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Date: Sun, 26 Apr 2015 00:31:49 +0300
From: Solar Designer <>
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 <>:
> > "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.


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