using System;

using System.Security.Cryptography;

using System.Text;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var transactionId = "123455";

        var language = 1 ;

        var message = transactionId + language;

        var publicKey = "EF48pcOY0Gt7q1ZlOyFB";

        var privateKey = "kfqA2yCeE4bpiH83uFcU";

        var theDigest = CalculateDigest(publicKey, privateKey, message);

        Console.WriteLine(theDigest);

    }

    public static string CalculateDigest(string publicKey, string privateKey, string message)

    {

        var digest = "";

        var hash = new System.Security.Cryptography.HMACSHA256(System.Text.Encoding.UTF8.GetBytes(privateKey));

        var correctHash = string.Join(string.Empty, hash.ComputeHash(System.Text.Encoding.UTF8.GetBytes(message)).Select(b => b.ToString("x2")));

        digest = publicKey + ":" + correctHash;

        return digest;

    }

}