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Date: Tue, 20 Dec 2005 01:00:39 +0100
From: Rembrandt <>
Subject: Re:  john improvement suggestions

Hash: SHA1

On Mon, 19 Dec 2005 21:48:30 +0000 (UTC)
Radim Horak <> wrote:

> Hi everyone
> and very special thanks to Solar Designer for the great John :)
> I've discovered this forum only recently, but I've been using John for quite 
> some time now, so I would like to share some ideas:
> 1. Bugs and annoyances
> - I have passwords (Traditional DES) from some old linux box, that are longer 
> than 16 chars, ie. consist of 3 hashes (crypt24?). John ignores such passwords 
> completely. I have tested them by manually cutting them. The 3rd hash uses salt 
> from the beginning of 2nd hash as 2nd hash uses the salt from beginning of the 
> 1st hash. I cannot provide the hashes nor I have access to that old linux box.
> - Is it possible to disable log to avoid very large log files (with certain 
> rules)?
> 2. Compilation
> - I have tested MSVC compiler with john.  
> (freely avail. here:
> I compiled the encryption routines with these parameters:
> cl /c /TC /G7 /Ox /O2 LM_fmt.c
> and the rest (I guess more POSIX dependent files) under the cygwin. The result 
> was notable improvement in Lanman DES cracking speed (around 19% increase), on 
> AthlonXP cpu (comparing to gcc -O3 -march=athlon-xp). Other algorithms were 
> performing at the same speed.
> - At this point, I'd like to see some way to increase the benchmarking time to 
> get more coherent/stable/exact figures.
> 3. Optimizations
> - In bigcrypt and other splitted psw. hashes, the first part(s) of the password 
> has known length of 8 (7 in LM). When cracking such passwords, the password 
> candidates (either from dictionary or incremental mode) that are shorter should 
> be filtered out (skipped).
> - Optimize regexp expansion order [a-z] according to some general/usage 
> statistics.
> - When there are psw. hashes cracked in session, does john skip cracking them 
> immediatelly? Or is there a session reload needed?
> 4. Other improvements
> - I use adhoc "wordlist" rules a lot, could there be some kind of this 
> functionality: -rules:wordlist_set_1 for selecting wordlist rules??
> - Is it possible to execute mmx and non-mmx instructions in x86 CPUs in 
> parallel? If so would it be possible get advantage of it in john?
> - The cygwin version of john can't access files (ie. wordlists) larger then 2 
> GB, would you consider a more win32 native/friendly version of john? (mingw?)
> - I think that the complexity gap between wordlist mode (even with rules) and 
> incremental modes is too big, there is a "undiscovered country" of various 
> optimizations/complexity reductions etc. Ie. like generating only "pronouncable" 
> passwords ( or the recent addition of 
> alpha-numeric charset. Another good thing to do would be to re-feed the cracked 
> passwords with the single-mode rules.
> 5. Time-memory trade-off for Traditional DES
> - I know. I know that there are salts that make it less effective, but I think 
> it's still worth (I assume 4096-times more memory needed for the equivalent of 
> non-salt performance, or 1024-times more memory for 1/16th of non-salt 
> performance. 
> Ophcrack ( uses 701 MB of 
> tables for alphanumeric LM passwords which is comparable to smallalphanumeric 
> Traditional Unix DES and 701 GB is quite acceptable storage space today, much 
> more tomorrow. Even pure smallalphabetical table would be beneficial and much 
> less demanding.)
> 6. There was mentioned a non-public sse-optimized version of john in this forum. 
>  Is there a chance we (public) will ever get our hands on it? If so, when?
> I hope to inspire
> and thanks in advance for any answers
> -Radim

Windows 9x had a limitation to 2GB for each file.
It's related to FAT. Maybe that's the problem? Because I can't imagine
why cygwin should have a filesize limit of 2GB.

- -- 
God did a bless on me,
So accapt the dark side in you.
Hate leads me to victory, so give me a war.
Version: GnuPG v1.4.1 (OpenBSD)


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