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BRSKI with Pledge in Responder Mode (BRSKI-PRM)
draft-ietf-anima-brski-prm-12

Document Type Active Internet-Draft (anima WG)
Authors Steffen Fries , Thomas Werner , Eliot Lear , Michael Richardson
Last updated 2024-03-04
Replaces draft-ietf-anima-brski-async-enroll
RFC stream Internet Engineering Task Force (IETF)
Intended RFC status Proposed Standard
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Stream WG state In WG Last Call
Document shepherd Matthias Kovatsch
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Send notices to ietf@kovatsch.net
draft-ietf-anima-brski-prm-12
ANIMA WG                                                        S. Fries
Internet-Draft                                                 T. Werner
Intended status: Standards Track                                 Siemens
Expires: 5 September 2024                                        E. Lear
                                                           Cisco Systems
                                                           M. Richardson
                                                Sandelman Software Works
                                                            4 March 2024

            BRSKI with Pledge in Responder Mode (BRSKI-PRM)
                     draft-ietf-anima-brski-prm-12

Abstract

   This document defines enhancements to Bootstrapping a Remote Secure
   Key Infrastructure (BRSKI, RFC8995) to enable bootstrapping in
   domains featuring no or only limited connectivity between a pledge
   and the domain registrar.  It specifically changes the interaction
   model from a pledge-initiated mode, as used in BRSKI, to a pledge-
   responding mode, where the pledge is in server role.  For this, BRSKI
   with Pledge in Responder Mode (BRSKI-PRM) introduces a new component,
   the Registrar-Agent, which facilitates the communication between
   pledge and registrar during the bootstrapping phase.  To establish
   the trust relation between pledge and registrar, BRSKI-PRM relies on
   object security rather than transport security.  The approach defined
   here is agnostic to the enrollment protocol that connects the domain
   registrar to the domain CA.

About This Document

   This note is to be removed before publishing as an RFC.

   Status information for this document may be found at
   https://datatracker.ietf.org/doc/draft-ietf-anima-brski-prm/.

   Source for this draft and an issue tracker can be found at
   https://github.com/anima-wg/anima-brski-prm.

Status of This Memo

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

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

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

   This Internet-Draft will expire on 5 September 2024.

Copyright Notice

   Copyright (c) 2024 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   Please review these documents carefully, as they describe your rights
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   6
   3.  Scope of Solution . . . . . . . . . . . . . . . . . . . . . .   7
     3.1.  Supported Environments and Use Case Examples  . . . . . .   8
       3.1.1.  Building Automation . . . . . . . . . . . . . . . . .   8
       3.1.2.  Infrastructure Isolation Policy . . . . . . . . . . .   9
       3.1.3.  Less Operational Security in the Target-Domain  . . .   9
     3.2.  Limitations . . . . . . . . . . . . . . . . . . . . . . .   9
   4.  Requirements Discussion and Mapping to Solution-Elements  . .   9
   5.  Architecture  . . . . . . . . . . . . . . . . . . . . . . . .  11
     5.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .  11
     5.2.  Nomadic Connectivity  . . . . . . . . . . . . . . . . . .  15
     5.3.  Co-located Registrar-Agent and Domain Registrar . . . . .  17
     5.4.  Agent-Proximity Assertion . . . . . . . . . . . . . . . .  18
   6.  System Components . . . . . . . . . . . . . . . . . . . . . .  19
     6.1.  Domain Registrar  . . . . . . . . . . . . . . . . . . . .  19
       6.1.1.  Domain Registrar with Combined Functionality  . . . .  19
     6.2.  Registrar-Agent . . . . . . . . . . . . . . . . . . . . .  20
       6.2.1.  Discovery of the Registrar  . . . . . . . . . . . . .  21
       6.2.2.  Discovery of the Pledge . . . . . . . . . . . . . . .  22
     6.3.  Pledge in Responder Mode  . . . . . . . . . . . . . . . .  23
       6.3.1.  Pledge with Combined Functionality  . . . . . . . . .  24
   7.  Exchanges and Artifacts . . . . . . . . . . . . . . . . . . .  24
     7.1.  Trigger Pledge Voucher-Request  . . . . . . . . . . . . .  28

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       7.1.1.  Request Artifact: Pledge Voucher-Request Trigger
               (tPVR)  . . . . . . . . . . . . . . . . . . . . . . .  30
       7.1.2.  Response Artifact: Pledge Voucher-Request (PVR) . . .  32
     7.2.  Trigger Pledge Enroll-Request . . . . . . . . . . . . . .  34
       7.2.1.  Request Artifact: Pledge Enroll-Request Trigger
               (tPER)  . . . . . . . . . . . . . . . . . . . . . . .  35
       7.2.2.  Response Artifact: Pledge Enroll-Request (PER)  . . .  36
     7.3.  Supply PVR to Registrar (including backend
            interaction) . . . . . . . . . . . . . . . . . . . . . .  39
       7.3.1.  Request Artifact: Pledge Voucher-Request (PVR)  . . .  40
       7.3.2.  Supply RVR to MASA (backend interaction)  . . . . . .  41
       7.3.3.  Issue Voucher by MASA (backend interaction) . . . . .  45
       7.3.4.  Supply Voucher to Registrar (backend interaction) . .  46
       7.3.5.  Response Artifact: Voucher  . . . . . . . . . . . . .  49
     7.4.  Supply PER to Registrar (including backend
            interaction) . . . . . . . . . . . . . . . . . . . . . .  50
       7.4.1.  Request Artifact: Pledge Enroll-Request (PER) . . . .  51
       7.4.2.  Enroll Pledge by Domain CA (backend interaction)  . .  51
       7.4.3.  Response Artifact: Enroll-Response (Enroll-Resp)  . .  52
     7.5.  Request CA Certificates . . . . . . . . . . . . . . . . .  52
       7.5.1.  Request Artifact: cACert-Request (cACert-Req) . . . .  53
       7.5.2.  Response Artifact: cACert-Response (cACert-Resp)  . .  53
     7.6.  Supply Voucher to Pledge  . . . . . . . . . . . . . . . .  54
       7.6.1.  Request Artifact: Voucher . . . . . . . . . . . . . .  55
       7.6.2.  Response Artifact: Voucher Status (vStatus) . . . . .  56
     7.7.  Supply CA Certificates to Pledge  . . . . . . . . . . . .  59
       7.7.1.  Request Artifact: . . . . . . . . . . . . . . . . . .  59
       7.7.2.  Response (no artifact)  . . . . . . . . . . . . . . .  60
     7.8.  Supply Enroll-Response to Pledge  . . . . . . . . . . . .  60
       7.8.1.  Request Artifact: Enroll-Response (Enroll-Resp) . . .  61
       7.8.2.  Response Artifact: Enroll Status (eStatus)  . . . . .  61
     7.9.  Voucher Status Telemetry (including backend
            interaction) . . . . . . . . . . . . . . . . . . . . . .  64
       7.9.1.  Request Artifact: Voucher Status (vStatus)  . . . . .  64
       7.9.2.  Response (no artifact)  . . . . . . . . . . . . . . .  65
     7.10. Enroll Status Telemetry . . . . . . . . . . . . . . . . .  65
       7.10.1.  Request Artifact: Enroll Status (eStatus)  . . . . .  66
       7.10.2.  Response (no artifact) . . . . . . . . . . . . . . .  66
     7.11. Query Pledge Status . . . . . . . . . . . . . . . . . . .  67
       7.11.1.  Request Artifact: Status Trigger (tStatus) . . . . .  68
       7.11.2.  Response Artifact: Pledge Status (pStatus) . . . . .  69
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  73
     8.1.  BRSKI .well-known Registry  . . . . . . . . . . . . . . .  73
     8.2.  DNS Service Names . . . . . . . . . . . . . . . . . . . .  73
   9.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  74
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  75
     10.1.  Denial of Service (DoS) Attack on Pledge . . . . . . . .  75
     10.2.  Misuse of acquired PVR and PER by Registrar-Agent  . . .  75

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     10.3.  Misuse of Registrar-Agent Credentials  . . . . . . . . .  76
     10.4.  Misuse of DNS-SD with mDNS to obtain list of pledges . .  76
     10.5.  YANG Module Security Considerations  . . . . . . . . . .  77
   11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  77
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  77
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  77
     12.2.  Informative References . . . . . . . . . . . . . . . . .  79
   Appendix A.  Examples . . . . . . . . . . . . . . . . . . . . . .  82
     A.1.  Example Pledge Voucher-Request (PVR) - from Pledge to
           Registrar-Agent . . . . . . . . . . . . . . . . . . . . .  82
     A.2.  Example Parboiled Registrar Voucher-Request (RVR) - from
           Registrar to MASA . . . . . . . . . . . . . . . . . . . .  84
     A.3.  Example Voucher - from MASA to Pledge, via Registrar and
           Registrar-Agent . . . . . . . . . . . . . . . . . . . . .  89
     A.4.  Example Voucher, MASA issued Voucher with additional
           Registrar signature (from MASA to Pledge, via Registrar and
           Registrar-Agent)  . . . . . . . . . . . . . . . . . . . .  90
   Appendix B.  HTTP-over-TLS operations between Registrar-Agent and
           Pledge  . . . . . . . . . . . . . . . . . . . . . . . . .  91
   Appendix C.  History of Changes [RFC Editor: please delete] . . .  92
   Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . . 104
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . 105

1.  Introduction

   BRSKI as defined in [RFC8995] specifies a solution for secure zero-
   touch (automated) bootstrapping of devices (pledges) in a customer
   domain, which may be associated to a specific installation location.
   This includes the discovery of the BRSKI registrar in the customer
   domain and the exchange of security information necessary to
   establish trust between a pledge and the domain.

   Security information about the customer domain, specifically the
   customer domain certificate, are exchanged and authenticated
   utilizing voucher-request and voucher-response artifacts as defined
   in [RFC8995].  Vouchers are signed objects from the Manufacturer
   Authorized Signing Authority (MASA).  The MASA issues the voucher and
   provides it via the domain registrar to the pledge.
   [I-D.ietf-anima-rfc8366bis] specifies the format of the voucher
   artifacts including the voucher-request.

   For the certificate enrollment of devices, BRSKI relies on EST
   [RFC7030] to request and distribute customer domain specific device
   certificates.  EST in turn relies for the authentication and
   authorization of the certification request on the credentials used by
   the underlying TLS between the EST client and the EST server.

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   BRSKI addresses scenarios in which the pledge initiates the
   bootstrapping acting as client (referred to as initiator mode by this
   document).  BRSKI with Pledge in Responder Mode (BRSKI-PRM) defined
   in this document allows the pledge to act as server, so that it can
   be triggered externally and at a specific time to generate
   bootstrapping requests in the customer domain.  For this approach,
   this document:

   *  introduces the Registrar-Agent as new component to facilitate the
      communication between the pledge and the domain registrar.  The
      Registrar-Agent may be implemented as an integrated functionality
      of a commissioning tool or be co-located with the domain registrar
      itself.  BRSKI-PRM supports the identification of the Registrar-
      Agent that was performing the bootstrapping allowing for
      accountability of the pledges installation, when the Registrar-
      Agent is a component used by an installer and not co-located with
      the domain registrar.

   *  specifies the interaction (data exchange and data objects) between
      a pledge acting as server, the Registrar-Agent acting as client,
      and the domain registrar.

   *  enables the usage of arbitrary transports between the pledge and
      the domain registrar via the Registrar-Agent; security is
      addressed at the application layer, and both IP-based and non-IP
      connectivity can be used between pledge and Registrar-Agent.

   *  allows the application of Registrar-Agent credentials to establish
      TLS connections to the domain registrar; these are different from
      the IDevID of the pledge.

   The term endpoint used in the context of this document is equivalent
   to resource in HTTP [RFC9110] and CoAP [RFC7252]; it is not used to
   describe a device.  Endpoints are accessible via Well-Known URIs
   [RFC8615].  For the interaction with the domain registrar, the
   Registrar-Agent will use existing BRSKI [RFC8995] endpoints as well
   as additional endpoints defined in this document.  To utilize the EST
   server endpoints on the domain registrar, the Registrar-Agent will
   act as client toward the registrar.

   The Registrar-Agent also acts as a client when communicating with a
   pledge that is in responder mode.  Here, TLS with server-side,
   certificate-based authentication is only optionally supported.  If
   TLS is optionally used between the Registrar-Agent and the pledge,
   the Registrar-Agent needs to identify the pledge based on its
   product-serial-number rather than the hostname, as the latter is not
   set in an IDevID certificate.

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   BRSKI-PRM is designed to rely on object security to support also for
   alternative transports for which TLS may not be available, e.g.,
   Bluetooth or NFC.  This is achieved through an additional signature
   wrapping of the exchanged data objects involving the Registrar-Agent
   for transport.

   To utilize EST [RFC7030] for enrollment, the domain registrar
   performs pre-processing of the wrapping signature before actually
   using EST as defined in [RFC7030].

   There may be pledges that can support both modes, initiator and
   responder mode.  In these cases BRSKI-PRM can be combined with BRSKI
   as defined in [RFC8995] or BRSKI-AE [I-D.ietf-anima-brski-ae] to
   allow for more bootstrapping flexibility.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   This document relies on the terminology defined in Section 1.2 of
   [RFC8995].  The following terms are defined in addition:

   authenticated self-contained object:  Describes an object, which is
      cryptographically bound to the end entity (EE) certificate.  The
      binding is assumed to be provided through a digital signature of
      the actual object using the corresponding private key of the
      certificate.

   CA:  Certification Authority, issues certificates.

   Commissioning tool:  Tool to interact with devices to provide
      configuration data.

   CSR:  Certificate Signing Request.

   EE:  End entity, as defined in [RFC9483].  Typically a device or
      service that owns a public-private key pair for which it manages a
      public key certificate.

   EE certificate:  Either IDevID certificate or LDevID certificate of
      the EE.

   endpoint:  Term equivalent to resource in HTTP [RFC9110] and CoAP

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      [RFC7252].  Endpoints are accessible via Well-Known URIs
      [RFC8615].

   mTLS:  mutual Transport Layer Security.

   PER:  Pledge Enroll-Request is a signature wrapped CSR, signed by the
      pledge that requests enrollment to a domain.

   POI:  Proof-of-Identity, as defined in [RFC5272].

   POP:  Proof-of-Possession (of a private key), as defined in
      [RFC5272].

   PVR:  Pledge Voucher-Request is a request for a voucher sent to the
      domain registrar.  The PVR is signed by the Pledge.

   RA:  Registration Authority, an optional system component to which a
      CA delegates certificate management functions such as
      authorization checks.  In BRSKI-PRM this is a functionality of the
      domain registrar, as in BRSKI [RFC8995].

   RER:  Registrar Enroll-Request is the CSR of a PER sent to the CA by
      the domain registrar (in its role as PKI RA).

   RVR:  Registrar Voucher-Request is a request for a voucher signed by
      the domain registrar to the MASA.  It may contain the PVR received
      from the pledge.

   This document uses the following encoding notations in the given JWS-
   signed artifact examples:

   BASE64URL(OCTETS):  Denotes the base64url encoding of OCTETS, per
      Section 2 of [RFC7515].

   UTF8(STRING):  Denotes the octets of the UTF-8 [RFC3629]
      representation of STRING, per Section 1 of [RFC7515].

   This document includes many examples that would contain many long
   sequences of base64-encoded objects with no content directly
   comprehensible to a human reader.  In order to keep those examples
   short, they use the token "base64encodedvalue==" as a placeholder for
   base64 data.  The full base64 data is included in the appendices of
   this document.

3.  Scope of Solution

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3.1.  Supported Environments and Use Case Examples

   BRSKI-PRM is applicable to scenarios where pledges may have no direct
   connection to the domain registrar, may have no continuous
   connection, or require coordination of the pledge requests to be
   provided to a domain registrar.

   This can be motivated by pledges deployed in environments not yet
   connected to the operational customer domain network, e.g., at a
   building construction site, or environments intentionally
   disconnected from the Internet, e.g., critical industrial facilities.
   Another example is the assembly of electrical cabinets, which are
   prepared in advance before the installation at a customer domain.

3.1.1.  Building Automation

   In building automation a typical use case exists where a detached
   building or the basement is equipped with sensors, actuators, and
   controllers, but with only limited or no connection to the central
   building management system.  This limited connectivity may exist
   during installation time or also during operation time.

   During the installation, for instance, a service technician collects
   the device-specific information from the basement network and
   provides them to the central building management system.  This could
   be done using a laptop, common mobile device, or dedicated
   commissioning tool to transport the information.  The service
   technician may successively collect device-specific information in
   different parts of the building before connecting to the domain
   registrar for bulk bootstrapping.

   A domain registrar may be part of the central building management
   system and already be operational in the installation network.  The
   central building management system can then provide operational
   parameters for the specific devices in the basement or other detached
   areas.  These operational parameters may comprise values and settings
   required in the operational phase of the sensors/actuators, among
   them a certificate issued by the operator to authenticate against
   other components and services.  These operational parameters are then
   provided to the devices in the basement facilitated by the service
   technician's laptop.  The Registrar-Agent, defined in this document,
   may be run on the technician's laptop to interact with pledges.

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3.1.2.  Infrastructure Isolation Policy

   This refers to any case in which the 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 a
   domain registrar may be allowed in carefully controlled short periods
   of time, for example when a batch of new devices are deployed, but
   prohibited at other times.

3.1.3.  Less Operational Security in the Target-Domain

   The registration authority (RA) performing the authorization of a
   certificate request is a critical PKI component and therefore
   requires higher operational security than other components utilizing
   the issued certificates.  CAs may also require higher security in the
   registration procedures.  There may be situations in which the
   customer domain does not offer enough physical security to operate a
   RA/CA and therefore this service is transferred to a backend that
   offers a higher level of operational security.

3.2.  Limitations

   The mechanism described in this document presumes the ability of the
   pledge and the Registrar-Agent to communicate with another.  This may
   not be possible in constrained environments where, in particular,
   power must be conserved.  In these situations, it is anticipated that
   the transceiver will be powered down most of the time.  This presents
   a rendezvous problem: the pledge is unavailable for certain periods
   of time, and the Registrar-Agent is similarly presumed to be
   unavailable for certain periods of time.  To overcome this situation,
   the pledges may need to be powered on, either manually or by sending
   a trigger signal.

4.  Requirements Discussion and Mapping to Solution-Elements

   Based on the intended target environment described in Section 3.1,
   the following requirements are derived to support bootstrapping of
   pledges in responder mode (acting as server):

   *  To facilitate the communication between a pledge in responder mode
      and the registrar, additional functionality is needed either on
      the registrar or as a stand-alone component.  This new
      functionality is defined as Registrar-Agent and acts as an agent
      of the registrar to trigger the pledge to generate requests for
      voucher and enrollment.  These requests are then provided by the
      Registrar-Agent to the registrar.  This requires the definition of
      pledge endpoints to allow interaction with the Registrar-Agent.

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   *  The security of communication between the Registrar-Agent and the
      pledge must not rely on Transport Layer Security (TLS) to enable
      application of BRSKI-PRM in environments, in which the
      communication between the Registrar-Agent and the pledge is done
      over other technologies like BTLE or NFC, which may not support
      TLS protected communication.  In addition, the pledge does not
      have a certificate that can easily be verified by [RFC9525]
      methods.

   *  The use of authenticated self-contained objects addresses both,
      the TLS challenges and the technology stack challenge.

   *  By contrast, the Registrar-Agent can be authenticated by the
      registrar as a component, acting on behalf of the registrar.  In
      addition the registrar must be able to verify, which Registrar-
      Agent was in direct contact with the pledge.

   *  It would be inaccurate for the voucher-request and voucher-
      response to use an assertion with value "proximity" in the
      voucher, as the pledge was not in direct contact with the
      registrar for bootstrapping.  Therefore, a new Agent-Proximity
      Assertion value {#agt_prx} is necessary for distinguishing
      assertions the MASA can state.

   At least the following properties are required for the voucher and
   enrollment processing:

   *  POI: provides data-origin authentication of a data object, e.g., a
      voucher-request or an Enroll-Request, utilizing an existing
      IDevID.  Certificate updates may utilize the certificate that is
      to be updated.

   *  POP: proves that an entity possesses and controls the private key
      corresponding to the public key contained in the certification
      request, typically by adding a signature computed using the
      private key to the certification request.

   Solution examples based on existing technology are provided with the
   focus on existing IETF RFCs:

   *  Voucher-Requests and Vouchers as used in [RFC8995] already provide
      both, POP and POI, through a digital signature to protect the
      integrity of the voucher, while the corresponding signing
      certificate contains the identity of the signer.

   *  Enroll-Requests are data structures containing the information
      from a requester for a CA to create a certificate.  The
      certification request format in BRSKI is PKCS#10 [RFC2986].  In

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      PKCS#10, the structure is signed to ensure integrity protection
      and POP of the private key of the requester that corresponds to
      the contained public key.  In the application examples, this POP
      alone is not sufficient.  A POI is also required for the
      certification request and therefore the certification request
      needs to be additionally bound to the existing credential of the
      pledge (IDevID).  This binding supports the authorization decision
      for the certification request and may be provided directly with
      the certification request.  While BRSKI uses the binding to TLS,
      BRSKI-PRM aims at an additional signature of the PKCS#10 using
      existing credentials on the pledge (IDevID).  This allows the
      process to be independent of the selected transport.

5.  Architecture

5.1.  Overview

   For BRSKI with Pledge in Responder Mode (BRSKI-PRM), the base system
   architecture defined in BRSKI [RFC8995] is enhanced to facilitate new
   use cases in which the pledge acts as server.  The responder mode
   allows delegated bootstrapping using a Registrar-Agent instead of a
   direct connection between the pledge and the domain registrar.

   Necessary enhancements to support authenticated self-contained
   objects for certificate enrollment are kept at a minimum to enable
   reuse of already defined architecture elements and interactions.  The
   format of the bootstrapping objects produced or consumed by the
   pledge is usually based on JSON Web Signature (JWS) [RFC7515] and
   further specified in Section 7 to address the requirements stated in
   Section 4 above.  In constrained environments, it may be based on
   COSE [RFC9052].

   An abstract overview of the BRSKI-PRM protocol can be found on slide
   8 of [BRSKI-PRM-abstract].

   To support mutual trust establishment between the domain registrar
   and pledges not directly connected to the customer domain, this
   document specifies the exchange of authenticated self-contained
   objects with the help of a Registrar-Agent.

   This leads to extensions of the logical components in the BRSKI
   architecture as shown in Figure 1.

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   Note that the Join Proxy is not shown in the figure.  In certain
   situations the Join Proxy may still be present and could be used by
   the Registrar-Agent to connect to the Registrar.  For example, a
   Registrar-Agent application on a smartphone often can connect to
   local Wi-Fi without giving up their cellular network connection
   [androidnsd], but only can make link-local connections.

   The Registrar-Agent interacts with the pledge to transfer the
   required data objects for bootstrapping, which are then also
   exchanged between the Registrar-Agent and the domain registrar.  The
   addition of the Registrar-Agent influences the sequences of the data
   exchange between the pledge and the domain registrar described in
   [RFC8995].  To enable reuse of BRSKI defined functionality as much as
   possible, BRSKI-PRM:

   *  uses existing endpoints where the required functionality is
      provided.

   *  enhances existing endpoints with new supported media types, e.g.,
      for JWS voucher.

   *  defines new endpoints where additional functionality is required,
      e.g., for wrapped certification request, CA certificates, or new
      status information.

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                                  +---------------------------+
             ..... Drop Ship .....| Vendor Services           |
             :                    +---------------+-----------+
             :                    | M anufacturer |           |
             :                    | A uthorized   | Ownership |
             :                    | S igning      | Tracker   |
             :                    | A uthority    |           |
             :                    +---------------+-----------+
             :                                         ^
             :                                         | BRSKI-
             :                                         | MASA
             :          ...............................|.........
             V          .                              v        .
         +--------+     .  +------------+        +-----------+  .
         |        |     .  |            |        |           |  .
         | Pledge | BRSKI- | Registrar- | BRSKI- | Domain    |  .
         |        |  PRM   | Agent      |  PRM   | Registrar |  .
         |        |<------>|            |<------>| (PKI RA)  |  .
         |        |     .  |    EE cert |        |           |  .
         |        |     .  +------------+        +-----+-----+  .
         | IDevID |     .                              |        .
         |        |     .           +------------------+-----+  .
         +--------+     .           | Key Infrastructure     |  .
                        .           | (e.g., PKI CA)         |  .
                        .           +------------------------+  .
                        .........................................
                                     Customer Domain

      Figure 1: BRSKI-PRM architecture overview using Registrar-Agent

   Figure 1 shows the relations between the following main components:

   *  Pledge: Is expected to respond with the necessary data objects for
      bootstrapping to the Registrar-Agent.  The protocol used between
      the pledge and the Registrar-Agent is assumed to be HTTP in the
      context of this document.  Any other protocols (including HTTPS)
      can be used as long as they support the exchange of the necessary
      data objects.  This includes CoAP or protocol to be used over
      Bluetooth or NFC connections A pledge acting as a server during
      bootstrapping leads to the following differences compared to
      BRSKI:

      -  The pledge is discovered by the Registrar-Agent as defined in
         {#discovery_uc2_ppa}.

      -  The pledge offers additional endpoints as defined in
         Section 6.3, so that the Registrar-Agent can request data
         required for bootstrapping the pledge.

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      -  The pledge includes additional data in the PVR, which is
         provided by the Registrar-Agent in the voucher-request trigger
         as defined in Section 7.1.  This allows the registrar to
         identify, with which Registrar-Agent the pledge was in contact.

      -  The order of exchanges in the BRSKI-PRM call flow is different
         from those in BRSKI [RFC8995], as the PVR and PER are collected
         simultaneously and provided to the registrar.  This enables
         bulk bootstrapping of several devices.

      -  The data objects utilized for the data exchange between the
         pledge and the registrar are self-contained authenticated
         objects (signature-wrapped objects).

   *  Registrar-Agent: Provides a store and forward communication path
      to exchange data objects between the pledge and the domain
      registrar.  The Registrar-Agent acts as a broker in situations in
      which the domain registrar is not directly reachable by the
      pledge.  This may be due to a different technology stack or due to
      missing connectivity.

      -  The Registrar-Agent triggers one or more pledges to create
         bootstrapping artifacts such as the voucher-request and the
         Enroll-Request.  It can then perform a (bulk) bootstrapping
         based on the collected data.

      -  The Registrar-Agent is expected to possess information about
         the domain registrar: the registrar EE certificate, LDevID(CA)
         certificate, and IP address, either by configuration or by
         using the discovery mechanism defined in [RFC8995].

      -  There is no trust assumption between the pledge and the
         Registrar-Agent as only authenticated self-contained objects
         are used, which are transported via the Registrar-Agent and
         provided either by the pledge or the domain registrar.

      -  The trust assumption between the Registrar-Agent and the domain
         registrar may be based on an LDevID, which is provided by the
         PKI responsible for the customer domain.

      -  The Registrar-Agent may be realized as stand-alone component
         supporting nomadic activities of a service technician moving
         between different installation sites.

      -  Alternatively, the Registrar-Agent may also be realized as co-
         located functionality for a registrar, to support pledges in
         responder mode.

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   *  Join Proxy (not shown): Has the same functionality as described in
      [RFC8995] if needed.  Note that a Registrar-Agent may use a join
      proxy to facilitate the TLS connection to the registrar in the
      same way that a BRSKI pledge would use a join proxy.  This is
      useful in cases where the Registrar-Agent does not have full IP
      connectivity via the domain network or cases where it has no other
      means to locate the registrar on the network.

   *  Domain Registrar: In general fulfills the same functionality
      regarding the bootstrapping of the pledge in a customer domain by
      facilitating the communication of the pledge with the MASA service
      and the domain key infrastructure (PKI).  In contrast to
      [RFC8995], a BRSKI-PRM domain registrar does not interact with a
      pledge directly, but through the Registrar-Agent.

   *  Vendor Services: Encompass MASA and Ownership Tracker and are used
      as defined in [RFC8995].  A MASA is able to support enrollment via
      Registrar-Agent without changes unless it checks the vouchers
      proximity indication, in which case it would need to be enhanced
      to support BRSKI-PRM to also accept the Agent-Proximity Assertion
      {#agt_prx}.

5.2.  Nomadic Connectivity

   In one example instance of the PRM architecture as shown in Figure 2,
   there is no connectivity between the location in which the pledge is
   installed and the location of the domain registrar.  This is often
   the case in the aforementioned building automation use case
   (Section 3.1.1).

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                                  +---------------------------+
             ..... Drop Ship .....| Vendor Services           |
             :                    +---------------------------+
             :                                         ^
         ........................................      |
         .   v                                  .      |
         . +--------+           .-.-.-.-.-.-.-. .      |
         . |        |           : Registrar-  : .      |
         . | Pledge |<--------->: Agent       : .      |
         . +--------+ L2 or L3  :-.-.-.-.-.-.-: .      |
         .          connectivity   ^            .      |
         ..........................!.............      |
            Pledge Installation    !                   |
            Location               ! Nomadic           |
                                   ! connectivity      |
                                   !                   |
                        ...........!...................|.........
                        .          v                   v        .
                        .  .-.-.-.-.-.-.-.       +-----------+  .
                        .  : Registrar-  :       | Domain    |  .
                        .  : Agent       :<----->| Registrar |  .
                        .  :-.-.-.-.-.-.-:       +-----+-----+  .
                        .                              |        .
                        .           +------------------+-----+  .
                        .           | Key Infrastructure     |  .
                        .           | (e.g., PKI CA)         |  .
                        .           +------------------------+  .
                        .........................................
                                     Customer Domain

           Figure 2: Registrar-Agent nomadic connectivity example

   PRM enables support of this case through nomadic connectivity of the
   Registrar-Agent.  To perform enrollment in this setup, multiple round
   trips of the Registrar-Agent between the pledge installation location
   and the domain registrar are required.

   1.  Connectivity to domain registrar: preparation tasks for pledge
       bootstrapping not part of the BRSKI-PRM protocol definition, like
       retrieval of list of pledges to enroll.

   2.  Connectivity to pledge installation location: retrieve
       information about available pledges (IDevID), collect request
       objects (i.e., Pledge Voucher-Requests and Pledge Enroll-Requests
       using the BRSKI-PRM approach described in Section 7.1 and
       Section 7.2.

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   3.  Connectivity to domain registrar, submit collected request
       information of pledges, retrieve response objects (i.e., Voucher
       and Enroll-Response) using the BRSKI-PRM approach described in
       Section 7.3 and Section 7.4.

   4.  Connectivity to pledge installation location, provide retrieved
       objects to the pledges to enroll pledges and collect status using
       the BRSKI-PRM approach described in Section 7.6, Section 7.7, and
       Section 7.8.

   5.  Connectivity to domain registrar, submit Voucher Status and
       Enrollment Status using the BRSKI-PRM approach described in
       Section 7.9 and Section 7.10.

   Variations of this setup include cases where the Registrar-Agent uses
   for example WiFi to connect to the pledge installation network, and
   mobile network connectivity to connect to the domain registrar.  Both
   connections may also be possible in a single location at the same
   time, based on installation building conditions.

5.3.  Co-located Registrar-Agent and Domain Registrar

   Compared to [RFC8995] BRSKI, pledges supporting BRSKI-PRM can be
   completely passive and only need to react when being requested to
   react by a Registrar-Agent.  In [RFC8995], pledges instead need to
   continuously request enrollment from a domain registrar, which may
   result in undesirable communications pattern and possible overload of
   a domain registrar.

                                  +---------------------------+
             ..... Drop Ship .....| Vendor Service            |
             :                    +---------------------------+
             :                                         ^
             :                                         |
             :          ...............................|.........
             :          .                              v        .
             v          .          +-------------------------+  .
          +--------+    .          |..............           |  .
          |        |    .          |. Registrar- . Domain    |  .
          | Pledge |<------------->|. Agent      . Registrar |  .
          +--------+ L2 or L3      |..............           |  .
                     connectivity  +-------------------+-----+  .
                        .                              |        .
                        .           +------------------+-----+  .
                        .           | Key Infrastructure     |  .
                        .           +------------------------+  .
                        .........................................
                                     Customer Domain

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     Figure 3: Registrar-Agent integrated into Domain Registrar example

   The benefits of BRSKI-PRM can be achieved even without the
   operational complexity of standalone Registrar-Agents by integrating
   the necessary functionality of the Registrar-Agent as a module into
   the domain registrar as shown in Figure 3 so that it can support the
   BRSKI-PRM communications to the pledge.

5.4.  Agent-Proximity Assertion

   "Agent-proximity" is a statement in the PVR and in the voucher, that
   the registrar certificate was provided via the Registrar-Agent as
   defined in Section 7 and not directly to the pledge.  Agent-proximity
   is therefore a different assertion than "proximity", which is defined
   in Section 4 of [RFC8366].  Agent-proximity is defined as additional
   assertion type in [I-D.ietf-anima-rfc8366bis].  This assertion can be
   verified by the registrar and also by the MASA during the voucher-
   request processing.

   In BRSKI, the pledge verifies POP of the registrar via the TLS
   handshake and pins that public key as the "proximity-registrar-cert"
   into the voucher request.  This allows the MASA to verify the
   proximity of the pledge and registrar, facilitating a decision to
   assign the pledge to that domain owner.  In BRSKI, the TLS connection
   is considered provisional until the pledge receives the voucher.

   In contrast, in BRSKI-PRM, the pledge has no direct connection to the
   registrar and MUST accept the registrar certificate provisionally
   until it receives the voucher as described in Section 7.6.  In a
   similar fashion, the pledge MUST accept the Registrar-Agent EE
   certificate provisionally.  See also Section 5 of [RFC8995] on
   "provisional state".

   For agent-proximity, the EE certificate of the Registrar-Agent MUST
   be an LDevID certificate signed by the domain owner.  Akin to the
   proximity assertion in the BRSKI case, the agent-proximity provides
   pledge proximity evidence to the MASA.  But additionally, agent-
   proximity allows the domain registrar to be sure that the PVR
   collected by the Registrar-Agent was in fact collected by the
   Registrar-Agent, to which the registrar is connected to.

   The provisioning of the Registrar-Agent LDevID certificate is out of
   scope for this document, but may be done in advance using a separate
   BRSKI run or by other means like configuration.  It is recommended to
   use short lived Registrar-Agent LDevIDs in the range of days or weeks
   as outlined in Section 10.3.

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6.  System Components

6.1.  Domain Registrar

   In BRSKI-PRM, the domain registrar provides the endpoints already
   specified in [RFC8995] (derived from EST [RFC7030]) where suitable.
   In addition, it MUST provide the endpoints defined in Table 1 within
   the BRSKI-defined "/.well-known/brski/" URI path.  These endpoints
   accommodate for the signature-wrapped objects used by BRSKI-PRM for
   the Pledge Enroll-Request (PER) and the provisioning of CA
   certificates.

   +================+=========================+========================+
   | Endpoint       | Operation               | Exchange and Artifacts |
   +================+=========================+========================+
   | requestenroll  | Supply PER              | Section 7.4            |
   |                | to Registrar            |                        |
   +----------------+-------------------------+------------------------+
   | wrappedcacerts | Request CA              | Section 7.5            |
   |                | Certificates            |                        |
   +----------------+-------------------------+------------------------+

     Table 1: Additional Well-Known Endpoints on a BRSKI-PRM Registrar

   According to Section 5.3 of [RFC8995], the domain registrar performs
   the pledge authorization for bootstrapping within his domain based on
   the Pledge Voucher-Request.  This behavior is retained in BRSKI-PRM.

   The domain registrar MUST possess and trust the IDevID (root or
   issuing) CA certificate of the pledge vendor/manufacturer.

   Further, the domain registrar MUST have its own EE credentials.

6.1.1.  Domain Registrar with Combined Functionality

   A registrar with combined BRSKI and BRSKI-PRM functionality MAY
   detect if the bootstrapping is performed by the pledge directly
   (BRSKI case) or by a Registrar-Agent (BRSKI-PRM case) based on the
   utilized credential for client authentication during the TLS session
   establishment and switch switch the operational mode from BRSKI to
   BRSKI-PRM.

   This may be supported by a specific naming in the SAN (subject
   alternative name) component of the EE certificate of the Registrar-
   Agent.

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   Alternatively, this may be supported by using an LDevID certificate
   signed by the domain owner for the client authentication of the
   Registrar-Agent.  Using an LDevID certificate also allows the
   registrar to verify that a Registrar-Agent is authorized to perform
   the bootstrapping of a pledge.  See also agent-proximity assertion in
   Section 5.4.

   Using an LDevID certificate for TLS client authentication of the
   Registrar-Agent is a deviation from [RFC8995], in which the IDevID
   credential of the pledge is used to perform TLS client
   authentication.

6.2.  Registrar-Agent

   The Registrar-Agent is a new component in BRSKI-PRM that provides a
   secure message passing service between pledges in responder mode and
   the domain registrar.

   It requires the EE certificate of the domain registrar for TLS server
   authentication when establishing a TLS session with the domain
   registrar and to provide the registrar EE certificate to the pledge
   for creating the Pledge Voucher-Request (PVR).

   The Registrar-Agent uses its own EE certificate for TLS client
   authentication when establishing a TLS session with the domain
   registrar and for signing agent-signed data.  This EE certificate
   MUST include a SubjectKeyIdentifier (SKID), which is used as
   reference in the context of an agent-signed-data object as defined in
   Section 7.1.

   Note that this is an additional requirement for issuing the
   certificate, as [IEEE-802.1AR] only requires the SKID to be included
   for intermediate CA certificates.  [RFC8995] has a similar
   requirement.  In BRSKI-PRM, the SKID is used in favor of providing
   the complete EE certificate of the Registrar-Agent to accommodate
   also constrained environments and reduce bandwidth needed for
   communication with the pledge.  In addition, it follows the
   recommendation from BRSKI to use SKID in favor of a certificate
   fingerprint to avoid additional computations.

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   In addition to the EE certificates, the Registrar-Agent is provided
   with the product serial number(s) of the pledge(s) to be
   bootstrapped.  This is necessary to allow the discovery of pledge(s)
   by the Registrar-Agent using DNS-SD with mDNS (see Section 6.2.2).
   The list may be provided by prior administrative means or the
   Registrar-Agent may get the information via an interaction with the
   pledge.  For instance, [RFC9238] describes scanning of a QR code,
   where the product serial number would be initialized from the 12N
   B005 Product Serial Number.

   In summary, the following information MUST be available at the
   Registrar-Agent before interaction with a pledge:

   *  Domain registrar EE certificate: certificate of the domain
      registrar to be provided to the pledge.

   *  Registrar-Agent EE certificate and corresponding private key: own
      operational key pair to sign agent-signed-data.

   *  Serial number(s): product serial number(s) of pledge(s) to be
      bootstrapped for discovery.

   Further, the Registrar-Agent SHOULD have synchronized time.

   Finally, the Registrar-Agent MAY possess the IDevID (root or issuing)
   CA certificate of the pledge vendor/manufacturer to validate the
   IDevID certificate on returned PVR or in case of TLS usage for pledge
   communication.  The distribution of IDevID CA certificates to the
   Registrar-Agent is out of scope of this document and may be done by a
   manual configuration.

6.2.1.  Discovery of the Registrar

   As a Registrar-Agent acts as representative of the domain registrar
   towards the pledge or may even be collocated with the domain
   registrar, a separate discovery of the registrar is likely not needed
   as Registrar-Agent and registrar are domain components and have a
   trust relation.  Moreover, other communication (not part of this
   document) between the Registrar-Agent and the registrar is assumed,
   e.g., to exchange information about product-serial-number(s) of
   pledges to be discovered as outlined in Section 5.2.  Moreover, as
   the standard discovery described in Section 4 of [RFC8995] and the
   Appendix A.2 of [RFC8995] does not support of registrars with an
   enhanced feature set (like the support of BRSKI-PRM), this standard
   discovery is not applicable.

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   As a more general solution, the BRSKI discovery mechanism can be
   extended to provide upfront information on the capabilities of
   registrars, such as the mode of operation (pledge-responder-mode or
   registrar-responder-mode).  Defining discovery extensions is out of
   scope of this document.  This may be provided in
   [I-D.eckert-anima-brski-discovery].

6.2.2.  Discovery of the Pledge

   The discovery of the pledge by Registrar-Agent in the context of this
   document describes the minimum discovery approach to be supported.  A
   more general discovery mechanism, also supporting GRASP besides DNS-
   SD with mDNS may be provided in [I-D.eckert-anima-brski-discovery].

   Discovery in BRSKI-PRM uses DNS-based Service Discovery [RFC6763]
   over Multicast DNS [RFC6762] to discover the pledge.  Note that
   [RFC6762] Section 9 provides support for conflict resolution in
   situations when an DNS-SD with mDNS responder receives a mDNS
   response with inconsistent data.  Note that [RFC8990] does not
   support conflict resolution of mDNS, which may be a limitation for
   its application.

   The pledge constructs a local host name based on device local
   information (product-serial-number), which results in "product-
   serial-number._brski-pledge._tcp.local".  The product-serial-number
   composition is manufacturer dependent and may contain information
   regarding the manufacturer, the product type, and further information
   specific to the product instance.  To allow distinction of pledges,
   the product-serial-number therefore needs to be sufficiently unique.

   In the absence of a more general discovery as defined in
   [I-D.eckert-anima-brski-discovery] the Registrar-Agent MUST use

   *  "<product-serial-number>._brski-pledge._tcp.local", to discover a
      specific pledge, e.g., when connected to a local network.

   *  "_brski-pledge._tcp.local" to get a list of pledges to be
      bootstrapped.

   A manufacturer may allow the pledge to react on DNS-SD with mDNS
   discovery without his product-serial-number contained.  This allows a
   commissioning tool to discover pledges to be bootstrapped in the
   domain.  The manufacturer support this functionality as outlined in
   Section 10.4.

   Establishing network connectivity of the pledge is out of scope of
   this document but necessary to apply DNS-SD with mDNS.  For Ethernet
   it is provided by simply connecting the network cable.  For WiFi

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   networks, connectivity can be provided by using a pre-agreed SSID for
   bootstrapping, e.g., as proposed in
   [I-D.richardson-emu-eap-onboarding].  The same approach can be used
   by 6LoWPAN/mesh using a pre-agreed PAN ID.  How to gain network
   connectivity is out of scope of this document.

6.3.  Pledge in Responder Mode

   The pledge is triggered by the Registrar-Agent to create the PVR and
   PER.  It is also triggered for processing of the responses and the
   generation of status information once the Registrar-Agent has
   received the responses from the registrar later in the process.

   To enable interaction as responder with the Registrar-Agent, pledges
   in responder mode MUST act as servers and MUST provide the endpoints
   defined in Table 2 within the BRSKI-defined "/.well-known/brski/" URI
   path.  The endpoints are defined with short names to also accommodate
   for resource-constrained devices.

      +==========+========================+========================+
      | Endpoint | Operation              | Exchange and Artifacts |
      +==========+========================+========================+
      | tpvr     | Trigger Pledge         | Section 7.1            |
      |          | Voucher-Request        |                        |
      +----------+------------------------+------------------------+
      | tper     | Trigger Pledge Enroll- | Section 7.2            |
      |          | Request                |                        |
      +----------+------------------------+------------------------+
      | svr      | Supply Voucher to      | Section 7.6            |
      |          | Pledge                 |                        |
      +----------+------------------------+------------------------+
      | scac     | Supply CA Certificates | Section 7.7            |
      |          | to Pledge              |                        |
      +----------+------------------------+------------------------+
      | ser      | Supply Enroll-Response | Section 7.8            |
      |          | to Pledge              |                        |
      +----------+------------------------+------------------------+
      | qps      | Query Pledge Status    | Section 7.11           |
      +----------+------------------------+------------------------+

       Table 2: Well-Known Endpoints on a Pledge in Responder Mode

   Section 7.2 of [RFC9110] makes the Host header field mandatory, so it
   will always be present.  The pledge MUST respond to all queries
   regardless of the Host header field provided by the client.

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   For instance, when the Registrar-Agent reaches out to the "tpvr"
   endpoint on a pledge in responder mode with the full URI
   "http://pledge.example.com/.well-known/brski/tpvr", it sets the Host
   header field to "pledge.example.com" and the absolute path "/.well-
   known/brski/tpbr".  In practice, however, the pledge often is only
   known by its IP address as returned by a discovery protocol, which
   will be included in the Host header field.

   As BRSKI-PRM uses authenticated self-contained data objects between
   the pledge and the domain registrar, the binding of the pledge
   identity to the requests is provided by the data object signature
   employing the IDevID of the pledge.  Hence, pledges MUST have an
   Initial Device Identifier (IDevID) installed in them at the factory.

6.3.1.  Pledge with Combined Functionality

   Pledges MAY support both initiator and responder mode.

   A pledge in initiator mode should listen for announcement messages as
   described in Section 4.1 of [RFC8995].  Upon discovery of a potential
   registrar, it initiates the bootstrapping to that registrar.  At the
   same time (so as to avoid the Slowloris-attack described in
   [RFC8995]), it SHOULD also respond to the triggers for responder mode
   described in this document.

   Once a pledge with combined functionality has been bootstrapped, it
   MAY act as client for enrollment of further certificates needed,
   e.g., using the enrollment protocol of choice.  If it still acts as
   server, the defined BRSKI-PRM endpoints to trigger a Pledge Enroll-
   Request (PER) or to provide an Enroll-Response can be used for
   further certificates.

7.  Exchanges and Artifacts

   The interaction of the pledge with the Registrar-Agent may be
   accomplished using different transports (i.e., protocols and/or
   network technologies).  This specification utilizes HTTP as default
   transport.  Other specifications may define alternative transports
   such as CoAP, Bluetooth Low Energy (BLE), or Near Field Communication
   (NFC).  These transports may differ from and are independent of the
   ones used between the Registrar-Agent and the registrar.

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   Transport independence is realized through data objects that are not
   bound to specific transport security and stay the same along the
   communication path from the pledge via the Registrar-Agent to the
   registrar.  Therefore, authenticated self-contained artifacts (e.g.,
   JWS-signed JSON structures or COSE-signed CBOR structures) are used
   for the data exchanges between the pledge and the registrar via the
   Registrar-Agent.

   Figure 4 provides an overview of the exchanges detailed in the
   following subsections.

 +--------+    +------------+    +-----------+    +--------+    +------+
 | Pledge |    | Registrar- |    |  Domain   |    | Domain |    | MASA |
 |        |    |   Agent    |    | Registrar |    |   CA   |    |      |
 +--------+    +------------+    +-----------+    +--------+    +------+
  |                  |                 |                 |   Internet |
  |     discover     |                 |                 |            |
  |      pledge      |                 |                 |            |
  |    mDNS query    |                 |                 |            |
  |<-----------------|                 |                 |            |
  |----------------->|                 |                 |            |
  |                  |                 |                 |            |
  ~                  ~                 ~                 ~            ~
 (1) Trigger Pledge Voucher-Request
  ~                  ~                 ~                 ~            ~
  |                  |                 |                 |            |
  |<----opt. TLS---->|                 |                 |            |
  |<------tPVR-------|                 |                 |            |
  |--------PVR------>|                 |                 |            |
  |                  |                 |                 |            |
  ~                  ~                 ~                 ~            ~
 (2) Trigger Pledge Enroll-Request
  ~                  ~                 ~                 ~            ~
  |                  |                 |                 |            |
  |<----opt. TLS---->|                 |                 |            |
  |<------tPER-------|                 |                 |            |
  |--------PER------>|                 |                 |            |
  |                  |                 |                 |            |
  ~                  ~                 ~                 ~            ~
 (3) Supply PVR to Registrar (including backend interaction)
  ~                  ~                 ~                 ~            ~
  |                  |                 |                 |            |
  |                  |<-----mTLS------>|                 |            |
  |                  |         [Registrar-Agent          |            |
  |                  |    authenticated&authorized?]     |            |
  |                  |-------PVR------>|                 |            |
  |                  |          [accept device?]         |            |
  |                  |          [contact vendor]         |            |

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  |                  |                 |                 |            |
  |                  |                 |<------------mTLS------------>|
  |                  |                 |--------------RVR------------>|
  |                  |                 |              [extract DomainID]
  |                  |                 |              [update audit log]
  |                  |                 |<-----------Voucher-----------|
  |                  |<----Voucher-----|                 |            |
  |                  |                 |                 |            |
  ~                  ~                 ~                 ~            ~
 (4) Supply PER to Registrar (including backend interaction)
  ~                  ~                 ~                 ~            ~
  |                  |                 |                 |            |
  |                  |<----(mTLS)----->|                 |            |
  |                  |-------PER------>|                 |            |
  |                  |                 |<-----mTLS------>|            |
  |                  |                 |-------RER------>|            |
  |                  |                 |<--Enroll-Resp---|            |
  |                  |<--Enroll-Resp---|                 |            |
  |                  |                 |                 |            |
  ~                  ~                 ~                 ~            ~
 (5) Request CA Certificates
  ~                  ~                 ~                 ~            ~
  |                  |                 |                 |            |
  |                  |<----(mTLS)----->|                 |            |
  |                  |---cACert-Req--->|                 |            |
  |                  |<--cACert-Resp---|                 |            |
  |                  |                 |                 |            |
  ~                  ~                 ~                 ~            ~
 (6) Supply Voucher to Pledge
  ~                  ~                 ~                 ~            ~
  |                  |                 |                 |            |
  |<----opt. TLS---->|                 |                 |            |
  |<-----Voucher-----|                 |                 |            |
  |------vStatus---->|                 |                 |            |
  |                  |                 |                 |            |
  ~                  ~                 ~                 ~            ~
 (7) Supply CA Certificates to Pledge
  ~                  ~                 ~                 ~            ~
  |                  |                 |                 |            |
  |<----opt. TLS---->|                 |                 |            |
  |<-----cACerts-----|                 |                 |            |
  |                  |                 |                 |            |
  ~                  ~                 ~                 ~            ~
 (8) Supply Enroll-Response to Pledge
  ~                  ~                 ~                 ~            ~
  |                  |                 |                 |            |
  |<----opt. TLS---->|                 |                 |            |
  |<---Enroll-Resp---|                 |                 |            |

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  |-----eStatus----->|                 |                 |            |
  |                  |                 |                 |            |
  ~                  ~                 ~                 ~            ~
 (9) Voucher Status Telemetry (including backend interaction)
  ~                  ~                 ~                 ~            ~
  |                  |                 |                 |            |
  |                  |<----(mTLS)----->|                 |            |
  |                  |-----vStatus---->|                 |            |
  |                  |                 |<-----------(mTLS)----------->|
  |                  |                 |-----req device audit log---->|
  |                  |                 |<------device audit log-------|
  |                  |        [verify audit log]         |            |
  |                  |                 |                 |            |
  ~                  ~                 ~                 ~            ~
 (10) Enroll Status Telemetry
  ~                  ~                 ~                 ~            ~
  |                  |                 |                 |            |
  |                  |<----(mTLS)----->|                 |            |
  |                  |-----eStatus---->|                 |            |
  |                  |                 |                 |            |
  ~                  ~                 ~                 ~            ~
 (11) Query Pledge Status
  ~                  ~                 ~                 ~            ~
  |                  |                 |                 |            |
  |<----opt. TLS---->|                 |                 |            |
  |<-----tStatus-----|                 |                 |            |
  |------pStatus---->|                 |                 |            |
  |                  |                 |                 |            |
  ~                  ~                 ~                 ~            ~

           Figure 4: Overview pledge-responder-mode exchanges

   The following sub sections split the interactions shown in Figure 4
   between the different components into:

   1.   Section 7.1 describes the acquisition exchange for the Pledge
        Voucher-Request initiated by the Registrar-Agent to the pledge.

   2.   Section 7.2 describes the acquisition exchange for the Pledge
        Enroll-Request initiated by the Registrar-Agent to the pledge.

   3.   Section 7.3 describes the issuing exchange for the Voucher
        initiated by the Registrar-Agent to the registrar, including the
        interaction of the registrar with the MASA using the RVR
        Section 7.3.2, as well as the artifact processing by these
        entities.

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   4.   Section 7.4 describes the enroll exchange initiated by the
        Registrar-Agent to the registrar including the interaction of
        the registrar with the CA using the PER as well as the artifact
        processing by these entities.

   5.   Section 7.5 describes the retrival exchange for the optional CA
        certificate provisioning to the pledge initiated by the
        Registrar-Agent to the CA.

   6.   Section 7.6 describes the Voucher exchange initiated by the
        Registrar-Agent to the pledge and the returned status
        information.

   7.   Section 7.7 describes the certificate provisioning exchange
        initiated by the Registrar-Agent to the pledge.

   8.   Section 7.8 describes the Enroll-Response exchange (containing
        the LDevID (Pledge) certificate) initiated by the Registrar-
        Agent to the pledge and the returned status information.

   9.   Section 7.9 describes the Voucher status telemetry exchange
        initiated by the Registrar-Agent to the registrar, including the
        interaction of the registrar with the MASA.

   10.  Section 7.10 describes the Enroll Status telemetry exchange
        initiated by the Registrar-Agent to the registrar.

   11.  Section 7.11 describes the Pledge Status exchange about the
        general bootstrapping state initiated by the Registrar-Agent to
        the pledge.

7.1.  Trigger Pledge Voucher-Request

   This exchange assumes that the Registrar-Agent has already discovered
   the pledge.  This may be done as described in Section 6.2.2 and
   Figure 4 based on DNS-SD or similar.

   Optionally, TLS MAY be used to provide privacy for this exchange
   between the Registrar-Agent and the pledge, see Appendix B.

   Figure 5 shows the acquisition of the Pledge Voucher-Request (PVR)
   and the following subsections describe the corresponding artifacts.

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 +--------+    +------------+    +-----------+    +--------+    +------+
 | Pledge |    | Registrar- |    |  Domain   |    | Domain |    | MASA |
 |        |    |   Agent    |    | Registrar |    |   CA   |    |      |
 +--------+    +------------+    +-----------+    +--------+    +------+
  |                  |                 |                 |   Internet |
  ~                  ~                 ~                 ~            ~
 (1) Trigger Pledge Voucher-Request
  ~                  ~                 ~                 ~            ~
  |                  |                 |                 |            |
  |<----opt. TLS---->|                 |                 |            |
  |<------tPVR-------|                 |                 |            |
  |--------PVR------>|                 |                 |            |
  |                  |                 |                 |            |
  ~                  ~                 ~                 ~            ~

                   Figure 5: PVR acquisition exchange

   The Registrar-Agent triggers the pledge to create the PVR via HTTP
   POST on the well-known pledge endpoint /.well-known/brski/tpvr.  The
   request body MUST contain the JSON-based Pledge Voucher-Request
   Trigger (tPVR) artifact.  The request header MUST set the Content-
   Type field to application/json.

   Upon receiving a valid tPVR, the pledge MUST reply with the PVR
   artifact in the body of a 200 OK response.  The Content-Type field
   header of the response MUST be set to application/voucher-jws+json as
   defined in [I-D.ietf-anima-jws-voucher].

   If the pledge is unable to create the PVR, it SHOULD respond with an
   HTTP error code.  The following client error responses MAY be used:

   *  400 Bad Request: if the pledge detected an error in the format of
      the request, e.g. missing field, wrong data types, etc. or if the
      request is not valid JSON even though the PVR media type was set
      to application/json.

   *  406 Not Acceptable: if the Accept request header field indicates a
      type that is unknown or unsupported, e.g., a type other than
      application/jose+json.

   *  415 Unsupported Media Type: if the Content-Type request header
      field indicates a type that is unknown or unsupported, e.g., a
      type other than application/json.

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7.1.1.  Request Artifact: Pledge Voucher-Request Trigger (tPVR)

   The Pledge Voucher-Request Trigger (tPVR) artifact is an unsigned
   JSON structure providing the trigger parameters.  The following CDDL
   [RFC8610] explains the Pledge Voucher-Request Trigger structure.

   <CODE BEGINS>
     pledgevoucherrequesttrigger = {
       "agent-provided-proximity-registrar-cert": bytes,
       "agent-signed-data": bytes
     }
   <CODE ENDS>

             Figure 6: CDDL for Pledge Voucher-Request Trigger

   The fields contained in the pledgevoucherrequesttrigger are:

   *  agent-provided-proximity-registrar-cert: X.509 v3 certificate
      structure of the domain registrar EE certificate (base64-encoded
      value); may be configured at the Registrar-Agent or may be fetched
      by the Registrar-Agent based on a prior TLS connection with this
      domain registrar

   *  agent-signed-data: base64-encoded JWS structure containing the
      SubjectKeyIdentifier of the EE (RegAgt) certificate and signing
      Data including the creation date and serial number of the pledge.
      Note that [I-D.ietf-anima-rfc8366bis] defines an opaque binary
      element for agent-signed data, for which the structure is defined
      in BRSKI-PRM.

   {
     "payload": BASE64URL(UTF8(prmasd)),
     "signatures": [
       {
         "protected": BASE64URL(UTF8(JWS Protected Header)),
         "signature": BASE64URL(JWS Signature)
       }
     ]
   }

        Figure 7: JWS structure for the agent-signed-data member in
                      General JWS Serialization syntax

   The BRSKI-PRM Agent Signed Data structure MUST be encoded in JSON as
   defined in [RFC8259] following the CDDL definition Figure 8.  The JWS
   Payload is further base64url-encoded to become the string value of
   the payload member as described in Section 3.2 of [RFC7515].

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   The following CDDL [RFC8610] explains the BRSKI-PRM Agent Signed Data
   structure.

   <CODE BEGINS>
     prmasd = {
       "created": tdate,
       "serial-number": text
     }
   <CODE ENDS>

               Figure 8: CDDL for BRSKI-PRM Agent Signed Data

   The fields contained in the prmasd are:

   *  created-on: creation date and time as standard date/time string as
      defined in [RFC3339]

   *  serial-number: product-serial-number in the X520SerialNumber field
      of the IDevID certificate of the pledge as string as defined in
      Section 2.3.1 of [RFC8995]

   Figure 9 below shows an example for unsigned BRSKI-PRM Agent Signed
   Data in JSON syntax.

   {
     "created-on": "2021-04-16T00:00:01.000Z",
     "serial-number": "callee4711"
   }

                     Figure 9: Data example for prmasd

   The JWS Protected Header of the agent-signed-data JWS structure MUST
   contain the following parameters (see Figure 10 for an example):

   *  alg: algorithm type used to create the signature, e.g., ES256 as
      defined in Section 4.1.1 of [RFC7515]

   *  kid: base64-encoded bytes of the SubjectKeyIdentifier (the
      "KeyIdentifier" OCTET STRING value) of the EE (RegAgt)
      certificate.

   {
     "alg": "ES256",
     "kid": "base64encodedvalue=="
   }

        Figure 10: Protected Header example inside agent-signed-data

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   Note that at the time of receiving the PVR trigger, the pledge cannot
   verify the registrar LDevID certificate and has no proof-of-
   possession of the corresponding private key for the certificate.
   Hence, the tPVR is an unsigned artifact and the pledge only accepts
   the registrar LDevID certificate provisionally until it receives the
   voucher as described in Section 7.6.

   The pledge will also be unable to verify the agent-signed-data itself
   as it does not possess the EE (RegAgt) certificate and the domain
   trust has not been established at this point of the communication.
   Verification SHOULD be done, after the voucher has been received.

   The trigger for the pledge to create a PVR is depicted in the
   following figure:

   {
     "agent-provided-proximity-registrar-cert": "base64encodedvalue==",
     "agent-signed-data": "base64encodedvalue=="
   }

             Figure 11: Representation of trigger to create PVR

7.1.2.  Response Artifact: Pledge Voucher-Request (PVR)

   The Pledge Voucher-Request (PVR) artifact is a JWS Voucher Request as
   defined in [I-D.ietf-anima-jws-voucher].  Its unsigned data SHALL be
   constructed similar to the Voucher-Request artifact defined in
   [RFC8995].  It will contain additional data provided by the
   Registrar-Agent as specified in the following.

   The payload of the PVR MUST contain the following parameters as part
   of the ietf-voucher-request:voucher as defined in
   [I-D.ietf-anima-rfc8366bis] and thus makes optional leaves in the
   YANG definition mandatory:

   *  created-on: SHALL contain the current date and time in yang:date-
      and-time format.  If the pledge does not have synchronized time,
      it SHALL use the created-on time from the agent-signed-data,
      received in the trigger to create a PVR.

   *  nonce: SHALL contain a cryptographically strong pseudo-random
      number.

   *  serial-number: SHALL contain the pledge product-serial-number as
      X520SerialNumber.

   *  assertion: SHALL contain the requested voucher assertion "agent-
      proximity" (different value as in RFC 8995)..

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   The ietf-voucher-request:voucher data is extended with two additional
   parameters that MUST be included:

   *  agent-provided-proximity-registrar-cert: base64-encoded registrar
      EE certificate (provided in tPVR by the Registrar-Agent); enables
      the registrar to verify that it is the desired registrar for
      handling the PVR

   *  agent-signed-data: base64-encoded agent-signed-data (provided in
      tPVR by the Registrar-Agent); enables the registrar to verify and
      log, which Registrar-Agent was in contact with the pledge, when
      verifying the PVR

   The enhancements of the YANG module for the ietf-voucher-request with
   these new leaves are defined in [I-D.ietf-anima-rfc8366bis].

   The PVR is signed using the pledge's IDevID credential contained as
   x5c parameter of the JOSE header.

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 # The PVR in General JWS Serialization syntax
 {
   "payload": BASE64URL(UTF8(ietf-voucher-request:voucher)),
   "signatures": [
     {
       "protected": BASE64URL(UTF8(JWS Protected Header)),
       "signature": BASE64URL(JWS Signature)
     }
   ]
 }

 # Example: Decoded Payload "ietf-voucher-request:voucher"
   representation in JSON syntax
 {
   "ietf-voucher-request:voucher": {
      "created-on": "2021-04-16T00:00:02.000Z",
      "nonce": "eDs++/FuDHGUnRxN3E14CQ==",
      "serial-number": "callee4711",
      "assertion": "agent-proximity",
      "agent-provided-proximity-registrar-cert": "base64encodedvalue==",
      "agent-signed-data": "base64encodedvalue=="
   }
 }

 # Example: Decoded "JWS Protected Header" representation
   in JSON syntax
 {
     "alg": "ES256",
     "typ": "voucher-jws+json",
     "x5c": [
       "base64encodedvalue==",
       "base64encodedvalue=="
     ]
 }

                    Figure 12: Representation of PVR

7.2.  Trigger Pledge Enroll-Request

   Once the Registrar-Agent has received the PVR it can trigger the
   pledge to generate a Pledge Enroll-Request (PER).

   Optionally, TLS MAY be used to provide privacy for this exchange
   between the Registrar-Agent and the pledge, see Appendix B.

   Figure 13 shows the the acquisition of the PER and the following
   subsections describe the corresponding artifacts.

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 +--------+    +------------+    +-----------+    +--------+    +------+
 | Pledge |    | Registrar- |    |  Domain   |    | Domain |    | MASA |
 |        |    |   Agent    |    | Registrar |    |   CA   |    |      |
 +--------+    +------------+    +-----------+    +--------+    +------+
  |                  |                 |                 |   Internet |
  ~                  ~                 ~                 ~            ~
 (2) Trigger Pledge Enroll-Request
  ~                  ~                 ~                 ~            ~
  |                  |                 |                 |            |
  |<----opt. TLS---->|                 |                 |            |
  |<------tPER-------|                 |                 |            |
  |--------PER------>|                 |                 |            |
  |                  |                 |                 |            |
  ~                  ~                 ~                 ~            ~

                  Figure 13: PER acquisition exchange

   The Registrar-Agent triggers the pledge to create the PER via HTTP
   POST on the well-known pledge endpoint /.well-known/brski/tper.  As
   the initial enrollment aims to request a generic certificate, no
   certificate attributes are provided to the pledge.  To avoid an empty
   request body an artifact is provided containing the description of
   the requested operation.

   Upon receiving a valid tPER, the pledge MUST reply with the PER
   artifact in the body of a 200 OK response.  The response header MUST
   have the Content-Type field set to application/jose+json.

   If the pledge is unable to create the PER, it SHOULD respond with an
   HTTP error code.  The following 4xx client error codes MAY be used:

   *  400 Bad Request: if the pledge detected an error in the format of
      the request.

   *  406 Not Acceptable: if the Accept request header field indicates a
      type that is unknown or unsupported.  For example, a type other
      than application/jose+json.

   *  415 Unsupported Media Type: if the Content-Type request header
      field indicates a type that is unknown or unsupported, e.g., a
      type other than application/json.

7.2.1.  Request Artifact: Pledge Enroll-Request Trigger (tPER)

   This document specifies the trigger for a generic certificate with no
   CSR attributes provided to the pledge.  If specific attributes in the
   certificate are required, they have to be inserted by the issuing RA/
   CA.

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   The Pledge Enroll-Request Trigger (tPVR) artifact is an unsigned JSON
   structure providing the trigger parameters (tPER-data).  The
   following CDDL [RFC8610] explains the Pledge Enroll-Request Trigger
   structure.

   <CODE BEGINS>
   pledgeenrollrequesttrigger = {
       "enroll-type": "enroll-generic-cert"
     }
   <CODE ENDS>

             Figure 14: CDDL for Pledge Enroll-Request Trigger

   The enroll-type field is an enum, identifying what is being enrolled.
   Currently only "enroll-generic-cert" for the LDevID certificate is
   defined.

   Figure 15 below shows an example for unsigned Pledge Enroll-Request
   Trigger in JSON syntax.

   {
     "enroll-type" : "enroll-generic-cert"
   }

           Figure 15: Data example for pledgeenrollrequesttrigger

   The Pledge Enroll-Request Trigger (tPER) artifact MUST be encoded in
   JSON as defined in [RFC8259] following the CDDL definition Figure 14.

   The Pledge Enroll-Request Trigger (tPER) artifact MAY be used to
   provide additional data, like CSR attributes.  How to provide and use
   such additional data is out of scope for this specification.

7.2.2.  Response Artifact: Pledge Enroll-Request (PER)

   The Pledge Enroll-Request (PER) artifact is a JWS-signed PKCS#10
   Certificate Signing Request (CSR) utilizing the csr-grouping of the
   ietf-ztp-types YANG module as defined in [I-D.ietf-netconf-sztp-csr].
   The CSR already assures POP of the private key corresponding to the
   contained public key.  In addition, based on the PER signature using
   the IDevID, POI is provided.

   The pledge constructs the Pledge Enroll-Request (PER) artifact as a
   JWS structure containing the PKCS#10 request wrapped in ietf-ztp-
   types YANG structrue as JWS payload.  Note,
   [I-D.ietf-netconf-sztp-csr] also allows for inclusion of
   certification requests in different formats used by CMP or CMC.

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   The pledge MUST construct the PER as PKCS#10 and MUST sign it
   additionally with its IDevID credentials to provide proof-of-identity
   bound to the PKCS#10 as described below.

   A successful enrollment will result in a generic LDevID certificate
   for the pledge in the new domain.  This generic LDevID certificate
   can be used to request further (application specific) LDevID
   certificates if necessary for operation.  The Registrar-Agent SHALL
   use the enrollment endpoint requestenroll specified in this document
   to provide the Pledge Enroll-Request artifact to the Registrar.

   The JWS Protected Header of the PER MUST contain the following
   parameters as defined in [RFC7515]:

   *  alg: algorithm type used to create the signature, e.g., ES256 as
      defined in Section 4.1.1 of [RFC7515]

   *  x5c: base64-encoded pledge IDevID certificate; it MAY optionally
      contain the certificate chain for this certificate; if the
      certificate chain is not included, it MUST be available at the
      registrar for verification of the IDevID certificate

   The body of the Pledge Enroll-Request SHOULD contain a P10 parameter
   (for PKCS#10) as defined for ietf-ztp-types:p10-csr in
   [I-D.ietf-netconf-sztp-csr]:

   *  p10-csr: base64-encoded PKCS#10 of the pledge.

   The JOSE object is signed using the pledge's IDevID credential, which
   corresponds to the certificate signaled in the JOSE header.

   While BRSKI-PRM targets the initial enrollment, re-enrollment SHOULD
   be supported as described in a similar way as for enrollment in this
   document, if no other re-enrollment mechanism is supported.  Note
   that in this case the current LDevID credential is used instead of
   the IDevID credential to create the signature of the PKCS#10 request.

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   # The PER in General JWS Serialization syntax
   {
     "payload": "BASE64URL(ietf-ztp-types)",
     "signatures": [
       {
         "protected": "BASE64URL(UTF8(JWS Protected Header))",
         "signature": BASE64URL(JWS Signature)
       }
     ]
   }

   # Example: Decoded Payload "ietf-ztp-types" Representation
     in JSON Syntax
   {
     "ietf-ztp-types": {
        "p10-csr": "base64encodedvalue=="
      }
   }

   # Example: Decoded "JWS Protected Header" Representation
     in JSON Syntax
   {
     "alg": "ES256",
     "x5c": [
       "base64encodedvalue==",
       "base64encodedvalue=="
     ],
     "crit":["created-on"],
     "created-on": "2022-09-13T00:00:02.000Z"
   }

                      Figure 16: Representation of PER

   With the collected PVR and PER, the Registrar-Agent starts the
   interaction with the domain registrar.

   The new protected header field "created-on" is introduced to reflect
   freshness of the PER.  The field is marked critical "crit" to ensure
   that it must be understood and validated by the receiver (here the
   domain registrar) according to Section 4.1.11 of [RFC7515].  It
   allows the registrar to verify the timely correlation between the PER
   and previously exchanged messages, i.e., created-on of PER >=
   created-on of PVR >= created-on of PVR trigger.  The registrar MAY
   consider to ignore any but the newest PER from the same pledge in the
   case the registrar has at any point in time more than one pending PER
   from the pledge.

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   As the Registrar-Agent is intended to facilitate communication
   between the pledge and the domain registrar, a collection of requests
   from more than one pledge is possible.  This allows bulk
   bootstrapping of several pledges using the same connection between
   the Registrar-Agent and the domain registrar.

7.3.  Supply PVR to Registrar (including backend interaction)

   Similar to BRSKI "requestvoucher" endpoint in Section 5.2 of
   [RFC8995].

   The Registrar-Agent has acquired one or more PVR and PER object pairs

   The Registrar-Agent establishes a TLS connection to the registrar.
   As already stated in [RFC8995], the use of TLS 1.3 (or newer) is
   encouraged.  TLS 1.2 or newer is REQUIRED on the Registrar-Agent
   side.  TLS 1.3 (or newer) SHOULD be available on the registrar, but
   TLS 1.2 MAY be used.  TLS 1.3 (or newer) SHOULD be available on the
   MASA, but TLS 1.2 MAY be used.

   In contrast to BRSKI [RFC8995] TLS client authentication to the
   registrar is achieved by using Registrar-Agent EE credentials instead
   of pledge IDevID credentials.  Consequently BRSKI (pledge-initiator-
   mode) is distinguishable from BRSKI-PRM (pledge-responder-mode) by
   the registrar.  The registrar SHOULD verify that the Registrar-Agent
   is authorized to establish a connection to the registrar based on the
   TLS client authentication.  If the connection from Registrar-Agent to
   registrar is established, the authorization SHOULD be verified again
   based on agent-signed-data contained in the PVR.  This ensures that
   the pledge has been triggered by an authorized Registrar-Agent.

   With BRSKI-PRM, the pledge generates PVR and PER as JSON-in-JWS
   objects and the Registrar-Agent forwards them to the registrar.  In
   [RFC8995], the pledge generates PVR as CMS-signed JSON and PER as
   PKCS#10 or PKCS#7 according to [RFC7030] and inherited by [RFC8995].

   Figure 17 shows the exchanges for the Voucher Request processing and
   the following subsections describe the corresponding artifacts.

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 +--------+    +------------+    +-----------+    +--------+    +------+
 | Pledge |    | Registrar- |    |  Domain   |    | Domain |    | MASA |
 |        |    |   Agent    |    | Registrar |    |   CA   |    |      |
 +--------+    +------------+    +-----------+    +--------+    +------+
  |                  |                 |                 |   Internet |
  ~                  ~                 ~                 ~            ~
 (3) Supply PVR to Registrar (including backend interaction)
  ~                  ~                 ~                 ~            ~
  |                  |                 |                 |            |
  |                  |<-----mTLS------>|                 |            |
  |                  |         [Registrar-Agent          |            |
  |                  |    authenticated&authorized?]     |            |
  |                  |-------PVR------>|                 |            |
  |                  |          [accept device?]         |            |
  |                  |          [contact vendor]         |            |
  |                  |                 |                 |            |
  |                  |                 |<------------mTLS------------>|
  |                  |                 |--------------RVR------------>|
  |                  |                 |              [extract DomainID]
  |                  |                 |              [update audit log]
  |                  |                 |<-----------Voucher-----------|
  |                  |<----Voucher-----|                 |            |
  |                  |                 |                 |            |
  ~                  ~                 ~                 ~            ~

                  Figure 17: Voucher issuing exchange

   The HTTP request Content-Type header field for JSON-in-JWS PVR is:
   application/voucher-jws+json (see Section 7.1 for the content
   definition), as defined in [I-D.ietf-anima-jws-voucher].

   The Registrar-Agent sets the Accept field in the request-header
   indicating the acceptable Content-Type for the Voucher.

   The HTTP response Content-Type header field is set to application/
   voucher-jws+json as defined in [I-D.ietf-anima-jws-voucher] if no
   content negotiation is used.

7.3.1.  Request Artifact: Pledge Voucher-Request (PVR)

   For BRSKI-PRM, the Registrar-Agent sends the PVR by HTTP POST to the
   same registrar endpoint as introduced by BRSKI: "/.well- known/brski/
   requestvoucher", but with a Content-Type header field for JSON-in-
   JWS"

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7.3.2.  Supply RVR to MASA (backend interaction)

   The registrar needs to convert the PVR to an RVR and supply it to the
   MASA.

   If the MASA address/URI is learned from the IDevID MASA URI extension
   (Section 2.3 of [RFC8995]), then the MASA on that URI MUST support
   the procedures defined in this document if the PVR used JSON-JWS
   encoding.  If the MASA is only configured on the registrar, then a
   registrar supporting BRKSI-PRM and other voucher encoding formats
   (such as those in [RFC8995]) SHOULD support per-message-format MASA
   address/URI configuration for the same IDevID trust anchor."

   The registrar SHALL construct the payload of the RVR as defined in
   [RFC8995], Section 5.5.  The RVR encoding SHALL be JSON-in-JWS as
   defined in [I-D.ietf-anima-jws-voucher].

   The header of the RVR SHALL contain the following parameter as
   defined for JWS [RFC7515]:

   *  alg: algorithm used to create the object signature

   *  x5c: base64-encoded registrar LDevID certificate(s) (It optionally
      contains the certificate chain for this certificate)

   The payload of the RVR MUST contain the following parameter as part
   of the voucher-request as defined in [RFC8995]:

   *  created-on: current date and time in yang:date-and-time format of
      RVR creation

   *  nonce: copied from the PVR

   *  serial-number: product-serial-number of pledge.  The registrar
      MUST verify that the IDevID certificate subject serialNumber of
      the pledge (X520SerialNumber) matches the serial-number value in
      the PVR.  In addition, it MUST be equal to the serial-number value
      contained in the agent-signed data of PVR.

   *  assertion: voucher assertion requested by the pledge (agent-
      proximity).  The registrar provides this information to assure
      successful verification of Registrar-Agent proximity based on the
      agent-signed-data.

   *  prior-signed-voucher-request: PVR as received from Registrar-
      Agent, see Section 7.1

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   The RVR MUST be extended with the following parameter, when the
   assertion "agent-proximity" is requested, as defined in
   [I-D.ietf-anima-rfc8366bis]:

   *  agent-sign-cert: EE (RegAgt) certificate or the EE (RegAgt)
      certificate including certificate chain.  In the context of this
      document it is a JSON array of base64encoded certificate
      information and handled in the same way as x5c header objects.  If
      only a single object is contained in the x5c it MUST be the
      base64-encoded EE (RegAgt) certificate.  If multiple certificates
      are included in the x5c, the first MUST be the base64-encoded EE
      (RegAgt) certificate.

   The MASA uses this information for verification that the Registrar-
   Agent is in proximity to the registrar to state the corresponding
   assertion "agent-proximity".

   The object is signed using the registrar LDevID credentials, which
   corresponds to the certificate referenced in the JOSE header.

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   # The RVR in General JWS Serialization syntax
   {
     "payload": BASE64URL(UTF8(ietf-voucher-request:voucher)),
     "signatures": [
       {
         "protected": BASE64URL(UTF8(JWS Protected Header)),
         "signature": BASE64URL(JWS Signature)
       }
     ]
   }

   # Example: Decoded payload "ietf-voucher-request:voucher"
     representation in JSON syntax
   {
     "ietf-voucher-request:voucher": {
        "created-on": "2022-01-04T02:37:39.235Z",
        "nonce": "eDs++/FuDHGUnRxN3E14CQ==",
        "serial-number": "callee4711",
        "assertion": "agent-proximity",
        "prior-signed-voucher-request": "base64encodedvalue==",
        "agent-sign-cert": [
          "base64encodedvalue==",
          "base64encodedvalue==",
          "..."
        ]
     }
   }

   # Example: Decoded "JWS Protected Header" representation
     in JSON syntax
   {
     "alg": "ES256",
     "x5c": [
       "base64encodedvalue==",
       "base64encodedvalue=="
     ],
     "typ": "voucher-jws+json"
   }

                      Figure 18: Representation of RVR

   The registrar SHALL send the RVR to the MASA endpoint by HTTP POST:
   "/.well-known/brski/requestvoucher"

   The RVR Content-Type header field is defined in
   [I-D.ietf-anima-jws-voucher] as: application/voucher-jws+json

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   The registrar SHOULD set the Accept header of the RVR indicating the
   desired media type for the voucher-response.  The media type is
   application/voucher-jws+json as defined in
   [I-D.ietf-anima-jws-voucher].

   This document uses the JSON-in-JWS format throughout the definition
   of exchanges and in the examples.  Nevertheless, alternative
   encodings of the voucher as used in BRSKI [RFC8995] with JSON-in-CMS
   or CBOR-in-COSE_Sign [RFC9052] for constraint environments are
   possible as well.  The assumption is that a pledge typically supports
   a single encoding variant and creates the PVR in the supported
   format.  To ensure that the pledge is able to process the voucher,
   the registrar MUST use the media type for Accept header in the RVR
   based on the media type used for the PVR.

   Once the MASA receives the RVR it SHALL perform the verification as
   described in Section 5.5 of [RFC8995].

   In addition, the following processing SHALL be performed for PVR
   contained in RVR "prior-signed-voucher-request" field:

   *  agent-provided-proximity-registrar-cert: The MASA MAY verify that
      this field contains the registrar LDevID certificate.  If so, it
      MUST correspond to the registrar LDevID credentials used to sign
      the RVR.  Note: Correspond here relates to the case that a single
      registrar LDevID certificate is used or that different registrar
      LDevID certificates are used, which are issued by the same CA.

   *  agent-signed-data: The MASA MAY verify this data to issue "agent-
      proximity" assertion.  If so, the agent-signed-data MUST contain
      the pledge product-serial-number, contained in the "serial-number"
      field of the PVR (from "prior-signed-voucher-request" field) and
      also in "serial-number" field of the RVR.  The EE (RegAgt)
      certificate to be used for signature verification is identified by
      the "kid" parameter of the JOSE header.  If the assertion "agent-
      proximity" is requested, the RVR MUST contain the corresponding EE
      (RegAgt) certificate data in the "agent-sign-cert" field of the
      RVR.  It MUST be verified by the MASA to the same domain CA as the
      registrar LDevID certificate.  If the "agent-sign-cert" field is
      not set, the MASA MAY state a lower level assertion value, e.g.:
      "logged" or "verified".  Note: Sub-CA certificate(s) MUST also be
      carried by "agent-sign-cert", in case the EE (RegAgt) certificate
      is issued by a sub-CA and not the domain CA known to the MASA.  As
      the "agent-sign-cert" field is defined as array (x5c), it can
      handle multiple certificates.

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   If validation fails, the MASA SHOULD respond with an HTTP 4xx client
   error status code to the registrar.  The HTTP error status codes are
   kept the same as defined in Section 5.6 of [RFC8995] and comprise the
   codes: 403, 404, 406, and 415.

   The registrar provides the EE certificate of the Registrar-Agent
   identified by the SubjectKeyIdentifier (SKID) in the header of the
   "agent-signed-data" from the PVR in its RVR (see also Section 7.3.2).

   The MASA in turn verifies the registrar LDevID certificate is
   included in the PVR (contained in the "prior-signed-voucher-request"
   field of RVR) in the "agent-provided-proximity-registrar-cert" leaf
   and may assert the PVR as "verified" or "logged".

   In addition, the MASA may issue the assertion "agent-proximity" as
   follows: The MASA verifies the signature of the "agent-signed-data"
   contained in the "prior-signed-voucher-request", based on the
   provided EE certificate of the Registrar-Agent in the "agent-sign-
   cert" leaf of the RVR.  If both can be verified successfully, the
   MASA can assert "agent-proximity" in the voucher.  The assertion of
   "agent-proximity" is similar to the proximity assertion by the MASA
   when using BRSKI.  Note that the different assertions do not provide
   a metric of strength as the security properties are not comparable.

   Depending on the MASA verification policy, it may also respond with a
   suitable 4xx or 5xx response status codes as described in Section 5.6
   of [RFC8995].  When successful, the Voucher will then be supplied via
   the registrar to the Registrar-Agent.

7.3.3.  Issue Voucher by MASA (backend interaction)

   The MASA creates a voucher with Media-Type of application/voucher-
   jws+json as defined in [I-D.ietf-anima-jws-voucher].  If the MASA
   detects that the Accept header of the PVR does not match application/
   voucher-jws+json it SHOULD respond with the HTTP status code "406 Not
   Acceptable" as the pledge will not be able to parse the response.
   The voucher is according to [I-D.ietf-anima-rfc8366bis] but uses the
   new assertion value specified Section 5.4.

   Figure 19 shows an example of the contents of a voucher.

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   # The MASA issued voucher in General JWS Serialization syntax
   {
     "payload": BASE64URL(UTF8(ietf-voucher:voucher)),
     "signatures": [
       {
         "protected": BASE64URL(UTF8(JWS Protected Header)),
         "signature": BASE64URL(JWS Signature)
       }
     ]
   }

   # Example: Decoded payload "ietf-voucher:voucher" representation
     in JSON syntax
   {
     "ietf-voucher:voucher": {
       "assertion": "agent-proximity",
       "serial-number": "callee4711",
       "nonce": "base64encodedvalue==",
       "created-on": "2022-01-04T00:00:02.000Z",
       "pinned-domain-cert": "base64encodedvalue=="
     }
   }

   # Example: Decoded "JWS Protected Header" representation
     in JSON syntax
   {
     "alg": "ES256",
     "x5c": [
       "base64encodedvalue==",
       "base64encodedvalue=="
     ],
     "typ": "voucher-jws+json"
   }

              Figure 19: Representation of MASA issued voucher

   The pinned-domain certificate to be put into the voucher is
   determined by the MASA as described in Section 5.5 of [RFC8995].  The
   MASA returns the voucher-response (voucher) to the registrar.

7.3.4.  Supply Voucher to Registrar (backend interaction)

   After receiving the voucher the registrar SHOULD evaluate it for
   transparency and logging purposes as outlined in Section 5.6 of
   [RFC8995].  The registrar MUST add an additional signature to the
   MASA provided voucher using its registrar EE credentials.

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   The signature is created by signing the original "JWS Payload"
   produced by MASA and the registrar added "JWS Protected Header" using
   the registrar EE credentials (see [RFC7515], Section 5.2 point 8.
   The x5c component of the "JWS Protected Header" MUST contain the
   registrar EE certificate as well as potential subordinate CA
   certificates up to (but not including) the pinned domain certificate.
   The pinned domain certificate is already contained in the voucher
   payload ("pinned-domain-cert").

   (For many installations, with a single registrar credential, the
   registrar credential is what is pinned)

   In [RFC8995], the Registrar proved possession of the it's credential
   when the TLS session was setup.  While the pledge could not, at the
   time, validate the certificate truly belonged the registrar, it did
   validate that the certificate it was provided was able to
   authenticate the TLS connection.

   In the BRSKI-PRM mode, with the Registrar-Agent mediating all
   communication, the Pledge has not as yet been able to witness that
   the intended Registrar really does possess the relevant private key.
   This second signature provides for the same level of assurance to the
   pledge, and that it matches the public key that the pledge received
   in the trigger for the PVR (see Figure 11).

   The registrar MUST use the same registrar EE credentials used for
   authentication in the TLS handshake to authenticate towards the
   Registrar-Agent.  This has some operational implications when the
   registrar may be part of a scalable framework as described in
   [I-D.richardson-anima-registrar-considerations], Section 1.3.1.

   The second signature MUST either be done with the private key
   associated with the registrar EE certificate provided to the
   Registrar-Agent, or the use of a certificate chain is necessary.
   This ensures that the same registrar EE certificate can be used to
   verify the signature as transmitted in the voucher-request as also
   transferred in the PVR in the "agent-provided-proximity-registrar-
   cert".

   Figure 20 below provides an example of the voucher with two
   signatures.

   # The MASA issued voucher with additional registrar signature in
     General JWS Serialization syntax
   {
     "payload": BASE64URL(ietf-voucher:voucher),
     "signatures": [
       {

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         "protected": BASE64URL(UTF8(JWS Protected Header (MASA))),
         "signature": BASE64URL(JWS Signature)
       },
       {
         "protected": BASE64URL(UTF8(JWS Protected Header (Reg))),
         "signature": BASE64URL(JWS Signature)
       }
     ]
   }

   # Example: Decoded payload "ietf-voucher:voucher" representation in
     JSON syntax
   {
     "ietf-voucher:voucher": {
        "assertion": "agent-proximity",
        "serial-number": "callee4711",
        "nonce": "base64encodedvalue==",
        "created-on": "2022-01-04T00:00:02.000Z",
        "pinned-domain-cert": "base64encodedvalue=="
     }
   }

   # Example: Decoded "JWS Protected Header (MASA)" representation
     in JSON syntax
   {
     "alg": "ES256",
     "typ": "voucher-jws+json",
     "x5c": [
       "base64encodedvalue==",
       "base64encodedvalue=="
     ]
   }

   # Example: Decoded "JWS Protected Header (Reg)" representation
     in JSON syntax
   {
     "alg": "ES256",
     "x5c": [
       "base64encodedvalue==",
       "base64encodedvalue=="
     ]
   }

      Figure 20: Representation of MASA issued voucher with additional
                            registrar signature

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   Depending on the security policy of the operator, this signature can
   also be interpreted by the pledge as explicit authorization of the
   registrar to install the contained trust anchor.  The registrar sends
   the voucher to the Registrar-Agent.

7.3.5.  Response Artifact: Voucher

   After receiving the PVR from Registrar-Agent, the registrar SHALL
   perform the verification as defined in Section 5.3 of [RFC8995].  In
   addition, the registrar SHALL verify the following parameters from
   the PVR:

   *  agent-provided-proximity-registrar-cert: MUST contain registrar's
      own registrar LDevID certificate to ensure the registrar in
      proximity of the Registrar-Agent is the desired registrar for this
      PVR.

   *  agent-signed-data: The registrar MUST verify that the Registrar-
      Agent provided data has been signed with the private key
      corresponding to the EE (RegAgt) certificate indicated in the
      "kid" JOSE header parameter.  The registrar MUST verify that the
      LDevID(ReAgt) certificate, corresponding to the signature, is
      still valid.  If the certificate is already expired, the registrar
      SHALL reject the request.  Validity of used signing certificates
      at the time of signing the agent-signed-data is necessary to avoid
      that a rogue Registrar-Agent generates agent-signed-data objects
      to onboard arbitrary pledges at a later point in time, see also
      Section 10.3.  The registrar MUST fetch the EE (RegAgt)
      certificate, based on the provided SubjectKeyIdentifier (SKID)
      contained in the "kid" header parameter of the agent-signed-data,
      and perform this verification.  This requires, that the registrar
      has access to the EE (RegAgt) certificate data (including
      intermediate CA certificates if existent) based on the SKID.
      Note, the registrar may have stored the EE (RegAgt) certificate if
      used during TLS establishment between Registrar-Agent and
      registrar or it may be provided via a repository.

   If the registrar is unable to validate the PVR, it SHOULD respond
   with a HTTP 4xx/5xx error code to the Registrar-Agent.

   The following 4xx client error codes SHOULD be used:

   *  403 Forbidden: if the registrar detected that one or more security
      related parameters are not valid or if the pledge-provided
      information could not be used with automated allowance.

   *  406 Not Acceptable: if the Content-Type indicated by the Accept
      header is unknown or unsupported.

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   If the validation succeeds, the registrar performs pledge
   authorization according to Section 5.3 of [RFC8995] followed by
   obtaining a voucher from the pledge's MASA according to Section 5.4
   of [RFC8995] with the modifications described below in Section 7.3.2.

7.4.  Supply PER to Registrar (including backend interaction)

   After receiving the voucher, the Registrar-Agent sends the PER to the
   registrar in the same HTTP-over-TLS connection.  Which is similar to
   the PER processing described in Section 5.2 of [RFC8995].  In case
   the PER cannot be send in the same HTTP-over-TLS connection the
   Registrar-Agent may send the PER in a new HTTP-over-TLS connection.
   The registrar is able to correlate the PVR and the PER based on the
   signatures and the contained product-serial-number information.
   Note, this also addresses situations in which a nonceless voucher is
   used and may be pre-provisioned to the pledge.

   Figure 21 depicts exchanges for the PER request handling and the
   following subsections describe the corresponding artifacts.

 +--------+    +------------+    +-----------+    +--------+    +------+
 | Pledge |    | Registrar- |    |  Domain   |    | Domain |    | MASA |
 |        |    |   Agent    |    | Registrar |    |   CA   |    |      |
 +--------+    +------------+    +-----------+    +--------+    +------+
  |                  |                 |                 |   Internet |
  ~                  ~                 ~                 ~            ~
 (4) Supply PER to Registrar (including backend interaction)
  ~                  ~                 ~                 ~            ~
  |                  |                 |                 |            |
  |                  |<----(mTLS)----->|                 |            |
  |                  |-------PER------>|                 |            |
  |                  |                 |<-----mTLS------>|            |
  |                  |                 |-------RER------>|            |
  |                  |                 |<--Enroll-Resp---|            |
  |                  |<--Enroll-Resp---|                 |            |
  |                  |                 |                 |            |
  ~                  ~                 ~                 ~            ~

                       Figure 21: Enroll exchange

   In case the TLS connection to the registrar is already closed, the
   Registrar-Agent opens a new TLS connection with the registrar as
   stated in Section 7.3.

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7.4.1.  Request Artifact: Pledge Enroll-Request (PER)

   As specified in Section 7.2 deviating from BRSKI the PER is not a raw
   PKCS#10.  As the Registrar-Agent is involved in the exchange, the
   PKCS#10 is wrapped in a JWS object by the pledge and signed with
   pledge's IDevID to ensure proof-of-identity as outlined in Figure 16.

   EST [RFC7030] standard endpoints (/simpleenroll, /simplereenroll,
   /serverkeygen, /cacerts) on the registrar cannot be used for BRSKI-
   PRM.  This is caused by the utilization of signature wrapped-objects
   in BRSKI-PRM.  As EST requires to sent a raw PKCS#10 request to e.g.,
   "/.well-known/est/simpleenroll" endpoint, this document makes an
   enhancement by utilizing EST but with the exception to transport a
   signature wrapped PKCS#10 request.  Therefore a new endpoint for
   BRSKI-PRM on the registrar is defined as "/.well-known/brski/
   requestenroll"

   The Registrar-Agent SHALL send the PER to the registrar by HTTP POST
   to the endpoint: "/.well-known/brski/requestenroll"

   The Content-Type header of PER is: application/jose+json.

   This is a deviation from the Content-Type header values used in
   [RFC7030] and results in additional processing at the domain
   registrar (as EST server).  Note, the registrar is already aware that
   the bootstrapping is performed in a pledge-responder-mode due to the
   use of the EE (RegAgt) certificate for TLS and the provided PVR as
   JSON-in-JWS object.

   *  If the registrar receives a PER with Content-Type header:
      application/jose+json, it MUST verify the wrapping signature using
      the certificate indicated in the JOSE header.

   *  The registrar verifies that the pledge's certificate (here
      IDevID), carried in "x5c" header field, is accepted to join the
      domain after successful validation of the PVR.

7.4.2.  Enroll Pledge by Domain CA (backend interaction)

   If both succeed, the registrar utilizes the PKCS#10 request contained
   in the JWS object body as "P10" parameter of "ietf-sztp-csr:csr" for
   further processing of the Enroll-Request with the corresponding
   domain CA.  It creates a Registrar Enroll-Request (RER) by utilizing
   the protocol expected by the domain CA.

   The domain registrar may either directly forward the provided PKCS#10
   request to the CA or provide additional information about attributes
   to be included by the CA into the requested LDevID certificate.

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   The approach of sending this information to the CA depends on the
   utilized certificate management protocol between the RA and the CA
   and is out of scope for this document.

7.4.3.  Response Artifact: Enroll-Response (Enroll-Resp)

   The registrar SHOULD respond with an HTTP 200 OK in the success case
   or fail with HTTP 4xx/5xx status codes as defined by the HTTP
   standard.

   A successful interaction with the domain CA will result in a pledge
   LDevID certificate, which is then forwarded by the registrar to the
   Registrar-Agent using the Content-Type header: application/
   pkcs7-mime.

   Note while BRSKI-PRM targets the initial enrollment, re-enrollment
   may be supported in a similar way with the exception that the current
   LDevID certificate is used instead of the IDevID certificate to
   verify the wrapping signature of the PKCS#10 request (see also
   Section 7.2).

7.5.  Request CA Certificates

   As the pledge will verify it own certificate LDevID certificate when
   received, it also needs the corresponding CA certificates.  This is
   done in EST [RFC7030] using the "/.well-known/est/cacerts" endpoint,
   which provides the CA certificates over a TLS protected connection.
   BRSKI-PRM requires a signature wrapped CA certificate object, to
   avoid that the pledge can be provided with arbitrary CA certificates
   in an authorized way.  The registrar signed CA certificate object
   will allow the pledge to verify the authorization to install the
   received CA certificate(s).  As the CA certificate(s) are provided to
   the pledge after the voucher, the pledge has the required information
   (the domain certificate) to verify the wrapped CA certificate object.

   Figure 22 shows the request and provisioning of CA certificates in
   the infrastructure.  The following subsections describe the
   corresponding artifacts.

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 +--------+    +------------+    +-----------+    +--------+    +------+
 | Pledge |    | Registrar- |    |  Domain   |    | Domain |    | MASA |
 |        |    |   Agent    |    | Registrar |    |   CA   |    |      |
 +--------+    +------------+    +-----------+    +--------+    +------+
  |                  |                 |                 |   Internet |
  ~                  ~                 ~                 ~            ~
 (5) Request CA Certificates
  ~                  ~                 ~                 ~            ~
  |                  |                 |                 |            |
  |                  |<----(mTLS)----->|                 |            |
  |                  |---cACert-Req--->|                 |            |
  |                  |<--cACert-Resp---|                 |            |
  |                  |                 |                 |            |
  ~                  ~                 ~                 ~            ~

              Figure 22: CA certificates retrival exchange

   In case the TLS connection to the registrar is already closed, the
   Registrar-Agent opens a new TLS connection with the registrar as
   stated in Section 7.3.

7.5.1.  Request Artifact: cACert-Request (cACert-Req)

   To support Registrar-Agents requesting a signature wrapped CA
   certificate(s) object, a new endpoint for BRSKI-PRM is defined on the
   registrar: "/.well-known/brski/wrappedcacerts"

   The Registrar-Agent SHALL requests the EST CA trust anchor database
   information (in form of CA certificates) by HTTP GET.

7.5.2.  Response Artifact: cACert-Response (cACert-Resp)

   The Content-Type header of the response SHALL be: application/
   jose+json.

   This is a deviation from the Content-Type header values used in EST
   [RFC7030] and results in additional processing at the domain
   registrar (as EST server).  The additional processing is to sign the
   CA certificate(s) information using the registrar LDevID credentials.
   This results in a signed CA certificate(s) object (JSON-in-JWS), the
   CA certificates are provided as base64-encoded "x5bag" (see
   definition in [RFC9360]) in the JWS payload.

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   # The CA certificates data with registrar signature in
   # General JWS Serialization syntax
   {
     "payload": BASE64URL(certs),
     "signatures": [
       {
         "protected": BASE64URL(UTF8(JWS Protected Header)),
         "signature": BASE64URL(JWS Signature)
       }
     ]
   }

   # Example: Decoded payload "certs" representation in JSON syntax
   {
     "x5bag": [
       "base64encodedvalue==",
       "base64encodedvalue=="
     ]
   }

   # Example: Decoded "JWS Protected Header" representation
     in JSON syntax
   {
     "alg": "ES256",
     "x5c": [
       "base64encodedvalue==",
       "base64encodedvalue=="
     ]
   }

          Figure 23: Representation of CA certificate(s) data with
                            registrar signature

7.6.  Supply Voucher to Pledge

   It is assumed that the Registrar-Agent already obtained the
   bootstrapping response objects from the domain registrar and can
   supply them to the pledge:

   *  voucher-response - Voucher (from MASA via Registrar)

   *  wrapped-CA-certificate(s)-response - CA certificates

   *  enrollment-response - LDevID (Pledge) certificate (from CA via
      registrar)

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   To deliver these response objects, the Registrar-Agent will re-
   connect to the pledge.  To contact the pledge, it may either discover
   the pledge as described in Section 6.2.2 or use stored information
   from the first contact with the pledge.

   Preconditions in addition to Section 7.3:

   *  Registrar-Agent: obtained voucher and LDevID certificate and
      optionally IDevID CA certificates.  The IDevID CA certificate is
      necessary, when the connection between the Registrar-Agent and the
      pledge is established using TLS to enable the Registrar-Agent to
      validate the pledges' IDevID certificate during the TLS handshake
      as described in Section 7.1.

   The Registrar-Agent MAY optionally use TLS to protect the
   communication as outlined in Section 7.1.

   The Registrar-Agent provides the information via distinct pledge
   endpoints as following.  Figure 24 shows the provisioning of the
   voucher to the pledge.  The following subsections describe the
   corresponding artifacts.

 +--------+    +------------+    +-----------+    +--------+    +------+
 | Pledge |    | Registrar- |    |  Domain   |    | Domain |    | MASA |
 |        |    |   Agent    |    | Registrar |    |   CA   |    |      |
 +--------+    +------------+    +-----------+    +--------+    +------+
  |                  |                 |                 |   Internet |
  ~                  ~                 ~                 ~            ~
 (6) Supply Voucher to Pledge
  ~                  ~                 ~                 ~            ~
  |                  |                 |                 |            |
  |<----opt. TLS---->|                 |                 |            |
  |<-----Voucher-----|                 |                 |            |
  |------vStatus---->|                 |                 |            |
  |                  |                 |                 |            |
  ~                  ~                 ~                 ~            ~

                      Figure 24: Voucher exchange

7.6.1.  Request Artifact: Voucher

   The Registrar-Agent SHALL send the voucher-response to the pledge by
   HTTP POST to the endpoint: "/.well-known/brski/svr".

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   The Registrar-Agent voucher-response Content-Type header is
   application/voucher-jws+json and contains the voucher as provided by
   the MASA.  An example is given in Figure 19 for a MASA signed voucher
   and in Figure 20 for the voucher with the additional signature of the
   registrar.

   A nonceless voucher may be accepted as in [RFC8995] and may be
   allowed by a manufacture's pledge implementation.

   To perform the validation of several signatures on the voucher
   object, the pledge SHALL perform the signature verification in the
   following order:

   1.  Verify MASA signature as described in Section 5.6.1 of [RFC8995],
       against pre-installed manufacturer trust anchor (IDevID).

   2.  Install trust anchor contained in the voucher ("pinned-domain-
       cert") provisionally

   3.  Validate the LDevID(Reg) certificate received in the agent-
       provided-proximity-registrar-cert in the Pledge-Voucher-Request
       trigger request (in the field "agent-provided-proximity-
       registrar-cert")

   4.  Verify registrar signature of the voucher similar as described in
       Section 5.6.1 of [RFC8995], but take the registrar certificate
       instead of the MASA certificate for the verification

   Step3 and step 4 have been introduced in BRSKI-PRM to enable
   verification of LDevID(Reg) certificate and also the proof-of-
   possession of the corresponding private key by the registrar, which
   is done in BRSKI based on the established TLS channel.  If all steps
   stated above have been performed successfully, the pledge SHALL
   terminate the "PROVISIONAL accept" state for the domain trust anchor
   and the registrar LDevID certificate.

   If an error occurs during the verification and validation of the
   voucher, this SHALL be reported in the reason field of the pledge
   voucher status.

7.6.2.  Response Artifact: Voucher Status (vStatus)

   After voucher verification and validation the pledge MUST reply with
   a status telemetry message as defined in Section 5.7 of [RFC8995].
   The pledge generates the voucher-status and provides it as signed
   JSON-in-JWS object in response to the Registrar-Agent.

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   The response has the Content-Type application/jose+json and is signed
   using the IDevID of the pledge as shown in Figure 25.  As the reason
   field is optional (see [RFC8995]), it MAY be omitted in case of
   success.

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   # The "pledge-voucher-status" telemetry in general JWS
     serialization syntax
   {
     "payload": BASE64URL(pledge-voucher-status),
     "signatures": [
       {
         "protected": BASE64URL(UTF8(JWS Protected Header)),
         "signature": BASE64URL(JWS Signature)
       }
     ]
   }

   # Example: Decoded payload "pledge-voucher-status" representation
     in JSON syntax for success case
   {
     "version": 1,
     "status": true,
     "reason": "Voucher successfully processed",
     "reason-context": {
       "pvs-details": "JSON"
     }
   }

   # Example: Decoded payload "pledge-voucher-status" representation
     in JSON syntax for error case
   {
     "version": 1,
     "status": false,
     "reason": "Failed to authenticate MASA certificate because
     it starts in the future (1/1/2023).",
     "reason-context": {
       "pvs-details": "Current date: 1/1/1970"
     }
   }

   # Example: Decoded "JWS Protected Header" representation
     in JSON syntax
   {
     "alg": "ES256",
     "x5c": [
       "base64encodedvalue==",
       "base64encodedvalue=="
     ]
   }

        Figure 25: Representation of pledge voucher status telemetry

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   If the pledge did not did not provide voucher status telemetry
   information after processing the voucher, the Registrar-Agent MAY
   query the pledge status explicitly as described in Section 7.11 and
   MAY resent the voucher depending on the Pledge status following the
   procedure described in Section 7.6.

7.7.  Supply CA Certificates to Pledge

   Figure 26 shows the provisioning of the CA certificates aquired by
   the pledge-agent to the pledge.  The following subsections describe
   the corresponding artifacts.

 +--------+    +------------+    +-----------+    +--------+    +------+
 | Pledge |    | Registrar- |    |  Domain   |    | Domain |    | MASA |
 |        |    |   Agent    |    | Registrar |    |   CA   |    |      |
 +--------+    +------------+    +-----------+    +--------+    +------+
  |                  |                 |                 |   Internet |
  ~                  ~                 ~                 ~            ~
 (7) Supply CA Certificates to Pledge
  ~                  ~                 ~                 ~            ~
  |                  |                 |                 |            |
  |<----opt. TLS---->|                 |                 |            |
  |<-----cACerts-----|                 |                 |            |
  |                  |                 |                 |            |
  ~                  ~                 ~                 ~            ~

              Figure 26: Certificate provisioning exchange

7.7.1.  Request Artifact:

   The Registrar-Agent SHALL provide the set of CA certificates
   requested from the registrar to the pledge by HTTP POST to the
   endpoint: "/.well-known/brski/scac".

   As the CA certificate provisioning is crucial from a security
   perspective, this provisioning SHOULD only be done, if the voucher-
   response has been successfully processed by pledge as reflected in
   the voucher status telemetry.

   The CA certificates message has the Content-Type application/
   jose+json and is signed using the credential of the registrar as
   shown in Figure 23.

   The CA certificates are provided as base64-encoded "x5bag".  The
   pledge SHALL install the received CA certificates as trust anchor
   after successful verification of the registrar's signature.

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7.7.2.  Response (no artifact)

   The verification comprises the following steps the pledge MUST
   perform.  Maintaining the order of versification steps as indicated
   allows to determine, which verification has already been passed:

   1.  Check content-type of the CA certificates message.  If no
       Content-Type is contained in the HTTP header, the default
       Content-Type utilized in this document (JSON-in-JWS) is used.  If
       the Content-Type of the response is in an unknown or unsupported
       format, the pledge SHOULD reply with a 415 Unsupported media type
       error code.

   2.  Check the encoding of the payload.  If the pledge detects errors
       in the encoding of the payload, it SHOULD reply with 400 Bad
       Request error code.

   3.  Verify that the wrapped CA certificate object is signed using the
       registrar certificate against the pinned-domain certificate.
       This MAY be done by comparing the hash that is indicating the
       certificate used to sign the message is that of the pinned-domain
       certificate.  If the validation against the pinned domain-
       certificate fails, the client SHOULD reply with a 401
       Unauthorized error code.  It signals that the authentication has
       failed and therefore the object was not accepted.

   4.  Verify signature of the received wrapped CA certificate object
       using the domain certificate contained in the voucher.  If the
       validation of the signature fails, the pledge SHOULD reply with a
       403 Forbidden.  It signals that the object could not be verified
       and has not been accepted.

   5.  If the received CA certificates are not self-signed, i.e., an
       intermediate CA certificate, verify them against an already
       installed trust anchor, as described in section 4.1.3 of
       [RFC7030].

   In case of success, the pledge SHOULD reply with HTTP 200 OK without
   a response body.

7.8.  Supply Enroll-Response to Pledge

   Figure 27 shows the supply of the Enroll-Response to the pledge.  The
   following subsections describe the corresponding artifacts.

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 +--------+    +------------+    +-----------+    +--------+    +------+
 | Pledge |    | Registrar- |    |  Domain   |    | Domain |    | MASA |
 |        |    |   Agent    |    | Registrar |    |   CA   |    |      |
 +--------+    +------------+    +-----------+    +--------+    +------+
  |                  |                 |                 |   Internet |
  ~                  ~                 ~                 ~            ~
 (8) Supply Enroll-Response to Pledge
  ~                  ~                 ~                 ~            ~
  |                  |                 |                 |            |
  |<----opt. TLS---->|                 |                 |            |
  |<---Enroll-Resp---|                 |                 |            |
  |-----eStatus----->|                 |                 |            |
  |                  |                 |                 |            |
  ~                  ~                 ~                 ~            ~

                  Figure 27: Enroll-Response exchange

7.8.1.  Request Artifact: Enroll-Response (Enroll-Resp)

   The Registrar-Agent SHALL send the Enroll-Response to the pledge by
   HTTP(S) POST to the endpoint: "/.well-known/brski/ser".

   The Content-Type header when using EST [RFC7030] as enrollment
   protocol between the Registrar-Agent and the infrastructure is
   application/pkcs7-mime.  Note: It only contains the LDevID
   certificate for the pledge, not the certificate chain.

   Upon reception, the pledge SHALL verify the received LDevID
   certificate.  The pledge SHALL generate the enroll status and provide
   it in the response to the Registrar-Agent.  If the verification of
   the LDevID certificate succeeds, the status property SHALL be set to
   "status": true, otherwise to "status": false

7.8.2.  Response Artifact: Enroll Status (eStatus)

   After enrollment processing the pledge MUST reply with a enrollment
   status telemetry message as defined in Section 5.9.4 of [RFC8995].
   The enroll-status is also a signed object in BRSKI-PRM and results in
   form of JSON-in-JWS here.  If the pledge verified the received LDevID
   certificate successfully it SHALL sign the enroll-status using its
   new LDevID credentials as shown in Figure 29.  In failure case, the
   pledge SHALL use its IDevID credentials.  Section 5.9.4 of [RFC8995]
   specifies the enrollment status telemetry message with two optional
   fields for "reason" and "reason-context".  In BRSKI-PRM the optional
   fields are mandated to have a clear distinction between other status
   messages and MUST be provided therefore.  This distinction is
   intended for better error handling on registrar side, as a status
   object could be send to a wrong status endpoint.

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   The following CDDL [RFC8610] explains enroll-status response
   structure.  It is similar as defined in Section 5.9.4 of [RFC8995]
   with the optional fields set to mandatory as described above.

   <CODE BEGINS>
   enrollstatus-trigger = {
       "version": uint,
       "status": bool,
       "reason": text,
       "reason-context" : { $$arbitrary-map }
     }
   <CODE ENDS>

           Figure 28: CDDL for pledge-enrollment-status response

   The response has the Content-Type application/jose+json.

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   # The "pledge-enroll-status" telemetry in General JWS Serialization
     syntax
   {
     "payload": BASE64URL(pledge-enroll-status),
     "signatures": [
       {
         "protected": BASE64URL(UTF8(JWS Protected Header)),
         "signature": BASE64URL(JWS Signature)
       }
     ]
   }

   # Example: Decoded payload "pledge-enroll-status" representation
     in JSON syntax for success case
   {
     "version": 1,
     "status": true,
     "reason": "Enroll-Response successfully processed",
     "reason-context": {
       "pes-details": "JSON"
     }
   }

   # Example: Decoded payload "pledge-voucher-status" representation
     in JSON syntax for error case
   {
     "version": 1,
     "status": false,
     "reason": "Enroll-Response could not be verified.",
     "reason-context": {
       "pes-details": "no matching trust anchor"
     }
   }

   # Example: Decoded "JWS Protected Header" representation
     in JSON syntax
   {
     "alg": "ES256",
     "x5c": [
       "base64encodedvalue==",
       "base64encodedvalue=="
     ]
   }

        Figure 29: Representation of pledge enroll status telemetry

   Once the Registrar-Agent has collected the information, it can
   connect to the registrar to provide it with the status responses.

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7.9.  Voucher Status Telemetry (including backend interaction)

   The following description requires that the Registrar-Agent has
   collected the status information from the pledge.  It SHALL provide
   the status information to the registrar for further processing.

   Preconditions in addition to Section 7.3:

   *  Registrar-Agent: obtained voucher status (vStatus) and enroll
      status (eStatus) from pledge.

 +--------+    +------------+    +-----------+    +--------+    +------+
 | Pledge |    | Registrar- |    |  Domain   |    | Domain |    | MASA |
 |        |    |   Agent    |    | Registrar |    |   CA   |    |      |
 +--------+    +------------+    +-----------+    +--------+    +------+
  |                  |                 |                 |   Internet |
  ~                  ~                 ~                 ~            ~
 (9) Voucher Status Telemetry (including backend interaction)
  ~                  ~                 ~                 ~            ~
  |                  |                 |                 |            |
  |                  |<----(mTLS)----->|                 |            |
  |                  |-----vStatus---->|                 |            |
  |                  |                 |<-----------(mTLS)----------->|
  |                  |                 |-----req device audit log---->|
  |                  |                 |<------device audit log-------|
  |                  |        [verify audit log]         |            |
  |                  |                 |                 |            |
  ~                  ~                 ~                 ~            ~

   {: #exchangesfig_uc2_9 title="Voucher Status telemetry exchange"
   artwork-align="center"}~~~~ aasvg

   In case the TLS connection to the registrar is already closed, the
   Registrar-Agent opens a new TLS connection with the registrar as
   stated in Section 7.3.

   The Registrar-Agent MUST provide the collected pledge voucher status
   to the registrar.  This status indicates if the pledge could process
   the voucher successfully or not.

7.9.1.  Request Artifact: Voucher Status (vStatus)

   The Registrar-Agent sends the pledge voucher status without
   modification to the registrar with an HTTP-over-TLS POST using the
   registrar endpoint "/.well-known/brski/voucher_status".  The Content-
   Type header is kept as application/jose+json as depicted in the
   example in Figure 25.

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   The registrar SHOULD log the transaction provided for a pledge via
   Registrar-Agent and include the identity of the Registrar-Agent in
   these logs.  For log analysis the following may be considered:

   *  The registrar knows the interacting Registrar-Agent from the
      authentication of the Registrar-Agent towards the registrar using
      LDevID (RegAgt) and can log it accordingly.

   *  The telemetry information from the pledge can be correlated to the
      voucher response provided from the registrar to the Registrar-
      Agent and further to the pledge.

   *  The telemetry information, when provided to the registrar is
      provided via the Registrar-Agent and can thus be correlated.

   The registrar SHALL verify the signature of the pledge voucher status
   and validate that it belongs to an accepted device of the domain
   based on the contained "serial-number" in the IDevID certificate
   referenced in the header of the voucher status.

7.9.2.  Response (no artifact)

   According to Section 5.7 of [RFC8995], the registrar SHOULD respond
   with an HTTP 200 OK without a response body in the success case or
   fail with HTTP 4xx/5xx status codes.  The Registrar-Agent may use the
   response status code to signal success/failure to the service
   technician operating the Registrar-Agent.  Within the server logs the
   server SHOULD capture this telemetry information.

   The registrar SHOULD proceed with collecting and logging status
   information by requesting the MASA audit-log from the MASA service as
   described in Section 5.8 of [RFC8995].

7.10.  Enroll Status Telemetry

   The Registrar-Agent MUST provide the pledge's enroll status to the
   registrar.  The status indicates the pledge could process the Enroll-
   Response (certificate) and holds the corresponding private key.

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 +--------+    +------------+    +-----------+    +--------+    +------+
 | Pledge |    | Registrar- |    |  Domain   |    | Domain |    | MASA |
 |        |    |   Agent    |    | Registrar |    |   CA   |    |      |
 +--------+    +------------+    +-----------+    +--------+    +------+
  |                  |                 |                 |   Internet |
  ~                  ~                 ~                 ~            ~
 (10) Enroll Status Telemetry
  ~                  ~                 ~                 ~            ~
  |                  |                 |                 |            |
  |                  |<----(mTLS)----->|                 |            |
  |                  |-----eStatus---->|                 |            |
  |                  |                 |                 |            |
  ~                  ~                 ~                 ~            ~

              Figure 30: Enroll Status telemetry exchange

   In case the TLS connection to the registrar is already closed, the
   Registrar-Agent opens a new TLS connection with the registrar as
   stated in Section 7.3.

7.10.1.  Request Artifact: Enroll Status (eStatus)

   The Registrar-Agent sends the pledge enroll status without
   modification to the registrar with an HTTP-over-TLS POST using the
   registrar endpoint "/.well-known/brski/enrollstatus".  The Content-
   Type header is kept as application/jose+json as depicted in the
   example in Figure 29.

   The registrar MUST verify the signature of the pledge enroll status.
   Also, the registrar SHALL validate that the pledge is an accepted
   device of the domain based on the contained product-serial-number in
   the LDevID certificate referenced in the header of the enroll status.
   The registrar SHOULD log this event.  In case the pledge enroll
   status indicates a failure, the pledge was unable to verify the
   received LDevID certificate and therefore signed the enroll status
   with its IDevID credential.  Note that the signature verification of
   the status information is an addition to the described handling in
   Section 5.9.4 of [RFC8995], and is replacing the pledges TLS client
   authentication by DevID credentials in [RFC8995].

7.10.2.  Response (no artifact)

   According to Section 5.9.4 of [RFC8995], the registrar SHOULD respond
   with an HTTP 200 OK in the success case or fail with HTTP 4xx/5xx
   status codes.

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   Based on the failure case the registrar MAY decide that for security
   reasons the pledge is not allowed to reside in the domain.  In this
   case the registrar MUST revoke the certificate.  An example case for
   the registrar revoking the issued LDevID for the pledge is when the
   pledge was not able to verify the received LDevID certificate and
   therefore did send a 406 (Not Acceptable) response.  In this case the
   registrar may revoke the LDevID certificate as the pledge did no
   accepted it for installation.

   The Registrar-Agent may use the response to signal success / failure
   to the service technician operating the Registrar-Agent.  Within the
   server log the registrar SHOULD capture this telemetry information.

7.11.  Query Pledge Status

   The following assumes that a Registrar-Agent may need to query the
   status of a pledge.  This information may be useful to solve errors,
   when the pledge was not able to connect to the target domain during
   the bootstrapping.  The pledge MAY provide the dedicated endpoint for
   the Query Pledge Status operation.

 +--------+    +------------+    +-----------+    +--------+    +------+
 | Pledge |    | Registrar- |    |  Domain   |    | Domain |    | MASA |
 |        |    |   Agent    |    | Registrar |    |   CA   |    |      |
 +--------+    +------------+    +-----------+    +--------+    +------+
  |                  |                 |                 |   Internet |
  ~                  ~                 ~                 ~            ~
 (11) Query Pledge Status
  ~                  ~                 ~                 ~            ~
  |                  |                 |                 |            |
  |<----opt. TLS---->|                 |                 |            |
  |<-----tStatus-----|                 |                 |            |
  |------pStatus---->|                 |                 |            |
  |                  |                 |                 |            |
  ~                  ~                 ~                 ~            ~

                   Figure 31: Pledge Status exchange

   The Registrar-Agent queries the Pledge Status via HTTP POST request
   on the well-known pledge endpoint /.well-known/brski/qps.  The
   request body MUST contain the JWS-signed Status Trigger (tStatus)
   artifact.  The request header MUST set the Content-Type field
   application/jose+json.

   If the pledge provides the Query Pledge Status endpoint, it MUST
   reply to this request with the Pledge Status (pStatus) artifact in
   the body of a 200 OK response.  The response header MUST have the
   Content-Type field set to application/jose+json.

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7.11.1.  Request Artifact: Status Trigger (tStatus)

   The Status Query artifact is a JWS structure signing information on
   the requested status-type, the time and date the request is created,
   and the product serial-number of the pledge contacted as shown in
   Figure 32.  The following Concise Data Definition Language (CDDL)
   [RFC8610] defines the structure of the unsigned Status Query data
   (i.e., JWS payload):

   <CODE BEGINS>
     statustrigger = {
         "version": uint,
         "created-on": tdate,
         "serial-number": text,
         "status-type": text
     }
   <CODE ENDS>

      Figure 32: CDDL for unsigned Status Trigger data (statustrigger)

   The version field is included to permit significant changes to the
   pledge status artifacts in the future.  The format and semantics in
   this document follow the status telemetry definitions of [RFC8995].
   Hence, the version MUST be set to 1.  A pledge (or Registrar-Agent)
   that receives a version larger than it knows about SHOULD log the
   contents and alert a human.

   The created-on field contains a standard date/time string following
   [RFC3339].

   The serial-number field takes the product-serial-number corresponding
   to the X520SerialNumber field of the IDevID certificate of the
   pledge.

   The status-type value defined for BRSKI-PRM Status Query is
   bootstrap.  This indicates the pledge to provide current status
   information regarding the bootstrapping status (voucher processing
   and enrollment of the pledge into the new domain).

   As the Status Query artifact is defined generic, it may be used by
   other specifications to request further status information using
   other status types, e.g., for onboarding to get further information
   about enrollment of application specific LDevIDs or other parameters.
   This is out of scope for this specification.

   Figure 33 below shows an example for unsigned Status Query data in
   JSON syntax using status-type bootstrap.

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   {
     "version": 1,
     "created-on": "2022-08-12T02:37:39.235Z",
     "serial-number": "pledge-callee4711",
     "status-type": "bootstrap"
   }

      Figure 33: Example of unsigned Status Query data in JSON syntax
         using status- type bootstrap for the Status Query artifact

   The Status Query data MUST be signed by the Registrar-Agent using its
   private key corresponding to the EE (RegAgt) certificate.  When using
   a JWS signature, the Status Query artifact looks as shown in
   Figure 34 and the Content-Type response header MUST be set to
   application/jose+json:

   {
     "payload": BASE64URL(UTF8(status-query)),
     "signatures": [
       {
         "protected": BASE64URL(UTF8(JWS Protected Header)),
         "signature": BASE64URL(JWS Signature)
       }
     ]
   }

         Figure 34: Status Query Representation in General JWS JSON
                            Serialization Syntax

   For details on JWS Protected Header and JWS Signature see
   [I-D.ietf-anima-jws-voucher] or [RFC7515].

7.11.2.  Response Artifact: Pledge Status (pStatus)

   When the pledge receives a Status Query with status-type bootstrap it
   SHALL respond with previously collected telemetry information (see
   Section 7.9 and Section 7.10) in a single Pledge Status artifact.

   The pledge-status response message is signed with IDevID or LDevID,
   depending on bootstrapping state of the pledge.

   The following CDDL defines the structure of the Pledge Status
   (pStatus) data:

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   <CODE BEGINS>
     pledgestatus = {
       "version": uint,
       "status":
         "factory-default" /
         "voucher-success" /
         "voucher-error" /
         "enroll-success" /
         "enroll-error" /
         "connect-success" /
         "connect-error",
       ?"reason" : text,
       ?"reason-context": { $$arbitrary-map }
     }
   <CODE ENDS>

       Figure 35: CDDL for unsigned Pledge Status data (pledgestatus)

   Different cases for pledge bootstrapping status may occur, which
   SHOULD be reflected using the status enumeration.  This document
   specifies the status values in the context of the bootstrapping
   process and credential application.  Other documents may enhance the
   above enumeration to reflect further status information.

   *  "factory-default": Pledge has not been bootstrapped.  Additional
      information may be provided in the reason or reason-context.  The
      pledge signs the response message using its IDevID(Pledge).

   *  "voucher-success": Pledge processed the voucher exchange
      successfully.  Additional information may be provided in the
      reason or reason-context.  The pledge signs the response message
      using its IDevID(Pledge).

   *  "voucher-error": Pledge voucher processing terminated with error.
      Additional information may be provided in the reason or reason-
      context.  The pledge signs the response message using its
      IDevID(Pledge).

   *  "enroll-success": Pledge has processed the enrollment exchange
      successfully.  Additional information may be provided in the
      reason or reason-context.  The pledge signs the response message
      using its LDevID(Pledge).

   *  "enroll-error": Pledge enrollment-response processing terminated
      with error.  Additional information may be provided in the reason
      or reason-context.  The pledge signs the response message using
      its IDevID(Pledge).

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   As the pledge is assumed to utilize its bootstrapped credentials
   (LDevID) in communication with other peers, additional status
   information is provided for the connectivity to other peers, which
   may be helpful in analyzing potential error cases.

   *  "connect-success": Pledge could successfully establish a
      connection to another peer.  Additional information may be
      provided in the reason or reason-context.  The pledge signs the
      response message using its LDevID(Pledge).

   *  "connect-error": Pledge connection establishment terminated with
      error.  Additional information may be provided in the reason or
      reason-context.  The pledge signs the response message using its
      LDevID(Pledge).

   The pledge-status responses are cumulative in the sense that connect-
   success implies enroll-success, which in turn implies voucher-
   success.

   Figure 36 provides an example for the bootstrapping-status
   information.

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   # The pledge "status-response" in General JWS Serialization syntax
   {
     "payload": BASE64URL(UTF8(status-response)),
     "signatures": [
       {
         "protected": BASE64URL(UTF8(JWS Protected Header)),
         "signature": BASE64URL(JWS Signature)
       }
     ]
   }

   # Example: Decoded payload "status-response" representation
     in JSON syntax
   {
     "version": 1,
     "status": "enroll-success",
     "reason-context": {
       "additional" : "JSON"
     }
   }

   # Example: Decoded "JWS Protected Header" representation
     in JSON syntax
   {
     "alg": "ES256",
     "x5c": [
       "base64encodedvalue==",
       "base64encodedvalue=="
     ],
     "typ": "jose+json
   }

                Figure 36: Example of pledge-status response

   *  In case "factory-default" the pledge does not possess the domain
      certificate resp. the domain trust-anchor.  It will not be able to
      verify the signature of the Registrar-Agent in the bootstrapping-
      status request.

   *  In cases "vouchered" and "enrolled" the pledge already possesses
      the domain certificate (has domain trust-anchor) and can therefore
      validate the signature of the Registrar-Agent.  If validation of
      the JWS signature fails, the pledge SHOULD respond with the HTTP
      403 Forbidden status code.

   *  The HTTP 406 Not Acceptable status code SHOULD be used, if the
      Accept header in the request indicates an unknown or unsupported
      format.

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   *  The HTTP 415 Unsupported Media Type status code SHOULD be used, if
      the Content-Type of the request is an unknown or unsupported
      format.

   *  The HTTP 400 Bad Request status code SHOULD be used, if the
      Accept/Content-Type headers are correct but nevertheless the
      status-request cannot be correctly parsed.

   The pledge SHOULD by default only respond to requests from nodes it
   can authenticate (such as registrar agent), once the pledge is
   enrolled with CA certificates and a matching domain certificate.

8.  IANA Considerations

   This document requires the following IANA actions.

8.1.  BRSKI .well-known Registry

   IANA is requested to enhance the Registry entitled: "BRSKI Well-Known
   URIs" with the following endpoints:

     +================+==================================+===========+
     | Path Segment   | Description                      | Reference |
     +================+==================================+===========+
     | requestenroll  | Supply PER to registrar          | [THISRFC] |
     +----------------+----------------------------------+-----------+
     | wrappedcacerts | Request wrapped CA certificates  | [THISRFC] |
     +----------------+----------------------------------+-----------+
     | tpvr           | Trigger Pledge Voucher-Request   | [THISRFC] |
     +----------------+----------------------------------+-----------+
     | tper           | Trigger Pledge Enroll-Request    | [THISRFC] |
     +----------------+----------------------------------+-----------+
     | svr            | Supply Voucher to pledge         | [THISRFC] |
     +----------------+----------------------------------+-----------+
     | scac           | Supply CA certificates to pledge | [THISRFC] |
     +----------------+----------------------------------+-----------+
     | ser            | Supply Enroll-Response to pledge | [THISRFC] |
     +----------------+----------------------------------+-----------+
     | qps            | Query Pledge Status              | [THISRFC] |
     +----------------+----------------------------------+-----------+

                  Table 3: BRSKI Well-Known URIs Additions

8.2.  DNS Service Names

   IANA has registered the following service names:

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   *Service Name:* brski-pledge
   *Transport Protocol(s):* tcp
   *Assignee:* IESG iesg@ietf.org (mailto:iesg@ietf.org)
   *Contact:* IESG iesg@ietf.org (mailto:iesg@ietf.org)
   *Description:* The Bootstrapping Remote Secure Key Infrastructure
   Pledge
   *Reference:* [THISRFC]

9.  Privacy Considerations

   In general, the privacy considerations of [RFC8995] apply for BRSKI-
   PRM also.  Further privacy aspects need to be considered for:

   *  the introduction of the additional component Registrar-Agent

   *  potentially no transport layer security between Registrar-Agent
      and pledge

   Section 7.1 describes to optional apply TLS to protect the
   communication between the Registrar-Agent and the pledge.  The
   following is therefore applicable to the communication without the
   TLS protection.

   The credential used by the Registrar-Agent to sign the data for the
   pledge SHOULD NOT contain any personal information.  Therefore, it is
   recommended to use an LDevID certificate associated with the
   commissioning device instead of an LDevID certificate associated with
   the service technician operating the device.  This avoids revealing
   potentially included personal information to Registrar and MASA.

   The communication between the pledge and the Registrar-Agent is
   performed over plain HTTP.  Therefore, it is subject to disclosure by
   a Dolev-Yao attacker (an "oppressive observer")[onpath].  Depending
   on the requests and responses, the following information is
   disclosed.

   *  the Pledge product-serial-number is contained in the trigger
      message for the PVR and in all responses from the pledge.  This
      information reveals the identity of the devices being bootstrapped
      and allows deduction of which products an operator is using in
      their environment.  As the communication between the pledge and
      the Registrar-Agent may be realized over wireless link, this
      information could easily be eavesdropped, if the wireless network
      is unencrypted.  Even if the wireless network is encrypted, if it
      uses a network-wide key, then layer-2 attacks (ARP/ND spoofing)
      could insert an on-path observer into the path.

   *  the Timestamp data could reveal the activation time of the device.

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   *  the Status data of the device could reveal information about the
      current state of the device in the domain network.

10.  Security Considerations

   In general, the security considerations of [RFC8995] apply for BRSKI-
   PRM also.  Further security aspects are considered here related to:

   *  the introduction of the additional component Registrar-Agent

   *  the reversal of the pledge communication direction (push mode,
      compared to BRSKI)

   *  no transport layer security between Registrar-Agent and pledge

10.1.  Denial of Service (DoS) Attack on Pledge

   Disrupting the pledge behavior by a DoS attack may prevent the
   bootstrapping of the pledge to a new domain.  Because in BRSKI-PRM,
   the pledge responds to requests from real or illicit Registrar-
   Agents, pledges are more subject to DoS attacks from Registrar-Agents
   in BRSKI-PRM than they are from illicit registrars in [RFC8995],
   where pledges do initiate the connections.

   A DoS attack with a faked Registrar-Agent may block the bootstrapping
   of the pledge due changing state on the pledge (the pledge may
   produce a voucher-request, and refuse to produce another one).  One
   mitigation may be that the pledge does not limited the number of
   voucher-requests it creates until at least one has finished.  An
   alternative may be that the onboarding state may expire after a
   certain time, if no further interaction has happened.

   In addition, the pledge may assume that repeated triggering for PVR
   are the result of a communication error with the Registrar-Agent.  In
   that case the pledge MAY simply resent the PVR previously sent.  Note
   that in case of resending, a contained nonce and also the contained
   agent-signed-data in the PVR would consequently be reused.

10.2.  Misuse of acquired PVR and PER by Registrar-Agent

   A Registrar-Agent that uses previously requested PVR and PER for
   domain-A, may attempt to onboard the device into domain-B.  This can
   be detected by the domain registrar while PVR processing.  The domain
   registrar needs to verify that the "proximity-registrar-cert" field
   in the PVR matches its own registrar LDevID certificate.  In
   addition, the domain registrar needs to verify the association of the
   pledge to its domain based on the product-serial-number contained in
   the PVR and in the IDevID certificate of the pledge.  (This is just

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   part of the supply chain integration).  Moreover, the domain
   registrar verifies if the Registrar-Agent is authorized to interact
   with the pledge for voucher-requests and enroll-requests, based on
   the EE (RegAgt) certificate data contained in the PVR.

   Misbinding of a pledge by a faked domain registrar is countered as
   described in BRSKI security considerations Section 11.4 of [RFC8995].

10.3.  Misuse of Registrar-Agent Credentials

   Concerns of misusage of a Registrar-Agent with a valid EE (RegAgt)
   certificate may be addressed by utilizing short-lived certificates
   (e.g., valid for a day) to authenticate the Registrar-Agent against
   the domain registrar.  The EE (RegAgt) certificate may have been
   acquired by a prior BRSKI run for the Registrar-Agent, if an IDevID
   is available on Registrar-Agent.  Alternatively, the EE (RegAgt)
   certificate may be acquired by a service technician from the domain
   PKI system in an authenticated way.

   In addition it is required that the EE (RegAgt) certificate is valid
   for the complete bootstrapping phase.  This avoids that a Registrar-
   Agent could be misused to create arbitrary "agent-signed-data"
   objects to perform an authorized bootstrapping of a rogue pledge at a
   later point in time.  In this misuse "agent-signed-data" could be
   dated after the validity time of the EE (RegAgt) certificate, due to
   missing trusted timestamp in the Registrar-Agents signature.  To
   address this, the registrar SHOULD verify the certificate used to
   create the signature on "agent-signed-data".  Furthermore the
   registrar also verifies the EE (RegAgt) certificate used in the TLS
   handshake with the Registrar-Agent.  If both certificates are
   verified successfully, the Registrar-Agent's signature can be
   considered as valid.

10.4.  Misuse of DNS-SD with mDNS to obtain list of pledges

   To discover a specific pledge a Registrar-Agent may request the
   service name in combination with the product-serial-number of a
   specific pledge.  The pledge reacts on this if its product-serial-
   number is part of the request message.

   If the Registrar-Agent performs DNS-based Service Discovery without a
   specific product-serial-number, all pledges in the domain react if
   the functionality is supported.  This functionality enumerates and
   reveals the information of devices available in the domain.  The
   information about this is provided here as a feature to support the
   commissioning of devices.  A manufacturer may decide to support this
   feature only for devices not possessing a LDevID or to not support
   this feature at all, to avoid an enumeration in an operative domain.

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10.5.  YANG Module Security Considerations

   The enhanced voucher-request described in [I-D.ietf-anima-rfc8366bis]
   is based on [RFC8995], but uses a different encoding based on
   [I-D.ietf-anima-jws-voucher].  The security considerations as
   described in Section 11.7 of [RFC8995] (Security Considerations)
   apply.

   The YANG module specified in [I-D.ietf-anima-rfc8366bis] defines the
   schema for data that is subsequently encapsulated by a JOSE signed-
   data Content-type as described in [I-D.ietf-anima-jws-voucher].  As
   such, all of the YANG-modeled data is protected against modification.

   The use of YANG to define data structures via the [RFC8971]
   "structure" statement, is relatively new and distinct from the
   traditional use of YANG to define an API accessed by network
   management protocols such as NETCONF [RFC6241] and RESTCONF
   [RFC8040].  For this reason, these guidelines do not follow the
   template described by Section 3.7 of [RFC8407] (Security
   Considerations).

11.  Acknowledgments

   We would like to thank the various reviewers, in particular Brian E.
   Carpenter, Charlie Kaufman (Early SECDIR review), Martin Björklund
   (Early YANGDOCTORS review), Marco Tiloca (Early IOTDIR review), Oskar
   Camenzind, Hendrik Brockhaus, and Ingo Wenda for their input and
   discussion on use cases and call flows.  Further review input was
   provided by Jesser Bouzid, Dominik Tacke, and Christian Spindler.
   Special thanks to Esko Dijk for the in deep review and the improving
   proposals.  Support in PoC implementations and comments resulting
   from the implementation was provided by Hong Rui Li and He Peng Jia.

12.  References

12.1.  Normative References

   [I-D.ietf-anima-jws-voucher]
              Werner, T. and M. Richardson, "JWS signed Voucher
              Artifacts for Bootstrapping Protocols", Work in Progress,
              Internet-Draft, draft-ietf-anima-jws-voucher-09, 29 August
              2023, <https://datatracker.ietf.org/doc/html/draft-ietf-
              anima-jws-voucher-09>.

   [I-D.ietf-anima-rfc8366bis]
              Watsen, K., Richardson, M., Pritikin, M., Eckert, T. T.,
              and Q. Ma, "A Voucher Artifact for Bootstrapping
              Protocols", Work in Progress, Internet-Draft, draft-ietf-

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              anima-rfc8366bis-11, 4 March 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-anima-
              rfc8366bis-11>.

   [I-D.ietf-netconf-sztp-csr]
              Watsen, K., Housley, R., and S. Turner, "Conveying a
              Certificate Signing Request (CSR) in a Secure Zero Touch
              Provisioning (SZTP) Bootstrapping Request", Work in
              Progress, Internet-Draft, draft-ietf-netconf-sztp-csr-14,
              2 March 2022, <https://datatracker.ietf.org/doc/html/
              draft-ietf-netconf-sztp-csr-14>.

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

   [RFC3339]  Klyne, G. and C. Newman, "Date and Time on the Internet:
              Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002,
              <https://www.rfc-editor.org/rfc/rfc3339>.

   [RFC6762]  Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
              DOI 10.17487/RFC6762, February 2013,
              <https://www.rfc-editor.org/rfc/rfc6762>.

   [RFC6763]  Cheshire, S. and M. Krochmal, "DNS-Based Service
              Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,
              <https://www.rfc-editor.org/rfc/rfc6763>.

   [RFC7030]  Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed.,
              "Enrollment over Secure Transport", RFC 7030,
              DOI 10.17487/RFC7030, October 2013,
              <https://www.rfc-editor.org/rfc/rfc7030>.

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

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.

   [RFC8259]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", STD 90, RFC 8259,
              DOI 10.17487/RFC8259, December 2017,
              <https://www.rfc-editor.org/rfc/rfc8259>.

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   [RFC8366]  Watsen, K., Richardson, M., Pritikin, M., and T. Eckert,
              "A Voucher Artifact for Bootstrapping Protocols",
              RFC 8366, DOI 10.17487/RFC8366, May 2018,
              <https://www.rfc-editor.org/rfc/rfc8366>.

   [RFC8610]  Birkholz, H., Vigano, C., and C. Bormann, "Concise Data
              Definition Language (CDDL): A Notational Convention to
              Express Concise Binary Object Representation (CBOR) and
              JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610,
              June 2019, <https://www.rfc-editor.org/rfc/rfc8610>.

   [RFC8615]  Nottingham, M., "Well-Known Uniform Resource Identifiers
              (URIs)", RFC 8615, DOI 10.17487/RFC8615, May 2019,
              <https://www.rfc-editor.org/rfc/rfc8615>.

   [RFC8995]  Pritikin, M., Richardson, M., Eckert, T., Behringer, M.,
              and K. Watsen, "Bootstrapping Remote Secure Key
              Infrastructure (BRSKI)", RFC 8995, DOI 10.17487/RFC8995,
              May 2021, <https://www.rfc-editor.org/rfc/rfc8995>.

   [RFC9360]  Schaad, J., "CBOR Object Signing and Encryption (COSE):
              Header Parameters for Carrying and Referencing X.509
              Certificates", RFC 9360, DOI 10.17487/RFC9360, February
              2023, <https://www.rfc-editor.org/rfc/rfc9360>.

12.2.  Informative References

   [androidnsd]
              "Android Developer: Connect devices wirelessly", archived
              at https://web.archive.org/web/20230000000000*/https://dev
              eloper.android.com/training/connect-devices-wirelessly,
              n.d., <https://developer.android.com/training/connect-
              devices-wirelessly>.

   [androidtrustfail]
              "Security with Network Protocols", archived at https://web
              .archive.org/web/20230326153937/https://developer.android.
              com/training/articles/security-ssl, n.d.,
              <https://developer.android.com/training/articles/security-
              ssl>.

   [BRSKI-PRM-abstract]
              "Abstract BRSKI-PRM Protocol Overview", March 2022,
              <https://datatracker.ietf.org/meeting/113/materials/
              slides-113-anima-update-on-brski-with-pledge-in-responder-
              mode-brski-prm-00>.

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   [I-D.eckert-anima-brski-discovery]
              Eckert, T. T., von Oheimb, D., and E. Dijk, "Discovery for
              BRSKI variations", Work in Progress, Internet-Draft,
              draft-eckert-anima-brski-discovery-01, 23 October 2023,
              <https://datatracker.ietf.org/doc/html/draft-eckert-anima-
              brski-discovery-01>.

   [I-D.ietf-anima-brski-ae]
              von Oheimb, D., Fries, S., and H. Brockhaus, "BRSKI-AE:
              Alternative Enrollment Protocols in BRSKI", Work in
              Progress, Internet-Draft, draft-ietf-anima-brski-ae-10, 1
              March 2024, <https://datatracker.ietf.org/doc/html/draft-
              ietf-anima-brski-ae-10>.

   [I-D.irtf-t2trg-taxonomy-manufacturer-anchors]
              Richardson, M., "A Taxonomy of operational security
              considerations for manufacturer installed keys and Trust
              Anchors", Work in Progress, Internet-Draft, draft-irtf-
              t2trg-taxonomy-manufacturer-anchors-03, 30 January 2024,
              <https://datatracker.ietf.org/doc/html/draft-irtf-t2trg-
              taxonomy-manufacturer-anchors-03>.

   [I-D.richardson-anima-registrar-considerations]
              Richardson, M. and W. Pan, "Operational Considerations for
              BRSKI Registrar", Work in Progress, Internet-Draft, draft-
              richardson-anima-registrar-considerations-08, 14 February
              2024, <https://datatracker.ietf.org/doc/html/draft-
              richardson-anima-registrar-considerations-08>.

   [I-D.richardson-emu-eap-onboarding]
              DeKok, A. and M. Richardson, "EAP defaults for devices
              that need to onboard", Work in Progress, Internet-Draft,
              draft-richardson-emu-eap-onboarding-03, 2 April 2023,
              <https://datatracker.ietf.org/doc/html/draft-richardson-
              emu-eap-onboarding-03>.

   [IEEE-802.1AR]
              Institute of Electrical and Electronics Engineers, "IEEE
              802.1AR Secure Device Identifier", IEEE 802.1AR, June
              2018.

   [onpath]   "can an on-path attacker drop traffic?", n.d.,
              <https://mailarchive.ietf.org/arch/msg/saag/
              m1r9uo4xYznOcf85Eyk0Rhut598/>.

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   [RFC2986]  Nystrom, M. and B. Kaliski, "PKCS #10: Certification
              Request Syntax Specification Version 1.7", RFC 2986,
              DOI 10.17487/RFC2986, November 2000,
              <https://www.rfc-editor.org/rfc/rfc2986>.

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

   [RFC5272]  Schaad, J. and M. Myers, "Certificate Management over CMS
              (CMC)", RFC 5272, DOI 10.17487/RFC5272, June 2008,
              <https://www.rfc-editor.org/rfc/rfc5272>.

   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
              <https://www.rfc-editor.org/rfc/rfc6241>.

   [RFC7252]  Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
              Application Protocol (CoAP)", RFC 7252,
              DOI 10.17487/RFC7252, June 2014,
              <https://www.rfc-editor.org/rfc/rfc7252>.

   [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
              <https://www.rfc-editor.org/rfc/rfc8040>.

   [RFC8407]  Bierman, A., "Guidelines for Authors and Reviewers of
              Documents Containing YANG Data Models", BCP 216, RFC 8407,
              DOI 10.17487/RFC8407, October 2018,
              <https://www.rfc-editor.org/rfc/rfc8407>.

   [RFC8792]  Watsen, K., Auerswald, E., Farrel, A., and Q. Wu,
              "Handling Long Lines in Content of Internet-Drafts and
              RFCs", RFC 8792, DOI 10.17487/RFC8792, June 2020,
              <https://www.rfc-editor.org/rfc/rfc8792>.

   [RFC8971]  Pallagatti, S., Ed., Mirsky, G., Ed., Paragiri, S.,
              Govindan, V., and M. Mudigonda, "Bidirectional Forwarding
              Detection (BFD) for Virtual eXtensible Local Area Network
              (VXLAN)", RFC 8971, DOI 10.17487/RFC8971, December 2020,
              <https://www.rfc-editor.org/rfc/rfc8971>.

   [RFC8990]  Bormann, C., Carpenter, B., Ed., and B. Liu, Ed., "GeneRic
              Autonomic Signaling Protocol (GRASP)", RFC 8990,
              DOI 10.17487/RFC8990, May 2021,
              <https://www.rfc-editor.org/rfc/rfc8990>.

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   [RFC9052]  Schaad, J., "CBOR Object Signing and Encryption (COSE):
              Structures and Process", STD 96, RFC 9052,
              DOI 10.17487/RFC9052, August 2022,
              <https://www.rfc-editor.org/rfc/rfc9052>.

   [RFC9110]  Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
              Ed., "HTTP Semantics", STD 97, RFC 9110,
              DOI 10.17487/RFC9110, June 2022,
              <https://www.rfc-editor.org/rfc/rfc9110>.

   [RFC9238]  Richardson, M., Latour, J., and H. Habibi Gharakheili,
              "Loading Manufacturer Usage Description (MUD) URLs from QR
              Codes", RFC 9238, DOI 10.17487/RFC9238, May 2022,
              <https://www.rfc-editor.org/rfc/rfc9238>.

   [RFC9483]  Brockhaus, H., von Oheimb, D., and S. Fries, "Lightweight
              Certificate Management Protocol (CMP) Profile", RFC 9483,
              DOI 10.17487/RFC9483, November 2023,
              <https://www.rfc-editor.org/rfc/rfc9483>.

   [RFC9525]  Saint-Andre, P. and R. Salz, "Service Identity in TLS",
              RFC 9525, DOI 10.17487/RFC9525, November 2023,
              <https://www.rfc-editor.org/rfc/rfc9525>.

Appendix A.  Examples

   These examples are folded according to [RFC8792] Single Backslash
   rule.

A.1.  Example Pledge Voucher-Request (PVR) - from Pledge to Registrar-
      Agent

   The following is an example request sent from a Pledge to the
   Registrar-Agent, in "General JWS JSON Serialization".  The message
   size of this PVR is: 4649 bytes

   =============== NOTE: '\' line wrapping per RFC 8792 ================

   {
     "payload":
       "eyJpZXRmLXZvdWNoZXItcmVxdWVzdC1wcm06dm91Y2hlciI6eyJhc3NlcnRpb24\
   iOiJhZ2VudC1wcm94aW1pdHkiLCJzZXJpYWwtbnVtYmVyIjoiMDEyMzQ1Njc4OSIsIm5\
   vbmNlIjoiTDNJSjZocHRIQ0lRb054YWFiOUhXQT09IiwiY3JlYXRlZC1vbiI6IjIwMjI\
   tMDQtMjZUMDU6MTY6MTcuNzA5WiIsImFnZW50LXByb3ZpZGVkLXByb3hpbWl0eS1yZWd\
   pc3RyYXItY2VydCI6Ik1JSUI0akNDQVlpZ0F3SUJBZ0lHQVhZNzJiYlpNQW9HQ0NxR1N\
   NNDlCQU1DTURVeEV6QVJCZ05WQkFvTUNrMTVRblZ6YVc1bGMzTXhEVEFMQmdOVkJBY01\
   CRk5wZEdVeER6QU5CZ05WQkFNTUJsUmxjM1JEUVRBZUZ3MHlNREV5TURjd05qRTRNVEp\
   hRncwek1ERXlNRGN3TmpFNE1USmFNRDR4RXpBUkJnTlZCQW9NQ2sxNVFuVnphVzVsYzN\

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   NeERUQUxCZ05WQkFjTUJGTnBkR1V4R0RBV0JnTlZCQU1NRDBSdmJXRnBibEpsWjJsemR\
   ISmhjakJaTUJNR0J5cUdTTTQ5QWdFR0NDcUdTTTQ5QXdFSEEwSUFCQmsxNksvaTc5b1J\
   rSzVZYmVQZzhVU1I4L3VzMWRQVWlaSE10b2tTZHFLVzVmbldzQmQrcVJMN1dSZmZlV2t\
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   VRkJ3TUJCZ2dyQmdFRkJRY0RIREFPQmdOVkhROEJBZjhFQkFNQ0I0QXdTQVlEVlIwUkJ\
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   aMmx6ZEhKaGNpMTBaWE4wTmk1emFXVnRaVzV6TFdKMExtNWxkREFLQmdncWhrak9QUVF\
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   hSURnSWhBTFNKYmdMbmdoYmJBZzBkY1dGVVZvL2dHTjAvand6SlowU2wyaDR4SVhrMSI\
   sImFnZW50LXNpZ25lZC1kYXRhIjoiZXlKd1lYbHNiMkZrSWpvaVpYbEtjRnBZVW0xTVd\
   GcDJaRmRPYjFwWVNYUmpiVlo0WkZkV2VtUkRNWGRqYlRBMldWZGtiR0p1VVhSak1teHV\
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   KRE1YVmtWekZwV2xoSmFVOXBTWGROVkVsNlRrUlZNazU2WnpWSmJqRTVJaXdpYzJsbmJ\
   tRjBkWEpsY3lJNlczc2ljSEp2ZEdWamRHVmtJam9pWlhsS2NtRlhVV2xQYVVwWlkwaHd\
   jMVJWZERSaVNFSkNUbXBvYWxaVVZrZFZWVEZaVmxoYWRWTldVVEpWV0dNNVNXbDNhVmx\
   YZUc1SmFtOXBVbFpOZVU1VVdXbG1VU0lzSW5OcFoyNWhkSFZ5WlNJNklrY3pWM2hHU0d\
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   VZER3RUIvd1FFQXdJQ0JEQWZCZ05WSFNNRUdEQVdnQlRvWklNelFkc0Qvai8rZ1gvN2N\
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   teFIzQ1hvWktHUXJVPSJdfX0",
       "signatures":[{
         "protected":"eyJ4NWMiOlsiTUlJQitUQ0NBYUNnQXdJQkFnSUdBWG5WanNVN\
   U1Bb0dDQ3FHU000OUJBTUNNRDB4Q3pBSkJnTlZCQVlUQWtGUk1SVXdFd1lEVlFRS0RBe\

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   EthVzVuU21sdVowTnZjbkF4RnpBVkJnTlZCQU1NRGtwcGJtZEthVzVuVkdWemRFTkJNQ\
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   yI6IkVTMjU2In0",
         "signature":"Y_ohapnmvbwjLuUicOB7NAmbGM7igBfpUlkKUuSNdG-eDI4BQ\
   yuXZ2aw93zZId45R7XxAK-12YKIx6qLjiPjMw"
     }]
   }

              Figure 37: Example Pledge-Voucher-Request - PVR

A.2.  Example Parboiled Registrar Voucher-Request (RVR) - from Registrar
      to MASA

   The term parboiled refers to food which is partially cooked.  In
   [RFC8995], the term refers to a pledge-voucher-request (PVR) which
   has been received by the Registrar, and then has been processed by
   the Registrar ("cooked"), and is now being forwarded to the MASA.

   The following is an example registrar-voucher-request (RVR) sent from
   the Registrar to the MASA, in "General JWS JSON Serialization".  Note
   that the previous PVR can be seen in the payload as "prior-signed-
   voucher-request".  The message size of this RVR is: 13257 bytes

   =============== NOTE: '\' line wrapping per RFC 8792 ================

   {
     "payload":
       "eyJpZXRmLXZvdWNoZXItcmVxdWVzdC1wcm06dm91Y2hlciI6eyJhc3NlcnRpb24\
   iOiJhZ2VudC1wcm94aW1pdHkiLCJzZXJpYWwtbnVtYmVyIjoiY2FmZmUtOTg3NDUiLCJ\
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   XbFBhVXBPVTFWc1JGSkdVa1JSTUVacFZESmtRbVF3YkVOUlYyUktVakJHV1ZkWVRuZFR\
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Fries, et al.           Expires 5 September 2024               [Page 85]
Internet-Draft                  BRSKI-PRM                     March 2024

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Fries, et al.           Expires 5 September 2024               [Page 86]
Internet-Draft                  BRSKI-PRM                     March 2024

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Fries, et al.           Expires 5 September 2024               [Page 87]
Internet-Draft                  BRSKI-PRM                     March 2024

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   hV0Z5ZVRFUE1BMEdBMVVFQnd3R1RYbFRhWFJsTVJFd0R3WURWUVFEREFoTmVWTnBkR1Z\
   EUVRBZUZ3MHlNREF5TWpBd05qQXlNak5hRncwek1EQXlNakF3TmpBeU1qTmFNRnd4Q3p\
   BSkJnTlZCQVlUQWtGUk1SSXdFQVlEVlFRS0RBbE5lVU52YlhCaGJua3hGVEFUQmdOVkJ\
   Bc01ERTE1VTNWaWMybGthV0Z5ZVRFUE1BMEdBMVVFQnd3R1RYbFRhWFJsTVJFd0R3WUR\
   WUVFEREFoTmVWTnBkR1ZEUVRCWk1CTUdCeXFHU000OUFnRUdDQ3FHU000OUF3RUhBMEl\
   BQkluQ3VoV1ZzZ2NONzFvWmVzMUZHXC9xZFZnTVBva01wZlMyNzFcL2V5SWNcL29EVmJ\
   NRkhDYmV2SjVMTTgxOTVOYVpLTlNvSFAzS3dMeXVCaDh2MncwOVp1alJUQkRNQklHQTF\
   VZEV3RUJcL3dRSU1BWUJBZjhDQVFFd0RnWURWUjBQQVFIXC9CQVFEQWdJRU1CMEdBMVV\
   kRGdRV0JCUXp4endwUnBMeVwvck1VWXphaDJzMTNlVTlnRnpBS0JnZ3Foa2pPUFFRREF\
   nTkhBREJFQWlCZGJIU212YW9qaDBpZWtaSUtOVzhRMGxTbGI1K0RLTlFcL05LY1I3dWx\
   6dGdJZ2RwejZiUkYyREZtcGlKb3JCMkd5VmE4YVdkd2xIc0RvRVdZY0k0UEdKYmc9Il0\
   sImFsZyI6IkVTMjU2In0",
       "signature":"67t3n8zyEek4IM2Ko3Y_UvE1hzp794QFNTqG-HzTrBQtE4_4-yS\
   yyFd3kP6YCn35YYJ7yK35d3styo_yoiPfKA"
     }]
   }

             Figure 38: Example Registrar-Voucher-Request - RVR

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A.3.  Example Voucher - from MASA to Pledge, via Registrar and
      Registrar-Agent

   The following is an example voucher-response from MASA to Pledge via
   Registrar and Registrar-Agent, in "General JWS JSON Serialization".
   The message size of this Voucher is: 1916 bytes

   =============== NOTE: '\' line wrapping per RFC 8792 ================

   {
     "payload":"eyJpZXRmLXZvdWNoZXI6dm91Y2hlciI6eyJhc3NlcnRpb24iOiJhZ2V\
   udC1wcm94aW1pdHkiLCJzZXJpYWwtbnVtYmVyIjoiMDEyMzQ1Njc4OSIsIm5vbmNlIjo\
   iTDNJSjZocHRIQ0lRb054YWFiOUhXQT09IiwiY3JlYXRlZC1vbiI6IjIwMjItMDQtMjZ\
   UMDU6MTY6MjguNzI2WiIsInBpbm5lZC1kb21haW4tY2VydCI6Ik1JSUJwRENDQVVtZ0F\
   3SUJBZ0lHQVcwZUx1SCtNQW9HQ0NxR1NNNDlCQU1DTURVeEV6QVJCZ05WQkFvTUNrMTV\
   RblZ6YVc1bGMzTXhEVEFMQmdOVkJBY01CRk5wZEdVeER6QU5CZ05WQkFNTUJsUmxjM1J\
   EUVRBZUZ3MHhPVEE1TVRFd01qTTNNekphRncweU9UQTVNVEV3TWpNM016SmFNRFV4RXp\
   BUkJnTlZCQW9NQ2sxNVFuVnphVzVsYzNNeERUQUxCZ05WQkFjTUJGTnBkR1V4RHpBTkJ\
   nTlZCQU1NQmxSbGMzUkRRVEJaTUJNR0J5cUdTTTQ5QWdFR0NDcUdTTTQ5QXdFSEEwSUF\
   CT2t2a1RIdThRbFQzRkhKMVVhSTcrV3NIT2IwVVMzU0FMdEc1d3VLUURqaWV4MDYvU2N\
   ZNVBKaWJ2Z0hUQitGL1FUamdlbEhHeTFZS3B3Y05NY3NTeWFqUlRCRE1CSUdBMVVkRXd\
   FQi93UUlNQVlCQWY4Q0FRRXdEZ1lEVlIwUEFRSC9CQVFEQWdJRU1CMEdBMVVkRGdRV0J\
   CVG9aSU16UWRzRC9qLytnWC83Y0JKdWNIL1htakFLQmdncWhrak9QUVFEQWdOSkFEQkd\
   BaUVBdHhRMytJTEdCUEl0U2g0YjlXWGhYTnVocVNQNkgrYi9MQy9mVllEalE2b0NJUUR\
   HMnVSQ0hsVnEzeWhCNThUWE1VYnpIOCtPbGhXVXZPbFJEM1ZFcURkY1F3PT0ifX0",
     "signatures":[{
       "protected":"eyJ4NWMiOlsiTUlJQmt6Q0NBVGlnQXdJQkFnSUdBV0ZCakNrWU1\
   Bb0dDQ3FHU000OUJBTUNNRDB4Q3pBSkJnTlZCQVlUQWtGUk1SVXdFd1lEVlFRS0RBeEt\
   hVzVuU21sdVowTnZjbkF4RnpBVkJnTlZCQU1NRGtwcGJtZEthVzVuVkdWemRFTkJNQjR\
   YRFRFNE1ERXlPVEV3TlRJME1Gb1hEVEk0TURFeU9URXdOVEkwTUZvd1R6RUxNQWtHQTF\
   VRUJoTUNRVkV4RlRBVEJnTlZCQW9NREVwcGJtZEthVzVuUTI5eWNERXBNQ2NHQTFVRUF\
   3d2dTbWx1WjBwcGJtZERiM0p3SUZadmRXTm9aWElnVTJsbmJtbHVaeUJMWlhrd1dUQVR\
   CZ2NxaGtqT1BRSUJCZ2dxaGtqT1BRTUJCd05DQUFTQzZiZUxBbWVxMVZ3NmlRclJzOFI\
   wWlcrNGIxR1d5ZG1XczJHQU1GV3diaXRmMm5JWEgzT3FIS1Z1OHMyUnZpQkdOaXZPS0d\
   CSEh0QmRpRkVaWnZiN294SXdFREFPQmdOVkhROEJBZjhFQkFNQ0I0QXdDZ1lJS29aSXp\
   qMEVBd0lEU1FBd1JnSWhBSTRQWWJ4dHNzSFAyVkh4XC90elVvUVwvU3N5ZEwzMERRSU5\
   FdGNOOW1DVFhQQWlFQXZJYjNvK0ZPM0JUbmNMRnNhSlpSQWtkN3pPdXNuXC9cL1pLT2F\
   FS2JzVkRpVT0iXSwiYWxnIjoiRVMyNTYifQ",
       "signature":"0TB5lr-cs1jqka2vNbQm3bBYWfLJd8zdVKIoV53eo2YgSITnKKY\
   TvHMUw0wx9wdyuNVjNoAgLysNIgEvlcltBw"
     }]
   }

               Figure 39: Example Voucher-Response from MASA

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A.4.  Example Voucher, MASA issued Voucher with additional Registrar
      signature (from MASA to Pledge, via Registrar and Registrar-Agent)

   The following is an example voucher-response from MASA to Pledge via
   Registrar and Registrar-Agent, in "General JWS JSON Serialization".
   The message size of this Voucher is: 3006 bytes

   =============== NOTE: '\' line wrapping per RFC 8792 ================

   {
     "payload":"eyJpZXRmLXZvdWNoZXI6dm91Y2hlciI6eyJhc3NlcnRpb24iOiJhZ2V\
   udC1wcm94aW1pdHkiLCJzZXJpYWwtbnVtYmVyIjoiMDEyMzQ1Njc4OSIsIm5vbmNlIjo\
   iUUJiSXMxNTJzbkFvVzdSeVFMWENvZz09IiwiY3JlYXRlZC1vbiI6IjIwMjItMDktMjl\
   UMDM6Mzc6MjYuMzgyWiIsInBpbm5lZC1kb21haW4tY2VydCI6Ik1JSUJwRENDQVVtZ0F\
   3SUJBZ0lHQVcwZUx1SCtNQW9HQ0NxR1NNNDlCQU1DTURVeEV6QVJCZ05WQkFvTUNrMTV\
   RblZ6YVc1bGMzTXhEVEFMQmdOVkJBY01CRk5wZEdVeER6QU5CZ05WQkFNTUJsUmxjM1J\
   EUVRBZUZ3MHhPVEE1TVRFd01qTTNNekphRncweU9UQTVNVEV3TWpNM016SmFNRFV4RXp\
   BUkJnTlZCQW9NQ2sxNVFuVnphVzVsYzNNeERUQUxCZ05WQkFjTUJGTnBkR1V4RHpBTkJ\
   nTlZCQU1NQmxSbGMzUkRRVEJaTUJNR0J5cUdTTTQ5QWdFR0NDcUdTTTQ5QXdFSEEwSUF\
   CT2t2a1RIdThRbFQzRkhKMVVhSTcrV3NIT2IwVVMzU0FMdEc1d3VLUURqaWV4MDYvU2N\
   ZNVBKaWJ2Z0hUQitGL1FUamdlbEhHeTFZS3B3Y05NY3NTeWFqUlRCRE1CSUdBMVVkRXd\
   FQi93UUlNQVlCQWY4Q0FRRXdEZ1lEVlIwUEFRSC9CQVFEQWdJRU1CMEdBMVVkRGdRV0J\
   CVG9aSU16UWRzRC9qLytnWC83Y0JKdWNIL1htakFLQmdncWhrak9QUVFEQWdOSkFEQkd\
   BaUVBdHhRMytJTEdCUEl0U2g0YjlXWGhYTnVocVNQNkgrYi9MQy9mVllEalE2b0NJUUR\
   HMnVSQ0hsVnEzeWhCNThUWE1VYnpIOCtPbGhXVXZPbFJEM1ZFcURkY1F3PT0ifX0",
     "signatures":[{
       "protected":"eyJ4NWMiOlsiTUlJQmt6Q0NBVGlnQXdJQkFnSUdBV0ZCakNrWU1\
   Bb0dDQ3FHU000OUJBTUNNRDB4Q3pBSkJnTlZCQVlUQWtGUk1SVXdFd1lEVlFRS0RBeEt\
   hVzVuU21sdVowTnZjbkF4RnpBVkJnTlZCQU1NRGtwcGJtZEthVzVuVkdWemRFTkJNQjR\
   YRFRFNE1ERXlPVEV3TlRJME1Gb1hEVEk0TURFeU9URXdOVEkwTUZvd1R6RUxNQWtHQTF\
   VRUJoTUNRVkV4RlRBVEJnTlZCQW9NREVwcGJtZEthVzVuUTI5eWNERXBNQ2NHQTFVRUF\
   3d2dTbWx1WjBwcGJtZERiM0p3SUZadmRXTm9aWElnVTJsbmJtbHVaeUJMWlhrd1dUQVR\
   CZ2NxaGtqT1BRSUJCZ2dxaGtqT1BRTUJCd05DQUFTQzZiZUxBbWVxMVZ3NmlRclJzOFI\
   wWlcrNGIxR1d5ZG1XczJHQU1GV3diaXRmMm5JWEgzT3FIS1Z1OHMyUnZpQkdOaXZPS0d\
   CSEh0QmRpRkVaWnZiN294SXdFREFPQmdOVkhROEJBZjhFQkFNQ0I0QXdDZ1lJS29aSXp\
   qMEVBd0lEU1FBd1JnSWhBSTRQWWJ4dHNzSFAyVkh4XC90elVvUVwvU3N5ZEwzMERRSU5\
   FdGNOOW1DVFhQQWlFQXZJYjNvK0ZPM0JUbmNMRnNhSlpSQWtkN3pPdXNuXC9cL1pLT2F\
   FS2JzVkRpVT0iXSwidHlwIjoidm91Y2hlci1qd3MranNvbiIsImFsZyI6IkVTMjU2In0\
   ",
       "signature":"ShqW8uFRkuAXIzjAhB4bolMMndcY7GYq3Kbo94yvGtjCaxEX3Hp\
   6QXZUTEJ_kulQ1G7DnaU4igDPdUGtcV9Lkw"},{
       "protected":"eyJ4NWMiOlsiTUlJQjRqQ0NBWWlnQXdJQkFnSUdBWFk3MmJiWk1\
   Bb0dDQ3FHU000OUJBTUNNRFV4RXpBUkJnTlZCQW9NQ2sxNVFuVnphVzVsYzNNeERUQUx\
   CZ05WQkFjTUJGTnBkR1V4RHpBTkJnTlZCQU1NQmxSbGMzUkRRVEFlRncweU1ERXlNRGN\
   3TmpFNE1USmFGdzB6TURFeU1EY3dOakU0TVRKYU1ENHhFekFSQmdOVkJBb01DazE1UW5\
   WemFXNWxjM014RFRBTEJnTlZCQWNNQkZOcGRHVXhHREFXQmdOVkJBTU1EMFJ2YldGcGJ\
   sSmxaMmx6ZEhKaGNqQlpNQk1HQnlxR1NNNDlBZ0VHQ0NxR1NNNDlBd0VIQTBJQUJCazE\
   2S1wvaTc5b1JrSzVZYmVQZzhVU1I4XC91czFkUFVpWkhNdG9rU2RxS1c1Zm5Xc0JkK3F\

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   STDdXUmZmZVdreWdlYm9KZklsbHVyY2kyNXduaGlPVkNHamV6QjVNQjBHQTFVZEpRUVd\
   NQlFHQ0NzR0FRVUZCd01CQmdnckJnRUZCUWNESERBT0JnTlZIUThCQWY4RUJBTUNCNEF\
   3U0FZRFZSMFJCRUV3UDRJZGNtVm5hWE4wY21GeUxYUmxjM1F1YzJsbGJXVnVjeTFpZEM\
   1dVpYU0NIbkpsWjJsemRISmhjaTEwWlhOME5pNXphV1Z0Wlc1ekxXSjBMbTVsZERBS0J\
   nZ3Foa2pPUFFRREFnTklBREJGQWlCeGxkQmhacTBFdjVKTDJQcldDdHlTNmhEWVcxeUN\
   PXC9SYXVicEM3TWFJRGdJaEFMU0piZ0xuZ2hiYkFnMGRjV0ZVVm9cL2dHTjBcL2p3ekp\
   aMFNsMmg0eElYazEiXSwidHlwIjoidm91Y2hlci1qd3MranNvbiIsImFsZyI6IkVTMjU\
   2In0",
       "signature":"N4oXV48V6umsHMKkhdSSmJYFtVb6agjD32uXpIlGx6qVE7Dh0-b\
   qhRRyjnxp80IV_Fy1RAOXIIzs3Q8CnMgBgg"
     }]
   }

       Figure 40: Example Voucher-Response from MASA, with additional
                            Registrar signature

Appendix B.  HTTP-over-TLS operations between Registrar-Agent and Pledge

   The use of HTTP-over-TLS between Registrar-Agent and pledge has been
   identified as an optional mechanism.

   Provided that the key-agreement in the underlying TLS protocol
   connection can be properly authenticated, the use of TLS provides
   privacy for the voucher and enrollment operations between the pledge
   and the Registrar-Agent.  The authenticity of the onboarding and
   enrollment is not dependant upon the security of the TLS connection.

   The use of HTTP-over-TLS is not mandated by this document for a
   number of reasons:

   1.  A certificate is generally required in order to do TLS.  While
       there are other modes of authentication including PSK, various
       EAP methods and raw public key, they do no help as there is no
       previous relationship between the Registrar-Agent.

   2.  The pledge can use it's IDevID certificate to authenticate
       itself, but [RFC9525] DNS-ID methods do not apply as the pledge
       does not have a FQDN.  Instead a new mechanism is required, which
       authenticates the X520SerialNumber DN attribute which must be
       present in every IDevID.

   If the Registrar-Agent has a preconfigured list of which product-
   serial-number(s), from which manufacturers it expects to see, then it
   can attempt to match this pledge against a list of potential devices.

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   In many cases only the list of manufacturers is known ahead of time,
   so at most the Registrar-Agent can show the X520SerialNumber to the
   (human) operator who may then attempt to confirm that they are
   standing in front of a device with that product-serial-number.  The
   use of scannable QRcodes may help automate this in some cases.

   1.  The CA used to sign the IDevID will be a manufacturer private PKI
       as described in [I-D.irtf-t2trg-taxonomy-manufacturer-anchors],
       Section 4.1.  The anchors for this PKI will never be part of the
       public WebPKI anchors which are distributed with most smartphone
       operating systems.  A Registrar-Agent application will need to
       use different APIs in order to initiate an HTTPS connection
       without performing WebPKI verification.  The application will
       then have to do it's own certificate chain verification against a
       store of manufacturer trust anchors.  In the Android ecosystem
       this involved use of a customer TrustManager: many application
       developers do not create these correctly, and there is
       significant push to remove this option as it has repeatedly
       resulted in security failures.  See [androidtrustfail]

   2.  The use of the Host: (or :authority in HTTP/2) is explained in
       [RFC9110], Section 7.2.  This header is mandatory, and so a
       compliant HTTPS client is going to insert it.  But, the contents
       of this header will at best be an IP address that came from the
       discovery process.  The pledge MUST therefore ignore the Host:
       header when it processes requests, and the pledge MUST NOT do any
       kind of name-base virtual hosting using the IP address/port
       combination.  Note that there is no requirement for the pledge to
       operate it's BRSKI-PRM service on port 80 or port 443, so if
       there is no reason for name-based virtual hosting.

   3.  Note that an Extended Key Usage (EKU) for TLS WWW Server
       authentication cannot be expected in the pledge's IDevID
       certificate.  IDevID certificates are intended to be widely
       useable and EKU does not support that use.

Appendix C.  History of Changes [RFC Editor: please delete]

   Proof of Concept Code available

   From IETF draft 11 -> IETF draft 12:

   *  Updated acknowledgements to reflect early reviews

   *  Addressed Shepherd review part 2 (Pull Request #132)

   From IETF draft 10 -> IETF draft 11:

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   *  issue #79, clarified that BRSKI discovery in the context of BRSKI-
      PRM is not needed in Section 6.2.1.

   *  issue #103, removed step 6 in verification handling for the
      wrapped CA certificate provisioning as only applicable after
      enrollment Section 7.7

   *  issue #128: included notation of nomadic operation of the
      Registrar-Agent in Section 5, including proposed text from PR #131

   *  issue #130, introduced DNS service discovery name for brski_pledge
      to enable discovery by the Registrar-Agent in Section 8

   *  removed unused reference RFC 5280

   *  removed site terminology

   *  deleted duplicated text in Section 6.3

   *  clarified registrar discovery and relation to BRSKI-Discovery in
      Section 6.2.1

   *  clarified discovery of pledges by the Registrar-Agent in
      Section 6.2.2, deleted reference to GRASP as handled in BRSKI-
      Discovery

   *  addressed comments from SECDIR early review

   From IETF draft 09 -> IETF draft 10:

   *  issue #79, clarified discovery in the context of BRSKI-PRM and
      included information about future discovery enhancements in a
      separate draft in Section 6.2.1.

   *  issue #93, included information about conflict resolution in mDNS
      and GRASP in Section 6.2.2

   *  issue #103, included verification handling for the wrapped CA
      certificate provisioning in Section 7.7

   *  issue #106, included additional text to elaborate more the
      registrar status handling in Section 7.9 and Section 7.10

   *  issue #116, enhanced DoS description in Section 10.1

   *  issue #120, included statement regarding pledge host header
      processing in Section 6.3

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   *  issue #122, availability of product-serial-number information on
      registrar agent clarified in Section 7.1

   *  issue #123, Clarified usage of alternative voucher formats in
      Section 7.3.2

   *  issue #124, determination of pinned domain certificate done as in
      RFC 8995 included in Section 7.3.3

   *  issue #125, remove strength comparison of voucher assertions in
      Section 5.4 and Section 7

   *  issue #130, aligned the usage of site and domain throughout the
      document

   *  changed naming of registrar certificate from LDevID(RegAgt) to EE
      (RegAgt) certificate throughout the document

   *  change x5b to x5bag according to [RFC9360]

   *  updated JSON examples -> "signature": BASE64URL(JWS Signature)

   From IETF draft 08 -> IETF draft 09:

   *  issue #80, enhanced Section 6.2.2 with clarification on the
      product-serial-number and the inclusion of GRASP

   *  issue #81, enhanced introduction with motivation for
      agent_signed_data

   *  issue #82, included optional TLS protection of the communication
      link between Registrar-Agent and pledge in the introduction
      Section 4, and Section 7.1

   *  issue #83, enhanced Section 7.2 and Section 7.3 with note to re-
      enrollment

   *  issue #87, clarified available information at the Registrar-Agent
      in Section 7.1

   *  issue #88, clarified, that the PVR in Section 7.1 and PER in
      Section 7.2 may contain the certificate chain.  If not contained
      it MUST be available at the registrar.

   *  issue #91, clarified that a separate HTTP connection may also be
      used to provide the PER in Section 7.4

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   *  resolved remaining editorial issues discovered after WGLC
      (responded to on the mailing list in Reply 1 and Reply 2)
      resulting in more consistent descriptions

   *  issue #92: kept separate endpoint for wrapped CSR on registrar
      Section 7.5

   *  issue #94: clarified terminology (possess vs. obtained)

   *  issue #95: clarified optional IDevID CA certificates on Registrar-
      Agent

   *  issue #96: updated exchangesfig_uc2_3 to correct to just one CA
      certificate provisioning

   *  issue #97: deleted format explanation in exchanges_uc2_3 as it may
      be misleading

   *  issue #99: motivated verification of second signature on voucher
      in Section 7.6

   *  issue #100: included negative example in Figure 25

   *  issue #101: included handling if Section 7.6 voucher telemetry
      information has not been received by the Registrar-Agent

   *  issue #102: relaxed requirements for CA certs provisioning in
      Section 7.7

   *  issue #105: included negative example in Figure 29

   *  issue #107: included example for certificate revocation in
      Section 7.10

   *  issue #108: renamed heading to Pledge-Status Request of
      Section 7.11

   *  issue #111: included pledge-status response processing for
      authenticated requests in Section 7.11

   *  issue #112: added "Example key word in pledge-status response in
      Figure 36

   *  issue #113: enhanced description of status reply for "factory-
      default" in Section 7.11

   *  issue #114: Consideration of optional TLS usage in Privacy
      Considerations

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   *  issue #115: Consideration of optional TLS usage in Privacy
      Considerations to protect potentially privacy related information
      in the bootstrapping like status information, etc.

   *  issue #116: Enhanced DoS description and mitigation options in
      security consideration section

   *  updated references

   From IETF draft 07 -> IETF draft 08:

   *  resolved editorial issues discovered after WGLC (still open issues
      remaining)

   *  resolved first comments from the Shepherd review as discussed in
      PR #85 on the ANIMA github

   From IETF draft 06 -> IETF draft 07:

   *  WGLC resulted in a removal of the voucher enhancements completely
      from this document to RFC 8366bis, containing all enhancements and
      augmentations of the voucher, including the voucher-request as
      well as the tree diagrams

   *  smaller editorial corrections

   From IETF draft 05 -> IETF draft 06:

   *  Update of list of reviewers

   *  Issue #67, shortened the pledge endpoints to prepare for
      constraint deployments

   *  Included table for new endpoints on the registrar in the overview
      of the Registrar-Agent

   *  addressed review comments from SECDIR early review (terminology
      clarifications, editorial improvements)

   *  addressed review comments from IOTDIR early review (terminology
      clarifications, editorial improvements)

   From IETF draft 04 -> IETF draft 05:

   *  Restructured document to have a distinct section for the object
      flow and handling and shortened introduction, issue #72

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   *  Added security considerations for using mDNS without a specific
      product-serial-number, issue #75

   *  Clarified pledge-status responses are cumulative, issue #73

   *  Removed agent-sign-cert from trigger data to save bandwidth and
      remove complexity through options, issue #70

   *  Changed terminology for LDevID(Reg) certificate to registrar
      LDevID certificate, as it does not need to be an LDevID, issue #66

   *  Added new protected header parameter (created-on) in PER to
      support freshness validation, issue #63

   *  Removed reference to CAB Forum as not needed for BRSKI-PRM
      specifically, issue #65

   *  Enhanced error codes in section 5.5.1, issue #39, #64

   *  Enhanced security considerations and privacy considerations, issue
      #59

   *  Issue #50 addressed by referring to the utilized enrollment
      protocol

   *  Issue #47 MASA verification of LDevID(RegAgt) to the same
      registrar LDevID certificate domain CA

   *  Reworked terminology of "enrollment object", "certification
      object", "enrollment request object", etc., issue #27

   *  Reworked all message representations to align with encoding

   *  Added explanation of MASA requiring domain CA cert in section
      5.5.1 and section 5.5.2, issue #36

   *  Defined new endpoint for pledge bootstrapping status inquiry,
      issue #35 in section Section 7.11, IANA considerations and section
      Section 6.3

   *  Included examples for several objects in section Appendix A
      including message example sizes, issue #33

   *  PoP for private key to registrar certificate included as
      mandatory, issues #32 and #49

   *  Issue #31, clarified that combined pledge may act as client/server
      for further (re)enrollment

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   *  Issue #42, clarified that Registrar needs to verify the status
      responses with and ensure that they match the audit log response
      from the MASA, otherwise it needs drop the pledge and revoke the
      certificate

   *  Issue #43, clarified that the pledge shall use the create time
      from the trigger message if the time has not been synchronized,
      yet.

   *  Several editorial changes and enhancements to increasing
      readability.

   From IETF draft 03 -> IETF draft 04:

   *  In deep Review by Esko Dijk lead to issues #22-#61, which are bein
      stepwise integrated

   *  Simplified YANG definition by augmenting the voucher-request from
      RFC 8995 instead of redefining it.

   *  Added explanation for terminology "endpoint" used in this
      document, issue #16

   *  Added clarification that Registrar-Agent may collect PVR or PER or
      both in one run, issue #17

   *  Added a statement that nonceless voucher may be accepted, issue
      #18

   *  Simplified structure in section Section 3.1, issue #19

   *  Removed join proxy in Figure 1 and added explanatory text, issue
      #20

   *  Added description of pledge-CAcerts endpoint plus further handling
      of providing a wrapped CA certs response to the pledge in section
      Section 7.7; also added new required registrar endpoint (section
      Section 7.3 and IANA considerations) for the registrar to provide
      a wrapped CA certs response, issue #21

   *  utilized defined abbreviations in the document consistently, issue
      #22

   *  Reworked text on discovery according to issue #23 to clarify scope
      and handling

   *  Added several clarifications based on review comments

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   From IETF draft 02 -> IETF draft 03:

   *  Updated examples to state "base64encodedvalue==" for x5c
      occurrences

   *  Include link to SVG graphic as general overview

   *  Restructuring of section 5 to flatten hierarchy

   *  Enhanced requirements and motivation in Section 4

   *  Several editorial improvements based on review comments

   From IETF draft 01 -> IETF draft 02:

   *  Issue #15 included additional signature on voucher from registrar
      in section Section 7.3 and section Section 5.4 The verification of
      multiple signatures is described in section Section 7.6

   *  Included representation for General JWS JSON Serialization for
      examples

   *  Included error responses from pledge if it is not able to create a
      Pledge-Voucher-Request or an enrollment request in section
      Section 7.1

   *  Removed open issue regarding handling of multiple CSRs and Enroll-
      Responses during the bootstrapping as the initial target it the
      provisioning of a generic LDevID certificate.  The defined
      endpoint on the pledge may also be used for management of further
      certificates.

   From IETF draft 00 -> IETF draft 01:

   *  Issue #15 lead to the inclusion of an option for an additional
      signature of the registrar on the voucher received from the MASA
      before forwarding to the Registrar-Agent to support verification
      of POP of the registrars private key in section Section 7.3 and
      exchanges_uc2_3.

   *  Based on issue #11, a new endpoint was defined for the registrar
      to enable delivery of the wrapped enrollment request from the
      pledge (in contrast to plain PKCS#10 in simple enroll).

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   *  Decision on issue #8 to not provide an additional signature on the
      enrollment-response object by the registrar.  As the Enroll-
      Response will only contain the generic LDevID certificate.  This
      credential builds the base for further configuration outside the
      initial enrollment.

   *  Decision on issue #7 to not support multiple CSRs during the
      bootstrapping, as based on the generic LDevID certificate the
      pledge may enroll for further certificates.

   *  Closed open issue #5 regarding verification of ietf-ztp-types
      usage as verified via a proof-of-concept in section Section 7.1.

   *  Housekeeping: Removed already addressed open issues stated in the
      draft directly.

   *  Reworked text in from introduction to section pledge-responder-
      mode

   *  Fixed "serial-number" encoding in PVR/RVR

   *  Added prior-signed-voucher-request in the parameter description of
      the registrar-voucher-request in Section 7.3.

   *  Note added in Section 7.3 if sub-CAs are used, that the
      corresponding information is to be provided to the MASA.

   *  Inclusion of limitation section (pledge sleeps and needs to be
      waked up.  Pledge is awake but Registrar-Agent is not available)
      (Issue #10).

   *  Assertion-type aligned with voucher in RFC8366bis, deleted related
      open issues.  (Issue #4)

   *  Included table for endpoints in Section 6.3 for better
      readability.

   *  Included registrar authorization check for Registrar-Agent during
      TLS handshake in section Section 7.3.  Also enhanced figure
      Figure 4 with the authorization step on TLS level.

   *  Enhanced description of registrar authorization check for
      Registrar-Agent based on the agent-signed-data in section
      Section 7.3.  Also enhanced figure Figure 4 with the authorization
      step on Pledge-Voucher-Request level.

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   *  Changed agent-signed-cert to an array to allow for providing
      further certificate information like the issuing CA cert for the
      LDevID(RegAgt) certificate in case the registrar and the
      Registrar-Agent have different issuing CAs in Figure 4 (issue
      #12).  This also required changes in the YANG module in
      [I-D.ietf-anima-rfc8366bis]

   *  Addressed YANG warning (issue #1)

   *  Inclusion of examples for a trigger to create a Pledge-Voucher-
      Request and an Pledge Enroll-Request.

   From IETF draft-ietf-anima-brski-async-enroll-03 -> IETF anima-brski-
   prm-00:

   *  Moved UC2 related parts defining the Pledge in Responder Mode from
      draft-ietf-anima-brski-async-enroll-03 to this document This
      required changes and adaptations in several sections to remove the
      description and references to UC1.

   *  Addressed feedback for voucher-request enhancements from YANG
      doctor early review, meanwhile moved to
      [I-D.ietf-anima-rfc8366bis] as well as in the security
      considerations (formerly named ietf-async-voucher-request).

   *  Renamed ietf-async-voucher-request to IETF-voucher-request-prm to
      to allow better listing of voucher related extensions; aligned
      with constraint voucher (#20)

   *  Utilized ietf-voucher-request-async instead of ietf-voucher-
      request in voucher exchanges to utilize the enhanced voucher-
      request.

   *  Included changes from draft-ietf-netconf-sztp-csr-06 regarding the
      YANG definition of csr-types into the enrollment request exchange.

   From IETF draft 02 -> IETF draft 03:

   *  Housekeeping, deleted open issue regarding YANG voucher-request in
      Section 7.1 as voucher-request was enhanced with additional leaf.

   *  Included open issues in YANG model in Section 5 regarding
      assertion value agent-proximity and csr encapsulation using SZTP
      sub module).

   From IETF draft 01 -> IETF draft 02:

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   *  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 Section 7.

   *  Terminology change: issue #2 pledge-agent -> Registrar-Agent to
      better underline Registrar-Agent relation.

   *  Terminology change: issue #3 PULL/PUSH -> pledge-initiator-mode
      and pledge-responder-mode to better address the pledge operation.

   *  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).

   *  Details on trust relationship between Registrar-Agent and
      registrar (issue #4, #5, #9) included in Section 5.

   *  Recommendation regarding short-lived certificates for Registrar-
      Agent authentication towards registrar (issue #7) in the security
      considerations.

   *  Introduction of reference to Registrar-Agent signing certificate
      using SKID in Registrar-Agent signed data (issue #37).

   *  Enhanced objects in exchanges between pledge and Registrar-Agent
      to allow the registrar to verify agent-proximity to the pledge
      (issue #1) in Section 7.

   *  Details on trust relationship between Registrar-Agent and pledge
      (issue #5) included in Section 5.

   *  Split of use case 2 call flow into sub sections in Section 7.

   From IETF draft 00 -> IETF draft 01:

   *  Update of scope in Section 3.1 to include in which the pledge acts
      as a server.  This is one main motivation for use case 2.

   *  Rework of use case 2 in Section 5 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.

   *  First description of exchanged object types (needs more work)

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   *  Clarification in discovery options for enrollment endpoints at the
      domain registrar based on well-known endpoints 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.

   *  Updated references.

   *  Included Thomas Werner as additional author for the document.

   From individual version 03 -> IETF draft 00:

   *  Inclusion of discovery options of enrollment endpoints at the
      domain registrar based on well-known endpoints in new section 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.

   *  Missing details provided for the description and call flow in
      pledge-agent use case Section 5, e.g. to accommodate distribution
      of CA certificates.

   *  Updated CMP example in to use lightweight CMP instead of CMP, as
      the draft already provides the necessary /.well-known endpoints.

   *  Requirements discussion moved to separate section in Section 4.
      Shortened description of proof of identity binding and mapping to
      existing protocols.

   *  Removal of copied call flows for voucher exchange and registrar
      discovery flow from [RFC8995] in UC1 to avoid doubling or text or
      inconsistencies.

   *  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.

   From individual version 02 -> 03:

   *  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.

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   *  Simplification of the architecture approach for the initial use
      case having an offsite PKI.

   *  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-PRM call flow.

   From individual version 01 -> 02:

   *  Update of introduction text to clearly relate to the usage of
      IDevID and LDevID.

   *  Update of description of architecture elements and changes to
      BRSKI in Section 5.

   *  Enhanced consideration of existing enrollment protocols in the
      context of mapping the requirements to existing solutions in
      Section 4.

   From individual version 00 -> 01:

   *  Update of examples, specifically for building automation as well
      as two new application use cases in Section 3.1.

   *  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 Section 5.

   *  Enhancement of description of architecture elements and changes to
      BRSKI in Section 5.

   *  Consideration of existing enrollment protocols in the context of
      mapping the requirements to existing solutions in Section 4.

   *  New section starting with the mapping to existing enrollment
      protocols by collecting boundary conditions.

Contributors

   Esko Dijk
   IoTconsultancy.nl
   Email: esko.dijk@iotconsultancy.nl

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   Toerless Eckert
   Futurewei
   Email: tte@cs.fau.de

   Matthias Kovatsch
   Siemens Schweiz AG
   Email: ietf@kovatsch.net

Authors' Addresses

   Steffen Fries
   Siemens AG
   Otto-Hahn-Ring 6
   81739 Munich
   Germany
   Email: steffen.fries@siemens.com
   URI:   https://www.siemens.com/

   Thomas Werner
   Siemens AG
   Otto-Hahn-Ring 6
   81739 Munich
   Germany
   Email: thomas-werner@siemens.com
   URI:   https://www.siemens.com/

   Eliot Lear
   Cisco Systems
   Richtistrasse 7
   CH-8304 Wallisellen
   Switzerland
   Phone: +41 44 878 9200
   Email: lear@cisco.com

   Michael C. Richardson
   Sandelman Software Works
   Email: mcr+ietf@sandelman.ca
   URI:   http://www.sandelman.ca/

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