Openwall GNU/*/Linux - a small security-enhanced Linux distro for servers
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Date: Mon, 19 Nov 2012 21:09:59 +0100
From: magnum <john.magnum@...hmail.com>
To: "john-users@...ts.openwall.com" <john-users@...ts.openwall.com>
Subject: Re: How does incremental mode works?

On 19 Nov, 2012, at 16:39 , Richard Miles <richard.k.miles@...glemail.com> wrote:
> B.1) Once a new password is cracked with Markov should not be useful to get this information to update the stats file and recalculate the probabilistic? It may be wrong, but I guess that for example with a good amount of passwords cracked with Markov if we used this data to modify the stats "on the fly" it could give better results, not?

You will never have a perfect stats file. Given that, your suggestion will amplify the errors instead of making things better: Let's say your stats file have too much weight for the letter 's' so you crack a lot of password containing 's'. While this is a good thing, the downside is you missed (for the sake of example) nearly all passwords containing a 'q'. Now, if you use these results to modify your stats file, you get even more weight to 's' and even less weight to 'q'.

This is why the RockYou list is so much better than any list of cracked passwords. Because the passwords were stored in the clear, the RockYou list is a complete list of passwords from a large user base, not just the ones that were cracked using some sort of method that will (always) have more or less of errors like the (extreme) example I gave above.

> D.1) This one is for Magnum again since he always improve jTr with amazing small features that make our files easier. Today calculate the time that Markov will run based on time is a bit of pain as described here http://openwall.info/wiki/john/markov
> 
> Do you think that you could add a new command-line option to automate it? For example, maybe we could do something like --markov=autoadjust-10800:0:0:13 whre jTr would calculate itself the best possibility of markov level based on the current password cracking speed of the target hash and autoadjust it to run during 3 hours (10800). What do you think?

That would be nice, but I currently don't have time and inspiration to do anything like that. Doing it inside JtR itself might be a lot more tricky than it might seem. It's probably a lot easier to make a trivial script that accomplishes what you want.

magnum

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