带密钥的sha1加密

private static string HmacSha1Sign(string jsonStr, string secretKey, string enCoding )
{ 
　　Encoding encoding = Encoding.GetEncoding(enCoding);
　　string encodedParam = Convert.ToBase64String(encoding.GetBytes(jsonStr));
　　byte[] bytes = encoding.GetBytes(jsonStr);
　　HMACSHA1 transform = new HMACSHA1(encoding.GetBytes(secretKey));
　　CryptoStream stream = new CryptoStream(Stream.Null, transform, CryptoStreamMode.Write);
　　stream.Write(bytes, 0, bytes.Length);
　　stream.Close();
　　return Convert.ToBase64String(transform.Hash);
}