Re: [Rats] New RATS Architecture document

[Simon Frost <[e-mail]>]

At a first pass through this, I'm concerned that the interaction model (Fig 1 etc) has been restricted to a single pattern, the 'passport' model to use the terminology from the TEEP/RATS  slides. I don't recall this restriction being discussed. Also allowing the 'background check' model allows the relying party to have much greater flexibility on selecting an appropriate verifier. While the origins of Attester and Known Good Values are going to have close alignment, multiple verifiers may exist. A relying party may choose an alternative verifier based upon the approach to appraisal, to the form that the attestation results are presented or due to business model.

Thanks
Simon

-----Original Message-----
From: Henk Birkholz <[e-mail]>
Sent: 10 September 2019 14:13
To: [e-mail]
Subject: [Rats] New RATS Architecture document

Hi all,

we created a fully revised architecture document that maps and represents the state of the current discussion and the material presented at the last IETF meeting.

The current Editor's version can be found here:

> https://ietf-rats.github.io/draft-birkholz-rats-architecture/draft-bir
> kholz-rats-architecture.html

We will submit a new version the day after the RATS virtual interim.

TL;DR
Below you can find a list of essential changes & a list of action items still to be addressed.


This version of the RATS Architecture document:

* does not define or uses the terms "root(s) of trust" (RoT) or "Trust
Anchor" (TA) at the moment. (Note: It is a fact that the Asserter Role
_is_ a TA for the Verifier Role and that an Attester Role _could_ rely
on RoTs. But - this content will not go into the main body of this
document),

* does define RATS Roles, Messages, and Principals formerly known as
"Actors" (borrowing heavily from ABLP),

* provides an even more "base" interaction model diagram for the RATS
Roles than presented in the last IETF meeting slide deck:

> https://datatracker.ietf.org/meeting/105/materials/slides-105-rats-sessb-rats-architecture-interaction-model-challange-response-yang-module-information-module-00.pdf

* introduces a framework for "level of confidence" in the
trustworthiness of an Attester and the endorsement of the protection
characteristics of its "Attesting Computing Context", allowing for other
entities to use this framework and fill it with, e.g., openly defined
levels of confidence metrics,

* is not based on the primitive of "trust" but the concept of
"trustworthiness" as illustrated by the RATS charter,

* simplifies the definitions of Attester and Verifier that seemed to
have caused some unfortunate confusion following the proposal of Giri
and starting with commonly-accepted definitions and then justify why
they may need to be modified,

* differentiates between the Attesting Computing Environment and the
Attested Computing Environment better, which both are components of an
Attester,

* uses the "Claim" concept as a building block to compose Evidence,
Known-Good-Values and Endorsements. Conversely, the "Assertion" concept
is dropped in this proposal (as initially suggested by Laurence, IIRC?).
(Note: this was done to simplify the discussion about the information
model. Please also note: Due to the {J|C}WT definition of "Claim", a
key/value pair is implied, which is already a data model decision and
not mandated by an information model), and

* analogously, now uses the term Known-Good-Values instead of
Attestation Assertions.


For future versions the authors intent:

* to elaborate on the use of RATS Principals, including more exemplary
diagrams of RATS Role composition and interaction between RATS
Principals based on the use case document (and by that address a unified
mapping to TEEP, RIV, and models that use EAT),

* to shift some of the focus on technical-trust as proposed by Thomas.
(the Endorsements provided by an Asserter are a first step into that
direction),

* still not to define the roots of trust terms nor invent new words for
them :) But - start to reference them on a minimal level and define a
base set of primitives they can provide in order to describe what they
actually are and can do in the context of RATS as proposed by Ira, Simon
and Thomas,

* to introduce and define a concise scope for layered attestation,
addressing, e.g., the staging of Computing Environments and the
(un-)availability of an Attesting Computing Environment at certain
points of time, or, another example given, addressing the
differentiation of an attested boot sequence of an Attester and an
Attester running TEEs or rich systems for years,

* to address the change of Roles of a Principal over time as proposed by
Ian,

* to move the remaining architectural sections in the EAT draft into the
RATS Architecture draft, and

* to shift some of the focus on the out-of-band trust establishment in
order to illustrate a coherent RATS ecosystem (e.g. the provisioning of
key material is not include in the "base diagram" anymore for now - this
will be more elaborated on in future section of the architecture).


Viele Grüße,

Henk







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