[Docs] [txt|pdf] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

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

TEEP                                                       H. Tschofenig
Internet-Draft                                                  Arm Ltd.
Intended status: Standards Track                                  M. Pei
Expires: January 14, 2021                                       Broadcom
                                                              D. Wheeler
                                                                   Intel
                                                               D. Thaler
                                                               Microsoft
                                                            A. Tsukamoto
                                                                    AIST
                                                           July 13, 2020


       Trusted Execution Environment Provisioning (TEEP) Protocol
                      draft-ietf-teep-protocol-03

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 January 14, 2021.








Tschofenig, et al.      Expires January 14, 2021                [Page 1]


Internet-Draft                TEEP Protocol                    July 2020


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.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  Message Overview  . . . . . . . . . . . . . . . . . . . . . .   3
   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  . . . . . . . . . . . . . . . . . . . . . .   6
     4.3.  QueryResponse . . . . . . . . . . . . . . . . . . . . . .   8
     4.4.  TrustedAppInstall . . . . . . . . . . . . . . . . . . . .  10
     4.5.  TrustedAppDelete  . . . . . . . . . . . . . . . . . . . .  11
     4.6.  Success . . . . . . . . . . . . . . . . . . . . . . . . .  11
     4.7.  Error . . . . . . . . . . . . . . . . . . . . . . . . . .  12
   5.  Mapping of TEEP Message Parameters to CBOR Labels . . . . . .  15
   6.  Ciphersuites  . . . . . . . . . . . . . . . . . . . . . . . .  15
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  16
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  18
     8.1.  Media Type Registration . . . . . . . . . . . . . . . . .  18
     8.2.  Error Code Registry . . . . . . . . . . . . . . . . . . .  19
     8.3.  Ciphersuite Registry  . . . . . . . . . . . . . . . . . .  19
     8.4.  CBOR Tag Registry . . . . . . . . . . . . . . . . . . . .  19
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  20
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  20
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  21
   A. Contributors . . . . . . . . . . . . . . . . . . . . . . . . .  21
   B. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  21
   C. Complete CDDL  . . . . . . . . . . . . . . . . . . . . . . . .  21
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  24






Tschofenig, et al.      Expires January 14, 2021                [Page 2]


Internet-Draft                TEEP Protocol                    July 2020


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 an TEE ecosystem, device vendors may use different operating
   systems in the REE and may use different types of TEEs.  When
   application providers 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, involving a TEEP Broker.

   The Trusted Execution Environment Provisioning (TEEP) architecture
   document [I-D.ietf-teep-architecture] has set to provide a design
   guidance for such an interoperable protocol and introduces the
   necessary terminology.  Note that the term Trusted Application may
   include more than code; it may also include configuration data and
   keys needed by the TA to operate correctly.

2.  Requirements Language

   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].

3.  Message Overview

   The TEEP protocol consists of a couple of messages exchanged between
   a TAM and a TEEP Agent via a TEEP Broker.  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 as well be encrypted and signed
   by the service provider.  The TEEP protocol not only re-use CBOR but
   also the respective security wrapper, namely COSE [RFC8152].
   Furthermore, for attestation the Entity Attestation Token (EAT)
   [I-D.ietf-rats-eat] and for software updates the SUIT manifest format
   [I-D.ietf-suit-manifest] are re-used.

   This specification defines six messages.




Tschofenig, et al.      Expires January 14, 2021                [Page 3]


Internet-Draft                TEEP Protocol                    July 2020


   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 TAs, 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
   subsequent message exchanges to install, update, or delete trusted
   applications shall be initiated.

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

       QueryRequest ------->

                              QueryResponse

                    <-------     or

                                Error

   With the TrustedAppInstall message a TAM can instruct a TEEP Agent to
   install a TA.  The TEEP Agent will process the message, determine
   whether the TAM is authorized and whether the TA has been signed by
   an authorized SP.  In addition to the binary, the TAM may also
   provide personalization data.  If the TrustedAppInstall message was
   processed successfully then a Success message is returned to the TAM,
   an Error message otherwise.

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

      TrustedAppInstall ---->

                               Success

                       <----    or

                               Error

   With the TrustedAppDelete message a TAM can instruct a TEEP Agent to
   delete one or multiple TA(s).  A Success message is returned when the
   operation has been completed successfully, and an Error message
   otherwise.






Tschofenig, et al.      Expires January 14, 2021                [Page 4]


Internet-Draft                TEEP Protocol                    July 2020


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

      TrustedAppDelete  ---->

                               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                => (QueryRequest /
                                       QueryResponse /
                                       TrustedAppInstall /
                                       TrustedAppDelete /
                                       Error /
                                       Success ),
   }

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.







Tschofenig, et al.      Expires January 14, 2021                [Page 5]


Internet-Draft                TEEP Protocol                    July 2020


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.

   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

   A QueryRequest message is used by the TAM to learn information from
   the TEEP Agent.  The TAM can learn 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 software (trusted apps), 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].






Tschofenig, et al.      Expires January 14, 2021                [Page 6]


Internet-Draft                TEEP Protocol                    July 2020


   query-request = [
     type: TEEP-TYPE-query-request,
     token: uint,
     options: {
       ? supported-cipher-suites => suite,
       ? nonce => bstr .size (8..64),
       ? version => [ + version ],
       ? oscp-data => bstr,
       * $$query-request-extensions
       * $$teep-option-extensions
     },
     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 particualrly useful when a TAM issues multiple
      concurrent requests to a TEEP Agent.

   request
      The request parameter indicates what information the TAM requests
      from the TEEP Agent in 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 an entity attestation token (EAT) in the response.
         If the TAM requests an attestation token to be returned by the
         TEEP Agent then it MUST also include the nonce in the message.
         The nonce is subsequently placed into the EAT token for replay
         protection.

      trusted_apps (2)  With this value the TAM queries the TEEP Agent
         for all installed TAs.

      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.






Tschofenig, et al.      Expires January 14, 2021                [Page 7]


Internet-Draft                TEEP Protocol                    July 2020


      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.

   cipher-suites
      The cipher-suites parameter lists the ciphersuite(s) supported by
      the TAM.  Details about the ciphersuite encoding can be found in
      Section 6.

   nonce
      The none field is an optional parameter used for ensuring the
      refreshness of the Entity Attestation Token (EAT) returned with a
      QueryResponse message.  When a nonce is provided in the
      QueryRequest and an EAT is returned with the QueryResponse message
      then the nonce contained in this request MUST be copied into the
      nonce claim found in the EAT token.

   version
      The version field parameter the version(s) supported by the TAM.
      For this version of the specification this field can be omitted.

   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

   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].







Tschofenig, et al.      Expires January 14, 2021                [Page 8]


Internet-Draft                TEEP Protocol                    July 2020


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

   The 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 protocol version
      selected by the TEEP Agent.

   eat
      The eat parameter contains an Entity Attestation Token following
      the encoding defined in [I-D.ietf-rats-eat].

   ta-list
      The ta-list parameter enumerates the trusted applications
      installed on the device in form of TA_ID byte strings.

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






Tschofenig, et al.      Expires January 14, 2021                [Page 9]


Internet-Draft                TEEP Protocol                    July 2020


4.4.  TrustedAppInstall

   The TrustedAppInstall message is used by the TAM to install software
   (trusted apps) via the TEEP Agent.

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

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

   The TrustedAppInstall message has the following fields:

   type
      The value of (3) corresponds to a TrustedAppInstall message sent
      from the TAM to the TEEP Agent.  In case of successful processing,
      an Success message is returned by the TEEP Agent.  In case of an
      error, an Error message is returned.  Note that the
      TrustedAppInstall message is used for initial TA installation but
      also for TA updates.

   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.  A manifest is a bundle of metadata about the trusted
      app, 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 is typically signed and encrypted by the SP.
      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 SP sign and/or encrypt the TA
      binary.







Tschofenig, et al.      Expires January 14, 2021               [Page 10]


Internet-Draft                TEEP Protocol                    July 2020


4.5.  TrustedAppDelete

   The TrustedAppDelete message is used by the TAM to remove software
   (trust apps) from the device.

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

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

   The TrustedAppDelete message has the following fields:

   type
      The value of (4) corresponds to a TrustedAppDelete message sent
      from the TAM to the TEEP Agent.  In case of successful processing,
      an 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.

   ta-list
      The ta-list parameter enumerates the TAs to be deleted.

4.6.  Success

   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 TrustedAppInstall and the
   TrustedAppDelete 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].







Tschofenig, et al.      Expires January 14, 2021               [Page 11]


Internet-Draft                TEEP Protocol                    July 2020


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

4.7.  Error

   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].

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

   The Error message has the following fields:

   type



Tschofenig, et al.      Expires January 14, 2021               [Page 12]


Internet-Draft                TEEP Protocol                    July 2020


      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 is populated with values listed in a
      registry (with the initial set of error codes listed below).  Only
      selected messages are applicable to each message.

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

   cipher-suites
      The cipher-suites parameter lists the ciphersuite(s) supported by
      the TEEP Agent.  This field is optional but MUST be returned with
      the ERR_UNSUPPORTED_CRYPTO_ALG error message.

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

   This specification defines the following initial error messages:

   ERR_ILLEGAL_PARAMETER (1)
      The TEEP Agent sends this error message when a request contains
      incorrect fields or fields that are inconsistent with other
      fields.

   ERR_UNSUPPORTED_EXTENSION (2)
      The TEEP Agent sends this error message when it recognizes an
      unsupported extension or unsupported message.

   ERR_REQUEST_SIGNATURE_FAILED (3)
      The TEEP Agent sends this error message when it fails to verify
      the signature of the message.

   ERR_UNSUPPORTED_MSG_VERSION (4)
      The TEEP Agent receives a message but does not support the
      indicated version.

   ERR_UNSUPPORTED_CRYPTO_ALG (5)




Tschofenig, et al.      Expires January 14, 2021               [Page 13]


Internet-Draft                TEEP Protocol                    July 2020


      The TEEP Agent receives a request message encoded with an
      unsupported cryptographic algorithm.

   ERR_BAD_CERTIFICATE (6)
      The TEEP Agent returns this error when 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)
      The TEEP Agent returns this error when a certificate was of an
      unsupported type.

   ERR_CERTIFICATE_REVOKED (8)
      The TEEP Agent returns this error when a certificate was revoked
      by its signer.

   ERR_CERTIFICATE_EXPIRED (9)
      The TEEP Agent returns this error when a certificate has expired
      or is not currently valid.

   ERR_INTERNAL_ERROR (10)
      The TEEP Agent returns this error when a miscellaneous internal
      error occurred while processing the request.

   ERR_RESOURCE_FULL (11)
      This error is reported when a device resource isn't available
      anymore, such as storage space is full.

   ERR_TA_NOT_FOUND (12)
      This error will occur when the target TA does not exist.  This
      error may happen when the TAM has stale information and tries to
      delete a TA that has already been deleted.

   ERR_TA_ALREADY_INSTALLED (13)
      While installing a TA, a TEE will return this error if the TA has
      already been installed.

   ERR_TA_UNKNOWN_FORMAT (14)
      The TEEP Agent returns this error when it does not recognize the
      format of the TA binary.

   ERR_TA_DECRYPTION_FAILED (15)
      The TEEP Agent returns this error when it fails to decrypt the TA
      binary.

   ERR_TA_DECOMPRESSION_FAILED (16)
      The TEEP Agent returns this error when it fails to decompress the
      TA binary.



Tschofenig, et al.      Expires January 14, 2021               [Page 14]


Internet-Draft                TEEP Protocol                    July 2020


   ERR_MANIFEST_PROCESSING_FAILED (17)
      The TEEP Agent returns this error when manifest processing
      failures occur that are less specific than ERR_TA_UNKNOWN_FORMAT,
      ERR_TA_UNKNOWN_FORMAT, and ERR_TA_DECOMPRESSION_FAILED.

   ERR_PD_PROCESSING_FAILED (18)
      The TEEP Agent returns this error when it fails to process the
      provided personalization data.

   Additional error code 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 |
                     +-----------------------+-------+
                     | cipher-suites         | 1     |
                     | nonce                 | 2     |
                     | version               | 3     |
                     | ocsp-data             | 4     |
                     | selected-cipher-suite | 5     |
                     | selected-version      | 6     |
                     | eat                   | 7     |
                     | ta-list               | 8     |
                     | ext-list              | 9     |
                     | manifest-list         | 10    |
                     | msg                   | 11    |
                     | err-msg               | 12    |
                     +-----------------------+-------+

6.  Ciphersuites

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







Tschofenig, et al.      Expires January 14, 2021               [Page 15]


Internet-Draft                TEEP Protocol                    July 2020


        +-------+------------------------------------------------+
        | 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 to by the TEEP Agent to authenticate the
      TAM and vice versa.

   Attestation
      A TAM may rely on the attestation information provided by the TEEP
      Agent and the Entity Attestation Token is re-used to convey this
      information.  To sign the Entity Attestation Token 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
      information or in the certificate used to sign the attestation
      token.  This uniqueness may raise privacy concerns.  To lower the
      privacy implications the TEEP Agent MUST present its attestation
      information only to an authenticated and authorized TAM and SHOULD
      use encryption in EATs 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.

   TA Binaries
      TA binaries are provided by the SP.  It is the responsibility of
      the TAM to relay only verified TAs from authorized SPs.  Delivery
      of that TA to the TEEP Agent is then the responsibility of the TAM
      and the TEEP Broker, using the security mechanisms provided by the
      TEEP protocol.  To protect the TA binary the SUIT manifest is re-
      used and it offers a varity of security features, including
      digitial signatures and symmetric encryption.

   Personalization Data





Tschofenig, et al.      Expires January 14, 2021               [Page 16]


Internet-Draft                TEEP Protocol                    July 2020


      An SP or a TAM can supply personalization data along with a TA.
      This data is also protected by a SUIT manifest.  The
      personalization data may be opaque to the TAM.

   TEEP Broker
      The TEEP protocol relies on the 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 the TEEP Agents are protected against such
      downgrading attacks based on features offered by the manifest
      itself.

   CA Compromise
      The QueryRequest message from a TAM to the TEEP Agent may include
      OCSP stapling data for the TAM's signer 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.  TEEP Agents will
      trust a TA signer certificate's validation status done by a TAM.

   CA Compromise
      The CA issuing certificates to a TAM or an SP may get compromised.
      A compromised intermediate CA certificates 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 device,
      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-provided 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 since OCSP stapling includes
      signature generation time, certificate validity dates are compared
      to the current time.







Tschofenig, et al.      Expires January 14, 2021               [Page 17]


Internet-Draft                TEEP Protocol                    July 2020


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

   Restrictions on usage:  none

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

   Change controller:  IETF



Tschofenig, et al.      Expires January 14, 2021               [Page 18]


Internet-Draft                TEEP Protocol                    July 2020


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

   o  Data Item: TEEP Message

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

   o  Reference: [[TBD: This RFC]]




Tschofenig, et al.      Expires January 14, 2021               [Page 19]


Internet-Draft                TEEP Protocol                    July 2020


   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-03 (work in progress), February 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-08
              (work in progress), July 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>.

   [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>.



Tschofenig, et al.      Expires January 14, 2021               [Page 20]


Internet-Draft                TEEP Protocol                    July 2020


9.2.  Informative References

   [I-D.ietf-teep-architecture]
              Pei, M., Tschofenig, H., Thaler, D., and D. Wheeler,
              "Trusted Execution Environment Provisioning (TEEP)
              Architecture", draft-ietf-teep-architecture-11 (work in
              progress), July 2020.

   [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>.

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




Tschofenig, et al.      Expires January 14, 2021               [Page 21]


Internet-Draft                TEEP Protocol                    July 2020


   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 /= trusted-app-install
   $teep-message-type /= trusted-app-delete
   $teep-message-type /= teep-error
   $teep-message-type /= teep-success

   ; message type numbers
   TEEP-TYPE-query-request = 1
   TEEP-TYPE-query-response = 2
   TEEP-TYPE-trusted-app-install = 3
   TEEP-TYPE-trusted-app-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-apps = 2
   $data-item-requested /= trusted-apps
   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,
       ? nonce => bstr .size (8..64),
       ? version => [ + version ],
       ? oscp-data => bstr,
       * $$query-request-extensions



Tschofenig, et al.      Expires January 14, 2021               [Page 22]


Internet-Draft                TEEP Protocol                    July 2020


       * $$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,
       ? selected-version => version,
       ? eat => bstr,
       ? ta-list  => [ + bstr ],
       ? ext-list => [ + ext-info ],
       * $$query-response-extensions,
       * $$teep-option-extensions
     }
   ]

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

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




Tschofenig, et al.      Expires January 14, 2021               [Page 23]


Internet-Draft                TEEP Protocol                    July 2020


   teep-success = [
     type: TEEP-TYPE-teep-success,
     token: uint,
     option: {
       ? msg => text,
       * $$teep-success-extensions,
       * $$teep-option-extensions
     }
   ]

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

   cipher-suites = 1
   nonce = 2
   versions = 3
   oscp-data = 4
   selected-cipher-suite = 5
   selected-version = 6
   eat = 7
   ta-list = 8
   ext-list = 9
   manifest-list = 10
   msg = 11
   err-msg = 12

Authors' Addresses

   Hannes Tschofenig
   Arm Ltd.
   Absam, Tirol  6067
   Austria

   Email: hannes.tschofenig@arm.com







Tschofenig, et al.      Expires January 14, 2021               [Page 24]


Internet-Draft                TEEP Protocol                    July 2020


   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


   Dave Thaler
   Microsoft
   US

   Email: dthaler@microsoft.com


   Akira Tsukamoto
   AIST
   JP

   Email: akira.tsukamoto@aist.go.jp























Tschofenig, et al.      Expires January 14, 2021               [Page 25]


Html markup produced by rfcmarkup 1.129d, available from https://tools.ietf.org/tools/rfcmarkup/