十六进制字符串异或实现

/// <summary>
        /// 十六进制字符串异或操作
        /// </summary>
        /// <param name="hex"></param>
        /// <param name="xor"></param>
        /// <returns></returns>
        public static string ConvertHexToXor2(string hex,string xor)
        {
            string newstring = "";
            for (int i = 0; i < hex.Length; i += 2)
            {
                string str = hex.Substring(i, 2);
                if (xor != "")
                {
                    newstring += (Convert.ToInt64(xor, 16) ^ Convert.ToInt64(str, 16)).ToString("X2");
                }
                else
                {
                    xor = str;
                }
            }
            return newstring;
        }