using System;

using System.Text;

public class Program

{

    public static void Main()

    {

        string plainText = "http://14.26.1.69:80/snapshot/1135444444/20190101-123ajie-0fjie-124.jpg";

        plainText = plainText.Replace("http://", "00").Replace(".jpg", "");

        var plainTextBytes = Encoding.UTF8.GetBytes(plainText);

        string encodedText = Convert.ToBase64String(plainTextBytes);

        Console.WriteLine("Plain Text : {0}", plainText);

        Console.WriteLine("Encoded Text : {0}", encodedText);

        var encodedTextBytes = Convert.FromBase64String(encodedText);

        string plainText1 = Encoding.UTF8.GetString(encodedTextBytes);

        string type = plainText1.Substring(0, 2);

        string result = "";

        if (type == "00")

        {

            result = "http://" + plainText1.Substring(2) + ".jpg";

        }

        Console.WriteLine("Encoded Text : {0}", encodedText);

        Console.WriteLine("Plain Text : {0}", result);

    }

}