public static byte[] HandleSessionKey(byte[] sessionKey, byte[] sharedSecret)
{
byte[] iv = new byte[16];
new SecureRandom().NextBytes(iv);
TwofishEngine engine = new TwofishEngine();
CtrBlockCipher blockCipher = new CtrBlockCipher(engine);
PaddedBufferedBlockCipher bufferedBlockCipher = new PaddedBufferedBlockCipher(blockCipher, new ZeroBytePadding());
KeyParameter secret = new KeyParameter(sharedSecret);
ParametersWithIV key = new ParametersWithIV(secret, iv);
bufferedBlockCipher.Init(true, key);
byte[] result = new byte[iv.Length + sessionKey.Length];
bufferedBlockCipher.ProcessBytes(sessionKey, 0, sessionKey.Length, result, 16);
Array.Copy(iv, result, iv.Length);
int pos = 0;
while (pos < sessionKey.Length)
{
int length = blockCipher.ProcessBlock(sessionKey, pos, result, pos + iv.Length);
pos += length;
}
return(result);
}
public static byte[] HandleUser(byte[] cipher, byte[] secretKey)
{
TwofishEngine engine = new TwofishEngine();
CtrBlockCipher blockCipher = new CtrBlockCipher(engine);
KeyParameter secret = new KeyParameter(secretKey);
ParametersWithIV key = new ParametersWithIV(secret, cipher, 0, 16);
int cipherLength = cipher.Length;
int blockSize = engine.GetBlockSize();
int fraction = cipherLength % blockSize;
cipherLength += blockSize - fraction;
byte[] input = new byte[cipherLength];
Array.Copy(cipher, input, cipher.Length);
blockCipher.Init(false, key);
byte[] result = new byte[cipherLength - 16];
int pos = 0;
while (pos < cipher.Length - 16)
{
int length = blockCipher.ProcessBlock(input, pos + 16, result, pos);
pos += length;
}
return(result);
}