using System.Security.Cryptography

using System.Text;

 private string hash_hmac2(string message, string secret)

        {

            secret = secret ?? "";

            var encoding = new System.Text.ASCIIEncoding();

            byte[] keyByte = encoding.GetBytes(secret);

            byte[] messageBytes = encoding.GetBytes(message);

            using (var hmacsha256 = new HMACSHA256(keyByte))

            {

                byte[] hashmessage = hmacsha256.ComputeHash(messageBytes);

                return Convert.ToBase64String(hashmessage);

            }

        }

           login  timespan=1546084445901;

           string appsec = "testappSecret";

           sign= hash_hmac2(timespan.ToString(),appsec);

        
           //此时sign为   HCbG3xNE3vzhO+u7qCUL1jS5hsu2n5r2cFhnTrtyDAE=
 

           Response.Write(sign);

  public long GetTimeStamp()

        {

            TimeSpan ts = DateTime.UtcNow - new DateTime(1970, 1, 1, 0, 0, 0, 0);

            return Convert.ToInt64(ts.TotalSeconds);

        }