AuthContextImpl.java

/*
 * otr4j, the open source java otr library.
 *
 * Distributable under LGPL license. See terms of license at gnu.org.
 */
package net.java.otr4j.session;

import java.io.IOException;
import java.math.BigInteger;
import java.nio.ByteBuffer;
import java.security.KeyPair;
import java.security.PublicKey;
import java.security.SecureRandom;
import java.util.Arrays;
import java.util.Vector;
import java.util.logging.Logger;

import javax.crypto.interfaces.DHPublicKey;

import net.java.otr4j.OtrException;
import net.java.otr4j.crypto.OtrCryptoEngine;
import net.java.otr4j.crypto.OtrCryptoEngineImpl;
import net.java.otr4j.io.SerializationUtils;
import net.java.otr4j.io.messages.AbstractEncodedMessage;
import net.java.otr4j.io.messages.AbstractMessage;
import net.java.otr4j.io.messages.DHCommitMessage;
import net.java.otr4j.io.messages.DHKeyMessage;
import net.java.otr4j.io.messages.QueryMessage;
import net.java.otr4j.io.messages.RevealSignatureMessage;
import net.java.otr4j.io.messages.SignatureM;
import net.java.otr4j.io.messages.SignatureMessage;
import net.java.otr4j.io.messages.SignatureX;

/** @author George Politis */
class AuthContextImpl implements AuthContext {

    public AuthContextImpl(Session session) {
        this.setSession(session);
        this.reset();
        //logger.addHandler(new AndroidLogHandler());

    }

    private Session session;

    private int authenticationState;
    SecureRandom secureRandom;
    private byte[] r;

    private DHPublicKey remoteDHPublicKey;
    private byte[] remoteDHPublicKeyEncrypted;
    private byte[] remoteDHPublicKeyHash;

    private KeyPair localDHKeyPair;
    private int localDHPrivateKeyID;
    private byte[] localDHPublicKeyBytes;
    private byte[] localDHPublicKeyHash;
    private byte[] localDHPublicKeyEncrypted;

    private BigInteger s;
    private byte[] c;
    private byte[] m1;
    private byte[] m2;
    private byte[] cp;
    private byte[] m1p;
    private byte[] m2p;

    private KeyPair localLongTermKeyPair;
    private Boolean isSecure = false;
    private int protocolVersion;

    private static Logger logger = Logger.getLogger(AuthContextImpl.class.getName());

    private int getProtocolVersion() {
        return this.protocolVersion;
    }

    private void setProtocolVersion(int protoVersion) {
        this.protocolVersion = protoVersion;
    }

    class MessageFactory {

        private QueryMessage getQueryMessage() {
            Vector<Integer> versions = new Vector<Integer>();
            versions.add(2);
            return new QueryMessage(versions);
        }

        private DHCommitMessage getDHCommitMessage() throws OtrException {
            return new DHCommitMessage(getProtocolVersion(), getLocalDHPublicKeyHash(),
                    getLocalDHPublicKeyEncrypted());
        }

        private DHKeyMessage getDHKeyMessage() throws OtrException {
            return new DHKeyMessage(getProtocolVersion(), (DHPublicKey) getLocalDHKeyPair()
                    .getPublic());
        }

        private RevealSignatureMessage getRevealSignatureMessage() throws OtrException {
            try {
                SignatureM m = new SignatureM((DHPublicKey) getLocalDHKeyPair().getPublic(),
                        getRemoteDHPublicKey(), getLocalLongTermKeyPair().getPublic(),
                        getLocalDHKeyPairID());

                OtrCryptoEngine otrCryptoEngine = new OtrCryptoEngineImpl();
                byte[] mhash = otrCryptoEngine.sha256Hmac(SerializationUtils.toByteArray(m),
                        getM1());
                byte[] signature = otrCryptoEngine.sign(mhash, getLocalLongTermKeyPair()
                        .getPrivate());

                SignatureX mysteriousX = new SignatureX(getLocalLongTermKeyPair().getPublic(),
                        getLocalDHKeyPairID(), signature);
                byte[] xEncrypted = otrCryptoEngine.aesEncrypt(getC(), null,
                        SerializationUtils.toByteArray(mysteriousX));

                byte[] tmp = SerializationUtils.writeData(xEncrypted);

                byte[] xEncryptedHash = otrCryptoEngine.sha256Hmac160(tmp, getM2());
                return new RevealSignatureMessage(getProtocolVersion(), xEncrypted, xEncryptedHash,
                        getR());
            } catch (IOException e) {
                throw new OtrException(e);
            }
        }

        private SignatureMessage getSignatureMessage() throws OtrException {
            SignatureM m = new SignatureM((DHPublicKey) getLocalDHKeyPair().getPublic(),
                    getRemoteDHPublicKey(), getLocalLongTermKeyPair().getPublic(),
                    getLocalDHKeyPairID());

            OtrCryptoEngine otrCryptoEngine = new OtrCryptoEngineImpl();
            byte[] mhash;
            try {
                mhash = otrCryptoEngine.sha256Hmac(SerializationUtils.toByteArray(m), getM1p());
            } catch (IOException e) {
                throw new OtrException(e);
            }

            byte[] signature = otrCryptoEngine.sign(mhash, getLocalLongTermKeyPair().getPrivate());

            SignatureX mysteriousX = new SignatureX(getLocalLongTermKeyPair().getPublic(),
                    getLocalDHKeyPairID(), signature);

            byte[] xEncrypted;
            try {
                xEncrypted = otrCryptoEngine.aesEncrypt(getCp(), null,
                        SerializationUtils.toByteArray(mysteriousX));
                byte[] tmp = SerializationUtils.writeData(xEncrypted);
                byte[] xEncryptedHash = otrCryptoEngine.sha256Hmac160(tmp, getM2p());
                return new SignatureMessage(getProtocolVersion(), xEncrypted, xEncryptedHash);
            } catch (IOException e) {
                throw new OtrException(e);
            }
        }
    }

    private MessageFactory messageFactory = new MessageFactory();

    public void reset() {
        logger.finest("Resetting authentication state.");
        authenticationState = AuthContext.NONE;
        r = null;

        remoteDHPublicKey = null;
        remoteDHPublicKeyEncrypted = null;
        remoteDHPublicKeyHash = null;

        localDHKeyPair = null;
        localDHPrivateKeyID = 1;
        localDHPublicKeyBytes = null;
        localDHPublicKeyHash = null;
        localDHPublicKeyEncrypted = null;

        s = null;
        c = m1 = m2 = cp = m1p = m2p = null;

        localLongTermKeyPair = null;
        protocolVersion = 0;
        setIsSecure(false);
    }

    private void setIsSecure(Boolean isSecure) {
        this.isSecure = isSecure;
    }

    public boolean getIsSecure() {
        return isSecure;
    }

    private void setAuthenticationState(int authenticationState) {
        this.authenticationState = authenticationState;
    }

    private int getAuthenticationState() {
        return authenticationState;
    }

    private byte[] getR() {
        if (secureRandom == null)
            secureRandom = new java.security.SecureRandom();
        if (r == null) {
            logger.finest("Picking random key r.");
            r = new byte[OtrCryptoEngine.AES_KEY_BYTE_LENGTH];
            secureRandom.nextBytes(r);
        }
        return r;
    }

    public void setRemoteDHPublicKey(DHPublicKey dhPublicKey) {
        // Verifies that Alice's gy is a legal value (2 <= gy <= modulus-2)
        if (dhPublicKey.getY().compareTo(OtrCryptoEngine.MODULUS_MINUS_TWO) > 0) {
            throw new IllegalArgumentException("Illegal D-H Public Key value, Ignoring message.");
        } else if (dhPublicKey.getY().compareTo(OtrCryptoEngine.BIGINTEGER_TWO) < 0) {
            throw new IllegalArgumentException("Illegal D-H Public Key value, Ignoring message.");
        }
        logger.finest("Received D-H Public Key is a legal value.");

        this.remoteDHPublicKey = dhPublicKey;
    }

    public DHPublicKey getRemoteDHPublicKey() {
        return remoteDHPublicKey;
    }

    private void setRemoteDHPublicKeyEncrypted(byte[] remoteDHPublicKeyEncrypted) {
        logger.finest("Storing encrypted remote public key.");
        this.remoteDHPublicKeyEncrypted = remoteDHPublicKeyEncrypted;
    }

    private byte[] getRemoteDHPublicKeyEncrypted() {
        return remoteDHPublicKeyEncrypted;
    }

    private void setRemoteDHPublicKeyHash(byte[] remoteDHPublicKeyHash) {
        logger.finest("Storing encrypted remote public key hash.");
        this.remoteDHPublicKeyHash = remoteDHPublicKeyHash;
    }

    private byte[] getRemoteDHPublicKeyHash() {
        return remoteDHPublicKeyHash;
    }

    public KeyPair getLocalDHKeyPair() throws OtrException {
        if (localDHKeyPair == null) {
            localDHKeyPair = new OtrCryptoEngineImpl().generateDHKeyPair();
            logger.finest("Generated local D-H key pair.");
        }
        return localDHKeyPair;
    }

    private int getLocalDHKeyPairID() {
        return localDHPrivateKeyID;
    }

    private byte[] getLocalDHPublicKeyHash() throws OtrException {
        if (localDHPublicKeyHash == null) {
            localDHPublicKeyHash = new OtrCryptoEngineImpl().sha256Hash(getLocalDHPublicKeyBytes());
            logger.finest("Hashed local D-H public key.");
        }
        return localDHPublicKeyHash;
    }

    private byte[] getLocalDHPublicKeyEncrypted() throws OtrException {
        if (localDHPublicKeyEncrypted == null) {
            localDHPublicKeyEncrypted = new OtrCryptoEngineImpl().aesEncrypt(getR(), null,
                    getLocalDHPublicKeyBytes());
            logger.finest("Encrypted our D-H public key.");
        }
        return localDHPublicKeyEncrypted;
    }

    public BigInteger getS() throws OtrException {
        if (s == null) {
            s = new OtrCryptoEngineImpl().generateSecret(this.getLocalDHKeyPair().getPrivate(),
                    this.getRemoteDHPublicKey());
            logger.finest("Generated shared secret.");
        }
        return s;
    }

    public byte[] getExtraSymmetricKey() throws OtrException {
        return h2(EXTRA_SYMMETRIC_KEY);
    }

    private byte[] getC() throws OtrException {
        if (c != null)
            return c;

        byte[] h2 = h2(C_START);
        ByteBuffer buff = ByteBuffer.wrap(h2);
        this.c = new byte[OtrCryptoEngine.AES_KEY_BYTE_LENGTH];
        buff.get(this.c);
        logger.finest("Computed c.");
        return c;

    }

    private byte[] getM1() throws OtrException {
        if (m1 != null)
            return m1;

        byte[] h2 = h2(M1_START);
        ByteBuffer buff = ByteBuffer.wrap(h2);
        byte[] m1 = new byte[OtrCryptoEngine.SHA256_HMAC_KEY_BYTE_LENGTH];
        buff.get(m1);
        logger.finest("Computed m1.");
        this.m1 = m1;
        return m1;
    }

    private byte[] getM2() throws OtrException {
        if (m2 != null)
            return m2;

        byte[] h2 = h2(M2_START);
        ByteBuffer buff = ByteBuffer.wrap(h2);
        byte[] m2 = new byte[OtrCryptoEngine.SHA256_HMAC_KEY_BYTE_LENGTH];
        buff.get(m2);
        logger.finest("Computed m2.");
        this.m2 = m2;
        return m2;
    }

    private byte[] getCp() throws OtrException {
        if (cp != null)
            return cp;

        byte[] h2 = h2(C_START);
        ByteBuffer buff = ByteBuffer.wrap(h2);
        byte[] cp = new byte[OtrCryptoEngine.AES_KEY_BYTE_LENGTH];
        buff.position(OtrCryptoEngine.AES_KEY_BYTE_LENGTH);
        buff.get(cp);
        logger.finest("Computed c'.");
        this.cp = cp;
        return cp;
    }

    private byte[] getM1p() throws OtrException {
        if (m1p != null)
            return m1p;

        byte[] h2 = h2(M1p_START);
        ByteBuffer buff = ByteBuffer.wrap(h2);
        byte[] m1p = new byte[OtrCryptoEngine.SHA256_HMAC_KEY_BYTE_LENGTH];
        buff.get(m1p);
        this.m1p = m1p;
        logger.finest("Computed m1'.");
        return m1p;
    }

    private byte[] getM2p() throws OtrException {
        if (m2p != null)
            return m2p;

        byte[] h2 = h2(M2p_START);
        ByteBuffer buff = ByteBuffer.wrap(h2);
        byte[] m2p = new byte[OtrCryptoEngine.SHA256_HMAC_KEY_BYTE_LENGTH];
        buff.get(m2p);
        this.m2p = m2p;
        logger.finest("Computed m2'.");
        return m2p;
    }

    public KeyPair getLocalLongTermKeyPair() {
        if (localLongTermKeyPair == null) {
            localLongTermKeyPair = getSession().getLocalKeyPair();
        }
        return localLongTermKeyPair;
    }

    private byte[] h2(byte b) throws OtrException {
        byte[] secbytes;
        try {
            secbytes = SerializationUtils.writeMpi(getS());
        } catch (IOException e) {
            throw new OtrException(e);
        }

        int len = secbytes.length + 1;
        ByteBuffer buff = ByteBuffer.allocate(len);
        buff.put(b);
        buff.put(secbytes);
        byte[] sdata = buff.array();
        return new OtrCryptoEngineImpl().sha256Hash(sdata);
    }

    private byte[] getLocalDHPublicKeyBytes() throws OtrException {
        if (localDHPublicKeyBytes == null) {
            try {
                this.localDHPublicKeyBytes = SerializationUtils
                        .writeMpi(((DHPublicKey) getLocalDHKeyPair().getPublic()).getY());

            } catch (IOException e) {
                throw new OtrException(e);
            }

        }
        return localDHPublicKeyBytes;
    }

    public void handleReceivingMessage(AbstractMessage m) throws OtrException {

        switch (m.messageType) {
        case AbstractEncodedMessage.MESSAGE_DH_COMMIT:
            handleDHCommitMessage((DHCommitMessage) m);
            break;
        case AbstractEncodedMessage.MESSAGE_DHKEY:
            handleDHKeyMessage((DHKeyMessage) m);
            break;
        case AbstractEncodedMessage.MESSAGE_REVEALSIG:
            handleRevealSignatureMessage((RevealSignatureMessage) m);
            break;
        case AbstractEncodedMessage.MESSAGE_SIGNATURE:
            handleSignatureMessage((SignatureMessage) m);
            break;
        default:
            throw new UnsupportedOperationException();
        }
    }

    private void handleSignatureMessage(SignatureMessage m) throws OtrException {
        Session session = getSession();
        SessionID sessionID = session.getSessionID();
       logger.finest(sessionID.getLocalUserId() + " received a signature message from "
                      + sessionID.getRemoteUserId() + " throught " + sessionID.getProtocolName() + ".");
        if (!session.getSessionPolicy().getAllowV2()) {
            logger.finest("Policy does not allow OTRv2, ignoring message.");
            return;
        }

        switch (this.getAuthenticationState()) {
        case AWAITING_SIG:
            // Verify MAC.
            if (!m.verify(this.getM2p())) {
                logger.finest("Signature MACs are not equal, ignoring message.");
                return;
            }

            // Decrypt X.
            byte[] remoteXDecrypted = m.decrypt(this.getCp());
            SignatureX remoteX;
            try {
                remoteX = SerializationUtils.toMysteriousX(remoteXDecrypted);
            } catch (IOException e) {
                throw new OtrException(e);
            }
            // Compute signature.
            PublicKey remoteLongTermPublicKey = remoteX.longTermPublicKey;
            SignatureM remoteM = new SignatureM(this.getRemoteDHPublicKey(), (DHPublicKey) this
                    .getLocalDHKeyPair().getPublic(), remoteLongTermPublicKey, remoteX.dhKeyID);
            OtrCryptoEngine otrCryptoEngine = new OtrCryptoEngineImpl();
            // Verify signature.
            byte[] signature;
            try {
                signature = otrCryptoEngine.sha256Hmac(SerializationUtils.toByteArray(remoteM),
                        this.getM1p());
            } catch (IOException e) {
                throw new OtrException(e);
            }
            if (!otrCryptoEngine.verify(signature, remoteLongTermPublicKey, remoteX.signature)) {
                session.showWarning("Bad signature");
                logger.finest("Signature verification failed.");
                return;
            }

            this.setIsSecure(true);
            this.setRemoteLongTermPublicKey(remoteLongTermPublicKey);
            break;
        default:
            logger.finest("We were not expecting a signature, ignoring message.");
            return;
        }
    }

    private void handleRevealSignatureMessage(RevealSignatureMessage m) throws OtrException {
        Session session = getSession();
        SessionID sessionID = session.getSessionID();
        logger.finest(sessionID.getLocalUserId() + " received a reveal signature message from "
                      + sessionID.getRemoteUserId() + " throught " + sessionID.getProtocolName() + ".");

        if (!session.getSessionPolicy().getAllowV2()) {
            logger.finest("Policy does not allow OTRv2, ignoring message.");
            return;
        }

        switch (this.getAuthenticationState()) {
        case AWAITING_REVEALSIG:
            // Use the received value of r to decrypt the value of gx
            // received
            // in the D-H Commit Message, and verify the hash therein.
            // Decrypt
            // the encrypted signature, and verify the signature and the
            // MACs.
            // If everything checks out:

            // * Reply with a Signature Message.
            // * Transition authstate to AUTHSTATE_NONE.
            // * Transition msgstate to MSGSTATE_ENCRYPTED.
            // * TODO If there is a recent stored message, encrypt it and
            // send
            // it as a Data Message.

            OtrCryptoEngine otrCryptoEngine = new OtrCryptoEngineImpl();
            // Uses r to decrypt the value of gx sent earlier
            byte[] remoteDHPublicKeyDecrypted = otrCryptoEngine.aesDecrypt(m.revealedKey, null,
                    this.getRemoteDHPublicKeyEncrypted());

            // Verifies that HASH(gx) matches the value sent earlier
            byte[] remoteDHPublicKeyHash = otrCryptoEngine.sha256Hash(remoteDHPublicKeyDecrypted);
            if (!Arrays.equals(remoteDHPublicKeyHash, this.getRemoteDHPublicKeyHash())) {
                logger.finest("Hashes don't match, ignoring message.");
                return;
            }

            // Verifies that Bob's gx is a legal value (2 <= gx <=
            // modulus-2)
            BigInteger remoteDHPublicKeyMpi;
            try {
                remoteDHPublicKeyMpi = SerializationUtils.readMpi(remoteDHPublicKeyDecrypted);
            } catch (IOException e) {
                throw new OtrException(e);
            }

            this.setRemoteDHPublicKey(otrCryptoEngine.getDHPublicKey(remoteDHPublicKeyMpi));

            // Verify received Data.
            if (!m.verify(this.getM2())) {
                logger.finest("Signature MACs are not equal, ignoring message.");
                return;
            }

            // Decrypt X.
            byte[] remoteXDecrypted = m.decrypt(this.getC());
            SignatureX remoteX;
            try {
                remoteX = SerializationUtils.toMysteriousX(remoteXDecrypted);
            } catch (IOException e) {
                throw new OtrException(e);
            }

            // Compute signature.
            PublicKey remoteLongTermPublicKey = remoteX.longTermPublicKey;
            SignatureM remoteM = new SignatureM(this.getRemoteDHPublicKey(), (DHPublicKey) this
                    .getLocalDHKeyPair().getPublic(), remoteLongTermPublicKey, remoteX.dhKeyID);

            // Verify signature.
            byte[] signature;
            try {
                signature = otrCryptoEngine.sha256Hmac(SerializationUtils.toByteArray(remoteM),
                        this.getM1());
            } catch (IOException e) {
                throw new OtrException(e);
            }

            if (!otrCryptoEngine.verify(signature, remoteLongTermPublicKey, remoteX.signature)) {
                session.showWarning("Bad revealed signature");
                logger.finest("Signature verification failed.");
                return;
            }

            logger.finest("Signature verification succeeded.");

            this.setAuthenticationState(AuthContext.NONE);
            this.setIsSecure(true);
            this.setRemoteLongTermPublicKey(remoteLongTermPublicKey);
            getSession().injectMessage(messageFactory.getSignatureMessage());
            break;
        default:
            logger.finest("Ignoring message.");
            break;
        }
    }

    private void handleDHKeyMessage(DHKeyMessage m) throws OtrException {
        Session session = getSession();
        SessionID sessionID = session.getSessionID();
        logger.finest(sessionID.getLocalUserId() + " received a D-H key message from "
                      + sessionID.getRemoteUserId() + " throught " + sessionID.getProtocolName() + ".");

        if (!session.getSessionPolicy().getAllowV2()) {
            logger.finest("If ALLOW_V2 is not set, ignore this message.");
            return;
        }

        switch (this.getAuthenticationState()) {
        case AWAITING_DHKEY:
            // Reply with a Reveal Signature Message and transition
            // authstate to
            // AUTHSTATE_AWAITING_SIG
            this.setRemoteDHPublicKey(m.dhPublicKey);
            this.setAuthenticationState(AuthContext.AWAITING_SIG);
            getSession().injectMessage(messageFactory.getRevealSignatureMessage());
            logger.finest("Sent Reveal Signature.");
            break;
        case AWAITING_SIG:

            if (m.dhPublicKey.getY().equals(this.getRemoteDHPublicKey().getY())) {
                // If this D-H Key message is the same the one you received
                // earlier (when you entered AUTHSTATE_AWAITING_SIG):
                // Retransmit
                // your Reveal Signature Message.
                getSession().injectMessage(messageFactory.getRevealSignatureMessage());
                logger.finest("Resent Reveal Signature.");
            } else {
                // Otherwise: Ignore the message.
                logger.finest("Ignoring message.");
            }
            break;
        default:
            // Ignore the message
            break;
        }
    }

    private void handleDHCommitMessage(DHCommitMessage m) throws OtrException {
        Session session = getSession();
        SessionID sessionID = session.getSessionID();
        logger.finest(sessionID.getLocalUserId() + " received a D-H commit message from "
                      + sessionID.getRemoteUserId() + " throught " + sessionID.getProtocolName() + ".");

        if (!session.getSessionPolicy().getAllowV2()) {
            logger.finest("ALLOW_V2 is not set, ignore this message.");
            return;
        }

        switch (this.getAuthenticationState()) {
        case NONE:
            // Reply with a D-H Key Message, and transition authstate to
            // AUTHSTATE_AWAITING_REVEALSIG.
            this.reset();
            this.setProtocolVersion(2);
            this.setRemoteDHPublicKeyEncrypted(m.dhPublicKeyEncrypted);
            this.setRemoteDHPublicKeyHash(m.dhPublicKeyHash);
            this.setAuthenticationState(AuthContext.AWAITING_REVEALSIG);
            getSession().injectMessage(messageFactory.getDHKeyMessage());
            logger.finest("Sent D-H key.");
            break;

        case AWAITING_DHKEY:
            // This is the trickiest transition in the whole protocol. It
            // indicates that you have already sent a D-H Commit message to
            // your
            // correspondent, but that he either didn't receive it, or just
            // didn't receive it yet, and has sent you one as well. The
            // symmetry
            // will be broken by comparing the hashed gx you sent in your
            // D-H
            // Commit Message with the one you received, considered as
            // 32-byte
            // unsigned big-endian values.
            BigInteger ourHash = new BigInteger(1, this.getLocalDHPublicKeyHash());
            BigInteger theirHash = new BigInteger(1, m.dhPublicKeyHash);

            if (theirHash.compareTo(ourHash) == -1) {
                // Ignore the incoming D-H Commit message, but resend your
                // D-H
                // Commit message.
                getSession().injectMessage(messageFactory.getDHCommitMessage());
                logger.finest("Ignored the incoming D-H Commit message, but resent our D-H Commit message.");
            } else {
                // *Forget* your old gx value that you sent (encrypted)
                // earlier,
                // and pretend you're in AUTHSTATE_NONE; i.e. reply with a
                // D-H
                // Key Message, and transition authstate to
                // AUTHSTATE_AWAITING_REVEALSIG.
                this.reset();
                this.setProtocolVersion(2);
                this.setRemoteDHPublicKeyEncrypted(m.dhPublicKeyEncrypted);
                this.setRemoteDHPublicKeyHash(m.dhPublicKeyHash);
                this.setAuthenticationState(AuthContext.AWAITING_REVEALSIG);
                getSession().injectMessage(messageFactory.getDHKeyMessage());
                logger.finest("Forgot our old gx value that we sent (encrypted) earlier, and pretended we're in AUTHSTATE_NONE -> Sent D-H key.");
            }
            break;

        case AWAITING_REVEALSIG:
            // Retransmit your D-H Key Message (the same one as you sent
            // when
            // you entered AUTHSTATE_AWAITING_REVEALSIG). Forget the old D-H
            // Commit message, and use this new one instead.
            this.setRemoteDHPublicKeyEncrypted(m.dhPublicKeyEncrypted);
            this.setRemoteDHPublicKeyHash(m.dhPublicKeyHash);
            getSession().injectMessage(messageFactory.getDHKeyMessage());
            logger.finest("Sent D-H key.");
            break;
        case AWAITING_SIG:
            // Reply with a new D-H Key message, and transition authstate to
            // AUTHSTATE_AWAITING_REVEALSIG
            this.reset();
            this.setRemoteDHPublicKeyEncrypted(m.dhPublicKeyEncrypted);
            this.setRemoteDHPublicKeyHash(m.dhPublicKeyHash);
            this.setAuthenticationState(AuthContext.AWAITING_REVEALSIG);
            getSession().injectMessage(messageFactory.getDHKeyMessage());
            logger.finest("Sent D-H key.");
            break;
        case V1_SETUP:
            throw new UnsupportedOperationException();
        }
    }

    public void startV2Auth() throws OtrException {
        logger.finest("Starting Authenticated Key Exchange, sending query message");
        getSession().injectMessage(messageFactory.getQueryMessage());
    }

    public void respondV2Auth() throws OtrException {
        logger.finest("Responding to Query Message");
        this.reset();
        this.setProtocolVersion(2);
        this.setAuthenticationState(AuthContext.AWAITING_DHKEY);
        logger.finest("Sending D-H Commit.");
        getSession().injectMessage(messageFactory.getDHCommitMessage());
    }

    private void setSession(Session session) {
        this.session = session;
    }

    private Session getSession() {
        return session;
    }

    private PublicKey remoteLongTermPublicKey;

    public PublicKey getRemoteLongTermPublicKey() {
        return remoteLongTermPublicKey;
    }

    private void setRemoteLongTermPublicKey(PublicKey pubKey) {
        this.remoteLongTermPublicKey = pubKey;
    }
}