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Date: Sun, 31 Mar 2013 12:20:10 +0400
From: Solar Designer <>
Subject: Re: De-duping NT ruleset


On Sat, Mar 30, 2013 at 08:02:59PM -0400, Rich Rumble wrote:
> I ran a small test on "NT" using a simple set of letters:
> aaaaaaaaaaaaA
> AaAaAaAaAaAaa
> aaaaa
> That produced 16448 cadidates, and half are repeats, it should be 8224
> unique cadidates. I changed NT to be like this instead (below), and it only
> produces 8224 like I believe it's supposed to.

You can't reliably adjust a JtR ruleset to avoid producing duplicates
stemming from similarities across multiple input words, without also
missing some desirable candidate passwords on other valid inputs.  This
is a fundamental problem, it is not specific to the NT ruleset.  Thus,
what you have done is introduce a bug: on other valid inputs, your
NT_Length will miss some passwords that NT would produce.  This is easy
to see:

$ cat w
$ ./john -w=w -ru=NT_Length -stdo|sort -u|wc -l 
words: 4096  time: 0:00:00:00 DONE (Sun Mar 31 12:10:09 2013)  w/s: 45511  current: AAAAAAAAAAAAa
$ ./john -w=w -ru=NT -stdo|sort -u|wc -l
words: 8192  time: 0:00:00:00 DONE (Sun Mar 31 12:10:11 2013)  w/s: 102400  current: AAAAAAAAAAAAa

... or is this on purpose, with NT_Length being intended for use on some
special cases of input files, not on all?  If so, that's inconsistent
with the original purpose of the NT ruleset; perhaps you'd need to call
your ruleset differently and explain what inputs it is valid for, then.


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