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Date: Fri, 24 Mar 2017 22:14:44 +0100
From: Patrick Proniewski <p+password@...atpro.net>
To: john-users@...ts.openwall.com
Cc: Frank Dittrich <frank.dittrich@...lbox.org>
Subject: Re: GPU performance

On 24 mars 2017, at 19:41, Frank Dittrich wrote:

> Am 24.03.2017 um 18:30 schrieb Patrick Proniewski:
>> Thanks, it's way faster:
>> 
>> $ ./john -test -format=raw-sha1-opencl --mask
>> Device 1: GeForce GTX 1080
>> ../..
>> Raw:	5778M c/s real, 5778M c/s virtual
>> 
>> Does it mean I have to use mask mode to get this kind of performance, and other modes would run in the 87M c/s range?
> 
> Yes, you have to use --mask to get optimal OpenCL performance for very
> fast hash formats.
> But you don't have to use standalone mask mode, you can also use hybrid
> modes, i.e., combine --mask with other modes.
> 
> While hashcat's GPU formats generate all password candidates on the GPU,
> john generates the candidates on the CPU, except for very fast hash
> formats which support --mask directly on the GPU.
> That way, --mask avoids a data transfer bottleneck which otherwise hurts
> GPU performance for those very fast hash formats.


Thanks for this explanation. I'll have to bench slow hashes to see how it behaves with and without --mask.
I don't use --mask so often, at least not during first cracking sessions.

patpro

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