anima Working Group                                        M. Richardson
Internet-Draft                                  Sandelman Software Works
Intended status: Standards Track                         P. van der Stok
Expires: 27 April 2023                            vanderstok consultancy
                                                           P. Kampanakis
                                                           Cisco Systems
                                                         24 October 2022


           Constrained Join Proxy for Bootstrapping Protocols
               draft-ietf-anima-constrained-join-proxy-13

Abstract

   This document extends the work of Bootstrapping Remote Secure Key
   Infrastructures (BRSKI) by replacing the (stateful) TLS Circuit proxy
   between Pledge and Registrar with a stateless or stateful Circuit
   proxy using CoAP which is called the constrained Join Proxy.  The
   constrained Join Proxy is a mesh neighbor of the Pledge and can relay
   a DTLS session originating from a Pledge with only link-local
   addresses to a Registrar which is not a mesh neighbor of the Pledge.

   Like the BRSKI Circuit proxy, this constrained Join Proxy eliminates
   the need of Pledges to have routeable IP addresses before enrolment
   by utilizing link-local addresses.  Use of the constrained Join Proxy
   also eliminates the need of the Pledge to authenticate to the network
   or perform network-wide Registrar discover before enrolment.

About This Document

   This note is to be removed before publishing as an RFC.

   Status information for this document may be found at
   https://datatracker.ietf.org/doc/draft-ietf-anima-constrained-join-
   proxy/.

   Discussion of this document takes place on the anima Working Group
   mailing list (mailto:anima@ietf.org), which is archived at
   https://mailarchive.ietf.org/arch/browse/anima/.

   Source for this draft and an issue tracker can be found at
   https://github.com/anima-wg/constrained-join-proxy.

Status of This Memo

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




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Copyright Notice

   Copyright (c) 2022 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   Please review these documents carefully, as they describe your rights
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  constrained Join Proxy functionality  . . . . . . . . . . . .   5
   4.  constrained Join Proxy specification  . . . . . . . . . . . .   7
     4.1.  Stateful Join Proxy . . . . . . . . . . . . . . . . . . .   8
     4.2.  Stateless Join Proxy  . . . . . . . . . . . . . . . . . .  10
     4.3.  Constraucting the extended token  . . . . . . . . . . . .  12
       4.3.1.  Processing by Registrar . . . . . . . . . . . . . . .  14
   5.  Discovery . . . . . . . . . . . . . . . . . . . . . . . . . .  14
     5.1.  Discovery operations by Join-Proxy  . . . . . . . . . . .  14
       5.1.1.  CoAP discovery  . . . . . . . . . . . . . . . . . . .  14
       5.1.2.  GRASP discovery . . . . . . . . . . . . . . . . . . .  15
     5.2.  Pledge discovers Join-Proxy . . . . . . . . . . . . . . .  16
       5.2.1.  CoAP discovery  . . . . . . . . . . . . . . . . . . .  16
       5.2.2.  GRASP discovery . . . . . . . . . . . . . . . . . . .  17
       5.2.3.  6tisch discovery  . . . . . . . . . . . . . . . . . .  17
   6.  Comparison of stateless and stateful modes  . . . . . . . . .  18
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  18
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  20
     8.1.  Resource Type Attributes registry . . . . . . . . . . . .  20



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     8.2.  service name and port number registry . . . . . . . . . .  20
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  21
   10. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  21
   11. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . .  21
     11.1.  14 to 13 . . . . . . . . . . . . . . . . . . . . . . . .  21
     11.2.  13 to 12 . . . . . . . . . . . . . . . . . . . . . . . .  21
     11.3.  12 to 11 . . . . . . . . . . . . . . . . . . . . . . . .  21
     11.4.  11 to 10 . . . . . . . . . . . . . . . . . . . . . . . .  22
     11.5.  10 to 09 . . . . . . . . . . . . . . . . . . . . . . . .  22
     11.6.  09 to 07 . . . . . . . . . . . . . . . . . . . . . . . .  22
     11.7.  06 to 07 . . . . . . . . . . . . . . . . . . . . . . . .  22
     11.8.  05 to 06 . . . . . . . . . . . . . . . . . . . . . . . .  22
     11.9.  04 to 05 . . . . . . . . . . . . . . . . . . . . . . . .  22
     11.10. 03 to 04 . . . . . . . . . . . . . . . . . . . . . . . .  22
     11.11. 02 to 03 . . . . . . . . . . . . . . . . . . . . . . . .  22
     11.12. 01 to 02 . . . . . . . . . . . . . . . . . . . . . . . .  22
     11.13. 00 to 01 . . . . . . . . . . . . . . . . . . . . . . . .  23
     11.14. 00 to 00 . . . . . . . . . . . . . . . . . . . . . . . .  23
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  23
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  23
     12.2.  Informative References . . . . . . . . . . . . . . . . .  25
   Appendix A.  Stateless CoAP payload examples  . . . . . . . . . .  27
   Appendix B.  Stateless Proxy payload examples . . . . . . . . . .  27
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  28

1.  Introduction

   The Bootstrapping Remote Secure Key Infrastructure (BRSKI) protocol
   described in [RFC8995] provides a solution for a secure zero-touch
   (automated) bootstrap of new (unconfigured) devices.  In the context
   of BRSKI, new devices, called "Pledges", are equipped with a factory-
   installed Initial Device Identifier (IDevID) (see [ieee802-1AR]), and
   are enrolled into a network.  BRSKI makes use of Enrollment over
   Secure Transport (EST) [RFC7030] with [RFC8366] vouchers to securely
   enroll devices.  A Registrar provides the security anchor of the
   network to which a Pledge enrolls.

   In this document, BRSKI is extended such that a Pledge connects to
   "Registrars" via a constrained Join Proxy.  In particular, this
   solution is intended to support mesh networks as described in
   [RFC4944].

   The constrained Join Proxy as specified in this document is one of
   the Join Proxy options referred to in [RFC8995] section 2.5.2 as
   future work.

   A complete specification of the terminology is pointed at in
   Section 2.



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   The specified solutions in [RFC8995] and [RFC7030] are based on POST
   or GET requests to the EST resources (/cacerts, /simpleenroll,
   /simplereenroll, /serverkeygen, and /csrattrs), and the brski
   resources (/requestvoucher, /voucher_status, and /enrollstatus).
   These requests use https and may be too large in terms of code space
   or bandwidth required for constrained devices.  Constrained devices
   which may be part of constrained networks [RFC7228], typically
   implement the IPv6 over Low-Power Wireless personal Area Networks
   (6LoWPAN) [RFC4944] and Constrained Application Protocol (CoAP)
   [RFC7252].

   CoAP can be run with the Datagram Transport Layer Security (DTLS)
   [RFC6347] as a security protocol for authenticity and confidentiality
   of the messages.  This is known as the "coaps" scheme.  A constrained
   version of EST, using CoAP and DTLS, is described in [RFC9148].

   The [I-D.ietf-anima-constrained-voucher] extends [RFC9148] with BRSKI
   artifacts such as voucher, request voucher, and the protocol
   extensions for constrained Pledges that use CoAP.

   However, in networks that require authentication, such as those using
   [RFC4944], the Pledge will not be IP routable over the mesh network
   until it is authenticated to the mesh network.  A new Pledge can only
   initially use a link-local IPv6 address to communicate with a mesh
   neighbor [RFC6775] until it receives the necessary network
   configuration parameters.  The Pledge receives these configuration
   parameters from the Registrar.  When the Registrar is not a direct
   neighbor of the Registrar but several hops away, the Pledge discovers
   a neighbor that is operating the constrained Join Proxy, which
   forwards DTLS protected messages between Pledge and Registrar.  The
   constrained Join Proxy must be enrolled previously such that the
   message from constrained Join Proxy to Registrar can be routed over
   one or more hops.

   An enrolled Pledge can act as constrained Join Proxy between other
   Pledges and the enrolling Registrar.

   Two modes of the constrained Join Proxy are specified:

1 A stateful Join Proxy that locally stores UDP connection state:
  IP addresses (link-local with interface and non-link-local and UDP port-numbers)
  during the connection.

2 A stateless Join Proxy where the connection state
  is replaced by a second layer of CoAP header in the
  UDP messages between constrained Join Proxy and Registrar.





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   This document is very much inspired by text published earlier in
   [I-D.kumar-dice-dtls-relay].
   [I-D.richardson-anima-state-for-joinrouter] outlined the various
   options for building a constrained Join Proxy.  [RFC8995] adopted
   only the Circuit Proxy method (1), leaving the other methods as
   future work.

   Similar to the difference between storing and non-storing Modes of
   Operations (MOP) in RPL [RFC6550], the stateful and stateless modes
   differ in the way that they store the state required to forward the
   return packet to the Pledge.  In the stateful method, the return
   forward state is stored in the Join Proxy.  In the stateless method,
   the return forward state is stored in the network using the CoAP
   extended token in a way identical to that described in [RFC9031].

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
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   The following terms are defined in [RFC8366], and are used
   identically as in that document: artifact, imprint, domain, Join
   Registrar/Coordinator (JRC), Pledge, and Voucher.

   In this document, the term "Registrar" is used throughout instead of
   "Join Registrar/Coordinator (JRC)".

   The "Constrained Join Proxy" enables a Pledge that is multiple hops
   away from the Registrar, to execute the BRSKI protocol [RFC8995]
   using a secure channel.

   The term "Join Proxy" is used interchangeably with the term
   "constrained Join Proxy" throughout this document.

   The [RFC8995] Circuit Proxy is referred to as a TCP circuit Join
   Proxy.

3.  constrained Join Proxy functionality

   As depicted in the Figure 1, the Pledge (P), in a network such as a
   Low-Power and Lossy Network (LLN) mesh [RFC7102] can be more than one
   hop away from the Registrar (R) and not yet authenticated into the
   network.





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   In this situation, the Pledge can only communicate one-hop to its
   nearest neighbor, the constrained Join Proxy (J) using link-local
   IPv6 addresses.  However, the Pledge needs to communicate using end-
   to-end security with a Registrar in order to onboard, authenticate
   and get the relevant system/network parameters.  If the Pledge,
   knowing the IP-address of the Registrar, initiates a DTLS connection
   to the Registrar, then the packets are dropped at the constrained
   Join Proxy since the Pledge is not yet admitted to the network or
   there is no IP routability to the Pledge for any returned messages
   from the Registrar.

                       multi-hop mesh
            .---.                         IPv6
            | R +---.    +----+    +---+ subnet +--+
            |   |    \   |6LR +----+ J |........|P |
            '---'     `--+    |    |   | clear  |  |
                         +----+    +---+        +--+
          Registrar             Join Proxy     Pledge

                      Figure 1: multi-hop enrollment.

   Without a routeable IPv6 address, the Pledge (P) cannot exchange
   IPv6/UDP/DTLS traffic with the Registrar (R), over multiple hops in
   the network.

   Furthermore, the Pledge may not even be able to discover the IP
   address of the Registrar over multiple hops to initiate a DTLS
   connection and perform authentication.

   To overcome the problems with non-routability of DTLS packets and the
   discovery of the destination address of the Registrar, the
   constrained Join Proxy is introduced.  This constrained Join Proxy
   functionality is also (auto) configured into all authenticated
   devices in the network which may act as a constrained Join Proxy for
   Pledges.

   The constrained Join Proxy allows for routing of the packets from the
   Pledge using IP routing to the intended Registrar.  An authenticated
   constrained Join Proxy can discover the routable IP address of the
   Registrar over multiple hops.  The following Section 4 specifies the
   two constrained Join Proxy modes.  A comparison is presented in
   Section 6.

   When a mesh network is set up, it consists of a Registrar and a set
   of connected Pledges.  No constrained Join Proxies are present.  Only
   some of these Pledges may be neighbors of the Registrar.  Others
   would need for their traffic to be routed across one or more enrolled
   devices to reach the Registrar.



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   The desired state of the installation is a network with a Registrar
   and all Pledges becoming enrolled devices.  Some of these enrolled
   devices can act as constrained Join Proxies.  Pledges can only employ
   link-local communication until they are enrolled.  A Pledge will
   regularly try to discover a constrained Join Proxy or a Registrar
   with link-local discovery requests.  The Pledges which are neighbors
   of the Registrar will discover the Registrar and be enrolled
   following the constrained BRSKI protocol.  An enrolled device can act
   as constrained Join Proxy.  The Pledges which are not a neighbor of
   the Registrar will eventually discover a constrained Join Proxy and
   follow the constrained BRSKI protocol to be enrolled.  While this
   goes on, more and more constrained Join Proxies with a larger hop
   distance to the Registrar will emerge.  The network should be
   configured such that at the end of the enrollment process, all
   Pledges have discovered a neighboring constrained Join Proxy or the
   Registrar, and all Pledges are enrolled.

   The constrained Join Proxy is as a packet-by-packet proxy for UDP
   packets between Pledge and Registrar.  The constrained BRSKI protocol
   between Pledge and Registrar described in
   [I-D.ietf-anima-constrained-voucher] which this Join Proxy supports
   uses UDP messages with DTLS payload, but the Join Proxy as described
   here is unaware of this payload.  It can therefore potentially also
   work for other UDP based protocols as long as they are agnostic to
   (or can be made to work with) the change of IP header by the
   constrained Join Proxy.

   In both Stateless and Stateful mode, the Join Proxy needs to be
   configured with or dynamically discover a Registrar to perform its
   service.  This specification does not discuss how a constrained Join
   Proxy selects a Registrar when it discovers 2 or more.

4.  constrained Join Proxy specification

   A Join Proxy can operate in two modes:

   *  Stateful mode

   *  Stateless mode

   The advantages and disadvantages of the two modes are presented in
   Section 6.

   A Registrar MUST implement both the stateful mode and the Stateless
   mode, but an operator MAY configure it to announce only one.  A Join
   Proxy MUST implement the stateless mode, but SHOULD implement the
   stateful mode if it has sufficient memory.




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   For a Join Proxy to be operational, the node on which it is running
   has to be able to talk to a Registrar (exchange UDP messages with
   it).  This can happen fully automatically by the Join Proxy node
   first enrolling itself as a Pledge, and then learning the IP address,
   the UDP port and the mode(s) (Stateful and/or Stateless) of the
   Registrar, through a discovery mechanism such as those described in
   Section 6.

   In mesh LLN networks like those based upon RPL ([RFC6550]), it would
   not be unusual for the 6LBR (the DODAG root) to have a wired network
   interface on which the Registrar can be found.  Or the Registrar may
   in fact be co-located with the 6LBR.  This 6LBR then becomes the
   first Join Proxy, and additional nodes attach to it in a concentric
   fashion.

   Other methods, such as provisioning the Join Proxy are out of scope
   of this document but equally feasible.

   Once the Join Proxy is operational, its mode is determined by the
   mode of the Registrar.  If the Registrar offers both Stateful and
   Stateless mode, the Join Proxy MUST use the stateless mode.

   Independent of the mode of the Join Proxy, the Pledge first discovers
   (see Section 6) and selects the most appropriate Join Proxy.  From
   the discovery, the Pledge learns the Join Proxies link-local scope IP
   address and UDP (join) port.  This discovery can also be based upon
   [RFC8995] section 4.1.  If the discovery method does not support
   discovery of the join-port, then the Pledge assumes the default CoAP
   over DTLS UDP port (5683).

4.1.  Stateful Join Proxy

   In stateful mode, the Join Proxy acts as a UDP "circuit" proxy that
   does not change the UDP payload (data octets according to [RFC768])
   but only rewrites the IP and UDP headers of each packet it receives
   from Pledge and Registrar.

   The stateful Join Proxy operates as a 'pseudo' UDP circuit proxy
   creating and utilizing connection mapping state to rewrite the IP
   address and UDP port number packet header fields of UDP packets that
   it forwards between Pledge and Registrar.  Figure 2 depiects how this
   state is used.









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   +------------+------------+-------------+--------------------------+
   |   Pledge   | Join Proxy |  Registrar  |          Message         |
   |    (P)     |     (J)    |    (R)      | Src_IP:port | Dst_IP:port|
   +------------+------------+-------------+-------------+------------+
   |      --ClientHello-->                 |   IP_P:p_P  | IP_Jl:p_Jl |
   |                    --ClientHello-->   |   IP_Jr:p_Jr| IP_R:5684  |
   |                                       |             |            |
   |                    <--ServerHello--   |   IP_R:5684 | IP_Jr:p_Jr |
   |                            :          |             |            |
   |       <--ServerHello--     :          |   IP_Jl:p_Jl| IP_P:p_P   |
   |               :            :          |             |            |
   |              [DTLS messages]          |       :     |    :       |
   |               :            :          |       :     |    :       |
   |        --Finished-->       :          |   IP_P:p_P  | IP_Jl:p_Jl |
   |                      --Finished-->    |   IP_Jr:p_Jr| IP_R:5684  |
   |                                       |             |            |
   |                      <--Finished--    |   IP_R:5684 | IP_Jr:p_Jr |
   |        <--Finished--                  |   IP_Jl:p_Jl| IP_P:p_P   |
   |              :             :          |      :      |     :      |
   +---------------------------------------+-------------+------------+
   IP_P:p_P = Link-local IP address and port of Pledge (DTLS Client)
   IP_R:5684 = Routable IP address and coaps port of Registrar
   IP_Jl:p_Jl = Link-local IP address and join-port of Join Proxy
   IP_Jr:p_Jr = Routable IP address and client port of Join Proxy

          Figure 2: constrained stateful joining message flow with
                   Registrar address known to Join Proxy.

   Because UDP does not have the notion of a connection, this document
   calls this a 'pseudo' connection, whose establishment is solely
   triggered by receipt of a packet from a Pledge with an IP_p%IF:p_P
   source for which no mapping state exists, and that is termined by a
   connection expiry timer E.

   If an untrusted Pledge that can only use link-local addressing wants
   to contact a trusted Registrar, and the Registrar is more than one
   hop away, it sends its DTLS messages to the Join Proxy.

   When a proxy receives an ICMP error message from the Registrar or
   Plege, for which mapping state exist, the proxy SHOULD map the ICMP
   message as it would map a UDP message and forward the ICMP message to
   the Registrar / Pledge.  Processing of ICMP messages SHOULD NOT reset
   the connection expiry timer.

   To protect itself and the Registrar against malfunctioning Pledges
   and or denial of service attacks, the join proxy SHOULD limit the
   number of simultaneous mapping states on per ip address to 2 and the
   number of simultaneous mapping states per interface to 10.  When



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   mapping state can not be built due to exhausted state, the proxy
   SHOULD return an ICMP error (1), "Destination Port Unreachable"
   message with code (1), "Communication with destination
   administratively prohibited".

4.2.  Stateless Join Proxy

   Stateless Join Proxy operation eliminates the need and complexity to
   maintain per UDP connection mapping state on the proxy and the state
   machinery to build, maintain and remove this mapping state.  It also
   removes the need to protect this mapping state against DoS attacks
   and may also reduce memory and CPU requirements on the proxy.

   Stateless Join Proxy operations works by encapsulating the DTLS
   messages into a new CoAP header [RFC7252].  This new CoAP header is
   designed to be as minimalistic as possible.  The use of CoAP here
   costs a XXX bytes more than a custom encapsulation, but simplies much
   of the operation, as well as permitting the result to pass through
   CoAP proxies, CoAP to HTTP proxies, and other mechanisms that might
   be introduced into a network.  This also eliminates custom code that
   is only rarely used, which may reduce bugs.

   The CoAP payload is configured much as [RFC9031], Section 8.1.1
   specifies:

   *  The request method is POST.

   *  The type is Confirmable (CON).

   *  The Proxy-Scheme option is set to "coap".

   *  No Uri_Host option is included, as none is technically required.

   *  No Uri-Path option is included.

   *  The payload is the DTLS payload as received from the Pledge.

   *  An extended token [RFC8974] is included to contain some encrypted
      state that allows replies to be returned to the Pledge.

   Appendix A shows an example CoAP header, assuming a 16-byte extended
   token, with the resulting overhead of 28 bytes.

   When the Join Proxy receives a UDP message from a Pledge, it encodes
   the Pledges link-local IP address, interface and UDP (source) port of
   the packet into the extended token.  The result is sent to the
   Registrar from a fixed source UDP port.




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   As described in [RFC7252], Section 5.3.1, when the Registrar sends
   packets for the Pledge, it MUST return the token field unchanged.
   This allows the Join Proxy to decode the saved Pledge state, and
   reconstruct the Pledges link-local IP address, interace and UDP
   (destination) port for the return packet.  Figure 3 shows this per-
   packet mapping on the Join Proxy.

   The Registrar transiently stores the extended token field information
   in case it needs to generate additional messages as a result of DTLS
   processing.

   The Registrar uses the payload field to execute the Registrar
   functionality.

   The Registrar SHOULD NOT assume that it can decode the Header Field,
   it should simply repeat it when responding.  The Header contains the
   original source link-local address and port of the Pledge from the
   transient state stored earlier and the Contents field contains the
   DTLS payload.

   On receiving the CoAP message, the Join Proxy processes the CoAP
   header.  It uses the extended token field to route the payload as a
   DTLS message to the Pledge.

   In the stateless Join Proxy mode, both the Registrar and the Join
   Proxy use discoverable UDP join-ports.  For the Join Proxy this may
   be a default CoAP port.
























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   +--------------+------------+---------------+-----------------------+
   |    Pledge    | Join Proxy |    Registrar  |        Message        |
   |     (P)      |     (J)    |      (R)      |Src_IP:port|Dst_IP:port|
   +--------------+------------+---------------+-----------+-----------+
   |      --ClientHello-->                     | IP_P:p_P  |IP_Jl:p_Jl |
   |                    --JPY[H(IP_P:p_P),-->  | IP_Jr:p_Jr|IP_R:p_Ra  |
   |                          C(ClientHello)]  |           |           |
   |                    <--JPY[H(IP_P:p_P),--  | IP_R:p_Ra |IP_Jr:p_Jr |
   |                         C(ServerHello)]   |           |           |
   |      <--ServerHello--                     | IP_Jl:p_Jl|IP_P:p_P   |
   |              :                            |           |           |
   |          [ DTLS messages ]                |     :     |    :      |
   |              :                            |     :     |    :      |
   |      --Finished-->                        | IP_P:p_P  |IP_Jr:p_Jr |
   |                    --JPY[H(IP_P:p_P),-->  | IP_Jl:p_Jl|IP_R:p_Ra  |
   |                          C(Finished)]     |           |           |
   |                    <--JPY[H(IP_P:p_P),--  | IP_R:p_Ra |IP_Jr:p_Jr |
   |                         C(Finished)]      |           |           |
   |      <--Finished--                        | IP_Jl:p_Jl|IP_P:p_P   |
   |              :                            |     :     |    :      |
   +-------------------------------------------+-----------+-----------+
   IP_P:p_P = Link-local IP address and port of the Pledge
   IP_R:p_Ra = Routable IP address and join-port of Registrar
   IP_Jl:p_Jl = Link-local IP address and join-port of Join Proxy
   IP_Jr:p_Jr = Routable IP address and port of Join Proxy

   JPY[H(),C()] = Join Proxy message with header H and content C

           Figure 3: constrained stateless joining message flow.

4.3.  Constraucting the extended token

   The Join Proxy cannot decrypt the DTLS payload and has no knowledge
   of the transported media type.  The contents are DTLS encrypted.

   The extended token payload is to be reflected by the Registrar when
   sending reply packets to the Join Proxy.  The extended token content
   is not standardized, but this section provides an non-normative
   example.

   As explained in [RFC8974], Section 5.2, the Join Proxy SHOULD encrypt
   the extended token with a symmetric key known only to the Join Proxy.
   This key need not persist on a long term basis, and MAY be changed
   periodically.







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   This is intended to be identical to the mechanism described in
   Section 7.1 of [RFC9031].  However, since the CoAP layer is inside of
   the DTLS layer (which is between the Pledge and the Registrar), it is
   not possible for the Join Proxy to act as an actual CoAP proxy.

   The context that is stored into the extended token might be
   constructed with the following CDDL grammar: (This is illustrative
   only: the contents are not subject to standardization)

       pledge_context_message = [
         family:  uint .bits 1,
         ifindex: uint .bits 8,
         srcport: uint .bits 16,
         iid:     bstr .bits 64,
       ]

   This results in a total of 96 bits, or 12 bytes.  The structure
   stores the srcport, the originating IPv6 Link-Local address, the
   IPv4/IPv6 family (as a single bit) and an ifindex to provide the
   link-local scope.  This fits nicely into a single AES128 CBC block
   for instance, resulting in a 16 byte token.  The Join Proxy MUST
   maintain the same context block for all communications from the same
   Pledge.  This implies that any encryption key either does not change
   during the communication, or that when it does, it is acceptable to
   break any onboarding connections which have not yet completed.  If
   using a context parameter like defined above, it should be easy for
   the Join Proxy to meet this requirement without maintaining any local
   state about the Pledge.

   Note: when IPv6 is used only the lower 64-bits of the origin IP need
   to be recorded, because they are all IPv6 Link-Local addresses, so
   the upper 64-bits are just "fe80::".  For IPv4, a Link-Local IPv4
   address [RFC3927] would be used, and it would fit into 64-bits.  On
   media where the IID is not 64-bits, a different arrangement will be
   necessary.

   For the join messages relayed to a particular Registrar, the Join
   Proxy SHOULD use the same UDP source port for all messages related to
   all Pledges.  A Join Proxy MAY change the UDP source port, but doing
   so creates more local state.  But, a Join Proxy with multiple CPUs
   (unlikely in a constrained system, but possible in some future)
   could, for instance, use different source port numbers to demultiplex
   connections across CPUs.








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4.3.1.  Processing by Registrar

   On reception of a CoAP encapsulated join message by the Registrar,
   the Registrar processes the CoAP header and extracts the extended
   token.  The extended token will need to be provided as input to a
   DTLS library [RFC9147], as the 5-tuple of the UDP connection alone
   does not provide enough context for the Registrar to pick an
   appropriate context.  Note that the socket will need to be used for
   multiple DTLS flows, which is atypical for how DTLS usually uses
   sockets.

   As an alternative, the Registrar could split out the state processing
   from the DTLS processing, creating new sockets that it maintains, but
   this just duplicates state across many places.  It may still be an
   advantage for some architectures.

   Examples are shown in Appendix B.

   At the CoAP level, within the Constrained BRSKI and the EST-COAP
   [RFC9148] level, the block option [RFC7959] is often used.  The
   Registrar and the Pledge MUST select a block size that would allow
   the addition of the additional CoAP header without violating MTU
   sizes.

5.  Discovery

5.1.  Discovery operations by Join-Proxy

   In order to accomodate automatic configuration of the Join-Proxy, it
   must discover the location and a capabilities of the Registar.
   Section 10.2 of [I-D.ietf-anima-constrained-voucher] explains the
   basic mechanism, and this section explains the extensions required to
   discover if stateless operation is supported.

5.1.1.  CoAP discovery

   Section 10.2.2 of [I-D.ietf-anima-constrained-voucher] describes how
   to use CoAP Discovery.  The stateless Join Proxy requires a different
   end point that can accept the second CoAP header encapsulation and
   extended token.

   The stateless Join Proxy can discover the join-port of the Registrar
   by sending a GET request to "/.well-known/core" including a resource
   type (rt) parameter with the value "brski.rjp" [RFC6690].  Upon
   success, the return payload will contain a port that contain process
   the CoAP encalsulated DTLS messages.





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     REQ: GET /.well-known/core?rt=brski.rjp

     RES: 2.05 Content
     <coap://[IP_address]:join-port>;rt=brski.rjp

   In the [RFC6690] link format, and [RFC3986], Section 3.2, the
   authority attribute can not include a port number unless it also
   includes the IP address.

   The returned join-port is expected to process the CoAP encapsulated
   DTLS messages described in section Section 4.3.  The scheme is now
   CoAP, as the outside protocol is CoAP and could be subject to further
   CoAP operations.

   An EST/Registrar server running at address 2001:db8:0:abcd::52, with
   the CoAP processing on port 7634, and the stateful Registrar on port
   5683 could reply to a multicast query as follows:

  REQ: GET /.well-known/core?rt=brski*

  RES: 2.05 Content
  <coap://[2001:db8:0:abcd::52]:7634>;rt=brski.rjp,
  <coaps://[2001:db8:0:abcd::52]/.well-known/brski>;rt=brski,
  <coaps://[2001:db8:0:abcd::52]/.well-known/brski/rv>;rt=brski.rv;ct=836,
  <coaps://[2001:db8:0:abcd::52]/.well-known/brski/vs>;rt=brski.vs;ct="50 60",
  <coaps://[2001:db8:0:abcd::52]/.well-known/brski/es>;rt=brski.es;ct="50 60",

5.1.2.  GRASP discovery

   Section 10.2.1 of [I-D.ietf-anima-constrained-voucher] describes how
   to use GRASP [RFC8990] discovery within the ACP to locate the
   stateful port of the Registrar.

   A Join Proxy which supports a stateless mode of operation using the
   mechanism described in Section 4.3 must know where to send the
   encoded content from the Pledge.  The Registrar announces its
   willingness to use the stateless mechanism by including an additional
   objective in it's M_FLOOD'ed AN_join_registrar announcements, but
   with a different objective value.

   The following changes are necessary with respect to figure 10 of
   [RFC8995]:

   *  The transport-proto is IPPROTO_UDP

   *  the objective is AN_join_registrar, identical to [RFC8995].

   *  the objective name is "BRSKI_RJP".



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   Here is an example M_FLOOD announcing the Registrar on example port
   5685, which is a port number chosen by the Registrar.

      [M_FLOOD, 51804231, h'fda379a6f6ee00000200000064000001', 180000,
      [["AN_join_registrar", 4, 255, "BRSKI_RJP"],
       [O_IPv6_LOCATOR,
        h'fda379a6f6ee00000200000064000001', IPPROTO_UDP, 5685]]]

            Figure 4: Example of Registrar announcement message

   Most Registrars will announce both a CoAP-stateless and stateful
   ports, and may also announce an HTTPS/TLS service:

      [M_FLOOD, 51840231, h'fda379a6f6ee00000200000064000001', 180000,
      [["AN_join_registrar", 4, 255, ""],
       [O_IPv6_LOCATOR,
        h'fda379a6f6ee00000200000064000001', IPPROTO_TCP, 8443],
       ["AN_join_registrar", 4, 255, "BRSKI_JP"],
       [O_IPv6_LOCATOR,
        h'fda379a6f6ee00000200000064000001', IPPROTO_UDP, 5684],
       ["AN_join_registrar", 4, 255, "BRSKI_RJP"],
       [O_IPv6_LOCATOR,
        h'fda379a6f6ee00000200000064000001', IPPROTO_UDP, 5685]]]

          Figure 5: Example of Registrar announcing three services

5.2.  Pledge discovers Join-Proxy

   Regardless of whether the Join Proxy operates in stateful or
   stateless mode, the Join Proxy is discovered by the Pledge
   identically.  When doing constrained onboarding with DTLS as
   security, the Pledge will always see an IPv6 Link-Local destination,
   with a single UDP port to which DTLS messages are to be sent.

5.2.1.  CoAP discovery

   In the context of a CoAP network without Autonomic Network support,
   discovery follows the standard CoAP policy.  The Pledge can discover
   a Join Proxy by sending a link-local multicast message to ALL CoAP
   Nodes with address FF02::FD.  Multiple or no nodes may respond.  The
   handling of multiple responses and the absence of responses follow
   section 4 of [RFC8995].

   The join-port of the Join Proxy is discovered by sending a GET
   request to "/.well-known/core" including a resource type (rt)
   parameter with the value "brski.jp" [RFC6690].  Upon success, the
   return payload will contain the join-port.




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   The example below shows the discovery of the join-port of the Join
   Proxy.

     REQ: GET coap://[FF02::FD]/.well-known/core?rt=brski.jp

     RES: 2.05 Content
     <coaps://[IP_address]:join-port>; rt="brski.jp"

   Port numbers are assumed to be the default numbers 5683 and 5684 for
   coap and coaps respectively (sections 12.6 and 12.7 of [RFC7252])
   when not shown in the response.  Discoverable port numbers are
   usually returned for Join Proxy resources in the <URI-Reference> of
   the payload (see section 4.1 of [RFC9148]).

5.2.2.  GRASP discovery

   This section is normative for uses with an ANIMA ACP.  In the context
   of autonomic networks, the Join-Proxy uses the DULL GRASP M_FLOOD
   mechanism to announce itself.  Section 4.1.1 of [RFC8995] discusses
   this in more detail.

   The following changes are necessary with respect to figure 10 of
   [RFC8995]:

   *  The transport-proto is IPPROTO_UDP

   *  the objective is AN_Proxy

   The Registrar announces itself using ACP instance of GRASP using
   M_FLOOD messages.  Autonomic Network Join Proxies MUST support GRASP
   discovery of Registrar as described in section 4.3 of [RFC8995] .

   Here is an example M_FLOOD announcing the Join-Proxy at fe80::1, on
   standard coaps port 5684.

        [M_FLOOD, 12340815, h'fe800000000000000000000000000001', 180000,
        [["AN_Proxy", 4, 1, ""],
        [O_IPv6_LOCATOR,
        h'fe800000000000000000000000000001', IPPROTO_UDP, 5684]]]

            Figure 6: Example of Registrar announcement message

5.2.3.  6tisch discovery

   The discovery of Join-Proxy by the Pledge uses the enhanced beacons
   as discussed in [RFC9032]. 6tisch does not use DTLS and so this
   specification does not apply to it.




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6.  Comparison of stateless and stateful modes

   The stateful and stateless mode of operation for the Join Proxy have
   their advantages and disadvantages.  This section should enable
   operators to make a choice between the two modes based on the
   available device resources and network bandwidth.

   +===============+============================+=====================+
   | Properties    | Stateful mode              | Stateless mode      |
   +===============+============================+=====================+
   | State         | The Join Proxy needs       | No information is   |
   | Information   | additional storage to      | maintained by the   |
   |               | maintain mapping between   | Join Proxy.         |
   |               | the address and port       | Registrar needs to  |
   |               | number of the Pledge and   | store the packet    |
   |               | those of the Registrar.    | header.             |
   +---------------+----------------------------+---------------------+
   | Packet size   | The size of the forwarded  | Size of the         |
   |               | message is the same as the | forwarded message   |
   |               | original message.          | is bigger than the  |
   |               |                            | original, it        |
   |               |                            | includes additional |
   |               |                            | information         |
   +---------------+----------------------------+---------------------+
   | Specification | The Join Proxy needs       | CoAP message to     |
   | complexity    | additional functionality   | encapsulate DTLS    |
   |               | to maintain state          | payload.  The       |
   |               | information, and specify   | Registrar and the   |
   |               | the source and destination | Join Proxy have to  |
   |               | addresses of the DTLS      | understand the CoAP |
   |               | handshake messages         | header in order to  |
   |               |                            | process it.         |
   +---------------+----------------------------+---------------------+
   | Ports         | Join Proxy needs           | Join Proxy and      |
   |               | discoverable join-port     | Registrar need      |
   |               |                            | discoverable join-  |
   |               |                            | ports               |
   +---------------+----------------------------+---------------------+

                                 Table 1

7.  Security Considerations

   All the concerns in [RFC8995] section 4.1 apply.  The Pledge can be
   deceived by malicious Join Proxy announcements.  The Pledge will only
   join a network to which it receives a valid [RFC8366] voucher
   [I-D.ietf-anima-constrained-voucher].  Once the Pledge joined, the
   payload between Pledge and Registrar is protected by DTLS.



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   A malicious constrained Join Proxy has a number of routing
   possibilities:

   *  It sends the message on to a malicious Registrar.  This is the
      same case as the presence of a malicious Registrar discussed in
      RFC 8995.

   *  It does not send on the request or does not return the response
      from the Registrar.  This is the case of the not responding or
      crashing Registrar discussed in RFC 8995.

   *  It uses the returned response of the Registrar to enroll itself in
      the network.  With very low probability it can decrypt the
      response because successful enrollment is deemed unlikely.

   *  It uses the request from the Pledge to appropriate the Pledge
      certificate, but then it still needs to acquire the private key of
      the Pledge.  This, too, is assumed to be highly unlikely.

   *  A malicious node can construct an invalid Join Proxy message.
      Suppose, the destination port is the coaps port.  In that case, a
      Join Proxy can accept the message and add the routing addresses
      without checking the payload.  The Join Proxy then routes it to
      the Registrar.  In all cases, the Registrar needs to receive the
      message at the join-port, checks that the message consists of two
      parts and uses the DTLS payload to start the BRSKI procedure.  It
      is highly unlikely that this malicious payload will lead to node
      acceptance.

   *  A malicious node can sniff the messages routed by the constrained
      Join Proxy.  It is very unlikely that the malicious node can
      decrypt the DTLS payload.  A malicious node can read the header
      field of the message sent by the stateless Join Proxy.  This
      ability does not yield much more information than the visible
      addresses transported in the network packets.

   It should be noted here that the contents of the CBOR array used to
   convey return address information is not DTLS protected.  When the
   communication between Join Proxy and Registrar passes over an
   unsecure network, an attacker can change the CBOR array, causing the
   Registrar to deviate traffic from the intended Pledge.  These
   concerns are also expressed in [RFC8974].  It is also pointed out
   that the encryption by the Join Proxy is a local matter.  Similarly
   to [RFC8974], the use of AES-CCM [RFC3610] with a 64-bit tag is
   recommended, combined with a sequence number and a replay window.






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   If such scenario needs to be avoided, the constrained Join Proxy MUST
   encrypt the CBOR array using a locally generated symmetric key.  The
   Registrar is not able to examine the encrypted result, but does not
   need to.  The Registrar stores the encrypted header in the return
   packet without modifications.  The constrained Join Proxy can decrypt
   the contents to route the message to the right destination.

8.  IANA Considerations

8.1.  Resource Type Attributes registry

   This specification registers two new Resource Type (rt=) Link Target
   Attributes in the "Resource Type (rt=) Link Target Attribute Values"
   subregistry under the "Constrained RESTful Environments (CoRE)
   Parameters" registry per the [RFC6690] procedure.

   Attribute Value: brski.jp
   Description: This BRSKI resource type is used to query and return
                the supported BRSKI resources of the constrained
                Join Proxy.
   Reference: [this document]

   Attribute Value: brski.rjp
   Description: This BRSKI resource type is used for the constrained
                Join Proxy to query and return Join Proxy specific
                BRSKI resources of a Registrar.
   Reference: [this document]

8.2.  service name and port number registry

   This specification registers two service names under the "Service
   Name and Transport Protocol Port Number" registry.



















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   Service Name: brski-jp
   Transport Protocol(s): udp
   Assignee:  IESG <iesg@ietf.org>
   Contact:  IESG <iesg@ietf.org>
   Description: Bootstrapping Remote Secure Key Infrastructure
                 constrained Join Proxy
   Reference: [this document]

   Service Name: brski-rjp
   Transport Protocol(s): udp
   Assignee:  IESG <iesg@ietf.org>
   Contact:  IESG <iesg@ietf.org>
   Description: Bootstrapping Remote Secure Key Infrastructure
                Registrar join-port used by stateless constrained
                Join Proxy
   Reference: [this document]

9.  Acknowledgements

   Many thanks for the comments by Carsten Bormann, Brian Carpenter,
   Spencer Dawkins, Esko Dijk, Toerless Eckert, Russ Housley, Ines
   Robles, Rich Salz, Jürgen Schönwälder, Mališa Vučinić, and Rob
   Wilton.

10.  Contributors

   Sandeep Kumar, Sye loong Keoh, and Oscar Garcia-Morchon are the co-
   authors of the draft-kumar-dice-dtls-relay-02.  Their draft has
   served as a basis for this document.

11.  Changelog

11.1.  14 to 13

   *  incorporated review comments from TTE

   *  jpy message changed to CoAP header

11.2.  13 to 12

   * jpy message encrypted and no longer standardized

11.3.  12 to 11

* many typos fixes and text re-organized
* core of GRASP and CoAP discovery moved to contrained-voucher document, only stateless extensions remain





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11.4.  11 to 10

   * Join-Proxy and Registrar discovery merged
   * GRASP discovery updated
   * ARTART review
   * TSVART review

11.5.  10 to 09

   * OPSDIR review
   * IANA review
   * SECDIR review
   * GENART review

11.6.  09 to 07

    * typos

11.7.  06 to 07

    * AD review changes

11.8.  05 to 06

    * RT value change to brski.jp and brski.rjp
    * new registry values for IANA
    * improved handling of jpy header array

11.9.  04 to 05

    * Join Proxy and join-port consistent spelling
    * some nits removed
    * restructured discovery
    * section
    * rephrased parts of security section

11.10.  03 to 04

   * mail address and reference

11.11.  02 to 03

   * Terminology updated
   * Several clarifications on discovery and routability
   * DTLS payload introduced

11.12.  01 to 02




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   *  Discovery of Join Proxy and Registrar ports

11.13.  00 to 01

   *  Registrar used throughout instead of EST server

   *  Emphasized additional Join Proxy port for Join Proxy and Registrar

   *  updated discovery accordingly

   *  updated stateless Join Proxy JPY header

   *  JPY header described with CDDL

   *  Example simplified and corrected

11.14.  00 to 00

   *  copied from vanderstok-anima-constrained-join-proxy-05

12.  References

12.1.  Normative References

   [family]   "Address Family Numbers", IANA, 19 October 2021,
              <https://www.iana.org/assignments/address-family-numbers/
              address-family-numbers.xhtml>.

   [I-D.ietf-anima-constrained-voucher]
              Richardson, M., Van der Stok, P., Kampanakis, P., and E.
              Dijk, "Constrained Bootstrapping Remote Secure Key
              Infrastructure (BRSKI)", Work in Progress, Internet-Draft,
              draft-ietf-anima-constrained-voucher-18, 11 July 2022,
              <https://www.ietf.org/archive/id/draft-ietf-anima-
              constrained-voucher-18.txt>.

   [ieee802-1AR]
              "IEEE 802.1AR Secure Device Identifier", IEEE Standard,
              2009,
              <https://standards.ieee.org/standard/802.1AR-2009.html>.

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






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   [RFC6347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
              January 2012, <https://www.rfc-editor.org/info/rfc6347>.

   [RFC6690]  Shelby, Z., "Constrained RESTful Environments (CoRE) Link
              Format", RFC 6690, DOI 10.17487/RFC6690, August 2012,
              <https://www.rfc-editor.org/info/rfc6690>.

   [RFC7252]  Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
              Application Protocol (CoAP)", RFC 7252,
              DOI 10.17487/RFC7252, June 2014,
              <https://www.rfc-editor.org/info/rfc7252>.

   [RFC768]   Postel, J., "User Datagram Protocol", STD 6, RFC 768,
              DOI 10.17487/RFC0768, August 1980,
              <https://www.rfc-editor.org/info/rfc768>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [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>.

   [RFC8949]  Bormann, C. and P. Hoffman, "Concise Binary Object
              Representation (CBOR)", STD 94, RFC 8949,
              DOI 10.17487/RFC8949, December 2020,
              <https://www.rfc-editor.org/info/rfc8949>.

   [RFC8990]  Bormann, C., Carpenter, B., Ed., and B. Liu, Ed., "GeneRic
              Autonomic Signaling Protocol (GRASP)", RFC 8990,
              DOI 10.17487/RFC8990, May 2021,
              <https://www.rfc-editor.org/info/rfc8990>.

   [RFC8995]  Pritikin, M., Richardson, M., Eckert, T., Behringer, M.,
              and K. Watsen, "Bootstrapping Remote Secure Key
              Infrastructure (BRSKI)", RFC 8995, DOI 10.17487/RFC8995,
              May 2021, <https://www.rfc-editor.org/info/rfc8995>.

   [RFC9147]  Rescorla, E., Tschofenig, H., and N. Modadugu, "The
              Datagram Transport Layer Security (DTLS) Protocol Version
              1.3", RFC 9147, DOI 10.17487/RFC9147, April 2022,
              <https://www.rfc-editor.org/info/rfc9147>.






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   [RFC9148]  van der Stok, P., Kampanakis, P., Richardson, M., and S.
              Raza, "EST-coaps: Enrollment over Secure Transport with
              the Secure Constrained Application Protocol", RFC 9148,
              DOI 10.17487/RFC9148, April 2022,
              <https://www.rfc-editor.org/info/rfc9148>.

12.2.  Informative References

   [I-D.kumar-dice-dtls-relay]
              Kumar, S. S., Keoh, S. L., and O. Garcia-Morchon, "DTLS
              Relay for Constrained Environments", Work in Progress,
              Internet-Draft, draft-kumar-dice-dtls-relay-02, 20 October
              2014, <https://www.ietf.org/archive/id/draft-kumar-dice-
              dtls-relay-02.txt>.

   [I-D.richardson-anima-state-for-joinrouter]
              Richardson, M., "Considerations for stateful vs stateless
              join router in ANIMA bootstrap", Work in Progress,
              Internet-Draft, draft-richardson-anima-state-for-
              joinrouter-03, 22 September 2020,
              <https://www.ietf.org/archive/id/draft-richardson-anima-
              state-for-joinrouter-03.txt>.

   [RFC3610]  Whiting, D., Housley, R., and N. Ferguson, "Counter with
              CBC-MAC (CCM)", RFC 3610, DOI 10.17487/RFC3610, September
              2003, <https://www.rfc-editor.org/info/rfc3610>.

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

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <https://www.rfc-editor.org/info/rfc3986>.

   [RFC4944]  Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
              "Transmission of IPv6 Packets over IEEE 802.15.4
              Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007,
              <https://www.rfc-editor.org/info/rfc4944>.

   [RFC6550]  Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J.,
              Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur,
              JP., and R. Alexander, "RPL: IPv6 Routing Protocol for
              Low-Power and Lossy Networks", RFC 6550,
              DOI 10.17487/RFC6550, March 2012,
              <https://www.rfc-editor.org/info/rfc6550>.



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   [RFC6775]  Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C.
              Bormann, "Neighbor Discovery Optimization for IPv6 over
              Low-Power Wireless Personal Area Networks (6LoWPANs)",
              RFC 6775, DOI 10.17487/RFC6775, November 2012,
              <https://www.rfc-editor.org/info/rfc6775>.

   [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>.

   [RFC7102]  Vasseur, JP., "Terms Used in Routing for Low-Power and
              Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January
              2014, <https://www.rfc-editor.org/info/rfc7102>.

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

   [RFC7959]  Bormann, C. and Z. Shelby, Ed., "Block-Wise Transfers in
              the Constrained Application Protocol (CoAP)", RFC 7959,
              DOI 10.17487/RFC7959, August 2016,
              <https://www.rfc-editor.org/info/rfc7959>.

   [RFC8610]  Birkholz, H., Vigano, C., and C. Bormann, "Concise Data
              Definition Language (CDDL): A Notational Convention to
              Express Concise Binary Object Representation (CBOR) and
              JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610,
              June 2019, <https://www.rfc-editor.org/info/rfc8610>.

   [RFC8974]  Hartke, K. and M. Richardson, "Extended Tokens and
              Stateless Clients in the Constrained Application Protocol
              (CoAP)", RFC 8974, DOI 10.17487/RFC8974, January 2021,
              <https://www.rfc-editor.org/info/rfc8974>.

   [RFC9031]  Vučinić, M., Ed., Simon, J., Pister, K., and M.
              Richardson, "Constrained Join Protocol (CoJP) for 6TiSCH",
              RFC 9031, DOI 10.17487/RFC9031, May 2021,
              <https://www.rfc-editor.org/info/rfc9031>.

   [RFC9032]  Dujovne, D., Ed. and M. Richardson, "Encapsulation of
              6TiSCH Join and Enrollment Information Elements",
              RFC 9032, DOI 10.17487/RFC9032, May 2021,
              <https://www.rfc-editor.org/info/rfc9032>.






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Appendix A.  Stateless CoAP payload examples

   This section shows how the CoAP header is arranged by the stateless
   proxy.

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |Ver|T=0|TKL=13 | Code=0.02 POST|          Message ID           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |0 0 0 0 0 0 1 1|
      |               16-bytes of extended token                      |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |1 1 0 1 0 1 0 0|0 0 0 1 1 0 1 0| four bytes: "coap"            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |1 1 1 1 1 1 1 1|    Payload (DTLS contents)
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Option is Proxy-Scheme, with a value 39, and must be encoded as
   an Option Delta of 13, followed by a single byte of (39-13=) 26.

   The total size of the header is 4,1+16,6,1 is 28 bytes.  A CBOR
   header would have taken 4+16 bytes or 20 bytes, for a difference of 8
   bytes.

Appendix B.  Stateless Proxy payload examples

   The examples show the request "GET coaps://192.168.1.200:5965/est/
   crts" to a Registrar.  The header generated between Join Proxy and
   Registrar and from Registrar to Join Proxy are shown in detail.  The
   DTLS payload is not shown.

   NOTE THESE ARE OLD.

   The request from Join Proxy to Registrar looks like:

      85                                   # array(5)
         50                                # bytes(16)
            FE800000000000000000FFFFC0A801C8 #
         19 BDA7                           # unsigned(48551)
         01                                # unsigned(1) IP
         00                                # unsigned(0)
         58 2D                             # bytes(45)
      <cacrts DTLS encrypted request>

   In CBOR Diagnostic:




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       [h'FE800000000000000000FFFFC0A801C8', 48551, 1, 0,
        h'<cacrts DTLS encrypted request>']

   The response is:

      85                                   # array(5)
         50                                # bytes(16)
            FE800000000000000000FFFFC0A801C8 #
         19 BDA7                           # unsigned(48551)
         01                                # unsigned(1) IP
         00                                # unsigned(0)
      59 026A                              # bytes(618)
         <cacrts DTLS encrypted response>

   In CBOR diagnostic:

       [h'FE800000000000000000FFFFC0A801C8', 48551, 1, 0,
       h'<cacrts DTLS encrypted response>']

Authors' Addresses

   Michael Richardson
   Sandelman Software Works
   Email: mcr+ietf@sandelman.ca


   Peter van der Stok
   vanderstok consultancy
   Email: stokcons@bbhmail.nl


   Panos Kampanakis
   Cisco Systems
   Email: pkampana@cisco.com

















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