[POSH] Comments/questions on draft-miller-posh-00

[Michael Procter <[e-mail]>]

I read draft-miller-posh-00 with interest, and have a couple of
questions about the expected usage.

In section 5, you discuss the relative timing of POSH operations and
the application TLS handshake, requiring the POSH operations to be
complete before the application handshake completes.  At the end of
the paragraph, you mention that all the POSH operations may in fact be
completed before the application handshake begins.  That sounds
reasonable, provided you know in advance that the POSH part is
required.  Is that inferred from DNS if the target hostname is not in
the original service domain or some other heuristic?  It seems fair to
me to only require the POSH part if the certificate presented is
invalid for reasons such as subjectAltName mismatch, which precludes
starting the POSH operations before the application handshake.
Similarly, I can't see anything obviously wrong with letting the
application handshake complete, then performing the POSH operations
before deciding the application connection is not suitable and should
be terminated before being used.  Is the MUST in this section
mandating the order of operations necessary for some other reason?

In section 6, you state that ideally, caching of the certificate
obtained via POSH should be based on the expiration time of the
certificate.  I think this might be a little too trusting, as it ties
delegation validity to certificate expiry.  If I trust
hosting.example.net to host my service today, that doesn't mean I will
continue to trust them until their certificate expires.  HTTP
cache-control headers might be a useful way of indicating a short term
trust though.

Regards,

Michael