Re: [Rats] Entity vs. role

[Thomas Fossati <[e-mail]>]

On Tue, Mar 22, 2022 at 6:42 PM Laurence Lundblade
<[e-mail]> wrote:
>
> Agree entirely with what’s below, but it doesn’t quite address what I am on about.
>
> RATS architecture clearly separates two polices:
>    1) Appraisal Policy for Evidence
>    2) Appraisal Policy for Results
>
> The first one is used only by the Verifier role and never by the Relying Party role. It can only be use to process Attestation Evidence, never to process Attestation Results. In a chain of Verifiers all the intermediate results are Attestation Evidence, never Attestation Results.
>
> When all the Verifiers are done, then you have Attestation Results.
>
> Similarly, the Appraisal Policy for Results is used only by the Relying Part role, never by the Verifier role. It can never be applied to Attestation Evidence.
>
> Since we are talking roles not entities, here, the Relying Party can *never* by definition receive Attestation Evidence. Again, since we’re talking *roles* not entities, a Relying Party can *never* host a Verifier.
>
> Said another way, the definition of the Verifier and Relying Party roles gives a hard one-way transition from Evidence to Results.
>
>
> I think the Verifier and the Appraisal Policy for Evidence is all about the device/implementation/attester.
>  - Who made the device?
>  - Is it configured correctly?
>  - Is it in the right state?
>  - Does it have the right SW?
>  - What certifications does it have?
>
> This is represented in the Attestation Results, perhaps in summary or in detail.
>
> Then the RP and the Appraisal Policy for Results is about the application-specific stuff:
>   - Is this device OK for this dollar amount (the RP knows the $ amount, not the Verifier)
>   - Can this content be played on this device — the RP knows which device and what characteristics it requires for the content
>   - Is the sensor data accurate — the RP knows which sensors it can trust

I think that the terminology choice made by the architecture is quite
precise: "AP for attestation results."

The appraisal logic you are describing above covers more ground than
just attestation results.  The way I picture myself the "complete"
appraisal process done by the RP looks more or less like:

          AP for AR
              |
       .------v-------.    .--------------------------------.
 AR -> | AR appraisal | -> | Application-specific appraisal | -> [0..1]
  :    '--------------'    '--^--------^---------^----------'
  :                           :        |         |
  '- - - - - - - - - - - - - -'        other     application-
                                       input     specific
                                                 policy

But otherwise, at least at a high level, I agree with the functional
split between evidence and ARs you are describing above.

There are grey areas though: for example, the RP may need to access
the software inventory in the evidence to decide whether the SW on the
attester needs updating.  And that is where your

> [...] as long as we’re open and flexible about what is in Attestation Results

(e.g., via passthrough) comes in the picture.

-- 
Thomas