Re: [Gnu-arch-users] GNU Arch review - am I accurate?

[Charles Duffy]

On Thu, 2004-03-04 at 05:00, Andrew Suffield wrote:
> On Wed, Mar 03, 2004 at 07:07:09AM +0000, David A. Wheeler wrote:
> > The signatures sign the revision number as well as the change itself
> > (they're both encoded in the signed tarball), so an attacker can't
> > just change the patch order and can't silently remove a patch and
> > renumber the later patches without detection. However, it appears to
> > me that such signatures (at least as currently implemented) cannot
> > detect the malicious substitution of whole signed patches (such as
> > the silent replacement of a previous security fix with a non-fix),
> > or removal of the "latest" fix before anyone else uses it.
> 
> This problem is not specific to arch. It's a fundamental limitation of
> cryptographic signatures. There is no way that you can ever tell
> whether you are looking at the latest copy of the tree, or whether
> you're looking at a snapshot that a hostile interloper took yesterday
> and has substituted for the new one. I don't believe it is even
> theoretically possible to solve this problem in any system that is
> based on signatures.

There are things that could be done about it, though: Signature 
chaining, for instance, would mean that substitution would have to be
done not on a single revision alone but on all future revisions as well.
Sure, it's not a complete solution, but it could well be better than
nothing.