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
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