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Date: Wed, 19 Aug 2015 00:25:01 +0300
From: Solar Designer <>
Subject: Re: 7z's KDF is unsalted (was: Re: Formats using non-SIMD SHA2 implementations)

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.

I went to:

and there you mention similarity to WPA-PSK.  But we don't have this for

[ run]$ GOMP_CPU_AFFINITY=0-31 ./john -test -form=wpapsk
Will run 32 OpenMP threads
Benchmarking: wpapsk, WPA/WPA2 PSK [PBKDF2-SHA1 128/128 AVX 4x]... (32xOMP) DONE
Raw:    10645 c/s real, 334 c/s virtual

... or do we?  And folks are generating per-SSID rainbow tables for
WPA-PSK, treating it as salted for that purpose.

So what did you mean by mentioning WPA-PSK in the same context?

And doesn't the AES step prevent rainbow tables for 7-Zip (even if it
doesn't prevent the speedup you've now implemented)?

BTW, I brought this to Twitter:

Also, this might be CVE-worthy, similarly to eCryptfs:

although that one was granted a CVE based on "the vendor" confirming
that they treat it as a vulnerability... so if you can get 7-Zip
upstream to treat it as a vulnerability and fix it (in a future
revision), then it'd also be CVE-worthy for the same reason.  Otherwise,
it's unclear.


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