Last Call Review of draft-drage-sipping-rfc3455bis-13
review-drage-sipping-rfc3455bis-13-genart-lc-thomson-2014-02-28-00

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Document: draft-drage-sipping-rfc3455bis-13
Reviewer: Martin Thomson
Review Date: 2014-02-27
IETF LC End Date: 2014-03-14
IESG Telechat date: (if known)

Summary: I find it strange that this 3GPP document is being published
on the standards track.  But since it's a -bis there is clearly
precedent, and it is otherwise sound.

Major issues:

This document doesn't include enough information for me to some of the
headers.  For example, there isn't enough information in the document
to allow me to interpret the contents of cgi-3gpp:
          cgi-3gpp     = "cgi-3gpp" EQUAL (token / quoted-string)
(I pick on P-Access-Network-Info, because I'm somewhat familiar with it.)

This can probably be addressed by the inclusion of appropriate
normative references.  I seem to recall there being a 3GPP TS that
covered at least some of these.

Minor issues:

RFC 4244 is now obsolete, see 7044.  (related nit: Change log entry #2
seems quite defensive, unnecessarily so.  This document only needs to
define P-Called-Party-ID, and reference History-Info as an alternative
mechanism.)

Change log entry #5, mentions a shortcoming of 3455 (no registry for
access network types), but the draft does nothing about it.  It seems
to be propagating the mistake it notes.

A lot has happened since RFC 3455 was published.  The privacy
considerations around the use of P-Access-Network-Info are unchanged
from their pre-Geopriv form.  In particular, I find the UA knowledge
part to be problematic; Geopriv definitions can probably help here.

S6.1 P-Associated-URI is a powerful linkability vector, which could be
a far more serious privacy leak than the text implies.  The following
seems like good advice, but is not sufficient:

   An eavesdropper could possibly collect the list of identities a user
   is registered.  This can have privacy implications.  To mitigate this
   problem, this extension SHOULD only be used in a secured environment,
   where encryption of SIP messages is provided either end-to-end or
   hop-by-hop.

You also have to trust the other end of the hop with the information.
I think that's implicit, but probably needs to be stated.

S6.4  This claim sounds false to me:

   However, there
   are no security problems resulting from a UA inserting incorrect
   information.  Networks providing services based on the information
   carried in the P-Access-Network-Info header field will therefore need
   to trust the UA sending the information.  A rogue UA sending false
   access network information will do no more harm than to restrict the
   user from using certain services.

Any parameter whereby changing it can cause loss of service is likely
to be true in the inverse.  The draft makes no claims that would make
me believe otherwise.

Nits/editorial comments:

S1 Having the disclaimer as the first section is a little strange.  I
don't know what it is disclaiming yet.

S1, S3 It looks like a few characters are missing from these sections:
"trust.These", "environment The", "[RFC3455]   This"

The change log contains a lot of normative language.  I expected to
see pointers to changes, and maybe some justification, but items
include normative-sounding text and no pointers(7), other contain
pointers and duplicate text (3&4)

Change log #6 notes the removal of a field; given that this is
extensible, why not just mark the CDMA 2000 item deprecated instead of
removing it?