using System;

using System.Text;

using System.Security.Cryptography;

public class Program

{

    public static void Main()

    {

        // var nonce = DateTime.UtcNow.ToString("yyyy-MM-ddTHH:mm:ss.fffZ");

        var nonce = "2011-10-05T14:48:00.000Z";

        var appkey = "OTtLfrHQmFmgf68n";

        using(SHA512 shaM = new SHA512Managed()) {

            var hash = shaM.ComputeHash(Encoding.UTF8.GetBytes(nonce + appkey));

            StringBuilder hex = new StringBuilder(hash.Length * 2);

            foreach(byte b in hash)

                hex.AppendFormat("{0:x2}", b);

​

            Console.WriteLine(hex.ToString());  // 371b6617540a434e23535a2881d4300cf528c79fb07118ad60ed21b1c01d6d74649fe701bfeb35ed7ebc5cf99ae803d5b8d059776e1f9f124072f338b8093253

        }

    }

}