Re: [Ace] Eric Rescorla's No Objection on draft-ietf-ace-cbor-web-token-13: (with COMMENT)

Mike Jones <> Wed, 14 March 2018 21:56 UTC

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From: Mike Jones <>
To: Eric Rescorla <>
CC: The IESG <>, "" <>, "" <>, "" <>, "" <>, "" <>
Thread-Topic: Eric Rescorla's No Objection on draft-ietf-ace-cbor-web-token-13: (with COMMENT)
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Subject: Re: [Ace] Eric Rescorla's No Objection on draft-ietf-ace-cbor-web-token-13: (with COMMENT)
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Thanks, Ekr.  One more reply to your last comment the bottom of the message…

From: Eric Rescorla <>
Sent: Wednesday, March 14, 2018 2:38 PM
To: Mike Jones <>
Cc: The IESG <>;;;;;
Subject: Re: Eric Rescorla's No Objection on draft-ietf-ace-cbor-web-token-13: (with COMMENT)

On Wed, Mar 14, 2018 at 2:34 PM, Mike Jones <<>> wrote:
Hi Ekr.  Thanks for the review comments.  Responses are inline below, prefixed by "Mike>"...

-----Original Message-----
From: Eric Rescorla <<>>
Sent: Wednesday, March 7, 2018 12:40 PM
To: The IESG <<>>
Subject: Eric Rescorla's No Objection on draft-ietf-ace-cbor-web-token-13: (with COMMENT)

Eric Rescorla has entered the following ballot position for
draft-ietf-ace-cbor-web-token-13: No Objection

When responding, please keep the subject line intact and reply to all email addresses included in the To and CC lines. (Feel free to cut this introductory paragraph, however.)

Please refer to
for more information about IESG DISCUSS and COMMENT positions.

The document, along with other ballot positions, can be found here:


   The claim values defined in this specification MUST NOT be prefixed
   with any CBOR tag.  For instance, while CBOR tag 1 (epoch-based date/
   time) could logically be prefixed to values of the "exp", "nbf", and
   "iat" claims, this is unnecessary, since the representation of the
   claim values is already specified by the claim definitions.  Tagging
   claim values would only take up extra space without adding
   information.  However, this does not prohibit future claim
   definitions from requiring the use of CBOR tags for those specific

Why do you need a MUST NOT here? This seems like not really an interop requirement
Mike> This requirement was added to simplify both producers and consumers of these tokens, after a working group discussion.  Not having to have code to validate, parse and then throw away tags prefixing claims of known types both makes representations smaller and requires less code.  Since the tags add no value for these claims, it seemed better to require that they be omitted.

Thanks. Seems reasonable.

  4.  Verify that the resulting COSE Header includes only parameters
       and values whose syntax and semantics are both understood and
       supported or that are specified as being ignored when not

I'm surprised to find that this is not a generic 8152 processing rule.
Can you explain why this is necessary here?

Mike> This intentionally parallels the same rule in JWT (, step 5).  It's saying that you have to validate that the parameters describing the parameters describing the cryptographic operations performed.

Sure. I don't think this is unreasonable, but why isn't a general rule for COSE messages rather than just CWT?

Mike> I’m sure that COSE has similar/overlapping requirements (that, or I didn’t adequately review it at the time before it became an RFC ;-) ).  As the Brits, say, this rule is “belt and suspenders” on top of that – and also reflects that CWT copies the syntax and semantics from JWT [RFC 7519] wherever applicable.

See you next week.

                                                       -- Mike


                                -- Mike