using System;

public class Program

{

    public static void Main()

    {

        string encode = Convert.ToBase64String(System.Text.Encoding.UTF8.GetBytes("https://secure-test.worldpay.com/jsp/merchant/xml/paymentService.jsp"));

         Console.WriteLine(encode);

        string decode =  System.Text.Encoding.UTF8.GetString(Convert.FromBase64String(encode));

            Console.WriteLine(decode);                                               

    }

}