phc-discussions - Re: [PHC] omegacrypt and timing

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Date: Wed, 17 Sep 2014 16:59:44 +0000
From: Brandon Enright <bmenrigh@...ndonenright.net>
To: Steve Thomas <steve@...tu.com>
Cc: discussions@...sword-hashing.net, bmenrigh@...ndonenright.net
Subject: Re: [PHC] omegacrypt and timing

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On Wed, 17 Sep 2014 11:36:57 -0500 (CDT)
Steve Thomas <steve@...tu.com> wrote:

> > However, AntCrypt, OmegaCrypt, and Schvrch all tried to introduce
> > data based branching for GPU defense, and "cyclomatic complexity".
> > I am not sure we've seen this idea implemented well yet, and
> > data-based branching has been considered a no-no for years
> > apparently. However, when 3 authors all invent the same thing, I
> > think we should take a closer look.
> >  
> 
> Adobe did this for encrypting PDFs
> (http://esec-lab.sogeti.com/post/The-undocumented-password-validation-algorithm-of-Adobe-Reader-X).
> This is why we see these submissions.

Interesting however I was not aware of any previous work on
data-dependent branching.  The Adobe implementation looks pretty naive
and not very effective because it does a lot of work between the
branches (a whole hash), and only 64 branches (rounds) in total.

Obviously I think the conventional wisdom that data-dependant branching
is a no-no is wrong.  We see passwords getting cracked very effectively
on GPUs and we're not likely to see ASICs become the primary attack
vector against password hashes anytime soon.  For this reason I created
an ani-GPU design.  It should also be hard two make an ASIC for it
that's any better than a general purpose computer.

Brandon

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