[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date: Wed, 19 Aug 2015 00:40:16 +0200
From: magnum <john.magnum@...hmail.com>
To: john-dev@...ts.openwall.com
Subject: Re: 7z's KDF is unsalted
On 2015-08-18 23:05, Solar Designer wrote:
> On Tue, Aug 18, 2015 at 10:59:43PM +0200, magnum wrote:
>> On 2015-08-18 10:52, magnum wrote:
>>> On another note, it seems 7z is actually unsalted within the KDF. So one
>>> could make extremely effective Rainbow tables for it.
>>
>> Issue #1679, PR #1681.
>>
>> We now take advantage of this. Almost on par with mschapv2 and netntlmv1 :-)
>>
>> $ ../run/john -test -form:7z
>> Will run 8 OpenMP threads
>> Benchmarking: 7z, 7-Zip (512K iterations) [SHA256 AES 32/64]... (8xOMP) DONE
>> Speed for cost 1 (iteration count) of 524288
>> Many salts: 7876 c/s real, 1085 c/s virtual
>> Only one salt: 42.1 c/s real, 5.5 c/s virtual
>>
>> For each additional salt, we can skip the (very heavy) KDF and only do
>> the AES checks. The speedup for 500 salts is "only" 187x here, we can
>
> In other words, one can crack passwords to 500 unrelated 7-Zip archives
> in only 2.7x the effort of cracking password to one archive (and we can
> optimize this further). Correct?
As discussed elsewhere we recalled incorrectly - it's actually just 256
salts tested, and a benchmark flaw calls for a longer benchmark test.
Also, I enabled our "own" AES-NI instead of using OpenSSL, and now test
without hyperthreading:
$ OMP_NUM_THREADS=4 ../run/john -test=7 -form:7z
Will run 4 OpenMP threads
Benchmarking: 7z, 7-Zip (512K iterations) [SHA256 AES 32/64]... (4xOMP) DONE
Speed for cost 1 (iteration count) of 524288
Many salts: 10781 c/s real, 2830 c/s virtual
Only one salt: 45.5 c/s real, 11.5 c/s virtual
This is 236x faster for 256 salts. So it actually wins "best many-salts
boost" over mschapv2 and ntlmv1.
From these figures you can crack passwords to 256 unrelated 7-zip
archives in only 1.1x the effort of cracking password to just one of
them. And the more archives, the more boost - I guess there's virtually
no limit.
magnum
Powered by blists - more mailing lists
Confused about mailing lists and their use?
Read about mailing lists on Wikipedia
and check out these
guidelines on proper formatting of your messages.
