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Date: Thu, 26 Oct 2023 20:41:38 +0200
From: Solar Designer <>
Subject: Re: very low cpu usage when cracking one password

On Thu, Oct 26, 2023 at 09:52:13AM -0700, jeff wrote:
> I am running a recent version of john, using descript on a single 
> unknown password.
> I have a 64 core amd epyc processor.
> John is running, but it seems to be using only 1 thread.
> My cpu usage is between 1 and 3 percent.
> Is there any way to use more threads when I have only 1 psssword to crack?

The issue is that while John is using 128 threads for hash computation,
it is only using 1 thread for generating candidate passwords (in your
case, going through the wordlist and applying rules).  descrypt is so
fast to compute, especially by 128 threads, that almost all real time
ends up being spent on generating the candidates.

You can remedy this by using the "--fork=128" option, so that separate
candidate password streams would be generated, one by each process.
It's also reasonable to try "--fork=64" and "--fork=32" - these will
likely be slower, but less cumbersome to manage.

I don't know how well that works on Windows, though.  Please try and let
us all know.


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