Re: Correct Session Authentication

["Balazs Attila-Mihaly (Cd-MaN)" <x_at_y_or_z () yahoo com>]

This method is fairly secure. My suggestions would be:
-use a salted hash (this means that if the users password is 'password', then you make a hash from 
'<somesecreetstring>password' and store that in the database. Of course <somesecreetstring> is hardcoded in the 
application. This guards against the scenario when somebody gets the hashes from the database and tries to do a 
dictionary attack - meaning that the attacker has precomputed the hash values for a set of common passwords and 
compares them to the ones got from your database. And use a long string (32 chars+))
-Read about session hijacking (and try to tie the sessions to a specific IP or user agent string - and be aware of the 
problems: users behind proxy servers and users who dinamically change proxies - this includes AFAIK AOL users who 
access the net from a few fixed ip addresses which can chenge during the browsing session)
-Timeout your sessions (mark when it began and timeout after a given period or after a given period of user inactivity 
- e.g. no pages requested)
-The session data is stored on the webserver, in the user cookie only the session ID is stored. You should be avare 
that if a shared host is used, the directory where the session data is stored is most probably available to all users, 
so other sites hosted on the same host can access your session data. You can either: encrypt the sessiond data before 
written to disk or better yet store it in the database

----- Original Message ----
From: xbennx () hotmail co uk
To: webappsec () securityfocus com
Sent: Saturday, 29 July, 2006 4:14:42 PM
Subject: Correct Session Authentication

I've been developing a shopping cart for my friends company and have just started using sessions to authenticate 
people. After reading many tutorials on the internet about sessions and PHP I coded a login page. I keep hearing about 
session id's but all the tutorials I read didn't mention them.

When a user logs on, the username and password are sent via SSL and the md5 hash is then checked against a hash stored 
in database. If the credentials are found in the database, the users id is return and stored in a session. If the 
credentials are not found this session value is 0. Every page that a user needs to be authenticated to see checks to 
see that the user id stored in the session is greater than 0, if not the user is classed as not authorised as 0 is not 
a valid user id.

Is this method secure or can it be easily bypassed? 

Another thing I was wondering is where are sessions values actually stored? I've read that they're stored in cookies 
but I always thought there was a seperate function in php to create cookies?

Sorry this is so long, any help will be much appreciated.

Thanks

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Sponsored by: Watchfire

AppScan 6.5 is now available! New features for Web Services Testing, 
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Reporting, Token Analysis, Authentication testing, Automated JavaScript 
execution and much more. 
Download a Free Trial of AppScan today!

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