The application's full source code - AJAX

If you’re a web developer who builds Ajax-driven applications and wants to learn how to use this technology for creating more secure web forms, then look no further. Welcome to the third part of a series focused on making web forms safer with Ajax. Made up of four comprehensive tutorials, this series explains how to generate different types of challenge strings via Ajax, which can be incorporated into any existing HTML form with the purpose of protecting it against attacks.

TABLE OF CONTENTS:

By: Alejandro Gervasio

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April 01, 2009

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As I said in the section that you just read, below I listed all of the source code that corresponds to this Ajax-based application, which implements a simple mathematical mechanism that protects a web form from possible hacks. Here are all of the files that comprise the program:

(definition of 'sample_form.htm' file)

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">

<head>

<title>Ajax-based challenge strings generator</title>

body{

padding: 0;

margin: 0;

background: #fff;

}

h1{

font: bold 16pt Arial, Helvetica, sans-serif;

color: #000;

}

font: bold 9pt Arial, Helvetica, sans-serif;

color: #000;

}

#formbox{

width: 380px;

text-align: right;

padding: 10px;

background: #eee;

}

#codebox{

font: bold 18pt Arial, Helvetica, sans-serif;

color: #00f;

}

.inputbox,textarea{

width: 300px;

border: 1px solid #999;

}

.checkingcode{

width: 50px;

border: 1px solid #999;

}

</style>

$(document).ready(function(){

// get verification code with Ajax

$.get('get_checkingcode.php',{data:'getting code'},function(checkingcode){$('#codebox').html(checkingcode);});

});

</script>

</head>

<body>

<h1>Ajax-based challenge strings generator</h1>

<p>First Name <input type="text" class="inputbox" title="Enter your first name" /></p>

<p>Email <input type="text" class="inputbox" title="Enter your email address" /></p>

<p>Enter your comments below:</p>

<p>Verification Code: <input type="text" name="code" class="checkingcode" title="Multiply the above digits and enter the result" /></p>

</form>

</div>

</body>

</html>

(definition of 'get_checkingcode.php' file)

<?php

session_start();

$valuea=rand(1,10);

$valueb=rand(1,10);

$_SESSION['checkcode']=$valuea*$valueb;

echo $valuea.' x '.$valueb;

(definition of 'check_form.php' file)

<?php

session_start();

if($_SESSION['checkcode']==$_POST['code']){

echo 'Correct verification code!';

}

else{

echo 'Incorrect verification code!';

}

Undoubtedly, the set of source files shown above demonstrates how easy it is to build an Ajax application that generates a multiplication problems to make a targeted web form a bit more secure.

Below I've included a couple of complementary images that show how these challenge calculations are displayed when the previous sample form is being filled in with some trivial data:

Of course, there's plenty of room for enhancing this Ajax-driven program, for instance, by embedding these operations directly into an image generated dynamically. But this improvement, and others, will be left as homework for you. In this case one thing is for sure: fun is already guaranteed!

Final thoughts

In this third episode of the series, I walked you through the development of an Ajax-driven application, which was capable of displaying multiplication problems within a targeted web form to protect it against malicious, automated submissions.

In the last chapter, I'll be building a similar program for protecting HTML forms, but this time it'll generate divisions as challenge strings. Thus, now that you've been warned about the subject of the next part, you won't want to miss it!