md5加密解密        public static string MD5(string input)        {            StringBuilder hash = new StringBuilder();            MD5CryptoServiceProvider md5provider = new MD5CryptoServiceProvider();            byte[] bytes = md5provider.ComputeHash(new UTF8Encoding().GetBytes(input));            for (int i = 0; i < bytes.Length; i++)            {                hash.Append(bytes[i].ToString("x2"));            }            return hash.ToString();        }