MCRYPT in .Net

I have come out with a solution in my blog.

Here is an excerpt :

    private static string CreateEncryptedString(string myString, string hexiv, string key)
    {
        RijndaelManaged alg = new RijndaelManaged();
        alg.Padding = PaddingMode.Zeros;
        alg.Mode = CipherMode.CBC;
        alg.BlockSize = 16 * 8;
        alg.Key = ASCIIEncoding.UTF8.GetBytes(key);
        alg.IV = StringToByteArray(hexiv);
        ICryptoTransform encryptor = alg.CreateEncryptor(alg.Key, alg.IV);

        MemoryStream msStream = new MemoryStream();
        CryptoStream mCSWriter = new CryptoStream(msStream, encryptor, CryptoStreamMode.Write);
        StreamWriter mSWriter = new StreamWriter(mCSWriter);
        mSWriter.Write(myString);
        mSWriter.Flush();
        mCSWriter.FlushFinalBlock();

        var EncryptedByte = new byte[msStream.Length];
        msStream.Position = 0;
        msStream.Read(EncryptedByte, 0, (int)msStream.Length);

        return ByteArrayToHexString(EncryptedByte);

    }

    public static byte[] StringToByteArray(String hex)
    {
        int NumberChars = hex.Length;
        byte[] bytes = new byte[NumberChars / 2];
        for (int i = 0; i < NumberChars; i += 2)
            bytes[i / 2] = Convert.ToByte(hex.Substring(i, 2), 16);
        return bytes;
    }

    public static string ByteArrayToHexString(byte[] ba)
    {
        StringBuilder hex = new StringBuilder(ba.Length * 2);
        foreach (byte b in ba)
            hex.AppendFormat("{0:x2}", b);
        return hex.ToString();
    }

There is one thing to note. The key size must be 16. Which means that key parameter must be a string with 16 characters. Or else the encryption won't work and will throw a CryptographicException.

On the PHP end, here's how you do the decoding:

$cipher_alg = MCRYPT_RIJNDAEL_128;
$decrypted_string = mcrypt_decrypt($cipher_alg, $key, 
$encrypted_string , MCRYPT_MODE_CBC, trim(hex2bin(trim($hexiv))));