oss-security - Re: Randomness Attacks Against PHP Applications

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Date: Mon, 17 Sep 2012 19:22:03 -0600
From: Kurt Seifried <kseifried@...hat.com>
To: oss-security@...ts.openwall.com
CC: Raphael Geissert <geissert@...ian.org>,
        argyros george <argyros.george@...il.com>,
        Aggelos Kiayias <aggelos@...yias.com>,
        Vladimir Vorontsov <vladimir.vorontsov@...ec.ru>,
        gifts <gifts.antichat@...il.com>
Subject: Re: Randomness Attacks Against PHP Applications

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On 09/17/2012 10:58 AM, Raphael Geissert wrote:
> On Monday 17 September 2012 10:36:46 Josh Bressers wrote:
>>> On Wed, Aug 22, 2012 at 02:31:07PM +0400, Solar Designer
>>> wrote: Maybe these PoCs will help convince someone.
> 
> Just a note regarding the sessionid case: IIRC since 5.4 
> session.entropy_length is set to, erm, 32 (bytes.) Basically it
> appends N bytes from /dev/urandom to the other input for the digest
> and then it is computed. (why 32 bytes, and why still use md5 by
> default, well...)
> 
>> I'm skeptical they will. I've been doing a lot of work for the
>> past year on various proactive security efforts. I keep coming
>> back to two basic things.
> [...]
>> Has anyone tried to talk to them about this further to see if the
>> issue is they don't understand, or are they being stubborn?
> 
> I think the main problem is education. For instance, there is no
> word about mt_rand not being suitable for criptographic pourposes
> (much less what that means.)

Agreed. One example of a similar problem with good images displaying
the issue clearly:

http://lcamtuf.coredump.cx/newtcp/

> Sure, searching for "crypt" in the page shows a few comments saying
> that it isn't suitable, but: a) there are far more "encryption
> functions", "random password generators", and similar stuff in the
> comments than those that do mention its weaknesses. b) the official
> documentation itself doesn't say a word. It should say it loud and
> clear.
> 
> Comments should also be moderated. Many examples available as
> comments in the documentation are incorrect.
> 
> Now, pointing it out is easy, but somebody has to actually do the
> work. *That* is another issue.
> 
> Cheers,
> 


- -- 
Kurt Seifried Red Hat Security Response Team (SRT)
PGP: 0x5E267993 A90B F995 7350 148F 66BF 7554 160D 4553 5E26 7993

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