Trusted Execution Environment Provisioning (TEEP) Protocol
draft-ietf-teep-protocol-06

Document Type Active Internet-Draft (teep WG)
Authors Hannes Tschofenig  , Mingliang Pei  , Dave Wheeler  , Dave Thaler  , Akira Tsukamoto 
Last updated 2021-07-12
Replaces draft-tschofenig-teep-protocol
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TEEP                                                       H. Tschofenig
Internet-Draft                                                  Arm Ltd.
Intended status: Standards Track                                  M. Pei
Expires: January 13, 2022                                       Broadcom
                                                              D. Wheeler
                                                                  Amazon
                                                               D. Thaler
                                                               Microsoft
                                                            A. Tsukamoto
                                                                    AIST
                                                           July 12, 2021

       Trusted Execution Environment Provisioning (TEEP) Protocol
                       draft-ietf-teep-protocol-06

Abstract

   This document specifies a protocol that installs, updates, and
   deletes Trusted Components in a device with a Trusted Execution
   Environment (TEE).  This specification defines an interoperable
   protocol for managing the lifecycle of Trusted Components.

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
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 13, 2022.

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
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of

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   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Message Overview  . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Detailed Messages Specification . . . . . . . . . . . . . . .   5
     4.1.  Creating and Validating TEEP Messages . . . . . . . . . .   5
       4.1.1.  Creating a TEEP message . . . . . . . . . . . . . . .   5
       4.1.2.  Validating a TEEP Message . . . . . . . . . . . . . .   6
     4.2.  QueryRequest Message  . . . . . . . . . . . . . . . . . .   6
     4.3.  QueryResponse Message . . . . . . . . . . . . . . . . . .   9
       4.3.1.  Evidence  . . . . . . . . . . . . . . . . . . . . . .  11
     4.4.  Update Message  . . . . . . . . . . . . . . . . . . . . .  12
     4.5.  Success Message . . . . . . . . . . . . . . . . . . . . .  14
     4.6.  Error Message . . . . . . . . . . . . . . . . . . . . . .  15
   5.  Mapping of TEEP Message Parameters to CBOR Labels . . . . . .  17
   6.  Behavior Specification  . . . . . . . . . . . . . . . . . . .  18
     6.1.  TAM Behavior  . . . . . . . . . . . . . . . . . . . . . .  18
     6.2.  TEEP Agent Behavior . . . . . . . . . . . . . . . . . . .  19
   7.  Ciphersuites  . . . . . . . . . . . . . . . . . . . . . . . .  20
   8.  Freshness Mechanisms  . . . . . . . . . . . . . . . . . . . .  21
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  21
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  23
     10.1.  Media Type Registration  . . . . . . . . . . . . . . . .  23
     10.2.  Ciphersuite Registry . . . . . . . . . . . . . . . . . .  24
     10.3.  Freshness Mechanism Registry . . . . . . . . . . . . . .  24
     10.4.  CBOR Tag Registry  . . . . . . . . . . . . . . . . . . .  25
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  25
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  25
     11.2.  Informative References . . . . . . . . . . . . . . . . .  26
   A. Contributors . . . . . . . . . . . . . . . . . . . . . . . . .  27
   B. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  27
   C. Complete CDDL  . . . . . . . . . . . . . . . . . . . . . . . .  27
   D. Examples of Diagnostic Notation and Binary Representation  . .  31
     D.1.  Some assumptions in examples  . . . . . . . . . . . . . .  31
     D.2.  QueryRequest Message  . . . . . . . . . . . . . . . . . .  31
       D.2.1.  CBOR Diagnostic Notation  . . . . . . . . . . . . . .  32
       D.2.2.  CBOR Binary Representation  . . . . . . . . . . . . .  32
     D.3.  Entity Attestation Token  . . . . . . . . . . . . . . . .  32
       D.3.1.  CBOR Diagnostic Notation  . . . . . . . . . . . . . .  33
     D.4.  QueryResponse Message . . . . . . . . . . . . . . . . . .  33

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       D.4.1.  CBOR Diagnostic Notation  . . . . . . . . . . . . . .  33
       D.4.2.  CBOR Binary Representation  . . . . . . . . . . . . .  34
     D.5.  Update Message  . . . . . . . . . . . . . . . . . . . . .  35
       D.5.1.  CBOR Diagnostic Notation  . . . . . . . . . . . . . .  35
       D.5.2.  CBOR Binary Representation  . . . . . . . . . . . . .  35
     D.6.  Success Message . . . . . . . . . . . . . . . . . . . . .  36
       D.6.1.  CBOR Diagnostic Notation  . . . . . . . . . . . . . .  36
       D.6.2.  CBOR Binary Representation  . . . . . . . . . . . . .  36
     D.7.  Error Message . . . . . . . . . . . . . . . . . . . . . .  36
       D.7.1.  CBOR Diagnostic Notation  . . . . . . . . . . . . . .  36
       D.7.2.  CBOR binary Representation  . . . . . . . . . . . . .  37
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  37

1.  Introduction

   The Trusted Execution Environment (TEE) concept has been designed to
   separate a regular operating system, also referred as a Rich
   Execution Environment (REE), from security-sensitive applications.
   In a TEE ecosystem, device vendors may use different operating
   systems in the REE and may use different types of TEEs.  When Trusted
   Component Developers or Device Administrators use Trusted Application
   Managers (TAMs) to install, update, and delete Trusted Applications
   and their dependencies on a wide range of devices with potentially
   different TEEs then an interoperability need arises.

   This document specifies the protocol for communicating between a TAM
   and a TEEP Agent.

   The Trusted Execution Environment Provisioning (TEEP) architecture
   document [I-D.ietf-teep-architecture] provides design guidance and
   introduces the necessary terminology.

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 specification re-uses the terminology defined in
   [I-D.ietf-teep-architecture].

   As explained in Section 4.4 of that document, the TEEP protocol
   treats each Trusted Application (TA), any dependencies the TA has,
   and personalization data as separate components that are expressed in
   SUIT manifests, and a SUIT manifest might contain or reference
   multiple binaries (see [I-D.ietf-suit-manifest] for more details).

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   As such, the term Trusted Component (TC) in this document refers to a
   set of binaries expressed in a SUIT manifest, to be installed in a
   TEE.  Note that a Trusted Component may include one or more TAs and/
   or configuration data and keys needed by a TA to operate correctly.

   Each Trusted Component is uniquely identified by a SUIT Component
   Identifier (see [I-D.ietf-suit-manifest] Section 8.7.2.2).

3.  Message Overview

   The TEEP protocol consists of messages exchanged between a TAM and a
   TEEP Agent.  The messages are encoded in CBOR and designed to provide
   end-to-end security.  TEEP protocol messages are signed by the
   endpoints, i.e., the TAM and the TEEP Agent, but Trusted Applications
   may also be encrypted and signed by a Trusted Component Developer or
   Device Administrator.  The TEEP protocol not only uses CBOR but also
   the respective security wrapper, namely COSE [RFC8152].  Furthermore,
   for software updates the SUIT manifest format
   [I-D.ietf-suit-manifest] is used, and for attestation the Entity
   Attestation Token (EAT) [I-D.ietf-rats-eat] format is supported
   although other attestation formats are also permitted.

   This specification defines five messages: QueryRequest,
   QueryResponse, Update, Success, and Error.

   A TAM queries a device's current state with a QueryRequest message.
   A TEEP Agent will, after authenticating and authorizing the request,
   report attestation information, list all Trusted Components, and
   provide information about supported algorithms and extensions in a
   QueryResponse message.  An error message is returned if the request
   could not be processed.  A TAM will process the QueryResponse message
   and determine whether to initiate subsequent message exchanges to
   install, update, or delete Trusted Applications.

     +------------+           +-------------+
     | TAM        |           |TEEP Agent   |
     +------------+           +-------------+

       QueryRequest ------->

                              QueryResponse

                    <-------     or

                                Error

   With the Update message a TAM can instruct a TEEP Agent to install
   and/or delete one or more Trusted Components.  The TEEP Agent will

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   process the message, determine whether the TAM is authorized and
   whether the Trusted Component has been signed by an authorized
   Trusted Component Signer.  A Success message is returned when the
   operation has been completed successfully, or an Error message
   otherwise.

    +------------+           +-------------+
    | TAM        |           |TEEP Agent   |
    +------------+           +-------------+

                Update  ---->

                               Success

                       <----    or

                               Error

4.  Detailed Messages Specification

   TEEP messages are protected by the COSE_Sign1 structure.  The TEEP
   protocol messages are described in CDDL format [RFC8610] below.

   {
       teep-message                => (query-request /
                                       query-response /
                                       update /
                                       teep-success /
                                       teep-error ),
   }

4.1.  Creating and Validating TEEP Messages

4.1.1.  Creating a TEEP message

   To create a TEEP message, the following steps are performed.

   1.  Create a TEEP message according to the description below and
       populate it with the respective content.  TEEP messages sent by
       TAMs (QueryRequest and Update) can include a "token".  The first
       usage of a token generated by a TAM MUST be randomly created.
       Subsequent token values MUST be different for each subsequent
       message created by a TAM.

   2.  Create a COSE Header containing the desired set of Header
       Parameters.  The COSE Header MUST be valid per the [RFC8152]
       specification.

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   3.  Create a COSE_Sign1 object using the TEEP message as the
       COSE_Sign1 Payload; all steps specified in [RFC8152] for creating
       a COSE_Sign1 object MUST be followed.

   4.  Prepend the COSE object with the TEEP CBOR tag to indicate that
       the CBOR-encoded message is indeed a TEEP message.

4.1.2.  Validating a TEEP Message

   When TEEP message is received (see the ProcessTeepMessage conceptual
   API defined in [I-D.ietf-teep-architecture] section 6.2.1), the
   following validation steps are performed.  If any of the listed steps
   fail, then the TEEP message MUST be rejected.

   1.  Verify that the received message is a valid CBOR object.

   2.  Remove the TEEP message CBOR tag and verify that one of the COSE
       CBOR tags follows it.

   3.  Verify that the message contains a COSE_Sign1 structure.

   4.  Verify that the resulting COSE Header includes only parameters
       and values whose syntax and semantics are both understood and
       supported or that are specified as being ignored when not
       understood.

   5.  Follow the steps specified in Section 4 of [RFC8152] ("Signing
       Objects") for validating a COSE_Sign1 object.  The COSE_Sign1
       payload is the content of the TEEP message.

   6.  Verify that the TEEP message is a valid CBOR map and verify the
       fields of the TEEP message according to this specification.

4.2.  QueryRequest Message

   A QueryRequest message is used by the TAM to learn information from
   the TEEP Agent, such as the features supported by the TEEP Agent,
   including ciphersuites, and protocol versions.  Additionally, the TAM
   can selectively request data items from the TEEP Agent via the
   request parameter.  Currently, the following features are supported:

   o  Request for attestation information,

   o  Listing supported extensions,

   o  Querying installed Trusted Components, and

   o  Listing supported SUIT commands.

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   Like other TEEP messages, the QueryRequest message is signed, and the
   relevant CDDL snippet is shown below.  The complete CDDL structure is
   shown in Appendix C.

   query-request = [
     type: TEEP-TYPE-query-request,
     options: {
       ? token => bstr .size (8..64),
       ? supported-cipher-suites => [ + suite ],
       ? supported-freshness-mechanisms => [ + freshness-mechanism ],
       ? challenge => bstr .size (8..512),
       ? versions => [ + version ],
       ? ocsp-data => bstr,
       * $$query-request-extensions
       * $$teep-option-extensions
     },
     data-item-requested: data-item-requested
   ]

   The message has the following fields:

   type
      The value of (1) corresponds to a QueryRequest message sent from
      the TAM to the TEEP Agent.

   token
      The value in the token parameter is used to match responses to
      requests.  This is particularly useful when a TAM issues multiple
      concurrent requests to a TEEP Agent.  The token MUST be present if
      and only if the attestation bit is clear in the data-item-
      requested value.  The size of the token is at least 8 bytes (64
      bits) and maximum of 64 bytes, which is the same as in an EAT
      Nonce Claim (see [I-D.ietf-rats-eat] Section 3.3).

   data-item-requested
      The data-item-requested parameter indicates what information the
      TAM requests from the TEEP Agent in the form of a bitmap.  Each
      value in the bitmap corresponds to an IANA registered information
      element.  This specification defines the following initial set of
      information elements:

      attestation (1)  With this value the TAM requests the TEEP Agent
         to return attestation evidence (e.g., an EAT) in the response.

      trusted-components (2)  With this value the TAM queries the TEEP
         Agent for all installed Trusted Components.

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      extensions (4)  With this value the TAM queries the TEEP Agent for
         supported capabilities and extensions, which allows a TAM to
         discover the capabilities of a TEEP Agent implementation.

      suit-commands (8)  With this value the TAM queries the TEEP Agent
         for supported commands offered by the SUIT manifest
         implementation.

      Further values may be added in the future via IANA registration.

   supported-cipher-suites
      The supported-cipher-suites parameter lists the ciphersuite(s)
      supported by the TAM.  If this parameter is not present, it is to
      be treated the same as if it contained both ciphersuites defined
      in this document.  Details about the ciphersuite encoding can be
      found in Section 7.

   supported-freshness-mechanisms
      The supported-freshness-mechanisms parameter lists the freshness
      mechanism(s) supported by the TAM.  Details about the encoding can
      be found in Section 8.  If this parameter is absent, it means only
      the nonce mechanism is supported.

   challenge
      The challenge field is an optional parameter used for ensuring the
      freshness of the attestation evidence returned with a
      QueryResponse message.  It MUST be absent if the attestation bit
      is clear (since the token is used instead in that case).  When a
      challenge is provided in the QueryRequest and an EAT is returned
      with the QueryResponse message then the challenge contained in
      this request MUST be copied into the nonce claim found in the EAT.
      If any format other than EAT is used, it is up to that format to
      define the use of the challenge field.

   versions
      The versions parameter enumerates the TEEP protocol version(s)
      supported by the TAM.  A value of 0 refers to the current version
      of the TEEP protocol.  If this field is not present, it is to be
      treated the same as if it contained only version 0.

   ocsp-data
      The ocsp-data parameter contains a list of OCSP stapling data
      respectively for the TAM certificate and each of the CA
      certificates up to, but not including, the trust anchor.  The TAM
      provides OCSP data so that the TEEP Agent can validate the status
      of the TAM certificate chain without making its own external OCSP
      service call.  OCSP data MUST be conveyed as a DER-encoded OCSP
      response (using the ASN.1 type OCSPResponse defined in [RFC6960]).

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      The use of OCSP is OPTIONAL to implement for both the TAM and the
      TEEP Agent.  A TAM can query the TEEP Agent for the support of
      this functionality via the capability discovery exchange, as
      described above.

4.3.  QueryResponse Message

   The QueryResponse message is the successful response by the TEEP
   Agent after receiving a QueryRequest message.

   Like other TEEP messages, the QueryResponse message is signed, and
   the relevant CDDL snippet is shown below.  The complete CDDL
   structure is shown in Appendix C.

   query-response = [
     type: TEEP-TYPE-query-response,
     options: {
       ? token => bstr .size (8..64),
       ? selected-cipher-suite => suite,
       ? selected-version => version,
       ? evidence-format => text,
       ? evidence => bstr,
       ? tc-list => [ + tc-info ],
       ? requested-tc-list => [ + requested-tc-info ],
       ? unneeded-tc-list => [ + SUIT_Component_Identifier ],
       ? ext-list => [ + ext-info ],
       * $$query-response-extensions,
       * $$teep-option-extensions
     }
   ]

   tc-info = {
     component-id => SUIT_Component_Identifier,
     ? tc-manifest-sequence-number => .within uint .size 8
   }

   requested-tc-info = {
     component-id => SUIT_Component_Identifier,
     ? tc-manifest-sequence-number => .within uint .size 8
     ? have-binary => bool
   }

   The QueryResponse message has the following fields:

   type
      The value of (2) corresponds to a QueryResponse message sent from
      the TEEP Agent to the TAM.

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   token
      The value in the token parameter is used to match responses to
      requests.  The value MUST correspond to the value received with
      the QueryRequest message if one was present, and MUST be absent if
      no token was present in the QueryRequest.

   selected-cipher-suite
      The selected-cipher-suite parameter indicates the selected
      ciphersuite.  Details about the ciphersuite encoding can be found
      in Section 7.

   selected-version
      The selected-version parameter indicates the TEEP protocol version
      selected by the TEEP Agent.  The absense of this parameter
      indicates the same as if it was present with a value of 0.

   evidence-format
      The evidence-format parameter indicates the IANA Media Type of the
      attestation evidence contained in the evidence parameter.  It MUST
      be present if the evidence parameter is present and the format is
      not an EAT.

   evidence
      The evidence parameter contains the attestation evidence.  This
      parameter MUST be present if the QueryResponse is sent in response
      to a QueryRequest with the attestation bit set.  If the evidence-
      format parameter is absent, the attestation evidence contained in
      this parameter MUST be an Entity Attestation Token following the
      encoding defined in [I-D.ietf-rats-eat].  See Section 4.3.1 for
      further discussion.

   tc-list
      The tc-list parameter enumerates the Trusted Components installed
      on the device in the form of tc-info objects.  This parameter MUST
      be present if the QueryResponse is sent in response to a
      QueryRequest with the trusted-components bit set.

   requested-tc-list
      The requested-tc-list parameter enumerates the Trusted Components
      that are not currently installed in the TEE, but which are
      requested to be installed, for example by an installer of an
      Untrusted Application that has a TA as a dependency, or by a
      Trusted Application that has another Trusted Component as a
      dependency.  Requested Trusted Components are expressed in the
      form of requested-tc-info objects.  A TEEP Agent can get this
      information from the UnrequestTA conceptual API defined in
      [I-D.ietf-teep-architecture] section 6.2.1.

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   unneeded-tc-list
      The unneeded-tc-list parameter enumerates the Trusted Components
      that are currently installed in the TEE, but which are no longer
      needed by any other application.  The TAM can use this information
      in determining whether a Trusted Component can be deleted.  Each
      unneeded Trusted Component is identified by its SUIT Component
      Identifier.  A TEEP Agent can get this information from the
      UnrequestTA conceptual API defined in [I-D.ietf-teep-architecture]
      section 6.2.1.

   ext-list
      The ext-list parameter lists the supported extensions.  This
      document does not define any extensions.

   The tc-info object has the following fields:

   component-id
      A SUIT Component Identifier.

   tc-manifest-sequence-number
      The suit-manifest-sequence-number value from the SUIT manifest for
      the Trusted Component, if a SUIT manifest was used.

   The requested-tc-info message has the following fields:

   component-id
      A SUIT Component Identifier.

   tc-manifest-sequence-number
      The minimum suit-manifest-sequence-number value from a SUIT
      manifest for the Trusted Component.  If not present, indicates
      that any sequence number will do.

   have-binary
      If present with a value of true, indicates that the TEEP agent
      already has the Trusted Component binary and only needs an Update
      message with a SUIT manifest that authorizes installing it.  If
      have-binary is true, the tc-manifest-sequence-number field MUST be
      present.

4.3.1.  Evidence

   Section 7.1 of [I-D.ietf-teep-architecture] lists information that
   may be required in the evidence depend on the circumstance.  When an
   Entity Attestation Token is used, the following claims can be used to
   meet those requirements:

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   +------------+---------------------+--------------------------------+
   | Requiremen | Claim               | Reference                      |
   | t          |                     |                                |
   +------------+---------------------+--------------------------------+
   | Device     | device-identifier   | [I-D.birkholz-rats-suit-claims |
   | unique     |                     | ] section 3.1.3                |
   | identifier |                     |                                |
   | Vendor of  | vendor-identifier   | [I-D.birkholz-rats-suit-claims |
   | the device |                     | ] section 3.1.1                |
   | Class of   | class-identifier    | [I-D.birkholz-rats-suit-claims |
   | the device |                     | ] section 3.1.2                |
   | TEE        | chip-version-scheme | [I-D.ietf-rats-eat] section    |
   | hardware   |                     | 3.7                            |
   | type       |                     |                                |
   | TEE        | chip-version-scheme | [I-D.ietf-rats-eat] section    |
   | hardware   |                     | 3.7                            |
   | version    |                     |                                |
   | TEE        | component-          | [I-D.birkholz-rats-suit-claims |
   | firmware   | identifier          | ] section 3.1.4                |
   | type       |                     |                                |
   | TEE        | version             | [I-D.birkholz-rats-suit-claims |
   | firmware   |                     | ] section 3.1.8                |
   | version    |                     |                                |
   | Freshness  | nonce               | [I-D.ietf-rats-eat] section    |
   | proof      |                     | 3.3                            |
   +------------+---------------------+--------------------------------+

4.4.  Update Message

   The Update message is used by the TAM to install and/or delete one or
   more Trusted Components via the TEEP Agent.

   Like other TEEP messages, the Update message is signed, and the
   relevant CDDL snippet is shown below.  The complete CDDL structure is
   shown in Appendix C.

   update = [
     type: TEEP-TYPE-update,
     options: {
       ? token => bstr .size (8..64),
       ? manifest-list => [ + bstr .cbor SUIT_Envelope ],
       * $$update-extensions,
       * $$teep-option-extensions
     }
   ]

   The Update message has the following fields:

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   type
      The value of (3) corresponds to an Update message sent from the
      TAM to the TEEP Agent.  In case of successful processing, a
      Success message is returned by the TEEP Agent.  In case of an
      error, an Error message is returned.  Note that the Update message
      is used for initial Trusted Component installation as well as for
      updates and deletes.

   token
      The value in the token field is used to match responses to
      requests.

   manifest-list
      The manifest-list field is used to convey one or multiple SUIT
      manifests to install.  A manifest is a bundle of metadata about a
      Trusted Component, such as where to find the code, the devices to
      which it applies, and cryptographic information protecting the
      manifest.  The manifest may also convey personalization data.
      Trusted Component binaries and personalization data can be signed
      and encrypted by the same Trusted Component Signer.  Other
      combinations are, however, possible as well.  For example, it is
      also possible for the TAM to sign and encrypt the personalization
      data and to let the Trusted Component Developer sign and/or
      encrypt the Trusted Component binary.

   Note that an Update message carrying one or more SUIT manifests will
   inherently involve multiple signatures, one by the TAM in the TEEP
   message and one from a Trusted Component signer inside each manifest.
   This is intentional as they are for different purposes.

   The TAM is what authorizes apps to be installed, updated, and deleted
   on a given TEE and so the TEEP signature is checked by the TEEP Agent
   at protocol message processing time.  (This same TEEP security
   wrapper is also used on messages like QueryRequest so that Agents
   only send potentially sensitive data such as evidence to trusted
   TAMs.)

   The Trusted Component signer on the other hand is what authorizes the
   Trusted Component to actually run, so the manifest signature could be
   checked at install time or load (or run) time or both, and this
   checking is done by the TEE independent of whether TEEP is used or
   some other update mechanism.  See section 5 of
   [I-D.ietf-teep-architecture] for further discussion.

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4.5.  Success Message

   The Success message is used by the TEEP Agent to return a success in
   response to an Update message.

   Like other TEEP messages, the Success message is signed, and the
   relevant CDDL snippet is shown below.  The complete CDDL structure is
   shown in Appendix C.

   teep-success = [
     type: TEEP-TYPE-teep-success,
     options: {
       ? token => bstr .size (8..64),
       ? msg => text .size (1..128),
       ? suit-reports => [ + suit-report ],
       * $$teep-success-extensions,
       * $$teep-option-extensions
     }
   ]

   The Success message has the following fields:

   type
      The value of (5) corresponds to corresponds to a Success message
      sent from the TEEP Agent to the TAM.

   token
      The value in the token parameter is used to match responses to
      requests.  It MUST match the value of the token parameter in the
      Update message the Success is in response to, if one was present.
      If none was present, the token MUST be absent in the Success
      message.

   msg
      The msg parameter contains optional diagnostics information
      encoded in UTF-8 [RFC3629] using Net-Unicode form [RFC5198] with
      max 128 bytes returned by the TEEP Agent.

   suit-reports
      If present, the suit-reports parameter contains a set of SUIT
      Reports as defined in Section 4 of [I-D.moran-suit-report].  If
      the suit-report-nonce field is present in the SUIT Report, is
      value MUST match the value of the token parameter in the Update
      message the Success message is in response to.

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4.6.  Error Message

   The Error message is used by the TEEP Agent to return an error in
   response to an Update message.

   Like other TEEP messages, the Error message is signed, and the
   relevant CDDL snippet is shown below.  The complete CDDL structure is
   shown in Appendix C.

   teep-error = [
     type: TEEP-TYPE-teep-error,
     options: {
        ? token => bstr .size (8..64),
        ? err-msg => text .size (1..128),
        ? supported-cipher-suites => [ + suite ],
        ? supported-freshness-mechanisms => [ + freshness-mechanism ],
        ? versions => [ + version ],
        ? suit-reports => [ + suit-report ],
        * $$teep-error-extensions,
        * $$teep-option-extensions
     },
     err-code: uint (0..23)
   ]

   The Error message has the following fields:

   type
      The value of (6) corresponds to an Error message sent from the
      TEEP Agent to the TAM.

   token
      The value in the token parameter is used to match responses to
      requests.  It MUST match the value of the token parameter in the
      Update message the Success is in response to, if one was present.
      If none was present, the token MUST be absent in the Error
      message.

   err-msg
      The err-msg parameter is human-readable diagnostic text that MUST
      be encoded using UTF-8 [RFC3629] using Net-Unicode form [RFC5198]
      with max 128 bytes.

   supported-cipher-suites
      The supported-cipher-suites parameter lists the ciphersuite(s)
      supported by the TEEP Agent.  Details about the ciphersuite
      encoding can be found in Section 7.  This field is optional but
      MUST be returned with the ERR_UNSUPPORTED_CRYPTO_ALG error
      message.

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   supported-freshness-mechanisms
      The supported-freshness-mechanisms parameter lists the freshness
      mechanism(s) supported by the TEEP Agent.  Details about the
      encoding can be found in Section 8.  If this parameter is absent,
      it means only the nonce mechanism is supported.

   versions
      The versions parameter enumerates the TEEP protocol version(s)
      supported by the TEEP Agent.  This otherwise optional parameter
      MUST be returned with the ERR_UNSUPPORTED_MSG_VERSION error
      message.

   suit-reports
      If present, the suit-reports parameter contains a set of SUIT
      Reports as defined in Section 4 of [I-D.moran-suit-report].  If
      the suit-report-nonce field is present in the SUIT Report, is
      value MUST match the value of the token parameter in the Update
      message the Error message is in response to.

   err-code
      The err-code parameter contains one of the error codes listed
      below).  Only selected values are applicable to each message.

   This specification defines the following initial error messages:

   ERR_PERMANENT_ERROR (1)
      The TEEP request contained incorrect fields or fields that are
      inconsistent with other fields.  For diagnosis purposes it is
      RECOMMMENDED to identify the failure reason in the error message.
      A TAM receiving this error might refuse to communicate further
      with the TEEP Agent for some period of time until it has reason to
      believe it is worth trying again, but it should take care not to
      give up on communication when there is no attestation evidence
      indicating that the error is genuine.  In contrast,
      ERR_TEMPORARY_ERROR is an indication that a more agressive retry
      is warranted.

   ERR_UNSUPPORTED_EXTENSION (2)
      The TEEP Agent does not support an extension included in the
      request message.  For diagnosis purposes it is RECOMMMENDED to
      identify the unsupported extension in the error message.  A TAM
      receiving this error might retry the request without using
      extensions.

   ERR_UNSUPPORTED_MSG_VERSION (4)
      The TEEP Agent does not support the TEEP protocol version
      indicated in the request message.  A TAM receiving this error
      might retry the request using a different TEEP protocol version.

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   ERR_UNSUPPORTED_CRYPTO_ALG (5)
      The TEEP Agent does not support the cryptographic algorithm
      indicated in the request message.  A TAM receiving this error
      might retry the request using a different cryptographic algorithm.

   ERR_BAD_CERTIFICATE (6)
      Processing of a certificate failed.  For diagnosis purposes it is
      RECOMMMENDED to include information about the failing certificate
      in the error message.  For example, the certificate was of an
      unsupported type, or the certificate was revoked by its signer.  A
      TAM receiving this error might attempt to use an alternate
      certificate.

   ERR_CERTIFICATE_EXPIRED (9)
      A certificate has expired or is not currently valid.  A TAM
      receiving this error might attempt to renew its certificate before
      using it again.

   ERR_TEMPORARY_ERROR (10)
      A miscellaneous temporary error, such as a memory allocation
      failure, occurred while processing the request message.  A TAM
      receiving this error might retry the same request at a later point
      in time.

   ERR_MANIFEST_PROCESSING_FAILED (17)
      The TEEP Agent encountered one or more manifest processing
      failures.  If the suit-reports parameter is present, it contains
      the failure details.  A TAM receiving this error might still
      attempt to install or update other components that do not depend
      on the failed manifest.

   New error codes should be added sparingly, not for every
   implementation error.  That is the intent of the err-msg field, which
   can be used to provide details meaningful to humans.  New error codes
   should only be added if the TAM is expected to do something
   behaviorally different upon receipt of the error message, rather than
   just logging the event.  Hence, each error code is responsible for
   saying what the behavioral difference is expected to be.

5.  Mapping of TEEP Message Parameters to CBOR Labels

   In COSE, arrays and maps use strings, negative integers, and unsigned
   integers as their keys.  Integers are used for compactness of
   encoding.  Since the word "key" is mainly used in its other meaning,
   as a cryptographic key, this specification uses the term "label" for
   this usage as a map key.

   This specification uses the following mapping:

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                +--------------------------------+-------+
                | Name                           | Label |
                +--------------------------------+-------+
                | supported-cipher-suites        | 1     |
                | challenge                      | 2     |
                | version                        | 3     |
                | ocsp-data                      | 4     |
                | selected-cipher-suite          | 5     |
                | selected-version               | 6     |
                | evidence                       | 7     |
                | tc-list                        | 8     |
                | ext-list                       | 9     |
                | manifest-list                  | 10    |
                | msg                            | 11    |
                | err-msg                        | 12    |
                | evidence-format                | 13    |
                | requested-tc-list              | 14    |
                | unneeded-tc-list               | 15    |
                | component-id                   | 16    |
                | tc-manifest-sequence-number    | 17    |
                | have-binary                    | 18    |
                | suit-reports                   | 19    |
                | token                          | 20    |
                | supported-freshness-mechanisms | 21    |
                +--------------------------------+-------+

6.  Behavior Specification

   Behavior is specified in terms of the conceptual APIs defined in
   section 6.2.1 of [I-D.ietf-teep-architecture].

6.1.  TAM Behavior

   When the ProcessConnect API is invoked, the TAM sends a QueryRequest
   message.

   When the ProcessTeepMessage API is invoked, the TAM first does
   validation as specified in Section 4.1.2, and drops the message if it
   is not valid.  Otherwise, it proceeds as follows.

   If the message includes a token, it can be used to match the response
   to a request previously sent by the TAM.  The TAM MUST expire the
   token value after receiving the first response from the device that
   has a valid signature and ignore any subsequent messages that have
   the same token value.  The token value MUST NOT be used for other
   purposes, such as a TAM to identify the devices and/or a device to
   identify TAMs or Trusted Components.

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   If a QueryResponse message is received that contains evidence, the
   evidence is passed to an attestation Verifier (see
   [I-D.ietf-rats-architecture]) to determine whether the Agent is in a
   trustworthy state.  Based on the results of attestation, and the
   lists of installed, requested, and unneeded Trusted Components
   reported in the QueryResponse, the TAM determines, in any
   implementation specific manner, which Trusted Components need to be
   installed, updated, or deleted, if any.  If any Trusted Components
   need to be installed, updated, or deleted, the TAM sends an Update
   message containing SUIT Manifests with command sequences to do the
   relevant installs, updates, or deletes.  It is important to note that
   the TEEP Agent's Update Procedure requires resolving and installing
   any dependencies indicated in the manifest, which may take some time,
   and the resulting Success or Error message is generated only after
   completing the Update Procedure.  Hence, depending on the freshness
   mechanism in use, the TAM may need to store data (e.g., a nonce) for
   some time.

   If a Success or Error message is received containing one or more SUIT
   Reports, the TAM also validates that the nonce in any SUIT Report
   matches the token sent in the Update message, and drops the message
   if it does not match.  Otherwise, the TAM handles the update in any
   implementation specific way, such as updating any locally cached
   information about the state of the TEEP Agent, or logging the
   results.

   If any other Error message is received, the TAM can handle it in any
   implementation specific way, but Section 4.6 provides recommendations
   for such handling.

6.2.  TEEP Agent Behavior

   When the RequestTA API is invoked, the TEEP Agent first checks
   whether the requested TA is already installed.  If it is already
   installed, the TEEP Agent passes no data back to the caller.
   Otherwise, if the TEEP Agent chooses to initiate the process of
   requesting the indicated TA, it determines (in any implementation
   specific way) the TAM URI based on any TAM URI provided by the
   RequestTA caller and any local configuration, and passes back the TAM
   URI to connect to.

   When the RequestPolicyCheck API is invoked, the TEEP Agent decides
   whether to initiate communication with any trusted TAMs (e.g., it
   might choose to do so for a given TAM unless it detects that it has
   already communicated with that TAM recently).  If so, it passes back
   a TAM URI to connect to.  If the TEEP Agent has multiple TAMs it
   needs to connect with, it just passes back one, with the expectation
   that RequestPolicyCheck API will be invoked to retrieve each one

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   successively until there are no more and it can pass back no data at
   that time.  Thus, once a TAM URI is returned, the TEEP Agent can
   remember that it has already initiated communication with that TAM.

   When the ProcessError API is invoked, the TEEP Agent can handle it in
   any implementation specific way, such as logging the error or using
   the information in future choices of TAM URI.

   When the ProcessTeepMessage API is invoked, the Agent first does
   validation as specified in Section 4.1.2, and drops the message if it
   is not valid.  Otherwise, processing continues as follows based on
   the type of message.

   When a QueryRequest message is received, the Agent responds with a
   QueryResponse message if all fields were understood, or an Error
   message if any error was encountered.

   When an Update message is received, the Agent attempts to update the
   Trusted Components specified in the SUIT manifests by following the
   Update Procedure specified in [I-D.ietf-suit-manifest], and responds
   with a Success message if all SUIT manifests were successfully
   installed, or an Error message if any error was encountered.  It is
   important to note that the Update Procedure requires resolving and
   installing any dependencies indicated in the manifest, which may take
   some time, and the Success or Error message is generated only after
   completing the Update Procedure.

7.  Ciphersuites

   A ciphersuite consists of an AEAD algorithm, a MAC algorithm, and a
   signature algorithm.  Each ciphersuite is identified with an integer
   value, which corresponds to an IANA registered ciphersuite (see
   Section 10.2.  This document specifies two ciphersuites.

        +-------+------------------------------------------------+
        | Value | Ciphersuite                                    |
        +-------+------------------------------------------------+
        | 1     | AES-CCM-16-64-128, HMAC 256/256, X25519, EdDSA |
        | 2     | AES-CCM-16-64-128, HMAC 256/256, P-256, ES256  |
        +-------+------------------------------------------------+

   A TAM MUST support both ciphersuites.  A TEEP Agent MUST support at
   least one of the two but can choose which one.  For example, a TEEP
   Agent might choose ciphersuite 2 if it has hardware support for it.

   Any ciphersuites without confidentiality protection can only be added
   if the associated specification includes a discussion of security
   considerations and applicability, since manifests may carry sensitive

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   information.  For example, Section 6 of [I-D.ietf-teep-architecture]
   permits implementations that terminate transport security inside the
   TEE and if the transport security provides confidentiality then
   additional encryption might not be needed in the manifest for some
   use cases.  For most use cases, however, manifest confidentiality
   will be needed to protect sensitive fields from the TAM as discussed
   in Section 9.8 of [I-D.ietf-teep-architecture].

8.  Freshness Mechanisms

   A freshness mechanism determines how a TAM can tell whether evidence
   provided in a Query Response is fresh.  There are multiple ways this
   can be done as discussed in Section 10 of
   [I-D.ietf-rats-architecture].

   Each freshness mechanism is identified with an integer value, which
   corresponds to an IANA registered freshness mechanism (see
   Section 10.3.  This document defines the following freshness
   mechanisms:

                      +-------+---------------------+
                      | Value | Freshness mechanism |
                      +-------+---------------------+
                      | 1     | Nonce               |
                      | 2     | Timestamp           |
                      | 3     | Epoch ID            |
                      +-------+---------------------+

   In the Nonce mechanism, the evidence MUST include a nonce provided in
   the QueryRequest challenge.  In other mechanisms, a timestamp or
   epoch ID determined via mechanisms outside the TEEP protocol is used,
   and the challenge is only needed in the QueryRequest message if a
   challenge is needed in generating evidence for reasons other than
   freshness.

9.  Security Considerations

   This section summarizes the security considerations discussed in this
   specification:

   Cryptographic Algorithms
      TEEP protocol messages exchanged between the TAM and the TEEP
      Agent are protected using COSE.  This specification relies on the
      cryptographic algorithms provided by COSE.  Public key based
      authentication is used by the TEEP Agent to authenticate the TAM
      and vice versa.

   Attestation

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      A TAM can rely on the attestation evidence provided by the TEEP
      Agent.  To sign the attestation evidence, it is necessary for the
      device to possess a public key (usually in the form of a
      certificate [RFC5280]) along with the corresponding private key.
      Depending on the properties of the attestation mechanism, it is
      possible to uniquely identify a device based on information in the
      attestation evidence or in the certificate used to sign the
      attestation evidence.  This uniqueness may raise privacy concerns.
      To lower the privacy implications the TEEP Agent MUST present its
      attestation evidence only to an authenticated and authorized TAM
      and when using EATS, it SHOULD use encryption as discussed in
      [I-D.ietf-rats-eat], since confidentiality is not provided by the
      TEEP protocol itself and the transport protocol under the TEEP
      protocol might be implemented outside of any TEE.  If any
      mechanism other than EATs is used, it is up to that mechanism to
      specify how privacy is provided.

   Trusted Component Binaries
      Each Trusted Component binary is signed by a Trusted Component
      Signer.  It is the responsibility of the TAM to relay only
      verified Trusted Components from authorized Trusted Component
      Signers.  Delivery of a Trusted Component to the TEEP Agent is
      then the responsibility of the TAM, using the security mechanisms
      provided by the TEEP protocol.  To protect the Trusted Component
      binary, the SUIT manifest format is used and it offers a variety
      of security features, including digitial signatures and symmetric
      encryption.

   Personalization Data
      A Trusted Component Signer or TAM can supply personalization data
      along with a Trusted Component.  This data is also protected by a
      SUIT manifest.  Personalization data signed and encrypted by a
      Trusted Component Signer other than the TAM is opaque to the TAM.

   TEEP Broker
      As discussed in section 6 of [I-D.ietf-teep-architecture], the
      TEEP protocol typically relies on a TEEP Broker to relay messages
      between the TAM and the TEEP Agent.  When the TEEP Broker is
      compromised it can drop messages, delay the delivery of messages,
      and replay messages but it cannot modify those messages.  (A
      replay would be, however, detected by the TEEP Agent.)  A
      compromised TEEP Broker could reorder messages in an attempt to
      install an old version of a Trusted Component.  Information in the
      manifest ensures that TEEP Agents are protected against such
      downgrade attacks based on features offered by the manifest
      itself.

   Trusted Component Signer Compromise

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      The QueryRequest message from a TAM to the TEEP Agent can include
      OCSP stapling data for the TAM's certificate and for intermediate
      CA certificates up to, but not including, the trust anchor so that
      the TEEP Agent can verify the certificate's revocation status.  A
      certificate revocation status check on a Trusted Component Signer
      certificate is OPTIONAL by a TEEP Agent.  A TAM is responsible for
      vetting a Trusted Component and before distributing them to TEEP
      Agents, so TEEP Agents can instead simply trust that a Trusted
      Component Signer certificate's status was done by the TAM.

   CA Compromise
      The CA issuing certificates to a TAM or a Trusted Component Signer
      might get compromised.  A compromised intermediate CA certificate
      can be detected by a TEEP Agent by using OCSP information,
      assuming the revocation information is available.  Additionally,
      it is RECOMMENDED to provide a way to update the trust anchor
      store used by the TEE, for example using a firmware update
      mechanism.  If the CA issuing certificates to devices gets
      compromised then these devices might be rejected by a TAM, if
      revocation is available to the TAM.

   Compromised TAM
      The TEEP Agent SHOULD use OCSP information to verify the validity
      of the TAM's certificate (as well as the validity of intermediate
      CA certificates).  The integrity and the accuracy of the clock
      within the TEE determines the ability to determine an expired or
      revoked certificate.  OCSP stapling data includes signature
      generation time, allowing certificate validity dates to be
      compared to the current time.

   Compromised Time Source
      As discussed above, certificate validity checks rely on comparing
      validity dates to the current time, which relies on having a
      trusted source of time, such as [RFC8915].  A compromised time
      source could thus be used to subvert such validity checks.

10.  IANA Considerations

10.1.  Media Type Registration

   IANA is requested to assign a media type for application/teep+cbor.

   Type name:  application

   Subtype name:  teep+cbor

   Required parameters:  none

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   Optional parameters:  none

   Encoding considerations:  Same as encoding considerations of
      application/cbor.

   Security considerations:  See Security Considerations Section of this
      document.

   Interoperability considerations:  Same as interoperability
      considerations of application/cbor as specified in [RFC7049].

   Published specification:  This document.

   Applications that use this media type:  TEEP protocol implementations

   Fragment identifier considerations:  N/A

   Additional information:

      Deprecated alias names for this type:  N/A

      Magic number(s):  N/A

      File extension(s):  N/A

      Macintosh file type code(s):  N/A

   Person to contact for further information:  teep@ietf.org

   Intended usage:  COMMON

   Restrictions on usage:  none

   Author:  See the "Authors' Addresses" section of this document

   Change controller:  IETF

10.2.  Ciphersuite Registry

   IANA is also requested to create a new registry for ciphersuites, as
   defined in Section 7.

10.3.  Freshness Mechanism Registry

   IANA is also requested to create a new registry for freshness
   mechanisms, as defined in Section 8.

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10.4.  CBOR Tag Registry

   IANA is requested to register a CBOR tag in the "CBOR Tags" registry
   for use with TEEP messages.

   The registry contents is:

   o  CBOR Tag: TBD1

   o  Data Item: TEEP Message

   o  Semantics: TEEP Message, as defined in draft-ietf-teep-protocol
      (TODO: replace with RFC once published)

   o  Reference: draft-ietf-teep-protocol (TODO: replace with RFC once
      published)

   o  Point of Contact: TEEP working group (teep@ietf.org)

11.  References

11.1.  Normative References

   [I-D.ietf-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.

   [I-D.ietf-rats-eat]
              Mandyam, G., Lundblade, L., Ballesteros, M., and J.
              O'Donoghue, "The Entity Attestation Token (EAT)", draft-
              ietf-rats-eat-10 (work in progress), June 2021.

   [I-D.ietf-suit-manifest]
              Moran, B., Tschofenig, H., Birkholz, H., and K. Zandberg,
              "A Concise Binary Object Representation (CBOR)-based
              Serialization Format for the Software Updates for Internet
              of Things (SUIT) Manifest", draft-ietf-suit-manifest-14
              (work in progress), July 2021.

   [I-D.moran-suit-report]
              Moran, B., "Secure Reporting of Update Status", draft-
              moran-suit-report-01 (work in progress), February 2021.

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   [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>.

   [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
              10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
              2003, <https://www.rfc-editor.org/info/rfc3629>.

   [RFC5198]  Klensin, J. and M. Padlipsky, "Unicode Format for Network
              Interchange", RFC 5198, DOI 10.17487/RFC5198, March 2008,
              <https://www.rfc-editor.org/info/rfc5198>.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
              <https://www.rfc-editor.org/info/rfc5280>.

   [RFC6960]  Santesson, S., Myers, M., Ankney, R., Malpani, A.,
              Galperin, S., and C. Adams, "X.509 Internet Public Key
              Infrastructure Online Certificate Status Protocol - OCSP",
              RFC 6960, DOI 10.17487/RFC6960, June 2013,
              <https://www.rfc-editor.org/info/rfc6960>.

   [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>.

   [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>.

11.2.  Informative References

   [I-D.birkholz-rats-suit-claims]
              Birkholz, H. and B. Moran, "Trustworthiness Vectors for
              the Software Updates of Internet of Things (SUIT) Workflow
              Model", draft-birkholz-rats-suit-claims-02 (work in
              progress), July 2021.

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   [I-D.ietf-teep-architecture]
              Pei, M., Tschofenig, H., Thaler, D., and D. Wheeler,
              "Trusted Execution Environment Provisioning (TEEP)
              Architecture", draft-ietf-teep-architecture-15 (work in
              progress), July 2021.

   [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>.

   [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>.

   [RFC8915]  Franke, D., Sibold, D., Teichel, K., Dansarie, M., and R.
              Sundblad, "Network Time Security for the Network Time
              Protocol", RFC 8915, DOI 10.17487/RFC8915, September 2020,
              <https://www.rfc-editor.org/info/rfc8915>.

A.  Contributors

   We would like to thank Brian Witten (Symantec), Tyler Kim (Solacia),
   Nick Cook (Arm), and Minho Yoo (IoTrust) for their contributions to
   the Open Trust Protocol (OTrP), which influenced the design of this
   specification.

B.  Acknowledgements

   We would like to thank Eve Schooler for the suggestion of the
   protocol name.

   We would like to thank Kohei Isobe (TRASIO/SECOM), Kuniyasu Suzaki
   (TRASIO/AIST), Tsukasa Oi (TRASIO), and Yuichi Takita (SECOM) for
   their valuable implementation feedback.

   We would also like to thank Carsten Bormann and Henk Birkholz for
   their help with the CDDL.

C.  Complete CDDL

   Valid TEEP messages MUST adhere to the following CDDL data
   definitions, except that "SUIT_Envelope" and
   "SUIT_Component_Identifier" are specified in
   [I-D.ietf-suit-manifest].

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   teep-message = $teep-message-type .within teep-message-framework

   SUIT_Envelope = any

   teep-message-framework = [
     type: uint (0..23) / $teep-type-extension,
     options: { * teep-option },
     * uint; further integers, e.g., for data-item-requested
   ]

   teep-option = (uint => any)

   ; messages defined below:
   $teep-message-type /= query-request
   $teep-message-type /= query-response
   $teep-message-type /= update
   $teep-message-type /= teep-success
   $teep-message-type /= teep-error

   ; message type numbers, uint (0..23)
   TEEP-TYPE-query-request = 1
   TEEP-TYPE-query-response = 2
   TEEP-TYPE-update = 3
   TEEP-TYPE-teep-success = 5
   TEEP-TYPE-teep-error = 6

   version = .within uint .size 4
   ext-info = .within uint .size 4

   ; data items as bitmaps
   data-item-requested = $data-item-requested .within uint .size 8
   attestation = 1
   $data-item-requested /= attestation
   trusted-components = 2
   $data-item-requested /= trusted-components
   extensions = 4
   $data-item-requested /= extensions
   suit-commands = 8
   $data-item-requested /= suit-commands

   query-request = [
     type: TEEP-TYPE-query-request,
     options: {
       ? token => bstr .size (8..64),
       ? supported-cipher-suites => [ + suite ],
       ? supported-freshness-mechanisms => [ + freshness-mechanism ],
       ? challenge => bstr .size (8..512),
       ? versions => [ + version ],

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       ? ocsp-data => bstr,
       * $$query-request-extensions
       * $$teep-option-extensions
     },
     data-item-requested: data-item-requested
   ]

   ; ciphersuites
   suite = $TEEP-suite .within uint .size 4

   TEEP-AES-CCM-16-64-128-HMAC256--256-X25519-EdDSA = 1
   TEEP-AES-CCM-16-64-128-HMAC256--256-P-256-ES256  = 2

   $TEEP-suite /= TEEP-AES-CCM-16-64-128-HMAC256--256-X25519-EdDSA
   $TEEP-suite /= TEEP-AES-CCM-16-64-128-HMAC256--256-P-256-ES256

   ; freshness-mechanisms

   freshness-mechanism = $TEEP-freshness-mechanism .within uint .size 4

   FRESHNESS_NONCE = 0
   FRESHNESS_TIMESTAMP = 1
   FRESHNESS_EPOCH_ID = 2

   $TEEP-freshness-mechanism /= FRESHNESS_NONCE
   $TEEP-freshness-mechanism /= FRESHNESS_TIMESTAMP
   $TEEP-freshness-mechanism /= FRESHNESS_EPOCH_ID

   query-response = [
     type: TEEP-TYPE-query-response,
     options: {
       ? token => bstr .size (8..64),
       ? selected-cipher-suite => suite,
       ? selected-version => version,
       ? evidence-format => text,
       ? evidence => bstr,
       ? tc-list => [ + tc-info ],
       ? requested-tc-list => [ + requested-tc-info ],
       ? unneeded-tc-list => [ + SUIT_Component_Identifier ],
       ? ext-list => [ + ext-info ],
       * $$query-response-extensions,
       * $$teep-option-extensions
     }
   ]

   tc-info = {
     component-id => SUIT_Component_Identifier,
     ? tc-manifest-sequence-number => .within uint .size 8

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   }

   requested-tc-info = {
     component-id => SUIT_Component_Identifier,
     ? tc-manifest-sequence-number => .within uint .size 8
     ? have-binary => bool
   }

   update = [
     type: TEEP-TYPE-update,
     options: {
       ? token => bstr .size (8..64),
       ? manifest-list => [ + bstr .cbor SUIT_Envelope ],
       * $$update-extensions,
       * $$teep-option-extensions
     }
   ]

   teep-success = [
     type: TEEP-TYPE-teep-success,
     options: {
       ? token => bstr .size (8..64),
       ? msg => text .size (1..128),
       ? suit-reports => [ + suit-report ],
       * $$teep-success-extensions,
       * $$teep-option-extensions
     }
   ]

   teep-error = [
     type: TEEP-TYPE-teep-error,
     options: {
        ? token => bstr .size (8..64),
        ? err-msg => text .size (1..128),
        ? supported-cipher-suites => [ + suite ],
        ? supported-freshness-mechanisms => [ + freshness-mechanism ],
        ? versions => [ + version ],
        ? suit-reports => [ + suit-report ],
        * $$teep-error-extensions,
        * $$teep-option-extensions
     },
     err-code: uint (0..23)
   ]

   ; The err-code parameter, uint (0..23)
   ERR_PERMANENT_ERROR = 1
   ERR_UNSUPPORTED_EXTENSION = 2
   ERR_UNSUPPORTED_MSG_VERSION = 4

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   ERR_UNSUPPORTED_CRYPTO_ALG = 5
   ERR_BAD_CERTIFICATE = 6
   ERR_CERTIFICATE_EXPIRED = 9
   ERR_TEMPORARY_ERROR = 10
   ERR_MANIFEST_PROCESSING_FAILED = 17

   ; labels of mapkey for teep message parameters, uint (0..23)
   supported-cipher-suites = 1
   challenge = 2
   versions = 3
   ocsp-data = 4
   selected-cipher-suite = 5
   selected-version = 6
   evidence = 7
   tc-list = 8
   ext-list = 9
   manifest-list = 10
   msg = 11
   err-msg = 12
   evidence-format = 13
   requested-tc-list = 14
   unneeded-tc-list = 15
   component-id = 16
   tc-manifest-sequence-number = 17
   have-binary = 18
   suit-reports = 19
   token = 20

D.  Examples of Diagnostic Notation and Binary Representation

D.1.  Some assumptions in examples

   o  OCSP stapling data = h'010203'

   o  TEEP Device will have two TCs with the following SUIT Component
      Identifiers:

      *  [ 0x000102030405060708090a0b0c0d0e0f ]

      *  [ 0x100102030405060708090a0b0c0d0e0f ]

   o  SUIT manifest-list is set empty only for example purposes

D.2.  QueryRequest Message

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D.2.1.  CBOR Diagnostic Notation

 / query-request = /
 [
   1,  / type : TEEP-TYPE-query-request = 1 (uint (0..23)) /
   / options : /
   {
     20 : 0xa0a1a2a3a4a5a6a7a8a9aaabacadaeaf,
             / token = 20 (mapkey) :
               h'a0a1a2a3a4a5a6a7a8a9aaabacadaeaf' (bstr .size (8..64)),
               generated by TAM /
     1 : [ 1 ], / supported-cipher-suites = 1 (mapkey) :
                  TEEP-AES-CCM-16-64-128-HMAC256--256-X25519-EdDSA =
                  [ 1 ] (array of .within uint .size 4) /
     3 : [ 0 ], / version = 3 (mapkey) :
                  [ 0 ] (array of .within uint .size 4) /
     4 : h'010203' / ocsp-data = 4 (mapkey) : 0x010203 (bstr) /
   },
   3   / data-item-requested :
         attestation | trusted-components = 3 (.within uint .size 8) /
 ]

D.2.2.  CBOR Binary Representation

   83                       # array(3)
     01                     # unsigned(1) uint (0..23)
     A4                     # map(4)
       14                   # unsigned(20) uint (0..23)
       4F                   # bytes(16) (8..64)
         A0A1A2A3A4A5A6A7A8A9AAABACADAEAF
       01                   # unsigned(1) uint (0..23)
       81                   # array(1)
         01                 # unsigned(1) within uint .size 4
       03                   # unsigned(3) uint (0..23)
       81                   # array(1)
         00                 # unsigned(0) within uint .size 4
       04                   # unsigned(4) uint (0..23)
       43                   # bytes(3)
         010203             # "\x01\x02\x03"
     03                     # unsigned(3) .within uint .size 8

D.3.  Entity Attestation Token

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

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D.3.1.  CBOR Diagnostic Notation

/ eat-claim-set = /
{
    / issuer /                   1: "joe",
    / timestamp (iat) /          6: 1(1526542894)
    / nonce /                   10: h'948f8860d13a463e8e',
    / secure-boot /             15: true,
    / debug-status /            16: 3, / disabled-permanently /
    / security-level /       <TBD>: 3, / secure-restricted /
    / device-identifier /    <TBD>: h'e99600dd921649798b013e9752dcf0c5',
    / vendor-identifier /    <TBD>: h'2b03879b33434a7ca682b8af84c19fd4',
    / class-identifier /     <TBD>: h'9714a5796bd245a3a4ab4f977cb8487f',
    / chip-version-scheme /  <TBD>: "MyTEE v1.0",
    / component-identifier / <TBD>: h'60822887d35e43d5b603d18bcaa3f08d',
    / version /              <TBD>: "v0.1"
}

D.4.  QueryResponse Message

D.4.1.  CBOR Diagnostic Notation

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 / query-response = /
 [
   2,  / type : TEEP-TYPE-query-response = 2 (uint (0..23)) /
   / options : /
   {
     20 : 0xa0a1a2a3a4a5a6a7a8a9aaabacadaeaf,
             / token = 20 (mapkey) :
               h'a0a1a2a3a4a5a6a7a8a9aaabacadaeaf' (bstr .size (8..64)),
               given from TAM's QueryRequest message /
     5 : 1,  / selected-cipher-suite = 5 (mapkey) :
               TEEP-AES-CCM-16-64-128-HMAC256--256-X25519-EdDSA =
               1 (.within uint .size 4) /
     6 : 0,  / selected-version = 6 (mapkey) :
               0 (.within uint .size 4) /
     7 : ... / evidence = 7 (mapkey) :
               Entity Attestation Token /
     8 : [   / tc-list = 8 (mapkey) : (array of tc-info) /
       {
         16 : [ 0x000102030405060708090a0b0c0d0e0f ] / component-id =
                16 (mapkey) : [ h'000102030405060708090a0b0c0d0e0f' ]
                (SUIT_Component_Identifier =  [* bstr]) /
       },
       {
         16 : [ 0x100102030405060708090a0b0c0d0e0f ] / component-id =
                16 (mapkey) : [ h'100102030405060708090a0b0c0d0e0f' ]
                (SUIT_Component_Identifier =  [* bstr]) /
       }
         ]
     }
 ]

D.4.2.  CBOR Binary Representation

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   82                       # array(2)
     02                     # unsigned(2) uint (0..23)
     A5                     # map(5)
       14                   # unsigned(20) uint (0..23)
       4F                   # bytes(16) (8..64)
         A0A1A2A3A4A5A6A7A8A9AAABACADAEAF
       05                   # unsigned(5) uint (0..23)
       01                   # unsigned(1) .within uint .size 4
       06                   # unsigned(6) uint (0..23)
       00                   # unsigned(0) .within uint .size 4
       07                   # unsigned(7) uint (0..23)
         ...                # Entity Attestation Token
       08                   # unsigned(8) uint (0..23)
       82                   # array(2)
         81                 # array(1)
           4F               # bytes(16)
             000102030405060708090A0B0C0D0E0F
         81                 # array(1)
           4F               # bytes(16)
             100102030405060708090A0B0C0D0E0F

D.5.  Update Message

D.5.1.  CBOR Diagnostic Notation

/ update = /
[
  3,  / type : TEEP-TYPE-update = 3 (uint (0..23)) /
  / options : /
  {
    20 : 0xa0a1a2a3a4a5a6a7a8a9aaabacadaeaf,
             / token = 20 (mapkey) :
               h'a0a1a2a3a4a5a6a7a8a9aaabacadaeaf' (bstr .size (8..64)),
               generated by TAM /
    10 : [ ] / manifest-list = 10 (mapkey) :
               [ ] (array of bstr wrapped SUIT_Envelope(any)) /
             / empty, example purpose only /
  }
]

D.5.2.  CBOR Binary Representation

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   82                       # array(2)
     03                     # unsigned(3) uint (0..23)
     A3                     # map(3)
       14                   # unsigned(20) uint (0..23)
       4F                   # bytes(16) (8..64)
         A0A1A2A3A4A5A6A7A8A9AAABACADAEAF
       0A                   # unsigned(10) uint (0..23)
       80                   # array(0)

D.6.  Success Message

D.6.1.  CBOR Diagnostic Notation

/ teep-success = /
[
  5,  / type : TEEP-TYPE-teep-success = 5 (uint (0..23)) /
  / options : /
  {
    20 : 0xa0a1a2a3a4a5a6a7a8a9aaabacadaeaf,
             / token = 20 (mapkey) :
               h'a0a1a2a3a4a5a6a7a8a9aaabacadaeaf' (bstr .size (8..64)),
               given from TAM's Update message /
  }
]

D.6.2.  CBOR Binary Representation

   82                       # array(2)
     05                     # unsigned(5) uint (0..23)
     A1                     # map(1)
       14                   # unsigned(20) uint (0..23)
       4F                   # bytes(16) (8..64)
         A0A1A2A3A4A5A6A7A8A9AAABACADAEAF

D.7.  Error Message

D.7.1.  CBOR Diagnostic Notation

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 / teep-error = /
 [
   6,  / type : TEEP-TYPE-teep-error = 6 (uint (0..23)) /
   / options : /
   {
     20 : 0xa0a1a2a3a4a5a6a7a8a9aaabacadaeaf,
            / token = 20 (mapkey) :
              h'a0a1a2a3a4a5a6a7a8a9aaabacadaeaf' (bstr .size (8..64)),
              given from TAM's Update message /
     12 : "disk-full"  / err-msg = 12 (mapkey) :
                         "disk-full" (text .size (1..128)) /
   },
   17, / err-code : ERR_MANIFEST_PROCESSING_FAILED = 17 (uint (0..23)) /
 ]

D.7.2.  CBOR binary Representation

   83                       # array(3)
     06                     # unsigned(6) uint (0..23)
     A2                     # map(2)
       14                   # unsigned(20) uint (0..23)
       4F                   # bytes(16) (8..64)
         A0A1A2A3A4A5A6A7A8A9AAABACADAEAF
       0C                   # unsigned(12) uint (0..23)
       69                   # text(9) (1..128)
         6469736B2D66756C6C # "disk-full"
     11                     # unsigned(17) uint (0..23)

Authors' Addresses

   Hannes Tschofenig
   Arm Ltd.
   Absam, Tirol  6067
   Austria

   Email: hannes.tschofenig@arm.com

   Mingliang Pei
   Broadcom
   350 Ellis St
   Mountain View, CA  94043
   USA

   Email: mingliang.pei@broadcom.com

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   David Wheeler
   Amazon
   US

   Email: davewhee@amazon.com

   Dave Thaler
   Microsoft
   US

   Email: dthaler@microsoft.com

   Akira Tsukamoto
   AIST
   JP

   Email: akira.tsukamoto@aist.go.jp

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