Internet DRAFT - draft-ietf-rats-eat
draft-ietf-rats-eat
RATS L. Lundblade
Internet-Draft Security Theory LLC
Intended status: Standards Track G. Mandyam
Expires: 18 July 2024
J. O'Donoghue
Qualcomm Technologies Inc.
C. Wallace
Red Hound Software, Inc.
15 January 2024
The Entity Attestation Token (EAT)
draft-ietf-rats-eat-25
Abstract
An Entity Attestation Token (EAT) provides an attested claims set
that describes state and characteristics of an entity, a device like
a smartphone, IoT device, network equipment or such. This claims set
is used by a relying party, server or service to determine the type
and degree of trust placed in the entity.
An EAT is either a CBOR Web Token (CWT) or JSON Web Token (JWT) with
attestation-oriented claims.
Status of This Memo
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This Internet-Draft will expire on 18 July 2024.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1. Entity Overview . . . . . . . . . . . . . . . . . . . . . 7
1.2. EAT as a Framework . . . . . . . . . . . . . . . . . . . 8
1.3. Operating Model and RATS Architecture . . . . . . . . . . 9
1.3.1. Relationship between Evidence and Attestation
Results . . . . . . . . . . . . . . . . . . . . . . . 9
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 10
3. Top-Level Token Definition . . . . . . . . . . . . . . . . . 12
4. The Claims . . . . . . . . . . . . . . . . . . . . . . . . . 13
4.1. eat_nonce (EAT Nonce) Claim . . . . . . . . . . . . . . . 14
4.2. Claims Describing the Entity . . . . . . . . . . . . . . 14
4.2.1. ueid (Universal Entity ID) Claim . . . . . . . . . . 15
4.2.1.1. Rules for Creating UEIDs . . . . . . . . . . . . 15
4.2.1.2. Rules for Consuming UEIDs . . . . . . . . . . . . 18
4.2.2. sueids (Semi-permanent UEIDs) Claim (SUEIDs) . . . . 18
4.2.3. oemid (Hardware OEM Identification) Claim . . . . . . 19
4.2.3.1. Random Number Based OEM ID . . . . . . . . . . . 19
4.2.3.2. IEEE Based OEM ID . . . . . . . . . . . . . . . . 20
4.2.3.3. IANA Private Enterprise Number Based OEM ID . . . 20
4.2.4. hwmodel (Hardware Model) Claim . . . . . . . . . . . 21
4.2.5. hwversion (Hardware Version) Claim . . . . . . . . . 22
4.2.6. swname (Software Name) Claim . . . . . . . . . . . . 22
4.2.7. swversion (Software Version) Claim . . . . . . . . . 22
4.2.8. oemboot (OEM Authorized Boot) Claim . . . . . . . . . 23
4.2.9. dbgstat (Debug Status) Claim . . . . . . . . . . . . 23
4.2.9.1. Enabled . . . . . . . . . . . . . . . . . . . . . 24
4.2.9.2. Disabled . . . . . . . . . . . . . . . . . . . . 24
4.2.9.3. Disabled Since Boot . . . . . . . . . . . . . . . 24
4.2.9.4. Disabled Permanently . . . . . . . . . . . . . . 24
4.2.9.5. Disabled Fully and Permanently . . . . . . . . . 25
4.2.10. location (Location) Claim . . . . . . . . . . . . . . 25
4.2.11. uptime (Uptime) Claim . . . . . . . . . . . . . . . . 26
4.2.12. bootcount (Boot Count) Claim . . . . . . . . . . . . 26
4.2.13. bootseed (Boot Seed) Claim . . . . . . . . . . . . . 26
4.2.14. dloas (Digital Letters of Approval) Claim . . . . . . 27
4.2.15. manifests (Software Manifests) Claim . . . . . . . . 28
4.2.16. measurements (Measurements) Claim . . . . . . . . . . 29
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4.2.17. measres (Software Measurement Results) Claim . . . . 30
4.2.18. submods (Submodules) . . . . . . . . . . . . . . . . 32
4.2.18.1. Submodule Claims-Set . . . . . . . . . . . . . . 35
4.2.18.2. Detached Submodule Digest . . . . . . . . . . . 36
4.2.18.3. Nested Tokens . . . . . . . . . . . . . . . . . 36
4.3. Claims Describing the Token . . . . . . . . . . . . . . . 36
4.3.1. iat (Timestamp) Claim . . . . . . . . . . . . . . . . 37
4.3.2. eat_profile (EAT Profile) Claim . . . . . . . . . . . 37
4.3.3. intuse (Intended Use) Claim . . . . . . . . . . . . . 38
5. Detached EAT Bundles . . . . . . . . . . . . . . . . . . . . 39
6. Profiles . . . . . . . . . . . . . . . . . . . . . . . . . . 40
6.1. Format of a Profile Document . . . . . . . . . . . . . . 41
6.2. Full and Partial Profiles . . . . . . . . . . . . . . . . 41
6.3. List of Profile Issues . . . . . . . . . . . . . . . . . 42
6.3.1. Use of JSON, CBOR or both . . . . . . . . . . . . . . 42
6.3.2. CBOR Map and Array Encoding . . . . . . . . . . . . . 42
6.3.3. CBOR String Encoding . . . . . . . . . . . . . . . . 43
6.3.4. CBOR Preferred Serialization . . . . . . . . . . . . 43
6.3.5. CBOR Tags . . . . . . . . . . . . . . . . . . . . . . 43
6.3.6. COSE/JOSE Protection . . . . . . . . . . . . . . . . 43
6.3.7. COSE/JOSE Algorithms . . . . . . . . . . . . . . . . 44
6.3.8. Detached EAT Bundle Support . . . . . . . . . . . . . 44
6.3.9. Key Identification . . . . . . . . . . . . . . . . . 44
6.3.10. Endorsement Identification . . . . . . . . . . . . . 45
6.3.11. Freshness . . . . . . . . . . . . . . . . . . . . . . 45
6.3.12. Claims Requirements . . . . . . . . . . . . . . . . . 45
6.4. The Constrained Device Standard Profile . . . . . . . . . 46
7. Encoding and Collected CDDL . . . . . . . . . . . . . . . . . 48
7.1. Claims-Set and CDDL for CWT and JWT . . . . . . . . . . . 48
7.2. Encoding Data Types . . . . . . . . . . . . . . . . . . . 48
7.2.1. Common Data Types . . . . . . . . . . . . . . . . . . 49
7.2.2. JSON Interoperability . . . . . . . . . . . . . . . . 49
7.2.3. Labels . . . . . . . . . . . . . . . . . . . . . . . 50
7.2.4. CBOR Interoperability . . . . . . . . . . . . . . . . 50
7.3. Collected CDDL . . . . . . . . . . . . . . . . . . . . . 50
7.3.1. Payload CDDL . . . . . . . . . . . . . . . . . . . . 50
7.3.2. CBOR-Specific CDDL . . . . . . . . . . . . . . . . . 55
7.3.3. JSON-Specific CDDL . . . . . . . . . . . . . . . . . 56
8. Privacy Considerations . . . . . . . . . . . . . . . . . . . 57
8.1. UEID and SUEID Privacy Considerations . . . . . . . . . . 57
8.2. Location Privacy Considerations . . . . . . . . . . . . . 58
8.3. Boot Seed Privacy Considerations . . . . . . . . . . . . 58
8.4. Replay Protection and Privacy . . . . . . . . . . . . . . 58
9. Security Considerations . . . . . . . . . . . . . . . . . . . 58
9.1. Claim Trustworthiness . . . . . . . . . . . . . . . . . . 58
9.2. Key Provisioning . . . . . . . . . . . . . . . . . . . . 59
9.2.1. Transmission of Key Material . . . . . . . . . . . . 59
9.3. Freshness . . . . . . . . . . . . . . . . . . . . . . . . 60
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9.4. Multiple EAT Consumers . . . . . . . . . . . . . . . . . 60
9.5. Detached EAT Bundle Digest Security Considerations . . . 60
9.6. Verification Keys . . . . . . . . . . . . . . . . . . . . 61
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 61
10.1. Reuse of CBOR and JSON Web Token (CWT and JWT) Claims
Registries . . . . . . . . . . . . . . . . . . . . . . . 61
10.2. CWT and JWT Claims Registered by This Document . . . . . 61
10.3. UEID URN Registered by this Document . . . . . . . . . . 68
10.4. CBOR Tag for Detached EAT Bundle Registered by this
Document . . . . . . . . . . . . . . . . . . . . . . . . 69
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 69
11.1. Normative References . . . . . . . . . . . . . . . . . . 69
11.2. Informative References . . . . . . . . . . . . . . . . . 72
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 74
A.1. Claims Set Examples . . . . . . . . . . . . . . . . . . . 74
A.1.1. Simple TEE Attestation . . . . . . . . . . . . . . . 74
A.1.2. Submodules for Board and Device . . . . . . . . . . . 76
A.1.3. EAT Produced by Attestation Hardware Block . . . . . 77
A.1.4. Key / Key Store Attestation . . . . . . . . . . . . . 78
A.1.5. Software Measurements of an IoT Device . . . . . . . 80
A.1.6. Attestation Results in JSON . . . . . . . . . . . . . 82
A.1.7. JSON-encoded Token with Submodules . . . . . . . . . 83
A.2. Signed Token Examples . . . . . . . . . . . . . . . . . . 84
A.2.1. Basic CWT Example . . . . . . . . . . . . . . . . . . 84
A.2.2. CBOR-encoded Detached EAT Bundle . . . . . . . . . . 85
A.2.3. JSON-encoded Detached EAT Bundle . . . . . . . . . . 87
Appendix B. UEID Design Rationale . . . . . . . . . . . . . . . 88
B.1. Collision Probability . . . . . . . . . . . . . . . . . . 88
B.2. No Use of UUID . . . . . . . . . . . . . . . . . . . . . 91
Appendix C. EAT Relation to IEEE.802.1AR Secure Device Identity
(DevID) . . . . . . . . . . . . . . . . . . . . . . . . . 91
C.1. DevID Used With EAT . . . . . . . . . . . . . . . . . . . 92
C.2. How EAT Provides an Equivalent Secure Device Identity . . 92
C.3. An X.509 Format EAT . . . . . . . . . . . . . . . . . . . 93
C.4. Device Identifier Permanence . . . . . . . . . . . . . . 93
Appendix D. CDDL for CWT and JWT . . . . . . . . . . . . . . . . 94
Appendix E. New Claim Design Considerations . . . . . . . . . . 96
E.1. Interoperability and Relying Party Orientation . . . . . 96
E.2. Operating System and Technology Neutral . . . . . . . . . 96
E.3. Security Level Neutral . . . . . . . . . . . . . . . . . 97
E.4. Reuse of Extant Data Formats . . . . . . . . . . . . . . 97
E.5. Proprietary Claims . . . . . . . . . . . . . . . . . . . 97
Appendix F. Endorsements and Verification Keys . . . . . . . . . 98
F.1. Identification Methods . . . . . . . . . . . . . . . . . 99
F.1.1. COSE/JWS Key ID . . . . . . . . . . . . . . . . . . . 99
F.1.2. JWS and COSE X.509 Header Parameters . . . . . . . . 99
F.1.3. CBOR Certificate COSE Header Parameters . . . . . . . 99
F.1.4. Claim-Based Key Identification . . . . . . . . . . . 100
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Appendix G. Changes from Previous Drafts . . . . . . . . . . . . 100
G.1. From draft-ietf-rats-eat-24 . . . . . . . . . . . . . . . 100
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 100
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 101
1. Introduction
An Entity Attestation Token (EAT) is a message made up of claims
about an entity. An entity may be a device, some hardware or some
software. The claims are ultimately used by a relying party who
decides if and how it will interact with the entity. The relying
party may choose to trust, not trust or partially trust the entity.
For example, partial trust may be allowing a monetary transaction
only up to a limit.
The security model and goal for attestation are unique and are not
the same as for other security standards like those for server
authentication, user authentication and secured messaging. To give
an example of one aspect of the difference, consider the association
and life-cycle of key material. For authentication, keys are
associated with a user or service and set up by actions performed by
a user or an operator of a service. For attestation, the keys are
associated with specific devices and are configured by device
manufacturers. The reader is assumed to be familiar with the goals
and security model for attestation as described in RATS Architecture
[RFC9334] and are not repeated here.
This document defines some common claims that are potentially of
broad use. EAT additionally allows proprietary claims and for
further claims to be standardized. Here are some examples:
* Make and model of manufactured consumer device
* Make and model of a chip or processor, particularly for a
security-oriented chip
* Identification and measurement of the software running on a device
* Configuration and state of a device
* Environmental characteristics of a device like its Global
Positioning Sytem (GPS) location
* Formal certifications received
EAT is constructed to support a wide range of use cases.
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No single set of claims can accommodate all use cases so EAT is
constructed as a framework for defining specific attestation tokens
for specific use cases. In particular, EAT provides a profile
mechanism to be able to clearly specify the claims needed, the
cryptographic algorithms that should be used, and other
characteristics for a particular token and use case. Section 6
describes profile contents and provides a profile that is suitable
for constrained device use cases.
The entity's EAT implementation generates the claims and typically
signs them with an attestation key. It is responsible for protecting
the attestation key. Some EAT implementations will use components
with very high resistance to attack like Trusted Platform Modules or
Secure Elements. Others may rely solely on simple software defenses.
Nesting of tokens and claims sets is accommodated for composite
devices that have multiple subsystems.
An EAT may be encoded in either JavaScript Object Notation (JSON)
[RFC8259] or Concise Binary Object Representation (CBOR) [RFC8949] as
needed for each use case. EAT is built on CBOR Web Token (CWT)
[RFC8392] and JSON Web Token (JWT) [RFC7519] and inherits all their
characteristics and their security mechanisms. Like CWT and JWT, EAT
does not imply any message flow.
Following is a very simple example. It is JSON format for easy
reading, but could also be CBOR. Only the Claims-Set, the payload
for the JWT, is shown.
{
"eat_nonce": "MIDBNH28iioisjPy",
"ueid": "AgAEizrK3Q",
"oemid": 76543,
"swname": "Acme IoT OS",
"swversion": "3.1.4"
}
This example has a nonce for freshness. This nonce is the base64url
encoding of a 12 byte random binary byte string. The ueid is
effectively a serial number uniquely identifying the device. This
ueid is the base64url encoding of a 48-bit MAC address preceded by
the type byte 0x02. The oemid identifies the manufacturer using a
Private Enterprise Number [PEN]. The software is identified by a
simple string name and version. It could be identified by a full
manifest, but this is a minimal example.
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1.1. Entity Overview
This document uses the term "entity" to refer to the target of an
EAT. Most of the claims defined in this document are claims about an
entity. An entity is equivalent to a target environment in an
attester as defined in [RFC9334].
Layered attestation and composite devices, as described in [RFC9334],
are supported by a submodule mechanism (see Section 4.2.18).
Submodules allow nesting of EATs and of claims-sets so that such
hierarchies can be modeled.
An entity is the same as a "system component", as defined in the
Internet Security Glossary [RFC4949].
Note that [RFC4949] defines "entity" and "system entity" as synonyms,
and that they may be a person or organization in addition to being a
system component. In the EAT context, "entity" never refers to a
person or organization. The hardware and software that implement a
web site server or service may be an entity in the EAT sense, but the
organization that operates, maintains or hosts the web site is not an
entity.
Some examples of entities:
* A Secure Element
* A Trusted Execution Environment (TEE)
* A network card in a router
* A router, perhaps with each network card in the router a submodule
* An Internet of Things (IoT) device
* An individual process
* An app on a smartphone
* A smartphone with many submodules for its many subsystems
* A subsystem in a smartphone like the modem or the camera
An entity may have strong security defenses against hardware invasive
attacks. It may also have low security, having no special security
defenses. There is no minimum security requirement to be an entity.
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1.2. EAT as a Framework
EAT is a framework for defining attestation tokens for specific use
cases, not a specific token definition. While EAT is based on and
compatible with CWT and JWT, it can also be described as:
* An identification and type system for claims in claims-sets
* Definitions of common attestation-oriented claims
* Claims defined in CDDL and serialized using CBOR or JSON
* Security envelopes based on CBOR Object Signing and Encryption
(COSE) and Javascript Object Signing and Encryption (JOSE)
* Nesting of claims sets and tokens to represent complex and
compound devices
* A profile mechanism for specifying and identifying specific tokens
for specific use cases
EAT uses the name/value pairs the same as CWT and JWT to identify
individual claims. Section 4 defines common attestation-oriented
claims that are added to the CWT and JWT IANA registries. As with
CWT and JWT, no claims are mandatory and claims not recognized should
be ignored.
Unlike, but compatible with CWT and JWT, EAT defines claims using
Concise Data Definition Language (CDDL) [RFC8610]. In most cases the
same CDDL definition is used for both the CBOR/CWT serialization and
the JSON/JWT serialization.
Like CWT and JWT, EAT uses COSE and JOSE to provide authenticity,
integrity and optionally confidentiality. EAT places no new
restrictions on cryptographic algorithms, retaining all the
cryptographic flexibility of CWT, COSE, JWT and JOSE.
EAT defines a means for nesting tokens and claims sets to accommodate
composite devices that have multiple subsystems and multiple
attesters. Tokens with security envelopes or bare claims sets may be
embedded in an enclosing token. The nested token and the enclosing
token do not have to use the same encoding (e.g., a CWT may be
enclosed in a JWT).
EAT adds the ability to detach claims sets and send them separately
from a security-enveloped EAT that contains a digest of the detached
claims set.
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This document registers no media or content types for the
identification of the type of EAT, its serialization encoding or
security envelope. The definition and registration of EAT media
types is addressed in [EAT.media-types].
Finally, the notion of an EAT profile is introduced that facilitates
the creation of narrowed definitions of EATs for specific use cases
in follow-on documents. One basic profile for constrained devices is
normatively defined.
1.3. Operating Model and RATS Architecture
EAT follows the operational model described in Figure 1 in RATS
Architecture [RFC9334]. To summarize, an attester generates evidence
in the form of a claims set describing various characteristics of an
entity. Evidence is usually signed by a key that proves the attester
and the evidence it produces are authentic. The claims set includes
a nonce or some other means to assure freshness.
A verifier confirms an EAT is valid by verifying the signature and
may vet some claims using reference values. The verifier then
produces attestation results, which may also be represented as an
EAT. The attestation results are provided to the relying party,
which is the ultimate consumer of the Remote Attestation Procedure.
The relying party uses the attestation results as needed for its use
case, perhaps allowing an entity to access a network, allowing a
financial transaction or such. In some cases, the verifier and
relying party are not distinct entities.
1.3.1. Relationship between Evidence and Attestation Results
Any claim defined in this document or in the IANA CWT or JWT registry
may be used in evidence or attestation results. The relationship of
claims in attestation results to evidence is fundamentally governed
by the verifier and the verifier's policy.
A common use case is for the verifier and its policy to perform
checks, calculations and processing with evidence as the input to
produce a summary result in attestation results that indicates the
overall health and status of the entity. For example, measurements
in evidence may be compared to reference values the results of which
are represented as a simple pass/fail in attestation results.
It is also possible that some claims in the Evidence will be
forwarded unmodified to the relying party in attestation results.
This forwarding is subject to the verifier's implementation and
policy. The relying party should be aware of the verifier's policy
to know what checks it has performed on claims it forwards.
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The verifier may modify claims it forwards, for example, to implement
a privacy preservation functionality. It is also possible the
verifier will put claims in the attestation results that give details
about the entity that it has computed or looked up in a database.
For example, the verifier may be able to put an "oemid" claim in the
attestation results by performing a look up based on a "ueid" claim
(e.g., serial number) it received in evidence.
This specification does not establish any normative rules for the
verifier to follow, as these are a matter of local policy. It is up
to each relying party to understand the processing rules of each
verifier to know how to interpret claims in attestation results.
2. Terminology
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.
In this document, the structure of data is specified in CDDL
[RFC8610] [RFC9165].
The examples in Appendix A use CBOR diagnostic notation defined in
Section 8 of [RFC8949] and Appendix G of [RFC8610].
This document reuses terminology from JWT [RFC7519] and CWT
[RFC8392]:
base64url-encoded: base64url-encoded is as described in [RFC7515],
i.e., using URL- and filename-safe character set [RFC4648] with
all trailing '=' characters omitted and without the inclusion of
any line breaks, whitespace, or other additional characters.
Claim: A piece of information asserted about a subject. A claim is
represented as pair with a value and either a name or key to
identify it.
Claim Name: A unique text string that identifies the claim. It is
used as the claim name for JSON encoding.
Claim Key: The CBOR map key used to identify a claim. (The term
"Claim Key" comes from CWT. This document, like COSE, uses the
term "label" to refer to CBOR map keys to avoid confusion with
cryptographic keys.)
Claim Value: The value portion of the claim. A claim value can be
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any CBOR data item or JSON value.
Claims Set: The CBOR map or JSON object that contains the claims
conveyed by the CWT or JWT.
This document reuses terminology from RATS Architecure [RFC9334]:
Attester: A role performed by an entity (typically a device) whose
evidence must be appraised in order to infer the extent to which
the attester is considered trustworthy, such as when deciding
whether it is authorized to perform some operation.
Verifier: A role that appraises the validity of evidence about an
attester and produces attestation results to be used by a relying
party.
Relying Party: A role that depends on the validity of information
about an attester, for purposes of reliably applying application
specific actions. Compare /relying party/ in [RFC4949].
Evidence: A set of claims generated by an attester to be appraised
by a verifier. Evidence may include configuration data,
measurements, telemetry, or inferences.
Attestation Results: The output generated by a verifier, typically
including information about an attester, where the verifier
vouches for the validity of the results
Reference Values: A set of values against which values of claims can
be compared as part of applying an appraisal policy for evidence.
Reference Values are sometimes referred to in other documents as
known-good values, golden measurements, or nominal values,
although those terms typically assume comparison for equality,
whereas here reference values might be more general and be used in
any sort of comparison.
Endorsement: A secure statement that an Endorser vouches for the
integrity of an attester's various capabilities such as claims
collection and evidence signing.
This document reuses terminology from CDDL [RFC8610]:
Group Socket: refers to the mechanism by which a CDDL definition is
extended, as described in [RFC8610] and [RFC9165]
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3. Top-Level Token Definition
An "EAT" is an encoded (serialized) message the purpose of which is
to transfer a Claims-Set between two parties. An EAT MUST always
contain a Claims-Set. In this document an EAT is always a CWT or JWT.
An EAT MUST have authenticity and integrity protection. CWT and JWT
provide that in this document.
Further documents may define other encodings and security mechanims
for EAT.
The identification of a protocol element as an EAT follows the
general conventions used for CWTs and JWTs. Identification depends
on the protocol carrying the EAT. In some cases it may be by media
type (e.g., in a HTTP Content-Type field). In other cases it may be
through use of CBOR tags. There is no fixed mechanism across all use
cases.
This document also defines another message, the detached EAT bundle
(see Section 5), which holds a collection of detached claims sets and
an EAT that provides integrity and authenticity protection for them.
Detached EAT bundles can be either CBOR or JSON encoded.
The following CDDL defines the top-level $EAT-CBOR-Tagged-Token,
$EAT-CBOR-Untagged-Token and $EAT-JSON-Token-Formats sockets (see
Section 3.9 of [RFC8610]), enabling future token formats to be
defined. Any new format that plugs into one or more of these sockets
MUST be defined by an IETF standards action. Of particular use may
be a token type that provides no direct authenticity or integrity
protection for use with transports mechanisms that do provide the
necessary security services [UCCS].
Nesting of EATs is allowed and defined in Section 4.2.18.3. This
includes the nesting of an EAT that is a different format than the
enclosing EAT, i.e., the nested EAT may be encoded using CBOR and the
enclosing EAT encoded using JSON or vice versa. The definition of
Nested-Token references the CDDL defined in this section. When new
token formats are defined, the means for identification in a nested
token MUST also be defined.
The top-level CDDL type for CBOR-encoded EATs is EAT-CBOR-Token and
for JSON is EAT-JSON-Token (while CDDL and CDDL tools provide enough
support for shared definitions of most items in this document, they
don’t provide enough support for this sharing at the top level).
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EAT-CBOR-Token = $EAT-CBOR-Tagged-Token / $EAT-CBOR-Untagged-Token
$EAT-CBOR-Tagged-Token /= CWT-Tagged-Message
$EAT-CBOR-Tagged-Token /= BUNDLE-Tagged-Message
$EAT-CBOR-Untagged-Token /= CWT-Untagged-Message
$EAT-CBOR-Untagged-Token /= BUNDLE-Untagged-Message
EAT-JSON-Token = $EAT-JSON-Token-Formats
$EAT-JSON-Token-Formats /= JWT-Message
$EAT-JSON-Token-Formats /= BUNDLE-Untagged-Message
4. The Claims
This section describes new claims defined for attestation that are to
be added to the CWT [IANA.CWT.Claims] and JWT [IANA.JWT.Claims] IANA
registries.
All definitions, requirements, creation and validation procedures,
security considerations, IANA registrations and so on from CWT and
JWT carry over to EAT.
This section also describes how several extant CWT and JWT claims
apply in EAT.
The set of claims that an EAT must contain to be considered valid is
context dependent and is outside the scope of this specification.
Specific applications of EATs will require implementations to
understand and process some claims in particular ways. However, in
the absence of such requirements, all claims that are not understood
by implementations MUST be ignored.
CDDL, along with a text description, is used to define each claim
independent of encoding. Each claim is defined as a CDDL group. In
Section 7 on encoding, the CDDL groups turn into CBOR map entries and
JSON name/value pairs.
Each claim defined in this document is added to the $$Claims-Set-
Claims group socket. Claims defined by other specifications MUST
also be added to the $$Claims-Set-Claims group socket.
All claims in an EAT MUST use the same encoding except where
otherwise explicitly stated (e.g., in a CBOR-encoded token, all
claims must be CBOR-encoded).
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This specification includes a CDDL definition of most of what is
defined in [RFC8392]. Similarly, this specification includes CDDL
for most of what is defined in [RFC7519]. These definitions are in
Appendix D and are not normative.
Each claim described has a unique text string and integer that
identifies it. CBOR-encoded tokens MUST use only the integer for
claim keys. JSON-encoded tokens MUST use only the text string for
claim names.
4.1. eat_nonce (EAT Nonce) Claim
An EAT nonce is either a byte or text string or an array of byte or
text strings. The array option supports multistage EAT verification
and consumption.
A claim named "nonce" was defined and registered with IANA for JWT,
but MUST NOT be used because it does not support multiple nonces. No
previous "nonce" claim was defined for CWT. To distinguish from the
previously defined JWT "nonce" claim, this claim is named "eat_nonce"
in JSON-encoded EATs. The CWT nonce defined here is intended for
general purpose use and retains the "Nonce" claim name instead of an
EAT-specific name.
An EAT nonce MUST have at least 64 bits of entropy. A maximum EAT
nonce size is set to limit the memory required for an implementation.
All receivers MUST be able to accommodate the maximum size.
In CBOR, an EAT nonce is a byte string between 8 and 64 bytes in
length. In JSON, an EAT nonce is a text string between 8 and 88
bytes in length.
$$Claims-Set-Claims //=
(nonce-label => nonce-type / [ 2* nonce-type ])
nonce-type = JC< tstr .size (8..88), bstr .size (8..64)>
4.2. Claims Describing the Entity
The claims in this section describe the entity itself. They describe
the entity whether they occur in evidence or occur in attestation
results. See Section 1.3.1 for discussion on how attestation results
relate to evidence.
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4.2.1. ueid (Universal Entity ID) Claim
The "ueid" claim conveys a UEID, which identifies an individual
manufactured entity like a mobile phone, a water meter, a Bluetooth
speaker or a networked security camera. It may identify the entire
entity or a submodule. It does not identify types, models or classes
of entities. It is akin to a serial number, though it does not have
to be sequential.
UEIDs MUST be universally and globally unique across manufacturers
and countries, as described in Section 4.2.1.1. UEIDs MUST also be
unique across protocols and systems, as tokens are intended to be
embedded in many different protocols and systems. No two products
anywhere, even in completely different industries made by two
different manufacturers in two different countries should have the
same UEID (if they are not global and universal in this way, then
relying parties receiving them will have to track other
characteristics of the entity to keep entities distinct between
manufacturers).
UEIDs are not designed for direct use by humans (e.g., printing on
the case of a device), so no such representation is defined.
There are privacy considerations for UEIDs. See Section 8.1.
A Device Identifier URN is registered for UEIDs. See Section 10.3.
$$Claims-Set-Claims //= (ueid-label => ueid-type)
ueid-type = JC<base64-url-text .size (10..44) , bstr .size (7..33)>
4.2.1.1. Rules for Creating UEIDs
These rules are solely for the creation of UEIDs. The EAT consumer
need not have any awareness of them.
A UEID is constructed of a single type byte followed by the unique
bytes for that type. The type byte assures global uniqueness of a
UEID even if the unique bytes for different types are accidentally
the same.
UEIDS are variable length to accommodate the types defined here and
future-defined types.
UEIDs SHOULD NOT be longer than 33 bytes. If they are longer, there
is no guarantee that a receiver will be able to accept them. See
Appendix B.
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A UEID is permanent. It MUST never change for a given entity.
The different types of UEIDs 1) accommodate different manufacturing
processes, 2) accommodate small UEIDs, 3) provide an option that
doesn't require registration fees and central administration.
In the unlikely event that a new UEID type is needed, it MUST be
defined in a standards-track update to this document.
A manufacturer of entities MAY use different types for different
products. They MAY also change from one type to another for a given
product or use one type for some items of a given produce and another
type for other.
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+======+======+=====================================================+
| Type | Type | Specification |
| Byte | Name | |
+======+======+=====================================================+
| 0x01 | RAND | This is a 128, 192 or 256-bit random number |
| | | generated once and stored in the entity. This |
| | | may be constructed by concatenating enough |
| | | identifiers to make up an equivalent number of |
| | | random bits and then feeding the concatenation |
| | | through a cryptographic hash function. It may |
| | | also be a cryptographic quality random number |
| | | generated once at the beginning of the life of |
| | | the entity and stored. It MUST NOT be smaller |
| | | than 128 bits. See the length analysis in |
| | | Appendix B. |
+------+------+-----------------------------------------------------+
| 0x02 | IEEE | This makes use of the device identification |
| | EUI | scheme operated by the IEEE. An EUI is either |
| | | an EUI-48, EUI-60 or EUI-64 and made up of an |
| | | OUI, OUI-36 or a CID, different registered |
| | | company identifiers, and some unique per-entity |
| | | identifier. EUIs are often the same as or |
| | | similar to MAC addresses. This type includes |
| | | MAC-48, an obsolete name for EUI-48. (Note that |
| | | while entities with multiple network interfaces |
| | | may have multiple MAC addresses, there is only |
| | | one UEID for an entity; changeable MAC addresses |
| | | that don't meet the permanence requirements in |
| | | this document MUST NOT be used for the UEID or |
| | | SUEID) [IEEE.802-2001], [OUI.Guide]. |
+------+------+-----------------------------------------------------+
| 0x03 | IMEI | This makes use of the International Mobile |
| | | Equipment Identity (IMEI) scheme operated by the |
| | | GSMA. This is a 14-digit identifier consisting |
| | | of an 8-digit Type Allocation Code (TAC) and a |
| | | 6-digit serial number allocated by the |
| | | manufacturer, which SHALL be encoded as byte |
| | | string of length 14 with each byte as the |
| | | digit's value (not the ASCII encoding of the |
| | | digit; the digit 3 encodes as 0x03, not 0x33). |
| | | The IMEI value encoded SHALL NOT include Luhn |
| | | checksum or SVN information. See |
| | | [ThreeGPP.IMEI]. |
+------+------+-----------------------------------------------------+
Table 1: UEID Composition Types
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4.2.1.2. Rules for Consuming UEIDs
For the consumer, a UEID is solely a globally unique opaque
identifier. The consumer does not and should not have any awareness
of the rules and structure used to achieve global uniqueness.
All implementations MUST be able to receive UEIDs up to 33 bytes
long. 33 bytes is the longest defined in this document and gives
necessary entropy for probabilistic uniqueness.
The consumer of a UEID MUST treat it as a completely opaque string of
bytes and MUST NOT make any use of its internal structure. The
reasons for this are:
* UEIDs types vary freely from one manufacturer to the next.
* New types of UEIDs may be defined.
* The manufacturer of an entity is allowed to change from one type
of UEID to another anytime they want.
For example, when the consumer receives a type 0x02 UEID, they should
not use the OUI part to identify the manufacturer of the device
because there is no guarantee all UEIDs will be type 0x02. Different
manufacturers may use different types. A manufacturer may make some
of their product with one type and others with a different type or
even change to a different type for newer versions of their product.
Instead, the consumer should use the "oemid" claim.
4.2.2. sueids (Semi-permanent UEIDs) Claim (SUEIDs)
The "sueids" claim conveys one or more semi-permanent UEIDs (SUEIDs).
An SUEID has the same format, characteristics and requirements as a
UEID, but MAY change to a different value on entity life-cycle
events. An entity MAY have both a UEID and SUEIDs, neither, one or
the other.
Examples of life-cycle events are change of ownership, factory reset
and on-boarding into an IoT device management system. It is beyond
the scope of this document to specify particular types of SUEIDs and
the life-cycle events that trigger their change. An EAT profile MAY
provide this specification.
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There MAY be multiple SUEIDs. Each has a text string label the
purpose of which is to distinguish it from others. The label MAY
name the purpose, application or type of the SUEID. For example, the
label for the SUEID used by XYZ Onboarding Protocol could thus be
"XYZ". It is beyond the scope of this document to specify any SUEID
labeling schemes. They are use case specific and MAY be specified in
an EAT profile.
If there is only one SUEID, the claim remains a map and there still
MUST be a label.
An SUEID provides functionality similar to an IEEE LDevID
[IEEE.802.1AR].
There are privacy considerations for SUEIDs. See Section 8.1.
A Device Identifier URN is registered for SUEIDs. See Section 10.3.
$$Claims-Set-Claims //= (sueids-label => sueids-type)
sueids-type = {
+ tstr => ueid-type
}
4.2.3. oemid (Hardware OEM Identification) Claim
The "oemid" claim identifies the Original Equipment Manufacturer
(OEM) of the hardware. Any of the three forms described below MAY be
used at the convenience of the claim sender. The receiver of this
claim MUST be able to handle all three forms.
Note that the "hwmodel" claim in Section 4.2.4, the "oemboot" claim
in Section 4.2.8 and "dbgstat" claim in Section 4.2.9 depend on this
claim.
Sometimes one manufacturer will acquire or merge with another.
Depending on the situation and use case newly manfactured devices may
continue to use the old OEM ID or switch to a new one. This is left
to the discretion of the manufacturers, but they should consider how
it affects the above-mentioned claims and the attestation eco-system
for their devices. The considerations are the same for all three
forms of this claim.
4.2.3.1. Random Number Based OEM ID
The random number based OEM ID MUST always be 16 bytes (128 bits)
long.
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The OEM may create their own ID by using a cryptographic-quality
random number generator. They would perform this only once in the
life of the company to generate the single ID for said company. They
would use that same ID in every entity they make. This uniquely
identifies the OEM on a statistical basis and is large enough should
there be ten billion companies.
In JSON-encoded tokens this MUST be base64url-encoded.
4.2.3.2. IEEE Based OEM ID
The IEEE operates a global registry for MAC addresses and company
IDs. This claim uses that database to identify OEMs. The contents
of the claim may be either an IEEE MA-L, MA-M, MA-S or an IEEE CID
[IEEE-RA]. An MA-L, formerly known as an OUI, is a 24-bit value used
as the first half of a MAC address. MA-M similarly is a 28-bit value
uses as the first part of a MAC address, and MA-S, formerly known as
OUI-36, a 36-bit value. Many companies already have purchased one of
these. A CID is also a 24-bit value from the same space as an MA-L,
but not for use as a MAC address. IEEE has published Guidelines for
Use of EUI, OUI, and CID [OUI.Guide] and provides a lookup service
[OUI.Lookup].
Companies that have more than one of these IDs or MAC address blocks
SHOULD select one and prefer that for all their entities.
Commonly, these are expressed in Hexadecimal Representation as
described in [IEEE.802-2001]. It is also called the Canonical
format. When this claim is encoded the order of bytes in the bstr
are the same as the order in the Hexadecimal Representation. For
example, an MA-L like "AC-DE-48" would be encoded in 3 bytes with
values 0xAC, 0xDE, 0x48.
This format is always 3 bytes in size in CBOR.
In JSON-encoded tokens, this MUST be base64url-encoded and always 4
bytes.
4.2.3.3. IANA Private Enterprise Number Based OEM ID
IANA maintains a registry for Private Enterprise Numbers (PEN) [PEN].
A PEN is an integer that identifies an enterprise and may be used to
construct an object identifier (OID) relative to the following OID
arc that is managed by IANA: iso(1) identified-organization(3) dod(6)
internet(1) private(4) enterprise(1).
For EAT purposes, only the integer value assigned by IANA as the PEN
is relevant, not the full OID value.
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In CBOR this value MUST be encoded as a major type 0 integer and is
typically 3 bytes. In JSON, this value MUST be encoded as a number.
$$Claims-Set-Claims //= (
oemid-label => oemid-pen / oemid-ieee / oemid-random
)
oemid-pen = int
oemid-ieee = JC<oemid-ieee-json, oemid-ieee-cbor>
oemid-ieee-cbor = bstr .size 3
oemid-ieee-json = base64-url-text .size 4
oemid-random = JC<oemid-random-json, oemid-random-cbor>
oemid-random-cbor = bstr .size 16
oemid-random-json = base64-url-text .size 24
4.2.4. hwmodel (Hardware Model) Claim
The "hwmodel" claim differentiates hardware models, products and
variants manufactured by a particular OEM, the one identified by OEM
ID in Section 4.2.3. It MUST be unique within a given OEM ID. The
concatenation of the OEM ID and "hwmodel" give a global identifier of
a particular product. The "hwmodel" claim MUST only be present if an
"oemid" claim described in Section 4.2.3 is present.
The granularity of the model identification is for each OEM to
decide. It may be very granular, perhaps including some version
information. It may be very general, perhaps only indicating top-
level products.
The "hwmodel" claim is for use in protocols and not for human
consumption. The format and encoding of this claim should not be
human-readable to discourage use other than in protocols. If this
claim is to be derived from an already-in-use human-readable
identifier, it can be run through a hash function.
There is no minimum length so that an OEM with a very small number of
models can use a one-byte encoding. The maximum length is 32 bytes.
All receivers of this claim MUST be able to receive this maximum
size.
The receiver of this claim MUST treat it as a completely opaque
string of bytes, even if there is some apparent naming or structure.
The OEM is free to alter the internal structure of these bytes as
long as the claim continues to uniquely identify its models.
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$$Claims-Set-Claims //= (
hardware-model-label => hardware-model-type
)
hardware-model-type = JC<base64-url-text .size (4..44),
bytes .size (1..32)>
4.2.5. hwversion (Hardware Version) Claim
The "hwversion" claim is a text string the format of which is set by
each manufacturer. The structure and sorting order of this text
string can be specified using the version-scheme item from CoSWID
[RFC9393]. It is useful to know how to sort versions so the newer
can be distinguished from the older. A "hwversion" claim MUST only
be present if a "hwmodel" claim described in Section 4.2.4 is
present.
$$Claims-Set-Claims //= (
hardware-version-label => hardware-version-type
)
hardware-version-type = [
version: tstr,
? scheme: $version-scheme
]
4.2.6. swname (Software Name) Claim
The "swname" claim contains a very simple free-form text value for
naming the software used by the entity. Intentionally, no general
rules or structure are set. This will make it unsuitable for use
cases that wish precise naming.
If precise and rigourous naming of the software for the entity is
needed, the "manifests" claim described in Section 4.2.15 may be used
instead.
$$Claims-Set-Claims //= ( sw-name-label => tstr )
4.2.7. swversion (Software Version) Claim
The "swversion" claim makes use of the CoSWID version-scheme defined
in [RFC9393] to give a simple version for the software. A
"swversion" claim MUST only be present if a "swname" claim described
in Section 4.2.6 is present.
The "manifests" claim Section 4.2.15 may be instead if this is too
simple.
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$$Claims-Set-Claims //= (sw-version-label => sw-version-type)
sw-version-type = [
version: tstr
? scheme: $version-scheme
]
4.2.8. oemboot (OEM Authorized Boot) Claim
An "oemboot" claim with value of true indicates the entity booted
with software authorized by the manufacturer of the entity as
indicated by the "oemid" claim described in Section 4.2.3. It
indicates the firmware and operating system are fully under control
of the OEM and may not be replaced by the end user or even the
enterprise that owns the device. The means of control may be by
cryptographic authentication of the software, by the software being
in Read-Only Memory (ROM), a combination of the two or other. If
this claim is present the "oemid" claim MUST be present.
$$Claims-Set-Claims //= (oem-boot-label => bool)
4.2.9. dbgstat (Debug Status) Claim
The "dbgstat" claim applies to entity-wide or submodule-wide debug
facilities of the entity like [JTAG] and diagnostic hardware built
into chips. It applies to any software debug facilities related to
privileged software that allows system-wide memory inspection,
tracing or modification of non-system software like user mode
applications.
This characterization assumes that debug facilities can be enabled
and disabled in a dynamic way or be disabled in some permanent way,
such that no enabling is possible. An example of dynamic enabling is
one where some authentication is required to enable debugging. An
example of permanent disabling is blowing a hardware fuse in a chip.
The specific type of the mechanism is not taken into account. For
example, it does not matter if authentication is by a global password
or by per-entity public keys.
As with all claims, the absence of the "dbgstat" claim means it is
not reported.
This claim is not extensible so as to provide a common interoperable
description of debug status. If a particular implementation
considers this claim to be inadequate, it can define its own
proprietary claim. It may consider including both this claim as a
coarse indication of debug status and its own proprietary claim as a
refined indication.
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The higher levels of debug disabling requires that all debug
disabling of the levels below it be in effect. Since the lowest
level requires that all of the target's debug be currently disabled,
all other levels require that too.
There is no inheritance of claims from a submodule to a superior
module or vice versa. There is no assumption, requirement or
guarantee that the target of a superior module encompasses the
targets of submodules. Thus, every submodule must explicitly
describe its own debug state. The receiver of an EAT MUST NOT assume
that debug is turned off in a submodule because there is a claim
indicating it is turned off in a superior module.
An entity may have multiple debug facilities. The use of plural in
the description of the states refers to that, not to any aggregation
or inheritance.
The architecture of some chips or devices may be such that a debug
facility operates for the whole chip or device. If the EAT for such
a chip includes submodules, then each submodule should independently
report the status of the whole-chip or whole-device debug facility.
This is the only way the receiver can know the debug status of the
submodules since there is no inheritance.
4.2.9.1. Enabled
If any debug facility, even manufacturer hardware diagnostics, is
currently enabled, then this level must be indicated.
4.2.9.2. Disabled
This level indicates all debug facilities are currently disabled. It
may be possible to enable them in the future. It may also be that
they were enabled in the past, but they are currently disabled.
4.2.9.3. Disabled Since Boot
This level indicates all debug facilities are currently disabled and
have been so since the entity booted/started.
4.2.9.4. Disabled Permanently
This level indicates all non-manufacturer facilities are permanently
disabled such that no end user or developer can enable them. Only
the manufacturer indicated in the "oemid" claim can enable them.
This also indicates that all debug facilities are currently disabled
and have been so since boot/start. If this debug state is reported,
the "oemid" claim MUST be present.
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4.2.9.5. Disabled Fully and Permanently
This level indicates that all debug facilities for the entity are
permanently disabled.
$$Claims-Set-Claims //= ( debug-status-label => debug-status-type )
debug-status-type = ds-enabled /
disabled /
disabled-since-boot /
disabled-permanently /
disabled-fully-and-permanently
ds-enabled = JC< "enabled", 0 >
disabled = JC< "disabled", 1 >
disabled-since-boot = JC< "disabled-since-boot", 2 >
disabled-permanently = JC< "disabled-permanently", 3 >
disabled-fully-and-permanently =
JC< "disabled-fully-and-permanently", 4 >
4.2.10. location (Location) Claim
The "location" claim gives the geographic position of the entity from
which the attestation originates. Latitude, longitude, altitude,
accuracy, altitude-accuracy, heading and speed MUST be as defined in
the W3C Geolocation API [W3C.GeoLoc] (which, in turn, is based on
[WGS84]). If the entity is stationary, the heading is NaN (floating-
point not-a-number). Latitude and longitude MUST always be provided.
If any other of these values are unknown, they are omitted.
The location may have been cached for a period of time before token
creation. For example, it might have been minutes or hours or more
since the last contact with a GNSS satellite. Either the timestamp
or age data item can be used to quantify the cached period. The
timestamp data item is preferred as it a non-relative time. If the
entity has no clock or the clock is unset but has a means to measure
the time interval between the acquisition of the location and the
token creation the age may be reported instead. The age is in
seconds.
See location-related privacy considerations in Section 8.2.
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$$Claims-Set-Claims //= (location-label => location-type)
location-type = {
latitude => number,
longitude => number,
? altitude => number,
? accuracy => number,
? altitude-accuracy => number,
? heading => number,
? speed => number,
? timestamp => ~time-int,
? age => uint
}
latitude = JC< "latitude", 1 >
longitude = JC< "longitude", 2 >
altitude = JC< "altitude", 3 >
accuracy = JC< "accuracy", 4 >
altitude-accuracy = JC< "altitude-accuracy", 5 >
heading = JC< "heading", 6 >
speed = JC< "speed", 7 >
timestamp = JC< "timestamp", 8 >
age = JC< "age", 9 >
4.2.11. uptime (Uptime) Claim
The "uptime" claim contains the number of seconds that have elapsed
since the entity or submodule was last booted.
$$Claims-Set-Claims //= (uptime-label => uint)
4.2.12. bootcount (Boot Count) Claim
The "bootcount" claim contains a count of the number times the entity
or submodule has been booted. Support for this claim requires a
persistent storage on the device.
$$Claims-Set-Claims //= (boot-count-label => uint)
4.2.13. bootseed (Boot Seed) Claim
The "bootseed" claim contains a value created at system boot time
that allows differentiation of attestation reports from different
boot sessions of a particular entity (e.g., a certain UEID).
This value is usually public. It is not a secret and MUST NOT be
used for any purpose that a secret seed is needed, such as seeding a
random number generator.
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There are privacy considerations for this claim. See Section 8.3.
$$Claims-Set-Claims //= (boot-seed-label => binary-data)
4.2.14. dloas (Digital Letters of Approval) Claim
The "dloas" claim conveys one or more Digital Letters of Approval
(DLOAs). A DLOA [DLOA] is a document that describes a certification
that an entity has received. Examples of certifications represented
by a DLOA include those issued by Global Platform and those based on
Common Criteria. The DLOA is unspecific to any particular
certification type or those issued by any particular organization.
This claim is typically issued by a verifier, not an attester.
Verifiers MUST NOT issue this claim unless the entity has received
the certification indicated by the DLOA.
This claim MAY contain more than one DLOA. If multiple DLOAs are
present, verifiers MUST NOT issue this claim unless the entity has
received all of the certifications.
DLOA documents are always fetched from a registrar that stores them.
This claim contains several data items used to construct a Uniform
Resource Locator (URL) for fetching the DLOA from the particular
registrar.
This claim MUST be encoded as an array with either two or three
elements. The first element MUST be the URL for the registrar. The
second element MUST be a platform label indicating which platform was
certified. If the DLOA applies to an application, then the third
element is added which MUST be an application label. The method of
constructing the registrar URL, platform label and possibly
application label is specified in [DLOA].
The retriever of a DLOA MUST follow the recommendation in [DLOA] and
use TLS or some other means to be sure the DLOA registrar they are
accessing is authentic. The platform and application labels in the
claim indicate the correct DLOA for the entity.
$$Claims-Set-Claims //= (
dloas-label => [ + dloa-type ]
)
dloa-type = [
dloa_registrar: general-uri
dloa_platform_label: text
? dloa_application_label: text
]
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4.2.15. manifests (Software Manifests) Claim
The "manifests" claim contains descriptions of software present on
the entity. These manifests are installed on the entity when the
software is installed or are created as part of the installation
process. Installation is anything that adds software to the entity,
possibly factory installation, the user installing elective
applications and so on. The defining characteristic of a manifest is
that it is created by the software manufacturer. The purpose of this
claim is to relay unmodified manifests to the verifier and possibly
to the relying party.
Some manifests are signed by their software manufacturer
independently, and some are not either because they do not support
signing or the manufacturer chose not to sign them. For example, a
CoSWID might be signed independently before it is included in an EAT.
When signed manifests are put into an EAT, the manufacturer's
signature SHOULD be included even though an EAT's signature will also
cover the manifest. This allows the receiver to directly verify the
manufacturer-originated manifest.
This claim allows multiple manifest formats. For example, the
manifest may be a CBOR-encoded CoSWID, an XML-encoded SWID or other.
Identification of the type of manifest is always by a Constrained
Application Protocol (CoAP) Content-Format integer [RFC7252]. If
there is no CoAP identifier registered for a manifest format, one
MUST be registered.
This claim MUST be an array of one or more manifests. Each manifest
in the claim MUST be an array of two. The first item in the array of
two MUST be an integer CoAP Content-Format identifier. The second
item is MUST be the actual manifest.
In JSON-encoded tokens the manifest, whatever encoding it is, MUST be
placed in a text string. When a non-text encoded manifest like a
CBOR-encoded CoSWID is put in a JSON-encoded token, the manifest MUST
be base-64 encoded.
This claim allows for multiple manifests in one token since multiple
software packages are likely to be present. The multiple manifests
MAY be of different encodings. In some cases EAT submodules may be
used instead of the array structure in this claim for multiple
manifests.
A CoSWID manifest MUST be a payload CoSWID, not an evidence CoSWID.
These are defined in [RFC9393].
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A Software Updates for Internet of Things (SUIT) Manifest
[SUIT.Manifest] may be used.
This claim is extensible for use of manifest formats beyond those
mentioned in this document. No particular manifest format is
preferred. For manifest interoperability, an EAT profile as defined
in Section 6, should be used to specify which manifest format(s) are
allowed.
$$Claims-Set-Claims //= (
manifests-label => manifests-type
)
manifests-type = [+ manifest-format]
manifest-format = [
content-type: coap-content-format,
content-format: JC< $manifest-body-json,
$manifest-body-cbor >
]
$manifest-body-cbor /= bytes .cbor untagged-coswid
$manifest-body-json /= base64-url-text
$manifest-body-cbor /= bytes .cbor SUIT_Envelope
$manifest-body-json /= base64-url-text
4.2.16. measurements (Measurements) Claim
The "measurements" claim contains descriptions, lists, evidence or
measurements of the software that exists on the entity or any other
measurable subsystem of the entity (e.g. hash of sections of a file
system or non-volatile memory). The defining characteristic of this
claim is that its contents are created by processes on the entity
that inventory, measure or otherwise characterize the software on the
entity. The contents of this claim do not originate from the
manufacturer of the measurable subsystem (e.g. developer of a
software library).
This claim can be a [RFC9393]. When the CoSWID format is used, it
MUST be an evidence CoSWID, not a payload CoSWID.
Formats other than CoSWID MAY be used. The identification of format
is by CoAP Content Format, the same as the "manifests" claim in
Section 4.2.15.
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$$Claims-Set-Claims //= (
measurements-label => measurements-type
)
measurements-type = [+ measurements-format]
measurements-format = [
content-type: coap-content-format,
content-format: JC< $measurements-body-json,
$measurements-body-cbor >
]
$measurements-body-cbor /= bytes .cbor untagged-coswid
$measurements-body-json /= base64-url-text
4.2.17. measres (Software Measurement Results) Claim
The "measres" claim is a general-purpose structure for reporting
comparison of measurements to expected reference values. This claim
provides a simple standard way to report the result of a comparison
as success, failure, fail to run, and absence.
It is the nature of measurement systems that they are specific to the
operating system, software and hardware of the entity that is being
measured. It is not possible to standardize what is measured and how
it is measured across platforms, OS's, software and hardware. The
recipient must obtain the information about what was measured and
what it indicates for the characterization of the security of the
entity from the provider of the measurement system. What this claim
provides is a standard way to report basic success or failure of the
measurement. In some use cases it is valuable to know if
measurements succeeded or failed in a general way even if the details
of what was measured is not characterized.
This claim MAY be generated by the verifier and sent to the relying
party. For example, it could be the results of the verifier
comparing the contents of the "measurements" claim, Section 4.2.16,
to reference values.
This claim MAY also be generated on the entity if the entity has the
ability for one subsystem to measure and evaluate another subsystem.
For example, a TEE might have the ability to measure the software of
the rich OS and may have the reference values for the rich OS.
Within an entity, attestation target or submodule, multiple results
can be reported. For example, it may be desirable to report the
results for measurements of the file system, chip configuration,
installed software, running software and so on.
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Note that this claim is not for reporting the overall result of a
verifier. It is solely for reporting the result of comparison to
reference values.
An individual measurement result (individual-result) is an array
consisting of two elements, an identifier of the measurement (result-
id) and an enumerated type of the result (result). Different
measurement systems will measure different things and perhaps measure
the same thing in different ways. It is up to each measurement
system to define identifiers (result-id) for the measurements it
reports.
Each individual measurement result is part of a group that may
contain many individual results. Each group has a text string that
names it, typically the name of the measurement scheme or system.
The claim itself consists of one or more groups.
The values for the results enumerated type are as follows:
1 -- comparison successful: Indicates successful comparison to
reference values.
2 -- comparison fail: The comparison was completed and did not
compare correctly to the reference values.
3 -- comparison not run: The comparison was not run. This includes
error conditions such as running out of memory.
4 -- measurement absent: The particular measurement was not
available for comparison.
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$$Claims-Set-Claims //= (
measurement-results-label =>
[ + measurement-results-group ] )
measurement-results-group = [
measurement-system: tstr,
measurement-results: [ + individual-result ]
]
individual-result = [
result-id: tstr / binary-data,
result: result-type,
]
result-type = comparison-successful /
comparison-fail /
comparison-not-run /
measurement-absent
comparison-successful = JC< "success", 1 >
comparison-fail = JC< "fail", 2 >
comparison-not-run = JC< "not-run", 3 >
measurement-absent = JC< "absent", 4 >
4.2.18. submods (Submodules)
Some devices are complex and have many subsystems. A mobile phone is
a good example. It may have subsystems for communications (e.g., Wi-
Fi and cellular), low-power audio and video playback, multiple
security-oriented subsystems like a TEE and a Secure Element, and
etc. The claims for a subsystem can be grouped together in a
submodule.
Submodules may be used in either evidence or attestation results.
Because system architecture will vary greatly from use case to use
case, there are no set requirements for what a submodule represents
either in evidence or in attestation results. Profiles, Section 6,
may wish to impose requirements. An attester that outputs evidence
with submodules should document the semantics it associates with
particular submodules for the verifier. Likewise, a verifier that
outputs attestation results with submodules should document the
semantics it associates with the submodules for the relying party.
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A submodule claim is a map that holds some number of submodules.
Each submodule is named by its label in the submodule claim map. The
value of each entry in a submodule may be a Claims-Set, nested token
or Detached-Submodule-Digest. This allows for the submodule to serve
as its own attester or not and allows for claims for each submodule
to be represented directly or indirectly, i.e., detached.
A submodule may include a submodule, allowing for arbitrary levels of
nesting. However, submodules do not inherit anything from the
containing token and must explicitly include all claims. Submodules
may contain claims that are present in any surrounding token or
submodule. For example, the top-level of the token may have a UEID,
a submodule may have a different UEID and a further subordinate
submodule may also have a UEID.
The following sub-sections define the three types for representing
submodules:
* A submodule Claims-Set
* The digest of a detached Claims-Set
* A nested token, which can be any EAT
The Submodule type definition and Nested-Token type definition vary
with the type of encoding. The definitions for CBOR-encoded EATs are
as follows:
Nested-Token = CBOR-Nested-Token
CBOR-Nested-Token =
JSON-Token-Inside-CBOR-Token /
CBOR-Token-Inside-CBOR-Token
CBOR-Token-Inside-CBOR-Token = bstr .cbor $EAT-CBOR-Tagged-Token
JSON-Token-Inside-CBOR-Token = tstr
$$Claims-Set-Claims //= (submods-label => { + text => Submodule })
Submodule = Claims-Set / CBOR-Nested-Token /
Detached-Submodule-Digest
The Submodule and Nested-Token definitions for JSON-encoded EATs is
as below. This difference in definitions vs. CBOR is necessary
because JSON has no tag mechanism and no byte string type to help
indicate the nested token is CBOR.
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Nested-Token = JSON-Selector
JSON-Selector = $JSON-Selector
$JSON-Selector /= [type: "JWT", nested-token: JWT-Message]
$JSON-Selector /= [type: "CBOR", nested-token: CBOR-Token-Inside-JSON-Token]
$JSON-Selector /= [type: "BUNDLE", nested-token: Detached-EAT-Bundle]
$JSON-Selector /= [type: "DIGEST", nested-token: Detached-Submodule-Digest]
CBOR-Token-Inside-JSON-Token = base64-url-text
$$Claims-Set-Claims //= (submods-label => { + text => Submodule })
Submodule = Claims-Set / JSON-Selector
The Detached-Submodule-Digest type is defined as follows:
Detached-Submodule-Digest = [
hash-algorithm : text / int,
digest : binary-data
]
Nested tokens can be one of three types as defined in this document
or types standardized in follow-on documents (e.g., [UCCS]). Nested
tokens are the only mechanism by which JSON can be embedded in CBOR
and vice versa.
The addition of further types is accomplished by augmenting the $EAT-
CBOR-Tagged-Token socket or the $JSON-Selector socket.
When decoding a JSON-encoded EAT, the type of submodule is determined
as follows. A JSON object indicates the submodule is a Claims-Set.
In all other cases, it is a JSON-Selector, which is an array of two
elements that indicates whether the submodule is a nested token or a
Detached-Submodule-Digest.The first element in the array indicates
the type present in the second element. If the value is “JWT”,
“CBOR”, “BUNDLE” or a future-standardized token types, e.g., [UCCS],
the submodule is a nested token of the indicated type, i.e., JWT-
Message, CBOR-Token-Inside-JSON-Token, Detached-EAT-Bundle, or a
future type. If the value is "DIGEST", the submodule is a Detached-
Submodule-Digest. Any other value indicates a standardized extension
to this specification.
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When decoding a CBOR-encoded EAT, the CBOR item type indicates the
type of the submodule as follows. A map indicates a CBOR-encoded
submodule Claims-Set. An array indicates a CBOR-encoded Detached-
Submodule-Digest. A byte string indicates a CBOR-encoded CBOR-
Nested-Token. A text string indicates a JSON-encoded JSON-Selector.
Where JSON-Selector is used in a CBOR-encoded EAT, the "DIGEST" type
and corresponding Detached-Submodule-Digest type MUST NOT be used.
The type of a CBOR-encoded nested token is always determined by the
CBOR tag encountered after the byte string wrapping is removed in a
CBOR-encoded enclosing token or after the base64 wrapping is removed
in JSON-encoded enclosing token.
The type of a JSON-encoded nested token is always determined by the
string name in JSON-Selector and is always “JWT”, “BUNDLE” or a new
name standardized outside this document for a further type (e.g.,
“UCCS”). This string name may also be “CBOR” to indicate the nested
token is CBOR-encoded.
"JWT": The second array item MUST be a JWT formatted according to
[RFC7519]
"CBOR": The second array item MUST be some base64url-encoded CBOR
that is a tag, typically a CWT or CBOR-encoded detached EAT bundle
"BUNDLE": The second array item MUST be a JSON-encoded Detached EAT
Bundle as defined in this document.
"DIGEST": The second array item MUST be a JSON-encoded Detached-
Submodule-Digest as defined in this document.
As noted elsewhere, additional EAT types may be defined by a
standards action. New type specifications MUST address the
integration of the new type into the Submodule claim type for
submodules.
4.2.18.1. Submodule Claims-Set
The Claims-Set type provides a means of representing claims from a
submodule that does not have its own attesting environment, i.e., it
has no keys distinct from the attester producing the surrounding
token. Claims are represented as a Claims-Set. Submodule claims
represented in this way are secured by the same mechanism as the
enclosing token (e.g., it is signed by the same attestation key).
The encoding of a submodule Claims-Set MUST be the same as the
encoding as the surrounding EAT, e.g., all submodule Claims-Sets in a
CBOR-encoded token must be CBOR-encoded.
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4.2.18.2. Detached Submodule Digest
The Detached-Submodule-Digest type is similar to a submodule Claims-
Set, except a digest of the Claims-Set is included in the claim with
the Claims-Set contents conveyed separately. The separately-conveyed
Claims-Set is called a detached claims set. The input to the digest
algorithm is directly the CBOR or JSON-encoded Claims-Set for the
submodule. There is no byte-string wrapping or base 64 encoding.
The data type for this type of submodule is an array consisting of
two data items: an algorithm identifier and a byte string containing
the digest. The hash algorithm identifier is always from the COSE
Algorithm registry, [IANA.COSE.Algorithms]. Either the integer or
string identifier may be used. The hash algorithm identifier is
never from the JOSE Algorithm registry.
A detached EAT bundle, described in Section 5, may be used to convey
detached claims sets and the EAT containing the corresponding
detached digests. EAT, however, doesn't require use of a detached
EAT bundle. Any other protocols may be used to convey detached
claims sets and the EAT containing the corresponding detached
digests. Detached Claims-Sets must not be modified in transit, else
validation will fail.
4.2.18.3. Nested Tokens
The CBOR-Nested-Token and JSON-Selector types provide a means of
representing claims from a submodule that has its own attesting
environment, i.e., it has keys distinct from the attester producing
the surrounding token. Claims are represented in a signed EAT token.
Inclusion of a signed EAT as a claim cryptographically binds the EAT
to the surrounding token. If it was conveyed in parallel with the
surrounding token, there would be no such binding and attackers could
substitute a good attestation from another device for the attestation
of an errant subsystem.
A nested token need not use the same encoding as the enclosing token.
This enables composite devices to be built without regards to the
encoding used by components. Thus, a CBOR-encoded EAT can have a
JSON-encoded EAT as a nested token and vice versa.
4.3. Claims Describing the Token
The claims in this section provide meta data about the token they
occur in. They do not describe the entity. They may appear in
evidence or attestation results.
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4.3.1. iat (Timestamp) Claim
The "iat" claim defined in CWT and JWT is used to indicate the date-
of-creation of the token, the time at which the claims are collected
and the token is composed and signed.
The data for some claims may be held or cached for some period of
time before the token is created. This period may be long, even
days. Examples are measurements taken at boot or a geographic
position fix taken the last time a satellite signal was received.
There are individual timestamps associated with these claims to
indicate their age is older than the "iat" timestamp.
CWT allows the use of floating-point for this claim. EAT disallows
the use of floating-point. An EAT token MUST NOT contain an "iat"
claim in floating-point format. Any recipient of a token with a
floating-point format "iat" claim MUST consider it an error.
A 64-bit integer representation of the CBOR epoch-based time
[RFC8949] used by this claim can represent a range of +/- 500 billion
years, so the only point of a floating-point timestamp is to have
precession greater than one second. This is not needed for EAT.
4.3.2. eat_profile (EAT Profile) Claim
See Section 6 for the detailed description of an EAT profile.
The "eat_profile" claim identifies an EAT profile by either a Uniform
Resource Identifier (URI) or an Object Identifier (OID). Typically,
the URI will reference a document describing the profile. An OID is
just a unique identifier for the profile. It may exist anywhere in
the OID tree. There is no requirement that the named document be
publicly accessible. The primary purpose of the "eat_profile" claim
is to uniquely identify the profile even if it is a private profile.
The OID is always absolute and never relative.
See Section 7.2.1 for OID and URI encoding.
$$Claims-Set-Claims //= (profile-label => general-uri / general-oid)
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4.3.3. intuse (Intended Use) Claim
EATs may be employed in the context of several different
applications. The "intuse" claim provides an indication to an EAT
consumer about the intended usage of the token. This claim can be
used as a way for an application using EAT to internally distinguish
between different ways it utilizes EAT. 5 possible values for
"intuse" are currently defined, but an IANA registry can be created
in the future to extend these values based on new use cases of EAT.
1 -- Generic: Generic attestation describes an application where the
EAT consumer requires the most up-to-date security assessment of
the attesting entity. It is expected that this is the most
commonly-used application of EAT.
2-- Registration: Entities that are registering for a new service
may be expected to provide an attestation as part of the
registration process. This "intuse" setting indicates that the
attestation is not intended for any use but registration.
3 -- Provisioning: Entities may be provisioned with different values
or settings by an EAT consumer. Examples include key material or
device management trees. The consumer may require an EAT to
assess entity security state of the entity prior to provisioning.
4 -- Certificate Issuance: Certification Authorities (CAs) may
require attestation results (which in a background check model
might require receiving evidence to be passed to a verifier) to
make decisions about the issuance of certificates. An EAT may be
used as part of the certificate signing request (CSR).
5 -- Proof-of-Possession: An EAT consumer may require an attestation
as part of an accompanying proof-of-possession (PoP) application.
More precisely, a PoP transaction is intended to provide to the
recipient cryptographically-verifiable proof that the sender has
possession of a key. This kind of attestation may be necessary to
verify the security state of the entity storing the private key
used in a PoP application.
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$$Claims-Set-Claims //= ( intended-use-label => intended-use-type )
intended-use-type = generic /
registration /
provisioning /
csr /
pop
generic = JC< "generic", 1 >
registration = JC< "registration", 2 >
provisioning = JC< "provisioning", 3 >
csr = JC< "csr", 4 >
pop = JC< "pop", 5 >
5. Detached EAT Bundles
A detached EAT bundle is a message to convey an EAT plus detached
claims sets secured by that EAT. It is a top-level message like a
CWT or JWT. It can occur in any place that a CWT or JWT occurs, for
example as a submodule nested token as defined in Section 4.2.18.3.
A detached EAT bundle may be either CBOR or JSON-encoded.
A detached EAT bundle consists of two parts.
The first part is an encoded EAT as follows:
* MUST have at least one submodule that is a detached submodule
digest as defined in Section 4.2.18.2
* MAY be either CBOR or JSON-encoded and doesn't have to the the
same as the encoding of the bundle
* MAY be a CWT, or JWT or some future-defined token type, but MUST
NOT be a detached EAT bundle
* MUST be authenticity and integrity protected
The same mechanism for distinguishing the type for nested token
submodules is employed here.
The second part is a map/object as follows:
* MUST be a Claims-Set
* MUST use the same encoding as the bundle
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* MUST be wrapped in a byte string when the encoding is CBOR and be
base64url-encoded when the encoding is JSON
For CBOR-encoded detached EAT bundles, tag TBD602 can be used to
identify it. The standard rules apply for use or non-use of a tag.
When it is sent as a submodule, it is always sent as a tag to
distinguish it from the other types of nested tokens.
The digests of the detached claims sets are associated with detached
Claims-Sets by label/name. It is up to the constructor of the
detached EAT bundle to ensure the names uniquely identify the
detached claims sets. Since the names are used only in the detached
EAT bundle, they can be very short, perhaps one byte.
BUNDLE-Messages = BUNDLE-Tagged-Message / BUNDLE-Untagged-Message
BUNDLE-Tagged-Message = #6.TBD602(BUNDLE-Untagged-Message)
BUNDLE-Untagged-Message = Detached-EAT-Bundle
Detached-EAT-Bundle = [
main-token : Nested-Token,
detached-claims-sets: {
+ tstr => JC<json-wrapped-claims-set,
cbor-wrapped-claims-set>
}
]
json-wrapped-claims-set = base64-url-text
cbor-wrapped-claims-set = bstr .cbor Claims-Set
6. Profiles
EAT makes normative use of CBOR, JSON, COSE, JOSE, CWT and JWT. Most
of these have implementation options to accommodate a range of use
cases.
For example, COSE doesn't require a particular set of cryptographic
algorithms so as to accommodate different usage scenarios and
evolution of algorithms over time. Section 10 of [RFC9052] describes
the profiling considerations for COSE.
The use of encryption is optional for both CWT and JWT. Section 8 of
[RFC7519] describes implementation requirement and recommendations
for JWT.
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Similarly, CBOR provides indefinite length encoding, which is not
commonly used, but valuable for very constrained devices. For EAT
itself, in a particular use case some claims will be used and others
will not. Section 4 of [RFC8949] describes serialization
considerations for CBOR.
For example a mobile phone use case may require the device make and
model, and prohibit UEID and location for privacy reasons. The
general EAT standard retains all this flexibility because it too is
aimed to accommodate a broad range of use cases.
It is necessary to explicitly narrow these implementation options to
guarantee interoperability. EAT chooses one general and explicit
mechanism, the profile, to indicate the choices made for these
implementation options for all aspects of the token.
Below is a list of the various issues that should be addressed by a
profile.
The "eat_profile" claim in Section 4.3.2 provides a unique identifier
for the profile a particular token uses.
A profile can apply to evidence or to attestation results or both.
6.1. Format of a Profile Document
A profile document doesn't have to be in any particular format. It
may be simple text, something more formal or a combination.
A profile may define, and possibly register, one or more new claims
if needed. A profile may also reuse one or more already defined
claims, either as-is or with values constrained to a subset or
subrange.
6.2. Full and Partial Profiles
For a "full" profile, the receiver will be able to decode and verify
every possible EAT sent when a sender and receiver both adhere to it.
For a "partial" profile, there are still some protocol options left
undecided.
For example, a profile that allows the use of signing algorithms by
the sender that the receiver is not required to support is a partial
profile. The sender might choose a signing algorithm that some
receivers don't support.
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Full profiles MUST be complete such that a complying receiver can
decode, verify and check for freshness every EAT created by a
complying sender. A full profile MAY or MAY NOT require the receiver
to fully handle every claim in an EAT from a complying sender.
Profile specifications may assume the receiver has access to the
necessary verification keys or may go into specific detail on the
means to access verification keys.
The "eat_profile" claim MUST NOT be used to identify partial
profiles.
While fewer profiles are preferrable, sometimes several may be needed
for a use case. One approach to handling variation in devices might
be to define several full profiles that are variants of each other.
It is relatively easy and inexpensive to define profiles as they
don't have to be standards track and don't have to be registered
anywhere. For example, flexibility for post-quantum algorithms can
be handled as follows. First, define a full profile for a set of
non-post-quantum algorithms for current use. Then, when post-quantum
algorithms are settled, define another full profile derived from the
first.
6.3. List of Profile Issues
The following is a list of EAT, CWT, JWT, COSE, JOSE and CBOR options
that a profile should address.
6.3.1. Use of JSON, CBOR or both
A profile should specify whether CBOR, JSON or both may be sent. A
profile should specify that the receiver can accept all encodings
that the sender is allowed to send.
This should be specified for the top-level and all nested tokens.
For example, a profile might require all nested tokens to be of the
same encoding of the top level token.
6.3.2. CBOR Map and Array Encoding
A profile should specify whether definite-length arrays/maps,
indefinite-length arrays/maps or both may be sent. A profile should
specify that the receiver be able to accept all length encodings that
the sender is allowed to send.
This applies to individual EAT claims, CWT and COSE parts of the
implementation.
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For most use cases, specifying that only definite-length arrays/maps
may be sent is suitable.
6.3.3. CBOR String Encoding
A profile should specify whether definite-length strings, indefinite-
length strings or both may be sent. A profile should specify that
the receiver be able to accept all types of string encodings that the
sender is allowed to send.
For most use cases, specifying that only definite-length strings may
be sent is suitable.
6.3.4. CBOR Preferred Serialization
A profile should specify whether or not CBOR preferred serialization
must be sent or not. A profile should specify the receiver be able
to accept preferred and/or non-preferred serialization so it will be
able to accept anything sent by the sender.
6.3.5. CBOR Tags
The profile should specify whether the token should be a CWT Tag or
not.
When COSE protection is used, the profile should specify whether COSE
tags are used or not. Note that RFC 8392 requires COSE tags be used
in a CWT tag.
Often a tag is unnecessary because the surrounding or carrying
protocol identifies the object as an EAT.
6.3.6. COSE/JOSE Protection
COSE and JOSE have several options for signed, MACed and encrypted
messages. JWT may use the JOSE NULL protection option. It is
possible to implement no protection, sign only, MAC only, sign then
encrypt and so on. All combinations allowed by COSE, JOSE, JWT, and
CWT are allowed by EAT.
A profile should specify all signing, encryption and MAC message
formats that may be sent. For example, a profile might allow only
COSE_Sign1 to be sent. For another example, a profile might allow
COSE_Sign and COSE_Encrypt to be sent to carry multiple signatures
for post quantum cryptography and to use encryption to provide
confidentiality.
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A profile should specify the receiver accepts all message formats
that are allowed to be sent.
When both signing and encryption are allowed, a profile should
specify which is applied first.
6.3.7. COSE/JOSE Algorithms
See the section on "Application Profiling Considerations" in
[RFC9052] for a discussion on selection of cryptographic algorithms
and related issues.
The profile MAY require the protocol or system using EAT provide an
algorithm negotiation mechanism.
If not, The profile document should list a set of algorithms for each
COSE and JOSE message type allowed by the profile per Section 6.3.6.
The verifier should implement all of them. The attester may
implement any of them it wishes, possibly just one for each message
type.
If detached submodule digests are used the profile should address the
determination of the hash algorithm(s) for the digests.
6.3.8. Detached EAT Bundle Support
A profile should specify whether or not a detached EAT bundle
(Section 5) can be sent. A profile should specify that a receiver be
able to accept a detached EAT bundle if the sender is allowed to send
it.
6.3.9. Key Identification
A profile should specify what must be sent to identify the
verification, decryption or MAC key or keys. If multiple methods of
key identification may be sent, a profile should require the receiver
support them all.
Appendix F describes a number of methods for identifying verification
keys. When encryption is used, there are further considerations. In
some cases key identification may be very simple and in others
involve multiple components. For example, it may be simple through
use of COSE key ID or it may be complex through use of an X.509
certificate hierarchy.
While not always possible, a profile should specify or make reference
to, a full end-end specification for key identification. For
example, a profile should specify in full detail how COSE key IDs are
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to be created, their lifecycle and such rather than just specifying
that a COSE key ID be used. For example, a profile should specify
the full details of an X.509 hierarchy including extension
processing, algorithms allowed and so on rather than just saying
X.509 certificates are used.
6.3.10. Endorsement Identification
Similar to, or perhaps the same as verification key identification,
the profile may wish to specify how endorsements are to be
identified. However note that endorsement identification is
optional, whereas key identification is not.
6.3.11. Freshness
Security considerations, see Section 9.3, require a mechanism to
provide freshness. This may be the EAT nonce claim in Section 4.1,
or some claim or mechanism defined outside this document. The
section on freshness in [RFC9334] describes several options. A
profile should specify which freshness mechanism or mechanisms can be
used.
If the EAT nonce claim is used, a profile should specify whether
multiple nonces may be sent. If a profile allows multiple nonces to
be sent, it should require the receiver to process multiple nonces.
6.3.12. Claims Requirements
A profile may define new claims that are not defined in this
document.
This document requires an EAT receiver must accept tokens with claims
it does not understand. A profile for a specific use case may
reverse this and allow a receiver to reject tokens with claims it
does not understand. A profile for a specific use case may specify
that specific claims are prohibited.
A profile for a specific use case may modify this and specify that
some claims are required.
A profile may constrain the definition of claims that are defined in
this document or elsewhere. For example, a profile may require the
EAT nonce be a certain length or the "location" claim always include
the altitude.
Some claims are "pluggable" in that they allow different formats for
their content. The "manifests" claim (Section 4.2.15) along with the
measurement and "measurements" (Section 4.2.16) claims are examples
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of this, allowing the use of CoSWID, SUIT Manifest and other formats.
A profile should specify which formats are allowed to be sent, with
the assumption that the corresponding CoAP content types have been
registered. A profile should require the receiver to accept all
formats that are allowed to be sent.
Further, if there is variation within a format that is allowed, the
profile should specify which variations can be sent. For example,
there are variations in the CoSWID format. A profile that require
the receiver to accept all variations that are allowed to be sent.
6.4. The Constrained Device Standard Profile
It is anticipated that there will be many profiles defined for EAT
for many different use cases. This section gives a normative
definition of one profile that is good for many constrained device
use cases.
The identifier for this profile is "urn:ietf:rfc:rfcTBD".
// RFC Editor: please replace rfcTBD with this RFC number and remove
// this note.
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+================+=============================================+
| Issue | Profile Definition |
+================+=============================================+
| CBOR/JSON | CBOR MUST be used |
+----------------+---------------------------------------------+
| CBOR Encoding | Definite length maps and arrays MUST be |
| | used |
+----------------+---------------------------------------------+
| CBOR Encoding | Definite length strings MUST be used |
+----------------+---------------------------------------------+
| CBOR | Preferred serialization MUST be used |
| Serialization | |
+----------------+---------------------------------------------+
| COSE | COSE_Sign1 MUST be used |
| Protection | |
+----------------+---------------------------------------------+
| Algorithms | The receiver MUST accept ES256, ES384 and |
| | ES512; the sender MUST send one of these |
+----------------+---------------------------------------------+
| Detached EAT | Detached EAT bundles MUST not be sent with |
| Bundle Usage | this profile |
+----------------+---------------------------------------------+
| Verification | Either the COSE kid or the UEID MUST be |
| Key | used to identify the verification key. If |
| Identification | both are present, the kid takes precedence. |
| | (It is assumed the receiver has access to a |
| | database of trusted verification keys which |
| | allows lookup of the verification key ID; |
| | the key format and means of distribution |
| | are beyond the scope of this profile) |
+----------------+---------------------------------------------+
| Endorsements | This profile contains no endorsement |
| | identifier |
+----------------+---------------------------------------------+
| Freshness | A new single unique nonce MUST be used for |
| | every token request |
+----------------+---------------------------------------------+
| Claims | No requirement is made on the presence or |
| | absence of claims other than requiring an |
| | EAT nonce. As per general EAT rules, the |
| | receiver MUST NOT error out on claims it |
| | doesn't understand. |
+----------------+---------------------------------------------+
Table 2: Constrained Device Profile Definition
Any profile with different requirements than those above MUST have a
different profile identifier.
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Note that many claims can be present for tokens conforming to this
profile, even claims not defined in this document. Note also that
even slight deviation from the above requirements is considered a
different profile that MUST have a different identifier. For
example, if a kid (key identifier) or UEID is not used for key
identification, it is not in conformance with this profile. For
another example, requiring the presence of some claim is also not in
conformance and requires another profile.
Derivations of this profile are encouraged. For example another
profile may be simply defined as The Constrained Device Standard
Profile plus the requirement for the presence of claim xxxx and claim
yyyy.
7. Encoding and Collected CDDL
An EAT is fundamentally defined using CDDL. This document specifies
how to encode the CDDL in CBOR or JSON. Since CBOR can express some
things that JSON can't (e.g., tags) or that are expressed differently
(e.g., labels) there is some CDDL that is specific to the encoding.
7.1. Claims-Set and CDDL for CWT and JWT
CDDL was not used to define CWT or JWT. It was not available at the
time.
This document defines CDDL for both CWT and JWT. This document does
not change the encoding or semantics of anything in a CWT or JWT.
A Claims-Set is the central data structure for EAT, CWT and JWT. It
holds all the claims and is the structure that is secured by signing
or other means. It is not possible to define EAT, CWT, or JWT in
CDDL without it. The CDDL definition of Claims-Set here is
applicable to EAT, CWT and JWT.
This document specifies how to encode a Claims-Set in CBOR or JSON.
With the exception of nested tokens and some other externally defined
structures (e.g., SWIDs) an entire Claims-Set must be in encoded in
either CBOR or JSON, never a mixture.
CDDL for the seven claims defined by [RFC8392] and [RFC7519] is
included here.
7.2. Encoding Data Types
This makes use of the types defined in [RFC8610] Appendix D, Standard
Prelude.
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7.2.1. Common Data Types
time-int is identical to the epoch-based time, but disallows
floating-point representation.
For CBOR-encoded tokens, OIDs are specified using the CDDL type name
"oid" from [RFC9090]. They are encoded without the tag number. For
JSON-encoded tokens, OIDs are a text string in the common form of
"nn.nn.nn...".
Unless expliclity indicated, URIs are not the URI tag defined in
[RFC8949]. They are just text strings that contain a URI conforming
to the format defined in [RFC3986].
time-int = #6.1(int)
binary-data = JC< base64-url-text, bstr>
base64-url-text = tstr .regexp "[A-Za-z0-9_-]+"
general-oid = JC< json-oid, ~oid >
json-oid = tstr .regexp "([0-2])((\\.0)|(\\.[1-9][0-9]*))*"
general-uri = JC< text, ~uri >
coap-content-format = uint .le 65535
7.2.2. JSON Interoperability
JSON should be encoded per [RFC8610], Appendix E. In addition, the
following CDDL types are encoded in JSON as follows:
* bstr -- MUST be base64url-encoded
* time -- MUST be encoded as NumericDate as described in Section 2
of [RFC7519].
* string-or-uri -- MUST be encoded as StringOrURI as described in
Section 2 of [RFC7519].
* uri -- MUST be a URI [RFC3986].
* oid -- MUST be encoded as a string using the well established
dotted-decimal notation (e.g., the text "1.2.250.1") [RFC2252].
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The CDDL generic "JC<>" is used in most places where there is a
variance between CBOR and JSON. The first argument is the CDDL for
JSON and the second is CDDL for CBOR.
7.2.3. Labels
Most map labels, Claims-Keys, Claim-Names and enumerated-type values
are integers for CBOR-encoded tokens and strings for JSON-encoded
tokens. When this is the case the "JC<>" CDDL construct is used to
give both the integer and string values.
7.2.4. CBOR Interoperability
CBOR allows data items to be serialized in more than one form to
accommodate a variety of use cases. This is addressed in Section 6.
7.3. Collected CDDL
7.3.1. Payload CDDL
This CDDL defines all the EAT Claims that are added to the main
definition of a Claim-Set in Appendix D. Claims-Set is the payload
for CWT, JWT and potentially other token types. This is for both
CBOR and JSON. When there is variation between CBOR and JSON, the
JC<> CDDL generic defined in Appendix D. Note that the JC<> generic
uses the CDDL ".feature" control operator defined in [RFC9165].
This CDDL uses, but doesn't define Submodule or nested tokens because
the definition for these types varies between CBOR and JSON and the
JC<> generic can't be used to define it. The submodule claim is the
one place where a CBOR token can be nested inside a JSON token and
vice versa. Encoding-specific definitions are provided in the
following sections.
time-int = #6.1(int)
binary-data = JC< base64-url-text, bstr>
base64-url-text = tstr .regexp "[A-Za-z0-9_-]+"
general-oid = JC< json-oid, ~oid >
json-oid = tstr .regexp "([0-2])((\\.0)|(\\.[1-9][0-9]*))*"
general-uri = JC< text, ~uri >
coap-content-format = uint .le 65535
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$$Claims-Set-Claims //=
(nonce-label => nonce-type / [ 2* nonce-type ])
nonce-type = JC< tstr .size (8..88), bstr .size (8..64)>
$$Claims-Set-Claims //= (ueid-label => ueid-type)
ueid-type = JC<base64-url-text .size (10..44) , bstr .size (7..33)>
$$Claims-Set-Claims //= (sueids-label => sueids-type)
sueids-type = {
+ tstr => ueid-type
}
$$Claims-Set-Claims //= (
oemid-label => oemid-pen / oemid-ieee / oemid-random
)
oemid-pen = int
oemid-ieee = JC<oemid-ieee-json, oemid-ieee-cbor>
oemid-ieee-cbor = bstr .size 3
oemid-ieee-json = base64-url-text .size 4
oemid-random = JC<oemid-random-json, oemid-random-cbor>
oemid-random-cbor = bstr .size 16
oemid-random-json = base64-url-text .size 24
$$Claims-Set-Claims //= (
hardware-version-label => hardware-version-type
)
hardware-version-type = [
version: tstr,
? scheme: $version-scheme
]
$$Claims-Set-Claims //= (
hardware-model-label => hardware-model-type
)
hardware-model-type = JC<base64-url-text .size (4..44),
bytes .size (1..32)>
$$Claims-Set-Claims //= ( sw-name-label => tstr )
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$$Claims-Set-Claims //= (sw-version-label => sw-version-type)
sw-version-type = [
version: tstr
? scheme: $version-scheme
]
$$Claims-Set-Claims //= (oem-boot-label => bool)
$$Claims-Set-Claims //= ( debug-status-label => debug-status-type )
debug-status-type = ds-enabled /
disabled /
disabled-since-boot /
disabled-permanently /
disabled-fully-and-permanently
ds-enabled = JC< "enabled", 0 >
disabled = JC< "disabled", 1 >
disabled-since-boot = JC< "disabled-since-boot", 2 >
disabled-permanently = JC< "disabled-permanently", 3 >
disabled-fully-and-permanently =
JC< "disabled-fully-and-permanently", 4 >
$$Claims-Set-Claims //= (location-label => location-type)
location-type = {
latitude => number,
longitude => number,
? altitude => number,
? accuracy => number,
? altitude-accuracy => number,
? heading => number,
? speed => number,
? timestamp => ~time-int,
? age => uint
}
latitude = JC< "latitude", 1 >
longitude = JC< "longitude", 2 >
altitude = JC< "altitude", 3 >
accuracy = JC< "accuracy", 4 >
altitude-accuracy = JC< "altitude-accuracy", 5 >
heading = JC< "heading", 6 >
speed = JC< "speed", 7 >
timestamp = JC< "timestamp", 8 >
age = JC< "age", 9 >
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$$Claims-Set-Claims //= (uptime-label => uint)
$$Claims-Set-Claims //= (boot-seed-label => binary-data)
$$Claims-Set-Claims //= (boot-count-label => uint)
$$Claims-Set-Claims //= ( intended-use-label => intended-use-type )
intended-use-type = generic /
registration /
provisioning /
csr /
pop
generic = JC< "generic", 1 >
registration = JC< "registration", 2 >
provisioning = JC< "provisioning", 3 >
csr = JC< "csr", 4 >
pop = JC< "pop", 5 >
$$Claims-Set-Claims //= (
dloas-label => [ + dloa-type ]
)
dloa-type = [
dloa_registrar: general-uri
dloa_platform_label: text
? dloa_application_label: text
]
$$Claims-Set-Claims //= (profile-label => general-uri / general-oid)
$$Claims-Set-Claims //= (
manifests-label => manifests-type
)
manifests-type = [+ manifest-format]
manifest-format = [
content-type: coap-content-format,
content-format: JC< $manifest-body-json,
$manifest-body-cbor >
]
$manifest-body-cbor /= bytes .cbor untagged-coswid
$manifest-body-json /= base64-url-text
$manifest-body-cbor /= bytes .cbor SUIT_Envelope
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$manifest-body-json /= base64-url-text
$$Claims-Set-Claims //= (
measurements-label => measurements-type
)
measurements-type = [+ measurements-format]
measurements-format = [
content-type: coap-content-format,
content-format: JC< $measurements-body-json,
$measurements-body-cbor >
]
$measurements-body-cbor /= bytes .cbor untagged-coswid
$measurements-body-json /= base64-url-text
$$Claims-Set-Claims //= (
measurement-results-label =>
[ + measurement-results-group ] )
measurement-results-group = [
measurement-system: tstr,
measurement-results: [ + individual-result ]
]
individual-result = [
result-id: tstr / binary-data,
result: result-type,
]
result-type = comparison-successful /
comparison-fail /
comparison-not-run /
measurement-absent
comparison-successful = JC< "success", 1 >
comparison-fail = JC< "fail", 2 >
comparison-not-run = JC< "not-run", 3 >
measurement-absent = JC< "absent", 4 >
Detached-Submodule-Digest = [
hash-algorithm : text / int,
digest : binary-data
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]
BUNDLE-Messages = BUNDLE-Tagged-Message / BUNDLE-Untagged-Message
BUNDLE-Tagged-Message = #6.TBD602(BUNDLE-Untagged-Message)
BUNDLE-Untagged-Message = Detached-EAT-Bundle
Detached-EAT-Bundle = [
main-token : Nested-Token,
detached-claims-sets: {
+ tstr => JC<json-wrapped-claims-set,
cbor-wrapped-claims-set>
}
]
json-wrapped-claims-set = base64-url-text
cbor-wrapped-claims-set = bstr .cbor Claims-Set
nonce-label = JC< "eat_nonce", 10 >
ueid-label = JC< "ueid", 256 >
sueids-label = JC< "sueids", 257 >
oemid-label = JC< "oemid", 258 >
hardware-model-label = JC< "hwmodel", 259 >
hardware-version-label = JC< "hwversion", 260 >
oem-boot-label = JC< "oemboot", 262 >
debug-status-label = JC< "dbgstat", 263 >
location-label = JC< "location", 264 >
profile-label = JC< "eat_profile",265 >
submods-label = JC< "submods", 266 >
uptime-label = JC< "uptime", TBD >
boot-seed-label = JC< "bootseed", TBD >
intended-use-label = JC< "intuse", TBD >
dloas-label = JC< "dloas", TBD >
sw-name-label = JC< "swname", TBD >
sw-version-label = JC< "swversion", TBD >
manifests-label = JC< "manifests", TBD >
measurements-label = JC< "measurements", TBD >
measurement-results-label = JC< "measres" , TBD >
boot-count-label = JC< "bootcount", TBD >
7.3.2. CBOR-Specific CDDL
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EAT-CBOR-Token = $EAT-CBOR-Tagged-Token / $EAT-CBOR-Untagged-Token
$EAT-CBOR-Tagged-Token /= CWT-Tagged-Message
$EAT-CBOR-Tagged-Token /= BUNDLE-Tagged-Message
$EAT-CBOR-Untagged-Token /= CWT-Untagged-Message
$EAT-CBOR-Untagged-Token /= BUNDLE-Untagged-Message
Nested-Token = CBOR-Nested-Token
CBOR-Nested-Token =
JSON-Token-Inside-CBOR-Token /
CBOR-Token-Inside-CBOR-Token
CBOR-Token-Inside-CBOR-Token = bstr .cbor $EAT-CBOR-Tagged-Token
JSON-Token-Inside-CBOR-Token = tstr
$$Claims-Set-Claims //= (submods-label => { + text => Submodule })
Submodule = Claims-Set / CBOR-Nested-Token /
Detached-Submodule-Digest
7.3.3. JSON-Specific CDDL
EAT-JSON-Token = $EAT-JSON-Token-Formats
$EAT-JSON-Token-Formats /= JWT-Message
$EAT-JSON-Token-Formats /= BUNDLE-Untagged-Message
Nested-Token = JSON-Selector
JSON-Selector = $JSON-Selector
$JSON-Selector /= [type: "JWT", nested-token: JWT-Message]
$JSON-Selector /= [type: "CBOR", nested-token: CBOR-Token-Inside-JSON-Token]
$JSON-Selector /= [type: "BUNDLE", nested-token: Detached-EAT-Bundle]
$JSON-Selector /= [type: "DIGEST", nested-token: Detached-Submodule-Digest]
CBOR-Token-Inside-JSON-Token = base64-url-text
$$Claims-Set-Claims //= (submods-label => { + text => Submodule })
Submodule = Claims-Set / JSON-Selector
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8. Privacy Considerations
Certain EAT claims can be used to track the owner of an entity;
therefore, implementations should consider privacy-preserving options
dependent on the usage of the EAT. For example, the location claim
might be suppressed in EATs sent to unauthenticated consumers.
8.1. UEID and SUEID Privacy Considerations
A UEID is usually not privacy-preserving. Relying parties receiving
tokens that happen to be from a particular entity will be able to
know the tokens are from the same entity and be able to identify the
entity issuing those tokens.
Thus the use of the claim may violate privacy policies. In other
usage situations a UEID will not be allowed for certain products like
browsers that give privacy for the end user. It will often be the
case that tokens will not have a UEID for these reasons.
An SUEID is also usually not privacy-preserving. In some cases it
may have fewer privacy issues than a UEID depending on when and how
and when it is generated.
There are several strategies that can be used to still be able to put
UEIDs and SUEIDs in tokens:
* The entity obtains explicit permission from the user of the entity
to use the UEID/SUEID. This may be through a prompt. It may also
be through a license agreement. For example, agreements for some
online banking and brokerage services might already cover use of a
UEID/SUEID.
* The UEID/SUEID is used only in a particular context or particular
use case. It is used only by one relying party.
* The entity authenticates the relying party and generates a derived
UEID/SUEID just for that particular relying party. For example,
the relying party could prove their identity cryptographically to
the entity, then the entity generates a UEID just for that relying
party by hashing a proofed relying party ID with the main entity
UEID/SUEID.
Note that some of these privacy preservation strategies result in
multiple UEIDs and SUEIDs per entity. Each UEID/SUEID is used in a
different context, use case or system on the entity. However, from
the view of the relying party, there is just one UEID and it is still
globally universal across manufacturers.
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8.2. Location Privacy Considerations
Geographic location is most always considered personally identifiable
information. Implementers should consider laws and regulations
governing the transmission of location data from end user devices to
servers and services. Implementers should consider using location
management facilities offered by the operating system on the entity
generating the attestation. For example, many mobile phones prompt
the user for permission before sending location data.
8.3. Boot Seed Privacy Considerations
The "bootseed" claim is effectively a stable entity identifier within
a given boot epoch. Therefore, it is not suitable for use in
attestation schemes that are privacy-preserving.
8.4. Replay Protection and Privacy
EAT defines the EAT nonce claim for replay protection and token
freshness. The nonce claim is based on a value usually derived
remotely (outside of the entity). This claim might be used to
extract and convey personally identifying information either
inadvertently or by intention. For instance, an implementor may
choose a nonce equivalent to a username associated with the device
(e.g., account login). If the token is inspected by a 3rd-party then
this information could be used to identify the source of the token or
an account associated with the token. To avoid the conveyance of
privacy-related information in the nonce claim, it should be derived
using a salt that originates from a true and reliable random number
generator or any other source of randomness that would still meet the
target system requirements for replay protection and token freshness.
9. Security Considerations
The security considerations provided in Section 8 of [RFC8392] and
Section 11 of [RFC7519] apply to EAT in its CWT and JWT form,
respectively. Moreover, Chapter 12 of [RFC9334] is also applicable
to implementations of EAT. In addition, implementors should consider
the following.
9.1. Claim Trustworthiness
This specification defines semantics for each claim. It does not
require any particular level of security in the implementation of the
claims or even the attester itself. Such specification is far beyond
the scope of this document which is about a message format not the
security level of an implementation.
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The receiver of an EAT comes to know the trustworthiness of the
claims in it by understanding the implementation made by the attester
vendor and/or understanding the checks and processing performed by
the verifier.
For example, this document says that a UEID is permanent and that it
must not change, but it doesn't say what degree of attack to change
it must be defended.
The degree of security will vary from use case to use case. In some
cases the receiver may only need to know something of the
implementation such as that it was implemented in a TEE. In other
cases the receiver may require the attester be certified by a
particular certification program. Or perhaps the receiver is content
with very little security.
9.2. Key Provisioning
Private key material can be used to sign and/or encrypt the EAT, or
can be used to derive the keys used for signing and/or encryption.
In some instances, the manufacturer of the entity may create the key
material separately and provision the key material in the entity
itself. The manufacturer of any entity that is capable of producing
an EAT should take care to ensure that any private key material be
suitably protected prior to provisioning the key material in the
entity itself. This can require creation of key material in an
enclave (see [RFC4949] for definition of "enclave"), secure
transmission of the key material from the enclave to the entity using
an appropriate protocol, and persistence of the private key material
in some form of secure storage to which (preferably) only the entity
has access.
9.2.1. Transmission of Key Material
Regarding transmission of key material from the enclave to the
entity, the key material may pass through one or more intermediaries.
Therefore some form of protection ("key wrapping") may be necessary.
The transmission itself may be performed electronically, but can also
be done by human courier. In the latter case, there should be
minimal to no exposure of the key material to the human (e.g.
encrypted portable memory). Moreover, the human should transport the
key material directly from the secure enclave where it was created to
a destination secure enclave where it can be provisioned.
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9.3. Freshness
All EAT use MUST provide a freshness mechanism to prevent replay and
related attacks. The extensive discussions on freshness in [RFC9334]
including security considerations apply here. The EAT nonce claim,
in Section 4.1, is one option to provide freshness.
9.4. Multiple EAT Consumers
In many cases, more than one EAT consumer may be required to fully
verify the entity attestation. Examples include individual consumers
for nested EATs, or consumers for individual claims with an EAT.
When multiple consumers are required for verification of an EAT, it
is important to minimize information exposure to each consumer. In
addition, the communication between multiple consumers should be
secure.
For instance, consider the example of an encrypted and signed EAT
with multiple claims. A consumer may receive the EAT (denoted as the
"receiving consumer"), decrypt its payload, verify its signature, but
then pass specific subsets of claims to other consumers for
evaluation ("downstream consumers"). Since any COSE encryption will
be removed by the receiving consumer, the communication of claim
subsets to any downstream consumer MUST leverage an equivalent
communication security protocol (e.g. Transport Layer Security).
However, assume the EAT of the previous example is hierarchical and
each claim subset for a downstream consumer is created in the form of
a nested EAT. Then the nested EAT is itself encrypted and
cryptographically verifiable (due to its COSE envelope) by a
downstream consumer (unlike the previous example where a claims set
without a COSE envelope is sent to a downstream consumer).
Therefore, Transport Layer Security between the receiving and
downstream consumers is not strictly required. Nevertheless,
downstream consumers of a nested EAT should provide a nonce unique to
the EAT they are consuming.
9.5. Detached EAT Bundle Digest Security Considerations
A detached EAT bundle is composed of a nested EAT and an claims set
as per Section 5. Although the attached claims set is vulnerable to
modification in transit, any modification can be detected by the
receiver through the associated digest, which is a claim fully
contained within an EAT. Moreover, the digest itself can only be
derived using an appropriate COSE hash algorithm, implying that an
attacker cannot induce false detection of modified detached claims
because the algorithms in the COSE registry are assumed to be of
sufficient cryptographic strength.
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9.6. Verification Keys
In all cases there must be some way that the verification key is
itself verified or determined to be trustworthy. The key
identification itself is never enough. This will always be by some
out-of-band mechanism that is not described here. For example, the
verifier may be configured with a root certificate or a master key by
the verifier system administrator.
Often an X.509 certificate or an endorsement carries more than just
the verification key. For example, an X.509 certificate might have
key usage constraints, and an endorsement might have reference
values. When this is the case, the key identifier must be either a
protected header or in the payload, such that it is cryptographically
bound to the EAT. This is in line with the requirements in section 6
on Key Identification in JSON Web Signature [RFC7515].
10. IANA Considerations
10.1. Reuse of CBOR and JSON Web Token (CWT and JWT) Claims Registries
Claims defined for EAT are compatible with those of CWT and JWT so
the CWT and JWT Claims Registries, [IANA.CWT.Claims] and
[IANA.JWT.Claims], are re-used. No new IANA registry is created.
All EAT claims defined in this document are placed in both
registries. All new EAT claims defined subsequently should be placed
in both registries.
Appendix E describes some considerations when defining new claims.
10.2. CWT and JWT Claims Registered by This Document
This specification adds the following values to the "JSON Web Token
Claims" registry established by [RFC7519] and the "CBOR Web Token
Claims Registry" established by [RFC8392]. Each entry below is an
addition to both registries.
The "Claim Description", "Change Controller" and "Specification
Documents" are common and equivalent for the JWT and CWT registries.
The "Claim Key" and "Claim Value Types(s)" are for the CWT registry
only. The "Claim Name" is as defined for the CWT registry, not the
JWT registry. The "JWT Claim Name" is equivalent to the "Claim Name"
in the JWT registry.
IANA is requested to register the following claims. The "Claim Value
Type(s)" here all name CDDL definitions and are only for the CWT
registry.
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// RFC editor: please see instructions in followg paragraph and
// remove for final publication
RFC Editor: Please make the following adjustments and remove this
paragraph. Replace "*this document*" with this RFC number. In the
following, the claims with "Claim Key: TBD" need to be assigned a
value in the Specification Required Range, preferably starting around
267. Those below already with a Claim Key number were given early
assignment. No change is requested for them except for Claim Key
262. Claim 262 should be renamed from "secboot" to "oemboot" in the
JWT registry and its description changed in both the CWT and JWT
registries.
* Claim Name: Nonce
* Claim Description: Nonce
* JWT Claim Name: "eat_nonce"
* Claim Key: 10
* Claim Value Type(s): bstr or array
* Change Controller: IETF
* Specification Document(s): *this document*
* Claim Name: UEID
* Claim Description: The Universal Entity ID
* JWT Claim Name: "ueid"
* CWT Claim Key: 256
* Claim Value Type(s): bstr
* Change Controller: IETF
* Specification Document(s): *this document*
* Claim Name: SUEIDs
* Claim Description: Semi-permanent UEIDs
* JWT Claim Name: "sueids"
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* CWT Claim Key: 257
* Claim Value Type(s): map
* Change Controller: IETF
* Specification Document(s): *this document*
* Claim Name: Hardware OEM ID
* Claim Description: Hardware OEM ID
* JWT Claim Name: "oemid"
* Claim Key: 258
* Claim Value Type(s): bstr or int
* Change Controller: IETF
* Specification Document(s): *this document*
* Claim Name: Hardware Model
* Claim Description: Model identifier for hardware
* JWT Claim Name: "hwmodel"
* Claim Key: 259
* Claim Value Type(s): bstr
* Change Controller: IETF
* Specification Document(s): *this document*
* Claim Name: Hardware Version
* Claim Description: Hardware Version Identifier
* JWT Claim Name: "hwversion"
* Claim Key: TBD 260
* Claim Value Type(s): array
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* Change Controller: IETF
* Specification Document(s): *this document*
* Claim Name: OEM Authorized Boot
* Claim Description: Indicates whether the software booted was OEM
authorized
* JWT Claim Name: "oemboot"
* Claim Key: 262
* Claim Value Type(s): bool
* Change Controller: IETF
* Specification Document(s): *this document*
* Claim Name: Debug Status
* Claim Description: Indicates status of debug facilities
* JWT Claim Name: "dbgstat"
* Claim Key: 263
* Claim Value Type(s): uint
* Change Controller: IETF
* Specification Document(s): *this document*
* Claim Name: Location
* Claim Description: The geographic location
* JWT Claim Name: "location"
* Claim Key: 264
* Claim Value Type(s): map
* Change Controller: IETF
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* Specification Document(s): *this document*
* Claim Name: EAT Profile
* Claim Description: Indicates the EAT profile followed
* JWT Claim Name: "eat_profile"
* Claim Key: 265
* Claim Value Type(s): uri or oid
* Change Controller: IETF
* Specification Document(s): *this document*
* Claim Name: Submodules Section
* Claim Description: The section containing submodules
* JWT Claim Name: "submods"
* Claim Key: 266
* Claim Value Type(s): map
* Change Controller: IETF
* Specification Document(s): *this document*
* Claim Name: Uptime
* Claim Description: Uptime
* JWT Claim Name: "uptime"
* Claim Key: TBD
* Claim Value Type(s): uint
* Change Controller: IETF
* Specification Document(s): *this document*
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* Claim Name: Boot Count
* Claim Description: The number times the entity or submodule has
been booted
* JWT Claim Name: "bootcount"
* Claim Key: TBD
* Claim Value Type(s): uint
* Change Controller: IETF
* Specification Document(s): *this document*
* Claim Name: Boot Seed
* Claim Description: Identifies a boot cycle
* JWT Claim Name: "bootseed"
* Claim Key: TBD
* Claim Value Type(s): bstr
* Change Controller: IETF
* Specification Document(s): *this document*
* Claim Name: DLOAs
* Claim Description: Certifications received as Digital Letters of
Approval
* JWT Claim Name: "dloas"
* Claim Key: TBD
* Claim Value Type(s): array
* Change Controller: IETF
* Specification Document(s): *this document*
* Claim Name: Software Name
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* Claim Description: The name of the software running in the entity
* JWT Claim Name: "swname"
* Claim Key: TBD
* Claim Value Type(s): tstr
* Change Controller: IETF
* Specification Document(s): *this document*
* Claim Name: Software Version
* Claim Description: The version of software running in the entity
* JWT Claim Name: "swversion"
* Claim Key: TBD
* Claim Value Type(s): array
* Change Controller: IETF
* Specification Document(s): *this document*
* Claim Name: Software Manifests
* Claim Description: Manifests describing the software installed on
the entity
* JWT Claim Name: "manifests"
* Claim Key: TBD
* Claim Value Type(s): array
* Change Controller: IETF
* Specification Document(s): *this document*
* Claim Name: Measurements
* Claim Description: Measurements of the software, memory
configuration and such on the entity
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* JWT Claim Name: "measurements"
* Claim Key: TBD
* Claim Value Type(s): array
* Change Controller: IETF
* Specification Document(s): *this document*
* Claim Name: Software Measurement Results
* Claim Description: The results of comparing software measurements
to reference values
* JWT Claim Name: "measres"
* Claim Key: TBD
* Claim Value Type(s): array
* Change Controller: IETF
* Specification Document(s): *this document*
* Claim Name: Intended Use
* Claim Description: Indicates intended use of the EAT
* JWT Claim Name: "intuse"
* Claim Key: TBD
* Claim Value Type(s): uint
* Change Controller: IETF
* Specification Document(s): *this document*
10.3. UEID URN Registered by this Document
IANA is requested to register the following new subtypes in the "DEV
URN Subtypes" registry under "Device Identification". See [RFC9039].
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+=========+=============================+===============+
| Subtype | Description | Reference |
+=========+=============================+===============+
| ueid | Universal Entity Identifier | This document |
+---------+-----------------------------+---------------+
| sueid | Semi-permanent Universal | This document |
| | Entity Identifier | |
+---------+-----------------------------+---------------+
Table 3: UEID URN Registration
ABNF for these two URNs is as follows where b64ueid is the base64url-
encoded binary byte-string for the UEID or SUEID:
body =/ ueidbody
ueidbody = %s”ueid:” b64ueid
10.4. CBOR Tag for Detached EAT Bundle Registered by this Document
In the registry [IANA.cbor-tags], IANA is requested to allocate the
following tag from the Specification Required space, with the present
document as the specification reference.
+========+============+===============================+
| Tag | Data Items | Semantics |
+========+============+===============================+
| TBD602 | array | Detached EAT Bundle Section 5 |
+--------+------------+-------------------------------+
Table 4: Detached EAT Bundle Tag Registration
11. References
11.1. Normative References
[DLOA] "Digital Letter of Approval", November 2015,
<https://globalplatform.org/wp-content/uploads/2015/12/
GPC_DigitalLetterOfApproval_v1.0.pdf>.
[IANA.cbor-tags]
IANA, "Concise Binary Object Representation (CBOR) Tags",
<https://www.iana.org/assignments/cbor-tags>.
[IANA.COSE.Algorithms]
IANA, "CBOR Object Signing and Encryption (COSE)",
<https://www.iana.org/assignments/cose>.
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[IANA.CWT.Claims]
IANA, "CBOR Web Token (CWT) Claims",
<https://www.iana.org/assignments/cwt>.
[IANA.JWT.Claims]
IANA, "JSON Web Token (JWT)",
<https://www.iana.org/assignments/jwt>.
[PEN] "Private Enterprise Number (PEN) Request", n.d.,
<https://pen.iana.org/pen/PenApplication.page>.
[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>.
[RFC2252] Wahl, M., Coulbeck, A., Howes, T., and S. Kille,
"Lightweight Directory Access Protocol (v3): Attribute
Syntax Definitions", RFC 2252, DOI 10.17487/RFC2252,
December 1997, <https://www.rfc-editor.org/info/rfc2252>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<https://www.rfc-editor.org/info/rfc4648>.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<https://www.rfc-editor.org/info/rfc7252>.
[RFC7515] Jones, M., Bradley, J., and N. Sakimura, "JSON Web
Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
2015, <https://www.rfc-editor.org/info/rfc7515>.
[RFC7519] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
(JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
<https://www.rfc-editor.org/info/rfc7519>.
[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>.
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[RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", STD 90, RFC 8259,
DOI 10.17487/RFC8259, December 2017,
<https://www.rfc-editor.org/info/rfc8259>.
[RFC8392] Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig,
"CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392,
May 2018, <https://www.rfc-editor.org/info/rfc8392>.
[RFC8610] Birkholz, H., Vigano, C., and C. Bormann, "Concise Data
Definition Language (CDDL): A Notational Convention to
Express Concise Binary Object Representation (CBOR) and
JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610,
June 2019, <https://www.rfc-editor.org/info/rfc8610>.
[RFC8792] Watsen, K., Auerswald, E., Farrel, A., and Q. Wu,
"Handling Long Lines in Content of Internet-Drafts and
RFCs", RFC 8792, DOI 10.17487/RFC8792, June 2020,
<https://www.rfc-editor.org/info/rfc8792>.
[RFC8949] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", STD 94, RFC 8949,
DOI 10.17487/RFC8949, December 2020,
<https://www.rfc-editor.org/info/rfc8949>.
[RFC9052] Schaad, J., "CBOR Object Signing and Encryption (COSE):
Structures and Process", STD 96, RFC 9052,
DOI 10.17487/RFC9052, August 2022,
<https://www.rfc-editor.org/info/rfc9052>.
[RFC9090] Bormann, C., "Concise Binary Object Representation (CBOR)
Tags for Object Identifiers", RFC 9090,
DOI 10.17487/RFC9090, July 2021,
<https://www.rfc-editor.org/info/rfc9090>.
[RFC9165] Bormann, C., "Additional Control Operators for the Concise
Data Definition Language (CDDL)", RFC 9165,
DOI 10.17487/RFC9165, December 2021,
<https://www.rfc-editor.org/info/rfc9165>.
[RFC9334] Birkholz, H., Thaler, D., Richardson, M., Smith, N., and
W. Pan, "Remote ATtestation procedureS (RATS)
Architecture", RFC 9334, DOI 10.17487/RFC9334, January
2023, <https://www.rfc-editor.org/info/rfc9334>.
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[RFC9393] Birkholz, H., Fitzgerald-McKay, J., Schmidt, C., and D.
Waltermire, "Concise Software Identification Tags",
RFC 9393, DOI 10.17487/RFC9393, June 2023,
<https://www.rfc-editor.org/info/rfc9393>.
[ThreeGPP.IMEI]
3GPP, "3rd Generation Partnership Project; Technical
Specification Group Core Network and Terminals; Numbering,
addressing and identification", 2019,
<https://portal.3gpp.org/desktopmodules/Specifications/
SpecificationDetails.aspx?specificationId=729>.
[WGS84] National Geospatial-Intelligence Agency (NGA), "WORLD
GEODETIC SYSTEM 1984, NGA.STND.0036_1.0.0_WGS84", 8 July
2014, <https://earth-info.nga.mil/php/
download.php?file=coord-wgs84>.
11.2. Informative References
[BirthdayAttack]
"Birthday attack",
<https://en.wikipedia.org/wiki/Birthday_attack.>.
[CBOR.Cert.Draft]
Mattsson, J. P., Selander, G., Raza, S., Höglund, J., and
M. Furuhed, "CBOR Encoded X.509 Certificates (C509
Certificates)", Work in Progress, Internet-Draft, draft-
ietf-cose-cbor-encoded-cert-07, 20 October 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-cose-
cbor-encoded-cert-07>.
[COSE.X509.Draft]
Schaad, J., "CBOR Object Signing and Encryption (COSE):
Header Parameters for Carrying and Referencing X.509
Certificates", Work in Progress, Internet-Draft, draft-
ietf-cose-x509-09, 13 October 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-cose-
x509-09>.
[EAT.media-types]
Lundblade, L., Birkholz, H., and T. Fossati, "EAT Media
Types", Work in Progress, Internet-Draft, draft-ietf-rats-
eat-media-type-05, 7 November 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-rats-
eat-media-type-05>.
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[IEEE-RA] "IEEE Registration Authority",
<https://standards.ieee.org/products-services/regauth/
index.html>.
[IEEE.802-2001]
"IEEE Standard for Local and Metropolitan Area Networks:
Overview and Architecture", IEEE standard,
DOI 10.1109/ieeestd.2014.6847097, July 2014,
<https://doi.org/10.1109/ieeestd.2014.6847097>.
[IEEE.802.1AR]
"IEEE Standard for Local and Metropolitan Area Networks -
Secure Device Identity", IEEE standard,
DOI 10.1109/ieeestd.2018.8423794, July 2018,
<https://doi.org/10.1109/ieeestd.2018.8423794>.
[JTAG] "IEEE Standard for Reduced-Pin and Enhanced-Functionality
Test Access Port and Boundary-Scan Architecture", February
2010, <https://ieeexplore.ieee.org/document/5412866>.
[OUI.Guide]
"Guidelines for Use of Extended Unique Identifier (EUI),
Organizationally Unique Identifier (OUI), and Company ID
(CID)", August 2017,
<https://standards.ieee.org/content/dam/ieee-
standards/standards/web/documents/tutorials/eui.pdf>.
[OUI.Lookup]
"IEEE Registration Authority Assignments",
<https://regauth.standards.ieee.org/standards-ra-web/pub/
view.html#registries>.
[RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally
Unique IDentifier (UUID) URN Namespace", RFC 4122,
DOI 10.17487/RFC4122, July 2005,
<https://www.rfc-editor.org/info/rfc4122>.
[RFC4949] Shirey, R., "Internet Security Glossary, Version 2",
FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007,
<https://www.rfc-editor.org/info/rfc4949>.
[RFC9039] Arkko, J., Jennings, C., and Z. Shelby, "Uniform Resource
Names for Device Identifiers", RFC 9039,
DOI 10.17487/RFC9039, June 2021,
<https://www.rfc-editor.org/info/rfc9039>.
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[SUIT.Manifest]
Moran, B., Tschofenig, H., Birkholz, H., Zandberg, K., and
O. Rønningstad, "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-24, 23 October
2023, <https://datatracker.ietf.org/doc/html/draft-ietf-
suit-manifest-24>.
[UCCS] Birkholz, H., O'Donoghue, J., Cam-Winget, N., and C.
Bormann, "A CBOR Tag for Unprotected CWT Claims Sets",
Work in Progress, Internet-Draft, draft-ietf-rats-uccs-07,
27 November 2023, <https://datatracker.ietf.org/doc/html/
draft-ietf-rats-uccs-07>.
[W3C.GeoLoc]
Popescu, A., Ed., "Geolocation API Specification", W3C
REC REC-geolocation-API-20131024, W3C REC-geolocation-API-
20131024, 24 October 2013, <https://www.w3.org/TR/2013/
REC-geolocation-API-20131024/>.
Appendix A. Examples
Most examples are shown as just a Claims-Set that would be a payload
for a CWT, JWT, detached EAT bundle or future token types. The
signing is left off so the Claims-Set is easier to see. Some
examples of signed tokens are also given.
// RFC Editor: When the IANA values are permanently assigned, please
// contact the authors so the examples can be regenerated.
// Regeneration is required because IANA-assigned values are inside
// hex and based-64 encoded data and some of these are signed.
A.1. Claims Set Examples
A.1.1. Simple TEE Attestation
This is a simple attestation of a TEE that includes a manifest that
is a payload CoSWID to describe the TEE's software.
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/ This is an EAT payload that describes a simple TEE. /
{
/ eat_nonce / 10: h'48df7b172d70b5a18935d0460a73dd71',
/ oemboot / 262: true,
/ dbgstat / 263: 2, / disabled-since-boot /
/ manifests / 273: [
[
121, / CoAP Content ID. A /
/ made up one until one /
/ is assigned for CoSWID /
/ This is byte-string wrapped /
/ payload CoSWID. It gives the TEE /
/ software name, the version and /
/ the name of the file it is in. /
/ {0: "3a24", /
/ 12: 1, /
/ 1: "Acme TEE OS", /
/ 13: "3.1.4", /
/ 2: [{31: "Acme TEE OS", 33: 1}, /
/ {31: "Acme TEE OS", 33: 2}], /
/ 6: { /
/ 17: { /
/ 24: "acme_tee_3.exe" /
/ } /
/ } /
/ } /
h' a60064336132340c01016b
41636d6520544545204f530d65332e31
2e340282a2181f6b41636d6520544545
204f53182101a2181f6b41636d652054
4545204f5318210206a111a118186e61
636d655f7465655f332e657865'
]
]
}
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/ A payload CoSWID created by the SW vendor. All this really does /
/ is name the TEE SW, its version and lists the one file that /
/ makes up the TEE. /
1398229316({
/ Unique CoSWID ID / 0: "3a24",
/ tag-version / 12: 1,
/ software-name / 1: "Acme TEE OS",
/ software-version / 13: "3.1.4",
/ entity / 2: [
{
/ entity-name / 31: "Acme TEE OS",
/ role / 33: 1 / tag-creator /
},
{
/ entity-name / 31: "Acme TEE OS",
/ role / 33: 2 / software-creator /
}
],
/ payload / 6: {
/ ...file / 17: {
/ ...fs-name / 24: "acme_tee_3.exe"
}
}
})
A.1.2. Submodules for Board and Device
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/ This example shows use of submodules to give information /
/ about the chip, board and overall device. /
/ /
/ The main attestation is associated with the chip with the /
/ CPU and running the main OS. It is what has the keys and /
/ produces the token. /
/ /
/ The board is made by a different vendor than the chip. /
/ Perhaps it is some generic IoT board. /
/ /
/ The device is some specific appliance that is made by a /
/ different vendor than either the chip or the board. /
/ /
/ Here the board and device submodules aren't the typical /
/ target environments as described by the RATS architecture /
/ document, but they are a valid use of submodules. /
{
/ eat_nonce / 10: h'e253cabedc9eec24ac4e25bcbeaf7765'
/ ueid / 256: h'0198f50a4ff6c05861c8860d13a638ea',
/ oemid / 258: h'894823', / IEEE OUI format OEM ID /
/ hwmodel / 259: h'549dcecc8b987c737b44e40f7c635ce8'
/ Hash of chip model name /,
/ hwversion / 260: ["1.3.4", 1], / Multipartnumeric /
/ swname / 271: "Acme OS",
/ swversion / 272: ["3.5.5", 1],
/ oemboot / 262: true,
/ dbgstat / 263: 3, / permanent-disable /
/ timestamp (iat) / 6: 1526542894,
/ submods / 266: {
/ A submodule to hold some claims about the circuit board /
"board" : {
/ oemid / 258: h'9bef8787eba13e2c8f6e7cb4b1f4619a',
/ hwmodel / 259: h'ee80f5a66c1fb9742999a8fdab930893'
/ Hash of board module name /,
/ hwversion / 260: ["2.0a", 2] / multipartnumeric+sfx /
},
/ A submodule to hold claims about the overall device /
"device" : {
/ oemid / 258: 61234, / PEN Format OEM ID /
/ hwversion / 260: ["4.0", 1] / Multipartnumeric /
}
}
}
A.1.3. EAT Produced by Attestation Hardware Block
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/ This is an example of a token produced by a HW block /
/ purpose-built for attestation. Only the nonce claim changes /
/ from one attestation to the next as the rest either come /
/ directly from the hardware or from one-time-programmable memory /
/ (e.g. a fuse). 47 bytes encoded in CBOR (8 byte nonce, 16 byte /
/ UEID). /
{
/ eat_nonce / 10: h'd79b964ddd5471c1393c8888',
/ ueid / 256: h'0198f50a4ff6c05861c8860d13a638ea',
/ oemid / 258: 64242, / Private Enterprise Number /
/ oemboot / 262: true,
/ dbgstat / 263: 3, / disabled-permanently /
/ hwversion / 260: [ "3.1", 1 ] / Type is multipartnumeric /
}
A.1.4. Key / Key Store Attestation
/ This is an attestation of a public key and the key store /
/ implementation that protects and manages it. The key store /
/ implementation is in a security-oriented execution /
/ environment separate from the high-level OS (HLOS), for /
/ example a Trusted Execution Environment (TEE). The key store /
/ is the Attester. /
/ /
/ There is some attestation of the high-level OS, just version /
/ and boot & debug status. It is a Claims-Set submodule because/
/ it has lower security level than the key store. The key /
/ store's implementation has access to info about the HLOS, so /
/ it is able to include it. /
/ /
/ A key and an indication of the user authentication given to /
/ allow access to the key is given. The labels for these are /
/ in the private space since this is just a hypothetical /
/ example, not part of a standard protocol. /
{
/ eat_nonce / 10: h'99b67438dba40743266f70bf75feb1026d5134
97a229bfe8'
/ oemboot / 262: true,
/ dbgstat / 263: 2, / disabled-since-boot /
/ manifests / 273: [
[ 121, / CoAP Content ID. A /
/ made up one until one /
/ is assigned for CoSWID /
h'a600683762623334383766
0c000169436172626f6e6974650d6331
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2e320e0102a2181f75496e6475737472
69616c204175746f6d6174696f6e1821
02'
]
/ Above is an encoded CoSWID /
/ with the following data /
/ SW Name: "Carbonite" /
/ SW Vers: "1.2" /
/ SW Creator: /
/ "Industrial Automation" /
],
/ exp / 4: 1634324274, / 2021-10-15T18:57:54Z /
/ iat / 6: 1634317080, / 2021-10-15T16:58:00Z /
-80000 : "fingerprint",
-80001 : { / The key -- A COSE_Key /
/ kty / 1: 2, / EC2, eliptic curve with x & y /
/ kid / 2: h'36675c206f96236c3f51f54637b94ced',
/ curve / -1: 2, / curve is P-256 /
/ x-coord / -2: h'65eda5a12577c2bae829437fe338701a
10aaa375e1bb5b5de108de439c08551d',
/ y-coord / -3: h'1e52ed75701163f7f9e40ddf9f341b3d
c9ba860af7e0ca7ca7e9eecd0084d19c'
},
/ submods / 266 : {
"HLOS" : { / submod for high-level OS /
/ eat_nonce / 10: h'8b0b28782a23d3f6',
/ oemboot / 262: true,
/ manifests / 273: [
[ 121, / CoAP Content ID. A /
/ made up one until one /
/ is assigned for CoSWID /
h'a600687337
6537346b78380c000168
44726f6964204f530d65
52322e44320e0302a218
1F75496E647573747269
616c204175746f6d6174
696f6e182102'
]
/ Above is an encoded CoSWID /
/ with the following data: /
/ SW Name: "Droid OS" /
/ SW Vers: "R2.D2" /
/ SW Creator: /
/ "Industrial Automation"/
]
}
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}
}
A.1.5. Software Measurements of an IoT Device
This is a simple token that might be for an IoT device. It includes
CoSWID format measurments of the SW. The CoSWID is in byte-string
wrapped in the token and also shown in diagnostic form.
/ This EAT payload is for an IoT device with a TEE. The attestation /
/ is produced by the TEE. There is a submodule for the IoT OS (the /
/ main OS of the IoT device that is not as secure as the TEE). The /
/ submodule contains claims for the IoT OS. The TEE also measures /
/ the IoT OS and puts the measurements in the submodule. /
{
/ eat_nonce / 10: h'5e19fba4483c7896'
/ oemboot / 262: true,
/ dbgstat / 263: 2, / disabled-since-boot /
/ oemid / 258: h'8945ad', / IEEE CID based /
/ ueid / 256: h'0198f50a4ff6c05861c8860d13a638ea',
/ submods / 266: {
"OS" : {
/ oemboot / 262: true,
/ dbgstat / 263: 2, / disabled-since-boot /
/ measurements / 274: [
[
121, / CoAP Content ID. A /
/ made up one until one /
/ is assigned for CoSWID /
/ This is a byte-string wrapped /
/ evidence CoSWID. It has /
/ hashes of the main files of /
/ the IoT OS. /
h'a600663463613234350c
17016d41636d6520522d496f542d4f
530d65332e312e3402a2181f724163
6d6520426173652041747465737465
7218210103a11183a318187161636d
655f725f696f745f6f732e65786514
1a0044b349078201582005f6b327c1
73b4192bd2c3ec248a292215eab456
611bf7a783e25c1782479905a31818
6d7265736f75726365732e72736314
1a000c38b10782015820c142b9aba4
280c4bb8c75f716a43c99526694caa
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be529571f5569bb7dc542f98a31818
6a636f6d6d6f6e2e6c6962141a0023
3d3b0782015820a6a9dcdfb3884da5
f884e4e1e8e8629958c2dbc7027414
43a913e34de9333be6'
]
]
}
}
}
/ An evidence CoSWID created for the "Acme R-IoT-OS" created by /
/ the "Acme Base Attester" (both fictious names). It provides /
/ measurements of the SW (other than the attester SW) on the /
/ device. /
1398229316({
/ Unique CoSWID ID / 0: "4ca245",
/ tag-version / 12: 23, / Attester-maintained counter /
/ software-name / 1: "Acme R-IoT-OS",
/ software-version / 13: "3.1.4",
/ entity / 2: {
/ entity-name / 31: "Acme Base Attester",
/ role / 33: 1 / tag-creator /
},
/ evidence / 3: {
/ ...file / 17: [
{
/ ...fs-name / 24: "acme_r_iot_os.exe",
/ ...size / 20: 4502345,
/ ...hash / 7: [
1, / SHA-256 /
h'05f6b327c173b419
2bd2c3ec248a2922
15eab456611bf7a7
83e25c1782479905'
]
},
{
/ ...fs-name / 24: "resources.rsc",
/ ...size / 20: 800945,
/ ...hash / 7: [
1, / SHA-256 /
h'c142b9aba4280c4b
b8c75f716a43c995
26694caabe529571
f5569bb7dc542f98'
]
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},
{
/ ...fs-name / 24: "common.lib",
/ ...size / 20: 2309435,
/ ...hash / 7: [
1, / SHA-256 /
h'a6a9dcdfb3884da5
f884e4e1e8e86299
58c2dbc702741443
a913e34de9333be6'
]
}
]
}
})
A.1.6. Attestation Results in JSON
This is a JSON-encoded payload that might be the output of a verifier
that evaluated the IoT Attestation example immediately above.
This particular verifier knows enough about the TEE attester to be
able to pass claims like debug status directly through to the relying
party. The verifier also knows the reference values for the measured
software components and is able to check them. It informs the
relying party that they were correct in the "measres" claim.
"Trustus Verifications" is the name of the services that verifies the
software component measurements.
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{
"eat_nonce": "jkd8KL-8=Qlzg4",
"oemboot": true,
"dbgstat": "disabled-since-boot",
"oemid": "iUWt",
"ueid": "AZj1Ck_2wFhhyIYNE6Y4",
"swname": "Acme R-IoT-OS",
"swversion": [
"3.1.4"
],
"measres": [
[
"Trustus Measurements",
[
[
"all",
"success"
]
]
]
]
}
A.1.7. JSON-encoded Token with Submodules
This example has its lines wrapped per [RFC8792].
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{
"eat_nonce": "lI-IYNE6Rj6O",
"ueid": "AJj1Ck_2wFhhyIYNE6Y46g==",
"secboot": true,
"dbgstat": "disabled-permanently",
"iat": 1526542894,
"submods": {
"Android App Foo": {
"swname": "Foo.app"
},
"Secure Element Eat": [
"CBOR",
"2D3ShEOhASagWGaoCkiUj4hg0TpGPhkBAFABmPUKT_bAWGHIhg0TpjjqGQ\
ECGfryGQEFBBkBBvUZAQcDGQEEgmMzLjEBGQEKoWNURUWCL1gg5c-V_ST6txRGdC3VjU\
Pa4XjlX-K5QpGpKRCC_8JjWgtYQPaQywOIZ3-mJKN3X9fLxOhAnsmBa-MvpHRzOw-Ywn\
-67bvJljuctezAPD41s6_At7NbSV3qwJlxIuqGfwe41es="
],
"Linux Android": {
"swname": "Android"
},
"Subsystem J": [
"JWT",
"eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJpc3MiOiJKLUF0dGVzd\
GVyIiwiaWF0IjoxNjUxNzc0ODY4LCJleHAiOm51bGwsImF1ZCI6IiIsInN1YiI6IiJ9.\
gjw4nFMhLpJUuPXvMPzK1GMjhyJq2vWXg1416XKszwQ"
]
}
}
A.2. Signed Token Examples
A.2.1. Basic CWT Example
This is a simple CWT-format token signed with the ECDSA algorithm.
/ This is a full CWT-format token with a very simple payloal. /
/ The main structure visible here is that of the COSE_Sign1. /
61( 18( [
h'A10126', / protected headers /
{}, / empty unprotected headers /
h'A20B46024A6B0978DE0A49000102030405060708', / payload /
h'9B9B2F5E470000F6A20C8A4157B5763FC45BE759
9A5334028517768C21AFFB845A56AB557E0C8973
A07417391243A79C478562D285612E292C622162
AB233787' / signature /
] ) )
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A.2.2. CBOR-encoded Detached EAT Bundle
In this detached EAT bundle, the main token is produced by a HW
attestation block. The detached Claims-Set is produced by a TEE and
is largely identical to the Simple TEE examples above. The TEE
digests its Claims-Set and feeds that digest to the HW block.
In a better example the attestation produced by the HW block would be
a CWT and thus signed and secured by the HW block. Since the
signature covers the digest from the TEE that Claims-Set is also
secured.
The detached EAT bundle itself can be assembled by untrusted
software.
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/ This is a detached EAT bundle tag. Note that 602, the tag /
/ identifying a detached EAT bundle is not yet registered /
/ with IANA /
602([
/ First part is a full EAT token with claims like nonce and /
/ UEID. Most importantly, it includes a submodule that is a /
/ detached digest which is the hash of the "TEE" claims set /
/ in the next section. The COSE payload follows: /
/ { /
/ 10: h'948F8860D13A463E', /
/ 256: h'0198F50A4FF6C05861C8860D13A638EA', /
/ 258: 64242, /
/ 262: true, /
/ 263: 3, /
/ 260: ["3.1", 1], /
/ 266: { /
/ "TEE": [ /
/ -16, /
/ h'8DEF652F47000710D9F466A4C666E209 /
/ DD74F927A1CEA352B03143E188838ABE' /
/ ] /
/ } /
/ } /
h'D83DD28443A10126A05866A80A48948F8860D13A463E1901
00500198F50A4FF6C05861C8860D13A638EA19010219FAF2
19010504190106F5190107031901048263332E310119010A
A163544545822F58208DEF652F47000710D9F466A4C666E2
09DD74F927A1CEA352B03143E188838ABE5840F690CB0388
677FA624A3775FD7CBC4E8409EC9816BE32FA474733B0F98
C27FBAEDBBC9963B9CB5ECC03C3E35B3AFC0B7B35B495DEA
C0997122EA867F07B8D5EB',
{
/ A CBOR-encoded byte-string wrapped EAT claims-set. It /
/ contains claims suitable for a TEE /
"TEE" : h'a40a48948f8860d13a463e190106f519010702
190111818218795858a60064336132340c0101
6b41636d6520544545204f530d65332e312e34
0282a2181f6b41636d6520544545204f531821
01a2181f6b41636d6520544545204f53182102
06a111a118186e61636d655f7465655f332e65
7865'
}
])
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/ This example contains submodule that is a detached digest, /
/ which is the hash of a Claims-Set convey outside this token. /
/ Other than that is is the other example of a token from an /
/ attestation HW block /
{
/ eat_nonce / 10: h'3515744961254b41a6cf9c02',
/ ueid / 256: h'0198f50a4ff6c05861c8860d13a638ea',
/ oemid / 258: 64242, / Private Enterprise Number /
/ oemboot / 262: true,
/ dbgstat / 263: 3, / disabled-permanently /
/ hwversion / 260: [ "3.1", 1 ], / multipartnumeric /
/ submods/ 266: {
"TEE": [ / detached digest submod /
-16, / SHA-256 /
h'e5cf95fd24fab7144674
2dd58d43dae178e55fe2
b94291a9291082ffc263
5a0b'
]
}
}
A.2.3. JSON-encoded Detached EAT Bundle
In this bundle there are two detached Claims-Sets, "Audio Subsystem"
and "Graphics Subsystem". The JWT at the start of the bundle has
detached signature submodules with hashes that cover these two
Claims-Sets. The JWT itself is protected using HMAC with a key of
"xxxxxx".
This example has its lines wrapped per [RFC8792].
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[
[
"JWT",
"eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJlYXRfbm9uY2UiOiJ5dT\
c2Tk44SXVWNmUiLCJzdWJtb2RzIjp7IkF1ZGlvIFN1YnN5c3RlbSI6WyJESUdFU1QiLF\
siU0hBLTI1NiIsIkZSRW4yVlR3aTk5cWNNRVFzYmxtTVFnM2I1b2ZYUG5OM1BJYW5CME\
5RT3MiXV0sIkdyYXBoaWNzIFN1YnN5c3RlbSI6WyJESUdFU1QiLFsiU0hBLTI1NiIsIk\
52M3NqUVU3Q1Z0RFRka0RTUlhWcFZDNUNMVFBCWmVQWWhTLUhoVlZWMXMiXV19fQ.FYs\
7R-TKhgAk85NyCOPQlbtGGjFM_3chnhBEOuM6qCo"
],
{
"Audio Subsystem" : "ewogICAgImVhdF9ub25jZSI6ICJsSStJWU5FNlJ\
qNk8iLAogICAgInVlaWQiOiAiQWROSlU0b1lYdFVwQStIeDNqQTcvRFEiCiAgICAib2V\
taWQiOiAiaVVXdCIsCiAgICAib2VtYm9vdCI6IHRydWUsIAogICAgInN3bmFtZSI6ICJ\
BdWRpbyBQcm9jZXNzb3IgT1MiCn0K",
"Graphics Subsystem" : "ewogICAgImVhdF9ub25jZSI6ICJZWStJWU5F\
NlJqNk8iLAogICAgInVlaWQiOiAiQWVUTUlRQ1NVMnhWQmtVdGlndHU3bGUiCiAgICAi\
b2VtaWQiOiA3NTAwMCwKICAgICJvZW1ib290IjogdHJ1ZSwgCiAgICAic3duYW1lIjog\
IkdyYXBoaWNzIE9TIgp9Cg"
}
]
Appendix B. UEID Design Rationale
B.1. Collision Probability
This calculation is to determine the probability of a collision of
type 0x01 UEIDs given the total possible entity population and the
number of entities in a particular entity management database.
Three different sized databases are considered. The number of
devices per person roughly models non-personal devices such as
traffic lights, devices in stores they shop in, facilities they work
in and so on, even considering individual light bulbs. A device may
have individually attested subsystems, for example parts of a car or
a mobile phone. It is assumed that the largest database will have at
most 10% of the world's population of devices. Note that databases
that handle more than a trillion records exist today.
The trillion-record database size models an easy-to-imagine reality
over the next decades. The quadrillion-record database is roughly at
the limit of what is imaginable and should probably be accommodated.
The 100 quadrillion database is highly speculative perhaps involving
nanorobots for every person, livestock animal and domesticated bird.
It is included to round out the analysis.
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Note that the items counted here certainly do not have IP address and
are not individually connected to the network. They may be connected
to internal buses, via serial links, Bluetooth and so on. This is
not the same problem as sizing IP addresses.
+=========+===========+============+==========+=================+
| People | Devices / | Subsystems | Database | Database Size |
| | Person | / Device | Portion | |
+=========+===========+============+==========+=================+
| 10 | 100 | 10 | 10% | trillion |
| billion | | | | (10^12) |
+---------+-----------+------------+----------+-----------------+
| 10 | 100,000 | 10 | 10% | quadrillion |
| billion | | | | (10^15) |
+---------+-----------+------------+----------+-----------------+
| 100 | 1,000,000 | 10 | 10% | 100 quadrillion |
| billion | | | | (10^17) |
+---------+-----------+------------+----------+-----------------+
Table 5: Entity Database Size Examples
This is conceptually similar to the Birthday Problem where m is the
number of possible birthdays, always 365, and k is the number of
people. It is also conceptually similar to the Birthday Attack where
collisions of the output of hash functions are considered.
The proper formula for the collision calculation is
p = 1 - e^{-k^2/(2n)}
p Collision Probability
n Total possible population
k Actual population
However, for the very large values involved here, this formula
requires floating point precision higher than commonly available in
calculators and software so this simple approximation is used. See
[BirthdayAttack].
p = k^2 / 2n
For this calculation:
p Collision Probability
n Total population based on number of bits in UEID
k Population in a database
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+=====================+==============+==============+==============+
| Database Size | 128-bit UEID | 192-bit UEID | 256-bit UEID |
+=====================+==============+==============+==============+
| trillion (10^12) | 2 * 10^-15 | 8 * 10^-35 | 5 * 10^-55 |
+---------------------+--------------+--------------+--------------+
| quadrillion (10^15) | 2 * 10^-09 | 8 * 10^-29 | 5 * 10^-49 |
+---------------------+--------------+--------------+--------------+
| 100 quadrillion | 2 * 10^-05 | 8 * 10^-25 | 5 * 10^-45 |
| (10^17) | | | |
+---------------------+--------------+--------------+--------------+
Table 6: UEID Size Options
Next, to calculate the probability of a collision occurring in one
year's operation of a database, it is assumed that the database size
is in a steady state and that 10% of the database changes per year.
For example, a trillion record database would have 100 billion states
per year. Each of those states has the above calculated probability
of a collision.
This assumption is a worst-case since it assumes that each state of
the database is completely independent from the previous state. In
reality this is unlikely as state changes will be the addition or
deletion of a few records.
The following tables gives the time interval until there is a
probability of a collision based on there being one tenth the number
of states per year as the number of records in the database.
t = 1 / ((k / 10) * p)
t Time until a collision
p Collision probability for UEID size
k Database size
+=====================+==============+==============+==============+
| Database Size | 128-bit UEID | 192-bit UEID | 256-bit UEID |
+=====================+==============+==============+==============+
| trillion (10^12) | 60,000 years | 10^24 years | 10^44 years |
+---------------------+--------------+--------------+--------------+
| quadrillion (10^15) | 8 seconds | 10^14 years | 10^34 years |
+---------------------+--------------+--------------+--------------+
| 100 quadrillion | 8 | 10^11 years | 10^31 years |
| (10^17) | microseconds | | |
+---------------------+--------------+--------------+--------------+
Table 7: UEID Collision Probability
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Clearly, 128 bits is enough for the near future thus the requirement
that type 0x01 UEIDs be a minimum of 128 bits.
There is no requirement for 256 bits today as quadrillion-record
databases are not expected in the near future and because this time-
to-collision calculation is a very worst case. A future update of
the standard may increase the requirement to 256 bits, so there is a
requirement that implementations be able to receive 256-bit UEIDs.
B.2. No Use of UUID
A UEID is not a Universally Unique Identifier (UUID) [RFC4122] by
conscious choice for the following reasons.
UUIDs are limited to 128 bits which may not be enough for some future
use cases.
Today, cryptographic-quality random numbers are available from common
CPUs and hardware. This hardware was introduced between 2010 and
2015. Operating systems and cryptographic libraries give access to
this hardware. Consequently, there is little need for
implementations to construct such random values from multiple sources
on their own.
Version 4 UUIDs do allow for use of such cryptographic-quality random
numbers, but do so by mapping into the overall UUID structure of time
and clock values. This structure is of no value here yet adds
complexity. It also slightly reduces the number of actual bits with
entropy.
The design of UUID accommodates the construction of a unique
identifier by combination of several identifiers that separately do
not provide sufficient uniqueness. UEID takes the view that this
construction is no longer needed, in particular because
cryptographic-quality random number generators are readily available.
It takes the view that hardware, software and/or manufacturing
process implement UEID in a simple and direct way.
Note also that that a type 2 UEID (EUI/MAC) is only 7 bytes compared
to 16 for a UUID.
Appendix C. EAT Relation to IEEE.802.1AR Secure Device Identity (DevID)
This section describes several distinct ways in which an IEEE IDevID
[IEEE.802.1AR] relates to EAT, particularly to UEID and SUEID.
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[IEEE.802.1AR] orients around the definition of an implementation
called a "DevID Module." It describes how IDevIDs and LDevIDs are
stored, protected and accessed using a DevID Module. A particular
level of defense against attack that should be achieved to be a DevID
is defined. The intent is that IDevIDs and LDevIDs can be used with
any network protocol or message format. In these protocols and
message formats the DevID secret is used to sign a nonce or similar
to prove the association of the DevID certificates with the device.
By contrast, EAT standardizes a message format that is sent to a
relying party, the very thing that is not defined in [IEEE.802.1AR].
Nor does EAT give details on how keys, data and such are stored
protected and accessed. EAT is intended to work with a variety of
different on-device implementations ranging from minimal protection
of assets to the highest levels of asset protection. It does not
define any particular level of defense against attack, instead
providing a set of security considerations.
EAT and DevID can be viewed as complimentary when used together or as
competing to provide a device identity service.
C.1. DevID Used With EAT
As just described, EAT standardizes a message format and
[IEEE.802.1AR] doesn't. Vice versa, EAT doesn't define a an device
implementation, but DevID does.
Hence, EAT can be the message format that a DevID is used with. The
DevID secret becomes the attestation key used to sign EATs. The
DevID and its certificate chain become the endorsement sent to the
verifier.
In this case, the EAT and the DevID are likely to both provide a
device identifier (e.g. a serial number). In the EAT it is the UEID
(or SUEID). In the DevID (used as an endorsement), it is a device
serial number included in the subject field of the DevID certificate.
It is probably a good idea in this use for them to be the same serial
number or for the UEID to be a hash of the DevID serial number.
C.2. How EAT Provides an Equivalent Secure Device Identity
The UEID, SUEID and other claims like OEM ID are equivalent to the
secure device identity put into the subject field of a DevID
certificate. These EAT claims can represent all the same fields and
values that can be put in a DevID certificate subject. EAT
explicitly and carefully defines a variety of useful claims.
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EAT secures the conveyance of these claims by having them signed on
the device by the attestation key when the EAT is generated. EAT
also signs the nonce that gives freshness at this time. Since these
claims are signed for every EAT generated, they can include things
that vary over time like GPS location.
DevID secures the device identity fields by having them signed by the
manufacturer of the device sign them into a certificate. That
certificate is created once during the manufacturing of the device
and never changes so the fields cannot change.
So in one case the signing of the identity happens on the device and
the other in a manufacturing facility, but in both cases the signing
of the nonce that proves the binding to the actual device happens on
the device.
While EAT does not specify how the signing keys, signature process
and storage of the identity values should be secured against attack,
an EAT implementation may have equal defenses against attack. One
reason EAT uses CBOR is because it is simple enough that a basic EAT
implementation can be constructed entirely in hardware. This allows
EAT to be implemented with the strongest defenses possible.
C.3. An X.509 Format EAT
It is possible to define a way to encode EAT claims in an X.509
certificate. For example, the EAT claims might be mapped to X.509 v3
extensions. It is even possible to stuff a whole CBOR-encoded
unsigned EAT token into a X.509 certificate.
If that X.509 certificate is an IDevID or LDevID, this becomes
another way to use EAT and DevID together.
Note that the DevID must still be used with an authentication
protocol that has a nonce or equivalent. The EAT here is not being
used as the protocol to interact with the rely party.
C.4. Device Identifier Permanence
In terms of permanence, an IDevID is similar to a UEID in that they
do not change over the life of the device. They cease to exist only
when the device is destroyed.
An SUEID is similar to an LDevID. They change on device life-cycle
events.
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[IEEE.802.1AR] describes much of this permanence as resistant to
attacks that seek to change the ID. IDevID permanence can be
described this way because [IEEE.802.1AR] is oriented around the
definition of an implementation with a particular level of defense
against attack.
EAT is not defined around a particular implementation and must work
on a range of devices that have a range of defenses against attack.
EAT thus can't be defined permanence in terms of defense against
attack. EAT's definition of permanence is in terms of operations and
device lifecycle.
Appendix D. CDDL for CWT and JWT
[RFC8392] was published before CDDL was available and thus is
specified in prose, not CDDL. Following is CDDL specifying CWT as it
is needed to complete this specification. This CDDL also covers the
Claims-Set for JWT.
Note that Section 4.3.1 requires that the iat claim be the type
~time-int (Section 7.2.1), not the type ~time when it is used in an
EAT as floating-point values are not allowed for the "iat" claim in
EAT.
The COSE-related types in this CDDL are defined in [RFC9052].
This however is NOT a normative or standard definition of CWT or JWT
in CDDL. The prose in CWT and JWT remain the normative definition.
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; This is replicated from draft-ietf-rats-uccs
Claims-Set = {
* $$Claims-Set-Claims
* Claim-Label .feature "extended-claims-label" => any
}
Claim-Label = int / text
string-or-uri = text
$$Claims-Set-Claims //= ( iss-claim-label => string-or-uri )
$$Claims-Set-Claims //= ( sub-claim-label => string-or-uri )
$$Claims-Set-Claims //= ( aud-claim-label => string-or-uri )
$$Claims-Set-Claims //= ( exp-claim-label => ~time )
$$Claims-Set-Claims //= ( nbf-claim-label => ~time )
$$Claims-Set-Claims //= ( iat-claim-label => ~time )
$$Claims-Set-Claims //= ( cti-claim-label => bytes )
iss-claim-label = JC<"iss", 1>
sub-claim-label = JC<"sub", 2>
aud-claim-label = JC<"aud", 3>
exp-claim-label = JC<"exp", 4>
nbf-claim-label = JC<"nbf", 5>
iat-claim-label = JC<"iat", 6>
cti-claim-label = CBOR-ONLY<7> ; jti in JWT: different name and text
JSON-ONLY<J> = J .feature "json"
CBOR-ONLY<C> = C .feature "cbor"
JC<J,C> = JSON-ONLY<J> / CBOR-ONLY<C>
; A JWT message is either a JWS or JWE in compact serialization form
; with the payload a Claims-Set. Compact serialization is the
; protected headers, payload and signature, each b64url encoded and
; separated by a ".". This CDDL simply matches top-level syntax of of
; a JWS or JWE since it is not possible to do more in CDDL.
JWT-Message =
text .regexp "[A-Za-z0-9_-]+\\.[A-Za-z0-9_-]+\\.[A-Za-z0-9_-]+"
; Note that the payload of a JWT is defined in claims-set.cddl. That
; definition is common to CBOR and JSON.
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; This is some CDDL describing a CWT at the top level This is
; not normative. RFC 8392 is the normative definition of CWT.
CWT-Messages = CWT-Tagged-Message / CWT-Untagged-Message
; The payload of the COSE_Message is always a Claims-Set
; The contents of a CWT Tag must always be a COSE tag
CWT-Tagged-Message = #6.61(COSE_Tagged_Message)
; An untagged CWT may be a COSE tag or not
CWT-Untagged-Message = COSE_Messages
Appendix E. New Claim Design Considerations
The following are design considerations that may be helpful to take
into account when creating new EAT claims. It is the product of
discussion in the working group.
EAT reuses the CWT and JWT claims registries. There is no registriy
exclusively for EAT claims. This is not an update to the expert
review criteria for the JWT and CWT claims registries as that would
be an overreach for this document.
E.1. Interoperability and Relying Party Orientation
It is a broad goal that EATs can be processed by relying parties in a
general way regardless of the type, manufacturer or technology of the
device from which they originate. It is a goal that there be
general-purpose verification implementations that can verify tokens
for large numbers of use cases with special cases and configurations
for different device types. This is a goal of interoperability of
the semantics of claims themselves, not just of the signing, encoding
and serialization formats.
This is a lofty goal and difficult to achieve broadly requiring
careful definition of claims in a technology neutral way. Sometimes
it will be difficult to design a claim that can represent the
semantics of data from very different device types. However, the
goal remains even when difficult.
E.2. Operating System and Technology Neutral
Claims should be defined such that they are not specific to an
operating system. They should be applicable to multiple large high-
level operating systems from different vendors. They should also be
applicable to multiple small embedded operating systems from multiple
vendors and everything in between.
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Claims should not be defined such that they are specific to a
software environment or programming language.
Claims should not be defined such that they are specific to a chip or
particular hardware. For example, they should not just be the
contents of some HW status register as it is unlikely that the same
HW status register with the same bits exists on a chip of a different
manufacturer.
The boot and debug state claims in this document are an example of a
claim that has been defined in this neutral way.
E.3. Security Level Neutral
Many use cases will have EATs generated by some of the most secure
hardware and software that exists. Secure Elements and smart cards
are examples of this. However, EAT is intended for use in low-
security use cases the same as high-security use case. For example,
an app on a mobile device may generate EATs on its own.
Claims should be defined and registered on the basis of whether they
are useful and interoperable, not based on security level. In
particular, there should be no exclusion of claims because they are
just used only in low-security environments.
E.4. Reuse of Extant Data Formats
Where possible, claims should use already standardized data items,
identifiers and formats. This takes advantage of the expertise put
into creating those formats and improves interoperability.
Often extant claims will not be defined in an encoding or
serialization format used by EAT. It is preferred to define a CBOR
and JSON encoding for them so that EAT implementations do not require
a plethora of encoders and decoders for serialization formats.
In some cases, it may be better to use the encoding and serialization
as is. For example, signed X.509 certificates and CRLs can be
carried as-is in a byte string. This retains interoperability with
the extensive infrastructure for creating and processing X.509
certificates and CRLs.
E.5. Proprietary Claims
It is not always possible or convenient to achieve the above goals,
so the definition and use of proprietary claims is an option.
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For example, a device manufacturer may generate a token with
proprietary claims intended only for verification by a service
offered by that device manufacturer. This is a supported use case.
In many cases proprietary claims will be the easiest and most obvious
way to proceed, however for better interoperability, use of general
standardized claims is preferred.
Appendix F. Endorsements and Verification Keys
The verifier must possess the correct key when it performs the
cryptographic part of an EAT verification (e.g., verifying the COSE/
JOSE signature). This section describes several ways to identify the
verification key. There is not one standard method.
The verification key itself may be a public key, a symmetric key or
something complicated in the case of a scheme like Direct Anonymous
Attestation (DAA).
RATS Architecture [RFC9334] describes what is called an endorsement.
This is an input to the verifier that is usually the basis of the
trust placed in an EAT and the attester that generated it. It may
contain the public key for verification of the signature on the EAT.
It may contain implied claims, those that are passed on to the
relying party in attestation results.
There is not yet any standard format(s) for an endorsement. One
format that may be used for an endorsement is an X.509 certificate.
Endorsement data like reference values and implied claims can be
carried in X.509 v3 extensions. In this use, the public key in the
X.509 certificate becomes the verification key, so identification of
the endorsement is also identification of the verification key.
The verification key identification and establishment of trust in the
EAT and the attester may also be by some other means than an
endorsement.
For the components (attester, verifier, relying party,...) of a
particular end-end attestation system to reliably interoperate, its
definition should specify how the verification key is identified.
Usually, this will be in the profile document for a particular
attestation system.
See also security consideration in Section 9.6.
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F.1. Identification Methods
Following is a list of possible methods of key identification. A
specific attestation system may employ any one of these or one not
listed here.
The following assumes endorsements are X.509 certificates or
equivalent and thus does not mention or define any identifier for
endorsements in other formats. If such an endorsement format is
created, new identifiers for them will also need to be created.
F.1.1. COSE/JWS Key ID
The COSE standard header parameter for Key ID (kid) may be used. See
[RFC9052] and [RFC7515]
COSE leaves the semantics of the key ID open-ended. It could be a
record locator in a database, a hash of a public key, an input to a
Key Derivation Function (KDF), an Authority Key Identifier (AKI) for
an X.509 certificate or other. The profile document should specify
what the key ID's semantics are.
F.1.2. JWS and COSE X.509 Header Parameters
COSE X.509 [COSE.X509.Draft] and JSON Web Signature [RFC7515] define
several header parameters (x5t, x5u,...) for referencing or carrying
X.509 certificates any of which may be used.
The X.509 certificate may be an endorsement and thus carrying
additional input to the verifier. It may be just an X.509
certificate, not an endorsement. The same header parameters are used
in both cases. It is up to the attestation system design and the
verifier to determine which.
F.1.3. CBOR Certificate COSE Header Parameters
Compressed X.509 and CBOR Native certificates are defined by CBOR
Certificates [CBOR.Cert.Draft]. These are semantically compatible
with X.509 and therefore can be used as an equivalent to X.509 as
described above.
These are identified by their own header parameters (c5t, c5u,...).
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F.1.4. Claim-Based Key Identification
For some attestation systems, a claim may be re-used as a key
identifier. For example, the UEID uniquely identifies the entity and
therefore can work well as a key identifier or endorsement
identifier.
This has the advantage that key identification requires no additional
bytes in the EAT and makes the EAT smaller.
This has the disadvantage that the unverified EAT must be
substantially decoded to obtain the identifier since the identifier
is in the COSE/JOSE payload, not in the headers.
Appendix G. Changes from Previous Drafts
// RFC editor: please remove this paragraph.
The following is a list of known changes since the immediately
previous drafts. This list is non-authoritative. It is meant to
help reviewers see the significant differences. A comprehensive
history is available via the IETF Datatracker's record for this
document.
G.1. From draft-ietf-rats-eat-24
* Use only CDDL definition names for "Claim Value Type" column in
CWT claim registry
* Correct the "Claim Value Type" for some claims
* Make SUIT reference informative (it use is optional in an optional
claim)
Contributors
Many thanks to the following contributors to draft versions of this
document:
Henk Birkholz
Fraunhofer SIT
Email: henk.birkholz@sit.fraunhofer.de
Thomas Fossati
Arm Limited
Email: thomas.fossati@arm.com
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Miguel Ballesteros
Michael Richardson
Sandelman Software Works
Email: mcr+ietf@sandelman.ca
Patrick Uiterwijk
Mathias Brossard
Hannes Tschofenig
Arm Limited
Email: hannes.tschofenig@arm.com
Paul Crowley
Authors' Addresses
Laurence Lundblade
Security Theory LLC
Email: lgl@securitytheory.com
Giridhar Mandyam
Email: giridhar.mandyam@gmail.com
Jeremy O'Donoghue
Qualcomm Technologies Inc.
279 Farnborough Road
Farnborough
GU14 7LS
United Kingdom
Phone: +44 1252 363189
Email: jodonogh@qti.qualcomm.com
Carl Wallace
Red Hound Software, Inc.
Email: carl@redhoundsoftware.com
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