private ChainKey getOrCreateChainKey(SessionState sessionState, ECPublicKey theirEphemeral)
{
try
{
if (sessionState.hasReceiverChain(theirEphemeral))
{
return sessionState.getReceiverChainKey(theirEphemeral);
}
else
{
RootKey rootKey = sessionState.getRootKey();
ECKeyPair ourEphemeral = sessionState.getSenderRatchetKeyPair();
Pair<RootKey, ChainKey> receiverChain = rootKey.createChain(theirEphemeral, ourEphemeral);
ECKeyPair ourNewEphemeral = Curve.generateKeyPair();
Pair<RootKey, ChainKey> senderChain = receiverChain.first().createChain(theirEphemeral, ourNewEphemeral);
sessionState.setRootKey(senderChain.first());
sessionState.addReceiverChain(theirEphemeral, receiverChain.second());
sessionState.setPreviousCounter(Math.Max(sessionState.getSenderChainKey().getIndex() - 1, 0));
sessionState.setSenderChain(ourNewEphemeral, senderChain.second());
return receiverChain.second();
}
}
catch (InvalidKeyException e)
{
throw new InvalidMessageException(e);
}
}
public static void initializeSession(SessionState sessionState,
uint sessionVersion,
AliceAxolotlParameters parameters)
{
try
{
sessionState.setSessionVersion(sessionVersion);
sessionState.setRemoteIdentityKey(parameters.getTheirIdentityKey());
sessionState.setLocalIdentityKey(parameters.getOurIdentityKey().getPublicKey());
ECKeyPair sendingRatchetKey = Curve.generateKeyPair();
MemoryStream secrets = new MemoryStream();
if (sessionVersion >= 3)
{
byte[] discontinuityBytes = getDiscontinuityBytes();
secrets.Write(discontinuityBytes, 0, discontinuityBytes.Length);
}
byte[] agree1 = Curve.calculateAgreement(parameters.getTheirSignedPreKey(),
parameters.getOurIdentityKey().getPrivateKey());
byte[] agree2 = Curve.calculateAgreement(parameters.getTheirIdentityKey().getPublicKey(),
parameters.getOurBaseKey().getPrivateKey());
byte[] agree3 = Curve.calculateAgreement(parameters.getTheirSignedPreKey(),
parameters.getOurBaseKey().getPrivateKey());
secrets.Write(agree1, 0, agree1.Length);
secrets.Write(agree2, 0, agree2.Length);
secrets.Write(agree3, 0, agree3.Length);
if (sessionVersion >= 3 && parameters.getTheirOneTimePreKey().HasValue)
{
byte[] agree4 = Curve.calculateAgreement(parameters.getTheirOneTimePreKey().ForceGetValue(),
parameters.getOurBaseKey().getPrivateKey());
secrets.Write(agree4, 0, agree4.Length);
}
DerivedKeys derivedKeys = calculateDerivedKeys(sessionVersion, secrets.ToArray());
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 Exception(e.Message);
}
}