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draft-ietf-anima-constrained-join-proxy-09.txt
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draft-ietf-anima-constrained-join-proxy-09.txt
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anima Working Group M. Richardson
Internet-Draft Sandelman Software Works
Intended status: Standards Track P. van der Stok
Expires: 26 September 2022 vanderstok consultancy
P. Kampanakis
Cisco Systems
25 March 2022
Constrained Join Proxy for Bootstrapping Protocols
draft-ietf-anima-constrained-join-proxy-09
Abstract
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.
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. It
relays join traffic from the Pledge to the Registrar.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 26 September 2022.
Copyright Notice
Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Requirements Language . . . . . . . . . . . . . . . . . . . . 4
4. Join Proxy functionality . . . . . . . . . . . . . . . . . . 5
5. Join Proxy specification . . . . . . . . . . . . . . . . . . 5
5.1. Stateful Join Proxy . . . . . . . . . . . . . . . . . . . 6
5.2. Stateless Join Proxy . . . . . . . . . . . . . . . . . . 7
5.3. Stateless Message structure . . . . . . . . . . . . . . . 9
6. Discovery . . . . . . . . . . . . . . . . . . . . . . . . . . 10
6.1. Join Proxy discovers Registrar . . . . . . . . . . . . . 11
6.1.1. CoAP discovery . . . . . . . . . . . . . . . . . . . 12
6.1.2. GRASP discovery . . . . . . . . . . . . . . . . . . . 12
6.1.3. 6tisch discovery . . . . . . . . . . . . . . . . . . 12
6.2. Pledge discovers Registrar . . . . . . . . . . . . . . . 12
6.2.1. CoAP discovery . . . . . . . . . . . . . . . . . . . 12
6.2.2. GRASP discovery . . . . . . . . . . . . . . . . . . . 13
6.2.3. 6tisch discovery . . . . . . . . . . . . . . . . . . 13
6.3. Pledge discovers Join Proxy . . . . . . . . . . . . . . . 13
6.3.1. CoAP discovery . . . . . . . . . . . . . . . . . . . 13
6.3.2. GRASP discovery . . . . . . . . . . . . . . . . . . . 14
6.3.3. 6tisch discovery . . . . . . . . . . . . . . . . . . 14
7. Comparison of stateless and stateful modes . . . . . . . . . 14
8. Security Considerations . . . . . . . . . . . . . . . . . . . 15
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
9.1. Resource Type Attributes registry . . . . . . . . . . . . 15
9.2. service name and port number registry . . . . . . . . . . 15
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 16
11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 16
12. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 16
12.1. 06 to 07 . . . . . . . . . . . . . . . . . . . . . . . . 16
12.2. 05 to 06 . . . . . . . . . . . . . . . . . . . . . . . . 16
12.3. 04 to 05 . . . . . . . . . . . . . . . . . . . . . . . . 16
12.4. 03 to 04 . . . . . . . . . . . . . . . . . . . . . . . . 17
12.5. 02 to 03 . . . . . . . . . . . . . . . . . . . . . . . . 17
12.6. 01 to 02 . . . . . . . . . . . . . . . . . . . . . . . . 17
12.7. 00 to 01 . . . . . . . . . . . . . . . . . . . . . . . . 17
12.8. 00 to 00 . . . . . . . . . . . . . . . . . . . . . . . . 17
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13. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
13.1. Normative References . . . . . . . . . . . . . . . . . . 17
13.2. Informative References . . . . . . . . . . . . . . . . . 18
Appendix A. Stateless Proxy payload examples . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21
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 Join
Proxy.
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 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
[I-D.ietf-ace-coap-est]. The [I-D.ietf-anima-constrained-voucher]
extends [I-D.ietf-ace-coap-est] 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 until it is authenticated
to the network. A new Pledge can only initially use a link-local
IPv6 address to communicate with a neighbor on the same link
[RFC6775] until it receives the necessary network configuration
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parameters. However, before the Pledge can receive these
configuration parameters, it needs to authenticate itself to the
network to which it connects.
During enrollment, a DTLS connection is required between Pledge and
Registrar.
Once a Pledge is enrolled, it can act as Join Proxy between other
Pledges and the enrolling Registrar.
This document specifies a new form of Join Proxy and protocol to act
as intermediary between Pledge and Registrar to relay DTLS messages
between Pledge and Registrar. Two versions of the Join Proxy are
specified:
1 A stateful Join Proxy that locally stores IP addresses
during the connection.
2 A stateless Join Proxy that 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 Join Proxy. [RFC8995] adopted only the
Circuit Proxy method (1), leaving the other methods as future work.
This document standardizes the CoAP/DTLS (method 4).
2. Terminology
The following terms are defined in [RFC8366], and are used
identically as in that document: artifact, imprint, domain, Join
Registrar/Coordinator (JRC), Manufacturer Authorized Signing
Authority (MASA), Pledge, Trust of First Use (TOFU), and Voucher.
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.
3. Requirements Language
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.
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4. 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 Join Proxy (J) using their link-local IPv6
addresses. However, the Pledge (P) needs to communicate with end-to-
end security with a Registrar to authenticate and get the relevant
system/network parameters. If the Pledge (P), knowing the IP-address
of the Registrar, initiates a DTLS connection to the Registrar, then
the packets are dropped at the Join Proxy (J) since the Pledge (P) is
not yet admitted to the network or there is no IP routability to
Pledge (P) for any returned messages from the Registrar.
++++ multi-hop
|R |---- mesh +--+ +--+
| | \ |J |........|P |
++++ \-----| | | |
+--+ +--+
Registrar Join Proxy Pledge
Figure 1: multi-hop enrollment.
Without routing the Pledge (P) cannot establish a secure connection
to the Registrar (R) over multiple hops in the network.
Furthermore, the Pledge (P) cannot discover the IP address of the
Registrar (R) 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 Join Proxy
is introduced. This Join Proxy functionality is configured into all
authenticated devices in the network which may act as a Join Proxy
for Pledges. The Join Proxy allows for routing of the packets from
the Pledge using IP routing to the intended Registrar. An
authenticated Join Proxy can discover the routable IP address of the
Registrar over multiple hops. The following Section 5 specifies the
two Join Proxy modes. A comparison is presented in Section 7.
5. Join Proxy specification
A Join Proxy can operate in two modes:
* Stateful mode
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* Stateless mode
A Join Proxy MUST implement one of the two modes. A Join Proxy MAY
implement both, with an unspecified mechanism to switch between the
two modes.
5.1. 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, for
example by using the discovery mechanism described in Section 6. The
Pledge first discovers (see Section 6) and selects the most
appropriate Join Proxy. (Discovery can also be based upon [RFC8995]
section 4.1). For service discovery via DNS-SD [RFC6763], this
document specifies the service names in Section 9.2. 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, and provides source and
destination addresses to forward the message to the intended
Registrar. The Join Proxy maintains a 4-tuple array to translate the
DTLS messages received from the Registrar and forwards it back to the
Pledge.
In Figure 2 the various steps of the message flow are shown, with
5684 being the standard coaps port:
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+------------+------------+-------------+--------------------------+
| Pledge | Join Proxy | Registrar | Message |
| (P) | (J) | (R) | Src_IP:port | Dst_IP:port|
+------------+------------+-------------+-------------+------------+
| --ClientHello--> | IP_P:p_P | IP_Jl:p_Jl |
| --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.
5.2. Stateless Join Proxy
The stateless Join Proxy aims to minimize the requirements on the
constrained Join Proxy device. Stateless operation requires no
memory in the Join Proxy device, but may also reduce the CPU impact
as the device does not need to search through a state table.
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.
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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.
5.3. Stateless Message structure
The JPY message is constructed as a payload with media-type
application/cbor
Header and Contents fields together are one CBOR array of 5 elements:
1. header field: containing a CBOR array [RFC8949] with the Pledge
IPv6 Link Local address as a CBOR byte string, the Pledge's UDP
port number as a CBOR integer, the IP address family (IPv4/IPv6)
as a CBOR integer, and the proxy's ifindex or other identifier
for the physical port as CBOR integer. The header field is not
DTLS encrypted.
2. Content field: containing the DTLS payload as a CBOR byte string.
The address family integer is defined in [family] with:
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1 IP (IP version 4)
2 IP6 (IP version 6)
The Join Proxy cannot decrypt the DTLS payload and has no knowledge
of the transported media type.
JPY_message =
[
ip : bstr,
port : int,
family : int,
index : int
content : bstr
]
Figure 4: CDDL representation of JPY message
The contents are DTLS encrypted. In CBOR diagnostic notation the
payload JPY[H(IP_P:p_P)], will look like:
[h'IP_p', p_P, family, ident, h'DTLS-payload']
On reception by the Registrar, the Registrar MUST verify that the
number of array elements is larger than or equal to 5, and reject the
message when the number of array elements is smaller than 5. After
replacing the 5th "content" element with the DTLS payload of the
response message and leaving all other array elements unchanged, the
Registrar returns the response message.
Examples are shown in Appendix A.
When additions are added to the array in later versions of this
protocol, any additional array elements (i.e., not specified by
current document) MUST be ignored by a receiver if it doesn't know
these elements. This approach allows evolution of the protocol while
maintaining backwards-compatibility. A version number isn't needed;
that number is defined by the length of the array. However, this
means that message elements are consistently added to earlier defined
elements to avoid ambiguities.
6. Discovery
It is assumed that Join Proxy seamlessly provides a coaps connection
between Pledge and Registrar. In particular this section extends
section 4.1 of [RFC8995] for the constrained case.
The discovery follows two steps with two alternatives for step 1:
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* Step 1. Two alternatives exist (near and remote):
- Near: the Pledge is one hop away from the Registrar. The
Pledge discovers the link-local address of the Registrar as
described in [I-D.ietf-ace-coap-est]. From then on, it follows
the BRSKI process as described in [I-D.ietf-ace-coap-est] and
[I-D.ietf-anima-constrained-voucher], using link-local
addresses.
- Remote: the Pledge is more than one hop away from a relevant
Registrar, and discovers the link-local address and join-port
of a Join Proxy. The Pledge then follows the BRSKI procedure
using the link-local address of the Join Proxy.
* Step 2. The enrolled Join Proxy discovers the join-port of the
Registrar.
The order in which the two alternatives of step 1 are tried is
installation dependent. The trigger for discovery in Step 2 in
implementation dependent.
Once a Pledge is enrolled, it may function as Join Proxy. The Join
Proxy functions are advertised as described below. In principle, the
Join Proxy functions are offered via a join-port, and not the
standard coaps port. Also, the Registrar offers a join-port to which
the stateless Join Proxy sends the JPY message. The Join Proxy and
Registrar show the extra join-port number when responding to a
/.well-known/core discovery request addressed to the standard coap/
coaps port.
Three discovery cases are discussed: Join Proxy discovers Registrar,
Pledge discovers Registrar, and Pledge discovers Join Proxy. Each
discovery case considers three alternatives: CoAP based discovery,
GRASP Based discovery, and 6tisch based discovery. The choice of
discovery mechanism depends on the type of installation, and
manufacturers can provide the pledge/join-proxy with support for more
than one discovery mechanism. The pledge/join-proxy can be designed
to dynamically try different discovery mechanisms until a successful
discovery mechanism is found, or the choice of discovery mechanism
could be configured during device installation.
6.1. Join Proxy discovers Registrar
In this section, the Join Proxy and Registrar are assumed to
communicate via Link-Local addresses. This section describes the
discovery of the Registrar by the Join Proxy.
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6.1.1. CoAP discovery
The discovery of the coaps Registrar, using coap discovery, by the
Join Proxy follows sections 6.3 and 6.5.1 of
[I-D.ietf-anima-constrained-voucher]. 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 coap://[IP_address]/.well-known/core?rt=brski.rjp
RES: 2.05 Content
<coaps://[IP_address]:join-port>; rt="brski.rjp"
The discoverable port numbers are usually returned for Join Proxy
resources in the <URI-Reference> of the payload (see section 5.1 of
[I-D.ietf-ace-coap-est]).
6.1.2. 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 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].
6.1.3. 6tisch discovery
The discovery of the Registrar by the Join Proxy uses the enhanced
beacons as discussed in [I-D.ietf-6tisch-enrollment-enhanced-beacon].
6.2. Pledge discovers Registrar
In this section, the Pledge and Registrar are assumed to communicate
via Link-Local addresses. This section describes the discovery of
the Registrar by the Pledge.
6.2.1. CoAP discovery
The discovery of the coaps Registrar, using coap discovery, by the
Pledge follows sections 6.3 and 6.5.1 of
[I-D.ietf-anima-constrained-voucher].
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6.2.2. GRASP discovery
This section is normative for uses with an ANIMA ACP. In the context
of autonomic networks, the Pledge uses the DULL GRASP M_FLOOD
mechanism to announce itself. Section 4.1.1 of [RFC8995] discusses
this in more detail. 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] .
6.2.3. 6tisch discovery
The discovery of Registrar by the Pledge uses the enhanced beacons as
discussed in [I-D.ietf-6tisch-enrollment-enhanced-beacon].
6.3. Pledge discovers Join Proxy
In this section, the Pledge and Join Proxy are assumed to communicate
via Link-Local addresses. This section describes the discovery of
the Join Proxy by the Pledge.
6.3.1. 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 [I-D.ietf-ace-coap-est]).
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6.3.2. GRASP discovery
This section is normative for uses with an ANIMA ACP. The Pledge
MUST listen for GRASP M_FLOOD [RFC8990] announcements of the
objective: "AN_Proxy". See section 4.1.1 [RFC8995] for the details
of the objective.
6.3.3. 6tisch discovery
The discovery of the Join Proxy by the Pledge uses the enhanced
beacons as discussed in [I-D.ietf-6tisch-enrollment-enhanced-beacon].
7. 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 to
make a choice between the two modes based on the available device
resources and network bandwidth.
+-------------+----------------------------+------------------------+
| Properties | Stateful mode | Stateless mode |
+-------------+----------------------------+------------------------+
| State |The Join Proxy needs | No information is |
| Information |additional storage to | maintained by the 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 5: Comparison between stateful and stateless mode
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8. 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.
It should be noted here that the contents of the CBOR map 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. If such
scenario needs to be avoided, then it is reasonable for the Join
Proxy to encrypt the CBOR array using a locally generated symmetric
key. The Registrar would not be able to examine the result, but it
does not need to do so. This is a topic for future work.
In some installations, level 2 protection is provided between all
member pairs of the mesh. In such an enviroment encryption of the
CBOR array is unnecessay because the level 2 protection already
provide it.
9. IANA Considerations
9.1. 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 (CoAP over DTLS) port of the constrained
Join Proxy.
Reference: [this document]
Attribute Value: brski.rjp
Description: This BRSKI resource type is used to query and return the
supported BRSKI JPY protocol port of the Registrar.
Reference: [this document]
9.2. service name and port number registry
This specification registers two service names under the "Service
Name and Transport Protocol Port Number" registry.
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Service Name: brski-jp
Transport Protocol(s): udp
Assignee: IESG <iesg@ietf.org>
Contact: IESG <iesg@ietf.org>
Description: Bootstrapping Remote Secure Key Infrastructure
constrained Join Proxy
Reference: [this document]
Service Name: brski-rjp
Transport Protocol(s): udp
Assignee: IESG <iesg@ietf.org>
Contact: IESG <iesg@ietf.org>
Description: Bootstrapping Remote Secure Key Infrastructure
Registrar join-port used by stateless constrained
Join Proxy
Reference: [this document]
10. Acknowledgements
Many thanks for the comments by Brian Carpenter, Esko Dijk, Russ
Housley, and Rob Wilton.
11. 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.
12. Changelog
12.1. 06 to 07
* AD review changes
12.2. 05 to 06
* RT value change to brski.jp and brski.rjp
* new registry values for IANA
* improved handling of jpy header array
12.3. 04 to 05
* Join Proxy and join-port consistent spelling
* some nits removed
* restructured discovery
* section
* rephrased parts of security section
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12.4. 03 to 04
* mail address and reference
12.5. 02 to 03
* Terminology updated
* Several clarifications on discovery and routability
* DTLS payload introduced
12.6. 01 to 02
* Discovery of Join Proxy and Registrar ports
12.7. 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
12.8. 00 to 00
* copied from vanderstok-anima-constrained-join-proxy-05
13. References
13.1. Normative References
[family] "Address Family Numbers", 19 October 2021,
<https://www.iana.org/assignments/address-family-numbers/
address-family-numbers.xhtml>.
[I-D.ietf-ace-coap-est]
Stok, P. V. D., Kampanakis, P., Richardson, M. C., and S.
Raza, "EST over secure CoAP (EST-coaps)", Work in
Progress, Internet-Draft, draft-ietf-ace-coap-est-18, 6
January 2020, <https://www.ietf.org/archive/id/draft-ietf-
ace-coap-est-18.txt>.
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[I-D.ietf-anima-constrained-voucher]
Richardson, M., Stok, P. V. D., Kampanakis, P., and E.
Dijk, "Constrained Bootstrapping Remote Secure Key
Infrastructure (BRSKI)", Work in Progress, Internet-Draft,
draft-ietf-anima-constrained-voucher-16, 14 February 2022,
<https://www.ietf.org/archive/id/draft-ietf-anima-
constrained-voucher-16.txt>.
[ieee802-1AR]
"IEEE 802.1AR Secure Device Identifier", 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>.
[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>.