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Versions: (draft-tschofenig-teep-protocol) 00 01 02 03 04 05

TEEP                                                       H. Tschofenig
Internet-Draft                                                  Arm Ltd.
Intended status: Standards Track                                  M. Pei
Expires: May 6, 2021                                            Broadcom
                                                              D. Wheeler
                                                                   Intel
                                                               D. Thaler
                                                               Microsoft
                                                            A. Tsukamoto
                                                                    AIST
                                                        November 2, 2020


       Trusted Execution Environment Provisioning (TEEP) Protocol
                      draft-ietf-teep-protocol-04

Abstract

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

   The protocol name is pronounced teepee.  This conjures an image of a
   wedge-shaped protective covering for one's belongings, which sort of
   matches the intent of this protocol.

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 http://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 May 6, 2021.








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Copyright Notice

   Copyright (c) 2020 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
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights 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 . . . . . . . . . . . . . . .   6
     4.1.  Creating and Validating TEEP Messages . . . . . . . . . .   6
       4.1.1.  Creating a TEEP message . . . . . . . . . . . . . . .   6
       4.1.2.  Validating a TEEP Message . . . . . . . . . . . . . .   6
     4.2.  QueryRequest Message  . . . . . . . . . . . . . . . . . .   7
     4.3.  QueryResponse Message . . . . . . . . . . . . . . . . . .   9
     4.4.  Install Message . . . . . . . . . . . . . . . . . . . . .  12
     4.5.  Delete Message  . . . . . . . . . . . . . . . . . . . . .  13
     4.6.  Success Message . . . . . . . . . . . . . . . . . . . . .  14
     4.7.  Error Message . . . . . . . . . . . . . . . . . . . . . .  14
   5.  Mapping of TEEP Message Parameters to CBOR Labels . . . . . .  17
   6.  Ciphersuites  . . . . . . . . . . . . . . . . . . . . . . . .  17
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  18
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  20
     8.1.  Media Type Registration . . . . . . . . . . . . . . . . .  20
     8.2.  Error Code Registry . . . . . . . . . . . . . . . . . . .  21
     8.3.  Ciphersuite Registry  . . . . . . . . . . . . . . . . . .  21
     8.4.  CBOR Tag Registry . . . . . . . . . . . . . . . . . . . .  21
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  22
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  22
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  23
   A. Contributors . . . . . . . . . . . . . . . . . . . . . . . . .  24
   B. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  24
   C. Complete CDDL  . . . . . . . . . . . . . . . . . . . . . . . .  24
   D. Examples of Diagnostic Notation and Binary Representation  . .  27
     D.1.  Some assumptions in examples  . . . . . . . . . . . . . .  27
     D.2.  QueryRequest Message  . . . . . . . . . . . . . . . . . .  28
       D.2.1.  CBOR Diagnostic Notation  . . . . . . . . . . . . . .  28



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       D.2.2.  CBOR Binary Representation  . . . . . . . . . . . . .  28
     D.3.  QueryResponse Message . . . . . . . . . . . . . . . . . .  29
       D.3.1.  CBOR Diagnostic Notation  . . . . . . . . . . . . . .  29
       D.3.2.  CBOR Binary Representation  . . . . . . . . . . . . .  29
     D.4.  Install Message . . . . . . . . . . . . . . . . . . . . .  29
       D.4.1.  CBOR Diagnostic Notation  . . . . . . . . . . . . . .  29
       D.4.2.  CBOR Binary Representation  . . . . . . . . . . . . .  30
     D.5.  Success Message (for Install) . . . . . . . . . . . . . .  30
       D.5.1.  CBOR Diagnostic Notation  . . . . . . . . . . . . . .  30
       D.5.2.  CBOR Binary Representation  . . . . . . . . . . . . .  30
     D.6.  Error Message (for Install) . . . . . . . . . . . . . . .  30
       D.6.1.  CBOR Diagnostic Notation  . . . . . . . . . . . . . .  30
       D.6.2.  CBOR binary Representation  . . . . . . . . . . . . .  31
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  31

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 TA
   Developers or Device Administrators use Trusted Application Managers
   (TAMs) to install, update, and delete Trusted Applications (TAs) 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 TA, any dependencies the TA has, and personalization data
   as separate components that are expressed in SUIT manifests, and a



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   SUIT manifest might contain or reference multiple binaries (see
   [I-D.ietf-suit-manifest] for more details).

   As such, the term Trusted Component 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 "component-id"
   byte string, such as a 16-byte UUID [RFC4122].  If Concise Software
   Identifiers [I-D.ietf-sacm-coswid] are used (e.g., in the suit-coswid
   field of SUIT manifests), the component-id value is the CoSWID tag-id
   value.

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 TA 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 six messages.

   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.













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

       QueryRequest ------->

                              QueryResponse

                    <-------     or

                                Error

   With the Install message a TAM can instruct a TEEP Agent to install a
   Trusted Component.  The TEEP Agent will process the message,
   determine whether the TAM is authorized and whether the Trusted
   Component has been signed by an authorized TA Signer.  If the Install
   message was processed successfully then a Success message is returned
   to the TAM, or an Error message otherwise.

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

                Install ---->

                               Success

                       <----    or

                               Error

   With the Delete message a TAM can instruct a TEEP Agent to delete one
   or multiple Trusted Components.  A Success message is returned when
   the operation has been completed successfully, or an Error message
   otherwise.

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

                Delete  ---->

                               Success

                       <----    or

                               Error




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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 /
                                       install /
                                       delete /
                                       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.

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

   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 validating a TEEP message, the following 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.





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   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 supporting SUIT commands.

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

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

   The message has the following fields:




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   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.

   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.

      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.  Details about the ciphersuite encoding can
      be found in Section 6.

   challenge
      The challenge field is an optional parameter used for ensuring the
      refreshness of the attestation evidence returned with a
      QueryResponse message.  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



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      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 the root certificate.  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 [RFC2560]).  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 [CDDL].

























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

   tc-info = {
     component-id: bstr,
     ? tc-manifest-sequence-number: uint
   }

   requested-ta-info = {
     component-id: bstr,
     ? tc-manifest-sequence-number: uint,
     ? 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.

   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.

   selected-cipher-suite
      The selected-cipher-suite parameter indicates the selected
      ciphersuite.  Details about the ciphersuite encoding can be found
      in Section 6.

   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.



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   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].

   tc-list
      The tc-list parameter enumerates the Trusted Components installed
      on the device in the form of tc-info objects.

   requested-ta-list
      The requested-ta-list parameter enumerates the Trusted
      Applications 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.
      Requested TAs are expressed in the form of requested-ta-info
      objects.

   unneeded-ta-list
      The unneeded-ta-list parameter enumerates the Trusted Applications
      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 TA can be deleted.  Each unneeded TA is
      expressed in the form of a component-id byte string.

   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 unique identifier encoded as a CBOR bstr.

   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-ta-info message has the following fields:




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   component-id
      A unique identifier encoded as a CBOR bstr.

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

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

4.4.  Install Message

   The Install message is used by the TAM to install a Trusted Component
   via the TEEP Agent.

   Like other TEEP messages, the Install message is signed, and the
   relevant CDDL snippet is shown below.  The complete CDDL structure is
   shown in [CDDL].

   install = [
     type: TEEP-TYPE-install,
     token: uint,
     option: {
       ? manifest-list => [ + SUIT_Envelope ],
       * $$install-extensions,
       * $$teep-option-extensions
     }
   ]

   The Install message has the following fields:

   type
      The value of (3) corresponds to an Install 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 Install
      message is used for initial Trusted Component installation as well
      as for updates.

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

   manifest-list



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      The manifest-list field is used to convey one or multiple SUIT
      manifests.  A manifest is a bundle of metadata about a TA, 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.  TA binaries and
      personalization data can be signed and encrypted by the same TA
      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 TA Developer sign and/or
      encrypt the TA binary.

4.5.  Delete Message

   The Delete message is used by the TAM to remove a Trusted Component
   from the device.

   Like other TEEP messages, the Delete message is signed, and the
   relevant CDDL snippet is shown below.  The complete CDDL structure is
   shown in [CDDL].

   delete = [
     type: TEEP-TYPE-delete,
     token: uint,
     option: {
       ? tc-list => [ + bstr ],
       * $$delete-extensions,
       * $$teep-option-extensions
     }
   ]

   The Delete message has the following fields:

   type
      The value of (4) corresponds to a Delete 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.

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

   tc-list
      The tc-list parameter enumerates the Trusted Components to be
      deleted, in the form of component-id byte strings.






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4.6.  Success Message

   The TEEP protocol defines two implicit success messages and this
   explicit Success message for the cases where the TEEP Agent cannot
   return another reply, such as for the Install and the Delete
   messages.

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

   teep-success = [
     type: TEEP-TYPE-teep-success,
     token: uint,
     option: {
       ? msg => text,
       ? 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.

   msg
      The msg parameter contains optional diagnostics information
      encoded in UTF-8 [RFC3629] 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].

4.7.  Error Message

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

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




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   teep-error = [
     type: TEEP-TYPE-teep-error,
     token: uint,
     err-code: uint,
     options: {
        ? err-msg => text,
        ? supported-cipher-suites => [ + suite ],
        ? versions => [ + version ],
        ? suit-reports => [ + suit-report ],
        * $$teep-error--extensions,
        * $$teep-option-extensions
     }
   ]

   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.

   err-code
      The err-code parameter contains one of the values listed in the
      registry defined in Section 8.2 (with the initial set of error
      codes listed below).  Only selected values are applicable to each
      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].

   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 6.  This field is optional but
      MUST be returned with the ERR_UNSUPPORTED_CRYPTO_ALG error
      message.

   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



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      If present, the suit-reports parameter contains a set of SUIT
      Reports as defined in Section 4 of [I-D.moran-suit-report].

   This specification defines the following initial error messages:

   ERR_ILLEGAL_PARAMETER (1)
      The TEEP request contained incorrect fields or fields that are
      inconsistent with other fields.

   ERR_UNSUPPORTED_EXTENSION (2)
      The TEEP Agent does not support the request message or an
      extension it indicated.

   ERR_REQUEST_SIGNATURE_FAILED (3)
      The TEEP Agent could not verify the signature of the request
      message.

   ERR_UNSUPPORTED_MSG_VERSION (4)
      The TEEP Agent does not support the TEEP protocol version
      indicated in the request message.

   ERR_UNSUPPORTED_CRYPTO_ALG (5)
      The TEEP Agent does not support the cryptographic algorithm
      indicated in the request message.

   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.

   ERR_UNSUPPORTED_CERTIFICATE (7)
      A certificate was of an unsupported type.

   ERR_CERTIFICATE_REVOKED (8)
      A certificate was revoked by its signer.

   ERR_CERTIFICATE_EXPIRED (9)
      A certificate has expired or is not currently valid.

   ERR_INTERNAL_ERROR (10)
      A miscellaneous internal error occurred while processing the
      request message.

   ERR_TC_NOT_FOUND (12)
      The target Trusted Component does not exist.  This error may
      happen when the TAM has stale information and tries to delete a
      Trusted Component that has already been deleted.




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   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.

   Additional error codes can be registered with IANA.

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:

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

6.  Ciphersuites

   A ciphersuite consists of an AEAD algorithm, an HMAC algorithm, and a
   signature algorithm.  Each ciphersuite is identified with an integer
   value, which corresponds to an IANA registered ciphersuite (see
   Section 8.3.  This document specifies two ciphersuites.




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

7.  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
      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) 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.

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

   Personalization Data




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      A TA Signer or TAM can supply personalization data along with a
      TA.  This data is also protected by a SUIT manifest.
      Personalization data signed and encrypted by a TA 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 TA.  Information in the manifest
      ensures that TEEP Agents are protected against such downgrade
      attacks based on features offered by the manifest itself.

   TA Signer Compromise
      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 the root certificate so that the TEEP Agent
      can verify the certificate's revocation status.  A certificate
      revocation status check on a TA Signer certificate is OPTIONAL by
      a TEEP Agent.  A TAM is responsible for vetting a TA and before
      distributing them to TEEP Agents, so TEEP Agents can instead
      simply trust that a TA Signer certificate's status was done by the
      TAM.

   CA Compromise
      The CA issuing certificates to a TAM or a TA 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.




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   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.

8.  IANA Considerations

8.1.  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

   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



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   Restrictions on usage:  none

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

   Change controller:  IETF

8.2.  Error Code Registry

   IANA is also requested to create a new registry for the error codes
   defined in Section 4.

   Registration requests are evaluated after a three-week review period
   on the teep-reg-review@ietf.org mailing list, on the advice of one or
   more Designated Experts [RFC8126].  However, to allow for the
   allocation of values prior to publication, the Designated Experts may
   approve registration once they are satisfied that such a
   specification will be published.

   Registration requests sent to the mailing list for review should use
   an appropriate subject (e.g., "Request to register an error code:
   example").  Registration requests that are undetermined for a period
   longer than 21 days can be brought to the IESG's attention (using the
   iesg@ietf.org mailing list) for resolution.

   Criteria that should be applied by the Designated Experts includes
   determining whether the proposed registration duplicates existing
   functionality, whether it is likely to be of general applicability or
   whether it is useful only for a single extension, and whether the
   registration description is clear.

   IANA must only accept registry updates from the Designated Experts
   and should direct all requests for registration to the review mailing
   list.

8.3.  Ciphersuite Registry

   IANA is also requested to create a new registry for ciphersuites, as
   defined in Section 6.

8.4.  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




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   o  Data Item: TEEP Message

   o  Semantics: TEEP Message, as defined in [[TBD: This RFC]]

   o  Reference: [[TBD: This RFC]]

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

9.  References

9.1.  Normative References

   [I-D.ietf-rats-eat]
              Mandyam, G., Lundblade, L., Ballesteros, M., and J.
              O'Donoghue, "The Entity Attestation Token (EAT)", draft-
              ietf-rats-eat-04 (work in progress), August 2020.

   [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-09
              (work in progress), July 2020.

   [I-D.moran-suit-report]
              Moran, B., "Secure Reporting of Update Status", draft-
              moran-suit-report-00 (work in progress), October 2020.

   [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>.

   [RFC2560]  Myers, M., Ankney, R., Malpani, A., Galperin, S., and C.
              Adams, "X.509 Internet Public Key Infrastructure Online
              Certificate Status Protocol - OCSP", RFC 2560,
              DOI 10.17487/RFC2560, June 1999, <https://www.rfc-
              editor.org/info/rfc2560>.

   [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>.





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   [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>.

9.2.  Informative References

   [I-D.ietf-sacm-coswid]
              Birkholz, H., Fitzgerald-McKay, J., Schmidt, C., and D.
              Waltermire, "Concise Software Identification Tags", draft-
              ietf-sacm-coswid-15 (work in progress), May 2020.

   [I-D.ietf-teep-architecture]
              Pei, M., Tschofenig, H., Thaler, D., and D. Wheeler,
              "Trusted Execution Environment Provisioning (TEEP)
              Architecture", draft-ietf-teep-architecture-12 (work in
              progress), July 2020.

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

   [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>.






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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" is specified in
   [I-D.ietf-suit-manifest].

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

   SUIT_Envelope = any

   teep-message-framework = [
     type: 0..23 / $teep-type-extension,
     token: uint,
     options: { * teep-option },
     * int; 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 /= install
   $teep-message-type /= delete
   $teep-message-type /= teep-success
   $teep-message-type /= teep-error

   ; message type numbers
   TEEP-TYPE-query-request = 1



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   TEEP-TYPE-query-response = 2
   TEEP-TYPE-install = 3
   TEEP-TYPE-delete = 4
   TEEP-TYPE-teep-success = 5
   TEEP-TYPE-teep-error = 6

   version = uint .size 4
   ext-info = uint

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

   ; ciphersuites as bitmaps
   suite = $TEEP-suite .within uint .size 8

   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

   query-response = [
     type: TEEP-TYPE-query-response,
     token: uint,
     options: {
       ? selected-cipher-suite => suite,



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       ? selected-version => version,
       ? evidence-format => text,
       ? evidence => bstr,
       ? tc-list => [ + tc-info ],
       ? requested-tc-list => [ + requested-tc-info ],
       ? unneeded-tc-list => [ + bstr ],
       ? ext-list => [ + ext-info ],
       * $$query-response-extensions,
       * $$teep-option-extensions
     }
   ]

   tc-info = {
     component-id: bstr,
     ? tc-manifest-sequence-number: uint
   }

   requested-ta-info = {
     component-id: bstr,
     ? tc-manifest-sequence-number: uint,
     ? have-binary: bool
   }

   install = [
     type: TEEP-TYPE-install,
     token: uint,
     option: {
       ? manifest-list => [ + SUIT_Envelope ],
       * $$install-extensions,
       * $$teep-option-extensions
     }
   ]

   delete = [
     type: TEEP-TYPE-delete,
     token: uint,
     option: {
       ? tc-list => [ + bstr ],
       * $$delete-extensions,
       * $$teep-option-extensions
     }
   ]

   teep-success = [
     type: TEEP-TYPE-teep-success,
     token: uint,
     option: {
       ? msg => text,



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       ? suit-reports => [ + suit-report ],
       * $$teep-success-extensions,
       * $$teep-option-extensions
     }
   ]

   teep-error = [
     type: TEEP-TYPE-teep-error,
     token: uint,
     err-code: uint,
     options: {
        ? err-msg => text,
        ? supported-cipher-suites => [ + suite ],
        ? versions => [ + version ],
        ? suit-reports => [ + suit-report ],
        * $$teep-error--extensions,
        * $$teep-option-extensions
     }
   ]

   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

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 2 TAs




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      *  TA-ID: 0x0102030405060708090a0b0c0d0e0f,
         0x1102030405060708090a0b0c0d0e0f

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

   o  Not including Entity Attestation Token (EAT) parameters for
      example purposes

D.2.  QueryRequest Message

D.2.1.  CBOR Diagnostic Notation

 / query-request = /
 [
     1,          / type : TEEP-TYPE-query-request = 1 (fixed int) /
     2004318071, / token : 0x77777777 (uint), generated by TAM /
     / options : /
     {
         1 : [ 1 ]  / supported-cipher-suites = 1 (mapkey) : /
                    / TEEP-AES-CCM-16-64-128-HMAC256--256-X25519-EdDSA =
                      [ 1 ] (array of uint .size 8) /
         3 : [ 0 ]  / version = 3 (mapkey) :
                      [ 0 ] (array of uint .size 4) /
         4 : h'010203' / ocsp-data = 4 (mapkey) : 0x010203 (bstr) /
     },
     2           / data-item-requested : trusted-components = 2 (uint) /
 ]

D.2.2.  CBOR Binary Representation

   84                        # array(4),
      01                     # unsigned(1)
      1A 77777777            # unsigned(2004318071, 0x77777777)
      A3                     # map(3)
         01                  # unsigned(1)
         81                  # array(1)
            01               # unsigned(1) within .size 8
         03                  # unsigned(3)
         81                  # array(1)
            00               # unsigned(0) within .size 4
         04                  # unsigned(4)
         43                  # bytes(3)
            010203           # "\x01\x02\x03"
      02                     # unsigned(2)







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D.3.  QueryResponse Message

D.3.1.  CBOR Diagnostic Notation

   / query-response = /
   [
       2,          / type : TEEP-TYPE-query-response = 2 (fixed int) /
       2004318071, / token : 0x77777777 (uint), from TAM's QueryRequest
                         message /
       / options : /
       {
           5 : 1,  / selected-cipher-suite = 5(mapkey) :/
                   / TEEP-AES-CCM-16-64-128-HMAC256--256-X25519-EdDSA =
                         1 (uint .size 8) /
           6 : 0,  / selected-version = 6 (mapkey) : 0 (uint .size 4) /
           8 : [ h'0102030405060708090a0b0c0d0e0f',
                 h'1102030405060708090a0b0c0d0e0f' ]
                   / ta-list = 8 (mapkey) :
                         [ 0x0102030405060708090a0b0c0d0e0f,
                           0x1102030405060708090a0b0c0d0e0f ]
                         (array of bstr) /
       }
   ]

D.3.2.  CBOR Binary Representation

   83                        # array(3)
      02                     # unsigned(2)
      1A 77777777            # unsigned(2004318071, 0x77777777)
      A3                     # map(3)
         05                  # unsigned(5)
         01                  # unsigned(1) within .size 8
         06                  # unsigned(6)
         00                  # unsigned(0) within .size 4
         08                  # unsigned(8)
         82                  # array(2)
            4F               # bytes(16)
               0102030405060708090A0B0C0D0D0F
            4F               # bytes(16)
               1102030405060708090A0B0C0D0D0F

D.4.  Install Message

D.4.1.  CBOR Diagnostic Notation







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   / install = /
   [
       3,          / type : TEEP-TYPE-install = 3 (fixed int) /
       2004318072,  / token : 0x777777778 (uint), generated by TAM /
       / options :  /
       {
           10 : [ ] / manifest-list = 10 (mapkey) :
                          [ ] (array of SUIT_Envelope(any)) /
                    / empty, example purpose only /
       }
   ]

D.4.2.  CBOR Binary Representation

   83                        # array(3)
      03                     # unsigned(3)
      1A 77777778            # unsigned(2004318072, 0x77777778)
      A1                     # map(1)
         0A                  # unsigned(10)
         80                  # array(0)

D.5.  Success Message (for Install)

D.5.1.  CBOR Diagnostic Notation

   / teep-success = /
   [
       5,          / type : TEEP-TYPE-teep-success = 5 (fixed int) /
       2004318072, / token : 0x777777778 (uint), from Install message /
   ]

D.5.2.  CBOR Binary Representation

   83                        # array(3)
       05                    # unsigned(5)
       1A 77777778           # unsigned(2004318072, 0x77777778)

D.6.  Error Message (for Install)

D.6.1.  CBOR Diagnostic Notation











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   / teep-error = /
   [
       6,          / type : TEEP-TYPE-teep-error = 6 (fixed int) /
       2004318072, / token : 0x777777778 (uint), from Install message /
       ERR_MANIFEST_PROCESSING_FAILED,
           / err-code : ERR_MANIFEST_PROCESSING_FAILED = 17 (uint) /
       / options :  /
       {
           12 : "disk-full"  / err-msg = 12 (mapkey) :
                                   "disk-full" (UTF-8 string) /
       }
   ]

D.6.2.  CBOR binary Representation

   83                        # array(3)
       06                    # unsigned(6)
       1A 77777778           # unsigned(2004318072, 0x77777778)
       11                    # unsigned(17)
       A1                    # map(1)
          0B                 # unsigned(12)
          69                 # text(9)
             6469736b2d66756c6c  # "disk-full"

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


   David Wheeler
   Intel
   US

   Email: david.m.wheeler@intel.com



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   Dave Thaler
   Microsoft
   US

   Email: dthaler@microsoft.com


   Akira Tsukamoto
   AIST
   JP

   Email: akira.tsukamoto@aist.go.jp







































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