Re: [Ace] Transporting different types of cnf objects - CBOR vs JSON

[Hannes Tschofenig <[e-mail]>]

There is unfortunately a problem.

With proof-of-possession keys there is more than just conveying the CWT/JWT over another transport.
In the PK-case, the client has to provide the public key to the server and get it bound to the PoP token.
In the symmetric key case, the server has to provide the token along with the symmetric key that is also included although encrypted) in the PoP token.

We have standardized the transport of this additional information in ACE for use with CoAP but for HTTP we decided to do the work on OAuth, where it got stuck because the IoT-interested people are not there and the Web folks want something else.

Ciao
Hannes

-----Original Message-----
From: Ace <[e-mail]> On Behalf Of Carsten Bormann
Sent: Mittwoch, 2. Oktober 2019 15:05
To: Cigdem Sengul <[e-mail]>
Cc: Jim Schaad <[e-mail]>; Ludwig Seitz <[e-mail]>; [e-mail]
Subject: Re: [Ace] Transporting different types of cnf objects - CBOR vs JSON

There is no strong interdependency between Web transfer protocol (HTTPS/CoAPS) and data format.
COSE works great over HTTPS, and if it must be, you can ship JOSE over CoAPS.

Grüße, Carsten


> On Oct 2, 2019, at 14:00, Cigdem Sengul <[e-mail]> wrote:
>
> Hello all,
>
> I am trying to implement this discussion in the draft.  A point is raised about COSE keys in JSON messages.
> Could it be possible to go with:
> (1) HTTPS - application/ace+json - jwt - jose - PoP for JWT or
> (2) CoAP - application/ace+cbor - cwt - cose - PoP for CWT without
> mixing anything?
>
> (1) we thought to describe by default in the document, and (2) we said MAY be supported.
> Is there a problem with this approach?
>
> Thanks,
> --Cigdem
>
>
> On Tue, Jun 4, 2019 at 9:29 PM Cigdem Sengul <[e-mail]> wrote:
> Hello,
> Yes, we thought supporting JSON option would be good, though indeed there is no issue with transporting CBOR..
> If there are no other concerns, we can define the new media type in the MQTT draft.
> Will add the issue to GitHub repo.
>
> --Cigdem
>
> On Tue, Jun 4, 2019 at 7:37 PM Jim Schaad <[e-mail]> wrote:
>
>
> > -----Original Message-----
> > From: Ace <[e-mail]> On Behalf Of Ludwig Seitz
> > Sent: Monday, June 3, 2019 11:51 PM
> > To: [e-mail]
> > Subject: Re: [Ace] Transporting different types of cnf objects -
> > CBOR vs JSON
> >
> > On 01/06/2019 02:51, Jim Schaad wrote:
> > > Ludwig,
> > >
> > > I have been doing some adaptions of my codebase for dealing with
> > > the MQTT specification.  In the process of this, I have identified
> > > the following items that I think needs some discussion.  They may
> > > not need changes in any documents and maybe should get a new document.
> > >
> > > 1.  The MQTT document is using the content type "application/json"
> > > over HTTPS for transporting messages.  Does there need to be an
> > > "application/ace+json" defined as a media type, but not
> > > necessarily a CBOR media type?  I think the answer may be yes, but
> > > it could be a new
> > document.
> > >
> > I would argue that the first draft using such a media type would be
> > the right place to specify it. However I'm not sure using JSON is
> > the right approach for an ACE specification at all, aren't we
> > supposed to cater for the constrained world?
> > What is there to prevent us from transporting CBOR over HTTP?
>
> There would be no reason that one cannot transport CBOR over HTTP.  During the discussions for these drafts Hannes was very explicit that he wanted to be able to use JSON rather than CBOR with the protocol that was defined by ACE.  This would mean that there needs to be an ability to use JSON with the ACE framework document.
>
> I would have no problems with the statement that the MQTT document would be a good place to define the new media type.
>
> >
> > > 2.  If I use a "COSE_Key" confirmation method inside of an
> > > application/ace+json message, there is a potential problem and it
> > > could be dealt with in a number of different ways.
> > > *  The JWT confirmation method is identified as "jwk".  The COSE
> > > key must be translated into JOSE even if there is no equivalent
> > > key in JOSE.  I.e. that is a fatal error
> > > *  This does not make sense and the confirmation method should be
> > > changed to "cwk" so that either key format could be used in either
> > encoding.
> > >
> >
> > If we use JSON messages mixing in COSE becomes awkward. If the use
> > case calls for JSON, I'd argue it should also use RFC7800 instead of
> > draft-ietf-ace- cwt-proof-of-possession.
>
> I would not have a problem with this, it was one of the options above.  I was just expanding my code to allow for JSON to be used and ran into this.  I just wanted to get a clear group decision on this before I put things into stone.
>
> Jim
>
> >
> > > 3.  If the confirmation is changed, you would need to convert the
> > > COSE key to a binary string, base64 encoded it and pass as a
> > > string when occurring in a JSON encoding.  There is not any other
> > > valid way to do this (except see above of just converting the key
> > > format).  However, the opposite of putting a JOSE key into a COSE
> > > confirmation has three different options that could be used.
> > > *  Encode the JOSE key to a string and pass as a string
> > > *  Encode the JOSE key top level map as CBOR but leave all of the
> > > elements alone.
> > > *  Encode the JOSE key in CBOR including conversion of base64
> > > strings to binary data.
> > > (My first preference is probably the second option, but either of
> > > the first two make sense.)
> > >
> > > Jim
> > >
> >
> > I'm still unsure that there is a good use case for transporting JOSE
> > keys in CBOR, but if such a case turns up, I would agree that
> > touching the encoding as little as possible is a good idea (=option 1 or 2).
> >
> > /Ludwig
> >
> > --
> > Ludwig Seitz, PhD
> > Security Lab, RISE
> > Phone [phone]
>
>
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