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Versions: (draft-thaler-rats-architecture) 00
01
RATS Working Group H. Birkholz
Internet-Draft Fraunhofer SIT
Intended status: Informational D. Thaler
Expires: 19 June 2020 Microsoft
M. Richardson
Sandelman Software Works
N. Smith
Intel
17 December 2019
Remote Attestation Procedures Architecture
draft-ietf-rats-architecture-00
Abstract
In network protocol exchanges, it is often the case that one entity
(a relying party) requires evidence about a remote peer to assess the
peer's trustworthiness, and a way to appraise such evidence. The
evidence is typically a set of claims about its software and hardware
platform. This document describes an architecture for such remote
attestation procedures (RATS).
Note to Readers
Discussion of this document takes place on the RATS Working Group
mailing list (rats@ietf.org), which is archived at
https://mailarchive.ietf.org/arch/browse/rats/
(https://mailarchive.ietf.org/arch/browse/rats/).
Source for this draft and an issue tracker can be found at
https://github.com/ietf-rats-wg/architecture (https://github.com/
ietf-rats-wg/architecture).
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
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This Internet-Draft will expire on 19 June 2020.
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Simplified BSD License text
as described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Reference Use Cases . . . . . . . . . . . . . . . . . . . . . 4
4. Architectural Overview . . . . . . . . . . . . . . . . . . . 4
5. Topological Models . . . . . . . . . . . . . . . . . . . . . 5
6. Two Types of Environments . . . . . . . . . . . . . . . . . . 5
7. Trust Model . . . . . . . . . . . . . . . . . . . . . . . . . 5
8. Conceptual Messages . . . . . . . . . . . . . . . . . . . . . 6
9. Freshness . . . . . . . . . . . . . . . . . . . . . . . . . . 6
10. Privacy Considerations . . . . . . . . . . . . . . . . . . . 7
11. Security Considerations . . . . . . . . . . . . . . . . . . . 7
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7
14. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
2. Terminology
The document defines the term "Remote Attestation" as follows: A
process by which one entity (the "Attester") provides evidence about
its identity and state to another remote entity (the "Relying
Party"), which then assesses the Attester's trustworthiness for the
Relying Party's own purposes.
This document then uses the following terms:
* Appraisal Policy for Evidence: A set of rules that direct how a
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verifier evaluates the validity of information about an Attester.
Compare /security policy/ in [RFC4949].
* Appraisal Policy for Attestation Result: A set of rules that
direct how a Relying Party evaluates the validity of information
about an Attester. Compare /security policy/ in [RFC4949].
* Attestation Result: The evaluation results generated by a
Verifier, typically including information about an Attester, where
the Verifier vouches for the validity of the results.
* Attester: An entity whose attributes must be evaluated in order to
determine whether the entity is considered trustworthy, such as
when deciding whether the entity is authorized to perform some
operation.
* Endorsement: A secure statement that some entity (typically a
manufacturer) vouches for the integrity of an Attester's signing
capability.
* Endorser: An entity that creates Endorsements that can be used to
help evaluate trustworthiness of Attesters.
* Evidence: A set of information about an Attester that is to be
evaluated by a Verifier.
* Relying Party: An entity that depends on the validity of
information about another entity, typically for purposes of
authorization. Compare /relying party/ in [RFC4949].
* Relying Party Owner: An entity, such as an administrator, that is
authorized to configure Appraisal Policy for Attestation Results
in a Relying Party.
* Verifier: An entity that evaluates the validity of Evidence about
an Attester.
* Verifier Owner: An entity, such as an administrator, that is
authorized to configure Appraisal Policy for Evidence in a
Verifier.
[EDITORIAL NOTE]
The term Attestation and Remote Attestation are not defined in this
document, at this time. This document will include pointers to
industry uses of the terms, in an attempt to gain consensus around
the term, and be consistent with the charter text defining this term.
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3. Reference Use Cases
<unclear if the WG wants this section in the arch doc>
4. Architectural Overview
Figure 1 depicts the data that flows between different roles,
independent of protocol or use case.
************ ************ *****************
* Endorser * * Verifier * * Relying Party *
************ * Owner * * Owner *
| ************ *****************
| | |
Endorsements| | |
| |Appraisal |
| |Policy for |
| |Evidence | Appraisal
| | | Policy for
| | | Attestation
| | | Result
v v |
.-----------------. |
.----->| Verifier |------. |
| '-----------------' | |
| | |
| Attestation| |
| Results | |
| Evidence | |
| | |
| v v
.----------. .-----------------.
| Attester | | Relying Party |
'----------' '-----------------'
Figure 1: Conceptual Data Flow
An Attester creates Evidence that is conveyed to a Verifier.
The Verifier uses the Evidence, and any Endorsements from Endorsers,
by applying an Evidence Appraisal Policy to assess the
trustworthiness of the Attester, and generates Attestation Results
for use by Relying Parties. The Evidence Appraisal Policy might be
obtained from an Endorser along with the Endorsements, or might be
obtained via some other mechanism such as being configured in the
Verifier by an administrator.
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The Relying Party uses Attestation Results by applying its own
Appraisal Policy to make application-specific decisions such as
authorization decisions. The Attestation Result Appraisal Policy
might, for example, be configured in the Relying Party by an
administrator.
5. Topological Models
<this section can include Message Flows from draft-birkholz-rats-architecture and
Architectural Models from draft-thaler-rats-architecture>
6. Two Types of Environments
An Attester consists of at least one Attesting Environment and
Attested Environment. In some implementations, the Attesting and
Attested Environments might be combined. Other implementations might
have multiple Attesting and Attested Environments.
<this section can include Two Types of Environments content from draft-birkholz-rats-architecture
but can we find a better name? also this could be a subsection of something else?>
7. Trust Model
The scope of this document is scenarios for which a Relying Party
trusts a Verifier that can evaluate the trustworthiness of
information about an Attester. Such trust might come by the Relying
Party trusting the Verifier (or its public key) directly, or might
come by trusting an entity (e.g., a Certificate Authority) that is in
the Verifier's certificate chain. The Relying Party might implicitly
trust a Verifier (such as in the Verifying Relying Party
combination). Or, for a stronger level of security, the Relying
Party might require that the Verifier itself provide information
about itself that the Relying Party can use to evaluate the
trustworthiness of the Verifier before accepting its Attestation
Results.
In solutions following the background-check model, the Attester is
assumed to trust the Verifier (again, whether directly or indirectly
via a Certificate Authority that it trusts), since the Attester
relies on an Attestation Result it obtains from the Verifier, in
order to access resources.
The Verifier trusts (or more specifically, the Verifier's security
policy is written in a way that configures the Verifier to trust) a
manufacturer, or the manufacturer's hardware, so as to be able to
evaluate the trustworthiness of that manufacturer's devices. In
solutions with weaker security, a Verifier might be configured to
implicitly trust firmware or even software (e.g., a hypervisor).
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That is, it might evaluate the trustworthiness of an application
component, or operating system component or service, under the
assumption that information provided about it by the lower-layer
hypervisor or firmware is true. A stronger level of security comes
when information can be vouched for by hardware or by ROM code,
especially if such hardware is physically resistant to hardware
tampering. The component that is implicitly trusted is often
referred to as a Root of Trust.
8. Conceptual Messages
<this section can include content from Serialization Formats and Conceptual Messages sections from
draft-thaler-rats-architecture, and Role Messages content from draft-birkholz-rats-architecture>
Evidence Attestation Results
.--------------. CWT CWT .-------------------.
| Attester-A |------------. .----------->| Relying Party V |
'--------------' v | `-------------------'
.--------------. JWT .------------. JWT .-------------------.
| Attester-B |-------->| Verifier |-------->| Relying Party W |
'--------------' | | `-------------------'
.--------------. X.509 | | X.509 .-------------------.
| Attester-C |-------->| |-------->| Relying Party X |
'--------------' | | `-------------------'
.--------------. TPM | | TPM .-------------------.
| Attester-D |-------->| |-------->| Relying Party Y |
'--------------' '------------' `-------------------'
.--------------. other ^ | other .-------------------.
| Attester-E |------------' '----------->| Relying Party Z |
'--------------' `-------------------'
Figure 2: Multiple Attesters and Relying Parties with Different
Formats
9. Freshness
<this section can include some high-level content from draft-birkholz-rats-reference-interaction-model>
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10. Privacy Considerations
The conveyance of Evidence and the resulting Attestation Results
reveal a great deal of information about the internal state of a
device. In many cases, the whole point of the Attestation process is
to provide reliable information about the type of the device and the
firmware/software that the device is running. This information is
particularly interesting to many attackers. For example, knowing
that a device is running a weak version of firmware provides a way to
aim attacks better.
Protocols that convey Evidence or Attestation Results are responsible
for detailing what kinds of information are disclosed, and to whom
they are exposed.
11. Security Considerations
<this section can include Security Considerations from draft-birkholz-rats-architecture
and draft-thaler-rats-architecture>
12. IANA Considerations
This document does not require any actions by IANA.
13. Acknowledgments
Special thanks go to David Wooten, Joerg Borchert, Hannes Tschofenig,
Laurence Lundblade, Diego Lopez, Jessica Fitzgerald-McKay, Frank Xia,
and Nancy Cam-Winget.
14. Contributors
Thomas Hardjono created older versions of the terminology section in
collaboration with Ned Smith. Eric Voit provided the conceptual
separation between Attestation Provision Flows and Attestation
Evidence Flows. Monty Wisemen created the content structure of the
first three architecture drafts. Carsten Bormann provided many of
the motivational building blocks with respect to the Internet Threat
Model.
Authors' Addresses
Henk Birkholz
Fraunhofer SIT
Rheinstrasse 75
64295 Darmstadt
Germany
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Email: henk.birkholz@sit.fraunhofer.de
Dave Thaler
Microsoft
United States of America
Email: dthaler@microsoft.com
Michael Richardson
Sandelman Software Works
Canada
Email: mcr+ietf@sandelman.ca
Ned Smith
Intel Corporation
United States of America
Email: ned.smith@intel.com
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