Re: Revocation list for old packages with security holes (was: Re: Revival of the signed debs discussion)
* Julian Mehnle (lists@mehnle.net) [031210 13:40]:
> Joey Hess <joeyh@debian.org> wrote:
> > Goswin von Brederlow wrote:
> > > What can we do with deb signatures?
> > >
> > > For our current problem, the integrity of the debian archive being
> > > questioned, the procedure would be easy and available to every user:
> > >
> > > 1. get any clean Debian keyring (or just the key signing the keyring)
> > > 2. verify the latest Debian keyring
> > > 3. verify that each deb was signed by a DD and the signature fits
> >
> > The canoical attack against signed debs in this situation is to find a
> > signed deb on snapshot.debian.net that contains a known security hole.
> > Now inject it into the compromised archive, with a changed filename, and
> > edit the Packages file to have its md5sum. Now a user's checks will
> > succeed -- the package is signed with a developer's key -- but they will
> > install the old, insecure .deb. The only hint will be a warning from
> > dpkg that it is downgrading the package, and a clever attacker might
> > avoid even that.
> We could use a revocation list where signatures of packages with known security holes are listed as being revoked. Of course, you'd
> need to be online to check it when installing/updating packages. And the revocation list would best be served from a server that's
> secure and separate from the archive servers to make attacks against it a bit more difficult.
Yes, that would also be a good enhancement.
However, verifying the actual control files of a package again the
information in Packages is also worth doing.
Cheers,
Andi
--
http://home.arcor.de/andreas-barth/
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