phc-discussions - Re: [PHC] Schvrch is broken

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Date: Mon, 15 Sep 2014 14:08:40 -0400
From: Bill Cox <waywardgeek@...hershed.org>
To: discussions@...sword-hashing.net
Subject: Re: [PHC] Schvrch is broken

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On 09/15/2014 01:05 PM, Steve Thomas wrote:
>> On September 14, 2014 at 11:06 PM Rade Vuckovac
>> <rade.vuckovac@...il.com> wrote:
>> 
>> Regarding time cost
>> 
>> As it stays (more details is needed perhaps) the statement about
>> PHC_Fast does not pass a basic logic.  Since PHS_Fast function is
>> allegedly time constant function it means that the time cost is
>> indifferent factor. In other words only input which is varied
>> through the initial search is the password. That leads that
>> PHC_Fast function, without even inspecting inner working 
>> (treating it as a black box) has multiple outputs for the same
>> input???
>> 
> 
> I guess I should of just posted code in my first message: 
> https://github.com/Sc00bz/break-schvrch
> 
> This takes about 3 minutes to run. With SSE or AVX it will be
> faster but this is a nice PoC. Note that the generation only needs
> to be done once per m_cost and once for each t_cost when m_cost is
> zero.
> 

Wow, you're good!  Really good... You considered *this* code too ugly
to post?  Generating the XORs and compiling them totally beats the
speed of what I was going to do (compute them on the fly as matrices).
 I see that I need to try and be an even more evil attacker :-)

While I have had some fun in attacks on this algorithm, it does bother
me that you've written over 500 lines of excellent code where I see no
bugs in order to attack a 117 line program with a lot of bugs.  At
least we got to practice our attack skills.

Bill
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