The Entity Attestation Token (EAT)
draft-ietf-rats-eat-02

RATS Working Group                                            G. Mandyam
Internet-Draft                                Qualcomm Technologies Inc.
Intended status: Standards Track                            L. Lundblade
Expires: July 12, 2020                               Security Theory LLC
                                                          M. Ballesteros
                                                           J. O'Donoghue
                                              Qualcomm Technologies Inc.
                                                        January 09, 2020

                   The Entity Attestation Token (EAT)
                         draft-ietf-rats-eat-02

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

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   This Internet-Draft will expire on July 12, 2020.

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Copyright Notice

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  CDDL, CWT and JWT . . . . . . . . . . . . . . . . . . . .   4
     1.2.  Entity Overview . . . . . . . . . . . . . . . . . . . . .   4
     1.3.  EAT Operating Models  . . . . . . . . . . . . . . . . . .   5
     1.4.  What is Not Standardized  . . . . . . . . . . . . . . . .   6
       1.4.1.  Transmission Protocol . . . . . . . . . . . . . . . .   6
       1.4.2.  Signing Scheme  . . . . . . . . . . . . . . . . . . .   7
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   7
   3.  The Claims Information Model  . . . . . . . . . . . . . . . .   8
     3.1.  Token ID Claim (cti and jti)  . . . . . . . . . . . . . .   8
     3.2.  Timestamp claim (iat) . . . . . . . . . . . . . . . . . .   8
     3.3.  Nonce Claim (nonce) . . . . . . . . . . . . . . . . . . .   8
       3.3.1.  CDDL  . . . . . . . . . . . . . . . . . . . . . . . .   9
     3.4.  Universal Entity ID Claim (ueid)  . . . . . . . . . . . .   9
       3.4.1.  CDDL  . . . . . . . . . . . . . . . . . . . . . . . .  11
     3.5.  Origination Claim (origination) . . . . . . . . . . . . .  11
       3.5.1.  CDDL  . . . . . . . . . . . . . . . . . . . . . . . .  12
     3.6.  OEM Identification by IEEE (oemid)  . . . . . . . . . . .  12
       3.6.1.  CDDL  . . . . . . . . . . . . . . . . . . . . . . . .  12
     3.7.  The Security Level Claim (security_level) . . . . . . . .  12
       3.7.1.  CDDL  . . . . . . . . . . . . . . . . . . . . . . . .  13
     3.8.  Secure Boot and Debug Enable State Claims (boot_state)  .  13
       3.8.1.  Secure Boot Enabled . . . . . . . . . . . . . . . . .  14
       3.8.2.  Debug Disabled  . . . . . . . . . . . . . . . . . . .  14
       3.8.3.  Debug Disabled Since Boot . . . . . . . . . . . . . .  14
       3.8.4.  Debug Permanent Disable . . . . . . . . . . . . . . .  14
       3.8.5.  Debug Full Permanent Disable  . . . . . . . . . . . .  14
       3.8.6.  CDDL  . . . . . . . . . . . . . . . . . . . . . . . .  14
     3.9.  The Location Claim (location) . . . . . . . . . . . . . .  15
       3.9.1.  CDDL  . . . . . . . . . . . . . . . . . . . . . . . .  15
     3.10. The Age Claim (age) . . . . . . . . . . . . . . . . . . .  15

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     3.11. The Uptime Claim (uptime) . . . . . . . . . . . . . . . .  15
       3.11.1.  CDDL . . . . . . . . . . . . . . . . . . . . . . . .  15
     3.12. Nested EATs, the EAT Claim (nested_eat) . . . . . . . . .  16
       3.12.1.  CDDL . . . . . . . . . . . . . . . . . . . . . . . .  16
     3.13. The Submods Claim (submods) . . . . . . . . . . . . . . .  16
       3.13.1.  The submod_name Claim  . . . . . . . . . . . . . . .  16
       3.13.2.  CDDL . . . . . . . . . . . . . . . . . . . . . . . .  17
   4.  Data Model  . . . . . . . . . . . . . . . . . . . . . . . . .  17
     4.1.  Common CDDL Types . . . . . . . . . . . . . . . . . . . .  17
     4.2.  CDDL for CWT-defined Claims . . . . . . . . . . . . . . .  17
     4.3.  JSON  . . . . . . . . . . . . . . . . . . . . . . . . . .  18
       4.3.1.  JSON Labels . . . . . . . . . . . . . . . . . . . . .  18
       4.3.2.  JSON Interoperability . . . . . . . . . . . . . . . .  19
     4.4.  CBOR  . . . . . . . . . . . . . . . . . . . . . . . . . .  19
       4.4.1.  Labels  . . . . . . . . . . . . . . . . . . . . . . .  19
       4.4.2.  CBOR Interoperability . . . . . . . . . . . . . . . .  20
     4.5.  Collected CDDL  . . . . . . . . . . . . . . . . . . . . .  21
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  22
     5.1.  Reuse of CBOR Web Token (CWT) Claims Registry . . . . . .  22
       5.1.1.  Claims Registered by This Document  . . . . . . . . .  22
   6.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  23
     6.1.  UEID Privacy Considerations . . . . . . . . . . . . . . .  23
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  24
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  24
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  24
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  25
   Appendix A.  Examples . . . . . . . . . . . . . . . . . . . . . .  27
     A.1.  Very Simple EAT . . . . . . . . . . . . . . . . . . . . .  27
     A.2.  Example with Submodules, Nesting and Security Levels  . .  27
   Appendix B.  Changes from Previous Drafts . . . . . . . . . . . .  28
     B.1.  From draft-mandyam-rats-eat-00  . . . . . . . . . . . . .  28
     B.2.  From draft-ietf-rats-eat-01 . . . . . . . . . . . . . . .  28
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  28

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

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   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

1.1.  CDDL, CWT and JWT

   An EAT token is either a CWT as defined in [RFC8392] or a JWT as
   defined in [RFC7519].  This specification defines additional claims
   for entity attestation.

   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 [RFC7049] or JSON [ECMAScript] representation.  In
   the case of JSON, Appendix E of [RFC8610] is followed.  Additional
   rules are given in Section 4.3.2 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).

1.2.  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.  It is assumed that any entity that can create an
   EAT does so by means of a dedicated root-of-trust (RoT).

   Modern devices such as a mobile phone have many different execution
   environments operating with different security levels.  For example,

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   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
   Secure Element) - a high security chip with defenses against HW
   attacks that can serve as a RoT.  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.

1.3.  EAT Operating Models

   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.

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   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
   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.

1.4.  What is Not Standardized

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

1.4.1.  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.

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1.4.2.  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,
   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 CBOR map or JSON object value representing the
      value of the claim.

   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

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      DevID [IDevID], 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 Information Model

   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

   o  No claims are mandatory

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

   CDDL along with text descriptions is used to define the information
   model.  Each claim is defined as a CDDL group (the group is a general
   aggregation and type definition feature of CDDL).  In the data model,
   described in the Section 4, the CDDL groups turn into CBOR map
   entries and JSON name/value pairs.

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.

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.

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   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.

3.3.1.  CDDL

   nonce_claim = (
       nonce => bstr .size (8..64)
   )

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
   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 6.1.

   The UEID should be permanent.  It should never change for a given
   device / entity.  In addition, it should not be reprogrammable.
   UEID's are variable length.  The recommended maximum is 33 bytes (1
   type byte and 256 bits).  The recommended minimum is 17 bytes (1 type
   and 128 bits) because fewer bytes endanger the universal uniqueness.

   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.

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

   +------+--------+---------------------------------------------------+
   | Type | Type   | Specification                                     |
   | Byte | Name   |                                                   |
   +------+--------+---------------------------------------------------+
   | 0x01 | RAND   | This is a 128- to 256-bit random number generated |
   |      |        | once and stored in the device. This may be        |
   |      |        | constructed by concatenating enough identifiers   |
   |      |        | to be universally unique and then feeding the     |
   |      |        | concatenation through a cryptographic hash        |
   |      |        | function. It may also be a cryptographic quality  |
   |      |        | random number generate once at the beginning of   |
   |      |        | the life of the device and stored.                |
   | 0x02 | IEEE   | This makes use of the IEEE company identification |
   |      | EUI    | registry. An EUI is made up of an OUI and 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. (Note that while devices with   |
   |      |        | multiple network interfaces may have multiple MAC |
   |      |        | addresses, there is only one UEID for a device)   |
   |      |        | TODO: normative references to IEEE.               |
   | 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 a binary integer over 48 bits. The  |
   |      |        | IMEI value encoded SHALL NOT include Luhn         |
   |      |        | checksum or SVN information.                      |
   | 0x04 | EUI-48 | This is a 48-bit identifier formed by             |
   |      |        | concatenating the 24-bit OUI with a 24-bit        |
   |      |        | identifier assigned by the organisation that      |
   |      |        | purchased the OUI.                                |
   | 0x05 | EUI-60 | This is a 60-bit identifier formed by             |
   |      |        | concatenating the 24-bit OUI with a 36-bit        |
   |      |        | identifier assigned by the organisation that      |
   |      |        | purchased the OUI.                                |
   | 0x06 | EUI-64 | This is a 64-bit identifier formed by             |
   |      |        | concatenating the 24-bit OUI with a 40-bit        |
   |      |        | identifier assigned by the organisation that      |
   |      |        | purchased the OUI.                                |
   +------+--------+---------------------------------------------------+

                      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.

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   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 OUI claim that is defined elsewhere.  The reasons
   for this are:

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

   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.  CDDL

    ueid_claim = (
    ueid: bstr )

3.5.  Origination Claim (origination)

   This claim describes the parts of the device or entity that are
   creating the EAT.  Often it will be tied back to the device or chip
   manufacturer.  The following table gives some examples:

   +-------------------+-----------------------------------------------+
   | Name              | Description                                   |
   +-------------------+-----------------------------------------------+
   | Acme-TEE          | The EATs are generated in the TEE authored    |
   |                   | and configured by "Acme"                      |
   | Acme-TPM          | The EATs are generated in a TPM manufactured  |
   |                   | by "Acme"                                     |
   | Acme-Linux-Kernel | The EATs are generated in a Linux kernel      |
   |                   | configured and shipped by "Acme"              |
   | Acme-TA           | The EATs are generated in a Trusted           |
   |                   | Application (TA) authored by "Acme"           |
   +-------------------+-----------------------------------------------+

   TODO: consider a more structure approach where the name and the URI
   and other are in separate fields.

   TODO: This needs refinement.  It is somewhat parallel to issuer claim
   in CWT in that it describes the authority that created the token.

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3.5.1.  CDDL

   origination_claim = (
   origination: string_or_uri )

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 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.  CDDL

   oemid_claim = (
   oemid: bstr )

3.7.  The Security Level Claim (security_level)

   EATs have a claim that roughly characterizes the device / entities
   ability to defend against attacks aimed at capturing the signing key,
   forging claims and at forging EATs.  This is done by roughly defining
   four security levels as described below.  This is similar to the
   security levels defined in the Metadata Service defined by the Fast
   Identity Online (FIDO) Alliance (TODO: reference).

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

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   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 (TODO:
      reference).  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.

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

3.7.1.  CDDL

   security_level_type = (
   unrestricted: 1,
   restricted: 2,
   secure_restricted: 3,
   hardware: 4
   )

   security_level_claim = (
   security_level: security_level_type )

3.8.  Secure Boot and Debug Enable State Claims (boot_state)

   This claim is an array of five Boolean values indicating the boot and
   debug state of the entity.

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3.8.1.  Secure Boot Enabled

   This indicates whether secure boot is enabled either for an entire
   device or an individual submodule.  If it appears at the device
   level, then this means that secure boot is enabled for all
   submodules.  Secure boot enablement allows a secure boot loader to
   authenticate software running either in a device or a submodule prior
   allowing execution.

3.8.2.  Debug Disabled

   This indicates whether debug capabilities are disabled for an entity
   (i.e. value of 'true').  Debug disablement is considered a
   prerequisite before an entity is considered operational.

3.8.3.  Debug Disabled Since Boot

   This claim indicates whether debug capabilities for the entity were
   not disabled in any way since boot (i.e. value of 'true').

3.8.4.  Debug Permanent Disable

   This claim indicates whether debug capabilities for the entity are
   permanently disabled (i.e. value of 'true').  This value can be set
   to 'true' also if only the manufacturer is allowed to enabled debug,
   but the end user is not.

3.8.5.  Debug Full Permanent Disable

   This claim indicates whether debug capabilities for the entity are
   permanently disabled (i.e. value of 'true').  This value can only be
   set to 'true' if no party can enable debug capabilities for the
   entity.  Often this is implemented by blowing a fuse on a chip as
   fuses cannot be restored once blown.

3.8.6.  CDDL

   boot_state_type = [
       secure_boot_enabled=> bool,
       debug_disabled=> bool,
       debug_disabled_since_boot=> bool,
       debug_permanent_disable=> bool,
       debug_full_permanent_disable=> bool
   ]

   boot_state_claim = (
   boot_state: boot_state_type
   )

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3.9.  The Location Claim (location)

   The location claim is a CBOR-formatted object that describes the
   location of the device entity from which the attestation originates.
   It is comprised of a map of additional sub claims that represent the
   actual location coordinates (latitude, longitude and altitude).  The
   location coordinate claims are consistent with the WGS84 coordinate
   system [WGS84].  In addition, a sub claim providing the estimated
   accuracy of the location measurement is defined.

3.9.1.  CDDL

   location_type = {
       latitude => number,
       longitude => number,
       altitude => number,
       accuracy => number,
       altitude_accuracy => number,
       heading => number,
       speed => number
   }

   location_claim = (
   location: location_type )

3.10.  The Age Claim (age)

   The "age" claim contains a value that represents the number of
   seconds that have elapsed since the token was created, measurement
   was made, or location was obtained.  Typical attestable values are
   sent as soon as they are obtained.  However, in the case that such a
   value is buffered and sent at a later time and a sufficiently
   accurate time reference is unavailable for creation of a timestamp,
   then the age claim is provided.

   age_claim = (
   age: uint)

3.11.  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.

3.11.1.  CDDL

   uptime_claim = (
   uptime: uint )

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3.12.  Nested EATs, the EAT Claim (nested_eat)

   It is allowed for one EAT to be embedded in another.  This is for
   complex devices that have more than one subsystem capable of
   generating an EAT.  For example, one might be the device-wide EAT
   that is low to medium security and another from a Secure Element or
   similar that is high security.

   The contents of the "nested_eat" claim must be a fully signed,
   optionally encrypted, EAT token.

3.12.1.  CDDL

   nested_eat_claim = (
   nested_eat: nested_eat_type)

   A nested_eat_type is defined in words rather than CDDL.  It is either
   a full CWT or JWT including the COSE or JOSE signing.

3.13.  The Submods Claim (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.

   Specifically, the "submods" claim is an array.  Each item in the
   array is a CBOR map containing all the claims for a particular
   submodule.

   The security level of the submod is assumed to be at the same level
   as the main entity unless there is a security level claim in that
   submodule indicating otherwise.  The security level of a submodule
   can never be higher (more secure) than the security level of the EAT
   it is a part of.

3.13.1.  The submod_name Claim

   Each submodule should have a submod_name claim that is descriptive
   name.  This name should be the CBOR txt type.

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3.13.2.  CDDL

   In the following a generic_claim_type is any CBOR map entry or JSON
   name/value pair.

   submod_name_type = (
   submod_name: tstr )

   submods_type = [ * submod_claims ]

   submod_claims = {
       submod_name_type,
       * generic_claim_type
   }

   submods_claim = (
   submods: submod_type )

4.  Data Model

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

4.1.  Common CDDL Types

string_or_uri = #6.32(tstr) / tstr; See JSON section below for JSON encoding of string_or_uri

4.2.  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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   cwt_claim = (
       issuer_claim //
       subject_claim //
       audience_claim //
       expiration_claim //
       not_before_claim //
       issued_at_calim //
       cwt_id_claim
   )

   issuer_claim = (
   issuer: string_or_uri )

   subject_claim = (
   subject: string_or_uri )

   audience_claim = (
   audience: string_or_uri )

   expiration_claim = (
   expiration: time )

   not_before_claim = (
   not_before: time )

   issued_at_calim = (
   issued_at: time )

   cwt_id_claim = (
   cwt_id: bstr )

   issuer = 1
   subject = 2
   audience = 3
   expiration = 4
   not_before = 5
   issued_at = 6
   cwt_id = 7

4.3.  JSON

4.3.1.  JSON Labels

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   ueid = "ueid"
   origination = "origination"
   oemid = "oemid"
   security_level = "security_level"
   boot_state = "boot_state"
   location = "location"
   age = "age"
   uptime = "uptime"
   nested_eat = "nested_eat"
   submods = "submods"

   latitude = "lat""
   longitude = "long""
   altitude = "alt"
   accuracy = "accry"
   altitude_accuracy = "alt_accry"
   heading = "heading"
   speed = "speed"

4.3.2.  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].

4.4.  CBOR

4.4.1.  Labels

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   ueid = 8
   origination = 9
   oemid = 10
   security_level = 11
   boot_state = 12
   location = 13
   age = 14
   uptime = 15
   nested_eat = 16
   submods = 17
   submod_name = 18
   nonce = 19

   latitude = 1
   longitude = 2
   altitude = 3
   accuracy = 4
   altitude_accuracy = 5
   heading = 6
   speed = 7

4.4.2.  CBOR Interoperability

   Variations in the CBOR serializations supported in CBOR encoding and
   decoding are allowed and suggests that CBOR-based protocols specify
   how this variation is handled.  This section specifies what formats
   MUST be supported in order to achieve interoperability.

   The assumption is that the entity is likely to be a constrained
   device and relying party is likely to be a very capable server.  The
   approach taken is that the entity generating the token can use
   whatever encoding it wants, specifically encodings that are easier to
   implement such as indefinite lengths.  The relying party receiving
   the token must support decoding all encodings.

   These rules cover all types used in the claims in this document.
   They also are recommendations for additional claims.

   Canonical CBOR encoding, Preferred Serialization and
   Deterministically Encoded CBOR are explicitly NOT required as they
   would place an unnecessary burden on the entity implementation,
   particularly if the entity implementation is implemented in hardware.

   o  Integer Encoding (major type 0, 1) - The entity may use any
      integer encoding allowed by CBOR.  The server MUST accept all
      integer encodings allowed by CBOR.

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   o  String Encoding (major type 2 and 3) - The entity can use any
      string encoding allowed by CBOR including indefinite lengths.  It
      may also encode the lengths of strings in any way allowed by CBOR.
      The server must accept all string encodings.

   o  Major type 2, bstr, SHOULD be have tag 21 to indicate conversion
      to base64url in case that conversion is performed.

   o  Map and Array Encoding (major type 4 and 5) - The entity can use
      any array or map encoding allowed by CBOR including indefinite
      lengths.  Sorting of map keys is not required.  Duplicate map keys
      are not allowed.  The server must accept all array and map
      encodings.  The server may reject maps with duplicate map keys.

   o  Date and Time - The entity should send dates as tag 1 encoded as
      64-bit or 32-bit integers.  The entity may not send floating-point
      dates.  The server must support tag 1 epoch-based dates encoded as
      64-bit or 32-bit integers.  The entity may send tag 0 dates,
      however tag 1 is preferred.  The server must support tag 0 UTC
      dates.

   o  URIs - URIs should be encoded as text strings and marked with tag
      32.

   o  Floating Point - The entity may use any floating-point encoding.
      The relying party must support decoding of all types of floating-
      point.

   o  Other types - Use of Other types like bignums, regular expressions
      and such, SHOULD NOT be used.  The server MAY support them but is
      not required to so interoperability is not guaranteed.

4.5.  Collected CDDL

   A generic_claim is any CBOR map entry or JSON name/value pair.

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eat_claims = {  ; the top-level payload that is signed using COSE or JOSE
        * claim
}

claim = (
    ueid_claim //
    origination_claim //
    oemid_claim //
    security_level_claim //
    boot_state_claim //
    location_claim //
    age_claim //
    uptime_claim //
    nested_eat_claim //
    cwt_claim //
    generic_claim_type //
    )

   TODO: copy the rest of the CDDL here (wait until the CDDL is more
   settled so as to avoid copying multiple times)

5.  IANA Considerations

5.1.  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.

5.1.1.  Claims Registered by This Document

   o  Claim Name: UEID

   o  Claim Description: The Universal Entity ID

   o  JWT Claim Name: N/A

   o  Claim Key: 8

   o  Claim Value Type(s): byte string

   o  Change Controller: IESG

   o  Specification Document(s): *this document*

   TODO: add the rest of the claims in here

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6.  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.

6.1.  UEID 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 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.

   There are several strategies that can be used to still be able to put
   UEID's in tokens:

   o  The device obtains explicit permission from the user of the device
      to use the UEID.  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.

   o  The UEID 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 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.

   Note that some of these privacy preservation strategies result in
   multiple UEIDs per device.  Each UEID 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.

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7.  Security Considerations

   TODO: Perhaps this can be the same as CWT / COSE, but not sure yet
   because it involves so much entity / device security that those do
   not.

8.  References

8.1.  Normative References

   [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>.

   [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>.

   [RFC7049]  Bormann, C. and P. Hoffman, "Concise Binary Object
              Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
              October 2013, <https://www.rfc-editor.org/info/rfc7049>.

   [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>.

   [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>.

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   [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>.

   [TIME_T]   The Open Group Base Specifications, "Vol. 1: Base
              Definitions, Issue 7", Section 4.15 'Seconds Since the
              Epoch', IEEE Std 1003.1, 2013 Edition, 2013,
              <http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/
              V1_chap04.html#tag_04_15>.

   [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>.

8.2.  Informative References

   [ASN.1]    International Telecommunication Union, "Information
              Technology -- ASN.1 encoding rules: Specification of Basic
              Encoding Rules (BER), Canonical Encoding Rules (CER) and
              Distinguished Encoding Rules (DER)", ITU-T Recommendation
              X.690, 1994.

   [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>.

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

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

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

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

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

   [Webauthn]
              Worldwide Web Consortium, "Web Authentication: A Web API
              for accessing scoped credentials", 2016.

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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.

{
   / nonce (cti) /            7:h'948f8860d13a463e8e',
   / UEID /                   8:h'0198f50a4ff6c05861c8860d13a638ea4fe2f',
   / boot_state /            12:{true, true, true, true, false}
   / time stamp (iat) /       6:1526542894,
}

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

{
   / nonce /                  7:h'948f8860d13a463e8e',
   / UEID /                   8:h'0198f50a4ff6c05861c8860d13a638ea4fe2f',
   / boot_state /            12:{true, true, true, true, false}
   / time stamp (iat) /       6:1526542894,
   / seclevel /              11:3, / secure restricted OS /

   / submods / 17:
      [
         / 1st submod, an Android Application / {
           / submod_name /   18:'Android App "Foo"',
           / seclevel /      11:1, / unrestricted /
           / app data /  -70000:'text string'
         },
         / 2nd submod, A nested EAT from a secure element / {
           / submod_name / 18:'Secure Element EAT',
           / eat /         16:61( 18(
              / an embedded EAT / [ /...COSE_Sign1 bytes with payload.../ ]
                           ))
         }
         / 3rd submod, information about Linux Android / {
            / submod_name/ 18:'Linux Android',
            / seclevel /   11:1, / unrestricted /
            / custom - release / -80000:'8.0.0',
            / custom - version / -80001:'4.9.51+'
         }
      ]
}

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Appendix B.  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.

B.1.  From draft-mandyam-rats-eat-00

   This is a fairly large change in the orientation of the document, but
   not 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

B.2.  From draft-ietf-rats-eat-01

   o  Clarifications and corrections for OEMID claim

   o  Minor spelling and other fixes

   o  Add the nonce claim, clarify jti claim

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

Mandyam, et al.           Expires July 12, 2020                [Page 28]
Internet-Draft                     EAT                      January 2020

   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

Mandyam, et al.           Expires July 12, 2020                [Page 29]