From: Stephan Mueller <smueller@chronox.de>
To: Clemens Ladisch <clemens@ladisch.de>
Cc: "Theodore Ts'o" <tytso@mit.edu>, Pavel Machek <pavel@ucw.cz>,
sandy harris <sandyinchina@gmail.com>,
linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org,
Nicholas Mc Guire <der.herr@hofr.at>
Subject: Re: [PATCH] CPU Jitter RNG: inclusion into kernel crypto API and /dev/random
Date: Thu, 14 Nov 2013 19:01:58 +0100 [thread overview]
Message-ID: <3127174.i8ueAho43m@tauon> (raw)
In-Reply-To: <5284AB17.5050802@ladisch.de>
Am Donnerstag, 14. November 2013, 11:51:03 schrieb Clemens Ladisch:
Hi Clemens,
>Stephan Mueller wrote:
>> Am Mittwoch, 13. November 2013, 12:51:44 schrieb Clemens Ladisch:
>>> (And any setting that increases accesses to main memory is likey to
>>> introduce more entropy due to clock drift between the processor and
>>> the memory bus. Or where do you assume the entropy comes from?)
>>
>> You nailed it. When I disable the caches using the CR0 setting, I get
>> a massive increase in variations and thus entropy.
>
>Now this would be an opportunity to use the number of main memory
>accesses to estimate entropy. (And when you're running out of the
>cache, i.e., deterministically, is there any entropy?)
>
I seem to have found the root cause with my bare metal tester, but I am
yet unable to make sense of it.
I will report back with more analyses.
>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. And then,
/dev/random is not so entropic any more for that attacker.
>
>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. And all I want and all I care about is that an
attacker has only the knowledge and ability to make measurements that
are less precise than 1 bit.
Ciao
Stephan
next prev parent reply other threads:[~2013-11-14 18:02 UTC|newest]
Thread overview: 61+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-10-11 18:38 [PATCH] CPU Jitter RNG: inclusion into kernel crypto API and /dev/random Stephan Mueller
2013-10-12 1:45 ` Sandy Harris
2013-10-12 3:28 ` Theodore Ts'o
2013-10-12 19:04 ` Stephan Mueller
2013-10-12 20:12 ` Stephan Mueller
[not found] ` <CACXcFm=_jmeKe2YYbHDi-jTGX-23hDsDeu_weWQkr2F_FpE_6g@mail.gmail.com>
2013-10-14 13:38 ` Fwd: " Sandy Harris
2013-10-14 14:12 ` Stephan Mueller
2013-10-14 14:26 ` Stephan Mueller
2013-10-14 14:14 ` Sandy Harris
2013-10-14 14:40 ` Stephan Mueller
2013-10-14 15:18 ` Sandy Harris
2013-10-14 15:26 ` Stephan Mueller
2013-10-14 15:46 ` Sandy Harris
2013-10-14 21:33 ` Sandy Harris
2013-10-15 6:23 ` Stephan Mueller
2013-10-28 15:40 ` Stephan Mueller
2013-10-28 16:06 ` Henrique de Moraes Holschuh
2013-10-28 16:15 ` Stephan Mueller
2013-10-28 21:45 ` Theodore Ts'o
2013-10-29 8:42 ` Stephan Mueller
2013-10-29 13:24 ` Theodore Ts'o
2013-10-29 14:00 ` Stephan Mueller
2013-10-29 22:25 ` Stephan Mueller
2013-11-02 11:01 ` Pavel Machek
2013-11-02 11:12 ` Pavel Machek
2013-11-03 7:20 ` Stephan Mueller
2013-11-03 12:41 ` Theodore Ts'o
2013-11-05 12:20 ` Stephan Mueller
2013-11-06 11:49 ` Stephan Mueller
2013-11-06 12:43 ` Theodore Ts'o
2013-11-06 12:51 ` Stephan Mueller
2013-11-06 13:04 ` Theodore Ts'o
2013-11-06 13:24 ` Pavel Machek
2013-11-07 0:36 ` Nicholas Mc Guire
2013-11-07 5:21 ` Stephan Mueller
2013-11-09 22:04 ` Clemens Ladisch
2013-11-10 1:10 ` Stephan Mueller
2013-11-10 16:31 ` Clemens Ladisch
2013-11-10 17:21 ` Stephan Mueller
2013-11-10 20:28 ` Clemens Ladisch
2013-11-13 3:12 ` Stephan Mueller
2013-11-13 11:51 ` Clemens Ladisch
2013-11-13 15:15 ` Stephan Mueller
2013-11-13 17:14 ` Pavel Machek
2013-11-14 10:51 ` Clemens Ladisch
2013-11-14 18:01 ` Stephan Mueller [this message]
2013-11-14 18:30 ` Clemens Ladisch
2013-11-14 18:34 ` Stephan Mueller
2013-11-11 2:58 ` H. Peter Anvin
2013-11-07 1:03 ` Nicholas Mc Guire
2013-11-07 5:26 ` Stephan Mueller
2013-11-09 22:04 ` Clemens Ladisch
2013-11-10 1:16 ` Stephan Mueller
2013-11-03 23:32 ` Pavel Machek
2013-11-05 12:25 ` Stephan Mueller
2013-11-05 13:45 ` Stephan Mueller
2013-11-06 11:42 ` Stephan Mueller
2013-11-06 13:26 ` Pavel Machek
2013-11-07 3:12 ` Stephan Mueller
2013-11-13 3:37 ` [PATCH] CPU Jitter RNG: Executing time variation tests on bare metal Stephan Mueller
2013-10-30 12:59 ` [PATCH] CPU Jitter RNG: inclusion into kernel crypto API and /dev/random Sandy Harris
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