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Date: Sun, 1 Apr 2012 13:38:57 +0400
From: Solar Designer <solar@...nwall.com>
To: john-dev@...ts.openwall.com
Subject: CUDA vs. OpenCL; approach to fast hashes (was: rawsha256.cu patch(using shared memory))

On Thu, Mar 29, 2012 at 05:16:21AM +0800, myrice wrote:
> I am sorry for lack my hardware details. GTX-580 is my lab's server. But
> recently it becomes unstable :(
> I tested this code on my laptop with GeForce 9600M GS card and P8600 CPU.
> So the performance is slow.

Do you expect to have access to faster cards during the summer?  Do you
intend to write any OpenCL code or only CUDA?  Efficient OpenCL code is
more desirable than CUDA code because AMD cards are simply about 3 times
faster than Nvidia at these tasks.  This is going to be partially
corrected with GTX 680, but I expect a difference of about 1.5x in favor
of AMD to remain (for optimized code).  And that's per-chip.  Now if we
consider that there are fast dual-GPU AMD cards on the market (6990,
5970), but no dual-GPU counterpart to GTX 680 available yet, that gives
AMD even further advantage this year (more GPUs per machine).  Perhaps a
new dual-GPU card from Nvidia will appear soon, though.

> However, I think If I implement candidate password generation and
> comparison on GPU, there are lots of work to do. I have to go
> through existing code on password generation(I guess they are mainly in
> Crakc.c?) and subtitute it with cuda.

That's one way to do it, but not the only one.  While there's obvious
usability advantage from being able to have all the same candidate
passwords generated on GPU that would be generated on CPU, it also makes
sense to have special cracking modes that are more suited to offloading
to GPU.

And no, this is not in cracker.c, but in per-cracking-mode source files.

Alexander

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