Subject: [Rats] my previous comments of the draft:// New RATS Architecture document

From: "Xialiang (Frank, Network Standard & Patent Dept)" <[email-masked]>
Date: Wed, 16 Oct 2019 01:52:56 +0000

Hi authors,
Please consider my below comments one month ago, most part of them are not received your feedback until now.

Thanks!

B.R.
Frank

-----邮件原件-----
发件人: Xialiang (Frank, Network Standard & Patent Dept) 
发送时间: 2019年9月17日 18:16
收件人: 'Henk Birkholz' <[email-masked]>
抄送: [email-masked]
主题: 答复: [Rats] New RATS Architecture document

Hi Henk, other draft authors,
Thanks for the efforts for largely simplifying this new version, which looks much more clear and understandable.

I have reviewed the draft through and have some comments as below:
Section 1.1
1. should "message digest" be "MAC"?
2. nit. s/A corresponding attestation provisioning workflow uses trustworthiness Claims/ A corresponding attestation provisioning workflow uses Reference Claims/ 3. the Endorsements definition in Section 4.3.2 seems to be more correct than the one in this section, but still be a little abstract. Is my understanding right: an example of Endorsements is manufacturer's CA?
4. In general, the overlapping exists for the RATS messages' definition in this section and section 4.3.2. Please combine them into one.

Section 3
The last sentence emphasis on the "change". Can you clarify what kind of change it is? The change of the Evidence with time or the change between Evidence and KGV? The former seems to be too narrow, the latter is better.

Section 3.2
Although I can understand, but some contents in it are not straightforward, like: " recursive trustworthiness properties and the need for termination. " and others. I suggest to re-write them using other well-known text such as: trust chain, root of trust, etc.

Section 4.2
1. Freshness is only for replay attack? No any time freshness meaning?
2. for the principle of Identity, do you consider the privacy protection issue: run remote attestation without revealing the device's identity?
3. Some confusing terminologies: does Provenance equal to source authentication? does Veracity equal to integrity protection? Validity seems to be like Freshness, right?

Section 5
I don't get your point why the last four bytes of a challenge nonce are replaced by the IPv4 address-value of the Attester in its response. Can you clarify?

B.R.
Frank

-----邮件原件-----
发件人: RATS [mailto:[email-masked]] 代表 Henk Birkholz
发送时间: 2019年9月10日 21:13
收件人: [email-masked]
主题: [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-ses
> sb-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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