OP_EQUAL (does PKH match refund PKH?)
+	 * OP_IF
+	 * 	OP_DROP (no need for duplicate PKH)
+	 * 	<push 4 bytes> <locktime>
+	 * 	OP_CHECKLOCKTIMEVERIFY (if this passes, leftover stack is <locktime> so script passes)
+	 * OP_ELSE
+	 * 	<push 20 bytes> <redeem PKH> OP_EQUALVERIFY (duplicate PKH must match redeem PKH or script fails)
+	 * 	OP_HASH160 (hash secret)
+	 * 	<push 20 bytes> <hash of secret> OP_EQUAL (do hashes of secrets match? if true, script passes else script fails)
+	 * OP_ENDIF
+	 */
+
+	private static final byte[] redeemScript1 = HashCode.fromString("7dada97614").asBytes(); // OP_TUCK OP_CHECKSIGVERIFY OP_HASH160 OP_DUP push(0x14 bytes)
+	private static final byte[] redeemScript2 = HashCode.fromString("87637504").asBytes(); // OP_EQUAL OP_IF OP_DROP push(0x4 bytes)
+	private static final byte[] redeemScript3 = HashCode.fromString("b16714").asBytes(); // OP_CHECKLOCKTIMEVERIFY OP_ELSE push(0x14 bytes)
+	private static final byte[] redeemScript4 = HashCode.fromString("88a914").asBytes(); // OP_EQUALVERIFY OP_HASH160 push(0x14 bytes)
+	private static final byte[] redeemScript5 = HashCode.fromString("8768").asBytes(); // OP_EQUAL OP_ENDIF
+
+	/**
+	 * Returns Bitcoin redeemScript used for cross-chain trading.
+	 * <p>
+	 * See comments in {@link BTCP2SH} for more details.
+	 * 
+	 * @param refunderPubKeyHash 20-byte HASH160 of P2SH funder's public key, for refunding purposes
+	 * @param lockTime seconds-since-epoch threshold, after which P2SH funder can claim refund
+	 * @param redeemerPubKeyHash 20-byte HASH160 of P2SH redeemer's public key
+	 * @param secretHash 20-byte HASH160 of secret, used by P2SH redeemer to claim funds
+	 * @return
+	 */
+	public static byte[] buildScript(byte[] refunderPubKeyHash, int lockTime, byte[] redeemerPubKeyHash, byte[] secretHash) {
+		return Bytes.concat(redeemScript1, refunderPubKeyHash, redeemScript2, BitTwiddling.toLEByteArray((int) (lockTime & 0xffffffffL)),
+				redeemScript3, redeemerPubKeyHash, redeemScript4, secretHash, redeemScript5);
+	}
+
+	/**
+	 * Builds a custom transaction to spend P2SH.
+	 * 
+	 * @param amount output amount, should be total of input amounts, less miner fees
+	 * @param spendKey key for signing transaction, and also where funds are 'sent' (output)
+	 * @param fundingOutput output from transaction that funded P2SH address
+	 * @param redeemScriptBytes the redeemScript itself, in byte[] form
+	 * @param lockTime (optional) transaction nLockTime, used in refund scenario
+	 * @param scriptSigBuilder function for building scriptSig using transaction input signature
+	 * @param outputPublicKeyHash PKH used to create P2PKH output
+	 * @return Signed Bitcoin transaction for spending P2SH
+	 */
+	public static Transaction buildP2shTransaction(Coin amount, ECKey spendKey, List<TransactionOutput> fundingOutputs, byte[] redeemScriptBytes,
+			Long lockTime, Function<byte[], Script> scriptSigBuilder, byte[] outputPublicKeyHash) {
+		NetworkParameters params = BTC.getInstance().getNetworkParameters();
+
+		Transaction transaction = new Transaction(params);
+		transaction.setVersion(2);
+
+		// Output is back to P2SH funder
+		transaction.addOutput(amount, ScriptBuilder.createP2PKHOutputScript(outputPublicKeyHash));
+
+		for (int inputIndex = 0; inputIndex < fundingOutputs.size(); ++inputIndex) {
+			TransactionOutput fundingOutput = fundingOutputs.get(inputIndex);
+
+			// Input (without scriptSig prior to signing)
+			TransactionInput input = new TransactionInput(params, null, redeemScriptBytes, fundingOutput.getOutPointFor());
+			if (lockTime != null)
+				input.setSequenceNumber(BTC.LOCKTIME_NO_RBF_SEQUENCE); // Use max-value - 1, so lockTime can be used but not RBF
+			else
+				input.setSequenceNumber(BTC.NO_LOCKTIME_NO_RBF_SEQUENCE); // Use max-value, so no lockTime and no RBF
+			transaction.addInput(input);
+		}
+
+		// Set locktime after inputs added but before input signatures are generated
+		if (lockTime != null)
+			transaction.setLockTime(lockTime);
+
+		for (int inputIndex = 0; inputIndex < fundingOutputs.size(); ++inputIndex) {
+			// Generate transaction signature for input
+			final boolean anyoneCanPay = false;
+			TransactionSignature txSig = transaction.calculateSignature(inputIndex, spendKey, redeemScriptBytes, SigHash.ALL, anyoneCanPay);
+
+			// Calculate transaction signature
+			byte[] txSigBytes = txSig.encodeToBitcoin();
+
+			// Build scriptSig using lambda and tx signature
+			Script scriptSig = scriptSigBuilder.apply(txSigBytes);
+
+			// Set input scriptSig
+			transaction.getInput(inputIndex).setScriptSig(scriptSig);
+		}
+
+		return transaction;
+	}
+
+	/**
+	 * Returns signed Bitcoin transaction claiming refund from P2SH address.
+	 * 
+	 * @param refundAmount refund amount, should be total of input amounts, less miner fees
+	 * @param refundKey key for signing transaction, and also where refund is 'sent' (output)
+	 * @param fundingOutput output from transaction that funded P2SH address
+	 * @param redeemScriptBytes the redeemScript itself, in byte[] form
+	 * @param lockTime transaction nLockTime - must be at least locktime used in redeemScript
+	 * @param receivingAccountInfo Bitcoin PKH used for output
+	 * @return Signed Bitcoin transaction for refunding P2SH
+	 */
+	public static Transaction buildRefundTransaction(Coin refundAmount, ECKey refundKey, List<TransactionOutput> fundingOutputs, byte[] redeemScriptBytes, long lockTime, byte[] receivingAccountInfo) {
+		Function<byte[], Script> refundSigScriptBuilder = (txSigBytes) -> {
+			// Build scriptSig with...
+			ScriptBuilder scriptBuilder = new ScriptBuilder();
+
+			// transaction signature
+			scriptBuilder.addChunk(new ScriptChunk(txSigBytes.length, txSigBytes));
+
+			// redeem public key
+			byte[] refundPubKey = refundKey.getPubKey();
+			scriptBuilder.addChunk(new ScriptChunk(refundPubKey.length, refundPubKey));
+
+			// redeem script
+			scriptBuilder.addChunk(new ScriptChunk(ScriptOpCodes.OP_PUSHDATA1, redeemScriptBytes));
+
+			return scriptBuilder.build();
+		};
+
+		// Send funds back to funding address
+		return buildP2shTransaction(refundAmount, refundKey, fundingOutputs, redeemScriptBytes, lockTime, refundSigScriptBuilder, receivingAccountInfo);
+	}
+
+	/**
+	 * Returns signed Bitcoin transaction redeeming funds from P2SH address.
+	 * 
+	 * @param redeemAmount redeem amount, should be total of input amounts, less miner fees
+	 * @param redeemKey key for signing transaction, and also where funds are 'sent' (output)
+	 * @param fundingOutput output from transaction that funded P2SH address
+	 * @param redeemScriptBytes the redeemScript itself, in byte[] form
+	 * @param secret actual 32-byte secret used when building redeemScript
+	 * @param receivingAccountInfo Bitcoin PKH used for output
+	 * @return Signed Bitcoin transaction for redeeming P2SH
+	 */
+	public static Transaction buildRedeemTransaction(Coin redeemAmount, ECKey redeemKey, List<TransactionOutput> fundingOutputs, byte[] redeemScriptBytes, byte[] secret, byte[] receivingAccountInfo) {
+		Function<byte[], Script> redeemSigScriptBuilder = (txSigBytes) -> {
+			// Build scriptSig with...
+			ScriptBuilder scriptBuilder = new ScriptBuilder();
+
+			// secret
+			scriptBuilder.addChunk(new ScriptChunk(secret.length, secret));
+
+			// transaction signature
+			scriptBuilder.addChunk(new ScriptChunk(txSigBytes.length, txSigBytes));
+
+			// redeem public key
+			byte[] redeemPubKey = redeemKey.getPubKey();
+			scriptBuilder.addChunk(new ScriptChunk(redeemPubKey.length, redeemPubKey));
+
+			// redeem script
+			scriptBuilder.addChunk(new ScriptChunk(ScriptOpCodes.OP_PUSHDATA1, redeemScriptBytes));
+
+			return scriptBuilder.build();
+		};
+
+		return buildP2shTransaction(redeemAmount, redeemKey, fundingOutputs, redeemScriptBytes, null, redeemSigScriptBuilder, receivingAccountInfo);
+	}
+
+	/** Returns 'secret', if any, given list of raw bitcoin transactions. */
+	public static byte[] findP2shSecret(String p2shAddress, List<byte[]> rawTransactions) {
+		NetworkParameters params = BTC.getInstance().getNetworkParameters();
+
+		for (byte[] rawTransaction : rawTransactions) {
+			Transaction transaction = new Transaction(params, rawTransaction);
+
+			// Cycle through inputs, looking for one that spends our P2SH
+			for (TransactionInput input : transaction.getInputs()) {
+				Script scriptSig = input.getScriptSig();
+				List<ScriptChunk> scriptChunks = scriptSig.getChunks();
+
+				// Expected number of script chunks for redeem. Refund might not have the same number.
+				int expectedChunkCount = 1 /*secret*/ + 1 /*sig*/ + 1 /*pubkey*/ + 1 /*redeemScript*/;
+				if (scriptChunks.size() != expectedChunkCount)
+					continue;
+
+				// We're expecting last chunk to contain the actual redeemScript
+				ScriptChunk lastChunk = scriptChunks.get(scriptChunks.size() - 1);
+				byte[] redeemScriptBytes = lastChunk.data;
+
+				// If non-push scripts, redeemScript will be null
+				if (redeemScriptBytes == null)
+					continue;
+
+				byte[] redeemScriptHash = Crypto.hash160(redeemScriptBytes);
+				Address inputAddress = LegacyAddress.fromScriptHash(params, redeemScriptHash);
+
+				if (!inputAddress.toString().equals(p2shAddress))
+					// Input isn't spending our P2SH
+					continue;
+
+				byte[] secret = scriptChunks.get(0).data;
+				if (secret.length != BTCP2SH.SECRET_LENGTH)
+					continue;
+
+				return secret;
+			}
+		}
+
+		return null;
+	}
+
+	/** Returns P2SH status, given P2SH address and expected redeem/refund amount, or throws BitcoinException if error occurs. */
+	public static Status determineP2shStatus(String p2shAddress, long minimumAmount) throws BitcoinException {
+		final BTC btc = BTC.getInstance();
+
+		List<TransactionHash> transactionHashes = btc.getAddressTransactions(p2shAddress, BTC.INCLUDE_UNCONFIRMED);
+
+		// Sort by confirmed first, followed by ascending height
+		transactionHashes.sort(TransactionHash.CONFIRMED_FIRST.thenComparing(TransactionHash::getHeight));
+
+		// Transaction cache
+		Map<String, BitcoinTransaction> transactionsByHash = new HashMap<>();
+		// HASH160(redeem script) for this p2shAddress
+		byte[] ourRedeemScriptHash = addressToRedeemScriptHash(p2shAddress);
+
+		// Check for spends first, caching full transaction info as we progress just in case we don't return in this loop
+		for (TransactionHash transactionInfo : transactionHashes) {
+			BitcoinTransaction bitcoinTransaction = btc.getTransaction(transactionInfo.txHash);
+
+			// Cache for possible later reuse
+			transactionsByHash.put(transactionInfo.txHash, bitcoinTransaction);
+
+			// Acceptable funding is one transaction output, so we're expecting only one input
+			if (bitcoinTransaction.inputs.size() != 1)
+				// Wrong number of inputs
+				continue;
+
+			String scriptSig = bitcoinTransaction.inputs.get(0).scriptSig;
+
+			List<byte[]> scriptSigChunks = extractScriptSigChunks(HashCode.fromString(scriptSig).asBytes());
+			if (scriptSigChunks.size() < 3 || scriptSigChunks.size() > 4)
+				// Not spending one of these P2SH
+				continue;
+
+			// Last chunk is redeem script
+			byte[] redeemScriptBytes = scriptSigChunks.get(scriptSigChunks.size() - 1);
+			byte[] redeemScriptHash = Crypto.hash160(redeemScriptBytes);
+			if (!Arrays.equals(redeemScriptHash, ourRedeemScriptHash))
+				// Not spending our specific P2SH
+				continue;
+
+			// If we have 4 chunks, then secret is present
+			return scriptSigChunks.size() == 4
+					? (transactionInfo.height == 0 ? Status.REDEEM_IN_PROGRESS : Status.REDEEMED)
+					: (transactionInfo.height == 0 ? Status.REFUND_IN_PROGRESS : Status.REFUNDED);
+		}
+
+		String ourScriptPubKey = HashCode.fromBytes(addressToScriptPubKey(p2shAddress)).toString();
+
+		// Check for funding
+		for (TransactionHash transactionInfo : transactionHashes) {
+			BitcoinTransaction bitcoinTransaction = transactionsByHash.get(transactionInfo.txHash);
+			if (bitcoinTransaction == null)
+				// Should be present in map!
+				throw new BitcoinException("Cached Bitcoin transaction now missing?");
+
+			// Check outputs for our specific P2SH
+			for (BitcoinTransaction.Output output : bitcoinTransaction.outputs) {
+				// Check amount
+				if (output.value < minimumAmount)
+					// Output amount too small (not taking fees into account)
+					continue;
+
+				String scriptPubKey = output.scriptPubKey;
+				if (!scriptPubKey.equals(ourScriptPubKey))
+					// Not funding our specific P2SH
+					continue;
+
+				return transactionInfo.height == 0 ? Status.FUNDING_IN_PROGRESS : Status.FUNDED;
+			}
+		}
+
+		return Status.UNFUNDED;
+	}
+
+	private static List<byte[]> extractScriptSigChunks(byte[] scriptSigBytes) {
+		List<byte[]> chunks = new ArrayList<>();
+
+		int offset = 0;
+		int previousOffset = 0;
+		while (offset < scriptSigBytes.length) {
+			byte pushOp = scriptSigBytes[offset++];
+
+			if (pushOp < 0 || pushOp > 0x4c)
+				// Unacceptable OP
+				return Collections.emptyList();
+
+			// Special treatment for OP_PUSHDATA1
+			if (pushOp == 0x4c) {
+				if (offset >= scriptSigBytes.length)
+					// Run out of scriptSig bytes?
+					return Collections.emptyList();
+
+				pushOp = scriptSigBytes[offset++];
+			}
+
+			previousOffset = offset;
+			offset += Byte.toUnsignedInt(pushOp);
+
+			byte[] chunk = Arrays.copyOfRange(scriptSigBytes, previousOffset, offset);
+			chunks.add(chunk);
+		}
+
+		return chunks;
+	}
+
+	private static byte[] addressToScriptPubKey(String p2shAddress) {
+		// We want the HASH160 part of the P2SH address
+		byte[] p2shAddressBytes = Base58.decode(p2shAddress);
+
+		byte[] scriptPubKey = new byte[1 + 1 + 20 + 1];
+		scriptPubKey[0x00] = (byte) 0xa9; /* OP_HASH160 */
+		scriptPubKey[0x01] = (byte) 0x14; /* PUSH 0x14 bytes */
+		System.arraycopy(p2shAddressBytes, 1, scriptPubKey, 2, 0x14);
+		scriptPubKey[0x16] = (byte) 0x87; /* OP_EQUAL */
+
+		return scriptPubKey;
+	}
+
+	private static byte[] addressToRedeemScriptHash(String p2shAddress) {
+		// We want the HASH160 part of the P2SH address
+		byte[] p2shAddressBytes = Base58.decode(p2shAddress);
+
+		return Arrays.copyOfRange(p2shAddressBytes, 1, 1 + 20);
+	}
+
+}

src/main/java/org/qortal/crosschain/BitcoinException.java

@@ -0,0 +1,57 @@
+package org.qortal.crosschain;
+
+@SuppressWarnings("serial")
+public class BitcoinException extends Exception {
+
+	public BitcoinException() {
+		super();
+	}
+
+	public BitcoinException(String message) {
+		super(message);
+	}
+
+	public static class NetworkException extends BitcoinException {
+		private final Integer daemonErrorCode;
+
+		public NetworkException() {
+			super();
+			this.daemonErrorCode = null;
+		}
+
+		public NetworkException(String message) {
+			super(message);
+			this.daemonErrorCode = null;
+		}
+
+		public NetworkException(int errorCode, String message) {
+			super(message);
+			this.daemonErrorCode = errorCode;
+		}
+
+		public Integer getDaemonErrorCode() {
+			return this.daemonErrorCode;
+		}
+	}
+
+	public static class NotFoundException extends BitcoinException {
+		public NotFoundException() {
+			super();
+		}
+
+		public NotFoundException(String message) {
+			super(message);
+		}
+	}
+
+	public static class InsufficientFundsException extends BitcoinException {
+		public InsufficientFundsException() {
+			super();
+		}
+
+		public InsufficientFundsException(String message) {
+			super(message);
+		}
+	}
+
+}

src/main/java/org/qortal/crosschain/BitcoinNetworkProvider.java

@@ -0,0 +1,31 @@
+package org.qortal.crosschain;
+
+import java.util.List;
+
+interface BitcoinNetworkProvider {
+
+	/** Returns current blockchain height. */
+	int getCurrentHeight() throws BitcoinException;
+
+	/** Returns a list of raw block headers, starting at <tt>startHeight</tt> (inclusive), up to <tt>count</tt> max. */
+	List<byte[]> getRawBlockHeaders(int startHeight, int count) throws BitcoinException;
+
+	/** Returns balance of address represented by <tt>scriptPubKey</tt>. */
+	long getConfirmedBalance(byte[] scriptPubKey) throws BitcoinException;
+
+	/** Returns raw, serialized, transaction bytes given <tt>txHash</tt>. */
+	byte[] getRawTransaction(String txHash) throws BitcoinException;
+
+	/** Returns unpacked transaction given <tt>txHash</tt>. */
+	BitcoinTransaction getTransaction(String txHash) throws BitcoinException;
+
+	/** Returns list of transaction hashes (and heights) for address represented by <tt>scriptPubKey</tt>, optionally including unconfirmed transactions. */
+	List<TransactionHash> getAddressTransactions(byte[] scriptPubKey, boolean includeUnconfirmed) throws BitcoinException;
+
+	/** Returns list of unspent transaction outputs for address represented by <tt>scriptPubKey</tt>, optionally including unconfirmed transactions. */
+	List<UnspentOutput> getUnspentOutputs(byte[] scriptPubKey, boolean includeUnconfirmed) throws BitcoinException;
+
+	/** Broadcasts raw, serialized, transaction bytes to network, returning success/failure. */
+	boolean broadcastTransaction(byte[] rawTransaction) throws BitcoinException;
+
+}

src/main/java/org/qortal/crosschain/BitcoinTransaction.java

@@ -0,0 +1,70 @@
+package org.qortal.crosschain;
+
+import java.util.List;
+import java.util.stream.Collectors;
+
+public class BitcoinTransaction {
+
+	public final String txHash;
+	public final int size;
+	public final int locktime;
+	// Not present if transaction is unconfirmed
+	public final Integer timestamp;
+
+	public static class Input {
+		public final String scriptSig;
+		public final int sequence;
+		public final String outputTxHash;
+		public final int outputVout;
+
+		public Input(String scriptSig, int sequence, String outputTxHash, int outputVout) {
+			this.scriptSig = scriptSig;
+			this.sequence = sequence;
+			this.outputTxHash = outputTxHash;
+			this.outputVout = outputVout;
+		}
+
+		public String toString() {
+			return String.format("{output %s:%d, sequence %d, scriptSig %s}",
+					this.outputTxHash, this.outputVout, this.sequence, this.scriptSig);
+		}
+	}
+	public final List<Input> inputs;
+
+	public static class Output {
+		public final String scriptPubKey;
+		public final long value;
+
+		public Output(String scriptPubKey, long value) {
+			this.scriptPubKey = scriptPubKey;
+			this.value = value;
+		}
+
+		public String toString() {
+			return String.format("{value %d, scriptPubKey %s}", this.value, this.scriptPubKey);
+		}
+	}
+	public final List<Output> outputs;
+
+	public BitcoinTransaction(String txHash, int size, int locktime, Integer timestamp,
+			List<Input> inputs, List<Output> outputs) {
+		this.txHash = txHash;
+		this.size = size;
+		this.locktime = locktime;
+		this.timestamp = timestamp;
+		this.inputs = inputs;
+		this.outputs = outputs;
+	}
+
+	public String toString() {
+		return String.format("txHash %s, size %d, locktime %d, timestamp %d\n"
+				+ "\tinputs: [%s]\n"
+				+ "\toutputs: [%s]\n",
+				this.txHash,
+				this.size,
+				this.locktime,
+				this.timestamp,
+				this.inputs.stream().map(Input::toString).collect(Collectors.joining(",\n\t\t")),
+				this.outputs.stream().map(Output::toString).collect(Collectors.joining(",\n\t\t")));
+	}
+}

src/main/java/org/qortal/crosschain/ElectrumX.java

@@ -14,8 +14,9 @@ import java.util.NoSuchElementException;
 import java.util.Random;
 import java.util.Scanner;
 import java.util.Set;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
 
-import javax.net.ssl.SSLSocket;
 import javax.net.ssl.SSLSocketFactory;
 
 import org.apache.logging.log4j.LogManager;
@@ -25,27 +26,37 @@ import org.json.simple.JSONObject;
 import org.json.simple.JSONValue;
 import org.qortal.crypto.Crypto;
 import org.qortal.crypto.TrustlessSSLSocketFactory;
-import org.qortal.utils.Pair;
 
 import com.google.common.hash.HashCode;
 import com.google.common.primitives.Bytes;
 
+/** ElectrumX network support for querying Bitcoin-related info like block headers, transaction outputs, etc. */
 public class ElectrumX {
 
 	private static final Logger LOGGER = LogManager.getLogger(ElectrumX.class);
 	private static final Random RANDOM = new Random();
 
+	private static final double MIN_PROTOCOL_VERSION = 1.2;
+
 	private static final int DEFAULT_TCP_PORT = 50001;
 	private static final int DEFAULT_SSL_PORT = 50002;
 
 	private static final int BLOCK_HEADER_LENGTH = 80;
 
+	private static final String MAIN_GENESIS_HASH = "000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f";
+	private static final String TEST3_GENESIS_HASH = "000000000933ea01ad0ee984209779baaec3ced90fa3f408719526f8d77f4943";
+	// We won't know REGTEST (i.e. local) genesis block hash
+
+	// "message": "daemon error: DaemonError({'code': -5, 'message': 'No such mempool or blockchain transaction. Use gettransaction for wallet transactions.'})"
+	private static final Pattern DAEMON_ERROR_REGEX = Pattern.compile("DaemonError\\(\\{.*'code': ?(-?[0-9]+).*\\}\\)\\z"); // Capture 'code' inside curly-brace content
+
+	// Key: Bitcoin network (e.g. "MAIN", "TEST3", "REGTEST"), value: ElectrumX instance
 	private static final Map<String, ElectrumX> instances = new HashMap<>();
 
-	static class Server {
+	private static class Server {
 		String hostname;
 
-		enum ConnectionType { TCP, SSL };
+		enum ConnectionType { TCP, SSL }
 		ConnectionType connectionType;
 
 		int port;
@@ -82,7 +93,9 @@ public class ElectrumX {
 		}
 	}
 	private Set<Server> servers = new HashSet<>();
+	private List<Server> remainingServers = new ArrayList<>();
 
+	private String expectedGenesisHash;
 	private Server currentServer;
 	private Socket socket;
 	private Scanner scanner;
@@ -93,20 +106,59 @@ public class ElectrumX {
 	private ElectrumX(String bitcoinNetwork) {
 		switch (bitcoinNetwork) {
 			case "MAIN":
-				servers.addAll(Arrays.asList());
+				this.expectedGenesisHash = MAIN_GENESIS_HASH;
+
+				this.servers.addAll(Arrays.asList(
+						// Servers chosen on NO BASIS WHATSOEVER from various sources!
+						new Server("enode.duckdns.org", Server.ConnectionType.SSL, 50002),
+						new Server("electrumx.ml", Server.ConnectionType.SSL, 50002),
+						new Server("electrum.bitkoins.nl", Server.ConnectionType.SSL, 50512),
+						new Server("btc.electroncash.dk", Server.ConnectionType.SSL, 60002),
+						new Server("electrumx.electricnewyear.net", Server.ConnectionType.SSL, 50002),
+						new Server("dxm.no-ip.biz", Server.ConnectionType.TCP, 50001),
+						new Server("kirsche.emzy.de", Server.ConnectionType.TCP, 50001),
+						new Server("2AZZARITA.hopto.org", Server.ConnectionType.TCP, 50001),
+						new Server("xtrum.com", Server.ConnectionType.TCP, 50001),
+						new Server("electrum.srvmin.network", Server.ConnectionType.TCP, 50001),
+						new Server("electrumx.alexridevski.net", Server.ConnectionType.TCP, 50001),
+						new Server("bitcoin.lukechilds.co", Server.ConnectionType.TCP, 50001),
+						new Server("electrum.poiuty.com", Server.ConnectionType.TCP, 50001),
+						new Server("horsey.cryptocowboys.net", Server.ConnectionType.TCP, 50001),
+						new Server("electrum.emzy.de", Server.ConnectionType.TCP, 50001),
+						new Server("electrum-server.ninja", Server.ConnectionType.TCP, 50081),
+						new Server("bitcoin.electrumx.multicoin.co", Server.ConnectionType.TCP, 50001),
+						new Server("esx.geekhosters.com", Server.ConnectionType.TCP, 50001),
+						new Server("bitcoin.grey.pw", Server.ConnectionType.TCP, 50003),
+						new Server("exs.ignorelist.com", Server.ConnectionType.TCP, 50001),
+						new Server("electrum.coinext.com.br", Server.ConnectionType.TCP, 50001),
+						new Server("bitcoin.aranguren.org", Server.ConnectionType.TCP, 50001),
+						new Server("skbxmit.coinjoined.com", Server.ConnectionType.TCP, 50001),
+						new Server("alviss.coinjoined.com", Server.ConnectionType.TCP, 50001),
+						new Server("electrum2.privateservers.network", Server.ConnectionType.TCP, 50001),
+						new Server("electrumx.schulzemic.net", Server.ConnectionType.TCP, 50001),
+						new Server("bitcoins.sk", Server.ConnectionType.TCP, 56001),
+						new Server("node.mendonca.xyz", Server.ConnectionType.TCP, 50001),
+						new Server("bitcoin.aranguren.org", Server.ConnectionType.TCP, 50001)));
 				break;
 
 			case "TEST3":
-				servers.addAll(Arrays.asList(
-						new Server("tn.not.fyi", Server.ConnectionType.TCP, 55001),
-						new Server("tn.not.fyi", Server.ConnectionType.SSL, 55002),
+				this.expectedGenesisHash = TEST3_GENESIS_HASH;
+
+				this.servers.addAll(Arrays.asList(
+						new Server("electrum.blockstream.info", Server.ConnectionType.TCP, 60001),
+						new Server("electrum.blockstream.info", Server.ConnectionType.SSL, 60002),
+						new Server("electrumx-test.1209k.com", Server.ConnectionType.SSL, 50002),
+						new Server("testnet.qtornado.com", Server.ConnectionType.TCP, 51001),
+						new Server("testnet.qtornado.com", Server.ConnectionType.SSL, 51002),
 						new Server("testnet.aranguren.org", Server.ConnectionType.TCP, 51001),
 						new Server("testnet.aranguren.org", Server.ConnectionType.SSL, 51002),
 						new Server("testnet.hsmiths.com", Server.ConnectionType.SSL, 53012)));
 				break;
 
 			case "REGTEST":
-				servers.addAll(Arrays.asList(
+				this.expectedGenesisHash = null;
+
+				this.servers.addAll(Arrays.asList(
 						new Server("localhost", Server.ConnectionType.TCP, DEFAULT_TCP_PORT),
 						new Server("localhost", Server.ConnectionType.SSL, DEFAULT_SSL_PORT)));
 				break;
@@ -116,9 +168,9 @@ public class ElectrumX {
 		}
 
 		LOGGER.debug(() -> String.format("Starting ElectrumX support for %s Bitcoin network", bitcoinNetwork));
-		rpc("server.banner");
 	}
 
+	/** Returns ElectrumX instance linked to passed Bitcoin network, one of "MAIN", "TEST3" or "REGTEST". */
 	public static synchronized ElectrumX getInstance(String bitcoinNetwork) {
 		if (!instances.containsKey(bitcoinNetwork))
 			instances.put(bitcoinNetwork, new ElectrumX(bitcoinNetwork));
@@ -128,25 +180,50 @@ public class ElectrumX {
 
 	// Methods for use by other classes
 
-	public Integer getCurrentHeight() {
-		JSONObject blockJson = (JSONObject) this.rpc("blockchain.headers.subscribe");
-		if (blockJson == null || !blockJson.containsKey("height"))
-			return null;
+	/**
+	 * Returns current blockchain height.
+	 * <p>
+	 * @throws BitcoinException if error occurs
+	 */
+	public int getCurrentHeight() throws BitcoinException {
+		Object blockObj = this.rpc("blockchain.headers.subscribe");
+		if (!(blockObj instanceof JSONObject))
+			throw new BitcoinException.NetworkException("Unexpected output from ElectrumX blockchain.headers.subscribe RPC");
 
-		return ((Long) blockJson.get("height")).intValue();
+		JSONObject blockJson = (JSONObject) blockObj;
+
+		Object heightObj = blockJson.get("height");
+
+		if (!(heightObj instanceof Long))
+			throw new BitcoinException.NetworkException("Missing/invalid 'height' in JSON from ElectrumX blockchain.headers.subscribe RPC");
+
+		return ((Long) heightObj).intValue();
 	}
 
-	public List<byte[]> getBlockHeaders(int startHeight, long count) {
-		JSONObject blockJson = (JSONObject) this.rpc("blockchain.block.headers", startHeight, count);
-		if (blockJson == null || !blockJson.containsKey("count") || !blockJson.containsKey("hex"))
-			return null;
+	/**
+	 * Returns list of raw block headers, starting from <tt>startHeight</tt> inclusive.
+	 * <p>
+	 * @throws BitcoinException if error occurs
+	 */
+	public List<byte[]> getBlockHeaders(int startHeight, long count) throws BitcoinException {
+		Object blockObj = this.rpc("blockchain.block.headers", startHeight, count);
+		if (!(blockObj instanceof JSONObject))
+			throw new BitcoinException.NetworkException("Unexpected output from ElectrumX blockchain.block.headers RPC");
 
-		Long returnedCount = (Long) blockJson.get("count");
-		String hex = (String) blockJson.get("hex");
+		JSONObject blockJson = (JSONObject) blockObj;
+
+		Object countObj = blockJson.get("count");
+		Object hexObj = blockJson.get("hex");
+
+		if (!(countObj instanceof Long) || !(hexObj instanceof String))
+			throw new BitcoinException.NetworkException("Missing/invalid 'count' or 'hex' entries in JSON from ElectrumX blockchain.block.headers RPC");
+
+		Long returnedCount = (Long) countObj;
+		String hex = (String) hexObj;
 
 		byte[] raw = HashCode.fromString(hex).asBytes();
 		if (raw.length != returnedCount * BLOCK_HEADER_LENGTH)
-			return null;
+			throw new BitcoinException.NetworkException("Unexpected raw header length in JSON from ElectrumX blockchain.block.headers RPC");
 
 		List<byte[]> rawBlockHeaders = new ArrayList<>(returnedCount.intValue());
 		for (int i = 0; i < returnedCount; ++i)
@@ -155,96 +232,220 @@ public class ElectrumX {
 		return rawBlockHeaders;
 	}
 
-	public Long getBalance(byte[] script) {
+	/**
+	 * Returns confirmed balance, based on passed payment script.
+	 * <p>
+	 * @return confirmed balance, or zero if script unknown
+	 * @throws BitcoinException if there was an error
+	 */
+	public long getConfirmedBalance(byte[] script) throws BitcoinException {
 		byte[] scriptHash = Crypto.digest(script);
 		Bytes.reverse(scriptHash);
 
-		JSONObject balanceJson = (JSONObject) this.rpc("blockchain.scripthash.get_balance", HashCode.fromBytes(scriptHash).toString());
-		if (balanceJson == null || !balanceJson.containsKey("confirmed"))
-			return null;
+		Object balanceObj = this.rpc("blockchain.scripthash.get_balance", HashCode.fromBytes(scriptHash).toString());
+		if (!(balanceObj instanceof JSONObject))
+			throw new BitcoinException.NetworkException("Unexpected output from ElectrumX blockchain.scripthash.get_balance RPC");
+
+		JSONObject balanceJson = (JSONObject) balanceObj;
+
+		Object confirmedBalanceObj = balanceJson.get("confirmed");
+
+		if (!(confirmedBalanceObj instanceof Long))
+			throw new BitcoinException.NetworkException("Missing confirmed balance from ElectrumX blockchain.scripthash.get_balance RPC");
 
 		return (Long) balanceJson.get("confirmed");
 	}
 
-	public List<Pair<byte[], Integer>> getUnspentOutputs(byte[] script) {
+	/**
+	 * Returns list of unspent outputs pertaining to passed payment script.
+	 * <p>
+	 * @return list of unspent outputs, or empty list if script unknown
+	 * @throws BitcoinException if there was an error.
+	 */
+	public List<UnspentOutput> getUnspentOutputs(byte[] script, boolean includeUnconfirmed) throws BitcoinException {
 		byte[] scriptHash = Crypto.digest(script);
 		Bytes.reverse(scriptHash);
 
-		JSONArray unspentJson = (JSONArray) this.rpc("blockchain.scripthash.listunspent", HashCode.fromBytes(scriptHash).toString());
-		if (unspentJson == null)
-			return null;
+		Object unspentJson = this.rpc("blockchain.scripthash.listunspent", HashCode.fromBytes(scriptHash).toString());
+		if (!(unspentJson instanceof JSONArray))
+			throw new BitcoinException("Expected array output from ElectrumX blockchain.scripthash.listunspent RPC");
 
-		List<Pair<byte[], Integer>> unspentOutputs = new ArrayList<>();
-		for (Object rawUnspent : unspentJson) {
+		List<UnspentOutput> unspentOutputs = new ArrayList<>();
+		for (Object rawUnspent : (JSONArray) unspentJson) {
 			JSONObject unspent = (JSONObject) rawUnspent;
 
+			int height = ((Long) unspent.get("height")).intValue();
+			// We only want unspent outputs from confirmed transactions (and definitely not mempool duplicates with height 0)
+			if (!includeUnconfirmed && height <= 0)
+				continue;
+
 			byte[] txHash = HashCode.fromString((String) unspent.get("tx_hash")).asBytes();
 			int outputIndex = ((Long) unspent.get("tx_pos")).intValue();
+			long value = (Long) unspent.get("value");
 
-			unspentOutputs.add(new Pair<>(txHash, outputIndex));
+			unspentOutputs.add(new UnspentOutput(txHash, outputIndex, height, value));
 		}
 
 		return unspentOutputs;
 	}
 
-	public byte[] getRawTransaction(byte[] txHash) {
-		String rawTransactionHex = (String) this.rpc("blockchain.transaction.get", HashCode.fromBytes(txHash).toString());
-		if (rawTransactionHex == null)
-			return null;
+	/**
+	 * Returns raw transaction for passed transaction hash.
+	 * <p>
+	 * @throws BitcoinException.NotFoundException if transaction not found
+	 * @throws BitcoinException if error occurs
+	 */
+	public byte[] getRawTransaction(byte[] txHash) throws BitcoinException {
+		Object rawTransactionHex;
+		try {
+			rawTransactionHex = this.rpc("blockchain.transaction.get", HashCode.fromBytes(txHash).toString());
+		} catch (BitcoinException.NetworkException e) {
+			// DaemonError({'code': -5, 'message': 'No such mempool or blockchain transaction. Use gettransaction for wallet transactions.'})
+			if (Integer.valueOf(-5).equals(e.getDaemonErrorCode()))
+				throw new BitcoinException.NotFoundException(e.getMessage());
 
-		return HashCode.fromString(rawTransactionHex).asBytes();
+			throw e;
+		}
+
+		if (!(rawTransactionHex instanceof String))
+			throw new BitcoinException.NetworkException("Expected hex string as raw transaction from ElectrumX blockchain.transaction.get RPC");
+
+		return HashCode.fromString((String) rawTransactionHex).asBytes();
 	}
 
-	public List<byte[]> getAddressTransactions(byte[] script) {
+	/**
+	 * Returns transaction info for passed transaction hash.
+	 * <p>
+	 * @throws BitcoinException.NotFoundException if transaction not found
+	 * @throws BitcoinException if error occurs
+	 */
+	public BitcoinTransaction getTransaction(String txHash) throws BitcoinException {
+		Object transactionObj;
+		try {
+			transactionObj = this.rpc("blockchain.transaction.get", txHash, true);
+		} catch (BitcoinException.NetworkException e) {
+			// DaemonError({'code': -5, 'message': 'No such mempool or blockchain transaction. Use gettransaction for wallet transactions.'})
+			if (Integer.valueOf(-5).equals(e.getDaemonErrorCode()))
+				throw new BitcoinException.NotFoundException(e.getMessage());
+
+			throw e;
+		}
+
+		if (!(transactionObj instanceof JSONObject))
+			throw new BitcoinException.NetworkException("Expected JSONObject as response from ElectrumX blockchain.transaction.get RPC");
+
+		JSONObject transactionJson = (JSONObject) transactionObj;
+
+		Object inputsObj = transactionJson.get("vin");
+		if (!(inputsObj instanceof JSONArray))
+			throw new BitcoinException.NetworkException("Expected JSONArray for 'vin' from ElectrumX blockchain.transaction.get RPC");
+
+		Object outputsObj = transactionJson.get("vout");
+		if (!(outputsObj instanceof JSONArray))
+			throw new BitcoinException.NetworkException("Expected JSONArray for 'vout' from ElectrumX blockchain.transaction.get RPC");
+
+		try {
+			int size = ((Long) transactionJson.get("size")).intValue();
+			int locktime = ((Long) transactionJson.get("locktime")).intValue();
+
+			// Timestamp might not be present, e.g. for unconfirmed transaction
+			Object timeObj = transactionJson.get("time");
+			Integer timestamp = timeObj != null
+					? ((Long) timeObj).intValue()
+					: null;
+
+			List<BitcoinTransaction.Input> inputs = new ArrayList<>();
+			for (Object inputObj : (JSONArray) inputsObj) {
+				JSONObject inputJson = (JSONObject) inputObj;
+
+				String scriptSig = (String) ((JSONObject) inputJson.get("scriptSig")).get("hex");
+				int sequence = ((Long) inputJson.get("sequence")).intValue();
+				String outputTxHash = (String) inputJson.get("txid");
+				int outputVout = ((Long) inputJson.get("vout")).intValue();
+
+				inputs.add(new BitcoinTransaction.Input(scriptSig, sequence, outputTxHash, outputVout));
+			}
+
+			List<BitcoinTransaction.Output> outputs = new ArrayList<>();
+			for (Object outputObj : (JSONArray) outputsObj) {
+				JSONObject outputJson = (JSONObject) outputObj;
+
+				String scriptPubKey = (String) ((JSONObject) outputJson.get("scriptPubKey")).get("hex");
+				long value = (long) (((Double) outputJson.get("value")) * 1e8);
+
+				outputs.add(new BitcoinTransaction.Output(scriptPubKey, value));
+			}
+
+			return new BitcoinTransaction(txHash, size, locktime, timestamp, inputs, outputs);
+		} catch (NullPointerException | ClassCastException e) {
+			// Unexpected / invalid response from ElectrumX server
+		}
+
+		throw new BitcoinException.NetworkException("Unexpected JSON format from ElectrumX blockchain.transaction.get RPC");
+	}
+
+	/**
+	 * Returns list of transactions, relating to passed payment script.
+	 * <p>
+	 * @return list of related transactions, or empty list if script unknown
+	 * @throws BitcoinException if error occurs
+	 */
+	public List<TransactionHash> getAddressTransactions(byte[] script, boolean includeUnconfirmed) throws BitcoinException {
 		byte[] scriptHash = Crypto.digest(script);
 		Bytes.reverse(scriptHash);
 
-		JSONArray transactionsJson = (JSONArray) this.rpc("blockchain.scripthash.get_history", HashCode.fromBytes(scriptHash).toString());
-		if (transactionsJson == null)
-			return null;
+		Object transactionsJson = this.rpc("blockchain.scripthash.get_history", HashCode.fromBytes(scriptHash).toString());
+		if (!(transactionsJson instanceof JSONArray))
+			throw new BitcoinException.NetworkException("Expected array output from ElectrumX blockchain.scripthash.get_history RPC");
 
-		List<byte[]> rawTransactions = new ArrayList<>();
+		List<TransactionHash> transactionHashes = new ArrayList<>();
 
-		for (Object rawTransactionInfo : transactionsJson) {
+		for (Object rawTransactionInfo : (JSONArray) transactionsJson) {
 			JSONObject transactionInfo = (JSONObject) rawTransactionInfo;
 
-			// We only want confirmed transactions
-			if (!transactionInfo.containsKey("height"))
+			Long height = (Long) transactionInfo.get("height");
+			if (!includeUnconfirmed && (height == null || height == 0))
+				// We only want confirmed transactions
 				continue;
 
 			String txHash = (String) transactionInfo.get("tx_hash");
-			String rawTransactionHex = (String) this.rpc("blockchain.transaction.get", txHash);
-			if (rawTransactionHex == null)
-				return null;
 
-			rawTransactions.add(HashCode.fromString(rawTransactionHex).asBytes());
+			transactionHashes.add(new TransactionHash(height.intValue(), txHash));
 		}
 
-		return rawTransactions;
+		return transactionHashes;
 	}
 
-	public boolean broadcastTransaction(byte[] transactionBytes) {
+	/**
+	 * Broadcasts raw transaction to Bitcoin network.
+	 * <p>
+	 * @throws BitcoinException if error occurs
+	 */
+	public void broadcastTransaction(byte[] transactionBytes) throws BitcoinException {
 		Object rawBroadcastResult = this.rpc("blockchain.transaction.broadcast", HashCode.fromBytes(transactionBytes).toString());
-		if (rawBroadcastResult == null)
-			return false;
 
-		// If result is a String, then it is simply transaction hash.
-		// Otherwise result is JSON and probably contains error info instead.
-		return rawBroadcastResult instanceof String;
+		// We're expecting a simple string that is the transaction hash
+		if (!(rawBroadcastResult instanceof String))
+			throw new BitcoinException.NetworkException("Unexpected response from ElectrumX blockchain.transaction.broadcast RPC");
 	}
 
 	// Class-private utility methods
 
-	private Set<Server> serverPeersSubscribe() {
+	/**
+	 * Query current server for its list of peer servers, and return those we can parse.
+	 * <p>
+	 * @throws BitcoinException
+	 * @throws ClassCastException to be handled by caller
+	 */
+	private Set<Server> serverPeersSubscribe() throws BitcoinException {
 		Set<Server> newServers = new HashSet<>();
 
-		JSONArray peers = (JSONArray) this.connectedRpc("server.peers.subscribe");
-		if (peers == null)
-			return newServers;
+		Object peers = this.connectedRpc("server.peers.subscribe");
 
-		for (Object rawPeer : peers) {
+		for (Object rawPeer : (JSONArray) peers) {
 			JSONArray peer = (JSONArray) rawPeer;
 			if (peer.size() < 3)
+				// We're expecting at least 3 fields for each peer entry: IP, hostname, features
 				continue;
 
 			String hostname = (String) peer.get(1);
@@ -265,9 +466,14 @@ public class ElectrumX {
 						connectionType = Server.ConnectionType.TCP;
 						port = DEFAULT_TCP_PORT;
 						break;
+
+					default:
+						// e.g. could be 'v' for protocol version, or 'p' for pruning limit
+						break;
 				}
 
 				if (connectionType == null)
+					// We couldn't extract any peer connection info?
 					continue;
 
 				// Possible non-default port?
@@ -287,7 +493,16 @@ public class ElectrumX {
 		return newServers;
 	}
 
-	private synchronized Object rpc(String method, Object...params) {
+	/**
+	 * Performs RPC call, with automatic reconnection to different server if needed.
+	 * <p>
+	 * @return "result" object from within JSON output
+	 * @throws BitcoinException if server returns error or something goes wrong
+	 */
+	private synchronized Object rpc(String method, Object...params) throws BitcoinException {
+		if (this.remainingServers.isEmpty())
+			this.remainingServers.addAll(this.servers);
+
 		while (haveConnection()) {
 			Object response = connectedRpc(method, params);
 			if (response != null)
@@ -302,17 +517,17 @@ public class ElectrumX {
 			this.scanner = null;
 		}
 
-		return null;
+		// Failed to perform RPC - maybe lack of servers?
+		throw new BitcoinException.NetworkException("Failed to perform Bitcoin RPC");
 	}
 
-	private boolean haveConnection() {
+	/** Returns true if we have, or create, a connection to an ElectrumX server. */
+	private boolean haveConnection() throws BitcoinException {
 		if (this.currentServer != null)
 			return true;
 
-		List<Server> remainingServers = new ArrayList<>(this.servers);
-
-		while (!remainingServers.isEmpty()) {
-			Server server = remainingServers.remove(RANDOM.nextInt(remainingServers.size()));
+		while (!this.remainingServers.isEmpty()) {
+			Server server = this.remainingServers.remove(RANDOM.nextInt(this.remainingServers.size()));
 			LOGGER.trace(() -> String.format("Connecting to %s", server));
 
 			try {
@@ -325,23 +540,41 @@ public class ElectrumX {
 
 				if (server.connectionType == Server.ConnectionType.SSL) {
 					SSLSocketFactory factory = TrustlessSSLSocketFactory.getSocketFactory();
-					this.socket = (SSLSocket) factory.createSocket(this.socket, server.hostname, server.port, true);
+					this.socket = factory.createSocket(this.socket, server.hostname, server.port, true);
 				}
 
 				this.scanner = new Scanner(this.socket.getInputStream());
 				this.scanner.useDelimiter("\n");
 
-				// Check connection works by asking for more servers
+				// Check connection is suitable by asking for server features, including genesis block hash
+				JSONObject featuresJson = (JSONObject) this.connectedRpc("server.features");
+
+				if (featuresJson == null || Double.valueOf((String) featuresJson.get("protocol_min")) < MIN_PROTOCOL_VERSION)
+					continue;
+
+				if (this.expectedGenesisHash != null && !((String) featuresJson.get("genesis_hash")).equals(this.expectedGenesisHash))
+					continue;
+
+				// Ask for more servers
 				Set<Server> moreServers = serverPeersSubscribe();
+				// Discard duplicate servers we already know
 				moreServers.removeAll(this.servers);
-				remainingServers.addAll(moreServers);
+				// Add to both lists
+				this.remainingServers.addAll(moreServers);
 				this.servers.addAll(moreServers);
 
 				LOGGER.debug(() -> String.format("Connected to %s", server));
 				this.currentServer = server;
 				return true;
-			} catch (IOException e) {
+			} catch (IOException | BitcoinException | ClassCastException | NullPointerException e) {
 				// Try another server...
+				if (this.socket != null && !this.socket.isClosed())
+					try {
+						this.socket.close();
+					} catch (IOException e1) {
+						// We did try...
+					}
+
 				this.socket = null;
 				this.scanner = null;
 			}
@@ -350,11 +583,20 @@ public class ElectrumX {
 		return false;
 	}
 
+	/**
+	 * Perform RPC using currently connected server.
+	 * <p>
+	 * @param method
+	 * @param params
+	 * @return response Object, or null if server fails to respond
+	 * @throws BitcoinException if server returns error
+	 */
 	@SuppressWarnings("unchecked")
-	private Object connectedRpc(String method, Object...params) {
+	private Object connectedRpc(String method, Object...params) throws BitcoinException {
 		JSONObject requestJson = new JSONObject();
 		requestJson.put("id", this.nextId++);
 		requestJson.put("method", method);
+		requestJson.put("jsonrpc", "2.0");
 
 		JSONArray requestParams = new JSONArray();
 		requestParams.addAll(Arrays.asList(params));
@@ -369,18 +611,52 @@ public class ElectrumX {
 			this.socket.getOutputStream().write(request.getBytes());
 			response = scanner.next();
 		} catch (IOException | NoSuchElementException e) {
+			// Unable to send, or receive -- try another server?
 			return null;
 		}
 
 		LOGGER.trace(() -> String.format("Response: %s", response));
 
 		if (response.isEmpty())
+			// Empty response - try another server?
 			return null;
 
-		JSONObject responseJson = (JSONObject) JSONValue.parse(response);
-		if (responseJson == null)
+		Object responseObj = JSONValue.parse(response);
+		if (!(responseObj instanceof JSONObject))
+			// Unexpected response - try another server?
 			return null;
 
+		JSONObject responseJson = (JSONObject) responseObj;
+
+		Object errorObj = responseJson.get("error");
+		if (errorObj != null) {
+			if (!(errorObj instanceof JSONObject))
+				throw new BitcoinException.NetworkException(String.format("Unexpected error response from ElectrumX RPC %s", method));
+
+			JSONObject errorJson = (JSONObject) errorObj;
+
+			Object messageObj = errorJson.get("message");
+
+			if (!(messageObj instanceof String))
+				throw new BitcoinException.NetworkException(String.format("Missing/invalid message in error response from ElectrumX RPC %s", method));
+
+			String message = (String) messageObj;
+
+			// Some error 'messages' are actually wrapped upstream bitcoind errors:
+			// "message": "daemon error: DaemonError({'code': -5, 'message': 'No such mempool or blockchain transaction. Use gettransaction for wallet transactions.'})"
+			// We want to detect these and extract the upstream error code for caller's use
+			Matcher messageMatcher = DAEMON_ERROR_REGEX.matcher(message);
+			if (messageMatcher.find())
+				try {
+					int daemonErrorCode = Integer.parseInt(messageMatcher.group(1));
+					throw new BitcoinException.NetworkException(daemonErrorCode, message);
+				} catch (NumberFormatException e) {
+					// We couldn't parse the error code integer? Fall-through to generic exception...
+				}
+
+			throw new BitcoinException.NetworkException(message);
+		}
+
 		return responseJson.get("result");
 	}
 

src/main/java/org/qortal/crosschain/TransactionHash.java

@@ -0,0 +1,31 @@
+package org.qortal.crosschain;
+
+import java.util.Comparator;
+
+public class TransactionHash {
+
+	public static final Comparator<TransactionHash> CONFIRMED_FIRST = (a, b) -> Boolean.compare(a.height != 0, b.height != 0);
+
+	public final int height;
+	public final String txHash;
+
+	public TransactionHash(int height, String txHash) {
+		this.height = height;
+		this.txHash = txHash;
+	}
+
+	public int getHeight() {
+		return this.height;
+	}
+
+	public String getTxHash() {
+		return this.txHash;
+	}
+
+	public String toString() {
+		return this.height == 0
+				? String.format("txHash %s (unconfirmed)", this.txHash)
+				: String.format("txHash %s (height %d)", this.txHash, this.height);
+	}
+
+}

src/main/java/org/qortal/crosschain/UnspentOutput.java

@@ -0,0 +1,16 @@
+package org.qortal.crosschain;
+
+/** Unspent output info as returned by ElectrumX network. */
+public class UnspentOutput {
+	public final byte[] hash;
+	public final int index;
+	public final int height;
+	public final long value;
+
+	public UnspentOutput(byte[] hash, int index, int height, long value) {
+		this.hash = hash;
+		this.index = index;
+		this.height = height;
+		this.value = value;
+	}
+}

src/main/java/org/qortal/crypto/Crypto.java

@@ -1,5 +1,6 @@
 package org.qortal.crypto;
 
+import java.nio.ByteBuffer;
 import java.security.MessageDigest;
 import java.security.NoSuchAlgorithmException;
 import java.util.Arrays;
@@ -42,6 +43,27 @@ public abstract class Crypto {
 		}
 	}
 
+	/**
+	 * Returns 32-byte SHA-256 digest of message passed in input.
+	 * 
+	 * @param input
+	 *            variable-length byte[] message
+	 * @return byte[32] digest, or null if SHA-256 algorithm can't be accessed
+	 */
+	public static byte[] digest(ByteBuffer input) {
+		if (input == null)
+			return null;
+
+		try {
+			// SHA2-256
+			MessageDigest sha256 = MessageDigest.getInstance("SHA-256");
+			sha256.update(input);
+			return sha256.digest();
+		} catch (NoSuchAlgorithmException e) {
+			throw new RuntimeException("SHA-256 message digest not available");
+		}
+	}
+
 	/**
 	 * Returns 32-byte digest of two rounds of SHA-256 on message passed in input.
 	 * 

src/main/java/org/qortal/crypto/MemoryPoW.java

@@ -29,6 +29,10 @@ public class MemoryPoW {
 		do {
 			++nonce;
 
+			// If we've been interrupted, exit fast with invalid value
+			if (Thread.currentThread().isInterrupted())
+				return -1;
+
 			seed *= seedMultiplier; // per nonce
 
 			state[0] = longHash[0] ^ seed;

src/main/java/org/qortal/data/account/EligibleQoraHolderData.java

@@ -0,0 +1,48 @@
+package org.qortal.data.account;
+
+public class EligibleQoraHolderData {
+
+	// Properties
+
+	private String address;
+
+	private long qoraBalance;
+	private long qortFromQoraBalance;
+
+	private Long finalQortFromQora;
+	private Integer finalBlockHeight;
+
+	// Constructors
+
+	public EligibleQoraHolderData(String address, long qoraBalance, long qortFromQoraBalance, Long finalQortFromQora,
+			Integer finalBlockHeight) {
+		this.address = address;
+		this.qoraBalance = qoraBalance;
+		this.qortFromQoraBalance = qortFromQoraBalance;
+		this.finalQortFromQora = finalQortFromQora;
+		this.finalBlockHeight = finalBlockHeight;
+	}
+
+	// Getters/Setters
+
+	public String getAddress() {
+		return this.address;
+	}
+
+	public long getQoraBalance() {
+		return this.qoraBalance;
+	}
+
+	public long getQortFromQoraBalance() {
+		return this.qortFromQoraBalance;
+	}
+
+	public Long getFinalQortFromQora() {
+		return this.finalQortFromQora;
+	}
+
+	public Integer getFinalBlockHeight() {
+		return this.finalBlockHeight;
+	}
+
+}

src/main/java/org/qortal/data/account/RewardShareData.java

@@ -1,11 +1,15 @@
 package org.qortal.data.account;
 
+import java.math.BigDecimal;
+
 import javax.xml.bind.annotation.XmlAccessType;
 import javax.xml.bind.annotation.XmlAccessorType;
 import javax.xml.bind.annotation.XmlElement;
 import javax.xml.bind.annotation.XmlTransient;
 import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;
 
+import org.qortal.utils.Base58;
+
 import io.swagger.v3.oas.annotations.media.Schema;
 
 // All properties to be converted to JSON via JAXB
@@ -71,4 +75,13 @@ public class RewardShareData {
 		return this.minter;
 	}
 
+	// For debugging
+
+	public String toString() {
+		if (this.minter.equals(this.recipient))
+			return String.format("Minter/recipient: %s, reward-share public key: %s", this.minter, Base58.encode(this.rewardSharePublicKey));
+		else
+			return String.format("Minter: %s, recipient: %s (%s %%), reward-share public key: %s", this.minter, this.recipient, BigDecimal.valueOf(this.sharePercent, 2), Base58.encode(this.rewardSharePublicKey));
+	}
+
 }

src/main/java/org/qortal/data/at/ATStateData.java

@@ -5,7 +5,6 @@ public class ATStateData {
 	// Properties
 	private String ATAddress;
 	private Integer height;
-	private Long creation;
 	private byte[] stateData;
 	private byte[] stateHash;
 	private Long fees;
@@ -14,10 +13,9 @@ public class ATStateData {
 	// Constructors
 
 	/** Create new ATStateData */
-	public ATStateData(String ATAddress, Integer height, Long creation, byte[] stateData, byte[] stateHash, Long fees, boolean isInitial) {
+	public ATStateData(String ATAddress, Integer height, byte[] stateData, byte[] stateHash, Long fees, boolean isInitial) {
 		this.ATAddress = ATAddress;
 		this.height = height;
-		this.creation = creation;
 		this.stateData = stateData;
 		this.stateHash = stateHash;
 		this.fees = fees;
@@ -26,21 +24,21 @@ public class ATStateData {
 
 	/** For recreating per-block ATStateData from repository where not all info is needed */
 	public ATStateData(String ATAddress, int height, byte[] stateHash, Long fees, boolean isInitial) {
-		this(ATAddress, height, null, null, stateHash, fees, isInitial);
+		this(ATAddress, height, null, stateHash, fees, isInitial);
 	}
 
 	/** For creating ATStateData from serialized bytes when we don't have all the info */
 	public ATStateData(String ATAddress, byte[] stateHash) {
 		// This won't ever be initial AT state from deployment as that's never serialized over the network,
 		// but generated when the DeployAtTransaction is processed locally.
-		this(ATAddress, null, null, null, stateHash, null, false);
+		this(ATAddress, null, null, stateHash, null, false);
 	}
 
 	/** For creating ATStateData from serialized bytes when we don't have all the info */
 	public ATStateData(String ATAddress, byte[] stateHash, Long fees) {
 		// This won't ever be initial AT state from deployment as that's never serialized over the network,
 		// but generated when the DeployAtTransaction is processed locally.
-		this(ATAddress, null, null, null, stateHash, fees, false);
+		this(ATAddress, null, null, stateHash, fees, false);
 	}
 
 	// Getters / setters
@@ -58,10 +56,6 @@ public class ATStateData {
 		this.height = height;
 	}
 
-	public Long getCreation() {
-		return this.creation;
-	}
-
 	public byte[] getStateData() {
 		return this.stateData;
 	}

src/main/java/org/qortal/data/block/BlockData.java

@@ -79,6 +79,25 @@ public class BlockData implements Serializable {
 				null, 0, null, null);
 	}
 
+	public BlockData(BlockData other) {
+		this.version = other.version;
+		this.reference = other.reference;
+		this.transactionCount = other.transactionCount;
+		this.totalFees = other.totalFees;
+		this.transactionsSignature = other.transactionsSignature;
+		this.height = other.height;
+		this.timestamp = other.timestamp;
+		this.minterPublicKey = other.minterPublicKey;
+		this.minterSignature = other.minterSignature;
+		this.atCount = other.atCount;
+		this.atFees = other.atFees;
+		this.encodedOnlineAccounts = other.encodedOnlineAccounts;
+		this.onlineAccountsCount = other.onlineAccountsCount;
+		this.onlineAccountsTimestamp = other.onlineAccountsTimestamp;
+		this.onlineAccountsSignatures = other.onlineAccountsSignatures;
+		this.signature = other.signature;
+	}
+
 	// Getters/setters
 
 	public byte[] getSignature() {

src/main/java/org/qortal/data/block/BlockSummaryData.java

@@ -3,8 +3,6 @@ package org.qortal.data.block;
 import javax.xml.bind.annotation.XmlAccessType;
 import javax.xml.bind.annotation.XmlAccessorType;
 
-import org.qortal.transform.block.BlockTransformer;
-
 @XmlAccessorType(XmlAccessType.FIELD)
 public class BlockSummaryData {
 
@@ -14,6 +12,10 @@ public class BlockSummaryData {
 	private byte[] minterPublicKey;
 	private int onlineAccountsCount;
 
+	// Optional, set during construction
+	private Long timestamp;
+	private Integer transactionCount;
+
 	// Optional, set after construction
 	private Integer minterLevel;
 
@@ -29,17 +31,23 @@ public class BlockSummaryData {
 		this.onlineAccountsCount = onlineAccountsCount;
 	}
 
+	public BlockSummaryData(int height, byte[] signature, byte[] minterPublicKey, int onlineAccountsCount, long timestamp, int transactionCount) {
+		this.height = height;
+		this.signature = signature;
+		this.minterPublicKey = minterPublicKey;
+		this.onlineAccountsCount = onlineAccountsCount;
+		this.timestamp = timestamp;
+		this.transactionCount = transactionCount;
+	}
+
 	public BlockSummaryData(BlockData blockData) {
 		this.height = blockData.getHeight();
 		this.signature = blockData.getSignature();
 		this.minterPublicKey = blockData.getMinterPublicKey();
+		this.onlineAccountsCount = blockData.getOnlineAccountsCount();
 
-		byte[] encodedOnlineAccounts = blockData.getEncodedOnlineAccounts();
-		if (encodedOnlineAccounts != null) {
-			this.onlineAccountsCount = BlockTransformer.decodeOnlineAccounts(encodedOnlineAccounts).size();
-		} else {
-			this.onlineAccountsCount = 0;
-		}
+		this.timestamp = blockData.getTimestamp();
+		this.transactionCount = blockData.getTransactionCount();
 	}
 
 	// Getters / setters
@@ -60,6 +68,14 @@ public class BlockSummaryData {
 		return this.onlineAccountsCount;
 	}
 
+	public Long getTimestamp() {
+		return this.timestamp;
+	}
+
+	public Integer getTransactionCount() {
+		return this.transactionCount;
+	}
+
 	public Integer getMinterLevel() {
 		return this.minterLevel;
 	}

src/main/java/org/qortal/data/crosschain/CrossChainTradeData.java

@@ -4,14 +4,14 @@ import javax.xml.bind.annotation.XmlAccessType;
 import javax.xml.bind.annotation.XmlAccessorType;
 import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;
 
+import org.qortal.crosschain.BTCACCT;
+
 import io.swagger.v3.oas.annotations.media.Schema;
 
 // All properties to be converted to JSON via JAXB
 @XmlAccessorType(XmlAccessType.FIELD)
 public class CrossChainTradeData {
 
-	public enum Mode { OFFER, TRADE };
-
 	// Properties
 
 	@Schema(description = "AT's Qortal address")
@@ -20,32 +20,40 @@ public class CrossChainTradeData {
 	@Schema(description = "AT creator's Qortal address")
 	public String qortalCreator;
 
+	@Schema(description = "AT creator's Qortal trade address")
+	public String qortalCreatorTradeAddress;
+
+	@Schema(description = "AT creator's Bitcoin trade public-key-hash (PKH)")
+	public byte[] creatorBitcoinPKH;
+
 	@Schema(description = "Timestamp when AT was created (milliseconds since epoch)")
 	public long creationTimestamp;
 
+	@Schema(description = "Suggested trade timeout (minutes)", example = "10080")
+	public int tradeTimeout;
+
 	@Schema(description = "AT's current QORT balance")
 	@XmlJavaTypeAdapter(value = org.qortal.api.AmountTypeAdapter.class)
 	public long qortBalance;
 
-	@Schema(description = "HASH160 of 32-byte secret")
-	public byte[] secretHash;
+	@Schema(description = "HASH160 of 32-byte secret-A")
+	public byte[] hashOfSecretA;
 
-	@Schema(description = "Initial QORT payment that will be sent to Qortal trade partner")
-	@XmlJavaTypeAdapter(value = org.qortal.api.AmountTypeAdapter.class)
-	public long initialPayout;
+	@Schema(description = "HASH160 of 32-byte secret-B")
+	public byte[] hashOfSecretB;
 
 	@Schema(description = "Final QORT payment that will be sent to Qortal trade partner")
 	@XmlJavaTypeAdapter(value = org.qortal.api.AmountTypeAdapter.class)
-	public long redeemPayout;
+	public long qortAmount;
 
 	@Schema(description = "Trade partner's Qortal address (trade begins when this is set)")
-	public String qortalRecipient;
+	public String qortalPartnerAddress;
 
 	@Schema(description = "Timestamp when AT switched to trade mode")
 	public Long tradeModeTimestamp;
 
-	@Schema(description = "How long from beginning trade until AT triggers automatic refund to AT creator (minutes)")
-	public long tradeRefundTimeout;
+	@Schema(description = "How long from AT creation until AT triggers automatic refund to AT creator (minutes)")
+	public Integer refundTimeout;
 
 	@Schema(description = "Actual Qortal block height when AT will automatically refund to AT creator (after trade begins)")
 	public Integer tradeRefundHeight;
@@ -54,10 +62,19 @@ public class CrossChainTradeData {
 	@XmlJavaTypeAdapter(value = org.qortal.api.AmountTypeAdapter.class)
 	public long expectedBitcoin;
 
-	public Mode mode;
+	public BTCACCT.Mode mode;
 
-	@Schema(description = "Suggested Bitcoin P2SH nLockTime based on trade timeout")
-	public Integer lockTime;
+	@Schema(description = "Suggested Bitcoin P2SH-A nLockTime based on trade timeout")
+	public Integer lockTimeA;
+
+	@Schema(description = "Suggested Bitcoin P2SH-B nLockTime based on trade timeout")
+	public Integer lockTimeB;
+
+	@Schema(description = "Trade partner's Bitcoin public-key-hash (PKH)")
+	public byte[] partnerBitcoinPKH;
+
+	@Schema(description = "Trade partner's Qortal receiving address")
+	public String qortalPartnerReceivingAddress;
 
 	// Constructors
 

src/main/java/org/qortal/data/crosschain/TradeBotData.java

@@ -0,0 +1,198 @@
+package org.qortal.data.crosschain;
+
+import static java.util.Arrays.stream;
+import static java.util.stream.Collectors.toMap;
+
+import java.util.Map;
+
+import javax.xml.bind.annotation.XmlAccessType;
+import javax.xml.bind.annotation.XmlAccessorType;
+import javax.xml.bind.annotation.XmlTransient;
+import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;
+
+import io.swagger.v3.oas.annotations.media.Schema;
+
+// All properties to be converted to JSON via JAXB
+@XmlAccessorType(XmlAccessType.FIELD)
+public class TradeBotData {
+
+	private byte[] tradePrivateKey;
+
+	public enum State {
+		BOB_WAITING_FOR_AT_CONFIRM(10), BOB_WAITING_FOR_MESSAGE(15), BOB_WAITING_FOR_P2SH_B(20), BOB_WAITING_FOR_AT_REDEEM(25), BOB_DONE(30), BOB_REFUNDED(35),
+		ALICE_WAITING_FOR_P2SH_A(80), ALICE_WAITING_FOR_AT_LOCK(85), ALICE_WATCH_P2SH_B(90), ALICE_DONE(95), ALICE_REFUNDING_B(100), ALICE_REFUNDING_A(105), ALICE_REFUNDED(110);
+
+		public final int value;
+		private static final Map<Integer, State> map = stream(State.values()).collect(toMap(state -> state.value, state -> state));
+
+		State(int value) {
+			this.value = value;
+		}
+
+		public static State valueOf(int value) {
+			return map.get(value);
+		}
+	}
+	private State tradeState;
+
+	private String creatorAddress;
+	private String atAddress;
+
+	private long timestamp;
+
+	@XmlJavaTypeAdapter(value = org.qortal.api.AmountTypeAdapter.class)
+	private long qortAmount;
+
+	private byte[] tradeNativePublicKey;
+	private byte[] tradeNativePublicKeyHash;
+	String tradeNativeAddress;
+
+	private byte[] secret;
+	private byte[] hashOfSecret;
+
+	private byte[] tradeForeignPublicKey;
+	private byte[] tradeForeignPublicKeyHash;
+
+	@XmlJavaTypeAdapter(value = org.qortal.api.AmountTypeAdapter.class)
+	private long bitcoinAmount;
+
+	// Never expose this via API
+	@XmlTransient
+	@Schema(hidden = true)
+	private String xprv58;
+
+	private byte[] lastTransactionSignature;
+
+	private Integer lockTimeA;
+
+	// Could be Bitcoin or Qortal...
+	private byte[] receivingAccountInfo;
+
+	protected TradeBotData() {
+		/* JAXB */
+	}
+
+	public TradeBotData(byte[] tradePrivateKey, State tradeState, String creatorAddress, String atAddress,
+			long timestamp, long qortAmount,
+			byte[] tradeNativePublicKey, byte[] tradeNativePublicKeyHash, String tradeNativeAddress,
+			byte[] secret, byte[] hashOfSecret,
+			byte[] tradeForeignPublicKey, byte[] tradeForeignPublicKeyHash,
+			long bitcoinAmount, String xprv58, byte[] lastTransactionSignature, Integer lockTimeA, byte[] receivingAccountInfo) {
+		this.tradePrivateKey = tradePrivateKey;
+		this.tradeState = tradeState;
+		this.creatorAddress = creatorAddress;
+		this.atAddress = atAddress;
+		this.timestamp = timestamp;
+		this.qortAmount = qortAmount;
+		this.tradeNativePublicKey = tradeNativePublicKey;
+		this.tradeNativePublicKeyHash = tradeNativePublicKeyHash;
+		this.tradeNativeAddress = tradeNativeAddress;
+		this.secret = secret;
+		this.hashOfSecret = hashOfSecret;
+		this.tradeForeignPublicKey = tradeForeignPublicKey;
+		this.tradeForeignPublicKeyHash = tradeForeignPublicKeyHash;
+		this.bitcoinAmount = bitcoinAmount;
+		this.xprv58 = xprv58;
+		this.lastTransactionSignature = lastTransactionSignature;
+		this.lockTimeA = lockTimeA;
+		this.receivingAccountInfo = receivingAccountInfo;
+	}
+
+	public byte[] getTradePrivateKey() {
+		return this.tradePrivateKey;
+	}
+
+	public State getState() {
+		return this.tradeState;
+	}
+
+	public void setState(State state) {
+		this.tradeState = state;
+	}
+
+	public String getCreatorAddress() {
+		return this.creatorAddress;
+	}
+
+	public String getAtAddress() {
+		return this.atAddress;
+	}
+
+	public void setAtAddress(String atAddress) {
+		this.atAddress = atAddress;
+	}
+
+	public long getTimestamp() {
+		return this.timestamp;
+	}
+
+	public void setTimestamp(long timestamp) {
+		this.timestamp = timestamp;
+	}
+
+	public long getQortAmount() {
+		return this.qortAmount;
+	}
+
+	public byte[] getTradeNativePublicKey() {
+		return this.tradeNativePublicKey;
+	}
+
+	public byte[] getTradeNativePublicKeyHash() {
+		return this.tradeNativePublicKeyHash;
+	}
+
+	public String getTradeNativeAddress() {
+		return this.tradeNativeAddress;
+	}
+
+	public byte[] getSecret() {
+		return this.secret;
+	}
+
+	public byte[] getHashOfSecret() {
+		return this.hashOfSecret;
+	}
+
+	public byte[] getTradeForeignPublicKey() {
+		return this.tradeForeignPublicKey;
+	}
+
+	public byte[] getTradeForeignPublicKeyHash() {
+		return this.tradeForeignPublicKeyHash;
+	}
+
+	public long getBitcoinAmount() {
+		return this.bitcoinAmount;
+	}
+
+	public String getXprv58() {
+		return this.xprv58;
+	}
+
+	public byte[] getLastTransactionSignature() {
+		return this.lastTransactionSignature;
+	}
+
+	public void setLastTransactionSignature(byte[] lastTransactionSignature) {
+		this.lastTransactionSignature = lastTransactionSignature;
+	}
+
+	public Integer getLockTimeA() {
+		return this.lockTimeA;
+	}
+
+	public void setLockTimeA(Integer lockTimeA) {
+		this.lockTimeA = lockTimeA;
+	}
+
+	public byte[] getReceivingAccountInfo() {
+		return this.receivingAccountInfo;
+	}
+
+	// Mostly for debugging
+	public String toString() {
+		return String.format("%s: %s", this.atAddress, this.tradeState.name());
+	}
+
+}

src/main/java/org/qortal/event/Event.java

@@ -0,0 +1,5 @@
+package org.qortal.event;
+
+public interface Event {
+
+}

src/main/java/org/qortal/event/EventBus.java

@@ -0,0 +1,48 @@
+package org.qortal.event;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public enum EventBus {
+	INSTANCE;
+
+	private static final List<Listener> LISTENERS = new ArrayList<>();
+
+	public void addListener(Listener newListener) {
+		synchronized (LISTENERS) {
+			LISTENERS.add(newListener);
+		}
+	}
+
+	public void removeListener(Listener listener) {
+		synchronized (LISTENERS) {
+			LISTENERS.remove(listener);
+		}
+	}
+
+	/**
+	 * <b>WARNING:</b> before calling this method,
+	 * make sure repository holds no locks, e.g. by calling
+	 * <tt>repository.discardChanges()</tt>.
+	 * <p>
+	 * This is because event listeners might open a new
+	 * repository session which will deadlock HSQLDB
+	 * if it tries to CHECKPOINT.
+	 * <p>
+	 * The HSQLDB deadlock occurs because the caller's
+	 * repository session blocks the CHECKPOINT until
+	 * their transaction is closed, yet event listeners
+	 * new sessions are blocked until CHECKPOINT is
+	 * completed, hence deadlock.
+	 */
+	public void notify(Event event) {
+		List<Listener> clonedListeners;
+
+		synchronized (LISTENERS) {
+			clonedListeners = new ArrayList<>(LISTENERS);
+		}
+
+		for (Listener listener : clonedListeners)
+			listener.listen(event);
+	}
+}

src/main/java/org/qortal/event/Listener.java

@@ -0,0 +1,6 @@
+package org.qortal.event;
+
+@FunctionalInterface
+public interface Listener {
+	void listen(Event event);
+}

src/main/java/org/qortal/globalization/Translator.java

@@ -10,12 +10,12 @@ import java.util.Set;
 
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
+import org.qortal.settings.Settings;
 
 public enum Translator {
 	INSTANCE;
 
 	private static final Logger LOGGER = LogManager.getLogger(Translator.class);
-	private static final String DEFAULT_LANG = Locale.getDefault().getLanguage();
 
 	private static final Map<String, ResourceBundle> resourceBundles = new HashMap<>();
 
@@ -34,7 +34,7 @@ public enum Translator {
 	}
 
 	public String translate(String className, String key) {
-		return this.translate(className, DEFAULT_LANG, key);
+		return this.translate(className, Settings.getInstance().getLocaleLang(), key);
 	}
 
 	public Set<String> keySet(String className, String lang) {

src/main/java/org/qortal/network/Handshake.java

@@ -1,6 +1,8 @@
 package org.qortal.network;
 
 import java.util.Arrays;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
@@ -13,7 +15,9 @@ import org.qortal.network.message.ChallengeMessage;
 import org.qortal.network.message.HelloMessage;
 import org.qortal.network.message.Message;
 import org.qortal.network.message.Message.MessageType;
+import org.qortal.settings.Settings;
 import org.qortal.network.message.ResponseMessage;
+import org.qortal.utils.DaemonThreadFactory;
 import org.qortal.utils.NTP;
 
 import com.google.common.primitives.Bytes;
@@ -27,6 +31,7 @@ public enum Handshake {
 
 		@Override
 		public void action(Peer peer) {
+			/* Never called */
 		}
 	},
 	HELLO(MessageType.HELLO) {
@@ -157,13 +162,20 @@ public enum Handshake {
 			}
 
 			int nonce = responseMessage.getNonce();
-			if (!MemoryPoW.verify2(data, POW_BUFFER_SIZE, POW_DIFFICULTY, nonce)) {
+			int powBufferSize = peer.getPeersVersion() < PEER_VERSION_131 ? POW_BUFFER_SIZE_PRE_131 : POW_BUFFER_SIZE_POST_131;
+			int powDifficulty = peer.getPeersVersion() < PEER_VERSION_131 ? POW_DIFFICULTY_PRE_131 : POW_DIFFICULTY_POST_131;
+			if (!MemoryPoW.verify2(data, powBufferSize, powDifficulty, nonce)) {
 				LOGGER.debug(() -> String.format("Peer %s sent incorrect RESPONSE nonce", peer));
 				return null;
 			}
 
 			peer.setPeersNodeId(Crypto.toNodeAddress(peersPublicKey));
 
+			// For inbound peers, we need to go into interim holding state while we compute RESPONSE
+			if (!peer.isOutbound())
+				return RESPONDING;
+
+			// Handshake completed!
 			return COMPLETED;
 		}
 
@@ -178,28 +190,52 @@ public enum Handshake {
 			final byte[] data = Crypto.digest(Bytes.concat(sharedSecret, peersChallenge));
 
 			// We do this in a new thread as it can take a while...
-			Thread responseThread = new Thread(() -> {
-				Integer nonce = MemoryPoW.compute2(data, POW_BUFFER_SIZE, POW_DIFFICULTY);
+			responseExecutor.execute(() -> {
+				// Are we still connected?
+				if (peer.isStopping())
+					// No point computing for dead peer
+					return;
+
+				int powBufferSize = peer.getPeersVersion() < PEER_VERSION_131 ? POW_BUFFER_SIZE_PRE_131 : POW_BUFFER_SIZE_POST_131;
+				int powDifficulty = peer.getPeersVersion() < PEER_VERSION_131 ? POW_DIFFICULTY_PRE_131 : POW_DIFFICULTY_POST_131;
+				Integer nonce = MemoryPoW.compute2(data, powBufferSize, powDifficulty);
 
 				Message responseMessage = new ResponseMessage(nonce, data);
 				if (!peer.sendMessage(responseMessage))
 					peer.disconnect("failed to send RESPONSE");
-			});
 
-			responseThread.setDaemon(true);
-			responseThread.start();
+				// For inbound peers, we should actually be in RESPONDING state.
+				// So we need to do the extra work to move to COMPLETED state.
+				if (!peer.isOutbound()) {
+					peer.setHandshakeStatus(COMPLETED);
+					Network.getInstance().onHandshakeCompleted(peer);
+				}
+			});
 		}
 	},
-	COMPLETED(null) {
+	// Interim holding state while we compute RESPONSE to send to inbound peer
+	RESPONDING(null) {
 		@Override
 		public Handshake onMessage(Peer peer, Message message) {
-			// Handshake completed
+			// Should never be called
 			return null;
 		}
 
 		@Override
 		public void action(Peer peer) {
-			// Note: this is only called when we've made outbound connection
+			// Should never be called
+		}
+	},
+	COMPLETED(null) {
+		@Override
+		public Handshake onMessage(Peer peer, Message message) {
+			// Should never be called
+			return null;
+		}
+
+		@Override
+		public void action(Peer peer) {
+			// Note: this is only called if we've made outbound connection
 		}
 	};
 
@@ -210,8 +246,16 @@ public enum Handshake {
 
 	private static final Pattern VERSION_PATTERN = Pattern.compile(Controller.VERSION_PREFIX + "(\\d{1,3})\\.(\\d{1,5})\\.(\\d{1,5})");
 
-	private static final int POW_BUFFER_SIZE = 8 * 1024 * 1024; // bytes
-	private static final int POW_DIFFICULTY = 8; // leading zero bits
+	private static final long PEER_VERSION_131 = 0x0100030001L;
+
+	private static final int POW_BUFFER_SIZE_PRE_131 = 8 * 1024 * 1024; // bytes
+	private static final int POW_DIFFICULTY_PRE_131 = 8; // leading zero bits
+	// Can always be made harder in the future...
+	private static final int POW_BUFFER_SIZE_POST_131 = 2 * 1024 * 1024; // bytes
+	private static final int POW_DIFFICULTY_POST_131 = 2; // leading zero bits
+
+
+	private static final ExecutorService responseExecutor = Executors.newFixedThreadPool(Settings.getInstance().getNetworkPoWComputePoolSize(), new DaemonThreadFactory("Network-PoW"));
 
 	private static final byte[] ZERO_CHALLENGE = new byte[ChallengeMessage.CHALLENGE_LENGTH];
 

src/main/java/org/qortal/network/Network.java

@@ -50,11 +50,11 @@ import org.qortal.repository.DataException;
 import org.qortal.repository.Repository;
 import org.qortal.repository.RepositoryManager;
 import org.qortal.settings.Settings;
-import org.qortal.transform.Transformer;
 import org.qortal.utils.ExecuteProduceConsume;
 // import org.qortal.utils.ExecutorDumper;
 import org.qortal.utils.ExecuteProduceConsume.StatsSnapshot;
 import org.qortal.utils.NTP;
+import org.qortal.utils.NamedThreadFactory;
 
 // For managing peers
 public class Network {
@@ -80,16 +80,9 @@ public class Network {
 	private static final byte[] TESTNET_MESSAGE_MAGIC = new byte[] { 0x71, 0x6f, 0x72, 0x54 }; // qorT
 
 	private static final String[] INITIAL_PEERS = new String[] {
-			"node1.qortal.org",
-			"node2.qortal.org",
-			"node3.qortal.org",
-			"node4.qortal.org",
-			"node5.qortal.org",
-			"node6.qortal.org",
-			"node7.qortal.org",
-			"node8.qortal.org",
-			"node9.qortal.org",
-			"node10.qortal.org"
+			"node1.qortal.org", "node2.qortal.org", "node3.qortal.org", "node4.qortal.org", "node5.qortal.org",
+			"node6.qortal.org", "node7.qortal.org", "node8.qortal.org", "node9.qortal.org", "node10.qortal.org",
+			"node.qortal.ru", "node2.qortal.ru", "node3.qortal.ru", "node.qortal.uk"
 	};
 
 	private static final long NETWORK_EPC_KEEPALIVE = 10L; // seconds
@@ -97,61 +90,47 @@ public class Network {
 	public static final int MAX_SIGNATURES_PER_REPLY = 500;
 	public static final int MAX_BLOCK_SUMMARIES_PER_REPLY = 500;
 
-	private final Ed25519PrivateKeyParameters edPrivateKeyParams;
-	private final Ed25519PublicKeyParameters edPublicKeyParams;
-	private final String ourNodeId;
+	// Generate our node keys / ID
+	private final Ed25519PrivateKeyParameters edPrivateKeyParams = new Ed25519PrivateKeyParameters(new SecureRandom());
+	private final Ed25519PublicKeyParameters edPublicKeyParams = edPrivateKeyParams.generatePublicKey();
+	private final String ourNodeId = Crypto.toNodeAddress(edPublicKeyParams.getEncoded());
 
 	private final int maxMessageSize;
+	private final int minOutboundPeers;
+	private final int maxPeers;
 
-	private List<PeerData> allKnownPeers;
-	private List<Peer> connectedPeers;
-	private List<PeerAddress> selfPeers;
+	private final List<PeerData> allKnownPeers = new ArrayList<>();
+	private final List<Peer> connectedPeers = new ArrayList<>();
+	private final List<PeerAddress> selfPeers = new ArrayList<>();
 
-	private ExecuteProduceConsume networkEPC;
+	private final ExecuteProduceConsume networkEPC;
 	private Selector channelSelector;
 	private ServerSocketChannel serverChannel;
 	private Iterator<SelectionKey> channelIterator = null;
 
-	private int minOutboundPeers;
-	private int maxPeers;
-	private long nextConnectTaskTimestamp;
+	// volatile because value is updated inside any one of the EPC threads
+	private volatile long nextConnectTaskTimestamp = 0L; // ms - try first connect once NTP syncs
 
-	private ExecutorService broadcastExecutor;
-	private long nextBroadcastTimestamp;
+	private ExecutorService broadcastExecutor = Executors.newCachedThreadPool();
+	// volatile because value is updated inside any one of the EPC threads
+	private volatile long nextBroadcastTimestamp = 0L; // ms - try first broadcast once NTP syncs
 
-	private Lock mergePeersLock;
+	private final Lock mergePeersLock = new ReentrantLock();
 
 	// Constructors
 
 	private Network() {
-		connectedPeers = new ArrayList<>();
-		selfPeers = new ArrayList<>();
-
-		// Generate our ID
-		byte[] seed = new byte[Transformer.PRIVATE_KEY_LENGTH];
-		new SecureRandom().nextBytes(seed);
-
-		edPrivateKeyParams = new Ed25519PrivateKeyParameters(seed, 0);
-		edPublicKeyParams = edPrivateKeyParams.generatePublicKey();
-		ourNodeId = Crypto.toNodeAddress(edPublicKeyParams.getEncoded());
-
 		maxMessageSize = 4 + 1 + 4 + BlockChain.getInstance().getMaxBlockSize();
 
 		minOutboundPeers = Settings.getInstance().getMinOutboundPeers();
 		maxPeers = Settings.getInstance().getMaxPeers();
 
-		nextConnectTaskTimestamp = 0; // First connect once NTP syncs
-
-		broadcastExecutor = Executors.newCachedThreadPool();
-		nextBroadcastTimestamp = 0; // First broadcast once NTP syncs
-
-		mergePeersLock = new ReentrantLock();
-
 		// We'll use a cached thread pool but with more aggressive timeout.
 		ExecutorService networkExecutor = new ThreadPoolExecutor(1,
 				Settings.getInstance().getMaxNetworkThreadPoolSize(),
 				NETWORK_EPC_KEEPALIVE, TimeUnit.SECONDS,
-				new SynchronousQueue<Runnable>());
+				new SynchronousQueue<Runnable>(),
+				new NamedThreadFactory("Network-EPC"));
 		networkEPC = new NetworkProcessor(networkExecutor);
 	}
 
@@ -182,7 +161,9 @@ public class Network {
 
 		// Load all known peers from repository
 		try (final Repository repository = RepositoryManager.getRepository()) {
-			allKnownPeers = repository.getNetworkRepository().getAllPeers();
+			synchronized (this.allKnownPeers) {
+				this.allKnownPeers.addAll(repository.getNetworkRepository().getAllPeers());
+			}
 		}
 
 		// Start up first networking thread
@@ -355,7 +336,7 @@ public class Network {
 
 		private Task maybeProducePeerPingTask(Long now) {
 			// Ask connected peers whether they need a ping
-			for (Peer peer : getConnectedPeers()) {
+			for (Peer peer : getHandshakedPeers()) {
 				Task peerTask = peer.getPingTask(now);
 				if (peerTask != null)
 					return peerTask;
@@ -450,35 +431,38 @@ public class Network {
 		private Task maybeProduceChannelTask(boolean canBlock) throws InterruptedException {
 			final SelectionKey nextSelectionKey;
 
-			// anything to do?
-			if (channelIterator == null) {
-				try {
-					if (canBlock)
-						channelSelector.select(1000L);
-					else
-						channelSelector.selectNow();
-				} catch (IOException e) {
-					LOGGER.warn(String.format("Channel selection threw IOException: %s", e.getMessage()));
-					return null;
+			// Synchronization here to enforce thread-safety on channelIterator
+			synchronized (channelSelector) {
+				// anything to do?
+				if (channelIterator == null) {
+					try {
+						if (canBlock)
+							channelSelector.select(1000L);
+						else
+							channelSelector.selectNow();
+					} catch (IOException e) {
+						LOGGER.warn(String.format("Channel selection threw IOException: %s", e.getMessage()));
+						return null;
+					}
+
+					if (Thread.currentThread().isInterrupted())
+						throw new InterruptedException();
+
+					channelIterator = channelSelector.selectedKeys().iterator();
 				}
 
-				if (Thread.currentThread().isInterrupted())
-					throw new InterruptedException();
+				if (channelIterator.hasNext()) {
+					nextSelectionKey = channelIterator.next();
+					channelIterator.remove();
+				} else {
+					nextSelectionKey = null;
+					channelIterator = null; // Nothing to do so reset iterator to cause new select
+				}
 
-				channelIterator = channelSelector.selectedKeys().iterator();
+				LOGGER.trace(() -> String.format("Thread %d, nextSelectionKey %s, channelIterator now %s",
+						Thread.currentThread().getId(), nextSelectionKey, channelIterator));
 			}
 
-			if (channelIterator.hasNext()) {
-				nextSelectionKey = channelIterator.next();
-				channelIterator.remove();
-			} else {
-				nextSelectionKey = null;
-				channelIterator = null; // Nothing to do so reset iterator to cause new select
-			}
-
-			LOGGER.trace(() -> String.format("Thread %d, nextSelectionKey %s, channelIterator now %s",
-					Thread.currentThread().getId(), nextSelectionKey, channelIterator));
-
 			if (nextSelectionKey == null)
 				return null;
 
@@ -635,7 +619,7 @@ public class Network {
 
 	/** Called when Peer's thread has setup and is ready to process messages */
 	public void onPeerReady(Peer peer) {
-		this.onMessage(peer, null);
+		onHandshakingMessage(peer, null, Handshake.STARTED);
 	}
 
 	public void onDisconnect(Peer peer) {
@@ -777,7 +761,7 @@ public class Network {
 		opportunisticMergePeers(peer.toString(), peerV2Addresses);
 	}
 
-	private void onHandshakeCompleted(Peer peer) {
+	/*pacakge*/ void onHandshakeCompleted(Peer peer) {
 		LOGGER.debug(String.format("Handshake completed with peer %s", peer));
 
 		// Are we already connected to this peer?

src/main/java/org/qortal/network/Peer.java

@@ -33,6 +33,7 @@ import org.qortal.settings.Settings;
 import org.qortal.utils.ExecuteProduceConsume;
 import org.qortal.utils.NTP;
 
+import com.google.common.hash.HashCode;
 import com.google.common.net.HostAndPort;
 import com.google.common.net.InetAddresses;
 
@@ -348,21 +349,37 @@ public class Peer {
 				if (this.byteBuffer == null)
 					this.byteBuffer = ByteBuffer.allocate(Network.getInstance().getMaxMessageSize());
 
+				final int priorPosition = this.byteBuffer.position();
 				final int bytesRead = this.socketChannel.read(this.byteBuffer);
 				if (bytesRead == -1) {
 					this.disconnect("EOF");
 					return;
 				}
 
-				LOGGER.trace(() -> String.format("Received %d bytes from peer %s", bytesRead, this));
+				LOGGER.trace(() -> {
+					if (bytesRead > 0) {
+						byte[] leadingBytes = new byte[Math.min(bytesRead, 8)];
+						this.byteBuffer.asReadOnlyBuffer().position(priorPosition).get(leadingBytes);
+						String leadingHex = HashCode.fromBytes(leadingBytes).toString();
+
+						return String.format("Received %d bytes, starting %s, into byteBuffer[%d] from peer %s",
+								bytesRead,
+								leadingHex,
+								priorPosition,
+								this);
+					} else {
+						return String.format("Received %d bytes into byteBuffer[%d] from peer %s", bytesRead, priorPosition, this);
+					}
+				});
 				final boolean wasByteBufferFull = !this.byteBuffer.hasRemaining();
 
 				while (true) {
 					final Message message;
 
 					// Can we build a message from buffer now?
+					ByteBuffer readOnlyBuffer = this.byteBuffer.asReadOnlyBuffer().flip();
 					try {
-						message = Message.fromByteBuffer(this.byteBuffer);
+						message = Message.fromByteBuffer(readOnlyBuffer);
 					} catch (MessageException e) {
 						LOGGER.debug(String.format("%s, from peer %s", e.getMessage(), this));
 						this.disconnect(e.getMessage());
@@ -372,9 +389,11 @@ public class Peer {
 					if (message == null && bytesRead == 0 && !wasByteBufferFull) {
 						// No complete message in buffer, no more bytes to read from socket even though there was room to read bytes
 
+						/* DISABLED
 						// If byteBuffer is empty then we can deallocate it, to save memory, albeit costing GC
 						if (this.byteBuffer.remaining() == this.byteBuffer.capacity())
 							this.byteBuffer = null;
+						*/
 
 						return;
 					}
@@ -385,6 +404,13 @@ public class Peer {
 
 					LOGGER.trace(() -> String.format("Received %s message with ID %d from peer %s", message.getType().name(), message.getId(), this));
 
+					// Tidy up buffers:
+					this.byteBuffer.flip();
+					// Read-only, flipped buffer's position will be after end of message, so copy that
+					this.byteBuffer.position(readOnlyBuffer.position());
+					// Copy bytes after read message to front of buffer, adjusting position accordingly, reset limit to capacity
+					this.byteBuffer.compact();
+
 					BlockingQueue<Message> queue = this.replyQueues.get(message.getId());
 					if (queue != null) {
 						// Adding message to queue will unblock thread waiting for response
@@ -397,7 +423,7 @@ public class Peer {
 
 					// Add message to pending queue
 					if (!this.pendingMessages.offer(message)) {
-						LOGGER.info(String.format("No room to queue message from peer %s - discarding", this));
+						LOGGER.info(() -> String.format("No room to queue message from peer %s - discarding", this));
 						return;
 					}
 
@@ -452,10 +478,24 @@ public class Peer {
 				while (outputBuffer.hasRemaining()) {
 					int bytesWritten = this.socketChannel.write(outputBuffer);
 
+					LOGGER.trace(() -> String.format("Sent %d bytes of %s message with ID %d to peer %s",
+							bytesWritten,
+							message.getType().name(),
+							message.getId(),
+							this));
+
 					if (bytesWritten == 0)
 						// Underlying socket's internal buffer probably full,
 						// so wait a short while for bytes to actually be transmitted over the wire
-						this.socketChannel.wait(1L);
+
+						/*
+						 * NOSONAR squid:S2276 - we don't want to use this.socketChannel.wait()
+						 * as this releases the lock held by synchronized() above
+						 * and would allow another thread to send another message,
+						 * potentially interleaving them on-the-wire, causing checksum failures
+						 * and connection loss.
+						 */
+						Thread.sleep(1L); //NOSONAR squid:S2276
 				}
 			}
 		} catch (MessageException e) {

src/main/java/org/qortal/network/message/BlockMessage.java

@@ -34,6 +34,7 @@ public class BlockMessage extends Message {
 		super(MessageType.BLOCK);
 
 		this.block = block;
+		this.blockData = block.getBlockData();
 		this.height = block.getBlockData().getHeight();
 	}
 
@@ -93,4 +94,10 @@ public class BlockMessage extends Message {
 		}
 	}
 
+	public BlockMessage cloneWithNewId(int newId) {
+		BlockMessage clone = new BlockMessage(this.block);
+		clone.setId(newId);
+		return clone;
+	}
+
 }

src/main/java/org/qortal/network/message/Message.java

@@ -160,80 +160,72 @@ public abstract class Message {
 	/**
 	 * Attempt to read a message from byte buffer.
 	 * 
-	 * @param byteBuffer
+	 * @param readOnlyBuffer
 	 * @return null if no complete message can be read
 	 * @throws MessageException
 	 */
-	public static Message fromByteBuffer(ByteBuffer byteBuffer) throws MessageException {
+	public static Message fromByteBuffer(ByteBuffer readOnlyBuffer) throws MessageException {
 		try {
-			byteBuffer.flip();
-
-			ByteBuffer readBuffer = byteBuffer.asReadOnlyBuffer();
-
 			// Read only enough bytes to cover Message "magic" preamble
 			byte[] messageMagic = new byte[MAGIC_LENGTH];
-			readBuffer.get(messageMagic);
+			readOnlyBuffer.get(messageMagic);
 
 			if (!Arrays.equals(messageMagic, Network.getInstance().getMessageMagic()))
 				// Didn't receive correct Message "magic"
 				throw new MessageException("Received incorrect message 'magic'");
 
 			// Find supporting object
-			int typeValue = readBuffer.getInt();
+			int typeValue = readOnlyBuffer.getInt();
 			MessageType messageType = MessageType.valueOf(typeValue);
 			if (messageType == null)
 				// Unrecognised message type
 				throw new MessageException(String.format("Received unknown message type [%d]", typeValue));
 
 			// Optional message ID
-			byte hasId = readBuffer.get();
+			byte hasId = readOnlyBuffer.get();
 			int id = -1;
 			if (hasId != 0) {
-				id = readBuffer.getInt();
+				id = readOnlyBuffer.getInt();
 
 				if (id <= 0)
 					// Invalid ID
 					throw new MessageException("Invalid negative ID");
 			}
 
-			int dataSize = readBuffer.getInt();
+			int dataSize = readOnlyBuffer.getInt();
 
 			if (dataSize > MAX_DATA_SIZE)
 				// Too large
 				throw new MessageException(String.format("Declared data length %d larger than max allowed %d", dataSize, MAX_DATA_SIZE));
 
+			// Don't have all the data yet?
+			if (dataSize > 0 && dataSize + CHECKSUM_LENGTH > readOnlyBuffer.remaining())
+				return null;
+
 			ByteBuffer dataSlice = null;
 			if (dataSize > 0) {
 				byte[] expectedChecksum = new byte[CHECKSUM_LENGTH];
-				readBuffer.get(expectedChecksum);
+				readOnlyBuffer.get(expectedChecksum);
 
-				// Remember this position in readBuffer so we can pass to Message subclass
-				dataSlice = readBuffer.slice();
-
-				// Consume data from buffer
-				byte[] data = new byte[dataSize];
-				readBuffer.get(data);
-
-				// We successfully read all the data bytes, so we can set limit on dataSlice
+				// Slice data in readBuffer so we can pass to Message subclass
+				dataSlice = readOnlyBuffer.slice();
 				dataSlice.limit(dataSize);
 
 				// Test checksum
-				byte[] actualChecksum = generateChecksum(data);
+				byte[] actualChecksum = generateChecksum(dataSlice);
 				if (!Arrays.equals(expectedChecksum, actualChecksum))
 					throw new MessageException("Message checksum incorrect");
+
+				// Reset position after being consumed by generateChecksum
+				dataSlice.position(0);
+				// Update position in readOnlyBuffer
+				readOnlyBuffer.position(readOnlyBuffer.position() + dataSize);
 			}
 
-			Message message = messageType.fromByteBuffer(id, dataSlice);
-
-			// We successfully read a message, so bump byteBuffer's position to reflect this
-			byteBuffer.position(readBuffer.position());
-
-			return message;
+			return messageType.fromByteBuffer(id, dataSlice);
 		} catch (BufferUnderflowException e) {
 			// Not enough bytes to fully decode message...
 			return null;
-		} finally {
-			byteBuffer.compact();
 		}
 	}
 
@@ -241,6 +233,10 @@ public abstract class Message {
 		return Arrays.copyOfRange(Crypto.digest(data), 0, CHECKSUM_LENGTH);
 	}
 
+	protected static byte[] generateChecksum(ByteBuffer dataBuffer) {
+		return Arrays.copyOfRange(Crypto.digest(dataBuffer), 0, CHECKSUM_LENGTH);
+	}
+
 	public byte[] toBytes() throws MessageException {
 		try {
 			ByteArrayOutputStream bytes = new ByteArrayOutputStream(256);

src/main/java/org/qortal/repository/ATRepository.java

@@ -15,6 +15,9 @@ public interface ATRepository {
 	/** Returns where AT with passed address exists in repository */
 	public boolean exists(String atAddress) throws DataException;
 
+	/** Returns AT creator's public key, or null if not found */
+	public byte[] getCreatorPublicKey(String atAddress) throws DataException;
+
 	/** Returns list of executable ATs, empty if none found */
 	public List<ATData> getAllExecutableATs() throws DataException;
 
@@ -54,6 +57,24 @@ public interface ATRepository {
 	 */
 	public ATStateData getLatestATState(String atAddress) throws DataException;
 
+	/**
+	 * Returns final ATStateData for ATs matching codeHash (required)
+	 * and specific data segment value (optional).
+	 * <p>
+	 * If searching for specific data segment value, both <tt>dataByteOffset</tt>
+	 * and <tt>expectedValue</tt> need to be non-null.
+	 * <p>
+	 * Note that <tt>dataByteOffset</tt> starts from 0 and will typically be
+	 * a multiple of <tt>MachineState.VALUE_SIZE</tt>, which is usually 8:
+	 * width of a long.
+	 * <p>
+	 * Although <tt>expectedValue</tt>, if provided, is natively an unsigned long,
+	 * the data segment comparison is done via unsigned hex string.
+	 */
+	public List<ATStateData> getMatchingFinalATStates(byte[] codeHash, Boolean isFinished,
+			Integer dataByteOffset, Long expectedValue, Integer minimumFinalHeight,
+			Integer limit, Integer offset, Boolean reverse) throws DataException;
+
 	/**
 	 * Returns all ATStateData for a given block height.
 	 * <p>
@@ -66,6 +87,21 @@ public interface ATRepository {
 	 */
 	public List<ATStateData> getBlockATStatesAtHeight(int height) throws DataException;
 
+	/** Returns height of first trimmable AT state. */
+	public int getAtTrimHeight() throws DataException;
+
+	/** Sets new base height for AT state trimming.
+	 * <p>
+	 * NOTE: performs implicit <tt>repository.saveChanges()</tt>.
+	 */
+	public void setAtTrimHeight(int trimHeight) throws DataException;
+
+	/** Hook to allow repository to prepare/cache info for AT state trimming. */
+	public void prepareForAtStateTrimming() throws DataException;
+
+	/** Trims full AT state data between passed heights. Returns number of trimmed rows. */
+	public int trimAtStates(int minHeight, int maxHeight, int limit) throws DataException;
+
 	/**
 	 * Save ATStateData into repository.
 	 * <p>
@@ -88,4 +124,28 @@ public interface ATRepository {
 	/** Delete state data for all ATs at this height */
 	public void deleteATStates(int height) throws DataException;
 
+	// Finding transactions for ATs to process
+
+	static class NextTransactionInfo {
+		public final int height;
+		public final int sequence;
+		public final byte[] signature;
+
+		public NextTransactionInfo(int height, int sequence, byte[] signature) {
+			this.height = height;
+			this.sequence = sequence;
+			this.signature = signature;
+		}
+	}
+
+	/**
+	 * Find next transaction for AT to process.
+	 * <p>
+	 * @param recipient AT address
+	 * @param height starting height
+	 * @param sequence starting sequence
+	 * @return next transaction info, or null if none found
+	 */
+	public NextTransactionInfo findNextTransaction(String recipient, int height, int sequence) throws DataException;
+
 }

src/main/java/org/qortal/repository/AccountRepository.java

@@ -4,6 +4,7 @@ import java.util.List;
 
 import org.qortal.data.account.AccountBalanceData;
 import org.qortal.data.account.AccountData;
+import org.qortal.data.account.EligibleQoraHolderData;
 import org.qortal.data.account.MintingAccountData;
 import org.qortal.data.account.QortFromQoraData;
 import org.qortal.data.account.RewardShareData;
@@ -89,6 +90,13 @@ public interface AccountRepository {
 	 */
 	public int modifyMintedBlockCount(String address, int delta) throws DataException;
 
+	/**
+	 * Modifies batch of accounts' minted block count only.
+	 * <p>
+	 * This is a one-shot, batch version of modifyMintedBlockCount(String, int) above.
+	 */
+	public void modifyMintedBlockCounts(List<String> addresses, int delta) throws DataException;
+
 	/** Delete account from repository. */
 	public void delete(String address) throws DataException;
 
@@ -106,6 +114,9 @@ public interface AccountRepository {
 	 */
 	public AccountBalanceData getBalance(String address, long assetId) throws DataException;
 
+	/** Returns all account balances for given assetID, optionally excluding zero balances. */
+	public List<AccountBalanceData> getAssetBalances(long assetId, Boolean excludeZero) throws DataException;
+
 	/** How to order results when fetching asset balances. */
 	public enum BalanceOrdering {
 		/** assetID first, then balance, then account address */
@@ -116,15 +127,18 @@ public interface AccountRepository {
 		ASSET_ACCOUNT
 	}
 
-	/** Returns all account balances for given assetID, optionally excluding zero balances. */
-	public List<AccountBalanceData> getAssetBalances(long assetId, Boolean excludeZero) throws DataException;
-
 	/** Returns account balances for matching addresses / assetIDs, optionally excluding zero balances, with pagination, used by API. */
 	public List<AccountBalanceData> getAssetBalances(List<String> addresses, List<Long> assetIds, BalanceOrdering balanceOrdering, Boolean excludeZero, Integer limit, Integer offset, Boolean reverse) throws DataException;
 
 	/** Modifies account's asset balance by <tt>deltaBalance</tt>. */
 	public void modifyAssetBalance(String address, long assetId, long deltaBalance) throws DataException;
 
+	/** Modifies a batch of account asset balances, treating AccountBalanceData.balance as <tt>deltaBalance</tt>. */
+	public void modifyAssetBalances(List<AccountBalanceData> accountBalanceDeltas) throws DataException;
+
+	/** Batch update of account asset balances. */
+	public void setAssetBalances(List<AccountBalanceData> accountBalances) throws DataException;
+
 	public void save(AccountBalanceData accountBalanceData) throws DataException;
 
 	public void delete(String address, long assetId) throws DataException;
@@ -156,6 +170,16 @@ public interface AccountRepository {
 	 */
 	public RewardShareData getRewardShareByIndex(int index) throws DataException;
 
+	/**
+	 * Returns list of reward-share data using array of indexes into list of reward-shares (sorted by reward-share public key).
+	 * <p>
+	 * This is a one-shot, batch form of the above <tt>getRewardShareByIndex(int)</tt> call.
+	 * 
+	 * @return list of reward-share data, or null if one (or more) index is invalid
+	 * @throws DataException
+	 */
+	public List<RewardShareData> getRewardSharesByIndexes(int[] indexes) throws DataException;
+
 	public boolean rewardShareExists(byte[] rewardSharePublicKey) throws DataException;
 
 	public void save(RewardShareData rewardShareData) throws DataException;
@@ -169,13 +193,13 @@ public interface AccountRepository {
 
 	public void save(MintingAccountData mintingAccountData) throws DataException;
 
-	/** Delete minting account info, used by BlockMinter, from repository using passed private key. */
-	public int delete(byte[] mintingAccountPrivateKey) throws DataException;
+	/** Delete minting account info, used by BlockMinter, from repository using passed public or private key. */
+	public int delete(byte[] mintingAccountKey) throws DataException;
 
 	// Managing QORT from legacy QORA
 
 	/**
-	 * Returns balance data for accounts with legacy QORA asset that are eligible
+	 * Returns full info for accounts with legacy QORA asset that are eligible
 	 * for more block reward (block processing) or for block reward removal (block orphaning).
 	 * <p>
 	 * For block processing, accounts that have already received their final QORT reward for owning
@@ -187,7 +211,7 @@ public interface AccountRepository {
 	 * @param blockHeight QORT reward must have be present at this height (for orphaning only)
 	 * @throws DataException
 	 */
-	public List<AccountBalanceData> getEligibleLegacyQoraHolders(Integer blockHeight) throws DataException;
+	public List<EligibleQoraHolderData> getEligibleLegacyQoraHolders(Integer blockHeight) throws DataException;
 
 	public QortFromQoraData getQortFromQoraInfo(String address) throws DataException;
 

src/main/java/org/qortal/repository/BlockRepository.java

@@ -60,6 +60,15 @@ public interface BlockRepository {
 	 */
 	public int getHeightFromTimestamp(long timestamp) throws DataException;
 
+	/**
+	 * Returns block timestamp for a given height.
+	 *
+	 * @param height
+	 * @return timestamp, or 0 if height is out of bounds.
+	 * @throws DataException
+	 */
+	public long getTimestampFromHeight(int height) throws DataException;
+
 	/**
 	 * Return highest block height from repository.
 	 * 
@@ -129,19 +138,33 @@ public interface BlockRepository {
 	public List<BlockSummaryData> getBlockSummaries(int firstBlockHeight, int lastBlockHeight) throws DataException;
 
 	/**
-	 * Trim online accounts signatures from blocks older than passed timestamp.
-	 * 
-	 * @param timestamp
-	 * @return number of blocks trimmed
+	 * Returns block summaries for the passed height range, for API use.
 	 */
-	public int trimOldOnlineAccountsSignatures(long timestamp) throws DataException;
+	public List<BlockSummaryData> getBlockSummaries(Integer startHeight, Integer endHeight, Integer count) throws DataException;
+
+	/** Returns height of first trimmable online accounts signatures. */
+	public int getOnlineAccountsSignaturesTrimHeight() throws DataException;
+
+	/** Sets new base height for trimming online accounts signatures.
+	 * <p>
+	 * NOTE: performs implicit <tt>repository.saveChanges()</tt>.
+	 */
+	public void setOnlineAccountsSignaturesTrimHeight(int trimHeight) throws DataException;
 
 	/**
-	 * Returns first (lowest height) block that doesn't link back to genesis block.
+	 * Trim online accounts signatures from blocks between passed heights.
 	 * 
+	 * @return number of blocks trimmed
+	 */
+	public int trimOldOnlineAccountsSignatures(int minHeight, int maxHeight) throws DataException;
+
+	/**
+	 * Returns first (lowest height) block that doesn't link back to specified block.
+	 * 
+	 * @param startHeight height of specified block
 	 * @throws DataException
 	 */
-	public BlockData getDetachedBlockSignature() throws DataException;
+	public BlockData getDetachedBlockSignature(int startHeight) throws DataException;
 
 	/**
 	 * Saves block into repository.

src/main/java/org/qortal/repository/CrossChainRepository.java

@@ -0,0 +1,18 @@
+package org.qortal.repository;
+
+import java.util.List;
+
+import org.qortal.data.crosschain.TradeBotData;
+
+public interface CrossChainRepository {
+
+	public TradeBotData getTradeBotData(byte[] tradePrivateKey) throws DataException;
+
+	public List<TradeBotData> getAllTradeBotData() throws DataException;
+
+	public void save(TradeBotData tradeBotData) throws DataException;
+
+	/** Delete trade-bot states using passed private key. */
+	public int delete(byte[] tradePrivateKey) throws DataException;
+
+}

src/main/java/org/qortal/repository/MessageRepository.java

@@ -0,0 +1,31 @@
+package org.qortal.repository;
+
+import java.util.List;
+
+import org.qortal.data.transaction.MessageTransactionData;
+
+public interface MessageRepository {
+
+	/**
+	 * Returns list of confirmed MESSAGE transaction data matching (some) participants.
+	 * <p>
+	 * At least one of <tt>senderPublicKey</tt> or <tt>recipient</tt> must be specified.
+	 * <p>
+	 * @throws DataException
+	 */
+	public List<MessageTransactionData> getMessagesByParticipants(byte[] senderPublicKey,
+			String recipient, Integer limit, Integer offset, Boolean reverse) throws DataException;
+
+	/**
+	 * Does a MESSAGE exist with matching sender (pubkey), recipient and message payload?
+	 * <p>
+	 * Includes both confirmed and unconfirmed transactions!
+	 * <p>
+	 * @param senderPublicKey
+	 * @param recipient
+	 * @param messageData
+	 * @return true if a message exists, false otherwise
+	 */
+	public boolean exists(byte[] senderPublicKey, String recipient, byte[] messageData) throws DataException;
+
+}