Trustworthiness Vectors for the Software Updates of Internet of Things (SUIT) Workflow Model
draft-birkholz-rats-suit-claims-03
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Henk Birkholz
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Brendan Moran
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RATS H. Birkholz
Internet-Draft Fraunhofer SIT
Intended status: Standards Track B. Moran
Expires: 16 July 2022 Arm Limited
12 January 2022
Trustworthiness Vectors for the Software Updates of Internet of Things
(SUIT) Workflow Model
draft-birkholz-rats-suit-claims-03
Abstract
The IETF Remote Attestation Procedures (RATS) architecture defines
Conceptual Messages as input and output of the appraisal process that
assesses the trustworthiness of remote peers: Evidence and
Attestation Results. Based on the Trustworthiness Vectors defined in
Trusted Path Routing, this document defines a core set of Claims to
be used in Evidence and Attestation Results for the Software Update
for the Internet of Things (SUIT) Workflow Model. Consecutively,
this document is in support of the Trusted Execution Environment
Provisioning (TEEP) architecture, which defines the assessment of
remote peers via RATS and uses SUIT for evidence generation as well
as a remediation measure to improve trustworthiness of given remote
peers.
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."
This Internet-Draft will expire on 16 July 2022.
Copyright Notice
Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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 Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. SUIT Workflow Model and Procedures . . . . . . . . . . . 3
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Trustworthiness Vectors . . . . . . . . . . . . . . . . . . . 4
3. SUIT Claims . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. System Properties Claims . . . . . . . . . . . . . . . . 5
3.1.1. vendor-identifier . . . . . . . . . . . . . . . . . . 6
3.1.2. class-identifier . . . . . . . . . . . . . . . . . . 6
3.1.3. device-identifier . . . . . . . . . . . . . . . . . . 6
3.1.4. image-digest . . . . . . . . . . . . . . . . . . . . 6
3.1.5. image-size . . . . . . . . . . . . . . . . . . . . . 6
3.1.6. version . . . . . . . . . . . . . . . . . . . . . . . 6
3.2. Interpreter Record Claims . . . . . . . . . . . . . . . . 7
3.2.1. record-success . . . . . . . . . . . . . . . . . . . 7
3.2.2. component-index . . . . . . . . . . . . . . . . . . . 7
3.2.3. dependency-index . . . . . . . . . . . . . . . . . . 7
3.2.4. command-index . . . . . . . . . . . . . . . . . . . . 7
3.2.5. nominal-parameters . . . . . . . . . . . . . . . . . 7
3.3. Generic Record Conditions (TBD) . . . . . . . . . . . . . 7
4. List of Commands (TBD) . . . . . . . . . . . . . . . . . . . 8
5. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
5.1. Normative References . . . . . . . . . . . . . . . . . . 9
5.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
Attestation Results are an essential output of Verifiers as defined
in the Remote ATtestation procedureS (RATS) architecture
[I-D.ietf-rats-architecture]. They are consumed by Relying Parties:
the entities that intend to build future decisions on trustworthiness
assessments of remote peers. Attestation Results must be easily
appraised by Relying Parties -- in contrast to the rather complex or
domain-specific Evidence appraised by Verifiers.
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In order to create Attestation Results, a Verifier must consume
Evidence generated by a given Attester (amongst other Conceptual
Messages, such as Endorsements and Attestation Policies). Both
Evidence and Attestation Results are composed of Claims. This
document highlights and defines a set of Claims to be used in
Evidence and Attestation Results that are based on the SUIT Workflow
Model [I-D.ietf-suit-manifest]. In the scope of this document, an
Attester takes on the role of a SUIT Recipient: the system that
receives a SUIT Manifest.
1.1. SUIT Workflow Model and Procedures
This document focuses on Evidence and Attestation Results that can be
generated based on the output of SUIT Procedures. The SUIT Workflow
Model allows for two types of SUIT Procedures generating Reports on
the Attester as defined in the SUIT Manifest specification
[I-D.ietf-suit-manifest]:
Update Procedures: A procedure that updates a device by fetching
dependencies, software images, and installing them.
An Update Procedure creates a Report about mutable software
components that are installed or updated on hardware components.
Boot Procedures: A procedure that boots a device by checking
dependencies and images, loading images, and invoking one or more
image.
A Boot Procedure creates a Report on measured boot events (e.g.
during Secure Boot).
The Records contained in each type of Report can be used as Claims in
Evidence generation on the Attester for Remote Attestation Procedures
as described in this document. Analogously, a corresponding Verifier
appraising that Evidence can generate Attestation Results using the
Claims defined in this document.
Both types of SUIT Procedures pass several stages (e.g. dependency-
checking is one stage). The type and sequence of stages are defined
by the Command Sequences included in a SUIT Manifest. For each stage
in which a Command from the Command Sequence is executed a Record is
created. All Records of a SUIT procedure contain binary results
limited to "fail" or "pass". The aggregated sequence of all Records
is composed into a Report.
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This document specifies new Claims derived from Command Sequence
Reports and relates them to Claims defined in Attestation Results for
Secure Interactions [I-D.ietf-rats-ar4si] -- if applicable to the
operational state of installed and updated software.
The Claims defined in this document are in support of the Trusted
Execution Environment Provisioning (TEEP) architecture. During TEEP,
the current operational state of an Attester is assessed via RATS.
If the corresponding Attestation Results -- as covered in this
document -- indicate insufficient Trustworthiness Tiers in a
Trustworthiness Vector with respect to installed software, the SUIT
Workflow Model is used for remediation.
1.2. Terminology
This document uses the terms and concepts defined in
[I-D.ietf-rats-architecture], [I-D.ietf-suit-manifest], and
[I-D.ietf-teep-architecture].
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. Trustworthiness Vectors
While there are usage scenarios where Attestation Results can be
binary decisions, more often than not the assessment of
trustworthiness is represented by a more fine-grained spectrum or
based on multiple factors. These shades of Attestation Results are
captured by the definition of Trustworthiness Vectors in Attestation
Results for Secure Interaction [I-D.ietf-rats-ar4si].
Trustworthiness Vectors are sets of Trustworthiness Claims
representing appraisal outputs produced by a Verifier (Attestation
Results). Each of these Trustworthiness Claims has a Trustworthiness
Tier ranging from Affirmed to None.
An Attester processing SUIT Manifests can manages three types of
information about it's Target Environments:
* installed manifests including initial state (e.g. factory
default),
* hardware component identifiers that represent identifiable targets
of updates, and
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* SUIT Interpreter results (e.g. test-failed) generated during
updates.
Every SUIT Manifest maps to a certain intended state of a device.
Every intended device composition of software components associated
with hardware components can therefore be expressed based on a SUIT
Manifest. The current operational state of a device can be
represented in the same form, including the initial state.
As a result, the Claims defined in this document are bundled by the
scope of the information represented in SUIT Manifests, i.e.,
dedicated blobs of software that are the payload of a SUIT Manifest.
All Claims associated with an identifiable SUIT Manifest MUST always
be bundled together in a Claims set that is limited to the Claims
defined in this document.
3. SUIT Claims
The Claim description in this document uses CDDL as the formal
modeling language for Claims. This approach is aligned with
[I-D.ietf-rats-eat]. All Claims are based on information elements as
used in the SUIT Manifest specification [I-D.ietf-suit-manifest].
For instance, a SUIT Class ID is represented as an UUID.
Analogously, the corresponding class-identifier Claim found below is
based on a UUID. SUIT Claims are differentiated in:
* software and hardware characteristics (System Properties), and
* reports about updates and their SUIT Commands (SUIT Records).
* success/failure reports
Each type of Claims is always bundled in a dedicated Claim Set.
Implementations can encode this information in various different ways
(data models), e.g., sets, sequences, or nested structures.
The SUIT Report is defined in [I-D.ietf-suit-report]. It is used
verbatim in this draft. The following subsections define the SUIT
Report Claims for RATS.
3.1. System Properties Claims
System Properties Claims are composed of:
* Hardware Component Claims and
* Software Component Claims.
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Correspondingly, the Claim definitions below highlight if a Claim is
generic or hw/sw-component specific.
3.1.1. vendor-identifier
A RFC 4122 UUID representing the vendor of the Attester or one of its
hardware and/or software components.
$$system-property-claim //= (vendor-identifier =>
(RFC4122_UUID / cbor-pen))
cbor-pen = #6.112(bstr)
3.1.2. class-identifier
A RFC 4122 UUID representing the class of the Attester or one of its
hardware and/or software components.
$$system-property-claim //= ( class-identifier => RFC4122_UUID )
3.1.3. device-identifier
A RFC 4122 UUID representing the Attester.
$$system-property-claim //= ( device-identifier => RFC4122_UUID )
3.1.4. image-digest
A fingerprint computed over a software component image on the
Attester. This Claim is always bundled with a component-identifier
or component-index.
$$system-property-claim //= ( image-digest => digest )
3.1.5. image-size
The size of a firmware image on the Attester.
$$system-property-claim //= ( image-size => size )
3.1.6. version
The Version of a hardware or software component of the Attester.
$$system-property-claim //= ( version => version-value )
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3.2. Interpreter Record Claims
This class of Claims represents the content of SUIT Records generated
by Interpreters running on Recipients. They are always bundled into
Claim Sets representing SUIT Reports and are intended to be included
in Evidence generated by an Attester. The Interpreter Record Claims
appraised by a Verifier can steer a corresponding a Firmware
Appraisal procedures that consumes this Evidence. Analogously, these
Claims can be re-used in generated Attestation Results as
Trustworthiness Vectors [I-D.ietf-rats-ar4si].
3.2.1. record-success
The result of a Command that was executed by the Interpreter on an
Attester.
$$interpreter-record-claim //= ( record-success => bool )
3.2.2. component-index
A positive integer representing an entry in a flat list of indices
mapped to software component identifiers to be updated.
$$system-property-claim //= ( component-index => uint )
3.2.3. dependency-index
A thumbprint of a software component that an update depends on.
$$interpreter-record-claim //= ( dependency-index => digest )
3.2.4. command-index
A positive integer representing an entry in a SUIT_Command_Sequence
identifying a Command encoded as a SUIT Manifest Directive or SUIT
Manifest Condition.
$$interpreter-record-claim //= ( command-index => uint )
3.2.5. nominal-parameters
A list of SUIT_Parameters associated with a specific Command that was
executed by the Interpreter on an Attester.
$$interpreter-record-claim //= ( actual-parameters => parameter-list )
3.3. Generic Record Conditions (TBD)
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* test-failed
* unsupported-command
* unsupported-parameter
* unsupported-component-id
* payload-unavailable
* dependency-unavailable
* critical-application-failure
* watchdog-timeout
4. List of Commands (TBD)
* Check Vendor Identifier
* Check Class Identifier
* Verify Image
* Set Component Index
* Override Parameters
* Set Dependency Index
* Set Parameters
* Process Dependency
* Run
* Fetch
* Use Before
* Check Component Offset
* Check Device Identifier
* Check Image Not Match
* Check Minimum Battery
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* Check Update Authorized
* Check Version
* Abort
* Try Each
* Copy
* Swap
* Wait For Event
* Run Sequence
* Run with Arguments
5. References
5.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
5.2. Informative References
[I-D.ietf-rats-ar4si]
Voit, E., Birkholz, H., Hardjono, T., Fossati, T., and V.
Scarlata, "Attestation Results for Secure Interactions",
Work in Progress, Internet-Draft, draft-ietf-rats-ar4si-
01, 2 December 2021, <https://www.ietf.org/archive/id/
draft-ietf-rats-ar4si-01.txt>.
[I-D.ietf-rats-architecture]
Birkholz, H., Thaler, D., Richardson, M., Smith, N., and
W. Pan, "Remote Attestation Procedures Architecture", Work
in Progress, Internet-Draft, draft-ietf-rats-architecture-
14, 9 December 2021, <https://www.ietf.org/archive/id/
draft-ietf-rats-architecture-14.txt>.
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[I-D.ietf-rats-eat]
Lundblade, L., Mandyam, G., and J. O'Donoghue, "The Entity
Attestation Token (EAT)", Work in Progress, Internet-
Draft, draft-ietf-rats-eat-11, 24 October 2021,
<https://www.ietf.org/archive/id/draft-ietf-rats-eat-
11.txt>.
[I-D.ietf-sacm-coswid]
Birkholz, H., Fitzgerald-McKay, J., Schmidt, C., and D.
Waltermire, "Concise Software Identification Tags", Work
in Progress, Internet-Draft, draft-ietf-sacm-coswid-19, 20
October 2021, <https://www.ietf.org/archive/id/draft-ietf-
sacm-coswid-19.txt>.
[I-D.ietf-suit-manifest]
Moran, B., Tschofenig, H., Birkholz, H., and K. Zandberg,
"A Concise Binary Object Representation (CBOR)-based
Serialization Format for the Software Updates for Internet
of Things (SUIT) Manifest", Work in Progress, Internet-
Draft, draft-ietf-suit-manifest-16, 25 October 2021,
<https://www.ietf.org/archive/id/draft-ietf-suit-manifest-
16.txt>.
[I-D.ietf-suit-report]
Moran, B., "Secure Reporting of Update Status", Work in
Progress, Internet-Draft, draft-ietf-suit-report-00, 12
July 2021, <https://www.ietf.org/archive/id/draft-ietf-
suit-report-00.txt>.
[I-D.ietf-teep-architecture]
Pei, M., Tschofenig, H., Thaler, D., and D. Wheeler,
"Trusted Execution Environment Provisioning (TEEP)
Architecture", Work in Progress, Internet-Draft, draft-
ietf-teep-architecture-15, 12 July 2021,
<https://www.ietf.org/archive/id/draft-ietf-teep-
architecture-15.txt>.
Authors' Addresses
Henk Birkholz
Fraunhofer SIT
Email: henk.birkholz@sit.fraunhofer.de
Brendan Moran
Arm Limited
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Email: Brendan.Moran@arm.com
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