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Delegated Authority for Bootstrap Voucher Artifacts

Document Type Active Internet-Draft (anima WG)
Authors Michael Richardson , Wei Pan
Last updated 2022-07-11
Replaces draft-richardson-anima-voucher-delegation
Stream Internet Engineering Task Force (IETF)
Intended RFC status Proposed Standard
Yang Validation 0 errors, 3 warnings
Stream WG state WG Document
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IESG IESG state I-D Exists
Consensus boilerplate Yes
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anima Working Group                                        M. Richardson
Internet-Draft                                  Sandelman Software Works
Intended status: Standards Track                                  W. Pan
Expires: 12 January 2023                             Huawei Technologies
                                                            11 July 2022

          Delegated Authority for Bootstrap Voucher Artifacts


   This document describes an extension of the RFC8366 Voucher Artifact
   in order to support delegation of signing authority.  The initial
   voucher pins a public identity, and that public indentity can then
   issue additional vouchers.  This chain of authorization can support
   permission-less resale of devices, as well as guarding against
   business failure of the BRSKI Manufacturer Authorized Signing
   Authority (MASA).

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

   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 12 January 2023.

Copyright Notice

   Copyright (c) 2022 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (
   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 Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Requirements for the Delegation . . . . . . . . . . . . .   3
       1.1.1.  Device Onboarding with Disconnected or Offline
               MASA  . . . . . . . . . . . . . . . . . . . . . . . .   3
       1.1.2.  Resale of Devices . . . . . . . . . . . . . . . . . .   3
       1.1.3.  Crypto-agility for Registrar  . . . . . . . . . . . .   4
       1.1.4.  Transparent Assemblers/Value-Added-Resellers  . . . .   4
     1.2.  Overview of Proposed Solution . . . . . . . . . . . . . .   4
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Delegation Voucher Artifact . . . . . . . . . . . . . . . . .   5
     3.1.  YANG Module . . . . . . . . . . . . . . . . . . . . . . .   6
     3.2.  Bundling of The Vouchers  . . . . . . . . . . . . . . . .   9
     3.3.  Delegation of Multiple Devices  . . . . . . . . . . . . .   9
   4.  Enhanced Pledge Behavior  . . . . . . . . . . . . . . . . . .   9
   5.  Changes to Registrar Behavior . . . . . . . . . . . . . . . .  10
     5.1.  Discovering The Most Recent Delegated Authority to Use  .  11
   6.  Applying The Delegation Voucher to Requirements . . . . . . .  12
     6.1.  Case 1: Resale  . . . . . . . . . . . . . . . . . . . . .  12
     6.2.  Case 2: Assembly  . . . . . . . . . . . . . . . . . . . .  13
   7.  Constraints on Pinning The Delegated Authority  . . . . . . .  13
   8.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  13
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
     9.1.  Delegation Vouchers do not expire . . . . . . . . . . . .  13
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
     10.1.  The IETF XML Registry  . . . . . . . . . . . . . . . . .  14
     10.2.  YANG Module Names Registry . . . . . . . . . . . . . . .  14
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  14
   12. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . .  14
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  14
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  14
     13.2.  Informative References . . . . . . . . . . . . . . . . .  15
   Appendix A.  Extra references . . . . . . . . . . . . . . . . . .  16
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  16

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1.  Introduction

   The [RFC8366] voucher artifact provides a proof from a manufacturer's
   authorizing signing authority (MASA) of the intended owner of a
   device.  This is used by an onboarding Pledge device in BRSKI
   ([RFC8995], [I-D.ietf-anima-constrained-voucher]), and SZTP

   There are a number of criticisms of the MASA concept.  They include:

   *  the MASA must be reachable to the Registar during the onboarding

   *  while the use of a nonceless voucher (see [RFC8366] section 4) can
      permit the MASA to be offline, it still requires the public key/
      certificate of the Registrar to be known at issuing time.  The
      device owner is always strongly dependent on the MASA service.

   *  the MASA must approve all transfers of ownership, impacting the
      rights of the supply chain distributors to transfer ownership as
      they see fit.

   *  if the Registrar has any nonceless vouchers, then it can not
      change it's public key, nor can it change which certification
      authority it uses.

   *  it is not possible for a MASA to pin ownership to a Registrar by
      Certification Authority plus DN.

   *  the creator of an assembly of parts/components can speak for the
      entire assembly of parts in a transparent way.

1.1.  Requirements for the Delegation

   This voucher artifact satisfies the following requirements:

1.1.1.  Device Onboarding with Disconnected or Offline MASA

   A Registrar wishes to onboard devices while it is not being connected
   to the Internet and MASA.

1.1.2.  Resale of Devices

   An owner of a device wishes to resale it which has previously been
   onboarded to a third party without specific authorization from the

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1.1.3.  Crypto-agility for Registrar

   The owner/manager of a registrar wishes to be able to replace its
   domain registration key.  Replacing the registration key would
   invalidate any previously acquired (nonceless) vouchers.  Any devices
   which have not been onboarded, or which need to be factory reset,
   would not trust a replacement key.

1.1.4.  Transparent Assemblers/Value-Added-Resellers

   An assembly may consist of a number of parts which are onboarded to a
   local controller during the manufacturing process.  Subsequent to
   this, the entire assembly will be shipped to a customer who wishes to
   onboard all the components.  The sub-components of the assembly needs
   to communicate with other sub-components, and so all the parts need
   to transparently onboarded.  (This is contrasted with an assembly
   where the controller acts as a security gateway.  Such a gateway
   might be a single point of failure)

   Assemblies may nest quite deeply.

1.2.  Overview of Proposed Solution

   The MASA will issue a voucher that delegates it's signing authority
   for one or more devices to a specific Registrar.  This is called a
   "delegation voucher".

   This Registrar can then operate as an authorized signing authority
   for the manufacturer, and can subsequently issue additional vouchers
   binding the pledge to new Registrars.

   This delegation can potentially be repeated multiple times to enable
   second, third, or n-th level of resale.

   The delegation voucher may be stored by the pledge for storage, to be
   included by the pledge in subsequent bootstrap operations.  The
   inclusion of the delegation voucher permits next Registrar with
   heuristics that permit it to find the delegated authorized signing
   authority (DASA).

   The delegation voucher pins the identity of the delegated authority
   using a variety of different mechanisms which are covered in
   Section 7.

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2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "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.

   Delegated Authorized Signing Authority :  the Delegated Authorized
      Signing Authority (DASA) is a service that can generate vouchers
      for one or more pledges to provide bootstrap authority, which is
      separated and delegated from the manufacturer.

   Delegation Voucher:  a Delegation Voucher is an [RFC8366] format
      voucher that has additional fields to provide details of the
      entity to which authority has been delegated.

   Intermediate Voucher:  a voucher that is not the final voucher
      linking a pledge to its owner.

   End Voucher:  a voucher that is the final voucher linking a pledge to
      its owner.

3.  Delegation Voucher Artifact

   The following tree diagram shows the extensions to the [RFC8366]

   There are a few new fields:

   delegation-enable-flag:  A global enable flag to the pledge that it
      can be delegated (true) or not (false).  With default, this flag
      is false, which is consistent with the voucher artifact in

   pinned-delegation-cert-authority:  An subject-public-key-info for a
      public key of the new DASA

   pinned-delegation-cert-name:  A string for the rfc822Name
      SubjectAltName contents of the new DASA; (XXX- is it enough,
      should other DNs be considered?)

   delegation-voucher:  One or a series of Intermediate Vouchers that
      delegate authority to the DASA.  For the latter case, the series
      of Intermediate Vouchers constitute a nested structure, and the
      most inner voucher is from the MASA, which is called terminal
      voucher here

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   intermediate-identities:  A set of voucher identities being
      consistent with the series of Intermediate Vouchers

   delegation-countdown:  Number of delegations still available.  If
      zero or omitted, then this is a terminal voucher and may not be
      further delegated.

   In addition, the serial-number field is no longer a plain leaf, but
   can also be an array (See Section 3.3).

   module: ietf-voucher-delegated

     grouping voucher-delegated-grouping:
       +-- voucher
          +-- created-on                          yang:date-and-time
          +-- expires-on?                         yang:date-and-time
          +-- assertion
          |       ianavat:voucher-assertion
          +-- serial-number                       string
          +-- idevid-issuer?                      binary
          +-- pinned-domain-cert?                 binary
          +-- domain-cert-revocation-checks?      boolean
          +-- nonce?                              binary
          +-- last-renewal-date?                  yang:date-and-time
          +-- delegation-enable-flag?             boolean
          +-- pinned-delegation-cert-authority?   binary
          +-- pinned-delegation-cert-name?        binary
          +-- delegation-voucher?                 binary
          +-- intermediate-identities?            binary
          +-- delegation-countdown?               int16

3.1.  YANG Module

   This module uses the grouping that was created in [RFC8366] to extend
   the definition.

   <CODE BEGINS> file "ietf-voucher-delegated@2020-01-06.yang"
   module ietf-voucher-delegated {
     yang-version 1.1;

     prefix "delegated";

     import ietf-restconf {
       prefix rc;
         "This import statement is only present to access

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          the yang-data extension defined in RFC 8040.";
       reference "RFC 8040: RESTCONF Protocol";

     // maybe should import from constrained-voucher instead!
     import ietf-voucher {
       prefix "v";

      "IETF ANIMA Working Group";

      "WG Web:   <>
       WG List:  <>
       Author:   Michael Richardson

     "This module extends the RFC8366 voucher format to provide
      a mechanism by which the authority to issue additional vouchers
      may be delegated to another entity

      The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL',
      and 'OPTIONAL' in the module text are to be interpreted as
      described in BCP 14 RFC 2119, and RFC8174.";

     revision "2020-01-06" {
        "Initial version";
        "RFC XXXX: Voucher Profile for Delegation Vouchers";

     rc:yang-data voucher-delegated-artifact {
       // YANG data template for a voucher.
       uses voucher-delegated-grouping;

     // Grouping defined for future usage
     grouping voucher-delegated-grouping {
         "Grouping to allow reuse/extensions in future work.";

       uses v:voucher-artifact-grouping {

         refine voucher/pinned-domain-cert {

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             mandatory  false;

         augment "voucher" {
           description "Base the delegated voucher
                        upon the regular one";

           leaf delegation-enable-flag {
             type boolean;
               "A global enable flag to the pledge that it can be
                delegated (true) or not (false). With default,
                this flag is false, which is consistent with
                the voucher artifact in RFC8366. ";

           leaf pinned-delegation-cert-authority {
             type binary;
               "An subject-public-key-info for a public key of the
                certificate authority that is to be trusted to issue
                a delegation voucher to the Registrar.
                This is not used by end-vouchers, and only valid
                when delegation-enable-flag is true.";

           leaf pinned-delegation-cert-name {
             type binary;
               "A string for the rfc822Name SubjectAltName contents
                which will be trusted to issue delegation vouchers.
                This is not used by end-vouchers, and only valid
                when delegation-enable-flag is true.";

           leaf delegation-voucher {
             type binary;
               "The intermediate voucher that delegates
                authority to the entity that signs this voucher
                is to be included here, and only valid
                when delegation-enable-flag is true.";

           leaf intermediate-identities {
             type binary;
               "A set of identities that will be needed to

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                validate the chain of vouchers, and only valid
                when delegation-enable-flag is true. MAY BE REDUNDANT";

           leaf delegation-countdown {
             type int16;
             "Number of delegations still available, and only valid
                when delegation-enable-flag is true. If zero
              or omitted, then this is a terminal voucher and
              may not be further delegated";

3.2.  Bundling of The Vouchers

   [RFC8995] defines a mechanism to return a single voucher to the

   This protocol requires a number of additional items to be returned to
   the pledge for evaluation: the series of Intermediate Vouchers that
   leads to the DASA, and the public keys (often as certificates) of the
   Registrars on the Delegation Path that leads to each Authority.

3.3.  Delegation of Multiple Devices

   A MASA MAY delegate multiple devices to the same Registrar by putting
   an array of items in the "serial-number" attributes.  (XXX-how to
   describe this in the YANG, and the detailed mechanism, are TBD)

4.  Enhanced Pledge Behavior

   The use of a Delegation Voucher requires changes to how the pledge
   evaluates the voucher that is returned to by the Registrar.

   There are no significant changes to the voucher-request that is made.
   The pledge continues to pin the identity of the Registrar to which it
   is connected, providing a nonce to establish freshness.

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   A pledge which has previously stored a Delegation Voucher and DASA ,
   SHOULD include it in its voucher request.  This will be in the form
   of a certificate provided by the "previous" owner.  This allows the
   Registrar to discover the previous authority for the pledge.  As the
   pledge has no idea if it connecting to an entity that it previously
   has connected to, it needs to include this certificate anyway.

   The pledge receives a voucher from the Registrar.  This voucher is
   called the zero voucher.  It will observe that the voucher is not
   signed with its built-in manufacturer trust anchor and it can not
   verify it.

   The pledge will examine the voucher to look for the "delegation-
   voucher" and the "intermediate-identities" attributes within the
   voucher.  A certificate from the set of intermediate-identities is
   expected to validate the signature on this zeroth end-entity voucher.
   (XXX- This attribute can be replaced by the CMS certificate chain)

   The contained delegation-voucher object is to be interpreted as an
   (Intermediate) Voucher.  This first voucher is called the first
   voucher, or "voucher[1]".  Generically, for voucher[i], the voucher
   found in the delegation-voucher is called voucher[i+1].

   If voucher[i] can be validated by a built-in trust anchor, then the
   process is done.  If not, then voucher[i] is examined in a recursive
   process until there are no further embedded vouchers.  The last
   voucher[n] is expected to be validated by a built-in manufacturer
   trust anchor.

   Once the top (n-th) voucher is found, then the pinned-certificate-
   authority is added to the working set of trust anchors.  The "pinned-
   certificate-name" attribute is used along with the trust anchor to
   validate the certificate chain provided with the (n-1)th voucher.
   This is repeated (unwinding the recursive processing) until the
   zeroth voucher has been validated.

5.  Changes to Registrar Behavior

   The Registrar is the component that authenticates the pledge, makes
   authorization decisions, and distributes vouchers.  If the vouchers
   is delegated, then the registrar need to co-ordinate MASA and DASA.

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5.1.  Discovering The Most Recent Delegated Authority to Use

   The pledge continues to use its manufacturer issued IDevID when
   performing BRSKI-style onboarding.  The IDevID contains an extension,
   the MASA URL (see [RFC8995] section 2.3.2).  The IDevID certificate
   is not expected to be updated when the device is resold, nor may it
   be practical for an intermediate owner to be able to replace the
   IDevID with their own.  (Some devices may support having an
   intermediate owner replace the IDevID, in which case this section
   does not apply)

   The Registrar needs to be informed that it should not contact a MASA
   using the URL in the IDevID, but rather to contact the previous
   owner's DASA.

   This can be accomplished by local override, as described in [RFC8995]
   section 5.4:

   Registrars MAY include a mechanism to override
   the MASA URL on a manufacturer-by-manufacturer basis, and within that
   override it is appropriate to provide alternate anchors.  This will
   typically used by some vendors to establish explicit (or private)
   trust anchors for validating their MASA that is part of a sales
   channel integration.

   The above override needs to be established on a per-device basis.  It
   requires per-device configuration which is very much non-autonomic.

   There are two other alternatives:

   1.  The Manufacturer could be aware of any Delegation Vouchers that
       it has issued for a particular device, and when contacted by the
       Registrar, it could redirect the Registrar to its DASA.  And the
       DASA may redirect the Registrar to its delegated DASA, this
       process is recursive to the final DASA.

   2.  The Pledge could provide a signed statement from the manufacturer
       providing the Registrar with a pointer to the DASA.

   Option 1 requires that the Registrar still contact the MASA,
   violating most of the goals from Section 1.1.

   Option 2 requires a signed artifact, and conveniently, the Delegation
   Voucher is exactly the item needed.  The most difficult problem is
   that the Pledge needs to (a) store one or more Delegation Vouchers in
   a non-volatile storage that survives factory reset operations, (b)
   attach these items to the pledge's voucher-request.

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   The extension to the [RFC8995] voucher-request described below
   provides for a contained for these Delegation Vouchers.

6.  Applying The Delegation Voucher to Requirements

6.1.  Case 1: Resale

   This case has many application scenarios.

   The simplest is that a device, previously owned by one entity is sold
   to another entity.  This would include many large home appliances
   (furnace, stove, refriderator) which are either sold with the home
   (because they are attached), or for which there is a frequent resale
   market.  Entire systems (HVAC, physical security, elevators) in
   commercial buildings also fall into this category.  Many of these
   devices exist for decades.

   The initial onboarder would obtain a delegated voucher, and would
   keep this voucher safe.  Should the device need to be resold, this
   voucher is provided to the new owner.  This protects the first owner
   from situations where the manufacturer is unwilling, or goes into

   A creditor, such as a bank, which may take the property, including
   required systems as collatoral for a loan could require that a
   delegated voucher be obtained.  A bank would find a building that
   needed new systems installed difficult to resale should the bank have
   to foreclose.  It is likely that this requirement would make devices
   which do not come with delegated vouchers significant liabilities,
   and that financial institutions (banks, insurance companies) might
   refuse to lend in this case.

   As a different example, an owner might initially start with some
   hosted Registrar (in the cloud perhaps, as a service).  Later on, the
   owner wishes to bring the Registrar in-house (or just change who is
   providing the Registrar service).  Such an activity is effectively a

   It is common when a company goes bankrupt that many of it's assets
   (routers, switches, desktops, as well as furniture) are sold by the
   court.  There are many resellers of digital equipment, and they
   typically take the devices, factory reset them, verify that they
   work, and then list them for resale.  Such an entity would want to
   have a delegated voucher for each device.  Whether the delegated
   voucher would be obtained from the original (bankrupt) company, by
   the court, or directly from the manufacturer is probably a legal

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   Further, the pledges may be resaled many times, and when onboarding,
   they will receive all vouchers in order with the sale chain, firstly
   masa vouchour, then 1st intermidate, 2nd intermidate, till to the
   final dealer.  In this case, the pledge's authorization form a signed
   voucher chain.

   The following illustrates a delegation voucher for a pledge: { "ietf-
   voucher-delegated:voucher": { "created-on": "2020-07-14T06:28:31Z",
   "expire-on": "2022-07-31T01:61:80Z", "assertion": "logged", "serial-
   number": "JADA123456789", "delegation-enable-flag": true, "pinned-
   delegation-cert-authority": "base64encodedvalue", "pinned-delegation-
   cert-name": "base64encodedvalue", "delegation-voucher":
   "base64encodedvalue", "intermediate-identities": "intermediateId1",
   "delegation-enable-flag": 1, } }

6.2.  Case 2: Assembly

   In some application, many pledges which come from multiple component
   assembled by a system integrated.  They need to to be assembled
   together in the first sale.  In this time, the owner is assembly
   controller, so the pledge's voucher need to include these delegation

   In addition, there are also transparent assembly, for example rail
   wagon scenario.  Firstly, the assembly onboards normally to get all
   pledges' vouchers, then this assembly acts as intermidate registrar,
   who "sell" these pledges to every rail wagon registrar.

7.  Constraints on Pinning The Delegated Authority


8.  Privacy Considerations


9.  Security Considerations

9.1.  Delegation Vouchers do not expire

   A significant feature of the [RFC8366] voucher is that it can be
   short-lived, and often renewed if needed.  This goes along with the
   arguments that renewal is better than revocation explained better in
   [RFC8739].  However, in order for a delegated voucher to be useful it
   has to have a life longer than the pessimistic expected life of the
   manufacturer (MASA).  This argues for the expiry time of a voucher to
   be rather long (decades), if not actually infinite.

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   [RFC8995] makes arguments for why a Pledge dos not need to have a
   clock that it can trust, because it can use a nonce to verify
   freshness of the resulting Voucher.  The Delegated Voucher can not
   use a nonce to verify the chain of delegated vouchers presented,
   although it can use a nonce for the last (non-delegated) voucher.

10.  IANA Considerations

   This document requires the following IANA actions:

10.1.  The IETF XML Registry

   This document registers a URI in the "IETF XML Registry" [RFC3688].
   IANA is asked to register the following:

        URI: urn:ietf:params:xml:ns:yang:ietf-voucher-delegated
        Registrant Contact: The ANIMA WG of the IETF.
        XML: N/A, the requested URI is an XML namespace.

10.2.  YANG Module Names Registry

   This document registers a YANG module in the "YANG Module Names"
   registry [RFC6020].  IANA is asked to register the following:

        name:         ietf-voucher-delegated
        namespace:    urn:ietf:params:xml:ns:yang:ietf-voucher-delegated
        prefix:       NONE
        reference:    THIS DOCUMENT

11.  Acknowledgements


12.  Changelog

13.  References

13.1.  Normative References

              Richardson, M., Stok, P. V. D., Kampanakis, P., and E.
              Dijk, "Constrained Bootstrapping Remote Secure Key
              Infrastructure (BRSKI)", Work in Progress, Internet-Draft,
              draft-ietf-anima-constrained-voucher-17, 7 April 2022,

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   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <>.

   [RFC8366]  Watsen, K., Richardson, M., Pritikin, M., and T. Eckert,
              "A Voucher Artifact for Bootstrapping Protocols",
              RFC 8366, DOI 10.17487/RFC8366, May 2018,

   [RFC8995]  Pritikin, M., Richardson, M., Eckert, T., Behringer, M.,
              and K. Watsen, "Bootstrapping Remote Secure Key
              Infrastructure (BRSKI)", RFC 8995, DOI 10.17487/RFC8995,
              May 2021, <>.

13.2.  Informative References

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              DOI 10.17487/RFC3688, January 2004,

   [RFC6020]  Bjorklund, M., Ed., "YANG - A Data Modeling Language for
              the Network Configuration Protocol (NETCONF)", RFC 6020,
              DOI 10.17487/RFC6020, October 2010,

   [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,

   [RFC8572]  Watsen, K., Farrer, I., and M. Abrahamsson, "Secure Zero
              Touch Provisioning (SZTP)", RFC 8572,
              DOI 10.17487/RFC8572, April 2019,

   [RFC8739]  Sheffer, Y., Lopez, D., Gonzalez de Dios, O., Pastor
              Perales, A., and T. Fossati, "Support for Short-Term,
              Automatically Renewed (STAR) Certificates in the Automated
              Certificate Management Environment (ACME)", RFC 8739,
              DOI 10.17487/RFC8739, March 2020,

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Appendix A.  Extra references

   RFC Editor, please remove this section.  This section lists
   references in the YANG.  [RFC8174], [RFC8040].

Authors' Addresses

   Michael Richardson
   Sandelman Software Works

   Wei Pan
   Huawei Technologies

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