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Message-ID: <20070704110001.GB13292@openwall.com>
Date: Wed, 4 Jul 2007 15:00:01 +0400
From: Solar Designer <solar@...nwall.com>
To: john-users@...ts.openwall.com
Subject: Re: Incremental mode limited to 8 character words?
On Wed, Jul 04, 2007 at 12:23:30AM +0200, Frank Dittrich wrote:
> I didn't study the source, but since CHARSET_MAX is < 128,
> you might get away with CHARSET_SCALE=128, or 0x80.
> (If possible, I would not set CHARSET_SCALE to a value which is
> not a power of 2, since I'd expect a performance impact otherwise.)
Actually, no, CHARSET_SCALE is not in any way connected with CHARSET_MAX
(except that we should avoid integer overflows) and almost arbitrary
values of CHARSET_SCALE are OK as long as it's at least 1 (since it's
used as a multiplier). There's no performance impact from any of this;
CHARSET_SCALE is only used while .chr files are being generated and it
affects the precision of fixed-point operations. Worse precision (lower
values of CHARSET_SCALE) means potentially less optimal order in which
the resulting .chr file will try candidate passwords.
Here are some working CHARSET_* settings:
For lengths up to 9: just increase CHARSET_LENGTH to 9. No other
changes are needed (default CHARSET_SCALE of 0x100 is OK). This is
because the requirement is actually a bit less strict than what the
comment says. Those who want to find out what it really is can refer to
charset.c: charset_self_test(). ;-)
For lengths up to 10, we can use a range of 84 ASCII codes:
#define CHARSET_MIN '\''
#define CHARSET_MAX 'z'
#define CHARSET_LENGTH 10
#define CHARSET_SCALE 9
For lengths up to 13, we can use either lowercase or uppercase letters:
#define CHARSET_MIN 'a'
#define CHARSET_MAX 'z'
#define CHARSET_LENGTH 13
#define CHARSET_SCALE 18
The above example is for lowercase letters. I've actually tested it by
first generating a fake john.pot from all.lst:
zcat all.gz | sed 's/^/:/' > john.pot
Then I generated a new .chr file with the patched build of JtR 1.7.2:
./john --make-charset=alpha13.chr
This has taken under a minute (and around 80 MB of RAM) and the output was:
Loaded 2783610 plaintexts
Generating charsets... 1 2 3 4 5 6 7 8 9 10 11 12 13 DONE
Generating cracking order... DONE
Successfully written charset file: alpha13.chr (26 characters)
Then I added a new section to john.conf:
[Incremental:Alpha13]
File = $JOHN/alpha13.chr
MinLen = 0
MaxLen = 13
CharCount = 26
Finally, I've tested this new "incremental" mode:
./john -i=alpha13 --stdout >&-
By pressing a key, I saw what candidate passwords it would be trying:
words: 1237066 time: 0:00:00:02 w/s: 618533 current: brimpaset
words: 1937544 time: 0:00:00:03 w/s: 645848 current: pangingatuur
words: 2654081 time: 0:00:00:04 w/s: 663520 current: sesslj
words: 4158186 time: 0:00:00:06 w/s: 693031 current: rozmarises
words: 6440073 time: 0:00:00:09 w/s: 715563 current: moretail
words: 9486464 time: 0:00:00:13 w/s: 729728 current: rivuletti
words: 11058620 time: 0:00:00:15 w/s: 737241 current: spichiserei
words: 12584642 time: 0:00:00:17 w/s: 740273 current: affenensker
words: 14092397 time: 0:00:00:19 w/s: 741705 current: podentuiset
words: 15634776 time: 0:00:00:21 w/s: 744513 current: kestllas
words: 17224298 time: 0:00:00:23 w/s: 748882 current: ammcgetu
words: 20371318 time: 0:00:00:27 w/s: 754493 current: bentykk
(This is on a fairly slow Pentium 3 system.)
> If password length 9 is OK, you could combine the incremental mode
> (MinLength = MaxLength = 8) and an external mode which always
> appends the same character.
This might actually be a reasonable thing to do.
Frank - thank you for helping address Tom's actual question while I
wasn't around.
--
Alexander Peslyak <solar at openwall.com>
GPG key ID: 5B341F15 fp: B3FB 63F4 D7A3 BCCC 6F6E FC55 A2FC 027C 5B34 1F15
http://www.openwall.com - bringing security into open computing environments
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