/// <summary>
/// generates new snonce0 object
/// resets state when necessary
/// </summary>
public Snonce0State GenerateOrGetExistingSnonce0(uint timeSec32UTC, ICcpRemoteEndpoint clientEndpoint)
{
if (timeSec32UTC > _nextPeriodSwitchTimeSec32UTC || _currentPeriodStates.Count > _config.Snonce0TableMaxSize)
{ // switch tables
_previousPeriodStates = _currentPeriodStates;
_currentPeriodStates = new Dictionary <ICcpRemoteEndpoint, Snonce0State>();
_nextPeriodSwitchTimeSec32UTC = timeSec32UTC + _config.Snonce0TablePeriodSec;
}
var existingSnonce0 = TryGetSnonce0(clientEndpoint);
if (existingSnonce0 != null)
{
return(existingSnonce0);
}
var r = new Snonce0State
{
Snonce0 = new byte[ServerHelloPacket0.Snonce0SupportedSize]
};
_rnd.NextBytes(r.Snonce0);
_currentPeriodStates.Add(clientEndpoint, r);
return(r);
}
void RespondToHello0(ICcpRemoteEndpoint clientEndpoint, ServerHello0Status status, byte[] cnonce0)
{
var response = new ServerHelloPacket0 {
Status = status, Cnonce0 = cnonce0
};
var responseBytes = response.Encode();
_ccpTransport.SendPacket(clientEndpoint, responseBytes);
}
public Snonce0State TryGetSnonce0(ICcpRemoteEndpoint clientEndpoint)
{
if (_currentPeriodStates.TryGetValue(clientEndpoint, out var r))
{
return(r);
}
if (_previousPeriodStates.TryGetValue(clientEndpoint, out r))
{
return(r);
}
return(null);
}
void ICcpTransportUser.ProcessPacket(ICcpRemoteEndpoint remoteEndpoint, byte[] data) // receiver thread(s)
{
lock (_packetsToProcess)
{
if (_packetsToProcess.Count > _config.PacketProcessingQueueMaxCount)
{
OnPacketProcessingQueueOverloaded();
return;
}
_packetsToProcess.Enqueue(new ReceivedPacket {
ClientEndpoint = remoteEndpoint, Data = data
});
}
}
void ProcessClientHello1(ICcpRemoteEndpoint clientEndpoint, BinaryReader reader, byte[] payloadData) // packets processor thread
{
var snonce0 = _snonce0Table.TryGetSnonce0(clientEndpoint);
if (snonce0 == null)
{
HandleBadSnonce0(clientEndpoint);
return;
}
var packet = new ClientHelloPacket1(reader, payloadData);
// check snonce0
if (!MiscProcedures.EqualByteArrays(packet.Snonce0, snonce0.Snonce0))
{
HandleBadSnonce0(clientEndpoint);
return;
}
///check stateful PoW result
var hash = _cryptoLibrary.GetHashSHA256(packet.OriginalPacketPayload);
// calculate hash, considering entire packet data (including stateful PoW result)
// verify hash result
if (!StatefulPowHashIsOK(hash))
{
HandleBadStatefulPowPacket(clientEndpoint);
// no response
return;
}
// questionable: hello1IPlimit table: limit number of requests per 1 minute from every IPv4 block: max 100? requests per 1 minute from 1 block
// ------------ possible attack on hello1IPlimit table???
var response = new ServerHelloPacket1 {
Status = ServerHello1Status.OKready, Cnonce1 = packet.StatefulProofOfWorkResponseData
};
var responseBytes = response.Encode();
_ccpTransport.SendPacket(clientEndpoint, responseBytes);
}
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();
}
}
void HandleBadStatefulPowPacket(ICcpRemoteEndpoint remoteEndpoint)
{
//todo
}
void HandleBadSnonce0(ICcpRemoteEndpoint remoteEndpoint)
{//todo
}
/// <summary>
/// possibly but not neccessarily malformed, because it created an exception
/// </summary>
void HandleMalformedPacket(ICcpRemoteEndpoint remoteEndpoint)
{
//todo
}
void ICcpTransport.SendPacket(ICcpRemoteEndpoint remoteEndpoint, byte[] data)
{
var ep = (CcpUdpRemoteEndpoint)remoteEndpoint;
_socket.Send(data, data.Length, ep.Endpoint);
}