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Date: Mon, 17 Aug 2015 14:02:45 +0300
From: Solar Designer <solar@...nwall.com>
To: john-users@...ts.openwall.com
Subject: Re: Merging rec sessions for --restore
On Sun, Aug 16, 2015 at 10:22:37PM +0100, Demian Smith wrote:
> I have a hash (truecrypt) that is, per default, saved as three possible
> hashtype (ripe, sha and whirlpool).
>
> I ran john (1.8.0.6-jumbo-1-639-gd647405) on it for some time (46 days,
> to be precise), specifying ripe to try. I have now, just to see would it
> be more successful, started another session for sha.
I hope you're not trying to run both at the same time on the same
machine and with OpenMP enabled in each. That would result in poor
performance, with much processing time lost in OpenMP implementation's
thread synchronization. (OpenMP only works well on an otherwise idle
system.) You may, however, halve the OpenMP thread count in each, with
the OMP_NUM_THREADS env var, in which case it'd be OK. (Still slightly
slower than --fork, though. And a lot slower than what you can achieve
with a GPU.)
> Of course this is anything but optimal, so I was wondering could the two
> sessions be merged= I'd remove the whirlpool hash from the hashfile and
> just restore the "merges" session, so that both hashes are tried
> simultaneous - or is that (both) not possible at all?
I doubt there's much to merge here. I am not familiar with TrueCrypt,
nor with the corresponding JtR format, but I think most processing time
is in fact spent on those different hashes. So even if some steps could
be merged (candidate password generation, decryption attempts with the
derived keys), the speedup from that would likely be negligible. Also,
you would have skipped all the most likely candidate passwords that you
already tested in those 46 days from being tested against the SHA hashes.
Alexander
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