Re: TPMs and random numbers

["Jörn Engel" <joern@logfs.org>]

On Thu, 12 September 2013 22:13:49 -0400, Theodore Ts'o wrote:
> On Thu, Sep 12, 2013 at 06:23:09PM -0400, Jörn Engel wrote:
> > It is worse in three ways:
> > - it costs performance,
> > - it may create a false sense of safety and
> > - it actively does harm if we credit it as entropy.
> > 
> > How much weight you assign to each of those is up to you.  So long as
> > we don't credit any of it as entropy, I am not too adverse to mixing
> > it in.  But I can equally see benefit in burning the bridges.
> 
> Well, mixing it in and using /dev/[u]random is certainly better than
> blindly using the output from the RNG from the TPM directly as a
> key.

Absolutely!

> I'm not sure what you mean by "burning the bridges"; what is the
> alternative that you are suggesting?

Not using hardware RNGs at all, see three messages back.  We know
those things can be compromised, we know a compromise cannot be
detected and we know of people/groups that have both a strong
motivation and likely the ability to pull it off.

I am not taking sides, but I can see good arguments for both
approaches.

Jörn

--
...one more straw can't possibly matter...
-- Kirby Bakken