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Date: Sun, 21 Aug 2011 21:05:28 +0400
From: Solar Designer <>
Subject: Re: John with Radeon graphical card supports?

On Fri, Aug 19, 2011 at 09:36:35AM +0200, Samuele Giovanni Tonon wrote:
> however bottleneck at the moment is not about COMPUTING power but
> transfer speed; ...

Our code should be made such that this would not be the case.  And when
it is the case, then I suspect that the CPU is also a bottleneck, likely
more so than the PCIe bandwidth.

> Also when you say multiple cards are you referring to SLI (or crossfire)
> or just a "put different gpu on the same motherboard" and make them work ?

Other password crackers don't rely on SLI/CrossFire, and we should neither.
Moreover, we should also try to minimize the bandwidth needs, to support
graphics cards in PCIe 1x slots - which is what people use to put 4 cards
onto inexpensive motherboards with only one 16x slot:

For slow hashes, this should be easy.  For fast hashes, I expect that
initially we'll be CPU- and bandwidth-bound, but we'll partially solve
this by optionally moving candidate password generation and hash
comparisons onto GPUs, likely at the expense of a less optimal order in
which candidate passwords are tried.

On Sun, Aug 21, 2011 at 02:16:07AM -0500, Richard Miles wrote:
> He also told that Radeon are much better for cracking in comparison
> with GeForce.

Yes, they're about 3x faster currently, but we need suitable code for
this to be seen.


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