Upgraded OnlineAccountsV3Message to new format (and fixed merge issues). Needs re-testing.

# Conflicts:
#	src/main/java/org/qortal/network/message/GetOnlineAccountsMessage.java
#	src/main/java/org/qortal/network/message/Message.java
#	src/main/java/org/qortal/network/message/OnlineAccountsMessage.java

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

@@ -85,7 +85,8 @@ public class Block {
 		ONLINE_ACCOUNT_UNKNOWN(71),
 		ONLINE_ACCOUNT_SIGNATURES_MISSING(72),
 		ONLINE_ACCOUNT_SIGNATURES_MALFORMED(73),
-		ONLINE_ACCOUNT_SIGNATURE_INCORRECT(74);
+		ONLINE_ACCOUNT_SIGNATURE_INCORRECT(74),
+		ONLINE_ACCOUNT_NONCE_INCORRECT(75);
 
 		public final int value;
 
@@ -313,6 +314,15 @@ public class Block {
 		int version = parentBlock.getNextBlockVersion();
 		byte[] reference = parentBlockData.getSignature();
 
+		// Qortal: minter is always a reward-share, so find actual minter and get their effective minting level
+		int minterLevel = Account.getRewardShareEffectiveMintingLevel(repository, minter.getPublicKey());
+		if (minterLevel == 0) {
+			LOGGER.error("Minter effective level returned zero?");
+			return null;
+		}
+
+		long timestamp = calcTimestamp(parentBlockData, minter.getPublicKey(), minterLevel);
+
 		// Fetch our list of online accounts
 		List<OnlineAccountData> onlineAccounts = OnlineAccountsManager.getInstance().getOnlineAccounts();
 		if (onlineAccounts.isEmpty()) {
@@ -355,26 +365,13 @@ public class Block {
 		byte[] encodedOnlineAccounts = BlockTransformer.encodeOnlineAccounts(onlineAccountsSet);
 		int onlineAccountsCount = onlineAccountsSet.size();
 
-		// Concatenate online account timestamp signatures (in correct order)
-		byte[] onlineAccountsSignatures = new byte[onlineAccountsCount * Transformer.SIGNATURE_LENGTH];
-		for (int i = 0; i < onlineAccountsCount; ++i) {
-			Integer accountIndex = accountIndexes.get(i);
-			OnlineAccountData onlineAccountData = indexedOnlineAccounts.get(accountIndex);
-			System.arraycopy(onlineAccountData.getSignature(), 0, onlineAccountsSignatures, i * Transformer.SIGNATURE_LENGTH, Transformer.SIGNATURE_LENGTH);
-		}
+		// Build the onlineAccountsSignatures byte array
+		byte[] onlineAccountsSignatures = BlockTransformer.encodeOnlineAccountSignatures(indexedOnlineAccounts,
+				accountIndexes, onlineAccountsCount, timestamp);
 
 		byte[] minterSignature = minter.sign(BlockTransformer.getBytesForMinterSignature(parentBlockData,
 				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());
-		if (minterLevel == 0) {
-			LOGGER.error("Minter effective level returned zero?");
-			return null;
-		}
-
-		long timestamp = calcTimestamp(parentBlockData, minter.getPublicKey(), minterLevel);
-
 		int transactionCount = 0;
 		byte[] transactionsSignature = null;
 		int height = parentBlockData.getHeight() + 1;
@@ -979,7 +976,10 @@ public class Block {
 		if (this.blockData.getOnlineAccountsSignatures() == null || this.blockData.getOnlineAccountsSignatures().length == 0)
 			return ValidationResult.ONLINE_ACCOUNT_SIGNATURES_MISSING;
 
-		if (this.blockData.getOnlineAccountsSignatures().length != onlineRewardShares.size() * Transformer.SIGNATURE_LENGTH)
+		// Verify the online account signatures length
+		int expectedLength = Block.getExpectedOnlineAccountsSignaturesLength(onlineRewardShares.size(), this.blockData.getTimestamp());
+
+		if (this.blockData.getOnlineAccountsSignatures().length != expectedLength)
 			return ValidationResult.ONLINE_ACCOUNT_SIGNATURES_MALFORMED;
 
 		// Check signatures
@@ -987,23 +987,31 @@ public class Block {
 		byte[] onlineTimestampBytes = Longs.toByteArray(onlineTimestamp);
 
 		// 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() - OnlineAccountsManager.ONLINE_TIMESTAMP_MODULUS
+		List<OnlineAccountData> currentOnlineAccounts = onlineTimestamp < NTP.getTime() - OnlineAccountsManager.getOnlineTimestampModulus()
 				? null
 				: OnlineAccountsManager.getInstance().getOnlineAccounts();
 		List<OnlineAccountData> latestBlocksOnlineAccounts = OnlineAccountsManager.getInstance().getLatestBlocksOnlineAccounts();
 
 		// Extract online accounts' timestamp signatures from block data
-		List<byte[]> onlineAccountsSignatures = BlockTransformer.decodeTimestampSignatures(this.blockData.getOnlineAccountsSignatures());
+		List<OnlineAccountData> onlineAccountsSignatures = BlockTransformer.decodeOnlineAccountSignatures(
+				this.blockData.getOnlineAccountsSignatures(), onlineRewardShares.size(), this.blockData.getTimestamp());
 
 		// 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);
+			// onlineAccountsSignatures will contain OnlineAccountData objects with at least a signature, and
+			// also a reduced block signature and nonce(s) if the mempow feature is active.
+			// It won't contain a public key or timestamp, so these must be added below.
+			OnlineAccountData onlineAccountSignatureData = onlineAccountsSignatures.get(i);
+			byte[] signature = onlineAccountSignatureData.getSignature();
+			byte[] reducedBlockSignature = onlineAccountSignatureData.getReducedBlockSignature();
+			List<Integer> nonces = onlineAccountSignatureData.getNonces();
 			byte[] publicKey = onlineRewardShares.get(i).getRewardSharePublicKey();
 
-			OnlineAccountData onlineAccountData = new OnlineAccountData(onlineTimestamp, signature, publicKey);
+			// It's simpler to create a new OnlineAccountData object rather than trying to modify the one we already have
+			OnlineAccountData onlineAccountData = new OnlineAccountData(onlineTimestamp, signature, publicKey, nonces, reducedBlockSignature);
 			ourOnlineAccounts.add(onlineAccountData);
 
 			// If signature is still current then no need to perform Ed25519 verify
@@ -1018,6 +1026,10 @@ public class Block {
 
 			if (!Crypto.verify(publicKey, signature, onlineTimestampBytes))
 				return ValidationResult.ONLINE_ACCOUNT_SIGNATURE_INCORRECT;
+
+			if (this.blockData.getTimestamp() >= BlockChain.getInstance().getOnlineAccountsMemoryPoWTimestamp())
+				if (!OnlineAccountsManager.getInstance().verifyMemoryPoW(onlineAccountData))
+					return ValidationResult.ONLINE_ACCOUNT_NONCE_INCORRECT;
 		}
 
 		// All online accounts valid, so save our list of online accounts for potential later use
@@ -2048,6 +2060,29 @@ public class Block {
 		return null;
 	}
 
+	/**
+	 * Expected length of serialized online accounts
+	 * @param onlineRewardSharesCount the number of reward shares in the serialized data
+	 * @param timestamp the block's timestamp, used for versioning / serialization differences
+	 * @return the number of bytes to expect
+	 */
+	public static int getExpectedOnlineAccountsSignaturesLength(int onlineRewardSharesCount, long timestamp) {
+		int expectedLength;
+
+		if (timestamp >= BlockChain.getInstance().getOnlineAccountsMemoryPoWTimestamp()) {
+			// byte array contains signatures, reduced signatures, and nonces
+			expectedLength = onlineRewardSharesCount *
+					(Transformer.SIGNATURE_LENGTH + Transformer.REDUCED_SIGNATURE_LENGTH + Transformer.INT_LENGTH +
+							(OnlineAccountsManager.MAX_NONCE_COUNT * Transformer.INT_LENGTH));
+		}
+		else {
+			// byte array contains signatures only
+			expectedLength = onlineRewardSharesCount * Transformer.SIGNATURE_LENGTH;
+		}
+
+		return expectedLength;
+	}
+
 	private void logDebugInfo() {
 		try {
 			// Avoid calculations if possible. We have to check against INFO here, since Level.isMoreSpecificThan() confusingly uses <= rather than just <

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

@@ -162,6 +162,14 @@ public class BlockChain {
 	/** Maximum time to retain online account signatures (ms) for block validity checks, to allow for clock variance. */
 	private long onlineAccountSignaturesMaxLifetime;
 
+	/** Feature trigger timestamp for ONLINE_ACCOUNTS_MODULUS time interval increase. Can't use
+	 * featureTriggers because unit tests need to set this value via Reflection. */
+	private long onlineAccountsModulusV2Timestamp;
+
+	/** Feature trigger timestamp for online accounts mempow verification. Can't use featureTriggers
+	 * because unit tests need to set this value via Reflection. */
+	private long onlineAccountsMemoryPoWTimestamp;
+
 	/** Settings relating to CIYAM AT feature. */
 	public static class CiyamAtSettings {
 		/** Fee per step/op-code executed. */
@@ -310,6 +318,15 @@ public class BlockChain {
 		return this.maxBlockSize;
 	}
 
+	// Online accounts
+	public long getOnlineAccountsModulusV2Timestamp() {
+		return this.onlineAccountsModulusV2Timestamp;
+	}
+
+	public long getOnlineAccountsMemoryPoWTimestamp() {
+		return this.onlineAccountsMemoryPoWTimestamp;
+	}
+
 	/** Returns true if approval-needing transaction types require a txGroupId other than NO_GROUP. */
 	public boolean getRequireGroupForApproval() {
 		return this.requireGroupForApproval;

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

@@ -1146,14 +1146,6 @@ public class Controller extends Thread {
 				TransactionImporter.getInstance().onNetworkTransactionSignaturesMessage(peer, message);
 				break;
 
-			case GET_ONLINE_ACCOUNTS:
-				OnlineAccountsManager.getInstance().onNetworkGetOnlineAccountsMessage(peer, message);
-				break;
-
-			case ONLINE_ACCOUNTS:
-				OnlineAccountsManager.getInstance().onNetworkOnlineAccountsMessage(peer, message);
-				break;
-
 			case GET_ONLINE_ACCOUNTS_V2:
 				OnlineAccountsManager.getInstance().onNetworkGetOnlineAccountsV2Message(peer, message);
 				break;
@@ -1162,6 +1154,10 @@ public class Controller extends Thread {
 				OnlineAccountsManager.getInstance().onNetworkOnlineAccountsV2Message(peer, message);
 				break;
 
+			case ONLINE_ACCOUNTS_V3:
+				OnlineAccountsManager.getInstance().onNetworkOnlineAccountsV3Message(peer, message);
+				break;
+
 			case GET_ARBITRARY_DATA:
 				// Not currently supported
 				break;

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

@@ -7,8 +7,10 @@ import org.qortal.account.Account;
 import org.qortal.account.PrivateKeyAccount;
 import org.qortal.account.PublicKeyAccount;
 import org.qortal.block.BlockChain;
+import org.qortal.crypto.MemoryPoW;
 import org.qortal.data.account.MintingAccountData;
 import org.qortal.data.account.RewardShareData;
+import org.qortal.data.block.BlockData;
 import org.qortal.data.network.OnlineAccountData;
 import org.qortal.network.Network;
 import org.qortal.network.Peer;
@@ -16,12 +18,18 @@ import org.qortal.network.message.*;
 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;
 
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
 import java.util.*;
+import java.util.concurrent.TimeoutException;
 import java.util.stream.Collectors;
 
+import static org.qortal.transform.Transformer.REDUCED_SIGNATURE_LENGTH;
+
 public class OnlineAccountsManager extends Thread {
 
     private class OurOnlineAccountsThread extends Thread {
@@ -47,14 +55,19 @@ public class OnlineAccountsManager extends Thread {
     private static OnlineAccountsManager instance;
     private volatile boolean isStopping = false;
 
+    // MemoryPoW
+    public final int POW_BUFFER_SIZE = 1 * 1024 * 1024; // bytes
+    public int POW_DIFFICULTY = 18; // leading zero bits
+    public static final int MAX_NONCE_COUNT = 1; // Maximum number of nonces to verify
+
     // 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
-    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);
+    public static final long ONLINE_TIMESTAMP_MODULUS_V1 = 5 * 60 * 1000L;
+    public static final long ONLINE_TIMESTAMP_MODULUS_V2 = 30 * 60 * 1000L;
     /** How many (latest) blocks' worth of online accounts we cache */
     private static final int MAX_BLOCKS_CACHED_ONLINE_ACCOUNTS = 2;
-    private static final long ONLINE_ACCOUNTS_V2_PEER_VERSION = 0x0300020000L;
+    private static final long ONLINE_ACCOUNTS_V3_PEER_VERSION = 0x0300030000L;
 
     private long onlineAccountsTasksTimestamp = Controller.startTime + ONLINE_ACCOUNTS_TASKS_INTERVAL; // ms
 
@@ -116,6 +129,13 @@ public class OnlineAccountsManager extends Thread {
         this.interrupt();
     }
 
+    public static long getOnlineTimestampModulus() {
+        if (NTP.getTime() >= BlockChain.getInstance().getOnlineAccountsModulusV2Timestamp()) {
+            return ONLINE_TIMESTAMP_MODULUS_V2;
+        }
+        return ONLINE_TIMESTAMP_MODULUS_V1;
+    }
+
 
     // Online accounts import queue
 
@@ -159,7 +179,7 @@ public class OnlineAccountsManager extends Thread {
         PublicKeyAccount otherAccount = new PublicKeyAccount(repository, onlineAccountData.getPublicKey());
 
         // Check timestamp is 'recent' here
-        if (Math.abs(onlineAccountData.getTimestamp() - now) > ONLINE_TIMESTAMP_MODULUS * 2) {
+        if (Math.abs(onlineAccountData.getTimestamp() - now) > getOnlineTimestampModulus() * 2) {
             LOGGER.trace(() -> String.format("Rejecting online account %s with out of range timestamp %d", otherAccount.getAddress(), onlineAccountData.getTimestamp()));
             return;
         }
@@ -186,8 +206,16 @@ public class OnlineAccountsManager extends Thread {
             return;
         }
 
+        // Validate mempow if feature trigger is active
+        if (now >= BlockChain.getInstance().getOnlineAccountsMemoryPoWTimestamp()) {
+            if (!this.verifyMemoryPoW(onlineAccountData)) {
+                LOGGER.trace(() -> String.format("Rejecting online reward-share for account %s due to invalid PoW nonce", mintingAccount.getAddress()));
+                return;
+            }
+        }
+
         synchronized (this.onlineAccounts) {
-            OnlineAccountData existingAccountData = this.onlineAccounts.stream().filter(account -> Arrays.equals(account.getPublicKey(), onlineAccountData.getPublicKey())).findFirst().orElse(null);
+            OnlineAccountData existingAccountData = this.onlineAccounts.stream().filter(account -> Arrays.equals(account.getPublicKey(), onlineAccountData.getPublicKey())).findFirst().orElse(null); // CME??
 
             if (existingAccountData != null) {
                 if (existingAccountData.getTimestamp() < onlineAccountData.getTimestamp()) {
@@ -203,10 +231,53 @@ public class OnlineAccountsManager extends Thread {
                 LOGGER.trace(() -> String.format("Added online account %s with timestamp %d", otherAccount.getAddress(), onlineAccountData.getTimestamp()));
             }
 
+            // Remove existing version of this online account data if the new one is superior
+            if (isOnlineAccountsDataSuperior(onlineAccountData)) {
+                this.onlineAccounts.remove(onlineAccountData);
+            }
+
             this.onlineAccounts.add(onlineAccountData);
         }
     }
 
+    /**
+     * Check if supplied onlineAccountData is superior (i.e. has a nonce value) than existing record.
+     * Two entries are considered equal even if the nonce and block signature differ, to prevent
+     * multiple variations co-existing. For this reason, we need to be able to check
+     * if a new OnlineAccountData should replace the existing one, which may be missing the nonce.
+     * @param onlineAccountData
+     * @return
+     */
+    private boolean isOnlineAccountsDataSuperior(OnlineAccountData onlineAccountData) {
+        if (onlineAccountData.getNonces() == null || onlineAccountData.getNonces().isEmpty()) {
+            // New online account data has no nonce value(s), so it won't be better than anything we already have
+            return false;
+        }
+
+        // New online account data has nonce value(s), so we need to check if the existing one does
+        OnlineAccountData existingOnlineAccountData = null;
+        for (OnlineAccountData acc : this.onlineAccounts) {
+            if (acc.equals(onlineAccountData)) {
+                // Found existing online account data
+                existingOnlineAccountData = acc;
+                break;
+            }
+        }
+
+        if (existingOnlineAccountData == null) {
+            // No existing online accounts data, so nothing to compare
+            return false;
+        }
+
+        if (existingOnlineAccountData.getNonces() == null || existingOnlineAccountData.getNonces().isEmpty()) {
+            // Existing data has no nonce value(s) so we want to replace it with the new one
+            return true;
+        }
+
+        // Both new and old data have nonce values so the new data isn't considered superior
+        return false;
+    }
+
     public void ensureTestingAccountsOnline(PrivateKeyAccount... onlineAccounts) {
         if (!BlockChain.getInstance().isTestChain()) {
             LOGGER.warn("Ignoring attempt to ensure test account is online for non-test chain!");
@@ -218,21 +289,21 @@ public class OnlineAccountsManager extends Thread {
             return;
 
         final long onlineAccountsTimestamp = toOnlineAccountTimestamp(now);
-        byte[] timestampBytes = Longs.toByteArray(onlineAccountsTimestamp);
+
+        List<MintingAccountData> mintingAccounts = new ArrayList<>();
 
         synchronized (this.onlineAccounts) {
             this.onlineAccounts.clear();
-
-            for (PrivateKeyAccount onlineAccount : onlineAccounts) {
-                // Check mintingAccount is actually reward-share?
-
-                byte[] signature = onlineAccount.sign(timestampBytes);
-                byte[] publicKey = onlineAccount.getPublicKey();
-
-                OnlineAccountData ourOnlineAccountData = new OnlineAccountData(onlineAccountsTimestamp, signature, publicKey);
-                this.onlineAccounts.add(ourOnlineAccountData);
-            }
         }
+
+        for (PrivateKeyAccount onlineAccount : onlineAccounts) {
+            // Check mintingAccount is actually reward-share?
+
+            MintingAccountData mintingAccountData = new MintingAccountData(onlineAccount.getPrivateKey(), onlineAccount.getPublicKey());
+            mintingAccounts.add(mintingAccountData);
+        }
+
+        computeOurAccountsForTimestamp(mintingAccounts, onlineAccountsTimestamp);
     }
 
     private void performOnlineAccountsTasks() {
@@ -241,7 +312,8 @@ public class OnlineAccountsManager extends Thread {
             return;
 
         // Expire old entries
-        final long cutoffThreshold = now - LAST_SEEN_EXPIRY_PERIOD;
+        final long lastSeenExpiryPeriod = (getOnlineTimestampModulus() * 2) + (1 * 60 * 1000L);
+        final long cutoffThreshold = now - lastSeenExpiryPeriod;
         synchronized (this.onlineAccounts) {
             Iterator<OnlineAccountData> iterator = this.onlineAccounts.iterator();
             while (iterator.hasNext()) {
@@ -265,12 +337,7 @@ public class OnlineAccountsManager extends Thread {
                 safeOnlineAccounts = new ArrayList<>(this.onlineAccounts);
             }
 
-            Message messageV1 = new GetOnlineAccountsMessage(safeOnlineAccounts);
-            Message messageV2 = new GetOnlineAccountsV2Message(safeOnlineAccounts);
-
-            Network.getInstance().broadcast(peer ->
-                    peer.getPeersVersion() >= ONLINE_ACCOUNTS_V2_PEER_VERSION ? messageV2 : messageV1
-            );
+            Network.getInstance().broadcast(peer -> new GetOnlineAccountsV2Message(safeOnlineAccounts));
         }
     }
 
@@ -280,6 +347,12 @@ public class OnlineAccountsManager extends Thread {
             return;
         }
 
+        // If we're not up-to-date, then there's no point in computing anything yet
+        // The exception being when we are in recovery mode, in which case we need some online accounts!
+        if (!Controller.getInstance().isUpToDate() && !Synchronizer.getInstance().getRecoveryMode()) {
+            return;
+        }
+
         List<MintingAccountData> mintingAccounts;
         try (final Repository repository = RepositoryManager.getRepository()) {
             mintingAccounts = repository.getAccountRepository().getMintingAccounts();
@@ -318,61 +391,206 @@ public class OnlineAccountsManager extends Thread {
             return;
         }
 
-        // 'current' timestamp
+        // 'next' timestamp (prioritize this as it's the most important)
+        final long nextOnlineAccountsTimestamp = toOnlineAccountTimestamp(now) + getOnlineTimestampModulus();
+        boolean success = computeOurAccountsForTimestamp(mintingAccounts, nextOnlineAccountsTimestamp);
+        if (!success) {
+            // We didn't compute the required nonce value(s), and so can't proceed until they have been retried
+            return;
+        }
+
+        // 'current' timestamp (if there's enough time after successfully computing the 'next' timestamps)
         final long onlineAccountsTimestamp = toOnlineAccountTimestamp(now);
-        boolean hasInfoChanged = false;
+        computeOurAccountsForTimestamp(mintingAccounts, onlineAccountsTimestamp);
+    }
 
-        byte[] timestampBytes = Longs.toByteArray(onlineAccountsTimestamp);
-        List<OnlineAccountData> ourOnlineAccounts = new ArrayList<>();
+    /**
+     * Compute a mempow nonce and signature for a given set of accounts and timestamp
+     * @param mintingAccounts - the online accounts
+     * @param onlineAccountsTimestamp - the online accounts timestamp
+     */
+    private boolean computeOurAccountsForTimestamp(List<MintingAccountData> mintingAccounts, long onlineAccountsTimestamp) {
+        try (final Repository repository = RepositoryManager.getRepository()) {
 
-        MINTING_ACCOUNTS:
-        for (MintingAccountData mintingAccountData : mintingAccounts) {
-            PrivateKeyAccount mintingAccount = new PrivateKeyAccount(null, mintingAccountData.getPrivateKey());
+            boolean hasInfoChanged = false;
 
-            byte[] signature = mintingAccount.sign(timestampBytes);
-            byte[] publicKey = mintingAccount.getPublicKey();
+            final long currentOnlineAccountsTimestamp = toOnlineAccountTimestamp(NTP.getTime());
 
-            // Our account is online
-            OnlineAccountData ourOnlineAccountData = new OnlineAccountData(onlineAccountsTimestamp, signature, publicKey);
-            synchronized (this.onlineAccounts) {
-                Iterator<OnlineAccountData> iterator = this.onlineAccounts.iterator();
+            List<OnlineAccountData> ourOnlineAccounts = new ArrayList<>();
+
+            MINTING_ACCOUNTS:
+            for (MintingAccountData mintingAccountData : mintingAccounts) {
+                PrivateKeyAccount mintingAccount = new PrivateKeyAccount(null, mintingAccountData.getPrivateKey());
+                byte[] publicKey = mintingAccount.getPublicKey();
+
+                // Our account is online
+                List<OnlineAccountData> safeOnlineAccounts;
+                synchronized (this.onlineAccounts) {
+                    safeOnlineAccounts = new ArrayList<>(this.onlineAccounts);
+                }
+
+                Iterator<OnlineAccountData> iterator = safeOnlineAccounts.iterator();
                 while (iterator.hasNext()) {
                     OnlineAccountData existingOnlineAccountData = iterator.next();
 
-                    if (Arrays.equals(existingOnlineAccountData.getPublicKey(), ourOnlineAccountData.getPublicKey())) {
+                    if (Arrays.equals(existingOnlineAccountData.getPublicKey(), publicKey)) {
                         // If our online account is already present, with same timestamp, then move on to next mintingAccount
                         if (existingOnlineAccountData.getTimestamp() == onlineAccountsTimestamp)
                             continue MINTING_ACCOUNTS;
 
                         // If our online account is already present, but with older timestamp, then remove it
-                        iterator.remove();
-                        break;
+                        if (existingOnlineAccountData.getTimestamp() < currentOnlineAccountsTimestamp) {
+                            this.onlineAccounts.remove(existingOnlineAccountData); // Safe because we are iterating through a copy
+                        }
                     }
                 }
 
-                this.onlineAccounts.add(ourOnlineAccountData);
+                // We need to add a new account
+
+                byte[] timestampBytes = Longs.toByteArray(onlineAccountsTimestamp);
+                int chainHeight = repository.getBlockRepository().getBlockchainHeight();
+                int referenceHeight = Math.max(1, chainHeight - 10);
+                BlockData recentBlockData = repository.getBlockRepository().fromHeight(referenceHeight);
+                if (recentBlockData == null || recentBlockData.getSignature() == null) {
+                    LOGGER.info("Unable to compute online accounts without having a recent block");
+                    return false;
+                }
+                byte[] reducedRecentBlockSignature = Arrays.copyOfRange(recentBlockData.getSignature(), 0, REDUCED_SIGNATURE_LENGTH);
+
+                byte[] mempowBytes;
+                try {
+                    mempowBytes = this.getMemoryPoWBytes(publicKey, onlineAccountsTimestamp, reducedRecentBlockSignature);
+                }
+                catch (IOException e) {
+                    LOGGER.info("Unable to create bytes for MemoryPoW. Moving on to next account...");
+                    continue MINTING_ACCOUNTS;
+                }
+
+                Integer nonce;
+                if (isMemoryPoWActive()) {
+                    try {
+                        nonce = this.computeMemoryPoW(mempowBytes, publicKey, onlineAccountsTimestamp);
+                        if (nonce == null) {
+                            // A nonce is required
+                            return false;
+                        }
+                    } catch (TimeoutException e) {
+                        LOGGER.info(String.format("Timed out computing nonce for account %.8s", Base58.encode(publicKey)));
+                        return false;
+                    }
+                }
+                else {
+                    // Send zero if we haven't computed a nonce due to feature trigger timestamp
+                    nonce = 0;
+                }
+
+                byte[] signature = mintingAccount.sign(timestampBytes); // TODO: include nonce and block signature?
+
+                OnlineAccountData ourOnlineAccountData = new OnlineAccountData(onlineAccountsTimestamp, signature, publicKey, Arrays.asList(nonce), reducedRecentBlockSignature);
+
+                // Make sure to verify before adding
+                if (verifyMemoryPoW(ourOnlineAccountData)) {
+                    this.onlineAccounts.add(ourOnlineAccountData);
+
+                    LOGGER.trace(() -> String.format("Added our online account %s with timestamp %d", mintingAccount.getAddress(), onlineAccountsTimestamp));
+                    ourOnlineAccounts.add(ourOnlineAccountData);
+                    hasInfoChanged = true;
+                }
             }
 
-            LOGGER.trace(() -> String.format("Added our online account %s with timestamp %d", mintingAccount.getAddress(), onlineAccountsTimestamp));
-            ourOnlineAccounts.add(ourOnlineAccountData);
-            hasInfoChanged = true;
+            if (!hasInfoChanged) {
+                // Nothing to do
+                return true;
+            }
+
+            Message messageV2 = new OnlineAccountsV2Message(ourOnlineAccounts);
+            Message messageV3 = new OnlineAccountsV3Message(ourOnlineAccounts);
+
+            Network.getInstance().broadcast(peer ->
+                    peer.getPeersVersion() >= ONLINE_ACCOUNTS_V3_PEER_VERSION ? messageV3 : messageV2
+            );
+
+            LOGGER.trace(() -> String.format("Broadcasted %d online account%s with timestamp %d", ourOnlineAccounts.size(), (ourOnlineAccounts.size() != 1 ? "s" : ""), onlineAccountsTimestamp));
+            return true;
+
+        } catch (DataException e) {
+            LOGGER.error(String.format("Repository issue while computing online accounts"), e);
+            return false;
+        }
+    }
+
+    private byte[] getMemoryPoWBytes(byte[] publicKey, long onlineAccountsTimestamp, byte[] reducedRecentBlockSignature) throws IOException {
+        byte[] timestampBytes = Longs.toByteArray(onlineAccountsTimestamp);
+
+        ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
+        outputStream.write(publicKey);
+        outputStream.write(timestampBytes);
+        outputStream.write(reducedRecentBlockSignature);
+
+        return outputStream.toByteArray();
+    }
+
+    private Integer computeMemoryPoW(byte[] bytes, byte[] publicKey, long onlineAccountsTimestamp) throws TimeoutException {
+        if (!isMemoryPoWActive()) {
+            LOGGER.info("Mempow start timestamp not yet reached, and onlineAccountsMemPoWEnabled not enabled in settings");
+            return null;
         }
 
-        if (!hasInfoChanged)
-            return;
+        LOGGER.info(String.format("Computing nonce for account %.8s and timestamp %d...", Base58.encode(publicKey), onlineAccountsTimestamp));
 
-        Message messageV1 = new OnlineAccountsMessage(ourOnlineAccounts);
-        Message messageV2 = new OnlineAccountsV2Message(ourOnlineAccounts);
+        // Calculate the time until the next online timestamp and use it as a timeout when computing the nonce
+        Long startTime = NTP.getTime();
+        final long nextOnlineAccountsTimestamp = toOnlineAccountTimestamp(startTime) + getOnlineTimestampModulus();
+        long timeUntilNextTimestamp = nextOnlineAccountsTimestamp - startTime;
 
-        Network.getInstance().broadcast(peer ->
-                peer.getPeersVersion() >= ONLINE_ACCOUNTS_V2_PEER_VERSION ? messageV2 : messageV1
-        );
+        Integer nonce = MemoryPoW.compute2(bytes, POW_BUFFER_SIZE, POW_DIFFICULTY, timeUntilNextTimestamp);
 
-        LOGGER.trace(() -> String.format("Broadcasted %d online account%s with timestamp %d", ourOnlineAccounts.size(), (ourOnlineAccounts.size() != 1 ? "s" : ""), onlineAccountsTimestamp));
+        double totalSeconds = (NTP.getTime() - startTime) / 1000.0f;
+        int minutes = (int) ((totalSeconds % 3600) / 60);
+        int seconds = (int) (totalSeconds % 60);
+        double hashRate = nonce / totalSeconds;
+
+        LOGGER.info(String.format("Computed nonce for timestamp %d and account %.8s: %d. Buffer size: %d. Difficulty: %d. " +
+                        "Time taken: %02d:%02d. Hashrate: %f", onlineAccountsTimestamp, Base58.encode(publicKey),
+                nonce, POW_BUFFER_SIZE, POW_DIFFICULTY, minutes, seconds, hashRate));
+
+        return nonce;
+    }
+
+    public boolean verifyMemoryPoW(OnlineAccountData onlineAccountData) {
+        List<Integer> nonces = onlineAccountData.getNonces();
+        if (nonces == null || nonces.isEmpty()) {
+            // Missing required nonce value(s)
+            return false;
+        }
+
+        if (nonces.size() > MAX_NONCE_COUNT) {
+            // More than the allowed nonce count
+            return false;
+        }
+
+        byte[] reducedBlockSignature = onlineAccountData.getReducedBlockSignature();
+        if (reducedBlockSignature == null) {
+            // Missing required block signature
+            return false;
+        }
+
+        byte[] mempowBytes;
+        try {
+            mempowBytes = this.getMemoryPoWBytes(onlineAccountData.getPublicKey(), onlineAccountData.getTimestamp(), reducedBlockSignature);
+        } catch (IOException e) {
+            return false;
+        }
+
+        // For now, we will only require a single nonce
+        int nonce = nonces.get(0);
+
+        // Verify the nonce
+        return MemoryPoW.verify2(mempowBytes, POW_BUFFER_SIZE, POW_DIFFICULTY, nonce);
     }
 
     public static long toOnlineAccountTimestamp(long timestamp) {
-        return (timestamp / ONLINE_TIMESTAMP_MODULUS) * ONLINE_TIMESTAMP_MODULUS;
+        return (timestamp / getOnlineTimestampModulus()) * getOnlineTimestampModulus();
     }
 
     /** Returns list of online accounts with timestamp recent enough to be considered currently online. */
@@ -411,56 +629,17 @@ public class OnlineAccountsManager extends Thread {
         }
     }
 
+    private boolean isMemoryPoWActive() {
+        Long now = NTP.getTime();
+        if (now < BlockChain.getInstance().getOnlineAccountsMemoryPoWTimestamp() || Settings.getInstance().isOnlineAccountsMemPoWEnabled()) {
+            return false;
+        }
+        return true;
+    }
+
 
     // Network handlers
 
-    public void onNetworkGetOnlineAccountsMessage(Peer peer, Message message) {
-        GetOnlineAccountsMessage getOnlineAccountsMessage = (GetOnlineAccountsMessage) message;
-
-        List<OnlineAccountData> excludeAccounts = getOnlineAccountsMessage.getOnlineAccounts();
-
-        // Send online accounts info, excluding entries with matching timestamp & public key from excludeAccounts
-        List<OnlineAccountData> accountsToSend;
-        synchronized (this.onlineAccounts) {
-            accountsToSend = new ArrayList<>(this.onlineAccounts);
-        }
-
-        Iterator<OnlineAccountData> iterator = accountsToSend.iterator();
-
-        SEND_ITERATOR:
-        while (iterator.hasNext()) {
-            OnlineAccountData onlineAccountData = iterator.next();
-
-            for (int i = 0; i < excludeAccounts.size(); ++i) {
-                OnlineAccountData excludeAccountData = excludeAccounts.get(i);
-
-                if (onlineAccountData.getTimestamp() == excludeAccountData.getTimestamp() && Arrays.equals(onlineAccountData.getPublicKey(), excludeAccountData.getPublicKey())) {
-                    iterator.remove();
-                    continue SEND_ITERATOR;
-                }
-            }
-        }
-
-        Message onlineAccountsMessage = new OnlineAccountsMessage(accountsToSend);
-        peer.sendMessage(onlineAccountsMessage);
-
-        LOGGER.trace(() -> String.format("Sent %d of our %d online accounts to %s", accountsToSend.size(), this.onlineAccounts.size(), peer));
-    }
-
-    public void onNetworkOnlineAccountsMessage(Peer peer, Message message) {
-        OnlineAccountsMessage onlineAccountsMessage = (OnlineAccountsMessage) message;
-
-        List<OnlineAccountData> peersOnlineAccounts = onlineAccountsMessage.getOnlineAccounts();
-        LOGGER.trace(() -> String.format("Received %d online accounts from %s", peersOnlineAccounts.size(), peer));
-
-        try (final Repository repository = RepositoryManager.getRepository()) {
-            for (OnlineAccountData onlineAccountData : peersOnlineAccounts)
-                this.verifyAndAddAccount(repository, onlineAccountData);
-        } catch (DataException e) {
-            LOGGER.error(String.format("Repository issue while verifying online accounts from peer %s", peer), e);
-        }
-    }
-
     public void onNetworkGetOnlineAccountsV2Message(Peer peer, Message message) {
         GetOnlineAccountsV2Message getOnlineAccountsMessage = (GetOnlineAccountsV2Message) message;
 
@@ -488,8 +667,10 @@ public class OnlineAccountsManager extends Thread {
             }
         }
 
-        Message onlineAccountsMessage = new OnlineAccountsV2Message(accountsToSend);
-        peer.sendMessage(onlineAccountsMessage);
+        Message messageV2 = new OnlineAccountsV2Message(accountsToSend);
+        Message messageV3 = new OnlineAccountsV3Message(accountsToSend);
+
+        peer.sendMessage(peer.getPeersVersion() >= ONLINE_ACCOUNTS_V3_PEER_VERSION ? messageV3 : messageV2);
 
         LOGGER.trace(() -> String.format("Sent %d of our %d online accounts to %s", accountsToSend.size(), this.onlineAccounts.size(), peer));
     }
@@ -502,6 +683,39 @@ public class OnlineAccountsManager extends Thread {
 
         int importCount = 0;
 
+        // Add any online accounts to the queue that aren't already present
+        for (OnlineAccountData onlineAccountData : peersOnlineAccounts) {
+
+            // Do we already know about this online account data?
+            if (onlineAccounts.contains(onlineAccountData)) {
+
+                // Don't import if it's no better than the one we already have
+                if (!isOnlineAccountsDataSuperior(onlineAccountData)) {
+                    // Do NOT remove the existing online account data - this takes place after validation
+                    continue;
+                }
+            }
+
+            // Is it already in the import queue?
+            if (onlineAccountsImportQueue.contains(onlineAccountData)) {
+                continue;
+            }
+
+            onlineAccountsImportQueue.add(onlineAccountData);
+            importCount++;
+        }
+
+        LOGGER.debug(String.format("Added %d online accounts to queue", importCount));
+    }
+
+    public void onNetworkOnlineAccountsV3Message(Peer peer, Message message) {
+        OnlineAccountsV3Message onlineAccountsMessage = (OnlineAccountsV3Message) message;
+
+        List<OnlineAccountData> peersOnlineAccounts = onlineAccountsMessage.getOnlineAccounts();
+        LOGGER.debug(String.format("Received %d online accounts from %s", peersOnlineAccounts.size(), peer));
+
+        int importCount = 0;
+
         // Add any online accounts to the queue that aren't already present
         for (OnlineAccountData onlineAccountData : peersOnlineAccounts) {
 

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

@@ -1,10 +1,25 @@
 package org.qortal.crypto;
 
+import org.qortal.utils.NTP;
+
 import java.nio.ByteBuffer;
+import java.util.concurrent.TimeoutException;
 
 public class MemoryPoW {
 
 	public static Integer compute2(byte[] data, int workBufferLength, long difficulty) {
+		try {
+			return MemoryPoW.compute2(data, workBufferLength, difficulty, null);
+
+		} catch (TimeoutException e) {
+			// This won't happen, because above timeout is null
+			return null;
+		}
+	}
+
+	public static Integer compute2(byte[] data, int workBufferLength, long difficulty, Long timeout) throws TimeoutException {
+		long startTime = NTP.getTime();
+
 		// Hash data with SHA256
 		byte[] hash = Crypto.digest(data);
 
@@ -33,6 +48,13 @@ public class MemoryPoW {
 			if (Thread.currentThread().isInterrupted())
 				return -1;
 
+			if (timeout != null) {
+				long now = NTP.getTime();
+				if (now > startTime + timeout) {
+					throw new TimeoutException("Timeout reached");
+				}
+			}
+
 			seed *= seedMultiplier; // per nonce
 
 			state[0] = longHash[0] ^ seed;

src/main/java/org/qortal/data/network/OnlineAccountData.java

@@ -1,6 +1,7 @@
 package org.qortal.data.network;
 
 import java.util.Arrays;
+import java.util.List;
 
 import javax.xml.bind.annotation.XmlAccessType;
 import javax.xml.bind.annotation.XmlAccessorType;
@@ -15,6 +16,8 @@ public class OnlineAccountData {
 	protected long timestamp;
 	protected byte[] signature;
 	protected byte[] publicKey;
+	protected List<Integer> nonces;
+	protected byte[] reducedBlockSignature;
 
 	// Constructors
 
@@ -22,10 +25,16 @@ public class OnlineAccountData {
 	protected OnlineAccountData() {
 	}
 
-	public OnlineAccountData(long timestamp, byte[] signature, byte[] publicKey) {
+	public OnlineAccountData(long timestamp, byte[] signature, byte[] publicKey, List<Integer> nonces, byte[] reducedBlockSignature) {
 		this.timestamp = timestamp;
 		this.signature = signature;
 		this.publicKey = publicKey;
+		this.nonces = nonces;
+		this.reducedBlockSignature = reducedBlockSignature;
+	}
+
+	public OnlineAccountData(long timestamp, byte[] signature, byte[] publicKey) {
+		this(timestamp, signature, publicKey, null, null);
 	}
 
 	public long getTimestamp() {
@@ -40,6 +49,14 @@ public class OnlineAccountData {
 		return this.publicKey;
 	}
 
+	public List<Integer> getNonces() {
+		return this.nonces;
+	}
+
+	public byte[] getReducedBlockSignature() {
+		return this.reducedBlockSignature;
+	}
+
 	// For JAXB
 	@XmlElement(name = "address")
 	protected String getAddress() {
@@ -69,6 +86,8 @@ public class OnlineAccountData {
 		if (!Arrays.equals(otherOnlineAccountData.publicKey, this.publicKey))
 			return false;
 
+		// Best not to consider additional properties for the purposes of uniqueness
+
 		return true;
 	}
 

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

@@ -1,69 +0,0 @@
-package org.qortal.network.message;
-
-import java.io.ByteArrayOutputStream;
-import java.io.IOException;
-import java.nio.ByteBuffer;
-import java.util.ArrayList;
-import java.util.List;
-import java.util.stream.Collectors;
-
-import org.qortal.data.network.OnlineAccountData;
-import org.qortal.transform.Transformer;
-
-import com.google.common.primitives.Ints;
-import com.google.common.primitives.Longs;
-
-public class GetOnlineAccountsMessage extends Message {
-	private static final int MAX_ACCOUNT_COUNT = 5000;
-
-	private List<OnlineAccountData> onlineAccounts;
-
-	public GetOnlineAccountsMessage(List<OnlineAccountData> onlineAccounts) {
-		super(MessageType.GET_ONLINE_ACCOUNTS);
-
-		ByteArrayOutputStream bytes = new ByteArrayOutputStream();
-
-		try {
-			bytes.write(Ints.toByteArray(onlineAccounts.size()));
-
-			for (OnlineAccountData onlineAccountData : onlineAccounts) {
-				bytes.write(Longs.toByteArray(onlineAccountData.getTimestamp()));
-
-				bytes.write(onlineAccountData.getPublicKey());
-			}
-		} catch (IOException e) {
-			throw new AssertionError("IOException shouldn't occur with ByteArrayOutputStream");
-		}
-
-		this.dataBytes = bytes.toByteArray();
-		this.checksumBytes = Message.generateChecksum(this.dataBytes);
-	}
-
-	private GetOnlineAccountsMessage(int id, List<OnlineAccountData> onlineAccounts) {
-		super(id, MessageType.GET_ONLINE_ACCOUNTS);
-
-		this.onlineAccounts = onlineAccounts.stream().limit(MAX_ACCOUNT_COUNT).collect(Collectors.toList());
-	}
-
-	public List<OnlineAccountData> getOnlineAccounts() {
-		return this.onlineAccounts;
-	}
-
-	public static Message fromByteBuffer(int id, ByteBuffer bytes) {
-		final int accountCount = bytes.getInt();
-
-		List<OnlineAccountData> onlineAccounts = new ArrayList<>(accountCount);
-
-		for (int i = 0; i < Math.min(MAX_ACCOUNT_COUNT, accountCount); ++i) {
-			long timestamp = bytes.getLong();
-
-			byte[] publicKey = new byte[Transformer.PUBLIC_KEY_LENGTH];
-			bytes.get(publicKey);
-
-			onlineAccounts.add(new OnlineAccountData(timestamp, null, publicKey));
-		}
-
-		return new GetOnlineAccountsMessage(id, onlineAccounts);
-	}
-
-}

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

@@ -38,10 +38,9 @@ public enum MessageType {
     BLOCK_SUMMARIES(70, BlockSummariesMessage::fromByteBuffer),
     GET_BLOCK_SUMMARIES(71, GetBlockSummariesMessage::fromByteBuffer),
 
-    ONLINE_ACCOUNTS(80, OnlineAccountsMessage::fromByteBuffer),
-    GET_ONLINE_ACCOUNTS(81, GetOnlineAccountsMessage::fromByteBuffer),
     ONLINE_ACCOUNTS_V2(82, OnlineAccountsV2Message::fromByteBuffer),
     GET_ONLINE_ACCOUNTS_V2(83, GetOnlineAccountsV2Message::fromByteBuffer),
+    ONLINE_ACCOUNTS_V3(84, OnlineAccountsV3Message::fromByteBuffer),
 
     ARBITRARY_DATA(90, ArbitraryDataMessage::fromByteBuffer),
     GET_ARBITRARY_DATA(91, GetArbitraryDataMessage::fromByteBuffer),

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

@@ -1,75 +0,0 @@
-package org.qortal.network.message;
-
-import java.io.ByteArrayOutputStream;
-import java.io.IOException;
-import java.nio.ByteBuffer;
-import java.util.ArrayList;
-import java.util.List;
-import java.util.stream.Collectors;
-
-import org.qortal.data.network.OnlineAccountData;
-import org.qortal.transform.Transformer;
-
-import com.google.common.primitives.Ints;
-import com.google.common.primitives.Longs;
-
-public class OnlineAccountsMessage extends Message {
-	private static final int MAX_ACCOUNT_COUNT = 5000;
-
-	private List<OnlineAccountData> onlineAccounts;
-
-	public OnlineAccountsMessage(List<OnlineAccountData> onlineAccounts) {
-		super(MessageType.ONLINE_ACCOUNTS);
-
-		ByteArrayOutputStream bytes = new ByteArrayOutputStream();
-
-		try {
-			bytes.write(Ints.toByteArray(onlineAccounts.size()));
-
-			for (OnlineAccountData onlineAccountData : onlineAccounts) {
-				bytes.write(Longs.toByteArray(onlineAccountData.getTimestamp()));
-
-				bytes.write(onlineAccountData.getSignature());
-
-				bytes.write(onlineAccountData.getPublicKey());
-			}
-		} catch (IOException e) {
-			throw new AssertionError("IOException shouldn't occur with ByteArrayOutputStream");
-		}
-
-		this.dataBytes = bytes.toByteArray();
-		this.checksumBytes = Message.generateChecksum(this.dataBytes);
-	}
-
-	private OnlineAccountsMessage(int id, List<OnlineAccountData> onlineAccounts) {
-		super(id, MessageType.ONLINE_ACCOUNTS);
-
-		this.onlineAccounts = onlineAccounts.stream().limit(MAX_ACCOUNT_COUNT).collect(Collectors.toList());
-	}
-
-	public List<OnlineAccountData> getOnlineAccounts() {
-		return this.onlineAccounts;
-	}
-
-	public static Message fromByteBuffer(int id, ByteBuffer bytes) {
-		final int accountCount = bytes.getInt();
-
-		List<OnlineAccountData> onlineAccounts = new ArrayList<>(accountCount);
-
-		for (int i = 0; i < Math.min(MAX_ACCOUNT_COUNT, accountCount); ++i) {
-			long timestamp = bytes.getLong();
-
-			byte[] signature = new byte[Transformer.SIGNATURE_LENGTH];
-			bytes.get(signature);
-
-			byte[] publicKey = new byte[Transformer.PUBLIC_KEY_LENGTH];
-			bytes.get(publicKey);
-
-			OnlineAccountData onlineAccountData = new OnlineAccountData(timestamp, signature, publicKey);
-			onlineAccounts.add(onlineAccountData);
-		}
-
-		return new OnlineAccountsMessage(id, onlineAccounts);
-	}
-
-}

src/main/java/org/qortal/network/message/OnlineAccountsV3Message.java

@@ -0,0 +1,134 @@
+package org.qortal.network.message;
+
+import com.google.common.primitives.Ints;
+import com.google.common.primitives.Longs;
+import org.qortal.data.network.OnlineAccountData;
+import org.qortal.transform.Transformer;
+
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+/**
+ * For sending online accounts info to remote peer.
+ *
+ * Same format as V2, but with added support for mempow nonce values and a recent block signature
+ */
+public class OnlineAccountsV3Message extends Message {
+	private List<OnlineAccountData> onlineAccounts;
+	private byte[] cachedData;
+
+	public OnlineAccountsV3Message(List<OnlineAccountData> onlineAccounts) {
+		super(MessageType.ONLINE_ACCOUNTS_V3);
+
+		// If we don't have ANY online accounts then it's an easier construction...
+		if (onlineAccounts.isEmpty()) {
+			// Always supply a number of accounts
+			this.dataBytes = Ints.toByteArray(0);
+			this.checksumBytes = Message.generateChecksum(this.dataBytes);
+			return;
+		}
+
+		// How many of each timestamp
+		Map<Long, Integer> countByTimestamp = new HashMap<>();
+
+		for (int i = 0; i < onlineAccounts.size(); ++i) {
+			OnlineAccountData onlineAccountData = onlineAccounts.get(i);
+			Long timestamp = onlineAccountData.getTimestamp();
+			countByTimestamp.compute(timestamp, (k, v) -> v == null ? 1 : ++v);
+		}
+
+		// We should know exactly how many bytes to allocate now
+		int byteSize = countByTimestamp.size() * (Transformer.INT_LENGTH + Transformer.TIMESTAMP_LENGTH)
+				+ onlineAccounts.size() * (Transformer.SIGNATURE_LENGTH + Transformer.PUBLIC_KEY_LENGTH);
+
+		ByteArrayOutputStream bytes = new ByteArrayOutputStream(byteSize);
+
+		try {
+			for (long timestamp : countByTimestamp.keySet()) {
+				bytes.write(Ints.toByteArray(countByTimestamp.get(timestamp)));
+
+				bytes.write(Longs.toByteArray(timestamp));
+
+				for (int i = 0; i < onlineAccounts.size(); ++i) {
+					OnlineAccountData onlineAccountData = onlineAccounts.get(i);
+
+					if (onlineAccountData.getTimestamp() == timestamp) {
+						bytes.write(onlineAccountData.getSignature());
+
+						bytes.write(onlineAccountData.getPublicKey());
+
+						bytes.write(onlineAccountData.getReducedBlockSignature());
+
+						int nonceCount = onlineAccountData.getNonces() != null ? onlineAccountData.getNonces().size() : 0;
+						bytes.write(Ints.toByteArray(nonceCount));
+
+						for (int n = 0; n < nonceCount; ++n) {
+							int nonce = onlineAccountData.getNonces().get(n);
+							bytes.write(Ints.toByteArray(nonce));
+						}
+					}
+				}
+			}
+		} catch (IOException e) {
+			throw new AssertionError("IOException shouldn't occur with ByteArrayOutputStream");
+		}
+
+		this.dataBytes = bytes.toByteArray();
+		this.checksumBytes = Message.generateChecksum(this.dataBytes);
+	}
+
+	private OnlineAccountsV3Message(int id, List<OnlineAccountData> onlineAccounts) {
+		super(id, MessageType.ONLINE_ACCOUNTS_V2);
+
+		this.onlineAccounts = onlineAccounts;
+	}
+
+	public List<OnlineAccountData> getOnlineAccounts() {
+		return this.onlineAccounts;
+	}
+
+	public static Message fromByteBuffer(int id, ByteBuffer bytes) {
+		int accountCount = bytes.getInt();
+
+		List<OnlineAccountData> onlineAccounts = new ArrayList<>(accountCount);
+
+		while (accountCount > 0) {
+			long timestamp = bytes.getLong();
+
+			for (int i = 0; i < accountCount; ++i) {
+				byte[] signature = new byte[Transformer.SIGNATURE_LENGTH];
+				bytes.get(signature);
+
+				byte[] publicKey = new byte[Transformer.PUBLIC_KEY_LENGTH];
+				bytes.get(publicKey);
+
+				byte[] reducedBlockSignature = new byte[Transformer.REDUCED_SIGNATURE_LENGTH];
+				bytes.get(reducedBlockSignature);
+
+				int nonceCount = bytes.getInt();
+				List<Integer> nonces = new ArrayList<>();
+				for (int n = 0; n < nonceCount; ++n) {
+					Integer nonce = bytes.getInt();
+					nonces.add(nonce);
+				}
+
+				onlineAccounts.add(new OnlineAccountData(timestamp, signature, publicKey, nonces, reducedBlockSignature));
+			}
+
+			if (bytes.hasRemaining()) {
+				accountCount = bytes.getInt();
+			} else {
+				// we've finished
+				accountCount = 0;
+			}
+		}
+
+		return new OnlineAccountsV3Message(id, onlineAccounts);
+	}
+
+}

src/main/java/org/qortal/settings/Settings.java

@@ -277,6 +277,11 @@ public class Settings {
 	/** Additional offset added to values returned by NTP.getTime() */
 	private Long testNtpOffset = null;
 
+	// Online accounts
+
+	/** Whether to opt-in to mempow computations for online accounts, ahead of general release */
+	private boolean onlineAccountsMemPoWEnabled = false;
+
 
 	// Data storage (QDN)
 
@@ -752,6 +757,10 @@ public class Settings {
 		return this.testNtpOffset;
 	}
 
+	public boolean isOnlineAccountsMemPoWEnabled() {
+		return this.onlineAccountsMemPoWEnabled;
+	}
+
 	public long getRepositoryBackupInterval() {
 		return this.repositoryBackupInterval;
 	}

src/main/java/org/qortal/transaction/PresenceTransaction.java

@@ -12,7 +12,6 @@ import java.util.function.Supplier;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 import org.qortal.account.Account;
-import org.qortal.controller.Controller;
 import org.qortal.controller.OnlineAccountsManager;
 import org.qortal.controller.tradebot.TradeBot;
 import org.qortal.crosschain.ACCT;
@@ -49,7 +48,7 @@ public class PresenceTransaction extends Transaction {
 		REWARD_SHARE(0) {
 			@Override
 			public long getLifetime() {
-				return OnlineAccountsManager.ONLINE_TIMESTAMP_MODULUS;
+				return OnlineAccountsManager.getOnlineTimestampModulus();
 			}
 		},
 		TRADE_BOT(1) {

src/main/java/org/qortal/transform/Transformer.java

@@ -18,6 +18,8 @@ public abstract class Transformer {
 	public static final int SIGNATURE_LENGTH = 64;
 	public static final int TIMESTAMP_LENGTH = LONG_LENGTH;
 
+	public static final int REDUCED_SIGNATURE_LENGTH = 4;
+
 	public static final int MD5_LENGTH = 16;
 	public static final int SHA256_LENGTH = 32;
 	public static final int AES256_LENGTH = 32;

src/main/java/org/qortal/transform/block/BlockTransformer.java

@@ -6,11 +6,13 @@ import java.nio.ByteBuffer;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
+import java.util.Map;
 
 import org.qortal.block.Block;
 import org.qortal.block.BlockChain;
 import org.qortal.data.at.ATStateData;
 import org.qortal.data.block.BlockData;
+import org.qortal.data.network.OnlineAccountData;
 import org.qortal.data.transaction.TransactionData;
 import org.qortal.repository.DataException;
 import org.qortal.transaction.Transaction;
@@ -27,6 +29,8 @@ import com.google.common.primitives.Longs;
 
 import io.druid.extendedset.intset.ConciseSet;
 
+import static org.qortal.controller.OnlineAccountsManager.MAX_NONCE_COUNT;
+
 public class BlockTransformer extends Transformer {
 
 	private static final int VERSION_LENGTH = INT_LENGTH;
@@ -213,7 +217,7 @@ public class BlockTransformer extends Transformer {
 			// Online accounts timestamp is only present if there are also signatures
 			onlineAccountsTimestamp = byteBuffer.getLong();
 
-			final int signaturesByteLength = onlineAccountsSignaturesCount * Transformer.SIGNATURE_LENGTH;
+			final int signaturesByteLength = Block.getExpectedOnlineAccountsSignaturesLength(onlineAccountsSignaturesCount, timestamp);
 			if (signaturesByteLength > BlockChain.getInstance().getMaxBlockSize())
 				throw new TransformationException("Byte data too long for online accounts signatures");
 
@@ -416,16 +420,101 @@ public class BlockTransformer extends Transformer {
 		return encodedSignatures;
 	}
 
-	public static List<byte[]> decodeTimestampSignatures(byte[] encodedSignatures) {
-		List<byte[]> signatures = new ArrayList<>();
+	public static byte[] encodeOnlineAccountSignatures(Map<Integer, OnlineAccountData> indexedOnlineAccounts,
+													   List<Integer> accountIndexes,
+													   int onlineAccountsCount,
+													   long timestamp) {
+		byte[] onlineAccountsSignatures;
 
-		for (int i = 0; i < encodedSignatures.length; i += Transformer.SIGNATURE_LENGTH) {
-			byte[] signature = new byte[Transformer.SIGNATURE_LENGTH];
-			System.arraycopy(encodedSignatures, i, signature, 0, Transformer.SIGNATURE_LENGTH);
-			signatures.add(signature);
+		if (timestamp >= BlockChain.getInstance().getOnlineAccountsMemoryPoWTimestamp()) {
+			// Online accounts must include at least one nonce and a reduced block signature from this time onwards
+
+			ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
+			for (int i = 0; i < onlineAccountsCount; ++i) {
+				Integer accountIndex = accountIndexes.get(i);
+				OnlineAccountData onlineAccountData = indexedOnlineAccounts.get(accountIndex);
+
+				List<Integer> nonces = onlineAccountData.getNonces();
+				byte[] reducedBlockSignature = onlineAccountData.getReducedBlockSignature();
+				if (nonces == null || nonces.isEmpty() || nonces.size() > MAX_NONCE_COUNT || reducedBlockSignature == null) {
+					// Missing or invalid data, so exclude this online account
+					continue;
+				}
+
+				try {
+					outputStream.write(onlineAccountData.getSignature());
+
+					outputStream.write(reducedBlockSignature);
+
+					outputStream.write(Ints.toByteArray(nonces.size()));
+
+					for (int n = 0; n < nonces.size(); ++n) {
+						Integer nonce = nonces.get(n);
+						outputStream.write(Ints.toByteArray(nonce));
+					}
+
+				} catch (IOException e) {
+					// Couldn't serialize this online account, so exclude it
+					continue;
+				}
+			}
+			onlineAccountsSignatures = outputStream.toByteArray();
+		}
+		else {
+			// Exclude nonce and reference block signature from online accounts data
+			// Concatenate online account timestamp signatures (in correct order)
+			onlineAccountsSignatures = new byte[onlineAccountsCount * Transformer.SIGNATURE_LENGTH];
+			for (int i = 0; i < onlineAccountsCount; ++i) {
+				Integer accountIndex = accountIndexes.get(i);
+				OnlineAccountData onlineAccountData = indexedOnlineAccounts.get(accountIndex);
+				System.arraycopy(onlineAccountData.getSignature(), 0, onlineAccountsSignatures, i * Transformer.SIGNATURE_LENGTH, Transformer.SIGNATURE_LENGTH);
+			}
 		}
 
-		return signatures;
+		return onlineAccountsSignatures;
+	}
+
+	public static List<OnlineAccountData> decodeOnlineAccountSignatures(byte[] encodedSignatures, int count, long timestamp) {
+		List<OnlineAccountData> onlineAccountSignatures = new ArrayList<>();
+
+		if (timestamp >= BlockChain.getInstance().getOnlineAccountsMemoryPoWTimestamp()) {
+			// byte array contains signatures, reduced signatures, and nonces
+			ByteBuffer byteBuffer = ByteBuffer.wrap(encodedSignatures);
+
+			for (int i = 0; i < count; ++i) {
+				byte[] signature = new byte[Transformer.SIGNATURE_LENGTH];
+				byteBuffer.get(signature);
+
+				byte[] reducedBlockSignature = new byte[Transformer.REDUCED_SIGNATURE_LENGTH];
+				byteBuffer.get(reducedBlockSignature);
+
+				int nonceCount = byteBuffer.getInt();
+
+				List<Integer> nonces = new ArrayList<>();
+				for (int n = 0; n < nonceCount; ++n) { // TODO: check against NONCE_COUNT in block validation
+					Integer nonce = byteBuffer.getInt();
+					nonces.add(nonce);
+				}
+
+				// Create an OnlineAccountData wrapper object containing the signature, nonce(s), and reduced block signature
+				OnlineAccountData onlineAccountDataWrapper = new OnlineAccountData(0, signature, null, nonces, reducedBlockSignature);
+				onlineAccountSignatures.add(onlineAccountDataWrapper);
+			}
+
+		}
+		else {
+			// byte array contains signatures only
+			for (int i = 0; i < encodedSignatures.length; i += Transformer.SIGNATURE_LENGTH) {
+				byte[] signature = new byte[Transformer.SIGNATURE_LENGTH];
+				System.arraycopy(encodedSignatures, i, signature, 0, Transformer.SIGNATURE_LENGTH);
+
+				// Create an OnlineAccountData wrapper object containing only the signature
+				OnlineAccountData onlineAccountDataWrapper = new OnlineAccountData(0, signature, null);
+				onlineAccountSignatures.add(onlineAccountDataWrapper);
+			}
+		}
+
+		return onlineAccountSignatures;
 	}
 
 }

src/main/resources/blockchain.json

@@ -19,6 +19,8 @@
 	"founderEffectiveMintingLevel": 10,
 	"onlineAccountSignaturesMinLifetime": 43200000,
 	"onlineAccountSignaturesMaxLifetime": 86400000,
+	"onlineAccountsModulusV2Timestamp": 9999999999999,
+	"onlineAccountsMemoryPoWTimestamp": 9999999999999,
 	"rewardsByHeight": [
 		{ "height": 1, "reward": 5.00 },
 		{ "height": 259201, "reward": 4.75 },

src/test/java/org/qortal/test/network/OnlineAccountsTests.java

@@ -1,22 +1,36 @@
 package org.qortal.test.network;
 
+import org.apache.commons.lang3.reflect.FieldUtils;
 import org.bouncycastle.jce.provider.BouncyCastleProvider;
 import org.bouncycastle.jsse.provider.BouncyCastleJsseProvider;
+import org.junit.Before;
 import org.junit.Test;
+import org.qortal.account.PrivateKeyAccount;
+import org.qortal.block.Block;
+import org.qortal.block.BlockChain;
+import org.qortal.controller.BlockMinter;
+import org.qortal.controller.OnlineAccountsManager;
 import org.qortal.data.network.OnlineAccountData;
 import org.qortal.network.message.*;
+import org.qortal.repository.DataException;
+import org.qortal.repository.Repository;
+import org.qortal.repository.RepositoryManager;
+import org.qortal.settings.Settings;
+import org.qortal.test.common.Common;
 import org.qortal.transform.Transformer;
+import org.qortal.utils.Base58;
+import org.qortal.utils.NTP;
 
+import java.io.IOException;
 import java.nio.ByteBuffer;
 import java.security.Security;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Random;
 
-import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.*;
 
-public class OnlineAccountsTests {
+public class OnlineAccountsTests extends Common {
 
     private static final Random RANDOM = new Random();
     static {
@@ -27,6 +41,12 @@ public class OnlineAccountsTests {
         Security.insertProviderAt(new BouncyCastleJsseProvider(), 1);
     }
 
+    @Before
+    public void beforeTest() throws DataException, IOException {
+        Common.useSettingsAndDb(Common.testSettingsFilename, false);
+        NTP.setFixedOffset(Settings.getInstance().getTestNtpOffset());
+    }
+
 
     @Test
     public void testGetOnlineAccountsV2() throws MessageException {
@@ -43,18 +63,6 @@ public class OnlineAccountsTests {
 
         assertEquals("size mismatch", onlineAccountsOut.size(), onlineAccountsIn.size());
         assertTrue("accounts mismatch", onlineAccountsIn.containsAll(onlineAccountsOut));
-
-        Message oldMessageOut = new GetOnlineAccountsMessage(onlineAccountsOut);
-        byte[] oldMessageBytes = oldMessageOut.toBytes();
-
-        long numTimestamps = onlineAccountsOut.stream().mapToLong(OnlineAccountData::getTimestamp).sorted().distinct().count();
-
-        System.out.println(String.format("For %d accounts split across %d timestamp%s: old size %d vs new size %d",
-                onlineAccountsOut.size(),
-                numTimestamps,
-                numTimestamps != 1 ? "s" : "",
-                oldMessageBytes.length,
-                messageBytes.length));
     }
 
     @Test
@@ -72,18 +80,6 @@ public class OnlineAccountsTests {
 
         assertEquals("size mismatch", onlineAccountsOut.size(), onlineAccountsIn.size());
         assertTrue("accounts mismatch", onlineAccountsIn.containsAll(onlineAccountsOut));
-
-        Message oldMessageOut = new OnlineAccountsMessage(onlineAccountsOut);
-        byte[] oldMessageBytes = oldMessageOut.toBytes();
-
-        long numTimestamps = onlineAccountsOut.stream().mapToLong(OnlineAccountData::getTimestamp).sorted().distinct().count();
-
-        System.out.println(String.format("For %d accounts split across %d timestamp%s: old size %d vs new size %d",
-                onlineAccountsOut.size(),
-                numTimestamps,
-                numTimestamps != 1 ? "s" : "",
-                oldMessageBytes.length,
-                messageBytes.length));
     }
 
     private List<OnlineAccountData> generateOnlineAccounts(boolean withSignatures) {
@@ -111,4 +107,136 @@ public class OnlineAccountsTests {
         return onlineAccounts;
     }
 
+    @Test
+    public void testOnlineAccountsModulusV1() throws IllegalAccessException, DataException {
+        try (final Repository repository = RepositoryManager.getRepository()) {
+
+            // Set feature trigger timestamp to MAX long so that it is inactive
+            FieldUtils.writeField(BlockChain.getInstance(), "onlineAccountsModulusV2Timestamp", Long.MAX_VALUE, true);
+
+            List<String> onlineAccountSignatures = new ArrayList<>();
+            long fakeNTPOffset = 0L;
+
+            // Mint a block and store its timestamp
+            Block block = BlockMinter.mintTestingBlock(repository, Common.getTestAccount(repository, "alice-reward-share"));
+            long lastBlockTimestamp = block.getBlockData().getTimestamp();
+
+            // Mint some blocks and keep track of the different online account signatures
+            for (int i = 0; i < 30; i++) {
+                block = BlockMinter.mintTestingBlock(repository, Common.getTestAccount(repository, "alice-reward-share"));
+
+                // Increase NTP fixed offset by the block time, to simulate time passing
+                long blockTimeDelta = block.getBlockData().getTimestamp() - lastBlockTimestamp;
+                lastBlockTimestamp = block.getBlockData().getTimestamp();
+                fakeNTPOffset += blockTimeDelta;
+                NTP.setFixedOffset(fakeNTPOffset);
+
+                String lastOnlineAccountSignatures58 = Base58.encode(block.getBlockData().getOnlineAccountsSignatures());
+                if (!onlineAccountSignatures.contains(lastOnlineAccountSignatures58)) {
+                    onlineAccountSignatures.add(lastOnlineAccountSignatures58);
+                }
+            }
+
+            // We expect at least 6 unique signatures over 30 blocks (generally 6-8, but could be higher due to block time differences)
+            System.out.println(String.format("onlineAccountSignatures count: %d", onlineAccountSignatures.size()));
+            assertTrue(onlineAccountSignatures.size() >= 6);
+        }
+    }
+
+    @Test
+    public void testOnlineAccountsModulusV2() throws IllegalAccessException, DataException {
+        try (final Repository repository = RepositoryManager.getRepository()) {
+
+            // Set feature trigger timestamp to 0 so that it is active
+            FieldUtils.writeField(BlockChain.getInstance(), "onlineAccountsModulusV2Timestamp", 0L, true);
+
+            List<String> onlineAccountSignatures = new ArrayList<>();
+            long fakeNTPOffset = 0L;
+
+            // Mint a block and store its timestamp
+            Block block = BlockMinter.mintTestingBlock(repository, Common.getTestAccount(repository, "alice-reward-share"));
+            long lastBlockTimestamp = block.getBlockData().getTimestamp();
+
+            // Mint some blocks and keep track of the different online account signatures
+            for (int i = 0; i < 30; i++) {
+                block = BlockMinter.mintTestingBlock(repository, Common.getTestAccount(repository, "alice-reward-share"));
+
+                // Increase NTP fixed offset by the block time, to simulate time passing
+                long blockTimeDelta = block.getBlockData().getTimestamp() - lastBlockTimestamp;
+                lastBlockTimestamp = block.getBlockData().getTimestamp();
+                fakeNTPOffset += blockTimeDelta;
+                NTP.setFixedOffset(fakeNTPOffset);
+
+                String lastOnlineAccountSignatures58 = Base58.encode(block.getBlockData().getOnlineAccountsSignatures());
+                if (!onlineAccountSignatures.contains(lastOnlineAccountSignatures58)) {
+                    onlineAccountSignatures.add(lastOnlineAccountSignatures58);
+                }
+            }
+
+            // We expect 1-3 unique signatures over 30 blocks
+            System.out.println(String.format("onlineAccountSignatures count: %d", onlineAccountSignatures.size()));
+            assertTrue(onlineAccountSignatures.size() >= 1 && onlineAccountSignatures.size() <= 3);
+        }
+    }
+
+    @Test
+    public void testBeforeMemoryPoW() throws IllegalAccessException, DataException {
+        try (final Repository repository = RepositoryManager.getRepository()) {
+
+            // Set feature trigger timestamp to MAX long so that it is inactive
+            FieldUtils.writeField(BlockChain.getInstance(), "onlineAccountsMemoryPoWTimestamp", Long.MAX_VALUE, true);
+
+            // Mint some blocks
+            for (int i = 0; i < 10; i++) {
+                BlockMinter.mintTestingBlock(repository, Common.getTestAccount(repository, "alice-reward-share"));
+            }
+        }
+    }
+
+    @Test
+    public void testMemoryPoW() throws IllegalAccessException, DataException {
+        try (final Repository repository = RepositoryManager.getRepository()) {
+
+            // Set feature trigger timestamp to 0 so that it is active
+            FieldUtils.writeField(BlockChain.getInstance(), "onlineAccountsMemoryPoWTimestamp", 0L, true);
+
+            // Set difficulty to 5, to speed up test
+            FieldUtils.writeField(OnlineAccountsManager.getInstance(), "POW_DIFFICULTY", 5, true);
+
+            // Mint some blocks
+            for (int i = 0; i < 10; i++) {
+                BlockMinter.mintTestingBlock(repository, Common.getTestAccount(repository, "alice-reward-share"));
+            }
+        }
+    }
+
+    @Test
+    public void testTransitionToMemoryPoW() throws IllegalAccessException, DataException {
+        try (final Repository repository = RepositoryManager.getRepository()) {
+
+            // Set feature trigger timestamp to now + 5 mins
+            long featureTriggerTimestamp = NTP.getTime() + (5 * 60 * 1000L);
+            FieldUtils.writeField(BlockChain.getInstance(), "onlineAccountsMemoryPoWTimestamp", featureTriggerTimestamp, true);
+
+            // Set difficulty to 5, to speed up test
+            FieldUtils.writeField(OnlineAccountsManager.getInstance(), "POW_DIFFICULTY", 5, true);
+
+            // Mint a block
+            Block block = BlockMinter.mintTestingBlock(repository, Common.getTestAccount(repository, "alice-reward-share"));
+            assertEquals(1, block.getBlockData().getOnlineAccountsCount());
+
+            // Ensure online accounts signatures are in legacy format (no nonce or reduced block signature)
+            assertEquals(64, block.getBlockData().getOnlineAccountsSignatures().length);
+
+            // Mint some blocks (at least 5 minutes' worth, to allow mempow to kick in)
+            for (int i = 0; i < 10; i++) {
+                block = BlockMinter.mintTestingBlock(repository, Common.getTestAccount(repository, "alice-reward-share"));
+                assertEquals(1, block.getBlockData().getOnlineAccountsCount());
+            }
+
+            // Ensure online accounts signatures are in new format (with 1 nonce and a reduced block signature)
+            assertEquals(80, block.getBlockData().getOnlineAccountsSignatures().length);
+        }
+    }
+
 }

src/test/resources/test-chain-v2-founder-rewards.json

@@ -14,6 +14,8 @@
 	"founderEffectiveMintingLevel": 10,
 	"onlineAccountSignaturesMinLifetime": 3600000,
 	"onlineAccountSignaturesMaxLifetime": 86400000,
+	"onlineAccountsModulusV2Timestamp": 9999999999999,
+	"onlineAccountsMemoryPoWTimestamp": 9999999999999,
 	"rewardsByHeight": [
 		{ "height": 1, "reward": 100 },
 		{ "height": 11, "reward": 10 },

src/test/resources/test-chain-v2-leftover-reward.json

@@ -14,6 +14,8 @@
 	"founderEffectiveMintingLevel": 10,
 	"onlineAccountSignaturesMinLifetime": 3600000,
 	"onlineAccountSignaturesMaxLifetime": 86400000,
+	"onlineAccountsModulusV2Timestamp": 9999999999999,
+	"onlineAccountsMemoryPoWTimestamp": 9999999999999,
 	"rewardsByHeight": [
 		{ "height": 1, "reward": 100 },
 		{ "height": 11, "reward": 10 },

src/test/resources/test-chain-v2-minting.json

@@ -14,6 +14,8 @@
 	"founderEffectiveMintingLevel": 10,
 	"onlineAccountSignaturesMinLifetime": 3600000,
 	"onlineAccountSignaturesMaxLifetime": 86400000,
+	"onlineAccountsModulusV2Timestamp": 9999999999999,
+	"onlineAccountsMemoryPoWTimestamp": 9999999999999,
 	"rewardsByHeight": [
 		{ "height": 1, "reward": 100 },
 		{ "height": 11, "reward": 10 },

src/test/resources/test-chain-v2-qora-holder-extremes.json

@@ -14,6 +14,8 @@
 	"founderEffectiveMintingLevel": 10,
 	"onlineAccountSignaturesMinLifetime": 3600000,
 	"onlineAccountSignaturesMaxLifetime": 86400000,
+	"onlineAccountsModulusV2Timestamp": 9999999999999,
+	"onlineAccountsMemoryPoWTimestamp": 9999999999999,
 	"rewardsByHeight": [
 		{ "height": 1, "reward": 100 },
 		{ "height": 11, "reward": 10 },

src/test/resources/test-chain-v2-qora-holder.json

@@ -14,6 +14,8 @@
 	"founderEffectiveMintingLevel": 10,
 	"onlineAccountSignaturesMinLifetime": 3600000,
 	"onlineAccountSignaturesMaxLifetime": 86400000,
+	"onlineAccountsModulusV2Timestamp": 9999999999999,
+	"onlineAccountsMemoryPoWTimestamp": 9999999999999,
 	"rewardsByHeight": [
 		{ "height": 1, "reward": 100 },
 		{ "height": 11, "reward": 10 },

src/test/resources/test-chain-v2-reward-levels.json

@@ -14,6 +14,8 @@
 	"founderEffectiveMintingLevel": 10,
 	"onlineAccountSignaturesMinLifetime": 3600000,
 	"onlineAccountSignaturesMaxLifetime": 86400000,
+	"onlineAccountsModulusV2Timestamp": 9999999999999,
+	"onlineAccountsMemoryPoWTimestamp": 9999999999999,
 	"rewardsByHeight": [
 		{ "height": 1, "reward": 100 },
 		{ "height": 11, "reward": 10 },

src/test/resources/test-chain-v2-reward-scaling.json

@@ -14,6 +14,8 @@
 	"founderEffectiveMintingLevel": 10,
 	"onlineAccountSignaturesMinLifetime": 3600000,
 	"onlineAccountSignaturesMaxLifetime": 86400000,
+	"onlineAccountsModulusV2Timestamp": 9999999999999,
+	"onlineAccountsMemoryPoWTimestamp": 9999999999999,
 	"rewardsByHeight": [
 		{ "height": 1, "reward": 100 },
 		{ "height": 11, "reward": 10 },

src/test/resources/test-chain-v2.json

@@ -14,6 +14,8 @@
 	"founderEffectiveMintingLevel": 10,
 	"onlineAccountSignaturesMinLifetime": 3600000,
 	"onlineAccountSignaturesMaxLifetime": 86400000,
+	"onlineAccountsModulusV2Timestamp": 9999999999999,
+	"onlineAccountsMemoryPoWTimestamp": 9999999999999,
 	"rewardsByHeight": [
 		{ "height": 1, "reward": 100 },
 		{ "height": 11, "reward": 10 },