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Date: Mon, 17 Sep 2012 13:20:07 -0400
From: Daniel Kahn Gillmor <dkg@...thhorseman.net>
To: oss-security@...ts.openwall.com
Subject: Re: Randomness Attacks Against PHP Applications

On 09/17/2012 12:58 PM, 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...)

32 bytes is 256 bits.  if the session entropy is from a truly random
source, cracking that by brute force is well beyond the capabilities of
any machinery i'm aware of.

i agree with the other concerns raised on this thread, though.

	--dkg


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