string GetKey(string appid, string privateKey, string areaId, string date, string type)

{

//HMAC using SHA1

HMAC hmac = HMACSHA1.Create();

var publicKey = "/data/?areaid={0}amp; type={1}amp; date={2}amp; appid= {3}";

var data = System.Text.Encoding.UTF8.GetBytes(string.Format(publicKey, areaId, type, date, appid));

// Key

var key = System.Text.Encoding.UTF8.GetBytes(privateKey);

hmac.Key = key;

//Perform data processing Signature

var signedData = hmac.ComputeHash(data);

return Convert.ToBase64String(signedData);

}

Reference materials ：blogs.com/aptdo2008/p/3566391.html