EAT Measured Component
draft-ietf-rats-eat-measured-component-10

Remote ATtestation ProcedureS                                   S. Frost
Internet-Draft                                                       Arm
Intended status: Standards Track                              T. Fossati
Expires: 16 July 2026                                             Linaro
                                                           H. Tschofenig
                                                                   H-BRS
                                                             H. Birkholz
                                                          Fraunhofer SIT
                                                         12 January 2026

                         EAT Measured Component
               draft-ietf-rats-eat-measured-component-10

Abstract

   The term "measured component" refers to an object within the
   attester's target environment whose state can be sampled and
   typically digested using a cryptographic hash function.  Examples of
   measured components include firmware stored in flash memory, software
   loaded into memory at start time, data stored in a file system, or
   values in a CPU register.  This document provides the information
   model for the "measured component" and two associated data models.
   This separation is intentional: the JSON and CBOR serializations,
   coupled with the media types and associated Constrained Application
   Protocol (CoAP) Content-Formats, enable the immediate use of the
   semantics within the Entity Attestation Token (EAT) framework.
   Meanwhile, the information model can be reused in future
   specifications to provide additional serializations, for example
   using ASN.1.

Discussion Venues

   This note is to be removed before publishing as an RFC.

   Discussion of this document takes place on the Remote ATtestation
   ProcedureS Working Group mailing list (rats@ietf.org), which is
   archived at https://mailarchive.ietf.org/arch/browse/rats/.

   Source for this draft and an issue tracker can be found at
   https://github.com/thomas-fossati/draft-fft-rats-eat-measured-
   component.

Status of This Memo

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

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Conventions and Definitions . . . . . . . . . . . . . . . . .   4
   3.  Information Model . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Data Model  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     4.1.   Common Types . . . . . . . . . . . . . . . . . . . . . .   6
     4.2.  The digest Type . . . . . . . . . . . . . . . . . . . . .   6
     4.3.  The measured-component Data Item  . . . . . . . . . . . .   6
       4.3.1.  Component Identifier  . . . . . . . . . . . . . . . .   7
       4.3.2.  Authority Identifier  . . . . . . . . . . . . . . . .   8
       4.3.3.  Profile-specific Flags  . . . . . . . . . . . . . . .   9
     4.4.  EAT measurements-format Extensions  . . . . . . . . . . .   9
     4.5.  measurements-format for CBOR EAT  . . . . . . . . . . . .   9
     4.6.  measurements-format for JSON EAT  . . . . . . . . . . . .  10
     4.7.  EAT Profiles and Measured Components  . . . . . . . . . .  10
     4.8.  Examples  . . . . . . . . . . . . . . . . . . . . . . . .  10
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  14
   6.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  14
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
     7.1.  Media Types Registrations . . . . . . . . . . . . . . . .  14
       7.1.1.  application/measured-component+cbor . . . . . . . . .  15

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       7.1.2.  application/measured-component+json . . . . . . . . .  15
     7.2.  Measured Component Content-Format Registrations . . . . .  16
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  16
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  16
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  17
   Appendix A.  Collected CDDL . . . . . . . . . . . . . . . . . . .  18
   Appendix B.  Open Issues  . . . . . . . . . . . . . . . . . . . .  19
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  19
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  19

1.  Introduction

   Section 4.2.16 of [RFC9711] defines a Measurements claim that:

      "[c]ontains descriptions, lists, evidence or measurements of the
      software that exists on the entity or any other measurable
      subsystem of the entity."

   This claim allows for different measurement formats, each identified
   by a different CoAP Content-Format (Section 12.3 of [RFC7252]).
   Currently, the only specified format is Concise Software
   Identification (CoSWID) Tags of type "evidence", as per Section 2.9.4
   of [RFC9393].  However, CoSWID is not suitable for measurements that
   cannot be anchored to a file system, such as those in early boot
   environments.  To address this gap, this document introduces a
   "measured component" format that can be used with the EAT
   Measurements claim alongside or instead of CoSWID.

   The term "measured component" refers to an object within the
   attester's target environment whose state can be sampled and
   typically digested using a cryptographic hash function.  This
   includes, for example: the invariant part of a firmware component
   that is loaded in memory at startup time, a run-time integrity check
   (RTIC), a file system object, or a CPU register.

   This document provides the information model for the "measured
   component" and two associated data models [RFC3444].  This separation
   is intentional: the JSON and CBOR serializations, coupled with the
   media types and associated CoAP Content-Formats, enable the immediate
   use of the semantics within the EAT framework.  Meanwhile, the
   information model can be reused in future specifications to provide
   additional serializations, for example using ASN.1.

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2.  Conventions and Definitions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   In this document, CDDL [RFC8610] [RFC9165] [RFC9741] is used to
   describe the data formats.

3.  Information Model

   This section presents the information model of a "measured
   component".

   A "measured component" information element includes the component's
   sampled state (in digested or raw form) along with metadata that
   helps in identifying the component.  Optionally, any entities
   responsible for signing the installed component can also be
   specified.

   The information elements (IE) that constitute a "measured component"
   are described in Table 1.

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   +=============+======================================+=============+
   | IE          | Description                          | Requirement |
   |             |                                      | Level       |
   +=============+======================================+=============+
   | Component   | The name given to the measured       | REQUIRED    |
   | Name        | component.  It is important that     |             |
   |             | this name remains consistent across  |             |
   |             | different releases to allow for      |             |
   |             | better tracking of the same measured |             |
   |             | item across updates.  When combined  |             |
   |             | with a consistent versioning scheme, |             |
   |             | it enables better signalling from    |             |
   |             | the appraisal procedure to the       |             |
   |             | relying parties.                     |             |
   +-------------+--------------------------------------+-------------+
   | Component   | A value representing the specific    | OPTIONAL    |
   | Version     | release or development version of    |             |
   |             | the measured component.  Using       |             |
   |             | Semantic Versioning [SEMVER] is      |             |
   |             | RECOMMENDED.                         |             |
   +-------------+--------------------------------------+-------------+
   | Digested or | Either the raw value or the digested | REQUIRED    |
   | Raw Value   | value of the measured component.     |             |
   +-------------+--------------------------------------+-------------+
   | Digest      | Hash algorithm used to compute the   | REQUIRED    |
   | Algorithm   | Digest Value.                        | only if the |
   |             |                                      | value is in |
   |             |                                      | the         |
   |             |                                      | digested    |
   |             |                                      | form        |
   +-------------+--------------------------------------+-------------+
   | Authorities | One or more entities that can        | OPTIONAL    |
   |             | authoritatively identify the         |             |
   |             | component being measured.            |             |
   +-------------+--------------------------------------+-------------+

             Table 1: Measured Component Information Elements

   A data model implementing this information model SHOULD also allow a
   limited amount of extensibility to accommodate profile-specific
   semantics.

4.  Data Model

   This section presents a JSON and CBOR data model that implements the
   information model outlined in Section 3.

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   The data model is inspired by the "PSA software component" claim
   (Section 4.4.1 of [RFC9783]), which has been refactored to take into
   account the recommendations about the design of new EAT claims
   described in Appendix E of [RFC9711].

   CDDL is used to express rules and constraints of the data model for
   both JSON and CBOR.  These rules must be strictly followed when
   creating or validating "measured component" data items.  When there
   is variation between CBOR and JSON, the CDDL generic JC<>, defined in
   Appendix D of [RFC9711], is used.

4.1.   Common Types

   The following three basic types are used at various places within the
   measured component data model:

   bytes-b64u = text .b64u bytes
   bytes8 = bytes .size 8
   bytes8-b64u = text .b64u bytes8

4.2.  The digest Type

   A digest represents the result of a hashing operation together with
   the hash algorithm used.  The type of the digest algorithm identifier
   can be either int or text and is interpreted according to the
   [IANA.named-information] registry.  Specifically, int values are
   matched against "ID" entries and text values are matched against
   "Hash Name String" entries.  Whenever possible, using the int
   encoding is RECOMMENDED.

   digest = [
     alg: (int / text)
     val: digest-value-type
   ]

   digest-value-type = eat.JC<bytes-b64u, bytes>

4.3.  The measured-component Data Item

   The measured-component data item is as follows:

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   measured-component = {
     component-id-label => component-id
     measurement
     ? authorities-label => [ + authority-id-type ]
     ? flags-label => flags-type
   }

   measurement //= ( digested-measurement-label => digest )
   measurement //= ( raw-measurement-label => bytes )

   authority-id-type = eat.JC<bytes-b64u, bytes>
   flags-type = eat.JC<bytes8-b64u, bytes8>

   component-id-label = eat.JC<"id", 1>
   digested-measurement-label = eat.JC<"digested-measurement", 2>
   raw-measurement-label = eat.JC<"raw-measurement", 5>
   authorities-label = eat.JC<"authorities", 3>
   flags-label = eat.JC<"flags", 4>

   The members of the measured-component CBOR map / JSON object are:

   "id" (index 1):
      The measured component identifier encoded according to the format
      described in Section 4.3.1.

   "measurement":
      Either a digest value and digest algorithm (index 2), encoded
      using the digest format (Section 4.2), or the "raw" measurement
      (index 5), encoded as a byte string.  Note that, while the size of
      the digested form is constrained by the digest function, the size
      of the raw form can vary greatly depending on what is being
      measured (it could be a CPU register or an entire configuration
      blob, for example).  Therefore, a decoder implementation may
      decide to limit the amount of memory it allocates to this specific
      field.

   "authorities" (index 3):
      One or more authorities, see Section 4.3.2.

   "flags" (index 4):
      a 64-bit field with profile-defined semantics, see Section 4.3.3.

4.3.1.  Component Identifier

   The component-id data item is as follows:

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   component-id = [
     name:      text
     ? version: version
   ]

   ;# import coswid.$version-scheme from rfc9393 as coswid

   version = [
     val:      text
     ? scheme: coswid.$version-scheme
   ]

   name  A string that provides a human readable identifier for the
      component in question.  Format and adopted conventions depend on
      the component type.

   version  A compound version data item that reuses the encoding and
      semantics of [RFC9711] sw-version-type, extending it to non-
      software components.

4.3.2.  Authority Identifier

   An authority is an entity that can authoritatively identify a given
   component by digitally signing it.  This signature is usually
   verified during installation, or when the measured component is
   executed by the boot ROM, operating system, or application launcher.
   For example, as in Unified Extensible Firmware Interface (UEFI)
   Secure Boot [UEFI2] and Arm Trusted Board Boot [TBBR-CLIENT].
   Another example may be the controlling entity in an app store.

   An authority is identified by its signing public key.  It could be an
   X.509 certificate, a raw public key, a public key thumbprint, or some
   other identifier that can be uniquely associated with the signing
   entity.  In some cases, multiple parties may need to sign a component
   to indicate their endorsement or approval.  This could include roles
   such as a firmware update system, fleet owner, or third-party
   auditor.  The specific purpose of each signature may depend on the
   deployment, and the order of authorities within the array could
   indicate meaning.

   If an EAT profile (Section 6 of [RFC9711]) uses measured components,
   it MUST specify whether the authorities field is used.  If it is
   used, the profile MUST also specify what each of the entries in the
   authorities array represents, and how to interpret the corresponding
   authority-id-type.

   The authority-id-type is defined as follows:

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   authority-id-type = eat.JC<bytes-b64u, bytes>

4.3.3.  Profile-specific Flags

   This optional field can contain up to 64 bits of profile-defined
   semantics, enabling a profile of this specification to encode
   additional information and extend the base type.  It can be used to
   carry information in fixed-size chunks, such as a bit mask or a
   single value within a predetermined set of codepoints.  Regardless of
   its internal structure, the size of this field is exactly 8 bytes.

   The flags-type is defined as follows:

   flags-type = eat.JC<bytes8-b64u, bytes8>

   If an EAT profile (Section 6 of [RFC9711]) uses measured components,
   it MUST specify whether the flags field is used.  If it is used, the
   profile MUST also specify how to interpret the 64 bits.

4.4.  EAT measurements-format Extensions

   The CDDL in Figure 1 extends the $measurements-body-cbor and
   $measurements-body-json EAT sockets to add support for measured-
   components to the Measurements claim.

   mc-cbor = bytes .cbor measured-component
   mc-json = text .json measured-component

   ; EAT CBOR (`.feature "cbor"`)
   $measurements-body-cbor /= mc-cbor ; native
   $measurements-body-cbor /= mc-json ; tunnel

   ; EAT JSON (`.feature "json"`)
   $measurements-body-json /= mc-json            ; native
   $measurements-body-json /= text .b64u mc-cbor ; tunnel

                Figure 1: EAT measurements-format Extensions

   Each socket is extended with two new types: a "native" representation
   that is used when measured-component and the EAT have the same
   serialization (e.g., they are both CBOR), and a "tunnel"
   representation that is used when the serializations differ.

4.5.  measurements-format for CBOR EAT

   The entries in Table 2 are the allowed content-type / content-format
   pairs when the measured-component is carried in a CBOR EAT.

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   Note the use of the "native" and "tunnel" formats from Figure 1, and
   how the associated CoAP Content-Format is used to describe the
   original serialization.

         +=====================================+================+
         | content-type (CoAP C-F equivalent)  | content-format |
         +=====================================+================+
         | application/measured-component+cbor | mc-cbor        |
         +-------------------------------------+----------------+
         | application/measured-component+json | mc-json        |
         +-------------------------------------+----------------+

                 Table 2: measurement-format for EAT CWT

4.6.  measurements-format for JSON EAT

   Table 3 is the equivalent of Table 2 for JSON-serialized EAT.

       +=====================================+====================+
       | content-type (CoAP C-F equivalent)  | content-format     |
       +=====================================+====================+
       | application/measured-component+json | mc-json            |
       +-------------------------------------+--------------------+
       | application/measured-component+cbor | tstr .b64u mc-cbor |
       +-------------------------------------+--------------------+

                 Table 3: measurement-format for EAT JWT

4.7.  EAT Profiles and Measured Components

   The semantics of the authorities and profile flags fields are defined
   by the applicable EAT profile, i.e., the profile of the wrapping EAT.

   If the profile of the EAT is not known to the consumer and one or
   more Measured Components within that EAT include authorities and/or
   profile flags, the consumer MUST reject the EAT.

4.8.  Examples

   The example in Figure 2 is a digested measured component with all the
   fields populated.

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   {
     / id / 1: [
       / name / "boot loader X",
       / version / [
         "1.2.3rc2",
         16384 / semver /
       ]
     ],
     / measurement / 2: [
       / alg / "sha-256",
       / val / h'3996003d486fb91ffb056f7d03f2b2992b215b31dbe7af4b37
                 3431fc7d319da3'
     ],
     / authorities / 3: [
       h'492e9b676c21f6012b1ceeb9032feb4141a880797355f6675015ec59c5
         1ca1ec',
       h'4277bb97ba7b51577a0d38151d3e08b40bdf946753f5b5bdeb814d6ff5
         7a8a5e'
     ],
     / flags / 4: h'0000000000000101'
   }

                   Figure 2: Complete Measured Component

   The example in Figure 3 is the same measured component as above but
   used as the format of a measurements claim in a EAT claims-set.

   This example uses TBD1 as the content-type value of the measurements-
   format entry.  (This will change to the value assigned by IANA to the
   mc+cbor Content-Format.)

   Note that the array contains only one measured component, but
   additional entries could be added if the measured TCB is made of
   multiple, individually measured components.

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   {
     273: [
       [
         TBD1, / mc+cbor /
         <<
           {
             / id / 1: [
               / name / "boot loader X",
               / version / [
                 "1.2.3rc2",
                 16384 / semver /
               ]
             ],
             / measurement / 2: [
               / alg / "sha-256",
               / val / h'3996003d486fb91ffb056f7d03f2b2992b215b31db
                         e7af4b373431fc7d319da3'
             ],
             / authorities / 3: [
               h'492e9b676c21f6012b1ceeb9032feb4141a880797355f66750
                 15ec59c51ca1ec',
               h'4277bb97ba7b51577a0d38151d3e08b40bdf946753f5b5bdeb
                 814d6ff57a8a5e'
             ]
           }
         >>
       ]
     ]
   }

     Figure 3: EAT Measurements Claim using a Measured Component (CBOR)

   The example in Figure 4 illustrates the inclusion of a JSON measured
   component inside a JSON EAT.

   This example uses TBD2 as the content-type value of the measurements-
   format entry.  (This will change to the value assigned by IANA to the
   mc+json Content-Format.)

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   =============== NOTE: '\' line wrapping per RFC 8792 ================

   {
     "measurements": [
       [
         TBD2, / mc+json /
         "{ \"id\": [ \"boot loader X\", [ \"1.2.3rc2\", 16384 ] ], \"\
   digested-measurement\": [ \"sha-256\", \"\
   OZYAPUhvuR_7BW99A_KymSshWzHb569LNzQx_H0xnaM\" ], \"authorities\": [ \
   \"SS6bZ2wh9gErHO65Ay_rQUGogHlzVfZnUBXsWcUcoew\", \"\
                      Qne7l7p7UVd6DTgVHT4ItAvflGdT9bW964FNb_V6il4\" ] }"
       ]
     ]
   }

     Figure 4: EAT Measurements Claim using a Measured Component (JSON)

   The example in Figure 5 is a measured component representing a boot
   loader identified by its path name:

   {
     / id / 1: [
       / name / "/boot/loader.bin"
     ],
     / measurement / 2: [
       / alg / "sha-384",
       / val / h'66ec2fb4e02d8c8b3eee320e750d9389d66c52c51db11cc6
                 9cc5e410816283ed60ba573795f5fcc85e513af57b3f6def'
     ],
     / flags / 4: h'0000000000000101'
   }

    Figure 5: Digested Measured Component using File Path as Identifier

   The example in Figure 6 is a raw measured component.

   {
     / id / 1: [
       / name / "hardware-config"
     ],
     / measurement / 5: h'4f6d616861'
   }

                      Figure 6: Raw Measured Component

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5.  Security Considerations

   Please review Sections 9.1 (Claim Trustworthiness), 9.4 (Multiple EAT
   Consumers) and 9.5 (Detached EAT Bundle Digest Security
   Considerations) of [RFC9711]; these considerations apply to this
   document as well.  Note that similar security considerations may
   apply when the Measured Component information model is serialized
   using different data models than the ones specified in this document.

   The Component Name and Component Version can give an attacker
   detailed information about the software running on a device and its
   configuration settings.  This information could offer an attacker
   valuable insights.

   Any textual fields (e.g., Component Name and Component Version) that
   are stored in a file, inserted into a database, or displayed to
   humans must be properly sanitized to prevent attacks and undesirable
   behavior.  Further discussion and references on this topic can be
   found in Section 7 of [RFC9839].

   If the component measurement is digested, the digest must be computed
   using a strong cryptographic hash function.

6.  Privacy Considerations

   Please review Section 9.1 (Multiple EAT Consumers) of [RFC9711]; the
   differential encryption considerations discussed there also apply to
   this document.

   The Component Name and Component Version could reveal private
   information about a device and its owner.

   Additionally, the stability requirement of the Component Name could
   enable tracking.

7.  IANA Considerations

   // RFC Editor: replace "RFCthis" with the RFC number assigned to this
   document.

7.1.  Media Types Registrations

   IANA is requested to add the following media types to the "Media
   Types" registry [IANA.media-types].

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       +=========+=====================================+===========+
       | Name    | Template                            | Reference |
       +=========+=====================================+===========+
       | mc+cbor | application/measured-component+cbor | RFCthis   |
       +---------+-------------------------------------+-----------+
       | mc+json | application/measured-component+json | RFCthis   |
       +---------+-------------------------------------+-----------+

                  Table 4: Measured Component Media Types

7.1.1.  application/measured-component+cbor

   Type name:  application
   Subtype name:  measured-component+cbor
   Required parameters:  n/a
   Optional parameters:  n/a
   Encoding considerations:  binary (CBOR)
   Security considerations:  Section 5 of RFCthis
   Interoperability considerations:  n/a
   Published specification:  RFCthis
   Applications that use this media type:  Attesters, Verifiers and
      Relying Parties
   Fragment identifier considerations:  The syntax and semantics of
      fragment identifiers are as specified for "application/cbor".  (No
      fragment identification syntax is currently defined for
      "application/cbor".)
   Person & email address to contact for further information:  RATS WG
      mailing list (rats@ietf.org)
   Intended usage:  COMMON
   Restrictions on usage:  none
   Author/Change controller:  IETF
   Provisional registration:  no

7.1.2.  application/measured-component+json

   Type name:  application
   Subtype name:  measured-component+json
   Required parameters:  n/a
   Optional parameters:  n/a
   Encoding considerations:  binary (JSON is UTF-8-encoded text)
   Security considerations:  Section 5 of RFCthis
   Interoperability considerations:  n/a
   Published specification:  RFCthis
   Applications that use this media type:  Attesters, Verifiers and
      Relying Parties
   Fragment identifier considerations:  The syntax and semantics of

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      fragment identifiers are as specified for "application/json".  (No
      fragment identification syntax is currently defined for
      "application/json".)
   Person & email address to contact for further information:  RATS WG
      mailing list (rats@ietf.org)
   Intended usage:  COMMON
   Restrictions on usage:  none
   Author/Change controller:  IETF
   Provisional registration:  no

7.2.  Measured Component Content-Format Registrations

   IANA is requested to register two Content-Format numbers in the "CoAP
   Content-Formats" sub-registry, within the "Constrained RESTful
   Environments (CoRE) Parameters" Registry [IANA.core-parameters], as
   follows:

      +=========================+================+======+===========+
      | Content-Type            | Content Coding | ID   | Reference |
      +=========================+================+======+===========+
      | application/measured-   | -              | TBD1 | RFCthis   |
      | component+cbor          |                |      |           |
      +-------------------------+----------------+------+-----------+
      | application/measured-   | -              | TBD2 | RFCthis   |
      | component+json          |                |      |           |
      +-------------------------+----------------+------+-----------+

                                  Table 5

   If possible, TBD1 and TBD2 should be assigned in the 256..9999 range.

8.  References

8.1.  Normative References

   [IANA.named-information]
              IANA, "Named Information",
              <https://www.iana.org/assignments/named-information>.

   [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/rfc/rfc2119>.

   [RFC7252]  Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
              Application Protocol (CoAP)", RFC 7252,
              DOI 10.17487/RFC7252, June 2014,
              <https://www.rfc-editor.org/rfc/rfc7252>.

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   [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/rfc/rfc8174>.

   [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/rfc/rfc8610>.

   [RFC9165]  Bormann, C., "Additional Control Operators for the Concise
              Data Definition Language (CDDL)", RFC 9165,
              DOI 10.17487/RFC9165, December 2021,
              <https://www.rfc-editor.org/rfc/rfc9165>.

   [RFC9711]  Lundblade, L., Mandyam, G., O'Donoghue, J., and C.
              Wallace, "The Entity Attestation Token (EAT)", RFC 9711,
              DOI 10.17487/RFC9711, April 2025,
              <https://www.rfc-editor.org/rfc/rfc9711>.

   [RFC9741]  Bormann, C., "Concise Data Definition Language (CDDL):
              Additional Control Operators for the Conversion and
              Processing of Text", RFC 9741, DOI 10.17487/RFC9741, March
              2025, <https://www.rfc-editor.org/rfc/rfc9741>.

   [SEMVER]   "Semantic Versioning 2.0.0", 2013,
              <https://semver.org/spec/v2.0.0.html>.

8.2.  Informative References

   [IANA.core-parameters]
              IANA, "Constrained RESTful Environments (CoRE)
              Parameters",
              <https://www.iana.org/assignments/core-parameters>.

   [IANA.media-types]
              IANA, "Media Types",
              <https://www.iana.org/assignments/media-types>.

   [RFC3444]  Pras, A. and J. Schoenwaelder, "On the Difference between
              Information Models and Data Models", RFC 3444,
              DOI 10.17487/RFC3444, January 2003,
              <https://www.rfc-editor.org/rfc/rfc3444>.

   [RFC9393]  Birkholz, H., Fitzgerald-McKay, J., Schmidt, C., and D.
              Waltermire, "Concise Software Identification Tags",
              RFC 9393, DOI 10.17487/RFC9393, June 2023,
              <https://www.rfc-editor.org/rfc/rfc9393>.

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   [RFC9783]  Tschofenig, H., Frost, S., Brossard, M., Shaw, A., and T.
              Fossati, "Arm's Platform Security Architecture (PSA)
              Attestation Token", RFC 9783, DOI 10.17487/RFC9783, June
              2025, <https://www.rfc-editor.org/rfc/rfc9783>.

   [RFC9839]  Bray, T. and P. Hoffman, "Unicode Character Repertoire
              Subsets", RFC 9839, DOI 10.17487/RFC9839, August 2025,
              <https://www.rfc-editor.org/rfc/rfc9839>.

   [TBBR-CLIENT]
              Arm Ltd, "Trusted Board Boot Requirements Client (TBBR-
              CLIENT) Armv8-A", ARM DEN0006D, September 2018,
              <https://developer.arm.com/documentation/den0006>.

   [UEFI2]    UEFI Forum, Inc., "Unified Extensible Firmware Interface
              (UEFI) Specification", August 2022,
              <https://uefi.org/sites/default/files/resources/
              UEFI_Spec_2_10_Aug29.pdf>.

Appendix A.  Collected CDDL

   This appendix contains all the CDDL definitions included in this
   specification.

   =============== NOTE: '\' line wrapping per RFC 8792 ================

   measured-component = {
     component-id-label => component-id,
     measurement,
     ? authorities-label => [+ authority-id-type],
     ? flags-label => flags-type,
   }
   measurement //= (digested-measurement-label => digest // raw-\
                                             measurement-label => bytes)
   authority-id-type = eat.JC<bytes-b64u, bytes>
   flags-type = eat.JC<bytes8-b64u, bytes8>
   component-id = [
     name: text,
     ? version: version,
   ]
   version = [
     val: text,
     ? scheme: coswid.$version-scheme,
   ]
   digest = [
     alg: int / text,
     val: digest-value-type,
   ]

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   digest-value-type = eat.JC<bytes-b64u, bytes>
   bytes-b64u = text .b64u bytes
   bytes8 = bytes .size 8
   bytes8-b64u = text .b64u bytes8
   component-id-label = eat.JC<"id", 1>
   digested-measurement-label = eat.JC<"digested-measurement", 2>
   raw-measurement-label = eat.JC<"raw-measurement", 5>
   authorities-label = eat.JC<"authorities", 3>
   flags-label = eat.JC<"flags", 4>
   mc-cbor = bytes .cbor measured-component
   mc-json = text .json measured-component
   $measurements-body-cbor /= mc-cbor / mc-json
   $measurements-body-json /= mc-json / text .b64u mc-cbor
   eat.JSON-ONLY<J> = J .feature "json"
   eat.CBOR-ONLY<C> = C .feature "cbor"
   eat.JC<J, C> = eat.JSON-ONLY<J> / eat.CBOR-ONLY<C>
   coswid.$version-scheme /= coswid.multipartnumeric / coswid.\
   multipartnumeric-suffix / coswid.alphanumeric / coswid.decimal / \
                                              coswid.semver / int / text
   coswid.multipartnumeric = 1
   coswid.multipartnumeric-suffix = 2
   coswid.alphanumeric = 3
   coswid.decimal = 4
   coswid.semver = 16384

Appendix B.  Open Issues

   The list of currently open issues for this documents can be found at
   https://github.com/ietf-rats-wg/draft-ietf-rats-eat-measured-
   component/issues.

   // Note to RFC Editor: please remove before publication.

Acknowledgments

   The authors would like to thank Carl Wallace, Carsten Bormann, Deb
   Cooley, Dionna Glaze, Giridhar Mandyam, Houda Labiod, Ionuț Mihalcea,
   Jun Zhang, Laurence Lundblade, Michael Richardson, Muhammad Usama
   Sardar and Yogesh Deshpande for providing comments, reviews and
   suggestions that greatly improved this document.

   The authors would also like to thank Ken Takayama for providing an
   implementation of this specification in the veraison/eat package.

Authors' Addresses

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   Simon Frost
   Arm
   Email: Simon.Frost@arm.com

   Thomas Fossati
   Linaro
   Email: Thomas.Fossati@linaro.org

   Hannes Tschofenig
   University of Applied Sciences Bonn-Rhein-Sieg
   Email: Hannes.Tschofenig@gmx.net

   Henk Birkholz
   Fraunhofer SIT
   Email: henk.birkholz@ietf.contact

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