//前臺通過js處理，獲取後臺設定的cookie

       //驗證驗證碼是否正確
        var checkCode = "";
        var cooks = document.cookie.split(";");
        for (var i = 0; i < cooks.length; i++) {
            var index = cooks[i].indexOf("CheckCode");
            if (index > -1) {
                checkCode = cooks[i].split("=")[1];
            }
        }
 

後臺，可以生成簡單的4字元的驗證碼

{
            StringBuilder checkCode = new StringBuilder();
            Random random = new Random();
            char[] letter =   {   
        '0','1','2','3','4','5','6','7','8','9',  
        'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z',   
        'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z'   
        };
            for (int i = 0; i < 4; i++)
            {
                int RandKey = random.Next(0, 20);
                checkCode.Append(letter[RandKey]);
            }
            //string str = System.Text.Encoding.UTF8.GetString(System.Text.Encoding.Default.GetBytes(checkCode.ToString()));
            //HttpCookie h = new HttpCookie("CheckCode", str);
            string str = HttpUtility.UrlEncode(checkCode.ToString());
            Response.Cookies.Add(new HttpCookie("CheckCode", str));

            return checkCode.ToString();
        }