The Entity Attestation Token (EAT)
draft-ietf-rats-eat-21



RATS                                                        L. Lundblade
Internet-Draft                                       Security Theory LLC
Intended status: Standards Track                              G. Mandyam
Expires: 1 January 2024                                    J. O'Donoghue
                                              Qualcomm Technologies Inc.
                                                              C. Wallace
                                                Red Hound Software, Inc.
                                                            30 June 2023

                   The Entity Attestation Token (EAT)
                         draft-ietf-rats-eat-21

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 how much
   it wishes to trust the entity.

   An EAT is either a CBOR Web Token (CWT) or JSON Web Token (JWT) with
   attestation-oriented claims.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on 1 January 2024.

Copyright Notice

   Copyright (c) 2023 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   5
     1.1.  Entity Overview . . . . . . . . . . . . . . . . . . . . .   6
     1.2.  EAT as a Framework  . . . . . . . . . . . . . . . . . . .   7
     1.3.  Operating Model and RATS Architecture . . . . . . . . . .   8
       1.3.1.  Relationship between Evidence and Attestation
               Results . . . . . . . . . . . . . . . . . . . . . . .   9
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .  10
   3.  Top-Level Token Definition  . . . . . . . . . . . . . . . . .  11
   4.  The Claims  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     4.1.  eat_nonce (EAT Nonce) Claim . . . . . . . . . . . . . . .  13
     4.2.  Claims Describing the Entity  . . . . . . . . . . . . . .  14
       4.2.1.  ueid (Universal Entity ID) Claim  . . . . . . . . . .  14
         4.2.1.1.  Rules for Creating UEIDs  . . . . . . . . . . . .  15
         4.2.1.2.  Rules for Consuming UEIDs . . . . . . . . . . . .  16
       4.2.2.  sueids (Semi-permanent UEIDs) Claim (SUEIDs)  . . . .  17
       4.2.3.  oemid (Hardware OEM Identification) Claim . . . . . .  18
         4.2.3.1.  Random Number Based OEMID . . . . . . . . . . . .  18
         4.2.3.2.  IEEE Based OEMID  . . . . . . . . . . . . . . . .  18
         4.2.3.3.  IANA Private Enterprise Number Based OEMID  . . .  19
       4.2.4.  hwmodel (Hardware Model) Claim  . . . . . . . . . . .  20
       4.2.5.  hwversion (Hardware Version) Claim  . . . . . . . . .  20
       4.2.6.  swname (Software Name) Claim  . . . . . . . . . . . .  21
       4.2.7.  swversion (Software Version) Claim  . . . . . . . . .  21
       4.2.8.  oemboot (OEM Authorized Boot) Claim . . . . . . . . .  21
       4.2.9.  dbgstat (Debug Status) Claim  . . . . . . . . . . . .  22
         4.2.9.1.  Enabled . . . . . . . . . . . . . . . . . . . . .  23
         4.2.9.2.  Disabled  . . . . . . . . . . . . . . . . . . . .  23
         4.2.9.3.  Disabled Since Boot . . . . . . . . . . . . . . .  23
         4.2.9.4.  Disabled Permanently  . . . . . . . . . . . . . .  23
         4.2.9.5.  Disabled Fully and Permanently  . . . . . . . . .  23
       4.2.10. location (Location) Claim . . . . . . . . . . . . . .  24
       4.2.11. uptime (Uptime) Claim . . . . . . . . . . . . . . . .  25
       4.2.12. bootcount (Boot Count) Claim  . . . . . . . . . . . .  25
       4.2.13. bootseed (Boot Seed) Claim  . . . . . . . . . . . . .  25
       4.2.14. dloas (Digital Letters of Approval) Claim . . . . . .  26
       4.2.15. manifests (Software Manifests) Claim  . . . . . . . .  27
       4.2.16. measurements (Measurements) Claim . . . . . . . . . .  28

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       4.2.17. measres (Software Measurement Results) Claim  . . . .  29
       4.2.18. submods (Submodules)  . . . . . . . . . . . . . . . .  31
         4.2.18.1.  Submodule Claims-Set . . . . . . . . . . . . . .  34
         4.2.18.2.  Detached Submodule Digest  . . . . . . . . . . .  35
         4.2.18.3.  Nested Tokens  . . . . . . . . . . . . . . . . .  35
     4.3.  Claims Describing the Token . . . . . . . . . . . . . . .  35
       4.3.1.  iat (Timestamp) Claim . . . . . . . . . . . . . . . .  36
       4.3.2.  eat_profile (EAT Profile) Claim . . . . . . . . . . .  36
       4.3.3.  intuse (Intended Use) Claim . . . . . . . . . . . . .  37
   5.  Detached EAT Bundles  . . . . . . . . . . . . . . . . . . . .  38
   6.  Profiles  . . . . . . . . . . . . . . . . . . . . . . . . . .  39
     6.1.  Format of a Profile Document  . . . . . . . . . . . . . .  40
     6.2.  List of Profile Issues  . . . . . . . . . . . . . . . . .  40
       6.2.1.  Use of JSON, CBOR or both . . . . . . . . . . . . . .  40
       6.2.2.  CBOR Map and Array Encoding . . . . . . . . . . . . .  41
       6.2.3.  CBOR String Encoding  . . . . . . . . . . . . . . . .  41
       6.2.4.  CBOR Preferred Serialization  . . . . . . . . . . . .  41
       6.2.5.  CBOR Tags . . . . . . . . . . . . . . . . . . . . . .  41
       6.2.6.  COSE/JOSE Protection  . . . . . . . . . . . . . . . .  42
       6.2.7.  COSE/JOSE Algorithms  . . . . . . . . . . . . . . . .  42
       6.2.8.  Detached EAT Bundle Support . . . . . . . . . . . . .  42
       6.2.9.  Key Identification  . . . . . . . . . . . . . . . . .  43
       6.2.10. Endorsement Identification  . . . . . . . . . . . . .  43
       6.2.11. Freshness . . . . . . . . . . . . . . . . . . . . . .  43
       6.2.12. Claims Requirements . . . . . . . . . . . . . . . . .  43
     6.3.  The Constrained Device Standard Profile . . . . . . . . .  44
   7.  Encoding and Collected CDDL . . . . . . . . . . . . . . . . .  46
     7.1.  Claims-Set and CDDL for CWT and JWT . . . . . . . . . . .  46
     7.2.  Encoding Data Types . . . . . . . . . . . . . . . . . . .  46
       7.2.1.  Common Data Types . . . . . . . . . . . . . . . . . .  47
       7.2.2.  JSON Interoperability . . . . . . . . . . . . . . . .  47
       7.2.3.  Labels  . . . . . . . . . . . . . . . . . . . . . . .  48
       7.2.4.  CBOR Interoperability . . . . . . . . . . . . . . . .  48
     7.3.  Collected CDDL  . . . . . . . . . . . . . . . . . . . . .  48
       7.3.1.  Payload CDDL  . . . . . . . . . . . . . . . . . . . .  48
       7.3.2.  CBOR-Specific CDDL  . . . . . . . . . . . . . . . . .  53
       7.3.3.  JSON-Specific CDDL  . . . . . . . . . . . . . . . . .  54
   8.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  55
     8.1.  UEID and SUEID Privacy Considerations . . . . . . . . . .  55
     8.2.  Location Privacy Considerations . . . . . . . . . . . . .  56
     8.3.  Boot Seed Privacy Considerations  . . . . . . . . . . . .  56
     8.4.  Replay Protection and Privacy . . . . . . . . . . . . . .  57
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  57
     9.1.  Claim Trustworthiness . . . . . . . . . . . . . . . . . .  57
     9.2.  Key Provisioning  . . . . . . . . . . . . . . . . . . . .  58
       9.2.1.  Transmission of Key Material  . . . . . . . . . . . .  58
     9.3.  Freshness . . . . . . . . . . . . . . . . . . . . . . . .  58
     9.4.  Multiple EAT Consumers  . . . . . . . . . . . . . . . . .  58

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     9.5.  Detached EAT Bundle Digest Security Considerations  . . .  59
     9.6.  Verification Keys . . . . . . . . . . . . . . . . . . . .  59
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  60
     10.1.  Reuse of CBOR and JSON Web Token (CWT and JWT) Claims
            Registries . . . . . . . . . . . . . . . . . . . . . . .  60
     10.2.  CWT and JWT Claims Registered by This Document . . . . .  60
     10.3.  UEID URN Registered by this Document . . . . . . . . . .  67
     10.4.  CBOR Tag for Detached EAT Bundle Registered by this
            Document . . . . . . . . . . . . . . . . . . . . . . . .  67
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  68
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  68
     11.2.  Informative References . . . . . . . . . . . . . . . . .  70
   Appendix A.  Examples . . . . . . . . . . . . . . . . . . . . . .  73
     A.1.  Claims Set Examples . . . . . . . . . . . . . . . . . . .  73
       A.1.1.  Simple TEE Attestation  . . . . . . . . . . . . . . .  73
       A.1.2.  Submodules for Board and Device . . . . . . . . . . .  75
       A.1.3.  EAT Produced by Attestation Hardware Block  . . . . .  76
       A.1.4.  Key / Key Store Attestation . . . . . . . . . . . . .  77
       A.1.5.  Software Measurements of an IoT Device  . . . . . . .  79
       A.1.6.  Attestation Results in JSON . . . . . . . . . . . . .  81
       A.1.7.  JSON-encoded Token with Sumodules . . . . . . . . . .  82
     A.2.  Signed Token Examples . . . . . . . . . . . . . . . . . .  83
       A.2.1.  Basic CWT Example . . . . . . . . . . . . . . . . . .  83
       A.2.2.  Detached EAT Bundle . . . . . . . . . . . . . . . . .  84
       A.2.3.  JSON-encoded Detached EAT Bundle  . . . . . . . . . .  86
   Appendix B.  UEID Design Rationale  . . . . . . . . . . . . . . .  87
     B.1.  Collision Probability . . . . . . . . . . . . . . . . . .  87
     B.2.  No Use of UUID  . . . . . . . . . . . . . . . . . . . . .  89
   Appendix C.  EAT Relation to IEEE.802.1AR Secure Device Identity
           (DevID) . . . . . . . . . . . . . . . . . . . . . . . . .  90
     C.1.  DevID Used With EAT . . . . . . . . . . . . . . . . . . .  91
     C.2.  How EAT Provides an Equivalent Secure Device Identity . .  91
     C.3.  An X.509 Format EAT . . . . . . . . . . . . . . . . . . .  92
     C.4.  Device Identifier Permanence  . . . . . . . . . . . . . .  92
   Appendix D.  CDDL for CWT and JWT . . . . . . . . . . . . . . . .  92
   Appendix E.  New Claim Design Considerations  . . . . . . . . . .  94
     E.1.  Interoperability and Relying Party Orientation  . . . . .  94
     E.2.  Operating System and Technology Neutral . . . . . . . . .  94
     E.3.  Security Level Neutral  . . . . . . . . . . . . . . . . .  95
     E.4.  Reuse of Extant Data Formats  . . . . . . . . . . . . . .  95
     E.5.  Proprietary Claims  . . . . . . . . . . . . . . . . . . .  95
   Appendix F.  Endorsements and Verification Keys . . . . . . . . .  96
     F.1.  Identification Methods  . . . . . . . . . . . . . . . . .  97
       F.1.1.  COSE/JWS Key ID . . . . . . . . . . . . . . . . . . .  97
       F.1.2.  JWS and COSE X.509 Header Parameters  . . . . . . . .  97
       F.1.3.  CBOR Certificate COSE Header Parameters . . . . . . .  97
       F.1.4.  Claim-Based Key Identification  . . . . . . . . . . .  98
   Appendix G.  Changes from Previous Drafts . . . . . . . . . . . .  98

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     G.1.  From draft-ietf-rats-eat-20 . . . . . . . . . . . . . . .  98
   Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .  98
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  99

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] 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 GPS location

   *  Formal certifications received

   EAT is constructed to support a wide range of use cases.

   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

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   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 TPMs 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 JSON [RFC8259] or 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.

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 [RATS.Architecture].

   Layered attestation and composite devices, as described in
   [RATS.Architecture], 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

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   *  A TEE

   *  A network card in a router

   *  A router, perhaps with each network card in the router a submodule

   *  An 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.

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 COSE and 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.

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   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.

   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].  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.

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   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.

   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 (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.

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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
      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
   [RATS.Architecture]:

   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.

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   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]

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

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   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).

   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

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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).

   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.

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   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.  The minimum size is 8 bytes.
   The maximum size is 64 bytes.

   In JSON, an EAT nonce is a text string.  It is assumed that only
   characters represented by the lower 7 bits of each byte will be used,
   so the text string must be one-seventh longer because the 8th bit
   doesn't contribute to entropy.  The minimum size for JSON-encoded
   EATs is 10 bytes and the maximum size is 74 bytes.

   $$Claims-Set-Claims //=
       (nonce-label => nonce-type / [ 2* nonce-type ])

   nonce-type = JC< tstr .size (10..74), 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.

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.  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

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   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 textual 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 (12..44) , bstr .size (7..33)>

4.2.1.1.  Rules for Creating UEIDs

   These rules are solely for the creation of UEIDs.  The 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.

   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 uses the IEEE company identification           |
   |      | EUI  | registry.  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) [IEEE.802-2001],    |
   |      |      | [OUI.Guide].                                        |
   +------+------+-----------------------------------------------------+
   | 0x03 | IMEI | This is a 14-digit identifier consisting of an      |
   |      |      | 8-digit Type Allocation Code 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

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.

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   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.

   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.

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   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.

4.2.3.1.  Random Number Based OEMID

   The random number based OEMID MUST always be 16 bytes (128 bits)
   long.

   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 OEMID

   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].

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   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 OEMID

   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.

   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

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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.

   $$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
   [CoSWID].  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.

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   $$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 item to
   give a simple version for the software.  A full CoSWID manifest or
   other type of manifest can be instead if this is too simple.  A
   "swversion" claim MUST only be present if a "swname" claim described
   in Section 4.2.6 is present.

   $$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 ROM, a combination of the two or other.  If this claim is present
   the "oemid" claim SHOULD always also be present.

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   $$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
   root, operating system or privileged software that allow 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.

   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.

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   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.

4.2.9.5.  Disabled Fully and Permanently

   This level indicates that all debug facilities for the entity are
   permanently disabled.

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   $$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 GPS 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 MUST contain a value that represents 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).

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   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.

   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 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 URI 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 URI, 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.

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   $$Claims-Set-Claims //= (
       dloas-label => [ + dloa-type ]
   )

   dloa-type = [
       dloa_registrar: general-uri
       dloa_platform_label: text
       ? dloa_application_label: text
   ]

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 is they are
   created by the software manufacturer.  The purpose of these claims in
   an EAT is to relay them without modification 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 claim allows multiple formats for the manifest.  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 CoAP
   Content-Format integer [RFC7252].  If there is no CoAP identifier
   registered for the 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.

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   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 [CoSWID].

   A [SUIT.Manifest] may be used as a manifest.

   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).

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   This claim can be a [CoSWID].  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.

   $$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, ...

   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.

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   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.

   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-Type /= "JWT" / "CBOR" / "BUNDLE" / "DIGEST"
   $JSON-Selector-Value /= JWT-Message /
                     CBOR-Token-Inside-JSON-Token /
                     Detached-EAT-Bundle /
                     Detached-Submodule-Digest

   JSON-Selector = [
      type : $JSON-Selector-Type,
      nested-token : $JSON-Selector-Value
   ]

   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-Type and $JSON-
   Selector-Value sockets.

   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 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 URL or
   an 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.TBD(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.  List of Profile Issues

   The following is a list of EAT, CWT, JWT, COSE, JOSE and CBOR options
   that a profile should address.

6.2.1.  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.

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6.2.2.  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.

   For most use cases, specifying that only definite-length arrays/maps
   may be sent is suitable.

6.2.3.  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.

6.2.4.  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.

6.2.5.  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.

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6.2.6.  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.

   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.

6.2.7.  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 6.2.6.
   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.

6.2.8.  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.

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6.2.9.  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
   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.

6.2.10.  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.

6.2.11.  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 [RATS.Architecture] 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.

6.2.12.  Claims Requirements

   A profile may define new claims that are not defined in this
   document.

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   This document requires an EAT receiver must accept all 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
   of this, allowing the use of CoSWID, TEEP Manifests 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.

6.3.  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 "https://www.rfc-editor.org/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   |
       | Bundle Usage   | with this profile                       |
       +----------------+-----------------------------------------+
       | Verification   | Either the COSE kid or the UEID MUST be |
       | Key            | used to identify the verification key.  |
       | Identification | If both are present, the kid takes      |
       |                | precedence                              |
       +----------------+-----------------------------------------+
       | Endorsements   | This profile contains no endorsement    |
       |                | identifier                              |
       +----------------+-----------------------------------------+
       | Nonce          | 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

   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.

   The OID encoding from [RFC9090] is used without the tag number in
   CBOR-encoded tokens.  In JSON 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].

   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.

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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.

   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 that that 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

   $$Claims-Set-Claims //=
       (nonce-label => nonce-type / [ 2* nonce-type ])

   nonce-type = JC< tstr .size (10..74), bstr .size (8..64)>

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   $$Claims-Set-Claims //= (ueid-label => ueid-type)

   ueid-type = JC<base64-url-text .size (12..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 )

   $$Claims-Set-Claims //= (sw-version-label => sw-version-type)

   sw-version-type = [
       version:  tstr
       ? scheme:  $version-scheme

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   ]

   $$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 >

   $$Claims-Set-Claims //= (uptime-label => uint)

   $$Claims-Set-Claims //=  (boot-seed-label => binary-data)

   $$Claims-Set-Claims //= (boot-count-label => uint)

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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 >

   $$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
   $manifest-body-json /= base64-url-text

   $$Claims-Set-Claims //= (
       measurements-label => measurements-type
   )

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   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
   ]

   BUNDLE-Messages = BUNDLE-Tagged-Message / BUNDLE-Untagged-Message

   BUNDLE-Tagged-Message   = #6.TBD(BUNDLE-Untagged-Message)
   BUNDLE-Untagged-Message = Detached-EAT-Bundle

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   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

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   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-Type /= "JWT" / "CBOR" / "BUNDLE" / "DIGEST"
   $JSON-Selector-Value /= JWT-Message /
                     CBOR-Token-Inside-JSON-Token /
                     Detached-EAT-Bundle /
                     Detached-Submodule-Digest

   JSON-Selector = [
      type : $JSON-Selector-Type,
      nested-token : $JSON-Selector-Value
   ]

   CBOR-Token-Inside-JSON-Token = base64-url-text

   $$Claims-Set-Claims //= (submods-label => { + text => Submodule })

   Submodule = Claims-Set / JSON-Selector

8.  Privacy Considerations

   Certain EAT claims can be used to track the owner of an entity and
   therefore, implementations should consider providing privacy-
   preserving options dependent on the intended usage of the EAT.
   Examples would include suppression of location claims for EAT's
   provided 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.

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   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.

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.

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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 [RATS.Architecture] 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.

   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.

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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.

9.3.  Freshness

   All EAT use MUST provide a freshness mechanism to prevent replay and
   related attacks.  The extensive discussions on freshness in
   [RATS.Architecture] 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.

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   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 unsigned
   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 a modified detached
   claims because the algorithms in the COSE registry are assumed to be
   of sufficient cryptographic strength.

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].

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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.

   // RFC editor: please remove this paragraph.

   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"

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   *  Claim Key: 10

   *  Claim Value Type(s): byte string

   *  Change Controller: IESG

   *  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): byte string

   *  Change Controller: IESG

   *  Specification Document(s): *this document*

   *  Claim Name: SUEIDs

   *  Claim Description: Semi-permanent UEIDs

   *  JWT Claim Name: "sueids"

   *  CWT Claim Key: 257

   *  Claim Value Type(s): map

   *  Change Controller: IESG

   *  Specification Document(s): *this document*

   *  Claim Name: Hardware OEMID

   *  Claim Description: Hardware OEM ID

   *  JWT Claim Name: "oemid"

   *  Claim Key: 258

   *  Claim Value Type(s): byte string or integer

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   *  Change Controller: IESG

   *  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): byte string

   *  Change Controller: IESG

   *  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

   *  Change Controller: IESG

   *  Specification Document(s): *this document*

   *  Claim Name: OEM Authortised Boot

   *  Claim Description: Indicate whether the software booted was OEM
      authorized

   *  JWT Claim Name: "oemboot"

   *  Claim Key: 262

   *  Claim Value Type(s): Boolean

   *  Change Controller: IESG

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   *  Specification Document(s): *this document*

   *  Claim Name: Debug Status

   *  Claim Description: Indicate status of debug facilities

   *  JWT Claim Name: "dbgstat"

   *  Claim Key: 263

   *  Claim Value Type(s): integer or string

   *  Change Controller: IESG

   *  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: IESG

   *  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: IESG

   *  Specification Document(s): *this document*

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   *  Claim Name: Submodules Section

   *  Claim Description: The section containing submodules

   *  JWT Claim Name: "submods"

   *  Claim Key: 266

   *  Claim Value Type(s): map

   *  Change Controller: IESG

   *  Specification Document(s): *this document*

   *  Claim Name: Uptime

   *  Claim Description: Uptime

   *  JWT Claim Name: "uptime"

   *  Claim Key: TBD

   *  Claim Value Type(s): unsigned integer

   *  Change Controller: IESG

   *  Specification Document(s): *this document*

   *  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: IESG

   *  Specification Document(s): *this document*

   *  Claim Name: Boot Seed

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   *  Claim Description: Identifies a boot cycle

   *  JWT Claim Name: "bootseed"

   *  Claim Key: TBD

   *  Claim Value Type(s): bytes

   *  Change Controller: IESG

   *  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: IESG

   *  Specification Document(s): *this document*

   *  Claim Name: Software Name

   *  Claim Description: The name of the software running in the entity

   *  JWT Claim Name: "swname"

   *  Claim Key: TBD

   *  Claim Value Type(s): map

   *  Change Controller: IESG

   *  Specification Document(s): *this document*

   *  Claim Name: Software Version

   *  Claim Description: The version of software running in the entity

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   *  JWT Claim Name: "swversion"

   *  Claim Key: TBD

   *  Claim Value Type(s): map

   *  Change Controller: IESG

   *  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: IESG

   *  Specification Document(s): *this document*

   *  Claim Name: Measurements

   *  Claim Description: Measurements of the software, memory
      configuration and such on the entity

   *  JWT Claim Name: "measurements"

   *  Claim Key: TBD

   *  Claim Value Type(s): array

   *  Change Controller: IESG

   *  Specification Document(s): *this document*

   *  Claim Name: Software Measurement Results

   *  Claim Description: The results of comparing software measurements
      to reference values

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   *  JWT Claim Name: "measres"

   *  Claim Key: TBD

   *  Claim Value Type(s): array

   *  Change Controller: IESG

   *  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): integer or string

   *  Change Controller: IESG

   *  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].

         +=========+=============================+===============+
         | Subtype | Description                 | Reference     |
         +=========+=============================+===============+
         | ueid    | Universal Entity Identifier | This document |
         +---------+-----------------------------+---------------+
         | sueid   | Semi-permanent Universal    | This document |
         |         | Entity Identifier           |               |
         +---------+-----------------------------+---------------+

                                  Table 3

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 FCFS space, with the present document as the
   specification reference.

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          +========+============+===============================+
          | Tag    | Data Items | Semantics                     |
          +========+============+===============================+
          | TBD602 | array      | Detached EAT Bundle Section 5 |
          +--------+------------+-------------------------------+

                                  Table 4

11.  References

11.1.  Normative References

   [CoSWID]   Birkholz, H., Fitzgerald-McKay, J., Schmidt, C., and D.
              Waltermire, "Concise Software Identification Tags", Work
              in Progress, Internet-Draft, draft-ietf-sacm-coswid-24, 24
              February 2023, <https://datatracker.ietf.org/doc/html/
              draft-ietf-sacm-coswid-24>.

   [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>.

   [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>.

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   [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>.

   [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>.

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   [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>.

   [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-22, 27 February
              2023, <https://datatracker.ietf.org/doc/html/draft-ietf-
              suit-manifest-22>.

   [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

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   [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-05, 10 January 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-cose-
              cbor-encoded-cert-05>.

   [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-02, 10 March 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-rats-
              eat-media-type-02>.

   [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>.

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   [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>.

   [RATS.Architecture]
              Birkholz, H., Thaler, D., Richardson, M., Smith, N., and
              W. Pan, "Remote ATtestation procedureS (RATS)
              Architecture", Work in Progress, Internet-Draft, draft-
              ietf-rats-architecture-22, 28 September 2022,
              <https://datatracker.ietf.org/doc/html/draft-ietf-rats-
              architecture-22>.

   [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>.

   [RFC7120]  Cotton, M., "Early IANA Allocation of Standards Track Code
              Points", BCP 100, RFC 7120, DOI 10.17487/RFC7120, January
              2014, <https://www.rfc-editor.org/info/rfc7120>.

   [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>.

   [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-05,
              1 February 2023, <https://datatracker.ietf.org/doc/html/
              draft-ietf-rats-uccs-05>.

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   [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.

   WARNING: These examples use tag and label numbers not yet assigned by
   IANA.

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, for example a   /
   / 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.                    /
   /                                                              /
   / This is similar to Android Key Attestation.                  /

   {
       / 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

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                                       0c000169436172626f6e6974650d6331
                                       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 and 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

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                                         280c4bb8c75f716a43c99526694caa
                                         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 Sumodules

   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 ECDSA signed CWT-format token.

   / 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.  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, "CS1" and "CS2".
   The JWT at the start of the bundle has detached signature submodules
   with hashes of "CS1" and "CS2".  TODO: make the JWT actually be
   correct verifiable JWT.

   This example has its lines wrapped per [RFC8792].

   [
      [
         "JWT",
         "eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJpc3MiOiJKLUF0dGVzdGVy\
   IiwiaWF0IjoxNjUxNzc0ODY4LCJleHAiOm51bGwsImF1ZCI6IiIsInN1YiI6IiJ9.gjw\
   4nFMhLpJUuPXvMPzK1GMjhyJq2vWXg1416XKszwQ"
      ],
      {
         "Audio Subsystem Claims": "ewogICAgICAgICAgICAibm9uY2UiOiAgICA\
   gImxJK0lZTkU2Umo2TyIsCiAgICAgICAgICAgICJpYXQiOiAgICAgIDE1MjY1NDI4OTQ\
   KICAgICAgICAgfQo=",
         "Graphics Subsystem Claims": "ewogICAgICAgICAgICAibm9uY2UiOiAg\
   ICJsSStJWU5FNlJqNk8iLAogICAgICAgICAgICAiaWF0IjogICAgIDE1MjY1NDI4OTQK\
   ICAgICAgICB9"
      }
   ]

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Appendix B.  UEID Design Rationale

B.1.  Collision Probability

   This calculation is to determine the probability of a collision of
   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.

   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

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   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

   +=====================+==============+==============+==============+
   | 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

   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.

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   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

   Clearly, 128 bits is enough for the near future thus the requirement
   that 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 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

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   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.

   [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.

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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 and 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.

   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.

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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.

   [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].

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   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.

   ; 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 [RATS.Architecture] 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
   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-20

   *  Uniformly use term "base64url-encoded"

   *  Add comment that MAC-based UEIDs are shorter than UUIDs

   *  Clarify that DLOAs must be authentic

   *  Require equivalent encryption when relaying between multiple EAT
      consumers

   *  "MUST" instead of "must" for freshness security considerations.

   *  Spelling and grammar fixes

Contributors

   Many thanks to the following contributors to draft versions of this
   document:

   Henk Birkholz
   Fraunhofer SIT
   Email: henk.birkholz@sit.fraunhofer.de

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   Thomas Fossati
   Arm Limited
   Email: thomas.fossati@arm.com

   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
   Qualcomm Technologies Inc.
   5775 Morehouse Drive
   San Diego, California
   United States of America
   Phone: +1 858 651 7200
   Email: mandyam@qti.qualcomm.com

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   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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