Wrong algorithm: AES or Rijndael required on c#

Question

I had andriod code and I tried to convert it to c#. It's a simple Encryption class. But when I try to decrypt data with it I catch: Wrong algorithm: AES or Rijndael required.
Here is my converted code:

public static string decrypt(string data)
{
    byte[] dataBytes = Convert.FromBase64String(data);
    SecretKey secretKey = getSecretKey(hashTheKey("ABCD"));

    Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");

    cipher.init(2, secretKey, new IvParameterSpec(new byte[16]),
            SecureRandom.getInstance("SHA1PRNG"));
    var x = cipher.doFinal(dataBytes);
    return System.Text.Encoding.UTF8.GetString(x);
}
public static SecretKey getSecretKey(char[] key)
{
    var secretKeyType = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1");
    var secretkey = secretKeyType.generateSecret(new PBEKeySpec(key,
            System.Text.Encoding.UTF8
                .GetBytes("ABCD"),
            100, 128)).getEncoded();

    return new SecretKeySpec(secretkey, "AES/CBC/PKCS5Padding");
}
public static char[] hashTheKey(string key)
{
    MessageDigest messageDigest = MessageDigest.getInstance("SHA1");
    messageDigest.update(System.Text.Encoding.UTF8.GetBytes(key));
    return Convert.ToBase64String(messageDigest.digest()).ToCharArray();
}

Here is my original android code:

private char[] hashTheKey(String key) throws UnsupportedEncodingException, NoSuchAlgorithmException {
    MessageDigest messageDigest = MessageDigest.getInstance("SHA1");
    messageDigest.update(key.getBytes());
    return Base64.encodeToString(messageDigest.digest(),
                                 Base64.NO_PADDING).toCharArray();
}

private SecretKey getSecretKey(char[] key) throws NoSuchAlgorithmException, UnsupportedEncodingException, InvalidKeySpecException {
    return new SecretKeySpec(
        SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1")
        .generateSecret(new PBEKeySpec(key,
                       "ABCD".getBytes("UTF8"),
                       100, 128)).getEncoded(), "AES");
}

public String decrypt(String data) throws NoSuchPaddingException, NoSuchAlgorithmException, InvalidAlgorithmParameterException, InvalidKeyException, BadPaddingException, IllegalBlockSizeException, UnsupportedEncodingException, InvalidKeySpecException {
    byte[] dataBytes = Base64.decode(data, Base64.DEFAULT);
    SecretKey secretKey = getSecretKey(hashTheKey("ABCD"));
    Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
    cipher.init(2, secretKey, new IvParameterSpec(new byte[16]),
            SecureRandom.getInstance("SHA1PRNG"));
    return new String(cipher.doFinal(dataBytes));
}

Answer 1

c# and java are using the same well-estabilished cryptography algorithms, but differs in approach how to invoke them. It is still possible to convert the code though.

One key point is difference in base64 encoding - C# always use padding.

Converted code goes like:

const int KeySize = 128;

static string HashTheKey(string key) {
  String hashKey;
  using (var sha = new SHA1Managed()) {
   hashKey = Convert.ToBase64String(sha.ComputeHash(Encoding.UTF8.GetBytes(key)));
  }
  // beware - you're on C# now so remove the padding and add the newline to match java
  return hashKey.Replace("=", "") + "\n";
}

static byte[] GetSecretKey(string password) {
  var salt = Encoding.UTF8.GetBytes("JVAaVhAiddKAaghraikhmaini");
  using (var pass = new Rfc2898DeriveBytes(password, salt, 65536)) {
    return pass.GetBytes(KeySize / 8);
  }
}

static void Main(string[] args) {
  string encrypted = "vtlkQHTz7/oz2weuAAkLz2Q5c2yj2LGukF7SHJjT+TA8oRLixTQSXQ7dG1O736hyT1HJxcz0P4DzzVaO5chWKKSJQ2uPEpDQJu/fZGguqDw=";
  byte[] encryptedBytes = Convert.FromBase64String(encrypted);
  using (var aes = new AesManaged()) {
    aes.KeySize = KeySize;
    aes.Padding = PaddingMode.PKCS7;
    aes.Key = GetSecretKey(HashTheKey("Android"));
    // you're using the same init vector in your android code
    aes.IV = new byte[16];
    using (var decryptor = aes.CreateDecryptor()) {
      // dumps {"barcode":"12345678","token":"cad603fc-1e53-4a95-9150-f1694baa07f9"}
      Console.Out.WriteLine(Encoding.UTF8.GetString(decryptor.TransformFinalBlock(encryptedBytes, 0, encryptedBytes.Length)));
    }
  }
}

Answer 2

C# does not handle the encryption algorithms as Android or java do you have to use either AES or Rijndael algorithm as you can see the error to covert to the simple text into Encrypted Base64 and vice versa you can use the following class in C#

public static class Stringcipher
    {
        // This constant is used to determine the keysize of the encryption algorithm in bits.
        // We divide this by 8 within the code below to get the equivalent number of bytes.
        private const int Keysize = 256;

        // This constant determines the number of iterations for the password bytes generation function.
        private const int DerivationIterations = 1000;

        public static string Encrypt(string plainText, string passPhrase)
        {
            // Salt and IV is randomly generated each time, but is preprended to encrypted cipher text
            // so that the same Salt and IV values can be used when decrypting.  
            var saltStringBytes = Generate256BitsOfRandomEntropy();
            var ivStringBytes = Generate256BitsOfRandomEntropy();
            var plainTextBytes = Encoding.UTF8.GetBytes(plainText);
            using (var password = new Rfc2898DeriveBytes(passPhrase, saltStringBytes, DerivationIterations))
            {
                var keyBytes = password.GetBytes(Keysize / 8);
                using (var symmetricKey = new RijndaelManaged())
                {
                    symmetricKey.BlockSize = 256;
                    symmetricKey.Mode = CipherMode.CBC;
                    symmetricKey.Padding = PaddingMode.PKCS7;
                    using (var encryptor = symmetricKey.CreateEncryptor(keyBytes, ivStringBytes))
                    {
                        using (var memoryStream = new MemoryStream())
                        {
                            using (var cryptoStream = new CryptoStream(memoryStream, encryptor, CryptoStreamMode.Write))
                            {
                                cryptoStream.Write(plainTextBytes, 0, plainTextBytes.Length);
                                cryptoStream.FlushFinalBlock();
                                // Create the final bytes as a concatenation of the random salt bytes, the random iv bytes and the cipher bytes.
                                var cipherTextBytes = saltStringBytes;
                                cipherTextBytes = cipherTextBytes.Concat(ivStringBytes).ToArray();
                                cipherTextBytes = cipherTextBytes.Concat(memoryStream.ToArray()).ToArray();
                                memoryStream.Close();
                                cryptoStream.Close();
                                return Convert.ToBase64String(cipherTextBytes);
                            }
                        }
                    }
                }
            }
        }

        public static string Decrypt(string cipherText, string passPhrase)
        {
            // Get the complete stream of bytes that represent:
            // [32 bytes of Salt] + [32 bytes of IV] + [n bytes of CipherText]
            var cipherTextBytesWithSaltAndIv = Convert.FromBase64String(cipherText);
            // Get the saltbytes by extracting the first 32 bytes from the supplied cipherText bytes.
            var saltStringBytes = cipherTextBytesWithSaltAndIv.Take(Keysize / 8).ToArray();
            // Get the IV bytes by extracting the next 32 bytes from the supplied cipherText bytes.
            var ivStringBytes = cipherTextBytesWithSaltAndIv.Skip(Keysize / 8).Take(Keysize / 8).ToArray();
            // Get the actual cipher text bytes by removing the first 64 bytes from the cipherText string.
            var cipherTextBytes = cipherTextBytesWithSaltAndIv.Skip((Keysize / 8) * 2).Take(cipherTextBytesWithSaltAndIv.Length - ((Keysize / 8) * 2)).ToArray();

            using (var password = new Rfc2898DeriveBytes(passPhrase, saltStringBytes, DerivationIterations))
            {
                var keyBytes = password.GetBytes(Keysize / 8);
                using (var symmetricKey = new RijndaelManaged())
                {
                    symmetricKey.BlockSize = 256;
                    symmetricKey.Mode = CipherMode.CBC;
                    symmetricKey.Padding = PaddingMode.PKCS7;
                    using (var decryptor = symmetricKey.CreateDecryptor(keyBytes, ivStringBytes))
                    {
                        using (var memoryStream = new MemoryStream(cipherTextBytes))
                        {
                            using (var cryptoStream = new CryptoStream(memoryStream, decryptor, CryptoStreamMode.Read))
                            {
                                var plainTextBytes = new byte[cipherTextBytes.Length];
                                var decryptedByteCount = cryptoStream.Read(plainTextBytes, 0, plainTextBytes.Length);
                                memoryStream.Close();
                                cryptoStream.Close();
                                return Encoding.UTF8.GetString(plainTextBytes, 0, decryptedByteCount);
                            }
                        }
                    }
                }
            }
        }

        private static byte[] Generate256BitsOfRandomEntropy()
        {
            var randomBytes = new byte[32]; // 32 Bytes will give us 256 bits.
            using (var rngCsp = new RNGCryptoServiceProvider())
            {
                // Fill the array with cryptographically secure random bytes.
                rngCsp.GetBytes(randomBytes);
            }
            return randomBytes;
        }
    }