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 Download attachment "signature.asc" of type "application/pgp-signature" (1031 bytes)
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