Using Netconf Pub/Sub Model for RATS Interaction Procedure
draft-xia-rats-pubsub-model-01

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Remote ATtestation ProcedureS                                     L. Xia
Internet-Draft                                                    W. Pan
Intended status: Standards Track                                  Huawei
Expires: April 23, 2020                                 October 21, 2019

       Using Netconf Pub/Sub Model for RATS Interaction Procedure
                     draft-xia-rats-pubsub-model-01

Abstract

   This draft defines the a new method of using the netconf pub/sub
   model in the RATS interaction procedure, to increse its flexibility,
   efficiency and scalability.

Status of This Memo

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

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions Used in This Document . . . . . . . . . . . . . .   3
   3.  Pub/sub Model for Remote Attestation Procedure  . . . . . . .   4
     3.1.  Solution Overview . . . . . . . . . . . . . . . . . . . .   4
     3.2.  Remote Attestation Event Stream Definition  . . . . . . .   7
     3.3.  Remote Attestation Subscription Definition  . . . . . . .   8
     3.4.  Remote Attestation Selection Filters Definition . . . . .   8
     3.5.  Remote Attestation Subscription Parameters Handling . . .   9
     3.6.  Remote Attestation Notification Distribution  . . . . . .   9
     3.7.  Summary . . . . . . . . . . . . . . . . . . . . . . . . .   9
   4.  The YANG Module for Sub/pub Model Remote Attestation
       Procedures  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     4.1.  Tree Format . . . . . . . . . . . . . . . . . . . . . . .  12
     4.2.  Raw Format  . . . . . . . . . . . . . . . . . . . . . . .  12
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  12
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  12
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   Remote attestation is for acquiring the evidence about various
   integrity information from remote endpoints to assess its
   trustworthiness (aka, behave in the expected manner).  These evidence
   should be about: system component identity, composition of system
   components, roots of trust, system component integrity, system
   component configuration, operational state and so on.
   [I-D.richardson-rats-usecases] describes possible use cases which
   remote attestation are using for different industries, like: network
   devices, FIDO authentication for onlline transaction, Cryptographic
   Key Attestation for mobile devices, and so on.

   [I-D.birkholz-rats-architecture] lays a foundation of RATS
   architecture about the key RATS roles (i.e., Relying Party, Verifier,
   Attester and asserter) and the messages they exchange, as well as
   some key concepts.  Based on it,
   [I-D.birkholz-rats-reference-interaction-model] specifies a basic
   challenge-response-based interaction model for the remote attestation
   procedure, which a complete remote attestation procedure is triggered
   by a challenge message originated from the verifier, and finished
   when the attester sends its response message back.  This is a very
   generic interaction model with wide adoption.  This document proposes
   an alternative interaction model for Remote attestation procedure, by

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   customizing the IETF NETCONF pub/sub model
   [RFC8639][RFC8640][RFC8641].  With its nature of asynchronous
   communication, the new pub/sub model for remote attestation procedure
   is optimal for large-scale and loosely coupled distributed systems,
   especially for the network devices, which has the advantages as:
   loose coupling, scalability, time delivery sensitivity, supporting
   filtering capability, and so on.  The pub/sub model can be used
   independently, or together with the challenge-response model to
   complement each other as a whole.  Note that in which way these
   models are combinded together are currently out of the scope of this
   draft.

   In summary, by untilizing the pub/sub model in remote attestation
   procedure, the gained benefits are as below:

   o  Flexibility: the verifier does not need to send the challenge
      message every time.  The whole thing of the verifier is to
      subscibe a topic to the attester and then to anticipate the period
      or timely on-change notification from the attester about its
      integrity evidence.

   o  Efficiency: once the verifier has subscribed its interested topics
      related with its triggering condition to the attester, it will get
      all the condition triggerd notifications on time, which are the
      integrity related evidence for remote attestation in fact.  It
      will ensure any integrity change/deviation of the remote endpoint
      to be detected with the minimum latency.

   o  Scalability: it will save a lot of challenge messages by replacing
      with single subscription message for one topic stream, and
      decrease the total number of stateful connection between the
      verifier and attester, especially for a very large scale network.
      Thus, the scalability of the solution will increase.

   This document is organized as follows.  Section 2 defines conventions
   and acronyms used.  Section 3 discusses pub/sub model of remote
   attestation procedure.

2.  Conventions Used in This Document

   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 document uses terminology defined in[I-D.birkholz-rats-architect
   ure][I-D.birkholz-rats-reference-interaction-model] for security
   related and RATS scoped terminology.

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3.  Pub/sub Model for Remote Attestation Procedure

3.1.  Solution Overview

   The following sequence diagram illustrates the reference remote
   attestation procedure by utilizing the netconf pub/sub model defined
   by this document.

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[Attester]                                                      [Verifier]
    |                                                               |
    | <--Sub(nonce,authSecID,assertionSelection, event/period)      |
    |                                                               |
collectAssertions(assertionSelection)                               |
    | => assertions                                                 |
    |                                                               |
signAttestationEvidence(authSecID, assertions, nonce)               |
    | => signedAttestationEvidence                                  |
    |                                                               |
    | signedAttestationEvidence ----------------------------------> |
    |                                                               |
    | verifyAttestationEvidence(signedAttestationEvidence, refAssertions)
    |                                          attestationResult <= |
    |                                                               |
    | ............................................................. |
    |                                                               |
collectAssertions(assertionSelection)                               |
    | => assertions                                                 |
    |                                                               |
signAttestationEvidence(authSecID, assertions, nonce)               |
    | => signedAttestationEvidence                                  |
    |                                                               |
    | signedAttestationEvidence ----------------------------------> |
    |                                                               |
    | verifyAttestationEvidence(signedAttestationEvidence, refAssertions)
    |                                          attestationResult <= |
    |                                                               |
    | ............................................................. |
    |                                                               |
    |                                                               |
    |on-change/event happens                                        |
    |     |                                                         |
    |    \|/                                                        |
collectAssertions(assertionSelection)                               |
    | => assertions                                                 |
    |                                                               |
signAttestationEvidence(authSecID, assertions, nonce)               |
    | => signedAttestationEvidence                                  |
    |                                                               |
    | signedAttestationEvidence ----------------------------------> |
    |                                                               |
    | verifyAttestationEvidence(signedAttestationEvidence, refAssertions)
    |                                          attestationResult <= |
    |                                                               |
    | ............................................................. |

               Figure 1: Pub/sub model of Remote Attestation

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   In short, the basic idea of pub/sub model for remote attestation is
   the verifier subscribes its interested event streams about the
   integrity evidence to the attester.  After the subscription succeeds,
   the attester sends the subscribed integrity evidence back to the
   verifier.  During subscription, the verifier may also specify how the
   attester returns the subscribed information, that is, the upate
   trigger as periodic subscription or on-change subscription.  And when
   the selection filters are applied to the subscription, only the
   information that pass the filter will be distributed out.

   More detailed, the key steps of the remote attestation workflow with
   this model can be summarized as below (using the network devices as
   the example):

   o  The verifier subscribes its interested event streams about the
      integrity evidence to the attester.  More specifically:

      *  The event stream here refers to various integrity evidence
         information related to device trustworthiness.  The basic event
         streams may include: software integrity information (including
         PCR values and system boot logs) of each layer of the trust
         chain recorded during device booting time; device identity
         certificates & Attestation Key certificate; operating system,
         application dynamic integrity information (e.g., IMA logs) and
         the device configuration information recorded during device
         running time.

      *  Periodic subscription is mainly used by the verifier for the
         general and non-critical information collection, which are not
         strictly time sensitive and aims for collecting the latest
         integrity evidence and checking the possible deviation.  In
         contrary, on-change subscription is basically used to to
         monitor the critical integrity evidence (e.g., integrity values
         and log files during device booting time, or integrity values
         of some key service processes).  If these integrity values
         change, notifications are sent immediately.

      *  The selection filters may be applied to the subscription, so
         that only the event records that pass the filter will be
         distributed out.  Some specific examples include: event records
         of a component (e.g., line card) in the composite device, the
         event records in a specific time period that includes a start
         time and an end time, and so on.

   o  Consider how to send the existing parameters (i.e., nonce, hash
      signature algorithm, and specified TPM name, etc.) carried in the
      challenge message of the previous challenge-response model to the
      attester through the subscription message of the new sub/pub model

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      in advance, and the follow-up usage of them.  A very important
      point is how to ensure that the nonce carried in every
      notification message is different, and both the attester and the
      verifier know the correct value in advance.

   o  Both configuration subscription and dynamic subscription are
      considered.  More specifically:

      *  Configure subscription is for the important security event
         stream.  For example, it enables the monitoring the important
         integrity information by using the on-change mode.

      *  Dynamic subscription is for the normal integrity information,
         that is, periodically receive those related information during
         NETCONF Session.  The corresponding subscription RPC needs to
         be established dynamically.  This way can reduce unnecessary
         NETCONF sessions.

   o  In addition to the update trigger of on-change, the other possible
      update trigger may be certain pre-defined events according to
      [I-D.bryskin-netconf-automation-yang], that is: When these events
      occur, the specified integrity information is triggered to be
      sent, which is the relevant event stream plus optional selection
      filter.  The events may include: device startup completion, device
      upgrade completion, specific attack event, active/standby
      switchover, line card insertion/removal/switchover, certificate
      life cycle event (expiration), etc.

   o  The attester notification delivery mechanisms thus vary as the
      above subscription mechanisms of verifier vary.

   The following sections decribe the above key steps one by one.

3.2.  Remote Attestation Event Stream Definition

   The event streams here refers to various integrity evidence
   information related to device trustworthiness.  The basic event
   streams may include: software integrity information (including PCR
   values and system boot logs) of each layer of the trust chain
   recorded during device booting time, device identity certificates &
   Attestation Key certificate generation, operating system and
   application dynamic integrity information (e.g., IMA logs) recorded
   during device running time.

   The event streams are created and managed by the attester.  And their
   formal definition should be conformed to the information model
   definition like Attestation Evidence or others in
   [I-D.birkholz-rats-information-model], and the claim data model

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   definition in [I-D.birkholz-rats-basic-yang-module] with YANG data
   format, and [I-D.ietf-rats-eat] with COSE data format.

3.3.  Remote Attestation Subscription Definition

   NETCONF pub/sub model provides several suscription types in which
   approriate one or more types are choosed and possibly used together
   to meet the service requirements.

   Particularly, periodic subscription is mainly used by the verifier
   for the general and non-critical information collection, which are
   not strictly time sensitive and aims for collecting the latest
   integrity information and checking the possible deviation.  In
   contrary, on-change subscription is basically used to monitor the
   critical integrity evidence (e.g., integrity values and log files
   during device booting time, or integrity values of some key service
   processes).  If these integrity values change, notifications are sent
   immediately.

   Besides, both configuration subscription and dynamic subscription are
   considered.  In which, configure subscription is for the important
   security data stream as it lasts even the NETCONF session is closed.
   For example, it enables the monitoring of the status of important
   security event stream by using the on-change mode.  On the other
   hand, dynamic subscription is for the general security event stream,
   that is, periodically receive those related information during
   NETCONF Session.  The corresponding subscription RPC needs to be
   established dynamically.  This way can reduce unnecessary NETCONF
   sessions.

   Furthermore, certain pre-defined events can be the update trigger
   too, that is: When these events occur, the specified integrity
   information is triggered to be sent, which is the relevant event
   stream plus optional selection filter.  The events may include:
   device startup completion, device upgrade completion, specific attack
   event, active/standby switchover, line card insertion/removal/
   switchover, certificate life cycle event (expiration), etc.

3.4.  Remote Attestation Selection Filters Definition

   The selection filters may be applied to the subscription, so that
   only the event that pass the filter will be distributed out.

   A concrete example of selection filter is limiting the delivered
   event stream to those originated from a specific component with id
   ("xxxxxxxxxx") of a designated vendor ("xxx-vendor-device").

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3.5.  Remote Attestation Subscription Parameters Handling

   Most of the parameters carried in the subscription message are not
   changed during the remote attestation procedure, like: hash signature
   algorithm, specified TPM name and so on.  Their main goal is to
   enable the dynamic negotiation with the attester about what
   information the verifier needs and how to construct them together.  A
   very important point is how to ensure that the nonce carried in every
   notification message is different, and both the attester and the
   verifier know the correct value in advance.  For this purpose, the
   basic idea is to ensure that the nonce in two sides of the
   communication is synchronously changed, and the randomness of the
   nonce is maintained.  Specifically, there may be several ways to do
   it:

   o  Verifier sends a seed with hash algorithm to the attester in the
      subscription message, and then perform the synchronization
      operation on both sides.

   o  In fact, the nonce does not need to be random every time.  As long
      as the receive endpoint (here for verifier) can identify
      duplicated packets, other means may be used.  For example: The
      timestamp and increasing count.

   o  The RATS TUDA mechanism [I-D.birkholz-rats-tuda] can also be used
      here to ensure the freshness of information.

3.6.  Remote Attestation Notification Distribution

   To be written.

3.7.  Summary

   Based on the above discussion, this section gives some examples to
   illustrate the overall application of sub/pub model to remote
   attestation procedure.

   Below is a configured subscription example with on-change update
   trigger, with specific contents as:

   o  There are 3 integrity evidence related event streams as follows:
      pcr-trust-evidence, bios-log-trust-evidence and ima-log-trust-
      evidence.  The subscribed one is pcr-trust-evidence.

   o  The other parameters of the subscription include: pcr-list: {{1,
      3, 7}}, tcg-hash-algo-id: TPM_ALG_SHA256, nonce-value: 0x564ac291,
      TPM_ALG_ID-value: TPM_ALG_ECDSA, pub-key-id: 0x784a22bf, tpms:
      {"tpm1"}.

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   o  The selection filter is set as follows: a specific component with
      id ("xxxxxxxxxx") of a designated vendor ("xxx-vendor-device").

<edit-config>
    <subscriptions
           xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications">
        <subscription>
            <id>100</id>
            <stream>pcr-trust-evidence</stream>
            <stream-subtree-filter>
                <xxx-vendor-device
                      xmlns="urn:xxx:params:xml:ns:yang:xxx-vendor-device ">
                    <device-id>xxxxxxxxxx</device-id>
                </xxx-vendor-device>
            </stream-subtree-filter>
            <pcr-list>
                <pcr>
                    <pcr-indices>1</pcr-indices>
                    <pcr-indices>3</pcr-indices>
                    <pcr-indices>7</pcr-indices>
                    <hash-algo>
                        <tcg-hash-algo-id>TPM_ALG_SHA256</tcg-hash-algo-id>
                    </hash-algo>
                </pcr>
            </pcr-list>
            <nonce-value>0x564ac291</nonce-value>
            <TPM_ALG_ID-value>TPM_ALG_ECDSA</TPM_ALG_ID-value>
            <pub-key-id>0x784a22bf</pub-key-id>
            <tpms>
                <tpm-name>tpm1</tpm-name>
            </tpms>
            <yp:on-change>
                <yp:dampening-period>100</yp:dampening-period>
            </yp:on-change>
        </subscription>
    </subscriptions>
</edit-config>

            Figure 2: Configured On-change Subscription Message

   Below is a dynamic subscription RPC example with periodic update
   trigger, with specific contents as:

   o  There are 3 integrity evidence related event streams as follows:
      pcr-trust-evidence, bios-log-trust-evidence and ima-log-trust-
      evidence.  The subscribed one is bios-log-trust-evidence.

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   o  The other parameters of the dynamic subscription include: tpms:
      {"tpm1"}, last-entry-value: 0xa34568baac79, log-type: bios, pcr-
      list: {{2, 4, 8}}, tcg-hash-algo-id: TPM_ALG_SHA256.

   o  The selection filter is set as follows: a specific component with
      id ("xxxxxxxxxx") of a designated vendor ("xxx-vendor-device").

   o  Subscription period: 500 centiseconds.

<rpc netconf:message-id="101"
       xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
    <establish-subscription
          xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications">
        <stream>bios-log-trust-evidence</stream>
        <stream-subtree-filter>
            <xxx-vendor-device
                  xmlns="urn:xxx:params:xml:ns:yang:xxx-vendor-device ">
                <device-id>xxxxxxxxxx</device-id>
            </xxx-vendor-device>
        </stream-subtree-filter>
        <tpms>
            <tpm-name>tpm1</tpm-name>
        </tpms>
        <last-entry-value>0xa34568baac79</last-entry-value>
        <log-type>bios</log-type>
        <pcr-list>
            <pcr>
                <pcr-indices>2</pcr-indices>
                <pcr-indices>4</pcr-indices>
                <pcr-indices>8</pcr-indices>
                <hash-algo>
                    <tcg-hash-algo-id>TPM_ALG_SHA256</tcg-hash-algo-id>
                </hash-algo>
            </pcr>
        </pcr-list>
        <yp:periodic>
            <yp:period>500</yp:period>
        </yp:periodic>
    </establish-subscription>
</rpc>

              Figure 3: Dynamic Periodic Subscription Message

   Below is a configured subscription RPC example with pre-defined
   events as the update trigger, with specific contents as:

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   o  There are 3 integrity evidence related event streams as follows:
      pcr-trust-evidence, bios-log-trust-evidence and ima-log-trust-
      evidence.  The subscribed one is pcr-trust-evidence.

   o  The other parameters of the subscription include: pcr-list: {{1,
      3, 7}}, tcg-hash-algo-id: TPM_ALG_SHA256, nonce-value: 0x564ac291,
      TPM_ALG_ID-value: TPM_ALG_ECDSA, pub-key-id: 0x784a22bf, tpms:
      {"tpm1"}.

   o  The selection filter is set as follows: a specific component with
      id ("xxxxxxxxxx") of a designated vendor ("xxx-vendor-device").

   o  The event which triggers the intergrity evidence delivery is
      defined as: id: 1001, type: master-slave-swithover

         Figure 4: Configured Event-triggered Subscription Message

4.  The YANG Module for Sub/pub Model Remote Attestation Procedures

4.1.  Tree Format

   To be written.

4.2.  Raw Format

   To be written.

5.  Security Considerations

   To be written

6.  Acknowledgements

   Thanks to ...

7.  IANA Considerations

   To be written, possibly.

8.  References

8.1.  Normative References

   [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>.

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   [RFC8639]  Voit, E., Clemm, A., Gonzalez Prieto, A., Nilsen-Nygaard,
              E., and A. Tripathy, "Subscription to YANG Notifications",
              RFC 8639, DOI 10.17487/RFC8639, September 2019,
              <https://www.rfc-editor.org/info/rfc8639>.

   [RFC8640]  Voit, E., Clemm, A., Gonzalez Prieto, A., Nilsen-Nygaard,
              E., and A. Tripathy, "Dynamic Subscription to YANG Events
              and Datastores over NETCONF", RFC 8640,
              DOI 10.17487/RFC8640, September 2019,
              <https://www.rfc-editor.org/info/rfc8640>.

   [RFC8641]  Clemm, A. and E. Voit, "Subscription to YANG Notifications
              for Datastore Updates", RFC 8641, DOI 10.17487/RFC8641,
              September 2019, <https://www.rfc-editor.org/info/rfc8641>.

8.2.  Informative References

   [I-D.birkholz-rats-architecture]
              Birkholz, H., Wiseman, M., Tschofenig, H., and N. Smith,
              "Remote Attestation Procedures Architecture", draft-
              birkholz-rats-architecture-02 (work in progress),
              September 2019.

   [I-D.birkholz-rats-basic-yang-module]
              Birkholz, H., Eckel, M., Bhandari, S., Sulzen, B., Voit,
              E., Xia, L., Laffey, T., and G. Fedorkow, "YANG Module for
              Basic Challenge-Response-based Remote Attestation
              Procedures", draft-birkholz-rats-basic-yang-module-01
              (work in progress), July 2019.

   [I-D.birkholz-rats-information-model]
              Birkholz, H. and M. Eckel, "An Information Model for
              Assertions used in RATS", draft-birkholz-rats-information-
              model-00 (work in progress), July 2019.

   [I-D.birkholz-rats-reference-interaction-model]
              Birkholz, H. and M. Eckel, "Reference Interaction Model
              for Challenge-Response-based Remote Attestation", draft-
              birkholz-rats-reference-interaction-model-01 (work in
              progress), July 2019.

   [I-D.birkholz-rats-tuda]
              Fuchs, A., Birkholz, H., McDonald, I., and C. Bormann,
              "Time-Based Uni-Directional Attestation", draft-birkholz-
              rats-tuda-01 (work in progress), September 2019.

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   [I-D.bryskin-netconf-automation-yang]
              Bryskin, I., Liu, X., Clemm, A., Birkholz, H., and T.
              Zhou, "Generalized Network Control Automation YANG Model",
              draft-bryskin-netconf-automation-yang-03 (work in
              progress), July 2019.

   [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.

   [I-D.richardson-rats-usecases]
              Richardson, M., Wallace, C., and W. Pan, "Use cases for
              Remote Attestation common encodings", draft-richardson-
              rats-usecases-05 (work in progress), October 2019.

Authors' Addresses

   Liang Xia (Frank)
   Huawei
   101 Software Avenue, Yuhuatai District,
   Nanjing, Jiangsu  210012
   China

   Email: frank.xialiang@huawei.com

   Wei Pan
   Huawei
   101 Software Avenue, Yuhuatai District
   Nanjing, Jiangsu  210012
   China

   Email: william.panwei@huawei.com

Xia & Pan                Expires April 23, 2020                [Page 14]