Re: Randomness Attacks Against PHP Applications

[Daniel Kahn Gillmor <dkg () fifthhorseman net>]

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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