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Date: Tue, 17 Aug 2010 12:18:56 +0400
From: Solar Designer <solar@...nwall.com>
To: john-users@...ts.openwall.com
Subject: Re: Consonant Vowel Patterns

On Thu, Aug 12, 2010 at 09:17:40AM -0400, Brad Tilley wrote:
> I wanted to ask if others had experimented with consonant vowel patterns
> in password cracking?

I briefly played with something like this in 1995 or so, and the code
stayed around for a few years longer (before being dropped).
Specifically, early revisions of what became JtR's incremental mode had
an optional builtin filter (called "wordlike") that would skip candidate
passwords that contain too many consecutive vowels or consonants.
It insisted on having no more than 2 consecutive consonants and no
consecutive vowels (OK, this wouldn't work for Dutch), although these
numbers were easy to edit in the code:

  bzero(vowels, sizeof(vowels));
  vowels['a']++; vowels['e']++; vowels['i']++; vowels['o']++; vowels['u']++;
  vowels['A']++; vowels['E']++; vowels['I']++; vowels['O']++; vowels['U']++;
[...]
        if (wordlike) {
          *(long *) & classcount = 0;
          for (wpos = 0; wpos < usecount; wpos++) {
            classcount[classindex = vowels[word[wpos]]]++;
            classcount[classindex ^ 1] = 0;
            if (classcount[0] > 2 || classcount[1] > 1) break;
          }
        }

This was of some help with pre-JtR and early JtR revisions of the code.
At the time, the sorted character lists were not per-position (there was
just one list initially, then three lists for beginning/middle/end).
Then per-position lists were introduced.  Then .chr files with
per-preceding-two-characters lists were introduced (effectively storing
info on trigraphs).  By this point, the "wordlike" filter was fully
obsoleted, so it was eventually not included into a new revision of the
code (written in 1997-1998, which became JtR 1.5+).

The above code snippet came from JtR 1.4 released in 1997, although
"wordlike" was already obsolete by then (JtR 1.4 already had support for
.chr files).  It's just that I did not drop the code separately from the
rewrite for 1.5+.

Alexander

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