From: clabbe.montjoie@gmail.com (Corentin Labbe)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH] nvmem: sunxi-sid: SID content is not a valid source of randomness
Date: Thu, 10 Nov 2016 16:14:34 +0100 [thread overview]
Message-ID: <20161110151434.GA1209@Red> (raw)
In-Reply-To: <20161025132648.txeo3rw6yz5wutrg@lukather>
On Tue, Oct 25, 2016 at 03:26:48PM +0200, Maxime Ripard wrote:
> 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.
>
Not the 3 leading digit and not the tailing zeros which are the same accross device.
So only 50% of data are really different accross devices.
Perhaps a "random-range" property could be used ?
Herbert, does it is safe to add that 50% duplicate content via add_device_randomness() ?
Reading add_device_randomness doc, it seems finally it is safe, but if you could confirm it.
Regards
prev parent reply other threads:[~2016-11-10 15:14 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
2016-11-10 15:14 ` Corentin Labbe [this message]
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