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Date: Thu, 18 Jul 2013 09:55:56 +0530
From: Sayantan Datta <std2048@...il.com>
To: john-dev@...ts.openwall.com
Subject: Re: md5 hash comparisons

Hi,

On Thu, Jul 18, 2013 at 6:00 AM, Michael Samuel <mik@...net.net> wrote:

> I had quite a bit of success with this approach with some otp-md5
> stuff I did, first because branches on GPUs are(/were?) really
> expensive and second because gpu->host transfers are async so the gpu
> can be computing the next batch while the transfer occurs.
>


This could have been a good idea for small number of hashes. But as solar
mentioned we will be checking more than a million hash against the millions
generated. I think a single cpu core will bottleneck at some point.

What I intend to do is use local memory for first 2 bitmap checks each of
size 4KB so that they fit inside LDS . Then the last two bitmap check will
use bitmap stored in global memory each of size 256MB.

However I did a little math which shows 99% of hashes are going through the
first two test. Mathematically the whole bitmap idea seems to be
ineffective. But the plus point is that the math I did was based on the
assumption that all possible hashes md5 hashes are loaded. But clearly this
will never be the case.

Regards,
Sayantan

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