News Feed
Sections




News Archive
Looking for more information on how to do PHP the right way? Check out PHP: The Right Way

Suspekt Blog:
mt_srand and not so random numbers
August 18, 2008 @ 13:49:31

Stefan Esser points out a problem with the mt_rand and rand methods in PHP that makes them not quite random enough for cryptographic uses.

PHP comes with two random number generators named rand() and mt_rand(). The first is just a wrapper around the libc rand() function and the second one is an implementation of the Mersenne Twister pseudo random number generator. Both of these algorithms are seeded by a single 32 bit dword when they are first used in a process or one of the seeding functions srand() or mt_srand() is called.

He looks at how its currently implemented, some examples of bad methods to get "random" numbers, how shared resources are a problem and an example of a cross-application attack (the application in more than once place using the same method for getting random numbers).

In the comments he recommends either grabbing from /dev/random (if you're on a unix-based system) or making the creation of your numbers a bit more complex to include things the outside world wouldn't know.

0 comments voice your opinion now!
mtrand random number rand cryptography problem


blog comments powered by Disqus

Similar Posts

Tony Bibbs' Blog: Oh So Familiar Problem with Zend Studio Neon (Eclipse-based)

PHPFreaks.com: PHP Add Text To Image

Martin Psinas' Blog: Switching to PDO

Sameer Borate's Blog: How not to create a Random string

Quinton Parker's Blog: Smarty. Solving the wrong problem since 2001


Community Events





Don't see your event here?
Let us know!


symfony community update series release introduction tool version security install voicesoftheelephpant language composer podcast package laravel framework interview opinion library

All content copyright, 2014 PHPDeveloper.org :: info@phpdeveloper.org - Powered by the Solar PHP Framework