基于CANVAS与MD5的客户端生成验证码

好久没写东西，工作太忙了！不想服务端请求太多，搞了个这玩意儿，不过项目中并不会用上，还是使用服务端生成的机制（会安全多少呢？）；我就想问个问题，除了图像识别来破解这样的简单验证码外，针对我这种例子，可以侦听到我的验证码吗？How？好吧，最简单的莫过于开发个浏览器插件，在页面注入脚本，修改我的所谓“md5的密码”的值。ヽ(*。>Д<)o゜

在线demo：verificationcod

<!DOCTYPE html><html lang="en">

<head>

    <meta charset="UTF-8">

    <title>Document</title>

</head>

<body>

    <input type="text" id="verificationCodeValue" /><button id="verificationCodeBtn">验证</button>

    <script type="text/javascript" src="md5.min.js"></script>

    <script type="text/javascript">

    var verificationCode="";

    function createVerificationCode (w,h){

        var codeLength = 4;

        var code=[];

        var random = new Array(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');

         for(var i = 0; i < codeLength; i++) {

            var index = Math.floor(Math.random()*36);

            code.push(random[index]);

        }

        verificationCode = md5(code.join(""));

        console.log(verificationCode);

        var colors = ["red","green","brown","blue","orange","purple","black"]; 

        var codeCanvas = document.createElement("canvas");

            codeCanvas.width = w;

            codeCanvas.height= h;

        var ctx = codeCanvas.getContext("2d");

        ctx.font = "18px Arial";

        var cx = (w-20-codeLength*4)/(codeLength-1),cy = h/2+18/2;

        var deg,cos,sin,dg;

        for(var j=0;j<codeLength;j++){

            ctx.fillStyle =colors[Math.floor(Math.random()*colors.length)];

            //产生一个正负30度以内的角度值以及一个用于变形的dg值

            dg = Math.random()*4.5/10;

            deg = Math.floor(Math.random()*60);

            deg = deg>30?(30-deg):deg;

            cos = Math.cos(deg*Math.PI/180);

            sin = Math.sin(deg*Math.PI/180);

            ctx.setTransform(cos,sin+dg,-sin+dg,cos,(j?cx:10)*j+10,cy);

            ctx.fillText(code[j], 0,0);

            console.log(sin);

        }

        var img = document.getElementById("verificationCodeImg");

        if(!img){

            img = new Image();

            img.id="verificationCodeImg";

            img.onload= function(){

                document.body.appendChild(img);

            }

        }

        img.src=codeCanvas.toDataURL("image/png");

    }

   window.onload=function(){

           createVerificationCode(120,40);

           document.getElementById("verificationCodeBtn").onclick=function(){

               var vlu = document.getElementById("verificationCodeValue").value;

               if(vlu.length!=4){

                   alert("请输入正确的验证码");

               }else if(md5(vlu.toUpperCase())===verificationCode){

                   alert("正确的验证码！");

               }else{

                   alert("错误的验证码！");

                   createVerificationCode(120,40);

               }

           }

   }

    </script>

</body>

</html>

本文原创，转载注明出处...博客园哥德