Re: [COSE] questions for the WG from 8152bis AUTH48

[Marco Tiloca <[e-mail]>]

Hi Ben and all,

On 2022-02-18 05:59, Benjamin Kaduk wrote:
> Hi all,
>
> The chairs and I are continuing to work through the AUTH48 process for the
> 8152bis drafts, and a couple topics have come up that would benefit from
> some broader input.
>
> The other question is in -algs; in
> https://eur05.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdatatracker.ietf.org%2Fdoc%2Fhtml%2Fdraft-ietf-cose-rfc8152bis-algs%23section-8&data=04%7C01%7Cmarco.tiloca%40ri.se%7C634eeebfc73d4bda82d108d9f29b9b26%7C5a9809cf0bcb413a838a09ecc40cc9e8%7C0%7C0%7C637807572981435893%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=A1x%2BuzSMoO%2FwsjO%2BjpLGCj%2BCRhK2BRRLCdqLrKFTw88%3D&reserved=0
> we start off with a rather awkward sentence "There are some situations that
> have been identified where identification of capabilities of an algorithm
> or a key type need to be specified."  In particular (at least to me), the
> "identification ... needs to be specified" seems like the verb tenses don't
> even match up properly, or something of that nature, but I can't properly
> describe exactly what seems off.  The current proposal from the RFC Editor
> is to dramatically replace this sentence with the bland "The capabilities of
> an algorithm or key type need to be specified in some situations".  Does
> anyone object to that change?

==>MT
On -algs, I agree with the proposed simplification for the first 
sentence, and I have now also had a deeper look into the following 
sentence, i.e.:

"One example of this is in [I-D.ietf-core-oscore-groupcomm] where the 
capabilities of the counter signature algorithm are mixed into the 
traffic key derivation process."

Note that the COSE -algs document is referring to version -09 of 
-core-oscore-groupcomm. That version was indeed still using COSE 
capabilities, but not as part of a key derivation process. Rather, they 
were used to build the OSCORE external_aad to bind requests and 
responses, see [1].

After a few revisions, we removed the explicit use of COSE capabilities 
altogether from -core-oscore-groupcomm. In fact, it was agreed to rather 
have the external_aad including full-fledged authentication credentials, 
i.e., the public key together with metadata related to the signature 
algorithm. This is the case in the latest version -13, see [2].

Practically, it is probably better to remove the following two sentences 
from the COSE -algs document:

* In Section 8, the second sentence of the first paragraph, also quoted 
above, i.e., "One example of this ... key derivation process."

* In Section 8.3, the second sentence of the first paragraph, i.e., 
"This is the approach that is being used by the group communication KDF 
in [I-D.ietf-core-oscore-groupcomm]."


For what is worth, the COSE capabilities are used with a descriptive 
purpose in the ACE documents [3] and [4] about key provisioning for 
group communication. That is, the Key Distribution Center responsible 
for a group can leverage COSE capabilities to provide a description of 
how the group works, in terms of signature algorithm parameters and 
signature key parameters. I am not suggesting to add these examples to 
the COSE -algs document :-)


Best,
/Marco


[1] 
https://datatracker.ietf.org/doc/html/draft-ietf-core-oscore-groupcomm-09#section-4.3.1

[2] 
https://datatracker.ietf.org/doc/html/draft-ietf-core-oscore-groupcomm-13#section-4.3

[3] https://datatracker.ietf.org/doc/html/draft-ietf-ace-key-groupcomm

[4] 
https://datatracker.ietf.org/doc/html/draft-ietf-ace-key-groupcomm-oscore
<==

> Thanks,
>
> Ben
>
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-- 
Marco Tiloca
Ph.D., Senior Researcher

Division: Digital System
Department: Computer Science
Unit: Cybersecurity

RISE Research Institutes of Sweden
https://www.ri.se

Phone: [phone]
Isafjordsgatan 22 / Kistagången 16
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