using System;

using System.Security.Cryptography;

using System.Text;

​

public class Program

{

    public static void Main()

    {

        Console.WriteLine("old URL = " + GetOldUrl("22400435070"));

    }

​

    public static string GetOldUrl(string panelNumber) {

        return "?panel=" + panelNumber + "&checksum=" + checksum; 

    }

​

    public static string GetChecksumForPanelNumber(string panelNumber) {

        StringBuilder sb = new StringBuilder();

        foreach (byte b in SHA256.Create().ComputeHash(Encoding.UTF8.GetBytes("salt_ntb" + panelNumber))) {

            sb.Append(b.ToString("X2"));

        }

        return sb.ToString();

    }

 }