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<rfc xmlns:xi="http://www.w3.org/2001/XInclude" ipr="trust200902" docName="draft-ietf-anima-brski-ae-13" number="9733" category="std" consensus="true" submissionType="IETF" tocInclude="true" sortRefs="true" symRefs="true"> symRefs="true" version="3" updates="" obsoletes="" xml:lang="en">

  <front>
    <title abbrev="BRSKI-AE">BRSKI-AE:

<!--[rfced] Please note that the title of the document has been updated as
follows. Abbreviations have been expanded per Section 3.6 of RFC 7322 ("RFC
Style Guide"). Please review and confirm that this is how you would like
"BRSKI-AE" to be expanded both in the title and throughout the rest of
this document.

Original:
BRSKI-AE: Alternative Enrollment Protocols in BRSKI</title> BRSKI

Current:
BRSKI-AE: Bootstrapping Remote Secure Key Infrastructure with Alternative Enrollment
-->

    <title abbrev="BRSKI-AE">BRSKI-AE: Bootstrapping Remote Secure Key Infrastructure with Alternative Enrollment</title>
    <seriesInfo name="RFC" value="9733"/>
    <author initials="D." surname="von&nbsp;Oheimb" surname="von Oheimb" fullname="David von&nbsp;Oheimb" von Oheimb" role="editor">
      <organization abbrev="Siemens">Siemens AG</organization>
      <address>
        <postal>
          <street>Otto-Hahn-Ring 6</street>
          <city>Munich</city>
          <code>81739</code>
          <country>Germany</country>
        </postal>
        <email>david.von.oheimb@siemens.com</email>
        <uri>https://www.siemens.com/</uri>
      </address>
    </author>
    <author initials="S." surname="Fries" fullname="Steffen Fries">
      <organization abbrev="Siemens">Siemens AG</organization>
      <address>
        <postal>
          <street>Otto-Hahn-Ring 6</street>
          <city>Munich</city>
          <code>81739</code>
          <country>Germany</country>
        </postal>
        <email>steffen.fries@siemens.com</email>
        <uri>https://www.siemens.com/</uri>
      </address>
    </author>
    <author initials="H." surname="Brockhaus" fullname="Hendrik Brockhaus">
      <organization abbrev="Siemens">Siemens AG</organization>
      <address>
        <postal>
          <street>Otto-Hahn-Ring 6</street>
          <city>Munich</city>
          <code>81739</code>
          <country>Germany</country>
        </postal>
        <email>hendrik.brockhaus@siemens.com</email>
        <uri>https://www.siemens.com/</uri>
      </address>
    </author>
    <date year="2024"/>

    <area>Operations and Management</area>
    <workgroup>ANIMA WG</workgroup>
    <keyword>Internet-Draft</keyword> year="2025" month="February"/>
    <area>OPS</area>
    <workgroup>anima</workgroup>

<!-- [rfced] Please insert any keywords (beyond those that appear in
the title) for use on https://www.rfc-editor.org/search. -->

<keyword>example</keyword>

    <abstract>

<?line 148?>
      <t>This document defines enhancements to the Bootstrapping Remote Secure
      Key Infrastructure (BRSKI) protocol, known as BRSKI-AE (Alternative Enrollment).<br /> BRSKI with Alternative
      Enrollment (BRSKI-AE).  BRSKI-AE extends BRSKI to support certificate
      enrollment mechanisms instead of the originally specified use of EST.
      Enrollment over Secure Transport (EST).  It supports certificate
      enrollment protocols, protocols such as CMP, the Certificate Management Protocol (CMP)
      that use authenticated self-contained signed objects for certification
      messages, allowing for flexibility in network device onboarding scenarios.<br />
      scenarios.  The enhancements address use cases where the existing
      enrollment mechanism may not be feasible or optimal, providing a
      framework for integrating suitable alternative enrollment protocols.<br /> protocols.
      This document also updates the BRSKI reference architecture to
      accommodate these alternative methods, ensuring secure and scalable
      deployment across a range of network environments.</t>
    </abstract>

    <note title="About This Document" removeInRFC="true">
      <t>
        Status information for this document may be found at <eref target="https://datatracker.ietf.org/doc/draft-ietf-anima-brski-ae/"/>.
      </t>
      <t>
        Discussion of this document takes place on the
        anima Working Group mailing list (<eref target="mailto:anima@ietf.org"/>),
        which is archived at <eref target="https://mailarchive.ietf.org/arch/browse/anima/"/>.
        Subscribe at <eref target="https://www.ietf.org/mailman/listinfo/anima/"/>.
      </t>
      <t>Source for this draft and an issue tracker can be found at
        <eref target="https://github.com/anima-wg/anima-brski-ae"/>.</t>
    </note>
  </front>

  <middle>

<?line 164?>
    <section anchor="introduction"><name>Introduction</name>

<t>BRSKI anchor="introduction">
      <name>Introduction</name>
      <t>Bootstrapping Remote Secure Key Infrastructure (BRSKI) <xref target="RFC8995"/> is typically used with Enrollment over Secure
      Transport
(EST, (EST) <xref target="RFC7030"/>) target="RFC7030"/> as the enrollment protocol for
      operator-specific device certificates, employing HTTP over TLS for
      secure message transfer.  BRSKI-AE is a variant using alternative
      enrollment protocols with authenticated self-contained objects for the
      device certificate enrollment.

<!--
This enhancement of BRSKI is named BRSKI-AE, where AE stands for
**A**lternative **E**nrollment.
(while originally it was used to abbreviate **A**synchronous **E**nrollment)
--></t>
-->
      </t>
      <t>This approach offers several distinct advantages.  It allows for the
      authentication of the origin of requests and responses independently of
      message transfer mechanisms.  This capability facilitates end-to-end
      authentication (i.e., end-to-end proof of origin) across multiple
      transport hops and supports the asynchronous operation of certificate
      enrollment. Consequently, this provides architectural flexibility in
      determining the location and timing for the ultimate authentication and
      authorization of certification requests, requests while ensuring that the
      integrity and authenticity of the enrollment messages
is are maintained with
      full cryptographic strength.</t>

      <t>This specification carries over the main characteristics of BRSKI,
      namely:</t>

<t><list style="symbols">
      <ul spacing="normal">
        <li>

<!-- [rfced] We have updated the text below to improve readability. Please
review to ensure these changes do not alter your intended meaning.

Original:
   It uses them to authenticate itself to the
   Manufacturer Authorized Signing Authority (MASA, [RFC8995]), and
   to the registrar, which is the access point of the target domain,
   and to possibly further components of the domain where it will be
   operated.

Current:
   It uses them to authenticate itself to the
   Manufacturer Authorized Signing Authority (MASA) [RFC8995] and the
   registrar (which is the access point of the target domain) and to
   possibly further components of the domain where it will be
   operated.
-->

          <t>The pledge is assumed to have received its Initial Device IDentifier
(IDevID,
          Identifier (IDevID) <xref target="IEEE_802.1AR-2018"/>) target="IEEE_802.1AR-2018"/> credentials
          during its manufacturing.  It uses them to authenticate itself to
          the Manufacturer Authorized Signing Authority (MASA, (MASA) <xref target="RFC8995"/>),
          target="RFC8995"/> and to the registrar, which registrar (which is the access point
          of the target domain, domain) and to possibly further components of the
          domain where it will be operated.</t>
        </li>
        <li>
          <t>The pledge first obtains via the voucher exchange <xref
          target="RFC8366"/> exchange a trust anchor for authenticating entities in the
          domain such as the domain registrar.</t>
        </li>
        <li>
          <t>The pledge then obtains its
Locally significant Local Device IDentifier (IDevID, Identifier
          (LDevID) <xref target="IEEE_802.1AR-2018"/>). target="IEEE_802.1AR-2018"/>.  To this end, the
          pledge generates a private key, called LDevID secret,
and an "LDevID secret". Then, it
          requests via the domain registrar from the PKI of its new domain a
          domain-specific device certificate, called LDevID certificate. an "LDevID certificate".
          On success, it receives the LDevID certificate along with its
          certificate chain.</t>
</list></t>
        </li>
      </ul>
      <t>The objectives of BRSKI-AE are to enhance BRSKI by enabling LDevID
      certificate enrollment through the use of an alternative protocol to EST
      that:</t>

<t><list style="symbols">
  <t>Supports
      <ul spacing="normal">
        <li>
          <t>supports end-to-end authentication over multiple transport hops.</t>
  <t>Facilitates hops and</t>
        </li>
        <li>
          <t>facilitates secure message exchange exchanges over any type of transfer
          mechanism, including asynchronous delivery.</t>
</list></t>
        </li>
      </ul>

      <!--- not really: and
* defining a certificate waiting indication and handling, for the case that the
  certifying component is (temporarily) not available.
-->

      <t>It may be observed that the BRSKI voucher exchange between the
      pledge, registrar, and MASA involves the use of authenticated
      self-contained objects, which inherently possess these properties.</t>

      <t>The existing well-known URI structure used for BRSKI and EST messages
      is extended by introducing an additional path element that specifies the
      enrollment protocol being employed.</t>

      <t>This specification allows the registrar to offer multiple enrollment
      protocols, enabling pledges and their developers to select the most
      appropriate one based on the defined overall approach and specific
      endpoints.</t>

      <t>It may be important to note that BRSKI (RFC 8995) <xref target="RFC8995"/>
      specifies the use of HTTP over TLS, but variations such as Constrained
      BRSKI <xref target="I-D.ietf-anima-constrained-voucher"/> target="I-D.ietf-anima-constrained-voucher"/>, which uses CoAP
      the Constrained Application Protocol (CoAP) over DTLS, are possible as well. In this context,
'HTTP' "HTTP" and 'TLS' "TLS"
      are used as references to the most common implementation, though
      variants using CoAP and/or DTLS are implied where applicable, as the
      distinctions are not pertinent here.</t>

      <t>This specification, together with its referenced documents, is
      sufficient to support BRSKI with the Certificate Management Protocol (CMP,
      (CMP) <xref target="RFC9480"/>) target="RFC9480"/> as profiled in the Lightweight CMP
      Profile (LCMPP, (LCMPP) <xref target="RFC9483"/>). target="RFC9483"/>.  Integrating BRSKI with an
      enrollment protocol or profile other than LCMPP will necessitate
      additional IANA registrations, as detailed in this document.
      Furthermore, additional specifications may be required for the details
      of the protocol or profile, which fall outside the scope of this
      document.</t>

      <section anchor="sup-env"><name>Supported anchor="sup-env">
        <name>Supported Scenarios</name>
        <t>BRSKI-AE is designed for use in scenarios such as the following:</t>

<t><list style="symbols">
  <t>Pledges
        <ul spacing="normal">
          <li>
            <t>When pledges and/or the target domain leverage an existing
            certificate enrollment protocol other than EST, such as CMP.</t>
  <t>The
          </li>
          <li>
            <t>When the application context precludes the use of EST for
            certificate enrollment due to factors such as:  <list style="symbols"> as when:</t>
            <ul spacing="normal">
              <li>
                <t>The Registration Authority (RA) is not co-located with the
                registrar and requires end-to-end authentication of
                requesters, which EST does not support over multiple transport
                hops.</t>
              </li>
              <li>
                <t>The RA or Certification Authority (CA) operator mandates
                auditable proof of origin for Certificate Signing Requests
                (CSRs), which cannot be provided by TLS as it only offers
                transient source authentication.</t>
              </li>
              <li>
                <t>Certificates are requested for key types, such as Key
                Encapsulation Mechanism (KEM) keys, that do not support
                signing or other single-shot proof-of-possession methods, methods as
                those described in <xref target="RFC6955"/>.  EST, which
                relies on CSRs in PKCS #10 format <xref target="RFC2986"/> format, target="RFC2986"/>,
                does not accommodate these key types because it necessitates
                proof-of-possession methods that operate within a single
                message, whereas proof of possession for KEM keys requires
                prior receipt of a fresh challenge value.</t>
              </li>
              <li>
                <t>The pledge implementation employs security libraries that
                do not support EST or uses a TLS library lacking support for
                the "tls-unique" value <xref target="RFC5929"/>, which EST
                requires for the strong binding of source authentication.</t>
    </list></t>
  <t>Full
              </li>
            </ul>
          </li>
          <li>
            <t>When full RA functionality is not available on-site within the
            target domain, and connectivity to an off-site RA may be
            intermittent or entirely offline.
<!-- in the latter case a message store-and-forward mechanism is needed. --></t>
  <t>Authoritative -->
            </t>
          </li>
          <li>
            <t>When authoritative actions by a local RA at the registrar are
            insufficient for fully and reliably authorizing pledge
            certification requests, potentially due to a lack of access to
            necessary data or inadequate security measures, such as the local
            storage of private keys.
<!-- Final authorization then is done by a RA residing in the backend. --></t>
</list></t> -->
            </t>
          </li>
        </ul>
        <t>Bootstrapping may be managed in various ways depending on the
        application domain.  <xref target="app-examples"/> provides
        illustrative examples from different industrial control system
        environments and operational contexts that motivate the support of
        alternative enrollment protocols.</t>
      </section>
    </section>

    <section anchor="terminology"><name>Terminology anchor="terminology">
      <name>Terminology and abbreviations</name>

<t>The Abbreviations</name>
            <t>
    The key words "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>",
    "<bcp14>REQUIRED</bcp14>", "<bcp14>SHALL</bcp14>", "<bcp14>SHALL NOT</bcp14>",
    "<bcp14>SHOULD</bcp14>", "<bcp14>SHOULD NOT</bcp14>",
    "<bcp14>RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>",
    "<bcp14>MAY</bcp14>", and "<bcp14>OPTIONAL</bcp14>" in this document are to be
    interpreted as described in BCP 14 BCP&nbsp;14 <xref target="RFC2119"/> <xref
    target="RFC8174"/> when, and only when, they appear in all capitals, as
    shown here.</t>

<?line -18?> here.
        </t>

	<t>This document relies on the terminology defined in <xref
	target="RFC8995"/>, <xref target="RFC5280"/>, and <xref
	target="IEEE_802.1AR-2018"/>, which is partly repeated here.
Also several Several
	further terms are also described here.</t>

	<t>To be independent of the terminology of a specific enrollment
	protocol, this document utilizes generic terminology regarding PKI
	management operations.</t>

<dl>

<!-- [rfced] Please review the following questions and changes regarding the
terminology list in Section 2:

a.) FYI - We have updated some list items to have a 1:1 relationship between
abbreviation and expansion. Please carefully review these changes and let us
know of any objections.

b.) As this list contains a mixture of definitions and abbreviations, may we
separate these items into two separate lists for readability?

c.) We note that several abbreviations appear in this document that are not
included in the terminology list in Section 2 (see some examples
below). Please review and let us know if these or any other terms should be
added.

(Note that we have already added a list item for Certification Authority (CA)
as this abbreviation appears in other definitions in this list.)

Key Encapsulation Mechanism (KEM)
Certificate Request Message Format (CRMF)
Simple Certificate Enrolment Protocol (SCEP)
Certificate Management over CMS (CMC)
Autonomic Control Plane (ACP)
-->

      <dl newline="false" spacing="normal">

        <dt>asynchronous:</dt>
  <dd>
    <t>time-wise
        <dd>the time-wise interrupted delivery of messages,<br />
here messages, here, between a
        pledge and some backend system (e.g., an RA)</t>
  </dd> RA).</dd>

        <dt>attribute request:</dt>
  <dd>
    <t>message
        <dd>a message requesting content to be included in the certification request</t>
  </dd> request.</dd>

        <dt>attribute response:</dt>
  <dd>
    <t>message
        <dd>a message providing the answer to the attribute request</t>
  </dd> request.</dd>

        <dt>authenticated self-contained object:</dt>
  <dd>
    <t>a
        <dd>a data structure that is cryptographically bound to the identity
        of its originator by an attached digital signature on the actual
        object, using a private key of the originator such as the IDevID secret.</t>
  </dd>
        secret.</dd>

        <dt>backend:</dt>
  <dd>
    <t>placement
        <dd>the placement of a domain component separately from the domain
        registrar; it may be on-site or off-site</t>
  </dd> off-site.</dd>

        <dt>BRSKI:</dt>
  <dd>
    <t>Bootstrapping
        <dd>Bootstrapping Remote Secure Key Infrastructure <xref target="RFC8995"/></t>
  </dd> target="RFC8995"/></dd>

        <dt>BRSKI-AE:</dt>
  <dd>
    <t>BRSKI
	<dd>BRSKI with <strong>A</strong>lternative <strong>E</strong>nrollment, Alternative Enrollment. Refers to a
        variation of BRSKI <xref target="RFC8995"/> in which BRSKI-EST, the
        enrollment protocol between the pledge and the registrar, is replaced
        by enrollment protocols that support end-to-end authentication of the
        pledge to the RA, such as Lightweight CMP (see LCMPP).</t>
  </dd> LCMPP).</dd>

	<dt>CA:</dt>
	<dd>Certification Authority</dd>

        <dt>CA certs request:</dt>
  <dd>
    <t>message
	<dd>a message requesting CA certificates</t>
  </dd> certificates.</dd>

        <dt>CA certs response:</dt>
  <dd>
    <t>message
	<dd>a message providing the answer to a CA certs request</t>
  </dd> request.</dd>

        <dt>certificate confirm:</dt>
  <dd>
    <t>message
	<dd>a message stating to the backend PKI that the requester of a
	certificate received the new certificate and accepted it</t>
  </dd> it.</dd>

        <dt>certification request:</dt>
  <dd>
    <t>message
	<dd>a message requesting a certificate with proof of identity</t>
  </dd> identity.</dd>

        <dt>certification response:</dt>
  <dd>
    <t>message
	<dd>a message providing the answer to a certification request</t>
  </dd> request.</dd>

        <dt>CMP:</dt>
  <dd>
    <t>Certificate
	<dd>Certificate Management Protocol <xref target="RFC4210"/> <xref target="RFC9480"/></t>
  </dd> target="RFC9480"/></dd>

        <dt>CSR:</dt>
  <dd>
    <t>Certificate
	<dd>Certificate Signing Request</t>
  </dd> Request</dd>

        <dt>EST:</dt>
  <dd>
    <t>Enrollment
	<dd>Enrollment over Secure Transport <xref target="RFC7030"/></t>
  </dd> target="RFC7030"/></dd>

        <dt>IDevID:</dt>
  <dd>
    <t>Initial
	<dd>Initial Device IDentifier of Identifier (of a pledge, provided by
        the manufacturer and comprising of a private key and the related X.509
        certificate with its chain</t>
  </dd> chain).</dd>

        <dt>LCMPP:</dt>
  <dd>
    <t>Lightweight
        <dd>Lightweight CMP Profile <xref target="RFC9483"/></t>
  </dd> target="RFC9483"/></dd>

        <dt>LDevID:</dt>
  <dd>
    <t>Locally significant
	<dd>Local Device IDentifier of Identifier (of a pledge, provided by
	its target domain and comprising of a private key and the related X.509
	certificate with its chain</t>
  </dd>
  <dt>local RA (LRA):</dt>
  <dd>
    <t>a chain).</dd>

        <dt>LRA:</dt>
        <dd>Local Registration Authority. A subordinate RA that is close to
        entities being enrolled and separate from a subsequent RA.  In BRSKI-AE
        BRSKI-AE, it is needed if a backend RA is used,
and used; in this case, the LRA
        is co-located with the registrar.</t>
  </dd> registrar.</dd>

        <dt>MASA:</dt>
  <dd>
    <t>Manufacturer
        <dd>Manufacturer Authorized Signing Authority, provides vouchers</t>
  </dd> Authority. Provides vouchers.</dd>

        <dt>off-site:</dt>
  <dd>
    <t>locality
	<dd>the locality of component or service a component, service, or functionality, such functionality (such as RA
	or CA, CA) that is not at the site of the registrar.  This may be a
	central site or a cloud service, to which connection may be intermittent.</t>
  </dd>
	intermittent.</dd>

        <dt>on-site:</dt>
  <dd>
    <t>locality
        <dd>the locality of a component or service component, service, or functionality at the site of
        the registrar</t>
  </dd> registrar.</dd>

        <dt>PKI/registrar confirm:</dt>
  <dd>
    <t>acknowledgment
        <dd>an acknowledgment of the PKI on the certificate confirm</t>
  </dd> confirm.</dd>

        <dt>pledge:</dt>
  <dd>
    <t>device
        <dd>a device that is to be bootstrapped into a target domain.  It
        requests an LDevID using IDevID credentials installed by its manufacturer.</t>
  </dd>
        manufacturer.</dd>

        <dt>RA:</dt>
  <dd>
    <t>Registration Authority, the
        <dd>Registration Authority. The PKI component to which a CA typically
        delegates certificate management functions such as authenticating
        pledges and performing authorization checks on certification requests</t>
  </dd>
        requests.</dd>

        <dt>registrar:</dt>
  <dd>
    <t>short
        <dd>short for domain registrar</t>
  </dd> registrar.</dd>

        <dt>site:</dt>
  <dd>
    <t>the
        <dd>the locality where an entity, entity such as a pledge, registrar, or PKI
        component is deployed.  The target domain may have multiple sites.</t>
  </dd> sites.</dd>

        <dt>synchronous:</dt>
  <dd>
    <t>time-wise
        <dd>the time-wise uninterrupted delivery of messages,
here here, between a
        pledge and a registrar or backend system (e.g., the MASA)</t>
  </dd> MASA).</dd>

        <dt>target domain:</dt>
  <dd>
    <t>the
        <dd>the domain that a pledge is going to be bootstrapped into</t>
  </dd> into.</dd>
      </dl>
    </section>

    <section anchor="req-sol"><name>Basic anchor="req-sol">
      <name>Basic Requirements and Mapping to Solutions</name>
      <t>Based on the intended target scenarios described in <xref
      target="sup-env"/> and the application examples described in <xref
      target="app-examples"/>, the following requirements are derived to
      support authenticated self-contained objects as containers carrying
      certification requests.</t>
      <t>The following properties are required for a certification request:</t>

<t><list style="symbols">
      <ul spacing="normal">
        <li>
          <t>Proof of possession: demonstrates access to the private key
          corresponding to the public key contained in a certification
          request.  This is typically achieved by a self-signature using the
          corresponding private key but can also be achieved indirectly, indirectly; see
          <xref section="4.3" sectionFormat="comma" target="RFC4210"/>.</t>
        </li>
        <li>
          <t>Proof of identity, also identity (also called proof "proof of origin: origin"): provides data
          origin authentication of the certification request.  Typically, this
          is achieved by a signature using the pledge IDevID secret over some
          data, which needs to include a sufficiently strong identifier of the
          pledge, such as the device serial number typically included in the
          subject of the IDevID certificate.</t>
</list></t>
        </li>
      </ul>
      <t>The remainder of this section gives a non-exhaustive list of solution
      examples, based on existing technology described in IETF documents.</t>

      <section anchor="solutions-PoP"><name>Solution anchor="solutions-PoP">
        <name>Solution Options for Proof of Possession</name>
        <t>Certificate signing request Signing Request (CSR) objects: CSRs objects are data structures
        protecting only the integrity of the contained data and providing
        proof of possession for a (locally generated) private key.  Important
        types of CSR data structures are:</t>

<t><list style="symbols">
  <t>PKCS
        <ul spacing="normal">
            <li>PKCS #10 <xref target="RFC2986"/>. target="RFC2986"/>: This very common form of
            CSR is self-signed to protect its integrity and to prove
            possession of the private key that corresponds to the public key
            included in the request.</t>
  <t>Certificate request.</li>
            <li>Certificate Request Message Format (CRMF, (CRMF) <xref target="RFC4211"/>).
            target="RFC4211"/>: This less common but more general CSR format
            supports several ways of integrity protection and proof of
            possession.  Typically a self-signature is used, which is
            generated over (part of) the structure with the private key
            corresponding to the included public key.  CRMF also supports
            further proof-of-possession methods for types of keys that do not
            have signing capability. For details details, see <xref section="4"
            sectionFormat="comma" target="RFC4211"/>.</t>
</list></t> target="RFC4211"/>.</li>
        </ul>
        <t>It should be noted that the integrity protection of CSRs includes
        the public key because it is part of the data signed by the
        corresponding private key.
  Yet  Yet, this signature does not provide data
        origin authentication, i.e., (i.e., proof of identity of the requester requester)
        because the key pair involved is new and therefore does not yet have a
        confirmed identity associated with it.
  <!-- already covered by the next paragraph:
  This extra property can be
  achieved by an additional binding to the IDevID of the pledge.
  This binding to the source authentication supports the
  authorization decision of the certification request.
  --></t>
  -->
        </t>
      </section>
      <section anchor="solutions-PoI"><name>Solution anchor="solutions-PoI">
        <name>Solution Options for Proof of Identity</name>

<t>Binding

<!-- [rfced] May we clarify the content in the parenthetical text below?

Original:
   Binding a certificate signing request (CSR) to an existing
   authenticated credential (the BRSKI context, the IDevID certificate)
   enables proof of origin...

Perhaps:
   Binding a Certificate Signing Request (CSR) to an existing
   authenticated credential (such as the BRSKI context or the IDevID certificate)
   enables proof of origin...
-->

<t>Binding a Certificate Signing Request (CSR) to an existing
        authenticated credential (the BRSKI context, the IDevID certificate)
        enables proof of origin, which in turn supports an authorization
        decision on the CSR.</t>
        <t>The binding of data origin authentication to the CSR is typically
        delegated to the protocol used for certificate management.  This
        binding may be achieved through security options in an underlying
        transport protocol such as TLS if the authorization of the
        certification request is (sufficiently) done at the next communication
        hop.  Depending on the key type, the binding can also be done in a
        stronger, transport-independent way by wrapping the CSR with a
        signature.</t>
        <t>This requirement is addressed by existing enrollment protocols in
        various ways, such as:</t>

<t><list style="symbols">
        <ul spacing="normal">
          <li>
            <t>EST <xref target="RFC7030"/>, also target="RFC7030"/> and its variant EST-coaps <xref target="RFC9148"/>,
utilizes
            target="RFC9148"/> utilize PKCS #10 to encode Certificate Signing Requests (CSRs). CSRs.  While such
            a CSR has not been designed to include proof of origin, there is a
            limited, indirect way of binding it to the source authentication
            of the underlying TLS session.  This is achieved by including in
            the CSR the tls-unique value <xref target="RFC5929"/> resulting
            from the TLS handshake.  As this is optionally supported by the
            EST <spanx style="verb">"/simpleenroll"</spanx> <tt>"/simpleenroll"</tt> endpoint used in BRSKI BRSKI, and the TLS
            handshake employed in BRSKI includes certificate-based client
            authentication of the pledge with its IDevID credentials, the
            proof of pledge identity being an authenticated TLS client can be
            bound to the CSR.  <vspace blankLines='1'/>
Yet CSR.</t>

<!-- [rfced] FYI - For ease of the reader, we have broken up the following
sentences below into two. Please let us know any objections.

Original:
   What the registrar needs to do is to authenticate and pre-authorize the
   pledge and to indicate this to the (second) RA by signing the forwarded
   certification request with its private key and a related certificate
   that has the id-kp- cmcRA extended key usage attribute.
   ...
   It will recognize whether the protocol
   it uses and the specific request it wants to perform are understood
   and supported by the domain registrar by sending the request to the
   respective endpoint according to the above addressing scheme and then
   evaluating the HTTP status code of the response.

Current:
   What the registrar needs to do is authenticate and pre-authorize the
   pledge and indicate this to the (second) RA.  This is done by signing the
   forwarded certification request with its private key and a related certificate
   that has the id-kp-cmcRA extended key usage attribute.
   ...
   It will recognize whether the protocol
   it uses and the specific request it wants to perform are understood
   and supported by the domain registrar.  This is done by sending the
   request to the respective endpoint according to the above addressing
   scheme and then evaluating the HTTP status code of the response.
-->

<t>Yet, this binding is only valid in the context of the TLS
            session established with the registrar acting as the EST server
            and typically also as an RA.  So even such a cryptographic binding
            of the authenticated pledge identity to the CSR is not visible nor
            verifiable to authorization points outside the registrar, such as
            a (second) RA in the backend.  What the registrar needs to do is to
            authenticate and pre-authorize the pledge and to indicate this to the
            (second) RA RA. This is done by signing the forwarded certification
            request with its private key and a related certificate that has
            the id-kp-cmcRA extended key usage attribute.  <vspace blankLines='1'/>
<xref attribute.</t>

<!--[rfced] To avoid the awkward hyphenation of "PKCS #10-formatted CSRs",
may we update the text as follows?

Original:
   [RFC7030], Section 2.5 sketches wrapping PKCS #10-formatted CSRs
   with a Full PKI Request message sent to the "/fullcmc" endpoint.

Perhaps:
   [RFC7030], Section 2.5 sketches wrapping CSRs formatted per PKCS #10
   with a Full PKI Request message sent to the "/fullcmc" endpoint.
-->

            <t><xref section="2.5" sectionFormat="comma" target="RFC7030"/>
            sketches wrapping PKCS #10-formatted CSRs with a Full PKI Request
            message sent to the <spanx style="verb">"/fullcmc"</spanx> <tt>"/fullcmc"</tt> endpoint.  This would
            allow for source authentication at the message level, such that
            the registrar could forward it to external RAs in a meaningful
            way.  This approach is so far not sufficiently described and
            likely has not been implemented.</t>
</list></t>
          </li>

        <!--
Note that, besides the existing enrollment protocols, there is
ongoing work in the ACE WG to define an encapsulation of EST messages
in OSCORE, which will result in a TLS-independent way of protecting EST.
This approach {{draft.selander-ace-coap-est-oscore}}
may be considered as a further variant.
-->

<t><list style="symbols">
  <t>SCEP

          <li>
            <t>The Simple Certificate Enrolment Protocol (SCEP) <xref
            target="RFC8894"/> supports using a shared secret (passphrase) or
            an existing certificate to protect CSRs based on SCEP Secure
            Message Objects using CMS Cryptographic Message Syntax (CMS) wrapping
(<xref target="RFC5652"/>). <xref target="RFC5652"/>. Note
            that the wrapping using an existing IDevID in SCEP is referred to
            as 'renewal'. "renewal".  This way way, SCEP does not rely on the security of the
            underlying message transfer.</t>
          </li>
          <li>
            <t>CMP <xref target="RFC4210"/> <xref target="RFC9480"/> supports
            using a shared secret (passphrase) or an existing certificate,
            which may be an IDevID credential, to authenticate certification
            requests via the PKIProtection structure in a PKIMessage.  The
            certification request is typically encoded utilizing CRMF, while
            PKCS #10 is supported as an alternative.  Thus, CMP does not rely
            on the security of the underlying message transfer.</t>
  <t>CMC
          </li>

<!-- [rfced] We note the use of "FullCMCRequest" in the following sentence;
however, RFC 7030 uses the term "Full CMC Request". May we update this instance for consistency with RFC 7030?

Original:
   The proof of identity can be provided as part of a FullCMCRequest, based on
   CMS [RFC5652] and signed with an existing IDevID secret.

Perhaps:
   The proof of identity can be provided as part of a Full CMC Request based on
   CMS [RFC5652] and signed with an existing IDevID secret.
-->

          <li>
            <t>Certificate Management over CMS (CMC) <xref target="RFC5272"/>
            also supports utilizing a shared secret (passphrase) or an
            existing certificate to protect certification requests, which can
            be either in a CRMF or PKCS #10 structure.  The proof of identity
            can be provided as part of a FullCMCRequest, FullCMCRequest based on CMS <xref
            target="RFC5652"/> and signed with an existing IDevID secret.
            Thus, CMC does not rely on the security of the underlying message
            transfer.</t>
</list></t>
          </li>
        </ul>
        <t>To sum up, EST does not meet the requirements for authenticated
        self-contained objects, but SCEP, CMP, and CMC do. This document
        primarily focuses on CMP as it has more industry adoption than CMC and
        SCEP has issues not detailed here.</t>
      </section>
    </section>

    <section anchor="uc1"><name>Adaptations anchor="uc1">
      <name>Adaptations to BRSKI</name>
      <t>To enable using alternative certificate enrollment protocols
      supporting end-to-end authentication, asynchronous enrollment, and more
      general system architectures, BRSKI-AE provides some generalizations on
      BRSKI <xref target="RFC8995"/>.  This way, authenticated self-contained
      objects such as those described in <xref target="req-sol"/> above can be
      used for certificate enrollment, and RA functionality can be deployed
      freely in the target domain.  Parts of the RA functionality can even be
      distributed over several nodes.</t>
      <t>The enhancements are kept to a minimum to ensure the reuse of already
      defined architecture elements and interactions.  In general, the
      communication follows the BRSKI model and utilizes the existing BRSKI
      architecture elements.  In particular, the pledge initiates
      communication with the domain registrar and interacts with the MASA as
      usual for voucher request and response processing.</t>

      <section anchor="architecture"><name>Architecture</name> anchor="architecture">
        <name>Architecture</name>
        <t>The key element of BRSKI-AE is that the authorization of a
        certification request <bcp14>MUST</bcp14> be performed based on an
        authenticated self-contained object.  The certification request is
        bound in a self-contained way to a proof of origin based on the IDevID
        credentials.  Consequently, the certification request
        <bcp14>MAY</bcp14> be transferred using any mechanism or
        protocol. Authentication and authorization of the certification
        request can be done by the domain registrar and/or by backend domain
        components.  As mentioned in <xref target="sup-env"/>, these
        components may be offline or off-site.  The registrar and other
        on-site domain components may have no or only temporary (intermittent)
        connectivity to them.</t>
        <t>This leads to generalizations in the placement and enhancements of
        the logical elements as shown in <xref target="uc1figure"/>.</t>
        <figure title="Architecture anchor="uc1figure">

          <name>Architecture Overview Using Backend PKI Components" anchor="uc1figure"><artset><artwork Components</name>
          <artset>
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                <g class="text">
                  <text x="184" y="52">Drop-Ship</text>
                  <text x="372" y="52">Vendor</text>
                  <text x="432" y="52">Service</text>
                  <text x="352" y="84">M</text>
                  <text x="408" y="84">anufacturer</text>
                  <text x="352" y="100">A</text>
                  <text x="400" y="100">uthorized</text>
                  <text x="496" y="100">Ownership</text>
                  <text x="352" y="116">S</text>
                  <text x="388" y="116">igning</text>
                  <text x="488" y="116">Tracker</text>
                  <text x="352" y="132">A</text>
                  <text x="396" y="132">uthority</text>
                  <text x="508" y="196">BRSKI-</text>
                  <text x="288" y="212">.........................................</text>
                  <text x="500" y="212">MASA</text>
                  <text x="128" y="228">.</text>
                  <text x="448" y="228">.</text>
                  <text x="128" y="244">.</text>
                  <text x="448" y="244">.</text>
                  <text x="44" y="260">Pledge</text>
                  <text x="128" y="260">.</text>
                  <text x="180" y="260">Join</text>
                  <text x="340" y="260">Domain</text>
                  <text x="184" y="276">Proxy</text>
                  <text x="352" y="276">Registrar</text>
                  <text x="448" y="276">.</text>
                  <text x="128" y="292">.</text>
                  <text x="324" y="292">w/</text>
                  <text x="352" y="292">LRA</text>
                  <text x="380" y="292">or</text>
                  <text x="404" y="292">RA</text>
                  <text x="448" y="292">.</text>
                  <text x="44" y="308">IDevID</text>
                  <text x="128" y="308">.</text>
                  <text x="448" y="308">.</text>
                  <text x="140" y="324">BRSKI-AE</text>
                  <text x="196" y="324">over</text>
                  <text x="232" y="324">TLS</text>
                  <text x="448" y="324">.</text>
                  <text x="132" y="340">using,</text>
                  <text x="184" y="340">e.g.,</text>
                  <text x="232" y="340">LCMPP</text>
                  <text x="448" y="340">.</text>
                  <text x="128" y="356">.</text>
                  <text x="448" y="356">.</text>
                  <text x="248" y="372">...............................</text>
                  <text x="416" y="372">.........</text>
                  <text x="128" y="388">on-site</text>
                  <text x="192" y="388">(local)</text>
                  <text x="252" y="388">domain</text>
                  <text x="324" y="388">components</text>
                  <text x="408" y="420">e.g.,</text>
                  <text x="456" y="420">LCMPP</text>
                  <text x="192" y="452">.............................................</text>
                  <text x="440" y="452">...............</text>
                  <text x="16" y="468">.</text>
                  <text x="68" y="468">Public-Key</text>
                  <text x="172" y="468">Infrastructure</text>
                  <text x="496" y="468">.</text>
                  <text x="16" y="484">.</text>
                  <text x="496" y="484">.</text>
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                  <text x="16" y="516">.</text>
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                </g>
              </svg>
</artwork><artwork
            </artwork>
            <artwork type="ascii-art" align="left"><![CDATA[
                                         +------------------------+
   +--------------Drop-Ship--------------| Vendor Service         |
   |                                     +------------------------+
   |                                     | M anufacturer|         |
   |                                     | A uthorized  |Ownership|
   |                                     | S igning     |Tracker  |
   |                                     | A uthority   |         |
   |                                     +--------------+---------+
   |                                                      ^
   |                                                      |
   V                                                      | BRSKI-
+--------+     .........................................  | MASA
|        |     .                                       .  |
|        |     .  +-------+          +--------------+  .  |
| Pledge |     .  | Join  |          | Domain       |<----+
|        |<------>| Proxy |<-------->| Registrar    |  .
|        |     .  |       |          | w/ LRA or RA |  .
| IDevID |     .  +-------+          +--------------+  .
|        |   BRSKI-AE over TLS                ^        .
+--------+   using, e.g., LCMPP               |        .
               .                              |        .
               ...............................|.........
            on-site (local) domain components |
                                              |
                                              | e.g., LCMPP
                                              |
 .............................................|...............
 . Public-Key Infrastructure                  v              .
 . +---------+     +---------------------------------------+ .
 . |         |<----+   Registration Authority RA           | .
 . |    CA   +---->|   (unless part of Domain Registrar)   | .
 . +---------+     +---------------------------------------+ .
 .............................................................
         backend (central or off-site) domain components
]]></artwork></artset></figure>
]]></artwork>
          </artset>
        </figure>

        <t>The architecture overview in <xref target="uc1figure"/> has the
        same logical elements as BRSKI, BRSKI but with a more flexible placement of
        the authentication and authorization checks on certification requests.
        Depending on the application scenario, the registrar
        <bcp14>MAY</bcp14> still do all of these checks (as is the case in BRSKI),
        BRSKI) or only do part of them.</t>
        <t>The following list describes the on-site components in the target
        domain of the pledge shown in <xref target="uc1figure"/>.</t>

<t><list style="symbols">
        <ul spacing="normal">
          <li>
            <t>Join Proxy: This has the same requirements as in BRSKI, see BRSKI (see
            <xref section="4" sectionFormat="comma" target="RFC8995"/></t> target="RFC8995"/>).</t>
          </li>

          <li>
            <t>Domain Registrar including (including LRA or RA functionality: in functionality): In
            BRSKI-AE, the domain registrar has mostly the same functionality
            as in BRSKI, namely to act as the gatekeeper of the domain for
            onboarding new devices and to facilitate the communication of
            pledges with their MASA and the domain PKI.
Yet  Yet, there are some
            generalizations and specific requirements:  <list style="numbers"> requirements:</t>
            <ol spacing="normal" type="1"><li>
            <t>The registrar <bcp14>MUST</bcp14> support at least one
            certificate enrollment protocol with authenticated self-contained
            objects for certification requests.  To this end, the URI scheme
            for addressing endpoints at the registrar is generalized (see
            <xref target="addressing"/>).</t>
              </li>
              <li>
		<t>Rather than having full RA functionality, the registrar
		<bcp14>MAY</bcp14> act as a local registration authority Local Registration Authority (LRA)
		and delegate part of its involvement in certificate enrollment
		to a backend RA.  In such scenarios, the registrar optionally
		checks certification requests it receives from pledges and
		forwards them to the backend RA, which performs the remaining
		parts of the enrollment request validation and authorization.
		Note that to this end end, the backend RA may need information
		regarding the authorization of pledges from the registrar or
		from other sources.  On the way back, the registrar forwards
		responses by the PKI to the pledge on the same channel.      <vspace blankLines='1'/>
To channel.</t>
                <t>To support end-to-end authentication of the pledge across
                the registrar to the backend RA, the certification request
                signed by the pledge needs to be upheld and forwarded by the
                registrar.  Therefore, the registrar cannot use for its communication with the PKI PKI, the
                registrar cannot use an enrollment protocol that is different
                from the enrollment protocol used between the pledge and the
                registrar.</t>
              </li>
              <li>
                <t>The use of a certificate enrollment protocol with
                authenticated self-contained objects gives freedom with how to
                transfer enrollment messages between the pledge and an RA.
                BRSKI demands that the RA accept certification requests for
                LDevIDs only with the consent of the registrar.  BRSKI-AE also
                guarantees this also in the case that the RA is not part of the
                registrar, even if the message exchange with backend systems
                is unprotected and involves further transport hops.  See <xref
                target="sec-consider"/> for details on how this can be
                achieved.</t>
    </list></t>
</list></t>
              </li>
            </ol>
          </li>
        </ul>
        <!-- is already covered by paragraph a little further below:
     Note:
     As far as (at least part of) the certificate enrollment traffic is routed
     via the registrar, BRSKI-AE re-uses during the certificate enrollment phase
     the channel that has been established in the BRSKI steps before between the
     pledge and the registrar.  Consequently, tunneling via this channel needs
     to be supported by the certificate enrollment protocol.
     By default, this channel is based on HTTP over TLS,
     but it may also be based on, for instance, CoAP over DTLS
     in the context of Constrained BRSKI {{I-D.ietf-anima-constrained-voucher}}.
-->
<!--
     In the latter scenario,
     the EST-specific parts of that specification do not apply.
-->

       <t>Despite the above generalizations to of the enrollment phase, the final
       step of BRSKI, namely the enrollment status telemetry, is kept as it
       is.</t>

        <t>The following list describes the components provided by the vendor
        or manufacturer outside the target domain.</t>

<t><list style="symbols">
        <ul spacing="normal">
          <li>
            <t>MASA: This has the functionality as described in BRSKI <xref
            target="RFC8995"/>.  The voucher exchange with the MASA via the
            domain registrar is performed as described in BRSKI.  <vspace blankLines='1'/> BRSKI.</t>

<!-- [rfced] In the sentence below, may we update "follows" for clarity?

Original:
      Note: From the definition of the interaction with the MASA in
      [RFC8995], Section 5 follows that it may be synchronous (using
      voucher request with nonces) or asynchronous (using nonceless
      voucher requests).

Perhaps:
      Note: From the definition of the interaction with the MASA in
      Section 5 of [RFC8995], it may be synchronous (using
      voucher requests with nonces) or asynchronous (using nonceless
      voucher requests).
-->

            <t>Note: From the definition of the interaction with the MASA in
            <xref section="5" sectionFormat="comma" target="RFC8995"/> follows
            that it may be synchronous (using voucher
request requests with nonces) or
            asynchronous (using nonceless voucher requests).</t>
          </li>
          <li>
            <t>Ownership tracker: Tracker: This is as defined in BRSKI.</t>
</list></t>
          </li>
        </ul>
        <t>The following list describes backend target domain components,
        which may be located on-site or off-site in the target domain.</t>

<t><list style="symbols">
        <ul spacing="normal">

<!-- [rfced] How may we clarify what "as not already done" and "it" refer to
in the text below?

Original:
   *  RA: performs centralized certificate management functions as a
      public-key infrastructure for the domain operator.  As far as not
      already done by the domain registrar, it performs the final
      validation and authorization of certification requests.

Perhaps:
   *  RA: This performs centralized certificate management functions as a
      public-key infrastructure for the domain operator.  As far as what is
      not already done by the domain registrar, the RA performs the final
      validation and authorization of certification requests.
-->

<!-- [rfced] Throughout this document, we note that RFCs 8895 and 9483 are
often referred to with shortened titles or nicknames such as "BRSKI" and
"LCMPP", respectively.

For clarity, because these names also represent protocols, we plan to update
these document nicknames to just their RFC number (in order to help the reader
distinguish between the RFC itself and the protocol). Please see some examples
below and let us know any objections.

Originals:
   In this document, references to CMP follow the Lightweight CMP
   Profile (LCMPP) [RFC9483] rather than [RFC4210] and [RFC9480], as the
   subset of CMP defined in LCMPP sufficiently meets the required
   functionality.

   *  MASA: functionality as described in BRSKI [RFC8995].  The voucher
      exchange with the MASA via the domain registrar is performed as
      described in BRSKI.

   *  Ownership tracker: This is as defined in BRSKI.

Perhaps:
   In this document, references to CMP follow [RFC9483] rather than
   [RFC4210] and [RFC9480], as the subset of CMP defined in [RFC9483]
   sufficiently meets the required functionality.

   *  MASA: This has the functionality as described in [RFC8995].
      The voucher exchange with the MASA via the domain registrar is
      performed as described in [RFC8995].

   *  Ownership Tracker: This is as defined in [RFC8995].
-->

<!-- [rfced] In Section 4.1, should "Discovery phase" and "Identification phase"
be updated to "Discover phase" and "Identity phase", respectively, to better
match the figure from Section 2.1 of RFC 8995?

Original:
   Based on the diagram in BRSKI [RFC8995], Section 2.1 and the
   architectural changes, the original protocol flow is divided into
   several phases showing commonalities and differences to the original
   approach as follows.

   *  Discovery phase: mostly as in BRSKI step (1).  For details see
      Section 4.2.1.

   *  Identification phase: same as in BRSKI step (2).

Perhaps:
   Based on the diagram in [RFC8995], Section 2.1 and the
   architectural changes, the original protocol flow is divided into
   several phases showing commonalities and differences to the original
   approach as follows.

   *  Discover phase: This is mostly as in step (1) of [RFC8995].  For
      details see Section 4.2.1.

   *  Identity phase: This is the same as in step (2) of [RFC8995].
-->

          <li>
            <t>RA: This performs centralized certificate management functions as a
            public-key infrastructure for the domain operator.  As far as not
            already done by the domain registrar, it performs the final
            validation and authorization of certification requests.
            Otherwise, the RA co-located with the domain registrar directly
            connects to the CA.</t>
  <t>CA, also
          </li>
          <li>
            <t>CA (also called domain CA: "domain CA"): This generates domain-specific
            certificates according to certification requests that have been
            authenticated and authorized by the registrar and/or an extra
            RA.</t>
</list></t>
          </li>
        </ul>
        <t>Based on the diagram in BRSKI <xref section="2.1"
        sectionFormat="comma" target="RFC8995"/> and the architectural
        changes, the original protocol flow is divided into several phases
       showing commonalities and differences to with the original approach as
        follows.</t>

<t><list style="symbols">

        <ul spacing="normal">
          <li>
            <t>Discovery phase: This is mostly as in BRSKI step (1). (1) of <xref target="RFC8995"/>. For details details, see
            <xref target="discovery"/>.</t>
          </li>
          <li>
            <t>Identification phase: This is the same as in BRSKI step (2).</t> (2) of <xref target="RFC8995"/>.</t>
          </li>
          <li>
            <t>Voucher exchange phase: This is the same as in BRSKI steps (3) and (4).</t> (4) of <xref target="RFC8995"/>.</t>
          </li>
          <li>
            <t>Voucher status telemetry: This is the same as in BRSKI directly after step (4).</t> (4) in <xref target="RFC8995"/>.</t>
          </li>
          <li>
            <t>Certificate enrollment phase: the The use of EST in step (5) is
            changed to employing a certificate enrollment protocol that uses
            an authenticated self-contained object for requesting the LDevID certificate.  <vspace blankLines='1'/>
            certificate.</t>

<!--[rfced] To improve the readability of the following sentence, may we update
it as follows?

Original:
   For transporting the certificate enrollment request and response
   messages, the (D)TLS channel established between pledge and
   registrar is REQUIRED to use.

Perhaps:
   It is REQUIRED to use the (D)TLS channel established between the
   pledge and registrar to transport the certificate enrollment request
   and response messages.
-->

            <t>For transporting the certificate enrollment request and
            response messages, the (D)TLS channel established between pledge
            and registrar is <bcp14>REQUIRED</bcp14> to use.  To this end, the
            enrollment protocol, the pledge, and the registrar need to support
            the use of this existing channel for certificate enrollment.  Due
            to this architecture, the pledge does not need to establish
            additional connections for certificate enrollment and the
            registrar retains full control over the certificate enrollment
            traffic.</t>
          </li>
          <li>
            <t>Enrollment status telemetry: This is the final exchange of BRSKI step (5).</t>
</list></t> (5) of <xref target="RFC8995"/>.</t>
          </li>
        </ul>
      </section>

      <section anchor="message_ex"><name>Message anchor="message_ex">
        <name>Message Exchange</name>
        <t>The behavior of a pledge described in BRSKI <xref section="2.1"
        sectionFormat="comma" target="RFC8995"/> is kept, with one major
        exception.  After finishing the Imprint step (4), the Enroll step (5)
        <bcp14>MUST</bcp14> be performed with an enrollment protocol utilizing
        authenticated self-contained objects, as explained in <xref
        target="req-sol"/>.
<!--
the certification request MUST be performed using an
authenticated self-contained object providing not only proof of possession
but also proof of identity (source authentication).
-->

<!-- [rfced] Should "options applicable" be updated to "applicable options"
in the text below?

Original:
   Section 5 discusses selected suitable enrollment protocols and options
   applicable.

Perhaps:
   Section 5 discusses selected suitable enrollment protocols and applicable
   options.
-->

        <xref target="exist_prot"/> discusses selected suitable enrollment
        protocols and options applicable.</t>
        <t>An abstract overview of the BRSKI-AE protocol can be found at <xref target="BRSKI-AE-overview"/>.</t>
        target="BRSKI-AE-OVERVIEW"/>.</t>

        <section anchor="discovery"><name>Pledge anchor="discovery">
          <name>Pledge - Registrar Discovery</name>
          <t>Discovery as specified in BRSKI <xref section="4" sectionFormat="comma"
          target="RFC8995"/> does not support the discovery of registrars with
          enhanced feature sets.  A pledge can not cannot find out in this way whether
          discovered registrars support the certificate enrollment protocol it
          expects, such as CMP.</t>

          <t>As a more general solution, the BRSKI discovery mechanism can be
          extended to provide up-front information on the capabilities of
          registrars.  For further discussion, see <xref
          target="I-D.ietf-anima-brski-discovery"/>.</t>

          <t>In the absence of such a generally applicable solution, BRSKI-AE
          deployments may use their particular way of doing discovery.  <xref
          target="brski-cmp-instance"/> defines a minimalist approach that
          <bcp14>MAY</bcp14> be used for CMP.</t>
        </section>

        <section anchor="pledge-registrar-masa-voucher-exchange"><name>Pledge anchor="pledge-registrar-masa-voucher-exchange">
          <name>Pledge - Registrar - MASA Voucher Exchange</name>
          <t>The voucher exchange is performed as specified in <xref
          target="RFC8995"/>.</t>
        </section>

        <section anchor="pledge-registrar-masa-voucher-status-telemetry"><name>Pledge anchor="pledge-registrar-masa-voucher-status-telemetry">
          <name>Pledge - Registrar - MASA Voucher Status Telemetry</name>
          <t>The voucher status telemetry is performed as specified in <xref
          section="5.7" sectionFormat="comma" target="RFC8995"/>.</t>
        </section>

<!-- [rfced] As this sentence begins Section 4.2.4, may we clarify what
"This" refers to?

Additionally, may we make a similar update in Appendix A.5?

Original:
4.2.4.  Pledge - Registrar - RA/CA Certificate Enrollment

   This replaces the EST integration for PKI bootstrapping described in
   [RFC8995], Section 5.9 (while [RFC8995], Section 5.9.4 remains as the
   final phase, see below).
...
A.5.  Infrastructure Isolation Policy

   This refers to any case in which network infrastructure is normally
   isolated from the Internet as a matter of policy, most likely for
   security reasons.

Perhaps:
4.2.4.  Pledge - Registrar - RA/CA Certificate Enrollment

    RA/CA certificate enrollment replaces the EST integration for PKI
    bootstrapping described in Section 5.9 of [RFC8995] (while Section 5.9.4
    of [RFC8995] remains as the final phase; see below).
...
A.5.  Infrastructure Isolation Policy

   The infrastructure isolation policy refers to any case in which...
-->

        <section anchor="pledge-registrar-raca-certificate-enrollment"><name>Pledge anchor="pledge-registrar-raca-certificate-enrollment">
          <name>Pledge - Registrar - RA/CA Certificate Enrollment</name>
          <t>This replaces the EST integration for PKI bootstrapping described
          in <xref section="5.9" sectionFormat="comma" target="RFC8995"/>
          (while <xref section="5.9.4" sectionFormat="comma"
          target="RFC8995"/> remains as the final phase, phase; see below).</t>

          <t>The certificate enrollment phase may involve the transmission of
          several messages.  Details can depend on the application scenario,
          the employed enrollment protocol, and other factors.
<!-- <br>
In line with the generalizations described in {{architecture}},
It is RECOMMENDED to transfer these messages
via the channel established between the pledge and the registrar.
--></t>
-->
          </t>
          <t>The only message exchange <bcp14>REQUIRED</bcp14> is for the
          actual certification request and response.  Further message
          exchanges <bcp14>MAY</bcp14> be performed as needed.</t>

          <t>Note: The message exchanges marked <bcp14>OPTIONAL</bcp14> in the below
          <xref target="enrollfigure"/> below cover all those supported by the
          use of EST in BRSKI.  The last <bcp14>OPTIONAL</bcp14> one, namely
          certificate confirmation, is not supported by EST, EST but by CMP and
          other enrollment protocols.</t>

          <figure title="Certificate anchor="enrollfigure">
            <name>Certificate Enrollment Message Flow" anchor="enrollfigure"><artset><artwork Flow</name>
            <artset>
              <artwork type="svg" align="left"><svg align="left">
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                  <g class="text">
                    <text x="36" y="52">Pledge</text>
                    <text x="308" y="52">Domain</text>
                    <text x="516" y="52">Operator</text>
                    <text x="320" y="68">Registrar</text>
                    <text x="504" y="68">RA/CA</text>
                    <text x="304" y="84">(JRC)</text>
                    <text x="504" y="84">(PKI)</text>
                    <text x="56" y="132">[OPTIONAL</text>
                    <text x="128" y="132">request</text>
                    <text x="172" y="132">of</text>
                    <text x="196" y="132">CA</text>
                    <text x="264" y="132">certificates]</text>
                    <text x="92" y="148">CA</text>
                    <text x="128" y="148">Certs</text>
                    <text x="184" y="148">Request</text>
                    <text x="232" y="148">(1)</text>
                    <text x="368" y="164">[OPTIONAL</text>
                    <text x="456" y="164">forwarding]</text>
                    <text x="364" y="180">CA</text>
                    <text x="400" y="180">Certs</text>
                    <text x="456" y="180">Request</text>
                    <text x="364" y="196">CA</text>
                    <text x="400" y="196">Certs</text>
                    <text x="460" y="196">Response</text>
                    <text x="92" y="212">CA</text>
                    <text x="128" y="212">Certs</text>
                    <text x="188" y="212">Response</text>
                    <text x="240" y="212">(2)</text>
                    <text x="56" y="244">[OPTIONAL</text>
                    <text x="128" y="244">request</text>
                    <text x="172" y="244">of</text>
                    <text x="228" y="244">attributes</text>
                    <text x="36" y="260">to</text>
                    <text x="80" y="260">include</text>
                    <text x="124" y="260">in</text>
                    <text x="192" y="260">Certification</text>
                    <text x="284" y="260">Request]</text>
                    <text x="120" y="276">Attribute</text>
                    <text x="192" y="276">Request</text>
                    <text x="240" y="276">(3)</text>
                    <text x="368" y="292">[OPTIONAL</text>
                    <text x="456" y="292">forwarding]</text>
                    <text x="392" y="308">Attribute</text>
                    <text x="464" y="308">Request</text>
                    <text x="392" y="324">Attribute</text>
                    <text x="468" y="324">Response</text>
                    <text x="120" y="340">Attribute</text>
                    <text x="196" y="340">Response</text>
                    <text x="248" y="340">(4)</text>
                    <text x="56" y="372">[REQUIRED</text>
                    <text x="152" y="372">certification</text>
                    <text x="244" y="372">request]</text>
                    <text x="136" y="388">Certification</text>
                    <text x="224" y="388">Request</text>
                    <text x="272" y="388">(5)</text>
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                    <text x="272" y="564">(8)</text>
                  </g>
                </svg>
</artwork><artwork
              </artwork>
              <artwork type="ascii-art" align="left"><![CDATA[
+------+                          +---------+              +--------+
|Pledge|                          |Domain   |              |Operator|
|      |                          |Registrar|              |RA/CA   |
|      |                          |(JRC)    |              |(PKI)   |
+------+                          +---------+              +--------+
 |                                     |                           |
 |[OPTIONAL request of CA certificates]|                           |
 |------- CA Certs Request (1) ------->|                           |
 |                                     | [OPTIONAL forwarding]     |
 |                                     |--- CA Certs Request ----->|
 |                                     |<-- CA Certs Response -----|
 |<------ CA Certs Response (2) -------|                           |
 |                                     |                           |
 |[OPTIONAL request of attributes      |                           |
 | to include in Certification Request]|                           |
 |------- Attribute Request (3) ------>|                           |
 |                                     | [OPTIONAL forwarding]     |
 |                                     |--- Attribute Request ---->|
 |                                     |<-- Attribute Response ----|
 |<------ Attribute Response (4) ------|                           |
 |                                     |                           |
 |[REQUIRED certification request]     |                           |
 |------- Certification Request (5) -->|                           |
 |                                     | [OPTIONAL forwarding]     |
 |                                     |---Certification Request-->|
 |                                     |<--Certification Resp.  ---|
 |<----- Certification Response (6) ---|                           |
 |                                     |                           |
 |[OPTIONAL certificate confirmation]  |                           |
 |------- Certificate Confirm (7) ---->|                           |
 |                                     | [OPTIONAL forwarding]     |
 |                                     |--- Certificate Confirm--->|
 |                                     |<-- PKI Confirm -----------|
 |<------ PKI/Registrar Confirm (8) ---|                           |
]]></artwork></artset></figure>
]]></artwork>
            </artset>
          </figure>
          <t>It may be noted that connections between the registrar and the PKI components
of the operator (RA, CA, etc.) may be intermittent or off-line. offline.
Messages should be sent as soon as sufficient transfer capacity is available.</t>
          <t>The label <spanx style="verb">[OPTIONAL forwarding]</spanx> <tt>[OPTIONAL forwarding]</tt> in <xref target="enrollfigure"/>
means that on receiving from a pledge a request message of the given type, type from a pledge,
the registrar <bcp14>MAY</bcp14> answer the request directly.
In this case, it <bcp14>MUST</bcp14> authenticate its responses with the same credentials
as used for authenticating itself at the TLS level for the voucher exchange.
Otherwise, the registrar <bcp14>MUST</bcp14> forward the request to the RA
and forward any resulting response back to the pledge.</t>

<!-- [rfced] To improve readability, may we update the list below as follows?

Original:
   They include the application scenario, the capabilities of the registrar
   and of the local RA possibly co-located with the registrar, the enrollment
   protocol being used, and the specific contents of the request.

Perhaps:
   They include the application scenario, the capabilities of the registrar,
   the capabilities of the local RA possibly co-located with the registrar,
   the enrollment protocol being used, and the specific contents of the
   request.
-->

<t>The decision of whether to forward a request or to answer it directly can depend
on various static and dynamic factors. They include the application scenario,
the capabilities of the registrar and of the local RA possibly co-located
with the registrar, the enrollment protocol being used, and the specific
contents of the request.</t>

<t>Note that there are several options for how the registrar could be able to directly answer
requests for CA certificates or for certification request attributes.
It could cache responses obtained from the domain PKI and
later use their contents for responding to requests asking for the same data.
The contents could also be explicitly provisioned at the registrar.</t>

<t>Further note that certification requests typically need to be handled by the backend PKI,
but the registrar can answer them directly with an error response
in case it determines that such a request should be rejected,
for instance, because it is not properly authenticated or not authorized.<!--br-->
Also, certificate confirmation messages
will usually be forwarded to the backend PKI,
but if the registrar knows that they are not needed or wanted there there,
it can acknowledge such messages directly.</t>

          <t>The following list provides an abstract description of the flow
	  depicted in <xref target="enrollfigure"/>.</t>

<t><list style="symbols">
          <ul spacing="normal">

            <li>
              <t>CA Certs Request (1): The pledge optionally requests the latest relevant
	      CA certificates. This ensures that the pledge has the
	      complete set of current CA certificates beyond the
	      pinned-domain-cert (which is contained in the voucher
	      and which may be just the domain registrar certificate).</t>
            </li>
            <li>
              <t>CA Certs Response (2): This <bcp14>MUST</bcp14> contain any intermediate CA certificates
	      that the pledge may need to validate certificates
	      and <bcp14>MAY</bcp14> contain the LDevID trust anchor.</t>
            </li>
            <li>
              <t>Attribute Request (3): Typically, the automated bootstrapping
              occurs without local administrative configuration of the pledge.
              Nevertheless, there are cases in which the pledge may also
              include in the Certification Request (5) additional attributes
              that are specific to the target domain. domain in the Certification Request (5). To get these attributes
              in advance, the attribute request may be used.</t>
            </li>

            <li>
              <t>Attribute Response (4): This <bcp14>MUST</bcp14> contain the
              attributes requested in (3) to be included in the subsequent
              Certification Request (5).  <vspace blankLines='1'/>
For (5).</t>

              <t>For example, <xref section="6.11.7.2" sectionFormat="comma"
              target="RFC8994"/> specifies how the attribute request is used
              to signal to the pledge the acp-node-name field required for
              enrollment into an ACP Autonomic Control Plane (ACP) domain.</t>
            </li>

            <li>
              <t>Certification Request (5): This <bcp14>MUST</bcp14> contain
              the authenticated self-contained object ensuring both the proof
              of possession of the corresponding private key and the proof of
              identity of the requester.</t>
            </li>
            <li>
              <t>Certification Response (6): This On success, this <bcp14>MUST</bcp14> contain on success
              the requested certificate and <bcp14>MAY</bcp14>
              include further information, like certificates of intermediate
              CAs and any additional trust anchors.</t>
            </li>
            <li>
              <t>Certificate Confirm (7): An This is an optional confirmation that is sent after
              the requested certificate has been received and validated.  If
              sent, it <bcp14>MUST</bcp14> contain a positive or negative
              confirmation by the pledge to the PKI whether the certificate
              was successfully enrolled and fits its needs.</t>
            </li>
            <li>
              <t>PKI/Registrar Confirm (8): An This is an acknowledgment by the PKI that
              <bcp14>MUST</bcp14> be sent on reception of the Certificate
              Confirm.</t>
</list></t>
            </li>
          </ul>
          <t>The generic messages described above may be implemented using any
          certificate enrollment protocol that supports authenticated
          self-contained objects for the certification request as described in
          <xref target="req-sol"/>.  Examples are available in <xref
          target="exist_prot"/>.</t>

          <t>Note that the optional certificate confirmation by the pledge to
          the PKI described above is independent of the mandatory enrollment
          status telemetry done between the pledge and the registrar in the
          final phase of BRSKI-AE, which is described next.</t>
        </section>

        <section anchor="pledge-registrar-enrollment-status-telemetry"><name>Pledge anchor="pledge-registrar-enrollment-status-telemetry">
          <name>Pledge - Registrar Enrollment Status Telemetry</name>
          <t>The enrollment status telemetry is performed as specified in
          <xref section="5.9.4" sectionFormat="comma" target="RFC8995"/>.</t>
          <t>In BRSKI BRSKI, this is described as part of the certificate enrollment
          step, but due to the generalization on of the enrollment protocol
          described in this document document, it is regarded as a separate phase
          here.</t>
        </section>
      </section>

      <section anchor="addressing"><name>Enhancements anchor="addressing">
        <name>Enhancements to the Endpoint Addressing Scheme of BRSKI</name>
        <t>BRSKI-AE extends the addressing scheme outlined in <xref
        section="5" sectionFormat="comma" target="RFC8995"/>, target="RFC8995"/> to support
        alternative enrollment protocols that utilize authenticated,
        self-contained objects for certification requests -- (also see also <xref
        target="exist_prot"/>).  These extensions are designed to be
        compatible with existing Registration Authorities (RAs) and
        Certification Authorities (CAs) that already support such enrollment
        protocols, enabling their use without requiring any modifications.</t>
        <t>The addressing scheme in BRSKI for certification requests and
the requests,
        related CA certificates certificates, and CSR attributes retrieval functions uses the
        definition from EST <xref target="RFC7030"/>.
Here is the  An example of
        simple enrollment: <spanx style="verb">"/.well-known/est/simpleenroll"</spanx>. enrollment is: <tt>"/.well-known/est/simpleenroll"</tt>.  This
        approach is generalized to the following notation:
<spanx style="verb">"/.well-known/&lt;enrollment-protocol&gt;/&lt;request&gt;"</spanx>
        <tt>"/.well-known/&lt;enrollment-protocol&gt;/&lt;request&gt;"</tt> in
        which <spanx style="verb">&lt;enrollment-protocol&gt;</spanx> <tt>&lt;enrollment-protocol&gt;</tt> refers to a certificate
        enrollment protocol.  Note that here, enrollment is considered here a
        message sequence that contains at least a certification request and a
        certification response.  The following conventions are used to provide
        maximal compatibility with BRSKI:</t>

<t><list style="symbols">
  <t><spanx style="verb">&lt;enrollment-protocol&gt;</spanx>:
        <ul spacing="normal">
          <li>
            <t><tt>&lt;enrollment-protocol&gt;</tt>: This <bcp14>MUST</bcp14>
            reference the protocol being used.  Existing values include '<spanx style="verb">est</spanx>'
            '<tt>est</tt>' <xref target="RFC7030"/> as in BRSKI and '<spanx style="verb">cmp</spanx>'
            '<tt>cmp</tt>' as in <xref target="RFC9483"/> and <xref
            target="brski-cmp-instance"/> below.  Values for other existing
            protocols such as CMC and SCEP, as well as for newly defined protocols
            protocols, are outside the scope of this document.  For use of the <spanx style="verb">&lt;enrollment-protocol&gt;</spanx>
            <tt>&lt;enrollment-protocol&gt;</tt> and <spanx style="verb">&lt;request&gt;</spanx> <tt>&lt;request&gt;</tt>
            URI components, they would need to be specified in a suitable RFC
            and placed into the Well-Known URIs "Well-Known URIs" registry, just as EST in <xref
            target="RFC7030"/>.</t>
  <t><spanx style="verb">&lt;request&gt;</spanx>: if
          </li>
          <li>
            <t><tt>&lt;request&gt;</tt>:  If present, this path component
            <bcp14>MUST</bcp14> describe, describe the operation requested depending on
            the enrollment protocol being used, the operation requested. used.  Enrollment protocols are
            expected to define their request endpoints, as is done by existing
            protocols (see also (also see <xref target="exist_prot"/>).</t>
</list></t>
          </li>
        </ul>
        <!-- ## Domain Registrar Support of Alternative Enrollment Protocols -->

	<t>Well-known URIs for various endpoints on the domain registrar are
	already defined as part of the base BRSKI specification or indirectly
	by EST.  In addition, alternative enrollment endpoints
	<bcp14>MAY</bcp14> be supported by the registrar.</t>

        <t>A pledge <bcp14>SHOULD</bcp14> use the endpoints defined for the
        enrollment protocol(s) that it can use.  It will recognize whether the
        protocol it uses and the specific request it wants to perform are
        understood and supported by the domain registrar registrar. This is done by
        sending the request to the respective endpoint according to the above
        addressing scheme and then evaluating the HTTP status code of the
        response.  If the pledge uses endpoints that are not standardized, it
        risks that the registrar does not recognize a request and thus may
        reject it, it even if the registrar supports the intended protocol and
        operation.</t>

        <t>The following list of endpoints provides an illustrative example of
        a domain registrar supporting several options for EST as well as for
        CMP to be used in BRSKI-AE. The listing contains the supported
        endpoints to which the pledge may connect for bootstrapping. This
        includes the voucher handling as well as the enrollment endpoints.
        The CMP-related enrollment endpoints are defined as well-known URIs in
        CMP Updates <xref target="RFC9480"/> and the Lightweight CMP Profile
        <xref target="RFC9483"/>.</t>

<figure><artwork

<!--[rfced] Should the following artwork element be reformatted as
a bulleted list, per text from the preceding paragraph?

Original:
   The following list of endpoints provides an illustrative example of a
   domain registrar supporting several options for EST as well as for
   CMP to be used in BRSKI-AE.
   ...
     /.well-known/brski/voucherrequest
     /.well-known/brski/voucher_status
     /.well-known/brski/enrollstatus
     /.well-known/est/cacerts
     /.well-known/est/csrattrs
     /.well-known/est/fullcmc
     /.well-known/cmp/getcacerts
     /.well-known/cmp/getcertreqtemplate
     /.well-known/cmp/initialization
     /.well-known/cmp/pkcs10
-->

        <artwork align="left"><![CDATA[
  /.well-known/brski/voucherrequest
  /.well-known/brski/voucher_status
  /.well-known/brski/enrollstatus
  /.well-known/est/cacerts
  /.well-known/est/csrattrs
  /.well-known/est/fullcmc
  /.well-known/cmp/getcacerts
  /.well-known/cmp/getcertreqtemplate
  /.well-known/cmp/initialization
  /.well-known/cmp/pkcs10
]]></artwork></figure>
]]></artwork>
      </section>
    </section>
    <section anchor="exist_prot"><name>Instantiation anchor="exist_prot">
      <name>Instantiation with Existing Enrollment Protocols</name>
      <t>This section maps the generic requirements to support proof of possession
and proof of identity to selected existing certificate enrollment protocols
and specifies further aspects of using such enrollment protocols in BRSKI-AE.</t>
      <section anchor="brski-cmp-instance"><name>BRSKI-CMP: anchor="brski-cmp-instance">
        <name>BRSKI-CMP: BRSKI-AE instantiated Instantiated with CMP</name>
        <t>In this document, references to CMP follow the Lightweight CMP Profile (LCMPP)
<xref target="RFC9483"/> rather than <xref target="RFC4210"/> and <xref target="RFC9480"/>, as the subset of CMP
defined in LCMPP sufficiently meets the required functionality.</t>
        <t>Adherence to the LCMPP <xref target="RFC9483"></xref> target="RFC9483"/> is <bcp14>REQUIRED</bcp14> when using CMP.
The following specific requirements apply (refer to <xref target="enrollfigure"/>):</t>

<t><list style="symbols">
        <ul spacing="normal">
          <li>
            <t>The validation of server response messages performed by the CMP
            client within the pledge <bcp14>MUST</bcp14> be based on the trust
            anchor established beforehand via the BRSKI voucher, i.e., on the pinned-domain-cert.  <vspace blankLines='1'/>
Note
            pinned-domain-cert.</t>
            <t>Note that the integrity and authenticity checks on the RA/CA by
            the CMP client can be stronger than for EST because they do not
            need to be performed hop-by-hop, hop-by-hop but are usually end-to-end.</t>
          </li>
          <li>
            <t>CA Certs Request (1) and Response (2):<br /> (2): Requesting CA
            certificates is <bcp14>OPTIONAL</bcp14>.<br /> <bcp14>OPTIONAL</bcp14>. If supported, it
            <bcp14>SHALL</bcp14> be implemented as specified in <xref
            section="4.3.1" sectionFormat="comma" target="RFC9483"/>.</t>
          </li>
          <li>
            <t>Attribute Request (3) and Response (4):<br /> (4): Requesting
            certification request attributes is <bcp14>OPTIONAL</bcp14>.<br /> <bcp14>OPTIONAL</bcp14>.  If
            supported, it <bcp14>SHALL</bcp14> be implemented as specified in
            <xref section="4.3.3" sectionFormat="comma" target="RFC9483"/>.  <vspace blankLines='1'/>
Alternatively, target="RFC9483"/>.</t>
            <t>Alternatively, the registrar <bcp14>MAY</bcp14> modify the
            requested certificate contents as specified in <xref
            section="5.2.3.2" sectionFormat="comma" target="RFC9483"/>.</t>
          </li>
          <li>
            <t>Certification Request (5) and Response (6):<br /> (6): Certificates
            <bcp14>SHALL</bcp14> be requested and provided as specified in
            LCMPP <xref section="4.1.1" sectionFormat="comma"
            target="RFC9483"/> (based on CRMF) or <xref section="4.1.4"
            sectionFormat="comma" target="RFC9483"/> (based on PKCS #10).  <vspace blankLines='1'/>
            </t>
            <t>
	      Proof of possession <bcp14>SHALL</bcp14> be provided in a manner
	      suitable for the key type.  Proof of identity
	      <bcp14>SHALL</bcp14> be provided by signature-based protection
	      of the certification request message as outlined in <xref
	      section="3.2" sectionFormat="comma" target="RFC9483"/>, target="RFC9483"/> using
	      the IDevID secret.  <vspace blankLines='1'/> secret.</t>
            <t>
	      When the registrar forwards a certification request from the
	      pledge to a backend RA/CA, it is <bcp14>RECOMMENDED</bcp14> that
	      the registrar wraps the original certification request in a
	      nested message signed with its own credentials, as described in
	      <xref section="5.2.2.1" sectionFormat="comma"
	      target="RFC9483"/>.  This approach explicitly conveys the
	      registrar's consent to the RA while retaining the original
	      certification request with the proof of origin provided by the
	      pledge's signature.  <vspace blankLines='1'/> </t>
            <t>
	      If additional trust anchors, anchors beyond the pinned-domain-cert, pinned-domain-cert need
	      to be conveyed to the pledge, this <bcp14>SHOULD</bcp14> be done
	      in the <spanx style="verb">caPubs</spanx> <tt>caPubs</tt> field of the certification response
	      rather than through a CA Certs Response.</t>
          </li>
          <li>
            <t>Certificate Confirm (7) and PKI/Registrar Confirm (8):<br /> (8): Explicit
            confirmation of new certificates to the RA/CA <bcp14>MAY</bcp14>
            be used as specified in <xref section="4.1.1"
            sectionFormat="comma" target="RFC9483"/>.  <vspace blankLines='1'/>
Note target="RFC9483"/>.</t>
            <t>Note that independent of the certificate confirmation within
            CMP, enrollment status telemetry with the registrar at the BRSKI
            level will be performed as described in <xref section="5.9.4"
            sectionFormat="comma" target="RFC8995"/>.</t>
          </li>
          <li>
            <t>If delayed delivery of CMP messages is needed (e.g., to support
            enrollment over an asynchronous channel), it <bcp14>SHALL</bcp14>
            be performed as specified in
Section Sections <xref target="RFC9483"
            section="4.4" sectionFormat="bare"/> and Section <xref
            target="RFC9483" section="5.1.2" sectionFormat="bare"/> of <xref
            target="RFC9483"/>.</t>
</list></t>
          </li>
        </ul>
        <t>The mechanisms for exchanging messages between the registrar and
        backend PKI components (i.e., RA and/or CA) are outside the scope of
        this document.  CMP's independence from the message transfer mechanism
        allows for flexibility in choosing the appropriate exchange method
        based on the application scenario.  For the applicable security and
        privacy considerations, refer to Sections <xref target="sec-consider"/> target="sec-consider" format="counter"/> and
        <xref target="priv-consider"/>. target="priv-consider" format="counter"/>.  Further guidance can be found in
        <xref section="6" sectionFormat="comma" target="RFC9483"/>.</t>
        <!--
CMP Updates {{RFC9480}} and
the LCMPP {{RFC9483}}
provide requirements for interoperability.
-->

	<t>BRSKI-AE with CMP can also be combined with Constrained BRSKI <xref
	target="I-D.ietf-anima-constrained-voucher"/>, using CoAP for
	enrollment message transport as described by CoAP Transport Transfer for CMP <xref target="RFC9482"/>.  In such scenarios, the EST-specific parts
	of <xref target="I-D.ietf-anima-constrained-voucher"/> do not
	apply.</t>

        <t>For BRSKI-AE scenarios where a general solution for discovering
        registrars with CMP support is not available (cf. <xref
        target="discovery"/>), the following minimalist approach
        <bcp14>MAY</bcp14> be used:
perform Perform discovery as defined in BRSKI <xref section="B"
        target="RFC8995" sectionFormat="comma" target="RFC8995"/>, section="B"/>, but use the service
        name <spanx style="verb">"brski-reg-cmp"</spanx> <tt>"brski-reg-cmp"</tt> (as defined in <xref
        target="iana-consider"/>) instead of <spanx style="verb">"brski-registrar"</spanx> <tt>"brski-registrar"</tt> (as
        defined in <xref section="8.6" sectionFormat="comma"
        target="RFC8995"/>).  Note that this approach does not support join
        proxies.</t>
      </section>

      <section anchor="support-of-other-enrollment-protocols"><name>Support anchor="support-of-other-enrollment-protocols">
        <name>Support of Other Enrollment Protocols</name>
        <t>Further instantiations of BRSKI-AE can be done.  They are left for
        future work.</t>

        <t>In particular, CMC <xref target="RFC5272"/> (using its in-band
        source authentication options) and SCEP <xref target="RFC8894"/>
        (using its 'renewal' option) could be used.</t>

        <t>The fullCMC variant of EST sketched in <xref section="2.5"
        sectionFormat="comma" target="RFC7030"/> might also be used here. For EST-fullCMC
        EST-fullCMC, further specification is necessary.
<!--
Yet most likely it will not be followed up
because, by now, no implementations of this EST variant are known,
and no reasons are known why it could be preferable over using BRSKI-CMP.
--></t>
-->
        </t>
        <!--
 ## BRSKI-EST-fullCMC: Application to EST

When using EST {{RFC7030}}, the following aspects and constraints
need to be considered and the given extra requirements need to be fulfilled,
which adapt BRSKI {{RFC8995, Section 5.9.3}}:

* Proof of possession is provided typically by using the specified PKCS #10
  structure in the request.
  Together with Full PKI requests, also CRMF can be used.

* Proof of identity needs to be achieved by signing the certification request
  object using the Full PKI Request option (including the /fullcmc endpoint).
  This provides sufficient information for the RA to authenticate the pledge
  as the origin of the request and to make an authorization decision on the
  received certification request.
  Note:
  EST references CMC {{RFC5272}} for the definition of the Full PKI Request.
  For proof of identity, the signature of the SignedData of the Full PKI Request
  is performed using the IDevID secret of the pledge.  The data signed
  must include include a sufficiently strong identifier of the pledge,
  e.g, the subject of its IDevID certificate.

  Note:
  In this case the binding to the underlying TLS channel is not necessary.

* When the RA is temporarily not available, as per {{RFC7030, Section 4.2.3}},
  an HTTP status code 202 should be returned by the registrar,
  and the pledge will repeat the initial Full PKI Request later.
-->

<!--
Note that the work in the ACE WG described in
{{draft-selander-ace-coap-est-oscore}} may be considered here as well,
as it also addresses the encapsulation of EST in a way that
makes it independent of the underlying TLS channel using OSCORE,
which also entails that authenticated self-contained objects are used.
-->

</section>
    </section>
    <section anchor="iana-consider"><name>IANA anchor="iana-consider">
      <name>IANA Considerations</name>

<t>This document requires one IANA action: register
      <t>IANA has registered the following service name in the <eref target="https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml">Service
      target="https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml" brackets="angle">"Service
      Name and Transport Protocol Port Number Registry</eref>
the following service name.</t>

<t><strong>Service Name:</strong> brski-reg-cmp<br />
<strong>Transport Protocol(s):</strong> tcp<br />
<strong>Assignee:</strong> IESG <eref target="mailto:iesg@ietf.org">iesg@ietf.org</eref><br />
<strong>Contact:</strong> IETF <eref target="mailto:chair@ietf.org">chair@ietf.org</eref><br />
<strong>Description:</strong> Bootstrapping Registry"</eref>.</t>
      <dl spacing="compact" newline="false">
	<dt>Service Name:</dt><dd>brski-reg-cmp</dd>
        <dt>Transport Protocol(s):</dt><dd>tcp</dd>
        <dt>Description:</dt><dd>Bootstrapping Remote Secure Key
        Infrastructure registrar with CMP capabilities according to the
        Lightweight CMP Profile (LCMPP, (LCMPP) <xref target="RFC9483"/>)<br />
<strong>Reference:</strong> [THISRFC]</t> target="RFC9483"/></dd>
        <dt>Assignee:</dt><dd>IESG <eref target="mailto:iesg@ietf.org">iesg@ietf.org</eref></dd>
        <dt>Contact:</dt><dd>IETF <eref target="mailto:chair@ietf.org">chair@ietf.org</eref></dd>
        <dt>Reference:</dt><dd>RFC 9733</dd>
      </dl>
      <t>Note: We chose here the suffix "cmp" here rather than some other
      abbreviation like "lcmpp" mainly because this document defines the
      normative CMP instantiation of BRSKI-AE, which implies adherence to
      LCMPP is necessary and sufficient.</t>
    </section>

    <section anchor="sec-consider"><name>Security anchor="sec-consider">
      <name>Security Considerations</name>
      <t>The security considerations laid out in BRSKI <xref section="11"
      sectionFormat="comma" target="RFC8995"/> apply to the discovery and
      voucher exchange as well as for the status exchange information.</t>
      <t>In particular, even if the registrar delegates part or all of its RA
      role during certificate enrollment to a separate system, it still must
      be made sure that the registrar takes part in the decision on accepting
      or declining a request to join the domain, as required in <xref
      section="5.3" sectionFormat="comma" target="RFC8995"/>.  As this pertains also
      pertains to obtaining a valid domain-specific certificate, it must
      be made sure that a pledge can not cannot circumvent the registrar in the
      decision of whether it is granted an LDevID certificate by the CA.
      There are various ways how to fulfill this, including:</t>

<t><list style="symbols">

      <ul spacing="normal">
        <li>
          <t>implicit consent</t> consent;</t>
        </li>
        <li>
          <t>the registrar signals signaling its consent to the RA out-of-band before or
          during the enrollment phase, for instance instance, by entering the pledge
          identity in a database.</t> database;</t>
        </li>
        <li>
          <t>the registrar provides providing its consent using an extra message that is
          transferred on the same channel as the enrollment messages, possibly
          in a TLS tunnel.</t> tunnel; and</t>
        </li>
        <li>
          <t>the registrar explicitly states stating its consent by signing, in addition to the pledge, signing the
          authenticated self-contained certificate enrollment request message.</t>
</list></t> message
          in addition to the pledge.</t>
        </li>
      </ul>
      <t>Note: If EST was used, the registrar could give implicit consent on a
      certification request by forwarding the request to a PKI entity using a
      connection authenticated with a certificate containing an id-kp-cmcRA
      extension.</t>
      <t>When CMP is used, the security considerations laid out in the LCMPP <xref target="RFC9483"/> apply.</t>
    </section>

    <section anchor="priv-consider"><name>Privacy anchor="priv-consider">
      <name>Privacy Considerations</name>
      <t>The privacy considerations laid out in BRSKI <xref section="10"
      sectionFormat="comma" target="RFC8995"/> apply as well.</t>
      <t>Note that CMP messages themselves are not encrypted.  This may give
      eavesdroppers insight into which devices are bootstrapped into the
      domain.
This in turn  In turn, this might also be used to selectively block the
      enrollment of certain devices.</t>
      <t>To prevent such issues, the underlying message transport channel can
      be encrypted.  This is already provided by TLS between the pledge and
      the registrar, and for the onward exchange with backend systems,
      encryption may need to be added.</t>
    </section>
<section anchor="acknowledgments"><name>Acknowledgments</name>

<t>We thank Eliot Lear
for his contributions as a co-author at an earlier draft stage.</t>

<t>We thank Brian E. Carpenter, Michael Richardson, and Giorgio Romanenghi
for their input and discussion on use cases and call flows.</t>

<t>Moreover,
we thank Toerless Eckert (document shepherd),
Barry Leiba (SECdir review),
Mahesh Jethanandani (IETF area director),
Meral Shirazipour (Gen-ART reviewer),
Reshad Rahman (YANGDOCTORS reviewer),
Deb Cooley, Gunter Van de Velde, John Scudder, Murray Kucherawy, Roman Danyliw,
and Éric Vyncke (IESG reviewers),
Michael Richardson (ANIMA design team member),
as well as Rajeev Ranjan, Rufus Buschart,
Andreas Reiter, and Szofia Fazekas-Zisch (Siemens colleagues)
for their reviews with suggestions for improvements.</t>

</section>

  </middle>
  <back>

<displayreference target="I-D.ietf-anima-brski-discovery" to="BRSKI-DISCOVERY"/>
<displayreference target="I-D.ietf-anima-constrained-voucher" to="cBRSKI"/>

<references>
      <name>References</name>
      <references title='Normative References' anchor="sec-normative-references">

<reference anchor="RFC5280">
  <front>
    <title>Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile</title>
    <author fullname="D. Cooper" initials="D." surname="Cooper"/>
    <author fullname="S. Santesson" initials="S." surname="Santesson"/>
    <author fullname="S. Farrell" initials="S." surname="Farrell"/>
    <author fullname="S. Boeyen" initials="S." surname="Boeyen"/>
    <author fullname="R. Housley" initials="R." surname="Housley"/>
    <author fullname="W. Polk" initials="W." surname="Polk"/>
    <date month="May" year="2008"/>
    <abstract>
      <t>This memo profiles the X.509 v3 certificate and X.509 v2 certificate revocation list (CRL) for use in the Internet. An overview of this approach and model is provided as an introduction. The X.509 v3 certificate format is described in detail, with additional information regarding the format and semantics of Internet name forms. Standard certificate extensions are described and two Internet-specific extensions are defined. A set of required certificate extensions is specified. The X.509 v2 CRL format is described in detail along with standard and Internet-specific extensions. An algorithm for X.509 certification path validation is described. An ASN.1 module and examples are provided in the appendices. [STANDARDS-TRACK]</t>
    </abstract>
  </front>
  <seriesInfo name="RFC" value="5280"/>
  <seriesInfo name="DOI" value="10.17487/RFC5280"/>
</reference>

<reference anchor="RFC8995">
  <front>
    <title>Bootstrapping Remote Secure Key Infrastructure (BRSKI)</title>
    <author fullname="M. Pritikin" initials="M." surname="Pritikin"/>
    <author fullname="M. Richardson" initials="M." surname="Richardson"/>
    <author fullname="T. Eckert" initials="T." surname="Eckert"/>
    <author fullname="M. Behringer" initials="M." surname="Behringer"/>
    <author fullname="K. Watsen" initials="K." surname="Watsen"/>
    <date month="May" year="2021"/>
    <abstract>
      <t>This document specifies automated bootstrapping of an Autonomic Control Plane. To do this, a Secure Key Infrastructure is bootstrapped. This is done using manufacturer-installed X.509 certificates, in combination with a manufacturer's authorizing service, both online and offline. We call this process the Bootstrapping Remote Secure Key Infrastructure (BRSKI) protocol. Bootstrapping a new device can occur when using a routable address and a cloud service, only link-local connectivity, or limited/disconnected networks. Support for deployment models with less stringent security requirements is included. Bootstrapping is complete when the cryptographic identity of the new key infrastructure is successfully deployed to the device. The established secure connection can be used to deploy a locally issued certificate to the device as well.</t>
    </abstract>
  </front>
  <seriesInfo name="RFC" value="8995"/>
  <seriesInfo name="DOI" value="10.17487/RFC8995"/>
</reference>

<reference anchor="RFC9483">
  <front>
    <title>Lightweight Certificate Management Protocol (CMP) Profile</title>
    <author fullname="H. Brockhaus" initials="H." surname="Brockhaus"/>
    <author fullname="D. von Oheimb" initials="D." surname="von Oheimb"/>
    <author fullname="S. Fries" initials="S." surname="Fries"/>
    <date month="November" year="2023"/>
    <abstract>
      <t>This document aims at simple, interoperable, and automated PKI management operations covering typical use cases of industrial and Internet of Things (IoT) scenarios. This is achieved by profiling the Certificate Management Protocol (CMP), the related Certificate Request Message Format (CRMF), and transfer based on HTTP or Constrained Application Protocol (CoAP) in a succinct but sufficiently detailed and self-contained way. To make secure certificate management for simple scenarios and constrained devices as lightweight as possible, only the most crucial types of operations and options are specified as mandatory. More specialized or complex use cases are supported with optional features.</t>
    </abstract>
  </front>
  <seriesInfo name="RFC" value="9483"/>
  <seriesInfo name="DOI" value="10.17487/RFC9483"/>
</reference>
        <name>Normative References</name>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5280.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8995.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9483.xml"/>

<!-- [IEEE_802.1AR-2018] -->
        <reference anchor="IEEE_802.1AR-2018" target="https://ieeexplore.ieee.org/document/8423794">
          <front>
            <title>IEEE Standard for Local and Metropolitan Area Networks - Secure Device Identity</title>
    <author >
            <author>
              <organization>IEEE</organization>
            </author>
            <date year="2018" month="August"/>
          </front>
          <seriesInfo name="IEEE" value="802.1AR-2018"/>
          <seriesInfo name="DOI" value="10.1109/IEEESTD.2018.8423794"/>
        </reference>

<reference anchor="RFC2119">
  <front>
    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
    <author fullname="S. Bradner" initials="S." surname="Bradner"/>
    <date month="March" year="1997"/>
    <abstract>
      <t>In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.</t>
    </abstract>
  </front>
  <seriesInfo name="BCP" value="14"/>
  <seriesInfo name="RFC" value="2119"/>
  <seriesInfo name="DOI" value="10.17487/RFC2119"/>
</reference>

<reference anchor="RFC8174">
  <front>
    <title>Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words</title>
    <author fullname="B. Leiba" initials="B." surname="Leiba"/>
    <date month="May" year="2017"/>
    <abstract>
      <t>RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings.</t>
    </abstract>
  </front>
  <seriesInfo name="BCP" value="14"/>
  <seriesInfo name="RFC" value="8174"/>
  <seriesInfo name="DOI" value="10.17487/RFC8174"/>
</reference>

        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.2119.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8174.xml"/>

      </references>

      <references title='Informative References' anchor="sec-informative-references">

<reference anchor="I-D.ietf-anima-constrained-voucher">
   <front>
      <title>Constrained Bootstrapping Remote Secure Key Infrastructure (cBRSKI)</title>
      <author fullname="Michael Richardson" initials="M." surname="Richardson">
         <organization>Sandelman Software Works</organization>
      </author>
      <author fullname="Peter Van der Stok" initials="P." surname="Van der Stok">
         <organization>vanderstok consultancy</organization>
      </author>
      <author fullname="Panos Kampanakis" initials="P." surname="Kampanakis">
         <organization>Cisco Systems</organization>
      </author>
      <author fullname="Esko Dijk" initials="E." surname="Dijk">
         <organization>IoTconsultancy.nl</organization>
      </author>
      <date day="8" month="July" year="2024"/>
      <abstract>
	 <t>   This document defines the Constrained Bootstrapping Remote Secure Key
   Infrastructure (cBRSKI) protocol, which provides a solution for
   secure zero-touch onboarding of resource-constrained (IoT) devices
   into the network
        <name>Informative References</name>

<!-- [I-D.ietf-anima-constrained-voucher] IESG State: I-D Exists as of a domain owner.  This protocol is designed for
   constrained networks, which may have limited data throughput or may
   experience frequent packet loss. cBRSKI is a variant 10/28/2024; WG State: In WG Last Call as of the BRSKI
   protocol, which uses an artifact signed by the device manufacturer
   called the &quot;voucher&quot; which enables a new device and the owner&#x27;s
   network to mutually authenticate.  While the BRSKI voucher data is
   encoded in JSON, cBRSKI uses a compact CBOR-encoded voucher.  The
   BRSKI voucher data definition is extended with new data types that
   allow for smaller voucher sizes.  The Enrollment over Secure
   Transport (EST) protocol, used in BRSKI, is replaced with EST-over-
   CoAPS; and HTTPS used in BRSKI is replaced with DTLS-secured CoAP
   (CoAPS).  This document Updates RFC 8995 and RFC 9148.

	 </t>
      </abstract>
   </front>
   <seriesInfo name="Internet-Draft" value="draft-ietf-anima-constrained-voucher-25"/>

</reference> 10/28/2024 -->
        <xi:include href="https://datatracker.ietf.org/doc/bibxml3/reference.I-D.ietf-anima-constrained-voucher.xml"/>

        <reference anchor="BRSKI-AE-overview" > anchor="BRSKI-AE-OVERVIEW" target="https://datatracker.ietf.org/meeting/116/materials/slides-116-anima-update-on-brski-ae-alternative-enrollment-protocols-in-brski-00">
          <front>
    <title>BRSKI-AE Protocol Overview</title>
    <author initials="" surname="S.&nbsp;Fries" fullname="S.&nbsp;Fries">
      <organization></organization>
    </author>
            <title>Update on BRSKI-AE: Alternative Enrollment Protocols in BRSKI</title>
            <author initials="D." surname="von&nbsp;Oheimb">
      <organization></organization> surname="von Oheimb" fullname="David von Oheimb" role="editor">
              <organization/>
            </author>
    <date year="2023" month="March"/>
  </front>
  <format type="PDF" target="https://datatracker.ietf.org/meeting/116/materials/slides-116-anima-update-on-brski-ae-alternative-enrollment-protocols-in-brski-00"/>
<annotation>Graphics on slide 4 of the status update on the BRSKI-AE draft 04 at IETF 116.</annotation></reference>

<reference anchor="RFC2986">
  <front>
    <title>PKCS #10: Certification Request Syntax Specification Version 1.7</title>
    <author fullname="M. Nystrom" initials="M." surname="Nystrom"/>
    <author fullname="B. Kaliski" initials="B." surname="Kaliski"/>
    <date month="November" year="2000"/>
    <abstract>
      <t>This memo represents a republication of PKCS #10 v1.7 from RSA Laboratories' Public-Key Cryptography Standards (PKCS) series, and change control is retained within the PKCS process. The body of this document, except for the security considerations section, is taken directly from the PKCS #9 v2.0 or the PKCS #10 v1.7 document. This memo provides information for the Internet community.</t>
    </abstract>
  </front>
  <seriesInfo name="RFC" value="2986"/>
  <seriesInfo name="DOI" value="10.17487/RFC2986"/>
</reference>

<reference anchor="RFC4210">
  <front>
    <title>Internet X.509 Public Key Infrastructure Certificate Management Protocol (CMP)</title>
    <author fullname="C. Adams" initials="C." surname="Adams"/>
            <author fullname="S. Farrell" initials="S." surname="Farrell"/>
    <author fullname="T. Kause" initials="T." surname="Kause"/>
    <author fullname="T. Mononen" initials="T." surname="Mononen"/>
    <date month="September" year="2005"/>
    <abstract>
      <t>This document describes the Internet X.509 Public Key Infrastructure (PKI) Certificate Management Protocol (CMP). Protocol messages are defined for X.509v3 certificate creation and management. CMP provides on-line interactions between PKI components, including an exchange between a Certification Authority (CA) and a client system. [STANDARDS-TRACK]</t>
    </abstract>
  </front>
  <seriesInfo name="RFC" value="4210"/>
  <seriesInfo name="DOI" value="10.17487/RFC4210"/>
</reference>

<reference anchor="RFC4211">
  <front>
    <title>Internet X.509 Public Key Infrastructure Certificate Request Message Format (CRMF)</title> surname="Fries" fullname="Steffen Fries">
              <organization/>
            </author>
            <author fullname="J. Schaad" initials="J." surname="Schaad"/> initials="H." surname="Brockhaus" fullname="Hendrik Brockhaus">
              <organization/>
            </author>
            <date month="September" year="2005"/>
    <abstract>
      <t>This document describes the Certificate Request Message Format (CRMF) syntax and semantics. This syntax is used to convey a request for a certificate to a Certification Authority (CA), possibly via a Registration Authority (RA), for the purposes of X.509 certificate production. The request will typically include a public key and the associated registration information. This document does not define a certificate request protocol. [STANDARDS-TRACK]</t>
    </abstract> year="2023" month="March"/>
          </front>
  <seriesInfo name="RFC" value="4211"/>
  <seriesInfo name="DOI" value="10.17487/RFC4211"/>
	  <refcontent>IETF 116 - ANIMA Working Group Presentation</refcontent>
        </reference>

<reference anchor="RFC5272">
  <front>
    <title>Certificate Management over CMS (CMC)</title>
    <author fullname="J. Schaad" initials="J." surname="Schaad"/>
    <author fullname="M. Myers" initials="M." surname="Myers"/>
    <date month="June" year="2008"/>
    <abstract>
      <t>This document defines the base syntax for CMC, a Certificate Management protocol using the Cryptographic Message Syntax (CMS). This protocol addresses two immediate needs within the Internet Public Key Infrastructure (PKI) community:</t>
      <t>1. The need for an interface to public key certification products and services based on CMS and PKCS #10 (Public Key Cryptography Standard), and</t>
      <t>2.

        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.2986.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.4210.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.4211.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5272.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5652.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5929.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.6955.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7030.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8366.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8894.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8994.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9148.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9480.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9482.xml"/>

<!-- TH TODO: The need for a PKI enrollment protocol for encryption only keys due to algorithm or hardware design.</t>
      <t>CMC also requires the use of the transport document and the requirements usage document along with this document for a full definition. [STANDARDS-TRACK]</t>
    </abstract>
  </front>
  <seriesInfo name="RFC" value="5272"/>
  <seriesInfo name="DOI" value="10.17487/RFC5272"/>
</reference>

<reference anchor="RFC5652">
  <front>
    <title>Cryptographic Message Syntax (CMS)</title>
    <author fullname="R. Housley" initials="R." surname="Housley"/>
    <date month="September" year="2009"/>
    <abstract>
      <t>This document describes the Cryptographic Message Syntax (CMS). This syntax is used to digitally sign, digest, authenticate, or encrypt arbitrary message content. [STANDARDS-TRACK]</t>
    </abstract>
  </front>
  <seriesInfo name="STD" value="70"/>
  <seriesInfo name="RFC" value="5652"/>
  <seriesInfo name="DOI" value="10.17487/RFC5652"/>
</reference>

<reference anchor="RFC5929">
  <front>
    <title>Channel Bindings for TLS</title>
    <author fullname="J. Altman" initials="J." surname="Altman"/>
    <author fullname="N. Williams" initials="N." surname="Williams"/>
    <author fullname="L. Zhu" initials="L." surname="Zhu"/>
    <date month="July" year="2010"/>
    <abstract>
      <t>This document defines three channel binding types for Transport Layer Security (TLS), tls-unique, tls-server-end-point, and tls-unique-for-telnet, in accordance with RFC 5056 (On Channel Binding).</t>
      <t>Note that based on implementation experience, this document changes the original definition of 'tls-unique' channel binding type in the channel binding type IANA registry. [STANDARDS-TRACK]</t>
    </abstract>
  </front>
  <seriesInfo name="RFC" value="5929"/>
  <seriesInfo name="DOI" value="10.17487/RFC5929"/>
</reference>

<reference anchor="RFC6955">
  <front>
    <title>Diffie-Hellman Proof-of-Possession Algorithms</title>
    <author fullname="J. Schaad" initials="J." surname="Schaad"/>
    <author fullname="H. Prafullchandra" initials="H." surname="Prafullchandra"/>
    <date month="May" year="2013"/>
    <abstract>
      <t>This document describes two methods for producing an integrity check value from a Diffie-Hellman key pair and one method for producing an integrity check value from an Elliptic Curve key pair. This behavior is needed normative references for such operations as creating the signature of a Public-Key Cryptography Standards (PKCS) #10 Certification Request. These algorithms are designed to provide a Proof-of-Possession of the private key and 2017 version do not to be a general purpose signing algorithm.</t>
      <t>This document obsoletes
include RFC 2875.</t>
    </abstract>
  </front>
  <seriesInfo name="RFC" value="6955"/>
  <seriesInfo name="DOI" value="10.17487/RFC6955"/>
</reference>

<reference anchor="RFC7030">
  <front>
    <title>Enrollment over Secure Transport</title>
    <author fullname="M. Pritikin" initials="M." role="editor" surname="Pritikin"/>
    <author fullname="P. Yee" initials="P." role="editor" surname="Yee"/>
    <author fullname="D. Harkins" initials="D." role="editor" surname="Harkins"/>
    <date month="October" year="2013"/>
    <abstract>
      <t>This document profiles certificate enrollment for clients using Certificate Management over CMS (CMC) messages over a secure transport. This profile, called Enrollment over Secure Transport (EST), describes a simple, yet functional, certificate management protocol targeting Public Key Infrastructure (PKI) clients that need to acquire client certificates and associated Certification Authority (CA) certificates. It also supports client-generated public/private key pairs as well as key pairs generated by the CA.</t>
    </abstract>
  </front>
  <seriesInfo name="RFC" value="7030"/>
  <seriesInfo name="DOI" value="10.17487/RFC7030"/>
</reference>

<reference anchor="RFC8366">
  <front>
    <title>A Voucher Artifact for Bootstrapping Protocols</title>
    <author fullname="K. Watsen" initials="K." surname="Watsen"/>
    <author fullname="M. Richardson" initials="M." surname="Richardson"/>
    <author fullname="M. Pritikin" initials="M." surname="Pritikin"/>
    <author fullname="T. Eckert" initials="T." surname="Eckert"/>
    <date month="May" year="2018"/>
    <abstract>
      <t>This document defines a strategy to securely assign a pledge to an owner using an artifact signed, directly or indirectly, by the pledge's manufacturer. This artifact is known as a "voucher".</t>
      <t>This document defines an artifact format as a YANG-defined JSON document that has been signed using a Cryptographic Message Syntax (CMS) structure. Other YANG-derived formats are possible. The voucher artifact is normally generated by the pledge's manufacturer (i.e., the Manufacturer Authorized Signing Authority (MASA)).</t>
      <t>This document only defines the voucher artifact, leaving it to other documents to describe specialized protocols for accessing it.</t>
    </abstract>
  </front>
  <seriesInfo name="RFC" value="8366"/>
  <seriesInfo name="DOI" value="10.17487/RFC8366"/>
</reference>

<reference anchor="RFC8894">
  <front>
    <title>Simple Certificate Enrolment Protocol</title>
    <author fullname="P. Gutmann" initials="P." surname="Gutmann"/>
    <date month="September" year="2020"/>
    <abstract>
      <t>This document specifies 8894 (SCEP). Rather, they reference the Simple Certificate Enrolment Protocol (SCEP), a PKI protocol that leverages existing technology by using Cryptographic Message Syntax (CMS, formerly known as PKCS #7) and PKCS #10 over HTTP. SCEP Internet-Draft. RFC
8894 is the evolution of the enrolment protocol sponsored by Cisco Systems, which enjoys wide support referenced in both client and server implementations, as well as being relied upon by numerous other industry standards that work with certificates.</t>
    </abstract>
  </front>
  <seriesInfo name="RFC" value="8894"/>
  <seriesInfo name="DOI" value="10.17487/RFC8894"/>
</reference>

<reference anchor="RFC8994">
  <front>
    <title>An Autonomic Control Plane (ACP)</title>
    <author fullname="T. Eckert" initials="T." role="editor" surname="Eckert"/>
    <author fullname="M. Behringer" initials="M." role="editor" surname="Behringer"/>
    <author fullname="S. Bjarnason" initials="S." surname="Bjarnason"/>
    <date month="May" year="2021"/>
    <abstract>
      <t>Autonomic functions need a control plane to communicate, which depends on some addressing and routing. This Autonomic Control Plane should ideally be self-managing and be as independent as possible of configuration. This document defines such a plane and calls it the "Autonomic Control Plane", with the primary use as a control plane for autonomic functions. It also serves as a "virtual out-of-band channel" for Operations, Administration, and Management (OAM) communications over a network that provides automatically configured, hop-by-hop authenticated and encrypted communications via automatically configured IPv6 even when the network is not configured or is misconfigured.</t>
    </abstract>
  </front>
  <seriesInfo name="RFC" value="8994"/>
  <seriesInfo name="DOI" value="10.17487/RFC8994"/>
</reference>

<reference anchor="RFC9148">
  <front>
    <title>EST-coaps: Enrollment over Secure Transport with the Secure Constrained Application Protocol</title>
    <author fullname="P. van der Stok" initials="P." surname="van der Stok"/>
    <author fullname="P. Kampanakis" initials="P." surname="Kampanakis"/>
    <author fullname="M. Richardson" initials="M." surname="Richardson"/>
    <author fullname="S. Raza" initials="S." surname="Raza"/>
    <date month="April" year="2022"/>
    <abstract>
      <t>Enrollment over Secure Transport (EST) is used as a certificate provisioning protocol over HTTPS. Low-resource devices often use the lightweight Constrained Application Protocol (CoAP) for message exchanges. This document defines how to transport EST payloads over secure CoAP (EST-coaps), which allows constrained devices to use existing EST functionality for provisioning certificates.</t>
    </abstract>
  </front>
  <seriesInfo name="RFC" value="9148"/>
  <seriesInfo name="DOI" value="10.17487/RFC9148"/>
</reference> 2023 version.-->

        <reference anchor="RFC9480"> anchor="IEC-62351-9" target="https://webstore.iec.ch/en/publication/30287">
          <front>
    <title>Certificate Management Protocol (CMP) Updates</title>
    <author fullname="H. Brockhaus" initials="H." surname="Brockhaus"/>
    <author fullname="D. von Oheimb" initials="D." surname="von Oheimb"/>
    <author fullname="J. Gray" initials="J." surname="Gray"/>
    <date month="November" year="2023"/>
    <abstract>
      <t>This document contains a set of updates to the syntax of Certificate Management Protocol (CMP) version 2
            <title>Power systems management and its HTTP transfer mechanism. This document updates RFCs 4210, 5912, associated information exchange - Data and 6712.</t>
      <t>The aspects of CMP updated in this document are using EnvelopedData instead of EncryptedValue, clarifying the handling of p10cr messages, improving the crypto agility, as well as adding new general message types, extended communications security - Part 9: Cyber security key usages to identify certificates management for use with CMP, and well-known URI path segments.</t>
      <t>CMP version 3 is introduced to enable signaling support of EnvelopedData instead of EncryptedValue and signal the use of an explicit hash AlgorithmIdentifier in certConf messages, as far as needed.</t>
    </abstract> power system equipment</title>
            <author>
              <organization>International Electrotechnical Commission</organization>
            </author>
            <date year="2017" month="May"/>
          </front>
          <seriesInfo name="RFC" value="9480"/>
  <seriesInfo name="DOI" value="10.17487/RFC9480"/> name="IEC" value="62351-9:2017"/>
        </reference>

<reference anchor="RFC9482">
  <front>
    <title>Constrained Application Protocol (CoAP) Transfer for the Certificate Management Protocol</title>
    <author fullname="M. Sahni" initials="M." role="editor" surname="Sahni"/>
    <author fullname="S. Tripathi" initials="S." role="editor" surname="Tripathi"/>
    <date month="November" year="2023"/>
    <abstract>
      <t>This document specifies the use of the Constrained Application Protocol (CoAP) as a transfer mechanism for the Certificate Management Protocol (CMP). CMP defines the interaction between various PKI entities

<!-- XML for the purpose of certificate creation and management. CoAP is an HTTP-like client-server protocol used by various constrained devices in the Internet 2023 version of Things space.</t>
    </abstract>
  </front>
  <seriesInfo name="RFC" value="9482"/>
  <seriesInfo name="DOI" value="10.17487/RFC9482"/>
</reference> [IEC-62351-9]:
        <reference anchor="IEC-62351-9" > target="https://webstore.iec.ch/en/publication/66864">
          <front>
    <title>IEC 62351 - Power
            <title>Power systems management and associated information exchange - Data and communications security - Part 9: Cyber security key management for power system equipment</title>
    <author >
            <author>
              <organization>International Electrotechnical Commission</organization>
            </author>
            <date year="2017" month="May"/> year="2023" month="June"/>
          </front>
          <seriesInfo name="IEC" value="62351-9 "/> value="62351-9:2023"/>
        </reference>
-->

        <reference anchor="NERC-CIP-005-5" > target="">
          <front>
            <title>Cyber Security - Electronic Security Perimeter</title>
    <author >
            <author>
              <organization>North American Electric Reliability Council</organization>
            </author>
            <date year="2013" month="December"/>
          </front>
          <seriesInfo name="CIP" value="005-5"/>
        </reference>

<!-- [ISO-IEC-15118-2] Note to PE: The correct series number for this
reference is "ISO 15118-2:2014", rather than "ISO/IEC 15118-2". Although some
sources say this reference is also an IEC doc (for example:
https://en.wikipedia.org/wiki/ISO_15118) the correct SDO is simply ISO. It may
be a good idea to update the cite tag to [ISO-15118-2], since I was unable to
find any versions of this reference which mention IEC. -->

        <reference anchor="ISO-IEC-15118-2" > target="https://www.iso.org/standard/55366.html">
          <front>
    <title>ISO/IEC 15118-2 Road
            <title>Road vehicles - Vehicle-to-Grid Communication Interface - Part 2: Network and application protocol requirements</title>
    <author >
            <author>
              <organization>International Standardization Organization / International Electrotechnical Commission</organization> for Standardization</organization>
            </author>
            <date year="2014" month="April"/>
          </front>
          <seriesInfo name="ISO/IEC" value="15118-2 "/> name="ISO" value="15118-2:2014"/>
        </reference>

<!-- [UNISIG-Subset-137]

For RE/PE during AUTH 48 - Updated XML for [UNISIG-Subset-137]:

        <reference anchor="UNISIG-Subset-137" target="">
          <front>
            <title>ERTMS/ETCS On-line Key Management FFFIS</title>
            <author>
              <organization>UNISIG</organization>
            </author>
            <date year="2023" month="May"/>
          </front>
	  <refcontent>Subset-137, Version 4.0.0</refcontent>
        </reference>

-->

        <reference anchor="UNISIG-Subset-137" > target="https://www.era.europa.eu/sites/default/files/filesystem/ertms/ccs_tsi_annex_a_-_mandatory_specifications/set_of_specifications_3_etcs_b3_r2_gsm-r_b1/index083_-_subset-137_v100.pdf">
          <front>
    <title>Subset-137; ERTMS/ETCS
            <title>ERTMS/ETCS On-line Key Management FFFIS; V1.0.0</title>
    <author > FFFIS</title>
            <author>
              <organization>UNISIG</organization>
            </author>
            <date year="2015" month="December"/>
          </front>
  <format type="PDF" target="https://www.era.europa.eu/sites/default/files/filesystem/ertms/ccs_tsi_annex_a_-_mandatory_specifications/set_of_specifications_3_etcs_b3_r2_gsm-r_b1/index083_-_subset-137_v100.pdf"/>
<annotation>http://www.kmc-subset137.eu/index.php/download/</annotation></reference>
	  <refcontent>Subset-137, Version 1.0.0</refcontent>
        </reference>

        <reference anchor="OCPP" > anchor="OCPP">
          <front>
            <title>Open Charge Point Protocol 2.0.1 (Draft)</title>
    <author >
            <author>
              <organization>Open Charge Alliance</organization>
            </author>
            <date year="2019" month="December"/>
          </front>
        </reference>

<reference anchor="I-D.ietf-anima-brski-discovery">
   <front>
      <title>Discovery for BRSKI variations</title>
      <author fullname="Toerless Eckert" initials="T. T." surname="Eckert">
         <organization>Futurewei USA</organization>
      </author>
      <author fullname="Esko Dijk" initials="E." surname="Dijk">
         <organization>IoTconsultancy.nl</organization>
      </author>
      <date day="25" month="July" year="2024"/>
      <abstract>
	 <t>   This document specifies how BRSKI entities, such as registrars,
   proxies, pledges or others that are acting as responders, can be
   discovered and selected by BRSKI entities acting

<!-- [I-D.ietf-anima-brski-discovery] IESG State: I-D Exists as initiators.

	 </t>
      </abstract>
   </front>
   <seriesInfo name="Internet-Draft" value="draft-ietf-anima-brski-discovery-04"/>

</reference> of 10/28/2024 -->
        <xi:include href="https://datatracker.ietf.org/doc/bibxml3/reference.I-D.ietf-anima-brski-discovery.xml"/>

      </references>
    </references>
    <?line 1287?>

<section anchor="app-examples"><name>Application anchor="app-examples">
      <name>Application Examples</name>
      <t>This informative annex provides some detail details about application examples.</t>

      <section anchor="rolling-stock"><name>Rolling anchor="rolling-stock">
        <name>Rolling Stock</name>
        <t>Rolling stock or railroad cars contain a variety of sensors,
        actuators, and controllers, which controllers. These communicate within the railroad car
        but also exchange information between railroad cars cars, forming a train, train
        with track-side equipment, equipment and/or possibly with backend systems.
        These devices are typically unaware of backend system connectivity.
        Enrolling certificates may be done during maintenance cycles of the
        railroad car, car but can already be prepared during operation.  Such
        asynchronous enrollment will include generating certification
        requests, which are collected and later forwarded for processing
        whenever the railroad car gets connectivity with the backend PKI of
        the operator.  The authorization of the certification request is then
        done based on the operator's asset/inventory information in the
        backend.</t>
        <t>UNISIG has included a CMP profile for the enrollment of TLS client
        and server X.509 certificates of on-board and track-side
        components in the Subset-137 specifying Subset-137, which specifies the ETRAM/ETCS online
        key management for train control systems <xref
        target="UNISIG-Subset-137"/>.</t>
      </section>

      <section anchor="building-automation"><name>Building anchor="building-automation">
        <name>Building Automation</name>
        <t>In building automation scenarios, a detached building or the
        basement of a building may be equipped with sensors, actuators, and
        controllers that are connected to each other in a local network but
        with only limited or no connectivity to a central building management
        system.  This problem may occur during installation time but also
        during operation.  In such a situation situation, a service technician collects
        the necessary data and transfers it between the local network and the
        central building management system, e.g., using a laptop or a mobile
        phone.  This data may comprise parameters and settings required in the
        operational phase of the sensors/actuators, like a component
        certificate issued by the operator to authenticate against other
        components and services.</t>
        <t>The collected data may be provided by a domain registrar already
        existing in the local network. In this case case, connectivity to the
        backend PKI may be facilitated by the service technician's laptop.
        Alternatively, the data can also be collected from the pledges
        directly and provided to a domain registrar deployed in a different
        network in preparation for the operational phase.  In this case,
        connectivity to the domain registrar may also be facilitated by the
        service technician's laptop.</t>
      </section>
      <section anchor="substation-automation"><name>Substation anchor="substation-automation">
        <name>Substation Automation</name>
        <t>In electrical substation automation scenarios, a control center
        typically hosts PKI services to issue certificates for Intelligent
        Electronic Devices (IEDs) operated in a substation. Communication
        between the substation and control center is performed through a
        proxy/gateway/DMZ, which terminates protocol flows.  Note that
        <xref target="NERC-CIP-005-5"/> requires inspection of protocols at
        the boundary of a security perimeter (the substation in (in this case). case, the substation).
        In addition, security management in substation automation assumes
        central support of several enrollment protocols to support the various
        capabilities of IEDs from different vendors.  The IEC standard
        IEC62351-9 <xref target="IEC-62351-9"/> specifies for the infrastructure side mandatory support of
        two enrollment protocols: protocols for the infrastructure side, SCEP <xref
        target="RFC8894"/> and EST <xref target="RFC7030"/>, while an Intelligent Electronic Device
        IED may support only one of them.</t>
      </section>
      <section anchor="electric-vehicle-charging-infrastructure"><name>Electric anchor="electric-vehicle-charging-infrastructure">
        <name>Electric Vehicle Charging Infrastructure</name>
        <t>For electric vehicle charging infrastructure, protocols have been
        defined for the interaction between the electric vehicle and the
        charging point (e.g., ISO 15118-2 <xref target="ISO-IEC-15118-2"/>) as
        well as between the charging point and the charging point operator
(e.g.
        (e.g., OCPP <xref target="OCPP"/>). Depending on the authentication
        model, unilateral or mutual authentication is required. In both cases,
        the charging point uses an X.509 certificate to authenticate itself in
        TLS channels between the electric vehicle and the charging point. The
        management of this certificate depends, among others, other things, on the selected
        backend connectivity protocol.  In the case of OCPP, this protocol is
        meant to be the only communication protocol between the charging point
        and the backend, carrying all information to control the charging
        operations and maintain the charging point itself. This means that the
        certificate management needs to be handled in-band of OCPP. This
        requires the ability to encapsulate the certificate management
        messages in a transport-independent way.  Authenticated
        self-containment will support this by allowing the transport without a
        separate enrollment protocol, binding the messages to the identity of
        the communicating endpoints.</t>
      </section>
      <section anchor="infrastructure-isolation"><name>Infrastructure anchor="infrastructure-isolation">
        <name>Infrastructure Isolation Policy</name>

        <t>This refers to any case in which network infrastructure is normally
        isolated from the Internet as a matter of policy, most likely for
        security reasons. In such a case, limited access to external PKI
        services will be allowed in carefully controlled short periods of
time, for example
        time (for example, when a batch of new devices is deployed, deployed) and
        forbidden or prevented at other times.</t>
      </section>

      <section anchor="sites-with-insufficient-level-of-operational-security"><name>Sites anchor="sites-with-insufficient-level-of-operational-security">
        <name>Sites with Insufficient Level Levels of Operational Security</name>
        <t>The RA performing (at least part of) the authorization of a
        certification request is a critical PKI component and therefore
        requires higher operational security than components utilizing the
        issued certificates for their security features. CAs may also demand
        higher security in the registration procedures from RAs, which domain
        registrars with co-located RAs may not be able to fulfill.
Especially  In
        particular, the CA/Browser forum currently increases the security
        requirements in the certificate issuance procedures for publicly
        trusted certificates, i.e., those placed in trust stores of browsers,
        which may be used to connect with devices in the domain.  In case the
        on-site components of the target domain can not cannot be operated securely
        enough for the needs of an RA, this service should be transferred to
        an off-site backend component that has a sufficient level of
        security.</t>
      </section>
    </section>
<section anchor="app_history"><name>History of Changes TBD RFC Editor: please delete</name>

<t>List of reviewers:</t>

<t><list style="symbols">
  <t>Toerless Eckert (document shepherd)</t>
  <t>Barry Leiba (SECdir)</t>
  <t>Mahesh Jethanandani (IETF area director)</t>
  <t>Meral Shirazipour (Gen-ART reviewer)</t>
  <t>Deb Cooley, Gunter Van de Velde, John Scudder, Murray Kucherawy, Roman Danyliw,
and Éric Vyncke (IESG reviewers)</t>
  <t>Michael Richardson (ANIMA design team)</t>
  <t>Rajeev Ranjan, Rufus Buschart, Szofia Fazekas-Zisch, etc. (Siemens)</t>
  <t>Reshad Rahman (YANGDOCTORS reviewer). Note that
<eref target="https://datatracker.ietf.org/doc/review-ietf-anima-brski-async-enroll-03-yangdoctors-early-rahman-2021-08-15/">YANGDOCTORS Early review of 2021-08-15</eref>
referred to the PRM aspect of <eref target="https://datatracker.ietf.org/doc/draft-ietf-anima-brski-async-enroll/03/">draft-ietf-anima-brski-async-enroll-03</eref>.
This has been carved out of the draft to a different one and thus is no more
applicable here.</t>
</list></t>

<t>IETF draft ae-12 -&gt; ae-13:</t>

<t><list style="symbols">
  <t>Due to IANA requirement, shorten service name <spanx style="verb">"brski-registrar-cmp"</spanx> to <spanx style="verb">"brski-reg-cmp"</spanx><br />
and change contact for service name registration from IESG to IETF</t>
  <t>Address Deb Cooley's DISCUSS by adding an item to the requirements list
<xref target="brski-cmp-instance"/> making the source of the initial trust anchor explicit.
<br />
Including the vouchers in <xref target="enrollfigure"/> would not fit because the figure
has a different scope (namely, certificate enrollment) and would get overloaded.</t>
  <t>Address Gunter Van de Velde's comments by taking over essentially all his
rewrites of text to help the structure and simplify reading the content,
while keeping the original message, as it helps improve document quality</t>
  <t>Address John Scudder's comments by tweaking <xref target="terminology"/>, fully alphabetizing terms</t>
  <t>Address Murray Kucherawy's comment
by adapting terminology entries, leaving out 'communication'
from 'asynchronous communication' and 'synchronous communication'</t>
  <t>Address Roman Danyliw's comments by updating reference<br />
I-D.eckert-anima-brski-discovery to I-D.ietf-anima-brski-discovery<br /> and
adding <xref target="priv-consider"/>, which refers to the BRSKI privacy considerations.</t>
  <t>Address Éric Vyncke's comment by replacing 'production' by 'manufacturing'</t>
</list></t>

<t>IETF draft ae-11 -&gt; ae-12:</t>

<t><list style="symbols">
  <t>Fix minor issues introduced during authors' response to the AD review,<br />
including nits spotted in the Gen-ART review by Meral Shirazipour</t>
</list></t>

<t>IETF draft ae-10 -&gt; ae-11:</t>

<t><list style="symbols">
  <t>In response to AD review by Mahesh Jethanandani,
  <list style="symbols">
      <t>replace most occurrences of 'Note:' by 'Note that' or the like</t>
      <t>move 2nd paragraph of abstract to the introduction</t>
      <t>remove section 1.2 and merge its first paragraph with the preceding section</t>
      <t>reconsider normative language, replacing one 'may' by '<bcp14>MAY</bcp14>' in section 4.1</t>
      <t>fix several ambiguities and hard-to-read sentences by re-phrasing them</t>
      <t>make wording more consistent, in particular: 'certification request'</t>
      <t>fix a number of (mostly grammar) nits</t>
    </list></t>
  <t>Improve item on limitations of PKCS#10 regarding keys that cannot sign</t>
</list></t>

<t>IETF draft ae-09 -&gt; ae-10:</t>

<t><list style="symbols">
  <t>Add reference to RFC 8633 at first occurrence of 'voucher' (fixes #37)</t>
  <t>Update reference of CoAP Transfer for CMP from I-D to RFC 9482</t>
  <t>Move RFC 4210 and RFC 9480 references from normative to informative</t>
  <t>Fix <spanx style="verb">p10</spanx> vs. <spanx style="verb">pkcs10</spanx> entry in list of example endpoints in <xref target="addressing"/></t>
  <t>Minor fix in <xref target="uc1figure"/> and few text tweaks due to Siemens-internal review</t>
  <t>Extend the list of reviewers and acknowledgments by two Siemens colleagues</t>
</list></t>

<t>IETF draft ae-08 -&gt; ae-09:</t>

<t><list style="symbols">
  <t>In response to review by Toerless,
  <list style="symbols">
      <t>tweak abstract to make meaning of 'alternative enrollment' more clear</t>
      <t>expand on first use not "well-known" abbreviations, such as 'EST',<br />
adding also a references on their first use</t>
      <t>add summary and reason for choosing CMP at end of <xref target="solutions-PoI"/></t>
      <t>remove paragraph on optimistic discovery in controlled environments</t>
      <t>mention role of reviewers also in acknowledgments section</t>
    </list></t>
  <t>A couple of grammar and spelling fixes</t>
</list></t>

<t>IETF draft ae-07 -&gt; ae-08:</t>

<t><list style="symbols">
  <t>Update references to service names in <xref target="brski-cmp-instance"/></t>
</list></t>

<t>IETF draft ae-06 -&gt; ae-07:</t>

<t><list style="symbols">
  <t>Update subsections on discovery according to discussion in the design team</t>
  <t>In <xref target="brski-cmp-instance"/>,
replace 'mandatory' by '<bcp14>REQUIRED</bcp14>' regarding adherence to LCMPP,<br />
in response to SECDIR Last Call Review of ae-06 by Barry Leiba</t>
</list></t>

<t>IETF draft ae-05 -&gt; ae-06:</t>

<t><list style="symbols">
  <t>Extend section on discovery according to discussion in the design team</t>
  <t>Make explicit that MASA voucher status telemetry is as in BRSKI</t>
  <t>Add note that on delegation, RA may need info on pledge authorization</t>
</list></t>

<t>IETF draft ae-04 -&gt; ae-05:</t>

<t><list style="symbols">
  <t>Remove entries from the terminology section that should be clear from BRSKI</t>
  <t>Tweak use of the terms IDevID and LDevID and replace PKI RA/CA by RA/CA</t>
  <t>Add the abbreviation 'LCMPP' for Lightweight CMP Profile to the terminology section</t>
  <t>State clearly in <xref target="brski-cmp-instance"/> that LCMPP is mandatory when using CMP</t>
  <t>Change URL of BRSKI-AE-overview graphics to slide on IETF 116 meeting material</t>
</list></t>

<t>IETF draft ae-03 -&gt; ae-04:</t>

<t><list style="symbols">
  <t>In response to SECDIR Early Review of ae-03 by Barry Leiba,
  <list style="symbols">
      <t>replace 'end-to-end security' by the more clear 'end-to-end authentication'</t>
      <t>restrict the meaning of the abbreviation 'AE' to 'Alternative Enrollment'</t>
      <t>replace '<bcp14>MAY</bcp14>' by 'may' in requirement on delegated registrar actions</t>
      <t>re-phrase requirement on certification request exchange, avoiding MANDATORY</t>
      <t>mention that further protocol names need be put in Well-Known URIs registry</t>
      <t>explain consequence of using non-standard endpoints, not following <bcp14>SHOULD</bcp14></t>
      <t>remove requirement that 'caPubs' field in CMP responses <bcp14>SHOULD NOT</bcp14> be used</t>
      <t>add paragraph in security considerations on additional use of TLS for CMP</t>
    </list></t>
  <t>In response to further internal reviews and suggestions for generalization,
  <list style="symbols">
      <t>significantly cut down the introduction because the original motivations and
most explanations are no more needed and would just make it lengthy to read</t>
      <t>sort out asynchronous vs. offline transfer, off-site vs. backend components</t>
      <t>improve description of CSRs and proof of possession vs. proof of origin</t>
      <t>clarify that the channel between pledge and registrar is not restricted
to TLS, but in connection with constrained BRSKI may also be DTLS.
Also move the references to Constrained BRSKI and CoAPS to better contexts.</t>
      <t>clarify that the registrar must not be circumvented in the decision to grant
and LDevID, and give hints and recommendations how to make sure this</t>
      <t>clarify that the cert enrollment phase may involve additional messages
and that BRSKI-AE replaces <xref section="5.9" sectionFormat="comma" target="RFC8995"/> (except Section 5.9.4)
<!--
clarify that messages of the cert enrollment phase are RECOMMENDED to be
transmitted on the existing channel between the pledge and the registrar
--></t>
      <t>the certificate enrollment protocol needs to support transport over (D)TLS
only as far as its messages are transported between pledge and registrar.</t>
      <t>the certificate enrollment protocol chosen between pledge and registrar
needs to be used also for the upstream enrollment exchange with the PKI only
if end-to-end authentication shall be achieved across the registrar to the PKI.</t>
      <t>add that with CMP, further trust anchors <bcp14>SHOULD</bcp14> be transported via <spanx style="verb">caPubs</spanx></t>
      <t>remove the former Appendix A: "Using EST for Certificate Enrollment",
moving relevant points to the list of scenarios in
<xref target="sup-env"/>: "Supported Scenarios",</t>
      <t>streamline the item on EST in
<xref target="solutions-PoI"/>: "Solution Options for Proof of Identity",</t>
      <t>various minor editorial improvements like making the wording more consistent</t>
    </list></t>
</list></t>

<t>IETF draft ae-02 -&gt; ae-03:</t>

<t><list style="symbols">
  <t>In response to review by Toerless Eckert,
  <list style="symbols">
      <t>many editorial improvements and clarifications as suggested, such as
the comparison to plain BRSKI, the description of offline vs. synchronous
message transfer and enrollment, and better differentiation of RA flavors.</t>
      <t>clarify that for transporting certificate enrollment messages between
pledge and registrar, the TLS channel established between these two
(via the join proxy) is used and the enrollment protocol <bcp14>MUST</bcp14> support this.</t>
      <t>clarify that the enrollment protocol chosen between pledge and registrar
<bcp14>MUST</bcp14> also be used for the upstream enrollment exchange with the PKI.</t>
      <t>extend the description and requirements on how during the certificate
enrollment phase the registrar <bcp14>MAY</bcp14> handle requests by the pledge itself and
otherwise <bcp14>MUST</bcp14> forward them to the PKI and forward responses to the pledge.</t>
    </list></t>
  <t>Change "The registrar <bcp14>MAY</bcp14> offer different enrollment protocols" to
"The registrar <bcp14>MUST</bcp14> support at least one certificate enrollment protocol ..."</t>
  <t>In response to review by Michael Richardson,
  <list style="symbols">
      <t>slightly improve the structuring of the Message Exchange <xref target="message_ex"/> and
add some detail on the request/response exchanges for the enrollment phase</t>
      <t>merge the 'Enhancements to the Addressing Scheme' <xref target="addressing"/>
with the subsequent one:
'Domain Registrar Support of Alternative Enrollment Protocols'</t>
      <t>add reference to SZTP (RFC 8572)</t>
      <t>extend venue information</t>
      <t>convert output of ASCII-art figures to SVG format</t>
      <t>various small other text improvements as suggested/provided</t>
    </list></t>
  <t>Remove the tentative informative application to EST-fullCMC</t>
  <t>Move Eliot Lear from co-author to contributor, add Eliot to the acknowledgments</t>
  <t>Add explanations for terms such as 'target domain' and 'caPubs'</t>
  <t>Fix minor editorial issues and update some external references</t>
</list></t>

<t>IETF draft ae-01 -&gt; ae-02:</t>

<t><list style="symbols">
  <t>Architecture: clarify registrar role including RA/LRA/enrollment proxy</t>
  <t>CMP: add reference to CoAP Transport for CMPV2 and Constrained BRSKI</t>
  <t>Include venue information</t>
</list></t>

<t>From IETF draft 05 -&gt; IETF draft ae-01:</t>

<t><list style="symbols">
  <t>Renamed the repo and files from 'anima-brski-async-enroll' to 'anima-brski-ae'</t>
  <t>Added graphics for abstract protocol overview as suggested by Toerless Eckert</t>
  <t>Balanced (sub-)sections and their headers</t>
  <t>Added details on CMP instance, now called BRSKI-CMP</t>
</list></t>

<t>From IETF draft 04 -&gt; IETF draft 05:</t>

<t><list style="symbols">
  <t>David von Oheimb became the editor.</t>
  <t>Streamline wording, consolidate terminology, improve grammar, etc.</t>
  <t>Shift the emphasis towards supporting alternative enrollment protocols.</t>
  <t>Update the title accordingly - preliminary change to be approved.</t>
  <t>Move comments on EST and detailed application examples to informative annex.</t>
  <t>Move the remaining text of section 3 as two new sub-sections of section 1.</t>
</list></t>

<t>From IETF draft 03 -&gt; IETF draft 04:</t>

<t><list style="symbols">
  <t>Moved UC2-related parts defining the pledge in responder mode to a
separate document. This required changes and adaptations in several
sections. Main changes concerned the removal of the subsection for UC2
as well as the removal of the YANG model related text as it is not
applicable in UC1.</t>
  <t>Updated references to the Lightweight CMP Profile (LCMPP).</t>
  <t>Added David von Oheimb as co-author.</t>
</list></t>

<t>From IETF draft 02 -&gt; IETF draft 03:</t>

<t><list style="symbols">
  <t>Housekeeping, deleted open issue regarding YANG voucher-request
in UC2 as voucher-request was enhanced with additional leaf.</t>
  <t>Included open issues in YANG model in UC2 regarding assertion
value agent-proximity and CSR encapsulation using SZTP sub module).</t>
</list></t>

<t>From IETF draft 01 -&gt; IETF draft 02:</t>

<t><list style="symbols">
  <t>Defined call flow and objects for interactions in UC2. Object format
based on draft for JOSE signed voucher artifacts and aligned the
remaining objects with this approach in UC2 .</t>
  <t>Terminology change: issue #2 pledge-agent -&gt; registrar-agent to
better underline agent relation.</t>
  <t>Terminology change: issue #3 PULL/PUSH -&gt; pledge-initiator-mode
and pledge-responder-mode to better address the pledge operation.</t>
  <t>Communication approach between pledge and registrar-agent
changed by removing TLS-PSK (former section TLS establishment)
and associated references to other drafts in favor of relying on
higher layer exchange of signed data objects. These data objects
are included also in the pledge-voucher-request and lead to an
extension of the YANG module for the voucher-request (issue #12).</t>
  <t>Details on trust relationship between registrar-agent and
registrar (issue #4, #5, #9) included in UC2.</t>
  <t>Recommendation regarding short-lived certificates for
registrar-agent authentication towards registrar (issue #7) in
the security considerations.</t>
  <t>Introduction of reference to agent signing certificate using SKID
in agent signed data (issue #11).</t>
  <t>Enhanced objects in exchanges between pledge and registrar-agent
to allow the registrar to verify agent-proximity to the pledge
(issue #1) in UC2.</t>
  <t>Details on trust relationship between registrar-agent and
pledge (issue #5) included in UC2.</t>
  <t>Split of use case 2 call flow into sub sections in UC2.</t>
</list></t>

<t>From IETF draft 00 -&gt; IETF draft 01:</t>

<t><list style="symbols">
  <t>Update of scope in <xref target="sup-env"/> to include in
which the pledge acts as a server. This is one main motivation
for use case 2.</t>
  <t>Rework of use case 2 to consider the
transport between the pledge and the pledge-agent. Addressed is
the TLS channel establishment between the pledge-agent and the
pledge as well as the endpoint definition on the pledge.</t>
  <t>First description of exchanged object types (needs more work)</t>
  <t>Clarification in discovery options for enrollment endpoints at
the domain registrar based on well-known endpoints in <xref target="addressing"/>
do not result in additional /.well-known URIs.
Update of the illustrative example.
Note that the change to /brski for the voucher-related endpoints
has been taken over in the BRSKI main document.</t>
  <t>Updated references.</t>
  <t>Included Thomas Werner as additional author for the document.</t>
</list></t>

<t>From individual version 03 -&gt; IETF draft 00:</t>

<t><list style="symbols">
  <t>Inclusion of discovery options of enrollment endpoints at
the domain registrar based on well-known endpoints in
<xref target="addressing"/> as replacement of section 5.1.3
in the individual draft. This is intended to support both use
cases in the document. An illustrative example is provided.</t>
  <t>Missing details provided for the description and call flow in
pledge-agent use case UC2, e.g. to
accommodate distribution of CA certificates.</t>
  <t>Updated CMP example in <xref target="exist_prot"/> to use
Lightweight CMP instead of CMP, as the draft already provides
the necessary /.well-known endpoints.</t>
  <t>Requirements discussion moved to separate section in
<xref target="req-sol"/>. Shortened description of proof-of-identity binding
and mapping to existing protocols.</t>
  <t>Removal of copied call flows for voucher exchange and registrar
discovery flow from <xref target="RFC8995"/> in <xref target="uc1"/> to avoid doubling or text or
inconsistencies.</t>
  <t>Reworked abstract and introduction to be more crisp regarding
the targeted solution. Several structural changes in the document
to have a better distinction between requirements, use case
description, and solution description as separate sections.
History moved to appendix.</t>
</list></t>

<t>From individual version 02 -&gt; 03:</t>

<t><list style="symbols">
  <t>Update of terminology from self-contained to authenticated
self-contained object to be consistent in the wording and to
underline the protection of the object with an existing
credential. Note that the naming of this object may be discussed.
An alternative name may be attestation object.</t>
  <t>Simplification of the architecture approach for the initial use
case having an off-site PKI.</t>
  <t>Introduction of a new use case utilizing authenticated
self-contain objects to onboard a pledge using a commissioning
tool containing a pledge-agent. This requires additional changes
in the BRSKI call flow sequence and led to changes in the
introduction, the application example,and also in the
related BRSKI-AE call flow.</t>
  <t>Update of provided examples of the addressing approach used in
BRSKI to allow for support of multiple enrollment protocols in
<xref target="addressing"/>.</t>
</list></t>

<t>From individual version 01 -&gt; 02:</t>

<t><list style="symbols">
  <t>Update of introduction text to clearly relate to the usage of
IDevID and LDevID.</t>
  <t>Definition of the addressing approach used in BRSKI to allow for
support of multiple enrollment protocols in <xref target="addressing"/>.  This
section also contains a first
discussion of an optional discovery mechanism to address
situations in which the registrar supports more than one enrollment
approach. Discovery should avoid that the pledge performs a trial
and error of enrollment protocols.</t>
  <t>Update of description of architecture elements and
changes to BRSKI in <xref target="architecture"/>.</t>
  <t>Enhanced consideration of existing enrollment protocols in the
context of mapping the requirements to existing solutions in
<xref target="req-sol"/> and in <xref target="exist_prot"/>.</t>
</list></t>

<t>From individual version 00 -&gt; 01:</t>

<t><list style="symbols">
  <t>Update of examples, specifically for building automation as
well as two new application use cases in <xref target="app-examples"/>.</t>
  <t>Deletion of asynchronous interaction with MASA to not
complicate the use case. Note that the voucher exchange can
already be handled in an asynchronous manner and is therefore
not considered further. This resulted in removal of the
alternative path the MASA in Figure 1 and the associated
description in <xref target="architecture"/>.</t>
  <t>Enhancement of description of architecture elements and
changes to BRSKI in <xref target="architecture"/>.</t>
  <t>Consideration of existing enrollment protocols in the context
of mapping the requirements to existing solutions in <xref target="req-sol"/>.</t>
  <t>New section starting <xref target="exist_prot"/> with the
mapping to existing enrollment protocols by collecting
boundary conditions.</t>
</list></t>
-->
<!--
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LocalWords: bcp uc prot vexchange enrollfigure req eo selander coap br iana tcp
LocalWords: oscore fullcmc simpleenroll tls env brski UC seriesinfo IDevID Resp
LocalWords: Attrib lt docname ipr toc anima async wg symrefs ann ae pkcs cert
LocalWords: sortrefs iprnotified Instantiation caPubs raVerified repo reqs Conf
LocalWords: IDentity IDentifier coaps aasvg acp cms json pkixcmp kp DOI abbrev
LocalWords: PoP PoI anufacturer uthorized igning uthority SECDIR nbsp passphrase
LocalWords: ietf cmp lcmpp submissionType kw std org uri cmpv app sol est Certs
LocalWords: github eckert lternative nrollment sec certs reg priv pledge's CMP's
LocalWords: Mahesh Jethanandani Gen ART Meral Shirazipour Deb Cooley's
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<section anchor="acknowledgments" numbered="false">
      <name>Acknowledgments</name>
      <t>We thank <contact fullname="Eliot Lear"/> for his contributions as a
      co-author at an earlier draft stage.</t>
      <t>We thank <contact fullname="Brian E. Carpenter"/>, <contact
      fullname="Michael Richardson"/>, and <contact fullname="Giorgio
      Romanenghi"/> for their input and discussion on use cases and call
      flows.</t>
      <t>Moreover, we thank <contact fullname="Toerless Eckert"/> (document
      shepherd); <contact fullname="Barry Leiba"/> (SECdir review); <contact
      fullname="Mahesh Jethanandani"/> (IETF area director); <contact
      fullname="Meral Shirazipour"/> (Gen-ART reviewer); <contact
      fullname="Reshad Rahman"/> (YANGDOCTORS reviewer); <contact
      fullname="Deb Cooley"/>, <contact fullname="Gunter Van de Velde"/>,
      <contact fullname="John Scudder"/>, <contact fullname="Murray
      Kucherawy"/>, <contact fullname="Roman Danyliw"/>, and <contact
      fullname="Éric Vyncke"/> (IESG reviewers); <contact fullname="Michael
      Richardson"/> (ANIMA design team member); and <contact
      fullname="Rajeev Ranjan"/>, <contact fullname="Rufus Buschart"/>,
      <contact fullname="Andreas Reiter"/>, and <contact fullname="Szofia
      Fazekas-Zisch"/> (Siemens colleagues) for their reviews with suggestions
      for improvements.</t>
</section>

    <section anchor="contributors" numbered="false" toc="include" removeInRFC="false">
      <name>Contributors</name>
      <contact initials="E." surname="Lear" fullname="Eliot Lear">
        <organization>Cisco Systems</organization>
        <address>
          <postal>
            <street>Richtistrasse 7</street>
            <city>Wallisellen</city>
          <code>CH-8304</code>
            <code>8304</code>
            <country>Switzerland</country>
          </postal>
          <phone>+41 44 878 9200</phone>
          <email>lear@cisco.com</email>
        </address>
      </contact>
    </section>
  </back>

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mq4+AQA= [rfced] Formatting and XML:

a.) There are several author comments present in the XML. Please
review and confirm that none of these comments still need to be
addressed. Note that the comments will be deleted prior to
publication.

b.) Please review whether any of the notes in this document
should be in the <aside> element. It is defined as "a container for
content that is semantically less important or tangential to the
content that surrounds it" (https://authors.ietf.org/en/rfcxml-vocabulary#aside).

c.) We note the following different uses regarding this document's use of <tt>
styling and quotation marks. In the HTML and PDF outputs, the text enclosed in
<tt> is output in fixed-width font. In the txt output, there are no changes to
the font. Please review carefully and let us know if any updates should be made
for consistency:

the <tt>caPubs</tt> field
the acp-node-name field  (no quotes or <tt> styling)

<tt>"brski-reg-cmp"</tt>
brski-reg-cmp (no quotes or <tt> styling)

<tt>"brski-registrar"</tt>
<tt>"/.well-known/est/simpleenroll"</tt>
<tt>"/.well-known/&lt;enrollment-protocol&gt;/&lt;request&gt;"</tt>
<tt>"/fullcmc"</tt> endpoint
<tt>"/simpleenroll"</tt> endpoint

'<tt>est</tt>'
'<tt>cmp</tt>'

<tt>&lt;enrollment-protocol&gt;</tt>
<tt>&lt;request&gt;</tt>
The label <tt>[OPTIONAL forwarding]</tt>

'renewal' option
"tls-unique" value
the tls-unique value (no quotes)
-->

<!-- [rfced] Abbreviations:

a.) FYI - We have updated the expansion of LDevID throughout the document
as follows. Please review and let us know of any objections.

Original:
   Locally significant Device IDentifier (LDevID)

Current:
   Local Device Identifier (LDevID)

b.) We note the following expanded forms of "PKI" are used after the
abbreviation is introduced. May we update these instances below to the
abbreviation?

Public-Key Infrastructure
public-key infrastructure

c.) May we update instances of "local RA" to the abbreviation "LRA"?

d.) FYI - We have added expansions for abbreviations upon first use
per Section 3.6 of RFC 7322 ("RFC Style Guide"). Please review each
expansion in the document carefully to ensure correctness.

 Autonomic Control Plane (ACP)
 Certificate Management over CMS (CMC)
 Cryptographic Message Syntax (CMS)
 Constrained Application Protocol (CoAP)
 Simple Certificate Enrollment Protocol (SCEP)
-->

<!-- [rfced] Please review the following changes and questions we have
regarding the References section:

a.) [UNISIG-Subset-137]

The provided URL returns the message: "The requested page could not be found."
We found the following URL from the European Union Agency for Railways (ERA)
website, which matches the specification described in this reference, but it
is a more up-to-date version from May 2023. Would you like to use this version
and URL instead?

<https://www.era.europa.eu/system/files/2023-09/index083_-_SUBSET-137_v400.pdf>

Current:
   [UNISIG-Subset-137]
              UNISIG, "ERTMS/ETCS On-line Key Management FFFIS", Subset-
              137, Version 1.0.0, December 2015,
              <https://www.era.europa.eu/sites/default/files/filesystem/
              ertms/ccs_tsi_annex_a_-_mandatory_specifications/
              set_of_specifications_3_etcs_b3_r2_gsm-r_b1/index083_-
              _subset-137_v100.pdf>.

b.) [BRSKI-AE-OVERVIEW]

FYI - We have removed the text below from the <annotation> element in this
reference. If you would like to include this note, we recommend placing it in
the document where this reference is cited (rather than in the references
section).

   "Graphics on slide 4 of the status update on the BRSKI-AE draft 04 at IETF 116."

c.) [IEC-62351-9]

Would you like to update to the newest version of this reference? The cited
version of this reference has been withdrawn. In addition, this version of the
document references the SCEP Internet-Draft rather than RFC 8894 (SCEP). RFC
8894 is cited in the 2023 version.

Current:
   [IEC-62351-9]
              International Electrotechnical Commission, "Power systems
              management and associated information exchange - Data and
              communications security - Part 9: Cyber security key
              management for power system equipment", IEC 62351-9:2017,
              May 2017, <https://webstore.iec.ch/en/publication/30287>.

-->

<!-- [rfced] Please review the "Inclusive Language" portion of the online
Style Guide <https://www.rfc-editor.org/styleguide/part2/#inclusive_language>
and let us know if any changes are needed.  Updates of this nature typically
result in more precise language, which is helpful for readers.

Note that our script did not flag any words in particular, but this should
still be reviewed as a best practice. -->

</rfc>