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Date: Wed, 21 Sep 2011 16:35:29 -0500
From: "jfoug" <>
To: <>
Subject: RE: False positives on zip (aes256)

There is a patch to add after the new Jumbo-7.  It is on the Wiki.  This
patch adds ability for a format to say that it finds 'false' positive
passwords, so the format will continue to search even if it finds one.

The patch page is:

The only format at the current time, using this code, is the zip-AES format
(the slow one).  Now, this format will continue to search, even after
finding a match.  It will be up to the user to really 'remove' the hash line
from the input file, once the 'real' password has been found.

This was implemented as a format flag (I used FMT_NOT_EXACT).

>From: Solar Designer []
>On Fri, Sep 02, 2011 at 08:38:30AM -0500, jfoug wrote:
>> I have added this as a 'wish list' item.  So if we do have formats
>> which end up outputting false ++ (and we cannot 'fix' them), then
>> an option like this will do just what you are seeing be performed
>> with your hard coded change.
>Alternatively, we could add a flag like FMT_MULTIGUESS, which we'd set
>for the current implementation of the WinZip/AES format, and which the
>rest of JtR code would interpret as a request to allow this format to
>produce multiple guesses.  It would affect (non-)removal of cracked
>hashes/ciphertexts both during cracking and on load.
>Besides false positives, another use may be for very weak
>hashes/ciphers/non-crypto where actual collisions are likely - e.g., if
>we ever introduce a way to crack CRC-32, BIOS passwords, etc. and want
>to let the user choose a good-looking one out of many valid passwords.
>This is becoming a topic for john-dev, though.

Since it was posted on john-users, I figured a notice of a working patch was
on-topic here.  There still are other ideas which may be added to this
sub-project, but that will be done on the other list.


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