Re: [Ace] [EXTERNAL] Re: Martin Duke's No Objection on draft-ietf-ace-oauth-params-13: (with COMMENT)

[Martin Duke <[e-mail]>]

LGTM. Thanks

On Wed, Mar 24, 2021 at 12:42 AM Seitz Ludwig <[e-mail]>
wrote:

> Hi Martin, Ben,
>
> If I were to change the offending sentence like so:
> "It is RECOMMENDED that an AS reject a request containing a symmetric key
> value ... (Note: this does not apply to key identifiers referencing a
> symmetric key)"
>
> (the "Note..." part being the new clarification), would that help making
> the intention distinction more visible?
>
> /Ludwig
>
>
> > -----Original Message-----
> > From: Benjamin Kaduk <[e-mail]>
> > Sent: den 21 mars 2021 03:17
> > To: Martin Duke <[e-mail]>
> > Cc: The IESG <[e-mail]>; [e-mail]; [e-mail];
> draft-ietf-
> > [e-mail]
> > Subject: [EXTERNAL] Re: [Ace] Martin Duke's No Objection on
> draft-ietf-ace-
> > oauth-params-13: (with COMMENT)
> >
> > Hi Martin,
> >
> > On Thu, Mar 18, 2021 at 11:44:53AM -0700, Martin Duke via Datatracker
> > wrote:
> > >
> > >
> > > ----------------------------------------------------------------------
> > > COMMENT:
> > > ----------------------------------------------------------------------
> > >
> > > In sec 3.1 it says the AS SHOULD reject req_cnf if the key is
> > > symmetric. But in Sec 5 it presents a totally reasonable use case
> > > where the C and RS hold a previously established (symmetric?) key.
> > > These observations are somewhat contradictory. Should 3.1 include a
> > > qualifier. Would the AS know about this key a priori so that it can
> > > ignore the recommendation? If not, how can this be done safely?
> >
> > I think there is a subtle distinction between the two cases, if I am
> > remembering correctly.  In particular, in Section 3.1 it says that "[i]t
> is
> > RECOMMENDED that an AS reject a request containing a symmetric key
> > value", and the last word ("value") is important!  This is saying, if
> the client
> > tries to propose to the AS the actual symmetric key to be (encapsulated
> in
> > the token and) used to secure C/RS communications, the AS typically
> should
> > reject it, since a constrained client is likely to have a much worse RNG
> than
> > the AS.  If, on the other hand, some out-of-band management system has
> > provisioned a symmetric key shared by C and RS, that key is presumed to
> be
> > strong, but in the scenario depicted in Section 5 it is "the
> key-identifier of a
> > previously established key between C and RS" that "req_cnf" conveys.
> > Note that this scenario is only the identifier, not the key value itself.
> >
> > This is clearly a pretty subtle distinction to make, and if you have any
> > suggestions for how to word things to make it more obvious, we'd love to
> > have them.
> >
> > Thanks,
> >
> > Ben
>