How can I decrypt an encrypted MCRYPT_RIJNDAEL_256 value in C#, that was encrypted by mcrypt in PHP?

Question

I am trying to read a Base64-Encoded value from a Database table managed on the Linux side. In that table there is a column called first_name. On the Linux side I can decrypt t

Answer 1

Post is old, but this might help somebody in a future. This function encrypt exactly like mcrypt_encrypt with parameters MCRYPT_RIJNDAEL_256 and MCRYPT_MODE_ECB

    static byte[] EncryptStringToBytes(string plainText, byte[] key)
    {
        if (plainText == null || plainText.Length <= 0)
            throw new ArgumentNullException("plainText");
        if (key == null || key.Length <= 0)
            throw new ArgumentNullException("key");

        byte[] encrypted;
        using (var rijAlg = new RijndaelManaged())
        {
            rijAlg.BlockSize = 256;
            rijAlg.Key = key;
            rijAlg.Mode = CipherMode.ECB;
            rijAlg.Padding = PaddingMode.Zeros;
            rijAlg.IV = new byte[] { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };

            ICryptoTransform encryptor = rijAlg.CreateEncryptor(rijAlg.Key, rijAlg.IV);
            using (var msEncrypt = new MemoryStream())
                using (var csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))
                {
                    using (var swEncrypt = new StreamWriter(csEncrypt))
                        swEncrypt.Write(plainText);
                    encrypted = msEncrypt.ToArray();
                }
        }
        return encrypted;
    }

And here is function to decrypt it

     static string DecryptStringFromBytes(byte[] cipherText, byte[] key)
     {
        if (cipherText == null || cipherText.Length <= 0)
            throw new ArgumentNullException("cipherText");
        if (key == null || key.Length <= 0)
            throw new ArgumentNullException("key");

        string plaintext;
        using (var rijAlg = new RijndaelManaged())
        {
            rijAlg.BlockSize = 256;
            rijAlg.Key = key;
            rijAlg.Mode = CipherMode.ECB;
            rijAlg.Padding = PaddingMode.Zeros;
            rijAlg.IV = new byte[] { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };

            ICryptoTransform decryptor = rijAlg.CreateDecryptor(rijAlg.Key, rijAlg.IV);
            using (var msDecrypt = new MemoryStream(cipherText))
                using (var csDecrypt = new CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Read))
                    using (var srDecrypt = new StreamReader(csDecrypt))
                        plaintext = srDecrypt.ReadToEnd();
        }
        return plaintext;
    }