The Entity Attestation Token (EAT)
draft-ietf-rats-eat-10

Document Type Active Internet-Draft (rats WG)
Authors Giridhar Mandyam  , Laurence Lundblade  , Miguel Ballesteros  , Jeremy O'Donoghue 
Last updated 2021-06-07
Replaces draft-mandyam-rats-eat
Stream Internet Engineering Task Force (IETF)
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Stream WG state WG Document (wg milestone: Mar 2021 - Submit EAT draft to ... )
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RATS Working Group                                            G. Mandyam
Internet-Draft                                Qualcomm Technologies Inc.
Intended status: Standards Track                            L. Lundblade
Expires: December 9, 2021                            Security Theory LLC
                                                          M. Ballesteros
                                                           J. O'Donoghue
                                              Qualcomm Technologies Inc.
                                                           June 07, 2021

                   The Entity Attestation Token (EAT)
                         draft-ietf-rats-eat-10

Abstract

   An Entity Attestation Token (EAT) provides a signed (attested) set of
   claims that describe state and characteristics of an entity,
   typically a device like a phone or an IoT device.  These claims are
   used by a relying party to determine how much it wishes to trust the
   entity.

   An EAT is either a CWT or JWT with some attestation-oriented claims.
   To a large degree, all this document does is extend CWT and JWT.

Contributing

   TBD

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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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on December 9, 2021.

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Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   5
     1.1.  CWT, JWT and UCCS . . . . . . . . . . . . . . . . . . . .   6
     1.2.  CDDL  . . . . . . . . . . . . . . . . . . . . . . . . . .   6
     1.3.  Entity Overview . . . . . . . . . . . . . . . . . . . . .   6
     1.4.  Use as Evidence and Attestation Results . . . . . . . . .   7
     1.5.  EAT Operating Models  . . . . . . . . . . . . . . . . . .   7
     1.6.  What is Not Standardized  . . . . . . . . . . . . . . . .   9
       1.6.1.  Transmission Protocol . . . . . . . . . . . . . . . .   9
       1.6.2.  Signing Scheme  . . . . . . . . . . . . . . . . . . .   9
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .  10
   3.  The Claims  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     3.1.  Token ID Claim (cti and jti)  . . . . . . . . . . . . . .  11
     3.2.  Timestamp claim (iat) . . . . . . . . . . . . . . . . . .  11
     3.3.  Nonce Claim (nonce) . . . . . . . . . . . . . . . . . . .  12
       3.3.1.  nonce CDDL  . . . . . . . . . . . . . . . . . . . . .  12
     3.4.  Universal Entity ID Claim (ueid)  . . . . . . . . . . . .  12
       3.4.1.  ueid CDDL . . . . . . . . . . . . . . . . . . . . . .  15
     3.5.  Semi-permanent UEIDs (SUEIDs) . . . . . . . . . . . . . .  15
     3.6.  OEM Identification by IEEE (oemid)  . . . . . . . . . . .  16
       3.6.1.  oemid CDDL  . . . . . . . . . . . . . . . . . . . . .  16
     3.7.  Hardware Version Claims (hardware-version-claims) . . . .  16
     3.8.  Software Description and Version  . . . . . . . . . . . .  17
     3.9.  The Security Level Claim (security-level) . . . . . . . .  17
       3.9.1.  security-level CDDL . . . . . . . . . . . . . . . . .  18
     3.10. Secure Boot Claim (secure-boot) . . . . . . . . . . . . .  19
       3.10.1.  secure-boot CDDL . . . . . . . . . . . . . . . . . .  19
     3.11. Debug Status Claim (debug-status) . . . . . . . . . . . .  19
       3.11.1.  Enabled  . . . . . . . . . . . . . . . . . . . . . .  20
       3.11.2.  Disabled . . . . . . . . . . . . . . . . . . . . . .  21
       3.11.3.  Disabled Since Boot  . . . . . . . . . . . . . . . .  21
       3.11.4.  Disabled Permanently . . . . . . . . . . . . . . . .  21

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       3.11.5.  Disabled Fully and Permanently . . . . . . . . . . .  21
       3.11.6.  debug-status CDDL  . . . . . . . . . . . . . . . . .  21
     3.12. Including Keys  . . . . . . . . . . . . . . . . . . . . .  22
     3.13. The Location Claim (location) . . . . . . . . . . . . . .  22
       3.13.1.  location CDDL  . . . . . . . . . . . . . . . . . . .  23
     3.14. The Uptime Claim (uptime) . . . . . . . . . . . . . . . .  24
       3.14.1.  uptime CDDL  . . . . . . . . . . . . . . . . . . . .  24
     3.15. The Boot Seed Claim (boot-seed) . . . . . . . . . . . . .  24
     3.16. The Intended Use Claim (intended-use) . . . . . . . . . .  24
       3.16.1.  intended-use CDDL  . . . . . . . . . . . . . . . . .  25
     3.17. The Profile Claim (profile) . . . . . . . . . . . . . . .  25
     3.18. The Software Manifests Claim (manifests)  . . . . . . . .  26
     3.19. The Software Evidence Claim {swevidence}  . . . . . . . .  27
     3.20. The Submodules Part of a Token (submods)  . . . . . . . .  28
       3.20.1.  Two Types of Submodules  . . . . . . . . . . . . . .  28
         3.20.1.1.  Non-token Submodules . . . . . . . . . . . . . .  29
         3.20.1.2.  Nested EATs  . . . . . . . . . . . . . . . . . .  29
         3.20.1.3.  Unsecured JWTs and UCCS Tokens as Submodules . .  30
       3.20.2.  No Inheritance . . . . . . . . . . . . . . . . . . .  30
       3.20.3.  Security Levels  . . . . . . . . . . . . . . . . . .  31
       3.20.4.  Submodule Names  . . . . . . . . . . . . . . . . . .  31
       3.20.5.  submods CDDL . . . . . . . . . . . . . . . . . . . .  31
   4.  Endorsements and Verification Keys  . . . . . . . . . . . . .  32
     4.1.  Identification Methods  . . . . . . . . . . . . . . . . .  33
       4.1.1.  COSE/JWS Key ID . . . . . . . . . . . . . . . . . . .  33
       4.1.2.  JWS and COSE X.509 Header Parameters  . . . . . . . .  34
       4.1.3.  CBOR Certificate COSE Header Parameters . . . . . . .  34
       4.1.4.  Claim-Based Key Identification  . . . . . . . . . . .  34
     4.2.  Other Considerations  . . . . . . . . . . . . . . . . . .  34
   5.  Profiles  . . . . . . . . . . . . . . . . . . . . . . . . . .  35
     5.1.  Format of a Profile Document  . . . . . . . . . . . . . .  35
     5.2.  List of Profile Issues  . . . . . . . . . . . . . . . . .  35
       5.2.1.  Use of JSON, CBOR or both . . . . . . . . . . . . . .  35
       5.2.2.  CBOR Map and Array Encoding . . . . . . . . . . . . .  35
       5.2.3.  CBOR String Encoding  . . . . . . . . . . . . . . . .  36
       5.2.4.  CBOR Preferred Serialization  . . . . . . . . . . . .  36
       5.2.5.  COSE/JOSE Protection  . . . . . . . . . . . . . . . .  36
       5.2.6.  COSE/JOSE Algorithms  . . . . . . . . . . . . . . . .  36
       5.2.7.  Verification Key Identification . . . . . . . . . . .  37
       5.2.8.  Endorsement Identification  . . . . . . . . . . . . .  37
       5.2.9.  Freshness . . . . . . . . . . . . . . . . . . . . . .  37
       5.2.10. Required Claims . . . . . . . . . . . . . . . . . . .  37
       5.2.11. Prohibited Claims . . . . . . . . . . . . . . . . . .  37
       5.2.12. Additional Claims . . . . . . . . . . . . . . . . . .  37
       5.2.13. Refined Claim Definition  . . . . . . . . . . . . . .  37
       5.2.14. CBOR Tags . . . . . . . . . . . . . . . . . . . . . .  38
       5.2.15. Manifests and Software Evidence Claims  . . . . . . .  38
   6.  Encoding  . . . . . . . . . . . . . . . . . . . . . . . . . .  38

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     6.1.  Common CDDL Types . . . . . . . . . . . . . . . . . . . .  38
     6.2.  CDDL for CWT-defined Claims . . . . . . . . . . . . . . .  38
     6.3.  JSON  . . . . . . . . . . . . . . . . . . . . . . . . . .  39
       6.3.1.  JSON Labels . . . . . . . . . . . . . . . . . . . . .  39
       6.3.2.  JSON Interoperability . . . . . . . . . . . . . . . .  40
     6.4.  CBOR  . . . . . . . . . . . . . . . . . . . . . . . . . .  41
       6.4.1.  CBOR Interoperability . . . . . . . . . . . . . . . .  41
         6.4.1.1.  EAT Constrained Device Serialization  . . . . . .  41
     6.5.  Collected CDDL  . . . . . . . . . . . . . . . . . . . . .  42
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  47
     7.1.  Reuse of CBOR Web Token (CWT) Claims Registry . . . . . .  47
     7.2.  Claim Characteristics . . . . . . . . . . . . . . . . . .  48
       7.2.1.  Interoperability and Relying Party Orientation  . . .  48
       7.2.2.  Operating System and Technology Neutral . . . . . . .  48
       7.2.3.  Security Level Neutral  . . . . . . . . . . . . . . .  49
       7.2.4.  Reuse of Extant Data Formats  . . . . . . . . . . . .  49
       7.2.5.  Proprietary Claims  . . . . . . . . . . . . . . . . .  49
     7.3.  Claims Registered by This Document  . . . . . . . . . . .  49
       7.3.1.  Claims for Early Assignment . . . . . . . . . . . . .  50
       7.3.2.  To be Assigned Claims . . . . . . . . . . . . . . . .  53
       7.3.3.  Version Schemes Registered by this Document . . . . .  53
   8.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  53
     8.1.  UEID and SUEID Privacy Considerations . . . . . . . . . .  53
     8.2.  Location Privacy Considerations . . . . . . . . . . . . .  54
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  54
     9.1.  Key Provisioning  . . . . . . . . . . . . . . . . . . . .  55
       9.1.1.  Transmission of Key Material  . . . . . . . . . . . .  55
     9.2.  Transport Security  . . . . . . . . . . . . . . . . . . .  55
     9.3.  Multiple EAT Consumers  . . . . . . . . . . . . . . . . .  56
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  56
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  56
     10.2.  Informative References . . . . . . . . . . . . . . . . .  59
   Appendix A.  Examples . . . . . . . . . . . . . . . . . . . . . .  61
     A.1.  Very Simple EAT . . . . . . . . . . . . . . . . . . . . .  61
     A.2.  Example with Submodules, Nesting and Security Levels  . .  61
   Appendix B.  UEID Design Rationale  . . . . . . . . . . . . . . .  61
     B.1.  Collision Probability . . . . . . . . . . . . . . . . . .  62
     B.2.  No Use of UUID  . . . . . . . . . . . . . . . . . . . . .  64
   Appendix C.  EAT Relation to IEEE.802.1AR Secure Device Identity
                (DevID)  . . . . . . . . . . . . . . . . . . . . . .  65
     C.1.  DevID Used With EAT . . . . . . . . . . . . . . . . . . .  65
     C.2.  How EAT Provides an Equivalent Secure Device Identity . .  66
     C.3.  An X.509 Format EAT . . . . . . . . . . . . . . . . . . .  66
     C.4.  Device Identifier Permanence  . . . . . . . . . . . . . .  67
   Appendix D.  Changes from Previous Drafts . . . . . . . . . . . .  67
     D.1.  From draft-rats-eat-01  . . . . . . . . . . . . . . . . .  67
     D.2.  From draft-mandyam-rats-eat-00  . . . . . . . . . . . . .  67
     D.3.  From draft-ietf-rats-eat-01 . . . . . . . . . . . . . . .  67

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     D.4.  From draft-ietf-rats-eat-02 . . . . . . . . . . . . . . .  68
     D.5.  From draft-ietf-rats-eat-03 . . . . . . . . . . . . . . .  68
     D.6.  From draft-ietf-rats-eat-04 . . . . . . . . . . . . . . .  68
     D.7.  From draft-ietf-rats-05 . . . . . . . . . . . . . . . . .  69
     D.8.  From draft-ietf-rats-06 . . . . . . . . . . . . . . . . .  69
     D.9.  From draft-ietf-rats-07 . . . . . . . . . . . . . . . . .  69
     D.10. From draft-ietf-rats-08 . . . . . . . . . . . . . . . . .  69
     D.11. From draft-ietf-rats-09 . . . . . . . . . . . . . . . . .  69
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  70

1.  Introduction

   Remote device attestation is a fundamental service that allows a
   remote device such as a mobile phone, an Internet-of-Things (IoT)
   device, or other endpoint to prove itself to a relying party, a
   server or a service.  This allows the relying party to know some
   characteristics about the device and decide whether it trusts the
   device.

   Remote attestation is a fundamental service that can underlie other
   protocols and services that need to know about the trustworthiness of
   the device before proceeding.  One good example is biometric
   authentication where the biometric matching is done on the device.
   The relying party needs to know that the device is one that is known
   to do biometric matching correctly.  Another example is content
   protection where the relying party wants to know the device will
   protect the data.  This generalizes on to corporate enterprises that
   might want to know that a device is trustworthy before allowing
   corporate data to be accessed by it.

   The notion of attestation here is large and may include, but is not
   limited to the following:

   o  Proof of the make and model of the device hardware (HW)

   o  Proof of the make and model of the device processor, particularly
      for security-oriented chips

   o  Measurement of the software (SW) running on the device

   o  Configuration and state of the device

   o  Environmental characteristics of the device such as its GPS
      location

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1.1.  CWT, JWT and UCCS

   For flexibility and ease of imlpementation in a wide variety of
   environments, EATs can be either CBOR [RFC8949] or JSON [ECMAScript]
   format.  This specification simultaneously describes both formats.

   An EAT is either a CWT as defined in [RFC8392], a UCCS as defined in
   [UCCS.Draft], or a JWT as defined in [RFC7519].  This specification
   extends those specifications with additional claims for attestation.

   The identification of a protocol element as an EAT, whether CBOR or
   JSON format, follows the general conventions used by CWT, JWT and
   UCCS.  Largely this depends on the protocol carrying the EAT.  In
   some cases it may be by content type (e.g., MIME type).  In other
   cases it may be through use of CBOR tags.  There is no fixed
   mechanism across all use cases.

1.2.  CDDL

   This specification uses CDDL, [RFC8610], as the primary formalism to
   define each claim.  The implementor then interprets the CDDL to come
   to either the CBOR [RFC8949] or JSON [ECMAScript] representation.  In
   the case of JSON, Appendix E of [RFC8610] is followed.  Additional
   rules are given in Section 6.3.2 of this document where Appendix E is
   insufficient.  (Note that this is not to define a general means to
   translate between CBOR and JSON, but only to define enough such that
   the claims defined in this document can be rendered unambiguously in
   JSON).

   The CWT specification was authored before CDDL was available and did
   not use it.  This specification includes a CDDL definition of most of
   what is described in [RFC8392].

1.3.  Entity Overview

   An "entity" can be any device or device subassembly ("submodule")
   that can generate its own attestation in the form of an EAT.  The
   attestation should be cryptographically verifiable by the EAT
   consumer.  An EAT at the device-level can be composed of several
   submodule EAT's.

   Modern devices such as a mobile phone have many different execution
   environments operating with different security levels.  For example,
   it is common for a mobile phone to have an "apps" environment that
   runs an operating system (OS) that hosts a plethora of downloadable
   apps.  It may also have a TEE (Trusted Execution Environment) that is
   distinct, isolated, and hosts security-oriented functionality like
   biometric authentication.  Additionally, it may have an eSE (embedded

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   Secure Element) - a high security chip with defenses against HW
   attacks that is used to produce attestations.  This device
   attestation format allows the attested data to be tagged at a
   security level from which it originates.  In general, any discrete
   execution environment that has an identifiable security level can be
   considered an entity.

1.4.  Use as Evidence and Attestation Results

   Here, normative reference is made to [RATS-Architecture],
   particularly the definition of Evidence, the Verifier, Attestation
   Results and the Relying Party.  Per Figure 1 in [RATS-Architecture],
   Evidence is a protocol message that goes from the Attester to the
   Verifier and Attestation Results a message that goes from the
   Verifier to the Relying Party.  EAT is defined such that it can be
   used to represent either Evidence, Attestation Results or both.  No
   claims defined here are considered exclusive to or are prohibited in
   either use.  It is useful to create EAT profiles as described in
   Section 5 for either use.

   It is useful to characterize the relationship of claims in Evidence
   to those in Attestation Results.

   Many claims in Evidence simply will pass through the Verifier to the
   Relying Party without modification.  They will be verified as
   authentic from the device by the Verifier just through normal
   verification of the Attester's signature.  They will be protected
   from modification when they are conveyed to the Relying Party by
   whatever means is used to protect Attestation Results.  (The details
   of that protection are out of scope of this document.)

   Some claims in Evidence will be verified by the Verifier by
   comparison to Reference Values.  In this case the claims in Evidence
   will not likely be conveyed to the Relying Party.  Instead, some
   claim indicating they were checked may be added to the Attestation
   Results or it may be tacitly known that the Verifier always does this
   check.

   In some cases the Verifier may provide privacy-preserving
   functionality by stripping or modifying claims that do not posses
   sufficient privacy-preserving characteristics.

1.5.  EAT Operating Models

   TODO: Rewrite (or eliminate) this section in light of the RATS
   architecture draft.

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   At least the following three participants exist in all EAT operating
   models.  Some operating models have additional participants.

   The Entity.  This is the phone, the IoT device, the sensor, the sub-
      assembly or such that the attestation provides information about.

   The Manufacturer.  The company that made the entity.  This may be a
      chip vendor, a circuit board module vendor or a vendor of finished
      consumer products.

   The Relying Party.  The server, service or company that makes use of
      the information in the EAT about the entity.

   In all operating models, the manufacturer provisions some secret
   attestation key material (AKM) into the entity during manufacturing.
   This might be during the manufacturer of a chip at a fabrication
   facility (fab) or during final assembly of a consumer product or any
   time in between.  This attestation key material is used for signing
   EATs.

   In all operating models, hardware and/or software on the entity
   create an EAT of the format described in this document.  The EAT is
   always signed by the attestation key material provisioned by the
   manufacturer.

   In all operating models, the relying party must end up knowing that
   the signature on the EAT is valid and consistent with data from
   claims in the EAT.  This can happen in many different ways.  Here are
   some examples.

   o  The EAT is transmitted to the relying party.  The relying party
      gets corresponding key material (e.g. a root certificate) from the
      manufacturer.  The relying party performs the verification.

   o  The EAT is transmitted to the relying party.  The relying party
      transmits the EAT to a verification service offered by the
      manufacturer.  The server returns the validated claims.

   o  The EAT is transmitted directly to a verification service, perhaps
      operated by the manufacturer or perhaps by another party.  It
      verifies the EAT and makes the validated claims available to the
      relying party.  It may even modify the claims in some way and re-
      sign the EAT (with a different signing key).

   All these operating models are supported and there is no preference
   of one over the other.  It is important to support this variety of
   operating models to generally facilitate deployment and to allow for
   some special scenarios.  One special scenario has a validation

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   service that is monetized, most likely by the manufacturer.  In
   another, a privacy proxy service processes the EAT before it is
   transmitted to the relying party.  In yet another, symmetric key
   material is used for signing.  In this case the manufacturer should
   perform the verification, because any release of the key material
   would enable a participant other than the entity to create valid
   signed EATs.

1.6.  What is Not Standardized

   The following is not standardized for EAT, just the same they are not
   standardized for CWT or JWT.

1.6.1.  Transmission Protocol

   EATs may be transmitted by any protocol the same as CWTs and JWTs.
   For example, they might be added in extension fields of other
   protocols, bundled into an HTTP header, or just transmitted as files.
   This flexibility is intentional to allow broader adoption.  This
   flexibility is possible because EAT's are self-secured with signing
   (and possibly additionally with encryption and anti-replay).  The
   transmission protocol is not required to fulfill any additional
   security requirements.

   For certain devices, a direct connection may not exist between the
   EAT-producing device and the Relying Party.  In such cases, the EAT
   should be protected against malicious access.  The use of COSE and
   JOSE allows for signing and encryption of the EAT.  Therefore, even
   if the EAT is conveyed through intermediaries between the device and
   Relying Party, such intermediaries cannot easily modify the EAT
   payload or alter the signature.

1.6.2.  Signing Scheme

   The term "signing scheme" is used to refer to the system that
   includes end-end process of establishing signing attestation key
   material in the entity, signing the EAT, and verifying it.  This
   might involve key IDs and X.509 certificate chains or something
   similar but different.  The term "signing algorithm" refers just to
   the algorithm ID in the COSE signing structure.  No particular
   signing algorithm or signing scheme is required by this standard.

   There are three main implementation issues driving this.  First,
   secure non-volatile storage space in the entity for the attestation
   key material may be highly limited, perhaps to only a few hundred
   bits, on some small IoT chips.  Second, the factory cost of
   provisioning key material in each chip or device may be high, with
   even millisecond delays adding to the cost of a chip.  Third,

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   privacy-preserving signing schemes like ECDAA (Elliptic Curve Direct
   Anonymous Attestation) are complex and not suitable for all use
   cases.

   Over time to faciliate interoperability, some signing schemes may be
   defined in EAT profiles or other documents either in the IETF or
   outside.

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.

   This document reuses terminology from JWT [RFC7519], COSE [RFC8152],
   and CWT [RFC8392].

   Claim Name.  The human-readable name used to identify a claim.

   Claim Key.  The CBOR map key or JSON name used to identify a claim.

   Claim Value.  The value portion of the claim.  A claim value can be
      any CBOR data item or JSON value.

   CWT Claims Set.  The CBOR map or JSON object that contains the claims
      conveyed by the CWT or JWT.

   Attestation Key Material (AKM).  The key material used to sign the
      EAT token.  If it is done symmetrically with HMAC, then this is a
      simple symmetric key.  If it is done with ECC, such as an IEEE
      DevID [IEEE.802.1AR], then this is the private part of the EC key
      pair.  If ECDAA is used, (e.g., as used by Enhanced Privacy ID,
      i.e. EPID) then it is the key material needed for ECDAA.

3.  The Claims

   This section describes new claims defined for attestation.  It also
   mentions several claims defined by CWT and JWT that are particularly
   important for EAT.

   Note also: * Any claim defined for CWT or JWT may be used in an EAT
   including those in the CWT [IANA.CWT.Claims] and JWT IANA
   [IANA.JWT.Claims] claims registries.

   o  All claims are optional

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   o  No claims are mandatory

   o  All claims that are not understood by implementations MUST be
      ignored

   There are no default values or meanings assigned to absent claims
   other than they are not reported.  The reason for a claim's absence
   may be the implementation not supporting the claim, an inability to
   determine its value, or a preference to report in a different way
   such as a proprietary claim.

   CDDL along with text descriptions is used to define each claim
   indepdent of encoding.  Each claim is defined as a CDDL group (the
   group is a general aggregation and type definition feature of CDDL).
   In the encoding section Section 6, the CDDL groups turn into CBOR map
   entries and JSON name/value pairs.

   Map labels are assigned both an integer and string value.  CBOR
   encoded tokens MUST use only integer labels.  JSON encoded tokens
   MUST use only string labels.

   TODO: add paragraph here about use for Attestation Evidence and for
   Results.

3.1.  Token ID Claim (cti and jti)

   CWT defines the "cti" claim.  JWT defines the "jti" claim.  These are
   equivalent to each other in EAT and carry a unique token identifier
   as they do in JWT and CWT.  They may be used to defend against re use
   of the token but are distinct from the nonce that is used by the
   relying party to guarantee freshness and defend against replay.

3.2.  Timestamp claim (iat)

   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.  No token may contain an iat claim in float-
   point format.  Any recipient of a token with a floating-point format

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   iat claim may consider it an error.  A 64-bit integer representation
   of epoch time 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.

3.3.  Nonce Claim (nonce)

   All EATs should have a nonce to prevent replay attacks.  The nonce is
   generated by the relying party, the end consumer of the token.  It is
   conveyed to the entity over whatever transport is in use before the
   token is generated and then included in the token as the nonce claim.

   This documents the nonce claim for registration in the IANA CWT
   claims registry.  This is equivalent to the JWT nonce claim that is
   already registered.

   The nonce must be at least 8 bytes (64 bits) as fewer are unlikely to
   be secure.  A maximum of 64 bytes is set to limit the memory a
   constrained implementation uses.  This size range is not set for the
   already-registered JWT nonce, but it should follow this size
   recommendation when used in an EAT.

   Multiple nonces are allowed to accommodate multistage verification
   and consumption.

3.3.1.  nonce CDDL

   nonce-type = bstr .size (8..64)

   nonce-claim = (
       nonce => nonce-type / [ 2* nonce-type ]
   )

3.4.  Universal Entity ID Claim (ueid)

   UEID's identify individual manufactured entities / devices such as a
   mobile phone, a water meter, a Bluetooth speaker or a networked
   security camera.  It may identify the entire device or a submodule or
   subsystem.  It does not identify types, models or classes of devices.
   It is akin to a serial number, though it does not have to be
   sequential.

   UEID's 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 device to keep devices
   distinct between manufacturers).

   There are privacy considerations for UEID's.  See Section 8.1.

   The UEID is permanent.  It never change for a given device / entity.

   UEIDs are variable length.  All implementations MUST be able to
   receive UEIDs that are 33 bytes long (1 type byte and 256 bits).  The
   recommended maximum sent is also 33 bytes.

   When the entity constructs the UEID, the first byte is a type and the
   following bytes the ID for that type.  Several types are allowed to
   accommodate different industries and different manufacturing
   processes and to give options to avoid paying fees for certain types
   of manufacturer registrations.

   Creation of new types requires a Standards Action [RFC8126].

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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 device. 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 device and      |
   |      |      | stored. It may not be smaller than 128 bits.        |
   | 0x02 | IEEE | This makes use of 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-device 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 devices with multiple network interfaces |
   |      |      | may have multiple MAC addresses, there is only one  |
   |      |      | UEID for a device) [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. [ThreeGPP.IMEI]   |
   +------+------+-----------------------------------------------------+

                      Table 1: UEID Composition Types

   UEID's are not designed for direct use by humans (e.g., printing on
   the case of a device), so no textual representation is defined.

   The consumer (the relying party) of a UEID MUST treat a UEID as a
   completely opaque string of bytes and not make any use of its
   internal structure.  For example, they should not use the OUI part of
   a type 0x02 UEID to identify the manufacturer of the device.  Instead
   they should use the oemid claim that is defined elsewhere.  The
   reasons for this are:

   o  UEIDs types may vary freely from one manufacturer to the next.

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   o  New types of UEIDs may be created.  For example, a type 0x07 UEID
      may be created based on some other manufacturer registration
      scheme.

   o  Device manufacturers are allowed to change from one type of UEID
      to another anytime they want.  For example, they may find they can
      optimize their manufacturing by switching from type 0x01 to type
      0x02 or vice versa.  The main requirement on the manufacturer is
      that UEIDs be universally unique.

3.4.1.  ueid CDDL

   ueid-type = bstr .size (7..33)

   ueid-claim = (
        ueid => ueid-type
   )

3.5.  Semi-permanent UEIDs (SUEIDs)

   An SEUID is of the same format as a UEID, but it may change to a
   different value on device life-cycle events.  Examples of these
   events are change of ownership, factory reset and on-boarding into an
   IoT device management system.  A device may have both a UEID and
   SUEIDs, neither, one or the other.

   There may be multiple SUEIDs.  Each one has a text string label the
   purpose of which is to distinguish it from others in the token.  The
   label may name the purpose, application or type of the SUEID.
   Typically, there will be few SUEDs so there is no need for a formal
   labeling mechanism like a registry.  The EAT profile may describe how
   SUEIDs should be labeled.  If there is only one SUEID, the claim
   remains a map and there still must be a label.  For example, the
   label for the SUEID used by FIDO Onboarding Protocol could simply be
   "FDO".

   There are privacy considerations for SUEID's.  See Section 8.1.

   sueids-type = {
       + tstr => ueid-type
   }

   sueids-claim = (
        sueids => sueids-type
   )

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3.6.  OEM Identification by IEEE (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 services
   [OUI.Lookup]

   Companies that have more than one of these IDs or MAC address blocks
   should pick one and prefer that for all their devices.

   Commonly, these are expressed in Hexadecimal Representation
   [IEEE.802-2001] 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.  For JSON
   encoded tokens, this is further base64url encoded.

3.6.1.  oemid CDDL

   oemid-claim = (
       oemid => bstr
   )

3.7.  Hardware Version Claims (hardware-version-claims)

   The hardware version can be claimed at three different levels, the
   chip, the circuit board and the final device assembly.  An EAT can
   include any combination these claims.

   The hardware version is a simple 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].

   The hardware version can also be given by a 13-digit [EAN-13].  A new
   CoSWID version scheme is registered with IANA by this document in
   Section 7.3.3.  An EAN-13 is also known as an International Article
   Number or most commonly as a bar code.

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   chip-version-claim = (
       chip-version => tstr
   )

   chip-version-scheme-claim = (
       chip-version-scheme => $version-scheme
   )

   board-version-claim = (
       board-version => tstr
   )

   board-version-scheme-claim = (
       board-version-scheme => $version-scheme
   )

   device-version-claim = (
       device-version => tstr
   )

   device-version-scheme-claim = (
       device-version-scheme => $version-scheme
   )

   hardware-version-claims = (
       ? chip-version-claim,
       ? board-version-claim,
       ? device-version-claim,
       ? chip-version-scheme-claim,
       ? board-version-scheme-claim,
       ? device-version-scheme-claim,
   )

3.8.  Software Description and Version

   TODO: Add claims that reference CoSWID.

3.9.  The Security Level Claim (security-level)

   This claim characterizes the device/entity ability to defend against
   attacks aimed at capturing the signing key, forging claims and at
   forging EATs.  This is done by defining four security levels as
   described below.  This is similar to the key protection types defined
   by the Fast Identity Online (FIDO) Alliance [FIDO.Registry].

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   These claims describe security environment and countermeasures
   available on the end-entity / client device where the attestation key
   reside and the claims originate.

   1 - Unrestricted  There is some expectation that implementor will
      protect the attestation signing keys at this level.  Otherwise the
      EAT provides no meaningful security assurances.

   2- Restricted  Entities at this level should not be general-purpose
      operating environments that host features such as app download
      systems, web browsers and complex productivity applications.  It
      is akin to the Secure Restricted level (see below) without the
      security orientation.  Examples include a Wi-Fi subsystem, an IoT
      camera, or sensor device.

   3 - Secure Restricted  Entities at this level must meet the criteria
      defined by FIDO Allowed Restricted Operating Environments
      [FIDO.AROE].  Examples include TEE's and schemes using
      virtualization-based security.  Like the FIDO security goal,
      security at this level is aimed at defending well against large-
      scale network / remote attacks against the device.

   4 - Hardware  Entities at this level must include substantial defense
      against physical or electrical attacks against the device itself.
      It is assumed any potential attacker has captured the device and
      can disassemble it.  Example include TPMs and Secure Elements.

   The entity should claim the highest security level it achieves and no
   higher.  This set is not extensible so as to provide a common
   interoperable description of security level to the relying party.  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 security and its own proprietary
   claim as a refined indication.

   This claim is not intended as a replacement for a proper end-device
   security certification schemes such as those based on FIPS 140
   [FIPS-140] or those based on Common Criteria [Common.Criteria].  The
   claim made here is solely a self-claim made by the Entity Originator.

3.9.1.  security-level CDDL

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security-level-cbor-type = &(
    unrestricted: 1,
    restricted: 2,
    secure-restricted: 3,
    hardware: 4
)

security-level-json-type =
    "unrestricted" /
    "restricted" /
    "secure-restricted" /
    "hardware"

security-level-claim = (
    security-level => security-level-cbor-type / security-level-json-type
)

3.10.  Secure Boot Claim (secure-boot)

   The value of true indicates secure boot is enabled.  Secure boot is
   considered enabled when base software, the firmware and operating
   system, are under control of the entity manufacturer identified in
   the oemid claimd described in Section 3.6.  This may because the
   software is in ROM or because it is cryptographically authenticated
   or some combination of the two or other.

3.10.1.  secure-boot CDDL

   secure-boot-claim = (
       secure-boot => bool
   )

3.11.  Debug Status Claim (debug-status)

   This applies to system-wide or submodule-wide debug facilities of the
   target device / submodule 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

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   example, it does not matter if authentication is by a global password
   or by per-device public keys.

   As with all claims, the absence of the debug level claim means it is
   not reported.  A conservative interpretation might assume the Not
   Disabled state.  It could however be that it is reported in a
   proprietary claim.

   This claim is not extensible so as to provide a common interoperable
   description of debug status to the relying party.  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 verifier or relying party
   receiving an EAT cannot assume that debug is turned off in a
   submodule because there is a claim indicating it is turned off in a
   superior module.

   An individual target device / submodule may have multiple debug
   facilities.  The use of plural in the description of the states
   refers to that, not to any aggregation or inheritance.

   The architecture of some chips or devices may be such that a debug
   facility operates for the whole chip or device.  If the EAT for such
   a chip includes submodules, then each submodule should independently
   report the status of the whole-chip or whole-device debug facility.
   This is the only way the relying party can know the debug status of
   the submodules since there is no inheritance.

3.11.1.  Enabled

   If any debug facility, even manufacturer hardware diagnostics, is
   currently enabled, then this level must be indicated.

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3.11.2.  Disabled

   This level indicates all debug facilities are currently disabled.  It
   may be possible to enable them in the future, and it may also be
   possible that they were enabled in the past after the target device/
   sub-system booted/started, but they are currently disabled.

3.11.3.  Disabled Since Boot

   This level indicates all debug facilities are currently disabled and
   have been so since the target device/sub-system booted/started.

3.11.4.  Disabled Permanently

   This level indicates all non-manufacturer facilities are permanently
   disabled such that no end user or developer cannot 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.

3.11.5.  Disabled Fully and Permanently

   This level indicates that all debug capabilities for the target
   device/sub-module are permanently disabled.

3.11.6.  debug-status CDDL

   debug-status-cbor-type = &(
       enabled: 0,
       disabled: 1,
       disabled-since-boot: 2,
       disabled-permanently: 3,
       disabled-fully-and-permanently: 4
   )

   debug-status-json-type =
       "enabled" /
       "disabled" /
       "disabled-since-boot" /
       "disabled-permanently" /
       "disabled-fully-and-permanently"

   debug-status-claim = (
       debug-status => debug-status-cbor-type / debug-status-json-type
   )

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3.12.  Including Keys

   An EAT may include a cryptographic key such as a public key.  The
   signing of the EAT binds the key to all the other claims in the
   token.

   The purpose for inclusion of the key may vary by use case.  For
   example, the key may be included as part of an IoT device onboarding
   protocol.  When the FIDO protocol includes a pubic key in its
   attestation message, the key represents the binding of a user, device
   and relying party.  This document describes how claims containing
   keys should be defined for the various use cases.  It does not define
   specific claims for specific use cases.

   Keys in CBOR format tokens SHOULD be the COSE_Key format [RFC8152]
   and keys in JSON format tokens SHOULD be the JSON Web Key format
   [RFC7517].  These two formats support many common key types.  Their
   use avoids the need to decode other serialization formats.  These two
   formats can be extended to support further key types through their
   IANA registries.

   The general confirmation claim format [RFC8747], [RFC7800] may also
   be used.  It provides key encryption.  It also allows for inclusion
   by reference through a key ID.  The confirmation claim format may
   employed in the definition of some new claim for a a particular use
   case.

   When the actual confirmation claim is included in an EAT, this
   document associates no use case semantics other than proof of
   posession.  Different EAT use cases may choose to associate further
   semantics.  The key in the confirmation claim MUST be protected the
   same as the key used to sign the EAT.  That is, the same, equivalent
   or better hardware defenses, access controls, key generation and such
   must be used.

3.13.  The Location Claim (location)

   The location claim gives the location of the device entity from which
   the attestation originates.  It is derived from the W3C Geolocation
   API [W3C.GeoLoc].  The latitude, longitude, altitude and accuracy
   must conform to [WGS84].  The altitude is in meters above the [WGS84]
   ellipsoid.  The two accuracy values are positive numbers in meters.
   The heading is in degrees relative to true north.  If the device is
   stationary, the heading is NaN (floating-point not-a-number).  The
   speed is the horizontal component of the device velocity in meters
   per second.

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   When encoding floating-point numbers half-precision should not be
   used.  It usually does not provide enough precision for a geographic
   location.  It is not a requirement that the receiver of an EAT
   implement half-precision, so the receiver may not be able to decode
   the location.

   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.

   The age data item can be used when the entity doesn't know what time
   it is either because it doesn't have a clock or it isn't set.  The
   entity must still have a "ticker" that can measure a time interval.
   The age is the interval between acquisition of the location data and
   token creation.

   See location-related privacy considerations in Section 8.2 below.

3.13.1.  location CDDL

   location-type = {
       latitude => number,
       longitude => number,
       ? altitude => number,
       ? accuracy => number,
       ? altitude-accuracy => number,
       ? heading => number,
       ? speed => number,
       ? timestamp => ~time-int,
       ? age => uint
   }

   latitude = 1 / "latitude"
   longitude = 2 / "longitude"
   altitude = 3 / "altitude"
   accuracy = 4 / "accuracy"
   altitude-accuracy = 5 / "altitude-accuracy"
   heading = 6 / "heading"
   speed = 7 / "speed"
   timestamp = 8 / "timestamp"
   age = 9 / "age"

   location-claim = (
       location-label => location-type
   )

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3.14.  The Uptime Claim (uptime)

   The "uptime" claim contains a value that represents the number of
   seconds that have elapsed since the entity or submod was last booted.

3.14.1.  uptime CDDL

   uptime-claim = (
       uptime => uint
   )

3.15.  The Boot Seed Claim (boot-seed)

   The Boot Seed claim is a random value created at system boot time
   that will allow differentiation of reports from different boot
   sessions.  This value is usually public and not protected.  It is not
   the same as a seed for a random number generator which must be kept
   secret.

   boot-seed-claim = (
       boot-seed => bytes
   )

3.16.  The Intended Use Claim (intended-use)

   EAT's may be used in the context of several different applications.
   The intended-use 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 uses EAT.

   1 - Generic  Generic attestation describes an application where the
      EAT consumer requres 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 intended-use 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 device security state of the entity prior to provisioning.

   4 - Certificate Issuance (Certificate Signing Request)  Certifying
      authorities (CA's) may require attestations prior to the issuance

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      of certificates related to keypairs hosted at the entity.  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) appication.
      More precisely, a PoP transaction is intended to provide to the
      recipient cryptographically-verifiable proof that the sender has
      posession of a key.  This kind of attestation may be neceesary to
      verify the security state of the entity storing the private key
      used in a PoP application.

3.16.1.  intended-use CDDL

   intended-use-cbor-type = &(
       generic: 1,
       registration: 2,
       provisioning: 3,
       csr: 4,
       pop:  5
   )

   intended-use-json-type =
       "generic" /
       "registration" /
       "provisioning" /
       "csr" /
       "pop"

   intended-use-claim = (
       intended-use => intended-use-cbor-type / intended-use-json-type
   )

3.17.  The Profile Claim (profile)

   See Section 5 for the detailed description of a profile.

   A profile is identified 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 profile claim is to
   uniquely identify the profile even if it is a private profile.

   The OID is encoded in CBOR according to [CBOR-OID] and the URI
   according to [RFC8949].  Both are unwrapped and thus not tags.  The
   OID is always absolute and never relative.  If the claims CBOR type
   is a text string it is a URI and if a byte string it is an OID.

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   Note that this named "eat_profile" for JWT and is distinct from the
   already registered "profile" claim in the JWT claims registry.

 oid = #6.4000(bstr) ; TODO: fill this in with correct CDDL from OID RFC

 profile-claim = (
     profile => ~uri / ~oid
 )

3.18.  The Software Manifests Claim (manifests)

   This claim contains descriptions of software that is present on the
   device.  These manifests are installed on the device when the
   software is installed or are created as part of the installation
   process.  Installation is anything that adds software to the device,
   possibly factory installation, the user installing elective
   applications and so on.  The defining characteristic is that 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/or
   the Relying Party.

   In some cases these will be signed by the software manufacturer
   independent of any signing for the purpose of EAT attestation.
   Manifest claims should include the manufacturer's signature (which
   will be signed over by the attestation signature).  In other cases
   the attestation signature will be the only one.

   This claim allows multiple formats for the manifest.  For example the
   manifest may be a CBOR-format CoSWID, an XML-format SWID or other.
   Identification of the type of manifest is always by a CBOR tag.  In
   many cases, for examples CoSWID, a tag will already be registered
   with IANA.  If not, a tag MUST be registered.  It can be in the
   first-come-first-served space which has minimal requirements for
   registration.

   The claim is an array of one or more manifests.  To facilitate hand
   off of the manifest to a decoding library, each manifest is contained
   in a byte string.  This occurs for CBOR-format manifests as well as
   non-CBOR format manifests.

   If a particular manifest type uses CBOR encoding, then the item in
   the array for it MUST be a byte string that contains a CBOR tag.  The
   EAT decoder must decode the byte string and then the CBOR within it
   to find the tag number to identify the type of manifest.  The
   contents of the byte string is then handed to the particular manifest
   processor for that type of manifest.  CoSWID and SUIT manifest are
   examples of this.

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   If a particular manifest type does not use CBOR encoding, then the
   item in the array for it must be a CBOR tag that contains a byte
   string.  The EAT decoder uses the tag to identify the processor for
   that type of manifest.  The contents of the tag, the byte string, are
   handed to the manifest processor.  Note that a byte string is used to
   contain the manifest whether it is a text based format or not.  An
   example of this is an XML format ISO/IEC 19770 SWID.

   It is not possible to describe the above requirements in CDDL so the
   type for an individual manifest is any in the CDDL below.  The above
   text sets the encoding requirement.

   This claim allows for multiple manifests in one token since multiple
   software packages are likely to be present.  The multiple manifests
   may be of multiple formats.  In some cases EAT submodules may be used
   instead of the array structure in this claim for multiple manifests.

   When the [CoSWID] format is used, it MUST be a payload CoSWID, not an
   evidence CoSWID.

   manifests-claim = (
       manifests => manifests-type
   )

   manifests-type = [+ $manifest-formats]

   ; Must be a CoSWID payload type
   $manifest-formats /= bytes .cbor concise-swid-tag

   $manifest-formats /= bytes .cbor SUIT_Envelope_Tagged

3.19.  The Software Evidence Claim {swevidence}

   This claim contains descriptions, lists, evidence or measurements of
   the software that exists on the device.  The defining characteristic
   of this claim is that its contents are created by processes on the
   device that inventory, measure or otherwise characterize the software
   on the device.  The contents of this claim do not originate from the
   software manufacturer.

   In most cases the contents of this claim are signed as part of
   attestation signing, but independent signing in addition to the
   attestation signing is not ruled out when a particular evidence
   format supports it.

   This claim uses the same mechanism for identification of the type of
   the swevidence as is used for the type of the manifest in the

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   manifests claim.  It also uses the same byte string based mechanism
   for containing the claim and easing the hand off to a processing
   library.  See the discussion above in the manifests claim.

   When the [CoSWID] format is used, it MUST be evidence CoSWIDs, not
   payload CoSWIDS.

   swevidence-claim = (
       swevidence => swevidence-type
   )

   swevidence-type = [+ $swevidence-formats]

   ; Must be a CoSWID evidence type
   $swevidence-formats /= bytes .cbor concise-swid-tag

3.20.  The Submodules Part of a Token (submods)

   Some devices are complex, having many subsystems or submodules.  A
   mobile phone is a good example.  It may have several connectivity
   submodules for communications (e.g., Wi-Fi and cellular).  It may
   have subsystems for low-power audio and video playback.  It may have
   one or more security-oriented subsystems like a TEE or a Secure
   Element.

   The claims for each these can be grouped together in a submodule.

   The submods part of a token are in a single map/object with many
   entries, one per submodule.  There is only one submods map in a
   token.  It is identified by its specific label.  It is a peer to
   other claims, but it is not called a claim because it is a container
   for a claim set rather than an individual claim.  This submods part
   of a token allows what might be called recursion.  It allows claim
   sets inside of claim sets inside of claims sets...

3.20.1.  Two Types of Submodules

   Each entry in the submod map is one of two types:

   o  A non-token submodule that is a map or object directly containing
      claims for the submodule.

   o  A nested EAT that is a fully formed, independently signed EAT
      token

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3.20.1.1.  Non-token Submodules

   This is simply a map or object containing claims about the submodule.

   It may contain claims that are the same as its surrounding token or
   superior submodules.  For example, the top-level of the token may
   have a UEID, a submod may have a different UEID and a further
   subordinate submodule may also have a UEID.

   It is signed/encrypted along with the rest of the token and thus the
   claims are secured by the same Attester with the same signing key as
   the rest of the token.

   If a token is in CBOR format (a CWT or a UCCS), all non-token
   submodules must be CBOR format.  If a token in in JSON format (a
   JWT), all non-token submodules must be in JSON format.

   When decoding, this type of submodule is recognized from the other
   type by being a data item of type map for CBOR or type object for
   JSON.

3.20.1.2.  Nested EATs

   This type of submodule is a fully formed secured EAT as defined in
   this document except that it MUST NOT be a UCCS or an unsecured JWT.
   A nested token that is one that is always secured using COSE or JOSE,
   usually by an independent Attester.  When the surrounding EAT is a
   CWT or secured JWT, the nested token becomes securely bound with the
   other claims in the surrounding token.

   It is allowed to have a CWT as a submodule in a JWT and vice versa,
   but this SHOULD be avoided unless necessary.

3.20.1.2.1.  Surrounding EAT is CBOR format

   They type of an EAT nested in a CWT is determined by whether the CBOR
   type is a text string or a byte string.  If a text string, then it is
   a JWT.  If a byte string, then it is a CWT.

   A CWT nested in a CBOR-format token is always wrapped by a byte
   string for easier handling with standard CBOR decoders and token
   processing APIs that will typically take a byte buffer as input.

   Nested CWTs may be either a CWT CBOR tag or a CWT Protocol Message.
   COSE layers in nested CWT EATs MUST be a COSE_Tagged_Message, never a
   COSE_Untagged_Message.  If a nested EAT has more than one level of
   COSE, for example one that is both encrypted and signed, a
   COSE_Tagged_message must be used at every level.

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3.20.1.2.2.  Surrounding EAT is JSON format

   When a CWT is nested in a JWT, it must be as a 55799 tag in order to
   distinguish it from a nested JWT.

   When a nested EAT in a JWT is decoded, first remove the base64url
   encoding.  Next, check to see if it starts with the bytes 0xd9d9f7.
   If so, then it is a CWT as a JWT will never start with these four
   bytes.  If not if it is a JWT.

   Other than the 55799 tag requirement, tag usage for CWT's nested in a
   JSON format token follow the same rules as for CWTs nested in CBOR-
   format tokens.  It may be a CWT CBOR tag or a CWT Protocol Message
   and COSE_Tagged_Message MUST be used at all COSE layers.

3.20.1.3.  Unsecured JWTs and UCCS Tokens as Submodules

   To incorporate a UCCS token as a submodule, it MUST be as a non-token
   submodule.  This can be accomplished inserting the content of the
   UCCS Tag into the submodule map.  The content of a UCCS tag is
   exactly a map of claims as required for a non-token submodule.  If
   the UCCS is not a UCCS tag, then it can just be inserted into the
   submodule map directly.

   The definition of a nested EAT type of submodule is that it is one
   that is secured (signed) by an Attester.  Since UCCS tokens are
   unsecured, they do not fulfill this definition and must be non-token
   submodules.

   To incorporate an Unsecured JWT as a submodule, the null-security
   JOSE wrapping should be removed.  The resulting claims set should be
   inserted as a non-token submodule.

   To incorporate a UCCS token in a surrounding JSON token, the UCCS
   token claims should be translated from CBOR to JSON.  To incorporate
   an Unsecured JWT into a surrounding CBOR-format token, the null-
   security JOSE should be removed and the claims translated from JSON
   to CBOR.

3.20.2.  No Inheritance

   The subordinate modules do not inherit anything from the containing
   token.  The subordinate modules must explicitly include all of their
   claims.  This is the case even for claims like the nonce and age.

   This rule is in place for simplicity.  It avoids complex inheritance
   rules that might vary from one type of claim to another.

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3.20.3.  Security Levels

   The security level of the non-token subordinate modules should always
   be less than or equal to that of the containing modules in the case
   of non-token submodules.  It makes no sense for a module of lesser
   security to be signing claims of a module of higher security.  An
   example of this is a TEE signing claims made by the non-TEE parts
   (e.g. the high-level OS) of the device.

   The opposite may be true for the nested tokens.  They usually have
   their own more secure key material.  An example of this is an
   embedded secure element.

3.20.4.  Submodule Names

   The label or name for each submodule in the submods map is a text
   string naming the submodule.  No submodules may have the same name.

3.20.5.  submods CDDL

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   ; The part of a token that contains all the submodules.  It is a peer
   ; with the claims in the token, but not a claim, only a map/object to
   ; hold all the submodules.

   submods-part = (
       submods => submods-type
   )

   submods-type = { + submod-type }

   ; The type of a submodule which can either be a nested claim set or a
   ; nested separately signed token. Nested tokens are wrapped in a bstr
   ; or a tstr.

   submod-type = (
       submod-name => eat-claim-set / nested-token
   )

   ; When this is a bstr, the contents are an eat-token in CWT or UCCS
   ; format.  When this is a tstr, the contents are an eat-token in JWT
   ; format.

   nested-token = bstr / tstr;

   ; Each submodule has a unique text string name.

   submod-name = tstr

4.  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
   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

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   on the EAT.  It may contain Reference Values to which EAT claims are
   compared as part of the verification process.  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.

4.1.  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.

4.1.1.  COSE/JWS Key ID

   The COSE standard header parameter for Key ID (kid) may be used.  See
   [RFC8152] 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.

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4.1.2.  JWS and COSE X.509 Header Parameters

   COSE X.509 [COSE.X509.Draft] and JSON Web Siganture [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.

4.1.3.  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,...).

4.1.4.  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 device 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.

4.2.  Other Considerations

   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

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   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].

5.  Profiles

   This EAT specification does not gaurantee that implementations of it
   will interoperate.  The variability in this specification is
   necessary to accommodate the widely varying use cases.  An EAT
   profile narrows the specification for a specific use case.  An ideal
   EAT profile will gauarantee interoperability.

   The profile can be named in the token using the profile claim
   described in Section 3.17.

5.1.  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.

   In some cases CDDL may be created that replaces CDDL in this or other
   document to express some profile requirements.  For example, to
   require the altitude data item in the location claim, CDDL can be
   written that replicates the location claim with the altitude no
   longer optional.

5.2.  List of Profile Issues

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

5.2.1.  Use of JSON, CBOR or both

   The profile should indicate whether the token format should be CBOR,
   JSON, both or even some other encoding.  If some other encoding, a
   specification for how the CDDL described here is serialized in that
   encoding is necessary.

   This should be addressed for the top-level token and for any nested
   tokens.  For example, a profile might require all nested tokens to be
   of the same encoding of the top level token.

5.2.2.  CBOR Map and Array Encoding

   The profile should indicate whether definite-length arrays/maps,
   indefinite-length arrays/maps or both are allowed.  A good default is
   to allow only definite-length arrays/maps.

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   An alternate is to allow both definite and indefinite-length arrays/
   maps.  The decoder should accept either.  Encoders that need to fit
   on very small hardware or be actually implement in hardware can use
   indefinite-length encoding.

   This applies to individual EAT claims, CWT and COSE parts of the
   implementation.

5.2.3.  CBOR String Encoding

   The profile should indicate whether definite-length strings,
   indefinite-length strings or both are allowed.  A good default is to
   allow only definite-length strings.  As with map and array encoding,
   allowing indefinite-length strings can be beneficial for some smaller
   implementations.

5.2.4.  CBOR Preferred Serialization

   The profile should indicate whether encoders must use preferred
   serialization.  The profile should indicate whether decoders must
   accept non-preferred serialization.

5.2.5.  COSE/JOSE Protection

   COSE and JOSE have several options for signed, MACed and encrypted
   messages.  EAT/CWT has the option to have no protection using UCCS
   and JOSE has a 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, CWT and UCCS are allowed by
   EAT.

   The profile should list the protections that must be supported by all
   decoders implementing the profile.  The encoders them must implement
   a subset of what is listed for the decoders, perhaps only one.

   Implementations may choose to sign or MAC before encryption so that
   the implementation layer doing the signing or MACing can be the
   smallest.  It is often easier to make smaller implementations more
   secure, perhaps even implementing in solely in hardware.  The key
   material for a signature or MAC is a private key, while for
   encryption it is likely to be a public key.  The key for encryption
   requires less protection.

5.2.6.  COSE/JOSE Algorithms

   The profile document should list the COSE algorithms that a Verifier
   must implement.  The Attester will select one of them.  Since there

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   is no negotiation, the Verifier should implement all algorithms
   listed in the profile.

5.2.7.  Verification Key Identification

   Section Section 4 describes a number of methods for identifying a
   verification key.  The profile document should specify one of these
   or one that is not described.  The ones described in this document
   are only roughly described.  The profile document should go into the
   full detail.

5.2.8.  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, where as key identification is not.

5.2.9.  Freshness

   Just about every use case will require some means of knowing the EAT
   is recent enough and not a replay of an old token.  The profile
   should describe how freshness is achieved.  The section on Freshness
   in [RATS-Architecture] describes some of the possible solutions to
   achieve this.

5.2.10.  Required Claims

   The profile can list claims whose absence results in Verification
   failure.

5.2.11.  Prohibited Claims

   The profile can list claims whose presence results in Verification
   failure.

5.2.12.  Additional Claims

   The profile may describe entirely new claims.  These claims can be
   required or optional.

5.2.13.  Refined Claim Definition

   The profile may lock down optional aspects of individual claims.  For
   example, it may require altitude in the location claim, or it may
   require that HW Versions always be described using EAN-13.

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5.2.14.  CBOR Tags

   The profile should specify whether the token should be a CWT Tag or
   not.  Similarly, the profile should specify whether the token should
   be a UCCS 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 unncessary because the surrounding or carrying
   protocol identifies the object as an EAT.

5.2.15.  Manifests and Software Evidence Claims

   The profile should specify which formats are allowed for the
   manifests and software evidence claims.  The profile may also go on
   to say which parts and options of these formats are used, allowed and
   prohibited.

6.  Encoding

   This makes use of the types defined in CDDL Appendix D, Standard
   Prelude.

   Some of the CDDL included here is for claims that are defined in CWT
   [RFC8392] or JWT [RFC7519] or are in the IANA CWT or JWT registries.
   CDDL was not in use when these claims where defined.

6.1.  Common CDDL Types

   time-int is identical to the epoch-based time, but disallows
   floating-point representation.

   Note that unless expliclity indicated, URIs are not the URI tag
   defined in [RFC8949].  They are just text strings that contain a URI.

   string-or-uri = tstr

   time-int = #6.1(int)

6.2.  CDDL for CWT-defined Claims

   This section provides CDDL for the claims defined in CWT.  It is non-
   normative as [RFC8392] is the authoritative definition of these
   claims.

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   Note that the subject, issue and audience claims may be a text string
   containing a URI per [RFC8392] and [RFC7519].  These are never the
   URI tag defined in [RFC8949].

   $$eat-extension //= (
       ? issuer => text,
       ? subject => text,
       ? audience => text,
       ? expiration => time,
       ? not-before => time,
       ? issued-at => time,
       ? cwt-id => bytes,
   )

   issuer = 1
   subject = 2
   audience = 3
   expiration = 4
   not-before = 5
   issued-at = 6
   cwt-id = 7

6.3.  JSON

6.3.1.  JSON Labels

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; The following are Claim Keys (labels) assigned for JSON-encoded tokens.

ueid /= "ueid"
sueids /= "sueids"
nonce /= "nonce"
oemid /= "oemid"
security-level /= "seclevel"
secure-boot /= "secboot"
debug-status /= "dbgstat"
location /= "location"
uptime /= "uptime"
profile /= "eat-profile"
intended-use /= "intuse"
boot-seed /= "bootseed"
submods /= "submods"
timestamp /= "timestamp"
manifests /= "manifests"
swevidence /= "swevidence"

latitude /= "lat"
longitude /= "long"
altitude /= "alt"
accuracy /= "accry"
altitude-accuracy /= "alt-accry"
heading /= "heading"
speed /= "speed"

6.3.2.  JSON Interoperability

   JSON should be encoded per RFC 8610 Appendix E.  In addition, the
   following CDDL types are encoded in JSON as follows:

   o  bstr - must be base64url encoded

   o  time - must be encoded as NumericDate as described section 2 of
      [RFC7519].

   o  string-or-uri - must be encoded as StringOrURI as described
      section 2 of [RFC7519].

   o  uri - must be a URI [RFC3986].

   o  oid - encoded as a string using the well established dotted-
      decimal notation (e.g., the text "1.2.250.1").

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6.4.  CBOR

6.4.1.  CBOR Interoperability

   CBOR allows data items to be serialized in more than one form.  If
   the sender uses a form that the receiver can't decode, there will not
   be interoperability.

   This specification gives no blanket requirements to narrow CBOR
   serialization for all uses of EAT.  This allows individual uses to
   tailor serialization to the environment.  It also may result in EAT
   implementations that don't interoperate.

   One way to guarantee interoperability is to clearly specify CBOR
   serialization in a profile document.  See Section 5 for a list of
   serialization issues that should be addressed.

   EAT will be commonly used where the device generating the attestation
   is constrained and the receiver/verifier of the attestation is a
   capacious server.  Following is a set of serialization requirements
   that work well for that use case and are guaranteed to interoperate.
   Use of this serialization is recommended where possible, but not
   required.  An EAT profile may just reference the following section
   rather than spell out serialization details.

6.4.1.1.  EAT Constrained Device Serialization

   o  Preferred serialization described in section 4.1 of [RFC8949] is
      not required.  The EAT decoder must accept all forms of number
      serialization.  The EAT encoder may use any form it wishes.

   o  The EAT decoder must accept indefinite length arrays and maps as
      described in section 3.2.2 of [RFC8949].  The EAT encoder may use
      indefinite length arrays and maps if it wishes.

   o  The EAT decoder must accept indefinite length strings as described
      in section 3.2.3 of [RFC8949].  The EAT encoder may use indefinite
      length strings if it wishes.

   o  Sorting of maps by key is not required.  The EAT decoder must not
      rely on sorting.

   o  Deterministic encoding described in Section 4.2 of [RFC8949] is
      not required.

   o  Basic validity described in section 5.3.1 of [RFC8949] must be
      followed.  The EAT encoder must not send duplicate map keys/labels
      or invalid UTF-8 strings.

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6.5.  Collected CDDL

; This is the top-level definition of the claims in EAT tokens.  To
; form an actual EAT Token, this claim set is enclosed in a COSE, JOSE
; or UCCS message.

eat-claim-set = {
    ? ueid-claim,
    ? sueids-claim,
    ? nonce-claim,
    ? oemid-claim,
    ? hardware-version-claims,
    ? security-level-claim,
    ? secure-boot-claim,
    ? debug-status-claim,
    ? location-claim,
    ? intended-use-claim,
    ? profile-claim,
    ? uptime-claim,
    ? manifests-claim,
    ? swevidence-claim,
    ? submods-part,
    * $$eat-extension,
}

; This is the top-level definition of an EAT Token.  It is a CWT, JWT
; or UCSS where the payload is an eat-claim-set. A JWT_Message is what
; is defined by JWT in RFC 7519. (RFC 7519 doesn't use CDDL so a there
; is no actual CDDL definition of JWT_Message).

eat-token = EAT_Tagged_Message / EAT_Untagged_Message / JWT_Message

; This is CBOR-format EAT token in the CWT or UCCS format that is a
; tag.  COSE_Tagged_message is defined in RFC 8152.  Tag 601 is
; proposed by the UCCS draft, but not yet assigned.

EAT_Tagged_Message = #6.61(COSE_Tagged_Message) / #6.601(eat-claim-set)

; This is a CBOR-format EAT token that is a CWT or UCSS that is not a
; tag COSE_Tagged_message and COSE_Untagged_Message are defined in RFC
; 8152.

EAT_Untagged_Message = COSE_Tagged_Message / COSE_Untagged_Message / UCCS_Untagged_Message

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; This is an "unwrapped" UCCS tag. Unwrapping a tag means to use the
; definition of its content without the preceding type 6 tag
; integer. Since a UCCS is nothing but a tag for an unsecured CWT
; claim set, unwrapping reduces to a bare eat-claim-set.

UCCS_Untagged_Message = eat-claim-set

string-or-uri = tstr

time-int = #6.1(int)
$$eat-extension //= (
    ? issuer => text,
    ? subject => text,
    ? audience => text,
    ? expiration => time,
    ? not-before => time,
    ? issued-at => time,
    ? cwt-id => bytes,
)

issuer = 1
subject = 2
audience = 3
expiration = 4
not-before = 5
issued-at = 6
cwt-id = 7

debug-status-cbor-type = &(
    enabled: 0,
    disabled: 1,
    disabled-since-boot: 2,
    disabled-permanently: 3,
    disabled-fully-and-permanently: 4
)

debug-status-json-type =
    "enabled" /
    "disabled" /
    "disabled-since-boot" /
    "disabled-permanently" /
    "disabled-fully-and-permanently"

debug-status-claim = (
    debug-status => debug-status-cbor-type / debug-status-json-type
)
location-type = {
    latitude => number,

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    longitude => number,
    ? altitude => number,
    ? accuracy => number,
    ? altitude-accuracy => number,
    ? heading => number,
    ? speed => number,
    ? timestamp => ~time-int,
    ? age => uint
}

latitude = 1 / "latitude"
longitude = 2 / "longitude"
altitude = 3 / "altitude"
accuracy = 4 / "accuracy"
altitude-accuracy = 5 / "altitude-accuracy"
heading = 6 / "heading"
speed = 7 / "speed"
timestamp = 8 / "timestamp"
age = 9 / "age"

location-claim = (
    location-label => location-type
)
nonce-type = bstr .size (8..64)

nonce-claim = (
    nonce => nonce-type / [ 2* nonce-type ]
)
oemid-claim = (
    oemid => bstr
)
chip-version-claim = (
    chip-version => tstr
)

chip-version-scheme-claim = (
    chip-version-scheme => $version-scheme
)

board-version-claim = (
    board-version => tstr
)

board-version-scheme-claim = (
    board-version-scheme => $version-scheme
)

device-version-claim = (

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    device-version => tstr
)

device-version-scheme-claim = (
    device-version-scheme => $version-scheme
)

hardware-version-claims = (
    ? chip-version-claim,
    ? board-version-claim,
    ? device-version-claim,
    ? chip-version-scheme-claim,
    ? board-version-scheme-claim,
    ? device-version-scheme-claim,
)

secure-boot-claim = (
    secure-boot => bool
)
security-level-cbor-type = &(
    unrestricted: 1,
    restricted: 2,
    secure-restricted: 3,
    hardware: 4
)

security-level-json-type =
    "unrestricted" /
    "restricted" /
    "secure-restricted" /
    "hardware"

security-level-claim = (
    security-level => security-level-cbor-type / security-level-json-type
)
; The part of a token that contains all the submodules.  It is a peer
; with the claims in the token, but not a claim, only a map/object to
; hold all the submodules.

submods-part = (
    submods => submods-type
)

submods-type = { + submod-type }

; The type of a submodule which can either be a nested claim set or a

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; nested separately signed token. Nested tokens are wrapped in a bstr
; or a tstr.

submod-type = (
    submod-name => eat-claim-set / nested-token
)

; When this is a bstr, the contents are an eat-token in CWT or UCCS
; format.  When this is a tstr, the contents are an eat-token in JWT
; format.

nested-token = bstr / tstr;

; Each submodule has a unique text string name.

submod-name = tstr

ueid-type = bstr .size (7..33)

ueid-claim = (
     ueid => ueid-type
)
sueids-type = {
    + tstr => ueid-type
}

sueids-claim = (
     sueids => sueids-type
)
intended-use-cbor-type = &(
    generic: 1,
    registration: 2,
    provisioning: 3,
    csr: 4,
    pop:  5
)

intended-use-json-type =
    "generic" /
    "registration" /
    "provisioning" /
    "csr" /
    "pop"

intended-use-claim = (

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    intended-use => intended-use-cbor-type / intended-use-json-type
)
oid = #6.4000(bstr) ; TODO: fill this in with correct CDDL from OID RFC

uptime-claim = (
    uptime => uint
)

manifests-claim = (
    manifests => manifests-type
)

manifests-type = [+ $manifest-formats]

; Must be a CoSWID payload type
$manifest-formats /= bytes .cbor concise-swid-tag

$manifest-formats /= bytes .cbor SUIT_Envelope_Tagged

swevidence-claim = (
    swevidence => swevidence-type
)

swevidence-type = [+ $swevidence-formats]

; Must be a CoSWID evidence type
$swevidence-formats /= bytes .cbor concise-swid-tag

oid = #6.4000(bstr) ; TODO: fill this in with correct CDDL from OID RFC

profile-claim = (
    profile => ~uri / ~oid
)

boot-seed-claim = (
    boot-seed => bytes
)

7.  IANA Considerations

7.1.  Reuse of CBOR Web Token (CWT) Claims Registry

   Claims defined for EAT are compatible with those of CWT so the CWT
   Claims Registry is re used.  No new IANA registry is created.  All
   EAT claims should be registered in the CWT and JWT Claims Registries.

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7.2.  Claim Characteristics

   The following is design guidance for creating new EAT claims,
   particularly those to be registered with IANA.

   Much of this guidance is generic and could also be considered when
   designing new CWT or JWT claims.

7.2.1.  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.

7.2.2.  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.

   Claims should not be defined such that they are specific to a SW
   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.

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7.2.3.  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.

7.2.4.  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 format 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.

7.2.5.  Proprietary Claims

   EAT allows the definition and use of proprietary claims.

   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.

7.3.  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

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   addition to both registries (except for the nonce claim which is
   already registered for JWT, but not registered for CWT).

   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.

7.3.1.  Claims for Early Assignment

   RFC Editor: in the final publication this section should be combined
   with the following section as it will no longer be necessary to
   distinguish claims with early assignment.  Also, the following
   paragraph should be removed.

   The claims in this section have been (requested for / given) early
   assignment according to [RFC7120].  They have been assigned values
   and registered before final publication of this document.  While
   their semantics is not expected to change in final publication, it is
   possible that they will.  The JWT Claim Names and CWT Claim Keys are
   not expected to change.

   o  Claim Name: Nonce

   o  Claim Description: Nonce

   o  JWT Claim Name: "nonce" (already registered for JWT)

   o  Claim Key: 10

   o  Claim Value Type(s): byte string

   o  Change Controller: IESG

   o  Specification Document(s): [OpenIDConnectCore], *this document*

   o  Claim Name: UEID

   o  Claim Description: The Universal Entity ID

   o  JWT Claim Name: "ueid"

   o  CWT Claim Key: 11

   o  Claim Value Type(s): byte string

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   o  Change Controller: IESG

   o  Specification Document(s): *this document*

   o  Claim Name: OEMID

   o  Claim Description: IEEE-based OEM ID

   o  JWT Claim Name: "oemid"

   o  Claim Key: 13

   o  Claim Value Type(s): byte string

   o  Change Controller: IESG

   o  Specification Document(s): *this document*

   o  Claim Name: Security Level

   o  Claim Description: Characterization of the security of an Attester
      or submodule

   o  JWT Claim Name: "seclevel"

   o  Claim Key: 14

   o  Claim Value Type(s): integer

   o  Change Controller: IESG

   o  Specification Document(s): *this document*

   o  Claim Name: Secure Boot

   o  Claim Description: Indicate whether the boot was secure

   o  JWT Claim Name: "secboot"

   o  Claim Key: 15

   o  Claim Value Type(s): Boolean

   o  Change Controller: IESG

   o  Specification Document(s): *this document*

   o  Claim Name: Debug Status

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   o  Claim Description: Indicate status of debug facilities

   o  JWT Claim Name: "dbgstat"

   o  Claim Key: 16

   o  Claim Value Type(s): integer

   o  Change Controller: IESG

   o  Specification Document(s): *this document*

   o  Claim Name: Location

   o  Claim Description: The geographic location

   o  JWT Claim Name: "location"

   o  Claim Key: 17

   o  Claim Value Type(s): map

   o  Change Controller: IESG

   o  Specification Document(s): *this document*

   o  Claim Name: Profile

   o  Claim Description: Indicates the EAT profile followed

   o  JWT Claim Name: "eat_profile"

   o  Claim Key: 18

   o  Claim Value Type(s): map

   o  Change Controller: IESG

   o  Specification Document(s): *this document*

   o  Claim Name: Submodules Section

   o  Claim Description: The section containing submodules (not actually
      a claim)

   o  JWT Claim Name: "submods"

   o  Claim Key: 20

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   o  Claim Value Type(s): map

   o  Change Controller: IESG

   o  Specification Document(s): *this document*

7.3.2.  To be Assigned Claims

   TODO: add the rest of the claims in here

7.3.3.  Version Schemes Registered by this Document

   IANA is requested to register a new value in the "Software Tag
   Version Scheme Values" established by [CoSWID].

   The new value is a version scheme a 13-digit European Article Number
   [EAN-13].  An EAN-13 is also known as an International Article Number
   or most commonly as a bar code.  This version scheme is the ASCII
   text representation of EAN-13 digits, the same ones often printed
   with a bar code.  This version scheme must comply with the EAN
   allocation and assignment rules.  For example, this requires the
   manufacturer to obtain a manufacture code from GS1.

              +-------+---------------------+---------------+
              | Index | Version Scheme Name | Specification |
              +-------+---------------------+---------------+
              | 5     | ean-13              | This document |
              +-------+---------------------+---------------+

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.  Any set of relying parties
   that receives tokens that happen to be from a single device will be
   able to know the tokens are all from the same device and be able to
   track the device.  Thus, in many usage situations UEID violates
   governmental privacy regulation.  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.

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   An SUEID is also usually not privacy-preserving.  In some cases it
   may have fewer privacy issues than a UEID depending on when and how
   and when it is generated.

   There are several strategies that can be used to still be able to put
   UEIDs and SUEIDs in tokens:

   o  The device obtains explicit permission from the user of the device
      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.

   o  The UEID/SUEID is used only in a particular context or particular
      use case.  It is used only by one relying party.

   o  The device 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 device, then the device generates a UEID just for that relying
      party by hashing a proofed relying party ID with the main device
      UEID/SUEID.

   Note that some of these privacy preservation strategies result in
   multiple UEIDs and SUEIDs per device.  Each UEID/SUEID is used in a
   different context, use case or system on the device.  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 device
   generating the attestation.  For example, many mobile phones prompt
   the user for permission when before sending location data.

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.  In addition, implementors should consider the
   following.

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9.1.  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 manfuacturer 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.

9.1.1.  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.

9.2.  Transport Security

   As stated in Section 8 of [RFC8392], "The security of the CWT relies
   upon on the protections offered by COSE".  Similar considerations
   apply to EAT when sent as a CWT.  However, EAT introduces the concept
   of a nonce to protect against replay.  Since an EAT may be created by
   an entity that may not support the same type of transport security as
   the consumer of the EAT, intermediaries may be required to bridge
   communications between the entity and consumer.  As a result, it is
   RECOMMENDED that both the consumer create a nonce, and the entity
   leverage the nonce along with COSE mechanisms for encryption and/or
   signing to create the EAT.

   Similar considerations apply to the use of EAT as a JWT.  Although
   the security of a JWT leverages the JSON Web Encryption (JWE) and
   JSON Web Signature (JWS) specifications, it is still recommended to
   make use of the EAT nonce.

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9.3.  Multiple EAT Consumers

   In many cases, more than one EAT consumer may be required to fully
   verify the entity attestation.  Examples include individual consumers
   for nested EATs, or consumers for individual claims with an EAT.
   When multiple consumers are required for verification of an EAT, it
   is important to minimize information exposure to each consumer.  In
   addition, the communication between multiple consumers should be
   secure.

   For instance, consider the example of an encrypted and signed EAT
   with multiple claims.  A consumer may receive the EAT (denoted as the
   "receiving consumer"), decrypt its payload, verify its signature, but
   then pass specific subsets of claims to other consumers for
   evaluation ("downstream consumers").  Since any COSE encryption will
   be removed by the receiving consumer, the communication of claim
   subsets to any downstream consumer should leverage a secure protocol
   (e.g.one that uses transport-layer security, i.e. TLS),

   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 transport 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.

10.  References

10.1.  Normative References

   [CBOR-OID]
              Bormann, C., "Concise Binary Object Representation (CBOR)
              Tags for Object Identifiers", draft-ietf-cbor-tags-oid-06
              (work in progress), March 2021.

   [CBOR.Cert.Draft]
              Raza, S., "CBOR Encoding of X.509 Certificates (CBOR
              Certificates)", 2020, <https://tools.ietf.org/html/draft-
              mattsson-cose-cbor-cert-compress-05>.

   [COSE.X509.Draft]
              Schaad, J., "CBOR Object Signing and Encryption (COSE):
              Header parameters for carrying and referencing X.509
              certificates", 2020,
              <https://tools.ietf.org/html/draft-ietf-cose-x509-08>.

   [CoSWID]   "Concise Software Identification Tags", November 2020,
              <https://tools.ietf.org/html/draft-ietf-sacm-coswid-16>.

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   [EAN-13]   GS1, "International Article Number - EAN/UPC barcodes",
              2019, <https://www.gs1.org/standards/barcodes/ean-upc>.

   [FIDO.AROE]
              The FIDO Alliance, "FIDO Authenticator Allowed Restricted
              Operating Environments List", November 2019,
              <https://fidoalliance.org/specs/fido-uaf-v1.0-fd-20191115/
              fido-allowed-AROE-v1.0-fd-20191115.html>.

   [IANA.CWT.Claims]
              IANA, "CBOR Web Token (CWT) Claims",
              <http://www.iana.org/assignments/cwt>.

   [IANA.JWT.Claims]
              IANA, "JSON Web Token (JWT) Claims",
              <https://www.iana.org/assignments/jwt>.

   [OpenIDConnectCore]
              Sakimura, N., Bradley, J., Jones, M., Medeiros, B. D., and
              C. Mortimore, "OpenID Connect Core 1.0 incorporating
              errata set 1", November 2014,
              <https://openid.net/specs/openid-connect-core-1_0.html>.

   [RATS-Architecture]
              Birkholz, H., Thaler, D., Richardson, M., Smith, N., and
              W. Pan, "Remote Attestation Procedures Architecture",
              draft-ietf-rats-architecture-12 (work in progress), April
              2021.

   [RATS.Architecture]
              Birkholz, H., "Remote Attestation Procedures
              Architecture", 2020, <https://tools.ietf.org/html/draft-
              ietf-rats-architecture-08>.

   [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>.

   [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>.

   [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>.

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   [RFC7517]  Jones, M., "JSON Web Key (JWK)", RFC 7517,
              DOI 10.17487/RFC7517, May 2015,
              <https://www.rfc-editor.org/info/rfc7517>.

   [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>.

   [RFC7800]  Jones, M., Bradley, J., and H. Tschofenig, "Proof-of-
              Possession Key Semantics for JSON Web Tokens (JWTs)",
              RFC 7800, DOI 10.17487/RFC7800, April 2016,
              <https://www.rfc-editor.org/info/rfc7800>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [RFC8152]  Schaad, J., "CBOR Object Signing and Encryption (COSE)",
              RFC 8152, DOI 10.17487/RFC8152, July 2017,
              <https://www.rfc-editor.org/info/rfc8152>.

   [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>.

   [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>.

   [RFC8747]  Jones, M., Seitz, L., Selander, G., Erdtman, S., and H.
              Tschofenig, "Proof-of-Possession Key Semantics for CBOR
              Web Tokens (CWTs)", RFC 8747, DOI 10.17487/RFC8747, March
              2020, <https://www.rfc-editor.org/info/rfc8747>.

   [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>.

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   [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>.

   [UCCS.Draft]
              Birkholz, H., "A CBOR Tag for Unprotected CWT Claims
              Sets", 2020,
              <https://tools.ietf.org/html/draft-birkholz-rats-uccs-01>.

   [WGS84]    National Imagery and Mapping Agency, "National Imagery and
              Mapping Agency Technical Report 8350.2, Third Edition",
              2000, <http://earth-
              info.nga.mil/GandG/publications/tr8350.2/wgs84fin.pdf>.

10.2.  Informative References

   [BirthdayAttack]
              "Birthday attack",
              <https://en.wikipedia.org/wiki/Birthday_attack.>.

   [Common.Criteria]
              "Common Criteria for Information Technology Security
              Evaluation", April 2017,
              <https://www.commoncriteriaportal.org/cc/>.

   [ECMAScript]
              "Ecma International, "ECMAScript Language Specification,
              5.1 Edition", ECMA Standard 262", June 2011,
              <http://www.ecma-international.org/ecma-262/5.1/ECMA-
              262.pdf>.

   [FIDO.Registry]
              The FIDO Alliance, "FIDO Registry of Predefined Values",
              December 2019, <https://fidoalliance.org/specs/common-
              specs/fido-registry-v2.1-ps-20191217.html>.

   [FIPS-140]
              National Institue of Standards, "Security Requirements for
              Cryptographic Modules", May 2001,
              <https://csrc.nist.gov/publications/detail/fips/140/2/
              final>.

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   [IEEE.802-2001]
              "IEEE Standard For Local And Metropolitan Area Networks
              Overview And Architecture", 2007,
              <https://webstore.ansi.org/standards/ieee/
              ieee8022001r2007>.

   [IEEE.802.1AR]
              "IEEE Standard, "IEEE 802.1AR Secure Device Identifier"",
              December 2009, <http://standards.ieee.org/findstds/
              standard/802.1AR-2009.html>.

   [IEEE.RA]  "IEEE Registration Authority",
              <https://standards.ieee.org/products-services/regauth/
              index.html>.

   [OUI.Guide]
              "Guidelines for Use of Extended Unique Identifier (EUI),
              Organizationally Unique Identifier (OUI), and Company ID
              (CID)", August 2017,
              <https://standards.ieee.org/content/dam/ieee-
              standards/standards/web/documents/tutorials/eui.pdf>.

   [OUI.Lookup]
              "IEEE Registration Authority Assignments",
              <https://regauth.standards.ieee.org/standards-ra-web/pub/
              view.html#registries>.

   [RFC4122]  Leach, P., Mealling, M., and R. Salz, "A Universally
              Unique IDentifier (UUID) URN Namespace", RFC 4122,
              DOI 10.17487/RFC4122, July 2005,
              <https://www.rfc-editor.org/info/rfc4122>.

   [RFC4949]  Shirey, R., "Internet Security Glossary, Version 2",
              FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007,
              <https://www.rfc-editor.org/info/rfc4949>.

   [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>.

   [W3C.GeoLoc]
              Worldwide Web Consortium, "Geolocation API Specification
              2nd Edition", January 2018, <https://www.w3.org/TR/
              geolocation-API/#coordinates_interface>.

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Appendix A.  Examples

A.1.  Very Simple EAT

   This is shown in CBOR diagnostic form.  Only the payload signed by
   COSE is shown.

   {
       / issuer /           1: "joe",
       / nonce /           10: h'948f8860d13a463e8e',
       / UEID /            11: h'0198f50a4ff6c05861c8860d13a638ea',
       / secure-boot /     15: true,
       / debug-disable /   16: 3, / permanent-disable /
       / timestamp (iat) /  6: 1(1526542894)
   }

A.2.  Example with Submodules, Nesting and Security Levels

  {
      / nonce /                 10: h'948f8860d13a463e8e',
      / UEID /                  11: h'0198f50a4ff6c05861c8860d13a638ea',
      / secure-boot /           15: true,
      / debug-disable /         16: 3, / permanent-disable  /
      / timestamp (iat) /        6: 1(1526542894),
      / security-level /        14: 3, / secure restricted OS /
      / submods / 20: {
          / first submod, an Android Application /
          "Android App Foo" :  {
              / security-level /  14: 1 / unrestricted /
          },

          / 2nd submod, A nested EAT from a secure element /
          "Secure Element Eat" :
              / an embedded EAT, bytes of which are not shown /
              h'420123',

          / 3rd submod, information about Linux Android /
          "Linux Android": {
              / security-level /  14: 1 / unrestricted /
          }
      }
  }

Appendix B.  UEID Design Rationale

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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 datadbase 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            |
   | billion |            |              |            | quadrillion    |
   |         |            |              |            | (10^17)        |
   +---------+------------+--------------+------------+----------------+

   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

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      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 SW 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)              |              |              |              |
   +----------------------+--------------+--------------+--------------+

   Next, to calculate the probability of a collision occurring in one
   year's operation of a database, it is assumed that the database size
   is in a steady state and that 10% of the database changes per year.
   For example, a trillion record database would have 100 billion states
   per year.  Each of those states has the above calculated probability
   of a collision.

   This assumption is a worst-case since it assumes that each state of
   the database is completely independent from the previous state.  In
   reality this is unlikely as state changes will be the addition or
   deletion of a few records.

   The following tables gives the time interval until there is a
   probability of a collision based on there being one tenth the number
   of states per year as the number of records in the database.

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     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  |              |              |
   +---------------------+---------------+--------------+--------------+

   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
   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.

   UUIDs seem to have been designed for scenarios where the implementor
   does not have full control over the environment and uniqueness has to
   be constructed from identifiers at hand.  UEID takes the view that

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   hardware, software and/or manufacturing process directly implement
   UEID in a simple and direct way.  It takes the view that
   cryptographic quality random number generators are readily available
   as they are implemented in commonly used CPU hardware.

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 are used with an
   open set of network protocols for authentication and such.  In these
   protocols the DevID secret is used to sign a nonce or similar to
   proof the association of the DevID certificates with the device.

   By contrast, EAT defines network protocol for proving trustworthiness
   to a relying party, the very thing that is not defined in
   [IEEE.802.1AR].  Nor does not give details on how keys, data and such
   are stored protected and accessed.  EAT is intended to work with a
   variety of different on-device implementations ranging from minimal
   protection of assets to the highest levels of asset protection.  It
   does not define any particular level of defense against attack,
   instead providing a set of security considerations.

   EAT and DevID can be viewed as complimentary when used together or as
   competing to provide a device identity service.

C.1.  DevID Used With EAT

   As just described, EAT defines a network protocol and [IEEE.802.1AR]
   doesn't.  Vice versa, EAT doesn't define a an device implementation
   and DevID does.

   Hence, EAT can be the network protocol 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.

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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.

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.

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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.  Changes from Previous Drafts

   The following is a list of known changes from the previous drafts.
   This list is non-authoritative.  It is meant to help reviewers see
   the significant differences.

D.1.  From draft-rats-eat-01

   o  Added UEID design rationale appendix

D.2.  From draft-mandyam-rats-eat-00

   This is a fairly large change in the orientation of the document, but
   no new claims have been added.

   o  Separate information and data model using CDDL.

   o  Say an EAT is a CWT or JWT

   o  Use a map to structure the boot_state and location claims

D.3.  From draft-ietf-rats-eat-01

   o  Clarifications and corrections for OEMID claim

   o  Minor spelling and other fixes

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   o  Add the nonce claim, clarify jti claim

D.4.  From draft-ietf-rats-eat-02

   o  Roll all EUIs back into one UEID type

   o  UEIDs can be one of three lengths, 128, 192 and 256.

   o  Added appendix justifying UEID design and size.

   o  Submods part now includes nested eat tokens so they can be named
      and there can be more tha one of them

   o  Lots of fixes to the CDDL

   o  Added security considerations

D.5.  From draft-ietf-rats-eat-03

   o  Split boot_state into secure-boot and debug-disable claims

   o  Debug disable is an enumerated type rather than Booleans

D.6.  From draft-ietf-rats-eat-04

   o  Change IMEI-based UEIDs to be encoded as a 14-byte string

   o  CDDL cleaned up some more

   o  CDDL allows for JWTs and UCCSs

   o  CWT format submodules are byte string wrapped

   o  Allows for JWT nested in CWT and vice versa

   o  Allows UCCS (unsigned CWTs) and JWT unsecured tokens

   o  Clarify tag usage when nesting tokens

   o  Add section on key inclusion

   o  Add hardware version claims

   o  Collected CDDL is now filled in.  Other CDDL corrections.

   o  Rename debug-disable to debug-status; clarify that it is not
      extensible

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   o  Security level claim is not extensible

   o  Improve specification of location claim and added a location
      privacy section

   o  Add intended use claim

D.7.  From draft-ietf-rats-05

   o  CDDL format issues resolved

   o  Corrected reference to Location Privacy section

D.8.  From draft-ietf-rats-06

   o  Added boot-seed claim

   o  Rework CBOR interoperability section

   o  Added profiles claim and section

D.9.  From draft-ietf-rats-07

   o  Filled in IANA and other sections for possible preassignment of
      claim keys for well understood claims

D.10.  From draft-ietf-rats-08

   o  Change profile claim to be either a URL or an OID rather than a
      test string

D.11.  From draft-ietf-rats-09

   o  Add SUEIDs

   o  Add appendix comparing IDevID to EAT

   o  Added section on use for Evidence and Attestation Results

   o  Fill in the key ID and endorsements identificaiton section

   o  Remove origination claim as it is replaced by key IDs and
      endorsements

   o  Added manifests and software evidence claims

   o  Add string labels non-claim labels for use with JSON (e.g. labels
      for members of location claim)

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Internet-Draft                     EAT                         June 2021

   o  EAN-13 HW versions are no longer a separate claim.  Now they are
      folded in as a CoSWID version scheme.

Authors' Addresses

   Giridhar Mandyam
   Qualcomm Technologies Inc.
   5775 Morehouse Drive
   San Diego, California
   USA

   Phone: +1 858 651 7200
   EMail: mandyam@qti.qualcomm.com

   Laurence Lundblade
   Security Theory LLC

   EMail: lgl@island-resort.com

   Miguel Ballesteros
   Qualcomm Technologies Inc.
   5775 Morehouse Drive
   San Diego, California
   USA

   Phone: +1 858 651 4299
   EMail: mballest@qti.qualcomm.com

   Jeremy O'Donoghue
   Qualcomm Technologies Inc.
   279 Farnborough Road
   Farnborough  GU14 7LS
   United Kingdom

   Phone: +44 1252 363189
   EMail: jodonogh@qti.qualcomm.com

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