Internet DRAFT - draft-ietf-anima-constrained-join-proxy
draft-ietf-anima-constrained-join-proxy
anima Working Group M. Richardson
Internet-Draft Sandelman Software Works
Intended status: Standards Track P. van der Stok
Expires: 9 May 2024 vanderstok consultancy
P. Kampanakis
Cisco Systems
6 November 2023
Join Proxy for Bootstrapping of Constrained Network Elements
draft-ietf-anima-constrained-join-proxy-15
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
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
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Please review these documents carefully, as they describe your rights
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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. Stateless Message structure example construction . . 11
4.3.2. Processing by Registrar . . . . . . . . . . . . . . . 12
5. Discovery . . . . . . . . . . . . . . . . . . . . . . . . . . 12
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 . . . . . . . . . . . . . . . . . . . 15
5.2.3. 6tisch Discovery . . . . . . . . . . . . . . . . . . 16
6. Comparison of stateless and stateful modes . . . . . . . . . 16
7. Security Considerations . . . . . . . . . . . . . . . . . . . 17
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
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8.1. Extensions to the "BRSKI AN_Proxy Objective Value"
Registry . . . . . . . . . . . . . . . . . . . . . . . . 19
8.2. Extensions to the "BRSKI AN_join_registrar Objective Value"
Registry . . . . . . . . . . . . . . . . . . . . . . . . 19
8.3. Resource Type Attributes registry . . . . . . . . . . . . 19
8.4. CoAPS+JPY Scheme Registration . . . . . . . . . . . . . . 19
8.5. Service name and port number registry . . . . . . . . . . 20
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 . . . . . . . . . . . . . . . . . . . . . . . . 21
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 . . . . . . . . . . . . . . . . . . . . . . . . 22
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.
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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).
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 challenged 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)
[RFC9147] 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 have been enrolled previously into the network, such
that the message from the constrained Join Proxy to the 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:
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1 A stateful Join Proxy that locally stores IP addresses during for the duration of the DTLS connection between Pledge and Registrar.
2 A stateless Join Proxy where the connection state is stored in the messages.
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, Pledge, and Voucher.
The term "Registrar" is used throughout this document instead of
"Join Registrar/Coordinator (JRC)" as defined in [RFC8366].
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 LLN mesh
.---.
| R +---. +----+ +---+ +--+
| | \ |6LR +----+ J |........|P |
'---' `--+ | | | clear | |
+----+ +---+ +--+
Registrar Join Proxy Pledge
Figure 1: multi-hop enrollment.
Without multi-hop 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.
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. Stateless Message structure example construction
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 Interface IDentifier (IID) is not 64-bits, a
different arrangement will be necessary.
4.3.2. 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.
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
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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 whether 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:
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 8.4, as per
[RFC7252], Section 6.2
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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:
[M_FLOOD, 51840231, h'fda379a6f6ee00000200000064000001', 180000,
[["AN_join_registrar", 4, 255, ""],
[O_IPv6_LOCATOR,
h'fda379a6f6ee00000200000064000001', IPPROTO_TCP, 8443],
["AN_join_registrar", 4, 255, "CMP"],
[O_IPv6_LOCATOR,
h'fda379a6f6ee00000200000064000001', IPPROTO_TCP, 8448],
["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]]]
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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]).
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]:
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* The transport-proto is IPPROTO_UDP
* the objective is AN_Proxy
* the objective-value is "DTLS-EST"
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, "DTLS-EST"],
[O_IPv6_LOCATOR,
h'fe800000000000000000000000000001', IPPROTO_UDP, 5684]]]
Figure 7: Example of Registrar announcement message
5.2.3. 6tisch Discovery
The discovery of CoJP [RFC9031] compatible 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.
The Enhanced Beason discovery mechanism used in 6tisch does not
convey a method to the pledge, (equivalent to an objective value, as
described above), so only the CoAP/OSCORE mechanism described in
[RFC9031] is announced.
A 6tisch network that wanted to use DTLS for security would need a
new attribute for the enhanced beacon that announced the availability
of a DTLS proxy as described in this document. Future work could
provide that capability.
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. Extensions to the "BRSKI AN_Proxy Objective Value" Registry
[I-D.ietf-anima-constrained-voucher] previously registered the
objective value DTLS-EST. This document makes use of it, and the
registry should be extended to reference this document as well.
8.2. Extensions to the "BRSKI AN_join_registrar Objective Value"
Registry
This document registers the objective-value: "BRSKI_RJP"
8.3. 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]
8.4. 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.
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8.5. Service name and port number registry
This specification registers two service names under the "Service
Name and Transport Protocol Port Number" registry.
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
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11.3. 11 to 10
* Join-Proxy and Registrar discovery merged
* GRASP discovery updated
* ARTART review
* TSVART review
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
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* 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
* 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-21, 7 July 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-anima-
constrained-voucher-21>.
[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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[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>.
[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>.
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[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://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
Richardson, et al. Expires 9 May 2024 [Page 26]