Swiftly following on from my last TripleDES-related question, here's my TripleDES wrapper code, which is used to encrypt and decrypt integers:
public static class Crypto {
private static Byte[] _fixedIv = new Byte[] { /* 8 random bytes, const */ };
private static TripleDES _tripleDes;
private static Byte[] _key;
static Crypto() {
_tripleDes = TripleDES.Create();
_tripleDes.Mode = CipherMode.CFB;
String key = ConfigurationManager.AppSettings["cryptoKeyId"];
_key = Convert.FromBase64String( key );
}
/// <summary>Encrypts the specified integer using the configuration-stored key.</summary>
public static String EncryptID(Int32 id) {
Byte[] input = new Byte[8]; // 64-bit block size
Byte[] inputLo = BitConverter.GetBytes( id );
for(int i=0;i<inputLo.Length;i++) input[i] = inputLo[i];
ICryptoTransform tr = _tripleDes.CreateEncryptor( _key, _fixedIv );
Byte[] output = new Byte[8];
tr.TransformBlock( input, 0, input.Length, output, 0 );
return Convert.ToBase64String( output );
}
/// <summary>Decrypts the specified string (storing an integer) using the configuration-stored key.</summary>
public static Int32 DecryptID(String s) {
Byte[] ciphertext = Convert.FromBase64String(s);
ICryptoTransform tr = _tripleDes.CreateDecryptor( _key, _fixedIv );
Byte[] output = new Byte[8];
tr.TransformBlock( ciphertext, 0, ciphertext.Length, output, 0 );
Byte[] outputLo = new Byte[4] { output[0], output[1], output[2], output[3] };
return BitConverter.ToInt32( outputLo, 0 );
}
}
When I run it, I get deterministic results for each input to EncryptID, but every call to DecryptID returns zero. I stepped into the code and say that the contents of the 'output' array are all zero (and tr.TransformBlock returns zero). Does anyone know what I'm doing wrong?
I tried calling tr.TransformFinalBlock but I got an exception:
'tr.TransformFinalBlock( ciphertext, 0, ciphertext.Length )' threw an exception of type System.Security.Cryptography.CryptographicException' base {System.SystemException}: {"Bad Data.\r\n"}
