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 Pei, et al. Expires January 9, 2020 [Page 1] Internet-Draft OTrP July 2019 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]. Pei, et al. Expires January 9, 2020 [Page 2] Internet-Draft OTrP July 2019 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. Pei, et al. Expires January 9, 2020 [Page 3] Internet-Draft OTrP July 2019 +------------+ +-------------+ | 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]). Pei, et al. Expires January 9, 2020 [Page 4] Internet-Draft OTrP July 2019 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, * $$extensions ) A QueryRequest message is signed by the TAM and has the following fields: TYPE TYPE = 1 corresponds to a QueryRequest message sent from the TAM to the OTrP Agent. Pei, et al. Expires January 9, 2020 [Page 5] Internet-Draft OTrP July 2019 TOKEN The value in the TOKEN field is used to match requests to responses. REQUEST The REQUEST field indicates what information the TAM requests from the OTrP Agent in form of a list of integer values. Each integer value corresponds to an IANA registered information element. This specification defines the initial set of information elements. With 'attestation' (1) the TAM requests the OTrP Agent to return an EAT entity attestation token in the response, with 'ta' (2) the TAM wants to query the OTrP Agent for all installed TAs, and with 'ext' (3) the TAM wants to query the OTrP Agent for supported extensions. Further values may be added in the future via IANA registration. CIPHER_SUITE The CIPHER_SUITE field lists the ciphersuite(s) supported by the TAM. NONCE NONCE is an optional field used for ensuring the refreshness of the Entity Attestation Token (EAT) contained in the response. VERSION The VERSION field lists the version(s) supported by the TAM. For this version of the specification this field can be omitted. OCSP_DATA The OCSP_DATA field contains a list of OCSP stapling data respectively for the TAM certificate and each of the CA certificates up to the root certificate. The TAM provides OCSP data so that the OTrP Agent can validate the status of the TAM certificate chain without making its own external OCSP service call. Pei, et al. Expires January 9, 2020 [Page 6] Internet-Draft OTrP July 2019 ta_id = ( Vendor_ID = bstr, Class_ID = bstr, Device_ID = bstr, * $$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], * $$extensions ) The QueryResponse message is signed and encrypted by the OTrP Agent and returned to the TAM. It has the following fields: TYPE TYPE = 2 corresponds to a QueryResponse message sent from the OTrP Agent to the TAM. TOKEN The value in the TOKEN field is used to match requests to responses. The value MUST correspond to the value received with the QueryRequest. SELECTED_CIPHER_SUITE The SELECTED_CIPHER_SUITE field indicates the selected ciphersuite. SELECTED_VERSION The SELECTED_VERSION field indicates the OTrP protocol version selected by the OTrP Agent. EAT The EAT field contains an Entity Attestation Token following the encoding defined in [I-D.ietf-rats-eat]. TA_LIST The TA_LIST field enumerates the trusted applications installed on the device in form of ta_ids, i.e., a vendor id/class id/device id triple. EXT_LIST The EXT_LIST field lists the supported extensions. This document does not define any extensions. Pei, et al. Expires January 9, 2020 [Page 7] Internet-Draft OTrP July 2019 TrustedAppInstall = ( TYPE : int, TOKEN : bstr, ? TA : [+SUIT_Outer_Wrapper], * $$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], * $$extensions ) The TrustedAppDelete message is MACed and encrypted by the TAM and has the following fields: TYPE TYPE = 4 corresponds to a TrustedAppDelete message sent from the TAM to the OTrP Agent. In case of successful processing, an Success message is returned by the OTrP Agent. In case of an error, an Error message is returned. TOKEN The value in the TOKEN field is used to match requests to responses. TA_LIST The TA_LIST field enumerates the TAs to be deleted. Pei, et al. Expires January 9, 2020 [Page 8] Internet-Draft OTrP July 2019 Success = ( TYPE : int, TOKEN : bstr, ? MSG : tstr, * $$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]. Pei, et al. Expires January 9, 2020 [Page 9] Internet-Draft OTrP July 2019 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. Pei, et al. Expires January 9, 2020 [Page 10] Internet-Draft OTrP July 2019 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. Pei, et al. Expires January 9, 2020 [Page 11] Internet-Draft OTrP July 2019 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. Pei, et al. Expires January 9, 2020 [Page 12] Internet-Draft OTrP July 2019 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 Pei, et al. Expires January 9, 2020 [Page 13] Internet-Draft OTrP July 2019 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 Pei, et al. Expires January 9, 2020 [Page 14] Internet-Draft OTrP July 2019 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, . [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November 2003, . Pei, et al. Expires January 9, 2020 [Page 15] Internet-Draft OTrP July 2019 [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006, . [RFC5198] Klensin, J. and M. Padlipsky, "Unicode Format for Network Interchange", RFC 5198, DOI 10.17487/RFC5198, March 2008, . [RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049, October 2013, . [RFC7159] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March 2014, . [RFC7515] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May 2015, . [RFC7516] Jones, M. and J. Hildebrand, "JSON Web Encryption (JWE)", RFC 7516, DOI 10.17487/RFC7516, May 2015, . [RFC7517] Jones, M., "JSON Web Key (JWK)", RFC 7517, DOI 10.17487/RFC7517, May 2015, . [RFC7518] Jones, M., "JSON Web Algorithms (JWA)", RFC 7518, DOI 10.17487/RFC7518, May 2015, . [RFC8152] Schaad, J., "CBOR Object Signing and Encryption (COSE)", RFC 8152, DOI 10.17487/RFC8152, July 2017, . 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. Pei, et al. Expires January 9, 2020 [Page 16] Internet-Draft OTrP July 2019 [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, . 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 Pei, et al. Expires January 9, 2020 [Page 17] Internet-Draft OTrP July 2019 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 Pei, et al. Expires January 9, 2020 [Page 18]