internal async Task <string> ReceiveShortSingleMessageAsync(UserCertificate senderUserCertificate)
{
if (Logger.WriteToLog_detail_enabled)
{
Logger.WriteToLog_detail(">>InviteSession.ReceiveShortSingleMessageAsync()");
}
if (!DerivedDirectChannelSharedDhSecretsAE)
{
throw new InvalidOperationException("DerivedDirectChannelSharedDhSecretsAE = false");
}
var messageSession = new MessageSession();
// wait for msgstart
if (Logger.WriteToLog_detail_enabled)
{
Logger.WriteToLog_detail("waiting for MSGSTART");
}
var messageStartUdpData = await _localDrpPeer.Engine.OptionallySendUdpRequestAsync_Retransmit_WaitForResponse("msgstart 480", "remote user", null, RemoteSessionDescription.DirectChannelEndPoint,
MessageStartPacket.GetScanner(LocalDirectChannelToken32, this) // scanner verifies MessageHMAC
);
var messageStart = MessageStartPacket.Decode(messageStartUdpData);
if (Logger.WriteToLog_detail_enabled)
{
Logger.WriteToLog_detail("decoded MSGSTART");
}
messageSession.DeriveKeys(_localDrpPeer.CryptoLibrary, SharedPingPongHmacKey, messageStart, DirectChannelSharedDhSecret);
// decrypt
var receivedMessage = messageSession.DecryptShortSingleMessage(_localDrpPeer.CryptoLibrary, messageStart.EncryptedMessageData);
// respond with msgack + ReceiverFinalNonce
if (messageSession.Status != MessageSessionStatusCode.encryptionDecryptionCompleted)
{
throw new InvalidOperationException();
}
var messageAck = new MessageAckPacket
{
MessageId32 = messageStart.MessageId32,
ReceiverStatus = messageSession.Status,
ReceiverFinalNonce = _localDrpPeer.CryptoLibrary.GetRandomBytes(MessageAckPacket.ReceiverFinalNonceSize),
};
messageAck.MessageHMAC = GetMessageHMAC(messageAck.GetSignedFieldsForMessageHMAC);
var messageAckUdpData = messageAck.Encode();
if (Logger.WriteToLog_detail_enabled)
{
Logger.WriteToLog_detail("responding with MSGACK to MSGSTART");
}
_localDrpPeer.Engine.RespondToRequestAndRetransmissions(messageStart.DecodedUdpData, messageAckUdpData, RemoteSessionDescription.DirectChannelEndPoint);
// wait for msgpart with status=encryptionDecryptionCompleted
if (Logger.WriteToLog_detail_enabled)
{
Logger.WriteToLog_detail("waiting for with MSGPART");
}
var messagePartUdpData = await _localDrpPeer.Engine.OptionallySendUdpRequestAsync_Retransmit_WaitForResponse("msgpart 42486", "remote user", null,
RemoteSessionDescription.DirectChannelEndPoint,
MessagePartPacket.GetScanner(messageStart.MessageId32, this, MessageSessionStatusCode.encryptionDecryptionCompleted)
// scanner verifies MessageHMAC
);
var messagePart = MessagePartPacket.Decode(messagePartUdpData);
// verify signature of sender user
if (!messagePart.SenderSignature.Verify(_localDrpPeer.CryptoLibrary, w =>
{
w.Write(MessageHMACkey);
w.Write(messageSession.AesKey);
w.Write(messageStart.EncryptedMessageData);
w.Write(messageAck.ReceiverFinalNonce);
}, senderUserCertificate))
{
throw new BadSignatureException("bad MSGPART sender signature 3408");
}
if (Logger.WriteToLog_detail_enabled)
{
Logger.WriteToLog_detail("verified sender signature");
}
// send msgack status=finalSignatureVerified
messageSession.Status = MessageSessionStatusCode.finalSignatureVerified;
var messageAck_finalSignatureVerified = new MessageAckPacket
{
MessageId32 = messageStart.MessageId32,
ReceiverStatus = messageSession.Status,
};
messageAck_finalSignatureVerified.MessageHMAC = GetMessageHMAC(messageAck_finalSignatureVerified.GetSignedFieldsForMessageHMAC);
var messageAck_finalSignatureVerified_UdpData = messageAck_finalSignatureVerified.Encode();
if (Logger.WriteToLog_detail_enabled)
{
Logger.WriteToLog_detail("sending MSGACK response to MSGPART");
}
_localDrpPeer.Engine.RespondToRequestAndRetransmissions(messagePart.DecodedUdpData, messageAck_finalSignatureVerified_UdpData, RemoteSessionDescription.DirectChannelEndPoint);
return(receivedMessage);
}