/// <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;
}
