diff -r 5315a5713dd5 -r b2e1b45382a4 src/net/java/otr4j/io/messages/SignatureMessage.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/net/java/otr4j/io/messages/SignatureMessage.java	Fri Apr 15 03:01:09 2011 +0200
@@ -0,0 +1,82 @@
+/*
+ * otr4j, the open source java otr library.
+ *
+ * Distributable under LGPL license.
+ * See terms of license at gnu.org.
+ */
+package net.java.otr4j.io.messages;
+
+import java.io.IOException;
+import java.util.Arrays;
+
+import net.java.otr4j.OtrException;
+import net.java.otr4j.crypto.OtrCryptoEngineImpl;
+import net.java.otr4j.io.SerializationUtils;
+
+/**
+ * 
+ * @author George Politis
+ */
+public class SignatureMessage extends AbstractEncodedMessage {
+	// Fields.
+	public byte[] xEncrypted;
+	public byte[] xEncryptedMAC;
+
+	// Ctor.
+	protected SignatureMessage(int messageType, int protocolVersion,
+			byte[] xEncrypted, byte[] xEncryptedMAC) {
+		super(messageType, protocolVersion);
+		this.xEncrypted = xEncrypted;
+		this.xEncryptedMAC = xEncryptedMAC;
+	}
+
+	public SignatureMessage(int protocolVersion, byte[] xEncrypted,
+			byte[] xEncryptedMAC) {
+		this(MESSAGE_SIGNATURE, protocolVersion, xEncrypted, xEncryptedMAC);
+	}
+
+	// Memthods.
+	public byte[] decrypt(byte[] key) throws OtrException {
+		return new OtrCryptoEngineImpl().aesDecrypt(key, null, xEncrypted);
+	}
+
+	public boolean verify(byte[] key) throws OtrException {
+		// Hash the key.
+		byte[] xbEncrypted;
+		try {
+			xbEncrypted = SerializationUtils.writeData(xEncrypted);
+		} catch (IOException e) {
+			throw new OtrException(e);
+		}
+
+		byte[] xEncryptedMAC = new OtrCryptoEngineImpl().sha256Hmac160(
+				xbEncrypted, key);
+		// Verify signature.
+		return Arrays.equals(xEncryptedMAC, xEncryptedMAC);
+	}
+
+	@Override
+	public int hashCode() {
+		final int prime = 31;
+		int result = super.hashCode();
+		result = prime * result + Arrays.hashCode(xEncrypted);
+		result = prime * result + Arrays.hashCode(xEncryptedMAC);
+		return result;
+	}
+
+	@Override
+	public boolean equals(Object obj) {
+		if (this == obj)
+			return true;
+		if (!super.equals(obj))
+			return false;
+		if (getClass() != obj.getClass())
+			return false;
+		SignatureMessage other = (SignatureMessage) obj;
+		if (!Arrays.equals(xEncrypted, other.xEncrypted))
+			return false;
+		if (!Arrays.equals(xEncryptedMAC, other.xEncryptedMAC))
+			return false;
+		return true;
+	}
+}