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ANIMA WG                                                     M. Pritikin
Internet-Draft                                                     Cisco
Intended status: Informational                             M. Richardson
Expires: May 4, 2017                                                 SSW
                                                            M. Behringer
                                                            S. Bjarnason
                                                                   Cisco
                                                               K. Watsen
                                                        Juniper Networks
                                                        October 31, 2016


        Bootstrapping Remote Secure Key Infrastructures (BRSKI)
               draft-ietf-anima-bootstrapping-keyinfra-04

Abstract

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

Status of This Memo

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

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

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

   This Internet-Draft will expire on May 4, 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
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include 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 . . . . . . . . . . . . . . . . . . . . . . .   5
     1.2.  Scope of solution . . . . . . . . . . . . . . . . . . . .   7
     1.3.  Trust bootstrap . . . . . . . . . . . . . . . . . . . . .   8
   2.  Architectural Overview  . . . . . . . . . . . . . . . . . . .   8
   3.  Functional Overview . . . . . . . . . . . . . . . . . . . . .  10
     3.1.  Behavior of a Pledge  . . . . . . . . . . . . . . . . . .  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 . . . . . . . . . . . . . . . .  20
       3.3.1.  Pledge Authentication . . . . . . . . . . . . . . . .  21
       3.3.2.  Pledge Authorization  . . . . . . . . . . . . . . . .  22
       3.3.3.  Claiming the New Entity . . . . . . . . . . . . . . .  23
       3.3.4.  Log Verification  . . . . . . . . . . . . . . . . . .  23
     3.4.  Behavior of the MASA Service  . . . . . . . . . . . . . .  24
       3.4.1.  Issue Audit Voucher and Log the event . . . . . . . .  24
       3.4.2.  Retrieve Audit Entries from Log . . . . . . . . . . .  24
     3.5.  Leveraging the new key infrastructure / next steps  . . .  25
       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  . . . .  26
     4.2.  Instantiating the Registrar . . . . . . . . . . . . . . .  26



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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  . . . . . . . . . . . . . . . . . . . . . .  28
     5.1.  Request Voucher from the Registrar  . . . . . . . . . . .  30
     5.2.  Request Voucher from MASA . . . . . . . . . . . . . . . .  32
     5.3.  Audit Voucher Response  . . . . . . . . . . . . . . . . .  33
       5.3.1.  Completing authentication of Provisional TLS
               connection  . . . . . . . . . . . . . . . . . . . . .  34
     5.4.  Voucher 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  . . . . . . . . . . . . . . . . .  37
       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  . . . . . . . . . . . . .  39
     6.1.  Trust Model . . . . . . . . . . . . . . . . . . . . . . .  40
     6.2.  New Entity security reductions  . . . . . . . . . . . . .  40
     6.3.  Registrar security reductions . . . . . . . . . . . . . .  41
     6.4.  MASA security reductions  . . . . . . . . . . . . . . . .  42
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  42
     7.1.  Security concerns with discovery process  . . . . . . . .  44
       7.1.1.  Discovery of Registrar by Proxy . . . . . . . . . . .  44
       7.1.2.  Discovery of Proxy by New Entity  . . . . . . . . . .  44
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  44
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  44
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  44
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  46
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  47

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 issued X.509 certificates and
   cryptographically signed "vouchers" issued by a new form of cloud
   service.





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   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
   device, or "pledge", being added:

   o  Pledge authentication: "Who is this?  What is its identity?"

   o  Pledge 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 an established key infrastructure(s).  The pledge's
   decisions are made according to verified communication with a trusted
   third-party.  The domain's decisions are made by comparing the
   pledge's authenticated identity against domain information such as a
   configured list of purchased devices supplimented by information
   provided by a trusted third-party.  The third-party is not required
   to provide sales channel ownership tracking nor is it required to
   authenticate the domain.

   Optimal security is achieved with X.509 certificates on each Pledge,
   accompanied by a third-party (e.g., vendor, manufacturer or
   integrator) 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
   pledge.

   The result of bootstrapping is that a domain specific key
   infrastructure is deployed.  Since X.509 PKI certificates are used
   for identifying the pledge, 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.








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1.1.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   [RFC2119].

   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
      Certification Authority subject key identifier (Section 4.2.1.2
      [RFC5280]) 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
      drop-ship.

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

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

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

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



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   Audit Voucher:  A voucher from the MASA service that indicates that
      the bootstrapping event has been successfully logged.  The
      Registrar is primarily responsible for verifying the logs and
      ensuring domain network security.

   Ownership Voucher:  A voucher from the MASA service that indicates
      the explicit owner identity.  The MASA is primarily responsible
      for tracking ownership using out-of-band sales channel integration
      (the definition of which is out-of-scope of this document).  It is
      defined in [I-D.ietf-netconf-zerotouch].

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

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

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

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

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

   Ownership Tracker  An Ownership Tracker service on the global
      internet.  The Ownership Tracker uses business processes to
      accurately track ownership of all devices shipped against domains
      that have purchased them.  Although optional this component allows
      vendors to provide additional value in cases where their sales and
      distribution channels allow for accurately tracking of such
      ownership.




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   IDevID  An Initial Device Identity X.509 certificate installed by the
      vendor on new equipment.  The [IDevID] certificate format is the
      primary example.  In particular the X.509 certificate needs to
      contain the device's serial number in a well known location in
      order to perform white list operations and in order to extract it
      for inclusion in messages to the MASA service.  The subject
      field's DN encoding MUST include the "serialNumber" attribute with
      the device's unique serial number.

1.2.  Scope of solution

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

   The 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 optimized for speed; the discovery
   process allows for the Pledge to avoid broadcasting for privacy
   reasons.  This protocol is not intended for low latency handoffs.

   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




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   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).

   The use of an IDevID that is consistant with [IDevID] allows for
   alignment with 802.1X network access control methods which could need
   to complete before bootstrapping can be initiated.  This document
   presumes that network access control has either already occured, is
   not required, or is integrated by the proxy and registrar in such a
   way that the device itself does not need to be aware of the details.
   Further integration is not in scope.

   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 a
   domain Registrar and the Pledge.  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 tokens.

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

   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
   vendors.

   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
   models.




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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 [RFC7575] for more information.

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

   A representative flow is shown in Figure 2:

     +--------+         +---------+    +------------+     +------------+
     | Pledge |         | Circuit |    | Domain     |     | Vendor     |
     |        |         | 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---X.509 client authentication---------->|                    |
      P                     |                   |                    |
      P---Request Voucher (include nonce)------>|                    |
      P                     |                   |                    |
      P                     |       /--->       |                    |
      P                     |       |      [accept device?]          |
      P                     |       |      [contact Vendor]          |
      P                     |       |           |--Pledge ID-------->|
      P                     |       |           |--Domain ID-------->|
      P                     |       |           |--optional:nonce--->|
      P                     |       |           |     [extract DomainID]
      P                     |       |           |                    |
      P                     |    optional:      |     [update audit log]
      P                     |       |can        |                    |
      P                     |       |occur      |                    |



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      P                     |       |in         |                    |
      P                     |       |advance    |                    |
      P                     |       |           |                    |
      P                     |       |           |<-device audit log--|
      P                     |       |           |<- voucher ---------|
      P                     |       \---->      |                    |
      P                     |                   |                    |
      P                     |       [verify audit log and voucher]   |
      P                     |                   |                    |
      P<------voucher---------------------------|                    |
  [verify voucher ]         |                   |                    |
  [verify provisional cert ]|                   |                    |
      |                     |                   |                    |
      |---------------------------------------->|                    |
      | Continue with RFC7030 enrollment        |                    |
      | using now bidirectionally authenticated |                    |
      | TLS session.        |                   |                    |
      |                     |                   |                    |
      |                     |                   |                    |
      |                     |                   |                    |

   Figure 2

3.1.  Behavior of a Pledge

   A pledge that has not yet been bootstrapped attempts to find a local
   domain and join it.  A pledge MUST NOT automatically initiate
   bootstrapping if it has already been configured or is in the process
   of being configured.

   States of a pledge are as follows:




















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


   Figure 3

   State descriptions for the pledge are as follows:

   1.  Discover a communication channel to a Registrar.

   2.  Identify itself.  This is done by presenting an IDevID X.509
       credential to the discovered Registrar (via the Proxy) in a TLS
       handshake.  (The Registrar 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 provided "Audit" or "Ownership" Voucher.  Either
       of these responses contains sufficient information for the pledge
       to complete authentication of a Registrar.  (The pledge can now
       finish authentication of the Registrar TLS server certificate)

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

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

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

3.1.1.  Discovery

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

   To discover the Registrar the Pledge 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.  The Plege MAY obtain an IP address via
       DHCP [RFC2131].  The DHCP provided parameters for the Domain Name
       System can be used to perform step (d) DNS operations if all
       local discovery attempts fail (see below).

   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 Pledge SHOULD listen
       for an unsolicited broadcast response as described in [RFC6762].
       This allows devices to avoid announcing their presence via mDNS
       broadcasts and instead silently join a network by watching for
       periodic unsolicited broadcast responses.





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   c.  MAY: Performs DNS-based Service Discovery [RFC6763] over normal
       DNS operations.  The service searched for is
       "_bootstrapks._tcp.example.com".  In this case the domain
       "example.com" 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 Pledge contacts a well known
       vendor provided bootstrapping server by performing a DNS lookup
       using a well known URI such as "bootstrapks.vendor-example.com".
       The details of the URI are vendor specific.  Vendors that
       leverage this method on the Pledge are responsible for providing
       the bootstrapks service.

   DNS-based service discovery communicates the local proxy IPv4 or IPv6
   address and port to the Pledge.  Once a proxy is discovered the
   Pledge communicates with a 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 Pledge returns to the
   Discovery state it picks up where it left off and continues
   attempting bootstrapping.  For example if the first Multicast DNS
   _bootstrapks._tcp.local response doesn't work then the second and
   third responses are tried.  If these fail the Pledge moves on to
   normal DNS-based Service Discovery.

   Each discovery method attempted SHOULD exponentially back-off
   attempts (to a maximum of one hour) to avoid overloading the network
   infrastructure with discovery.  The back-off timer for each method
   MUST be independent of other methods.  Methods SHOULD be run in
   parallel to avoid head of queue problems.  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 Pledge may prioritize selection order as appropriate
   for the anticipated environment.

3.1.2.  Identity

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

   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.
   This is aligned with the existing provisional mode of EST [RFC7030]



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   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 Pledge POSTs a request to join the domain to the Bootstrapping
   server.  This request contains a Pledge generated nonce and informs
   the Bootstrapping server which imprint methods the Pledge 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 Pledge has resorted to a well known vendor URI and is
   communicating with the vendor's Registrar directly.  In this case the
   Pledge 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 Pledge 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 Pledge during the
   bootstrapping protocol methods in the form of a 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
      involved),






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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
      autonomic),

   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 autonomic methods that MUST be supported by
   the Pledge:

   Audit Voucher  Audit Vouchers are obtained by a Registrar from the
      MASA service and presented to the Pledge for validation.  These
      indicate to the Pledge that joining the domain has been logged by
      a logging service.

   Ownership Voucher  Ownership Vouchers are obtained by a Registrar
      from the MASA service and explicitly indicate the owner of the
      Pledge.  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 Voucher contains the domain's public key material as
   provided to the MASA service by a Registrar.  This provides
   sufficient information to the client to complete automated
   bootstrapping with the local key infrastructure.  The Ownership
   Voucher contains the Owner Certificate which the Pledge uses to
   authenticate the TLS connection.

   If the autonomic methods fail the Pledge returns to discovery state
   and attempts bootstrapping with the next available discovered
   Registrar.

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 Pledge maintaining a concept of the current "window"




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   of presumed time validity that is continually refined throughout the
   bootstrapping process as follows:

   o  Initially the Pledge does not know the current time.

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

   o  Once the Audit Voucher is accepted the validity period of the
      domainCAcert in the voucher (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 certificate is assumed to be valid by the Pledge.
      The Pledge is now willing to use this credential for client
      authentication.

   Once in this state the Pledge 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.

   The nonce included in join attempts provides an alternate mechanism
   for the Pledge to ensure Audit Voucher responses are associated with
   a particular bootstrapping attempt.  Nonceless Audit Vouchers from
   the MASA server are always valid and thus time is not needed.

   Ownership Vouchers include time information and MUST be validated
   using a realtime clock.

3.1.6.  Enrollment

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






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   Enrollment proceeds as described in [RFC7030].  Authentication of the
   EST server is done using the Voucher rather than the methods defined
   in EST.

   Once the Audit or Ownership Voucher is received, as specified in this
   document, the client has sufficient information to leverage the
   existing communication channel with a Registrar to continue an EST
   RFC7030 enrollment.  Enrollment picks up at RFC7030 section 4.1.1.
   bootstrapping where the Audit Voucher 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 Pledge 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 Pledge and a Registrar that has been
   configured on the Proxy.  The Proxy does not terminate the TLS
   handshake.  A Proxy is always assumed even if directly integrated
   into a Registrar.

   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.

   If the Proxy joins an Autonomic Control Plane
   ([I-D.ietf-anima-autonomic-control-plane]) it SHOULD use Autonomic



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   Control Plane secured GRASP ([I-D.ietf-anima-grasp]) to discovery the
   Registrar address and port.  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 stateless.

   In order to permit the proxy functionality to be implemented on the
   maximum variety of devices the chosen mechanism SHOULD use the
   minimum amount of state on the proxy device.  While many devices in
   the ANIMA target space will be rather large routers, the proxy
   function is likely to be implemented in the control plane CPU 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.]]

   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 (link-
   local) 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 Pledge to a Registrar.

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





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   When the Proxy provides a stateless IPIP encapsulation to a
   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

   A Registrar listens for Pledges and determines if they can join the
   domain.  A Registrar obtains a Voucher from the MASA service and
   delivers them to the Pledge as well as facilitating enrollment with
   the domain PKI.

   A Registrar is typically configured manually.  If the Registrar joins
   an Autonomic Control Plane ([I-D.ietf-anima-autonomic-control-plane])
   it MUST use Autonomic Control Plane secured GRASP
   ([I-D.ietf-anima-grasp]) to broadcast the Registrar's address and
   port to potential Proxies.

   Registrar behavior is as follows:























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

   Figure 4

3.3.1.  Pledge Authentication

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

   o  the use of an IDevID X.509 credential during the TLS client
      authentication,

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

   In order to validate the IDevID X.509 credential a 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.



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3.3.2.  Pledge Authorization

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

   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 X.509
      IDevID),

   o  allow any device from a specific vendor (as determined by the
      X.509 IDevID),

   o  allow a specific device from a vendor (as determined by the X.509
      IDevID) against a domain white list.  (The mechanism for checking
      a shared white list potentiatlly used by multiple Registrars is
      out of scope).

   To look the Pledge up in a domain white list a consistent method for
   extracting device identity from the X.509 certificate is required.
   RFC6125 describes Domain-Based Application Service identity but here
   we require Vendor Device-Based identity.  The subject field's DN
   encoding MUST include the "serialNumber" attribute with the device's
   unique serial number.  In the language of RFC6125 this provides for a
   SERIALNUM-ID category of identifier that can be included in a
   certificate and therefore that can also be used for matching
   purposes.  The SERIALNUM-ID whitelist is collated according to vendor
   trust anchor since serial numbers are not globally unique.

   Since all Pledges accept Audit Vouchers a 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, a Registrar of that domain would show
   in the log.

   If a Pledge is accepted into the domain, it is expected to 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 be used for
   other methods, for example boundary detection, auto-securing
   protocols, etc.).  The authorization performed during this phase is
   used for EST enrollment requests.







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3.3.3.  Claiming the New Entity

   Claiming an entity establishes an audit log at the MASA server and
   provides a Registrar with proof, in the form of a MASA Audit Voucher,
   that the log entry has been inserted.  As indicated in Section 3.1.4
   a Pledge will only proceed with bootstrapping if a validated MASA
   Audit Voucher has been received.  The Pledge 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 Registrar.

   Registrar's obtain the Vendor URI via static configuration or by
   extracting it from the X.509 IDevID credential.  The imprint method
   supported by the Pledge is known from the X.509 IDevID 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 Pledge provides a nonce specific to
   the particular bootstrapping attempt.  The Registrar SHOULD include
   this nonce when claiming the Pledge 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 Pledge that is not online by forming the
   request using the entities unique identifier and not including a
   nonce in the claim request.  Audit Voucher 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
   although no requirement is implied that the MASA associates this
   authentication with ownership.

   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.  A MASA ignores or reports failures when an
   attempt is made to claim a device that has a an Ownership Voucher.

3.3.4.  Log Verification

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

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



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

   If any of these criteria are unacceptable to a Registrar the entity
   is rejected.  A Registrar MAY be configured to ignore the history of
   the device but it is RECOMMENDED that this only be configured if
   hardware assisted NEA [RFC5209] is supported.

   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 Voucher
   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 X.509 IDevID extension (a "MASA Audit Voucher
   Distribution Point" extension).

   The MASA service provides the following functionalities to
   Registrars:

3.4.1.  Issue Audit Voucher 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 Voucher.  For the simple log format defined in this
   document using the DomainID is considered sufficient privacy.  Future
   work to improve the logging mechanism could include additional
   privacy protections.

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

3.4.2.  Retrieve Audit Entries from Log

   When determining if a Pledge 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



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   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.

   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 Pledge 's X.509 IDevID 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
   exchange.

4.  Domain Operator Activities

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





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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
   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 Pledge 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 a 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 a 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




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       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.

   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.








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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 Pledge, 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
   3.2.2.

   The Pledge 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 "Pledge" 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
   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 Pledge client are as follows:

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

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

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

   o  The Pledge completes bootstrapping as detailed in EST section
      4.1.1.

   In order to obtain a validated Audit Voucher and Audit Log a
   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 /requestvoucher          |                |
   Data        +--------------------nonce------>                |
               |               .               | /requestvoucher|
               |               .               +---------------->
               |                               <----------------+
               |                               | /requestlog    |
               |                               +---------------->
               |            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   |
              |           | |          | |           | |          |
              ++----------+ +--+-------+ +-----+-----+ +--------+-+
               |               |               |                |
               |               |               |                |
               |               |               | /requestvoucher|
               |               |  (nonce       +---------------->
               |               |  unknown)     <----------------+
               |               |               | /requestlog    |
               |               |               +---------------->
               |               |               <----------------+
               |   TLS hello   |  TLS hello    |                |
   Establish   +---------------C--------------->                |
   TLS         |               |               |                |
   connection  |               | Server Cert   |                |
               <---------------C---------------+                |
               | Client Cert   |               |                |
               |               |               |                |
   HTTP REST   | POST /requestvoucher          |                |
   Data        +----------------------nonce---->   (discard     |
               |            voucher            |   nonce)       |
               <-------------------------------+                |
               | (optional config information) |                |
               |               .               |                |
               |               .               |                |

   Figure 6

   The extensions for a Registrar server are as follows:

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

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

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

5.1.  Request Voucher from the Registrar

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

   This is done with an HTTPS POST using the operation path value of
   "/requestvoucher".



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   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 Pledge that
   the Audit Voucher 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:

   {
    "version":"1",
    "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 Pledge 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 Voucher from the MASA service (see Section 5.2).

   The received Voucher is forwarded to the Pledge.

   As indicated in EST [RFC7030] the bootstrapping server can redirect
   the client to an alternate server.  If the Pledge authenticated a
   Registrar using the well known URI method then the Pledge MUST follow
   the redirect automatically and authenticate the new Registrar against
   the redirect URI provided.  If the Pledge had not yet authenticated a
   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.

   Recall that during this communication with the Registar the TLS
   authentication is only provisional.  The Pledge client MUST handle
   all data from the Registrar with upmost care.  In particular the
   Pledge MUST only allow a single redirection and MUST only support a



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   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 Pledge restarts
   the state machine and tries again.  So a Registrar that is unable to
   complete the transaction the first time will have future chances.

5.2.  Request Voucher from MASA

   A Registrar requests a Voucher from the MASA service using a REST
   interface.  For simplicity this is defined as an optional EST message
   between a Registrar and an EST server running on the MASA service
   although the Registrar is not required to make use of any other EST
   functionality when communicating with the MASA service.  (The MASA
   service MUST properly reject any EST functionality requests it does
   not wish to service; a requirement that holds for any REST
   interface).

   This is done with an HTTP POST using the operation path value of
   "/requestvoucher".

   The request format is a JSON object optionally containing the nonce
   value (as obtained from the bootstrap request) and the X.509 IDevID
   extracted 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 Pledge's serial number
   is extracted from the X.509 IDevID subject name id-at-serialNumber or
   it is the base64 encoded RFC4108 hardwareModuleName hwSerialNum:

   {
    "version":"1",
    "nonce":"<64bit nonce value>",
    "IDevIDAuthorityKeyIdentifier":"<base64 encoded keyIdentifier">,
    "DevIDSerialNumber":"<id-at-serialNumber or base64 encoded
                          hardwareModuleName hwSerialNum>",
   }

   A Registrar MAY exclude the nonce from the request.  Doing so allows
   the Registrar to request a Voucher when the Pledge 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 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.  A Registrar performs
   authorization as detailed in Section 3.3.2.  If authorization is




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   successful the Registrar obtains an Voucher 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 root certificate is extracted and used to populate the Audit
   Voucher.  The domain ID (e.g. hash of the public key of the domain)
   is extracted from the root certificate and is used to update the
   audit log.

5.3.  Audit Voucher Response

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

   If the the join operation is successful, the server response MUST
   contain an HTTP 200 response code with a content-type of
   "application/authorizationvoucher".  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 Audit Voucher consists of the nonce, if supplied, the serial
   number information identifying the device and the domain CA
   certificate extracted from the request:

   {
    "version":"1",
    "nonce":"<64bit nonce value>",
    "IDevIDAuthorityKeyIdentifier":"<base64 encoded keyIdentifier>",
    "DevIDSerialNumber":"<id-at-serialNumber>",
    "domainCAcert":"<the base64 encoded domain CA's certificate>"
   }



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   The Audit Voucher response is encapsulated in a [RFC5652] Signed-data
   that is signed by the MASA server.  The Pledge verifies this signed
   message using the manufacturer installed trust anchor assocaited with
   the X.509 IDevID.  [[EDNOTE: As detailed in netconf-zerotouch this
   might be a distinct trust anchor rather than re-using the trust
   anchor for the IDevID.  This concept will need to be detailed in this
   document as well.]]

   [[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 Voucher response that does not contain a 'domainCAcert'
   field at all.

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

   The Pledge 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 Pledge MUST use the domainCAcert
   trust anchor to immediately validate the currently provisional TLS
   connection to a Registrar.

5.3.1.  Completing authentication of Provisional TLS connection

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

   The following behaviors on a Registrar and Pledge are in addition to
   normal PKIX operations:





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   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 Pledge PKIX path validation of a 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 Pledge SHOULD avoid additional discovery
   operations.  Instead the Pledge SHOULD communicate directly with the
   Registrar as the EST server to complete PKI local certificate
   enrollment.  Additionally the Pledge 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.  Voucher 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 Pledge status regarding the Audit Voucher the client
   SHOULD post a status message.

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

   {
     "version":"1",
     "Status":FALSE /* TRUE=Success, FALSE=Fail"
     "Reason":"Informative human readable message"
   }



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   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
   "/requestauditlog".

   The client HTTP POSTs the same Voucher Request as for requesting an
   audit token but now posts it to the /requestauditlog 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
   example:

  {
    "version":"1",
    "events":[
      {
       "date":"<date/time of the entry>",
       "domainID":"<domainID as extracted from the domain CA certificate
                    within the CMS of the audit voucher 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 voucher request>",
       "nonce":"<any nonce if supplied (or the exact string 'NULL')>"
      }
    ]
  }

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

   A Registrar uses this log information to make an informed decision
   regarding the continued bootstrapping of the Pledge.  For example if
   the log includes unexpected domainIDs this is indicative of



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   problematic imprints by the Pledge.  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 Voucher 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 Pledge to obtain a
   trust anchor representative of the Domain.  The following section
   describe using EST to obtain a locally issued PKI certificate.  The
   Pledge SHOULD leverage the discovered Registrar to proceed with
   certificate enrollment and, if they do, MUST implement the EST
   options described in this section.  The Pledge MAY perform
   alternative enrollment methods including discovering an alternate EST
   server, or proceed to use its IDevID credential indefinitely.

5.7.1.  EST Distribution of CA Certificates

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

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

5.7.2.  EST CSR Attributes

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



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   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 Pledge MUST request the EST
   "CSR Attributes" from the EST server.  This allows the local
   infrastructure to inform the Pledge 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
   guidance.

5.7.3.  EST Client Certificate Request

   The Pledge 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
   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




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   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.

  {
    "version":"1",
    "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 Pledge 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
   message sizes necessary for bootstrapping will require support for
   [draft-ietf-core-block].]]

6.  Reduced security operational modes

   A common requirement of bootstrapping is to support less secure
   operational modes for support specific use cases.  The following




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   sections detail specific ways that the Pledge, Registrar and MASA can
   be configured to run in a less secure mode for the indicated reasons.

6.1.  Trust Model

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

   Figure 7

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

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

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

6.2.  New Entity security reductions

   The Pledge MAY support "trust on first use" on physical interfaces
   but MUST NOT support "trust on first use" on network interfaces.
   This is because "trust on first use" permanently degrades the
   security for all other use cases.

   The Pledge MAY have an operational mode where it skips Voucher
   validation one time.  For example if a physical button is depressed
   during the bootstrapping operation.  This can be useful if the vendor



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   service is unavailable.  This behavior SHOULD be available via local
   configuration or physical presence methods to ensure new entities can
   always be deployed even when autonomic methods fail.  This allows for
   unsecured imprint.

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

6.3.  Registrar security reductions

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

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

   2.  A registrar MAY choose to accept devices that claim a unique
       identity without the benefit of authenticating that claimed
       identity.  This could occur when the Pledge does not include an
       X.509 IDevID factory installed credential.  New Entities without
       an IDevID credential MAY form the Section 5.1 request using the
       Section 5.2 format to ensure the Pledge's serial number
       information is provided to the Registar (this includes the
       IDevIDAuthorityKeyIdentifier value which would be statically
       configured on the Pledge).  The Pledge MAY refused to provide a
       TLS client certificate (as one is not available).  The Pledge
       SHOULD support HTTP-based or certificate-less TLS authentication
       as described in EST RFC7030 section 3.3.2.  A Registrar MUST NOT
       accept unauthenticated New Entities unless it has been configured
       to do so by an administrator that has verified that only expected
       new entities can communicate with a Registrar (presumably via a
       physically secured perimeter).

   3.  A Registrar MAY request nonce-less Audit Vouchers from the MASA
       service (by not including a nonce in the request).  These Audit
       Vouchers 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 Pledge
       deployment.

   4.  A registrar MAY ignore unrecognized nonce-less Audit Log entries.
       This could occur when used equipment is purchased with a valid




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       history being deployed in air gap networks that required
       permanent Audit Vouchers.

   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
   by:

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

   2.  Not verifying ownership before responding with an Audit Voucher.
       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.  A Registrar uses the audit
       log information as a defense in depth strategy to ensure that
       this does not occur unexpectedly (for example when purchasing new
       equipment the Registrar would throw an error if any audit log
       information is reported).

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
   claim.  The MASA service is required to authenticate such Registrars
   but no programmatic method is provided to ensure good behavior by the



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   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 a 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 Voucher to take control of the
   Pledge 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 logging and administrative oversight the Pledge reports
   on Audit Voucher parsing status to the Registrar.  In the case of a
   failure this information is informative to a potentially malicious
   Registar but this is RECOMMENDED anyway because of the operational
   benefits of an informed administrator in cases where the failure is
   indicative of a problem.

   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 voucher
   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 Audit Vouchers.

7.1.  Security concerns with discovery process

7.1.1.  Discovery of Registrar by Proxy

   As described in section Section 3.2, the RECOMMENDED mechanism is for
   the proxy to discover the address of the registrar via GRASP
   [I-D.ietf-anima-grasp]

   GRASP is intended to run over a secured, and private Autonomic
   Control Plan [I-D.ietf-anima-autonomic-control-plane].  This
   discovery is between the already registered Registrar, and the
   already registered Proxy.  There are no GRASP security issues with
   this part, as both entities will have already joined the secured ACP.

7.1.2.  Discovery of Proxy by New Entity

   [[EDNOTE: To be discussed]]

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, <http://standards.ieee.org/findstds/
              standard/802.1AR-2009.html>.

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







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   [RFC3542]  Stevens, W., Thomas, M., Nordmark, E., and T. Jinmei,
              "Advanced Sockets Application Program Interface (API) for
              IPv6", RFC 3542, DOI 10.17487/RFC3542, May 2003,
              <http://www.rfc-editor.org/info/rfc3542>.

   [RFC3927]  Cheshire, S., Aboba, B., and E. Guttman, "Dynamic
              Configuration of IPv4 Link-Local Addresses", RFC 3927,
              DOI 10.17487/RFC3927, May 2005,
              <http://www.rfc-editor.org/info/rfc3927>.

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862,
              DOI 10.17487/RFC4862, September 2007,
              <http://www.rfc-editor.org/info/rfc4862>.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
              <http://www.rfc-editor.org/info/rfc5280>.

   [RFC5386]  Williams, N. and M. Richardson, "Better-Than-Nothing
              Security: An Unauthenticated Mode of IPsec", RFC 5386,
              DOI 10.17487/RFC5386, November 2008,
              <http://www.rfc-editor.org/info/rfc5386>.

   [RFC5652]  Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
              RFC 5652, DOI 10.17487/RFC5652, September 2009,
              <http://www.rfc-editor.org/info/rfc5652>.

   [RFC5660]  Williams, N., "IPsec Channels: Connection Latching",
              RFC 5660, DOI 10.17487/RFC5660, October 2009,
              <http://www.rfc-editor.org/info/rfc5660>.

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

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

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





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   [RFC7228]  Bormann, C., Ersue, M., and A. Keranen, "Terminology for
              Constrained-Node Networks", RFC 7228,
              DOI 10.17487/RFC7228, May 2014,
              <http://www.rfc-editor.org/info/rfc7228>.

9.2.  Informative References

   [I-D.behringer-homenet-trust-bootstrap]
              Behringer, M., Pritikin, M., and S. Bjarnason,
              "Bootstrapping Trust on a Homenet", draft-behringer-
              homenet-trust-bootstrap-02 (work in progress), February
              2014.

   [I-D.ietf-ace-actors]
              Gerdes, S., Seitz, L., Selander, G., and C. Bormann, "An
              architecture for authorization in constrained
              environments", draft-ietf-ace-actors-04 (work in
              progress), September 2016.

   [I-D.ietf-anima-autonomic-control-plane]
              Behringer, M., Eckert, T., and S. Bjarnason, "An Autonomic
              Control Plane", draft-ietf-anima-autonomic-control-
              plane-03 (work in progress), July 2016.

   [I-D.ietf-anima-grasp]
              Bormann, C., Carpenter, B., and B. Liu, "A Generic
              Autonomic Signaling Protocol (GRASP)", draft-ietf-anima-
              grasp-08 (work in progress), October 2016.

   [I-D.ietf-netconf-zerotouch]
              Watsen, K. and M. Abrahamsson, "Zero Touch Provisioning
              for NETCONF or RESTCONF based Management", draft-ietf-
              netconf-zerotouch-09 (work in progress), July 2016.

   [I-D.lear-mud-framework]
              Lear, E., "Manufacturer Usage Description Framework",
              draft-lear-mud-framework-00 (work in progress), January
              2016.

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

   [imprinting]
              Wikipedia, , "Wikipedia article: Imprinting", July 2015,
              <https://en.wikipedia.org/wiki/Imprinting_(psychology)>.




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   [pledge]   Dictionary.com, , "Dictionary.com Unabridged", July 2015,
              <http://dictionary.reference.com/browse/pledge>.

   [RFC7575]  Behringer, M., Pritikin, M., Bjarnason, S., Clemm, A.,
              Carpenter, B., Jiang, S., and L. Ciavaglia, "Autonomic
              Networking: Definitions and Design Goals", RFC 7575,
              DOI 10.17487/RFC7575, June 2015,
              <http://www.rfc-editor.org/info/rfc7575>.

   [Stajano99theresurrecting]
              Stajano, F. and R. Anderson, "The resurrecting duckling:
              security issues for ad-hoc wireless networks", 1999,
              <https://www.cl.cam.ac.uk/~fms27/papers/1999-StajanoAnd-
              duckling.pdf>.

Authors' Addresses

   Max Pritikin
   Cisco

   Email: pritikin@cisco.com


   Michael C. Richardson
   Sandelman Software Works

   Email: mcr+ietf@sandelman.ca
   URI:   http://www.sandelman.ca/


   Michael H. Behringer
   Cisco

   Email: mbehring@cisco.com


   Steinthor Bjarnason
   Cisco

   Email: sbjarnas@cisco.com


   Kent Watsen
   Juniper Networks

   Email: kwatsen@juniper.net





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