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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
Last updated 2016-06-30
Replaces draft-pritikin-anima-bootstrapping-keyinfra
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IESG IESG state Became RFC 8995 (Proposed Standard)
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ANIMA WG                                                     M. Pritikin
Internet-Draft                                                     Cisco
Intended status: Informational                             M. Richardson
Expires: January 1, 2017                                             SSW
                                                            M. Behringer
                                                            S. Bjarnason
                                                           June 30, 2016

        Bootstrapping Remote Secure Key Infrastructures (BRSKI)


   This document specifies automated bootstrapping of a remote secure
   key infrastructure (BRSKI) using vendor installed IEEE 802.1AR
   manufacturing installed certificates, in combination with a vendor
   based service on the Internet.  Before being authenticated, a new
   device has only link-local connectivity, and does not require a
   routable address.  When a vendor provides an Internet based service
   devices can be redirected to a local service.  In limited/
   disconnected networks or legacy environments we describe a variety of
   options that allow bootstrapping to proceed.  Support for lower
   security models, including devices with minimal identity, is
   described for legacy reasons but not encouraged.

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 January 1, 2017.

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Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
     1.2.  Scope of solution . . . . . . . . . . . . . . . . . . . .   6
     1.3.  Trust bootstrap . . . . . . . . . . . . . . . . . . . . .   7
   2.  Architectural Overview  . . . . . . . . . . . . . . . . . . .   7
   3.  Functional Overview . . . . . . . . . . . . . . . . . . . . .   9
     3.1.  Behavior of a New Entity  . . . . . . . . . . . . . . . .  11
       3.1.1.  Discovery . . . . . . . . . . . . . . . . . . . . . .  13
       3.1.2.  Identity  . . . . . . . . . . . . . . . . . . . . . .  14
       3.1.3.  Request Join  . . . . . . . . . . . . . . . . . . . .  15
       3.1.4.  Imprint . . . . . . . . . . . . . . . . . . . . . . .  15
       3.1.5.  Lack of realtime clock  . . . . . . . . . . . . . . .  16
       3.1.6.  Enrollment  . . . . . . . . . . . . . . . . . . . . .  17
       3.1.7.  Being Managed . . . . . . . . . . . . . . . . . . . .  18
     3.2.  Behavior of a Proxy . . . . . . . . . . . . . . . . . . .  18
       3.2.1.  CoAP connection to Registrar  . . . . . . . . . . . .  19
       3.2.2.  HTTPS proxy connection to Registrar . . . . . . . . .  19
     3.3.  Behavior of the Registrar (Bootstrap Server)  . . . . . .  20
       3.3.1.  Entity Authentication . . . . . . . . . . . . . . . .  21
       3.3.2.  Entity Authorization  . . . . . . . . . . . . . . . .  21
       3.3.3.  Claiming the New Entity . . . . . . . . . . . . . . .  22
       3.3.4.  Log Verification  . . . . . . . . . . . . . . . . . .  23
     3.4.  Behavior of the MASA Service  . . . . . . . . . . . . . .  24
       3.4.1.  Issue Authorization Token and Log the event . . . . .  24
       3.4.2.  Retrieve Audit Entries from Log . . . . . . . . . . .  24
     3.5.  Leveraging the new key infrastructure / next steps  . . .  24
       3.5.1.  Network boundaries  . . . . . . . . . . . . . . . . .  25
     3.6.  Interactions with Network Access Control  . . . . . . . .  25
   4.  Domain Operator Activities  . . . . . . . . . . . . . . . . .  25
     4.1.  Instantiating the Domain Certification Authority  . . . .  25
     4.2.  Instantiating the Registrar . . . . . . . . . . . . . . .  25

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     4.3.  Accepting New Entities  . . . . . . . . . . . . . . . . .  26
     4.4.  Automatic Enrollment of Devices . . . . . . . . . . . . .  27
     4.5.  Secure Network Operations . . . . . . . . . . . . . . . .  27
   5.  Protocol Details  . . . . . . . . . . . . . . . . . . . . . .  27
     5.1.  Request Audit Token from the Registrar  . . . . . . . . .  30
     5.2.  Request Audit Token from MASA . . . . . . . . . . . . . .  32
     5.3.  Audit Token Response  . . . . . . . . . . . . . . . . . .  33
       5.3.1.  Completing authentication of Provisional TLS
               connection  . . . . . . . . . . . . . . . . . . . . .  34
     5.4.  Audit Token Status Telemetry  . . . . . . . . . . . . . .  35
     5.5.  MASA authorization log Request  . . . . . . . . . . . . .  36
     5.6.  MASA authorization log Response . . . . . . . . . . . . .  36
     5.7.  EST Integration for PKI bootstrapping . . . . . . . . . .  37
       5.7.1.  EST Distribution of CA Certificates . . . . . . . . .  37
       5.7.2.  EST CSR Attributes  . . . . . . . . . . . . . . . . .  38
       5.7.3.  EST Client Certificate Request  . . . . . . . . . . .  38
       5.7.4.  Enrollment Status Telemetry . . . . . . . . . . . . .  38
       5.7.5.  EST over CoAP . . . . . . . . . . . . . . . . . . . .  39
   6.  Reduced security operational modes  . . . . . . . . . . . . .  40
     6.1.  Trust Model . . . . . . . . . . . . . . . . . . . . . . .  40
     6.2.  New Entity security reductions  . . . . . . . . . . . . .  41
     6.3.  Registrar security reductions . . . . . . . . . . . . . .  41
     6.4.  MASA security reductions  . . . . . . . . . . . . . . . .  42
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  42
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  44
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  44
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  44
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  45
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  46

1.  Introduction

   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 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.  This document describes a zero-touch approach to
   bootstrapping an entity by securing the initial distribution of key
   material using third-party generic keying material, such as a
   manufacturer installed IEEE 802.1AR certificate [IDevID], and a
   corresponding third-party service on the Internet.

   The two sides of an association being bootstrapped authenticate each
   other and then determine appropriate authorization.  This process is
   described as four distinct steps between the existing domain and the
   new entity being added:

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   o  New entity authentication: "Who is this?  What is its identity?"

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

   o  Domain authentication: "What is this domain's claimed identity?"

   o  Domain authorization: "Should I join it?"

   A precise answer to these questions can not be obtained without
   leveraging some established key infrastructure(s).  A complexity that
   this protocol deals with are dealing with devices from a variety of
   vendors, and a network infrastructure (the domain) that is operated
   by parties that do not have any priviledged relationship with the
   device vendors.  The domain's decisions are based on the new entity's
   authenticated identity, as established by verification of previously
   installed credentials such as a manufacturer installed IEEE 802.1AR
   certificate, and verified back-end information such as a configured
   list of purchased devices or communication with a (unidirectionally)
   trusted third-party.  The new entity's decisions are made according
   to verified communication with a trusted third-party or in a strictly
   auditable fashion.

   Optimal security is achieved with IEEE 802.1AR certificates on each
   new entity, accompanied by a third-party Internet based service for
   verification.  Bootstrapping concepts run to completion with less
   requirements, but are then less secure.  A domain can choose to
   accept lower levels of security when a trusted third-party is not
   available so that bootstrapping proceeds even at the risk of reduced
   security.  Only the domain can make these decisions based on
   administrative input and known behavior of the new entity.

   The result of bootstrapping is that a domain specific key
   infrastructure is deployed.  Since IEEE 802.1AR PKI certificates are
   used for identifying the new entity, and the public key of the domain
   identity is leveraged during communications with an Internet based
   service, which is itself authenticated using HTTPS, bootstrapping of
   a domain specific Public Key Infrastructure (PKI) is described.
   Sufficient agility to support bootstrapping alternative key
   infrastructures (such as symmetric key solutions) is considered
   although no such alternate key infrastructure is described.

1.1.  Terminology

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

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   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 domain trust anchor that is
      stored by the Domain CA.  This is consistent with the RFC5280
      Certification Authority subject key identifier of the Domain CA's
      self signed root certificate.  (A string value bound to the Domain
      CA's self signed root certificate subject and issuer fields is
      often colloquially used as a humanized identity value but during
      protocol discussions the more exact term as defined here is used).

   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 identity 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].

   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 the identity provided to
      at the factory.  Neither the device nor the network knows if the
      device yet knows if this device belongs with this network.  This
      is definition 6, according to [pledge]

   Audit Token:  A signed token from the manufacturer authorized signing
      authority indicating that the bootstrapping event has been
      successfully logged.  This has been referred to as an
      "authorization token" indicating that it authorizes bootstrapping
      to proceed.

   Ownership Voucher:  A signed voucher from the vendor vouching that a
      specific domain "owns" the new entity as defined in

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1.2.  Scope of solution

   Questions have been posed as to whether this solution is suitable in
   general for Internet of Things (IoT) networks.  In general the answer
   is no, but the terminology of [RFC7228] is best used to describe the

   The entire 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 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 bootstraping process can take minutes to complete depending on
   the network infrastructure and device processing speed.  The network
   communication itself is not "chatty" but there can be delays for
   privacy reasons.  This protocol is not intended for low latency

   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.

   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).

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   Some aspects are in scope for constrained devices on challenged
   networks: the certificate contents, and the process by which the four
   questions above are resolved is in scope.  It is simply the actual
   on-the-wire imprint protocol which is likely inappropriate.

1.3.  Trust bootstrap

   The imprint protocol results in a secure relationship between the
   domain registrar and the new device.  If the new device is
   sufficiently constrained that the ACE protocol should be leveraged
   for operation, (see [I-D.ietf-ace-actors]), and the domain registrar
   is also the Client Authorization Server or the Authorization Server,
   then it may be appropriate to use this secure channel to exchange ACE

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   |         |
      |                                      .+--------------+---------+
      |                                      ..............  ^
      V                                                      |
   +-------+     ............................................|...
   |       |     .                                           |  .
   |       |     .  +------------+       +-----------+       |  .
   |       |     .  |            |       |           |       |  .
   |       |     .  |            |       |           <-------+  .
   |       |     .  |   Proxy    |       | Registrar |          .
   |       <-------->            <------->           |          .
   | New   |     .  |            |       |           |          .
   | Entity|     .  +------------+       +-----+-----+          .
   |       |     .                             |                .
   |       |     .           +-----------------+----------+     .
   |       |     .           | Domain Certification       |     .
   |       |     .           | Authority                  |     .
   +-------+     .           | Management and etc         |     .
                 .           +----------------------------+     .
                 .                                              .
                               "Domain" components

   Figure 1

   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 the Registrar and stores
      the trust anchor that defines the domain.  Optionally, it
      certifies all elements.

   Registrar:  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

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      with a Registrar to control this process.  Typically a Registrar
      is "inside" its domain.

   New Entity:  A new device or virtual machine or software component
      that is not yet part of the domain.

   Proxy:  A domain entity that helps the New Entity 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 New Entity
      is unaware that they are communicating with a proxy rather than
      directly with the Registrar.

   MASA Service:  A Manufacturer Authorized Signing Authority (MASA)
      service on the global Internet.  The MASA provides a repository
      for audit log information concerning privacy protected
      bootstrapping events.

   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

   We assume a multi-vendor network.  In such an environment there could
   be a MASA or Ownership Tracker for each vendor that supports devices
   following this document's specification, or an integrator could
   provide a MASA service for all devices.  It is unlikely that an
   integrator could provide Ownership Tracking services for multiple

   This document describes a secure zero-touch approach to bootstrapping
   a key infrastructure; if certain devices in a network do not support
   this approach, they can still be bootstrapped manually.  Although
   manual deployment is not scalable and is not a focus of this document
   the necessary mechanisms are called out in this document to ensure
   such edge conditions are covered by the architectural and protocol

3.  Functional Overview

   Entities behave in an autonomic fashion.  They discover each other
   and autonomically bootstrap into a key infrastructure delineating the
   autonomic domain.  See [I-D.irtf-nmrg-autonomic-network-definitions]
   for more information.

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   This section details the state machine and operational flow for each
   of the main three entities.  The New Entity, the Domain (primarily
   the Registrar) and the MASA service.

   A representative flow is shown in Figure 2:

     +--------+         +---------+    +------------+     +------------+
     | New    |         | Circuit |    | Domain     |     | Vendor     |
     | Entity |         | Proxy   |    | Registrar  |     | Service    |
     |        |         |         |    |            |     | (Internet  |
     +--------+         +---------+    +------------+     +------------+
      |                     |                   |                    |
      |<-RFC3927 IPv4 adr   |                   |                    |
    or|<-RFC4862 IPv6 adr   |                   |                    |
      |                     |                   |                    |
      |-------------------->|                   |                    |
      | optional: mDNS query|                   |                    |
      | RFC6763/RFC6762     |                   |                    |
      |                     |                   |                    |
      |<--------------------|                   |                    |
      | mDNS broadcast      |                   |                    |
      | response or periodic|                   |                    |
      |                     |                   |                    |
      |<------------------->C<----------------->|                    |
      |            TLS via the Circuit Proxy    |                    |
      |<--Registrar TLS server authentication---|                    |
  [PROVISIONAL accept of server cert]           |                    |
      P---IEEE 802.1AR client authentication--->|                    |
      P                     |                   |                    |
      P---Request Audit Token (include nonce)-->|                    |
      P                     |                   |                    |
      P                     |       /--->       |                    |
      P                     |       |      [accept device?]          |
      P                     |       |      [contact Vendor]          |
      P                     |       |           |--New Entity ID---->|
      P                     |       |           |--Domain ID-------->|
      P                     |       |           |--optional:nonce--->|
      P                     |       |           |     [extract DomainID]
      P                     |       |           |                    |
      P                     |    optional:      |     [update audit log]
      P                     |       |can        |                    |
      P                     |       |occur      |     optional: is   |
      P                     |       |in         |     an ownership   |
      P                     |       |advance    |     voucher available?
      P                     |       |           |                    |
      P                     |       |           |<-device audit log--|
      P                     |       |           |                    |
      P                     |       |           |  choice:           |

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      P                     |       |           |<-audit token-------|
      P                     |       |           |<-or: ownership-----|
      P                     |       \---->      |      voucher       |
      P                     |                   |                    |
      P                     |       [verify audit log or voucher]    |
      P                     |                   |                    |
      P<--Audit token and/or ownership voucher--|                    |
  [verify response         ]|                   |                    |
  [verify provisional cert ]|                   |                    |
      |                     |                   |                    |
      |---------------------------------------->|                    |
      | Continue with RFC7030 enrollment        |                    |
      | using now bidirectionally authenticated |                    |
      | TLS session.        |                   |                    |
      |                     |                   |                    |
      |                     |                   |                    |
      |                     |                   |                    |

   Figure 2

3.1.  Behavior of a New Entity

   A New Entity that has not yet been bootstrapped attempts to find a
   local domain and join it.  A New Entity MUST NOT automatically
   initiate bootstrapping if it has already been configured.

   States of a New Entity are as follows:

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                |   Start      |
                |              |
                |  Discover    |
   +------------>              |
   |            +------+-------+
   |                   |
   |            +------v-------+
   |            |  Identity    |
   ^------------+              |
   | rejected   +------+-------+
   |                   |
   |            +------v-------+
   |            | Request      |
   |            | Join         |
   |            +------+-------+
   |                   |
   |            +------v-------+
   |            |  Imprint     |   Optional
   ^------------+              <--+Manual input
   | Bad Vendor +------+-------+
   | response          |
   |            +------v-------+
   |            |  Enroll      |
   ^------------+              |
   | Enroll     +------+-------+
   | Failure           |
   |            +------v-------+
   |            |  Being       |
   ^------------+  Managed     |
    Factory     +--------------+

   Figure 3

   State descriptions for the New Entity are as follows:

   1.  Discover a communication channel to the "closest" Registrar.

   2.  Identify itself.  This is done by presenting an IEEE 802.1AR
       credentials to the discovered Registrar (via the Proxy) in a TLS
       handshake.  (Although the Registrar is also authenticated these
       credentials are only provisionally accepted at this time).

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   3.  Requests to Join the discovered Registrar.  A unique nonce is
       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 "Audit Token" or the validation of the vendor
       service "Ownership Voucher".  Either of these responses contains
       sufficient information for the New Entity to complete
       authentication of the Registrar.  (The New Entity can now finish
       authentication of the Registrar TLS server certificate)

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

   6.  The New Entity 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.

   The following sections describe each of these steps in more detail.

3.1.1.  Discovery

   The result of discovery is logically communication with a Proxy
   instead of a Domain Registrar but in such a case the proxy
   facilitates communication with the actual Domain Registrar in a
   manner that is transparent to the New Entity.  Therefore or clarity a
   Proxy is always assumed.

   To discover the Domain Bootstrap Server the New Entity performs the
   following actions:

   a.  MUST: Obtains a local address using either IPv4 or IPv6 methods
       as described in [RFC4862] IPv6 Stateless Address
       AutoConfiguration or [RFC3927] Dynamic Configuration of IPv4
       Link-Local Addresses.

   b.  MUST: Performs DNS-based Service Discovery [RFC6763] over
       Multicast DNS [RFC6762] searching for the service
       "_bootstrapks._tcp.local.".  To prevent unaccceptable levels of
       network traffic the congestion avoidance mechanisms specified in
       [RFC6762] section 7 MUST be followed.  The New Entity 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 responses.

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   c.  MAY: 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.

   d.  MAY: If no local bootstrapks service is located using the DNS-
       based Service Discovery methods the New Entity contacts a well
       known vendor provided bootstrapping server by performing a DNS
       lookup using a well known URI such as "bootstrapks.vendor-".  The details of the URI are vendor specific.
       Vendors that leverage this method SHOULD provision appropriately.

   DNS-based service discovery communicates the local proxy IPv4 or IPv6
   address and port to the New Entity.  Once a proxy is discovered the
   New Entity communicates with the Registrar through the proxy using
   the bootstrapping protocol defined in Section 5.  The current DNS
   services returned during each query is maintained until bootstrapping
   is completed.  If bootstrapping fails and the New Entity 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 New Entity moves on to
   normal DNS-based Service Discovery.

   Each discovery method attempted SHOULD exponentially back-off
   attempts (to a maximum of one hour) to avoid overloading that
   discovery methods network infrastructure.  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.  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 5.1.

   Once all discovered services are attempted the device SHOULD return
   to Multicast DNS.  It should periodically retry the vendor specific
   mechanisms.  The New Entity may prioritize selection order as
   appropriate for the anticipated environment.

3.1.2.  Identity

   The New Entity identifies itself during the communication protocol
   handshake.  If the client identity is rejected the New Entity repeats
   the Discovery process using the next proxy or discovery method

   The bootstrapping protocol server is not initially authenticated.
   Thus the connection is provisional and all data received is untrusted
   until sufficiently validated even though it is over a TLS connection.

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   This is aligned with the existing provisional mode of EST [RFC7030]
   during s4.1.1 "Bootstrap Distribution of CA Certificates".  See
   Section 5.3 for more information about when the TLS connection
   authenticated is completed.

   All security associations established are between the new device and
   the Bootstrapping server regardless of proxy operations.

3.1.3.  Request Join

   The New Entity POSTs a request to join the domain to the
   Bootstrapping server.  This request contains a New Entity generated
   nonce and informs the Bootstrapping server which imprint methods the
   New Entity will accept.

   As indicated in EST [RFC7030] the bootstrapping server MAY redirect
   the client to an alternate server.  This is most useful in the case
   where the New Entity has resorted to a well known vendor URI and is
   communicating with the vendor's Registrar directly.  In this case the
   New Entity has authenticated the Registrar using the local Implicit
   Trust Anchor database and can therefore treat the redirect URI as a
   trusted URI which can also be validated using the Implicit Trust
   Anchor database.  Since client authentication occurs during the TLS
   handshake the bootstrapping server has sufficient information to
   apply appropriate policy concerning which server to redirect to.

   The nonce ensures the New Entity can verify that responses are
   specific to this bootstrapping attempt.  This minimizes the use of
   global time and provides a substantial benefit for devices without a
   valid clock.

3.1.4.  Imprint

   The domain trust anchor is received by the New Entity during the
   bootstrapping protocol methods in the form of either an Audit Token
   containing the domain CA cert or an explicit ownership voucher.  The
   goal of the imprint state is to securely obtain a copy of this trust
   anchor without involving human interaction.

   The enrollment protocol EST [RFC7030] details a set of non-autonomic
   bootstrapping methods such as:

   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

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   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).

   This document describes additional autonomic methods:

   MASA audit token  Audit tokens are obtained by the Registrar from the
      MASA service and presented to the New Entity for validation.
      These indicate to the New Entity that joining the domain has been
      logged by a logging service.

   Ownership Voucher  Ownership Vouchers are obtained by the Registrar
      from the MASA service and explicitly indicate the fully qualified
      domain name of the domain the new entity currently belongs to.
      The Ownership Voucher is defined in [I-D.ietf-netconf-zerotouch].

   Since client authentication occurs during the TLS handshake the
   bootstrapping server has sufficient information to apply appropriate
   policy concerning which method to use.

   The audit token contains the domain's public key material as provided
   to the MASA service by the Registrar.  This provides sufficient
   information to the client to complete automated bootstrapping with
   the local key infrastructure.

   If the autonomic methods fail the New Entity returns to discovery
   state and attempts bootstrapping with the next available discovered

3.1.5.  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 New Entity maintaining a concept of the current
   "window" of presumed time validity that is continually refined
   throughout the bootstrapping process as follows:

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   o  Initially the New Entity does not know the current time.  The
      nonce included in join attempts provides an alternate mechanism
      for the New Entity to ensure responses are associated with a
      particular bootstrapping attempt.  Nonceless audit tokens from the
      MASA server are always valid and thus time is not needed.

   o  In accordance with IEEE 802.1AR and RFC5280 all manufacturing
      installed certificates and trust anchors are assumed to have
      infinite lifetimes.  All such certificates "SHOULD be assigned the
      GeneralizedTime value of 99991231235959Z" [RFC5280].  The New
      Entity, Registrar and MASA server MUST ignore any other validity
      period information in these credentials and treat the effective
      lifetime as 99991231235959Z.  This ensures that client
      authentication (see Section 3.3.1) and the audit token signature
      (see Section 5.3) can always be verified during RFC5280 path

   o  Once the audit token is accepted the validity period of the
      domainCAcert in the token (see Section 5.3) now describes 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 end entity certificate is assumed to be valid by
      the New Entity.  The New Entity is now willing to use this
      credential for client authentication.

   Once in this state the New Entity has a valid trust anchor with the
   local domain and has a locally issued credential.  These MAY be used
   to secure distribution of more accurate time information although
   specification of such a protocol is out-of-scope of this document.

3.1.6.  Enrollment

   As the final step of bootstrapping a Registrar helps to issue a
   domain specific credential to the New Entity.  For simplicity in this
   document, a Registrar primarily facilitates issuing a credential by
   acting as an RFC5280 Registration Authority for the Domain
   Certification Authority.

   Enrollment proceeds as described in Enrollment over Secure Transport
   (EST) [RFC7030].  The New Entity contacts the Registrar using EST as

   o  The New Entity is authenticated using the IEEE 802.1AR

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   o  The EST section 4.1.3 CA Certificates Response is verified using
      either the Audit Token which provided the domain identity -or-

   o  The EST server is authenticated by using the Ownership Voucher
      indicated fully qualified domain name to build the EST URI such
      that EST section 4.1.1 bootstrapping using the New Entity implicit
      Trust Anchor database can be used.

   Once the Audit Token is received, as specified in this document, the
   client has sufficient information to leverage the existing
   communication channel with the Registrar to continue an EST RFC7030
   enrollment.  Enrollment picks up at RFC7030 section 4.1.1.
   bootstrapping where the audit token provides the "out-of-band" CA
   certificate fingerprint (in this case the full CA certificate) such
   that the client can now complete the TLS server authentication.  At
   this point the client continues with EST enrollment operations
   including "CA Certificates Request", "CSR Attributes" and "Client
   Certificate Request" or "Server-Side Key Generation".

3.1.7.  Being Managed

   Functionality to provide generic "configuration" information is
   supported.  The parsing of this data and any subsequent use of the
   data, for example communications with a Network Management System is
   out of scope but is expected to occur after bootstrapping enrollment
   is complete.  This ensures that all communications with management
   systems which can divulge local security information (e.g. network
   topology or raw key material) is secured using the local credentials
   issued during enrollment.

   The New Entity uses bootstrapping to join only one domain.
   Management by multiple domains is out-of-scope of bootstrapping.
   After the device has successfully joined a domain and is being
   managed it is plausible that the domain can insert credentials for
   other domains depending on the device capabilities.

   See Section 3.5.

3.2.  Behavior of a Proxy

   The role of the Proxy is to facilitate communications.  The Proxy
   forwards packets between the New Entity and the Registrar that has
   been configured on the Proxy.  The Proxy does not terminate the TLS

   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

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   the ANIMA target space will be rather large routers, the proxy
   function is likely to be implemented in the control plane CPU 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 of the alternative proxy methods.

3.2.1.  CoAP connection to Registrar

   The proxy MUST implement an IPIP (protocol 41) encapsulation function
   for CoAP traffic to the configured UDP port on the registrar.  The
   proxy does not terminate the CoAP DTLS connection.  [[EDNOTE: The
   choice of CoAP as the mandatory to implement protocol rather than
   HTTP maximizes code reuse on the smallest of devices.  Unfortunately
   this means this document will have to include the EST over CoAP
   details as additional sections.  The alternative is to make 'HTTPS
   proxy' method the mandatory to implement and provide a less friendly
   environment for the smallest of devices.  This is a decision we'll
   have to see addressed by the broader team.]]

   As a result of the Proxy Discovery process in section Section 3.1.1,
   the port number exposed by the proxy does not need to be well known,
   or require an IANA allocation.

   The address and port of the Registrar to which the packets will be
   forwarded will be discovered by the GRASP protocol inside the ACP.
   For the IPIP encapsulation methods, the port announced by the Proxy
   MUST be the same as on the registrar in order for the proxy to remain

   The IPIP encapsulation allows the proxy to forward traffic which is
   otherwise not to be forwarded, as the traffic between New Node and
   Proxy use IPv6 Link Local addresses.

   If the Proxy device has more than one interface on which it offers
   the proxy function, then it must select a unique (ACP) IP address per
   interface in order so that the proxy can stateless return the reply
   packets to the correct link.

3.2.2.  HTTPS proxy connection to Registrar

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

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

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   When the Proxy provides a stateless IPIP encapsulation to the
   Registrar, then the Registrar will have to perform IPIP
   decapsulation, remembering the originating outer IPIP source address
   in order to qualify the inner link-local address.  This is a kind of
   encapsulation and processing which is similar in many ways to how
   mobile IP works.

   Being able to connect a TCP (HTTP) or UDP (CoAP) socket to a link-
   local address with an encapsulated IPIP header requires API
   extensions beyond [RFC3542] for UDP use, and requires a form of
   connection latching (see section 4.1 of [RFC5386] and all of
   [RFC5660], except that a simple IPIP tunnel is used rather than an
   IPsec tunnel).

3.3.  Behavior of the Registrar (Bootstrap Server)

   Once a Registrar is established it listens for new entities and
   determines if they can join the domain.  The registrar delivers any
   necessary authorization information to the new device and facilitates
   enrollment with the domain PKI.

   Registrar behavior is as follows:

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   Contacted by New Entity
   | Entity           | fail?
   | Authentication   +---------+
   +-------+----------+         |
           |                    |
   +-------v----------+         |
   | Entity           | fail?   |
   | Authorization    +--------->
   +-------+----------+         |
           |                    |
   +-------v----------+         |
   | Claiming the     | fail?   |
   | Entity           +--------->
   +-------+----------+         |
           |                    |
   +-------v----------+         |
   | Log Verification | fail?   |
   |                  +--------->
   +-------+----------+         |
           |                    |
   +-------v----------+    +----v-------+
   | Forward          |    |            |
   | Audit            |    | Reject     |
   | token + config   |    | Device     |
   | to the Entity    |    |            |
   +------------------+    +------------+

   Figure 4

3.3.1.  Entity Authentication

   The applicable authentication methods detailed in EST [RFC7030] are:

   o  the use of an IEEE 802.1AR IDevID credential during the TLS client

   o  or the use of a secret that is transmitted out of band between the
      New Entity and the Registrar (this use case is not autonomic).

3.3.2.  Entity Authorization

   In a fully automated network all devices must be securely identified
   and authorized to join the domain.

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   A Registrar accepts or declines a request to join the domain, based
   on the authenticated identity presented.  Automated acceptance
   criteria include:

   o  allow any device of a specific type (as determined by the IEEE
      802.1AR device identity),

   o  allow any device from a specific vendor (as determined by the IEEE
      802.1AR identity),

   o  allow a specific device from a vendor (as determined by the IEEE
      802.1AR identity)

   Since all New Entities accept Audit Tokens the Registrar MUST use the
   vendor provided MASA service to verify that the device's history log
   does not include unexpected Registrars.  If a device had previously
   registered with another domain, the Registrar of that domain would
   show in the log.

   In order to validate the IEEE 802.1AR device identity the Registrar
   maintains a database of vendor trust anchors (e.g. vendor root
   certificates or keyIdentifiers for vendor root public keys).  For
   user interface purposes this database can be mapped to colloquial
   vendor names.  Registrars can be shipped with the trust anchors of a
   significant number of third-party vendors within the target market.

   If a device is accepted into the domain, it is expected request a
   domain certificate through a certificate enrollment process.  The
   result is a common trust anchor and device certificates for all
   autonomic devices in a domain (these certificates can subsequently be
   used to determine the boundaries of the homenet, to authenticate
   other domain nodes, and to autonomically enable services on the
   homenet).  The authorization performed during this phase MAY be
   cached for the TLS session and applied to subsequent EST enrollment
   requests so long as the session lasts.

3.3.3.  Claiming the New Entity

   Claiming an entity establishes an audit log at the MASA server and
   provides the Registrar with proof, in the form of a MASA
   authorization token, that the log entry has been inserted.  As
   indicated in Section 3.1.4 a New Entity will only proceed with
   bootstrapping if a validated MASA authorization token has been
   received.  The New Entity therefore enforces that bootstrapping only
   occurs if the claim has been logged.  There is no requirement for the
   vendor to definitively know that the device is owned by the

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   Registrar's obtain the Vendor URI via static configuration or by
   extracting it from the IEEE 802.1AR credential.  The imprint method
   supported by the New Entity is known from the IEEE 802.1AR
   credential.  [[EDNOTE: An appropriate extension for indicating the
   Vendor URI and imprint method could be defined using the methods
   described in [I-D.lear-mud-framework]]].

   During initial bootstrapping the New Entity provides a nonce specific
   to the particular bootstrapping attempt.  The Registrar SHOULD
   include this nonce when claiming the New Entity from the MASA
   service.  Claims from an unauthenticated Registrar are only serviced
   by the MASA resource if a nonce is provided.

   The Registrar can claim a New Entity that is not online by forming
   the request using the entities unique identifier and not including a
   nonce in the claim request.  Audit Tokens obtained in this way do not
   have a lifetime and they provide a permanent method for the domain to
   claim the device.  Evidence of such a claim is provided in the audit
   log entries available to any future Registrar.  Such claims reduce
   the ability for future domains to secure bootstrapping and therefore
   the Registrar MUST be authenticated by the MASA service.

   An ownership voucher requires the vendor to definitively know that a
   device is owned by a specific domain.  The method used to "claim"
   this are out-of-scope.  The Registrar simply requests an ownership
   validation token and the New Entity trusts the response.

3.3.4.  Log Verification

   The Registrar requests the log information for the new entity from
   the MASA service.  The log is verified to confirm that the following
   is true to the satisfaction of the Registrar's configured policy:

   o  Any nonceless entries in the log are associated with domainIDs
      recognized by the registrar.

   o  Any nonce'd entries are older than when the domain is known to
      have physical possession of the new entity or that the domainIDs
      are recognized by the registrar.

   If any of these criteria are unacceptable to the registrar the entity
   is rejected.  The 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.

   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 the audit token

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   with a current 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 for future work.

3.4.  Behavior of the MASA Service

   The MASA service is provided by the Factory provider on the global
   Internet.  The URI of this service is well known.  The URI SHOULD
   also be provided as an IEEE 802.1AR IDevID X.509 extension (a "MASA
   Audit Token Distribution Point" extension).

   The MASA service provides the following functionalities to

3.4.1.  Issue Authorization Token and Log the event

   A Registrar POSTs a claim message optionally containing the bootstrap
   nonce to the MASA server.

   If a nonce is provided the MASA service responds to all requests.
   The MASA service verifies the Registrar is representative of the
   domain and generates a privacy protected log entry before responding
   with the Audit Token.

   If a nonce is not provided then the MASA service MUST authenticate
   the Registrar as a valid customer.  This prevents denial of service

3.4.2.  Retrieve Audit Entries from Log

   When determining if a New Entity should be accepted into a domain the
   Registrar retrieves a copy of the audit log from the MASA service.
   This contains a list of privacy protected domain identities that have
   previously claimed the device.  Included in the list is an indication
   of the time the entry was made and if the nonce was included.

3.5.  Leveraging the new key infrastructure / next steps

   As the devices have a common trust anchor, device identity can be
   securely established, making it possible to automatically deploy
   services across the domain in a secure manner.

   Examples of services:

   o  Device management.

   o  Routing authentication.

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   o  Service discovery.

3.5.1.  Network boundaries

   When a device has joined the domain, it can validate the domain
   membership of other devices.  This makes it possible to create trust
   boundaries where domain members have higher level of trusted than
   external devices.  Using the autonomic User Interface, specific
   devices can be grouped into to sub domains and specific trust levels
   can be implemented between those.

3.6.  Interactions with Network Access Control

   The assumption is that Network Access Control (NAC) completes using
   the New Entity 802.1AR credentials and results in the device having
   sufficient connectivity to discovery and communicate with the proxy.
   Any additional connectivity or quarantine behavior by the NAC
   infrastructure is out-of-scope.  After the devices has completed
   bootstrapping the mechanism to trigger NAC to re-authenticate the
   device and provide updated network privileges is also out-of-scope.

   This achieves the goal of a bootstrap architecture that can integrate
   with NAC but does not require NAC within the network where it wasn't
   previously required.  Future optimizations can be achieved by
   integrating the bootstrapping protocol directly into an initial EAP

4.  Domain Operator Activities

   This section describes how an operator interacts with a domain that
   supports the bootstrapping as described in this document.

4.1.  Instantiating the Domain Certification Authority

   This is a one time step by the domain administrator.  This is an "off
   the shelf" CA with the exception that it is designed to work as an
   integrated part of the security solution.  This precludes the use of
   3rd party certification authority services that do not provide
   support for delegation of certificate issuance decisions to a domain
   managed Registration Authority.

4.2.  Instantiating the Registrar

   This is a one time step by the domain administrator.  One or more
   devices in the domain are configured take on a Registrar function.

   A device can be configured to act as a Registrar or a device can
   auto-select itself to take on this function, using a detection

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   mechanism to resolve potential conflicts and setup communication with
   the Domain Certification Authority.  Automated Registrar selection is
   outside scope for this document.

4.3.  Accepting New Entities

   For each New Entity the Registrar is informed of the unique
   identifier (e.g. serial number) along with the manufacturer's
   identifying information (e.g. manufacturer root certificate).  This
   can happen in different ways:

   1.  Default acceptance: In the simplest case, the new device asserts
       its unique identity to the registrar.  The registrar accepts all
       devices without authorization checks.  This mode does not provide
       security against intruders and is not recommended.

   2.  Per device acceptance: The new device asserts its unique identity
       to the registrar.  A non-technical human validates the identity,
       for example by comparing the identity displayed by the registrar
       (for example using a smartphone app) with the identity shown on
       the packaging of the device.  Acceptance may be triggered by a
       click on a smartphone app "accept this device", or by other forms
       of pairing.  See also [I-D.behringer-homenet-trust-bootstrap] for
       how the approach could work in a homenet.

   3.  Whitelist acceptance: In larger networks, neither of the previous
       approaches is acceptable.  Default acceptance is not secure, and
       a manual per device methods do not scale.  Here, the registrar is
       provided a priori with a list of identifiers of devices that
       belong to the network.  This list can be extracted from an
       inventory database, or sales records.  If a device is detected
       that is not on the list of known devices, it can still be
       manually accepted using the per device acceptance methods.

   4.  Automated Whitelist: an automated process that builds the
       necessary whitelists and inserts them into the larger network
       domain infrastructure is plausible.  Once set up, no human
       intervention is required in this process.  Defining the exact
       mechanisms for this is out of scope although the registrar
       authorization checks is identified as the logical integration
       point of any future work in this area.

   None of these approaches require the network to have permanent
   Internet connectivity.  Even when the Internet based MASA service is
   used, it is possible to pre-fetch the required information from the
   MASA a priori, for example at time of purchase such that devices can
   enroll later.  This supports use cases where the domain network may
   be entirely isolated during device deployment.

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   Additional policy can be stored for future authorization decisions.
   For example an expected deployment time window or that a certain
   Proxy must be used.

4.4.  Automatic Enrollment of Devices

   The approach outlined in this document provides a secure zero-touch
   method to enroll new devices without any pre-staged configuration.
   New devices communicate with already enrolled devices of the domain,
   which proxy between the new device and a Registrar.  As a result of
   this completely automatic operation, all devices obtain a domain
   based certificate.

4.5.  Secure Network Operations

   The certificate installed in the previous step can be used for all
   subsequent operations.  For example, to determine the boundaries of
   the domain: If a neighbor has a certificate from the same trust
   anchor it can be assumed "inside" the same organization; if not, as
   outside.  See also Section 3.5.1.  The certificate can also be used
   to securely establish a connection between devices and central
   control functions.  Also autonomic transactions can use the domain
   certificates to authenticate and/or encrypt direct interactions
   between devices.  The usage of the domain certificates is outside
   scope for this document.

5.  Protocol Details

   A bootstrapping protocol could be implemented as an independent
   protocol from EST, but for simplicity and to reduce the number of TLS
   connections and crypto operations required on the New Entity, it is
   described specifically as extensions to EST.  These extensions MUST
   be supported by the Registrar EST server within the same .well-known
   URI tree as the existing EST URIs as described in [RFC7030] section

   The new entity establishes a TLS connection with the Registrar
   through the circuit proxy (see Section 3.2) but the TLS connection is
   with the Registar; so for this section the "New Entity" is the TLS
   client and the "Registrar" is the TLS server.

   Establishment of the TLS connection for bootstrapping is as specified
   for EST [RFC7030].  In particular server identity and client identity
   are as described in EST [RFC7030] section 3.3.  In EST [RFC7030]
   provisional server authentication for bootstrapping is described in
   section 4.1.1 wherein EST clients can "engage a human user to
   authorize the CA certificate using out-of-band data such as a CA
   certificate" or wherein a human user configures the URI of the EST

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   server for Implicit TA based authentication.  As described in this
   document, Section 5.3.1, a new method of bootstrapping now provides a
   completely automating method of bootstrapping PKI.

   The extensions for the New Entity client are as follows:

   o  The New Entity provisionally accept the EST server certificate
      during the TLS handshake as detailed in Section 5.3.1.

   o  The New Entity requests and validates the Audit Token as described
      below.  At this point the New Entity has sufficient information to
      validate domain credentials.

   o  The New Entity calls the EST defined /cacerts method to obtain the
      current CA certificate.  These are validated using the Audit

   o  The New Entity completes bootstrapping as detailed in EST section

   In order to obtain a validated Audit Token and Audit Log the
   Registrar contacts the MASA service Service using REST calls:

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              +-----------+ +----------+ +-----------+ +----------+
              | New       | | Circuit  | |           | |          |
              | Entity    | | Proxy    | | Registrar | | Vendor   |
              |           | |          | |           | |          |
              ++----------+ +--+-------+ +-----+-----+ +--------+-+
               |               |               |                |
               |               |               |                |
               |   TLS hello   |  TLS hello    |                |
   Establish   +---------------C--------------->                |
   TLS         |               |               |                |
   connection  |               | Server Cert   |                |
               <---------------C---------------+                |
               | Client Cert   |               |                |
               +---------------C--------------->                |
               |               |               |                |
   HTTP REST   | POST /requestaudittoken       |                |
   Data        +--------------------nonce------>                |
               |               .               | /requestaudittoken
               |               .               +---------------->
               |                               <----------------+
               |                               | /requestauditlog
               |                               +---------------->
               | audit token or owner voucher  <----------------+
               <-------------------------------+                |
               | (optional config information) |                |
               |               .               |                |
               |               .               |                |

   Figure 5

   In some use cases the Registrar may need to contact the Vendor in
   advanced, for example when the target network is air-gapped.  The
   nonceless request format is provided for this and the resulting flow
   is slightly different.  The security differences associated with not
   knowing the nonce are discussed below:

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              +-----------+ +----------+ +-----------+ +----------+
              | New       | | Circuit  | |           | |          |
              | Entity    | | Proxy    | | Registrar | | Vendor   |
              |           | |          | |           | |          |
              ++----------+ +--+-------+ +-----+-----+ +--------+-+
               |               |               |                |
               |               |               |                |
               |               |               | /requestaudittoken
               |               |  (nonce       +---------------->
               |               |  unknown)     <----------------+
               |               |               | /requestauditlog
               |               |               +---------------->
               |               |               <----------------+
               |   TLS hello   |  TLS hello    |                |
   Establish   +---------------C--------------->                |
   TLS         |               |               |                |
   connection  |               | Server Cert   |                |
               <---------------C---------------+                |
               | Client Cert   |               |                |
               |               |               |                |
   HTTP REST   | POST /requestaudittoken       |                |
   Data        +----------------------nonce---->   (discard     |
               | audit token or owner Voucher  |   nonce)       |
               <-------------------------------+                |
               | (optional config information) |                |
               |               .               |                |
               |               .               |                |

   Figure 6

   The extensions for the Registrar server are as follows:

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

   o  The Registrar forwards the Audit Token to the New Entity when

   o  The Registar performs log verifications in addition to local
      authorization checks before accepting the New Entity device.

5.1.  Request Audit Token from the Registrar

   When the New Entity reaches the EST section 4.1.1 "Bootstrap
   Distribution of CA Certificates" state but wishes to proceed in a
   fully automated fashion it makes a request for a MASA authorization
   token from the Registrar.

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

   The request format is JSON object containing a 64bit nonce generated
   by the client for each request.  This nonce MUST be a
   cryptographically strong random or pseudo-random number that can not
   be easily predicted.  The nonce MUST NOT be reused for multiple
   attempts to join a network domain.  The nonce assures the New Entity
   that the audit token response is associated with this bootstrapping
   attempt and is not a replay.

   Request media type: application/auditnonce

   Request format: a JSON file with the following:

    "nonce":"<64bit nonce value>",

   [[EDNOTE: Even if the nonce was signed it would provide no defense
   against rogue registrars; although it would assure the MASA that a
   certified new entity exists.  To protect against rogue registrars a
   nonce component generated by the MASA (a new round trip) would be
   required).  Instead this is addressed by requiring MASA & Registrar
   authentications but it is worth exploring additional protections.
   This to be explored more at IETF96.]]

   The Registrar validates the client identity as described in EST
   [RFC7030] section 3.3.2.  The registrar performs authorization as
   detailed in Section 3.3.2.  If authorization is successful the
   Registrar obtains an Audit Token from the MASA service (see
   Section 5.2).

   The received MASA authorization token is returned to the New Entity.

   As indicated in EST [RFC7030] the bootstrapping server can redirect
   the client to an alternate server.  If the New Entity authenticated
   the Registrar using the well known URI method then the New Entity
   MUST follow the redirect automatically and authenticate the new
   Registrar against the redirect URI provided.  If the New Entity had
   not yet authenticated the Registrar because it was discovered and was
   not a known-to-be-valid URI then the new Registrar must be
   authenticated using one of the two autonomic methods described in
   this document.  Similarly 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.

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   Recall that during this communication with the Registar the TLS
   authentication is only provisional.  The New Entity client MUST
   handle all data from the Registrar with upmost care.  In particular
   the New Entity MUST only allow a single redirection and MUST only
   support a delay of five seconds before declaring the Registrar a
   failure and moving on to the next discovered Registrar.  As detailed
   in Section 3.1.1 if no suitable Registrar is found the New Entity
   restarts the state machine and tries again.  So a Registrar that is
   unable to complete the transaction the first time will have future

5.2.  Request Audit Token from MASA

   The Registrar requests the Audit Token from the MASA service using a
   REST interface.  For simplicity this is defined as an optional EST
   message between the 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

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

   The request format is a JSON object optionally containing the nonce
   value (as obtained from the bootstrap request) and the IEEE 802.1AR
   identity of the device as a serial number (the full certificate is
   not needed and no proof-of-possession information for the device
   identity is included).  The AuthorityKeyIdentifier value from the
   certificate is included to ensure a statistically unique identity.
   The New Entity's serial number is extracted from the IEEE 802.1AR
   subject name id-at-serialNumber or it is the base64 encoded RFC4108
   hardwareModuleName hwSerialNum:

    "nonce":"<64bit nonce value>",
    "IDevIDAuthorityKeyIdentifier":"<base64 encoded keyIdentifier">,
    "DevIDSerialNumber":"<id-at-serialNumber or base64 encoded
                          hardwareModuleName hwSerialNum>",

   The Registrar MAY exclude the nonce from the request.  Doing so
   allows the Registrar to request an authorization token when the New
   Entity is not online, or when the target bootstrapping environment is
   not on the same network as the MASA server (this requires the
   Registrar to learn the appropriate DevIDSerialNumber field from the

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   physical device labeling or from the sales channel -- how this occurs
   is out-of-scope of this document).  If a nonce is not provided the
   MASA server MUST authenticate the client as described in EST
   [RFC7030] section 3.3.2 to reduce the risk of DDoS attacks.  The
   registrar performs authorization as detailed in Section 3.3.2.  If
   authorization is successful the Registrar obtains an Audit Token from
   the MASA service (see Section 5.2).

   The JSON message information is encapsulated in a [RFC5652] Signed-
   data that is signed by the Registrar.  The entire certificate chain,
   up to and including the Domain CA, MUST be included in the
   CertificateSet structure.  The MASA service checks the internal
   consistency of the CMS but does not authenticate the domain identity
   information.  The domain is not know to the MASA server in advance
   and a shared trust anchor is not implied.  The MASA server MUST
   verify that the CMS is signed by a Registrar certificate (by checking
   for the cmc-idRA field) that was issued by a the root certificate
   included in the CMS.  This ensures that the Registrar making the
   claim is an authorized Registrar of the unauthenticated domain.  The
   EST style client authentication (TLS and HTTP) is used to provide a
   DDoS prevention strategy.

   The domain ID (e.g. hash of the public key of the domain) is
   extracted from the root certificate and is used to populate the MASA
   authorization token and to update the audit log.

5.3.  Audit Token Response

   The authorization token response to requests from the device and
   requests from the Registrar are in the same format.  The Registrar
   either caches prior MASA responses or dynamically requests a new
   Audit Token based on local policy.

   If the the join operation is successful, the server response MUST
   contain an HTTP 200 response code with a content-type of
   "application/authorization-token".  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 error message containing explanatory information describing
   why the request was rejected.

   The authorization token consists of the nonce, if supplied, the
   serial number information identifying the device and the domain CA
   certificate extracted from the request:

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    "nonce":"<64bit nonce value>",
    "IDevIDAuthorityKeyIdentifier":"<base64 encoded keyIdentifier>",
    "domainCAcert":"<the base64 encoded domain CA's certificate>"

   The audit token response is encapsulated in a [RFC5652] Signed-data
   that is signed by the MASA server.  The New Entity verifies this
   signed message using the IEEE 802.1AR manufacturer installed trust

   [[EDNOTE: Using CMS is consistent with the alignment of this
   bootstrapping document with EST, a PKIX enrollment protocol that
   includes Certificate Management over CMS.  An alternative format
   would be the RFC7515 JSON Web Signature (JWS), which would allow
   clients that do not use fullCMC messages to avoid CMS entirely.  Use
   of JWS would likely include a discussion of CBOR in order ensure the
   base64 expansions of the certs and signatures within the JWS message
   are of minimal size -- it is not yet clear to this author how that
   would work out]]

   The 'domainCAcert' element of this message contains the domain CA's
   public key.  This is specific to bootstrapping a public key
   infrastructure.  To support bootstrapping other key infrastructures
   additional domain identity types might be defined in the future.
   Clients MUST be prepared to ignore additional fields they do not
   recognize.  Clients MUST be prepared to parse and fail gracefully
   from an audit token response that does not contain a 'domainCAcert'
   field at all.

   To minimize the size of the audit token response message the
   domainCAcert is not a complete distribution of the EST section 4.1.3
   CA Certificate Response.

   The New Entity installs the domainCAcert trust anchor.  As indicated
   in Section 3.1.2 the newly installed trust anchor is used as an EST
   RFC7030 Explicit Trust Anchor.  The New Entity MUST use the
   domainCAcert trust anchor to immediately validate the currently
   provisional TLS connection to the Registrar.

5.3.1.  Completing authentication of Provisional TLS connection

   If the Registrar's credential can not be verified using the
   domainCAcert trust anchor the TLS connection is immediately discarded
   and the New Entity abandons attempts to bootstrap with this
   discovered registrar.

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   The following behaviors on the Registrar and New Entity are in
   addition to normal PKIX operations:

   o  The EST server MUST use a certificate that chains to the
      domainCAcert.  This means that when the EST server obtains renewed
      credentials the credentials included in the Section 5.2 request
      match the chain used in the current provisional TLS connection.

   o  The New Entity PKIX path validation of the Registrar validity
      period information is as described in Section 3.1.5.

   Because the domainCAcert trust anchor is installed as an Explicit
   Trust Anchor it 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 New Entity SHOULD avoid additional discovery
   operations.  Instead the New entity SHOULD communicate directly with
   the Registrar as the EST server to complete PKI local certificate
   enrollment.  Additionally the New Entity SHOULD use the existing TLS
   connection to proceed with EST enrollment, thus reducing the total
   amount of cryptographic and round trip operations required during
   bootstrapping.  [[EDNOTE: It is reasonable to mandate that the
   existing TLS connection be re-used? e.g.  MUST >> SHOULD?]]

5.4.  Audit Token Status Telemetry

   For automated bootstrapping of devices the adminstrative elements
   providing bootstrapping also provide indications to the system
   administrators concerning device lifecycle status.  To facilitate
   this those elements need telemetry information concerning the
   device's status.

   To indicate New Entity status regarding the audit token the client
   SHOULD post a status message.

   The client HTTP POSTs the following to the server at the EST well
   known URI /requestaudittoken_status.  The Status field indicates if
   the audit token 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 audit
   token was ignored by a client the registar expected to continue
   joining the domain.

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     "Status":FALSE /* TRUE=Success, FALSE=Fail"
     "Reason":"Informative human readable message"

   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.

5.5.  MASA authorization log Request

   A registrar requests the MASA authorization log from the MASA service
   using this EST extension.

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

   The client HTTP POSTs the same Audit Token Request as for requesting
   an audit token but now posts it the /requestMASAlog URI instead.  The
   IDevIDAuthorityKeyIdentifier and DevIDSerialNumber informs the MASA
   server which log is requested so the appropriate log can be prepared
   for the response.

5.6.  MASA authorization log Response

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

       "date":"<date/time of the entry>",
       "domainID":"<domainID as extracted from the domain CA certificate
                    within the CMS of the audit token request>",
       "nonce":"<any nonce if supplied (or the exact string 'NULL')>"
       "date":"<date/time of the entry>",
       "domainID":"<domainID as extracted from the domain CA certificate
                    within the CMS of the audit token request>",
       "nonce":"<any nonce if supplied (or the exact string 'NULL')>"

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

   The Registrar uses this log information to make an informed decision
   regarding the continued bootstrapping of the New Entity.  For example
   if the log includes unexpected domainIDs this is indicative of
   problematic imprints by the new entity.  If the log includes nonce-
   less entries this is indicative of the permanent ability for the
   indicated domain to trigger a reset of the device and take over
   management of it.  Equipment that is purchased pre-owned can be
   expected to have an extensive history.

   Log entries containing the Domain's ID can be compared against local
   history logs in search of discrepancies.

5.7.  EST Integration for PKI bootstrapping

   The prior sections describe EST extensions necessary to enable fully
   automated bootstrapping.  Although the audit token request/response
   structure members IDevIDAuthorityKeyIdentifier and DevIDSerialNumber
   are specific to PKI bootstrapping these are the only PKI specific
   aspects of the extensions and future work might replace them with
   non-PKI structures.

   The prior sections provide functionality for the New Entity to obtain
   a trust anchor representative of the Domain.  The following section
   describe using EST to obtain a locally issued PKI certificate.  The
   New Entity MAY perform alternative enrollment methods or proceed to
   use its IDevID credential indefinately, but those that leverage the
   discovered Registrar to proceed with certificate enrollment MUST
   implement the following EST choices.

5.7.1.  EST Distribution of CA Certificates

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

   This ensures that the New Entity has the complete set of current CA
   certificates beyond the domainCAcert (see Section 5.3 for a
   discussion of the limitations).  Although these restrictions are
   acceptable for the Registrar integrated with initial bootstrapping
   they are not appropriate for ongoing PKIX end entity certificate

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5.7.2.  EST CSR Attributes

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

   To alleviate operational difficulty the New Entity MUST request the
   EST "CSR Attributes" from the EST server.  This allows the local
   infrastructure to inform the New Entity of the proper fields to
   include in the generated CSR.

   [[EDNOTE: The following is specific to anima purposes and should be
   moved to an appropriate anima document so as to keep bootstrapping as
   generic as possible: What we want are a 'domain name' stored in [TBD]
   and an 'ACP IPv6 address' stored in the iPAddress field as specified
   in RFC5208 s4.2.1.6. ref ACP draft where certificate verification
   [TBD].  These should go into the subjectaltname in the [TBD]
   fields.]].  If the hardwareModuleName in the IDevID is populated then
   it SHOULD by default be propagated to the LDevID along with the
   hwSerialNum.  The registar SHOULD support local policy concerning
   this functionality.  [[EDNOTE: extensive use of EST CSR Attributes
   might need an new OID definition]].]]

   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

5.7.3.  EST Client Certificate Request

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

5.7.4.  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
   include information concerning attempted bootstrapping messages seen

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   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 failure 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 this field is ommited from the status telemetry.

   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"
    "SubjectKeyIdentifier":"<base64 encoded subjectkeyidentifier for the
                             enrollment that failed>"

   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
   recieved over an TLS session with a matching client certificate.
   This allows for clients that wish to minimize their crypto operations
   to simpy 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.

5.7.5.  EST over CoAP

   [[EDNOTE: In order to support smaller devices the above section on
   Proxy behavior introduces mandatory to implement support for CoAP
   support by the Proxy.  This implies similar support by the New Entity
   and Registrar and means that the EST protocol operation encapsulation
   into CoAP needs to be described.  EST is HTTP based and "CoaP is
   designed to easily interface with HTTP for integration" [RFC7252].
   Use of CoAP implies Datagram TLS (DTLS) wherever this document
   describes TLS handshake specifics.  A complexity is that the large

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   message sizes necessary for bootstrapping will require support for

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 New Entity, Registrar and MASA
   can be configured to run in a less secure mode for the indicated

6.1.  Trust Model

   +--------+         +---------+    +------------+     +------------+
   | New    |         | Circuit |    | Domain     |     | Vendor     |
   | Entity |         | Proxy   |    | Registrar  |     | Service    |
   |        |         |         |    |            |     | (Internet  |
   +--------+         +---------+    +------------+     +------------+

   Figure 7

   New Entity:  The New Entity 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 document.

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

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

   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
      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.

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6.2.  New Entity security reductions

   Although New Entity can choose to run in less secure modes this is
   MUST NOT be the default state because it permanently degrades the
   security for all other uses cases.

   The device may have an operational mode where it skips Audit Token or
   Ownership 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 unsecure imprint.

   It is RECOMMENDED that this only be available if hardware assisted
   NEA [RFC5209] is supported.

6.3.  Registrar security reductions

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

   2.  The registrar MAY choose to accept devices that claim a unique
       identity without the benefit of authenticating that claimed
       identity.  This could occur when the New Entity does not include
       an IEEE 802.1AR factory installed credential.  New Entities
       without an IDevID credential MAY form the Section 5.1 request
       using the Section 5.2 format to ensure the New Entity's serial
       number information is provided to the Registar (this includes the
       IDevIDAuthorityKeyIdentifier value which would be statically
       configured on the New Entity).  The New Entity MAY refused to
       provide a TLS client certificate (as one is not available).  The
       New Entity SHOULD support HTTP-based or certificate-less TLS
       authentication as described in EST RFC7030 section 3.3.2.

   3.  The registrar MAY request nonce-less Audit Tokens from the MASA
       service.  These tokens can then be transmitted to the Registrar
       and stored 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 New
       Entity deployment.

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   4.  The registrar MAY ignore unrecognized nonce-less Audit Log
       entries.  This could occur when used equipment is purchased with
       a valid history being deployed in air gap networks that required
       permanent Audit Tokens.

   These modes are not available for devices that require a vendor
   Ownership Voucher.  The methods vendors use to determine which
   devices are owned by which domains is out-of-scope.

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 Audit Token.  This results
       in distribution of Audit Tokens that never expire and in effect
       makes the Domain an always trusted entity to the New Entity
       during any subsequent bootstrapping attempts.  That this occurred
       is captured in the log information so that the Domain registrar
       can make appropriate security decisions when a New Entity 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 Audit Tokens and do not require the
       proof that the device is online this is only accepted when the
       Registrar is authenticated by the MASA server and authorized to
       provide this functionality.  The MASA server is RECOMMENDED to
       use this functionality only in concert with Ownership Validation

   2.  Not verifying ownership before responding with an Audit Token.
       This is expected to be a common operational model because doing
       so relieves the vendor providing MASA services from having to
       tracking ownership during shipping and supply chain and allows
       for a very low overhead MASA service.  The 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).

7.  Security Considerations

   In order to support a wide variety of use cases, devices can be
   claimed by a registrar without proving possession of the device in
   question.  This would result in a nonceless, and thus always valid,
   claim.  Or would result in an invalid nonce being associated with a

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   claim.  The MASA service is required to authenticate such Registrars
   but no programmatic method is provided to ensure good behavior by the
   MASA service.  Nonceless entries into the audit log therefore
   permanently reduce the value of a device because future Registrars,
   during future bootstrap attempts, would now have to be configured
   with policy to ignore previously (and potentially unknown) domains.

   Future registrars are recommended to take the audit history of a
   device into account when deciding to join such devices into their
   network.  If the MASA server were to have allowed a significantly
   large number of claims this might become onerous to the MASA server
   which must maintain all the extra log entries.  Ensuring the
   Registrar is representative of a valid customer domain even without
   validating ownership helps to mitigate this.

   It is possible for an attacker to send an authorization request to
   the MASA service directly after the real Registrar obtains an
   authorization log.  If the attacker could also force the
   bootstrapping protocol to reset there is a theoretical opportunity
   for the attacker to use the Audit Token to take control of the New
   Entity but then proceed to enroll with the target domain.  Possible
   prevention mechanisms include:

   o  Per device rate limits on the MASA service ensure such timing
      attacks are difficult.

   o  In the advent of an unexpectedly lost bootstrapping connection the
      Registrar repeats the request for audit log information.

   To facilitate auditing the New Entity reports on audit token parsing
   status.  In the case of a failure this information is informative to
   the potentially malicious Registar but this is included because the
   operational benefits are concidered beneficial.

   As indicated in EST [RFC7030] the connection is provisional and
   untrusted until the server is successfully authorized.  If the server
   provides a redirect response the client MUST follow the redirect but
   the connection remains provisional.  If the client uses a well known
   URI for contacting a well known Registrar the EST Implicit Trust
   Anchor database is used as is described in RFC6125 to authenticate
   the well known URI.  In this case the connection is not provisional
   and RFC6125 methods can be used for each subsequent redirection.

   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 clients only
   "SHOULD" support such a model.  This reflects current (not great)
   practices but is NOT RECOMMENDED.

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   The MASA service could lock a claim and refuse to issue a new token
   or the MASA service could go offline (for example if a vendor went
   out of business).  This functionality provides benefits such as theft
   resistance, but it also implies an operational risk to the Domain
   that Vendor behavior could limit future bootstrapping of the device
   by the Domain.  This can be mitigated by Registrars that request
   nonce-less authorization tokens.

8.  Acknowledgements

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

9.  References

9.1.  Normative References

   [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, May 2003.

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

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

   [RFC5386]  Williams, N. and M. Richardson, "Better-Than-Nothing
              Security: An Unauthenticated Mode of IPsec", RFC 5386,
              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, October 2009.

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

   [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,

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

9.2.  Informative References

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

              Gerdes, S., Seitz, L., Selander, G., and C. Bormann, "An
              architecture for authorization in constrained
              environments", draft-ietf-ace-actors-03 (work in
              progress), March 2016.

              Watsen, K. and M. Abrahamsson, "Zero Touch Provisioning
              for NETCONF or RESTCONF based Management", draft-ietf-
              netconf-zerotouch-08 (work in progress), April 2016.

              Behringer, M., Pritikin, M., Bjarnason, S., Clemm, A.,
              Carpenter, B., Jiang, S., and L. Ciavaglia, "Autonomic
              Networking - Definitions and Design Goals", draft-irtf-
              nmrg-autonomic-network-definitions-07 (work in progress),
              March 2015.

              Lear, E., "Manufacturer Usage Description Framework",
              draft-lear-mud-framework-00 (work in progress), January

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              Richardson, M., "Considerations for stateful vs stateless
              join router in ANIMA bootstrap", draft-richardson-anima-
              state-for-joinrouter-00 (work in progress), January 2016.

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

   [pledge], , " Unabridged", July 2015,

Authors' Addresses

   Max Pritikin


   Michael C. Richardson
   Sandelman Software Works
   470 Dawson Avenue
   Ottawa, ON  K1Z 5V7


   Michael H. Behringer


   Steinthor Bjarnason


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