[libvirt-users] virRandomBits - not very random

[Eric Blake]

On 05/25/2018 09:17 AM, Michal Privoznik wrote:

>>> We should probably seed it with data from /dev/urandom, and/or the new
>>> Linux getrandom() syscall (or BSD equivalent).
> 
> I'm not quite sure that right after reboot there's going to be enough
> entropy. Every service that's starting wants some random bits. But it's
> probably better than what we have now.

Here's where we left things last time it came up:

https://www.redhat.com/archives/libvir-list/2014-December/msg00573.html

If gnutls has an interface that will give us random bits 
(gnutls_key_generate() in 3.0, perhaps), we should use THAT for all of 
our random bits (and forget about a seed), except when we are mocking 
things in our testsuite, and need a deterministic PRNG from a 
deterministic seed.

If not (including if we are not linked with gnutls), then we should 
prefer the new Linux syscall but fall back to /dev/urandom for JUST 
enough bits for a seed; once we're seeded, stick with using our existing 
PRNG for all future bits (after all, we aren't trying to generate 
cryptographically secure keys using virRandomBits - and the places where 
we DO need crypto-strong randomness such as setting up TLS migration is 
where we are relying on gnutls to provide it rather than virRandomBits).

So at this point, it's just a matter of someone writing the patches.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org