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Message-Id: <1195009929.8441.34.camel@localhost>
Date: Tue, 13 Nov 2007 21:12:09 -0600
From: jmk <jmk@...fus.net>
To: john-users@...ts.openwall.com
Subject: Re: advice requested about NTLMv1 implementation
On Tue, 2007-11-13 at 09:54 +0100, Simon Marechal wrote:
> Hello,
>
> as most people know it's quite easy once you have a valid account on a
> window computer (not vista) to retrieve an NTLMv1 response to an
> arbitrary challenge. This makes it quite useful when looking for a valid
> user password.
>
> This response is made of 3 chunks, based on the LM hash (which is made
> of 2 chunks). The dependency is:
>
> C/R LM
> 1st chunk 7 first bytes of the first LM chunk
> 2nd chunk last byte of 1st LM chunk and 6 first bytes of 2nd chunk
> 3rd chunk 2 last bytes of the second LM chunk
>
> It should be clear here that there are only 2^16 3rd chunks for a given
> challenge. Getting the last 2 bytes of the 2nd chunk's LM hash is thus
> quite fast. In the same way, once you know the 2nd LM chunk, it's quite
> easy to retrieve the last byte of the 1st.
>
> It thus makes sense to only compute the LM hash, and do the full
> computation on passwords whose last bytes match (with a false positive
> rate of 1/2^16 and 1/2^8 for the 2nd and 1st chunk).
>
> It's straightforward to alter the LM cipher to crack either the last
> chunk or the first chunk, but I can't see a smart way to attack both in
> the same cipher, as the split() function would retrieve chunks that are
> computed differently. Would someone have a good advice on that?
I don't have any good advice for you on this specifically. ;)
At the risk of pointing out the obvious, have you seen the basic
implementation of LMv1/NTLMv1 posted here:
http://openwall.com/john/contrib/john-1.7.0.2-netlm-netntlm-jmk-3.diff.gz
http://openwall.com/john/contrib/john-1.7.2-all-8.diff.gz
I've found coupling LMv1 (1st chunk) Rainbow Table look-ups with NTLMv1
brute-force guessing to be relatively quick for cracking a user's
password.
Joe
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