From: maxime.ripard@free-electrons.com (Maxime Ripard)
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 15:26:48 +0200 [thread overview]
Message-ID: <20161025132648.txeo3rw6yz5wutrg@lukather> (raw)
In-Reply-To: <20161025053855.GA901@Red>
On Tue, Oct 25, 2016 at 07:38:55AM +0200, LABBE Corentin wrote:
> 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's constant across reboots, but not across devices. Each device have
a different SID content, therefore it's a relevant source of entropy
in the system.
Maxime
--
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
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next prev parent reply other threads:[~2016-10-25 13:26 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
2016-10-25 7:06 ` Jean-Francois Moine
2016-10-28 12:37 ` LABBE Corentin
2016-10-25 13:26 ` Maxime Ripard [this message]
2016-11-10 15:14 ` Corentin Labbe
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