/// <summary>
/// Decrypt using XTEA algo and verify CRC
/// </summary>
/// <returns>true for success, false for failure</returns>
internal bool DecryptSymmetric(NetBuffer buffer)
{
int bufLen = buffer.LengthBytes;
if (bufLen % 8 != 0)
{
if (NetBase.CurrentContext != null && NetBase.CurrentContext.Log != null)
NetBase.CurrentContext.Log.Info("Bad buffer size in DecryptSymmetricInPlace()");
return false;
}
//NetBase.CurrentContext.Log.Debug.Debug("Decrypting using key: " + Convert.ToBase64String(m_xtea.Key));
// decrypt
for (int i = 0; i < bufLen; i += 8)
m_xtea.DecryptBlock(buffer.Data, i, buffer.Data, i);
int numPadBits = buffer.Data[bufLen - 1];
buffer.Data[bufLen - 1] = 0; // zap for correct crc calculation
int dataBits = (bufLen * 8) - (24 + numPadBits); // include pad and crc
buffer.ResetReadPointer(dataBits);
ushort statedCrc = buffer.ReadUInt16();
// zap crc to be able to compare
buffer.ResetWritePointer(dataBits);
buffer.Write((ushort)0);
ushort dataCrc = Checksum.Adler16(buffer.Data, 0, bufLen);
//NetBase.CurrentContext.Log.Debug("Plain (len " + bufLen + "): " + Convert.ToBase64String(buffer.Data, 0, bufLen) + " Stated CRC: " + statedCrc + " Calc: " + realCrc);
if (statedCrc != dataCrc)
{
if (NetBase.CurrentContext != null && NetBase.CurrentContext.Log != null)
NetBase.CurrentContext.Log.Warning("CRC failure; expected " + dataCrc + " found " + statedCrc + " dropping packet!");
return false;
}
// clean up
buffer.LengthBits = dataBits;
buffer.ResetReadPointer();
return true;
}
internal void Encode(NetConnection connection, NetBuffer intoBuffer)
{
if (m_type == NetMessageType.None)
m_type = NetMessageType.User;
intoBuffer.Write((byte)m_type, 3);
switch(m_type)
{
case NetMessageType.UserFragmented:
case NetMessageType.User:
case NetMessageType.Acknowledge:
case NetMessageType.AcknowledgeBitField:
intoBuffer.Write((byte)m_sequenceChannel, 5); // encode channel
intoBuffer.Write(m_sequenceNumber, 12); // encode sequence number
break;
}
int byteLen = (m_buffer == null ? 0 : m_buffer.LengthBytes);
if (m_type == NetMessageType.UserFragmented || m_type == NetMessageType.User || m_type == NetMessageType.Discovery || m_type == NetMessageType.Handshake)
intoBuffer.Write(byteLen, 12); // encode length
// encode payload
if (byteLen > 0)
intoBuffer.Write(m_buffer.Data, 0, byteLen);
return;
}
/// <summary>
/// Append a CRC checksum and encrypt data in place using XTEA
/// </summary>
internal void EncryptSymmetric(NetBuffer buffer)
{
//string plain = Convert.ToBase64String(buffer.Data, 0, buffer.LengthBytes);
int bufferLen = buffer.LengthBytes;
// calculate number of pad bits
int dataBits = buffer.LengthBits;
int bitsNeeded = dataBits + 24; // 24 extra for crc and num-pad-bits
int totalBits = bitsNeeded + (64 - (bitsNeeded % 64));
int padBits = totalBits - bitsNeeded;
// write to ensure zeroes in buffer (crc and num-pad-bits space)
buffer.Write((uint)0, 24);
if (padBits > 0)
buffer.Write((ulong)0, padBits);
int writePadBitsPosition = buffer.LengthBits - 8;
// write crc
ushort crc = Checksum.Adler16(buffer.Data, 0, buffer.LengthBytes);
buffer.ResetWritePointer(dataBits);
buffer.Write(crc);
// write num-pad-bits in LAST byte
buffer.ResetWritePointer(writePadBitsPosition);
buffer.Write((byte)padBits);
// encrypt in place
int ptr = 0;
bufferLen = buffer.LengthBytes;
while (ptr < bufferLen)
{
m_xtea.EncryptBlock(buffer.Data, ptr, buffer.Data, ptr);
ptr += 8;
}
return;
}
