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Versions: 00

TEEP                                                              M. Pei
Internet-Draft                                                  Symantec
Intended status: Standards Track                           H. Tschofenig
Expires: January 9, 2020                                        Arm Ltd.
                                                              D. Wheeler
                                                                   Intel
                                                            July 8, 2019


                   The Open Trust Protocol (OTrP) v2
                    draft-tschofenig-teep-otrp-v2-00

Abstract

   This document specifies the Open Trust Protocol (OTrP) version 2, a
   protocol that provisions and installs, updates, and deletes Trusted
   Applications in a device with a Trusted Execution Environment (TEE).

Status of This Memo

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

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

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

   This Internet-Draft will expire on January 9, 2020.

Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   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




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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   2
   3.  OTrP Message Overview . . . . . . . . . . . . . . . . . . . .   3
   4.  Detailed Messages Specification . . . . . . . . . . . . . . .   4
   5.  Security Consideration  . . . . . . . . . . . . . . . . . . .  11
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  15
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  16
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .  17
   Appendix B.  Contributors . . . . . . . . . . . . . . . . . . . .  17
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  17

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, different 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 version 2 of the Open Trust Protocol (OTrP),
   a protocol for communicating between an OTrP server (as part of a
   TAM) and an OTrP client (which is a client-side component running in
   the REE).

   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.

2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

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




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3.  OTrP Message Overview

   OTrP consists of a couple of messages exchanged between a TAM and an
   OTrP Agent via an OTrP Broker.  The messages are encoded either in
   JSON or CBOR and designed to provide end-to-end security.  OTrP
   messages are signed and/or encrypted by the endpoints, i.e., TAM and
   OTrP Agent, but trusted applications may as well be encrypted and
   signed by the service provider.  OTrP not only re-uses JSON and CBOR
   but also the respective security wrappers, namely JOSE (JWS [RFC7515]
   and JWE [RFC7516], to be more specific) and COSE [RFC8152].
   Furthermore, for attestation the Entity Attestation Token (EAT) and
   for software updates the SUIT manifest format is re-used.

   This specification defines six messages.

   A TAM queries a device's current state with a QueryRequest message.
   An OTrP 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        |           |OTrP Agent   |
     +------------+           +-------------+

       QueryRequest ------->

                              QueryResponse

                    <-------     or

                                Error

   With the TrustedAppInstall message a TAM can instruct an OTrP Agent
   to install a TA.  The OTrP 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.








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    +------------+           +-------------+
    | TAM        |           |OTrP Agent   |
    +------------+           +-------------+

      TrustedAppInstall ---->

                               Success

                       <----    or

                               Error

   With the TrustedAppDelete message a TAM can instruct an OTrP 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.

    +------------+           +-------------+
    | TAM        |           |OTrP Agent   |
    +------------+           +-------------+

      TrustedAppDelete  ---->

                               Success

                       <----    or

                               Error

4.  Detailed Messages Specification

   For a CBOR-based encoding the following security wrapper is used
   (described in CDDL format [I-D.ietf-cbor-cddl]).


















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   Outer_Wrapper = {
       msg-authenc-wrapper         => bstr .cbor
                                      Msg_AuthEnc_Wrapper / nil,
       otrp-message                => (QueryRequest /
                                       QueryResponse /
                                       TrustedAppInstall /
                                       TrustedAppDelete /
                                       Error /
                                       Success ),
   }

   msg-authenc-wrapper = 1
   otrp-message = 2

   Msg_AuthEnc_Wrapper = [ * (COSE_Mac_Tagged /
                              COSE_Sign_Tagged /
                              COSE_Mac0_Tagged /
                              COSE_Sign1_Tagged)]

   A future version of this specification will also describe the
   security wrapper for JSON (in CDDL format).

   suite = int

   version = int

   data_items = (
      attestation: 1,
      ta: 2,
      ext: 3
   )

   QueryRequest = (
        TYPE : int,
        TOKEN : bstr,
        REQUEST : [+data_items],
        ? CIPHER_SUITE : [+suite],
        ? NONCE : bstr,
        ? VERSION : [+version],
        ? OCSP_DATA : bstr,
        * $$extensions
   )

   A QueryRequest message is signed by the TAM and has the following
   fields:

   TYPE  TYPE = 1 corresponds to a QueryRequest message sent from the
      TAM to the OTrP Agent.



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

   REQUEST  The REQUEST field indicates what information the TAM
      requests from the OTrP Agent in form of a list of integer values.
      Each integer value corresponds to an IANA registered information
      element.  This specification defines the initial set of
      information elements.  With 'attestation' (1) the TAM requests the
      OTrP Agent to return an EAT entity attestation token in the
      response, with 'ta' (2) the TAM wants to query the OTrP Agent for
      all installed TAs, and with 'ext' (3) the TAM wants to query the
      OTrP Agent for supported extensions.  Further values may be added
      in the future via IANA registration.

   CIPHER_SUITE  The CIPHER_SUITE field lists the ciphersuite(s)
      supported by the TAM.

   NONCE  NONCE is an optional field used for ensuring the refreshness
      of the Entity Attestation Token (EAT) contained in the response.

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

   OCSP_DATA  The OCSP_DATA field 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 OTrP Agent can validate the status of the TAM
      certificate chain without making its own external OCSP service
      call.






















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   ta_id = (
      Vendor_ID = bstr,
      Class_ID = bstr,
      Device_ID = bstr,
      * $$extensions
   )

   ext_info = int

   QueryResponse = (
        TYPE : int,
        TOKEN : bstr,
        ? SELECTED_CIPHER_SUITE : suite,
        ? SELECTED_VERSION : version,
        ? EAT : bstr,
        ? TA_LIST  : [+ta_id],
        ? EXT_LIST : [+ext_info],
        * $$extensions
   )

   The QueryResponse message is signed and encrypted by the OTrP Agent
   and returned to the TAM.  It has the following fields:

   TYPE  TYPE = 2 corresponds to a QueryResponse message sent from the
      OTrP Agent to the TAM.

   TOKEN  The value in the TOKEN field is used to match requests to
      responses.  The value MUST correspond to the value received with
      the QueryRequest.

   SELECTED_CIPHER_SUITE  The SELECTED_CIPHER_SUITE field indicates the
      selected ciphersuite.

   SELECTED_VERSION  The SELECTED_VERSION field indicates the OTrP
      protocol version selected by the OTrP Agent.

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

   TA_LIST  The TA_LIST field enumerates the trusted applications
      installed on the device in form of ta_ids, i.e., a vendor id/class
      id/device id triple.

   EXT_LIST  The EXT_LIST field lists the supported extensions.  This
      document does not define any extensions.






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   TrustedAppInstall = (
        TYPE : int,
        TOKEN : bstr,
        ? TA  : [+SUIT_Outer_Wrapper],
        * $$extensions
   )

   The TrustedAppInstall message is MACed and encrypted by the TAM and
   has the following fields:

   TYPE  TYPE = 3 corresponds to a TrustedAppInstall message sent from
      the TAM to the OTrP Agent.  In case of successful processing, an
      Success message is returned by the OTrP 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 requests to
      responses.

   TA The TA field is used to convey one or multiple SUIT manifests.
      The SUIT manifest contains the code for the trusted app but may
      also convey personalization data.  TA binaries and personalization
      data is often 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.

   TrustedAppDelete  = (
        TYPE : int,
        TOKEN : bstr,
        ? TA_LIST  : [+ta_id],
        * $$extensions
   )

   The TrustedAppDelete message is MACed and encrypted by the TAM and
   has the following fields:

   TYPE  TYPE = 4 corresponds to a TrustedAppDelete message sent from
      the TAM to the OTrP Agent.  In case of successful processing, an
      Success message is returned by the OTrP Agent.  In case of an
      error, an Error message is returned.

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

   TA_LIST  The TA_LIST field enumerates the TAs to be deleted.




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   Success = (
        TYPE : int,
        TOKEN : bstr,
        ? MSG : tstr,
        * $$extensions
   )

   The Success message is MACed and encrypted by the OTrP Agent and has
   the following fields:

   TYPE  TYPE = 5 corresponds to a Error message sent from the OTrP
      Agent to the TAM.

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

   MSG  The MSG field contains optional diagnostics information encoded
      in UTF-8 [RFC3629] returned by the OTrP Agent.

   Error = (
        TYPE : int,
        TOKEN : bstr,
        ERR_CODE : int,
        ? ERR_MSG : tstr,
        ? CIPHER_SUITE : [+suite],
        ? VERSION : [+version],
        * $$extensions
   )

   If possible, the Error message is MACed and encrypted by the OTrP
   Agent.  Unprotected Error messages MUST be handled with care by the
   TAM due to possible downgrading attacks.  It has the following
   fields:

   TYPE  TYPE = 6 corresponds to a Error message sent from the OTrP
      Agent to the TAM.

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

   ERR_CODE  The ERR_CODE field 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 message is a human-readable diagnostic message
      that MUST be encoded using UTF-8 [RFC3629] using Net-Unicode form
      [RFC5198].




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   VERSION  The VERSION field enumerates the protocol version(s)
      supported by the OTrP Agent.  This field is optional but MUST be
      returned with the ERR_UNSUPPORTED_MSG_VERSION error message.

   CIPHER_SUITE  The CIPHER_SUITE field lists the ciphersuite(s)
      supported by the OTrP Agent.  This field is optional but MUST be
      returned with the ERR_UNSUPPORTED_CRYPTO_ALG error message.

   This specification defines the following initial error messages.
   Additional error code can be registered with IANA.

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

   ERR_UNSUPPORTED_EXTENSION  The OTrP Agent sends this error message
      when it recognizes an unsupported extension or unsupported
      message.

   ERR_REQUEST_SIGNATURE_FAILED  The OTrP Agent sends this error message
      when it fails to verify the signature of the message.

   ERR_UNSUPPORTED_MSG_VERSION  The OTrP Agent receives a message but
      does not support the indicated version.

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

   ERR_BAD_CERTIFICATE  The OTrP 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  The OTrP Agent returns this error when a
      certificate was of an unsupported type.

   ERR_CERTIFICATE_REVOKED  The OTrP Agent returns this error when a
      certificate was revoked by its signer.

   ERR_CERTIFICATE_EXPIRED  The OTrP Agent returns this error when a
      certificate has expired or is not currently valid.

   ERR_INTERNAL_ERROR  The OTrP Agent returns this error when a
      miscellaneous internal error occurred while processing the
      request.

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



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   ERR_TA_NOT_FOUND  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  While installing a TA, a TEE will return
      this error if the TA has already been installed.

   ERR_TA_UNKNOWN_FORMAT  The OTrP Agent returns this error when it does
      not recognize the format of the TA binary.

   ERR_TA_DECRYPTION_FAILED  The OTrP Agent returns this error when it
      fails to decrypt the TA binary.

   ERR_TA_DECOMPRESSION_FAILED  The OTrP Agent returns this error when
      it fails to decompress the TA binary.

   ERR_MANIFEST_PROCESSING_FAILED  The OTrP 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  The OTrP Agent returns this error when it
      fails to process the provided personalization data.

5.  Security Consideration

   This section summarizes the security considerations discussed in this
   specification:

   Cryptographic Algorithms  This specification relies on the
      cryptographic algorithms provided by the security wrappers JOSE
      and COSE, respectively.  A companion document makes algorithm
      recommendations but this document is written in an algorithm-
      agnostic way.  OTrP messages between the TAM and the OTrP Agent
      are protected using JWS and JWE (for JSON-encoded messages) and
      COSE (for CBOR-encoded messages).  Public key based authentication
      is used to by the OTrP Agent to authenticate the TAM and vice
      versa.

   Attestation  A TAM may rely on the attestation information provided
      by the OTrP 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.



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      To lower the privacy implications the OTrP Agent MUST present its
      attestation information only to an authenticated and authorized
      TAM.

   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 OTrP Agent is then the
      responsibility of the TAM and the OTrP Broker, using the security
      mechanisms provided by the OTrP.  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  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 itself is (or can be) opaque to
      the TAM.

   OTrP Broker  OTrP relies on the OTrP Broker to relay messages between
      the TAM and the OTrP Agent.  When the OTrP Broker is compromised
      it can drop, relay, and replay messages but it cannot modify those
      messages.  A compromised OTrP Broker could reorder TAM messages to
      install an old version of a TA.  Information in the manifest
      ensures that the OTrP Agents are protected against such
      downgrading attacks.

   CA Compromise  The QueryRequest message from a TAM to the OTrP 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 OTrP Agent can verify the certificate's revocation
      status.

      A certificate revocation status check on a TA signer certificate
      is OPTIONAL by an OTrP Agent.  A TAM is responsible for vetting a
      TA and before distributing them to OTrP Agents.  The OTrP 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 an OTrP 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.




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   Compromised TAM  The OTrP 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.

6.  IANA Considerations

   There are two IANA requests: a media type and list of error codes.

   IANA is requested to assign a media type for application/otrpv2+json.

   Type name:  application

   Subtype name:  otrp+json

   Required parameters:  none

   Optional parameters:  none

   Encoding considerations:  Same as encoding considerations of
     application/json as specified in Section 11 of [RFC7159]

   Security considerations:  See Security Considerations Section of this
     document.

   Interoperability considerations:  Same as interoperability
     considerations of application/json as specified in [RFC7159]

   Published specification:  This document.

   Applications that use this media type:  OTrPv2 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



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   Intended usage:  COMMON

   Restrictions on usage:  none

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

   Change controller:  IETF

   IANA is requested to assign a media type for application/otrpv2+cbor.

   Type name:  application

   Subtype name:  otrpv2+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:  OTrPv2 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



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

   Change controller:  IETF

   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 otrp-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.

7.  References

7.1.  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-01 (work in progress), July 2019.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

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




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   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
              <https://www.rfc-editor.org/info/rfc4648>.

   [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>.

   [RFC7159]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
              2014, <https://www.rfc-editor.org/info/rfc7159>.

   [RFC7515]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web
              Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
              2015, <https://www.rfc-editor.org/info/rfc7515>.

   [RFC7516]  Jones, M. and J. Hildebrand, "JSON Web Encryption (JWE)",
              RFC 7516, DOI 10.17487/RFC7516, May 2015,
              <https://www.rfc-editor.org/info/rfc7516>.

   [RFC7517]  Jones, M., "JSON Web Key (JWK)", RFC 7517,
              DOI 10.17487/RFC7517, May 2015,
              <https://www.rfc-editor.org/info/rfc7517>.

   [RFC7518]  Jones, M., "JSON Web Algorithms (JWA)", RFC 7518,
              DOI 10.17487/RFC7518, May 2015,
              <https://www.rfc-editor.org/info/rfc7518>.

   [RFC8152]  Schaad, J., "CBOR Object Signing and Encryption (COSE)",
              RFC 8152, DOI 10.17487/RFC8152, July 2017,
              <https://www.rfc-editor.org/info/rfc8152>.

7.2.  Informative References

   [I-D.ietf-cbor-cddl]
              Birkholz, H., Vigano, C., and C. Bormann, "Concise data
              definition language (CDDL): a notational convention to
              express CBOR and JSON data structures", draft-ietf-cbor-
              cddl-08 (work in progress), March 2019.








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   [I-D.ietf-teep-architecture]
              Pei, M., Tschofenig, H., Wheeler, D., Atyeo, A., and D.
              Liu, "Trusted Execution Environment Provisioning (TEEP)
              Architecture", draft-ietf-teep-architecture-02 (work in
              progress), March 2019.

   [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>.

Appendix A.  Acknowledgements

   This work is based on the initial version of OTrP and hence credits
   go to those who have contributed to it.

Appendix B.  Contributors

   We would like to thank the following individuals for their
   contributions to an earlier version of this specification.

   - Brian Witten
     Symantec
     brian_witten@symantec.com

   - Tyler Kim
     Solacia
     tylerkim@iotrust.kr

   - Nick Cook
     Arm Ltd.
     nicholas.cook@arm.com

   - Minho Yoo
     IoTrust
     minho.yoo@iotrust.kr

Authors' Addresses

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

   Email: mingliang_pei@symantec.com





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   Hannes Tschofenig
   Arm Ltd.
   110 Fulbourn Rd
   Cambridge, CB1  9NJ
   Great Britain

   Email: hannes.tschofenig@arm.com


   David Wheeler
   Intel
   US

   Email: david.m.wheeler@intel.com





































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