Re: [Qemu-devel] RFC: virtio-rng and /dev/urandom

[Hubert Kario]

On Friday 15 April 2016 09:47:51 Eric Blake wrote:
> On 04/15/2016 04:41 AM, Cole Robinson 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#0
> > 0023
> > 
> > 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?
> That I'm not sure about - and the answer may be context-dependent (for
> example a FIPS user may care more than an ordinary user)

/dev/urandom use is FIPS compliant, no FIPS-validated protocol or 
cryptographic primitive requires the "fresh" entropy provided by 
/dev/random. All primitives are designed to work with weaker entropy 
guarantees than what /dev/urandom provides.

-- 
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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