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Message-ID: <20130127231701.GA6692@openwall.com>
Date: Mon, 28 Jan 2013 03:17:01 +0400
From: Solar Designer <solar@...nwall.com>
To: john-dev@...ts.openwall.com
Subject: Re: Bug in a number of "crack array" formats
magnum, Dhiru -
On Sun, Jan 27, 2013 at 11:35:44PM +0100, magnum wrote:
> You can't reset the array in set_salt() because if we only have one salt, set_salt() will only be called once and never again. I get a deja-vu now, I am pretty sure we have told you this before.
We discussed similar issues before, but maybe not this specific one.
> I think you should do this:
>
> 1. If using an "any_cracked" variable, reset it in crypt_all() before the OMP loop.
I agree.
> 2. Always set *or reset* cracked[index] in crypt_all(). Ie. do not just set it on successfull crack but also reset it otherwise.
This may have performance impact with fast (non-)hashes and OpenMP, due
to false sharing, which may occur due to the cracked[] elements being
tiny and thus close together.
It may be better to memset() the entire cracked array to 0, but only if
any_cracked was previously set. That is, crypt_all() may start with:
if (any_cracked) {
memset(cracked, 0, cracked_size);
any_cracked = 0;
}
before it proceeds with the loop and OpenMP stuff.
IIRC, it's the exact same code that is currently in set_salt() in some
formats. It only needs to be moved to the beginning of crypt_all(),
because of the special case of having only one salt.
Thanks,
Alexander
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