From: Corentin Labbe <clabbe.montjoie@gmail.com>
To: Maxime Ripard <maxime.ripard@free-electrons.com>,
herbert@gondor.apana.org.au
Cc: srinivas.kandagatla@linaro.org, wens@csie.org,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
linux-crypto@vger.kernel.org
Subject: Re: [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
WARNING: multiple messages have this Message-ID (diff)
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
next prev parent reply other threads:[~2016-11-10 15:14 UTC|newest]
Thread overview: 16+ 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
2016-10-22 13:53 ` Corentin Labbe
2016-10-24 20:10 ` Maxime Ripard
2016-10-24 20:10 ` Maxime Ripard
2016-10-25 5:38 ` LABBE Corentin
2016-10-25 5:38 ` LABBE Corentin
2016-10-25 7:06 ` Jean-Francois Moine
2016-10-25 7:06 ` Jean-Francois Moine
2016-10-28 12:37 ` LABBE Corentin
2016-10-28 12:37 ` LABBE Corentin
2016-10-28 12:37 ` LABBE Corentin
2016-10-25 13:26 ` Maxime Ripard
2016-10-25 13:26 ` Maxime Ripard
2016-10-25 13:26 ` Maxime Ripard
2016-11-10 15:14 ` Corentin Labbe [this message]
2016-11-10 15:14 ` Corentin Labbe
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20161110151434.GA1209@Red \
--to=clabbe.montjoie@gmail.com \
--cc=herbert@gondor.apana.org.au \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-crypto@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=maxime.ripard@free-electrons.com \
--cc=srinivas.kandagatla@linaro.org \
--cc=wens@csie.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.