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Message-ID: <20150507141611.GD11074@openwall.com>
Date: Thu, 7 May 2015 17:16:11 +0300
From: Solar Designer <solar@...nwall.com>
To: john-dev@...ts.openwall.com
Subject: Re: get_binary_*() and get_hash_*() methods
On Thu, May 07, 2015 at 02:02:36PM +0300, Aleksey Cherepanov wrote:
> get_hash[]() should be called for each computed hash, cmp_all()
> without get_hash[]() should be called for each loaded hash.
>
> It would be possible to remove get_hash[]() calls if crypt_all
> returned the values in array: john provides a pointer to array of ints
> (BTW why not unsigned int?) of length MAX_KEYS_PER_CRYPT to
> crypt_all(), and crypt_all fills the array with values like from
> get_hash[6](). Though the length of array should be a separate field
> in the format structure because crypt_all() may produce more
> candidates.
The caller will not always need those partial hashes. For some formats,
e.g. for bitslice DES, they are costly to produce. When cracking only a
handful of hashes, it is quicker to call cmp_all() right away, without
going through get_hash[]() first.
loader.c:
threshold = password_hash_thresholds[0];
if (db->format && (db->format->params.flags & FMT_BS)) {
/*
* Estimate the complexity of DES_bs_get_hash() for each computed hash (but
* comparing it against less than 1 loaded hash on average due to the use of a
* hash table) vs. the complexity of DES_bs_cmp_all() for all computed hashes
* at once (but calling it for each loaded hash individually).
*/
threshold = 5 * ARCH_BITS / ARCH_BITS_LOG + 1;
}
Alexander
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