[Sidrops] Re: Notification for draft-spaghetti-sidrops-rpki-ta-tiebreaker

[Martin Hoffmann <[e-mail]>]

Job Snijders wrote:
> 
> Tim and I had a meeting and talked this draft over, Tim suggested to
> remove the notion of 'local policy' (as this introduces ambiguity).
> Instead: if the validity period is considered equal, and the signature
> is good, use the newly-retrieved cert (if it differs from the locally
> cached copy).

Given that the aim here is to avoid replaying (either maliciously or
accidentally) an older certificate and that we can trust that TA
operators take a fair amount of care, I think only looking at notBefore
time and using the new certificate if it is greater or equal should be
good enough. As a safeguard, you could add a line instructing TA
operators to never issue TA certificates with identical notBefore.

One thing to possibly consider to make it more unlikely that a new
certificate is withheld (again either maliciously or accidentally) is
to require trying different URIs listed on the TAL if the fetched
certificate is rejected for any of the reasons in the list and only use
the stored certificate if all of them are rejected.

Routinator currently doesn’t do that -- it uses a stored certificate
for that particular URI if fetching a new one fails --, but that’s
mostly because we don’t want to fall back from the safer HTTPS
transport to rsync where replaying an old certificate is easier. But
with the proposed protection mechanism, this won’t be necessary any
more.

  -- Martin