Review: code verification system with Ajax - AJAX

As you know, Ajax is a technology that can be used to perform all sorts of clever tasks; this includes building web forms that are less vulnerable to attacks from malicious web bots. Indeed, it’s pretty simple to develop certain mechanisms that permit the dynamic generation of verification codes via Ajax, which must be entered manually by a user before submitting an HTML form. This is the second part of a four-part series that shows you how to make your web forms safer with Ajax.

TABLE OF CONTENTS:

By: Alejandro Gervasio

Poor Best

Rating:

/ 3

March 25, 2009

print this article

SEARCH DEV SHED

TOOLS YOU CAN USE

Before we develop this new application, I will show you the complete source code of the example built in the preceding article. As I mentioned, it dynamically generated a few random values each time a user attempted to submit a contact web form.

The source files that comprised this application looked like this:

(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 Random Code Generator System</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 Random Code Generator System</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="Enter the above four-digit verification code" /></p>

</form>

</div>

</body>

</html>

(definition of 'get_checkingcode.php' file)

<?php

function RandomGenerator($length=4){

$chars="ABCDEFGHIJKLMNPQRSTUVWXYZ123456789";

if(!is_int($length)||$length<1){

$length=4;

}

$rndstr='';

$maxvalue=strlen($chars)-1;

for($i=0;$i<$length;$i++){

$rndstr.=substr($chars,rand(0,$maxvalue),1);

}

return $rndstr;

}

session_start();

$_SESSION['checkcode']=RandomGenerator();

echo $_SESSION['checkcode'];

(definition of 'check_form.php' file)

<?php

session_start();

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

echo 'Correct verification code!';

}

else{

echo 'Incorrect verification code!';

}

As you'll possibly recall, the three files shown above are all the source code required to get this web form protection mechanism working correctly. In this case, the first file is charged with displaying the sample web form that incorporates this protective system, and is also tasked with fetching, via Ajax, the PHP file that actually generates the corresponding random values.

On the server side, there's one PHP file that echoes to the browser the random strings, while another one simple checks to see if the user entered the correct challenge value or not. Simple to code and read, isn't it?

So far, so good. At this point, you're hopefully familiar with the way that the previous Ajax application generates random codes for protecting a targeted web form. Thus, it's time to see how the same logic can be applied to displaying elemental mathematical sums as challenge strings.

Curious about how this will be achieved? Then click on the link below and read the following section.

Next: Displaying basic mathematical sums as challenge strings >>