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Message-ID: <20130626082511.GA29575@debian>
Date: Wed, 26 Jun 2013 12:25:11 +0400
From: Aleksey Cherepanov <aleksey.4erepanov@...il.com>
To: john-users@...ts.openwall.com
Subject: Re: [dhiru] write up for Hash Runner 2013
On Mon, May 27, 2013 at 10:13:20AM +0530, Dhiru Kholia wrote:
> I was able to write (and commit) a format for cracking SHA3-256 hashes
> in a short time (10 minutes). I think this is only contribution I made
> this time. I also wrote a format for cracking md5-broken hashes but I
> don't believe it was used much.
I am happy to say that your format was used despite alternative
implementation. I recracked all md5-broken found with your format and
it works well. Good work!
Alternative implementation was not an obvious must-have also it was
not an obvious waste of time. Now I think we were able to stick to
your implementation so the alternative implementation seems to have
the secondary role. Nevertheless alternative implementation allowed us
to use experimental code for generation of candidates on gpu without
effort. But it was important to have your implementation!
I think it would be great to have a post with your format on john-dev
and wiki to have an example how to do such things.
After all I got the idea how to improve speed of your format in place
of comparison. If I understand correctly you compare computed hash
with all hashes to crack. You could use hash function and table to
reduce the list of candidates for comparison. Usual hash function for
comparison in john uses first bytes from computed hash. Due to unknown
bits in input hashes you need different hash function - it should use
only bits known in all input hashes. In case there are no such bits or
their amount is not enough, you could create more tricky hash function
to meet following criteria: this hash function should give you the
same results on hashes with all bits and with question marks inside.
In good case you could craft a hash function to pick only one
candidate for comparison (perfect hash function). Though you would
need to generate a hash function for a defined set of hashes (i.e. per
input file) - there could not be one hash function suitable for all
sets.
Thanks!
--
Regards,
Aleksey Cherepanov
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