diff --git a/test/build.xml b/test/build.xml
index 2791cc2a029c6e1bb278c112185650a450cd6bae..d008290f4224b3453dee129229e291d929aa16a2 100644
--- a/test/build.xml
+++ b/test/build.xml
@@ -32,6 +32,7 @@
 			<test name='net.sf.briar.serial.ReaderImplTest'/>
 			<test name='net.sf.briar.serial.WriterImplTest'/>
 			<test name='net.sf.briar.setup.SetupWorkerTest'/>
+			<test name='net.sf.briar.transport.ConnectionRecogniserImplTest'/>
 			<test name='net.sf.briar.transport.ConnectionWindowImplTest'/>
 			<test name='net.sf.briar.transport.PacketEncrypterImplTest'/>
 			<test name='net.sf.briar.transport.PacketWriterImplTest'/>
diff --git a/test/net/sf/briar/transport/ConnectionRecogniserImplTest.java b/test/net/sf/briar/transport/ConnectionRecogniserImplTest.java
new file mode 100644
index 0000000000000000000000000000000000000000..7ec47deb53e50043c37a41a811f03538b7ef14d5
--- /dev/null
+++ b/test/net/sf/briar/transport/ConnectionRecogniserImplTest.java
@@ -0,0 +1,98 @@
+package net.sf.briar.transport;
+
+import java.util.Collection;
+import java.util.Collections;
+
+import javax.crypto.Cipher;
+import javax.crypto.SecretKey;
+
+import junit.framework.TestCase;
+import net.sf.briar.api.ContactId;
+import net.sf.briar.api.crypto.CryptoComponent;
+import net.sf.briar.api.db.DatabaseComponent;
+import net.sf.briar.api.transport.ConnectionWindow;
+import net.sf.briar.crypto.CryptoModule;
+
+import org.jmock.Expectations;
+import org.jmock.Mockery;
+import org.junit.Test;
+
+import com.google.inject.Guice;
+import com.google.inject.Injector;
+
+public class ConnectionRecogniserImplTest extends TestCase {
+
+	private final CryptoComponent crypto;
+	private final ContactId contactId;
+	private final byte[] secret;
+	private final int transportId;
+	private final ConnectionWindow connectionWindow;
+
+	public ConnectionRecogniserImplTest() {
+		super();
+		Injector i = Guice.createInjector(new CryptoModule());
+		crypto = i.getInstance(CryptoComponent.class);
+		contactId = new ContactId(1);
+		secret = new byte[18];
+		transportId = 123;
+		connectionWindow = new ConnectionWindowImpl(0L, 0);
+	}
+
+	@Test
+	public void testUnexpectedTag() throws Exception {
+		Mockery context = new Mockery();
+		final DatabaseComponent db = context.mock(DatabaseComponent.class);
+		context.checking(new Expectations() {{
+			oneOf(db).addListener(with(any(ConnectionRecogniserImpl.class)));
+			oneOf(db).getContacts();
+			will(returnValue(Collections.singleton(contactId)));
+			oneOf(db).getSharedSecret(contactId);
+			will(returnValue(secret));
+			oneOf(db).getConnectionWindow(contactId, transportId);
+			will(returnValue(connectionWindow));
+		}});
+		final ConnectionRecogniserImpl c =
+			new ConnectionRecogniserImpl(transportId, crypto, db);
+		assertNull(c.acceptConnection(new byte[16]));
+		context.assertIsSatisfied();
+	}
+
+	@Test
+	public void testExpectedTag() throws Exception {
+		// Calculate the expected tag for connection number 3
+		SecretKey tagKey = crypto.deriveTagKey(secret);
+		Cipher tagCipher = crypto.getTagCipher();
+		tagCipher.init(Cipher.ENCRYPT_MODE, tagKey);
+		byte[] tag = TagEncoder.encodeTag(transportId, 3L, 0);
+		byte[] encryptedTag = tagCipher.doFinal(tag);
+
+		Mockery context = new Mockery();
+		final DatabaseComponent db = context.mock(DatabaseComponent.class);
+		context.checking(new Expectations() {{
+			oneOf(db).addListener(with(any(ConnectionRecogniserImpl.class)));
+			oneOf(db).getContacts();
+			will(returnValue(Collections.singleton(contactId)));
+			oneOf(db).getSharedSecret(contactId);
+			will(returnValue(secret));
+			oneOf(db).getConnectionWindow(contactId, transportId);
+			will(returnValue(connectionWindow));
+			oneOf(db).setConnectionWindow(contactId, transportId,
+					connectionWindow);
+		}});
+		final ConnectionRecogniserImpl c =
+			new ConnectionRecogniserImpl(transportId, crypto, db);
+		// First time - the tag should be expected
+		assertEquals(contactId, c.acceptConnection(encryptedTag));
+		// Second time - the tag should no longer be expected
+		assertNull(c.acceptConnection(encryptedTag));
+		// The window should have advanced
+		assertEquals(4L, connectionWindow.getCentre());
+		Collection<Long> unseen = connectionWindow.getUnseenConnectionNumbers();
+		assertEquals(19, unseen.size());
+		for(int i = 0; i < 19; i++) {
+			if(i == 3) continue;
+			assertTrue(unseen.contains(Long.valueOf(i)));
+		}
+		context.assertIsSatisfied();
+	}
+}