Re: [Suit] [sacm] [Rats] CoSWID and EAT and CWT

Henk Birkholz <henk.birkholz@sit.fraunhofer.de> Tue, 03 December 2019 13:09 UTC

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To: Michael Richardson <mcr+ietf@sandelman.ca>, "rats@ietf.org" <rats@ietf.org>, "suit@ietf.org" <suit@ietf.org>, sacm <sacm@ietf.org>
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From: Henk Birkholz <henk.birkholz@sit.fraunhofer.de>
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Subject: Re: [Suit] [sacm] [Rats] CoSWID and EAT and CWT
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As the I-D is trying to stay close to the ISO/IEC spec & as COSE is an 
"envelope" encapsulating a CoSWID tag, the guidance on signing is 
actually a bit detached to the structure of a CoSWID.

Having said that. CoSWID can be measurements of installed SW components 
on an Attester and be part of Attestation Evidence. For this, they do 
not have to be signed - this depends on the level of assurance the 
Attest-ING Environment of the Attester can provide (e.g. via 
Endorsements from Endorsers, formerly known as Asserters).

On 03.12.19 14:04, Michael Richardson wrote:
> 
> Smith, Ned <ned.smith@intel.com> wrote:
>      > The architecture slides presented at Singapore showed Attester-Verifier
>      > interactions supporting multiple signed formats. Therefore, it could be
>      > reasonable to consider [Co]SWID as yet another payload format the Verifier
>      > needs to handle.
> 
> That's an interesting take on things.
> My reading of CoSWID is that COSE signatures are almost an afterthought
> (appendix A), and in any case, would be produced by manufacturers rather than
> as evidence.
> 
> It seems that inclusion of an unsigned CoSWID into a SUIT Manifest is
> appropriate as the manufacturer is authoritative for both.
> 
>      > Another consideration might question whether it makes sense for [Co]SWID to
>      > be regarded as Evidence. Maybe it should be restricted to Endorsements?
> 
> I think that it makes more sense as Endorsement only, as such it falls
> outside of the normative part of the RATS architecture.
> 
>      > The important distinction from the perspective of the RATS architecture is
>      > that Endorsements (signed by a mfg – aka “Endorser”) are still Endorsements
>      > even if they are stored on the Attester and conveyed to a Verifier over a
>      > conveyance protocol that supports conveyance of Evidence. Evidence and
>      > Endorsements are signed by different keys. How they are conveyed isn’t
>      > interesting to the Verifier per se. except where freshness is a
>      > consideration.
> 
> If the manufacturer-signed Endorsement is communicated within EAT, then it's
> not a seperate token format. It's just payload for a Evidence carrying EAT.
> 
> --
> Michael Richardson <mcr+IETF@sandelman.ca>ca>, Sandelman Software Works
>   -= IPv6 IoT consulting =-
> 
> 
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