Bootstrapping Remote Secure Key Infrastructure (BRSKI) Cloud Registrar
draft-ietf-anima-brski-cloud-19

Network Working Group                                           O. Friel
Internet-Draft                                                     Cisco
Updates: 8995 (if approved)                               R. Shekh-Yusef
Intended status: Standards Track                                   Ciena
Expires: 13 March 2026                                     M. Richardson
                                                Sandelman Software Works
                                                        9 September 2025

 Bootstrapping Remote Secure Key Infrastructure (BRSKI) Cloud Registrar
                    draft-ietf-anima-brski-cloud-19

Abstract

   Bootstrapping Remote Secure Key Infrastructures (BRSKI) defines how
   to onboard a device securely into an operator-maintained
   infrastructure.  It assumes that there is local network
   infrastructure for the device to discover.  On networks without that,
   there is nothing present to help onboard the device.

   This document extends BRSKI and defines behavior for bootstrapping
   devices for deployments where no local infrastructure is available,
   such as in a home or remote office.  This document defines how the
   device can use a well-defined "call-home" mechanism to find the
   operator-maintained infrastructure.

   This document defines how to contact a well-known Cloud Registrar,
   and two ways in which the device may be redirected towards the
   operator-maintained infrastructure.  The Cloud Registrar enables
   discovery of the operator-maintained infrastructure, and may enable
   establishment of trust with operator-maintained infrastructure that
   does not support BRSKI mechanisms.

   This document updates RFC 8995 (BRSKI).

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-cloud/.

   Discussion of this document takes place on the anima Working Group
   mailing list (mailto:anima@ietf.org), which is archived at
   https://mailarchive.ietf.org/arch/browse/anima/.  Subscribe at
   https://www.ietf.org/mailman/listinfo/anima/.

Friel, et al.             Expires 13 March 2026                 [Page 1]
Internet-Draft                 BRSKI-CLOUD                September 2025

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

Status of This Memo

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

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

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

   This Internet-Draft will expire on 13 March 2026.

Copyright Notice

   Copyright (c) 2025 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
     1.2.  Use Cases . . . . . . . . . . . . . . . . . . . . . . . .   6
       1.2.1.  Bootstrap via Cloud Registrar and Owner Registrar . .   7
       1.2.2.  Bootstrap via Cloud Registrar and Owner EST
               Service . . . . . . . . . . . . . . . . . . . . . . .   8
   2.  Architecture  . . . . . . . . . . . . . . . . . . . . . . . .   8
     2.1.  Network Connectivity  . . . . . . . . . . . . . . . . . .  11
     2.2.  Pledge Certificate Identity Considerations  . . . . . . .  11
     2.3.  YANG extension for Voucher based redirect . . . . . . . .  12
   3.  Protocol Operation  . . . . . . . . . . . . . . . . . . . . .  12
     3.1.  Pledge Sends Voucher Request to Cloud Registrar . . . . .  13

Friel, et al.             Expires 13 March 2026                 [Page 2]
Internet-Draft                 BRSKI-CLOUD                September 2025

       3.1.1.  Cloud Registrar Discovery . . . . . . . . . . . . . .  13
       3.1.2.  Pledge - Cloud Registrar TLS Establishment Details  .  13
       3.1.3.  Pledge Sends Voucher Request Message  . . . . . . . .  14
     3.2.  Cloud Registrar Processes Voucher Request Message . . . .  14
       3.2.1.  Pledge Ownership Look Up  . . . . . . . . . . . . . .  15
       3.2.2.  Bootstrap via Cloud Registrar and Owner Registrar . .  15
       3.2.3.  Bootstrap via Cloud Registrar and Owner EST
               Service . . . . . . . . . . . . . . . . . . . . . . .  15
     3.3.  Pledge Handles Cloud Registrar Response . . . . . . . . .  16
       3.3.1.  Bootstrap via Cloud Registrar and Owner Registrar . .  16
       3.3.2.  Bootstrap via Cloud Registrar and Owner EST
               Service . . . . . . . . . . . . . . . . . . . . . . .  18
   4.  Protocol Details  . . . . . . . . . . . . . . . . . . . . . .  18
     4.1.  Bootstrap via Cloud Registrar and Owner Registrar . . . .  18
     4.2.  Bootstrap via Cloud Registrar and Owner EST Service . . .  20
   5.  Lifecycle Considerations  . . . . . . . . . . . . . . . . . .  23
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  24
   7.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  24
   8.  Implementation Considerations . . . . . . . . . . . . . . . .  24
     8.1.  Captive Portals . . . . . . . . . . . . . . . . . . . . .  24
     8.2.  Multiple HTTP Redirects . . . . . . . . . . . . . . . . .  25
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  26
     9.1.  Security Updates for the Pledge . . . . . . . . . . . . .  26
     9.2.  Trust Anchors for Cloud Registrar . . . . . . . . . . . .  27
     9.3.  Considerations for HTTP Redirect  . . . . . . . . . . . .  27
     9.4.  Considerations for Voucher est-domain . . . . . . . . . .  28
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  29
   References  . . . . . . . . . . . . . . . . . . . . . . . . . . .  29
     Normative References  . . . . . . . . . . . . . . . . . . . . .  29
     Informative References  . . . . . . . . . . . . . . . . . . . .  30
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  32

1.  Introduction

   Bootstrapping Remote Secure Key Infrastructures [BRSKI] (BRSKI)
   specifies automated and secure provisioning of nodes (which are
   called Pledges) with cryptographic keying material (trust anchors and
   certificates) to enable authenticated and confidential communication
   with other similarly enrolled nodes.  This bootstrapping process is
   also called enrollment.

   In BRSKI, the Pledge performs enrollment by communicating with a
   BRSKI Registrar belonging to the owner of the Pledge.  The Pledge
   does not know who its owner will be when manufactured.  Instead, in
   BRSKI it is assumed that the network to which the Pledge connects
   belongs to the owner of the Pledge and therefore network-supported
   discovery mechanisms can resolve generic, non-owner specific names to
   the owner's Registrar.

Friel, et al.             Expires 13 March 2026                 [Page 3]
Internet-Draft                 BRSKI-CLOUD                September 2025

   To support enrollment of Pledges without such an owner based access
   network, the mechanisms of BRSKI Cloud are required, which assume
   that Pledge and Registrar simply connect to the Internet.

   This entire work is an update to [BRSKI].

   Specifically, it extends [BRSKI], Section 2.7 to describe describes
   how a Pledge may contact a well-known URI of a Cloud Registrar if a
   local Registrar cannot be discovered or if the Pledge is deployed in
   a network that does not include a local Registrar.

   This kind of non-network onboarding is sometimes called "Application
   Onboarding", as the purpose is typically to deploy a credential that
   will be used by the device in its intended use.  For instance, a SIP
   [RFC3261] phone might have a client certificate to be used with a SIP
   proxy.

   This document updates [BRSKI] by clarifying operations that are left
   out of scope in [BRSKI].  Two modes of operation are specified in
   this document.  The Cloud Registrar can choose between redirecting
   the Pledge to the owner's Registrar, or it may issue a voucher to the
   Pledge that includes the domain of the owner's Enrollment over Secure
   Transport [RFC7030] (EST) server.

1.1.  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 uses the terms Domain, Pledge, Registrar, Manufacturer
   Authorized Signing Authority (MASA), and Voucher from [BRSKI] and
   [RFC8366bis].

   Cloud Registrar:  The default Registrar that is deployed at a URI
      that is well known to the Pledge.

   Cloud VAR Registrar:  The non-default Registrar that is operated by a
      value added reseller (VAR).

   CSR:  Certificate Signing Request

   DHCP  refers to DHCPv4 [RFC2131] or DHCPv6 [RFC8914].

   EST:  Enrollment over Secure Transport [RFC7030].

Friel, et al.             Expires 13 March 2026                 [Page 4]
Internet-Draft                 BRSKI-CLOUD                September 2025

   IDevID:  An initial device identity certificate as described in
      [IDEVID]

   LDevID:  A local device identity certificate as described in [IDEVID]

   Local Domain:  The domain where the Pledge is physically located and
      bootstrapping from.  This may be different from the Pledge owner's
      domain.

   Manufacturer:  The term manufacturer is used throughout this document
      as the entity that created the Pledge.  This is typically the
      original equipment manufacturer (OEM), but in more complex
      situations, it could be a value added retailer (VAR), or possibly
      even a systems integrator.  Refer to [BRSKI] for more detailed
      descriptions of manufacturer, VAR and OEM.

   OEM:  Original Equipment Manufacturer.  The company that manufactured
      the device.

   Owner:  The owner is the organization that has purchased the new
      device (the pledge).  The device might be deployed in a network
      that the owner does not control.

   Owner Delegate:  The owner delegate is an entity distinct from the
      Owner that has been contracted to operate/manage the devices in
      question.  For instance, an IT maintenance and support-desk
      company.

   Owner Domain:  The domain that the Pledge needs to discover and
      bootstrap with.

   Owner Registrar:  The Registrar that is operated by the Owner, or the
      Owner's delegate.  There may not be an Owner Registrar in all
      deployment scenarios.

   Pledge operator:  The person or organization that removes the device
      from the shipping box and connects power and network to it.

   Provisional TLS:  A mechanism defined in [BRSKI], Section 5.1 whereby
      a Pledge establishes a provisional TLS connection with a Registrar
      before the Pledge is provisioned with a trust anchor that can be
      used for verifying the Registrar identity.

   SIP:  Session Initiation Protocol defined in [RFC3261]

   VAR:  Value Added Reseller.  A VAR will often collect products from

Friel, et al.             Expires 13 March 2026                 [Page 5]
Internet-Draft                 BRSKI-CLOUD                September 2025

      many OEMs, creating a complete solution, and then sells that
      composite solution to end customers.  A VAR will often need to
      provision products to operate in a specific manner.  For instance,
      a VoIP phone might have SIP functionality as well as MGCP
      functionality, but in a particular deployment, only one will be
      used.

1.2.  Use Cases

   This document specifies procedures for two high-level use cases.

   *  Bootstrap via Cloud Registrar and Owner Registrar: The operator-
      maintained infrastructure supports BRSKI and has a BRSKI Registrar
      deployed.  More details are provided in Section 1.2.1.

   *  Bootstrap via Cloud Registrar and Owner EST Service: The operator-
      maintained infrastructure does not support BRSKI, does not have a
      BRSKI Registrar deployed, but does have an Enrollment over Secure
      Transport (EST) [RFC7030] service deployed.  More detailed are
      provided in Section 1.2.2.

   There are existing DHCP options that network operators use to
   configure devices such as a VoIP phone.  This includes DHCP options
   66 [RFC2132], 150 (TFTP/HTTP server names) [RFC5859], and 120 (SIP
   Server) [RFC3361], which inform a VoIP phone about how to do
   application onboarding.  A network with an operator that is able to
   provision these options would also be able to use BRSKI without
   changes.  Such a network has no need for the mechanisms described in
   this document!

   Where the need for the mechanism is needed is to allow the use of
   BRSKI in many small sites, such as teleworkers working from home,
   with minimum expectations against their network infrastructure.  In
   particular, the home office user is not qualified or authorized to
   change DHCP options for the local network.

   The procedures defined in this document support situations where a
   Manufacturer sells a number of devices (in bulk) to a Value Added
   Reseller (VAR).  The Manufacturer knows which devices have been sold
   to which VAR, but not who the ultimate owner will be.  The VAR then
   sells devices to other entities, such as enterprises, and records
   this in the VARs Cloud Registrar.  Specifically, the VAR will record
   that a specific device has been sold to an enterprise, and will know
   that when this device bootstraps, it should be redirected to the
   enterprise's Owner Registrar or Owner EST Service.

Friel, et al.             Expires 13 March 2026                 [Page 6]
Internet-Draft                 BRSKI-CLOUD                September 2025

   One example is a VoIP phone Manufacturer provides telephones to a
   local system integration company (a VAR).  The VAR records this sale
   in its Cloud VAR Registrar system.  The VAR has sold a VoIP system to
   an enterprise (e.g., a SIP PBX).  When a new employee needs a phone
   at their home office, the VAR ships that unit across town to the
   employee.  When the employee plugs in the device and turns it on, the
   device will be provisioned with a LDevID [IDEVID] and configuration
   that connections the phone with the Enterprises' VoIP PBX.  The home
   employee's network has no special provisions.

   The procedures defined in this document also support a chain of VARs
   through chained HTTP redirects.  This also supports a situation where
   in effect, a large enterprise might also stock devices in a central
   location.

   The Pledge is not expected to know whether the operator-maintained
   infrastructure has a BRSKI Registrar deployed or not.  The Pledge
   determines this based upon the response to its Voucher Request
   message that it receives from the Cloud Registrar.  The Cloud
   Registrar is expected to determine whether the operator-maintained
   infrastructure has a BRSKI Registrar deployed based upon the identity
   presented by the Pledge.

   A Cloud Registrar will receive BRSKI communications from all devices
   configured with its URI.  This could be, for example, all devices of
   a particular product line from a particular Manufacturer.  When this
   is a significantly large number, a Cloud Registrar may need to be
   scaled with the usual web-service scaling mechanisms.

1.2.1.  Bootstrap via Cloud Registrar and Owner Registrar

   A Pledge is bootstrapping from a location with no Local Domain
   Registrar (for example, the small site or teleworker use case with no
   local infrastructure to provide for automated discovery), and needs
   to discover its Owner Registrar.  The Cloud Registrar is used by the
   Pledge to discover the Owner Registrar.  The Cloud Registrar
   redirects the Pledge to the Owner Registrar, and the Pledge completes
   bootstrap against the Owner Registrar.

   This mechanism is useful to help an employee who is deploying a
   Pledge in a home or small branch office, where the Pledge belongs to
   the employer.  As there is no Local Domain Registrar in the
   employee's local network, the Pledge needs to discover and bootstrap
   with the employer's Registrar which is deployed within the employer's
   network, and the Pledge needs the keying material to trust the
   Registrar.  As a very specific example, an employee is deploying an
   IP phone in a home office and the phone needs to register to an IP
   PBX deployed in their employer's office.

Friel, et al.             Expires 13 March 2026                 [Page 7]
Internet-Draft                 BRSKI-CLOUD                September 2025

   Protocol details for this use case are provided in Section 4.1.

1.2.2.  Bootstrap via Cloud Registrar and Owner EST Service

   A Pledge is bootstrapping where the owner organization does not yet
   have an Owner Registrar deployed, but does have an EST service
   deployed.  The Cloud Registrar issues a voucher, and the Pledge
   completes trust bootstrap using the Cloud Registrar.  The voucher
   issued by the Cloud Registrar includes domain information for the
   owner's EST service that the Pledge should use for certificate
   enrollment.

   For example, an organization has an EST service deployed, but does
   not yet have a BRSKI-capable Registrar service deployed.  The Pledge
   is deployed in the organization's domain, but does not discover a
   Local Domain Registrar or Owner Registrar.  The Pledge uses the Cloud
   Registrar to bootstrap, and the Cloud Registrar provides a voucher
   that includes instructions on finding the organization's EST service.

   This option can be used to introduce the benefits of BRSKI for an
   initial period when BRSKI is not available in existing EST Servers.
   Additionally, it can also be used long-term as a security-equivalent
   solution in which BRSKI and EST Server are set up in a modular
   fashion.

   The use of an EST Server instead of a BRSKI Registrar may mean that
   not all the EST options required by [BRSKI] may be available and
   hence this option may not support all BRSKI deployment cases.  For
   example, certificates to enroll into an ACP [RFC8994] needs to
   include an AcpNodeName.  See [RFC8994], Section 6.2.2, which non-
   BRSKI-capable EST Servers may not support.

   Protocol details for this use case are provided in Section 4.2.

2.  Architecture

   The high-level architectures for the two high-level use cases are
   illustrated in Figure 1 and Figure 2.

   In both use cases, the Pledge connects to the Cloud Registrar during
   bootstrap.

   For the first use case, as described in Section 1.2.1, the Cloud
   Registrar redirects the Pledge to an Owner Registrar in order to
   complete bootstrap with the Owner Registrar.  When bootstrapping
   against an Owner Registrar, the Owner Registrar will interact with a
   CA to assist in issuing certificates to the Pledge.  This is
   illustrated in Figure 1.

Friel, et al.             Expires 13 March 2026                 [Page 8]
Internet-Draft                 BRSKI-CLOUD                September 2025

   |<--------------OWNER--------------------------->|   MANUFACTURER

    On-site                Cloud
   +--------+                                          +-----------+
   | Pledge |------------------------------------------| Cloud     |
   +--------+          307 redirect                    | Registrar |
       |                                               +-----------+
       |
       |                 +-----------+                 +-----------+
       +---------------->|  Owner    |-----------------|   MASA    |
           VR-sign(N)    | Registrar |sign(VR-sign(N)) +-----------+
                         +-----------+
                               |    +-----------+
                               +----|    CA     |
                                    +-----------+

      Figure 1: Architecture: Bootstrap via Cloud Registrar and Owner
                                 Registrar

   As depicted in Figure 1 and Figure 2, there are a number of parties
   involved in the process.  The Manufacturer, or Original Equipment
   Manufacturer (OEM) builds the device, but also is expected to run the
   MASA, or arrange for it to exist.  The interaction between the Cloud
   Registrar and the MASA is described by [BRSKI], Section 5.4.

   In Figure 1 the two signatures that the Pledge and the Owner
   Registrar place on the Voucher Request (VR) are shown as VR-sign(N)
   and sign(VR-sign(N)) This is as described in [BRSKI], Section 3.
   There are also signatures from Pledge to Cloud Registrar and to MASA
   in Figure 2, but they are omitted as they would make the diagram too
   busy.

   For the second use case, as described Section 1.2.2, the Cloud
   Registrar issues a voucher itself without redirecting the Pledge to
   an Owner Registrar.  The Cloud Registrar will inform the Pledge what
   domain to use for accessing EST services in the voucher response.  In
   this model, the Pledge interacts directly with the EST service to
   enroll.  The EST service will interact with a CA to assist in issuing
   a certificate to the Pledge.  This is illustrated in Figure 2.

Friel, et al.             Expires 13 March 2026                 [Page 9]
Internet-Draft                 BRSKI-CLOUD                September 2025

   |<--------------OWNER--------------------------->|   MANUFACTURER

    On-site                Cloud
   +--------+                                          +-----------+
   | Pledge |------------------------------------------| Cloud     |
   +--------+        referral via est-domain           | Registrar |
       |                                               +--+--------+
       |                                                  | BRSKI-MASA
       |                                               +--+--------+
       |                                               |   MASA    |
       |                                               +-----------+
       |                 +-----------+
       +-----------------| EST       |
                         | Server    |
                         +-----------+
                               |    +-----------+
                               +--->|    CA     |
                                    +-----------+

      Figure 2: Architecture: Bootstrap via Cloud Registrar and Owner
                                EST Service

   It is also possible for the Cloud Registrar to redirect the Pledge to
   another Cloud Registrar operated by a VAR, with that VAR's Cloud
   Registrar then redirecting the Pledge to the Owner Registrar.  This
   scenario is discussed further in Section 8.2 and 9.3.

   The mechanisms and protocols by which the Registrar or EST service
   interacts with the CA are transparent to the Pledge and are outside
   the scope of this document.

   The architectures show the Cloud Registrar and MASA as being
   logically separate entities.  The two functions could of course be
   integrated into a single entity.

   In the two use cases, there are different mechanisms for a Cloud
   Registrar to handle voucher requests.

   It can redirect the request to the Owner Registrar for handling, or
   it can return a voucher that includes an "est-domain" attribute that
   points to the Owner EST Service.  When returning a voucher,
   additional bootstrapping information can be embedded in the voucher
   using the additional-configuration-url attribute.  The contents of
   this additional configuration are device and Manufacturer specific.
   Both mechanisms are described in detail later in this document.

Friel, et al.             Expires 13 March 2026                [Page 10]
Internet-Draft                 BRSKI-CLOUD                September 2025

   The network operator or enterprise is the intended owner of the new
   device: the Pledge.  This could be the enterprise itself, or in many
   cases there is some outsourced IT department that might be involved.
   They are the operator of the Registrar or EST Server.  They may also
   operate the CA, or they may contract those services from another
   entity.

   There is a potential additional party involved who may operate the
   Cloud Registrar: the value added reseller (VAR).  The VAR works with
   the OEM to ship products with the right configuration to the owner.
   For example, SIP telephones or other conferencing systems may be
   installed by this VAR, often shipped directly from a warehouse to the
   customer's remote office location.  The VAR and manufacturer are
   aware of which devices have been shipped to the VAR through sales
   channel integrations, and so the manufacturer's Cloud Registrar is
   able to redirect the Pledge through a chain of Cloud Registrars, as
   explained in Section 3.3.1.

2.1.  Network Connectivity

   The assumption is that the Pledge already has network connectivity
   prior to connecting to the Cloud Registrar.  The Pledge must have an
   IP address that is able to reach a recursive DNS server, and be able
   to send requests to the Cloud Registrar.  There are many ways to
   accomplish this, from using routable IPv4 or IPv6 addresses, to use
   of NAT44, to using HTTP or SOCKS proxies.

   The Pledge operator has already connected the Pledge to the network,
   and the mechanism by which this has happened is out of scope of this
   document.

   For many telephony applications, this is typically going to be a
   wired connection.  For wireless use cases, existing Wi-Fi onboarding
   mechanisms such as [WPS] can be used.

   Similarly, what address space the IP address belongs to, whether it
   is an IPv4 or IPv6 address, or if there are firewalls or proxies
   deployed between the Pledge and the cloud registrar are all out of
   scope of this document.

2.2.  Pledge Certificate Identity Considerations

   [BRSKI], Section 5.9.2 specifies that the Pledge MUST send an EST
   [RFC7030] Certificate Signing Request (CSR) Attributes request to the
   EST server before it requests a client certificate.  For the use case
   described in Section 1.2.1, the Owner Registrar operates as the EST
   server as described in [BRSKI], Section 2.5.3, and the Pledge sends
   the CSR Attributes request to the Owner Registrar.  For the use case

Friel, et al.             Expires 13 March 2026                [Page 11]
Internet-Draft                 BRSKI-CLOUD                September 2025

   described in Section 1.2.2, the EST server operates as described in
   [RFC7030], and the Pledge sends the CSR Attributes request to the EST
   server.  Note that the Pledge only sends the CSR Attributes request
   to the entity acting as the EST server as per [RFC7030], Section 2.6,
   and MUST NOT send the CSR Attributes request to the Cloud Registrar,
   because the Cloud Registrar does not have authority to issue a
   certificate for the customer domain.  (The Cloud Registrar is not a
   full EST server) If a Pledge erroneously sends a CSR Attributes
   request to the Cloud Registrar, then the Cloud Registrar MUST reply
   with 404 response code.

   The EST server MAY use this mechanism to instruct the Pledge about
   the identities it should include in the CSR request it sends as part
   of enrollment.  The EST server MAY use this mechanism to tell the
   Pledge what Subject or Subject Alternative Name identity information
   to include in its CSR request.  This can be useful if the Subject or
   Subject Alternative Name identity must have a specific value in order
   to complete enrollment with the CA.

   EST [RFC7030] is not clear on how the CSR Attributes response should
   be structured, and in particular is not clear on how a server can
   instruct a client to include specific attribute values in its CSR.
   [I-D.ietf-lamps-rfc7030-csrattrs] clarifies how a server can use CSR
   Attributes response to specify specific values for attributes that
   the client should include in its CSR.

   For example, the Pledge may only be aware of its IDevID Subject which
   includes a Manufacturer serial number, but must include a specific
   fully qualified domain name in the CSR in order to complete domain
   ownership proofs required by the CA.

   As another example, the Registrar may deem the Manufacturer serial
   number in an IDevID as personally identifiable information, and may
   want to specify a new random opaque identifier that the Pledge should
   use in its CSR.

2.3.  YANG extension for Voucher based redirect

   [RFC8366bis] contains the two needed voucher attributes: est-domain
   and additional-configuration-url which are needed when a client is
   redirected to a local EST server.

3.  Protocol Operation

   This section outlines the high-level protocol requirements and
   operations that take place.  Section 4 outlines the exact sequence of
   message interactions between the Pledge, the Cloud Registrar, the
   Owner Registrar and the Owner EST server.

Friel, et al.             Expires 13 March 2026                [Page 12]
Internet-Draft                 BRSKI-CLOUD                September 2025

3.1.  Pledge Sends Voucher Request to Cloud Registrar

3.1.1.  Cloud Registrar Discovery

   BRSKI defines how a Pledge contacts a well-known URI of a Cloud
   Registrar if a Local Domain Registrar cannot be discovered.
   Additionally, certain Pledge types might never attempt to discover a
   Local Domain Registrar and might automatically bootstrap against a
   Cloud Registrar.

   The details of the URI are Manufacturer specific.  If the Pledge
   fails to connect to the Cloud Registrar for any reason, it should
   consider that this is a bootstrapping failure, and indicate this.

3.1.2.  Pledge - Cloud Registrar TLS Establishment Details

   According to [BRSKI], Section 2.7, the Pledge MUST use an Implicit
   Trust Anchor database (see EST [RFC7030]) to authenticate the Cloud
   Registrar service.  The Pledge MUST establish a mutually
   authenticated TLS connection with the Cloud Registrar.  Unlike the
   Provisional TLS procedures documented in [BRSKI], Section 5.1, the
   Pledge MUST NOT establish a Provisional TLS connection with the Cloud
   Registrar.

   Pledges MUST and Cloud/Owner Registrars SHOULD support the use of the
   "server_name" TLS extension (SNI, [RFC6066]) when using TLS 1.2.
   Support for SNI is mandatory with TLS 1.3.

   Pledges SHOULD send a valid "server_name" extension (SNI) whenever
   they know the domain name of the registrar they connect to.  A Pledge
   creating a Provisional TLS connection according to [BRSKI] will often
   only know the link-local IPv6 address of a Join Proxy that connects
   it to the Registrar.  Registrars are accordingly expected to ignore
   SNI information, as in most cases, the Pledge will not know how to
   set the SNI correctly.

   The Pledge MUST be manufactured with preloaded trust anchors that are
   used to verify the identity of the Cloud Registrar when establishing
   the TLS connection.  The TLS connection can be verified using a
   public Web PKI trust anchor using [RFC9525] DNS-ID mechanisms or a
   pinned certification authority.  This is a local implementation
   decision.  Refer to Section 9.2 for trust anchor security
   considerations.

Friel, et al.             Expires 13 March 2026                [Page 13]
Internet-Draft                 BRSKI-CLOUD                September 2025

   The Cloud Registrar MUST verify the identity of the Pledge by sending
   a TLS CertificateRequest message to the Pledge during TLS session
   establishment.  The Cloud Registrar MAY include a
   certificate_authorities field in the message to specify the set of
   allowed IDevID issuing CAs that Pledges MAY use when establishing
   connections with the Cloud Registrar.

   In addition to other protections against DoS attacks, the Cloud
   Registrar is able to reject TLS connections when it can determine
   during TLS authentication that it cannot support the Pledge.  For
   example, the Pledge cannot provide an IDevID signed by a CA
   recognized/supported by the Cloud Registrar.

3.1.3.  Pledge Sends Voucher Request Message

   After the Pledge has established a mutually authenticated TLS
   connection with the Cloud Registrar, the Pledge generates a voucher
   request message as outlined in [BRSKI], Section 5.2, and sends the
   voucher request message to the Cloud Registrar.

3.2.  Cloud Registrar Processes Voucher Request Message

   The Cloud Registrar MUST determine Pledge ownership.  Prior to
   ownership determination, the Registrar checks the request for
   correctness and if it is unwilling or unable to handle the request,
   it MUST return a suitable 4xx or 5xx error response to the Pledge as
   defined by [BRSKI] and HTTP [RFC9110].  The Registrar returns the
   following errors:

   *  in the case of an unknown Pledge, a 404 is returned.

   *  for a malformed request, 400 is returned.

   *  in case of server overload, 503 is returned.

   If the request is correct and the Registrar is able to handle it, but
   unable to determine ownership at that time, then it MUST return a 401
   Unauthorized response to the Pledge.  This signals to the Pledge that
   there is currently no known owner domain for it, but that retrying
   later might resolve this situation.  In this scenario, the Registrar
   SHOULD include a Retry-After [RFC9110] header that includes a time to
   defer.  The absence of a Retry-After header indicates to the Pledge
   not to attempt again.  The Pledge MUST restart the bootstrapping
   process from the beginning.

   A Pledge with some kind of indicator (such as a screen or LED) SHOULD
   consider all 4xx and 5xx errors to be a bootstrapping failure, and
   indicate this.

Friel, et al.             Expires 13 March 2026                [Page 14]
Internet-Draft                 BRSKI-CLOUD                September 2025

   If the Cloud Registrar successfully determines ownership, then it
   MUST take one of the following actions:

   *  error: return a suitable 4xx or 5xx error response (as defined by
      [BRSKI] and HTTP) to the Pledge if the request processing failed
      for any reason.

   *  redirect to Owner Registrar: redirect the Pledge to an Owner
      Registrar via 307 response code.

   *  redirect to Owner EST server: issue a voucher (containing an "est-
      domain" attribute) and return a 200 response code.

3.2.1.  Pledge Ownership Look Up

   The Cloud Registrar needs some suitable mechanism for knowing the
   correct owner of a connecting Pledge based on the presented identity
   certificate.  For example, if the Pledge establishes TLS using an
   IDevID that is signed by a known manufacturing CA, the Registrar
   could extract the serial number from the IDevID and use this to look
   up a database of Pledge IDevID serial numbers to owners.

   The mechanism by which the Cloud Registrar determines Pledge
   ownership is, however, outside the scope of this document.  The Cloud
   Registrar is strongly tied to the Manufacturers' processes for device
   identity.

3.2.2.  Bootstrap via Cloud Registrar and Owner Registrar

   Once the Cloud Registrar has determined Pledge ownership, the Cloud
   Registrar MAY redirect the Pledge to the Owner Registrar in order to
   complete bootstrap.  If the owner wants the Cloud Registrar to
   redirect Pledges to their Owner Registrar, the owner must register
   their Owner Registrar URI with cloud Registrar.  The mechanism by
   which Pledge owners register their Owner Registrar URI with the Cloud
   Registrar is outside the scope of this document.

   In case of redirection, the Cloud Registrar replies to the voucher
   request with an HTTP 307 Temporary Redirect response code, including
   the owner's Local Domain in the HTTP Location header.

3.2.3.  Bootstrap via Cloud Registrar and Owner EST Service

   If the Cloud Registrar issues a voucher, it returns the voucher in an
   HTTP response with a 200 response code.

   The Cloud Registrar MAY issue a 202 response code if it is willing to
   issue a voucher, but will take some time to prepare the voucher.

Friel, et al.             Expires 13 March 2026                [Page 15]
Internet-Draft                 BRSKI-CLOUD                September 2025

   The voucher MUST include the new "est-domain" field as defined in
   [RFC8366bis].  This tells the Pledge where the domain of the EST
   service to use for completing certificate enrollment.

   The voucher MAY include the new additional-configuration-url field.
   This field points the Pledge to a URI where Pledge specific
   additional configuration information SHOULD be retrieved.  For
   example, a SIP user agent (a UA, such as a desk phone) might retrieve
   a Manufacturer specific configuration file that contains information
   about how to do SIP Registration.  One advantage of this mechanism
   over current mechanisms like DHCP options 120 defined in [RFC3361] or
   option 125 defined in [RFC3925] is that the voucher is returned in a
   confidential (TLS-protected) transport, and so can include device-
   specific credentials for retrieval of the configuration.

   The exact Pledge and Registrar behavior for handling and specifying
   the additional-configuration-url field is outside the scope of this
   document.

3.3.  Pledge Handles Cloud Registrar Response

3.3.1.  Bootstrap via Cloud Registrar and Owner Registrar

   The Cloud Registrar has returned a 307 response to a voucher request.
   The Cloud Registrar MAY be redirecting the Pledge to the Owner
   Registrar, or to a different Cloud Registrar operated by a VAR.

   The Pledge MUST restart its bootstrapping process by sending a new
   voucher request message (with a fresh nonce) using the location
   provided in the HTTP redirect.

   The Pledge MUST attempt to validate the identity of the Cloud VAR
   Registrar specified in the 307 response using its Implicit Trust
   Anchor Database.  If validation of this identity succeeds using the
   Implicit Trust Anchor Database, then the Pledge MAY accept a
   subsequent 307 response from this Cloud VAR Registrar.

   The Pledge MAY continue to follow a number of 307 redirects provided
   that each 307 redirect target Registrar identity is validated using
   the Implicit Trust Anchor Database.  The Manufacturer MAY enforce a
   Manufacturer-specific limit on the number of 307 redirects that the
   Pledge will follow.  The Pledge MAY be redirected to an Owner
   Register that then redirects the Pledge via a 3xx response.  The
   Pledge MUST follow the rules outlined in [BRSKI], Section 5.6 for any
   redirections other than 307 and MUST NOT follow more than one non-307
   redirection (3xx code other than 307) to another web origin.

Friel, et al.             Expires 13 March 2026                [Page 16]
Internet-Draft                 BRSKI-CLOUD                September 2025

   However, if validation of a 307 redirect target Registrar identity
   using the Implicit Trust Anchor Database fails, then the Pledge MUST
   NOT accept the 307 responses from the Registrar.  At this point, the
   TLS connection that has been established is considered a Provisional
   TLS, as per [BRSKI], Section 5.1.

   The Pledge then (re)sends a voucher-request on this connection.  As
   explained by [BRSKI], the connection is validated using the pinned
   credential from the voucher.

   The Pledge MUST process any error messages as defined in [BRSKI], and
   in case of error MUST restart the process from its provisioned Cloud
   Registrar.  The exception is that a 401 Unauthorized code SHOULD
   cause the Pledge to retry a number of times over a period of a few
   hours.

   In order to avoid permanent bootstrap cycles, the Pledge MUST NOT
   revisit a prior location on the same attempt.  If a loop is detected,
   then the Pledge MUST abort the current attempt, returning to the
   initial state where it looks for local Registrars (as per [BRSKI]),
   starting again with the initial Cloud Registrar if none are found.

   Section 8.2 further outlines risks associated with redirects.
   However, in some scenarios, Pledges MAY visit the current location
   multiple times, for example when handling a 401 Unauthorized
   response, or when handling a 503 Service Unavailable that includes a
   Retry-After HTTP header.  If it happens that a location is repeated,
   then the Pledge MUST fail the bootstrapping attempt and go back to
   the beginning, which includes listening to other sources of
   bootstrapping information as specified in [BRSKI] section 4.1 and
   5.0.  The Pledge MUST also have a limit on the total number of
   redirects it will follow, as the cycle detection requires that it
   keep track of the places it has been.  That limit MUST be in the
   dozens or more redirects such that no reasonable delegation path
   would be affected.

   When the Pledge cannot validate the connection, then it MUST
   establish a Provisional TLS connection with the specified Local
   Domain Registrar at the location specified.

   The Pledge then sends a voucher request message via the Local Domain
   Registrar.

   After the Pledge receives the voucher, it verifies the TLS connection
   to the Local Domain Registrar and continues with enrollment and
   bootstrap as per standard BRSKI operation.

Friel, et al.             Expires 13 March 2026                [Page 17]
Internet-Draft                 BRSKI-CLOUD                September 2025

   The Pledge MUST process any error messages as defined in [BRSKI], and
   in case of error MUST restart the process from its provisioned Cloud
   Registrar.

   The exception is that a 401 Unauthorized code SHOULD cause the Pledge
   to retry a number of times over a period of a few hours.

3.3.2.  Bootstrap via Cloud Registrar and Owner EST Service

   The Cloud Registrar returned a voucher to the Pledge.  The Pledge
   MUST perform voucher verification as per [BRSKI], Section 5.6.1.

   The Pledge SHOULD extract the "est-domain" field from the voucher,
   and SHOULD continue with EST enrollment as per standard EST
   operation.  Note that the Pledge has been instructed to connect to
   the EST server specified in the "est-domain" field, and therefore
   SHOULD use EST mechanisms, and not BRSKI mechanisms, when connecting
   to the EST server.

4.  Protocol Details

4.1.  Bootstrap via Cloud Registrar and Owner Registrar

   This flow illustrates the "Bootstrap via Cloud Registrar and Owner
   Registrar" use case.  A Pledge is bootstrapping in a remote location
   with no Local Domain Registrar.  The assumption is that the Owner
   Registrar domain is accessible, and the Pledge can establish a
   network connection with the Owner Registrar.  This may require that
   the owner network firewall exposes the Owner Registrar on the public
   internet.

Friel, et al.             Expires 13 March 2026                [Page 18]
Internet-Draft                 BRSKI-CLOUD                September 2025

   +--------+                                       +----------+
   | Pledge |                                       | Cloud    |
   |        |                                       |Registrar |
   +--------+                                       +----------+
       |                                                 |
       | 1. Mutually-authenticated TLS                   |
       |<----------------------------------------------->|
       |                                                 |
       | 2. Voucher Request                              |
       |------------------------------------------------>|
       |                                                 |
       | 3. 307 Location: owner-ra.example.com           |
       |<------------------------------------------------|
       |                                                 |
       |
       |                  +-----------+             +---------+
       |                  | Owner     |             |  MASA   |
       |                  | Registrar |             |         |
       |                  +-----------+             +---------+
       | 4. Provisional TLS   |                          |
       |<-------------------->|                          |
       |                      |                          |
       | 5. Voucher Request   |                          |
       |--------------------->| 6. Voucher Request       |
       |                      |------------------------->|
       |                      |                          |
       |                      | 7. Voucher Response      |
       |                      |<-------------------------|
       | 8. Voucher Response  |                          |
       |<---------------------|                          |
       |                      |                          |
       | 9. Verify TLS        |                          |
       |<-------------------->|                          |
       |                      |                          |
       | 10. EST enroll       |
       |--------------------->|
       |<---------------------|

   The process starts, in step 1, when the Pledge establishes a Mutual
   TLS channel with the Cloud Registrar using the IDevID certificate and
   the trust anchors created during the manufacturing process of the
   Pledge.

   In step 2, the Pledge sends a voucher request to the Cloud Registrar.

Friel, et al.             Expires 13 March 2026                [Page 19]
Internet-Draft                 BRSKI-CLOUD                September 2025

   The Cloud Registrar determines Pledge ownership look up as outlined
   in Section 3.2.1, and determines the Owner Registrar domain.  In step
   3, the Cloud Registrar redirects the Pledge to the Owner Registrar
   domain.

   Steps 4 and onwards follow the standard BRSKI flow, which includes
   doing EST enroll operations.  The Pledge establishes a Provisional
   TLS connection with the Owner Registrar, and sends a voucher request
   to the Owner Registrar.  The Registrar forwards the voucher request
   to the MASA.  Assuming the MASA issues a voucher, then the Pledge
   verifies the TLS connection with the Registrar using the pinned-
   domain-cert from the voucher and completes the BRSKI flow.

4.2.  Bootstrap via Cloud Registrar and Owner EST Service

   This flow illustrates the "Bootstrap via Cloud Registrar and Owner
   EST Service" use case.  A Pledge is bootstrapping in a location with
   no Local Domain Registrar.  The Cloud Registrar is instructing the
   Pledge to connect directly to an EST server for enrollment using EST
   mechanisms.  The assumption is that the EST domain is accessible, and
   the Pledge can establish a network connection with the EST server.

Friel, et al.             Expires 13 March 2026                [Page 20]
Internet-Draft                 BRSKI-CLOUD                September 2025

   +--------+                                       +----------+
   | Pledge |                                       | Cloud    |
   |        |                                       |Registrar |
   |        |                                       | / MASA   |
   +--------+                                       +----------+
       |                                                 |
       | 1. Mutually-authenticated TLS                   |
       |<----------------------------------------------->|
       |                                                 |
       | 2. Voucher Request                              |
       |------------------------------------------------>|
       |                                                 |
       | 3. Voucher Response  {est-domain:fqdn}          |
       |<------------------------------------------------|
       |                                                 |
       |                 +----------+                    |
       |                 | RFC7030  |                    |
       |                 | EST      |                    |
       |                 | Server   |                    |
       |                 +----------+                    |
       |                      |                          |
       | 4. Authenticate TLS  |                          |
       |<-------------------->|                          |
       |                                                 |
       | 5a. On success: POST /voucher_status success    |
       | 5b. On failure: POST /voucher_status failure    |
       |------------------------------------------------>|
       |                                                 |
       | 6. CSR Attributes    |                          |
       |    Request           |                          |
       |--------------------->|                          |
       | 7. CSR Attributes    |                          |
       |    Response          |                          |
       |<---------------------|                          |
       |                      |                          |
       | 8. EST Enroll        |                          |
       |--------------------->|                          |
       |                      |                          |
       | 9. Certificate       |                          |
       |<---------------------|                          |
       |                      |                          |
       | 10. /enrollstatus    |                          |
       |--------------------->|                          |

   The process starts, in step 1, when the Pledge establishes a Mutual
   TLS channel with the Cloud Registrar/MASA using artifacts created
   during the manufacturing process of the Pledge.

Friel, et al.             Expires 13 March 2026                [Page 21]
Internet-Draft                 BRSKI-CLOUD                September 2025

   In step 2, the Pledge sends a voucher request to the Cloud Registrar/
   MASA.

   In step 3, the Cloud Registrar/MASA replies to the Pledge with an
   [RFC8366bis] format voucher that includes its assigned EST domain in
   the "est-domain" attribute.

   In step 4, the Pledge establishes a TLS connection with the EST RA
   that was specified in the voucher "est-domain" attribute.  The
   connection may involve crossing the Internet requiring a DNS look up
   on the provided name.  The resulting IP address can be of any scope:
   a globally unique IP address, or a local IP address.  An IP address
   literal MAY be used in the est-domain attributes, including a local
   address that includes an IP address literal including both IPv4
   [RFC1918] and IPv6 Unique Local Addresses [RFC4193].

   The Pledge attempts to authenticate the TLS connection and verify the
   EST server identity.  The artifact provided in the pinned-domain-cert
   is trusted as a trust anchor, and is used to verify the EST server
   identity.  The EST server identity MUST be verified using the pinned-
   domain-cert value provided in the voucher as described in [RFC7030]
   section 3.3.1.

   There is a case where the pinned-domain-cert is the identical End-
   Entity (EE) Certificate as the EST server.  It also explicitly
   includes the case where the EST server has a self-signed EE
   Certificate, but it MAY also be an EE certificate that is part of a
   larger PKI.  If the certificate is not a self-signed or EE
   certificate, then the Pledge SHOULD apply [RFC9525] DNS-ID
   verification on the certificate against the domain provided in the
   "est-domain" attribute.  If the "est-domain" was provided with an IP
   address literal, then it is unlikely that it can be verified, and in
   that case, it is expected that either a self-signed certificate or an
   EE certificate will be pinned by the voucher.

   In steps 5.a and 5.b, the Pledge MAY optionally notify the Cloud
   Registrar/MASA of the success or failure of its attempt to establish
   a secure TLS channel with the EST server.  This is described in
   [BRSKI], Section 5.7 This telemetry returns allow for the Registrar
   to better provide diagnostics in the event of failure to onboard. if
   the Pledge fails to verify the identity of the EST server, it MUST
   drop the connection and MUST NOT continue with a CSR Attributes
   request or an EST Enroll request.

   In step 6, the Pledge follows the procedures outlined in Section 2.2
   and sends a CSR Attributes request to the EST server before sending
   the EST Enroll request.

Friel, et al.             Expires 13 March 2026                [Page 22]
Internet-Draft                 BRSKI-CLOUD                September 2025

   In step 7, the EST server returns the CSR Attributes response.

   In step 8, the Pledge sends an EST Enroll request with the CSR.

   In step 9, the EST server returns the requested certificate.

   Step 10 is described in [BRSKI], Section 5.9.4 as the Enrollment
   Status Telemetry.  This telemetry return also allows for better
   diagnostics in the event of a failure.

5.  Lifecycle Considerations

   BRSKI and the Cloud Registrar support provided in this document are
   dependent upon the Manufacturer maintaining the required
   infrastructure.  [BRSKI], Section 10.7 outlines additional
   considerations about Manufacturer life span.

   Sections 11.5 and 11.6 of [BRSKI] outline additional considerations
   about device trust anchors and how devices establish trust.

   The well-known URL that is used is specified by the Manufacturer when
   designing its firmware, and is therefore completely under the
   Manufacturer's control.  If the Manufacturer wishes to change the
   URL, or discontinue the service, then the Manufacturer will need to
   arrange for a firmware update where appropriate changes are made.

   Often the firmware can not be updated because there is significant
   inventory in a warehouse.  If the Pledge were powered on and
   connected, then it would get firmware updates.  Since it is not, any
   URLs built-in to the old firmware need to be maintained until all
   copies of that firmware have been replaced.  This could be a
   challenge if a company is going out of business, and in which case
   the considerations from [BRSKI], Section 10.7 apply.

   If a merger between two companies happens, then it is possible to
   consolidate the MASA of each company into a single system.  The
   consolidated MASA will need access to a MASA signing key for both
   companies to operate correctly.  One way is for both MASA names (such
   as masa.company1.example, and masa.company2.example) to be added as
   SubjectAltNames for the HTTPS certificates used by the MASA.  The
   Cloud Registrar will need a similar treatment.  As an alternative to
   operating a Registrar under two names, all access to one Cloud
   Registrar could be replaced with a 307 redirect as described in
   Section 8.2.

   Additionally, in the hosted Registrar use case, with an Owner EST
   Server Section 4.2 use case, the Cloud Registrar MUST know the
   certificate for the EST Server in order to pin it properly.  In that

Friel, et al.             Expires 13 March 2026                [Page 23]
Internet-Draft                 BRSKI-CLOUD                September 2025

   case, when the owner of the EST Server wishes to change their
   certificate, then they MUST coordinate this with the upstream Cloud
   Registrar operator.

6.  IANA Considerations

   This document makes no IANA requests.

7.  Privacy Considerations

   All privacy considerations outlined in [BRSKI], Section 10 are
   applicable.

   There are additional privacy considerations as the Pledge connects to
   a default Cloud Registrar during bootstrap.  In particular, [BRSKI],
   Section 10.3 documents the information that is revealed to the MASA.
   When Pledges use the mechansisms described in this document, a subset
   of this information is revealed to the Cloud Registrar, namely:

   *  the identity of the device being enrolled

   *  the time the device is activated

   *  the IP address of the device, or if the Pledge is behind a NAT,
      the public IP of the NAT

   Refer to [BRSKI], Section 10 for more comprehensive information.

8.  Implementation Considerations

8.1.  Captive Portals

   A Pledge might find itself deployed in a network where a captive
   portal or an intelligent home gateway that provides access control on
   all connections are also deployed.  Captive portals that do not
   follow the requirements of Section 1 of [RFC8952] might forcibly
   redirect HTTPS connections.  While this is a deprecated practice as
   it breaks TLS in a way that most users can not deal with, it is still
   common in many networks.

   When the Pledge attempts to connect to any Cloud Registrar, an
   incorrect connection will be detected because the Pledge will be
   unable to verify the TLS connection to its Cloud Registrar via DNS-ID
   check [RFC9525], Section 6.3.  That is, the certificate returned from
   the captive portal will not match.

Friel, et al.             Expires 13 March 2026                [Page 24]
Internet-Draft                 BRSKI-CLOUD                September 2025

   At this point a network operator who controls the captive portal,
   noticing the connection to what seems a legitimate destination (the
   Cloud Registrar), MAY then permit that connection.  This enables the
   first connection to go through.

   The connection is then redirected to the Registrar via 307, or to an
   EST server via "est-domain" in a voucher.  If it is a 307 redirect,
   then a Provisional TLS connection will be initiated, and it will
   succeed.  The Provisional TLS connection does not do DNS-ID
   verification ([RFC9525], Section 6.3), so the forced redirection to a
   captive portal system will not be detected.  However, the subsequent
   BRSKI POST of a voucher request will most likely be met by a 404 or
   500 HTTP code.  Even if somehow it did work (because the captive
   portal was in fact an attacker), any returned voucher would not be
   signed by a trusted MASA.

   It is RECOMMENDED therefore that the Pledge look for Captive-Portal
   Identification attributes [RFC8910] in DHCP, and if present, use the
   Captive-Portal API [RFC8908] to learn if it is captive.

   The scenarios outlined here when a Pledge is deployed behind a
   captive portal may result in failure scenarios, but do not constitute
   a security risk, so long as the Pledge is correctly verifying all TLS
   connections as per [BRSKI].

8.2.  Multiple HTTP Redirects

   If the Redirect to Registrar method is used, as described in
   Section 4.1, there MAY be a series of 307 redirects.  An example of
   why this might occur is that the Manufacturer only knows that it
   resold the device to a particular value added reseller (VAR), and
   there MAY be a chain of such VARs.  It is important the Pledge avoid
   being drawn into a loop of redirects.  This could happen if a VAR
   does not think they are authoritative for a particular device.  A
   "helpful" programmer might instead decide to redirect back to the
   Manufacturer in an attempt to restart at the top: perhaps there is
   another process that updates the Manufacturer's database and this
   process is underway.  Instead, the VAR MUST return a 404 error if it
   cannot process the device.  This will force the device to stop,
   timeout, and then try all mechanisms again.

   There are additional considerations regarding TLS certificate
   validation as outlined in Section 3.3.1.  If the Registrar returns a
   307 response, the Pledge MUST NOT follow this redirect if the
   Registrar identity was not validated using its Implicit Trust Anchor
   Database.  If the Registrar identity was validated using the Implicit
   Trust Anchor Database, then the Pledge MAY follow the redirect.

Friel, et al.             Expires 13 March 2026                [Page 25]
Internet-Draft                 BRSKI-CLOUD                September 2025

9.  Security Considerations

   The Cloud Registrar described in this document inherits all the
   strong security properties that are described in [BRSKI], and none of
   the security mechanisms that are defined in [BRSKI] are bypassed or
   weakened by this document.  The Cloud Registrar also inherits all the
   potential issues that are described in [BRSKI].  This includes
   dependency upon continued operation of the Manufacturer provided
   MASA, as well as potential complications where a Manufacturer might
   interfere with resale of a device.

   In addition to the dependency upon the MASA, the successful
   enrollment of a device using a Cloud Registrar depends upon the
   correct and continued operation of this new service.  This internet
   accessible service might be operated by the Manufacturer and/or by
   one or more value-added-resellers.  All the considerations for
   operation of the MASA also apply to the operation of the Cloud
   Registrar.

9.1.  Security Updates for the Pledge

   Unlike many other uses of BRSKI, in the Cloud Registrar case it is
   assumed that the Pledge has connected to a network, such as the
   public Internet, on which some amount of connectivity is possible,
   but there is no other local configuration available.  (Note: there
   are many possible configurations in which the device might not have
   unlimited connectivity to the public Internet, but for which there
   might be some connectivity possible)

   The Pledge SHOULD NOT assume that the network is protecting the
   device.  In a majority of cases, the Pledge will be connected to a
   network behind an enterprise firewall, or a home router, with typical
   restrictions on incoming TCP connections due to NAT44 [RFC6144] and
   [RFC7084], Section 3.1, and [RFC6092], Section 4.  In such
   situations, the Pledge might think it can be assured that it can not
   be attacked, but this is not the case!

   Pledges could be deployed on networks

   *  with unfiltered connectivity, including public IPv4 and IPv6

   *  where incoming connections are enabled via explicit rules

   *  where there could be malicious devices within this network

   The Pledge SHOULD contact the Manufacturer before bootstrapping in
   order to apply any available firmware patches.  Firmware patches need
   to validated before being applied.  This is best done via signatures

Friel, et al.             Expires 13 March 2026                [Page 26]
Internet-Draft                 BRSKI-CLOUD                September 2025

   on the firmware updates, such as described in [RFC9019] or an
   equivalent mechanism.  Origin authentication of updates is also
   sometimes enough.

   In order to best protect the Pledge from attacks of all kinds,
   Manufacturers are encouraged to make MUD [RFC8520] files available.
   Care needs to be taken in those definitions to allow for retrieval of
   firmware updates.  This may also include updates to the Implicit list
   of Trust Anchors.  In this way, a Pledge that may have been in a
   dusty box in a warehouse for a long time can be updated to the latest
   (exploit-free) firmware before attempting bootstrapping.

9.2.  Trust Anchors for Cloud Registrar

   The HTTPS connections that the Pledge makes to the Cloud Registrar,
   and any subsequent Registrars that it may be redirected to, MUST be
   validated using the Implicit Trust Anchor database as described in
   [RFC7030], Section 3.6.1.  Manufacturers MUST include all necessary
   trust anchors in a Pledge's Implicit Trust Anchor database so that
   all expected Registrars can be validated.

   Registars may use public (WebPKI) or private PKI Trust Anchors.
   While there is no requirement that Registrar's certificates are part
   of any public (WebPKI) Trust Anchor lists, it may be simpler and
   cheaper for Registrars to use these easily obtained certificates,
   rather than use a private PKI.  It is recommended for Manufacturers
   to work with their VARs to determine the subset of publicly trusted
   (Web) PKI Trust Anchors and / or private PKI Trust Anchors that would
   satisfy all their VARs, and to ship only that minimal set in the
   Implicit Trust Anchor database.

9.3.  Considerations for HTTP Redirect

   When the default Cloud Registrar redirects a Pledge using HTTP 307 to
   an Owner Registrar, or another Cloud Registrar operated by a VAR, the
   Pledge MUST have validated the TLS connection using an Implicit Trust
   Anchor.

   However, when connecting to the target Owner Registrar, a provisional
   TLS connection is required as explained in [BRSKI], Section 5.1.

   Provisional TLS connections are not immediately validated.  A
   provisional TLS connection can be intercepted by an attacker, as
   unlike in [BRSKI], this connection crosses the Internet.  There can
   be IP address hijacks, possibly DNS attacks that could send the
   Pledge to the wrong place.  Such a diversion would be detected when
   the resulting Voucher can not be validated.

Friel, et al.             Expires 13 March 2026                [Page 27]
Internet-Draft                 BRSKI-CLOUD                September 2025

   There is a conflict between these requirements: one says to validate,
   and the other one says not to.  This is resolved by having the Pledge
   attempt validation, and if it succeeds, then and only then, an HTTP
   307 redirect will be accepted.  If validation fails, then an HTTP 307
   redirect MUST be rejected as an error.  If that occurs, then the
   onboarding process SHOULD restart after a delay.  This failure should
   be reported to the initial Cloud Registrar via the mechanism
   described in [BRSKI], Section 5.7.

   If the Pledge were to accept a 307 Redirect from a malicious entity,
   then it could be directed to connect to some other Registrar-like
   entity.  This could be used to turn the Pledge into part of a
   distributed denial of service (DDoS) attack.  As the Pledge will send
   it's details in the Voucher Request that it does send, there is also
   a possible disclosure of the Pledge's identifiable private
   information.

   Note that for use case two, in which redirection to an EST Server
   occurs, then there is no provisional TLS connection at all.  The
   connection to the last Cloud Registrar is validated using the
   Implicit Trust Database, while the EST Server connection is validated
   by the certificate pinned by the Voucher artifact.

9.4.  Considerations for Voucher est-domain

   A Cloud Registrar supporting the same set of Pledges as a MASA MAY be
   integrated with the MASA to avoid the need for a network based API
   between them, and without changing their external behavior as
   specified here.

   When a Cloud Registrar handles the scenario described in
   Section 1.2.2 by the returning "est-domain" attribute in the voucher,
   the Cloud Registrar MUST do all the voucher processing as specified
   in [BRSKI].  This is an example deployment scenario where the Cloud
   Registrar MAY be operated by the same entity as the MASA, and it MAY
   even be integrated with the MASA.

   When a voucher is issued by the Cloud Registrar and that voucher
   contains an "est-domain" attribute, the Pledge MUST verify the TLS
   connection with this EST server using the "pinned-domain-cert"
   attribute in the voucher.

   The reduced operational security mechanisms outlined in Sections 7.3
   and 11 of [BRSKI] MAY be supported when the Pledge connects with the
   EST server.  These mechanisms reduce the security checks that take
   place when the Pledge enrolls with the EST server.  Refer to [BRSKI]
   sections 7.3 and 11 for further details.

Friel, et al.             Expires 13 March 2026                [Page 28]
Internet-Draft                 BRSKI-CLOUD                September 2025

Acknowledgements

   The authors would like to thank for following for their detailed
   reviews: (ordered by last name): Esko Dijk, Toerless Eckert, Sheng
   Jiang.

References

Normative References

   [BRSKI]    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>.

   [I-D.ietf-lamps-rfc7030-csrattrs]
              Richardson, M., Friel, O., von Oheimb, D., and D. Harkins,
              "Clarification and enhancement of RFC7030 CSR Attributes
              definition", Work in Progress, Internet-Draft, draft-ietf-
              lamps-rfc7030-csrattrs-23, 28 June 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-lamps-
              rfc7030-csrattrs-23>.

   [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>.

   [RFC6066]  Eastlake 3rd, D., "Transport Layer Security (TLS)
              Extensions: Extension Definitions", RFC 6066,
              DOI 10.17487/RFC6066, January 2011,
              <https://www.rfc-editor.org/rfc/rfc6066>.

   [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>.

   [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>.

Friel, et al.             Expires 13 March 2026                [Page 29]
Internet-Draft                 BRSKI-CLOUD                September 2025

   [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-
              anima-rfc8366bis-14, 1 April 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-anima-
              rfc8366bis-14>.

   [RFC8994]  Eckert, T., Ed., Behringer, M., Ed., and S. Bjarnason, "An
              Autonomic Control Plane (ACP)", RFC 8994,
              DOI 10.17487/RFC8994, May 2021,
              <https://www.rfc-editor.org/rfc/rfc8994>.

   [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>.

Informative References

   [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-11, 22 July 2025,
              <https://datatracker.ietf.org/doc/html/draft-irtf-t2trg-
              taxonomy-manufacturer-anchors-11>.

   [IDEVID]   IEEE Standard, "IEEE 802.1AR Secure Device Identifier",
              2018, <https://1.ieee802.org/security/802-1ar/>.

   [RFC1918]  Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.
              J., and E. Lear, "Address Allocation for Private
              Internets", BCP 5, RFC 1918, DOI 10.17487/RFC1918,
              February 1996, <https://www.rfc-editor.org/rfc/rfc1918>.

   [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol",
              RFC 2131, DOI 10.17487/RFC2131, March 1997,
              <https://www.rfc-editor.org/rfc/rfc2131>.

   [RFC2132]  Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
              Extensions", RFC 2132, DOI 10.17487/RFC2132, March 1997,
              <https://www.rfc-editor.org/rfc/rfc2132>.

Friel, et al.             Expires 13 March 2026                [Page 30]
Internet-Draft                 BRSKI-CLOUD                September 2025

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              DOI 10.17487/RFC3261, June 2002,
              <https://www.rfc-editor.org/rfc/rfc3261>.

   [RFC3361]  Schulzrinne, H., "Dynamic Host Configuration Protocol
              (DHCP-for-IPv4) Option for Session Initiation Protocol
              (SIP) Servers", RFC 3361, DOI 10.17487/RFC3361, August
              2002, <https://www.rfc-editor.org/rfc/rfc3361>.

   [RFC3925]  Littlefield, J., "Vendor-Identifying Vendor Options for
              Dynamic Host Configuration Protocol version 4 (DHCPv4)",
              RFC 3925, DOI 10.17487/RFC3925, October 2004,
              <https://www.rfc-editor.org/rfc/rfc3925>.

   [RFC4193]  Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
              Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005,
              <https://www.rfc-editor.org/rfc/rfc4193>.

   [RFC5859]  Johnson, R., "TFTP Server Address Option for DHCPv4",
              RFC 5859, DOI 10.17487/RFC5859, June 2010,
              <https://www.rfc-editor.org/rfc/rfc5859>.

   [RFC6092]  Woodyatt, J., Ed., "Recommended Simple Security
              Capabilities in Customer Premises Equipment (CPE) for
              Providing Residential IPv6 Internet Service", RFC 6092,
              DOI 10.17487/RFC6092, January 2011,
              <https://www.rfc-editor.org/rfc/rfc6092>.

   [RFC6144]  Baker, F., Li, X., Bao, C., and K. Yin, "Framework for
              IPv4/IPv6 Translation", RFC 6144, DOI 10.17487/RFC6144,
              April 2011, <https://www.rfc-editor.org/rfc/rfc6144>.

   [RFC7084]  Singh, H., Beebee, W., Donley, C., and B. Stark, "Basic
              Requirements for IPv6 Customer Edge Routers", RFC 7084,
              DOI 10.17487/RFC7084, November 2013,
              <https://www.rfc-editor.org/rfc/rfc7084>.

   [RFC8520]  Lear, E., Droms, R., and D. Romascanu, "Manufacturer Usage
              Description Specification", RFC 8520,
              DOI 10.17487/RFC8520, March 2019,
              <https://www.rfc-editor.org/rfc/rfc8520>.

   [RFC8908]  Pauly, T., Ed. and D. Thakore, Ed., "Captive Portal API",
              RFC 8908, DOI 10.17487/RFC8908, September 2020,
              <https://www.rfc-editor.org/rfc/rfc8908>.

Friel, et al.             Expires 13 March 2026                [Page 31]
Internet-Draft                 BRSKI-CLOUD                September 2025

   [RFC8910]  Kumari, W. and E. Kline, "Captive-Portal Identification in
              DHCP and Router Advertisements (RAs)", RFC 8910,
              DOI 10.17487/RFC8910, September 2020,
              <https://www.rfc-editor.org/rfc/rfc8910>.

   [RFC8914]  Kumari, W., Hunt, E., Arends, R., Hardaker, W., and D.
              Lawrence, "Extended DNS Errors", RFC 8914,
              DOI 10.17487/RFC8914, October 2020,
              <https://www.rfc-editor.org/rfc/rfc8914>.

   [RFC8952]  Larose, K., Dolson, D., and H. Liu, "Captive Portal
              Architecture", RFC 8952, DOI 10.17487/RFC8952, November
              2020, <https://www.rfc-editor.org/rfc/rfc8952>.

   [RFC9019]  Moran, B., Tschofenig, H., Brown, D., and M. Meriac, "A
              Firmware Update Architecture for Internet of Things",
              RFC 9019, DOI 10.17487/RFC9019, April 2021,
              <https://www.rfc-editor.org/rfc/rfc9019>.

   [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>.

   [WPS]      Wi-Fi Alliance, "Wi-Fi Protected Setup (WPS)", January
              2025, <https://www.wi-fi.org/discover-wi-fi/wi-fi-
              protected-setup>.

Authors' Addresses

   Owen Friel
   Cisco
   Email: ofriel@cisco.com

   Rifaat Shekh-Yusef
   Ciena
   Email: rifaat.s.ietf@gmail.com

   Michael Richardson
   Sandelman Software Works
   Email: mcr+ietf@sandelman.ca

Friel, et al.             Expires 13 March 2026                [Page 32]