using System;

using System.Security.Cryptography;

using System.IO;

public class Program

{

    public static void Main()

    {

        RijndaelManaged alg = new RijndaelManaged();

        alg.GenerateKey();

        alg.GenerateIV();

        var encodedString = EncodeString("Hello, Dev!", alg.Key, alg.IV);

        Console.WriteLine(encodedString);

    }

    static string EncodeString(string text, byte[] key, byte[] iv) {

        RijndaelManaged alg = new RijndaelManaged();

        var encryptor = alg.CreateEncryptor(key, iv);

        using (var s = new MemoryStream())

        using (var cs = new CryptoStream(s, encryptor, CryptoStreamMode.Write))

        {

            using (var sw = new StreamWriter(cs))

            {

                // encrypt the string

                sw.Write(text);

            }

            return Convert.ToBase64String(s.ToArray());

        }

    }

}