Re: [Ksummit-discuss] [TOPIC] Secure/verified boot and roots of trust

[Ben Hutchings <ben@decadent.org.uk>]

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On Thu, 2016-08-04 at 00:01 +0100, Ben Hutchings wrote:
> On Wed, 2016-08-03 at 09:46 -0700, Andy Lutomirski wrote:
> [...]
> > 
> > And it gets rid of the IMO extremely nasty temporary key.  I
> > personally think that reproducible builds would add considerable
> > value
> > to many use cases, and we currently can't simultaneously support
> > reproducible builds and Secure Boot without a big mess involving
> > trusted parties, and the whole point of reproducible builds is to
> > avoid needed to trust the packager.
> [...]
> 
> You need that trusted party to supply a signature for the kernel, so
> why is it so much worse to have them do that for the modules as well?
[...]

I think I can now answer this myself.

Where there's a separate certificate store, the signing stage can be
entirely independent of the initial build.  A user of a distribution
can reproduce the distribution's unsigned binaries and then use their
own keys to build signed binaries for their own use.

However, the module signing certificate embedded in the kernel - even
if it refers to a persistent signing key, making it reproducible - has
to be established before the initial build, so it doesn't allow for
users to use a different root of trust.  So there ought to be an option
to require signatures but without defining any trusted keys at build
time.

Ben.

-- 
Ben Hutchings
Kids!  Bringing about Armageddon can be dangerous.  Do not attempt it
in
your own home. - Terry Pratchett and Neil Gaiman, `Good Omens'

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