linux-kernel - Re: [PATCH] CPU Jitter RNG: inclusion into kernel crypto API and /dev/random

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Date:	Tue, 29 Oct 2013 09:24:48 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Stephan Mueller <smueller@...onox.de>
Cc:	sandy harris <sandyinchina@...il.com>,
	linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org
Subject: Re: [PATCH] CPU Jitter RNG: inclusion into kernel crypto API and
 /dev/random

On Tue, Oct 29, 2013 at 09:42:30AM +0100, Stephan Mueller wrote:
> Based on this suggestion, I now added the tests in Appendix F.46.8 where 
> I disable the caches and the tests in Appendix F.46.9 where I disable 
> the caches and interrupts.

What you've added in F.46 is a good start, but as a suggestiom,
instead of disabling one thing at a time, try disabling *everything*
and then see what you get, and then enabling one thing at a time.  The
best thing is if you can get to the point where the amount of entropy
is close to zero.  Then as you add things back, there's a much better
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.

Regards,

						- Ted
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