New network handshaking. NOT backwards compatible!

Old Qora v1 message types removed.
Message type values changed.

Network handshaking reworked to fix multiple-connections issue.
Instead of using some random peerID, we now use proper keypairs and a challenge-response handshake to prevent doppelgangers/ID-theft.
This results in simpler handshaking code as we don't have to perform some arcane doppelganger resolution.

Handshaking still uses proof-of-work for challenge-response, but switched to newer MemoryPoW.

API call GET /peers no longer has 'buildTimestamp' field, but does now have 'nodeId' field.

Network no longer has a whole raft of getXXXpeers() due to simplified handshaking.
Quite a few method calls changed to simply Network.getHandshakedPeers(), which is also faster.

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

@@ -25,7 +25,8 @@ public class ConnectedPeer {
 
 	public String address;
 	public String version;
-	public Long buildTimestamp;
+
+	public String nodeId;
 
 	public Integer lastHeight;
 	@Schema(example = "base58")
@@ -45,10 +46,9 @@ public class ConnectedPeer {
 		this.peersConnectedWhen = peer.getPeersConnectionTimestamp();
 
 		this.address = peerData.getAddress().toString();
-		if (peer.getVersionMessage() != null) {
+
-			this.version = peer.getVersionMessage().getVersionString();
+		this.version = peer.getPeersVersionString();
-			this.buildTimestamp = peer.getVersionMessage().getBuildTimestamp();
+		this.nodeId = peer.getPeersNodeId();
-		}
 
 		PeerChainTipData peerChainTipData = peer.getChainTipData();
 		if (peerChainTipData != null) {

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

@@ -10,6 +10,7 @@ public class NodeInfo {
 	public long uptime;
 	public String buildVersion;
 	public long buildTimestamp;
+	public String nodeId;
 
 	public NodeInfo() {
 	}

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

@@ -117,6 +117,7 @@ public class AdminResource {
 		nodeInfo.uptime = System.currentTimeMillis() - Controller.startTime;
 		nodeInfo.buildVersion = Controller.getInstance().getVersionString();
 		nodeInfo.buildTimestamp = Controller.getInstance().getBuildTimestamp();
+		nodeInfo.nodeId = Network.getInstance().getOurNodeId();
 
 		return nodeInfo;
 	}

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

@@ -128,7 +128,7 @@ public class BlockMinter extends Thread {
 					}
 				}
 
-				List<Peer> peers = Network.getInstance().getUniqueHandshakedPeers();
+				List<Peer> peers = Network.getInstance().getHandshakedPeers();
 				BlockData lastBlockData = blockRepository.getLastBlock();
 
 				// Disregard peers that have "misbehaved" recently

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

@@ -60,11 +60,9 @@ import org.qortal.network.message.GetBlockMessage;
 import org.qortal.network.message.GetBlockSummariesMessage;
 import org.qortal.network.message.GetOnlineAccountsMessage;
 import org.qortal.network.message.GetPeersMessage;
-import org.qortal.network.message.GetSignaturesMessage;
 import org.qortal.network.message.GetSignaturesV2Message;
 import org.qortal.network.message.GetTransactionMessage;
 import org.qortal.network.message.GetUnconfirmedTransactionsMessage;
-import org.qortal.network.message.HeightMessage;
 import org.qortal.network.message.HeightV2Message;
 import org.qortal.network.message.Message;
 import org.qortal.network.message.OnlineAccountsMessage;
@@ -501,7 +499,7 @@ public class Controller extends Thread {
 	};
 
 	private void potentiallySynchronize() throws InterruptedException {
-		List<Peer> peers = Network.getInstance().getUniqueHandshakedPeers();
+		List<Peer> peers = Network.getInstance().getHandshakedPeers();
 
 		// Disregard peers that have "misbehaved" recently
 		peers.removeIf(hasMisbehaved);
@@ -626,7 +624,7 @@ public class Controller extends Thread {
 			return;
 		}
 
-		final int numberOfPeers = Network.getInstance().getUniqueHandshakedPeers().size();
+		final int numberOfPeers = Network.getInstance().getHandshakedPeers().size();
 
 		final int height = getChainHeight();
 
@@ -782,32 +780,11 @@ public class Controller extends Thread {
 	public void onPeerHandshakeCompleted(Peer peer) {
 		// Only send if outbound
 		if (peer.isOutbound()) {
-			if (peer.getVersion() < 2) {
+			// Request peer's unconfirmed transactions
-				// Legacy mode
+			Message message = new GetUnconfirmedTransactionsMessage();
-
+			if (!peer.sendMessage(message)) {
-				// Send our unconfirmed transactions
+				peer.disconnect("failed to send request for unconfirmed transactions");
-				try (final Repository repository = RepositoryManager.getRepository()) {
+				return;
-					List<TransactionData> transactions = repository.getTransactionRepository().getUnconfirmedTransactions();
-
-					for (TransactionData transactionData : transactions) {
-						Message transactionMessage = new TransactionMessage(transactionData);
-						if (!peer.sendMessage(transactionMessage)) {
-							peer.disconnect("failed to send unconfirmed transaction");
-							return;
-						}
-					}
-				} catch (DataException e) {
-					LOGGER.error("Repository issue while sending unconfirmed transactions", e);
-				}
-			} else {
-				// V2 protocol
-
-				// Request peer's unconfirmed transactions
-				Message message = new GetUnconfirmedTransactionsMessage();
-				if (!peer.sendMessage(message)) {
-					peer.disconnect("failed to send request for unconfirmed transactions");
-					return;
-				}
 			}
 		}
 
@@ -823,22 +800,10 @@ public class Controller extends Thread {
 
 		// Ordered by message type value
 		switch (message.getType()) {
-			case HEIGHT:
-				onNetworkHeightMessage(peer, message);
-				break;
-
-			case GET_SIGNATURES:
-				onNetworkGetSignaturesMessage(peer, message);
-				break;
-
 			case GET_BLOCK:
 				onNetworkGetBlockMessage(peer, message);
 				break;
 
-			case BLOCK:
-				onNetworkBlockMessage(peer, message);
-				break;
-
 			case TRANSACTION:
 				onNetworkTransactionMessage(peer, message);
 				break;
@@ -884,56 +849,11 @@ public class Controller extends Thread {
 				break;
 
 			default:
-				LOGGER.debug(String.format("Unhandled %s message [ID %d] from peer %s", message.getType().name(), message.getId(), peer));
+				LOGGER.debug(() -> String.format("Unhandled %s message [ID %d] from peer %s", message.getType().name(), message.getId(), peer));
 				break;
 		}
 	}
 
-	private void onNetworkHeightMessage(Peer peer, Message message) {
-		HeightMessage heightMessage = (HeightMessage) message;
-
-		// Update all peers with same ID
-
-		List<Peer> connectedPeers = Network.getInstance().getHandshakedPeers();
-		for (Peer connectedPeer : connectedPeers) {
-			if (connectedPeer.getPeerId() == null || !Arrays.equals(connectedPeer.getPeerId(), peer.getPeerId()))
-				continue;
-
-			// Update peer chain tip data
-			PeerChainTipData newChainTipData = new PeerChainTipData(heightMessage.getHeight(), null, null, null);
-			connectedPeer.setChainTipData(newChainTipData);
-		}
-
-		// Potentially synchronize
-		requestSync = true;
-	}
-
-	private void onNetworkGetSignaturesMessage(Peer peer, Message message) {
-		GetSignaturesMessage getSignaturesMessage = (GetSignaturesMessage) message;
-		byte[] parentSignature = getSignaturesMessage.getParentSignature();
-
-		try (final Repository repository = RepositoryManager.getRepository()) {
-			List<byte[]> signatures = new ArrayList<>();
-
-			do {
-				BlockData blockData = repository.getBlockRepository().fromReference(parentSignature);
-
-				if (blockData == null)
-					break;
-
-				parentSignature = blockData.getSignature();
-				signatures.add(parentSignature);
-			} while (signatures.size() < Network.MAX_SIGNATURES_PER_REPLY);
-
-			Message signaturesMessage = new SignaturesMessage(signatures);
-			signaturesMessage.setId(message.getId());
-			if (!peer.sendMessage(signaturesMessage))
-				peer.disconnect("failed to send signatures");
-		} catch (DataException e) {
-			LOGGER.error(String.format("Repository issue while sending signatures after %s to peer %s", Base58.encode(parentSignature), peer), e);
-		}
-	}
-
 	private void onNetworkGetBlockMessage(Peer peer, Message message) {
 		GetBlockMessage getBlockMessage = (GetBlockMessage) message;
 		byte[] signature = getBlockMessage.getSignature();
@@ -957,40 +877,6 @@ public class Controller extends Thread {
 		}
 	}
 
-	private void onNetworkBlockMessage(Peer peer, Message message) {
-		// From a v1 peer, with no message ID, this is a broadcast of peer's latest block
-		// v2 peers announce new blocks using HEIGHT_V2
-
-		// Not version 1?
-		if (peer.getVersion() == null || peer.getVersion() > 1)
-			return;
-
-		// Message ID present?
-		// XXX Why is this test here? If BLOCK had an ID then surely it would be a response to GET_BLOCK
-		// and hence captured by Peer's reply queue?
-		if (message.hasId())
-			return;
-
-		BlockMessage blockMessage = (BlockMessage) message;
-		BlockData blockData = blockMessage.getBlockData();
-
-		// Update all peers with same ID
-
-		List<Peer> connectedPeers = Network.getInstance().getHandshakedPeers();
-		for (Peer connectedPeer : connectedPeers) {
-			// Skip connectedPeer if they have no ID or their ID doesn't match sender's ID
-			if (connectedPeer.getPeerId() == null || !Arrays.equals(connectedPeer.getPeerId(), peer.getPeerId()))
-				continue;
-
-			// Update peer chain tip data
-			PeerChainTipData newChainTipData = new PeerChainTipData(blockData.getHeight(), blockData.getSignature(), blockData.getTimestamp(), blockData.getMinterPublicKey());
-			connectedPeer.setChainTipData(newChainTipData);
-		}
-
-		// Potentially synchronize
-		requestSync = true;
-	}
-
 	private void onNetworkTransactionMessage(Peer peer, Message message) {
 		TransactionMessage transactionMessage = (TransactionMessage) message;
 		TransactionData transactionData = transactionMessage.getTransactionData();
@@ -1096,18 +982,9 @@ public class Controller extends Thread {
 		if (!peer.isOutbound() && (peer.getChainTipData() == null || peer.getChainTipData().getLastHeight() == null))
 			peer.sendMessage(Network.getInstance().buildHeightMessage(peer, getChainTip()));
 
-		// Update all peers with same ID
+		// Update peer chain tip data
-
+		PeerChainTipData newChainTipData = new PeerChainTipData(heightV2Message.getHeight(), heightV2Message.getSignature(), heightV2Message.getTimestamp(), heightV2Message.getMinterPublicKey());
-		List<Peer> connectedPeers = Network.getInstance().getHandshakedPeers();
+		peer.setChainTipData(newChainTipData);
-		for (Peer connectedPeer : connectedPeers) {
-			// Skip connectedPeer if they have no ID or their ID doesn't match sender's ID
-			if (connectedPeer.getPeerId() == null || !Arrays.equals(connectedPeer.getPeerId(), peer.getPeerId()))
-				continue;
-
-			// Update peer chain tip data
-			PeerChainTipData newChainTipData = new PeerChainTipData(heightV2Message.getHeight(), heightV2Message.getSignature(), heightV2Message.getTimestamp(), heightV2Message.getMinterPublicKey());
-			connectedPeer.setChainTipData(newChainTipData);
-		}
 
 		// Potentially synchronize
 		requestSync = true;
@@ -1561,7 +1438,7 @@ public class Controller extends Thread {
 		getArbitraryDataMessage.setId(id);
 
 		// Broadcast request
-		Network.getInstance().broadcast(peer -> peer.getVersion() < 2 ? null : getArbitraryDataMessage);
+		Network.getInstance().broadcast(peer -> getArbitraryDataMessage);
 
 		// Poll to see if data has arrived
 		final long singleWait = 100;
@@ -1593,7 +1470,7 @@ public class Controller extends Thread {
 		if (minLatestBlockTimestamp == null)
 			return null;
 
-		List<Peer> peers = Network.getInstance().getUniqueHandshakedPeers();
+		List<Peer> peers = Network.getInstance().getHandshakedPeers();
 
 		// Filter out unsuitable peers
 		Iterator<Peer> iterator = peers.iterator();
@@ -1639,7 +1516,7 @@ public class Controller extends Thread {
 		if (latestBlockData == null || latestBlockData.getTimestamp() < minLatestBlockTimestamp)
 			return false;
 
-		List<Peer> peers = Network.getInstance().getUniqueHandshakedPeers();
+		List<Peer> peers = Network.getInstance().getHandshakedPeers();
 		if (peers == null)
 			return false;
 

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

@@ -22,7 +22,6 @@ import org.qortal.network.message.BlockMessage;
 import org.qortal.network.message.BlockSummariesMessage;
 import org.qortal.network.message.GetBlockMessage;
 import org.qortal.network.message.GetBlockSummariesMessage;
-import org.qortal.network.message.GetSignaturesMessage;
 import org.qortal.network.message.GetSignaturesV2Message;
 import org.qortal.network.message.Message;
 import org.qortal.network.message.SignaturesMessage;
@@ -372,12 +371,7 @@ public class Synchronizer {
 				return SynchronizationResult.TOO_DIVERGENT;
 			}
 
-			if (peer.getVersion() >= 2) {
+			step <<= 1;
-				step <<= 1;
-			} else {
-				// Old v1 peers are hard-coded to return 500 signatures so we might as well go backward by 500 too
-				step = 500;
-			}
 			step = Math.min(step, MAXIMUM_BLOCK_STEP);
 
 			testHeight = Math.max(testHeight - step, 1);
@@ -415,8 +409,7 @@ public class Synchronizer {
 	}
 
 	private List<byte[]> getBlockSignatures(Peer peer, byte[] parentSignature, int numberRequested) throws InterruptedException {
-		// numberRequested is v2+ feature
+		Message getSignaturesMessage = new GetSignaturesV2Message(parentSignature, numberRequested);
-		Message getSignaturesMessage = peer.getVersion() >= 2 ? new GetSignaturesV2Message(parentSignature, numberRequested) : new GetSignaturesMessage(parentSignature);
 
 		Message message = peer.getResponse(getSignaturesMessage);
 		if (message == null || message.getType() != MessageType.SIGNATURES)

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

@@ -1,158 +1,193 @@
 package org.qortal.network;
 
 import java.util.Arrays;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
 
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 import org.qortal.controller.Controller;
+import org.qortal.crypto.Crypto;
+import org.qortal.crypto.MemoryPoW;
+import org.qortal.network.message.ChallengeMessage;
+import org.qortal.network.message.HelloMessage;
 import org.qortal.network.message.Message;
-import org.qortal.network.message.PeerIdMessage;
-import org.qortal.network.message.PeerVerifyMessage;
-import org.qortal.network.message.ProofMessage;
-import org.qortal.network.message.VerificationCodesMessage;
-import org.qortal.network.message.VersionMessage;
 import org.qortal.network.message.Message.MessageType;
+import org.qortal.network.message.ResponseMessage;
+import org.qortal.utils.NTP;
+
+import com.google.common.primitives.Bytes;
 
 public enum Handshake {
 	STARTED(null) {
 		@Override
 		public Handshake onMessage(Peer peer, Message message) {
-			return SELF_CHECK;
+			return HELLO;
 		}
 
 		@Override
 		public void action(Peer peer) {
 		}
 	},
-	SELF_CHECK(MessageType.PEER_ID) {
+	HELLO(MessageType.HELLO) {
 		@Override
 		public Handshake onMessage(Peer peer, Message message) {
-			PeerIdMessage peerIdMessage = (PeerIdMessage) message;
+			HelloMessage helloMessage = (HelloMessage) message;
-			byte[] peerId = peerIdMessage.getPeerId();
 
-			if (Arrays.equals(peerId, Network.ZERO_PEER_ID)) {
+			long peersConnectionTimestamp = helloMessage.getTimestamp();
-				if (peer.isOutbound()) {
+			long now = NTP.getTime();
-					// Peer has indicated they already have an outbound connection to us
-					LOGGER.trace(String.format("Peer %s already connected to us - discarding this connection", peer));
-				} else {
-					// Not sure this should occur so log it
-					LOGGER.info(String.format("Inbound peer %s claims we also have outbound connection to them?", peer));
-				}
 
+			long timestampDelta = Math.abs(peersConnectionTimestamp - now);
+			if (timestampDelta > MAX_TIMESTAMP_DELTA) {
+				LOGGER.debug(() -> String.format("Peer %s HELLO timestamp %d too divergent (± %d > %d) from ours %d",
+						peer, peersConnectionTimestamp, timestampDelta, MAX_TIMESTAMP_DELTA, now));
 				return null;
 			}
 
-			if (Arrays.equals(peerId, Network.getInstance().getOurPeerId())) {
+			String versionString = helloMessage.getVersionString();
-				// Connected to self!
+
+			Matcher matcher = VERSION_PATTERN.matcher(versionString);
+			if (!matcher.lookingAt()) {
+				LOGGER.debug(() -> String.format("Peer %s sent invalid HELLO version string '%s'", peer, versionString));
+				return null;
+			}
+
+			// We're expecting 3 positive shorts, so we can convert 1.2.3 into 0x0100020003
+			long version = 0;
+			for (int g = 1; g <= 3; ++g) {
+				long value = Long.parseLong(matcher.group(g));
+
+				if (value < 0 || value > Short.MAX_VALUE)
+					return null;
+
+				version <<= 16;
+				version |= value;
+			}
+
+			peer.setPeersConnectionTimestamp(peersConnectionTimestamp);
+			peer.setPeersVersion(versionString, version);
+
+			return CHALLENGE;
+		}
+
+		@Override
+		public void action(Peer peer) {
+			String versionString = Controller.getInstance().getVersionString();
+			long timestamp = NTP.getTime();
+
+			Message helloMessage = new HelloMessage(timestamp, versionString);
+			if (!peer.sendMessage(helloMessage))
+				peer.disconnect("failed to send HELLO");
+		}
+	},
+	CHALLENGE(MessageType.CHALLENGE) {
+		@Override
+		public Handshake onMessage(Peer peer, Message message) {
+			ChallengeMessage challengeMessage = (ChallengeMessage) message;
+
+			byte[] peersPublicKey = challengeMessage.getPublicKey();
+			byte[] peersChallenge = challengeMessage.getChallenge();
+
+			// If public key matches our public key then we've connected to self
+			byte[] ourPublicKey = Network.getInstance().getOurPublicKey();
+			if (Arrays.equals(ourPublicKey, peersPublicKey)) {
 				// If outgoing connection then record destination as self so we don't try again
 				if (peer.isOutbound()) {
 					Network.getInstance().noteToSelf(peer);
-					// Handshake failure - caller will deal with disconnect
+					// Handshake failure, caller will handle disconnect
 					return null;
 				} else {
 					// We still need to send our ID so our outbound connection can mark their address as 'self'
-					sendMyId(peer);
+					challengeMessage = new ChallengeMessage(ourPublicKey, ZERO_CHALLENGE);
-					// We return SELF_CHECK here to prevent us from closing connection, which currently preempts
+					if (!peer.sendMessage(challengeMessage))
-					// remote end from reading any pending messages, specifically the PEER_ID message we just sent above.
+						peer.disconnect("failed to send CHALLENGE to self");
-					// When our 'remote' outbound counterpart reads our message, they will close both connections.
+
-					// Failing that, our connection will timeout or a future handshake error will occur.
+					/*
-					return SELF_CHECK;
+					 * We return CHALLENGE here to prevent us from closing connection. Closing
+					 * connection currently preempts remote end from reading any pending messages,
+					 * specifically the CHALLENGE message we just sent above. When our 'remote'
+					 * outbound counterpart reads our message, they will close both connections.
+					 * Failing that, our connection will timeout or a future handshake error will
+					 * occur.
+					 */
+					return CHALLENGE;
 				}
 			}
 
-			// Is this ID already connected inbound or outbound?
+			// Are we already connected to this peer?
-			Peer otherInboundPeer = Network.getInstance().getInboundPeerWithId(peerId);
+			Peer existingPeer = Network.getInstance().getHandshakedPeerWithPublicKey(peersPublicKey);
-			Peer otherOutboundPeer = Network.getInstance().getOutboundHandshakedPeerWithId(peerId);
+			if (existingPeer != null) {
-
+				LOGGER.info(() -> String.format("We already have a connection with peer %s - discarding", peer));
-			// Extra checks on inbound peers with known IDs, to prevent ID stealing
-			if (!peer.isOutbound() && otherInboundPeer != null) {
-				if (otherOutboundPeer == null) {
-					// We already have an inbound peer with this ID, but no outgoing peer with which to request verification
-					LOGGER.trace(String.format("Discarding inbound peer %s with existing ID", peer));
-
-					// Let peer know by sending special zero peer ID. This avoids peer keeping connection open until timeout.
-					peerIdMessage = new PeerIdMessage(Network.ZERO_PEER_ID);
-					peer.sendMessage(peerIdMessage);
-
-					return null;
-				} else {
-					// Use corresponding outbound peer to verify inbound
-					LOGGER.trace(String.format("We will be using outbound peer %s to verify inbound peer %s with same ID", otherOutboundPeer, peer));
-
-					// Discard peer's ID
-					// peer.setPeerId(peerId);
-
-					// Generate verification codes for later
-					peer.generateVerificationCodes();
-				}
-			} else if (peer.isOutbound() && otherOutboundPeer != null) {
-				// We already have an outbound connection to this peer?
-				LOGGER.info(String.format("We already have another outbound connection to peer %s - discarding", peer));
 				// Handshake failure - caller will deal with disconnect
 				return null;
-			} else {
-				// Set peer's ID
-				peer.setPeerId(peerId);
 			}
 
-			return VERSION;
+			peer.setPeersPublicKey(peersPublicKey);
+			peer.setPeersChallenge(peersChallenge);
+
+			return RESPONSE;
 		}
 
 		@Override
 		public void action(Peer peer) {
-			sendMyId(peer);
+			// Send challenge
+			byte[] publicKey = Network.getInstance().getOurPublicKey();
+			byte[] challenge = peer.getOurChallenge();
+
+			Message challengeMessage = new ChallengeMessage(publicKey, challenge);
+			if (!peer.sendMessage(challengeMessage))
+				peer.disconnect("failed to send CHALLENGE");
 		}
 	},
-	VERSION(MessageType.VERSION) {
+	RESPONSE(MessageType.RESPONSE) {
 		@Override
 		public Handshake onMessage(Peer peer, Message message) {
-			peer.setVersionMessage((VersionMessage) message);
+			ResponseMessage responseMessage = (ResponseMessage) message;
 
-			// If we're both version 2 peers then next stage is proof
+			byte[] peersPublicKey = peer.getPeersPublicKey();
-			if (peer.getVersion() >= 2)
+			byte[] ourChallenge = peer.getOurChallenge();
-				return PROOF;
+
+			byte[] sharedSecret = Network.getInstance().getSharedSecret(peersPublicKey);
+			final byte[] expectedData = Crypto.digest(Bytes.concat(sharedSecret, ourChallenge));
+
+			byte[] data = responseMessage.getData();
+			if (!Arrays.equals(expectedData, data)) {
+				LOGGER.debug(() -> String.format("Peer %s sent incorrect RESPONSE data", peer));
+				return null;
+			}
+
+			int nonce = responseMessage.getNonce();
+			if (!MemoryPoW.verify2(data, POW_BUFFER_SIZE, POW_DIFFICULTY, nonce)) {
+				LOGGER.debug(() -> String.format("Peer %s sent incorrect RESPONSE nonce", peer));
+				return null;
+			}
+
+			peer.setPeersNodeId(Crypto.toNodeAddress(peersPublicKey));
 
-			// Fall-back for older clients (for now)
 			return COMPLETED;
 		}
 
 		@Override
 		public void action(Peer peer) {
-			sendVersion(peer);
+			// Send response
-		}
-	},
-	PROOF(MessageType.PROOF) {
-		@Override
-		public Handshake onMessage(Peer peer, Message message) {
-			ProofMessage proofMessage = (ProofMessage) message;
 
-			// Check peer's timestamp is within acceptable bounds
+			byte[] peersPublicKey = peer.getPeersPublicKey();
-			if (Math.abs(proofMessage.getTimestamp() - peer.getConnectionTimestamp()) > MAX_TIMESTAMP_DELTA) {
+			byte[] peersChallenge = peer.getPeersChallenge();
-				LOGGER.debug(String.format("Rejecting PROOF from %s as timestamp delta %d greater than max %d", peer, Math.abs(proofMessage.getTimestamp() - peer.getConnectionTimestamp()), MAX_TIMESTAMP_DELTA));
-				return null;
-			}
 
-			// Save peer's value for connectionTimestamp
+			byte[] sharedSecret = Network.getInstance().getSharedSecret(peersPublicKey);
-			peer.setPeersConnectionTimestamp(proofMessage.getTimestamp());
+			final byte[] data = Crypto.digest(Bytes.concat(sharedSecret, peersChallenge));
 
-			// If we connected outbound to peer, then this is a faked confirmation response, so we're good
+			// We do this in a new thread as it can take a while...
-			if (peer.isOutbound())
+			Thread responseThread = new Thread(() -> {
-				return COMPLETED;
+				Integer nonce = MemoryPoW.compute2(data, POW_BUFFER_SIZE, POW_DIFFICULTY);
 
-			// Check salt hasn't been seen before - this stops multiple peers reusing same nonce in a Sybil-like attack
+				Message responseMessage = new ResponseMessage(nonce, data);
-			if (Proof.seenSalt(proofMessage.getSalt()))
+				if (!peer.sendMessage(responseMessage))
-				return null;
+					peer.disconnect("failed to send RESPONSE");
+			});
 
-			if (!Proof.check(proofMessage.getTimestamp(), proofMessage.getSalt(), proofMessage.getNonce()))
+			responseThread.setDaemon(true);
-				return null;
+			responseThread.start();
-
-			// Proof valid
-			return COMPLETED;
-		}
-
-		@Override
-		public void action(Peer peer) {
-			sendProof(peer);
 		}
 	},
 	COMPLETED(null) {
@@ -166,40 +201,6 @@ public enum Handshake {
 		public void action(Peer peer) {
 			// Note: this is only called when we've made outbound connection
 		}
-	},
-	PEER_VERIFY(null) {
-		@Override
-		public Handshake onMessage(Peer peer, Message message) {
-			// We only accept PEER_VERIFY messages
-			if (message.getType() != Message.MessageType.PEER_VERIFY)
-				return PEER_VERIFY;
-
-			// Check returned code against expected
-			PeerVerifyMessage peerVerifyMessage = (PeerVerifyMessage) message;
-
-			if (!Arrays.equals(peerVerifyMessage.getVerificationCode(), peer.getVerificationCodeExpected()))
-				return null;
-
-			// Drop other inbound peers with the same ID
-			for (Peer otherPeer : Network.getInstance().getConnectedPeers())
-				if (!otherPeer.isOutbound() && otherPeer.getPeerId() != null && Arrays.equals(otherPeer.getPeerId(), peer.getPendingPeerId()))
-					otherPeer.disconnect("doppelganger");
-
-			// Tidy up
-			peer.setVerificationCodes(null, null);
-			peer.setPeerId(peer.getPendingPeerId());
-			peer.setPendingPeerId(null);
-
-			// Completed for real this time
-			return COMPLETED;
-		}
-
-		@Override
-		public void action(Peer peer) {
-			// Send VERIFICATION_CODE to other peer (that we connected to)
-			// Send PEER_VERIFY to peer
-			sendVerificationCodes(peer);
-		}
 	};
 
 	private static final Logger LOGGER = LogManager.getLogger(Handshake.class);
@@ -207,6 +208,13 @@ public enum Handshake {
 	/** Maximum allowed difference between peer's reported timestamp and when they connected, in milliseconds. */
 	private static final long MAX_TIMESTAMP_DELTA = 30 * 1000L; // ms
 
+	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 = 12; // leading zero bits
+
+	private static final byte[] ZERO_CHALLENGE = new byte[ChallengeMessage.CHALLENGE_LENGTH];
+
 	public final MessageType expectedMessageType;
 
 	private Handshake(MessageType expectedMessageType) {
@@ -217,47 +225,4 @@ public enum Handshake {
 
 	public abstract void action(Peer peer);
 
-	private static void sendVersion(Peer peer) {
-		long buildTimestamp = Controller.getInstance().getBuildTimestamp();
-		String versionString = Controller.getInstance().getVersionString();
-
-		Message versionMessage = new VersionMessage(buildTimestamp, versionString);
-		if (!peer.sendMessage(versionMessage))
-			peer.disconnect("failed to send version");
-	}
-
-	private static void sendMyId(Peer peer) {
-		Message peerIdMessage = new PeerIdMessage(Network.getInstance().getOurPeerId());
-		if (!peer.sendMessage(peerIdMessage))
-			peer.disconnect("failed to send peer ID");
-	}
-
-	private static void sendProof(Peer peer) {
-		if (peer.isOutbound()) {
-			// For outbound connections we need to generate real proof
-			new Proof(peer).start(); // Calculate & send in a new thread to free up networking processing
-		} else {
-			// For incoming connections we only need to send a fake proof message as confirmation
-			Message proofMessage = new ProofMessage(peer.getConnectionTimestamp(), 0, 0);
-			if (!peer.sendMessage(proofMessage))
-				peer.disconnect("failed to send proof");
-		}
-	}
-
-	private static void sendVerificationCodes(Peer peer) {
-		Peer otherOutboundPeer = Network.getInstance().getOutboundHandshakedPeerWithId(peer.getPendingPeerId());
-
-		// Send VERIFICATION_CODES to peer
-		Message verificationCodesMessage = new VerificationCodesMessage(peer.getVerificationCodeSent(), peer.getVerificationCodeExpected());
-		if (!otherOutboundPeer.sendMessage(verificationCodesMessage)) {
-			peer.disconnect("failed to send verification codes"); // give up with this peer instead
-			return;
-		}
-
-		// Send PEER_VERIFY to peer
-		Message peerVerifyMessage = new PeerVerifyMessage(peer.getVerificationCodeSent());
-		if (!peer.sendMessage(peerVerifyMessage))
-			peer.disconnect("failed to send verification code");
-	}
-
 }

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

@@ -1,7 +1,6 @@
 package org.qortal.network;
 
 import java.io.IOException;
-import java.net.Inet6Address;
 import java.net.InetAddress;
 import java.net.InetSocketAddress;
 import java.net.StandardSocketOptions;
@@ -32,28 +31,26 @@ import java.util.stream.Collectors;
 
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
+import org.bouncycastle.crypto.params.Ed25519PrivateKeyParameters;
+import org.bouncycastle.crypto.params.Ed25519PublicKeyParameters;
 import org.qortal.block.BlockChain;
 import org.qortal.controller.Controller;
+import org.qortal.crypto.Crypto;
 import org.qortal.data.block.BlockData;
 import org.qortal.data.network.PeerData;
 import org.qortal.data.transaction.TransactionData;
 import org.qortal.network.message.GetPeersMessage;
 import org.qortal.network.message.GetUnconfirmedTransactionsMessage;
-import org.qortal.network.message.HeightMessage;
 import org.qortal.network.message.HeightV2Message;
 import org.qortal.network.message.Message;
-import org.qortal.network.message.PeerVerifyMessage;
-import org.qortal.network.message.PeersMessage;
 import org.qortal.network.message.PeersV2Message;
 import org.qortal.network.message.PingMessage;
-import org.qortal.network.message.TransactionMessage;
 import org.qortal.network.message.TransactionSignaturesMessage;
-import org.qortal.network.message.VerificationCodesMessage;
-import org.qortal.network.message.Message.MessageType;
 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;
@@ -99,10 +96,11 @@ public class Network {
 
 	public static final int MAX_SIGNATURES_PER_REPLY = 500;
 	public static final int MAX_BLOCK_SUMMARIES_PER_REPLY = 500;
-	public static final int PEER_ID_LENGTH = 128;
-	public static final byte[] ZERO_PEER_ID = new byte[PEER_ID_LENGTH];
 
-	private final byte[] ourPeerId;
+	private final Ed25519PrivateKeyParameters edPrivateKeyParams;
+	private final Ed25519PublicKeyParameters edPublicKeyParams;
+	private final String ourNodeId;
+
 	private final int maxMessageSize;
 
 	private List<PeerData> allKnownPeers;
@@ -129,10 +127,13 @@ public class Network {
 		connectedPeers = new ArrayList<>();
 		selfPeers = new ArrayList<>();
 
-		ourPeerId = new byte[PEER_ID_LENGTH];
+		// Generate our ID
-		new SecureRandom().nextBytes(ourPeerId);
+		byte[] seed = new byte[Transformer.PRIVATE_KEY_LENGTH];
-		// Set bit to make sure our peer ID is not 0
+		new SecureRandom().nextBytes(seed);
-		ourPeerId[ourPeerId.length - 1] |= 0x01;
+
+		edPrivateKeyParams = new Ed25519PrivateKeyParameters(seed, 0);
+		edPublicKeyParams = edPrivateKeyParams.generatePublicKey();
+		ourNodeId = Crypto.toNodeAddress(edPublicKeyParams.getEncoded());
 
 		maxMessageSize = 4 + 1 + 4 + BlockChain.getInstance().getMaxBlockSize();
 
@@ -201,8 +202,12 @@ public class Network {
 		return Settings.getInstance().isTestNet() ? TESTNET_MESSAGE_MAGIC : MAINNET_MESSAGE_MAGIC;
 	}
 
-	public byte[] getOurPeerId() {
+	public String getOurNodeId() {
-		return this.ourPeerId;
+		return this.ourNodeId;
+	}
+
+	/*package*/ byte[] getOurPublicKey() {
+		return this.edPublicKeyParams.getEncoded();
 	}
 
 	/** Maximum message size (bytes). Needs to be at least maximum block size + MAGIC + message type, etc. */
@@ -241,25 +246,6 @@ public class Network {
 		}
 	}
 
-	/** Returns list of connected peers that have completed handshaking, with inbound duplicates removed. */
-	public List<Peer> getUniqueHandshakedPeers() {
-		List<Peer> peers = getHandshakedPeers();
-
-		// Returns true if this peer is inbound and has corresponding outbound peer with same ID
-		Predicate<Peer> hasOutboundWithSameId = peer -> {
-			// Peer is outbound so return fast
-			if (peer.isOutbound())
-				return false;
-
-			return peers.stream().anyMatch(otherPeer -> otherPeer.isOutbound() && Arrays.equals(otherPeer.getPeerId(), peer.getPeerId()));
-		};
-
-		// Filter out inbound peers that have corresponding outbound peer with the same ID
-		peers.removeIf(hasOutboundWithSameId);
-
-		return peers;
-	}
-
 	/** Returns list of peers we connected to that have completed handshaking. */
 	public List<Peer> getOutboundHandshakedPeers() {
 		synchronized (this.connectedPeers) {
@@ -267,21 +253,13 @@ public class Network {
 		}
 	}
 
-	/** Returns Peer with inbound connection and matching ID, or null if none found. */
+	/** Returns first peer that has completed handshaking and has matching public key. */
-	public Peer getInboundPeerWithId(byte[] peerId) {
+	public Peer getHandshakedPeerWithPublicKey(byte[] publicKey) {
 		synchronized (this.connectedPeers) {
-			return this.connectedPeers.stream().filter(peer -> !peer.isOutbound() && peer.getPeerId() != null && Arrays.equals(peer.getPeerId(), peerId)).findAny().orElse(null);
+			return this.connectedPeers.stream().filter(peer -> peer.getHandshakeStatus() == Handshake.COMPLETED && Arrays.equals(peer.getPeersPublicKey(), publicKey)).findFirst().orElse(null);
 		}
 	}
 
-	/** Returns handshake-completed Peer with outbound connection and matching ID, or null if none found. */
-	public Peer getOutboundHandshakedPeerWithId(byte[] peerId) {
-		synchronized (this.connectedPeers) {
-			return this.connectedPeers.stream().filter(peer -> peer.isOutbound() && peer.getHandshakeStatus() == Handshake.COMPLETED && peer.getPeerId() != null && Arrays.equals(peer.getPeerId(), peerId)).findAny().orElse(null);
-		}
-	}
-
-
 	// Peer list filters
 
 	/** Must be inside <tt>synchronized (this.selfPeers) {...}</tt> */
@@ -639,10 +617,22 @@ public class Network {
 
 	// Peer callbacks
 
-	/* package */ void wakeupChannelSelector() {
+	/*package*/ void wakeupChannelSelector() {
 		this.channelSelector.wakeup();
 	}
 
+	/*package*/ boolean verify(byte[] signature, byte[] message) {
+		return Crypto.verify(this.edPublicKeyParams.getEncoded(), signature, message);
+	}
+
+	/*package*/ byte[] sign(byte[] message) {
+		return Crypto.sign(this.edPrivateKeyParams, message);
+	}
+
+	/*package*/ byte[] getSharedSecret(byte[] publicKey) {
+		return Crypto.getSharedSecret(this.edPrivateKeyParams.getEncoded(), publicKey);
+	}
+
 	/** Called when Peer's thread has setup and is ready to process messages */
 	public void onPeerReady(Peer peer) {
 		this.onMessage(peer, null);
@@ -692,17 +682,13 @@ public class Network {
 				onGetPeersMessage(peer, message);
 				break;
 
-			case PEERS:
-				onPeersMessage(peer, message);
-				break;
-
 			case PING:
 				onPingMessage(peer, message);
 				break;
 
-			case VERSION:
+			case HELLO:
-			case PEER_ID:
+			case CHALLENGE:
-			case PROOF:
+			case RESPONSE:
 				LOGGER.debug(() -> String.format("Unexpected handshaking message %s from peer %s", message.getType().name(), peer));
 				peer.disconnect("unexpected handshaking message");
 				return;
@@ -711,14 +697,6 @@ public class Network {
 				onPeersV2Message(peer, message);
 				break;
 
-			case PEER_VERIFY:
-				onPeerVerifyMessage(peer, message);
-				break;
-
-			case VERIFICATION_CODES:
-				onVerificationCodesMessage(peer, message);
-				break;
-
 			default:
 				// Bump up to controller for possible action
 				Controller.getInstance().onNetworkMessage(peer, message);
@@ -731,12 +709,6 @@ public class Network {
 			// Still handshaking
 			LOGGER.trace(() -> String.format("Handshake status %s, message %s from peer %s", handshakeStatus.name(), (message != null ? message.getType().name() : "null"), peer));
 
-			// v1 nodes are keen on sending PINGs early. Send to back of queue so we'll process right after handshake
-			if (message != null && message.getType() == MessageType.PING) {
-				peer.queueMessage(message);
-				return;
-			}
-
 			// Check message type is as expected
 			if (handshakeStatus.expectedMessageType != null && message.getType() != handshakeStatus.expectedMessageType) {
 				LOGGER.debug(() -> String.format("Unexpected %s message from %s, expected %s", message.getType().name(), peer, handshakeStatus.expectedMessageType));
@@ -775,22 +747,6 @@ public class Network {
 			peer.disconnect("failed to send peers list");
 	}
 
-	private void onPeersMessage(Peer peer, Message message) {
-		PeersMessage peersMessage = (PeersMessage) message;
-
-		List<PeerAddress> peerAddresses = new ArrayList<>();
-
-		// v1 PEERS message doesn't support port numbers so we have to add default port
-		for (InetAddress peerAddress : peersMessage.getPeerAddresses())
-			// This is always IPv4 so we don't have to worry about bracketing IPv6.
-			peerAddresses.add(PeerAddress.fromString(peerAddress.getHostAddress()));
-
-		// Also add peer's details
-		peerAddresses.add(PeerAddress.fromString(peer.getPeerData().getAddress().getHost()));
-
-		opportunisticMergePeers(peer.toString(), peerAddresses);
-	}
-
 	private void onPingMessage(Peer peer, Message message) {
 		PingMessage pingMessage = (PingMessage) message;
 
@@ -821,45 +777,7 @@ public class Network {
 		opportunisticMergePeers(peer.toString(), peerV2Addresses);
 	}
 
-	private void onPeerVerifyMessage(Peer peer, Message message) {
-		// Remote peer wants extra verification
-		possibleVerificationResponse(peer);
-	}
-
-	private void onVerificationCodesMessage(Peer peer, Message message) {
-		VerificationCodesMessage verificationCodesMessage = (VerificationCodesMessage) message;
-
-		// Remote peer is sending the code it wants to receive back via our outbound connection to it
-		Peer ourUnverifiedPeer = Network.getInstance().getInboundPeerWithId(Network.getInstance().getOurPeerId());
-		ourUnverifiedPeer.setVerificationCodes(verificationCodesMessage.getVerificationCodeSent(), verificationCodesMessage.getVerificationCodeExpected());
-
-		possibleVerificationResponse(ourUnverifiedPeer);
-	}
-
-	private void possibleVerificationResponse(Peer peer) {
-		// Can't respond if we don't have the codes (yet?)
-		if (peer.getVerificationCodeExpected() == null)
-			return;
-
-		PeerVerifyMessage peerVerifyMessage = new PeerVerifyMessage(peer.getVerificationCodeExpected());
-		if (!peer.sendMessage(peerVerifyMessage)) {
-			peer.disconnect("failed to send verification code");
-			return;
-		}
-
-		peer.setVerificationCodes(null, null);
-		peer.setHandshakeStatus(Handshake.COMPLETED);
-		this.onHandshakeCompleted(peer);
-	}
-
 	private void onHandshakeCompleted(Peer peer) {
-		// Do we need extra handshaking because of peer doppelgangers?
-		if (peer.getPendingPeerId() != null) {
-			peer.setHandshakeStatus(Handshake.PEER_VERIFY);
-			peer.getHandshakeStatus().action(peer);
-			return;
-		}
-
 		LOGGER.debug(String.format("Handshake completed with peer %s", peer));
 
 		// Make a note that we've successfully completed handshake (and when)
@@ -930,86 +848,44 @@ public class Network {
 		};
 		knownPeers.removeIf(notRecentlyConnected);
 
-		if (peer.getVersion() >= 2) {
+		List<PeerAddress> peerAddresses = new ArrayList<>();
-			List<PeerAddress> peerAddresses = new ArrayList<>();
 
-			for (PeerData peerData : knownPeers) {
+		for (PeerData peerData : knownPeers) {
-				try {
+			try {
-					InetAddress address = InetAddress.getByName(peerData.getAddress().getHost());
+				InetAddress address = InetAddress.getByName(peerData.getAddress().getHost());
 
-					// Don't send 'local' addresses if peer is not 'local'. e.g. don't send localhost:9084 to node4.qortal.org
+				// Don't send 'local' addresses if peer is not 'local'. e.g. don't send localhost:9084 to node4.qortal.org
-					if (!peer.getIsLocal() && Peer.isAddressLocal(address))
+				if (!peer.isLocal() && Peer.isAddressLocal(address))
-						continue;
+					continue;
 
-					peerAddresses.add(peerData.getAddress());
+				peerAddresses.add(peerData.getAddress());
-				} catch (UnknownHostException e) {
+			} catch (UnknownHostException e) {
-					// Couldn't resolve hostname to IP address so discard
+				// Couldn't resolve hostname to IP address so discard
-				}
 			}
-
-			// New format PEERS_V2 message that supports hostnames, IPv6 and ports
-			return new PeersV2Message(peerAddresses);
-		} else {
-			// Map to socket addresses
-			List<InetAddress> peerAddresses = new ArrayList<>();
-
-			for (PeerData peerData : knownPeers) {
-				try {
-					// We have to resolve to literal IP address to check for IPv4-ness.
-					// This isn't great if hostnames have both IPv6 and IPv4 DNS entries.
-					InetAddress address = InetAddress.getByName(peerData.getAddress().getHost());
-
-					// Legacy PEERS message doesn't support IPv6
-					if (address instanceof Inet6Address)
-						continue;
-
-					// Don't send 'local' addresses if peer is not 'local'. e.g. don't send localhost:9084 to node4.qortal.org
-					if (!peer.getIsLocal() && !Peer.isAddressLocal(address))
-						continue;
-
-					peerAddresses.add(address);
-				} catch (UnknownHostException e) {
-					// Couldn't resolve hostname to IP address so discard
-				}
-			}
-
-			// Legacy PEERS message that only sends IPv4 addresses
-			return new PeersMessage(peerAddresses);
 		}
+
+		// New format PEERS_V2 message that supports hostnames, IPv6 and ports
+		return new PeersV2Message(peerAddresses);
 	}
 
 	public Message buildHeightMessage(Peer peer, BlockData blockData) {
-		if (peer.getVersion() < 2) {
-			// Legacy height message
-			return new HeightMessage(blockData.getHeight());
-		}
-
 		// HEIGHT_V2 contains way more useful info
 		return new HeightV2Message(blockData.getHeight(), blockData.getSignature(), blockData.getTimestamp(), blockData.getMinterPublicKey());
 	}
 
 	public Message buildNewTransactionMessage(Peer peer, TransactionData transactionData) {
-		if (peer.getVersion() < 2) {
-			// Legacy TRANSACTION message
-			return new TransactionMessage(transactionData);
-		}
-
 		// In V2 we send out transaction signature only and peers can decide whether to request the full transaction
 		return new TransactionSignaturesMessage(Collections.singletonList(transactionData.getSignature()));
 	}
 
 	public Message buildGetUnconfirmedTransactionsMessage(Peer peer) {
-		// V2 only
-		if (peer.getVersion() < 2)
-			return null;
-
 		return new GetUnconfirmedTransactionsMessage();
 	}
 
 	// Peer-management calls
 
 	public void noteToSelf(Peer peer) {
-		LOGGER.info(String.format("No longer considering peer address %s as it connects to self", peer));
+		LOGGER.info(() -> String.format("No longer considering peer address %s as it connects to self", peer));
 
 		synchronized (this.selfPeers) {
 			this.selfPeers.add(peer.getPeerData().getAddress());
@@ -1230,7 +1106,7 @@ public class Network {
 		}
 
 		try {
-			broadcastExecutor.execute(new Broadcaster(this.getUniqueHandshakedPeers(), peerMessageBuilder));
+			broadcastExecutor.execute(new Broadcaster(this.getHandshakedPeers(), peerMessageBuilder));
 		} catch (RejectedExecutionException e) {
 			// Can't execute - probably because we're shutting down, so ignore
 		}

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

@@ -24,9 +24,9 @@ import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 import org.qortal.data.network.PeerChainTipData;
 import org.qortal.data.network.PeerData;
+import org.qortal.network.message.ChallengeMessage;
 import org.qortal.network.message.Message;
 import org.qortal.network.message.PingMessage;
-import org.qortal.network.message.VersionMessage;
 import org.qortal.network.message.Message.MessageException;
 import org.qortal.network.message.Message.MessageType;
 import org.qortal.settings.Settings;
@@ -42,7 +42,7 @@ public class Peer {
 	private static final Logger LOGGER = LogManager.getLogger(Peer.class);
 
 	/** Maximum time to allow <tt>connect()</tt> to remote peer to complete. (ms) */
-	private static final int CONNECT_TIMEOUT = 1000; // ms
+	private static final int CONNECT_TIMEOUT = 2000; // ms
 
 	/** Maximum time to wait for a message reply to arrive from peer. (ms) */
 	private static final int RESPONSE_TIMEOUT = 2000; // ms
@@ -54,9 +54,6 @@ public class Peer {
 	 */
 	private static final int PING_INTERVAL = 20_000; // ms
 
-	/** Threshold for buildTimestamp in VERSION messages where we consider peer to be using v2 protocol. */
-	private static final long V2_PROTOCOL_TIMESTAMP_THRESHOLD = 1546300800L; // midnight starting 1st Jan 2019
-
 	private volatile boolean isStopping = false;
 
 	private SocketChannel socketChannel = null;
@@ -65,41 +62,48 @@ public class Peer {
 	private boolean isLocal;
 
 	private final Object byteBufferLock = new Object();
-	private volatile ByteBuffer byteBuffer;
+	private ByteBuffer byteBuffer;
+
 	private Map<Integer, BlockingQueue<Message>> replyQueues;
 	private LinkedBlockingQueue<Message> pendingMessages;
 
 	/** True if we created connection to peer, false if we accepted incoming connection from peer. */
 	private final boolean isOutbound;
-	/** Numeric protocol version, typically 1 or 2. */
-	private volatile Integer version;
-	private volatile byte[] peerId;
 
-	private volatile Handshake handshakeStatus = Handshake.STARTED;
+	private final Object handshakingLock = new Object();
+	private Handshake handshakeStatus = Handshake.STARTED;
 	private volatile boolean handshakeMessagePending = false;
 
-	private volatile byte[] pendingPeerId;
-	private volatile byte[] verificationCodeSent;
-	private volatile byte[] verificationCodeExpected;
-
-	private volatile PeerData peerData = null;
-
 	/** Timestamp of when socket was accepted, or connected. */
-	private volatile Long connectionTimestamp = null;
+	private Long connectionTimestamp = null;
-
-	/** Peer's value of connectionTimestamp. */
-	private volatile Long peersConnectionTimestamp = null;
-
-	/** Version info as reported by peer. */
-	private volatile VersionMessage versionMessage = null;
 
 	/** Last PING message round-trip time (ms). */
-	private volatile Long lastPing = null;
+	private Long lastPing = null;
 	/** When last PING message was sent, or null if pings not started yet. */
-	private volatile Long lastPingSent;
+	private Long lastPingSent;
+
+	byte[] ourChallenge;
+
+	// Peer info
+
+	private final Object peerInfoLock = new Object();
+
+	private String peersNodeId;
+	private byte[] peersPublicKey;
+	private byte[] peersChallenge;
+
+	private PeerData peerData = null;
+
+	/** Peer's value of connectionTimestamp. */
+	private Long peersConnectionTimestamp = null;
+
+	/** Version string as reported by peer. */
+	private String peersVersionString = null;
+	/** Numeric version of peer. */
+	private Long peersVersion = null;
 
 	/** Latest block info as reported by peer. */
-	private volatile PeerChainTipData chainTipData;
+	private PeerChainTipData peersChainTipData;
 
 	// Constructors
 
@@ -124,16 +128,20 @@ public class Peer {
 
 	// Getters / setters
 
-	public SocketChannel getSocketChannel() {
-		return this.socketChannel;
-	}
-
 	public boolean isStopping() {
 		return this.isStopping;
 	}
 
-	public PeerData getPeerData() {
+	public SocketChannel getSocketChannel() {
-		return this.peerData;
+		return this.socketChannel;
+	}
+
+	public InetSocketAddress getResolvedAddress() {
+		return this.resolvedAddress;
+	}
+
+	public boolean isLocal() {
+		return this.isLocal;
 	}
 
 	public boolean isOutbound() {
@@ -141,103 +149,131 @@ public class Peer {
 	}
 
 	public Handshake getHandshakeStatus() {
-		return this.handshakeStatus;
+		synchronized (this.handshakingLock) {
-	}
+			return this.handshakeStatus;
-
-	public void setHandshakeStatus(Handshake handshakeStatus) {
-		this.handshakeStatus = handshakeStatus;
-	}
-
-	public void resetHandshakeMessagePending() {
-		this.handshakeMessagePending = false;
-	}
-
-	public VersionMessage getVersionMessage() {
-		return this.versionMessage;
-	}
-
-	public void setVersionMessage(VersionMessage versionMessage) {
-		this.versionMessage = versionMessage;
-
-		if (this.versionMessage.getBuildTimestamp() >= V2_PROTOCOL_TIMESTAMP_THRESHOLD) {
-			this.version = 2; // enhanced protocol
-		} else {
-			this.version = 1; // legacy protocol
 		}
 	}
 
-	public Integer getVersion() {
+	/*package*/ void setHandshakeStatus(Handshake handshakeStatus) {
-		return this.version;
+		synchronized (this.handshakingLock) {
+			this.handshakeStatus = handshakeStatus;
+		}
+	}
+
+	/*package*/ void resetHandshakeMessagePending() {
+		this.handshakeMessagePending = false;
+	}
+
+	public PeerData getPeerData() {
+		synchronized (this.peerInfoLock) {
+			return this.peerData;
+		}
 	}
 
 	public Long getConnectionTimestamp() {
-		return this.connectionTimestamp;
+		synchronized (this.peerInfoLock) {
+			return this.connectionTimestamp;
+		}
+	}
+
+	public String getPeersVersionString() {
+		synchronized (this.peerInfoLock) {
+			return this.peersVersionString;
+		}
+	}
+
+	public Long getPeersVersion() {
+		synchronized (this.peerInfoLock) {
+			return this.peersVersion;
+		}
+	}
+
+	/*package*/ void setPeersVersion(String versionString, long version) {
+		synchronized (this.peerInfoLock) {
+			this.peersVersionString = versionString;
+			this.peersVersion = version;
+		}
 	}
 
 	public Long getPeersConnectionTimestamp() {
-		return this.peersConnectionTimestamp;
+		synchronized (this.peerInfoLock) {
+			return this.peersConnectionTimestamp;
+		}
 	}
 
-	/* package */ void setPeersConnectionTimestamp(Long peersConnectionTimestamp) {
+	/*package*/ void setPeersConnectionTimestamp(Long peersConnectionTimestamp) {
-		this.peersConnectionTimestamp = peersConnectionTimestamp;
+		synchronized (this.peerInfoLock) {
+			this.peersConnectionTimestamp = peersConnectionTimestamp;
+		}
 	}
 
 	public Long getLastPing() {
-		return this.lastPing;
+		synchronized (this.peerInfoLock) {
+			return this.lastPing;
+		}
 	}
 
-	public void setLastPing(long lastPing) {
+	/*package*/ void setLastPing(long lastPing) {
-		this.lastPing = lastPing;
+		synchronized (this.peerInfoLock) {
+			this.lastPing = lastPing;
+		}
 	}
 
-	public InetSocketAddress getResolvedAddress() {
+	/*package*/ byte[] getOurChallenge() {
-		return this.resolvedAddress;
+		return this.ourChallenge;
 	}
 
-	public boolean getIsLocal() {
+	public String getPeersNodeId() {
-		return this.isLocal;
+		synchronized (this.peerInfoLock) {
+			return this.peersNodeId;
+		}
 	}
 
-	public byte[] getPeerId() {
+	/*package*/ void setPeersNodeId(String peersNodeId) {
-		return this.peerId;
+		synchronized (this.peerInfoLock) {
+			this.peersNodeId = peersNodeId;
+		}
 	}
 
-	public void setPeerId(byte[] peerId) {
+	public byte[] getPeersPublicKey() {
-		this.peerId = peerId;
+		synchronized (this.peerInfoLock) {
+			return this.peersPublicKey;
+		}
 	}
 
-	public byte[] getPendingPeerId() {
+	/*package*/ void setPeersPublicKey(byte[] peerPublicKey) {
-		return this.pendingPeerId;
+		synchronized (this.peerInfoLock) {
+			this.peersPublicKey = peerPublicKey;
+		}
 	}
 
-	public void setPendingPeerId(byte[] peerId) {
+	public byte[] getPeersChallenge() {
-		this.pendingPeerId = peerId;
+		synchronized (this.peerInfoLock) {
+			return this.peersChallenge;
+		}
 	}
 
-	public byte[] getVerificationCodeSent() {
+	/*package*/ void setPeersChallenge(byte[] peersChallenge) {
-		return this.verificationCodeSent;
+		synchronized (this.peerInfoLock) {
-	}
+			this.peersChallenge = peersChallenge;
-
+		}
-	public byte[] getVerificationCodeExpected() {
-		return this.verificationCodeExpected;
-	}
-
-	public void setVerificationCodes(byte[] sent, byte[] expected) {
-		this.verificationCodeSent = sent;
-		this.verificationCodeExpected = expected;
 	}
 
 	public PeerChainTipData getChainTipData() {
-		return this.chainTipData;
+		synchronized (this.peerInfoLock) {
+			return this.peersChainTipData;
+		}
 	}
 
 	public void setChainTipData(PeerChainTipData chainTipData) {
-		this.chainTipData = chainTipData;
+		synchronized (this.peerInfoLock) {
+			this.peersChainTipData = chainTipData;
+		}
 	}
 
-	/* package */ void queueMessage(Message message) {
+	/*package*/ void queueMessage(Message message) {
 		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));
 	}
 
 	@Override
@@ -248,14 +284,6 @@ public class Peer {
 
 	// Processing
 
-	public void generateVerificationCodes() {
-		verificationCodeSent = new byte[Network.PEER_ID_LENGTH];
-		new SecureRandom().nextBytes(verificationCodeSent);
-
-		verificationCodeExpected = new byte[Network.PEER_ID_LENGTH];
-		new SecureRandom().nextBytes(verificationCodeExpected);
-	}
-
 	private void sharedSetup(Selector channelSelector) throws IOException {
 		this.connectionTimestamp = NTP.getTime();
 		this.socketChannel.setOption(StandardSocketOptions.TCP_NODELAY, true);
@@ -264,6 +292,10 @@ public class Peer {
 		this.byteBuffer = null; // Defer allocation to when we need it, to save memory. Sorry GC!
 		this.replyQueues = Collections.synchronizedMap(new HashMap<Integer, BlockingQueue<Message>>());
 		this.pendingMessages = new LinkedBlockingQueue<>();
+
+		Random random = new SecureRandom();
+		this.ourChallenge = new byte[ChallengeMessage.CHALLENGE_LENGTH];
+		random.nextBytes(this.ourChallenge);
 	}
 
 	public SocketChannel connect(Selector channelSelector) {
@@ -378,9 +410,11 @@ public class Peer {
 	}
 
 	/* package */ ExecuteProduceConsume.Task getMessageTask() {
-		// If we are still handshaking and there is a message yet to be processed
+		/*
-		// then don't produce another message task.
+		 * If we are still handshaking and there is a message yet to be processed then
-		// This allows us to process handshake messages sequentially.
+		 * don't produce another message task. This allows us to process handshake
+		 * messages sequentially.
+		 */
 		if (this.handshakeMessagePending)
 			return null;
 
@@ -454,9 +488,10 @@ public class Peer {
 		BlockingQueue<Message> blockingQueue = new ArrayBlockingQueue<>(1);
 
 		// Assign random ID to this message
+		Random random = new Random();
 		int id;
 		do {
-			id = new Random().nextInt(Integer.MAX_VALUE - 1) + 1;
+			id = random.nextInt(Integer.MAX_VALUE - 1) + 1;
 
 			// Put queue into map (keyed by message ID) so we can poll for a response
 			// If putIfAbsent() doesn't return null, then this ID is already taken

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

@@ -1,126 +0,0 @@
-package org.qortal.network;
-
-import java.security.MessageDigest;
-import java.security.NoSuchAlgorithmException;
-import java.security.SecureRandom;
-import java.util.HashSet;
-
-import org.apache.logging.log4j.LogManager;
-import org.apache.logging.log4j.Logger;
-import org.qortal.network.message.ProofMessage;
-
-import com.google.common.primitives.Longs;
-
-public class Proof extends Thread {
-
-	private static final int MIN_PROOF_ZEROS = 2;
-	private static final HashSet<Long> seenSalts = new HashSet<>();
-	private static final Logger LOGGER = LogManager.getLogger(Proof.class);
-
-	private Peer peer;
-
-	public Proof(Peer peer) {
-		this.peer = peer;
-		setDaemon(true);
-	}
-
-	public static boolean seenSalt(long salt) {
-		synchronized (seenSalts) {
-			return seenSalts.contains(salt);
-		}
-	}
-
-	public static void addSalt(long salt) {
-		synchronized (seenSalts) {
-			seenSalts.add(salt);
-		}
-	}
-
-	@Override
-	public void run() {
-		setName("Proof for peer " + this.peer);
-
-		// Do proof-of-work calculation to gain acceptance with remote end
-		final long startTime = LOGGER.isTraceEnabled() ? System.currentTimeMillis() : 0;
-
-		// Remote end knows this (approximately)
-		long timestamp = this.peer.getConnectionTimestamp();
-
-		// Needs to be unique on the remote end
-		long salt = new SecureRandom().nextLong();
-
-		byte[] message = new byte[8 + 8 + 8]; // nonce + salt + timestamp
-
-		byte[] saltBytes = Longs.toByteArray(salt);
-		System.arraycopy(saltBytes, 0, message, 8, saltBytes.length);
-
-		byte[] timestampBytes = Longs.toByteArray(timestamp);
-		System.arraycopy(timestampBytes, 0, message, 8 + 8, timestampBytes.length);
-
-		MessageDigest sha256;
-		try {
-			sha256 = MessageDigest.getInstance("SHA256");
-		} catch (NoSuchAlgorithmException e) {
-			// Can't progress
-			throw new RuntimeException("Message digest SHA256 not available");
-		}
-
-		long nonce;
-		for (nonce = 0; nonce < Long.MAX_VALUE; ++nonce) {
-			// Check whether we're shutting down every so often
-			if ((nonce & 0xff) == 0 && (this.peer.isStopping() || Thread.currentThread().isInterrupted()))
-				// throw new InterruptedException("Interrupted during peer proof calculation");
-				return;
-
-			byte[] nonceBytes = Longs.toByteArray(nonce);
-			System.arraycopy(nonceBytes, 0, message, 0, nonceBytes.length);
-
-			byte[] digest = sha256.digest(message);
-
-			if (check(digest))
-				break;
-
-			sha256.reset();
-		}
-
-		LOGGER.trace(() -> String.format("Proof for peer %s took %dms", this.peer, System.currentTimeMillis() - startTime));
-
-		ProofMessage proofMessage = new ProofMessage(timestamp, salt, nonce);
-		peer.sendMessage(proofMessage);
-	}
-
-	private static boolean check(byte[] digest) {
-		int idx;
-		for (idx = 0; idx < MIN_PROOF_ZEROS; ++idx)
-			if (digest[idx] != 0)
-				break;
-
-		return idx == MIN_PROOF_ZEROS;
-	}
-
-	public static boolean check(long timestamp, long salt, long nonce) {
-		byte[] message = new byte[8 + 8 + 8];
-
-		byte[] saltBytes = Longs.toByteArray(salt);
-		System.arraycopy(saltBytes, 0, message, 8, saltBytes.length);
-
-		byte[] timestampBytes = Longs.toByteArray(timestamp);
-		System.arraycopy(timestampBytes, 0, message, 8 + 8, timestampBytes.length);
-
-		byte[] nonceBytes = Longs.toByteArray(nonce);
-		System.arraycopy(nonceBytes, 0, message, 0, nonceBytes.length);
-
-		MessageDigest sha256;
-		try {
-			sha256 = MessageDigest.getInstance("SHA256");
-		} catch (NoSuchAlgorithmException e) {
-			// Can't progress
-			throw new RuntimeException("Message digest SHA256 not available");
-		}
-
-		byte[] digest = sha256.digest(message);
-
-		return check(digest);
-	}
-
-}

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

@@ -0,0 +1,56 @@
+package org.qortal.network.message;
+
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.nio.ByteBuffer;
+
+import org.qortal.transform.Transformer;
+
+public class ChallengeMessage extends Message {
+
+	public static final int CHALLENGE_LENGTH = 32;
+
+	private final byte[] publicKey;
+	private final byte[] challenge;
+
+	private ChallengeMessage(int id, byte[] publicKey, byte[] challenge) {
+		super(id, MessageType.CHALLENGE);
+
+		this.publicKey = publicKey;
+		this.challenge = challenge;
+	}
+
+	public ChallengeMessage(byte[] publicKey, byte[] challenge) {
+		this(-1, publicKey, challenge);
+	}
+
+	public byte[] getPublicKey() {
+		return this.publicKey;
+	}
+
+	public byte[] getChallenge() {
+		return this.challenge;
+	}
+
+	public static Message fromByteBuffer(int id, ByteBuffer byteBuffer)  {
+		byte[] publicKey = new byte[Transformer.PUBLIC_KEY_LENGTH];
+		byteBuffer.get(publicKey);
+
+		byte[] challenge = new byte[CHALLENGE_LENGTH];
+		byteBuffer.get(challenge);
+
+		return new ChallengeMessage(id, publicKey, challenge);
+	}
+
+	@Override
+	protected byte[] toData() throws IOException {
+		ByteArrayOutputStream bytes = new ByteArrayOutputStream();
+
+		bytes.write(this.publicKey);
+
+		bytes.write(this.challenge);
+
+		return bytes.toByteArray();
+	}
+
+}

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

@@ -1,54 +0,0 @@
-package org.qortal.network.message;
-
-import java.io.ByteArrayOutputStream;
-import java.io.IOException;
-import java.io.UnsupportedEncodingException;
-import java.nio.ByteBuffer;
-
-import org.qortal.transform.block.BlockTransformer;
-
-public class GetSignaturesMessage extends Message {
-
-	private static final int BLOCK_SIGNATURE_LENGTH = BlockTransformer.BLOCK_SIGNATURE_LENGTH;
-
-	private byte[] parentSignature;
-
-	public GetSignaturesMessage(byte[] parentSignature) {
-		this(-1, parentSignature);
-	}
-
-	private GetSignaturesMessage(int id, byte[] parentSignature) {
-		super(id, MessageType.GET_SIGNATURES);
-
-		this.parentSignature = parentSignature;
-	}
-
-	public byte[] getParentSignature() {
-		return this.parentSignature;
-	}
-
-	public static Message fromByteBuffer(int id, ByteBuffer bytes) throws UnsupportedEncodingException {
-		if (bytes.remaining() != BLOCK_SIGNATURE_LENGTH)
-			return null;
-
-		byte[] parentSignature = new byte[BLOCK_SIGNATURE_LENGTH];
-
-		bytes.get(parentSignature);
-
-		return new GetSignaturesMessage(id, parentSignature);
-	}
-
-	@Override
-	protected byte[] toData() {
-		try {
-			ByteArrayOutputStream bytes = new ByteArrayOutputStream();
-
-			bytes.write(this.parentSignature);
-
-			return bytes.toByteArray();
-		} catch (IOException e) {
-			return null;
-		}
-	}
-
-}

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

@@ -0,0 +1,65 @@
+package org.qortal.network.message;
+
+import static java.util.Arrays.stream;
+import static java.util.stream.Collectors.toMap;
+
+import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.util.Map;
+
+import com.google.common.primitives.Ints;
+
+public class GoodbyeMessage extends Message {
+
+	public enum Reason {
+		NO_HELLO(1),
+		BAD_HELLO(2),
+		BAD_HELLO_VERSION(3),
+		BAD_HELLO_TIMESTAMP(4);
+
+		public final int value;
+
+		private static final Map<Integer, Reason> map = stream(Reason.values())
+				.collect(toMap(reason -> reason.value, reason -> reason));
+
+		private Reason(int value) {
+			this.value = value;
+		}
+
+		public static Reason valueOf(int value) {
+			return map.get(value);
+		}
+	}
+
+	private final Reason reason;
+
+	private GoodbyeMessage(int id, Reason reason) {
+		super(id, MessageType.GOODBYE);
+
+		this.reason = reason;
+	}
+
+	public GoodbyeMessage(Reason reason) {
+		this(-1, reason);
+	}
+
+	public Reason getReason() {
+		return this.reason;
+	}
+
+	public static Message fromByteBuffer(int id, ByteBuffer byteBuffer) {
+		int reasonValue = byteBuffer.getInt();
+
+		Reason reason = Reason.valueOf(reasonValue);
+		if (reason == null)
+			return null;
+
+		return new GoodbyeMessage(id, reason);
+	}
+
+	@Override
+	protected byte[] toData() throws IOException {
+		return Ints.toByteArray(this.reason.value);
+	}
+
+}

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

@@ -1,47 +0,0 @@
-package org.qortal.network.message;
-
-import java.io.ByteArrayOutputStream;
-import java.io.IOException;
-import java.io.UnsupportedEncodingException;
-import java.nio.ByteBuffer;
-
-import com.google.common.primitives.Ints;
-
-public class HeightMessage extends Message {
-
-	private int height;
-
-	public HeightMessage(int height) {
-		this(-1, height);
-	}
-
-	private HeightMessage(int id, int height) {
-		super(id, MessageType.HEIGHT);
-
-		this.height = height;
-	}
-
-	public int getHeight() {
-		return this.height;
-	}
-
-	public static Message fromByteBuffer(int id, ByteBuffer bytes) throws UnsupportedEncodingException {
-		int height = bytes.getInt();
-
-		return new HeightMessage(id, height);
-	}
-
-	@Override
-	protected byte[] toData() {
-		try {
-			ByteArrayOutputStream bytes = new ByteArrayOutputStream();
-
-			bytes.write(Ints.toByteArray(this.height));
-
-			return bytes.toByteArray();
-		} catch (IOException e) {
-			return null;
-		}
-	}
-
-}

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

@@ -0,0 +1,55 @@
+package org.qortal.network.message;
+
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.nio.ByteBuffer;
+
+import org.qortal.transform.TransformationException;
+import org.qortal.utils.Serialization;
+
+import com.google.common.primitives.Longs;
+
+public class HelloMessage extends Message {
+
+	private final long timestamp;
+	private final String versionString;
+
+	private HelloMessage(int id, long timestamp, String versionString) {
+		super(id, MessageType.HELLO);
+
+		this.timestamp = timestamp;
+		this.versionString = versionString;
+	}
+
+	public HelloMessage(long timestamp, String versionString) {
+		this(-1, timestamp, versionString);
+	}
+
+	public long getTimestamp() {
+		return this.timestamp;
+	}
+
+	public String getVersionString() {
+		return this.versionString;
+	}
+
+	public static Message fromByteBuffer(int id, ByteBuffer byteBuffer) throws TransformationException {
+		long timestamp = byteBuffer.getLong();
+
+		String versionString = Serialization.deserializeSizedString(byteBuffer, 255);
+
+		return new HelloMessage(id, timestamp, versionString);
+	}
+
+	@Override
+	protected byte[] toData() throws IOException {
+		ByteArrayOutputStream bytes = new ByteArrayOutputStream();
+
+		bytes.write(Longs.toByteArray(this.timestamp));
+
+		Serialization.serializeSizedString(bytes, this.versionString);
+
+		return bytes.toByteArray();
+	}
+
+}

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

@@ -4,6 +4,7 @@ import java.util.Map;
 
 import org.qortal.crypto.Crypto;
 import org.qortal.network.Network;
+import org.qortal.transform.TransformationException;
 
 import com.google.common.primitives.Ints;
 
@@ -45,32 +46,41 @@ public abstract class Message {
 	}
 
 	public enum MessageType {
-		GET_PEERS(1),
+		// Handshaking
-		PEERS(2),
+		HELLO(0),
-		HEIGHT(3),
+		GOODBYE(1),
-		GET_SIGNATURES(4),
+		CHALLENGE(2),
-		SIGNATURES(5),
+		RESPONSE(3),
-		GET_BLOCK(6),
+
-		BLOCK(7),
+		// Status / notifications
-		TRANSACTION(8),
+		HEIGHT_V2(10),
-		PING(9),
+		PING(11),
-		VERSION(10),
+		PONG(12),
-		PEER_ID(11),
+
-		PROOF(12),
+		// Requesting data
-		PEERS_V2(13),
+		PEERS_V2(20),
-		GET_BLOCK_SUMMARIES(14),
+		GET_PEERS(21),
-		BLOCK_SUMMARIES(15),
+
-		GET_SIGNATURES_V2(16),
+		TRANSACTION(30),
-		PEER_VERIFY(17),
+		GET_TRANSACTION(31),
-		VERIFICATION_CODES(18),
+
-		HEIGHT_V2(19),
+		TRANSACTION_SIGNATURES(40),
-		GET_TRANSACTION(20),
+		GET_UNCONFIRMED_TRANSACTIONS(41),
-		GET_UNCONFIRMED_TRANSACTIONS(21),
+
-		TRANSACTION_SIGNATURES(22),
+		BLOCK(50),
-		GET_ARBITRARY_DATA(23),
+		GET_BLOCK(51),
-		ARBITRARY_DATA(24),
+
-		GET_ONLINE_ACCOUNTS(25),
+		SIGNATURES(60),
-		ONLINE_ACCOUNTS(26);
+		GET_SIGNATURES_V2(61),
+
+		BLOCK_SUMMARIES(70),
+		GET_BLOCK_SUMMARIES(71),
+
+		ONLINE_ACCOUNTS(80),
+		GET_ONLINE_ACCOUNTS(81),
+
+		ARBITRARY_DATA(90),
+		GET_ARBITRARY_DATA(91);
 
 		public final int value;
 		public final Method fromByteBufferMethod;
@@ -263,11 +273,11 @@ public abstract class Message {
 				throw new MessageException(String.format("About to send message with length %d larger than allowed %d", bytes.size(), MAX_DATA_SIZE));
 
 			return bytes.toByteArray();
-		} catch (IOException e) {
+		} catch (IOException | TransformationException e) {
 			throw new MessageException("Failed to serialize message", e);
 		}
 	}
 
-	protected abstract byte[] toData();
+	protected abstract byte[] toData() throws IOException, TransformationException;
 
 }

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

@@ -1,52 +0,0 @@
-package org.qortal.network.message;
-
-import java.io.ByteArrayOutputStream;
-import java.io.IOException;
-import java.io.UnsupportedEncodingException;
-import java.nio.ByteBuffer;
-
-import org.qortal.network.Network;
-
-public class PeerIdMessage extends Message {
-
-	private byte[] peerId;
-
-	public PeerIdMessage(byte[] peerId) {
-		this(-1, peerId);
-	}
-
-	private PeerIdMessage(int id, byte[] peerId) {
-		super(id, MessageType.PEER_ID);
-
-		this.peerId = peerId;
-	}
-
-	public byte[] getPeerId() {
-		return this.peerId;
-	}
-
-	public static Message fromByteBuffer(int id, ByteBuffer bytes) throws UnsupportedEncodingException {
-		if (bytes.remaining() != Network.PEER_ID_LENGTH)
-			return null;
-
-		byte[] peerId = new byte[Network.PEER_ID_LENGTH];
-
-		bytes.get(peerId);
-
-		return new PeerIdMessage(id, peerId);
-	}
-
-	@Override
-	protected byte[] toData() {
-		try {
-			ByteArrayOutputStream bytes = new ByteArrayOutputStream();
-
-			bytes.write(this.peerId);
-
-			return bytes.toByteArray();
-		} catch (IOException e) {
-			return null;
-		}
-	}
-
-}

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

@@ -1,51 +0,0 @@
-package org.qortal.network.message;
-
-import java.io.ByteArrayOutputStream;
-import java.io.IOException;
-import java.io.UnsupportedEncodingException;
-import java.nio.ByteBuffer;
-
-import org.qortal.network.Network;
-
-public class PeerVerifyMessage extends Message {
-
-	private byte[] verificationCode;
-
-	public PeerVerifyMessage(byte[] verificationCode) {
-		this(-1, verificationCode);
-	}
-
-	private PeerVerifyMessage(int id, byte[] verificationCode) {
-		super(id, MessageType.PEER_VERIFY);
-
-		this.verificationCode = verificationCode;
-	}
-
-	public byte[] getVerificationCode() {
-		return this.verificationCode;
-	}
-
-	public static Message fromByteBuffer(int id, ByteBuffer bytes) throws UnsupportedEncodingException {
-		if (bytes.remaining() != Network.PEER_ID_LENGTH)
-			return null;
-
-		byte[] verificationCode = new byte[Network.PEER_ID_LENGTH];
-		bytes.get(verificationCode);
-
-		return new PeerVerifyMessage(id, verificationCode);
-	}
-
-	@Override
-	protected byte[] toData() {
-		try {
-			ByteArrayOutputStream bytes = new ByteArrayOutputStream();
-
-			bytes.write(this.verificationCode);
-
-			return bytes.toByteArray();
-		} catch (IOException e) {
-			return null;
-		}
-	}
-
-}

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

@@ -1,79 +0,0 @@
-package org.qortal.network.message;
-
-import java.io.ByteArrayOutputStream;
-import java.io.IOException;
-import java.io.UnsupportedEncodingException;
-import java.net.Inet6Address;
-import java.net.InetAddress;
-import java.net.UnknownHostException;
-import java.nio.ByteBuffer;
-import java.util.ArrayList;
-import java.util.List;
-
-import com.google.common.primitives.Ints;
-
-// NOTE: this legacy message only supports 4-byte IPv4 addresses and doesn't send port number either
-public class PeersMessage extends Message {
-
-	private static final int ADDRESS_LENGTH = 4;
-
-	private List<InetAddress> peerAddresses;
-
-	public PeersMessage(List<InetAddress> peerAddresses) {
-		super(MessageType.PEERS);
-
-		this.peerAddresses = new ArrayList<>(peerAddresses);
-
-		// Legacy PEERS message doesn't support IPv6
-		this.peerAddresses.removeIf(address -> address instanceof Inet6Address);
-	}
-
-	private PeersMessage(int id, List<InetAddress> peerAddresses) {
-		super(id, MessageType.PEERS);
-
-		this.peerAddresses = peerAddresses;
-	}
-
-	public List<InetAddress> getPeerAddresses() {
-		return this.peerAddresses;
-	}
-
-	public static Message fromByteBuffer(int id, ByteBuffer bytes) throws UnsupportedEncodingException {
-		int count = bytes.getInt();
-
-		if (bytes.remaining() != count * ADDRESS_LENGTH)
-			return null;
-
-		List<InetAddress> peerAddresses = new ArrayList<>();
-
-		byte[] addressBytes = new byte[ADDRESS_LENGTH];
-
-		try {
-			for (int i = 0; i < count; ++i) {
-				bytes.get(addressBytes);
-				peerAddresses.add(InetAddress.getByAddress(addressBytes));
-			}
-		} catch (UnknownHostException e) {
-			return null;
-		}
-
-		return new PeersMessage(id, peerAddresses);
-	}
-
-	@Override
-	protected byte[] toData() {
-		try {
-			ByteArrayOutputStream bytes = new ByteArrayOutputStream();
-
-			bytes.write(Ints.toByteArray(this.peerAddresses.size()));
-
-			for (InetAddress peerAddress : this.peerAddresses)
-				bytes.write(peerAddress.getAddress());
-
-			return bytes.toByteArray();
-		} catch (IOException e) {
-			return null;
-		}
-	}
-
-}

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

@@ -1,63 +0,0 @@
-package org.qortal.network.message;
-
-import java.io.ByteArrayOutputStream;
-import java.io.IOException;
-import java.io.UnsupportedEncodingException;
-import java.nio.ByteBuffer;
-
-import com.google.common.primitives.Longs;
-
-public class ProofMessage extends Message {
-
-	private long timestamp;
-	private long salt;
-	private long nonce;
-
-	public ProofMessage(long timestamp, long salt, long nonce) {
-		this(-1, timestamp, salt, nonce);
-	}
-
-	private ProofMessage(int id, long timestamp, long salt, long nonce) {
-		super(id, MessageType.PROOF);
-
-		this.timestamp = timestamp;
-		this.salt = salt;
-		this.nonce = nonce;
-	}
-
-	public long getTimestamp() {
-		return this.timestamp;
-	}
-
-	public long getSalt() {
-		return this.salt;
-	}
-
-	public long getNonce() {
-		return this.nonce;
-	}
-
-	public static Message fromByteBuffer(int id, ByteBuffer bytes) throws UnsupportedEncodingException {
-		long timestamp = bytes.getLong();
-		long salt = bytes.getLong();
-		long nonce = bytes.getLong();
-
-		return new ProofMessage(id, timestamp, salt, nonce);
-	}
-
-	@Override
-	protected byte[] toData() {
-		try {
-			ByteArrayOutputStream bytes = new ByteArrayOutputStream();
-
-			bytes.write(Longs.toByteArray(this.timestamp));
-			bytes.write(Longs.toByteArray(this.salt));
-			bytes.write(Longs.toByteArray(this.nonce));
-
-			return bytes.toByteArray();
-		} catch (IOException e) {
-			return null;
-		}
-	}
-
-}

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

@@ -0,0 +1,55 @@
+package org.qortal.network.message;
+
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.nio.ByteBuffer;
+
+import com.google.common.primitives.Ints;
+
+public class ResponseMessage extends Message {
+
+	public static final int DATA_LENGTH = 32;
+
+	private final int nonce;
+	private final byte[] data;
+
+	private ResponseMessage(int id, int nonce, byte[] data) {
+		super(id, MessageType.RESPONSE);
+
+		this.nonce = nonce;
+		this.data = data;
+	}
+
+	public ResponseMessage(int nonce, byte[] data) {
+		this(-1, nonce, data);
+	}
+
+	public int getNonce() {
+		return this.nonce;
+	}
+
+	public byte[] getData() {
+		return this.data;
+	}
+
+	public static Message fromByteBuffer(int id, ByteBuffer byteBuffer) {
+		int nonce = byteBuffer.getInt();
+
+		byte[] data = new byte[DATA_LENGTH];
+		byteBuffer.get(data);
+
+		return new ResponseMessage(id, nonce, data);
+	}
+
+	@Override
+	protected byte[] toData() throws IOException {
+		ByteArrayOutputStream bytes = new ByteArrayOutputStream(4 + DATA_LENGTH);
+
+		bytes.write(Ints.toByteArray(this.nonce));
+
+		bytes.write(data);
+
+		return bytes.toByteArray();
+	}
+
+}

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

@@ -1,64 +0,0 @@
-package org.qortal.network.message;
-
-import java.io.ByteArrayOutputStream;
-import java.io.IOException;
-import java.io.UnsupportedEncodingException;
-import java.nio.ByteBuffer;
-
-import org.qortal.network.Network;
-
-public class VerificationCodesMessage extends Message {
-
-	private static final int TOTAL_LENGTH = Network.PEER_ID_LENGTH + Network.PEER_ID_LENGTH;
-
-	private byte[] verificationCodeSent;
-	private byte[] verificationCodeExpected;
-
-	public VerificationCodesMessage(byte[] verificationCodeSent, byte[] verificationCodeExpected) {
-		this(-1, verificationCodeSent, verificationCodeExpected);
-	}
-
-	private VerificationCodesMessage(int id, byte[] verificationCodeSent, byte[] verificationCodeExpected) {
-		super(id, MessageType.VERIFICATION_CODES);
-
-		this.verificationCodeSent = verificationCodeSent;
-		this.verificationCodeExpected = verificationCodeExpected;
-	}
-
-	public byte[] getVerificationCodeSent() {
-		return this.verificationCodeSent;
-	}
-
-	public byte[] getVerificationCodeExpected() {
-		return this.verificationCodeExpected;
-	}
-
-	public static Message fromByteBuffer(int id, ByteBuffer bytes) throws UnsupportedEncodingException {
-		if (bytes.remaining() != TOTAL_LENGTH)
-			return null;
-
-		byte[] verificationCodeSent = new byte[Network.PEER_ID_LENGTH];
-		bytes.get(verificationCodeSent);
-
-		byte[] verificationCodeExpected = new byte[Network.PEER_ID_LENGTH];
-		bytes.get(verificationCodeExpected);
-
-		return new VerificationCodesMessage(id, verificationCodeSent, verificationCodeExpected);
-	}
-
-	@Override
-	protected byte[] toData() {
-		try {
-			ByteArrayOutputStream bytes = new ByteArrayOutputStream();
-
-			bytes.write(this.verificationCodeSent);
-
-			bytes.write(this.verificationCodeExpected);
-
-			return bytes.toByteArray();
-		} catch (IOException e) {
-			return null;
-		}
-	}
-
-}

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

@@ -1,68 +0,0 @@
-package org.qortal.network.message;
-
-import java.io.ByteArrayOutputStream;
-import java.io.IOException;
-import java.io.UnsupportedEncodingException;
-import java.nio.ByteBuffer;
-import java.nio.charset.StandardCharsets;
-
-import org.qortal.utils.Serialization;
-
-import com.google.common.primitives.Longs;
-
-public class VersionMessage extends Message {
-
-	private long buildTimestamp;
-	private String versionString;
-
-	public VersionMessage(long buildTimestamp, String versionString) {
-		this(-1, buildTimestamp, versionString);
-	}
-
-	private VersionMessage(int id, long buildTimestamp, String versionString) {
-		super(id, MessageType.VERSION);
-
-		this.buildTimestamp = buildTimestamp;
-		this.versionString = versionString;
-	}
-
-	public long getBuildTimestamp() {
-		return this.buildTimestamp;
-	}
-
-	public String getVersionString() {
-		return this.versionString;
-	}
-
-	public static Message fromByteBuffer(int id, ByteBuffer bytes) throws UnsupportedEncodingException {
-		long buildTimestamp = bytes.getLong();
-
-		int versionStringLength = bytes.getInt();
-
-		if (versionStringLength != bytes.remaining())
-			return null;
-
-		byte[] versionBytes = new byte[versionStringLength];
-		bytes.get(versionBytes);
-
-		String versionString = new String(versionBytes, StandardCharsets.UTF_8);
-
-		return new VersionMessage(id, buildTimestamp, versionString);
-	}
-
-	@Override
-	protected byte[] toData() {
-		try {
-			ByteArrayOutputStream bytes = new ByteArrayOutputStream();
-
-			bytes.write(Longs.toByteArray(this.buildTimestamp));
-
-			Serialization.serializeSizedString(bytes, this.versionString);
-
-			return bytes.toByteArray();
-		} catch (IOException e) {
-			return null;
-		}
-	}
-
-}