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Security and Sessions in PHP


Learn how to secure your PHP pages swiftly using a simple include file that should be included at the top of every page. Read more ...

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By: Jason D. Agostoni
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August 21, 2003

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Learn how to secure your PHP pages swiftly using a simple include file that should be included at the top of every page. Read more ...This article demonstrates an easy way to maintain sessions and security (or authorization) in PHP. It does NOT use the PHP built in session support.

The following method will allow you to easily secure any PHP page by simply including a file at the top of every page. In this tutorial you will:

a) Create your database structure
b) Create a login page
c) Create your security check include file
d) Secure your site

There are many different ways you can modify this technique to suit your own needs. Some of these ideas will be listed at the end of this article.

Step 1: Store your data

In order to authenticate your users, you must store their information somewhere. That location can be a flat text file or a database server. In this tutorial, we will use a MySql database. Given that you probably already have a database you wish to use, this article will focus just on one table: tblUsers.

This table will store all of your user information but we will only focus on the fields necessary to this article. The following fields are required:

iUser - This will be a unique ID used in the table.
sEmail - We will use the email address as the login
sPassword - We will need this to authenticate the user
sGUID - This is the field to store the users current session ID
sData - This is where you can store various session information about the user.

To create this table in MySql, execute the following DDL:

CREATE TABLE tblUsers (
iUser int(10) unsigned NOT NULL auto_increment,
sEmail varchar(255) NOT NULL,
sPassword varchar(255) NOT NULL,
sGUID varchar(32),
sData text,
PRIMARY KEY (iUser)
) TYPE=MyISAM;


In the interest of space and time, this article will assume you can build your own "Add User" form and we will use the following DML to add a user for demonstration purposes:

INSERT INTO tblUsers Values
(
Null,
'test@user.com',
password('testpass'),
Null,
Null
)


Note the use of MySql's Password() function. This is a one-way function so you will not be able to "retrieve" the user's password. There are other options you can use besides the Password() function such as a md5 hash or your own cipher. The Null value for the iUser field triggers the auto_number function and will generate a unique ID for us. The user we just created has an email/username of test@user.com and a password of testpass.

Step 2: Create a login page

You will need a way to authenticate your users as they enter the system. You will create a login page in such a manner that it can intercept a user going to any secured page in your system. Once the user has logged in they will be redirected back to the page they were attempting to access.

First, we need a simple HTML form so save the following HTML as Login.php:

<html>
<head><title>Login</title></head>
<body>
<form action="LoginAction.php" method="Post">
Email Address:<br />
<input type="Text" name="psEmail" />
<br />
Password:<br />
<input type="password" name="psPassword" />
<br />
<input type="submit" value="Login" />
<input type="hidden" name="psRefer" value="<? echo($refer) ?>"
</form>
</body>
</html>


The obvious parts of this login page are the email and password. The hidden field psRefer will be a query string variable that is passed to this page, which represents from where the user entered the web site.

Next, we need a page that will actually authenticate the user against the data in the database. If the user is successfully authenticated a GUID will be generated and they will be on their way. If they are NOT authenticated they will be sent back to the login page. The following code should be saved as LoginAction.php:

<?php
// Check if the information has been filled in
if($psEmail == '' || $psPassword == '') {
// No login information
header('Location: Login.php?refer='.urlencode($psRefer));
} else {
// Authenticate user
$hDB = mysql_connect('server', 'user', 'pass');
mysql_select_db('database', $hDB);
$sQuery = "
Select iUser, MD5(UNIX_TIMESTAMP() + iUser + RAND(UNIX_TIMESTAMP())) sGUID
From tblUsers
Where sEmail = '$psEmail'
And sPassword = password('$psPassword')";
$hResult = mysql_query($sQuery, $hDB);
if(mysql_affected_rows($hDB)) {
$aResult = mysql_fetch_row($hResult);
// Update the user record
$sQuery = "
Update tblUsers
Set sGUID = '$aResult[1]'
Where iUser = $aResult[0]";
mysql_query($sQuery, $hDB);
// Set the cookie and redirect
setcookie("session_id", $aResult[1]);
if(!$psRefer) $psRefer = 'index.php';
header('Location: '.$psRefer);
} else {
// Not authenticated
header('Location: Login.php?refer='.urlencode($psRefer));
}
}
?>


The first objective of this code is to verify that a username and password were sent and otherwise return to the login page. This is just some rudimentary protection against some hacking. Next, the code connects to a database and tries to retrieve the user data matching the credentials sent from the Login.php page. If there is no match in the database the user is returned to the login page.

If there is a match the user record is updated with a GUID and a cookie is set on the user's computer. You do not have to use cookies here but this prevents you from having to put the session id on the URL of every page. After the cookie is set, the user is either sent to the referring page or to a default page (in this example: index.php).

To generate the GUID or session ID, you need to generate a unique number and hash it to protect would-be hackers from brute-forcing their way into your application. This article used MySql's built in MD5 function with a formula to help generate a random seed. You can use PHP's hashing functions or any other method of generating random hashes here.

Step 3: Create an include file

Now that you have a login mechanism, you need to create a page that will easily protect any page in your web site by simply including it. To make this "smart" page you just need to check the user's session ID that is stored in their cookie against the database. If there is a match then the user has logged in otherwise they should be redirected to the Login.php page. Here is the PHP code to perform that (call it incSession.php):

<?php
// Check for a cookie, if none got to login page
if(!isset($HTTP_COOKIE_VARS['session_id'])) {
header('Location: Login.php?refer='.urlencode($PHP_SELF.'?'.$HTTP_SERVER_VARS['QUERY_STRING']));
}
// Try to find a match in the database
$sGUID = $HTTP_COOKIE_VARS['session_id'];
$hDB = mysql_connect('server', 'username', 'password');
mysql_select_db('database', $hDB);
$sQuery = "
Select iUser
From tblUsers
Where sGUID = '$sGUID'";
$hResult = mysql_query($sQuery, $hDB);
if(!mysql_affected_rows($hDB)) {
// No match for guid
header('Location: Login.php?refer='.urlencode($PHP_SELF.'?'.$HTTP_SERVER_VARS['QUERY_STRING']));
}
?>


The first part of the code checks to see if there is a cookie set with the session ID otherwise it will redirect the user to the Login.php page. If there is a valid session ID the script will try and match it against the database. If there is not a match the user is redirected to a Login.php page. Otherwise, the user is allowed to continue onto the page they were trying to access. To add this security to a page in your application, simply add the following code to the top of the page:

<?PHP require('incSession.php'); ?>


Now you have secured your application! Once you get over the initial creation of the Login and actions pages you only need to add the one line of code above to secure any page in your web. Here is a list of modifications you can make to the above implementation to make the script even better:

Expiration - You can have the login expire by adding a logged-in date field to tblUsers. You would need to check that date against your "timeout" in incSession.php.

Security Levels - You can add a field to tblUsers to specify the user's security clearence. Then you can compare that value against a variable that you have defined on each secured page. For example you could put the following at the top of your secured page:

<?PHP
$giSecurityLevel = 3;
require('incSession.php');
?>


After that, the script could return the user's security level in incSession.php and compare it against $giSecurityLevel. If the user's level is below the required level the script can redirect them to a "no access" page.

Store/Retrieve Session Data - You can use the sData field to store the user's session information (like a shopping cart, for example) as a formatted string or even XML data. The choice is entirely yours since it is a large text field.

Conclusion

Using the script above will assure that you have a simple and foolproof method of securing your web site. There are many other methods available (PHP sessions, .htaccess, etc.) and each has their strengths and weaknesses. I believe this method to be one of the most portable and easily customized methods available.


DISCLAIMER: The content provided in this article is not warranted or guaranteed by Developer Shed, Inc. The content provided is intended for entertainment and/or educational purposes in order to introduce to the reader key ideas, concepts, and/or product reviews. As such it is incumbent upon the reader to employ real-world tactics for security and implementation of best practices. We are not liable for any negative consequences that may result from implementing any information covered in our articles or tutorials. If this is a hardware review, it is not recommended to open and/or modify your hardware.

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