linux-kernel - Re: [RFC][PATCH 0/6] /dev/random

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Sun, 24 Apr 2016 23:25:00 +0200
From:	Pavel Machek <pavel@....cz>
To:	Stephan Mueller <smueller@...onox.de>
Cc:	Ted Tso <tytso@....edu>, herbert@...dor.apana.org.au,
	linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
	sandyinchina@...il.com
Subject: Re: [RFC][PATCH 0/6] /dev/random - a new approach

Hi!

> > So you are relying on high-resolution timestamps. Ok. then you do kind
> > of the check on the timestamps... ok, why not. But then you mix in the
> > data regardless, saying that "they are not dependent" and thus can't
> > hurt.
> > 
> > But you already know they _are_ dependent, that's what your stuck test
> > told you:
> 
> The stuck test says that there is a pattern, but not that the pattern shows a 
> dependency.
...
> > Now. I could imagine cases where interrupts are correlated... like
> > some hardware may generate two interrupts for each event or something
> > like that...
> 
> But I see what you are referring to and I think you have a valid point in a 
> worst case assessment.
> 
> Thus, any stuck value should not be mixed into the pool.

Thanks.

> /* This RNG does not work if no high-resolution timer is available */
> BUG_ON(!random_get_entropy() && !random_get_entropy());

Heh, does this cause BUG() with 2^-64 probability? :-).

> If there is no high-resolution timer, the LRNG will not produce good entropic 
> random numbers. The current kernel code implements high-resolution timers for 
> all but the following architectures where neither random_get_entropy nor 
> get_cycles are implemented:

Ok, what about stuff like Intel 486 (no RDTSC)?

> Thus, for all large-scale architectures, the LRNG would be applicable.
> 
> Please note that also the legacy /dev/random will have hard time to obtain 
> entropy for these environments. The majority of the entropy comes
> from high-

Understood.

> Though, the patch I offer leaves the legacy /dev/random in peace for those 
> architectures to not touch the status quo.

Well -- that's the major problem -- right? Makes it tricky to tell
what changed, and we had two RNGs to maintain.

Best regards,
								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html