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Versions: (draft-pritikin-bootstrapping-keyinfrastructures) 00 01 02 draft-ietf-anima-bootstrapping-keyinfra

ANIMA WG                                                     M. Pritikin
Internet-Draft                                                     Cisco
Intended status: Informational                             M. Richardson
Expires: January 7, 2016                                             SSW
                                                            M. Behringer
                                                            S. Bjarnason
                                                                   Cisco
                                                            July 6, 2015


                   Bootstrapping Key Infrastructures
             draft-pritikin-anima-bootstrapping-keyinfra-02

Abstract

   This document specifies automated bootstrapping of an key
   infrastructure using vendor installed IEEE 802.1AR manufacturing
   installed certificates, in combination with a vendor based service on
   the Internet.  Before being authenticated, a new device has only
   link-local connectivity, and does not require a routable address.
   When a vendor provides an Internet based service, devices can be
   forced to join only specific domains but for constrained environments
   we describe a variety of options that allow bootstrapping to proceed.

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at 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 January 7, 2016.

Copyright Notice

   Copyright (c) 2015 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



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   (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
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.












































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  5
   2.  Architectural Overview . . . . . . . . . . . . . . . . . . . .  5
   3.  Functional Overview  . . . . . . . . . . . . . . . . . . . . .  7
     3.1.  Behavior of a new entity . . . . . . . . . . . . . . . . .  8
       3.1.1.  Discovery and Identity . . . . . . . . . . . . . . . . 10
       3.1.2.  Imprint  . . . . . . . . . . . . . . . . . . . . . . . 11
       3.1.3.  Enrollment . . . . . . . . . . . . . . . . . . . . . . 12
       3.1.4.  Being Managed  . . . . . . . . . . . . . . . . . . . . 12
     3.2.  Behavior of a proxy  . . . . . . . . . . . . . . . . . . . 13
     3.3.  Behavior of the Registrar  . . . . . . . . . . . . . . . . 13
       3.3.1.  Entity Authentication  . . . . . . . . . . . . . . . . 14
       3.3.2.  Entity Authorization . . . . . . . . . . . . . . . . . 14
       3.3.3.  Claiming the New Entity  . . . . . . . . . . . . . . . 15
       3.3.4.  Log Verification . . . . . . . . . . . . . . . . . . . 16
       3.3.5.  Forwarding Authorization Token plus Configuration  . . 16
     3.4.  Behavior of the MASA Service . . . . . . . . . . . . . . . 16
       3.4.1.  Issue Authorization Token and Log the event  . . . . . 17
       3.4.2.  Retrieve Audit Entries from Log  . . . . . . . . . . . 17
     3.5.  Leveraging the new key infrastructure / next steps . . . . 17
       3.5.1.  Network boundaries . . . . . . . . . . . . . . . . . . 17
   4.  Domain Operator Activities . . . . . . . . . . . . . . . . . . 18
     4.1.  Instantiating the Domain Certification Authority . . . . . 18
     4.2.  Instantiating the Registrar  . . . . . . . . . . . . . . . 18
     4.3.  Accepting New Entities . . . . . . . . . . . . . . . . . . 18
     4.4.  Automatic Enrolment of Devices . . . . . . . . . . . . . . 19
     4.5.  Secure Network Operations  . . . . . . . . . . . . . . . . 19
   5.  Protocol Details . . . . . . . . . . . . . . . . . . . . . . . 20
     5.1.  EAP-EST  . . . . . . . . . . . . . . . . . . . . . . . . . 21
     5.2.  Request bootstrap token  . . . . . . . . . . . . . . . . . 21
     5.3.  Request MASA authorization token . . . . . . . . . . . . . 21
     5.4.  Basic Configuration Information Package  . . . . . . . . . 22
     5.5.  Request MASA authorization log . . . . . . . . . . . . . . 23
   6.  Reduced security operational modes . . . . . . . . . . . . . . 23
     6.1.  New Entity security reductions . . . . . . . . . . . . . . 24
     6.2.  Registrar security reductions  . . . . . . . . . . . . . . 24
     6.3.  MASA security reductions . . . . . . . . . . . . . . . . . 25
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 25
     7.1.  Trust Model  . . . . . . . . . . . . . . . . . . . . . . . 26
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 26
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 26
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 26
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 27
   Appendix A.  Editor notes  . . . . . . . . . . . . . . . . . . . . 27
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 28




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1.  Introduction

   To literally "pull yourself up by the bootstraps" is an impossible
   action.  Similarly the secure establishment of a key infrastructure
   without external help is also an impossibility.  Today it is accepted
   that the initial connections between nodes are insecure, until key
   distribution is complete, or that domain-specific keying material is
   pre-provisioned on each new device in a costly and non-scalable
   manner.  This document describes a zero-touch approach to
   bootstrapping an entity by securing the initial distribution of key
   material using third-party generic keying material, such as a
   manufacturer installed IEEE 802.1AR certificate [IDevID], and a
   corresponding third-party service on the Internet.

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

   o  New entity authentication: "Who is this?  What is its identity?"
   o  New entity authorization: "Is it mine?  Do I want it?  What are
      the chances it has been compromised?"
   o  Domain authentication: "What is this domain's claimed identity?"
   o  Domain authorization: "Should I join it?"

   A precise answer to these questions can not be obtained without
   leveraging an established key infrastructure(s).  The domain's
   decisions are based on the new entity's authenticated identity, as
   established by verification of previously installed credentials such
   as a manufacturer installed IEEE 802.1AR certificate, and verified
   back-end information such as a configured list of purchased devices
   or communication with a trusted third-party.  The new entity's
   decisions are made according to verified communication with a trusted
   third-party or in a strictly auditable fasion.

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

   The result of bootstrapping is that a domain specific key
   infrastructure is deployed.  Since IEEE 802.1AR PKI certificates are
   used for identifying the new entity and the public key of the domain
   identity is leveraged during communiciations with an Internet based



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   service, which is itself authenticated using HTTPS, bootstrapping of
   a domain specific Public Key Infrastructure (PKI) is fully described.
   Sufficient agility to support bootstrapping alternative key
   infrastructures (such as symmetric key solutions) is considered
   although no such key infrastructure is described.

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:

   Domain Identity:  The domain identity is the 160-bit SHA-1 hash of
      the BIT STRING of the subjectPublicKey of the domain trust anchor
      that is stored by the Domain CA.  This is consistent with the
      RFC5280 Certification Authority subject key identifier of the
      Domain CA's self signed root certificate.  (A string value bound
      to the Domain CA's self signed root certificate subject and issuer
      fields is often colloquially used as a humanized identity value
      but during protocol discussions the more exact term as defined
      here is used).
   drop ship  The physical distribution of equipment containing the
      "factory default" configuration to a final destination.  In zero-
      touch scenarios there is no staging or pre-configuration during
      drop-ship.
   imprint  the process where a device that wishes to join a network
      acquires it's domain specific identity.  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.  [imprinting]
   pledge  the prospective device, which has the identity provided to at
      the factory.  Neither the device nor the network knows if the
      device yet knows if this device belongs with this network.  This
      is definition 6, according to [pledge]


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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                                                       Vendor components
                                                      .
                                                      .+---------------+
      +--------------Drop Ship------------------------.| Manufacturer  |
      |                                               .+---------------+
      |                                               .| M anufacturer |
      |                                               .| A uthorized   |
      |                                               .| S igning      |
      |                                               .| A uthority    |
      |                                               .+---------------+
      V                                               ......   ^
   +-------+                                                   |
   | New   |        +------------+       +-----------+         |
   | Entity|<--L2-->|    Proxy   |<----->|           |         |
   |       |        +------------+       |           |         |
   |       |                             | Registrar |         |
   |       |                             |           |         |
   |       |<-----L3---------------------( may proxy )---------+
   |       |                             +-----------+
   |       |                                   |
   |       |                 +----------------------------+
   |       |<-----Enroll---->| Domain Certification       | ^
   |       |<-----Config---->|      Authority             | .
   +-------+        .        | Management and etc         | .
                    .        +----------------------------+ .
                    .                                       .
                    .........................................
                                     "domain" components


   Figure 1

   Domain:  The set of entities that trust a common key infrastructure
      trust anchor.
   Domain CA:  The domain Certification Authority (CA) provides
      certification functionalities to the domain.  At a minimum it
      provides certification functionalities to the Registrar and stores
      the trust anchor that defines the domain.  Optionally, it
      certifies all elements.
   Registrar:  A representative of the domain that is configured,
      perhaps autonomically, to decide whether a new device is allowed
      to join the domain.  The administrator of the domain interfaces
      with a Registrar to control this process.  Typically a Registrar
      is "inside" its domain.







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   New Entity:  A new device or virtual machine or software component
      that is not yet part of the domain.
   Proxy:  A domain entity that helps the New Entity join the domain.  A
      Proxy facilitates communication for devices that find themselves
      in an environment where they are not provided L3 connectivity
      until after they are validated as members of the domain.
   MASA Service:  A Manufacturer Authorized Signing Authority (MASA)
      service on the global Internet.  At a minimum the MASA provides a
      trusted repository for audit information concerning privacy
      protected bootstrapping events.  The MASA is recommended to
      provide ownership validation services which allows for fully
      secure zero-touch bootstrap of domain certificates with mutual
      authentication.

   We assume a multi-vendor network.  In such an environment, there
   could a MASA for each vendor that supports devices following this
   document's specification, or an integrator could provide a MASA
   service for all devices.

   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
   all such edge conditions are covered by the architectural and
   protocol models.


3.  Functional Overview

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

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

   The overall flow is shown in Figure 2:











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   +---------+                +----------+                +-----------+
   |  New    |                |          |                |  MASA     |
   | Entity  |                |  Domain  |                |  Service  |
   |         |                |          |                | (Internet)|
   +---------+                +----------+                +-----------+
       |                           |                            |
       |<-------discovery--------->|                            |
       |---802.1AR credential----->|                            |
       |                           |                            |
       |                    [ accept device? ]                  |
       |                           |                            |
       |                           |---802.1AR identity-------->|
       |                           |---Domain ID--------------->|
       |                           |                            |
       |                           |                    [device belongs]
       |                           |                    [to domain?    ]
       |                           |                            |
       |                           |                  [update audit log]
       |                           |                            |
       |                           |<---device history log------|
       |                           |<-- authorization token-----|
       |                           |                            |
       |                  [ still accept device?]               |
       |                           |                            |
       |<----authorization token---|                            |
       |<----config information----|                            |
       |                           |                            |
  [authorization token valid?]     |                            |
  [apply config information]       |                            |
       |                           |                            |
       |----domain enrolment------>|                            |
       |<----domain certificate----|                            |
       |                           |                            |
   Figure 2

3.1.  Behavior of a new entity

   A New Entity that has not yet been bootstrapped attempts to find a
   local domain and join it.

   States of a New Entity are as follows:










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


   Figure 3

   State descriptions are as follows:

   1.  Discover a communication channel to the "closest" Registrar by
       trying the following steps in this order:
       A.  Search for a Proxy on the local link using a link local
           discovery protocol (no routable addresses are required for
           this approach).  If multiple local proxies are discovered
           attempt communications with each before widening the search
           to other options.  The proxy relays information to the
           registrar.  If this fails:
       B.  Obtain an IP address using existing methods, such as SLAAC or
           DHCPv6, and search for a local registrar using DNS service
           discovery.  If this fails:




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       C.  Obtain an IP address (as above), and search for the domain
           registrar using a pre-defined Factory provided Internet based
           re-direct service.  Various methods could be used, such as
           DNS or RESTful APIs.
   2.  Identify itself.  This is done by presenting an IEEE 802.1AR
       credentials to the discovered Registrar (via a Proxy if
       necessary).  Included is a generated nonce that is specific to
       this attempt.
   3.  Imprint on the Registrar.  This requires verification of the MASA
       service generated authorization token as provided by the
       contacted Registrar.  The authorization token contains the valid
       domain(s) for this device and is signed by the MASA service.  The
       device uses a pre-installed certificate of the MASA service to
       validate the signature of the MASA.  The nonce information
       previously provided is also checked, if it was not removed by the
       Registrar.
   4.  Enroll by accepting the domain specific information from the
       registrar, and by enrolling a domain certificate from the
       registrar using a standard enrollment protocol, e.g.  Enrolment
       over Secure Transport (EST) [RFC7030].
   5.  The New Entity is now a member of and Being 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 and Identity

   Existing architectures provide the functionality for discovery of the
   Domain Registrar.  Use of an existing architecture is preferred over
   development of a new architecture.  Discovering of a Domain Proxy
   that facilitates communication through to the Domain Registrar is
   simplified as "discovery of the domain".  A proxy is included in
   Figure 1 although the simplified flow in Figure 2 does not include a
   proxy - under the assuption that the proxy forwarding is mostly
   transparent to the New Entity.  Existing architectures for
   investigation include:

   IEEE 802.1X  Where the New Entity can be cast as the "supplicant" and
      the Proxy is the "authenticator".  The bootstrapping protocol
      messages are encapsulated as EAP methods.  The "authenticator"
      reencapsulates the EAPOL frames and forwards them to the
      "Authentication Server", which provides Registrar functionalities.
   PANA [RFC5191]  [[EDNOTE: TBD]]
   ND [RFC2461] / [RFC4861]  [[EDNOTE: TBD]] NOTE: Neighbor Discovery
      protocols do not describe a mechanism for forwarding messages.
   Each provides a method for the New Entity to discover and initiate
   communication with a local neighbor which is assumed to be a member
   of the domain infrastructure.  In each protocol methods are available



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   to support encapsulation of the bootstrapping protocol messages
   described elsewhere in this document.  Other protocols for
   transporting bootstrapping messages can be added in future
   references.

   All security assocaitions established are between the new device and
   the Registrar regardless of proxy operations.  [[EDNOTE: this is the
   simplest and most direct threat model but should be evaluated against
   the anima use cases.  It may be preferable to engage in secure
   communications with the proxy itself?]]

   The New Entity is expected to identify itself during one of the
   communication protocol exchanges.  For example using EAP-TLS.  If the
   client identity is rejected the New Entity repeats the Discovery
   process using the next proxy or discovery method available.  If
   multiple proxies are available the New Entity tries each until a
   successful bootstrapping occurs.  The New Entity may prioritize
   proxies selection order as appropriate for the anticipated
   environment.

   If Proxy discovery fails the New Entity moves on to discovering a
   Registrar directly using an appropriate L3 protocol mechanisms.

   [[EDNOTE: it is unclear yet if discovery happens on a per interface
   basis or once per device.  What is the requirement around joining
   multiple domains; is this a bootstrapping requirement or is this a
   broader autonomic requirement]]

3.1.2.  Imprint

   The domain trust anchor is received by the New Entity during the
   boostrapping protocol methods in the form of a MASA authorization
   token containing the domainID.  The goal of the imprint state is to
   securely obtain a copy of this trust anchor without involving human
   interaction.

   An enrollment protocol such as 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),
   o  using a configured Explicit TA database (not an autonomic solution
      because the distribution of an explicit TA database is not
      autonomic),




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   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 an additional autonomic method:

   MASA authorization token  Authorization tokens are obtained by the
      Registrar from the MASA service and presented to the New Entity
      for validation.

   An arbitrary basic configuration information package that is signed
   by the domain can be delivered alongside the authorization token.
   This information is signed by the domain private keys and is a one
   time delivery containing information such as which enrollment server
   to communicate with and which management system to communicate with.
   It is intended as a limited basic configuration for these purposes
   and is not intended to deliver entire final configuration to the
   device.

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

3.1.3.  Enrollment

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

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

   o  The New Entity is authenticated using the IEEE 802.1AR
      credentials.
   o  The EST section 4.1.3 CA Certificates Response is verified using
      the MASA authorization token provided domain identity.

3.1.4.  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



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   issued during enrollment.

   See Section 3.5.

3.2.  Behavior of a proxy

   The role of the Proxy is to facilitate communications.  The Proxy
   forwards messages between the New Entity and a Registrar.  Where
   existing protocols, as detailed in Section 3.1.1, already provide
   this functionality nothing additional is defined.

3.3.  Behavior of the Registrar

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

   Registrar behavior is as follows:
































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   Contacted by New Entity
           +
           |
   +-------v----------+
   | Entity           | fail?
   | Authentication   +---------+
   +-------+----------+         |
           |                    |
   +-------v----------+         |
   | Entity           | fail?   |
   | Authorization    +--------->
   +-------+----------+         |
           |                    |
   +-------v----------+         |
   | Claiming the     | fail?   |
   | Entity           +--------->
   +-------+----------+         |
           |                    |
   +-------v----------+         |
   | Log Verification | fail?   |
   |                  +--------->
   +-------+----------+         |
           |                    |
   +-------v----------+    +----v-------+
   | Forward          |    |            |
   | Authorization    |    | Reject     |
   | token + config   |    | Device     |
   | to the Entity    |    |            |
   +------------------+    +------------+
   Figure 4

3.3.1.  Entity Authentication

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

   o  the use of an IEEE 802.1AR IDevID credential,
   o  or the use of a secret that is transmitted out of band between the
      New Entity and the Registrar (this use case is not autonomic).

3.3.2.  Entity Authorization

   In a fully automated network all devices must be securely identified.

   A Registrar accepts or declines a request to join the domain, based
   on the authenticated identity presented and other policy defined
   criteria such as Proxy identity.  Automated acceptance criteria
   include:




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   o  allow any device of a specific type (as determined by the IEEE
      802.1AR device identity),
   o  allow any device from a specific Factory (as determined by the
      IEEE 802.1AR identity),
   o  allow a specific device from a Factory (as determined by the IEEE
      802.1AR identity)
   In all cases a Registrar must use the globally available MASA service
   to verify that the device's history log does not include unexpected
   Registrars.  Because if a device had previously registered with
   another domain, the registrar of that domain would show in the log.

   If a device is accepted into the domain, it is then invited to
   request a domain certificate through a certificate enrolment process.
   The result is a common trust anchor and device certificates for all
   autonomic devices in a domain.  These certificates can subsequently
   be used to determine the boundaries of the homenet, to authenticate
   other domain nodes, and to autonomically enable services on the
   homenet.

   For each entity that will be accepted a Registrar maintains the
   Factory CA identity and the entity's unique identifier.  The Factory
   CA identity could be implemented as the Factory CA root certificate
   keyIdentifier (the 160-bit SHA-1 hash of the value of the BIT STRING
   subjectPublicKey).  For user interface purposes the keyIdentifier
   information can be mapped to a colloquial Factory name (Registrars
   can be shipped with the keyIdentifier of a significant number of
   third-party manufacturers).

3.3.3.  Claiming the New Entity

   During initial bootstrapping the New Entity provides a nonce specific
   to the particular bootstrapping attempt.  The registrar should
   include this nonce when claiming the New Entity from the Internet
   based MASA service.  If a nonce is provided by the Registrar, then
   claims from an unauthenticated Registrar are serviced by the MASA
   resource.

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

   Claiming an entity establishes an audit log at the MASA server and



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   provides the Registrar with proof, in the form of a MASA
   authorization token, that the log entry has been inserted.  As
   indicated in Section 3.1.2 a New Entity will only proceed with
   bootstrapping if a validated MASA authorization token has been
   recieved.  The New Entity therefore enforces that bootstrapping only
   occurs if the claim has been logged.

3.3.4.  Log Verification

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

   o  Any nonceless entries in the log are associated with domainIDs
      recognized by the registrar.  The registar MAY be configured to
      ignore the history of the device but it is RECOMMENDED that this
      only be configured if the MASA server is known to perform
      ownership validation or if Trusted Computing Group secure boot and
      remote attestation is available.
   o  Any nonce'd entries are older than when the domain is known to
      have physical possession of the new entity or that the domainIDs
      are recognized by the registrar.
   If any of these criteria are unacceptable to the registrar the entity
   is rejected.

3.3.5.  Forwarding Authorization Token plus Configuration

   The Registrar forwards the received authorization token to the new
   entity.  To simplify the message flows an initial configuration
   package can be delivered at this time which is signed by a
   representative of the domain.

   [[EDNOTE: format TBD.  The configuration package signature data must
   contain the full certificate path sufficient for the new entity to
   use the domainID information (as a trust anchor) to accept and
   validate the configuration)]]

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 be
   provided as an IEEE 802.1AR IDevID X.509 extension (a "MASA
   authorization token Distribution Point" extension).

   The MASA service provides the following functionalities to
   Registrars:





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3.4.1.  Issue Authorization Token and Log the event

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

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

   If a nonce is not provided then the MASA service MUST authenticate
   the Registrar as a valid customer.  This prevents denial of service
   attacks.  The specific level of authentication provided by the
   customer is not defined here.  An MASA Practice Statement (MPS)
   similar to the Certification Authority CPS, as defined in RFC5280, is
   provided by the Factory such that Registrar's can determine the level
   of trust they have in the Factory.

3.4.2.  Retrieve Audit Entries from Log

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

3.5.  Leveraging the new key infrastructure / next steps

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

   Examples of services:
   o  Device management.
   o  Routing authentication.
   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.






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4.  Domain Operator Activities

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

4.1.  Instantiating the Domain Certification Authority

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

4.2.  Instantiating the Registrar

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

   A device can be configured to act as a Registrar or a device can
   auto-select itself to take on this function, using a detection
   mechanism to resolve potential conflicts and setup communication with
   the Domain Certification Authority.  Automated Registrar selection is
   outside scope for this document.

4.3.  Accepting New Entities

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

   1.  Default acceptance: In the simplest case, the new device asserts
       its unique identity to the registrar.  The registrar accepts all
       devices without authorization checks.  This mode does not provide
       security against intruders and is not recommended.
   2.  Per device acceptance: The new device asserts its unique identity
       to the registrar.  A non-technical human validates the identity,
       for example by comparing the identity displayed by the registrar
       (for example using a smartphone app) with the identity shown on
       the packaging of the device.  Acceptance may be triggered by a
       click on a smartphone app "accept this device", or by other forms
       of pairing.  See also [I-D.behringer-homenet-trust-bootstrap] for
       how the approach could work in a homenet.
   3.  Whitelist acceptance: In larger networks, neither of the previous
       approaches is acceptable.  Default acceptance is not secure, and
       a manual per device methods do not scale.  Here, the registrar is
       provided a priori with a list of identifiers of devices that



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       belong to the network.  This list can be extracted from an
       inventory database, or sales records.  If a device is detected
       that is not on the list of known devices, it can still be
       manually accepted using the per device acceptance methods.
   4.  Automated Whitelist: an automated process that builds the
       necessary whitelists and inserts them into the larger network
       domain infrastructure is plausible.  Once set up, no human
       intervention is required in this process.  Defining the exact
       mechanisms for this is out of scope although the registrar
       authorization checks is identified as the logical integration
       point of any future work in this area.

   None of these approaches require the network to have permanent
   Internet connectivity.  Even when the Internet based MASA service is
   used, it is possible to pre-fetch the required information from the
   MASA a priori, for example at time of purchase such that devices can
   enrol 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 Enrolment of Devices

   The approach outlined in this document provides a secure zero-touch
   method to enrol 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

   For simplicity the bootstrapping protocol is described as extensions
   to EST [RFC7030].

   EST provides a bootstrapping mechanism for new entities that are
   configured with the URI of the EST server such that the Implicit TA
   database can be used to authenticate the EST server.  Alternatively
   EST clients can "engage a human user to authorize the CA certificate
   using out-of-band data such as a CA certificate".  EST does not
   provide a completely automated method of bootstrapping the PKI as
   both of these methods require some user input (either of the URI or
   authorizing the CA certificate).

   This section details additional EST functionality that support
   automated bootstrapping of the public key infrastructure.  These
   additions provide for fully automated bootstrapping.  These additions
   are to be optionally supported by the EST server within the same
   .well-known URI tree as the existing EST URIs.

   The "New Entity" is the EST client and the "Registrar" is the EST
   server.

   The extensions for the client are as follows:

   o  The New Entity provisionally accept the EST server certificate
      during the TLS handshake as detailed in EST section 4.1.1
      ("Bootstrap Distribution of CA Certificates").
   o  The New Entity request and validates a "bootstrap token" as
      described below.  At this point the New Entity has sufficient
      information to validate domain credentials.
   o  The New Entity calls the EST defined /cacerts method to obtain the
      current CA certificate.  These are validated using the "bootstrap
      token".
   o  The New Entity completes bootstrapping as detailed in EST section
      4.1.1.

   These extensions could be implemented as an independent protocol from
   EST but since the overlap with basic enrollment is extensive,
   particularly with respect to client authorization, they are presented
   here as additions to EST.

   In order to obtain a validated bootstrap token and history logs the
   Registrar contacts the MASA service Service using REST calls.







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5.1.  EAP-EST

   In order to support Proxy environments EAP-EST is defined.

   [[EDNOTE: TBD.  EST is TLS with some data.  EAP-TLS and other similar
   protocols provide an example framework for filling out this section]]

5.2.  Request bootstrap token

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

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

   The request format is JSON object containing a nonce.

   Request media type: application/masanonce

   Request format: a json file with the following:

   {"nonce":"<64bit nonce value>"}

   [[EDNOTE: exact format TBD.  There is an advantage to having the
   client sign the nonce (similar to a PKI Certification Signing
   Request) since this allows the MASA service to confirm the actual
   device identity.  It is not clear that there is a security benefit
   from this.]]

   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 a MASA authorization token from the MASA service
   (see Section 5.3).

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

5.3.  Request MASA authorization token

   A registrar requests the MASA authorization token from the MASA
   service using a REST interface.

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

   The request format is a JSON object optionally containing the nonce



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   value (as obtained from the bootstrap request) and the IEEE 802.1AR
   identity of the device as a serial number (the full certificate is
   not needed and no proof-of-possession information for the device
   identity is included).  The New Entity's serial number is extracted
   from the subject name :

   {"nonce":"<64bit nonce value>", "serialnumber", "<subjectname/
   subjectaltname serial number>"}

   Inclusion of the nonce is optional because the Registar might request
   an authorization token when the New Entity is not online, or when the
   target bootstrapping environment is not on the same network as the
   MASA server.

   This information is encapsulated in a PKCS7 signed data structure
   that is signed by the Registrar.  The entire certificate chain, up to
   and including the Domain CA, is included in the PKCS7.

   The MASA service checks the internal consistency of the PKCS7 but is
   unable to actually 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 verifies that the PKCS7 is
   signed by a Registrar (by checking for the cmc-idRA field in the
   Registrar certificate) certificate that was issued by the root
   certificate included in the PKCS7.

   The domain ID is extracted from the root certificate and is used to
   generate the MASA authorization token and to update the audit log.

   [[EDNOTE: The authorization token response format needs to be defined
   here.  It consists of the nonce, if supplied, the serialnumber and
   the trust anchor of the domain.  For example:

   {"nonce":"<64bit nonce value>", "serialnumber", "<subjectname/
   subjectaltname serial number>","domainID":}

   ]]

   [[EDNOTE: This assumes the Registrar can extract the serial number
   successfullly from the cilent certificate.  The RFC4108
   hardwareModuleName is likely the best known location.]]

5.4.  Basic Configuration Information Package

   When the MASA authorization token is returned to the New Entity an
   arbitrary information package can be signed and delivered along side
   it.  This is signed by the Domain Registar.  The New Entity first
   verifies the MASA authorization token and, if it is valid, then uses



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   the domain's TA to validate the Information Package.

   [[EDNOTE: The package format to be specified here.  Any signed format
   is viable and ideally one can simply be specified from netconf.  The
   Registar knows the New Entity device type from the 802.1AR credential
   and so is able to determine the proper format for the configuration]]

5.5.  Request MASA authorization log

   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
   "/requestMASAlog".

   The log data returned is a file consisting of all previous log
   entries.  For example:

   "log":[
     {"date":"<date/time of the entry>"},
      "domainID":"<domainID as extracted from the root
                   certificate within the PKCS7 of the
                   authorization token request>",
      "nonce":"<any nonce if supplied (or NULL)>"},

     {"date":"<date/time of the entry>"},
      "domainID":"<domainID as extracted from the root
                   certificate within the PKCS7 of the
                   authorization token request>",
      "nonce":"<any nonce if supplied (or NULL)>"},
   ]

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

   The Registrar uses this log information to make an informed decision
   regarding the continued bootstrapping of the New Entity.

   [[EDNOTE: certificate transparency might offer an alternative log
   entry method]]


6.  Reduced security operational modes

   A common requirement of bootstrapping is to support less secure



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   operational modes for support specific use cases.  The following
   sections detail specific ways that the New Entity, Registrar and MASA
   can be configured to run in a less secure mode for the indicated
   reasons.

6.1.  New Entity security reductions

   Although New Entity can choose to run in less secure modes this is
   MUST NOT be the default state because it permanently degrades the
   security for all other uses cases.  When configured into lower
   security modes by a trusted administrator:

   1.  The device may have an operational mode where it skips
       authorization token validation.  For example if a physical button
       is depressed during the bootstrapping operation.  This may occur
       when: A device Factory goes out of business or otherwise fails to
       provide a reliable MASA service or when local staging has pre-
       configured the New Entity with a known good Trust Anchor.
   2.  The device may be configured during staging or requested from the
       factory to not require the MASA service authorization token.  An
       entity that does not validate the domain identity is inherently
       dangerous as it may have had malware installed on it by a man-in-
       the-middle.  This risk should be mitigated using attestation and
       measurement technologies.  In order to support an unsecured
       imprint the New Entity MUST support remote attestation
       technologies such as is defined by the Trusted Computing Group.
       [[EDNOTE: How to include remote attestation into the boostrapping
       protocol exchange is TBD]].  This may occur when: The device
       Factory does not provide a MASA service.

6.2.  Registrar security reductions

   The Registrar can choose to accept devices using less secure methods.
   These methods are RECOMMENDED when low security models are needed as
   the security decisions are being made by the local administrator:
   1.  The registrar may choose to accept all devices, or all devices of
       a particular type, at the administrator's discretion.  This may
       occur when: Informing the Registrar of unique identifiers of new
       entities might be operationally difficult.
   2.  The registrar may choose to accept devices that claim a unique
       identity without the benefit of authenticating that claimed
       identity.  This may occur when: The New Entity does not include
       an IEEE 802.1AR factory installed credential.
   3.  The registrar may request nonce-less authorization tokens from
       the MASA service.  These tokens can then be transmitted to the
       Registrar and stored until they are needed during bootstrapping
       operations.  This is for use cases where target network is
       protected by an air gap and therefore can not contact the MASA



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       service during New Entity deployment.

6.3.  MASA security reductions

   Lower security modes chosen by the MASA service effect all device
   deployments unless paired with strict device ownership validation, 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 authorization token.  This
       results in distribution of authorization tokens that never expire
       and effectly makes the Domain an always trusted entity to the New
       Entity during any subsequent bootstrapping attempts.  That this
       occured is captured in the log information so that the Domain
       registrar can make appropriate security decisions when a new
       device joins the domain.  This is useful to support use cases
       where Registrars might not be online during actual device
       deployment.
   2.  Not verifying ownership before responding with an authorization
       token.  Doing so relieves the vendor providing MASA services from
       having to tracking ownership during shipping and supply chain.
       The registrar uses the log information as a defense in depth
       strategy to ensure that this does not occur unexpectedly.  For
       example when purchasing used equipment a MASA response is
       necessary for autonomic provisioning but the greatest level of
       security is achieved when the MASA server is also performing
       ownership validation.


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
   MASA service.  Nonceless entries into the audit log therefore
   permanently reduce the value of a device because future Registrars,
   during future bootstrap attempts, would now have to be configured
   with policy to ignore previously (and potentially unknown) domains.

   Future registrars are recommended to take the audit history of a
   device into account when deciding to join such devices into their
   network.  If the MASA server were to have allowed a significantly
   large number of claims this might become onerous to the MASA server
   which must maintain all the extra log entries.  Ensuring the registar



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   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 authorization token to take control of
   the New Entity but then proceed to enrol with the target domain.  To
   prevent this the MASA service is rate limited to only generate
   authorization tokens at a rate of 1 per minute.  The Registrar
   therefore has at least 1 minute to get the response back to the New
   Entity.  [[EDNOTE: a better solution can likely be found.  This text
   captures the issue for now.  Binding the logs via a ]] Also the
   Registrar can double check the log information after enrolling the
   New Entity.

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

7.1.  Trust Model

   [[EDNOTE: (need to describe that we need to trust the device h/w.  To
   be completed.)]]


8.  Acknowledgements

   We would like to thank the various reviewers for their input, in
   particular Markus Stenberg, Brian Carpenter, Fuyu Eleven.


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, March 1997.

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



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

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

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


Appendix A.  Editor notes

   [[EDNOTE: This section is to capturing rough notes between editors
   and Anima Bootstrapping design team members.  This entire section to
   be removed en masse before finalization]]

   Change Discussion:

   02 Moved sections for readability, Updated introduction, simplified
      functional overview to avoid distractions from optional elements,
      addressed updated security considerations, fleshed out state
      machines.

   The following is a non-prioritized list of work items currently
   identified:
   o  Continue to address gaps/opportunities highlighted by community
      work on bootstrappping.  Refs: IETF92 "Survey of Security
      Bootstrapping", Aana Danping He, behcet Sarikaya.  "NETCONF Zero
      Touch Update for ANIMA"
      https://www.ietf.org/proceedings/92/anima.html and "Bootstrapping
      Key Infrastructures", Pritikin, Behringer, Bjarnason
   o  Intergrate "Ownership Voucher" as a valid optional format for the
      MASA response.  So long as the issuance of this is logged and
      captured in the log response then the basic flow and threat model
      is substantially the same.



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   o  Attempt to re-use existing work as per the charter: Toerless
      notes: a) are existing [eap] options? or too complex? or doens't
      work? b) our own method (e.g.  EAP-ANIMA c) if b then investigate
      using signaling protocol).
   o


Authors' Addresses

   Max Pritikin
   Cisco

   Email: pritikin@cisco.com


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

   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
















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