Re: Keys/Signature use in OSTree/Flatpak/Flathub

[Alexander Larsson <alexl redhat com>]

On Wed, 2016-10-05 at 08:46 +0200, Alexander Larsson wrote:
> On tis, 2016-10-04 at 10:55 -0400, Colin Walters wrote:
> >  
> > So basically I assert that combining two well known and proven
> > technologies:
> >
> > - GPG signatures for *static* assertions (yes, no revocation, but
> > that's
> >   just how it works and everyone understands that)
> >   (Alternatively, one can use something other than GPG, like
> > alpine's
> >   use of simple ed25519 signatures)
> > - pubkey-pinned TLS to a centralized (metadata) server
> >
> > Mostly addresses the TUF threat model.
>
> Oh, wait, do you mean that we would have *unsigned* summaries, and
> instead relying on TLS for MITM protection, and the metadata public-
> facing server security (rather than the signature on the summaries)
> for
> protecting the metadata? 

What about keeping the single gpg key that signs everything, but just
allowing the delegation of keys?

For instance, the main key (call it A) would sign the commit, but the
summary could be signed with a different key (call it B) plus it
contains a statement "key B is allowed to sign the summary" signed by
key A. That could also be used in the summary file to say "branches
starting with foo can be signed by key C".

That way we would only ever need one key on the client side, but on the
server side one could chose to delegate signatures such that the main
key doesn't have to be on the system that signs the summary, or such
that a 3rd party can sign his app builds.