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SubjectRe: [PATCH] CPU Jitter RNG: inclusion into kernel crypto API and /dev/random
On Sat 2013-11-02 12:01:12, Pavel Machek wrote:
> Hi!
>
> > >sense of where the unpredictability might be coming from, and whether
> > >the unpredictability is coming from something which is fundamentally
> > >arising from something which is chaotic or quantum effect, or just
> > >because we don't have a good way of modelling the behavior of the
> > >L1/L2 cache (for example) and that is spoofing your entropy estimator.
> >
> > Please note: if the jitter really comes from the oscillator effect of
> > the RAM clock vs. the CPU clock (which I suspect), we will not be able
> > to alter the jitter software wise.
>
> Well... if it is really oscillator effect, there should be _no_
> entropy when running with L1/L2 enabled (because DRAM will not be
> accessed at all at that case).
>
> There should be way to extract entropy more directly from various
> oscillator effects, no?

Actually... bogomips calibrating loop already has jitter, measured
from difference between CPU clock and system clock... Could that be
used as entropy source? As a bonus, we should have it on most
platforms...
Pavel
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html


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