md5

         //　MD5加密函数
        public static string MD5(String str)
        {
            MD5 md5 = new MD5CryptoServiceProvider();
            byte[] data = System.Text.Encoding.Default.GetBytes(str);
            byte[] result = md5.ComputeHash(data);
            String ret = "";
            for (int i = 0; i < result.Length; i++)
                ret += result[i].ToString("x").PadLeft(2, '0');
            return ret;
        }