void ProcessClientHello0(ICcpRemoteEndpoint clientEndpoint, BinaryReader reader, byte[] payloadData) // packets processor thread
{
var packet = new ClientHelloPacket0(reader, payloadData);
if (!PassStatelessPoWfilter(clientEndpoint, packet))
{
return;
}
// create snonce0 state
var snonce0 = _snonce0Table.GenerateOrGetExistingSnonce0(TimeSec32UTC, clientEndpoint);
var response = new ServerHelloPacket0
{
Cnonce0 = packet.Cnonce0,
Snonce0 = snonce0.Snonce0,
Status = ServerHello0Status.OK,
StatefulProofOfWorkType = StatefulProofOfWorkType._2019_06
};
var responseBytes = response.Encode();
_ccpTransport.SendPacket(clientEndpoint, responseBytes);
}
bool PassStatelessPoWfilter(ICcpRemoteEndpoint clientEndpoint, ClientHelloPacket0 packet)// packets processor thread // sends responses
{
switch (packet.StatelessProofOfWorkType)
{
case StatelessProofOfWorkType._2019_06:
// verify size of PoW data
if (packet.StatelessProofOfWorkData.Length < 12 || packet.StatelessProofOfWorkData.Length > 64)
{
throw new CcpBadPacketException();
}
// verify datetime ("period")
// return err code if time is wrong, with correct server's UTC time
uint receivedTimeSec32;
unsafe
{
fixed(byte *statelessProofOfWorkDataPtr = packet.StatelessProofOfWorkData)
{
fixed(byte *addressBytesPtr = clientEndpoint.AddressBytes)
{
receivedTimeSec32 = *((uint *)statelessProofOfWorkDataPtr);
if (addressBytesPtr[0] != statelessProofOfWorkDataPtr[4] ||
addressBytesPtr[1] != statelessProofOfWorkDataPtr[5] ||
addressBytesPtr[2] != statelessProofOfWorkDataPtr[6] ||
addressBytesPtr[3] != statelessProofOfWorkDataPtr[7]
)
{
if (_config.RespondErrors)
{
RespondToHello0(clientEndpoint, ServerHello0Status.ErrorBadStatelessProofOfWork_BadSourceIp, packet.Cnonce0);
}
return(false);
}
}
}
}
var localTimeSec32 = TimeSec32UTC;
var diffSec = Math.Abs((int)unchecked (localTimeSec32 - receivedTimeSec32));
if (diffSec > _config.StatelessPoW_MaxClockDifferenceS)
{
// respond with error "try again with valid clock" - legitimate user has to get valid clock from some time server and synchronize itself with the server
if (_config.RespondErrors)
{
RespondToHello0(clientEndpoint, ServerHello0Status.ErrorBadStatelessProofOfWork_BadClock, packet.Cnonce0);
}
return(false);
}
var hash = _cryptoLibrary.GetHashSHA256(packet.OriginalPacketPayload);
// calculate hash, considering entire packet data (including stateless PoW result)
// verify hash result
if (!StatelessPowHashIsOK(hash))
{
HandleBadStatelessPowPacket(clientEndpoint);
// no response
return(false);
}
// check if hash is unique
var dataIsUnique = _recentUniquePowData.TryInputData(hash, localTimeSec32);
if (dataIsUnique)
{
return(true);
}
else
{
// respond with error "try again with unique PoW data"
if (_config.RespondErrors)
{
RespondToHello0(clientEndpoint, ServerHello0Status.ErrorTryAgainRightNowWithThisServer, packet.Cnonce0);
}
return(false);
}
default:
throw new CcpBadPacketException();
}
}