private MessageKeys getOrCreateMessageKeys(SessionState sessionState,
ECPublicKey theirEphemeral,
ChainKey chainKey, uint counter)
{
if (chainKey.getIndex() > counter)
{
if (sessionState.hasMessageKeys(theirEphemeral, counter))
{
return sessionState.removeMessageKeys(theirEphemeral, counter);
}
else
{
throw new DuplicateMessageException($"Received message with old counter: {chainKey.getIndex()} , {counter}");
}
}
//Avoiding a uint overflow
uint chainKeyIndex = chainKey.getIndex();
if ((counter > chainKeyIndex) && (counter - chainKeyIndex > 2000))
{
throw new InvalidMessageException("Over 2000 messages into the future!");
}
while (chainKey.getIndex() < counter)
{
MessageKeys messageKeys = chainKey.getMessageKeys();
sessionState.setMessageKeys(theirEphemeral, messageKeys);
chainKey = chainKey.getNextChainKey();
}
sessionState.setReceiverChainKey(theirEphemeral, chainKey.getNextChainKey());
return chainKey.getMessageKeys();
}