Re: [COSE] Newly Submitted Draft - CBOR Web Token (CWT) Claims in COSE Headers

[Tobias Looker <[e-mail]>]

Hi Hannes,

I can elaborate.

Encrypted CWTs - In some circumstances CWT claims can be useful to have available for processing prior to decryption. For example the iss claim can be used to indicate to a recipient of an encrypted CWT how it should be decrypted, by informing the recipient who encrypted (and potentially signed) it.

Detached Signature - In cases where a detached signature COSE structure is being used the payload can be un-available (or of invalid form) to express CWT claims. A concrete example is being able to express who signed the detached signature structure (using the iss claim) and when it expires (using the exp claim).


Thanks,

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Tobias Looker

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________________________________
From: Hannes Tschofenig <[e-mail]>
Sent: 12 March 2022 01:45
To: Mike Jones <[e-mail]>om>; Anders Rundgren <[e-mail]>om>; Laurence Lundblade <[e-mail]>
Cc: Tobias Looker <[e-mail]>al>; [e-mail] <[e-mail]>
Subject: RE: [COSE] Newly Submitted Draft - CBOR Web Token (CWT) Claims in COSE Headers

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Hi Mike,



maybe you can give examples of where this feature is used in JWTs, which would explain why you want to have it in CWTs as well.



Ciao

Hannes



From: Mike Jones <[e-mail]>
Sent: Thursday, March 3, 2022 6:02 PM
To: Hannes Tschofenig <[e-mail]>om>; Anders Rundgren <[e-mail]>om>; Laurence Lundblade <[e-mail]>
Cc: Tobias Looker <[e-mail]>al>; [e-mail]
Subject: RE: [COSE] Newly Submitted Draft - CBOR Web Token (CWT) Claims in COSE Headers



We are *definitely* not attempting to change anything about COSE message processing, including how encryption is done.  We are defining an additional header parameter that can be used – that’s it.



                                                       -- Mike



From: Hannes Tschofenig <[e-mail]<mailto:[e-mail]>>
Sent: Thursday, March 3, 2022 1:45 AM
To: Anders Rundgren <[e-mail]<mailto:[e-mail]>>; Laurence Lundblade <[e-mail]<mailto:[e-mail]>>; Mike Jones <[e-mail]<mailto:[e-mail]>>
Cc: Tobias Looker <[e-mail]<mailto:[e-mail]>>; [e-mail]<mailto:[e-mail]>
Subject: RE: [COSE] Newly Submitted Draft - CBOR Web Token (CWT) Claims in COSE Headers



Hi Anders,



Thanks for jumping in.



The example you provide below is actually quite interesting and related to a question I posted to the list a few days ago (see https://mailarchive.ietf.org/arch/msg/cose/9nowDz5kbfUvrGR-o6U1Tm31XAA/).



I am not sure whether the intention of Tobias & Mike are actually to re-define the way how encryption is accomplished. They should confirm.



Ciao

Hannes



From: Anders Rundgren <[e-mail]<mailto:[e-mail]>>
Sent: Thursday, March 3, 2022 8:39 AM
To: Laurence Lundblade <[e-mail]<mailto:[e-mail]>>; Mike Jones <Michael.Jones=[e-mail]<mailto:Michael.Jones=[e-mail]>>
Cc: Hannes Tschofenig <[e-mail]<mailto:[e-mail]>>; Tobias Looker <tobias.looker=[e-mail]<mailto:tobias.looker=[e-mail]>>; [e-mail]<mailto:[e-mail]>
Subject: Re: [COSE] Newly Submitted Draft - CBOR Web Token (CWT) Claims in COSE Headers



On 2022-03-02 19:33, Laurence Lundblade wrote:

Makes sense to me. Helps out for the EAT claim named “profile” which gives information about the type of the token you might want before fully verifying it. Addresses an issue Anders brought up about the profile claim.

Not so fast  :)  I brought up a bunch of things which can be illustrated by this (just implemented...) example of an encryption object:

211(["https://example.com/myobject"<https://example.com/myobject>com/myobject>, {
  / COSE content encryption algorithm = A256GCM /
  1: 3,
  / Key encryption container /
  2: {
    / COSE Key encryption algorithm = ECDH-ES+A256KW /
    1: -31,
    / Key identifier /
    3: "mykey",
    / Ephemeral key /
    5: {
      / COSE Key type = OKP /
      1: 1,
      / COSE Curve = X25519 /
      -1: 4,
      / COSE X coordinate /
      -2: h'33a04b83d4428824b6d5477522d4a88fac4441122bc46136c0203faa308c3929'
    },
    / Encrypted key /
    10: h'e08977c25aeccaecd63b3367de2e2b8f700c82e098ad1e5099d9db510920ccff14debf820427e4ba'
  },
  / Tag /
  8: h'59a84826983e3247fbec4295f75cc138',
  / IV /
  9: h'fd8556c122cff2bc128d5119',
  / Encrypted data /
  10: h'e16b16c29da5163eb0131dd1f10f080f8850f55df2ae9d89a3b839ad50952858445f290dfb60'
}])

The core of this builds on Deterministic CBOR which unleashes the true power of CBOR in a way legacy solutions do not.   The enhancements include:

  *   Eliminating wrapping of header and (unencrypted) application data.
  *   Using the entire container (modulo the algorithm output variables which are added lastly) as input to a signature process and to the authentication part of an encryption process.  In the example that includes the top-level CBOR tag as well.  cryptoOperation(cborObject.encode()) is all that it takes on the encoder's side.

This is pretty much what the X.509 folks have been doing from the very start so there is close to zero innovation here ??

In the example I have also used a URL as profile/object type indicator since IANA CBOR custom tag 1537244 or whatever you end-up with, simply isn't pretty enough :)  To be more serious: URLs are decentralized and would in this context probably be browseable as well.

Cheers,
Anders

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