Re: [PATCH v4 0/5] /dev/random - a new approach

Tomas Mraz
2016-06-21T13:27:44Z

On Út, 2016-06-21 at 09:05 -0400, Austin S. Hemmelgarn wrote:
> On 2016-06-20 14:32, Stephan Mueller wrote:
> >
> > [1] http://www.chronox.de/jent/doc/CPU-Jitter-NPTRNG.pdf
> Specific things I notice about this:
> 1. QEMU systems are reporting higher values than almost anything
> else
> with the same ISA.  This makes sense, but you don't appear to have
> accounted for the fact that you can't trust almost any of the entropy
> in
> a VM unless you have absolute trust in the host system, because the
> host
> system can do whatever the hell it wants to you, including
> manipulating
> timings directly (with a little patience and some time spent working
> on
> it, you could probably get those number to show whatever you want
> just
> by manipulating scheduling parameters on the host OS for the VM
> software).

You have to trust the host for anything, not just for the entropy in
timings. This is completely invalid argument unless you can present a
method that one guest can manipulate timings in other guest in such a
way that _removes_ the inherent entropy from the host.

--
Tomas Mraz
No matter how far down the wrong road you've gone, turn back.
Turkish proverb
(You'll never know whether the road is wrong though.)