c中使用云解析api签名机制老是错误

老是报签名字符串与阿里计算后的不匹配~，有点晕了，实在找不出在那个计算中出问题了。请大家帮忙看看吧。
下面为核心代码：
       public string HTTP_METHOD = "GET";
        public string SEPARATOR = "&";
        //参数集合
        public SortedDictionary<string, string> parameters = new SortedDictionary<string, string>(StringComparer.Ordinal);



private void Form2_Load(object sender, EventArgs e)
        {
            //初始化http url 参数
            parameters.Add("Format", "json");
            parameters.Add("Version", "2015-01-09");
            parameters.Add("AccessKeyId", "testid");
            parameters.Add("SignatureMethod", "HMAC-SHA1");
            parameters.Add("Timestamp", CreateTimestamp());
            parameters.Add("SignatureVersion", "1.0");
            parameters.Add("SignatureNonce",CreateSignatureNonce());
            parameters.Add("Action", "DescribeDomainRecords");
            parameters.Add("DomainName","test.com");
            //构造出规范化请求字符串CanonicalizedQueryString
            string CanonicalizedQueryString = "";
            foreach (var item in parameters)
            {
                if (CanonicalizedQueryString != "") CanonicalizedQueryString += SEPARATOR;
                CanonicalizedQueryString += string.Format("{0}{1}{2}", percentEncode(item.Key),("="), percentEncode(item.Value));
            }
            //构造出用于签名的字符串StringToSign
            string StringToSign = HTTP_METHOD + SEPARATOR + percentEncode("/") + SEPARATOR + percentEncode(CanonicalizedQueryString);
            //计算签名
            string ALGORITHM = "HmacSHA1";
            string ENCODING = "UTF-8";
            string key = "testsecret" + SEPARATOR;


            string signature = HmacSha1Sign(StringToSign,key);
            CanonicalizedQueryString += string.Format("{0}{1}={2}", SEPARATOR, "Signature",percentEncode(signature));
            httpitem = new HttpItem() { URL = url + CanonicalizedQueryString };
            httpresult = httphelper.GetHtml(httpitem);



        }





        /// <summary>
        /// 根据阿里云的要求进行编码
        /// </summary>
        /// <param name="value"></param>
        /// <returns></returns>
        public string percentEncode(string value)
        {
            return value!=null?HttpHelper.URLEncode(value,UTF8Encoding.UTF8).Replace("+","%20").Replace("*","%2A").Replace("%7E","~"):null;
        }
        /// <summary>
        /// 生成时间戳UTC时间ISO8601规范
        /// </summary>
        /// <returns>字符串</returns>
        public string CreateTimestamp()
        {
            var dt = DateTime.UtcNow;


            return (dt.ToString(@"yyyy-MM-dd\THH:mm:ss\Z"));
        }
        /// <summary>
        /// 创建唯一标示
        /// </summary>
        /// <returns>字符串</returns>
        public string CreateSignatureNonce()
        {
            return Guid.NewGuid().ToString();
        }
        /// <summary>
        /// HmacSha1算法
        /// </summary>
        /// <param name="text"></param>
        /// <param name="key"></param>
        /// <returns></returns>
        private string HmacSha1Sign(string text, string key)
        {
            Encoding encode = Encoding.UTF8;
            byte[] byteData = encode.GetBytes(text);
            byte[] byteKey = encode.GetBytes(key);
            HMACSHA1 hmac = new HMACSHA1(byteKey);
            CryptoStream cs = new CryptoStream(Stream.Null, hmac, CryptoStreamMode.Write);
            cs.Write(byteData, 0, byteData.Length);
            cs.Close();
            return Convert.ToBase64String(hmac.Hash);
        }