Subject: [Ace] gerdes-ace-dcaf-authorize

From: Alper Yegin <[email-masked]>
Date: Thu, 19 Mar 2015 16:19:44 +0200

Hello dear authors of gerdes-ace-dcaf-authorize,

      Implicit authorization:   SAM authenticates the Client for the Server
      without specifying the privileges in detail.  This can be used for
      binary or unrestricted authorization (cf section 4 of
      [I-D.gerdes-ace-actors]).

I'd not call this "implicit". I'd call this "unlimited authorization", or "unrestricted authorization".
Authorization is explicitly there, it's just lacking any constrains. 

Also, don't you need a protocol exchanges between S and SAM, triggered by the S receiving an authenticated request from C? After all, SAM knows the Ticket but S does not.

And what protocol are you thinking of using between C and CAM, and between S and SAM?

Cheers,

Alper

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From: Olaf Bergmann <[email-masked]>
Date: Sat, 21 Mar 2015 15:19:56 +0100

Alper,

Thanks for your comments on dcaf which I will try address here:

> Authorization is explicitly there, it's just lacking any constrains. 

Well, we had the impression that many people we were talking to did not
see that authorization indeed is in effect here. I think, this was the
reason for that somehow misleading term.

> Also, don't you need a protocol exchanges between S and SAM, triggered
> by the S receiving an authenticated request from C? After all, SAM
> knows the Ticket but S does not.

The protocol exchange between S and SAM is tunneled through CAM and
C. Eventually, C puts the ticket face (that contains the authz
information) into the psk_identity field of the ClientKeyExchange. This
is all that S needs to validate that SAM has authorized C to access
certain resources on S.

> And what protocol are you thinking of using between C and CAM, and

For the ticket request and transfer between C and CAM, we envision DCAF
of DTLS as described in the draft. (DTLS is not a MUST here but a
natural choice. If, e.g., C and CAM happen to be combined into one
entity (e.g., a smartphone used as a control device), no explicit
communication is required whatsoever as described in Section 11.1 of
draft-gerdes-ace-dcaf-authorize.)

Direct interaction between S and SAM is not required for the DCAF
protocol flow as the DCAF messaging is tunneled through CAM and C.
However, a prerequisite for DCAF is the existence of a shared secret
between SAM and S (because this is used for integrity protection of the
ticket face). DCAF makes no assumptions on the protocol or configuration
method that is used to "bootstrap" this initial security relationship
between SAM and S (and the same holds for CAM and C).

Grüße
Olaf

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From: Stefanie Gerdes <[email-masked]>
Date: Mon, 23 Mar 2015 10:53:43 +0100

Hi Alper,

Thank you for your comments.

> Authorization is explicitly there, it's just lacking any constrains.

We called it implicit because the authorization information is not 
transmitted. S can still have own means for authorization.

Best regards,
Steffi