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Re: [Qemu-devel] RFC: virtio-rng and /dev/urandom
From: |
Hubert Kario |
Subject: |
Re: [Qemu-devel] RFC: virtio-rng and /dev/urandom |
Date: |
Fri, 15 Apr 2016 18:06:17 +0200 |
User-agent: |
KMail/4.14.10 (Linux/4.4.6-201.fc22.x86_64; KDE/4.14.17; x86_64; ; ) |
On Friday 15 April 2016 08:56:59 H. Peter Anvin wrote:
> On April 15, 2016 3:41:34 AM PDT, Cole Robinson <address@hidden>
wrote:
> >Libvirt currently rejects using host /dev/urandom as an input source
> >for a
> >virtio-rng device. The only accepted sources are /dev/random and
> >/dev/hwrng.
> >This is the result of discussions on qemu-devel around when the
> >feature was
> >first added (2013). Examples:
> >
> >http://lists.gnu.org/archive/html/qemu-devel/2012-09/msg02387.html
> >https://lists.gnu.org/archive/html/qemu-devel/2013-03/threads.html#00
> >023
> >
> >libvirt's rejection of /dev/urandom has generated some complaints
> >from users:
> >
> >https://bugzilla.redhat.com/show_bug.cgi?id=1074464
> >* cited: http://www.2uo.de/myths-about-urandom/
> >http://www.redhat.com/archives/libvir-list/2016-March/msg01062.html
> >http://www.redhat.com/archives/libvir-list/2016-April/msg00186.html
> >
> >I think it's worth having another discussion about this, at least
> >with a
> >recent argument in one place so we can put it to bed. I'm CCing a
> >bunch of
> >people. I think the questions are:
> >
> >1) is the original recommendation to never use
> >virtio-rng+/dev/urandom correct?
> >
> >2) regardless of #1, should we continue to reject that config in
> >libvirt?
> >
> >Thanks,
> >Cole
>
> Using /dev/urandom for virtio-rng, *except* perhaps for a small seed,
> it a complete waste of cycles. There is absolutely no reason to have
> one prng feed another.
/dev/random is a prng too, both /dev/random and /dev/urandom use exact
same algorithm
and yes, there are multiple reason for feeding one prng with another,
all cryptographic protocols do that all the time (e.g. TLS Pseudo-Random
Function output is fed as key to AES-GCM, both PRF and AES-GCM are
essentially PRNGs)
--
Regards,
Hubert Kario
Senior Quality Engineer, QE BaseOS Security team
Web: www.cz.redhat.com
Red Hat Czech s.r.o., Purkyňova 99/71, 612 45, Brno, Czech Republic
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- Re: [Qemu-devel] RFC: virtio-rng and /dev/urandom, (continued)
- Re: [Qemu-devel] RFC: virtio-rng and /dev/urandom, Hubert Kario, 2016/04/15
- Re: [Qemu-devel] RFC: virtio-rng and /dev/urandom, H. Peter Anvin, 2016/04/15
- Re: [Qemu-devel] RFC: virtio-rng and /dev/urandom, H. Peter Anvin, 2016/04/15
- Re: [Qemu-devel] RFC: virtio-rng and /dev/urandom, Paolo Bonzini, 2016/04/16
- Re: [Qemu-devel] RFC: virtio-rng and /dev/urandom, H. Peter Anvin, 2016/04/17
- Re: [Qemu-devel] RFC: virtio-rng and /dev/urandom, H. Peter Anvin, 2016/04/17
- Re: [Qemu-devel] RFC: virtio-rng and /dev/urandom, Hubert Kario, 2016/04/18
- Re: [Qemu-devel] RFC: virtio-rng and /dev/urandom, Hubert Kario, 2016/04/18
Re: [Qemu-devel] [libvirt] RFC: virtio-rng and /dev/urandom, Yaniv Kaul, 2016/04/19
Re: [Qemu-devel] RFC: virtio-rng and /dev/urandom, H. Peter Anvin, 2016/04/15
Re: [Qemu-devel] RFC: virtio-rng and /dev/urandom, Cole Robinson, 2016/04/20