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Message-ID: <20120701101213.7QAX8.322862.imail@eastrmwml302>
Date: Sun, 1 Jul 2012 10:12:13 -0400
From: <jfoug@....net>
To: john-dev@...ts.openwall.com
Subject: Re: raw-sha1-ng reduced binary size (was: asan report)
---- magnum <john.magnum@...hmail.com> wrote:
> On 2012-07-01 13:20, Tavis Ormandy wrote:
> > I understand, I'm just not sure it's worth the performance penalty (because
> > I can't treat it like a dqword in cmp_all).
I have not looked at the code, but would you not simply load the 4 byte DWORD, into a reg:
ABCDxxxxxxxxxxxx
then replicate this to the entire register
ABCDABCDABCDABCD
Then simply do comparison using that to the first register load of each group of 4 ? A register load hear being the first DWORD of each hash, in packed format.
I have not looked at the code, so I am not sure if your SSE buffers setup differently than the interleaved DWORDS, but would I think it is done that way.
> > I can think of a faster format
> > if I store it redundantly, like:
> >
> > SHA1 =00112233 44556677 aabbccdd eeff3344 eeaa1122
> > BINARY=EEAA1122 EEAA1122 EEAA1122 EEAA1122
> >
> > Then I only have to shuffle it once, instead of once per cmp_all. That's a
> > saving of 4 bytes per hash, and I can still use it like a dqword, is that
> > ok?
>
> Sure, I did not realize you would end up with a slower cmp_all. There
> should be some way around that.
the cmp_all is simply a 'better' hash check. It 'can' be an exact check, (if you are testing all 20 bytes, it is an exact check), but it does not have to be. There are many formats which have used the cmp_all to do a full compare, when really it should be written to as quickly as possible return that there is no way at all, that any of the passwords were cracked. Same thing for cmp_one. It should as quickly as possible state that 'this is not the one'. Any candidates that do squeeze by cmp_one can be fully tested in cmp_all.
Jim.
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