public static byte[] Decrypt(byte[] key, byte[] ciphertext)
{
if (key == null) throw new ArgumentNullException("key");
if (key.Length != 16)
throw new ArgumentOutOfRangeException("key length must be 16 bytes");
if (ciphertext == null) throw new ArgumentNullException("ciphertext");
if ((ciphertext.Length % 8) != 0)
throw new Exception("ciphertext length must be a multiple of 8 bytes");
byte[] input_whitening_key = new byte[8];
Buffer.BlockCopy(key, 8, input_whitening_key, 0, 8);
byte[] output_whitening_key = BuildOutputWhiteningKey(key);
XOR input_whitener = new XOR(input_whitening_key);
XOR output_whitener = new XOR(output_whitening_key);
byte[] plaintext = new byte[ciphertext.Length];
byte[] desKey = new byte[8];
Buffer.BlockCopy(key, 0, desKey, 0, 8);
for (int i = 0; i < (ciphertext.Length / 8); i++)
{
byte[] ciphertextBytes = new byte[8];
Buffer.BlockCopy(ciphertext, i * 8, ciphertextBytes, 0, 8);
byte[] whitenedCiphertextBytes = output_whitener.Crypt(ciphertextBytes);
byte[] decryptedBytes =
input_whitener.Crypt(DecryptBytes(desKey, new byte[8], whitenedCiphertextBytes));
Buffer.BlockCopy(decryptedBytes, 0, plaintext, i * 8, decryptedBytes.Length);
}
return plaintext;
}