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Date: Wed, 23 Nov 2005 03:30:39 +0300
From: Solar Designer <>
Subject: Re: Speed up John

On Wed, Nov 23, 2005 at 02:55:49AM +0300, Solar Designer wrote:
> On Tue, Nov 22, 2005 at 11:36:58PM +0100, Frank Dittrich wrote:
> > The master could just once precompute all password candidates,
> Unfortunately, it would take one of the fastest CPUs available today
> almost 30 years to do that with the code currently in John.

A clarification: this estimate _includes_ the overhead of stdio and the
kernel (with output into /dev/null) since Frank's proposal was to abuse
the --stdout option without code modifications.

Simply commenting out the puts() line triples the performance, bringing
the rate up to 20M candidates/second (on the fastest CPUs currently
available) and the time to generate them all down to 10 years.
Commenting out even more stuff in crk_process_key(), except for the
events check and the status_update_crypts() call, makes the performance
almost 10x better than the original, for a rate of up to 70M candidates
per second (but the .rec file is not getting updated, then).

Alexander Peslyak <solar at>
GPG key ID: B35D3598  fp: 6429 0D7E F130 C13E C929  6447 73C3 A290 B35D 3598 - bringing security into open computing environments

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