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ANIMA WG                                                        S. Fries
Internet-Draft                                              H. Brockhaus
Intended status: Standards Track                                 Siemens
Expires: January 11, 2021                                        E. Lear
                                                           Cisco Systems
                                                           July 10, 2020


         Support of asynchronous Enrollment in BRSKI (BRSKI-AE)
                 draft-ietf-anima-brski-async-enroll-00

Abstract

   This document describes enhancements of bootstrapping a remote secure
   key infrastructure (BRSKI) to also operate in domains featuring no or
   only timely limited connectivity between involved components.  It
   addresses connectivity to backend services supporting enrollment like
   a Public Key Infrastructure (PKI) and also to the connectivity
   between pledge and registrar.  For this it enhances the use of
   authenticated self-contained objects in BRSKI also for request and
   distribution of deployment domain specific device certificates.  The
   defined approach is agnostic regarding the utilized enrollment
   protocol allowing the application of existing and potentially new
   certificate management protocols.

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 https://datatracker.ietf.org/drafts/current/.

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

   This Internet-Draft will expire on January 11, 2021.

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.





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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include 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
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   6
   3.  Scope of solution . . . . . . . . . . . . . . . . . . . . . .   7
     3.1.  Supported environment . . . . . . . . . . . . . . . . . .   7
     3.2.  Application Examples  . . . . . . . . . . . . . . . . . .   7
       3.2.1.  Rolling stock . . . . . . . . . . . . . . . . . . . .   7
       3.2.2.  Building automation . . . . . . . . . . . . . . . . .   8
       3.2.3.  Substation automation . . . . . . . . . . . . . . . .   8
       3.2.4.  Electric vehicle charging infrastructure  . . . . . .   8
       3.2.5.  Infrastructure isolation policy . . . . . . . . . . .   9
       3.2.6.  Less operational security in the deployment domain  .   9
   4.  Requirement discussion and mapping to solution elements . . .   9
   5.  Architectural Overview and Communication Exchanges  . . . . .  12
     5.1.  Use Case 1: Support of off-site PKI service . . . . . . .  12
       5.1.1.  Behavior of a pledge  . . . . . . . . . . . . . . . .  15
       5.1.2.  Pledge - Registrar discovery and voucher exchange . .  15
       5.1.3.  Registrar - MASA voucher exchange . . . . . . . . . .  16
       5.1.4.  Pledge - Registrar - RA/CA certificate enrollment . .  16
       5.1.5.  Addressing Scheme Enhancements  . . . . . . . . . . .  19
     5.2.  Use Case 2: pledge-agent  . . . . . . . . . . . . . . . .  19
       5.2.1.  Behavior of a pledge  . . . . . . . . . . . . . . . .  23
       5.2.2.  Behavior of a pledge-agent  . . . . . . . . . . . . .  24
       5.2.3.  Registrar discovery . . . . . . . . . . . . . . . . .  24
       5.2.4.  Handling voucher request and certification requests .  24
     5.3.  Discovery of supported enrollment options at domain
           registrar . . . . . . . . . . . . . . . . . . . . . . . .  27
   6.  Example mappings to existing enrollment protocols . . . . . .  28
     6.1.  EST Handling  . . . . . . . . . . . . . . . . . . . . . .  29
     6.2.  Lightweight CMP Handling  . . . . . . . . . . . . . . . .  29
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  30
   8.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  30
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  30
   10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  30
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  30
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  30
     11.2.  Informative References . . . . . . . . . . . . . . . . .  31



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   Appendix A.  History of changes [RFC Editor: please delete] . . .  32
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  34

1.  Introduction

   BRSKI as defined in [I-D.ietf-anima-bootstrapping-keyinfra] specifies
   a solution for secure zero-touch (automated) bootstrapping of devices
   (pledges) in a target deployment domain.  This includes the discovery
   of network elements in the deployment domain, time synchronization,
   and the exchange of security information necessary to establish trust
   between a pledge and the domain and to adopt a pledge as new network
   and application element.  Security information about the deployment
   domain, specifically the deployment domain certificate (domain root
   certificate), is exchanged utilizing voucher objects as defined in
   [RFC8366].  These vouchers are authenticated self-contained (signed)
   objects, which may be provided online (synchronous) or offline
   (asynchronous) via the domain registrar to the pledge and originate
   from a Manufacturer's Authorized Signing Authority (MASA).  The MASA
   signed voucher contains the target domain certificate and can be
   verified by the pledge due to the possession of a manufacturer root
   certificate.  It facilitates the enrollment of the pledge in the
   deployment domain and is used to establish trust from the pledge to
   the domain.

   For the enrollment of devices BRSKI relies on EST [RFC7030] to
   request and distribute deployment domain specific device
   certificates.  EST in turn relies on a binding of the certification
   request to an underlying TLS connection between the EST client and
   the EST server.  According to BRSKI the domain registrar acts as EST
   server and is also acting as registration authority (RA) or local
   registration authority (LRA).  The binding to TLS is used to protect
   the exchange of a certification request (for an LDevID certificate)
   and to provide data origin authentication to support the
   authorization decision for processing the certification request.  The
   TLS connection is mutually authenticated and the client side
   authentication utilizes the pledge's manufacturer issued device
   certificate (IDevID certificate).  This approach requires an on-site
   availability of a local asset or inventory management system
   performing the authorization decision based on tuple of the
   certification request and the pledge authentication using the IDevID
   certificate, to issue a domain specific certificate to the pledge.
   The reason bases on the EST server (the domain registrar) terminating
   the security association with the pledge and thus the local binding
   between the certification request and the authentication of the
   pledge.  This type of enrollment utilizing an online connection to
   the PKI is considered as synchronous enrollment.





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   For certain use cases on-site support of a RA/CA component and/or an
   asset management is not available and rather provided by an
   operator's backend and may be provided timely limited or completely
   through offline interactions.  This may be due to higher security
   requirements for operating the certification authority.  The
   authorization of a certification request based on an asset management
   in this case will not / can not be performed on-site at enrollment
   time.  Enrollment, which cannot be performed in a (timely) consistent
   fashion is considered as asynchronous enrollment in this document.
   It requires the support of a store and forward functionality of
   certification request together with the requester authentication
   information.  This enables processing of the request at a later point
   in time.  A similar situation may occur through network segmentation,
   which is utilized in industrial systems to separate domains with
   different security needs.  Here, a similar requirement arises if the
   communication channel carrying the requester authentication is
   terminated before the RA/CA authorization handling of the
   certification request.  If a second communication channel is opened
   to forward the certification request to the issuing RA/ CA, the
   requester authentication information needs to be retained and ideally
   bound to the certification request.  This uses case is independent
   from timely limitations of the first use case.  For both cases, it is
   assumed that the requester authentication information is utilized in
   the process of authorization of a certification request.  There are
   different options to perform store and forward of certification
   requests including the requester authentication information:

   o  Providing a trusted component (e.g., an LRA) in the deployment
      domain, which stores the certification request combined with the
      requester authentication information (based on the IDevID) and
      potentially the information about a successful proof of possession
      (of the corresponding private key) in a way prohibiting changes to
      the combined information.  Note that the assumption is that the
      information elements may not be cryptographically bound together.
      Once connectivity to the backend is available, the trusted
      component forwards the certification request together with the
      requester information (authentication and proof of possession) to
      the off-site PKI for further processing.  It is assumed that the
      off-site PKI in this case relies on the local pledge
      authentication result and thus performs the authorization and
      issues the requested certificate.  In BRSKI the trusted component
      may be the EST server residing co-located with the registrar in
      the deployment domain.

   o  Utilization of authenticated self-contained objects for the
      enrollment, binding the certification request and the requester
      authentication in a cryptographic way.  This approach reduces the
      necessary trust in a domain component to storage and delivery.



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      Unauthorized modifications of the requester information (request
      and authentication) can be detected during the verification of the
      authenticated self-contained object.  An example for such an
      object is a signed CMS wrapped object (as the voucher).

   This targets environments, in which connectivity to a PKI is only
   temporary or not directly available, by specifying support for
   handling authenticated self-contained objects for enrollment.  As it
   is intended to enhance BRSKI it is named BRSKI-AE, where AE stands
   for asynchronous enrollment.  As BRSKI, BRSKI-AE results in the
   pledge storing a X.509 root certificate sufficient for verifying the
   domain registrar / proxy identity (LDevID CA Certificate) as well as
   an domain specific X.509 device certificate (LDevID EE certificate).

   Based on the proposed approach, a second set of scenarios can be
   addressed, in which the pledge has no direct communication path to
   the domain registrar, e.g., due to no network connectivity or a
   different technology stack as the domain registrar, but is considered
   to be managed by the domain registrar regarding the pledge domain
   credentials.  For this, an additional component is introduced acting
   as an agent for the pledge towards the domain registrar, e.g., a
   commissioning tool.  In contrast to BRSKI here the credentials may be
   pushed to the pledge instead of the pull approach taken by BRSKI.

   The goal is to enhance BRSKI to either allow other existing
   certificate management protocols supporting authenticated self-
   contained objects to be applied or to allow other types of encoding
   for the certificate management information exchange.  This is
   addressed by

   o  enhancing the well-known URI approach with additional path' for
      the utilized enrollment protocol.

   o  defining a certificate waiting indication and handling, if the
      certifying component is (temporarily) not available.

   o  allowing to utilize credentials different from the pledge's IDevID
      to establish a connection to the domain registrar.

   Note that in contrast to BRSKI, BRSKI-AE assumes support of multiple
   enrollment protocols on the infrastructure side, allowing the pledge
   manufacturer to select the most appropriate.  Thus, BRSKI-AE can be
   applied for both, asynchronous and synchronous enrollment.








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2.  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].

   This document relies on the terminology defined in
   [I-D.ietf-anima-bootstrapping-keyinfra].  The following terms are
   defined additionally:

   CA:  Certification authority, issues certificates.

   RA:  Registration authority, an optional system component to which a
      CA delegates certificate management functions such as
      authorization checks.

   LRA:  Local registration authority, an optional RA system component
      with proximity to end entities.

   IED:  Intelligent Electronic Device (in essence a pledge).

   on-site:  Describes a component or service or functionality available
      in the target deployment domain.

   off-site:  Describes a component or service or functionality
      available in an operator domain different from the target
      deployment domain.  This may be a central side, to which only a
      temporarily connection is available, or which is in a different
      administrative domain.

   asynchronous communication:  Describes a timely interrupted
      communication between an end entity and a PKI component.

   synchronous communication:  Describes a timely uninterrupted
      communication between an end entity and a PKI component.

   authenticated self-contained object:  Describes an object, which is
      cryptographically bound to the IDevID EE credential of a pledge.
      The binding is assumed to be provided through a digital signature
      using the corresponding private key of the IDevID to wrap the
      actual object.  Note that depending on the availability of a
      LDevID EE credential, the binding may also be achieved using
      corresponding private key of the LDevID.  This can be utilized in
      for instance in the context of an initial certification request or
      a certificate update.





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3.  Scope of solution

3.1.  Supported environment

   This solution is intended to be used in domains with limited support
   of on-site PKI services and comprises use cases in which:

   o  there is no registration authority available in the deployment
      domain.  The connectivity to the backend RA may only be
      temporarily available.  A local store and forward device is used
      for the communication with the backend services.

   o  authoritative actions of a LRA are limited and may not comprise
      authorization of certification requests of pledges.  Final
      authorization is done at the RA residing in the backend operator
      domain.

   o  the target deployment domain already uses a certificate management
      approach that shall be reused to be consistent throughout the life
      cycle.

   In addition, the solution is intended to be applicable in domains in
   which pledges have no direct connection to the domain registrar, but
   are expected to be managed by the registrar.  This can be motivated
   by pledges featuring a different technology stack or by pledges
   without an existing connection to the domain registrar during
   onboarding.

3.2.  Application Examples

   The following examples are intended to motivate the support of
   different enrollment approaches in general and asynchronous
   enrollment specifically, by introducing industrial applications
   cases, which could leverage BRSKI as such but also require support of
   asynchronous operation as intended with BRSKI-AE.

3.2.1.  Rolling stock

   Rolling stock or railroad cars contain a variety of sensors,
   actuators, and controller, which communicate within the railroad car
   but also exchange information between railroad cars building a train
   or with a backend.  These devices are typically unaware of backend
   connectivity.  Managing certificates may be done during maintenance
   cycles of the railroad car, but can already be prepared during
   operation.  The preparation may comprise the generation of
   certification requests by the components, which are collected and
   forwarded for processing once the railroad car is connected to the
   operator backend.  The authorization of the certification request is



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   then done based on the operator's asset/inventory information in the
   backend.

3.2.2.  Building automation

   In building automation a use case can be described by a detached
   building or the basement of a building equipped with sensor,
   actuators, and controllers connected, but with only limited or no
   connection to the centralized building management system.  This
   limited connectivity may be during the installation time but also
   during operation time.  During the installation in the basement, a
   service technician collects the necessary information from the
   basement network and provides them to the central building management
   system, e.g., using a laptop or even a mobile phone to transport the
   information.  This information may comprise parameters and settings
   required in the operational phase of the sensors/actuators, like a
   certificate issued by the operator to authenticate against other
   components and services.

   The collected information may be provided by a domain registrar
   already existing in the installation network.  In this case
   connectivity to the backend PKI may be facilitated by the service
   technician's laptop.  Contrary, the information can also be collected
   from the pledges directly and provided to a domain registrar deployed
   in the main network.  In this cases connectivity to the domain
   registrar may be facilitated by the service technician's laptop.

3.2.3.  Substation automation

   In substation automation a control center typically hosts PKI
   services to issue certificates for Intelligent Electronic Devices
   (IED)s in a substation.  Communication between the substation and
   control center is done through a proxy/gateway/DMZ, which terminates
   protocol flows.  Note that NERC CIP-005-5 [NERC-CIP-005-5] requires
   inspection of protocols at the boundary of a security perimeter (the
   substation in this case).  In addition, security management in
   substation automation assumes central support of different enrollment
   protocols to facilitate the capabilities of IEDs from different
   vendors.  The IEC standard IEC62351-9 [IEC-62351-9] specifies the
   mandatory support of two enrollment protocols, SCEP
   [I-D.gutmann-scep] and EST [RFC7030] for the infrastructure side,
   while the IED must only support one of the two.

3.2.4.  Electric vehicle charging infrastructure

   For the electric vehicle charging infrastructure protocols have been
   defined for the interaction between the electric vehicle (EV) and the
   charging point (e.g., ISO 15118-2 [ISO-IEC-15118-2]) as well as



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   between the charging point and the charging point operator (e.g.
   OCPP [OCPP]).  Depending on the authentication model, unilateral or
   mutual authentication is required.  In both cases the charging point
   authenticates uses an X.509 certificate to authenticate in the
   context of a TLS connection between the EV and the charging point.
   The management of this certificate depends (beyond others) on the
   selected backend connectivity protocol.  Specifically, in case of
   OCPP it is intended as single communication protocol between the
   charging point and the backend carrying all information to control
   the charging operations and maintain the charging point itself.  This
   means that the certificate management is intended to be handled in-
   band of OCPP.  This requires to be able to encapsulate the
   certificate management exchanges in a transport independent way.
   Authenticated self-containment will ease this by allowing the
   transport without a separate communication protocol.  For the purpose
   of certificate management CMP [RFC4210] is intended to be used.

3.2.5.  Infrastructure isolation policy

   This refers to any case in which network infrastructure is normally
   isolated from the Internet as a matter of policy, most likely for
   security reasons.  In such a case, limited access to external PKI
   resources will be allowed in carefully controlled short periods of
   time, for example when a batch of new devices are deployed, but
   impossible at other times.

3.2.6.  Less operational security in the deployment domain

   The registration point performing the authorization of a certificate
   request is a critical PKI component and therefore implicates higher
   operational security than other components utilizing the issued
   certificates for their security features.  CAs may also demand higher
   security in the registration procedures.  Especially the CA/Browser
   forum currently increases the security requirements in the
   certificate issuance procedures for publicly trusted certificates.
   There may be the situation that the deployment domain does not offer
   enough security to operate a registration point and therefore wants
   to transfer this service to a backend.

4.  Requirement discussion and mapping to solution elements

   For the requirements discussion it is assumed that the domain
   registrar receiving a certification request as authenticated self-
   contained object is not the authorization point for this
   certification request.  If the domain registrar is the authorization
   point, BRSKI can be used directly.  Note that BRSKI-AE could also be
   used in this case.




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   Based on the intended deployment environment described in Section 3.1
   and the motivated application examples described in Section 3.2 the
   following base requirements are derived to support authenticated
   self-contained objects as container carrying the certification
   request and further information to support asynchronous operation.

   At least the following properties are required:

   o  Proof of Possession: utilizing the private key corresponding to
      the public key contained in the certification request.

   o  Proof of Identity: utilizing an existing IDevID credential bound
      to the certification request.  Certificate updates may utilize the
      LDevID credential.

   Solution examples (not complete) based on existing technology are
   provided with the focus on existing IETF documents:

   o  Certification request objects: Certification requests are
      structures protecting only the integrity of the contained data
      providing a proof-of-private-key-possession for locally generated
      key pairs.  Examples for certification requests are:

      *  PKCS#10 [RFC2986]: Defines a structure for a certification
         request.  The structure is signed to ensure integrity
         protection and proof of possession of the private key of the
         requester that corresponds to the contained public key.

      *  CRMF [RFC4211]: Defines a structure for the certification
         request message.  The structure supports integrity protection
         and proof of possession, through a signature generated over
         parts of the structure by using the private key corresponding
         to the contained public key.

      Note that the integrity of the certification request is bound to
      the public key contained in the certification request by
      performing the signature operation with the corresponding private
      key.  In the considered application examples, this is not
      sufficient and needs to be bound to the existing credential of the
      pledge (IDevID) additionally.  This binding supports the
      authorization decision for the certification request through the
      provisioning of a proof of identity.  The binding of data origin
      authentication to the certification request may be delegated to
      the protocol used for certificate management.

   o  Proof of Identity options: The certification request should be
      bound to an existing credential (here IDevID) to enable a proof of
      identity and based on it an the authorization of the certification



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      request.  The binding may be realized through a security options
      in an underlying transport protocol if the authorization of the
      the certification request is done at the next communication hop.
      Alternatively, this binding can be done by a wrapping signature
      employing an existing credential (initial: IDevID, renewal:
      LDevID).  This requirement is addressed by existing enrollment
      protocols in different ways, for instance:

      *  EST [RFC7030]: Utilizes PKCS#10 to encode the certification
         request.  The Certificate Signing Request (CSR) may contain a
         binding to the underlying TLS by including the tls-unique value
         in the self-signed CSR structure.  The tls-unique value is one
         result of the TLS handshake.  As the TLS handshake is performed
         mutually authenticated and the pledge utilized its IDevID for
         it, the proof of identity can be provided by the binding to the
         TLS session.  This is supported in EST using simpleenroll.  To
         avoid the binding to the underlying authentication in the
         transport layer EST offers the support of a wrapping the CSR
         with an existing certificate by using fullcmc.

      *  SCEP [I-D.gutmann-scep]: Provides the option to utilize either
         an existing secret (password) or an existing certificate to
         protect the CSR based on SCEP Secure Message Objects using CMS
         wrapping ([RFC5652]).  Note that the wrapping using an existing
         IDevID credential in SCEP is referred to as renewal.  SCEP
         therefore does not rely on the security of an underlying
         transport.

      *  CMP [RFC4210] Provides the option to utilize either an existing
         secret (password) or an existing certificate to protect the
         PKIMessage containing the certification request.  The
         certification request is encoded utilizing CRMF.  PKCS#10 is
         optionally supported.  The proof of identity of the PKIMessage
         containing the certification request can be achieved by using
         IDevID credentials to calculate a signature over the header and
         the body of the PKIMessage utilizing the protectionAlg signaled
         in the PKIMessage header and the PKIProtection carrying the
         actual signature value.  CMP therefore does not rely on the
         security of an underlying transport.

      *  CMC [RFC5272] Provides the option to utilize either an existing
         secret (password) or an existing certificate to protect the
         certification request (either in CRMF or PKCS#10) based on CMS
         [RFC5652]).  Here a FullCMCRequest can be used, which allows
         signing with an existing IDevID credential to provide a proof
         of identity.  CMC therefore does not rely on the security of an
         underlying transport.




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   Note that besides the already existing enrollment protocols there
   ongoing work in the ACE WG to define an encapsulation of EST in
   OSCORE to result in a TLS independent way of protecting EST.  This
   approach [I-D.selander-ace-coap-est-oscore] may be considered as
   further variant.

5.  Architectural Overview and Communication Exchanges

   To support asynchronous enrollment, the base system architecture
   defined in BRSKI [I-D.ietf-anima-bootstrapping-keyinfra] is enhanced
   to facilitate the two target use cases.

   o  Use case 1 (PULL case): the pledge requests certificates from a
      PKI operated off-site via the domain registrar.

   o  Use case 2 (PUSH/PULL case): allows delayed (delegated) onboarding
      using a pledge-agent instead a direct connection to the domain
      registrar.  The communication model between pledge-agent and
      pledge depends on the specified interface and may use a PULL or
      PUSH approach.  This interaction in terms of a protocol
      specification is out of scope of this document.

   Note that the terminology PUSH and PULL relates to the pledge
   behavior.  In PULL the pledge requests data objects as in BRSKI,
   while in the PUSH case the pledge may be provisioned with the
   necessary data objects.  The pledge-agent as it represents the pledge
   always acts in a PULL mode to the domain registrar.  Both use cases
   are described in the next subsections.  They utilize the existing
   BRSKI architecture elements as much as possible.  Necessary
   enhancements to support authenticated self-contained objects for
   certificate enrollment are kept on a minimum to ensure reuse of
   already defined architecture elements and interactions.

   For the authenticated self-contained objects used for the
   certification request, BRSKI-AE relies on the defined message
   wrapping mechanisms of the enrollment protocols stated in Section 4
   above.

5.1.  Use Case 1: Support of off-site PKI service

   One assumption of BRSKI-AE is that the authorization of a
   certification request is performed based on an authenticated self-
   contained object, binding the certification request to the
   authentication using the IDevID.  This supports interaction with off-
   site or off-line PKI (RA/CA) components.  In addition, the
   authorization of the certification request may not be done by the
   domain registrar but by a PKI residing in the backend of the domain
   operator (off-site) as described in Section 3.1.  This leads to



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   changes in the placement or enhancements of the logical elements as
   shown in Figure 1.

                                              +------------------------+
      +--------------Drop Ship--------------->| Vendor Service         |
      |                                       +------------------------+
      |                                       | M anufacturer|         |
      |                                       | A uthorized  |Ownership|
      |                                       | S igning     |Tracker  |
      |                                       | A uthority   |         |
      |                                       +--------------+---------+
      |                                                      ^
      |                                                      |
      V                                                      |
   +--------+     .........................................  |
   |        |     .                                       .  | BRSKI-
   |        |     .  +------------+       +------------+  .  | MASA
   | Pledge |     .  |   Join     |       | Domain     <-----+
   |        |     .  |   Proxy    |       | Registrar/ |  .
   |        <-------->............<-------> Enrollment |  .
   |        |     .  |        BRSKI-AE    | Proxy      |  .
   | IDevID |     .  |            |       +------^-----+  .
   |        |     .  +------------+              |        .
   |        |     .                              |        .
   +--------+     ...............................|.........
                   "on-site domain" components   |
                                                 |e.g., RFC 7030,
                                                 |      RFC 4210, ...
    .............................................|.....................
    . +---------------------------+     +--------v------------------+ .
    . | Public Key Infrastructure |<----+ PKI RA                    | .
    . | PKI CA                    |---->+                           | .
    . +---------------------------+     +---------------------------+ .
    ...................................................................
            "off-site domain" components

       Figure 1: Architecture overview using off-site PKI components

   The architecture overview in Figure 1 utilizes the same logical
   elements as BRSKI but with a different placement in the deployment
   architecture for some of the elements.  The main difference is the
   placement of the PKI RA/CA component, which is performing the
   authorization decision for the certification request message.  It is
   placed in the off-site domain of the operator (not the deployment
   site directly), which may have no or only temporary connectivity to
   the deployment or on-site domain of the pledge.  This is to underline
   the authorization decision for the certification request in the




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   backend rather than on-site.  The following list describes the
   components in the deployment domain:

   o  Join Proxy: same functionality as described in BRSKI.

   o  Domain Registrar / Enrollment Proxy: In general the domain
      registrar proxy has a similar functionality regarding the
      imprinting of the pledge in the deployment domain to facilitate
      the communication of the pledge with the MASA and the PKI.
      Different is the authorization of the certification request.
      BRSKI-AE allows to perform this in the operators backend (off-
      site), and not directly at the domain registrar.

      *  Voucher exchange: The voucher exchange with the MASA via the
         domain registrar is performed as described in BRSKI
         [I-D.ietf-anima-bootstrapping-keyinfra] .

      *  Certificate enrollment: For the pledge enrollment the domain
         registrar in the deployment domain supports the adoption of the
         pledge in the domain based on the voucher request.
         Nevertheless, it may not have sufficient information for
         authorizing the certification request.  If the authorization is
         done in the off-site domain, the domain registrar forwards the
         certification request to the RA to perform the authorization.
         The domain registrar in this acts as an enrollment proxy or
         local registration authority.  It is also able to handle the
         case having temporarily no connection to an off-site PKI by
         storing the certification request and forwarding it to the RA
         upon regaining connectivity.  As authenticated self-contained
         objects are used, it requires an enhancement of the domain
         registrar.  This is done by supporting alternative enrollment
         approaches (protocol options, protocols, encoding) by enhancing
         the addressing scheme to communicate with the domain registrar
         (see Section 5.1.5) and also by providing a discover scheme to
         allow the pledge to enumerate the supported enrollment options
         (see Section 5.3).

   The following list describes the vendor related components/service
   outside the deployment domain:

   o  MASA: general functionality as described in BRSKI.  Assumption
      that the interaction with the MASA may be synchronous (voucher
      request with nonce) or asynchronous (voucher request without
      nonce).

   o  Ownership tracker: as defined in BRSKI.





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   The following list describes the operator related components/service
   operated in the backend:

   o  PKI RA: Performs certificate management functions (validation of
      certification requests, interaction with inventory/asset
      management for authorization of certification requests, etc.) for
      issuing, updating, and revoking certificates for a domain as a
      centralized infrastructure for the domain operator.  The inventory
      (asset) management may be a separate component or integrated into
      the RA directly.

   o  PKI CA: Performs certificate generation by signing the certificate
      structure provided in the certification request.

   Based on BRSKI and the architectural changes the original protocol
   flow is divided into three phases showing commonalities and
   differences to the original approach as depicted in the following.

   o  Discovery phase (same as BRSKI)

   o  Voucher exchange with deployment domain registrar (same as BRSKI).

   o  Enrollment phase (changed to accompany the application of
      authenticated self-contained objects).

5.1.1.  Behavior of a pledge

   The behavior of a pledge as described in
   [I-D.ietf-anima-bootstrapping-keyinfra] is kept with one exception.
   After finishing the imprinting phase (4) the enrollment phase (5) is
   performed with a method supporting authenticated self-contained
   objects.  Using EST with simpleenroll cannot be applied here, as it
   binds the pledge authentication with the existing IDevID to the
   transport channel (TLS) rather than to the certification request
   object directly.  This authentication in the transport layer is not
   visible / verifiable at the authorization point in the off-site
   domain.  Section 6 discusses potential enrollment protocols and
   options applicable.

5.1.2.  Pledge - Registrar discovery and voucher exchange

   The discovery phase is applied as specified in
   [I-D.ietf-anima-bootstrapping-keyinfra].








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5.1.3.  Registrar - MASA voucher exchange

   The voucher exchange is performed as specified in
   [I-D.ietf-anima-bootstrapping-keyinfra].

5.1.4.  Pledge - Registrar - RA/CA certificate enrollment

   As stated in Section 4 the enrollment shall be performed using an
   authenticated self-contained object providing:

   o  Proof of Possession: utilizing the private key corresponding to
      the public key contained in the certification request.

   o  Proof of Identity: utilizing the existing IDevID credential to
      generate a signature of the initial certification request.
      Certificate updates may utilize the LDevID credential.



































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   +--------+         +---------+    +------------+     +------------+
   | Pledge |         | Circuit |    | Domain     |     | Operator   |
   |        |         | Join    |    | Registrar  |     | RA/CA      |
   |        |         | Proxy   |    |  (JRC)     |     | (OPKI)     |
   +--------+         +---------+    +------------+     +------------+
     /-->                                      |                    |
   [Request of CA Certificates]                |                    |
     |---------- CA Certs Request ------------>|                    |
     |              [if connection to operator domain is available] |
     |                                         |-Request CA Certs ->|
     |                                         |<- CA Certs Response|
     |<-------- CA Certs Response--------------|                    |
     /-->                                      |                    |
   [Request of Certificate Attributes to be included]               |
     |---------- Attribute Request ----------->|                    |
     |              [if connection to operator domain is available] |
     |                                         |Attribute Request ->|
     |                                         |<-Attribute Response|
     |<--------- Attribute Response -----------|                    |
     /-->                                      |                    |
   [Certification request]                     |                    |
     |-------------- Cert Request ------------>|                    |
     |              [if connection to operator domain is available] |
     |                                         |--- Cert Request -->|
     |                                         |<-- Cert Response --|
   [Optional Certification waiting indication] |                    |
     /-->                                      |                    |
     |<---------- Cert Waiting ----------------|                    |
     |-- Cert Polling (with orig request ID) ->|                    |
     |              [if connection to operator domain is available] |
     |                                         |--- Cert Request -->|
     |                                         |<-- Cert Response --|
     /-->                                      |                    |
     |<------------- Cert Response ------------|                    |
     /-->                                      |                    |
   [Certification confirmation]                |                    |
     |-------------- Cert Confirm ------------>|                    |
     |                                         /-->                 |
     |                                         |[optional]          |
     |                                         |--- Cert Confirm -->|
     |                                         |<-- PKI Confirm ----|
     |<------------- PKI/Registrar Confirm ----|                    |

                     Figure 2: Certificate enrollment

   The following list provides an abstract description of the flow
   depicted in Figure 2.




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   o  CA Cert Request: The pledge SHOULD request the full distribution
      of CA Certificates.  This ensures that the pledge has the complete
      set of current CA certificates beyond the pinned-domain-cert.

   o  CA Cert Response: Contains at least one CA certificate of the
      issuing CA.

   o  Attribute Request: Typically, the automated bootstrapping occurs
      without local administrative configuration of the pledge.
      Nevertheless, there are cases, in which the pledge may also
      include additional attributes specific to the deployment domain
      into the certification request.  To get these attributes in
      advance, the attribute request SHOULD be used.

   o  Attribute Response: Contains the attributes to be included in the
      certification request message.

   o  Cert Request: Depending on the utilized enrollment protocol, this
      certification request contains the authenticated self-contained
      object ensuring both, proof-of-possession of the corresponding
      private key and proof-of-identity of the requester.

   o  Cert Response: certification response message containing the
      requested certificate and potentially further information like
      certificates of intermediary CAs on the certification path.

   o  Cert Waiting: waiting indication for the pledge to retry after a
      given time.  For this a request identifier is necessary.  This
      request identifier may bei either part of the enrollment protocol
      or build based on the certification request.

   o  Cert Polling: querying the registrar, if the certificate request
      was already processed; can be answered either with another Cert
      Waiting, or a Cert Response.

   o  Cert Confirm: confirmation message from pledge after receiving and
      verifying the certificate.

   o  PKI/Registrar Confirm: confirmation message from PKI/registrar
      about reception of the pledge's certificate confirmation.

   [RFC Editor: please delete] /*

   Open Issues:

   o  Description of certificate waiting and retries.





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   o  Message exchange description is expected to be done by the
      utilized enrollment protocol based on the addressing scheme (see
      also Section 6.

   o  Handling of certificate/PKI confirmation message between pledge
      and domain registrar and PKI (treated optional?).

   */

5.1.5.  Addressing Scheme Enhancements

   BRSKI-AE requires enhancements to the addressing scheme defined in
   [I-D.ietf-anima-bootstrapping-keyinfra] to accommodate the additional
   handling of authenticated self-contained objects for the
   certification request.  As this is supported by different enrollment
   protocols, they can be directly employed (see also Section 6).  For
   the support of different enrollment options at the domain registrar,
   the addressing approach of BRSKI using a "/.well-known" tree from
   [RFC5785] is enhanced.

   The current addressing scheme in BRSKI for the client certificate
   request function during the enrollment is using the definition from
   EST [RFC7030], here on the example on simple enroll: "/.well-
   known/est/simpleenroll" This approach is generalized to the following
   notation: "/.well-known/enrollment-protocol/request" in which
   enrollment-protocol may be an already existing protocol or a newly
   defined approach.  Note that enrollment is considered here as a
   sequence of at least a certification request and a certification
   response.  In case of existing enrollment protocols the following
   notation is used proving compatibility to BRSKI:

   o  enrollment-protocol: references either EST [RFC7030] as in BRSKI
      or CMP, CMC, SCEP, or newly defined approaches as alternatives.
      Note: the IANA registration of the well-known URI is expected to
      be done by the enrollment protocol.  For CMP a lightweight profile
      is defined, which provides the definition of the well-known URI in
      Lightweight CMP Profile [I-D.ietf-lamps-lightweight-cmp-profile].

   o  request: depending on the utilized enrollment protocol, the
      request describes the required operation at the registrar side.
      Enrollment protocols are expected to define the request endpoints
      as done by existing protocols (see also Section 6).

5.2.  Use Case 2: pledge-agent

   To support mutual trust establishment of pledges, not directly
   connected to the domain registrar, a similar approach is applied as
   discussed for the use case 1.  It relies on the exchange of



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   authenticated self-contained objects (the voucher request/response
   objects as known from BRSKI and the certification request/response
   objects as introduced by BRSKI-AE).  This allows independence from
   the protection provided by the underlying transport.

   In contrast to BRSKI, the exchange of these objects is performed with
   the help of a pledge-agent, supporting the interaction of the pledge
   with the domain registrar.  It may be an integrated functionality of
   a commissioning tool.  This leads to enhancements of the logical
   elements in the BRSKI architecture as shown in Figure 3.  The pledge-
   agent provides an interface to the pledge to enable creation or
   consumption of required data objects, which are exchanged with the
   domain registrar.  Moreover, the addition of the pledge-agent also
   influences the sequences for the data exchange between the pledge and
   the domain registrar described in
   [I-D.ietf-anima-bootstrapping-keyinfra].  The general goal for the
   pledge-agent application is the reuse of already defined endpoints on
   the domain registrar side.  The behavior of the endpoint may need to
   be adapted.
































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                                             +------------------------+
      +--------------Drop Ship---------------| Vendor Service         |
      |                                      +------------------------+
      |                                      | M anufacturer|         |
      |                                      | A uthorized  |Ownership|
      |                                      | S igning     |Tracker  |
      |                                      | A uthority   |         |
      |                                      +--------------+---------+
      |                                                     ^
      |                                                     |  BRSKI-
      V                                                     |   MASA
   +-------+     +-------+     .............................|.........
   |       |     |       |     .                            |        .
   |       |     |       |     .  +-----------+       +-----v-----+  .
   |       |     |Pledge |     .  |           |       |           |  .
   |Pledge |     | Agent |     .  |   Join    |       | Domain    |  .
   |       |     |       |     .  |   Proxy   |       | Registrar |  .
   |       <----->.......<-------->...........<-------> (PKI RA)  |  .
   |       |     |       |     .  |       BRSKI-AE    |           |  .
   |       |     |       |     .  |           |       +-----+-----+  .
   |IDevID |     |opt.   |     .  +-----------+             |        .
   |       |     |IDevID |     .         +------------------+-----+  .
   |       |     |or     |     .         | Key Infrastructure     |  .
   |       |     |LDevID |     .         | (e.g., PKI Certificate |  .
   +-------+     +-------+     .         |       Authority)       |  .
                               .         +------------------------+  .
                               .......................................
                                         "Domain" components

           Figure 3: Architecture overview using a pledge-agent

   The architecture overview in Figure 3 utilizes the same logical
   elements as BRSKI with the addition of the pledge-agent.  The pledge-
   agent, may originate from the pledge manufacturer and may have either
   an own IDevID credential issued by the manufacturer or an LDevID
   issued already by the deployment (on-site) domain.

   For authentication towards the domain registrar, the pledge-agent may
   use the IDevID or LDevID credentials, which are verified by the
   domain registrar as part of the TLS establishment.  The provisioning
   of this credential to the pledge-agent is out of scope for this
   specification.  Alternatively, the domain registrar may authenticate
   the user operating the pledge-agent to perform authorization of
   pledge onboarding.  Examples for such a user level authentication are
   the application of HTTP authentication or the usage of SAML tokens or
   the application of a user related certificates in the TLS handshake
   or other.  If the pledge-agent utilizes a certificate, the domain




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   registrar must be able to verify the certificate by possessing the
   corresponding root certificate.

   The following list describes the components in the deployment domain:

   o  Pledge: The pledge is expected to communicate with the pledge-
      agent for providing the necessary data objects for onboarding.
      The exact protocol used between the pledge and the pledge-agent is
      out of scope for this document but may consider: If the pledge is
      triggered/PUSHED by the pledge-agent, it becomes a callee.  There
      are some differences to BRSKI:

      *  Discovery of the domain registrar will be omitted as the pledge
         is expected to be triggered by the pledge-agent.

      *  The pledge-agent is expected to provide an option to trigger
         the onboarding by pushing data objects to the pledge.

      *  Order of exchanges in the call flow is different as the pledge-
         agent collects both voucher request objects and certification
         request objects at once.

      *  The data objects utilized are the same objects already applied
         in use case 1 Section 5.1.

   o  Pledge-Agent: provides a communication path to exchange data
      objects between the pledge and the domain registrar.  The pledge-
      agent facilitates situations, in which the domain registrar is not
      directly reachable by the pledge, either due to a different
      technology stack or due to missing connectivity (e.g., if the
      domain registrar resides in the cloud and the pledge has no
      connectivity, yet).  The pledge-agent in this cases can easily
      collect voucher request objects and certification request objects
      from one or multiple pledges at once and perform a bulk onboarding
      based on the collected data.  The pledge-agent may be configured
      with the domain registrar information or may use the discovery
      mechanism.

   o  Join Proxy: same functionality as described in BRSKI.

   o  Domain Registrar: In general the domain registrar fulfills the
      same functionality regarding the onboarding of the pledge in the
      deployment domain by facilitating the communication of the pledge
      with the MASA and the PKI.  In contrast to BRSKI, the domain
      registrar does not interact with a pledge directly but through the
      pledge-agent.  This prohibits a pledge authentication using its
      IDevID during TLS establishment towards the registrar.  If the
      pledge-agent has an IDevID or is already possessing a LDevID valid



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      in the deployment domain, it is expected to use this
      authentication towards the domain registrar.

   The manufacturer provided components/services (MASA and Ownership
   tracker) are used as defined in BRSKI.

5.2.1.  Behavior of a pledge

   The behavior of a pledge as described for use case 1 Section 5.1 is
   basically kept regarding the generation of voucher request/response
   objects and certificate request/response objects.  Due to the use of
   the pledge-agent, the interaction with the domain registrar is
   changed as shown in Figure 4.

   The interaction of the pledge with the pledge-agent in terms of
   utilized protocols or discovery options is out of scope of this
   document.  This document concentrates on the exchanged data objects
   between the pledge and the domain registrar via the pledge-agent.

   The pledge-agent should be able to authenticate the pledge-agent
   either based on security mechanisms as part of the communication
   channel between the pledge and the pledge-agent or based on the data
   (request) objects.

   The pledge-agent should provide the proximity-registrar-cert to the
   pledge to enable embedding in the voucher request object.  The
   registrar certificate may be configured at the pledge-agent or may be
   fetched by the pledge-agent based on the TLS connection establishment
   with the domain registrar.

   The pledge interacts with the pledge-agent, to generate a voucher
   request object (VouReq) and a certification request object (CR),
   which are provided to the domain registrar through the pledge-agent.

   The pledge shall generate the voucher request object as described in
   [I-D.ietf-anima-bootstrapping-keyinfra] and provide this information
   to the pledge-agent.

   After the voucher request exchange the pledge will be triggered by to
   generate a certification request object.  For this, the pledge-agent
   may have been pre-configured with the certification request
   attributes, that it may provide to the pledge.  The certification
   request is generated as authenticated self-signed object, which
   assures proof of possession of the private key corresponding to the
   contained public key in the certification request as well as a proof
   of identity, based on the IDevID of the pledge.  This is done as
   described for use case 1 Section 5.1.




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5.2.2.  Behavior of a pledge-agent

   The pledge-agent is a new component in the BRSKI context.  It
   provides connectivity between the pledge and the domain registrar and
   utilizes the endpoints already specified in
   [I-D.ietf-anima-bootstrapping-keyinfra].  The pledge-agent is
   expected to interact with the pledge independent of the domain
   registrar.  As stated before, data exchange is only defined based on
   the data objects, which are the voucher request/response objects and
   the certification request/response objects.  The transport mechanism
   is out of scope here.  This changes the general interaction as shown
   in Figure 4.

   The pledge-agent may have an own IDevID or a deployment domain issued
   LDevID to be utilized in the TLS communication establishment towards
   the domain registrar.  Note that the pledge-agent may also be used
   without client side authentication if no suitable credential is
   available on transport layer.  As BRSKI-AE utilizes authenticated
   self-contained data objects, which bind the pledge authentication
   (proof of identity) directly to the objects (voucher request and
   certification request), the TLS client authentication may be
   neglected.  This is a deviation from the BRSKI approach in which the
   pledge's IDevID credential is used to perform TLS client
   authentication.  According to [I-D.ietf-anima-bootstrapping-keyinfra]
   section 5.3, the domain registrar performs the pledge authorization
   for onboarding within his domain based on the provided voucher
   request.

5.2.3.  Registrar discovery

   The discovery phase may be applied as specified in
   [I-D.ietf-anima-bootstrapping-keyinfra] with the deviation that it is
   done between the pledge-agent and the domain registrar.
   Alternatively, the domain registrar may be configured in the pledge-
   agent.

   The discovery of the pledge-agent by the pledge belongs to the
   communication between the two instances and is out of scope for this
   specification.

5.2.4.  Handling voucher request and certification requests

   The BRSKI-AE exchange of voucher requests and certification requests
   utilizes authenticated self-contained objects independent of
   transport protection.

   +--------+      +-------+    +-----------+   +--------+   +---------+
   | Pledge |      | Pledge|    | Domain    |   | Domain |   | Vendor  |



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   |        |      | Agent |    | Registrar |   | CA     |   | Service |
   |        |      |       |    |  (JRC)    |   |        |   | (MASA)  |
   +--------+      +-------+    +-----------+   +--------+   +---------+
     |                   |              |               |    Internet |
     |       opt: configure             |               |             |
     |       - proximity-registrar-cert |               |             |
     |       - CSR attributes           |               |             |
     |                   |              |               |             |
   [example: trigger voucher and certification request generation ]   |
     |                   |              |               |             |
     |<--trigger VouReq--|              |               |             |
     |(o: proximity-cert)|              |               |             |
     |- Voucher Request->|              |               |             |
     |                   |              |               |             |
     |<--trigger CR------|              |               |             |
     |(o: attributes)    |              |               |             |
     |----Cert Request-->|              |               |             |
     |                   |<---- TLS --->|               |             |
     |                   |              |               |             |
   [Start known BRSKI interaction ]     |               |             |
     |                   |              |               |             |
     |                   |--- VouReq -->|               |             |
     |                   |       [accept device?]       |             |
     |                   |       [contact vendor]       |             |
     |                   |              |----- Voucher Request ------>|
     |                   |              |----- Pledge ID ------------>|
     |                   |              |----- Domain ID ------------>|
     |                   |              |----- optional: nonce ------>|
     |                   |              |             [extract DomainID]
     |                   |              |             [update audit log]
     |                   |              |<--------- Voucher  ---------|
     |                   |<-- Voucher --|               |             |
     |                   |              |<----- device audit log  ----|
     |                   |              |               |             |
   [optional retrieve CA certs]         |               |             |
     |                   |- CACertReq ->|               |             |
     |                   |              |- CACertReq -->|             |
     |                   |              |<-CACertResp --|             |
     |                   |< CACertResp -|               |             |
     |                   |              |               |             |
   [certification request]              |               |             |
     |                   |-- CertReq -->|               |             |
     |                   |              |-- CertReq --->|             |
     |                   |              |<--CertResp----|             |
     |                   |<-- CertResp -|               |             |
     |                   |              |               |             |
   [Stop known BRSKI interaction ]      |               |             |
     |                   |              |               |             |



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   [push voucher and certificate to pledge, optionally push CA certs] |
     |                   |              |               |             |
     |<---post Voucher---|              |               |             |
     |- Voucher Status-->|              |               |             |
     |         |              |               |             |
     |<---post CACerts---|              |               |             |
     |- CACerts Status-->|              |               |             |
     |                   |              |               |             |
     |                   |              |               |             |
     |<--post CertResp---|              |               |             |
     |---- CertConf ---->|              |               |             |
     |                   |              |               |             |
     |                 [voucher status telemetry ]      |             |
     |                   |VoucherStatus>|               |             |
     |                   |[verify audit log and voucher]|             |
     |                   |              |               |             |
     |                   |     [enroll Status]          |             |
     |                   |-- CertConf ->|               |             |
     |                   |              |-- CertConf -->|             |
     |                   |              |               |             |

       Figure 4: Request handling of the pledge using a pledge-agent

   As shown in Figure 4 the pledge-agent collects the voucher request
   and certification request objects from a pledge.  As the pledge-agent
   (e.g., as part of a commissioning tool) is intended to work between
   the pledge and the domain registrar, a collection of requests from
   multiple pledges is possible, allowing a bulk onboarding of multiple
   pledges using the connection between the pledge-agent and the domain
   registrar.

   The information exchange between the pledge-agent and the domain
   registrar resembles the exchanges between the pledge and the domain
   registrar from BRSKI with one exception.  As authenticated self-
   contained objects are used consequently, the authentication of the
   pledge-agent to the domain registrar may be neglected.  Note that
   this allows to employ simple applications as pledge-agent.  The
   authentication of the pledge-agent is recommended if it is desired to
   perform the onboarding with an authorized pledge-agent or to support
   advanced auditing in case a user based authentication is done.  As
   stated above, the authentication may be realized by device (IDevID or
   LDevID) or user related credentials in the context of the TLS
   handshake, HTTP based authentication, SAML tokens or other.

   [RFC Editor: please delete] /* to be discussed: Description on how
   the registrar makes the decision if he is connected with pledge
   directly or with a pledge-agent.  This may result in a case statement
   (client side authentication in TLS, user authentication above TLS,



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   etc.) for the TLS connection establishment in the original BRSKI
   document in section 5.1 */

   Once the pledge-agent has finished the exchanges with the domain
   registrar to get the voucher and the certificate object, it can close
   the TLS connection to the domain registrar and provide the objects to
   the pledge(s).  The transport of the objects to the pledge is out of
   scope.  The content of the response objects is defined through the
   voucher [RFC8366] and the certificate [RFC5280].

5.3.  Discovery of supported enrollment options at domain registrar

   Well-know URIs for different endpoints on the domain registrar are
   already defined as part of the base BRSKI specification.  In
   addition, this document utilizes well-known URIs to allow for
   alternative enrollment options at the domain registrar.  The
   discovery of supported endpoints will therefore provide the
   information to the pledge, how to contact the domain registrar.

   Querying the registrar, the pledge will get a list of potential
   endpoints supported by the domain registrar.  To allow for a BRSKI
   specific discovery of endpoints/resources, this document specifies a
   new URI for the discovery as "/.well-known/brski".

   Performing a GET on "/.well-known/brski" to the default port returns
   a set of links to endpoints available from the server.  In addition
   to the link also the expected format of the data object is provided
   as content type (ct).

   The following provides an illustrative example for a domain registrar
   supporting different options for EST as well as CMP to be used in
   BRSKI-AE.  The listing contains the supported endpoints for the
   onboarding:

   REQ: GET /.well-known/brski
















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   RES: Content
     </brski/voucherrequest>,ct=voucher-cms+json
     </brski/voucher_status>,ct=json
     </brski/requestauditlog>,ct=json
     </brski/enrollstatus>,ct=json
     </est/cacerts>;ct=pkcs7-mime
     </est/cacerts>;ct=pkcs7-mime
     </est/simpleenroll>;ct=pkcs7-mime
     </est/simplereenroll>;ct=pkcs7-mime
     </est/fullcmc>;ct=pkcs7-mime
     </est/serverkeygen>;ct= pkcs7-mime
     </est/csrattrs>;ct=pkcs7-mime
     </cmp/initialization>;ct=pkixcmp
     </cmp/certification>;ct=pkixcmp
     </cmp/keyupdate>;ct=pkixcmp
     </cmp/p10>;ct=pkixcmp
     </cmp/getCAcert>;ct=pkixcmp
     </cmp/getCSRparam>;ct=pkixcmp


   [RFC Editor: please delete] /*

   Open Issues:

   o  Change path from /est to /brski to be protocol agnostic

   o  Define new well-know URI as above or reuse core approach as
      described in RFC 6690 with /.well-known/core and the already
      defined functionality?

   o  In addition to the current content types, we may specify that the
      response provide information about different content types as
      multiple values.  This would allow to further adopt the encoding
      of the objects exchanges (ASN.1, JSON, CBOR, ...).

   */

6.  Example mappings to existing enrollment protocols

   This sections maps the requirements to support proof of possession
   and proof of identity to selected existing enrollment protocols.
   Note that that the work in the ACE WG described in
   [I-D.selander-ace-coap-est-oscore] may be considered here as well, as
   it also addresses the encapsulation of EST in a way to make it
   independent from the underlying TLS using OSCORE resulting in an
   authenticated self-contained object.





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6.1.  EST Handling

   When using EST [RFC7030], the following constrains should be
   considered:

   o  Proof of possession is provided by using the specified PKCS#10
      structure in the request.

   o  Proof of identity is achieved by signing the certification request
      object, which is only supported when the /fullcmc endpoint is
      used.  This contains sufficient information for the RA to make an
      authorization decision on the received certification request.
      Note: EST references CMC [RFC5272] for the definition of the Full
      PKI Request.  For proof of identity, the signature of the
      SignedData of the Full PKI Request would be calculated using the
      IDevID credential of the pledge.

   o  [RFC Editor: please delete] /* TBD: in this case the binding to
      the underlying TLS connection is not be necessary. */

   o  When the RA is not available, as per [RFC7030] Section 4.2.3, a
      202 return code should be returned by the Registrar.  The pledge
      in this case would retry a simpleenroll with a PKCS#10 request.
      Note that if the TLS connection is teared down for the waiting
      time, the PKCS#10 request would need to be rebuild if it contains
      the unique identifier (tls_unique) from the underlying TLS
      connection for the binding.

   o  [RFC Editor: please delete] /* TBD: clarification of retry for
      fullcmc is necessary as not specified in the context of EST */

6.2.  Lightweight CMP Handling

   Instead of using CMP [RFC4210], this specification refers to the
   lightweight CMP profile [I-D.ietf-lamps-lightweight-cmp-profile], as
   it restricts the full featured CMP to the functionality needed here.
   For this, the following constrains should be observed:

   o  For proof of possession, the defined approach in Lightweight CMP
      section 5.1.1 (based on CRMF) and 5.1.5 based on PCKS#10 should be
      supported.

   o  Proof of identity can be provided by using the signatures to
      protect the certificate request message as outlined in section
      4.2.

   o  When the RA/CA is not available, a waiting indication should be
      returned in the PKIStatus by the Registrar.  The pledge in this



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      case would retry using the PollReqContent with a request
      identifier certReqId provided in the initial CertRequest message
      as specified in section 6.1.4 with delayed enrollemnt.

7.  IANA Considerations

   This document requires the following IANA actions:

   [RFC Editor: please delete] /* to be done: IANA consideration to be
   included for the defined namespaces in Section 5.1.5 and Section 5.3
   .  */

8.  Privacy Considerations

   [RFC Editor: please delete] /* to be done: clarification necessary */

9.  Security Considerations

   [RFC Editor: please delete] /* to be done: clarification necessary */

10.  Acknowledgments

   We would like to thank the various reviewers for their input, in
   particular Brian E.  Carpenter, Giorgio Romanenghi, Oskar Camenzind,
   for their input and discussion on use cases and call flows.

11.  References

11.1.  Normative References

   [I-D.ietf-anima-bootstrapping-keyinfra]
              Pritikin, M., Richardson, M., Eckert, T., Behringer, M.,
              and K. Watsen, "Bootstrapping Remote Secure Key
              Infrastructures (BRSKI)", draft-ietf-anima-bootstrapping-
              keyinfra-41 (work in progress), April 2020.

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

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






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   [RFC8366]  Watsen, K., Richardson, M., Pritikin, M., and T. Eckert,
              "A Voucher Artifact for Bootstrapping Protocols",
              RFC 8366, DOI 10.17487/RFC8366, May 2018,
              <https://www.rfc-editor.org/info/rfc8366>.

11.2.  Informative References

   [I-D.gutmann-scep]
              Gutmann, P., "Simple Certificate Enrolment Protocol",
              draft-gutmann-scep-16 (work in progress), March 2020.

   [I-D.ietf-lamps-lightweight-cmp-profile]
              Brockhaus, H., Fries, S., and D. Oheimb, "Lightweight CMP
              Profile", draft-ietf-lamps-lightweight-cmp-profile-01
              (work in progress), March 2020.

   [I-D.selander-ace-coap-est-oscore]
              Selander, G., Raza, S., Furuhed, M., Vucinic, M., and T.
              Claeys, "Protecting EST Payloads with OSCORE", draft-
              selander-ace-coap-est-oscore-03 (work in progress), March
              2020.

   [IEC-62351-9]
              International Electrotechnical Commission, "IEC 62351 -
              Power systems management and associated information
              exchange - Data and communications security - Part 9:
              Cyber security key management for power system equipment",
              IEC 62351-9 , May 2017.

   [ISO-IEC-15118-2]
              International Standardization Organization / International
              Electrotechnical Commission, "ISO/IEC 15118-2 Road
              vehicles - Vehicle-to-Grid Communication Interface - Part
              2: Network and application protocol requirements", ISO/
              IEC 15118 , April 2014.

   [NERC-CIP-005-5]
              North American Reliability Council, "Cyber Security -
              Electronic Security Perimeter", CIP 005-5, December 2013.

   [OCPP]     Open Charge Alliance, "Open Charge Point Protocol 2.0
              (Draft)", April 2018.

   [RFC2986]  Nystrom, M. and B. Kaliski, "PKCS #10: Certification
              Request Syntax Specification Version 1.7", RFC 2986,
              DOI 10.17487/RFC2986, November 2000,
              <https://www.rfc-editor.org/info/rfc2986>.




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   [RFC4210]  Adams, C., Farrell, S., Kause, T., and T. Mononen,
              "Internet X.509 Public Key Infrastructure Certificate
              Management Protocol (CMP)", RFC 4210,
              DOI 10.17487/RFC4210, September 2005,
              <https://www.rfc-editor.org/info/rfc4210>.

   [RFC4211]  Schaad, J., "Internet X.509 Public Key Infrastructure
              Certificate Request Message Format (CRMF)", RFC 4211,
              DOI 10.17487/RFC4211, September 2005,
              <https://www.rfc-editor.org/info/rfc4211>.

   [RFC5272]  Schaad, J. and M. Myers, "Certificate Management over CMS
              (CMC)", RFC 5272, DOI 10.17487/RFC5272, June 2008,
              <https://www.rfc-editor.org/info/rfc5272>.

   [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,
              <https://www.rfc-editor.org/info/rfc5280>.

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

   [RFC5785]  Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known
              Uniform Resource Identifiers (URIs)", RFC 5785,
              DOI 10.17487/RFC5785, April 2010,
              <https://www.rfc-editor.org/info/rfc5785>.

Appendix A.  History of changes [RFC Editor: please delete]

   From individual version 03 -> IETF draft 00:

   o  Inclusion of discovery options of enrollment endpoints at the
      domain registrar based on well-known endpoints in Section 5.3 as
      replacement of section 5.1.3 in the individual draft.  This is
      intended to support both use cases in the document.  An
      illustrative example is provided.

   o  Missing details provided for the description and call flow in
      pledge-agent use case Section 5.2, e.g. to accommodate
      distribution of CA certificates.

   o  Updated CMP example in Section 6 to use lightweight CMP instead of
      CMP, as the draft already provides the necessary /.well-known
      endpoints.




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   o  Requirements discussion moved to separate section in Section 4.
      Shortened description of proof of identity binding and mapping to
      existing protocols.

   o  Removal of copied call flows for voucher exchange and registrar
      discovery flow from [I-D.ietf-anima-bootstrapping-keyinfra] in
      Section 5.1 to avoid doubling or text or inconsistencies.

   o  Reworked abstract and introduction to be more crisp regarding the
      targeted solution.  Several structural changes in the document to
      have a better distinction between requirements, use case
      description, and solution description as separate sections.
      History moved to appendix.

   From individual version 02 -> 03:

   o  Update of terminology from self-contained to authenticated self-
      contained object to be consistent in the wording and to underline
      the protection of the object with an existing credential.  Note
      that the naming of this object may be discussed.  An alternative
      name may be attestation object.

   o  Simplification of the architecture approach for the initial use
      case having an offsite PKI.

   o  Introduction of a new use case utilizing authenticated self-
      contain objects to onboard a pledge using a commissioning tool
      containing a pledge-agent.  This requires additional changes in
      the BRSKI call flow sequence and led to changes in the
      introduction, the application example,and also in the related
      BRSKI-AE call flow.

   o  Update of provided examples of the addressing approach used in
      BRSKI to allow for support of multiple enrollment protocols in
      Section 5.1.5.

   From individual version 01 -> 02:

   o  Update of introduction text to clearly relate to the usage of
      IDevID and LDevID.

   o  Definition of the addressing approach used in BRSKI to allow for
      support of multiple enrollment protocols in Section 5.1.5.  This
      section also contains a first discussion of an optional discovery
      mechanism to address situations in which the registrar supports
      more than one enrollment approach.  Discovery should avoid that
      the pledge performs a trial and error of enrollment protocols.




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   o  Update of description of architecture elements and changes to
      BRSKI in Section 5.

   o  Enhanced consideration of existing enrollment protocols in the
      context of mapping the requirements to existing solutions in
      Section 4 and in Section 6.

   From individual version 00 -> 01:

   o  Update of examples, specifically for building automation as well
      as two new application use cases in Section 3.2.

   o  Deletion of asynchronous interaction with MASA to not complicate
      the use case.  Note that the voucher exchange can already be
      handled in an asynchronous manner and is therefore not considered
      further.  This resulted in removal of the alternative path the
      MASA in Figure 1 and the associated description in Section 5.

   o  Enhancement of description of architecture elements and changes to
      BRSKI in Section 5.

   o  Consideration of existing enrollment protocols in the context of
      mapping the requirements to existing solutions in Section 4.

   o  New section starting Section 6 with the mapping to existing
      enrollment protocols by collecting boundary conditions.

Authors' Addresses

   Steffen Fries
   Siemens AG
   Otto-Hahn-Ring 6
   Munich, Bavaria  81739
   Germany

   Email: steffen.fries@siemens.com
   URI:   http://www.siemens.com/


   Hendrik Brockhaus
   Siemens AG
   Otto-Hahn-Ring 6
   Munich, Bavaria  81739
   Germany

   Email: hendrik.brockhaus@siemens.com
   URI:   http://www.siemens.com/




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   Eliot Lear
   Cisco Systems
   Richtistrasse 7
   Wallisellen  CH-8304
   Switzerland

   Phone: +41 44 878 9200
   Email: lear@cisco.com











































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