Merge branch 'multiple-transport-keys' into 'master'

Support multiple sets of transport keys per contact

See merge request akwizgran/briar!745

bramble-core/src/main/java/org/briarproject/bramble/contact/ContactManagerImpl.java

@@ -50,7 +50,7 @@ class ContactManagerImpl implements ContactManager {
 
 	@Override
 	public ContactId addContact(Transaction txn, Author remote, AuthorId local,
-			SecretKey master,long timestamp, boolean alice, boolean verified,
+			SecretKey master, long timestamp, boolean alice, boolean verified,
 			boolean active) throws DbException {
 		ContactId c = db.addContact(txn, remote, local, verified, active);
 		keyManager.addContact(txn, c, master, timestamp, alice);
@@ -60,6 +60,16 @@ class ContactManagerImpl implements ContactManager {
 		return c;
 	}
 
+	@Override
+	public ContactId addContact(Transaction txn, Author remote, AuthorId local,
+			boolean verified, boolean active) throws DbException {
+		ContactId c = db.addContact(txn, remote, local, verified, active);
+		Contact contact = db.getContact(txn, c);
+		for (AddContactHook hook : addHooks)
+			hook.addingContact(txn, contact);
+		return c;
+	}
+
 	@Override
 	public ContactId addContact(Author remote, AuthorId local, SecretKey master,
 			long timestamp, boolean alice, boolean verified, boolean active)

bramble-core/src/main/java/org/briarproject/bramble/crypto/TransportCryptoImpl.java

@@ -36,7 +36,8 @@ class TransportCryptoImpl implements TransportCrypto {
 
 	@Override
 	public TransportKeys deriveTransportKeys(TransportId t,
-			SecretKey master, long rotationPeriod, boolean alice) {
+			SecretKey master, long rotationPeriod, boolean alice,
+			boolean active) {
 		// Keys for the previous period are derived from the master secret
 		SecretKey inTagPrev = deriveTagKey(master, t, !alice);
 		SecretKey inHeaderPrev = deriveHeaderKey(master, t, !alice);
@@ -57,7 +58,7 @@ class TransportCryptoImpl implements TransportCrypto {
 		IncomingKeys inNext = new IncomingKeys(inTagNext, inHeaderNext,
 				rotationPeriod + 1);
 		OutgoingKeys outCurr = new OutgoingKeys(outTagCurr, outHeaderCurr,
-				rotationPeriod);
+				rotationPeriod, active);
 		// Collect and return the keys
 		return new TransportKeys(t, inPrev, inCurr, inNext, outCurr);
 	}
@@ -71,6 +72,7 @@ class TransportCryptoImpl implements TransportCrypto {
 		IncomingKeys inNext = k.getNextIncomingKeys();
 		OutgoingKeys outCurr = k.getCurrentOutgoingKeys();
 		long startPeriod = outCurr.getRotationPeriod();
+		boolean active = outCurr.isActive();
 		// Rotate the keys
 		for (long p = startPeriod + 1; p <= rotationPeriod; p++) {
 			inPrev = inCurr;
@@ -80,7 +82,7 @@ class TransportCryptoImpl implements TransportCrypto {
 			inNext = new IncomingKeys(inNextTag, inNextHeader, p + 1);
 			SecretKey outCurrTag = rotateKey(outCurr.getTagKey(), p);
 			SecretKey outCurrHeader = rotateKey(outCurr.getHeaderKey(), p);
-			outCurr = new OutgoingKeys(outCurrTag, outCurrHeader, p);
+			outCurr = new OutgoingKeys(outCurrTag, outCurrHeader, p, active);
 		}
 		// Collect and return the keys
 		return new TransportKeys(k.getTransportId(), inPrev, inCurr, inNext,

bramble-core/src/main/java/org/briarproject/bramble/db/Database.java

@@ -21,6 +21,8 @@ import org.briarproject.bramble.api.sync.Message;
 import org.briarproject.bramble.api.sync.MessageId;
 import org.briarproject.bramble.api.sync.MessageStatus;
 import org.briarproject.bramble.api.sync.ValidationManager.State;
+import org.briarproject.bramble.api.transport.KeySet;
+import org.briarproject.bramble.api.transport.KeySetId;
 import org.briarproject.bramble.api.transport.TransportKeys;
 
 import java.util.Collection;
@@ -123,9 +125,16 @@ interface Database<T> {
 			throws DbException;
 
 	/**
-	 * Stores transport keys for a newly added contact.
+	 * Stores the given transport keys, optionally binding them to the given
+	 * contact, and returns a key set ID.
 	 */
-	void addTransportKeys(T txn, ContactId c, TransportKeys k)
+	KeySetId addTransportKeys(T txn, @Nullable ContactId c, TransportKeys k)
+			throws DbException;
+
+	/**
+	 * Binds the given keys for the given transport to the given contact.
+	 */
+	void bindTransportKeys(T txn, ContactId c, TransportId t, KeySetId k)
 			throws DbException;
 
 	/**
@@ -486,15 +495,14 @@ interface Database<T> {
 	 * <p/>
 	 * Read-only.
 	 */
-	Map<ContactId, TransportKeys> getTransportKeys(T txn, TransportId t)
+	Collection<KeySet> getTransportKeys(T txn, TransportId t)
 			throws DbException;
 
 	/**
-	 * Increments the outgoing stream counter for the given contact and
-	 * transport in the given rotation period.
+	 * Increments the outgoing stream counter for the given transport keys.
 	 */
-	void incrementStreamCounter(T txn, ContactId c, TransportId t,
-			long rotationPeriod) throws DbException;
+	void incrementStreamCounter(T txn, TransportId t, KeySetId k)
+			throws DbException;
 
 	/**
 	 * Marks the given messages as not needing to be acknowledged to the
@@ -584,6 +592,12 @@ interface Database<T> {
 	 */
 	void removeTransport(T txn, TransportId t) throws DbException;
 
+	/**
+	 * Removes the given transport keys from the database.
+	 */
+	void removeTransportKeys(T txn, TransportId t, KeySetId k)
+			throws DbException;
+
 	/**
 	 * Resets the transmission count and expiry time of the given message with
 	 * respect to the given contact.
@@ -619,12 +633,18 @@ interface Database<T> {
 	void setMessageState(T txn, MessageId m, State state) throws DbException;
 
 	/**
-	 * Sets the reordering window for the given contact and transport in the
+	 * Sets the reordering window for the given key set and transport in the
 	 * given rotation period.
 	 */
-	void setReorderingWindow(T txn, ContactId c, TransportId t,
+	void setReorderingWindow(T txn, KeySetId k, TransportId t,
 			long rotationPeriod, long base, byte[] bitmap) throws DbException;
 
+	/**
+	 * Marks the given transport keys as usable for outgoing streams.
+	 */
+	void setTransportKeysActive(T txn, TransportId t, KeySetId k)
+		throws DbException;
+
 	/**
 	 * Updates the transmission count and expiry time of the given message
 	 * with respect to the given contact, using the latency of the transport
@@ -636,6 +656,5 @@ interface Database<T> {
 	/**
 	 * Stores the given transport keys, deleting any keys they have replaced.
 	 */
-	void updateTransportKeys(T txn, Map<ContactId, TransportKeys> keys)
-			throws DbException;
+	void updateTransportKeys(T txn, Collection<KeySet> keys) throws DbException;
 }

bramble-core/src/main/java/org/briarproject/bramble/db/DatabaseComponentImpl.java

@@ -51,15 +51,15 @@ import org.briarproject.bramble.api.sync.event.MessageToAckEvent;
 import org.briarproject.bramble.api.sync.event.MessageToRequestEvent;
 import org.briarproject.bramble.api.sync.event.MessagesAckedEvent;
 import org.briarproject.bramble.api.sync.event.MessagesSentEvent;
+import org.briarproject.bramble.api.transport.KeySet;
+import org.briarproject.bramble.api.transport.KeySetId;
 import org.briarproject.bramble.api.transport.TransportKeys;
 
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
-import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
-import java.util.Map.Entry;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.locks.ReentrantReadWriteLock;
 import java.util.logging.Logger;
@@ -234,15 +234,27 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 	}
 
 	@Override
-	public void addTransportKeys(Transaction transaction, ContactId c,
-			TransportKeys k) throws DbException {
+	public KeySetId addTransportKeys(Transaction transaction,
+			@Nullable ContactId c, TransportKeys k) throws DbException {
+		if (transaction.isReadOnly()) throw new IllegalArgumentException();
+		T txn = unbox(transaction);
+		if (c != null && !db.containsContact(txn, c))
+			throw new NoSuchContactException();
+		if (!db.containsTransport(txn, k.getTransportId()))
+			throw new NoSuchTransportException();
+		return db.addTransportKeys(txn, c, k);
+	}
+
+	@Override
+	public void bindTransportKeys(Transaction transaction, ContactId c,
+			TransportId t, KeySetId k) throws DbException {
 		if (transaction.isReadOnly()) throw new IllegalArgumentException();
 		T txn = unbox(transaction);
 		if (!db.containsContact(txn, c))
 			throw new NoSuchContactException();
-		if (!db.containsTransport(txn, k.getTransportId()))
+		if (!db.containsTransport(txn, t))
 			throw new NoSuchTransportException();
-		db.addTransportKeys(txn, c, k);
+		db.bindTransportKeys(txn, c, t, k);
 	}
 
 	@Override
@@ -586,8 +598,8 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 	}
 
 	@Override
-	public Map<ContactId, TransportKeys> getTransportKeys(
-			Transaction transaction, TransportId t) throws DbException {
+	public Collection<KeySet> getTransportKeys(Transaction transaction,
+			TransportId t) throws DbException {
 		T txn = unbox(transaction);
 		if (!db.containsTransport(txn, t))
 			throw new NoSuchTransportException();
@@ -595,15 +607,13 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 	}
 
 	@Override
-	public void incrementStreamCounter(Transaction transaction, ContactId c,
-			TransportId t, long rotationPeriod) throws DbException {
+	public void incrementStreamCounter(Transaction transaction, TransportId t,
+			KeySetId k) throws DbException {
 		if (transaction.isReadOnly()) throw new IllegalArgumentException();
 		T txn = unbox(transaction);
-		if (!db.containsContact(txn, c))
-			throw new NoSuchContactException();
 		if (!db.containsTransport(txn, t))
 			throw new NoSuchTransportException();
-		db.incrementStreamCounter(txn, c, t, rotationPeriod);
+		db.incrementStreamCounter(txn, t, k);
 	}
 
 	@Override
@@ -779,6 +789,16 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 		db.removeTransport(txn, t);
 	}
 
+	@Override
+	public void removeTransportKeys(Transaction transaction,
+			TransportId t, KeySetId k) throws DbException {
+		if (transaction.isReadOnly()) throw new IllegalArgumentException();
+		T txn = unbox(transaction);
+		if (!db.containsTransport(txn, t))
+			throw new NoSuchTransportException();
+		db.removeTransportKeys(txn, t, k);
+	}
+
 	@Override
 	public void setContactVerified(Transaction transaction, ContactId c)
 			throws DbException {
@@ -858,31 +878,35 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 	}
 
 	@Override
-	public void setReorderingWindow(Transaction transaction, ContactId c,
+	public void setReorderingWindow(Transaction transaction, KeySetId k,
 			TransportId t, long rotationPeriod, long base, byte[] bitmap)
 			throws DbException {
 		if (transaction.isReadOnly()) throw new IllegalArgumentException();
 		T txn = unbox(transaction);
-		if (!db.containsContact(txn, c))
-			throw new NoSuchContactException();
 		if (!db.containsTransport(txn, t))
 			throw new NoSuchTransportException();
-		db.setReorderingWindow(txn, c, t, rotationPeriod, base, bitmap);
+		db.setReorderingWindow(txn, k, t, rotationPeriod, base, bitmap);
+	}
+
+	@Override
+	public void setTransportKeysActive(Transaction transaction, TransportId t,
+			KeySetId k) throws DbException {
+		if (transaction.isReadOnly()) throw new IllegalArgumentException();
+		T txn = unbox(transaction);
+		if (!db.containsTransport(txn, t))
+			throw new NoSuchTransportException();
+		db.setTransportKeysActive(txn, t, k);
 	}
 
 	@Override
 	public void updateTransportKeys(Transaction transaction,
-			Map<ContactId, TransportKeys> keys) throws DbException {
+			Collection<KeySet> keys) throws DbException {
 		if (transaction.isReadOnly()) throw new IllegalArgumentException();
 		T txn = unbox(transaction);
-		Map<ContactId, TransportKeys> filtered = new HashMap<>();
-		for (Entry<ContactId, TransportKeys> e : keys.entrySet()) {
-			ContactId c = e.getKey();
-			TransportKeys k = e.getValue();
-			if (db.containsContact(txn, c)
-					&& db.containsTransport(txn, k.getTransportId())) {
-				filtered.put(c, k);
-			}
+		Collection<KeySet> filtered = new ArrayList<>();
+		for (KeySet ks : keys) {
+			TransportId t = ks.getTransportKeys().getTransportId();
+			if (db.containsTransport(txn, t)) filtered.add(ks);
 		}
 		db.updateTransportKeys(txn, filtered);
 	}

bramble-core/src/main/java/org/briarproject/bramble/db/JdbcDatabase.java

@@ -25,6 +25,8 @@ import org.briarproject.bramble.api.sync.MessageStatus;
 import org.briarproject.bramble.api.sync.ValidationManager.State;
 import org.briarproject.bramble.api.system.Clock;
 import org.briarproject.bramble.api.transport.IncomingKeys;
+import org.briarproject.bramble.api.transport.KeySet;
+import org.briarproject.bramble.api.transport.KeySetId;
 import org.briarproject.bramble.api.transport.OutgoingKeys;
 import org.briarproject.bramble.api.transport.TransportKeys;
 
@@ -223,37 +225,44 @@ abstract class JdbcDatabase implements Database<Connection> {
 					+ " maxLatency INT NOT NULL,"
 					+ " PRIMARY KEY (transportId))";
 
+	private static final String CREATE_OUTGOING_KEYS =
+			"CREATE TABLE outgoingKeys"
+					+ " (transportId _STRING NOT NULL,"
+					+ " keySetId _COUNTER,"
+					+ " rotationPeriod BIGINT NOT NULL,"
+					+ " contactId INT," // Null if keys are not bound
+					+ " tagKey _SECRET NOT NULL,"
+					+ " headerKey _SECRET NOT NULL,"
+					+ " stream BIGINT NOT NULL,"
+					+ " active BOOLEAN NOT NULL,"
+					+ " PRIMARY KEY (transportId, keySetId),"
+					+ " FOREIGN KEY (transportId)"
+					+ " REFERENCES transports (transportId)"
+					+ " ON DELETE CASCADE,"
+					+ " UNIQUE (keySetId),"
+					+ " FOREIGN KEY (contactId)"
+					+ " REFERENCES contacts (contactId)"
+					+ " ON DELETE CASCADE)";
+
 	private static final String CREATE_INCOMING_KEYS =
 			"CREATE TABLE incomingKeys"
-					+ " (contactId INT NOT NULL,"
-					+ " transportId _STRING NOT NULL,"
+					+ " (transportId _STRING NOT NULL,"
+					+ " keySetId INT NOT NULL,"
 					+ " rotationPeriod BIGINT NOT NULL,"
+					+ " contactId INT," // Null if keys are not bound
 					+ " tagKey _SECRET NOT NULL,"
 					+ " headerKey _SECRET NOT NULL,"
 					+ " base BIGINT NOT NULL,"
 					+ " bitmap _BINARY NOT NULL,"
-					+ " PRIMARY KEY (contactId, transportId, rotationPeriod),"
-					+ " FOREIGN KEY (contactId)"
-					+ " REFERENCES contacts (contactId)"
-					+ " ON DELETE CASCADE,"
+					+ " PRIMARY KEY (transportId, keySetId, rotationPeriod),"
 					+ " FOREIGN KEY (transportId)"
 					+ " REFERENCES transports (transportId)"
-					+ " ON DELETE CASCADE)";
-
-	private static final String CREATE_OUTGOING_KEYS =
-			"CREATE TABLE outgoingKeys"
-					+ " (contactId INT NOT NULL,"
-					+ " transportId _STRING NOT NULL,"
-					+ " rotationPeriod BIGINT NOT NULL,"
-					+ " tagKey _SECRET NOT NULL,"
-					+ " headerKey _SECRET NOT NULL,"
-					+ " stream BIGINT NOT NULL,"
-					+ " PRIMARY KEY (contactId, transportId),"
+					+ " ON DELETE CASCADE,"
+					+ " FOREIGN KEY (keySetId)"
+					+ " REFERENCES outgoingKeys (keySetId)"
+					+ " ON DELETE CASCADE,"
 					+ " FOREIGN KEY (contactId)"
 					+ " REFERENCES contacts (contactId)"
-					+ " ON DELETE CASCADE,"
-					+ " FOREIGN KEY (transportId)"
-					+ " REFERENCES transports (transportId)"
 					+ " ON DELETE CASCADE)";
 
 	private static final String INDEX_CONTACTS_BY_AUTHOR_ID =
@@ -415,8 +424,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			s.executeUpdate(insertTypeNames(CREATE_OFFERS));
 			s.executeUpdate(insertTypeNames(CREATE_STATUSES));
 			s.executeUpdate(insertTypeNames(CREATE_TRANSPORTS));
-			s.executeUpdate(insertTypeNames(CREATE_INCOMING_KEYS));
 			s.executeUpdate(insertTypeNames(CREATE_OUTGOING_KEYS));
+			s.executeUpdate(insertTypeNames(CREATE_INCOMING_KEYS));
 			s.close();
 		} catch (SQLException e) {
 			tryToClose(s);
@@ -865,61 +874,105 @@ abstract class JdbcDatabase implements Database<Connection> {
 	}
 
 	@Override
-	public void addTransportKeys(Connection txn, ContactId c, TransportKeys k)
-			throws DbException {
+	public KeySetId addTransportKeys(Connection txn, @Nullable ContactId c,
+			TransportKeys k) throws DbException {
 		PreparedStatement ps = null;
+		ResultSet rs = null;
 		try {
-			// Store the incoming keys
-			String sql = "INSERT INTO incomingKeys (contactId, transportId,"
-					+ " rotationPeriod, tagKey, headerKey, base, bitmap)"
+			// Store the outgoing keys
+			String sql = "INSERT INTO outgoingKeys (contactId, transportId,"
+					+ " rotationPeriod, tagKey, headerKey, stream, active)"
 					+ " VALUES (?, ?, ?, ?, ?, ?, ?)";
 			ps = txn.prepareStatement(sql);
-			ps.setInt(1, c.getInt());
-			ps.setString(2, k.getTransportId().getString());
-			// Previous rotation period
-			IncomingKeys inPrev = k.getPreviousIncomingKeys();
-			ps.setLong(3, inPrev.getRotationPeriod());
-			ps.setBytes(4, inPrev.getTagKey().getBytes());
-			ps.setBytes(5, inPrev.getHeaderKey().getBytes());
-			ps.setLong(6, inPrev.getWindowBase());
-			ps.setBytes(7, inPrev.getWindowBitmap());
-			ps.addBatch();
-			// Current rotation period
-			IncomingKeys inCurr = k.getCurrentIncomingKeys();
-			ps.setLong(3, inCurr.getRotationPeriod());
-			ps.setBytes(4, inCurr.getTagKey().getBytes());
-			ps.setBytes(5, inCurr.getHeaderKey().getBytes());
-			ps.setLong(6, inCurr.getWindowBase());
-			ps.setBytes(7, inCurr.getWindowBitmap());
-			ps.addBatch();
-			// Next rotation period
-			IncomingKeys inNext = k.getNextIncomingKeys();
-			ps.setLong(3, inNext.getRotationPeriod());
-			ps.setBytes(4, inNext.getTagKey().getBytes());
-			ps.setBytes(5, inNext.getHeaderKey().getBytes());
-			ps.setLong(6, inNext.getWindowBase());
-			ps.setBytes(7, inNext.getWindowBitmap());
-			ps.addBatch();
-			int[] batchAffected = ps.executeBatch();
-			if (batchAffected.length != 3) throw new DbStateException();
-			for (int rows : batchAffected)
-				if (rows != 1) throw new DbStateException();
-			ps.close();
-			// Store the outgoing keys
-			sql = "INSERT INTO outgoingKeys (contactId, transportId,"
-					+ " rotationPeriod, tagKey, headerKey, stream)"
-					+ " VALUES (?, ?, ?, ?, ?, ?)";
-			ps = txn.prepareStatement(sql);
-			ps.setInt(1, c.getInt());
+			if (c == null) ps.setNull(1, INTEGER);
+			else ps.setInt(1, c.getInt());
 			ps.setString(2, k.getTransportId().getString());
 			OutgoingKeys outCurr = k.getCurrentOutgoingKeys();
 			ps.setLong(3, outCurr.getRotationPeriod());
 			ps.setBytes(4, outCurr.getTagKey().getBytes());
 			ps.setBytes(5, outCurr.getHeaderKey().getBytes());
 			ps.setLong(6, outCurr.getStreamCounter());
+			ps.setBoolean(7, outCurr.isActive());
 			int affected = ps.executeUpdate();
 			if (affected != 1) throw new DbStateException();
 			ps.close();
+			// Get the new (highest) key set ID
+			sql = "SELECT keySetId FROM outgoingKeys"
+					+ " ORDER BY keySetId DESC LIMIT 1";
+			ps = txn.prepareStatement(sql);
+			rs = ps.executeQuery();
+			if (!rs.next()) throw new DbStateException();
+			KeySetId keySetId = new KeySetId(rs.getInt(1));
+			if (rs.next()) throw new DbStateException();
+			rs.close();
+			ps.close();
+			// Store the incoming keys
+			sql = "INSERT INTO incomingKeys (keySetId, contactId, transportId,"
+					+ " rotationPeriod, tagKey, headerKey, base, bitmap)"
+					+ " VALUES (?, ?, ?, ?, ?, ?, ?, ?)";
+			ps = txn.prepareStatement(sql);
+			ps.setInt(1, keySetId.getInt());
+			if (c == null) ps.setNull(2, INTEGER);
+			else ps.setInt(2, c.getInt());
+			ps.setString(3, k.getTransportId().getString());
+			// Previous rotation period
+			IncomingKeys inPrev = k.getPreviousIncomingKeys();
+			ps.setLong(4, inPrev.getRotationPeriod());
+			ps.setBytes(5, inPrev.getTagKey().getBytes());
+			ps.setBytes(6, inPrev.getHeaderKey().getBytes());
+			ps.setLong(7, inPrev.getWindowBase());
+			ps.setBytes(8, inPrev.getWindowBitmap());
+			ps.addBatch();
+			// Current rotation period
+			IncomingKeys inCurr = k.getCurrentIncomingKeys();
+			ps.setLong(4, inCurr.getRotationPeriod());
+			ps.setBytes(5, inCurr.getTagKey().getBytes());
+			ps.setBytes(6, inCurr.getHeaderKey().getBytes());
+			ps.setLong(7, inCurr.getWindowBase());
+			ps.setBytes(8, inCurr.getWindowBitmap());
+			ps.addBatch();
+			// Next rotation period
+			IncomingKeys inNext = k.getNextIncomingKeys();
+			ps.setLong(4, inNext.getRotationPeriod());
+			ps.setBytes(5, inNext.getTagKey().getBytes());
+			ps.setBytes(6, inNext.getHeaderKey().getBytes());
+			ps.setLong(7, inNext.getWindowBase());
+			ps.setBytes(8, inNext.getWindowBitmap());
+			ps.addBatch();
+			int[] batchAffected = ps.executeBatch();
+			if (batchAffected.length != 3) throw new DbStateException();
+			for (int rows : batchAffected)
+				if (rows != 1) throw new DbStateException();
+			ps.close();
+			return keySetId;
+		} catch (SQLException e) {
+			tryToClose(rs);
+			tryToClose(ps);
+			throw new DbException(e);
+		}
+	}
+
+	@Override
+	public void bindTransportKeys(Connection txn, ContactId c, TransportId t,
+			KeySetId k) throws DbException {
+		PreparedStatement ps = null;
+		try {
+			String sql = "UPDATE outgoingKeys SET contactId = ?"
+					+ " WHERE keySetId = ?";
+			ps = txn.prepareStatement(sql);
+			ps.setInt(1, c.getInt());
+			ps.setInt(2, k.getInt());
+			int affected = ps.executeUpdate();
+			if (affected < 0) throw new DbStateException();
+			ps.close();
+			sql = "UPDATE incomingKeys SET contactId = ?"
+					+ " WHERE keySetId = ?";
+			ps = txn.prepareStatement(sql);
+			ps.setInt(1, c.getInt());
+			ps.setInt(2, k.getInt());
+			affected = ps.executeUpdate();
+			if (affected < 0) throw new DbStateException();
+			ps.close();
 		} catch (SQLException e) {
 			tryToClose(ps);
 			throw new DbException(e);
@@ -2078,8 +2131,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 	}
 
 	@Override
-	public Map<ContactId, TransportKeys> getTransportKeys(Connection txn,
-			TransportId t) throws DbException {
+	public Collection<KeySet> getTransportKeys(Connection txn, TransportId t)
+			throws DbException {
 		PreparedStatement ps = null;
 		ResultSet rs = null;
 		try {
@@ -2088,7 +2141,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 					+ " base, bitmap"
 					+ " FROM incomingKeys"
 					+ " WHERE transportId = ?"
-					+ " ORDER BY contactId, rotationPeriod";
+					+ " ORDER BY keySetId, rotationPeriod";
 			ps = txn.prepareStatement(sql);
 			ps.setString(1, t.getString());
 			rs = ps.executeQuery();
@@ -2105,29 +2158,34 @@ abstract class JdbcDatabase implements Database<Connection> {
 			rs.close();
 			ps.close();
 			// Retrieve the outgoing keys in the same order
-			sql = "SELECT contactId, rotationPeriod, tagKey, headerKey, stream"
+			sql = "SELECT keySetId, contactId, rotationPeriod,"
+					+ " tagKey, headerKey, stream, active"
 					+ " FROM outgoingKeys"
 					+ " WHERE transportId = ?"
-					+ " ORDER BY contactId, rotationPeriod";
+					+ " ORDER BY keySetId";
 			ps = txn.prepareStatement(sql);
 			ps.setString(1, t.getString());
 			rs = ps.executeQuery();
-			Map<ContactId, TransportKeys> keys = new HashMap<>();
+			Collection<KeySet> keys = new ArrayList<>();
 			for (int i = 0; rs.next(); i++) {
 				// There should be three times as many incoming keys
 				if (inKeys.size() < (i + 1) * 3) throw new DbStateException();
-				ContactId contactId = new ContactId(rs.getInt(1));
-				long rotationPeriod = rs.getLong(2);
-				SecretKey tagKey = new SecretKey(rs.getBytes(3));
-				SecretKey headerKey = new SecretKey(rs.getBytes(4));
-				long streamCounter = rs.getLong(5);
+				KeySetId keySetId = new KeySetId(rs.getInt(1));
+				ContactId contactId = new ContactId(rs.getInt(2));
+				if (rs.wasNull()) contactId = null;
+				long rotationPeriod = rs.getLong(3);
+				SecretKey tagKey = new SecretKey(rs.getBytes(4));
+				SecretKey headerKey = new SecretKey(rs.getBytes(5));
+				long streamCounter = rs.getLong(6);
+				boolean active = rs.getBoolean(7);
 				OutgoingKeys outCurr = new OutgoingKeys(tagKey, headerKey,
-						rotationPeriod, streamCounter);
+						rotationPeriod, streamCounter, active);
 				IncomingKeys inPrev = inKeys.get(i * 3);
 				IncomingKeys inCurr = inKeys.get(i * 3 + 1);
 				IncomingKeys inNext = inKeys.get(i * 3 + 2);
-				keys.put(contactId, new TransportKeys(t, inPrev, inCurr,
-						inNext, outCurr));
+				TransportKeys transportKeys = new TransportKeys(t, inPrev,
+						inCurr, inNext, outCurr);
+				keys.add(new KeySet(keySetId, contactId, transportKeys));
 			}
 			rs.close();
 			ps.close();
@@ -2140,17 +2198,15 @@ abstract class JdbcDatabase implements Database<Connection> {
 	}
 
 	@Override
-	public void incrementStreamCounter(Connection txn, ContactId c,
-			TransportId t, long rotationPeriod) throws DbException {
+	public void incrementStreamCounter(Connection txn, TransportId t,
+			KeySetId k) throws DbException {
 		PreparedStatement ps = null;
 		try {
 			String sql = "UPDATE outgoingKeys SET stream = stream + 1"
-					+ " WHERE contactId = ? AND transportId = ?"
-					+ " AND rotationPeriod = ?";
+					+ " WHERE transportId = ? AND keySetId = ?";
 			ps = txn.prepareStatement(sql);
-			ps.setInt(1, c.getInt());
-			ps.setString(2, t.getString());
-			ps.setLong(3, rotationPeriod);
+			ps.setString(1, t.getString());
+			ps.setInt(2, k.getInt());
 			int affected = ps.executeUpdate();
 			if (affected != 1) throw new DbStateException();
 			ps.close();
@@ -2626,6 +2682,27 @@ abstract class JdbcDatabase implements Database<Connection> {
 		}
 	}
 
+	@Override
+	public void removeTransportKeys(Connection txn, TransportId t, KeySetId k)
+			throws DbException {
+		PreparedStatement ps = null;
+		try {
+			// Delete any existing outgoing keys - this will also remove any
+			// incoming keys with the same key set ID
+			String sql = "DELETE FROM outgoingKeys"
+					+ " WHERE transportId = ? AND keySetId = ?";
+			ps = txn.prepareStatement(sql);
+			ps.setString(1, t.getString());
+			ps.setInt(2, k.getInt());
+			int affected = ps.executeUpdate();
+			if (affected < 0) throw new DbStateException();
+			ps.close();
+		} catch (SQLException e) {
+			tryToClose(ps);
+			throw new DbException(e);
+		}
+	}
+
 	@Override
 	public void resetExpiryTime(Connection txn, ContactId c, MessageId m)
 			throws DbException {
@@ -2791,18 +2868,18 @@ abstract class JdbcDatabase implements Database<Connection> {
 	}
 
 	@Override
-	public void setReorderingWindow(Connection txn, ContactId c, TransportId t,
+	public void setReorderingWindow(Connection txn, KeySetId k, TransportId t,
 			long rotationPeriod, long base, byte[] bitmap) throws DbException {
 		PreparedStatement ps = null;
 		try {
 			String sql = "UPDATE incomingKeys SET base = ?, bitmap = ?"
-					+ " WHERE contactId = ? AND transportId = ?"
+					+ " WHERE transportId = ? AND keySetId = ?"
 					+ " AND rotationPeriod = ?";
 			ps = txn.prepareStatement(sql);
 			ps.setLong(1, base);
 			ps.setBytes(2, bitmap);
-			ps.setInt(3, c.getInt());
-			ps.setString(4, t.getString());
+			ps.setString(3, t.getString());
+			ps.setInt(4, k.getInt());
 			ps.setLong(5, rotationPeriod);
 			int affected = ps.executeUpdate();
 			if (affected < 0 || affected > 1) throw new DbStateException();
@@ -2813,6 +2890,23 @@ abstract class JdbcDatabase implements Database<Connection> {
 		}
 	}
 
+	@Override
+	public void setTransportKeysActive(Connection txn, TransportId t,
+			KeySetId k) throws DbException {
+		PreparedStatement ps = null;
+		try {
+			String sql = "UPDATE outgoingKeys SET active = true"
+					+ " WHERE transportId = ? AND keySetId = ?";
+			ps = txn.prepareStatement(sql);
+			int affected = ps.executeUpdate();
+			if (affected < 0 || affected > 1) throw new DbStateException();
+			ps.close();
+		} catch (SQLException e) {
+			tryToClose(ps);
+			throw new DbException(e);
+		}
+	}
+
 	@Override
 	public void updateExpiryTime(Connection txn, ContactId c, MessageId m,
 			int maxLatency) throws DbException {
@@ -2848,45 +2942,12 @@ abstract class JdbcDatabase implements Database<Connection> {
 	}
 
 	@Override
-	public void updateTransportKeys(Connection txn,
-			Map<ContactId, TransportKeys> keys) throws DbException {
-		PreparedStatement ps = null;
-		try {
-			// Delete any existing incoming keys
-			String sql = "DELETE FROM incomingKeys"
-					+ " WHERE contactId = ?"
-					+ " AND transportId = ?";
-			ps = txn.prepareStatement(sql);
-			for (Entry<ContactId, TransportKeys> e : keys.entrySet()) {
-				ps.setInt(1, e.getKey().getInt());
-				ps.setString(2, e.getValue().getTransportId().getString());
-				ps.addBatch();
-			}
-			int[] batchAffected = ps.executeBatch();
-			if (batchAffected.length != keys.size())
-				throw new DbStateException();
-			ps.close();
-			// Delete any existing outgoing keys
-			sql = "DELETE FROM outgoingKeys"
-					+ " WHERE contactId = ?"
-					+ " AND transportId = ?";
-			ps = txn.prepareStatement(sql);
-			for (Entry<ContactId, TransportKeys> e : keys.entrySet()) {
-				ps.setInt(1, e.getKey().getInt());
-				ps.setString(2, e.getValue().getTransportId().getString());
-				ps.addBatch();
-			}
-			batchAffected = ps.executeBatch();
-			if (batchAffected.length != keys.size())
-				throw new DbStateException();
-			ps.close();
-		} catch (SQLException e) {
-			tryToClose(ps);
-			throw new DbException(e);
-		}
-		// Store the new keys
-		for (Entry<ContactId, TransportKeys> e : keys.entrySet()) {
-			addTransportKeys(txn, e.getKey(), e.getValue());
+	public void updateTransportKeys(Connection txn, Collection<KeySet> keys)
+			throws DbException {
+		for (KeySet ks : keys) {
+			TransportKeys k = ks.getTransportKeys();
+			removeTransportKeys(txn, k.getTransportId(), ks.getKeySetId());
+			addTransportKeys(txn, ks.getContactId(), k);
 		}
 	}
 }

bramble-core/src/main/java/org/briarproject/bramble/transport/KeyManagerImpl.java

@@ -19,6 +19,7 @@ import org.briarproject.bramble.api.plugin.TransportId;
 import org.briarproject.bramble.api.plugin.duplex.DuplexPluginFactory;
 import org.briarproject.bramble.api.plugin.simplex.SimplexPluginFactory;
 import org.briarproject.bramble.api.transport.KeyManager;
+import org.briarproject.bramble.api.transport.KeySetId;
 import org.briarproject.bramble.api.transport.StreamContext;
 
 import java.util.HashMap;
@@ -104,6 +105,67 @@ class KeyManagerImpl implements KeyManager, Service, EventListener {
 			m.addContact(txn, c, master, timestamp, alice);
 	}
 
+	@Override
+	public Map<TransportId, KeySetId> addUnboundKeys(Transaction txn,
+			SecretKey master, long timestamp, boolean alice)
+			throws DbException {
+		Map<TransportId, KeySetId> ids = new HashMap<>();
+		for (Entry<TransportId, TransportKeyManager> e : managers.entrySet()) {
+			TransportId t = e.getKey();
+			TransportKeyManager m = e.getValue();
+			ids.put(t, m.addUnboundKeys(txn, master, timestamp, alice));
+		}
+		return ids;
+	}
+
+	@Override
+	public void bindKeys(Transaction txn, ContactId c,
+			Map<TransportId, KeySetId> keys) throws DbException {
+		for (Entry<TransportId, KeySetId> e : keys.entrySet()) {
+			TransportId t = e.getKey();
+			TransportKeyManager m = managers.get(t);
+			if (m == null) {
+				if (LOG.isLoggable(INFO)) LOG.info("No key manager for " + t);
+			} else {
+				m.bindKeys(txn, c, e.getValue());
+			}
+		}
+	}
+
+	@Override
+	public void activateKeys(Transaction txn, Map<TransportId, KeySetId> keys)
+			throws DbException {
+		for (Entry<TransportId, KeySetId> e : keys.entrySet()) {
+			TransportId t = e.getKey();
+			TransportKeyManager m = managers.get(t);
+			if (m == null) {
+				if (LOG.isLoggable(INFO)) LOG.info("No key manager for " + t);
+			} else {
+				m.activateKeys(txn, e.getValue());
+			}
+		}
+	}
+
+	@Override
+	public void removeKeys(Transaction txn, Map<TransportId, KeySetId> keys)
+			throws DbException {
+		for (Entry<TransportId, KeySetId> e : keys.entrySet()) {
+			TransportId t = e.getKey();
+			TransportKeyManager m = managers.get(t);
+			if (m == null) {
+				if (LOG.isLoggable(INFO)) LOG.info("No key manager for " + t);
+			} else {
+				m.removeKeys(txn, e.getValue());
+			}
+		}
+	}
+
+	@Override
+	public boolean canSendOutgoingStreams(ContactId c, TransportId t) {
+		TransportKeyManager m = managers.get(t);
+		return m == null ? false : m.canSendOutgoingStreams(c);
+	}
+
 	@Override
 	public StreamContext getStreamContext(ContactId c, TransportId t)
 			throws DbException {
@@ -114,7 +176,7 @@ class KeyManagerImpl implements KeyManager, Service, EventListener {
 			if (LOG.isLoggable(INFO)) LOG.info("No key manager for " + t);
 			return null;
 		}
-		StreamContext ctx = null;
+		StreamContext ctx;
 		Transaction txn = db.startTransaction(false);
 		try {
 			ctx = m.getStreamContext(txn, c);
@@ -133,7 +195,7 @@ class KeyManagerImpl implements KeyManager, Service, EventListener {
 			if (LOG.isLoggable(INFO)) LOG.info("No key manager for " + t);
 			return null;
 		}
-		StreamContext ctx = null;
+		StreamContext ctx;
 		Transaction txn = db.startTransaction(false);
 		try {
 			ctx = m.getStreamContext(txn, tag);

bramble-core/src/main/java/org/briarproject/bramble/transport/MutableKeySet.java

@@ -0,0 +1,34 @@
+package org.briarproject.bramble.transport;
+
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.transport.KeySetId;
+
+import javax.annotation.Nullable;
+
+public class MutableKeySet {
+
+	private final KeySetId keySetId;
+	@Nullable
+	private final ContactId contactId;
+	private final MutableTransportKeys transportKeys;
+
+	public MutableKeySet(KeySetId keySetId, @Nullable ContactId contactId,
+			MutableTransportKeys transportKeys) {
+		this.keySetId = keySetId;
+		this.contactId = contactId;
+		this.transportKeys = transportKeys;
+	}
+
+	public KeySetId getKeySetId() {
+		return keySetId;
+	}
+
+	@Nullable
+	public ContactId getContactId() {
+		return contactId;
+	}
+
+	public MutableTransportKeys getTransportKeys() {
+		return transportKeys;
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/transport/MutableOutgoingKeys.java

@@ -13,17 +13,19 @@ class MutableOutgoingKeys {
 	private final SecretKey tagKey, headerKey;
 	private final long rotationPeriod;
 	private long streamCounter;
+	private boolean active;
 
 	MutableOutgoingKeys(OutgoingKeys out) {
 		tagKey = out.getTagKey();
 		headerKey = out.getHeaderKey();
 		rotationPeriod = out.getRotationPeriod();
 		streamCounter = out.getStreamCounter();
+		active = out.isActive();
 	}
 
 	OutgoingKeys snapshot() {
 		return new OutgoingKeys(tagKey, headerKey, rotationPeriod,
-				streamCounter);
+				streamCounter, active);
 	}
 
 	SecretKey getTagKey() {
@@ -45,4 +47,12 @@ class MutableOutgoingKeys {
 	void incrementStreamCounter() {
 		streamCounter++;
 	}
+
+	boolean isActive() {
+		return active;
+	}
+
+	void activate() {
+		active = true;
+	}
 }

bramble-core/src/main/java/org/briarproject/bramble/transport/TransportKeyManager.java

@@ -5,6 +5,7 @@ import org.briarproject.bramble.api.crypto.SecretKey;
 import org.briarproject.bramble.api.db.DbException;
 import org.briarproject.bramble.api.db.Transaction;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.transport.KeySetId;
 import org.briarproject.bramble.api.transport.StreamContext;
 
 import javax.annotation.Nullable;
@@ -17,8 +18,19 @@ interface TransportKeyManager {
 	void addContact(Transaction txn, ContactId c, SecretKey master,
 			long timestamp, boolean alice) throws DbException;
 
+	KeySetId addUnboundKeys(Transaction txn, SecretKey master, long timestamp,
+			boolean alice) throws DbException;
+
+	void bindKeys(Transaction txn, ContactId c, KeySetId k) throws DbException;
+
+	void activateKeys(Transaction txn, KeySetId k) throws DbException;
+
+	void removeKeys(Transaction txn, KeySetId k) throws DbException;
+
 	void removeContact(ContactId c);
 
+	boolean canSendOutgoingStreams(ContactId c);
+
 	@Nullable
 	StreamContext getStreamContext(Transaction txn, ContactId c)
 			throws DbException;

bramble-core/src/main/java/org/briarproject/bramble/transport/TransportKeyManagerImpl.java

@@ -11,19 +11,24 @@ import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.TransportId;
 import org.briarproject.bramble.api.system.Clock;
 import org.briarproject.bramble.api.system.Scheduler;
+import org.briarproject.bramble.api.transport.KeySet;
+import org.briarproject.bramble.api.transport.KeySetId;
 import org.briarproject.bramble.api.transport.StreamContext;
 import org.briarproject.bramble.api.transport.TransportKeys;
 import org.briarproject.bramble.transport.ReorderingWindow.Change;
 
+import java.util.ArrayList;
+import java.util.Collection;
 import java.util.HashMap;
 import java.util.Iterator;
 import java.util.Map;
-import java.util.Map.Entry;
 import java.util.concurrent.Executor;
 import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.locks.ReentrantLock;
 import java.util.logging.Logger;
 
+import javax.annotation.Nullable;
 import javax.annotation.concurrent.ThreadSafe;
 
 import static java.util.concurrent.TimeUnit.MILLISECONDS;
@@ -47,12 +52,13 @@ class TransportKeyManagerImpl implements TransportKeyManager {
 	private final Clock clock;
 	private final TransportId transportId;
 	private final long rotationPeriodLength;
-	private final ReentrantLock lock;
+	private final AtomicBoolean used = new AtomicBoolean(false);
+	private final ReentrantLock lock = new ReentrantLock();
 
 	// The following are locking: lock
-	private final Map<Bytes, TagContext> inContexts;
-	private final Map<ContactId, MutableOutgoingKeys> outContexts;
-	private final Map<ContactId, MutableTransportKeys> keys;
+	private final Map<KeySetId, MutableKeySet> keys = new HashMap<>();
+	private final Map<Bytes, TagContext> inContexts = new HashMap<>();
+	private final Map<ContactId, MutableKeySet> outContexts = new HashMap<>();
 
 	TransportKeyManagerImpl(DatabaseComponent db,
 			TransportCrypto transportCrypto, Executor dbExecutor,
@@ -65,20 +71,16 @@ class TransportKeyManagerImpl implements TransportKeyManager {
 		this.clock = clock;
 		this.transportId = transportId;
 		rotationPeriodLength = maxLatency + MAX_CLOCK_DIFFERENCE;
-		lock = new ReentrantLock();
-		inContexts = new HashMap<>();
-		outContexts = new HashMap<>();
-		keys = new HashMap<>();
 	}
 
 	@Override
 	public void start(Transaction txn) throws DbException {
+		if (used.getAndSet(true)) throw new IllegalStateException();
 		long now = clock.currentTimeMillis();
 		lock.lock();
 		try {
 			// Load the transport keys from the DB
-			Map<ContactId, TransportKeys> loaded =
-					db.getTransportKeys(txn, transportId);
+			Collection<KeySet> loaded = db.getTransportKeys(txn, transportId);
 			// Rotate the keys to the current rotation period
 			RotationResult rotationResult = rotateKeys(loaded, now);
 			// Initialise mutable state for all contacts
@@ -93,41 +95,48 @@ class TransportKeyManagerImpl implements TransportKeyManager {
 		scheduleKeyRotation(now);
 	}
 
-	private RotationResult rotateKeys(Map<ContactId, TransportKeys> keys,
-			long now) {
+	private RotationResult rotateKeys(Collection<KeySet> keys, long now) {
 		RotationResult rotationResult = new RotationResult();
 		long rotationPeriod = now / rotationPeriodLength;
-		for (Entry<ContactId, TransportKeys> e : keys.entrySet()) {
-			ContactId c = e.getKey();
-			TransportKeys k = e.getValue();
+		for (KeySet ks : keys) {
+			TransportKeys k = ks.getTransportKeys();
 			TransportKeys k1 =
 					transportCrypto.rotateTransportKeys(k, rotationPeriod);
+			KeySet ks1 = new KeySet(ks.getKeySetId(), ks.getContactId(), k1);
 			if (k1.getRotationPeriod() > k.getRotationPeriod())
-				rotationResult.rotated.put(c, k1);
-			rotationResult.current.put(c, k1);
+				rotationResult.rotated.add(ks1);
+			rotationResult.current.add(ks1);
 		}
 		return rotationResult;
 	}
 
 	// Locking: lock
-	private void addKeys(Map<ContactId, TransportKeys> m) {
-		for (Entry<ContactId, TransportKeys> e : m.entrySet())
-			addKeys(e.getKey(), new MutableTransportKeys(e.getValue()));
+	private void addKeys(Collection<KeySet> keys) {
+		for (KeySet ks : keys) {
+			addKeys(ks.getKeySetId(), ks.getContactId(),
+					new MutableTransportKeys(ks.getTransportKeys()));
+		}
 	}
 
 	// Locking: lock
-	private void addKeys(ContactId c, MutableTransportKeys m) {
-		encodeTags(c, m.getPreviousIncomingKeys());
-		encodeTags(c, m.getCurrentIncomingKeys());
-		encodeTags(c, m.getNextIncomingKeys());
-		outContexts.put(c, m.getCurrentOutgoingKeys());
-		keys.put(c, m);
+	private void addKeys(KeySetId keySetId, @Nullable ContactId contactId,
+			MutableTransportKeys m) {
+		MutableKeySet ks = new MutableKeySet(keySetId, contactId, m);
+		keys.put(keySetId, ks);
+		if (contactId != null) {
+			encodeTags(keySetId, contactId, m.getPreviousIncomingKeys());
+			encodeTags(keySetId, contactId, m.getCurrentIncomingKeys());
+			encodeTags(keySetId, contactId, m.getNextIncomingKeys());
+			considerReplacingOutgoingKeys(ks);
+		}
 	}
 
 	// Locking: lock
-	private void encodeTags(ContactId c, MutableIncomingKeys inKeys) {
+	private void encodeTags(KeySetId keySetId, ContactId contactId,
+			MutableIncomingKeys inKeys) {
 		for (long streamNumber : inKeys.getWindow().getUnseen()) {
-			TagContext tagCtx = new TagContext(c, inKeys, streamNumber);
+			TagContext tagCtx =
+					new TagContext(keySetId, contactId, inKeys, streamNumber);
 			byte[] tag = new byte[TAG_LENGTH];
 			transportCrypto.encodeTag(tag, inKeys.getTagKey(), PROTOCOL_VERSION,
 					streamNumber);
@@ -135,6 +144,17 @@ class TransportKeyManagerImpl implements TransportKeyManager {
 		}
 	}
 
+	// Locking: lock
+	private void considerReplacingOutgoingKeys(MutableKeySet ks) {
+		// Use the active outgoing keys with the highest key set ID
+		if (ks.getTransportKeys().getCurrentOutgoingKeys().isActive()) {
+			MutableKeySet old = outContexts.get(ks.getContactId());
+			if (old == null ||
+					old.getKeySetId().getInt() < ks.getKeySetId().getInt())
+				outContexts.put(ks.getContactId(), ks);
+		}
+	}
+
 	private void scheduleKeyRotation(long now) {
 		long delay = rotationPeriodLength - now % rotationPeriodLength;
 		scheduler.schedule((Runnable) this::rotateKeys, delay, MILLISECONDS);
@@ -159,20 +179,82 @@ class TransportKeyManagerImpl implements TransportKeyManager {
 	@Override
 	public void addContact(Transaction txn, ContactId c, SecretKey master,
 			long timestamp, boolean alice) throws DbException {
+		deriveAndAddKeys(txn, c, master, timestamp, alice, true);
+	}
+
+	@Override
+	public KeySetId addUnboundKeys(Transaction txn, SecretKey master,
+			long timestamp, boolean alice) throws DbException {
+		return deriveAndAddKeys(txn, null, master, timestamp, alice, false);
+	}
+
+	private KeySetId deriveAndAddKeys(Transaction txn, @Nullable ContactId c,
+			SecretKey master, long timestamp, boolean alice, boolean active)
+			throws DbException {
 		lock.lock();
 		try {
 			// Work out what rotation period the timestamp belongs to
 			long rotationPeriod = timestamp / rotationPeriodLength;
 			// Derive the transport keys
 			TransportKeys k = transportCrypto.deriveTransportKeys(transportId,
-					master, rotationPeriod, alice);
+					master, rotationPeriod, alice, active);
 			// Rotate the keys to the current rotation period if necessary
 			rotationPeriod = clock.currentTimeMillis() / rotationPeriodLength;
 			k = transportCrypto.rotateTransportKeys(k, rotationPeriod);
-			// Initialise mutable state for the contact
-			addKeys(c, new MutableTransportKeys(k));
 			// Write the keys back to the DB
-			db.addTransportKeys(txn, c, k);
+			KeySetId keySetId = db.addTransportKeys(txn, c, k);
+			// Initialise mutable state for the contact
+			addKeys(keySetId, c, new MutableTransportKeys(k));
+			return keySetId;
+		} finally {
+			lock.unlock();
+		}
+	}
+
+	@Override
+	public void bindKeys(Transaction txn, ContactId c, KeySetId k)
+			throws DbException {
+		lock.lock();
+		try {
+			MutableKeySet ks = keys.get(k);
+			if (ks == null) throw new IllegalArgumentException();
+			// Check that the keys haven't already been bound
+			if (ks.getContactId() != null) throw new IllegalArgumentException();
+			MutableTransportKeys m = ks.getTransportKeys();
+			addKeys(k, c, m);
+			db.bindTransportKeys(txn, c, m.getTransportId(), k);
+		} finally {
+			lock.unlock();
+		}
+	}
+
+	@Override
+	public void activateKeys(Transaction txn, KeySetId k) throws DbException {
+		lock.lock();
+		try {
+			MutableKeySet ks = keys.get(k);
+			if (ks == null) throw new IllegalArgumentException();
+			// Check that the keys have been bound
+			if (ks.getContactId() == null) throw new IllegalArgumentException();
+			MutableTransportKeys m = ks.getTransportKeys();
+			m.getCurrentOutgoingKeys().activate();
+			considerReplacingOutgoingKeys(ks);
+			db.setTransportKeysActive(txn, m.getTransportId(), k);
+		} finally {
+			lock.unlock();
+		}
+	}
+
+	@Override
+	public void removeKeys(Transaction txn, KeySetId k) throws DbException {
+		lock.lock();
+		try {
+			MutableKeySet ks = keys.remove(k);
+			if (ks == null) throw new IllegalArgumentException();
+			// Check that the keys haven't been bound
+			if (ks.getContactId() != null) throw new IllegalArgumentException();
+			TransportId t = ks.getTransportKeys().getTransportId();
+			db.removeTransportKeys(txn, t, k);
 		} finally {
 			lock.unlock();
 		}
@@ -183,12 +265,29 @@ class TransportKeyManagerImpl implements TransportKeyManager {
 		lock.lock();
 		try {
 			// Remove mutable state for the contact
-			Iterator<Entry<Bytes, TagContext>> it =
-					inContexts.entrySet().iterator();
-			while (it.hasNext())
-				if (it.next().getValue().contactId.equals(c)) it.remove();
+			Iterator<TagContext> it = inContexts.values().iterator();
+			while (it.hasNext()) if (it.next().contactId.equals(c)) it.remove();
 			outContexts.remove(c);
-			keys.remove(c);
+			Iterator<MutableKeySet> it1 = keys.values().iterator();
+			while (it1.hasNext()) {
+				ContactId c1 = it1.next().getContactId();
+				if (c1 != null && c1.equals(c)) it1.remove();
+			}
+		} finally {
+			lock.unlock();
+		}
+	}
+
+	@Override
+	public boolean canSendOutgoingStreams(ContactId c) {
+		lock.lock();
+		try {
+			MutableKeySet ks = outContexts.get(c);
+			if (ks == null) return false;
+			MutableOutgoingKeys outKeys =
+					ks.getTransportKeys().getCurrentOutgoingKeys();
+			if (!outKeys.isActive()) throw new AssertionError();
+			return outKeys.getStreamCounter() <= MAX_32_BIT_UNSIGNED;
 		} finally {
 			lock.unlock();
 		}
@@ -200,8 +299,11 @@ class TransportKeyManagerImpl implements TransportKeyManager {
 		lock.lock();
 		try {
 			// Look up the outgoing keys for the contact
-			MutableOutgoingKeys outKeys = outContexts.get(c);
-			if (outKeys == null) return null;
+			MutableKeySet ks = outContexts.get(c);
+			if (ks == null) return null;
+			MutableOutgoingKeys outKeys =
+					ks.getTransportKeys().getCurrentOutgoingKeys();
+			if (!outKeys.isActive()) throw new AssertionError();
 			if (outKeys.getStreamCounter() > MAX_32_BIT_UNSIGNED) return null;
 			// Create a stream context
 			StreamContext ctx = new StreamContext(c, transportId,
@@ -209,8 +311,7 @@ class TransportKeyManagerImpl implements TransportKeyManager {
 					outKeys.getStreamCounter());
 			// Increment the stream counter and write it back to the DB
 			outKeys.incrementStreamCounter();
-			db.incrementStreamCounter(txn, c, transportId,
-					outKeys.getRotationPeriod());
+			db.incrementStreamCounter(txn, transportId, ks.getKeySetId());
 			return ctx;
 		} finally {
 			lock.unlock();
@@ -238,8 +339,9 @@ class TransportKeyManagerImpl implements TransportKeyManager {
 				byte[] addTag = new byte[TAG_LENGTH];
 				transportCrypto.encodeTag(addTag, inKeys.getTagKey(),
 						PROTOCOL_VERSION, streamNumber);
-				inContexts.put(new Bytes(addTag), new TagContext(
-						tagCtx.contactId, inKeys, streamNumber));
+				TagContext tagCtx1 = new TagContext(tagCtx.keySetId,
+						tagCtx.contactId, inKeys, streamNumber);
+				inContexts.put(new Bytes(addTag), tagCtx1);
 			}
 			// Remove tags for any stream numbers removed from the window
 			for (long streamNumber : change.getRemoved()) {
@@ -250,9 +352,19 @@ class TransportKeyManagerImpl implements TransportKeyManager {
 				inContexts.remove(new Bytes(removeTag));
 			}
 			// Write the window back to the DB
-			db.setReorderingWindow(txn, tagCtx.contactId, transportId,
+			db.setReorderingWindow(txn, tagCtx.keySetId, transportId,
 					inKeys.getRotationPeriod(), window.getBase(),
 					window.getBitmap());
+			// If the outgoing keys are inactive, activate them
+			MutableKeySet ks = keys.get(tagCtx.keySetId);
+			MutableOutgoingKeys outKeys =
+					ks.getTransportKeys().getCurrentOutgoingKeys();
+			if (!outKeys.isActive()) {
+				LOG.info("Activating outgoing keys");
+				outKeys.activate();
+				considerReplacingOutgoingKeys(ks);
+				db.setTransportKeysActive(txn, transportId, tagCtx.keySetId);
+			}
 			return ctx;
 		} finally {
 			lock.unlock();
@@ -264,9 +376,11 @@ class TransportKeyManagerImpl implements TransportKeyManager {
 		lock.lock();
 		try {
 			// Rotate the keys to the current rotation period
-			Map<ContactId, TransportKeys> snapshot = new HashMap<>();
-			for (Entry<ContactId, MutableTransportKeys> e : keys.entrySet())
-				snapshot.put(e.getKey(), e.getValue().snapshot());
+			Collection<KeySet> snapshot = new ArrayList<>(keys.size());
+			for (MutableKeySet ks : keys.values()) {
+				snapshot.add(new KeySet(ks.getKeySetId(), ks.getContactId(),
+						ks.getTransportKeys().snapshot()));
+			}
 			RotationResult rotationResult = rotateKeys(snapshot, now);
 			// Rebuild the mutable state for all contacts
 			inContexts.clear();
@@ -285,12 +399,14 @@ class TransportKeyManagerImpl implements TransportKeyManager {
 
 	private static class TagContext {
 
+		private final KeySetId keySetId;
 		private final ContactId contactId;
 		private final MutableIncomingKeys inKeys;
 		private final long streamNumber;
 
-		private TagContext(ContactId contactId, MutableIncomingKeys inKeys,
-				long streamNumber) {
+		private TagContext(KeySetId keySetId, ContactId contactId,
+				MutableIncomingKeys inKeys, long streamNumber) {
+			this.keySetId = keySetId;
 			this.contactId = contactId;
 			this.inKeys = inKeys;
 			this.streamNumber = streamNumber;
@@ -299,11 +415,7 @@ class TransportKeyManagerImpl implements TransportKeyManager {
 
 	private static class RotationResult {
 
-		private final Map<ContactId, TransportKeys> current, rotated;
-
-		private RotationResult() {
-			current = new HashMap<>();
-			rotated = new HashMap<>();
-		}
+		private final Collection<KeySet> current = new ArrayList<>();
+		private final Collection<KeySet> rotated = new ArrayList<>();
 	}
 }