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Date: Sat, 19 Sep 2015 16:33:37 +0300
From: Solar Designer <>
Subject: Re: fast hash early exit vs. large hash list

On Sat, Sep 19, 2015 at 12:17:13PM +0300, Aleksey Cherepanov wrote:
> Similarly, we know b61 here. b61 becomes a64 in the end. So it is
> possible to check 1 int 3 rounds earlier.

This is what we're doing now, but when cracking a large hash list this
lets a bit too many passwords proceed further.

> Check of 2 ints needs 1 more round.

This is probably something we should implement, unless we end up
reversing more rounds first.

> Check against millions of hashes may just need 2 ints, not fully
> stored state.

Yes, although in Fred's testcase 1.7+ million correct passwords (and
more than that with --fork and some duplication in post-rules
candidates) would proceed all the way to cmp_*() where we'd want to
check the full 128 bits.  Testing them with scalar code may consume a
second, which is like a few percent of the total running time, thus is
"significant". ;-)

> I did not try these formulas, they may be wrong.

john-devkit produced them for you?  Can it produce anything for
reversing beyond step 61?  Maybe if you tell it that some input words
are zero?  (Just curious of its capabilities.)


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