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Date: Tue, 13 Aug 2013 09:21:27 +0400
From: Solar Designer <solar@...nwall.com>
To: john-dev@...ts.openwall.com
Subject: Re: key-length for mask mode.

Hi Sayantan,

On Tue, Aug 13, 2013 at 10:40:41AM +0530, Sayantan Datta wrote:
> I have introduced a few changes to raw-md5-kernel. Now we can achieve
> nearly 2700Mc/s with around 12k loaded hashes.

That's good news, but have you reviewed myrice's PG-test and
experimented with it by now (with a variety of loaded hash counts
ranging from one to millions)?  If not yet, please stop all other work
and do that now!  It is wrong to abandon previous attempts without even
using the opportunity to learn from them (both what was done right and
what was done wrong).  And yes, myrice's code achieved a similar speed,
including with more hashes - IIRC, we were testing with 1M and 10M, as
well as with a few thousand, and the speed somehow varied between
invocations, sometimes being above 3000M c/s and sometimes below.  (This
is twice slower than hashcat's, though.)

> More optimizations are possible if we could limit the key length to 16.
> Current key length limit of 55 seems to be unnecessary. This should free up
> some more registers and allow me to introduce few more bitmpas.

No, we should be supporting long passwords.  55 is essential (max for
one MD5 block), anything less is artificial (speaking of raw MD5 only).
Actually, I think hashcat went in the opposite direction - getting rid
of those length limits - after CMIYC 2012, where the average password
length was 27 (I think the contest organizers said so).

I think there's no good excuse for us to sacrifice support for longer
passwords while still achieving only at most one half of the potential
speed.  (I say "at most" because hashcat's speed, while very good, is
most likely not the absolute maximum speed one can achieve.)

Thanks,

Alexander

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