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/**
* Copyright (C) 2014 Open Whisper Systems
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
package org.whispersystems.libaxolotl.ratchet;
import org.whispersystems.libaxolotl.InvalidKeyException;
import org.whispersystems.libaxolotl.ecc.Curve;
import org.whispersystems.libaxolotl.ecc.ECKeyPair;
import org.whispersystems.libaxolotl.ecc.ECPublicKey;
import org.whispersystems.libaxolotl.kdf.HKDF;
import org.whispersystems.libaxolotl.state.SessionState;
import org.whispersystems.libaxolotl.util.ByteUtil;
import org.whispersystems.libaxolotl.util.Pair;
import org.whispersystems.libaxolotl.util.guava.Optional;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.util.Arrays;
public class RatchetingSession {
public static void initializeSession(SessionState sessionState,
int sessionVersion,
SymmetricAxolotlParameters parameters)
throws InvalidKeyException
{
if (isAlice(parameters.getOurBaseKey().getPublicKey(), parameters.getTheirBaseKey())) {
AliceAxolotlParameters.Builder aliceParameters = AliceAxolotlParameters.newBuilder();
aliceParameters.setOurBaseKey(parameters.getOurBaseKey())
.setOurIdentityKey(parameters.getOurIdentityKey())
.setTheirRatchetKey(parameters.getTheirRatchetKey())
.setTheirIdentityKey(parameters.getTheirIdentityKey())
.setTheirSignedPreKey(parameters.getTheirBaseKey())
.setTheirOneTimePreKey(Optional.<ECPublicKey>absent());
RatchetingSession.initializeSession(sessionState, sessionVersion, aliceParameters.create());
} else {
BobAxolotlParameters.Builder bobParameters = BobAxolotlParameters.newBuilder();
bobParameters.setOurIdentityKey(parameters.getOurIdentityKey())
.setOurRatchetKey(parameters.getOurRatchetKey())
.setOurSignedPreKey(parameters.getOurBaseKey())
.setOurOneTimePreKey(Optional.<ECKeyPair>absent())
.setTheirBaseKey(parameters.getTheirBaseKey())
.setTheirIdentityKey(parameters.getTheirIdentityKey());
RatchetingSession.initializeSession(sessionState, sessionVersion, bobParameters.create());
}
}
public static void initializeSession(SessionState sessionState,
int sessionVersion,
AliceAxolotlParameters parameters)
throws InvalidKeyException
{
try {
sessionState.setSessionVersion(sessionVersion);
sessionState.setRemoteIdentityKey(parameters.getTheirIdentityKey());
sessionState.setLocalIdentityKey(parameters.getOurIdentityKey().getPublicKey());
ECKeyPair sendingRatchetKey = Curve.generateKeyPair();
ByteArrayOutputStream secrets = new ByteArrayOutputStream();
if (sessionVersion >= 3) {
secrets.write(getDiscontinuityBytes());
}
secrets.write(Curve.calculateAgreement(parameters.getTheirSignedPreKey(),
parameters.getOurIdentityKey().getPrivateKey()));
secrets.write(Curve.calculateAgreement(parameters.getTheirIdentityKey().getPublicKey(),
parameters.getOurBaseKey().getPrivateKey()));
secrets.write(Curve.calculateAgreement(parameters.getTheirSignedPreKey(),
parameters.getOurBaseKey().getPrivateKey()));
if (sessionVersion >= 3 & parameters.getTheirOneTimePreKey().isPresent()) {
secrets.write(Curve.calculateAgreement(parameters.getTheirOneTimePreKey().get(),
parameters.getOurBaseKey().getPrivateKey()));
}
DerivedKeys derivedKeys = calculateDerivedKeys(sessionVersion, secrets.toByteArray());
Pair<RootKey, ChainKey> sendingChain = derivedKeys.getRootKey().createChain(parameters.getTheirRatchetKey(), sendingRatchetKey);
sessionState.addReceiverChain(parameters.getTheirRatchetKey(), derivedKeys.getChainKey());
sessionState.setSenderChain(sendingRatchetKey, sendingChain.second());
sessionState.setRootKey(sendingChain.first());
} catch (IOException e) {
throw new AssertionError(e);
}
}
public static void initializeSession(SessionState sessionState,
int sessionVersion,
BobAxolotlParameters parameters)
throws InvalidKeyException
{
try {
sessionState.setSessionVersion(sessionVersion);
sessionState.setRemoteIdentityKey(parameters.getTheirIdentityKey());
sessionState.setLocalIdentityKey(parameters.getOurIdentityKey().getPublicKey());
ByteArrayOutputStream secrets = new ByteArrayOutputStream();
if (sessionVersion >= 3) {
secrets.write(getDiscontinuityBytes());
}
secrets.write(Curve.calculateAgreement(parameters.getTheirIdentityKey().getPublicKey(),
parameters.getOurSignedPreKey().getPrivateKey()));
secrets.write(Curve.calculateAgreement(parameters.getTheirBaseKey(),
parameters.getOurIdentityKey().getPrivateKey()));
secrets.write(Curve.calculateAgreement(parameters.getTheirBaseKey(),
parameters.getOurSignedPreKey().getPrivateKey()));
if (sessionVersion >= 3 && parameters.getOurOneTimePreKey().isPresent()) {
secrets.write(Curve.calculateAgreement(parameters.getTheirBaseKey(),
parameters.getOurOneTimePreKey().get().getPrivateKey()));
}
DerivedKeys derivedKeys = calculateDerivedKeys(sessionVersion, secrets.toByteArray());
sessionState.setSenderChain(parameters.getOurRatchetKey(), derivedKeys.getChainKey());
sessionState.setRootKey(derivedKeys.getRootKey());
} catch (IOException e) {
throw new AssertionError(e);
}
}
private static byte[] getDiscontinuityBytes() {
byte[] discontinuity = new byte[32];
Arrays.fill(discontinuity, (byte) 0xFF);
return discontinuity;
}
private static DerivedKeys calculateDerivedKeys(int sessionVersion, byte[] masterSecret) {
HKDF kdf = HKDF.createFor(sessionVersion);
byte[] derivedSecretBytes = kdf.deriveSecrets(masterSecret, "WhisperText".getBytes(), 64);
byte[][] derivedSecrets = ByteUtil.split(derivedSecretBytes, 32, 32);
return new DerivedKeys(new RootKey(kdf, derivedSecrets[0]),
new ChainKey(kdf, derivedSecrets[1], 0));
}
private static boolean isAlice(ECPublicKey ourKey, ECPublicKey theirKey) {
return ourKey.compareTo(theirKey) < 0;
}
private static class DerivedKeys {
private final RootKey rootKey;
private final ChainKey chainKey;
private DerivedKeys(RootKey rootKey, ChainKey chainKey) {
this.rootKey = rootKey;
this.chainKey = chainKey;
}
public RootKey getRootKey() {
return rootKey;
}
public ChainKey getChainKey() {
return chainKey;
}
}
}
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