using System;

using System.Security.Cryptography;

using System.Text;

using System.IO;

​

public class Program

{

    private static string key = "NKu84HvQaPRr";

    private static string encryptedValue = "G/jBikRLNfxTlr3WAL/iOg==";

    private static string iv = "abcdef987654";

    public static void Main()

    {

        // Console.WriteLine(OpenSslDecrypt(encryptedValue, key));

        Console.WriteLine(DecryptPHP(encryptedValue));

    //Console.WriteLine(HMACThing());

    }

​

    public static string HMACThing()

    {

        using (var hmacsha256 = new HMACSHA256(System.Text.ASCIIEncoding.UTF8.GetBytes("15081947")))

        {

            hmacsha256.ComputeHash(System.Text.ASCIIEncoding.UTF8.GetBytes("state_code=4"));

            return ByteToString(hmacsha256.Hash);

        }

    }

​

    static string ByteToString(byte[] buff)

    {

        string sbinary = "";

        for (int i = 0; i < buff.Length; i++)

            sbinary += buff[i].ToString("X2"); /* hex format */

        return sbinary;

    }

​

    public static string DecryptPHP(string encrypted)

    {

        //get the encrypted data and decrypt

        byte[] encryptedBytes = Convert.FromBase64String(encryptedValue);

        byte[] keyBytes = System.Text.ASCIIEncoding.UTF8.GetBytes(key);

        byte[] keyBytesFixed = new byte[16];

        keyBytes.CopyTo(keyBytesFixed, 0);

        byte[] ivBytes = System.Text.ASCIIEncoding.UTF8.GetBytes(iv);

        byte[] ivBytesFixed = new byte[16];

        ivBytes.CopyTo(ivBytesFixed, 0);

        return DecryptStringFromBytesAes(encryptedBytes, keyBytesFixed, ivBytesFixed);

    }

​

    public static string DecryptStringFromBytesAes(byte[] cipherText, byte[] key, byte[] iv)

    {

        // Check arguments.

        if (cipherText == null || cipherText.Length <= 0)

            throw new ArgumentNullException("cipherText");

        if (key == null || key.Length <= 0)

            throw new ArgumentNullException("key");

        if (iv == null || iv.Length <= 0)

            throw new ArgumentNullException("iv");

        // Declare the RijndaelManaged object

        // used to decrypt the data.

        RijndaelManaged aesAlg = null;

        // Declare the string used to hold

        // the decrypted text.

        string plaintext;

        // Create a RijndaelManaged object

        // with the specified key and IV.

        aesAlg = new RijndaelManaged{Mode = CipherMode.CBC, Padding = PaddingMode.Zeros, KeySize = 256, BlockSize = 128, Key = key, IV = iv};

        // Create a decrytor to perform the stream transform.

        ICryptoTransform decryptor = aesAlg.CreateDecryptor(aesAlg.Key, aesAlg.IV);

        // Create the streams used for decryption.

        using (MemoryStream msDecrypt = new MemoryStream(cipherText))

        {

            using (CryptoStream csDecrypt = new CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Read))

            {

                using (StreamReader srDecrypt = new StreamReader(csDecrypt))

                {

                    // Read the decrypted bytes from the decrypting stream

                    // and place them in a string.

                    plaintext = srDecrypt.ReadToEnd();

                    srDecrypt.Close();

                }

            }

        }

​

        return plaintext;

    }

}