From: clabbe.montjoie@gmail.com (LABBE Corentin)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH] nvmem: sunxi-sid: SID content is not a valid source of randomness
Date: Tue, 25 Oct 2016 07:38:55 +0200 [thread overview]
Message-ID: <20161025053855.GA901@Red> (raw)
In-Reply-To: <20161024201020.h6akyqad2o42xkhq@lukather>
On Mon, Oct 24, 2016 at 10:10:20PM +0200, Maxime Ripard wrote:
> On Sat, Oct 22, 2016 at 03:53:28PM +0200, Corentin Labbe wrote:
> > Since SID's content is constant over reboot,
>
> That's not true, at least not across all the Allwinner SoCs, and
> especially not on the A10 and A20 that this driver supports.
>
On my cubieboard2 (A20)
hexdump -C /sys/devices/platform/soc\@01c00000/1c23800.eeprom/sunxi-sid0/nvmem
00000000 16 51 66 83 80 48 50 72 56 54 48 48 03 c2 75 72 |.Qf..HPrVTHH..ur|
00000010 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
00000100 16 51 66 83 80 48 50 72 56 54 48 48 03 c2 75 72 |.Qf..HPrVTHH..ur|
00000110 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
00000200
cubiedev ~ # reboot
cubiedev ~ # hexdump -C /sys/devices/platform/soc\@01c00000/1c23800.eeprom/sunxi-sid0/nvmem
00000000 16 51 66 83 80 48 50 72 56 54 48 48 03 c2 75 72 |.Qf..HPrVTHH..ur|
00000010 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
00000100 16 51 66 83 80 48 50 72 56 54 48 48 03 c2 75 72 |.Qf..HPrVTHH..ur|
00000110 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
00000200
So clearly for me its constant.
> > it must not be used as source of randomness.
>
> And I don't think that's true either. A constant entropy provider will
> not add any entropy, but will not remove any, would it?
I cced linux-crypto at the begining for confirmation on that.
But the problem is increased as a part of the content is predicatable over same type of device (at least the thirst bytes and all the zeros).
next prev parent reply other threads:[~2016-10-25 5:38 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-22 13:53 [PATCH] nvmem: sunxi-sid: SID content is not a valid source of randomness Corentin Labbe
2016-10-24 20:10 ` Maxime Ripard
2016-10-25 5:38 ` LABBE Corentin [this message]
2016-10-25 7:06 ` Jean-Francois Moine
2016-10-28 12:37 ` LABBE Corentin
2016-10-25 13:26 ` Maxime Ripard
2016-11-10 15:14 ` Corentin Labbe
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