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);
}
}