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

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Date:	Thu, 14 Nov 2013 19:34:04 +0100
From:	Stephan Mueller <smueller@...onox.de>
To:	Clemens Ladisch <clemens@...isch.de>
Cc:	Theodore Ts'o <tytso@....edu>, Pavel Machek <pavel@....cz>,
	sandy harris <sandyinchina@...il.com>,
	linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
	Nicholas Mc Guire <der.herr@...r.at>
Subject: Re: [PATCH] CPU Jitter RNG: inclusion into kernel crypto API and /dev/random

Am Donnerstag, 14. November 2013, 19:30:22 schrieb Clemens Ladisch:

Hi Clemens,

>Stephan Mueller wrote:
>> Am Donnerstag, 14. November 2013, 11:51:03 schrieb Clemens Ladisch:
>>> An attacker would not try to detect patterns; he would apply
>>> knowledge
>>> of the internals.
>> 
>> I do not buy that argument, because if an attacker can detect or
>> deduce the internals of the CPU, he surely can detect the state of
>> the input_pool or the other entropy pools behind /dev/random.
>
>With "internals", I do not mean the actual state of the CPU, but the
>behaviour of all the CPU's execution engines.
>
>An Intel engineer might know how to affect the CPU so that the CPU
>jitter code measures a deterministic pattern, but he will not know the
>contents of my memory.

Here I agree fully.
>
>>> Statistical tests are useful only for detecting the absence of
>>> entropy, not for the opposite.
>> 
>> Again, I fully agree. But it is equally important to understand that
>> entropy is relative.
>
>In cryptography, we care about absolute entropy, i.e., _nobody_ must be
>able to predict the RNG output, not even any CPU engineer.

With your clarification above, I agree here fully.

And now my task is to verify the root cause which I seem to have found.

Let me do my homework.

Ciao
Stephan
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