On Friday 15 April 2016 08:56:59 H. Peter Anvin wrote: > On April 15, 2016 3:41:34 AM PDT, Cole Robinson <crobinso@xxxxxxxxxx> 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
Attachment:
signature.asc
Description: This is a digitally signed message part.
-- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list