using System;

using System.IO;

using System.Security.Cryptography;

using System.Text;

​

public class Program

{

    public static void Main()

    {

        // Example OAuth2 bearer token

        var str = "4321";

        var encryptedAndEncodedStr = str.Encrypt().Base64UrlEncode();

        var decodedAndDecryptedStr = encryptedAndEncodedStr.Base64UrlDecode().Decrypt();

        Console.WriteLine("Original string: " + str);

        Console.WriteLine("Original string length: " + str.Length);

        Console.WriteLine("\nEncrypted string: " + encryptedAndEncodedStr);

        Console.WriteLine("Encrypted string length: " + encryptedAndEncodedStr.Length);

        Console.WriteLine("\nDecrypted string: " + decodedAndDecryptedStr);

        Console.WriteLine("\n\nDecrypted string is the same as original string: " + str.Equals(decodedAndDecryptedStr));

    }

}

​

// Taken from Stack answer: http://stackoverflow.com/a/5518092/654708

public static class Aes

{

    /*

        Replace 999999999 with a random numer less than 256 

    */  

​

​

    // Change these keys

    private static byte[] key =

    {

        123, 217, 19, 11, 24, 26, 85, 45, 114, 184, 27, 162, 37, 112, 222, 209, 241, 24, 175, 144, 173, 53, 196, 29, 24, 26, 17, 218, 131, 236, 53, 255

    }

​

    ;

    // 

    private static byte[] vector =

    {

        146, 64, 191, 111, 23, 3, 113, 119, 231, 121, 1, 112, 79, 32, 114, 22

    };

    private static readonly ICryptoTransform encryptor;

    private static readonly ICryptoTransform decryptor;

    private static readonly UTF8Encoding encoder;

    static Aes()

    {

        using (var rm = new RijndaelManaged())

        {

            encryptor = rm.CreateEncryptor(key, vector);

            decryptor = rm.CreateDecryptor(key, vector);

        }

​

        encoder = new UTF8Encoding();

    }

​

    public static string Encrypt(this string unencrypted)

    {

        return Convert.ToBase64String(Encrypt(encoder.GetBytes(unencrypted)));

    }

​

    public static string Decrypt(this string encrypted)

    {

        return encoder.GetString(Decrypt(Convert.FromBase64String(encrypted)));

    }

​

    public static byte[] Encrypt(byte[] buffer)

    {

        return Transform(buffer, encryptor);

    }

​

    public static byte[] Decrypt(byte[] buffer)

    {

        return Transform(buffer, decryptor);

    }

​

    private static byte[] Transform(byte[] buffer, ICryptoTransform transform)

    {

        using (var stream = new MemoryStream())

        {

            using (var cs = new CryptoStream(stream, transform, CryptoStreamMode.Write))

            {

                cs.Write(buffer, 0, buffer.Length);

            }

​

            return stream.ToArray();

        }

    }

}

​

public static class Helper

{

    public static string Base64UrlEncode(this string value)

    {

        var bytes = Encoding.UTF8.GetBytes(value);

        var s = Convert.ToBase64String(bytes); // Regular base64 encoder

        s = s.Split('=')[0]; // Remove any trailing '='s

        s = s.Replace('+', '-'); // 62nd char of encoding

        s = s.Replace('/', '_'); // 63rd char of encoding

        return s;

    }

​

    public static string Base64UrlDecode(this string value)

    {

        var s = value;

        s = s.Replace('-', '+'); // 62nd char of encoding

        s = s.Replace('_', '/'); // 63rd char of encoding

        switch (s.Length % 4) // Pad with trailing '='s

        {

            case 0:

                break; // No pad chars in this case

            case 2:

                s += "==";

                break; // Two pad chars

            case 3:

                s += "=";

                break; // One pad char

            default:

                throw new Exception("Illegal base64 url string!");

        }

​

        var bytes = Convert.FromBase64String(s); // Standard base64 decoder

        return Encoding.UTF8.GetString(bytes);

    }

}