Constrained Join Proxy for Bootstrapping Protocols
draft-ietf-anima-constrained-join-proxy-14

anima Working Group                                        M. Richardson
Internet-Draft                                  Sandelman Software Works
Intended status: Standards Track                         P. van der Stok
Expires: 28 October 2023                          vanderstok consultancy
                                                           P. Kampanakis
                                                           Cisco Systems
                                                           26 April 2023

           Constrained Join Proxy for Bootstrapping Protocols
               draft-ietf-anima-constrained-join-proxy-14

Abstract

   This document extends the work of Bootstrapping Remote Secure Key
   Infrastructures (BRSKI) by replacing the Circuit-proxy between Pledge
   and Registrar by a stateless/stateful 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.

   This document defines a protocol to securely assign a Pledge to a
   domain, represented by a Registrar, using an intermediary node
   between Pledge and Registrar.  This intermediary node is known as a
   "constrained Join Proxy".  An enrolled Pledge can act as a
   constrained Join Proxy.

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) 2023 IETF Trust and the persons identified as the
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  constrained Join Proxy functionality  . . . . . . . . . . . .   6
   4.  constrained Join Proxy specification  . . . . . . . . . . . .   7
     4.1.  Stateful Join Proxy . . . . . . . . . . . . . . . . . . .   7
     4.2.  Stateless Join Proxy  . . . . . . . . . . . . . . . . . .   8
     4.3.  Stateless Message structure . . . . . . . . . . . . . . .  10
       4.3.1.  Processing by Registrar . . . . . . . . . . . . . . .  12
   5.  Discovery . . . . . . . . . . . . . . . . . . . . . . . . . .  13
     5.1.  Discovery operations by Join-Proxy  . . . . . . . . . . .  13
       5.1.1.  CoAP discovery  . . . . . . . . . . . . . . . . . . .  13
       5.1.2.  GRASP discovery . . . . . . . . . . . . . . . . . . .  14
     5.2.  Pledge discovers Join-Proxy . . . . . . . . . . . . . . .  15
       5.2.1.  CoAP discovery  . . . . . . . . . . . . . . . . . . .  15
       5.2.2.  GRASP discovery . . . . . . . . . . . . . . . . . . .  16
       5.2.3.  6tisch discovery  . . . . . . . . . . . . . . . . . .  16
   6.  Comparison of stateless and stateful modes  . . . . . . . . .  16
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  17
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  19
     8.1.  Resource Type Attributes registry . . . . . . . . . . . .  19

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     8.2.  CoAPS+JPY Scheme Registration . . . . . . . . . . . . . .  19
     8.3.  service name and port number registry . . . . . . . . . .  19
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  20
   10. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  20
   11. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . .  20
     11.1.  13 to 12 . . . . . . . . . . . . . . . . . . . . . . . .  20
     11.2.  12 to 11 . . . . . . . . . . . . . . . . . . . . . . . .  20
     11.3.  11 to 10 . . . . . . . . . . . . . . . . . . . . . . . .  20
     11.4.  10 to 09 . . . . . . . . . . . . . . . . . . . . . . . .  21
     11.5.  09 to 07 . . . . . . . . . . . . . . . . . . . . . . . .  21
     11.6.  06 to 07 . . . . . . . . . . . . . . . . . . . . . . . .  21
     11.7.  05 to 06 . . . . . . . . . . . . . . . . . . . . . . . .  21
     11.8.  04 to 05 . . . . . . . . . . . . . . . . . . . . . . . .  21
     11.9.  03 to 04 . . . . . . . . . . . . . . . . . . . . . . . .  21
     11.10. 02 to 03 . . . . . . . . . . . . . . . . . . . . . . . .  21
     11.11. 01 to 02 . . . . . . . . . . . . . . . . . . . . . . . .  21
     11.12. 00 to 01 . . . . . . . . . . . . . . . . . . . . . . . .  21
     11.13. 00 to 00 . . . . . . . . . . . . . . . . . . . . . . . .  22
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  22
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  22
     12.2.  Informative References . . . . . . . . . . . . . . . . .  23
   Appendix A.  Stateless Proxy payload examples . . . . . . . . . .  25
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  26

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, the underlying IP network is
   assumed to be a mesh network as described in [RFC4944], although
   other IP-over-foo networks are not excluded.  An example network is
   shown in Figure 1.

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

   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).

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   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.

   DTLS is a client-server protocol relying on the underlying IP layer
   to perform the routing between the DTLS Client and the DTLS Server.
   However, 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 constrained Join Proxy, which transmits the DTLS protected
   request coming from the Pledge to the 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.

   During enrollment, a DTLS connection is required between Pledge and
   Registrar.

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

   This document specifies a new form of constrained Join Proxy and
   protocol to act as intermediary between Pledge and Registrar to relay
   DTLS messages between Pledge and Registrar.  Two modes of the
   constrained Join Proxy are specified:

   1 A stateful Join Proxy that locally stores IP addresses
     during the connection.
   2 A stateless Join Proxy where the connection state
    is stored in the messages.

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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.

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 term "installation network" refers to all devices in the
   installation and the network connections between them.  The term
   "installation IP_address" refers to an address out of the set of
   addresses which are routable over the whole installation network.

   The "Constrained Join Proxy" enables a pledge that is multiple hops
   away from the Registrar, to securely execute the BRSKI protocol
   [RFC8995] over 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.

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3.  constrained Join Proxy functionality

   As depicted in the Figure 1, the Pledge (P), in 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.

   In this situation, the Pledge can only communicate one-hop to its
   nearest neighbor, the constrained Join Proxy (J) using their link-
   local IPv6 addresses.  However, the Pledge needs to communicate with
   end-to-end security with a Registrar to 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 Pledge for any returned messages from the Registrar.

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

                      Figure 1: multi-hop enrollment.

   Without routing the Pledge cannot establish a secure connection to
   the Registrar over multiple hops in the network.

   Furthermore, the Pledge cannot 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/or
   discovery of the destination address of the Registrar, the
   constrained Join Proxy is introduced.  This constrained Join Proxy
   functionality is 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.  The
   wanted end-state is a network with a Registrar and a set of enrolled

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   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 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 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.

4.  constrained Join Proxy specification

   A Join Proxy can operate in two modes:

   *  Stateful mode

   *  Stateless mode

   A Join Proxy MUST implement both.  A Registrar MUST implement the
   stateful mode and SHOULD implement the Stateless mode.

   A mechanism to switch between modes is out of scope of this document.
   It is recommended that a Join Proxy uses only one of these modes at
   any given moment during an installation lifetime.

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

4.1.  Stateful Join Proxy

   In stateful mode, the Join Proxy forwards the DTLS messages to the
   Registrar.

   Assume that the Pledge does not know the IP address of the Registrar
   it needs to contact.  The Join Proxy has been enrolled via the
   Registrar and learns the IP address and port of the Registrar, by
   using a discovery mechanism such as described in Section 5.  The
   Pledge first discovers (see Section 5) and selects the most
   appropriate Join Proxy.  (Discovery can also be based upon [RFC8995]
   section 4.1).  The Pledge initiates its request as if the Join Proxy
   is the intended Registrar.  The Join Proxy receives the message at a
   discoverable join-port.  The Join Proxy constructs an IP packet by
   copying the DTLS payload from the message received from the Pledge,

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   and provides source and destination addresses to forward the message
   to the intended Registrar.  The Join Proxy stores the 4-tuple array
   of the messages received from the Registrar and copies it back to the
   header of the message returned to the Pledge.

   In Figure 2 the various steps of the message flow are shown, with
   5684 being the standard coaps port.  The columns "SRc_IP:port" and
   "Dst_IP:port" show the IP address and port values for the source and
   destination of the message.

   +------------+------------+-------------+--------------------------+
   |   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.

4.2.  Stateless Join Proxy

   The JPY Encapsulation Protocol allows the stateless Join Proxy to
   minimize memory requirements on a constrained Join Proxy device.  The
   use of a stateless operation requires no memory in the Join Proxy
   device because it stores the state in a special encapsulation in the
   packet.  This may also reduce the CPU impact as the device does not
   need to search through a state table.

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   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 Pledge attempts a DTLS connection to the Join Proxy, it uses
   its link-local IP address as its IP source address.  This message is
   transmitted one-hop to a neighboring (Join Proxy) node.  Under normal
   circumstances, this message would be dropped at the neighbor node
   since the Pledge is not yet IP routable or is not yet authenticated
   to send messages through the network.  However, if the neighbor
   device has the Join Proxy functionality enabled; it routes the DTLS
   message to its Registrar of choice.

   The Join Proxy transforms the DTLS message to a JPY message which
   includes the DTLS data as payload, and sends the JPY message to the
   join-port of the Registrar.

   The JPY message payload consists of two parts:

   *  Header (H) field: consisting of the source link-local address and
      port of the Pledge (P), and

   *  Contents (C) field: containing the original DTLS payload.

   On receiving the JPY message, the Registrar (or proxy) retrieves the
   two parts.

   The Registrar transiently stores the Header field information.  The
   Registrar uses the Contents field to execute the Registrar
   functionality.  However, when the Registrar replies, it also extends
   its DTLS message with the header field in a JPY message and sends it
   back to the Join Proxy.  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 JPY message, the Join Proxy retrieves the two parts.
   It uses the Header field to route the DTLS message containing the
   DTLS payload retrieved from the Contents field to the Pledge.

   In this scenario, both the Registrar and the Join Proxy use
   discoverable join-ports, for the Join Proxy this may be a default
   CoAP port.

   The Figure 3 depicts the message flow diagram:

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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.  Stateless Message structure

   The JPY message is constructed as a payload directly above UDP.
   There is no CoAP or DTLS layer as both are within the relayed
   payload.

   Header and Contents fields together are consist of one CBOR [RFC8949]
   array of 2 elements, explained in CDDL [RFC8610]:

   1.  The context payload.  This is a CBOR byte string.  It SHOULD be
       between 8 and 32 bytes in size.

   2.  Content field: containing the DTLS payload as a CBOR byte string.

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       JPY_message =
       [
          pledge_context_message : bstr,
          content   : bstr
       ]

                Figure 4: CDDL representation of JPY message

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

   The context payload is to be reflected by the Registrar when sending
   reply packets to the Join Proxy.  The context payload is not
   standardized.  It is to be used by the Join Proxy to record which
   pledge the traffic came from.

   The Join Proxy SHOULD encrypt this context 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.  The considerations of
   Section 5.2 of [RFC8974] apply.

   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 a CoAP proxy.

   A typical context parameter 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,
       ]

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

4.3.1.  Processing by Registrar

   On reception of a JPY message by the Registrar, the Registrar MUST
   verify that the number of array elements is 2 or more.  The
   pledge_content field must be provided as input to a DTLS library
   [RFC9147], which along with the 5-tuple of the UDP connection
   provides 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.  The
   pledge_context_message can be used to select an appropriate DTLS
   context, as DTLS headers do not contain any kind of of per session
   context.  The pledge_context_message needs to be linked to the DTLS
   context, and when DTLS records need to be sent, then the
   pledge_context_message needs to be prepended to the data that is
   sent.

   Examples are shown in Appendix A.

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   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 JPY_message 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 JPY encapsulation.

   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 the join-port of the
   Registrar.

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

     RES: 2.05 Content
     <coaps+jpy://[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 encapsulated JPY
   messages described in section Section 4.3.  The scheme remains coaps,
   as the inside protocol is still CoAP and DTLS.

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

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

  RES: 2.05 Content
  <coaps+jpy://[2001:db8:0:abcd::52]:7634>;rt=brski.rjp,
  <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",

   The coaps+jpy scheme is registered is defined in Section 8.2, as per
   [RFC7252], Section 6.2

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".

   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 5: Example of Registrar announcement message

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

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      [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 6: Example of Registrar announcing two 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.

   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 5.1 of [RFC9148]).

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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 7: 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.

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.

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

          Figure 8: Comparison between stateful and stateless mode

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.

   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.

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   *  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 in the source 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.

   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.

   In some installations, layer 2 protection is provided between all
   member pairs of the mesh.  In such an environment encryption of the
   CBOR array is unnecessary because the layer 2 protection already
   provide it.

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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.  CoAPS+JPY Scheme Registration

Scheme name: coaps+jpy
Status: permanent
Applications/protocols that use this scheme name: Constrained BRSKI Join Proxy
Contact: ANIMA WG
Change controller: IESG
References: [THIS RFC]
Scheme syntax: identical to coaps
Scheme semantics: The encapsulation mechanism described in {{stateless-jpy}} is used with coaps.
Security considerations: The new encapsulation allows traffic to be returned to a calling node
   behind a proxy.  The form of the encapsulation can include privacy and integrity protection
   under the control of the proxy system.

8.3.  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.  Much text from their draft is
   copied over to this draft.

11.  Changelog

11.1.  13 to 12

   * jpy message encrypted and no longer standardized

11.2.  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

11.3.  11 to 10

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

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11.4.  10 to 09

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

11.5.  09 to 07

    * typos

11.6.  06 to 07

    * AD review changes

11.7.  05 to 06

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

11.8.  04 to 05

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

11.9.  03 to 04

   * mail address and reference

11.10.  02 to 03

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

11.11.  01 to 02

   *  Discovery of Join Proxy and Registrar ports

11.12.  00 to 01

   *  Registrar used throughout instead of EST server

   *  Emphasized additional Join Proxy port for Join Proxy and Registrar

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   *  updated discovery accordingly

   *  updated stateless Join Proxy JPY header

   *  JPY header described with CDDL

   *  Example simplified and corrected

11.13.  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-20, 13 March 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-anima-
              constrained-voucher-20>.

   [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>.

   [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>.

   [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>.

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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>.

   [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>.

   [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>.

   [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>.

   [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://datatracker.ietf.org/doc/html/draft-kumar-
              dice-dtls-relay-02>.

   [I-D.richardson-anima-state-for-joinrouter]
              Richardson, M., "Considerations for stateful vs stateless
              join router in ANIMA bootstrap", Work in Progress,

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              Internet-Draft, draft-richardson-anima-state-for-
              joinrouter-03, 22 September 2020,
              <https://datatracker.ietf.org/doc/html/draft-richardson-
              anima-state-for-joinrouter-03>.

   [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>.

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

   [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>.

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   [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>.

   [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>.

   [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>.

Appendix A.  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.

   The request from Join Proxy to Registrar looks like:

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      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:

       [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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