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Bootstrapping Remote Secure Key Infrastructures (BRSKI)

The information below is for an old version of the document.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 8995.
Authors Max Pritikin , Michael Richardson , Michael H. Behringer , Steinthor Bjarnason , Kent Watsen
Last updated 2017-10-30 (Latest revision 2017-10-13)
Replaces draft-pritikin-anima-bootstrapping-keyinfra
RFC stream Internet Engineering Task Force (IETF)
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Stream WG state WG Document
Document shepherd Toerless Eckert
IESG IESG state Became RFC 8995 (Proposed Standard)
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ANIMA WG                                                     M. Pritikin
Internet-Draft                                                     Cisco
Intended status: Standards Track                           M. Richardson
Expires: May 3, 2018                                                 SSW
                                                            M. Behringer
                                                            S. Bjarnason
                                                          Arbor Networks
                                                               K. Watsen
                                                        Juniper Networks
                                                        October 30, 2017

        Bootstrapping Remote Secure Key Infrastructures (BRSKI)


   This document specifies automated bootstrapping of a remote secure
   key infrastructure (BRSKI) using vendor installed X.509 certificate,
   in combination with a vendor's authorizing service, both online and
   offline.  Bootstrapping a new device can occur using a routable
   address and a cloud service, or using only link-local connectivity,
   or on limited/disconnected networks.  Support for lower security
   models, including devices with minimal identity, is described for
   legacy reasons but not encouraged.  Bootstrapping is complete when
   the cryptographic identity of the new key infrastructure is
   successfully deployed to the device but the established secure
   connection can be used to deploy a locally issued certificate to the
   device as well.

Status of This Memo

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

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

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

   This Internet-Draft will expire on May 3, 2018.

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Copyright Notice

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   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   ( in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
     1.1.  Other Bootstrapping Approaches  . . . . . . . . . . . . .   5
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   6
     1.3.  Scope of solution . . . . . . . . . . . . . . . . . . . .   8
     1.4.  Leveraging the new key infrastructure / next steps  . . .   9
   2.  Architectural Overview  . . . . . . . . . . . . . . . . . . .   9
     2.1.  Behavior of a Pledge  . . . . . . . . . . . . . . . . . .  11
     2.2.  Secure Imprinting using Vouchers  . . . . . . . . . . . .  12
     2.3.  Initial Device Identifier . . . . . . . . . . . . . . . .  13
     2.4.  Protocol Flow . . . . . . . . . . . . . . . . . . . . . .  14
       2.4.1.  Architectural component: Pledge . . . . . . . . . . .  16
       2.4.2.  Architectural component: Circuit Proxy  . . . . . . .  16
       2.4.3.  Architectural component: Domain Registrar . . . . . .  16
       2.4.4.  Architectural component: Vendor Service . . . . . . .  16
     2.5.  Lack of realtime clock  . . . . . . . . . . . . . . . . .  16
     2.6.  Cloud Registrar . . . . . . . . . . . . . . . . . . . . .  17
     2.7.  Determining the MASA to contact . . . . . . . . . . . . .  17
   3.  Voucher-Request artifact  . . . . . . . . . . . . . . . . . .  18
     3.1.  Tree Diagram  . . . . . . . . . . . . . . . . . . . . . .  18
     3.2.  Examples  . . . . . . . . . . . . . . . . . . . . . . . .  19
     3.3.  YANG Module . . . . . . . . . . . . . . . . . . . . . . .  21
   4.  Proxy details . . . . . . . . . . . . . . . . . . . . . . . .  23
     4.1.  Pledge discovery of Proxy . . . . . . . . . . . . . . . .  24
       4.1.1.  Proxy Grasp announcements . . . . . . . . . . . . . .  25
     4.2.  CoAP connection to Registrar  . . . . . . . . . . . . . .  26
     4.3.  HTTPS proxy connection to Registrar . . . . . . . . . . .  26
     4.4.  Proxy discovery of Registrar  . . . . . . . . . . . . . .  26
   5.  Protocol Details  . . . . . . . . . . . . . . . . . . . . . .  28
     5.1.  BRSKI-EST TLS establishment details . . . . . . . . . . .  30
     5.2.  Pledge Requests Voucher from the Registrar  . . . . . . .  30
     5.3.  BRSKI-MASA TLS establishment details  . . . . . . . . . .  31

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     5.4.  Registrar Requests Voucher from MASA  . . . . . . . . . .  32
     5.5.  Voucher Response  . . . . . . . . . . . . . . . . . . . .  35
       5.5.1.  Completing authentication of Provisional TLS
               connection  . . . . . . . . . . . . . . . . . . . . .  36
     5.6.  Voucher Status Telemetry  . . . . . . . . . . . . . . . .  37
     5.7.  MASA authorization log Request  . . . . . . . . . . . . .  38
       5.7.1.  MASA authorization log Response . . . . . . . . . . .  39
     5.8.  EST Integration for PKI bootstrapping . . . . . . . . . .  40
       5.8.1.  EST Distribution of CA Certificates . . . . . . . . .  40
       5.8.2.  EST CSR Attributes  . . . . . . . . . . . . . . . . .  40
       5.8.3.  EST Client Certificate Request  . . . . . . . . . . .  41
       5.8.4.  Enrollment Status Telemetry . . . . . . . . . . . . .  41
       5.8.5.  EST over CoAP . . . . . . . . . . . . . . . . . . . .  43
   6.  Reduced security operational modes  . . . . . . . . . . . . .  43
     6.1.  Trust Model . . . . . . . . . . . . . . . . . . . . . . .  43
     6.2.  Pledge security reductions  . . . . . . . . . . . . . . .  44
     6.3.  Registrar security reductions . . . . . . . . . . . . . .  44
     6.4.  MASA security reductions  . . . . . . . . . . . . . . . .  45
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  46
     7.1.  PKIX Registry . . . . . . . . . . . . . . . . . . . . . .  46
     7.2.  Voucher Status Telemetry  . . . . . . . . . . . . . . . .  46
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  47
     8.1.  Freshness in Voucher-Requests . . . . . . . . . . . . . .  48
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  50
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  50
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  50
     10.2.  Informative References . . . . . . . . . . . . . . . . .  52
   Appendix A.  IPv4 operations  . . . . . . . . . . . . . . . . . .  54
     A.1.  IPv4 Link Local addresses . . . . . . . . . . . . . . . .  54
     A.2.  Use of DHCPv4 . . . . . . . . . . . . . . . . . . . . . .  54
   Appendix B.  mDNS / DNSSD proxy discovery options . . . . . . . .  54
   Appendix C.  IPIP Join Proxy mechanism  . . . . . . . . . . . . .  55
     C.1.  Multiple Join networks on the Join Proxy side . . . . . .  55
     C.2.  Automatic configuration of tunnels on Registrar . . . . .  56
     C.3.  Proxy Neighbor Discovery by Join Proxy  . . . . . . . . .  56
     C.4.  Use of connected sockets; or IP_PKTINFO for CoAP on
           Registrar . . . . . . . . . . . . . . . . . . . . . . . .  57
     C.5.  Use of socket extension rather than virtual interface . .  57
   Appendix D.  MUD Extension  . . . . . . . . . . . . . . . . . . .  57
   Appendix E.  Example Vouchers . . . . . . . . . . . . . . . . . .  59
     E.1.  Keys involved . . . . . . . . . . . . . . . . . . . . . .  59
       E.1.1.  MASA key pair for voucher signatures  . . . . . . . .  59
       E.1.2.  Manufacturer key pair for IDevID signatures . . . . .  59
       E.1.3.  Registrar key pair  . . . . . . . . . . . . . . . . .  60
       E.1.4.  Pledge key pair . . . . . . . . . . . . . . . . . . .  62
     E.2.  Example process . . . . . . . . . . . . . . . . . . . . .  64
       E.2.1.  Pledge to Registrar . . . . . . . . . . . . . . . . .  64
       E.2.2.  Registrar to MASA . . . . . . . . . . . . . . . . . .  66

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       E.2.3.  MASA to Registrar . . . . . . . . . . . . . . . . . .  67
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  69

1.  Introduction

   BRSKI provides a foundation to securely answer the following
   questions between an element of the network domain called the
   "Registrar" and an unconfigured and untouched device called a

   o  Registrar authenticating the Pledge: "Who is this device?  What is
      its identity?"

   o  Registrar authorization the Pledge: "Is it mine?  Do I want it?
      What are the chances it has been compromised?"

   o  Pledge authenticating the Registrar/Domain: "What is this domain's

   o  Pledge authorization the Registrar: "Should I join it?"

   This document details protocols and messages to the endpoints to
   answer the above questions.  The Registrar actions derive from Pledge
   identity, third party cloud service communications, and local access
   control lists.  The Pledge actions derive from a cryptographically
   protected "voucher" message delivered through the Registrar but
   originating at a Manufacturer Authorized Signing Authority.

   The syntactic details of vouchers are described in detail in
   [I-D.ietf-anima-voucher].  This document details automated protocol
   mechanisms to obtain vouchers, including the definition of a
   'voucher-request' message that is a minor extension to the voucher
   format (see Section 3).

   BRSKI results in the Pledge storing an X.509 root certificate
   sufficient for verifying the Registrar identity.  In the process a
   TLS connection is established which can be directly used for
   Enrollment over Secure Transport (EST).  In effect BRSKI provides an
   automated mechanism for the "Bootstrap Distribution of CA
   Certificates" described in [RFC7030] Section 4.1.1 wherein the Pledge
   "MUST [...]. engage a human user to authorize the CA certificate
   using out-of-band" information".  With BRSKI the Pledge now can
   automate this process using the voucher.  Integration with a complete
   EST enrollment is optional but trivial.

   BRSKI is agile enough to support bootstrapping alternative key
   infrastructures, such as a symmetric key solutions, but no such
   system is described in this document.

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1.1.  Other Bootstrapping Approaches

   To literally "pull yourself up by the bootstraps" is an impossible
   action.  Similarly the secure establishment of a key infrastructure
   without external help is also an impossibility.  Today it is commonly
   accepted that the initial connections between nodes are insecure,
   until key distribution is complete, or that domain-specific keying
   material is pre-provisioned on each new device in a costly and non-
   scalable manner.  Existing mechanisms are known as non-secured 'Trust
   on First Use' (TOFU) [RFC7435], 'resurrecting duckling'
   [Stajano99theresurrecting] or 'pre-staging'.

   Another approach is to try and minimize user actions during
   bootstrapping.  The enrollment protocol EST [RFC7030] details a set
   of non-autonomic bootstrapping methods in this vein:

   o  using the Implicit Trust Anchor database (not an autonomic
      solution because the URL must be securely distributed),

   o  engaging a human user to authorize the CA certificate using out-
      of-band data (not an autonomic solution because the human user is

   o  using a configured Explicit TA database (not an autonomic solution
      because the distribution of an explicit TA database is not

   o  and using a Certificate-Less TLS mutual authentication method (not
      an autonomic solution because the distribution of symmetric key
      material is not autonomic).

   These "touch" methods do not meet the requirements for zero-touch.

   There are "call home" technologies where the Pledge first establishes
   a connection to a well known vendor service using a common client-
   server authentication model.  After mutual authentication appropriate
   credentials to authenticate the target domain are transfered to the
   Pledge.  This creates serveral problems and limitations:

   o  the pledge requires realtime connectivity to the vendor service,

   o  the domain identity is exposed to the vendor service (this is a
      privacy concern),

   o  the vendor is responsible for making the authorization decisions
      (this is a liability concern),

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   BRSKI addresses these issues by defining extensions to the EST
   protocol for the automated distribution of vouchers.

1.2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "OPTIONAL" in this document are to be interpreted as described in

   The following terms are defined for clarity:

   domainID:  The domain IDentity is the 160-bit SHA-1 hash of the BIT
      STRING of the subjectPublicKey of the root certificate for the
      registrars in the domain.  This is consistent with the subject key
      identifier (Section [RFC5280]).

   drop ship:  The physical distribution of equipment containing the
      "factory default" configuration to a final destination.  In zero-
      touch scenarios there is no staging or pre-configuration during

   imprint:  The process where a device obtains the cryptographic key
      material to identify and trust future interactions with a network.
      This term is taken from Konrad Lorenz's work in biology with new
      ducklings: during a critical period, the duckling would assume
      that anything that looks like a mother duck is in fact their
      mother.  An equivalent for a device is to obtain the fingerprint
      of the network's root certification authority certificate.  A
      device that imprints on an attacker suffers a similar fate to a
      duckling that imprints on a hungry wolf.  Securely imprinting is a
      primary focus of this document.[imprinting].  The analogy to
      Lorenz's work was first noted in [Stajano99theresurrecting].

   enrollment:  The process where a device presents key material to a
      network and acquires a network specific identity.  For example
      when a certificate signing request is presented to a certification
      authority and a certificate is obtained in response.

   Pledge:  The prospective device, which has an identity installed by a
      third-party (e.g., vendor, manufacturer or integrator).

   Voucher  A signed statement from the MASA service that indicates to a
      Pledge the cryptographic identity of the Registrar it should
      trust.  There are different types of vouchers depending on how
      that trust asserted.  Multiple voucher types are defined in

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   Domain:  The set of entities that trust a common key infrastructure
      trust anchor.  This includes the Proxy, Registrar, Domain
      Certificate Authority, Management components and any existing
      entity that is already a member of the domain.

   Domain CA:  The domain Certification Authority (CA) provides
      certification functionalities to the domain.  At a minimum it
      provides certification functionalities to a Registrar and stores
      the trust anchor that defines the domain.  Optionally, it
      certifies all elements.

   Join Registrar (and Coordinator):  A representative of the domain
      that is configured, perhaps autonomically, to decide whether a new
      device is allowed to join the domain.  The administrator of the
      domain interfaces with a Join Registrar (and Coordinator) to
      control this process.  Typically a Join Registrar is "inside" its
      domain.  For simplicity this document often refers to this as just
      "Registrar".  The term JRC is used in common with other bootstrap

   Join Proxy:  A domain entity that helps the pledge join the domain.
      A Proxy facilitates communication for devices that find themselves
      in an environment where they are not provided connectivity until
      after they are validated as members of the domain.  The pledge is
      unaware that they are communicating with a proxy rather than
      directly with a Registrar.

   MASA Service:  A third-party Manufacturer Authorized Signing
      Authority (MASA) service on the global Internet.  The MASA signs
      vouchers.  It also provides a repository for audit log information
      of privacy protected bootstrapping events.  It does not track

   Ownership Tracker:  An Ownership Tracker service on the global
      internet.  The Ownership Tracker uses business processes to
      accurately track ownership of all devices shipped against domains
      that have purchased them.  Although optional this component allows
      vendors to provide additional value in cases where their sales and
      distribution channels allow for accurately tracking of such
      ownership.  Ownership tracking information is indicated in
      vouchers as described in [I-D.ietf-anima-voucher]

   IDevID:  An Initial Device Identity X.509 certificate installed by
      the vendor on new equipment.

   TOFU:  Trust on First Use. Used similarly to [RFC7435].  This is
      where a Pledge device makes no security decisions but rather

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      simply trusts the first Registrar it is contacted by.  This is
      also known as the "resurrecting duckling" model.

1.3.  Scope of solution

   Questions have been posed as to whether this solution is suitable in
   general for Internet of Things (IoT) networks.  This depends on the
   capabilities of the devices in question.  The terminology of
   [RFC7228] is best used to describe the boundaries.

   The solution described in this document is aimed in general at non-
   constrained (i.e. class 2+) devices operating on a non-Challenged
   network.  The entire solution as described here is not intended to be
   useable as-is by constrained devices operating on challenged networks
   (such as 802.15.4 LLNs).

   In many target applications, the systems involved are large router
   platforms with multi-gigabit inter-connections, mounted in controlled
   access data centers.  But this solution is not exclusive to the
   large, it is intended to scale to thousands of devices located in
   hostile environments, such as ISP provided CPE devices which are
   drop-shipped to the end user.  The situation where an order is
   fulfilled from distributed warehouse from a common stock and shipped
   directly to the target location at the request of the domain owner is
   explicitly supported.  That stock ("SKU") could be provided to a
   number of potential domain owners, and the eventual domain owner will
   not know a-priori which device will go to which location.

   The bootstrapping process can take minutes to complete depending on
   the network infrastructure and device processing speed.  The network
   communication itself is not optimized for speed; for privacy reasons,
   the discovery process allows for the Pledge to avoid announcing it's
   presence through broadcasting.

   This protocol is not intended for low latency handoffs.  In networks
   requiring such things, the pledge SHOULD already have been enrolled.

   Specifically, there are protocol aspects described here which might
   result in congestion collapse or energy-exhaustion of intermediate
   battery powered routers in an LLN.  Those types of networks SHOULD
   NOT use this solution.  These limitations are predominately related
   to the large credential and key sizes required for device
   authentication.  Defining symmetric key techniques that meet the
   operational requirements is out-of-scope but the underlying protocol
   operations (TLS handshake and signing structures) have sufficient
   algorithm agility to support such techniques when defined.

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   The imprint protocol described here could, however, be used by non-
   energy constrained devices joining a non-constrained network (for
   instance, smart light bulbs are usually mains powered, and speak
   802.11).  It could also be used by non-constrained devices across a
   non-energy constrained, but challenged network (such as 802.15.4).
   The certificate contents, and the process by which the four questions
   above are resolved do apply to constrained devices.  It is simply the
   actual on-the-wire imprint protocol which could be inappropriate.

   This document presumes that network access control has either already
   occurred, is not required, or is integrated by the proxy and
   registrar in such a way that the device itself does not need to be
   aware of the details.  Although the use of an X.509 Initial Device
   Identity is consistant with IEEE 802.1AR [IDevID], and allows for
   alignment with 802.1X network access control methods, its use here is
   for Pledge authentication rather than network access control.
   Integrating this protocol with network access control, perhaps as an
   Extensible Authentication Protocol (EAP) method (see [RFC3748]), is

1.4.  Leveraging the new key infrastructure / next steps

   As a result of the protocol described herein the bootstrapped devices
   have a common trust anchor and a certificate has optionally been
   issued from a local PKI.  This makes it possible to automatically
   deploy services across the domain in a secure manner.

   Services which benefit from this:

   o  Device management.

   o  Routing authentication.

   o  Service discovery.

   The major beneficiary is that it possible to use the credentials
   deployed by this protocol to secure the Autonomic Control Plane (ACP)

2.  Architectural Overview

   The logical elements of the bootstrapping framework are described in
   this section.  Figure 1 provides a simplified overview of the
   components.  Each component is logical and may be combined with other
   components as necessary.

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      +--------------Drop Ship--------------->| Vendor Service         |
      |                                       +------------------------+
      |                                       | M anufacturer|         |
      |                                       | A uthorized  |Ownership|
      |                                       | S igning     |Tracker  |
      |                                       | A uthority   |         |
      |                                       +--------------+---------+
      |                                                      ^
      |                                                      |  BRSKI-
      V                                                      |   MASA
   +-------+     ............................................|...
   |       |     .                                           |  .
   |       |     .  +------------+       +-----------+       |  .
   |       |     .  |            |       |           |       |  .
   |Pledge |     .  |   Circuit  |       | Domain    <-------+  .
   |       |     .  |   Proxy    |       | Registrar |          .
   |       <-------->............<-------> (PKI RA)  |          .
   |       |        |        BRSKI-EST   |           |          .
   |       |     .  |            |       +-----+-----+          .
   |IDevID |     .  +------------+             | EST RFC7030    .
   |       |     .           +-----------------+----------+     .
   |       |     .           | Key Infrastructure         |     .
   |       |     .           | (e.g. PKI Certificate      |     .
   +-------+     .           |       Authority)           |     .
                 .           +----------------------------+     .
                 .                                              .
                               "Domain" components

   Figure 1

   We assume a multi-vendor network.  In such an environment there could
   be a Vendor Service for each vendor that supports devices following
   this document's specification, or an integrator could provide a
   generic service authorized by multiple vendors.  It is unlikely that
   an integrator could provide Ownership Tracking services for multiple
   vendors due to the required sales channel integrations necessary to
   track ownership.

   The domain is the managed network infrastructure with a Key
   Infrastructure the Pledge is joining.  The a domain provides initial
   device connectivity sufficient for bootstrapping with a Circuit
   Proxy.  The Domain Registrar authenticates the Pledge, makes
   authorization decisions, and distributes vouchers obtained from the
   Vendor Service.  Optionally the Registrar also acts as a PKI
   Registration Authority.

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2.1.  Behavior of a Pledge

   The pledge goes through a series of steps which are outlined here at
   a high level.

                |   Factory    |
                |   default    |
                |  Discover    |
   +------------>              |
   |            +------+-------+
   |                   |
   |            +------v-------+
   |            |  Identity    |
   ^------------+              |
   | rejected   +------+-------+
   |                   |
   |            +------v-------+
   |            | Request      |
   |            | Join         |
   |            +------+-------+
   |                   |
   |            +------v-------+
   |            |  Imprint     |   Optional
   ^------------+              <--+Manual input (Appendix C)
   | Bad Vendor +------+-------+
   | response          |  send Voucher Status Telemetry
   |            +------v-------+
   |            |  Enroll      |
   ^------------+              |
   | Enroll     +------+-------+
   | Failure           |
   |            +------v-------+
   |            |  Enrolled    |
   ^------------+              |
    Factory     +--------------+

   Figure 2

   State descriptions for the pledge are as follows:

   1.  Discover a communication channel to a Registrar.

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   2.  Identify itself.  This is done by presenting an X.509 IDevID
       credential to the discovered Registrar (via the Proxy) in a TLS
       handshake.  (The Registrar credentials are only provisionally
       accepted at this time).

   3.  Requests to Join the discovered Registrar.  A unique nonce can be
       included ensuring that any responses can be associated with this
       particular bootstrapping attempt.

   4.  Imprint on the Registrar.  This requires verification of the
       vendor service provided voucher.  A voucher contains sufficient
       information for the Pledge to complete authentication of a
       Registrar.  (It enables the Pledge to finish authentication of
       the Registrar TLS server certificate).

   5.  Enroll.  By accepting the domain specific information from a
       Registrar, and by obtaining a domain certificate from a Registrar
       using a standard enrollment protocol, e.g.  Enrollment over
       Secure Transport (EST) [RFC7030].

   6.  The Pledge is now a member of, and can be managed by, the domain
       and will only repeat the discovery aspects of bootstrapping if it
       is returned to factory default settings.

2.2.  Secure Imprinting using Vouchers

   A voucher is a cryptographically protected statement to the Pledge
   device authorizing a zero-touch imprint on the Registrar domain.

   The format and cryptographic mechanism of vouchers is described in
   detail in [I-D.ietf-anima-voucher].

   Vouchers provide a flexible mechanism to secure imprinting: the
   Pledge device only imprints when a voucher can be validated.  At the
   lowest security levels the MASA server can indiscriminately issue
   vouchers.  At the highest security levels issuance of vouchers can be
   integrated with complex sales channel integrations that are beyond
   the scope of this document.  This provides the flexibility for a
   number of use cases via a single common protocol mechanism on the
   Pledge and Registrar devices that are to be widely deployed in the
   field.  The MASA vendor services have the flexibility to leverage
   either the currently defined claim mechanisms or to experiment with
   higher or lower security levels.

   Vouchers provide a signed but non-encrypted communication channel
   between the Pledge, the MASA, and the Registrar.  The Registrar
   maintains control over the transport and policy decisions allowing
   the local security policy of the domain network to be enforced.

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2.3.  Initial Device Identifier

   Pledge authentication and Pledge voucher-request signing is via an
   X.509 certificate installed during the manufacturing process.  This
   Initial Device Identifier provides a basis for authenticating the
   Pledge during subsequent protocol exchanges and informing the
   Registrar of the MASA URI.  There is no requirement for a common root
   PKI hierarchy.  Each device vendor can generate their own root

   The following previously defined fields are in the X.509 IDevID

   o  The subject field's DN encoding MUST include the "serialNumber"
      attribute with the device's unique serial number.

   o  The subject-alt field's encoding SHOULD include a non-critical
      version of the RFC4108 defined HardwareModuleName.

   In order to build the voucher "serial-number" field these IDevID
   fields need to be converted into a serial-number of "type string".
   The following methods is used depending on the first available IDevID
   certificate field (attempted in this order):

   o  An RFC4514 String Representation of the Distinguished Name
      "serialNumber" attribute.

   o  The HardwareModuleName hwSerialNum OCTET STRING base64 encoded.

   o  The RFC4514 String Representation of the Distinguished Name
      "common name" attribute.

   The following newly defined field SHOULD be in the X.509 IDevID
   certificate: An X.509 non-critical certificate extension that
   contains a single Uniform Resource Identifier (URI) that points to an
   on-line Manufacturer Authorized Signing Authority.  The URI is
   represented as described in Section 7.4 of [RFC5280].

   Any Internationalized Resource Identifiers (IRIs) MUST be mapped to
   URIs as specified in Section 3.1 of [RFC3987] before they are placed
   in the certificate extension.  The URI provides the authority
   information.  The BRSKI .well-known tree is described in Section 5

   The new extension is identified as follows:

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   MASAURLExtnModule-2016 { iso(1) identified-organization(3) dod(6)
   internet(1) security(5) mechanisms(5) pkix(7)
   id-mod(0) id-mod-MASAURLExtn2016(TBD) }


   -- EXPORTS ALL --

   FROM PKIX-CommonTypes-2009
   { iso(1) identified-organization(3) dod(6) internet(1)
   security(5) mechanisms(5) pkix(7) id-mod(0)
   id-mod-pkixCommon-02(57) }

   FROM PKIX1Explicit-2009
   { iso(1) identified-organization(3) dod(6) internet(1)
   security(5) mechanisms(5) pkix(7) id-mod(0)
   id-mod-pkix1-explicit-02(51) } ;
   MASACertExtensions EXTENSION ::= { ext-MASAURL, ... }
   IDENTIFIED BY id-pe-masa-url }

   id-pe-masa-url OBJECT IDENTIFIER ::= { id-pe TBD }

   MASAURLSyntax ::= IA5String



   The choice of id-pe is based on guidance found in Section 4.2.2 of
   [RFC5280], "These extensions may be used to direct applications to
   on-line information about the issuer or the subject".  The MASA URL
   is precisely that: online information about the particular subject.

2.4.  Protocol Flow

   A representative flow is shown in Figure 3:

   +--------+         +---------+    +------------+     +------------+
   | Pledge |         | Circuit |    | Domain     |     | Vendor     |
   |        |         | Proxy   |    | Registrar  |     | Service    |
   |        |         |         |    |  (JRC)     |     | (MASA)     |
   +--------+         +---------+    +------------+     +------------+

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     |                     |                   |           Internet |
     |<-RFC4862 IPv6 addr  |                   |                    |
     |<-RFC3927 IPv4 addr  | Appendix A        |                    |
     |                     |                   |                    |
     |-------------------->|                   |                    |
     | optional: mDNS query| Appendix B        |                    |
     | RFC6763/RFC6762     |                   |                    |
     |                     |                   |                    |
     |<--------------------|                   |                    |
     | GRASP M_FLOOD       |                   |                    |
     |   periodic broadcast|                   |                    |
     |                     |                   |                    |
     |<------------------->C<----------------->|                    |
     |              TLS via the Circuit Proxy  |                    |
     |<--Registrar TLS server authentication---|                    |
   [PROVISIONAL accept of server cert]         |                    |
     P---X.509 client authentication---------->|                    |
     P                     |                   |                    |
     P---Voucher Request (include nonce)------>|                    |
     P                     |                   |                    |
     P                     |       /--->       |                    |
     P                     |       |      [accept device?]          |
     P                     |       |      [contact Vendor]          |
     P                     |       |           |--Pledge ID-------->|
     P                     |       |           |--Domain ID-------->|
     P                     |       |           |--optional:nonce--->|
     P                     |       |           |     [extract DomainID]
     P                     |       |           |                    |
     P                     |    optional:      |     [update audit log]
     P                     |       |can        |                    |
     P                     |       |occur      |                    |
     P                     |       |in         |                    |
     P                     |       |advance    |                    |
     P                     |       |if         |                    |
     P                     |       |nonceless  |                    |
     P                     |       |           |<- voucher ---------|
     P                     |       \---->      |                    |
     P                     |                   |                    |
     P<------voucher---------------------------|                    |
   [verify voucher ]       |                   |                    |
   [verify provisional cert|                   |                    |
     |                     |                   |                    |
     |---------------------------------------->|                    |
     |      [voucher status telemetry]         |<-device audit log--|
     |                     |       [verify audit log and voucher]   |
     |                     |                   |                    |
     |<--------------------------------------->|                    |
     | Continue with RFC7030 enrollment        |                    |

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     | using now bidirectionally authenticated |                    |
     | TLS session.        |                   |                    |
     |                     |                   |                    |

   Figure 3

2.4.1.  Architectural component: Pledge

   The Pledge is the device which is attempting to join.  Until the
   pledge completes the enrollment process, it does has network
   connectivity only to the Proxy.

2.4.2.  Architectural component: Circuit Proxy

   The (Circuit) Proxy provides HTTPS connectivity between the pledge
   and the registrar.  The proxy mechanism is described in Section 4,
   with an optional stateless mechanism described in Appendix C.

2.4.3.  Architectural component: Domain Registrar

   The Domain Registrar (having the formal name Join Registrar/
   Coordinator (JRC)), operates as a CMC Registrar, terminating the EST
   and BRSKI connections.  The Registrar is manually configured or
   distributed with a list of trust anchors necessary to authenticate
   any Pledge device expected on the network.  The Registrar
   communicates with the Vendor supplied MASA to establish ownership.

2.4.4.  Architectural component: Vendor Service

   The Vendor Service provides two logically seperate functions: the
   Manufacturer Authorized Signing Authority (MASA), and an ownership
   tracking/auditing function.

2.5.  Lack of realtime clock

   Many devices when bootstrapping do not have knowledge of the current
   time.  Mechanisms like Network Time Protocols can not be secured
   until bootstrapping is complete.  Therefore bootstrapping is defined
   in a method that does not require knowledge of the current time.

   Unfortunately there are moments during bootstrapping when
   certificates are verified, such as during the TLS handshake, where
   validity periods are confirmed.  This paradoxical "catch-22" is
   resolved by the Pledge maintaining a concept of the current "window"
   of presumed time validity that is continually refined throughout the
   bootstrapping process as follows:

   o  Initially the Pledge does not know the current time.

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   o  During Pledge authentiation by the Registrar a realtime clock can
      be used by the Registrar.  This bullet expands on a closely
      related issue regarding Pledge lifetimes.  RFC5280 indicates that
      long lived Pledge certifiates "SHOULD be assigned the
      GeneralizedTime value of 99991231235959Z" [RFC7030] so the
      Registrar MUST support such lifetimes and SHOULD support ignoring
      Pledge lifetimes if they did not follow the RFC5280

   o  The Pledge authenticates the voucher presented to it.  During this
      authentication the Pledge ignores certificate lifetimes (by
      necessity because it does not have a realtime clock).

   o  If the voucher contains a nonce then the Pledge MUST confirm the
      nonce matches the original Pledge voucher-request.  This ensures
      the voucher is fresh.  See / (Section 5.2).

   o  Once the voucher is accepted the validity period of the pinned-
      domain-cert in the voucher now serves as a valid time window.  Any
      subsequent certificate validity periods checked during RFC5280
      path validation MUST occur within this window.

   o  When accepting an enrollment certificate the validity period
      within the new certificate is assumed to be valid by the Pledge.
      The Pledge is now willing to use this credential for client

2.6.  Cloud Registrar

   The Pledge MAY contact a well known URI of a cloud Registrar if a
   local Registrar can not be discovered or if the Pledge's target use
   cases do not include a local Registrar.

   If the Pledge uses a well known URI for contacting a cloud Registrar
   an Implicit Trust Anchor database (see [RFC7030]) MUST be used to
   authenticate service as described in RFC6125.  This is consistent
   with the human user configuration of an EST server URI in [RFC7030]
   which also depends on RFC6125.

2.7.  Determining the MASA to contact

   The registrar needs to be able to contact a MASA that is trusted by
   the Pledge in order to obtain vouchers.  There are three mechanisms

   The device's Initial Device Identifier will normally contain the MASA
   URL as detailed in Section 2.3.  This is the RECOMMENDED mechanism.

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   If the Registrar is integrated with [I-D.ietf-opsawg-mud] and the
   Pledge IDevID contains the id-pe-mud-url then the Registrar MAY
   attempt to obtain the MASA URL from the MUD file.  The MUD file
   extension for the MASA URL is defined in Appendix D.

   It can be operationally difficult to ensure the necessary X.509
   extensions are in the Pledge's' IDevID due to the difficulty of
   aligning current Pledge manufacturing with software releases and
   development.  As a final fallback the Registrar MAY be manually
   configured or distributed with a MASA URL for each vendor.  Note that
   the Registrar can only select the configured MASA URL based on the
   trust anchor -- so vendors can only leverage this approach if they
   ensure a single MASA URL works for all Pledge's associated with each
   trust anchor.

3.  Voucher-Request artifact

   The Pledge voucher-request is how a Pledge requests a voucher.  The
   Pledge forms a voucher-request and submits it to the Registrar.  The
   Registrar in turn submits a voucher-request to the MASA server.  To
   help differentiate this document refers to "Pledge voucher-request"
   and "Registrar voucher-request" when indicating the source is
   beneficial.  The "proximity-registrar-cert" leaf is used in Pledge
   voucher-requests.  The "prior-signed-voucher-request" is used in
   Registrar voucher-requests that include a Pledge voucher-request.

   Unless otherwise signaled (outside the voucher-request artifact), the
   signing structure is as defined for vouchers, see

3.1.  Tree Diagram

   The following tree diagram illustrates a high-level view of a
   voucher-request document.  The notation used in this diagram is
   described in [I-D.ietf-anima-voucher].  Each node in the diagram is
   fully described by the YANG module in Section 3.3.  Please review the
   YANG module for a detailed description of the voucher-request format.

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   module: ietf-voucher-request

     grouping voucher-request-grouping
       +---- voucher
          +---- created-on?                      yang:date-and-time
          +---- expires-on?                      yang:date-and-time
          +---- assertion                        enumeration
          +---- serial-number                    string
          +---- idevid-issuer?                   binary
          +---- pinned-domain-cert?              binary
          +---- domain-cert-revocation-checks?   boolean
          +---- nonce?                           binary
          +---- last-renewal-date?               yang:date-and-time
          +---- prior-signed-voucher-request?    binary
          +---- proximity-registrar-cert?        binary

3.2.  Examples

   This section provides voucher examples for illustration purposes.
   That these examples conform to the encoding rules defined in

   Example (1)  The following example illustrates a Pledge voucher-
                request.  The assertion leaf is indicated as 'proximity'
                and the Registrar's TLS server certificate is included
                in the 'proximity-registrar-cert' leaf.  See
                Section 5.2.

       "ietf-voucher-request:voucher": {
           "nonce": "62a2e7693d82fcda2624de58fb6722e5",
           "created-on": "2017-01-01T00:00:00.000Z",
           "assertion": "proximity",
           "proximity-registrar-cert": "base64encodedvalue=="

   Example (2)  The following example illustrates a Registrar voucher-
                request.  The 'prior-signed-voucher-request' leaf is
                populated with the Pledge's voucher-request (such as the
                prior example).  See Section 5.4.

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       "ietf-voucher-request:voucher": {
           "nonce": "62a2e7693d82fcda2624de58fb6722e5",
           "created-on": "2017-01-01T00:00:02.000Z",
           "assertion": "proximity",
           "idevid-issuer": "base64encodedvalue=="
           "serial-number": "JADA123456789"
           "prior-signed-voucher": "base64encodedvalue=="

   Example (3)  The following example illustrates a Registrar voucher-
                request.  The 'prior-signed-voucher-request' leaf is not
                populated with the Pledge's voucher-request nor is the
                nonce leaf.  This form might be used by a Registrar
                requesting a voucher when the Pledge is offline or when
                the Registrar expects to be offline during deployment.
                See Section 5.4.

       "ietf-voucher-request:voucher": {
           "created-on": "2017-01-01T00:00:02.000Z",
           "assertion": "TBD",
           "idevid-issuer": "base64encodedvalue=="
           "serial-number": "JADA123456789"

   Example (4)  The following example illustrates a Registrar voucher-
                request.  The 'prior-signed-voucher-request' leaf is not
                populated with the Pledge voucher-request because the
                Pledge did not sign it's own request.  This form might
                be used when more constrained Pledges are being
                deployed.  The nonce is populated from the Pledge's
                request.  See Section 5.4.

       "ietf-voucher-request:voucher": {
           "nonce": "62a2e7693d82fcda2624de58fb6722e5",
           "created-on": "2017-01-01T00:00:02.000Z",
           "assertion": "proximity",
           "idevid-issuer": "base64encodedvalue=="
           "serial-number": "JADA123456789"

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3.3.  YANG Module

   Following is a YANG [RFC7950] module formally extending the
   [I-D.ietf-anima-voucher] voucher into a voucher-request.

<CODE BEGINS> file "ietf-voucher-request@2017-10-30.yang"
module ietf-voucher-request {
  yang-version 1.1;

  prefix "vch";

  import ietf-restconf {
    prefix rc;
      "This import statement is only present to access
       the yang-data extension defined in RFC 8040.";
    reference "RFC 8040: RESTCONF Protocol";

  import ietf-voucher {
    prefix v;
    reference "RFC ????: Voucher Profile for Bootstrapping Protocols";

   "IETF ANIMA Working Group";

   "WG Web:   <>
    WG List:  <>
    Author:   Kent Watsen
    Author:   Max Pritikin
    Author:   Michael Richardson
    Author:   Toerless Eckert

   "This module... FIXME

    The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL NOT',

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    the module text are to be interpreted as described in RFC 2119.

    Copyright (c) 2017 IETF Trust and the persons identified as
    authors of the code. All rights reserved.

    Redistribution and use in source and binary forms, with or without
    modification, is permitted pursuant to, and subject to the license
    terms contained in, the Simplified BSD License set forth in Section
    4.c of the IETF Trust's Legal Provisions Relating to IETF Documents

    This version of this YANG module is part of RFC XXXX; see the RFC
    itself for full legal notices.";

  revision "2017-10-30" {
     "Initial version";
     "RFC XXXX: Voucher Profile for Bootstrapping Protocols";

  // Top-level statement
  rc:yang-data voucher-request-artifact {
    uses voucher-request-grouping;

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

    uses v:voucher-artifact-grouping {
      refine "voucher/created-on" {
        mandatory false;

      refine "voucher/pinned-domain-cert" {
        mandatory false;

      augment "voucher"  {
          "Adds leaf nodes appropriate for requesting vouchers.";

        leaf prior-signed-voucher-request {
          type binary;
            "If it is necessary to change a voucher, or re-sign and

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             forward a voucher that was previously provided along a
             protocol path, then the previously signed voucher SHOULD be
             included in this field.

             For example, a pledge might sign a proximity voucher, which
             an intermediate registrar then re-signs to make its own
             proximity assertion.  This is a simple mechanism for a
             chain of trusted parties to change a voucher, while
             maintaining the prior signature information.

             The pledge MUST ignore all prior voucher information when
             accepting a voucher for imprinting. Other parties MAY
             examine the prior signed voucher information for the
             purposes of policy decisions. For example this information
             could be useful to a MASA to determine that both pledge and
             registrar agree on proximity assertions. The MASA SHOULD
             remove all prior-signed-voucher information when signing
             a voucher for imprinting so as to minimize the final
             voucher size.";

        leaf proximity-registrar-cert {
          type binary;
            "An X.509 v3 certificate structure as specified by RFC 5280,
             Section 4 encoded using the ASN.1 distinguished encoding
             rules (DER), as specified in ITU-T X.690.

             The first certificate in the Registrar TLS server
             certificate_list sequence  (see [RFC5246]) presented by
             the Registrar to the Pledge. This MUST be populated in a
             Pledge's voucher request if the proximity assertion is



4.  Proxy details

   The role of the Proxy is to facilitate communications.  The Proxy
   forwards packets between the Pledge and a Registrar that has been
   configured on the Proxy.

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   The Proxy does not terminate the TLS handshake: it passes streams of
   bytes onward without examination.

   A proxy MAY assume TLS framing for auditing purposes, but MUST NOT
   assume any TLS version.

   A Proxy is always assumed even if it is directly integrated into a
   Registrar.  (In a completely autonomic network, the Registrar MUST
   provide proxy functionality so that it can be discovered, and the
   network can grow concentrically around the Registrar)

   As a result of the Proxy Discovery process in section Section 4.1.1,
   the port number exposed by the proxy does not need to be well known,
   or require an IANA allocation.

   If the Proxy joins an Autonomic Control Plane
   ([I-D.ietf-anima-autonomic-control-plane]) it SHOULD use Autonomic
   Control Plane secured GRASP ([I-D.ietf-anima-grasp]) to discovery the
   Registrar address and port.  As part of the discovery process, the
   proxy mechanism (Circuit Proxy vs IPIP encapsulation) is agreed to
   between the Registrar and Join Proxy.

   For the IPIP encapsulation methods (described in Appendix C), the
   port announced by the Proxy SHOULD be the same as on the registrar in
   order for the proxy to remain stateless.

   In order to permit the proxy functionality to be implemented on the
   maximum variety of devices the chosen mechanism SHOULD use the
   minimum amount of state on the proxy device.  While many devices in
   the ANIMA target space will be rather large routers, the proxy
   function is likely to be implemented in the control plane CPU of such
   a device, with available capabilities for the proxy function similar
   to many class 2 IoT devices.

   The document [I-D.richardson-anima-state-for-joinrouter] provides a
   more extensive analysis and background of the alternative proxy

4.1.  Pledge discovery of Proxy

   The result of discovery is a logical communication with a Registrar,
   through a Proxy.  The Proxy is transparent to the Pledge but is
   always assumed to exist.

   To discover the Proxy the Pledge performs the following actions:

   1.  MUST: Obtains a local address using IPv6 methods as described in
       [RFC4862] IPv6 Stateless Address AutoConfiguration.  Use of

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       [RFC4941] temporary addresses is encouraged.  A new temporary
       address SHOULD be allocated whenever the discovery process is
       forced to restart due to failures.  Pledges will generally prefer
       use of IPv6 Link-Local addresses, and discovery of Proxy will be
       by Link-Local mechanisms.  IPv4 methods are described in
       Appendix A

   2.  MUST: Listen for GRASP M_FLOOD ([I-D.ietf-anima-grasp])
       announcements of the objective: "AN_Proxy".  See section
       Section 4.1.1 for the details of the objective.  The Pledge may
       listen concurrently for other sources of information, see
       Appendix B.

   Once a proxy is discovered the Pledge communicates with a Registrar
   through the proxy using the bootstrapping protocol defined in
   Section 5.

   Each discovery method attempted SHOULD exponentially back-off
   attempts (to a maximum of one hour) to avoid overloading the network
   infrastructure with discovery.  The back-off timer for each method
   MUST be independent of other methods.

   Methods SHOULD be run in parallel to avoid head of queue problems
   wherein an attacker running a fake proxy or registrar can operate
   protocol actions intentionally slowly.

   Once a connection to a Registrar is established (e.g. establishment
   of a TLS session key) there are expectations of more timely
   responses, see Section 5.2.

   Once all discovered services are attempted the device SHOULD return
   to listening for GRASP M_FLOOD.  It should periodically retry the
   vendor specific mechanisms.  The Pledge MAY prioritize selection
   order as appropriate for the anticipated environment.

4.1.1.  Proxy Grasp announcements

   A proxy uses the GRASP M_FLOOD mechanism to announce itself.  The
   pledge SHOULD listen for messages of these form.  This announcement
   can be within the same message as the ACP announcement detailed in

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    proxy-objective = ["AN_Proxy", [ O_IPv6_LOCATOR, ipv6-address,
    transport-proto, port-number ] ]

    ipv6-address       - the v6 LL of the proxy
    transport-proto    - 6, for TCP 17 for UDP
    port-number        - the TCP or UDP port number to find the proxy

   Figure 5

4.2.  CoAP connection to Registrar

   The use of CoAP to connect from Pledge to Registrar is out of scope
   for this document, and may be described in future work.

4.3.  HTTPS proxy connection to Registrar

   The proxy SHOULD also provide one of: an IPIP encapsulation of HTTP
   traffic to the registrar, or a TCP circuit proxy that connects the
   Pledge to a Registrar.

   When the Proxy provides a circuit proxy to a Registrar the Registrar
   MUST accept HTTPS connections.

4.4.  Proxy discovery of Registrar

   The Registrar SHOULD announce itself so that proxies can find it and
   determine what kind of connections can be terminated.

   The registrar announces itself using GRASP M_FLOOD messages.  The
   M_FLOOD is formatted as follows:

   [M_FLOOD, 12340815, h'fda379a6f6ee0000200000064000001', 180000,
               ["AN_join_registrar", 4, 255, "EST-TLS"],
                    h'fda379a6f6ee0000200000064000001', TCP, 80

   Figure 6: Registrar Discovery

   The formal CDDL definition is:

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   flood-message = [M_FLOOD, session-id, initiator, ttl,
                    +[objective, (locator-option / [])]]

   objective = ["AN_join_registrar", objective-flags, loop-count,

   initiator = ACP address to contact Registrar
   objective-flags = sync-only  ; as in GRASP spec
   sync-only =  4               ; M_FLOOD only requires synchronization
   loop-count      = 255        ; mandatory maximum
   objective-value = text       ; name of the (list of) of supported
                                ; protocols: "EST-TLS" for RFC7030.

   Figure 7: AN_join_registrar CDDL

   The M_FLOOD message MUST be sent periodically.  The period is subject
   to network administrator policy (EST server configuration).  It must
   be so low that the aggregate amount of periodic M_FLOODs from all EST
   servers causes negligible traffic across the ACP.

   The locators are to be interpreted as follows:

   locator1  = [O_IPv6_LOCATOR, fd45:1345::6789, 6,  443]
   locator2  = [O_IPv6_LOCATOR, fd45:1345::6789, 17, 5683]
   locator3  = [O_IPv6_LOCATOR, fe80::1234, 41, nil]

   Figure 7: Registrar Response

   The set of locators is to be interpreted as follows.  A protocol of 6
   indicates that TCP proxying on the indicated port is desired.  A
   protocol of 17 indicates that UDP proxying on the indicated port is
   desired.  In each case, the traffic SHOULD be proxied to the same
   port at the ULA address provided.

   A protocol of 41 indicates that packets may be IPIP proxy'ed.  In the
   case of that IPIP proxying is used, then the provided link-local
   address MUST be advertised on the local link using proxy neighbour
   discovery.  The Join Proxy MAY limit forwarded traffic to the
   protocol (6 and 17) and port numbers indicated by locator1 and
   locator2.  The address to which the IPIP traffic should be sent is
   the initiator address (an ACP address of the Registrar), not the
   address given in the locator.

   Registrars MUST accept TCP / UDP traffic on the ports given at the
   ACP address of the Registrar.  If the Registrar supports IPIP
   ntunnelling, it MUST also accept traffic encapsulated with IPIP.

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   Registrars MUST accept HTTPS/EST traffic on the TCP ports indicated.
   Registrars MAY accept DTLS/CoAP/EST traffic on the UDP in addition to
   TCP traffic.

5.  Protocol Details

   The Pledge MUST initiate BRSKI after boot if it is unconfigured.  The
   Pledge MUST NOT automatically initiate BRSKI if it has been
   configured or is in the process of being configured.

   BRSKI is described as extensions to EST [RFC7030] to reduce the
   number of TLS connections and crypto operations required on the
   Pledge.  The Registrar implements the BRSKI REST interface within the
   same .well-known URI tree as the existing EST URIs as described in
   EST [RFC7030] section 3.2.2.  The communication channel between the
   Pledge and the Registrar is referred to as "BRSKI-EST" (see
   Figure 1).

   The communication channel between the Registrar and MASA is similarly
   described as extensions to EST within the same ./well-known tree.
   For clarity this channel is referred to as "BRSKI-MASA".  (See
   Figure 1).

   MASA URI is "https:// authority "./well-known/est".

   BRSKI uses EST message formats for existing operations, uses JSON
   [RFC7159] for all new operations defined here, and voucher formats.

   While EST section 3.2 does not insist upon use of HTTP 1.1 persistent
   connections, BRSKI-EST connections SHOULD use persistent connections.
   The intention of this guidance is to ensure the provisional TLS
   authentication occurs only once and is properly managed.

   Summarized automation extensions for the BRSKI-EST flow are:

   o  The Pledge provisionally accepts the Registrar certificate during
      the TLS handshake as detailed in Section 5.1.

   o  If the Registrar responds with a redirection to other web origins
      the Pledge MUST follow only a single redirection.  (EST supports
      redirection but does not allow redirections to other web origins
      without user input).

   o  The Registar MAY respond with an HTTP 202 ("the request has been
      accepted for processing, but the processing has not been
      completed") as described in EST [RFC7030] section 4.2.3 wherein
      the client "MUST wait at least the specified 'retry-after' time
      before repeating the same request".  The Pledge is RECOMMENDED to

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      provide local feed (blinked LED etc) during this wait cycle if
      mechanisms for this are available.  To prevent an attacker
      Registrar from significantly delaying bootstrapping the Pledge
      MUST limit the 'retry-after' time to 60 seconds.  To avoid
      blocking on a single erroneous Registrar the Pledge MUST drop the
      connection after 5 seconds in which there has been no progress on
      the TCP connection.  It should proceed to other discovered
      Registrars if there are any.  If there were no other Registrars
      discovered, the pledge MAY continue to wait, as long as it is
      concurrently listening for new proxy announcements.

   o  Ideally the Pledge could keep track of the appropriate retry-after
      value for any number of outstanding Registrars but this would
      involve a large state table on the Pledge.  Instead the pledge MAY
      ignore the exact retry-after value in favor of a single hard coded
      value that takes effect between discovery ([[ProxyDiscovery]])
      attempts.  A Registrar that is unable to complete the transaction
      the first time due to timing reasons will have future chances.

   o  The Pledge requests and validates a voucher using the new REST
      calls described below.

   o  If necessary the Pledge calls the EST defined /cacerts method to
      obtain the domain owners' CA certificate.  The pinned-domain-
      certificate element from the voucher should validate this
      certificate, or be identical to it.

   o  The Pledge completes authentication of the server certificate as
      detailed in Section 5.5.1.  This moves the BRSKI-EST TLS
      connection out of the provisional state.  Optionally, the BRSKI-
      EST TLS connection can now be used for EST enrollment.

   The extensions for a Registrar (equivalent to EST server) are:

   o  Client authentication is automated using Initial Device Identity
      (IDevID) as per the EST certificate based client authentication.
      The subject field's DN encoding MUST include the "serialNumber"
      attribute with the device's unique serial number.  In the language
      of RFC6125 this provides for a SERIALNUM-ID category of identifier
      that can be included in a certificate and therefore that can also
      be used for matching purposes.  The SERIALNUM-ID whitelist is
      collated according to vendor trust anchor since serial numbers are
      not globally unique.

   o  The Registrar requests and validates the Voucher from the vendor
      authorized MASA service.

   o  The Registrar forwards the Voucher to the Pledge when requested.

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   o  The Registar performs log verifications in addition to local
      authorization checks before accepting optional Pledge device
      enrollment requests.

5.1.  BRSKI-EST TLS establishment details

   The Pledge establishes the TLS connection with the Registrar through
   the circuit proxy (see Section 4) but the TLS handshake is with the
   Registar.  The BRSKI-EST Pledge is the TLS client and the BRSKI-EST
   Registrar is the TLS server.  All security associations established
   are between the Pledge and the Registrar regardless of proxy

   Establishment of the BRSKI-EST TLS connection is as specified in EST
   [RFC7030] section 4.1.1 "Bootstrap Distribution of CA Certificates"
   [RFC7030] wherein the client is authenticated with the IDevID
   certificate, and the EST server (the Registrar) is provisionally
   authenticated with a unverified server certificate.

   The Pledge maintains a security paranoia concerning the provisional
   state, and all data received, until a voucher is received and
   verified as specified in Section 5.5.1

5.2.  Pledge Requests Voucher from the Registrar

   When the Pledge bootstraps it makes a request for a Voucher from a

   This is done with an HTTPS POST using the operation path value of

   The request media types are:

   application/pkcs7-mime; smime-type=voucher-request  The request is a
      "YANG-defined JSON document that has been signed using a PKCS#7
      structure" as described in Section 3 using the JSON encoding
      described in [RFC7951].  The Pledge SHOULD sign the request using
      the Section 2.3 credential.

   application/json  The request is the "YANG-defined JSON document" as
      described in Section 3 with exception that it is not within a
      PKCS#7 structure.  It is protected only by the TLS client
      authentication.  This reduces the cryptographic requirements on
      the Pledge.

   For simplicity the term 'voucher-request' is used to refer to either
   of these media types.  Registrar impementations SHOULD anticipate

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   future media types but of course will simply fail the request if
   those types are not yet known.

   The Pledge populates the voucher-request fields as follows:

   created-on:  Pledges that have a realtime clock are RECOMMENDED to
      populate this field.  This provides additional information to the

   nonce:  The Pledge voucher-request MUST contain a cryptographically
      strong random or pseudo-random number nonce.  Doing so ensures
      Section 2.5 functionality.  The nonce MUST NOT be reused for
      bootstrapping attempts.

   assertion:  The Pledge voucher-request MAY contain an assertion of

   proximity-registrar-cert:  In a Pledge voucher-request this is the
      first certificate in the TLS server 'certificate_list' sequence
      (see [RFC5246]) presented by the Registrar to the Pledge.  This
      MUST be populated in a Pledge voucher-request if the "proximity"
      assertion is populated.

   All other fields MAY be omitted in the Pledge voucher-request.

   An example JSON payload of a Pledge voucher-request is in Section 3.2
   Example 1.

   The Registrar validates the client identity as described in EST
   [RFC7030] section 3.3.2.  If the request is signed the Registrar
   confirms the 'proximity' asserion and associated 'proximity-
   registrar-cert' are correct.  The registrar performs authorization as
   detailed in [[EDNOTE: UNRESOLVED.  See Appendix D "Pledge
   Authorization"]].  If these validations fail the Registrar SHOULD
   respond with an appropriate HTTP error code.

   If authorization is successful the Registrar obtains a voucher from
   the MASA service (see Section 5.4) and returns that MASA signed
   voucher to the pledge as described in Section 5.5.

5.3.  BRSKI-MASA TLS establishment details

   The BRSKI-MASA TLS connection is a 'normal' TLS connection
   appropriate for HTTPS REST interfaces.  The Registrar initiates the
   connection and uses the MASA URL obtained as described in Section 2.7
   for RFC6125 authentication of the MASA server.

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   The primary method of Registrar "authentication" by the MASA is
   detailed in Section 5.4.  As detailed in Section 8 the MASA might
   find it necessary to request additional Registrar authentication.
   Registrars MUST be prepared to support TLS client certificate
   authentication and HTTP Basic or Digest authentication as described
   in RFC7030 for EST clients.  Implementors are advised that contacting
   the MASA is to establish a secured REST connection with a web service
   and that there are a number of authentication models being explored
   within the industry.  Registrars are RECOMMENDED to fail gracefully
   and generate useful administrative notifications or logs in the
   advent of unexpected HTTP 401 (Unauthorized) responses from the MASA.

5.4.  Registrar Requests Voucher from MASA

   When a Registrar receives a Pledge voucher-request it in turn submits
   a Registrar voucher-request to the MASA service.  For simplicity this
   is defined as an optional EST message between a Registrar and an EST
   server running on the MASA service although the Registrar is not
   required to make use of any other EST functionality when
   communicating with the MASA service.  (The MASA service MUST properly
   reject any EST functionality requests it does not wish to service; a
   requirement that holds for any REST interface).

   This is done with an HTTP POST using the operation path value of

   The request media type is:

   application/pkcs7-mime; smime-type=voucher-request  The voucher-
      request is a "YANG-defined JSON document that has been signed
      using a PKCS#7 structure" as described in [I-D.ietf-anima-voucher]
      using the JSON encoding described in [RFC7951].  The Registrar
      MUST sign the Registrar voucher-request.  The entire Registrar
      certificate chain, up to and including the Domain CA, MUST be
      included in the PKCS#7 structure.

   MASA impementations SHOULD anticipate future media types but of
   course will simply fail the request if those types are not yet known.

   The Registrar populates the voucher-request fields as follows:

   created-on:  Registrars are RECOMMENDED to populate this field.  This
      provides additional information to the MASA.

   nonce:  The optional nonce value from the Pledge request if desired
      (see below).

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   serial-number:  The serial number of the Pledge the Registrar would
      like a voucher for.

   idevid-issuer:  The idevid-issuer value from the pledge certificate
      is included to ensure a statistically unique identity.  The
      Pledge's serial number is extracted from the X.509 IDevID.  See
      Section 2.3.

   prior-signed-voucher:  If a signed Pledge voucher-request was
      received then it SHOULD be included in the Registrar voucher-
      request.  (NOTE: what is included is the complete Pledge voucher-
      request, inclusive of the 'assertion', 'proximity-registrar-cert',
      etc wrapped by the pledge's original signature).

   A nonceless Registrar voucher-request MAY be submitted to the MASA.
   Doing so allows the Registrar to request a Voucher when the Pledge is
   offline, or when the Registrar is expected to be offline when the
   Pledge is being deployed.  These use cases require the Registrar to
   learn the appropriate IDevID SerialNumber field from the physical
   device labeling or from the sales channel (out-of-scope of this
   document).  If a nonceless voucher-reqeust is submitted the MASA
   server MUST authenticate the Registrar as described in either EST
   [RFC7030] section 3.2, section 3.3, or by validating the Registrar's
   certificate used to sign the Registrar voucher-request.  Any of these
   methods reduce the risk of DDoS attacks and provide an authenticated
   identity as an input to sales channel integration and authorizations
   (the actual sale-channel integration is also out-of-scope of this

   All other fields MAY be omitted in the Registrar voucher-request.

   Example JSON payloads of Registrar voucher-requests are in
   Section 3.2 Example 2 through 4.

   The MASA verifies that the Registrar voucher-request is internally
   consistent but does not necessarily authenticate the Registrar
   certificate since the registrar is not know to the MASA server in
   advance.  The MASA validation checks before issuing a voucher are as

   Renew for expired voucher:  As described in [I-D.ietf-anima-voucher]
      vouchers are normally short lived to avoid revocation issues.  If
      the request is for a previous (expired) voucher using the same
      Registrar (as determined by the Registrar pinned-domain-cert) and
      the MASA has not been informed that the claim is invalid then the
      request for a renewed voucher SHOULD be automatically authorized.

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   Voucher signature consistency:  The MASA MUST verify that the
      Registrar voucher-request is signed by a Registrar.  This is
      confirmed by verifying that the id-kp-cmcRA extended key usage
      extension field (as detailed in EST RFC7030 section 3.6.1) exists
      in the certificate of the entity that signed the Registrar
      voucher-request.  This verification is only a consistency check
      that the unauthenticated domain CA intended this to be a
      Registrar.  Performing this check provides value to domain PKI by
      assuring the domain administrator that the MASA service will only
      respect claims from authorized Registration Authorities of the
      domain.  (The requirement for the Registrar to include the Domain
      CA certificate in the signature structure was stated above).

   Registrar revocation consistency:  The MASA SHOULD check for
      revocation of the Registrar certificate.  The maximum lifetime of
      the voucher issued SHOULD NOT exceed the lifetime of the
      Registrar's revocation validation (for example if the Registrar
      revocation status is indicated in a CRL that is valid for two
      weeks then that is an appropriate lifetime for the voucher).
      Because the Registar certificate authority is unknown to the MASA
      in advance this is only an extended consistency check and is not
      required.  The maximum lifetime of the voucher issued SHOULD NOT
      exceed the lifetime of the Registrar's revocation validation (for
      example if the Registrar revocation status is indicated in a CRL
      that is valid for two weeks then that is an appropriate lifetime
      for the voucher).

   Pledge proximity assertion:  The MASA server MAY verify that the
      Registrar voucher-request includes the 'prior-signed-voucher'
      field populated with a Pledge voucher-request that includes a
      'proximity-registrar-cert' that is consistent with the certificate
      used to sign the Registrar voucher-request.  The MASA server is
      aware of which Pledge's support signing of their voucher requests
      and can use this information to confirm proximity of the Pledge
      with the Registrar.

   Registar (certificate) authentication:  This only occurs if the
      Registrar voucher-request is nonceless.  As noted above the
      details concerning necessary sales-channel integration for the
      MASA to authenticate a Registrar certificate is out-of-scope.

   The Registrar's certificate chain is extracted from the signature
   method and the root certificate is used to populate the "pinned-
   domain-cert" of the Voucher being issued.  The domainID (e.g. hash of
   the root public key) is determined from the pinned-domain-cert and is
   used to update the audit log.

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5.5.  Voucher Response

   The voucher response to requests from the Pledge and requests from a
   Registrar are in the same format.  A Registrar either caches prior
   MASA responses or dynamically requests a new Voucher based on local

   If the join operation is successful, the server response MUST contain
   an HTTP 200 response code.  The server MUST answer with a suitable
   4xx or 5xx HTTP [RFC2616] error code when a problem occurs.  The
   response data from the MASA server MUST be a plaintext human-readable
   (ASCII, english) error message containing explanatory information
   describing why the request was rejected.

   A 403 (Forbidden) response is appropriate if the voucher-request is
   not signed correctly, stale, or if the pledge has another outstanding
   voucher which can not be overridden.

   A 404 (Not Found) response is appropriate when the request is for a
   device which is not known to the MASA.

   A 406 (Not Acceptable) response is appropriate if a voucher of the
   desired type, or using the desired algorithms (as indicated by the
   Accept: headers, and algorithms used in the signature) can not be
   issued, such as because the MASA knows the pledge can not process
   that type.

   A 415 (Unsupported Media Type) response is approriate for a request
   that has a voucher encoding that is not understood.

   The response media type is:

   application/pkcs7-mime; smime-type=voucher  The response is a "YANG-
      defined JSON document that has been signed using a PKCS#7
      structure" as described in [I-D.ietf-anima-voucher] using the JSON
      encoded described in [RFC7951].  The MASA MUST sign the request.

   The syntactic details of vouchers are described in detail in
   [I-D.ietf-anima-voucher].  For example, the voucher consists of:

     "ietf-voucher:voucher": {
       "nonce": "62a2e7693d82fcda2624de58fb6722e5",
       "assertion": "logging"
       "pinned-domain-cert": "base64encodedvalue=="
       "serial-number": "JADA123456789"

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   The Pledge verifies the signed voucher using the manufacturer
   installed trust anchor associated with the vendor's selected
   Manufacturer Authorized Signing Authority.

   The 'pinned-domain-cert' element of the voucher contains the domain
   CA's public key.  The Pledge MUST use the 'pinned-domain-cert' trust
   anchor to immediately complete authentication of the provisional TLS

   The Pledge MUST be prepared to parse and fail gracefully from a
   Voucher response that does not contain a 'pinned-domain-cert' field.
   The Pledge MUST be prepared to ignore additional fields it does not

5.5.1.  Completing authentication of Provisional TLS connection

   If a Registrar's credentials can not be verified using the pinned-
   domain-cert trust anchor from the voucher then the TLS connection is
   immediately discarded and the Pledge abandons attempts to bootstrap
   with this discovered registrar.  The pledge SHOULD send voucher
   status telemetry (described below) before closing the TLS connection.
   The pledge MUST attempt to enroll using any other proxies it has
   found.  It SHOULD return to the same proxy again after attempting
   with other proxies.  Attempts should be attempted in the exponential
   backoff described earlier.  Attempts SHOULD be repeated as failure
   may be the result of a temporary inconsistently (an inconsistently
   rolled Registrar key, or some other mis-configuration).  The
   inconsistently could also be the result an active MITM attack on the
   EST connection.

   The Registrar MUST use a certificate that chains to the pinned-
   domain-cert as its TLS server certificate.

   The Pledge's PKIX path validation of a Registrar certificate's
   validity period information is as described in Section 2.5.  Once the
   PKIX path validation is successful the TLS connection is no longer

   The pinned-domain-cert is installed as an Explicit Trust Anchor for
   future operations.  It can therefore can be used to authenticate any
   dynamically discovered EST server that contain the id-kp-cmcRA
   extended key usage extension as detailed in EST RFC7030 section
   3.6.1; but to reduce system complexity the Pledge SHOULD avoid
   additional discovery operations.  Instead the Pledge SHOULD
   communicate directly with the Registrar as the EST server.  The '
   pinned-domain-cert' is not a complete distribution of the EST section
   4.1.3 CA Certificate Response which is an additional justification
   for the recommendation to proceed with EST key management operations.

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   Once a full CA Certificate Response is obtained it is more
   authoritative for the domain than the limited 'pinned-domain-cert'

5.6.  Voucher Status Telemetry

   The domain is expected to provide indications to the system
   administrators concerning device lifecycle status.  To facilitate
   this it needs telemetry information concerning the device's status.

   To indicate Pledge status regarding the Voucher, the pledge MUST post
   a status message.

   The posted data media type: application/json

   The client HTTP POSTs the following to the server at the EST well
   known URI /voucher_status.  The Status field indicates if the Voucher
   was acceptable.  If it was not acceptable the Reason string indicates
   why.  In the failure case this message is being sent to an
   unauthenticated, potentially malicious Registrar and therefore the
   Reason string SHOULD NOT provide information beneficial to an
   attacker.  The operational benefit of this telemetry information is
   balanced against the operational costs of not recording that an
   Voucher was ignored by a client the registar expected to continue
   joining the domain.

     "Status":FALSE /* TRUE=Success, FALSE=Fail"
     "Reason":"Informative human readable message"
     "reason-context": { additional JSON }

   The server SHOULD respond with an HTTP 200 but MAY simply fail with
   an HTTP 404 error.  The client ignores any response.  Within the
   server logs the server SHOULD capture this telemetry information.

   The reason-context attribute is an arbitrary JSON object (literal
   value or hash of values) which provides additional information
   specific to this pledge.  The contents of this field are not subject
   to standardization."

   Additional standard responses MAY be added via Specification

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5.7.  MASA authorization log Request

   After receiving the voucher status telemetry Section 5.6, the
   Registrar SHOULD request the MASA authorization log from the MASA
   service using this EST extension.  If a device had previously
   registered with another domain, a Registrar of that domain would show
   in the log.

   This is done with an HTTP GET using the operation path value of

   The Registrar MUST HTTP POSTs the same Registrar voucher-request as
   it did when requesting a Voucher.  It is posted to the
   /requestauditlog URI instead.  The "idevid-issuer" and "serial-
   number" informs the MASA server which log is requested so the
   appropriate log can be prepared for the response.  Using the same
   media type and message minimizes cryptographic and message operations
   although it results in additional network traffic.  The relying MASA
   server implementation MAY leverage internal state to associate this
   request with the original, and by now already validated, Registrar
   voucher-request so as to avoid an extra crypto validation.

   A MASA which receives a request for a device which does not exist, or
   for which the requesting owner was never an owner returns an HTTP 404
   ("Not found") code.

   Rather than returning the audit log as a response to the POST (with a
   return code 200), the MASA MAY instead return a 201 ("Created")
   RESTful response ([RFC7231] section 7.1) containing a URL to the
   prepared (and easily cachable) audit response.

   MASA servers that return URLs SHOULD take care to make the returned
   URL unguessable.  URLs containing a database number such as or the EUI of the device such, would be easily
   enumerable by an attacker.  It is recommended put to put some
   meaningless randomly generated slug that indexes a database instead.

   A MASA that returns a code 200 MAY also include a Location: header
   for future reference by the Registrar.

   The request media type is:

   application/pkcs7-mime; smime-type=voucher-request  The request is a
      "YANG-defined JSON document that has been signed using a PKCS#7
      structure" as described in Section 3 using the JSON encoded
      described in [RFC7951].  The Registrar MUST sign the request.  The

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      entire Registrar certificate chain, up to and including the Domain
      CA, MUST be included in the PKCS#7 structure.

5.7.1.  MASA authorization log Response

   A log data file is returned consisting of all log entries.  For

        "date":"<date/time of the entry>",
        "domainID":"<domainID extracted from voucher-request>",
        "nonce":"<any nonce if supplied (or the exact string 'NULL')>"
        "date":"<date/time of the entry>",
        "domainID":"<domainID extracted from voucher-request>",
        "nonce":"<any nonce if supplied (or the exact string 'NULL')>"

   Distribution of a large log is less than ideal.  This structure can
   be optimized as follows: All nonceless entries for the same domainID
   MAY be condensed into the single most recent nonceless entry.

   A Registrar SHOULD use this log information to make an informed
   decision regarding the continued bootstrapping of the Pledge.  For
   example if the log includes an unexpected domainID then the Pledge
   could have imprinted on an unexpected domain.  If the log includes
   nonceless entries then any registrar in the same domain could
   theoretically trigger a reset of the device and take over management
   of the Pledge.  Equipment that is purchased pre-owned can be expected
   to have an extensive history.  A Registrar MAY request logs at future
   times.  A Registrar MAY be configured to ignore the history of the
   device but it is RECOMMENDED that this only be configured if hardware
   assisted NEA [RFC5209] is supported.

   Log entries can be compared against local history logs in search of

   This document specifies a simple log format as provided by the MASA
   service to the registar.  This format could be improved by
   distributed consensus technologies that integrate vouchers with a
   technologies such as block-chain or hash trees or the like.  Doing so
   is out of the scope of this document but are anticipated improvements

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   for future work.  As such, the Registrar client SHOULD anticipate new
   kinds of responses, and SHOULD provide operator controls to indicate
   how to process unknown responses.

5.8.  EST Integration for PKI bootstrapping

   The Pledge SHOULD follow the BRSKI operations with EST enrollment
   operations including "CA Certificates Request", "CSR Attributes" and
   "Client Certificate Request" or "Server-Side Key Generation" etc.
   This is a relatively seamless integration since BRSKI REST calls
   provide an automated alternative to the manual bootstrapping method
   described in [RFC7030].  As noted above, use of HTTP 1.1 persistent
   connections simplifies the Pledge state machine.

   The Pledge is also RECOMMENDED to implement the following EST
   automation extensions.  They supplement the RFC7030 EST to better
   support automated devices that do not have an end user.

   Although EST allows clients to obtain multiple certificates by
   sending multiple CSR requests BRSKI mandates use of the CSR
   Attributes request and mandates that the Registrar validate the CSR
   against the expected attributes.  This implies that client requests
   will "look the same" and therefore result in a single logical
   certificate being issued even if the client were to make multiple
   requests.  Registrars MAY contain more complex logic but doing so is
   out-of-scope of this specification.  BRSKI does not signal any
   enhancement or restriction to this capability.  Pledges that require
   multiple certificates could establish direct EST connections to the

5.8.1.  EST Distribution of CA Certificates

   The Pledge MUST request the full EST Distribution of CA Certificates
   message.  See RFC7030, section 4.1.

   This ensures that the Pledge has the complete set of current CA
   certificates beyond the pinned-domain-cert (see Section 5.5.1 for a
   discussion of the limitations inherent in having a single certificate
   instead of a full CA Certificates response).  Although these
   limitations are acceptable during initial bootstrapping they are not
   appropriate for ongoing PKIX end entity certificate validation.

5.8.2.  EST CSR Attributes

   Automated bootstrapping occurs without local administrative
   configuration of the Pledge.  In some deployments its plausible that
   the Pledge generates a certificate request containing only identity
   information known to the Pledge (essentially the X.509 IDevID

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   information) and ultimately receives a certificate containing domain
   specific identity information.  Conceptually the CA has complete
   control over all fields issued in the end entity certificate.
   Realistically this is operationally difficult with the current status
   of PKI certificate authority deployments where the CSR is submitted
   to the CA via a number of non-standard protocols.  Even with all
   standardized protocols used, it could operationally be problematic to
   expect that service specific certificate fields can be created by a
   CA that is likely operated by a group that has no insight into
   different network services/protocols used.  For example, the CA could
   even be outsourced.

   To alleviate these operational difficulties, the Pledge MUST request
   the EST "CSR Attributes" from the EST server and the EST server needs
   to be able to reply with the attributes necessary for use of the
   certificate in its intended protocols/services.  This approach allows
   for minimal CA integrations and instead the local infrastructure (EST
   server) informs the Pledge of the proper fields to include in the
   generated CSR.  This approach is beneficial to automated boostrapping
   in the widest number of environments.

   If the hardwareModuleName in the X.509 IDevID is populated then it
   SHOULD by default be propagated to the LDevID along with the
   hwSerialNum.  The EST server SHOULD support local policy concerning
   this functionality.

   In networks using the BRSKI enrolled certificate to authenticate the
   ACP (Autonomic Control Plane), the EST attributes MUST include the
   "ACP information" field.  See
   [I-D.ietf-anima-autonomic-control-plane] for more details.

   The Registar MUST also confirm the resulting CSR is formatted as
   indicated before forwarding the request to a CA.  If the Registar is
   communicating with the CA using a protocol like full CMC which
   provides mechanisms to override the CSR attributes, then these
   mechanisms MAY be used even if the client ignores CSR Attribute

5.8.3.  EST Client Certificate Request

   The Pledge MUST request a new client certificate.  See RFC7030,
   section 4.2.

5.8.4.  Enrollment Status Telemetry

   For automated bootstrapping of devices the adminstrative elements
   providing bootstrapping also provide indications to the system
   administrators concerning device lifecycle status.  This might

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   include information concerning attempted bootstrapping messages seen
   by the client, MASA provides logs and status of credential
   enrollment.  The EST protocol assumes an end user and therefore does
   not include a final success indication back to the server.  This is
   insufficient for automated use cases.

   To indicate successful enrollment the client SHOULD re-negotiate the
   EST TLS session using the newly obtained credentials.  This occurs by
   the client initiating a new TLS ClientHello message on the existing
   TLS connection.  The client MAY simply close the old TLS session and
   start a new one.  The server MUST support either model.

   In the case of a FAIL the Reason string indicates why the most recent
   enrollment failed.  The SubjectKeyIdentifier field MUST be included
   if the enrollment attempt was for a keypair that is locally known to
   the client.  If EST /serverkeygen was used and failed then the field
   is omitted from the status telemetry.

   In the case of a SUCCESS the Reason string is omitted.  The
   SubjectKeyIdentifier is included so that the server can record the
   successful certificate distribution.

   Status media type: application/json

   The client HTTP POSTs the following to the server at the new EST well
   known URI /enrollstatus.

     "Status":TRUE /* TRUE=Success, FALSE=Fail"
     "Reason":"Informative human readable message"
     "reason-context": "Additional information"

   The server SHOULD respond with an HTTP 200 but MAY simply fail with
   an HTTP 404 error.

   Within the server logs the server MUST capture if this message was
   received over an TLS session with a matching client certificate.
   This allows for clients that wish to minimize their crypto operations
   to simply POST this response without renegotiating the TLS session -
   at the cost of the server not being able to accurately verify that
   enrollment was truly successful.

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5.8.5.  EST over CoAP

   This document describes extensions to EST for the purposes of
   bootstrapping of remote key infrastructures.  Bootstrapping is
   relevant for CoAP enrollment discussions as well.  The defintion of
   EST and BRSKI over CoAP is not discussed within this document beyond
   ensuring proxy support for CoAP operations.  Instead it is
   anticipated that a definition of CoAP mappings will occur in
   subsequent documents such as [I-D.vanderstok-ace-coap-est] and that
   CoAP mappings for BRSKI will be discussed either there or in future

6.  Reduced security operational modes

   A common requirement of bootstrapping is to support less secure
   operational modes for support specific use cases.  The following
   sections detail specific ways that the Pledge, Registrar and MASA can
   be configured to run in a less secure mode for the indicated reasons.

6.1.  Trust Model

   +--------+         +---------+    +------------+     +------------+
   | Pledge |         | Circuit |    | Domain     |     | Vendor     |
   |        |         | Proxy   |    | Registrar  |     | Service    |
   |        |         |         |    |            |     | (Internet  |
   +--------+         +---------+    +------------+     +------------+

   Figure 10

   Pledge:  The Pledge could be compromised and providing an attack
      vector for malware.  The entity is trusted to only imprint using
      secure methods described in this document.  Additional endpoint
      assessment techniques are RECOMMENDED but are out-of-scope of this

   Proxy:  Provides proxy functionalities but is not involved in
      security considerations.

   Registrar:  When interacting with a MASA server a Registrar makes all
      decisions.  When Ownership Vouchers are involved a Registrar is
      only a conduit and all security decisions are made on the vendor

   Vendor Service, MASA:  This form of vendor service is trusted to
      accurately log all claim attempts and to provide authoritative log
      information to Registrars.  The MASA does not know which devices
      are associated with which domains.  These claims could be
      strengthened by using cryptographic log techniques to provide

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      append only, cryptographic assured, publicly auditable logs.
      Current text provides only for a trusted vendor.

   Vendor Service, Ownership Validation:  This form of vendor service is
      trusted to accurately know which device is owned by which domain.

6.2.  Pledge security reductions

   The Pledge can choose to accept vouchers using less secure methods.
   These methods enable offline and emergency (touch based) deployment
   use cases:

   1.  The Pledge MUST accept nonceless vouchers.  This allows for
       offline use cases.  Logging and validity periods address the
       inherent security considerations of supporting these use cases.

   2.  The Pledge MAY support "trust on first use" for physical
       interfaces such as a local console port or physical user
       interface but MUST NOT support "trust on first use" on network
       interfaces.  This is because "trust on first use" permanently
       degrades the security for all use cases.

   3.  The Pledge MAY have an operational mode where it skips Voucher
       validation one time.  For example if a physical button is
       depressed during the bootstrapping operation.  This can be useful
       if the vendor service is unavailable.  This behavior SHOULD be
       available via local configuration or physical presence methods to
       ensure new entities can always be deployed even when autonomic
       methods fail.  This allows for unsecured imprint.

   It is RECOMMENDED that "trust on first use" or skipping voucher
   validation only be available if hardware assisted Network Endpoint
   Assessment [RFC5209] is supported.  This recommendation ensures that
   domain network monitoring can detect innappropriate use of offline or
   emergency deployment procedures.

6.3.  Registrar security reductions

   A Registrar can choose to accept devices using less secure methods.
   These methods are acceptable when low security models are needed, as
   the security decisions are being made by the local administrator, but
   they MUST NOT be the default behavior:

   1.  A registrar MAY choose to accept all devices, or all devices of a
       particular type, at the administrator's discretion.  This could
       occur when informing all Registrars of unique identifiers of new
       entities might be operationally difficult.

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   2.  A registrar MAY choose to accept devices that claim a unique
       identity without the benefit of authenticating that claimed
       identity.  This could occur when the Pledge does not include an
       X.509 IDevID factory installed credential.  New Entities without
       an X.509 IDevID credential MAY form the Section 5.2 request using
       the Section 5.4 format to ensure the Pledge's serial number
       information is provided to the Registar (this includes the IDevID
       AuthorityKeyIdentifier value which would be statically configured
       on the Pledge).  The Pledge MAY refuse to provide a TLS client
       certificate (as one is not available).  The Pledge SHOULD support
       HTTP-based or certificate-less TLS authentication as described in
       EST RFC7030 section 3.3.2.  A Registrar MUST NOT accept
       unauthenticated New Entities unless it has been configured to do
       so by an administrator that has verified that only expected new
       entities can communicate with a Registrar (presumably via a
       physically secured perimeter).

   3.  A Registrar MAY submit a nonceless voucher-requests to MASA
       service (by not including a nonce in the voucher-request).  The
       resulting Vouchers can then be stored by the Registrar until they
       are needed during bootstrapping operations.  This is for use
       cases where target network is protected by an air gap and
       therefore can not contact the MASA service during Pledge

   4.  A registrar MAY ignore unrecognized nonceless log entries.  This
       could occur when used equipment is purchased with a valid history
       being deployed in air gap networks that required permanent

6.4.  MASA security reductions

   Lower security modes chosen by the MASA service effect all device
   deployments unless bound to the specific device identities.  In which
   case these modes can be provided as additional features for specific
   customers.  The MASA service can choose to run in less secure modes

   1.  Not enforcing that a nonce is in the Voucher.  This results in
       distribution of Voucher that never expires and in effect makes
       the Domain an always trusted entity to the Pledge during any
       subsequent bootstrapping attempts.  That this occurred is
       captured in the log information so that the Registrar can make
       appropriate security decisions when a Pledge joins the Domain.
       This is useful to support use cases where Registrars might not be
       online during actual device deployment.  Because this results in
       long lived Voucher and does not require the proof that the device
       is online this is only accepted when the Registrar is

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       authenticated by the MASA server and authorized to provide this
       functionality.  The MASA server is RECOMMENDED to use this
       functionality only in concert with an enhanced level of ownership
       tracking (out-of-scope).  If the Pledge device is known to have a
       real-time-clock that is set from the factory use of a voucher
       validity period is RECOMMENDED.

   2.  Not verifying ownership before responding with an Voucher.  This
       is expected to be a common operational model because doing so
       relieves the vendor providing MASA services from having to track
       ownership during shipping and supply chain and allows for a very
       low overhead MASA service.  A Registrar uses the audit log
       information as a defense in depth strategy to ensure that this
       does not occur unexpectedly (for example when purchasing new
       equipment the Registrar would throw an error if any audit log
       information is reported).  The MASA should verify the 'prior-
       signed-voucher' information for Pledge's that support that
       functionality.  This provides a proof-of-proximity check that
       reduces the need for ownership verification.

7.  IANA Considerations

   This document requests the following Parameter Values for the "smime-
   type" Parameters:

   o  voucher-request

   o  voucher

7.1.  PKIX Registry

   IANA is requested to register the following:

   This document requests a number for id-mod-MASAURLExtn2016(TBD) from
   the pkix(7) id-mod(0) Registry.  [[EDNOTE: fix names]]

   This document requests a number from the id-pe registry for id-pe-
   masa-url.  XXX

7.2.  Voucher Status Telemetry

   IANA is requested to create a registry entitled: _Voucher Status
   Telemetry Attributes_.  New items can be added using the
   Specification Required.  The following items are to be in the initial
   registration, with this document as the reference:

   o  version

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   o  Status

   o  Reason

   o  reason-context

8.  Security Considerations

   There are uses cases where the MASA could be unavailable or
   uncooperative to the Registrar.  They include planned and unplanned
   network partitions, changes to MASA policy, or other instances where
   MASA policy rejects a claim.  These introduce an operational risk to
   the Registrar owner that MASA/vendor behavior might limit the ability
   to re-boostrap a Pledge device.  For example this might be an issue
   during disaster recovery.  This risk can be mitigated by Registrars
   that request and maintain long term copies of "nonceless" Vouchers.
   In that way they are guaranteed to be able to repeat bootstrapping
   for their devices.

   The issuance of nonceless vouchers themselves create a security
   concern.  If the Registrar of a previous domain can intercept
   protocol communications then it can use a previously issued nonceless
   voucher to establish management control of a pledge device even after
   having sold it.  This risk is mitigated by recording the issuance of
   such vouchers in the MASA audit log that is verified by the
   subsequent Registrar.  This reduces the resale value of the equipment
   because future owners will detect the lowered security inherent in
   the existence of a nonceless voucher that would be trusted by their
   Pledge.  This reflects a balance between partition resistant recovery
   and security of future bootstrapping.  Registrars take the Pledge's
   audit history into account when applying policy to new devices.

   The MASA server is exposed to DoS attacks wherein attackers claim an
   unbounded number of devices.  Ensuring a Registrar is representative
   of a valid vendor customer, even without validating ownership of
   specific Pledge devices, helps to mitigate this.  Pledge signatures
   on the Pledge voucher-request, as forwarded by the Registrar in the
   prior-signed-voucher field of the Registrar voucher-request,
   significantly reduce this risk by ensuring the MASA can confirm
   proximity between the Pledge and the Registrar making the request.
   This mechanism is optional to allow for constrained devices.

   To facilitate logging and administrative oversight in addition to
   triggering Registration verification of MASA logs the Pledge reports
   on Voucher parsing status to the Registrar.  In the case of a failure
   this information is informative to a potentially malicious Registar
   but this is mandated anyway because of the operational benefits of an
   informed administrator in cases where the failure is indicative of a

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   problem.  The Registrar is RECOMMENDED to verify MASA logs if voucher
   status telemetry is not received.

   The MASA authorization log includes a hash of the domainID for each
   registrar a voucher has been issued to.  This information is closely
   related to the actual domain identity, especially when paired with
   the anti-DDoS authentication information the MASA might collect.
   This could provide sufficient information for the MASA service to
   build a detailed understanding the devices that have been provisioned
   within a domain.  There are a number of design choices that mitigate
   this risk.  The domain can maintain some privacy since it has not
   necessarily been authenticated and is not authoritatively bound to
   the supply chain.  Additionally the domainID captures only the
   unauthenticated subject key identifier of the domain.  A privacy
   sensitive domain could theoretically generate a new domainID for each
   device being deployed.  Similarly a privacy sensitive domain would
   likely purchase devices that support proximity assertions from a
   vendor that does not require sales channel integrations.  This would
   result in a significant level of privacy while maintaining the
   security characteristics provided by Registrar based audit log

   To facilitate truely limited clients EST RFC7030 section 3.3.2
   requirements that the client MUST support a client authentication
   model have been reduced in Section 6 to a statement that the
   Registrar "MAY" choose to accept devices that fail cryptographic
   authentication.  This reflects current (poor) practices in shipping
   devices without a cryptographic identity that are NOT RECOMMENDED.

   During the provisional period of the connection the Pledge MUST treat
   all HTTP header and content data as untrusted data.  HTTP libraries
   are regularly exposed to non-secured HTTP traffic: mature libraries
   should not have any problems.

   Pledge's might chose to engage in protocol operations with multiple
   discovered Registrars in parallel.  As noted above they will only do
   so with distinct nonce values, but the end result could be multiple
   voucher's issued from the MASA if all registrars attempt to claim the
   device.  This is not a failure and the Pledge choses whichever
   voucher to accept based on internal logic.  The Registrar's verifying
   log information will see multiple entries and take this into account
   for their analytics purposes.

8.1.  Freshness in Voucher-Requests

   A concern has been raised that the Pledge voucher-request should
   contain some content (a nonce) provided by the Registrar and/or MASA

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   in order for those actors to verify that the Pledge voucher-request
   is fresh.

   There are a number of operational problems with getting a nonce from
   the MASA to the pledge.  It is somewhat easier to collect a random
   value from the Registrar, but as the Registrar is not yet vouched
   for, such a Registrar nonce has little value.  There are privacy and
   logistical challenges to addressing these operational issues, so if
   such a thing were to be considered, it would have to provide some
   clear value.  This section examines the impacts of not having a fresh
   Pledge voucher-request.

   Because the Registrar authenticates the Pledge a full Man-in-the-
   Middle attack is not possible, despite the provisional TLS
   authentication by the Pledge (see Section 5).  Instead we examine the
   case of a fake Registrar (Rm) that communicates with the Pledge in
   parallel or in close time proximity with the intended Registrar.
   (This scenario is intentionally supported as described in
   Section 4.1).

   The fake Registrar (Rm) can obtain a voucher signed by the MASA
   either directly or through arbitrary intermediaries.  Assuming that
   the MASA accepts the Registar voucher-request (either because Rm is
   collaborating with a legitimate Registrar according to supply chain
   information, or because the MASA is in audit-log only mode), then a
   voucher linking the pledge to the Registrar Rm is issued.

   Such a voucher, when passed back to the Pledge, would link the pledge
   to Registrar Rm, and would permit the Pledge to end the provisional
   state.  It now trusts Rm and, if it has any security vulnerabilities
   leveragable by an Rm with full administrative control, can be assumed
   to be a threat against the intended Registrar.

   This flow is mitigated by the intended Registar verifying the audit
   logs available from the MASA as described in Section 5.7.  Rm might
   chose to wait until after the intended Registrar completes the
   authorization process before submitting the now-stale Pledge voucher-
   request.  The Rm would need to remove the Pledge's nonce.

   In order to successfully use the resulting "stale voucher" Rm would
   have to attack the Pledge and return it to a bootstrapping enabled
   state.  This would require wiping the Pledge of current configuration
   and triggering a re-bootstrapping of the Pledge.  This is no more
   likely than simply taking control of the Pledge directly but if this
   is a consideration the target network is RECOMMENDED to take the
   following steps:

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   o  Ongoing network monitoring for unexpected bootstrapping attempts
      by Pledges.

   o  Retreival and examination of MASA log information upon the
      occurance of any such unexpected events.  Rm will be listed in the

9.  Acknowledgements

   We would like to thank the various reviewers for their input, in
   particular Brian Carpenter, Toerless Eckert, Fuyu Eleven, Eliot Lear,
   Sergey Kasatkin, Markus Stenberg, and Peter van der Stok

10.  References

10.1.  Normative References

              Behringer, M., Eckert, T., and S. Bjarnason, "An Autonomic
              Control Plane (ACP)", draft-ietf-anima-autonomic-control-
              plane-12 (work in progress), October 2017.

              Bormann, C., Carpenter, B., and B. Liu, "A Generic
              Autonomic Signaling Protocol (GRASP)", draft-ietf-anima-
              grasp-15 (work in progress), July 2017.

              Watsen, K., Richardson, M., Pritikin, M., and T. Eckert,
              "Voucher Profile for Bootstrapping Protocols", draft-ietf-
              anima-voucher-06 (work in progress), October 2017.

   [IDevID]   IEEE Standard, "IEEE 802.1AR Secure Device Identifier",
              December 2009, <

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

   [RFC3542]  Stevens, W., Thomas, M., Nordmark, E., and T. Jinmei,
              "Advanced Sockets Application Program Interface (API) for
              IPv6", RFC 3542, DOI 10.17487/RFC3542, May 2003,

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   [RFC3748]  Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
              Levkowetz, Ed., "Extensible Authentication Protocol
              (EAP)", RFC 3748, DOI 10.17487/RFC3748, June 2004,

   [RFC3927]  Cheshire, S., Aboba, B., and E. Guttman, "Dynamic
              Configuration of IPv4 Link-Local Addresses", RFC 3927,
              DOI 10.17487/RFC3927, May 2005,

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862,
              DOI 10.17487/RFC4862, September 2007,

   [RFC4941]  Narten, T., Draves, R., and S. Krishnan, "Privacy
              Extensions for Stateless Address Autoconfiguration in
              IPv6", RFC 4941, DOI 10.17487/RFC4941, September 2007,

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,

   [RFC5386]  Williams, N. and M. Richardson, "Better-Than-Nothing
              Security: An Unauthenticated Mode of IPsec", RFC 5386,
              DOI 10.17487/RFC5386, November 2008,

   [RFC5652]  Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
              RFC 5652, DOI 10.17487/RFC5652, September 2009,

   [RFC5660]  Williams, N., "IPsec Channels: Connection Latching",
              RFC 5660, DOI 10.17487/RFC5660, October 2009,

   [RFC6762]  Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
              DOI 10.17487/RFC6762, February 2013,

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   [RFC6763]  Cheshire, S. and M. Krochmal, "DNS-Based Service
              Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,

   [RFC7030]  Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed.,
              "Enrollment over Secure Transport", RFC 7030,
              DOI 10.17487/RFC7030, October 2013,

   [RFC7159]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
              2014, <>.

   [RFC7228]  Bormann, C., Ersue, M., and A. Keranen, "Terminology for
              Constrained-Node Networks", RFC 7228,
              DOI 10.17487/RFC7228, May 2014,

   [RFC7950]  Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
              RFC 7950, DOI 10.17487/RFC7950, August 2016,

   [RFC7951]  Lhotka, L., "JSON Encoding of Data Modeled with YANG",
              RFC 7951, DOI 10.17487/RFC7951, August 2016,

10.2.  Informative References

              Behringer, M., Pritikin, M., and S. Bjarnason,
              "Bootstrapping Trust on a Homenet", draft-behringer-
              homenet-trust-bootstrap-02 (work in progress), February

              Watsen, K., Abrahamsson, M., and I. Farrer, "Zero Touch
              Provisioning for NETCONF or RESTCONF based Management",
              draft-ietf-netconf-zerotouch-19 (work in progress),
              October 2017.

              Lear, E., Droms, R., and D. Romascanu, "Manufacturer Usage
              Description Specification", draft-ietf-opsawg-mud-13 (work
              in progress), October 2017.

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              Richardson, M., "Considerations for stateful vs stateless
              join router in ANIMA bootstrap", draft-richardson-anima-
              state-for-joinrouter-01 (work in progress), July 2016.

              Kumar, S., Stok, P., Kampanakis, P., Furuhed, M., and S.
              Raza, "EST over secure CoAP (EST-coaps)", draft-
              vanderstok-ace-coap-est-02 (work in progress), June 2017.

              Wikipedia, "Wikipedia article: Imprinting", July 2015,

   [RFC2473]  Conta, A. and S. Deering, "Generic Packet Tunneling in
              IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473,
              December 1998, <>.

   [RFC7217]  Gont, F., "A Method for Generating Semantically Opaque
              Interface Identifiers with IPv6 Stateless Address
              Autoconfiguration (SLAAC)", RFC 7217,
              DOI 10.17487/RFC7217, April 2014,

   [RFC7231]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
              DOI 10.17487/RFC7231, June 2014,

   [RFC7435]  Dukhovni, V., "Opportunistic Security: Some Protection
              Most of the Time", RFC 7435, DOI 10.17487/RFC7435,
              December 2014, <>.

   [RFC7575]  Behringer, M., Pritikin, M., Bjarnason, S., Clemm, A.,
              Carpenter, B., Jiang, S., and L. Ciavaglia, "Autonomic
              Networking: Definitions and Design Goals", RFC 7575,
              DOI 10.17487/RFC7575, June 2015,

              Stajano, F. and R. Anderson, "The resurrecting duckling:
              security issues for ad-hoc wireless networks", 1999,

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Appendix A.  IPv4 operations

A.1.  IPv4 Link Local addresses

   Instead of an IPv6 link-local address, an IPv4 address may be
   generated using [RFC3927]  Dynamic Configuration of IPv4 Link-Local

   In the case that an IPv4 Local-Local address is formed, then the
   bootstrap process would continue as in the IPv6 case by looking for a
   (circuit) proxy.

A.2.  Use of DHCPv4

   The Plege MAY obtain an IP address via DHCP [RFC2131].  The DHCP
   provided parameters for the Domain Name System can be used to perform
   DNS operations if all local discovery attempts fail.

Appendix B.  mDNS / DNSSD proxy discovery options

   The Pledge MAY perform DNS-based Service Discovery [RFC6763] over
   Multicast DNS [RFC6762] searching for the service

   To prevent unaccceptable levels of network traffic the congestion
   avoidance mechanisms specified in [RFC6762] section 7 MUST be
   followed.  The Pledge SHOULD listen for an unsolicited broadcast
   response as described in [RFC6762].  This allows devices to avoid
   announcing their presence via mDNS broadcasts and instead silently
   join a network by watching for periodic unsolicited broadcast

   Performs DNS-based Service Discovery [RFC6763] over normal DNS
   operations.  The service searched for is
   "".  In this case the domain
   "" is discovered as described in [RFC6763] section 11.
   This method is only available if the host has received a useable IPv4
   address via DHCPv4 as suggested in Appendix A.

   If no local bootstrapks service is located using the GRASP
   mechanisms, or the above mentioned DNS-based Service Discovery
   methods the Pledge MAY contact a well known vendor provided
   bootstrapping server by performing a DNS lookup using a well known
   URI such as "".  The details of the URI
   are vendor specific.  Vendors that leverage this method on the Pledge
   are responsible for providing the bootstrapks service.

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   The current DNS services returned during each query is maintained
   until bootstrapping is completed.  If bootstrapping fails and the
   Pledge returns to the Discovery state it picks up where it left off
   and continues attempting bootstrapping.  For example if the first
   Multicast DNS _bootstrapks._tcp.local response doesn't work then the
   second and third responses are tried.  If these fail the Pledge moves
   on to normal DNS-based Service Discovery.

Appendix C.  IPIP Join Proxy mechanism

   The Circuit Proxy mechanism suffers from requiring a state on the
   Join Proxy for each connection that is relayed.  The Circuit Proxy
   can be considered a kind of Algorithm Gateway [FIND-good-REF].

   An alternative to proxying at the TCP layer is to selectively forward
   at the IP layer.  This moves all per-connection to the Join
   Registrar.  The IPIP tunnel statelessly forwards packets.  This
   section provides some explanation of some of the details of the
   Registrar discovery procotol which are not important to Circuit
   Proxy, and some implementation advice.

   The IPIP tunnel is described in [RFC2473].  Each such tunnel is
   considered a unidirectional construct, but two tunnels may be
   associated to form a bidirectional mechanism.  An IPIP tunnel is
   setup as follows.  The outer addresses are an ACP address of the Join
   Proxy, and the ACP address of the Join Registrar.  The inner
   addresses seen in the tunnel are the link-local addresses of the
   network on which the join activity is occuring.

   One way to look at this construct is to consider that the Registrar
   is extending attaching an interface to the network on which the Join
   Proxy is physically present.  The Registrar then interacts as if it
   were present on that network using link-local (fe80::) addresses.
   The Join node is unaware that the traffic is being proxied through a
   tunnel, and does not need any special routing.

   There are a number of considerations with this mechanism which
   require cause some minor amounts of complexity.  Note that due to the
   tunnels, the Registrar sees multiple connections to a fe80::/10
   network on not just physical interfaces, but on each of the virtual
   interfaces represending the tunnels.

C.1.  Multiple Join networks on the Join Proxy side

   The Join Proxy will in the general case be a routing device with
   multiple interfaces.  Even a device as simple as a wifi access point
   may have wired, and multiple frequencies of wireless interfaces,
   potentially with multiple ESSIDs.

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   Each of these interfaces on the Join Proxy may be seperate L3 routing
   domains, and therefore will have a unique set of link-local
   addresses.  An IPIP packet being returned by the Registrar needs to
   be forwarded to the correct interface, so the Join Proxy needs an
   additional key to distinguish which network the packet should be
   returned to.

   The simplest way to get this additional key is to allocate an
   additional ACP address; one address for each network on which join
   traffic is occuring.  The Join Proxy SHOULD do a GRASP M_NEG_SYN for
   each interface which they wish to relay traffic, as this allows the
   Registrar to do any static tunnel configuration that may be required.

C.2.  Automatic configuration of tunnels on Registrar

   The Join Proxy is expected to do a GRASP negotiation with the proxy
   for each Join Interface that it needs to relay traffic from.  This is
   to permit Registrars to configure the appropriate virtual interfaces
   before join traffic arrives.

   A Registrar serving a large number of interfaces may not wish to
   allocate resources to every interface at all times, but can instead
   dynamically allocate interfaces.  It can do this by monitoring IPIP
   traffic that arrives on it's ACP interface, and when packets arrive
   from new Join Proxys, it can dynamically configure virtual

   A more sophisticated Registrar willing to modify the behaviour of
   it's TCP and UDP stack could note the IPIP traffic origination in the
   socket control block and make information available to the TCP layer
   (for HTTPS connections), or to the application (for CoAP connections)
   via a proprietary extension to the socket API.

C.3.  Proxy Neighbor Discovery by Join Proxy

   The Join Proxy MUST answer neighbor discovery messages for the
   address given by the Registrar as being it's link-local address.  The
   Join Proxy must also advertise this address as the address to which
   to connect to when advertising it's existence.

   This proxy neighbor discovery means that the pledge will create TCP
   and UDP connections to the correct Registrar address.  This matters
   as the TCP and UDP pseudo-header checksum includes the destination
   address, and for the proxy to remain completely stateless, it must
   not be necessary for the checksum to be updated.

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C.4.  Use of connected sockets; or IP_PKTINFO for CoAP on Registrar

   TCP connections on the registrar SHOULD properly capture the ifindex
   of the incoming connection into the socket structure.  This is normal
   IPv6 socket API processing.  The outgoing responses will go out on
   the same (virtual) interface by ifindex.

   When using UDP sockets with CoAP, the application will have to pay
   attention to the incoming ifindex on the socket.  Access to this
   information is available using the IP_PKTINFO auxiliary extension
   which is a standard part of the IPv6 sockets API.

   A registrar application could, after receipt of an initial CoAP
   message from the Pledge, create a connected UDP socket (including the
   ifindex information).  The kernel would then take care of accurate
   demultiplexing upon receive, and subsequent transmission to the
   correct interface.

C.5.  Use of socket extension rather than virtual interface

   Some operating systems on which a Registrar need be implemented may
   find need for a virtual interface per Join Proxy to be problematic.
   There are other mechanism which can make be done.

   If the IPIP decapsulator can mark the (SYN) packet inside the kernel
   with the address of the Join Proxy sending the traffic, then an
   interface per Join Proxy may not be needed.  The outgoing path need
   just pay attention to this extra information and add an appropriate
   IPIP header on outgoing.  A CoAP over UDP mechanism may need to
   expose this extra information to the application as the UDP sockets
   are often not connected, and the application will need to specify the
   outgoing path on each packet send.

   Such an additional socket mechanism has not been standardized.
   Terminating L2TP connections over IPsec transport mode suffers from
   the same challenges.

Appendix D.  MUD Extension

   The following extension augments the MUD model to include a single
   node, as described in [I-D.ietf-opsawg-mud] section 3.6, using the
   following sample module that has the following tree structure:

   module: ietf-mud-brski-masa
   augment /ietf-mud:mud:
   +--rw masa-server?   inet:uri

   The model is defined as follows:

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   module ietf-mud-brski-masa {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:ietf-mud-brski-masa";
     prefix ietf-mud-brski-masa;
     import ietf-mud {
       prefix ietf-mud;
     import ietf-inet-types {
       prefix inet;

       "IETF ANIMA (Autonomic Networking Integrated Model and
       Approach) Working Group";
       "WG Web:
       WG List:
       "BRSKI extension to a MUD file to indicate the
       MASA URL.";

     revision 2017-10-09 {
       "Initial revision.";
       "RFC XXXX: Manufacturer Usage Description

     augment "/ietf-mud:mud" {
       "BRSKI extension to a MUD file to indicate the
       MASA URL.";
       leaf masa-server {
         type inet:uri;
         "This value is the URI of the MASA server";

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Appendix E.  Example Vouchers

   Three entities are involved in a voucher: the MASA issues (signs) it,
   the registrar's public key is mentioned in the voucher, and the
   pledge validates it.  In order to provide reproduceable examples the
   public and private keys for an example MASA and Registrar are first

E.1.  Keys involved

   The Manufacturer has a Certificate Authority that signs the Pledge's
   IDevID.  In addition the Manufacturer's signing authority (the MASA)
   signs the vouchers, and that certificate must distributed to the
   devices at manufacturing time so that vouchers can be validated.

E.1.1.  MASA key pair for voucher signatures

   This private key signs vouchers:

   -----END EC PRIVATE KEY-----

   This public key validates vouchers:

   -----END CERTIFICATE-----

E.1.2.  Manufacturer key pair for IDevID signatures

   This private key signs IDevID certificates:

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   -----END EC PRIVATE KEY-----

   This public key validates IDevID certificates:

   -----END CERTIFICATE-----

E.1.3.  Registrar key pair

   The registrar key (or chain) is the representative of the domain
   owner.  This key signs Registrar voucher-requests:

   -----END EC PRIVATE KEY-----

   The public key is indicated in a pledge voucher-request to show

   -----END CERTIFICATE-----

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   The registrar public certificate as decoded by openssl's x509
   utility.  Note that the registrar certificate is marked with the
   cmcRA extension.

           Version: 3 (0x2)
           Serial Number: 3 (0x3)
           Signature Algorithm: ecdsa-with-SHA384
           Issuer: DC=ca, DC=sandelman, CN=Unstrung Fountain CA
               Not Before: Sep  5 01:12:45 2017 GMT
               Not After : Sep  5 01:12:45 2019 GMT
           Subject: DC=ca, DC=sandelman, CN=localhost
           Subject Public Key Info:
               Public Key Algorithm: id-ecPublicKey
               EC Public Key:
                   ASN1 OID: prime256v1
           X509v3 extensions:
               X509v3 Basic Constraints:
       Signature Algorithm: ecdsa-with-SHA384

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E.1.4.  Pledge key pair

   The pledge has an IDevID key pair built in at manufacturing time:

   -----END EC PRIVATE KEY-----

   The public key is used by the registrar to find the MASA.  The MASA
   URL is in an extension described in Section 2.3.  RFC-EDITOR: Note
   that these certificates are using a Private Enterprise Number for the
   not-yet-assigned by IANA MASA URL, and need to be replaced before

   -----END CERTIFICATE-----

   The pledge public certificate as decoded by openssl's x509 utility so
   that the extensions can be seen.  A second custom Extension is
   included to provided to contain the EUI48/EUI64 that the pledge will

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           Version: 3 (0x2)
           Serial Number: 12 (0xc)
           Signature Algorithm: ecdsa-with-SHA256
           Issuer: DC=ca, DC=sandelman, CN=Unstrung Highway CA
               Not Before: Oct 12 13:52:52 2017 GMT
               Not After : Dec 31 00:00:00 2999 GMT
           Subject: DC=ca, DC=sandelman, CN=00-D0-E5-F2-00-02
           Subject Public Key Info:
               Public Key Algorithm: id-ecPublicKey
               EC Public Key:
                   ASN1 OID: prime256v1
           X509v3 extensions:
               X509v3 Subject Key Identifier:
               X509v3 Basic Constraints:
               X509v3 Subject Alternative Name:
       Signature Algorithm: ecdsa-with-SHA256

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E.2.  Example process

   RFC-EDITOR: these examples will need to be replaced with CMS versions
   once IANA has assigned the eContentType in [I-D.ietf-anima-voucher].

E.2.1.  Pledge to Registrar

   As described in Section 5.2, the pledge will sign a pledge voucher-
   request containing the Registrar's public key in the proximity-
   registrar-cert field.  The base64 has been wrapped at 60 characters
   for presentation reasons.

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   file: examples/vr_00-D0-E5-F2-00-02.pkcs

   The ASN1 decoding of the artifact:

   The JSON contained in the voucher request:

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E.2.2.  Registrar to MASA

   As described in Section 5.4 the Registrar will sign a registrar
   voucher-request, and will include pledge's voucher request in the


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   file: examples/parboiled_vr_00-D0-E5-F2-00-02.pkcs

   The ASN1 decoding of the artifact:

E.2.3.  MASA to Registrar

   The MASA will return a voucher to the Registrar, to be relayed to the

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   file: examples/voucher_00-D0-E5-F2-00-02.pkcs

   The ASN1 decoding of the artifact:

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Authors' Addresses

   Max Pritikin


   Michael C. Richardson
   Sandelman Software Works


   Michael H. Behringer


   Steinthor Bjarnason
   Arbor Networks


   Kent Watsen
   Juniper Networks


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