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Message-ID: <20150425213149.GA23167@openwall.com>
Date: Sun, 26 Apr 2015 00:31:49 +0300
From: Solar Designer <solar@...nwall.com>
To: john-dev@...ts.openwall.com
Subject: Re: [GSoC] John the Ripper support for PHC finalists
On Sat, Apr 25, 2015 at 10:28:31PM +0200, Agnieszka Bielec wrote:
> 2015-04-25 21:20 GMT+02:00 Solar Designer <solar@...nwall.com>:
> > "4 GPU units" sounded weird and confusing to me.
> > If you put a hash of a known password in a text file, and put the
> > password somewhere down a wordlist, and run "john" with pomelo-opencl
> > against that, will it crack the hash?
>
> It works
Can you explain how/why it works? I am probably missing something.
I would expect it to fail most of the time.
> > You don't actually have any test vectors in
> > opencl_pomelo_fmt_plug.c, so when you --test you don't actually test,
> > right? :-(
>
> no, now I keep in fmt_tests many hashes with various costs
> and it's 100 lines of code. Before I was generating hashes to structure
> fmt_test dynamically because it was convenient for me.
> this version of code was rather intended for experiments
Oh, I looked at the gpu4_cache branch. Now I see you do have test
vectors in the main branch. That's good.
> > Also, I think you're over-using "unsigned long", such as for loop
> > variables. This may have performance impact on GPUs. You should prefer
> > "uint" except where a wider type is actually needed.
>
> unsigned long is necessary where m_cost is equal to 21 or bigger
> I can test if it will increase the speed but I'm sceptic about that
We don't need m_cost >= 21 in the OpenCL-enabled format. OpenCL
typically means running lots of concurrent instances, and m_cost = 21 is
way too high for that on current devices. That's 16 GB per instance!
Please check for this in the OpenCL-enabled format's valid(), print a
warning (at most once), and have valid() return 0 to skip such hashes.
Alexander
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