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Date: Mon, 17 Jun 2013 08:19:01 +0400
From: Solar Designer <solar@...nwall.com>
To: john-dev@...ts.openwall.com
Subject: Re: Mask mode for GPU

Sayantan,

On Mon, Jun 17, 2013 at 09:19:14AM +0530, Sayantan Datta wrote:
> Generating password for each work item on host and repeating aa to zz in 
> each work item doesn't works very good with descrypt. There is a lot of 
> performance loss(30-40%) due to looping inside the kernel. But I think 
> this works great with md5 and other fast hashes(haven't tested myself 
> though).

I don't see why it would result in extra overhead for descrypt (and
compared to what).  Can you explain this in some detail, perhaps with
examples?

> So for descrypt I think we should generate one key on the host 
> and generate the remaining on GPU with each work item generating a 
> different set of password.

I don't see how what you wrote here is different from the approach I had
proposed.  You're talking about generating a set of passwords (not just
one password) per work-item anyway.

> One key issue with this is fitting the mask with GWS.

I had thought of this, and it's one of the reasons why I suggested the
approach I did suggest.  It lets us keep the portion of mask to search
on GPU independent from GWS.

Alexander

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