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Date: Mon, 06 Apr 2015 11:16:15 +0300
From: Alexander Cherepanov <>
Subject: Re: Advice on proposal: John the Ripper jumbo robustness

On 02.04.2015 12:49, Kai Zhao wrote:
>> 7x:
>> $ echo '[Options]' > john.conf
>> $ echo garbage >
>> $ time ../run/john --format=7z --config=./john.conf
>> No password hashes loaded (see FAQ)
>> real    0m0.015s
> I tried to change the john.conf to "[Options]" and run afl-fuzz, it does
> have more than
> 100 execs per second. However, there is a problem that when john reach
> single.c:single_init() function, it will exit and print message "No
> "Single" mode rules
> found in ./john.conf".  Even though the speed is faster, but we can only
> fuzz few functions.

Sure, if we disable some functionality we will not be able to use this 
functionality. What I had described is not a magic way to make john 
generally faster. It's a trick permitting a specific task to run faster. 
You will need other tricks for other tasks.

If you want to fuzz functions specific to a format like 7z then you can 
disable single mode.

If you want to fuzz functions used by single mode then enable single 
mode rules  and choose one simple format (like dummy). No need to fuzz 
single mode functionality with all formats. More precisely you have to 
take a look at single mode implementation to know if it has 
format-specific parts.

If you want to fuzz a dynamic format then enable it in the config file.

No need to enable all features simultaneously in your scenario.

Alexander Cherepanov

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