using System;

​

public class Program

{

    public static void Main()

    {

        Guid gg = Guid.NewGuid();

        string ss = Encode(gg);

        Console.WriteLine(ss);

        Console.WriteLine(Decode(ss));

    }

​

    public static string Encode(Guid guid)

    {

        string encoded = Convert.ToBase64String(guid.ToByteArray());

        encoded = encoded.Replace("/", "_").Replace("+", "-");

        return encoded.Substring(0, 22);

    }

​

    public static Guid Decode(string value)

    {

        value = value.Replace("_", "/").Replace("-", "+");

        byte[] buffer = Convert.FromBase64String(value + "==");

        return new Guid(buffer);

    }

}