Subject: [Rats] Thinking about Attestation Results

From: Laurence Lundblade <[email-masked]>
Date: Mon, 28 Feb 2022 14:42:48 -0800

This is an attempt to step back and think about Attestation Results (AR) in a broad and general way.

TLDR: RATS ought to focus on the semantics of the stuff in AR, not the encoding or securing of it.

LL

AR Security
When the Verifier is not combined into the RP, then there is network transfer of AR to the RP and it must be secured. 

AR mostly seems like a B2B backend transfer. Pretty sure TLS is they way to do this. There are enormous amounts of stuff transferred B2B like this these days. IT people know how to secure it so we probably don’t have to specify it or discuss it much.

It’s OK to have other ways to secure AR other than TLS, but I don’t think we need to worry too much about them. 

It’s fine that we say how to use EAT, CWT, JWT, X.509 and such to secure AR in RATS, but it’s not critical.

AR Encoding

When the Verifier is not combined with the RP, then there is network transfer of the AR to the RP that must be encoded.

CBOR, JSON, XML, ASN.1, … All seem possible and not something we have to lock down. 

JSON is at the top of my list because that seems the very common practice for B2B, but we have to expect lots of people will define lots of Web APIs I lots of ways for this. We can also say how to do it with JWT and CWT and such. 

I think it’s good that ar4si isn’t picking any specific encoding or security mechanism.

I think name-value pair claims are a good way to structure most AR.

AR Contents
This is the output from SW measurements verification, device identity, claims passed through from the Evidence, the general Verification results and such.

This is what really matters in RATS! They exist whether or not the RP is combined with the Verifier. This is THE output from RATS. 

These seem candidate for standardization in AR:
- the overall result of a Verifier, perhaps detailed, perhaps simple summary
- SW measurements results
- device identity
- representing claims passed through (location, cryptographic keys…)
- certifications received

Below is a picture from from the RATS architecture document. At this point it seems kind of a mis characterization because it doesn’t mention JSON over TLS and/or Web APIs for AR.

LL