Internet DRAFT - draft-ietf-anima-constrained-voucher
draft-ietf-anima-constrained-voucher
anima Working Group M. Richardson
Internet-Draft Sandelman Software Works
Updates: 8366, 8995 (if approved) P. van der Stok
Intended status: Standards Track vanderstok consultancy
Expires: 14 September 2023 P. Kampanakis
Cisco Systems
E. Dijk
IoTconsultancy.nl
13 March 2023
Constrained Bootstrapping Remote Secure Key Infrastructure (BRSKI)
draft-ietf-anima-constrained-voucher-20
Abstract
This document defines the Constrained Bootstrapping Remote Secure Key
Infrastructure (Constrained BRSKI) protocol, which provides a
solution for secure zero-touch bootstrapping of resource-constrained
(IoT) devices into the network of a domain owner. This protocol is
designed for constrained networks, which may have limited data
throughput or may experience frequent packet loss. Constrained BRSKI
is a variant of the BRSKI protocol, which uses an artifact signed by
the device manufacturer called the "voucher" which enables a new
device and the owner's network to mutually authenticate. While the
BRSKI voucher is typically encoded in JSON, Constrained BRSKI uses a
compact CBOR-encoded voucher. The BRSKI voucher is extended with new
data types that allow for smaller voucher sizes. The Enrollment over
Secure Transport (EST) protocol, used in BRSKI, is replaced with EST-
over-CoAPS; and HTTPS used in BRSKI is replaced with CoAPS. This
document Updates RFC 8366 and RFC 8995.
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-
voucher/.
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/. Subscribe at
https://www.ietf.org/mailman/listinfo/anima/.
Source for this draft and an issue tracker can be found at
https://github.com/anima-wg/constrained-voucher.
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Status of This Memo
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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
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 5
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Requirements Language . . . . . . . . . . . . . . . . . . . . 6
4. Overview of Protocol . . . . . . . . . . . . . . . . . . . . 6
5. Updates to RFC8366 and RFC8995 . . . . . . . . . . . . . . . 8
6. BRSKI-EST Protocol . . . . . . . . . . . . . . . . . . . . . 9
6.1. DTLS Connection . . . . . . . . . . . . . . . . . . . . . 9
6.1.1. DTLS Version . . . . . . . . . . . . . . . . . . . . 9
6.1.2. TLS Client Certificates: IDevID authentication . . . 9
6.1.3. DTLS Handshake Fragmentation Considerations . . . . . 10
6.1.4. Registrar and the Server Name Indicator (SNI) . . . . 10
6.2. Resource Discovery, URIs and Content Formats . . . . . . 11
6.2.1. RFC8995 Telemetry Returns . . . . . . . . . . . . . . 14
6.3. Join Proxy options . . . . . . . . . . . . . . . . . . . 14
6.4. Extensions to BRSKI . . . . . . . . . . . . . . . . . . . 15
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6.4.1. CoAP EST Resource Discovery and BRSKI . . . . . . . . 15
6.4.2. CoAP responses . . . . . . . . . . . . . . . . . . . 16
6.5. Extensions to EST-coaps . . . . . . . . . . . . . . . . . 16
6.5.1. Pledge Extensions . . . . . . . . . . . . . . . . . . 17
6.5.2. EST-client Extensions . . . . . . . . . . . . . . . . 18
6.5.3. Registrar Extensions . . . . . . . . . . . . . . . . 20
7. BRSKI-MASA Protocol . . . . . . . . . . . . . . . . . . . . . 21
7.1. Protocol and Formats . . . . . . . . . . . . . . . . . . 21
7.2. Registrar Voucher Request . . . . . . . . . . . . . . . . 22
7.3. MASA and the Server Name Indicator (SNI) . . . . . . . . 22
7.3.1. Registrar Certificate Requirement . . . . . . . . . . 23
8. Pinning in Voucher Artifacts . . . . . . . . . . . . . . . . 23
8.1. Registrar Identity Selection and Encoding . . . . . . . . 23
8.2. MASA Pinning Policy . . . . . . . . . . . . . . . . . . . 24
8.3. Pinning of Raw Public Keys . . . . . . . . . . . . . . . 25
8.4. Considerations for use of IDevID-Issuer . . . . . . . . . 26
9. Artifacts . . . . . . . . . . . . . . . . . . . . . . . . . . 27
9.1. Example Artifacts . . . . . . . . . . . . . . . . . . . . 28
9.1.1. Example Pledge voucher request (PVR) artifact . . . . 28
9.1.2. Example Registrar voucher request (RVR) artifact . . 28
9.1.3. Example voucher artifacts . . . . . . . . . . . . . . 29
9.2. Signing voucher and voucher request artifacts with
COSE . . . . . . . . . . . . . . . . . . . . . . . . . . 30
9.2.1. Signing of Registrar Voucher Request (RVR) . . . . . 31
9.2.2. Signing of Pledge Voucher Request (PVR) . . . . . . . 32
9.2.3. Signing of voucher by MASA . . . . . . . . . . . . . 33
10. Extensions to Discovery . . . . . . . . . . . . . . . . . . . 34
10.1. Discovery operations by Pledge . . . . . . . . . . . . . 35
10.1.1. GRASP discovery . . . . . . . . . . . . . . . . . . 36
10.1.2. CoAP Discovery . . . . . . . . . . . . . . . . . . . 37
10.2. Discovery operations by Join Proxy . . . . . . . . . . . 37
10.2.1. GRASP Discovery . . . . . . . . . . . . . . . . . . 38
10.2.2. CoAP discovery . . . . . . . . . . . . . . . . . . . 38
11. Deployment-specific Discovery Considerations . . . . . . . . 38
11.1. 6TSCH Deployments . . . . . . . . . . . . . . . . . . . 39
11.2. Generic networks using GRASP . . . . . . . . . . . . . . 39
11.3. Generic networks using mDNS . . . . . . . . . . . . . . 39
11.4. Thread networks using Mesh Link Establishment (MLE) . . 39
12. Design Considerations . . . . . . . . . . . . . . . . . . . . 40
13. Raw Public Key Use Considerations . . . . . . . . . . . . . . 40
13.1. The Registrar Trust Anchor . . . . . . . . . . . . . . . 40
13.2. The Pledge Voucher Request . . . . . . . . . . . . . . . 41
13.3. The Voucher Response . . . . . . . . . . . . . . . . . . 41
14. Use of constrained vouchers with HTTPS . . . . . . . . . . . 41
15. Security Considerations . . . . . . . . . . . . . . . . . . . 42
15.1. Duplicate serial-numbers . . . . . . . . . . . . . . . . 42
15.2. IDevID security in Pledge . . . . . . . . . . . . . . . 43
15.3. Security of CoAP and UDP protocols . . . . . . . . . . . 44
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15.4. Registrar Certificate may be self-signed . . . . . . . . 45
15.5. Use of RPK alternatives to proximity-registrar-cert . . 45
15.6. MASA support of CoAPS . . . . . . . . . . . . . . . . . 45
16. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 46
16.1. GRASP Discovery Registry . . . . . . . . . . . . . . . . 46
16.2. Resource Type Registry . . . . . . . . . . . . . . . . . 46
16.3. Media Types Registry . . . . . . . . . . . . . . . . . . 47
16.3.1. application/voucher-cose+cbor . . . . . . . . . . . 47
16.4. CoAP Content-Format Registry . . . . . . . . . . . . . . 47
16.5. Update to BRSKI Parameters Registry . . . . . . . . . . 48
17. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 48
18. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 49
19. References . . . . . . . . . . . . . . . . . . . . . . . . . 49
19.1. Normative References . . . . . . . . . . . . . . . . . . 49
19.2. Informative References . . . . . . . . . . . . . . . . . 52
Appendix A. Library Support for BRSKI . . . . . . . . . . . . . 55
A.1. OpensSSL . . . . . . . . . . . . . . . . . . . . . . . . 55
A.2. mbedTLS . . . . . . . . . . . . . . . . . . . . . . . . . 56
Appendix B. Constrained BRSKI-EST Message Examples . . . . . . . 57
B.1. enrollstatus . . . . . . . . . . . . . . . . . . . . . . 57
B.2. voucher_status . . . . . . . . . . . . . . . . . . . . . 58
Appendix C. COSE-signed Voucher (Request) Examples . . . . . . . 59
C.1. Pledge, Registrar and MASA Keys . . . . . . . . . . . . . 59
C.1.1. Pledge IDevID private key . . . . . . . . . . . . . . 59
C.1.2. Registrar private key . . . . . . . . . . . . . . . . 60
C.1.3. MASA private key . . . . . . . . . . . . . . . . . . 60
C.2. Pledge, Registrar, Domain CA and MASA Certificates . . . 61
C.2.1. Pledge IDevID Certificate . . . . . . . . . . . . . . 61
C.2.2. Registrar Certificate . . . . . . . . . . . . . . . . 63
C.2.3. Domain CA Certificate . . . . . . . . . . . . . . . . 65
C.2.4. MASA Certificate . . . . . . . . . . . . . . . . . . 67
C.3. COSE-signed Pledge Voucher Request (PVR) . . . . . . . . 69
C.4. COSE-signed Registrar Voucher Request (RVR) . . . . . . . 70
C.5. COSE-signed Voucher from MASA . . . . . . . . . . . . . . 73
Appendix D. Generating Certificates with OpenSSL . . . . . . . . 76
Appendix E. Pledge Device Class Profiles . . . . . . . . . . . . 80
E.1. Minimal Pledge . . . . . . . . . . . . . . . . . . . . . 80
E.2. Typical Pledge . . . . . . . . . . . . . . . . . . . . . 81
E.3. Full-featured Pledge . . . . . . . . . . . . . . . . . . 81
E.4. Comparison Chart of Pledge Classes . . . . . . . . . . . 81
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 82
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1. Introduction
Secure enrollment of new nodes into constrained networks with
constrained nodes presents unique challenges. As explained in
[RFC7228], such networks may have limited data throughput or may
experience frequent packet loss. In addition, its nodes may be
constrained by energy availability, memory space, and code size.
The Bootstrapping Remote Secure Key Infrastructure (BRSKI) protocol
described in [RFC8995] provides a solution for secure zero-touch
(automated) bootstrap of new (unconfigured) devices. In it, new
devices, such as IoT devices, are called "pledges", and equipped with
a factory-installed Initial Device Identifier (IDevID) (see
[ieee802-1AR]), are enrolled into a network.
The BRSKI solution described in [RFC8995] was designed to be modular,
and this document describes a version scaled to the constraints of
IoT deployments.
Therefore, this document uses a constrained version of the voucher
and voucher request artifacts described in [RFC8366bis], along with a
constrained version of the BRSKI protocol. This Constrained BRSKI
protocol makes use of the constrained CoAP-based version of EST (EST-
coaps from [RFC9148]) rather than the EST over HTTPS [RFC7030].
Constrained BRSKI is itself scalable to multiple resource levels
through the definition of optional functions. Appendix E illustrates
this.
In BRSKI, the [RFC8366] voucher is by default serialized to JSON with
a signature in CMS [RFC5652]. This document uses the new CBOR
[RFC8949] voucher serialization, as defined by [RFC8366bis], and
applies a new COSE [RFC9052] signature format.
This COSE-signed CBOR-encoded voucher is transported using both
secured CoAP and HTTPS. The CoAP connection (between Pledge and
Registrar) is to be protected by either OSCORE+EDHOC
[I-D.ietf-lake-edhoc] or DTLS (CoAPS). The HTTP connection (between
Registrar and MASA) is to be protected using TLS (HTTPS).
2. Terminology
The following terms are defined in [RFC8366bis], and are used
identically as in that document: artifact, domain, imprint, Join
Registrar/Coordinator (JRC), Manufacturer Authorized Signing
Authority (MASA), Pledge, Registrar, Trust of First Use (TOFU), and
Voucher.
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The following terms from [RFC8995] are used identically as in that
document: Domain CA, enrollment, IDevID, Join Proxy, LDevID,
manufacturer, nonced, nonceless, PKIX.
The term Pledge Voucher Request, or acronym PVR, is introduced to
refer to the voucher request between the Pledge and the Registrar.
The term Registrar Voucher Request, or acronym RVR, is introduced to
refer to the voucher request between the Registrar and the MASA.
This document uses the term "PKIX Certificate" to refer to the
X.509v3 profile described in [RFC5280].
In code examples, the string "<CODE BEGINS>" denotes the start of a
code example and "<CODE ENDS>" the end of the code example. Four
dots ("....") in a CBOR diagnostic notation byte string denotes a
further sequence of bytes that is not shown for brevity.
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.
4. Overview of Protocol
[RFC8366bis] defines a voucher that can assert proximity,
authenticates the Registrar, and can offer varying levels of anti-
replay protection. The proximity proof provided by a voucher is an
assertion that the Pledge and the Registrar are believed to be close
together, from a network topology point of view. Similar to BRSKI
[RFC8995], proximity is proven by making a DTLS connection between a
Pledge and a Registrar. The Pledge initiates this connection using a
link-local source address.
The secure DTLS connection is then used by the Pledge to make a
Pledge Voucher Request (PVR). The Registrar then includes the PVR
into its own Registrar Voucher Request (RVR), sent to an agent (MASA)
of the Pledge's manufacturer. The MASA verifies the PVR and RVR and
issues a signed voucher. The voucher provides an authorization
statement from the manufacturer indicating that the Registrar is the
intended owner of the Pledge. The voucher refers to the Registrar
through pinning of the Registrar's identity.
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After verification of the voucher, the Pledge enrolls into the
Registrar's domain by obtaining a certificate using the EST-coaps
[RFC9148] protocol, suitable for constrained devices. Once the
Pledge has obtained its domain identity (LDevID) in this manner, it
can use this identity to obtain network access credentials, to join
the local IP network. The method to obtain such credentials depends
on the particular network technology used and is outside the scope of
this document.
This document does not make any extensions to the semantic meaning of
vouchers, only the a new signature method based on COSE [RFC9052] is
defined to optimize for constrained devices and networks.
The two main parts of the BRSKI protocol are named separately in this
document: BRSKI-EST for the protocol between Pledge and Registrar,
and BRSKI-MASA for the protocol between the Registrar and the MASA.
Time-based vouchers are supported, but given that constrained devices
are extremely unlikely to have accurate time, their use will be
uncommon. Most Pledges using constrained vouchers will be online
during enrollment and will use live nonces to provide anti-replay
protection rather than expiry times.
[RFC8366bis] defines the two artifacts of a constrained voucher and a
constrained voucher request, which are used by Constrained BRSKI.
The constrained voucher request MUST be signed by the Pledge. It
signs using the private key associated with its IDevID certificate.
This also holds for the most constrained types of Pledges that are
unable to perform certain PKIX operations (such as certificate chain
validation). These types of Pledge still contain an IDevID identity
that is used for authentication. See Section 13 for additional
details on PKIX-less operations.
The constrained voucher MUST be signed by the MASA.
For the constrained voucher request (PVR) this document defines two
distinct methods for the Pledge to identify the Registrar: using
either the Registrar's full PKIX certificate, or using a Raw Public
Key (RPK). The method depends on which type of Registrar identity is
obtained by the Pledge during the DTLS handshake process. Normally,
the Pledge obtains the PKIX certificate. But when operating PKIX-
less as described in Section 13, the Registrar's RPK is obtained.
For the constrained voucher also both methods are supported to
indicate (pin) a trusted domain identity: using either a pinned
domain PKIX certificate, or a pinned RPK.
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The BRSKI architectures mandates that the MASA be aware of the
capabilities of the Pledge. This is not a drawback as a Pledges is
constructed by a manufacturer which also arranges for the MASA to be
aware of the inventory of devices. The MASA therefore knows if the
Pledge supports PKIX operations, or if it is limited to Raw Public
Key (RPK) operations only. Based upon this, the MASA can select
which attributes to use in the voucher for certain operations, like
the pinning of the Registrar identity.
5. Updates to RFC8366 and RFC8995
This section details the ways in which this document updates other
RFCs. The terminology for Updates is taken from
[I-D.kuehlewind-update-tag].
This document Updates [RFC8366]. It Extends [RFC8366] by creating a
new serialization format, and creates a mechanism to pin a Raw Public
Key (RPK).
This document Updates [RFC8995]. It Amends [RFC8995]
* by clarifying how pinning is done,
* adopts clearer explanation of the TLS Server Name Indicator (SNI),
see Section 6.1.4 and Section 7.3,
* clarifies when new trust anchors should be retrieved
(Section 6.5.1),
* clarifies what kinds of Extended Key Usage attributes are
appropriate for each certificate (Section 7.3.1).
It Extends [RFC8995] as follows:
* defines the CoAP version of the BRSKI protocol,
* makes some messages optional if the results can be inferred from
other validations (Section 6.5),
* provides the option to return trust anchors in a simpler format
(Section 6.5.3),
* extends the BRSKI-MASA protocol to carry the new voucher-cose+cbor
format.
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6. BRSKI-EST Protocol
This section describes the constrained BRSKI extensions to EST-coaps
[RFC9148] to transport the voucher between Registrar and Pledge
(optionally via a Join Proxy) over CoAP. The extensions are
targeting low-resource networks with small packets.
The constrained BRSKI-EST protocol described in this section is
between the Pledge and the Registrar only.
6.1. DTLS Connection
A DTLS connection is established between the Pledge and the
Registrar, similar to the TLS connection described in Section 5.1 of
[RFC8995]. This may occur via a Join Proxy as described in
Section 6.3. Regardless of the Join Proxy presence or particular
mechanism used, the DTLS connection should operate identically. The
Constrained BRSKI and EST-coaps requests and responses for
bootstrapping are carried over this DTLS connection.
6.1.1. DTLS Version
DTLS version 1.3 [RFC9147] SHOULD be used in any implementation of
this specification. An exception case where DTLS 1.2 [RFC6347] MAY
be used is in a Pledge that uses a software platform where DTLS 1.3
is not available (yet). This may occur for example if a legacy
device gets software-upgraded to support Constrained BRSKI. For this
reason, a Registrar MUST by default support both DTLS 1.3 and DTLS
1.2 client connections. However, for security reasons the Registrar
MAY be administratively configured to support only a particular DTLS
version or higher.
An EST-coaps server [RFC9148] that implements this specification also
MUST support both DTLS 1.3 and DTLS 1.2 client connections by
default. However, for security reasons the EST-coaps server MAY be
administratively configured to support only a particular DTLS version
or higher.
6.1.2. TLS Client Certificates: IDevID authentication
As described in Section 5.1 of [RFC8995], the Pledge makes a
connection to the Registrar using a TLS Client Certificate for
authentication. This is the Pledge's IDevID certificate.
Subsequently the Pledge will send a Pledge Voucher Request (PVR).
Further elements of Pledge authentication may be present in the PVR,
as detailed in Section 9.2.
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6.1.3. DTLS Handshake Fragmentation Considerations
DTLS includes a mechanism to fragment handshake messages. This is
described in Section 4.4 of [RFC9147]. Constrained BRSKI will often
be used with a Join Proxy, described in
[I-D.ietf-anima-constrained-join-proxy], which relays each DTLS
message to the Registrar. A stateless Join Proxy will need some
additional space to wrap each DTLS message inside a CoAP request,
while the wrapped result needs to fit in the maximum packet sized
guaranteed on 6LoWPAN networks, which is 1280 bytes.
For this reason it is RECOMMENDED that a PMTU of 1024 bytes be
assumed for the DTLS handshake and appropriate DTLS fragmentation is
used. It is unlikely that any Packet Too Big indications [RFC4443]
will be relayed by the Join Proxy back to the Pledge.
During the operation of the constrained BRSKI-EST protocol, the CoAP
Blockwise transfer mechanism will be used when message sizes exceed
the PMTU. A Pledge/EST-client on a constrained network MUST use the
(D)TLS maximum fragment length extension ("max_fragment_length")
defined in Section 4 of [RFC6066] with the maximum fragment length
set to a value of either 2^9 or 2^10.
6.1.4. Registrar and the Server Name Indicator (SNI)
The SNI issue described below affects [RFC8995] as well, and is
reported in errata: https://www.rfc-editor.org/errata/eid6648
As the Registrar is discovered by IP address, and typically connected
via a Join Proxy, the name of the Registrar is not known to the
Pledge. The Pledge will not know what the hostname for the Registrar
is, so it cannot do DNS-ID validation ([I-D.ietf-uta-rfc6125bis]) on
the Registrar's certificate. Instead, it must do validation using
the voucher.
As the Pledge does not know the name of the Registrar, the Pledge
cannot put any reasonable value into the [RFC6066] Server Name
Indicator (SNI). Threfore the Pledge SHOULD omit the SNI extension
as per Section 9.2 of [RFC8446].
In some cases, particularly while testing BRSKI, a Pledge may be
given the hostname of a particular Registrar to connect to directly.
Such a bypass of the discovery process may result in the Pledge
taking a different code branch to establish a DTLS connection, and
may result in the SNI being inserted by a library. The Registrar
MUST ignore any SNI seen.
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A primary motivation for making the SNI ubiquitous in the public web
is because it allows for multi-tenant hosting of HTTPS sites on a
single (scarce) IPv4 address. This consideration does not apply to
the server function in the Registrar because:
* it uses DTLS and CoAP, not HTTPS
* it typically uses IPv6, often [RFC4193] Unique Local Address,
which are plentiful
* the server port number is typically discovered, so multiple
tenants can be accomodated via unique port numbers.
As per Section 3.6.1 of [RFC7030], the Registrar certificate MUST
have the Extended Key Usage (EKU) id-kp-cmcRA. This certificate is
also used as a TLS Server Certificate, so it MUST also have the EKU
id-kp-serverAuth. See Appendix C.2.2 for an example of a Registrar
certificate with these EKUs set.
6.2. Resource Discovery, URIs and Content Formats
To keep the protocol messages small the EST-coaps and Constrained
BRSKI URIs are shorter than the respective EST and BRSKI URIs.
The EST-coaps server URIs differ from the EST URIs by replacing the
scheme https by coaps and by specifying shorter resource path names.
Below are some examples; the first two using a discovered short path
name and the last one using the well-known URI of EST which requires
no resource discovery by the EST client.
coaps://estserver.example.com/est/<short-name>
coaps://estserver.example.com/e/<short-name>
coaps://estserver.example.com/.well-known/est/<short-name>
Similarly the constrained BRSKI Registrar URIs differ from the RFC
8995 BRSKI URIs by replacing the scheme https by coaps and by
specifying shorter resource path names. Below are some examples; the
first two are using a discovered short path name and the last one is
using the well-known URI prefix which requires no resource discovery
by the Pledge. This is the same "/.well-known/brski" prefix as
defined in Section 5 of [RFC8995].
coaps://registrar.example.com/brski/<short-name>
coaps://registrar.example.com/b/<short-name>
coaps://registrar.example.com/.well-known/brski/<short-name>
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Figure 5 in Section 3.2.2 of [RFC7030] enumerates the operations
supported by EST, for which Table 1 in Section 5.1 of [RFC9148]
enumerates the corresponding EST-coaps short path names. Similarly,
Table 1 below provides the mapping from the supported BRSKI extension
URI paths to the Constrained BRSKI URI paths.
+=================+============================+
| BRSKI resource | Constrained BRSKI resource |
+=================+============================+
| /requestvoucher | /rv |
+-----------------+----------------------------+
| /voucher_status | /vs |
+-----------------+----------------------------+
| /enrollstatus | /es |
+-----------------+----------------------------+
Table 1: BRSKI URI paths mapping to
Constrained BRSKI URI paths
Note that /requestvoucher occurs between the Pledge and Registrar (in
scope of the BRSKI-EST protocol), but it also occurs between
Registrar and MASA. However, as described in Section 6, this section
and above table addresses only the BRSKI-EST protocol.
Pledges that wish to discover the available BRSKI bootstrap options/
formats, or reduce the size of the CoAP headers by eliminating the
"/.well-known/brski" path, can do a discovery operation using
Section 4 of [RFC6690] by sending a discovery query to the Registrar
over the secured DTLS connection.
For example, if the Registrar supports a short BRSKI URL (/b) and
supports the voucher format "application/voucher-cose+cbor" (836),
and status reporting in both CBOR and JSON formats, a CoAP resource
discovery request and response may look as follows:
REQ: GET /.well-known/core?rt=brski*
RES: 2.05 Content
Content-Format: 40
Payload:
</b>;rt=brski,
</b/rv>;rt=brski.rv;ct=836,
</b/vs>;rt=brski.vs;ct="50 60",
</b/es>;rt=brski.es;ct="50 60"
The Registrar is under no obligation to provide shorter URLs, and MAY
respond to this query with only the "/.well-known/brski/<short-name>"
resources for the short names as defined in Table 1.
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When responding to a discovery request for BRSKI resources, the
Registrar MAY in addition return the full resource paths and the
content types which are supported by these resources as shown in
above example. This is useful when multiple content types are
specified for a particular resource on the Registrar.
Registrars that have implemented shorter URLs MUST also respond in
equivalent ways to the corresponding "/.well-known/brski/<short-
name>" URLs, and MUST NOT distinguish between them. In particular, a
Pledge MAY use the longer (e.g. well-known) and shorter URLs in any
combination.
In case the client queries for only rt=brski type resources, the
Registrar responds with only the root path for the BRSKI resources
(rt=brski, resource /b in above example) and no others. (So, a query
for rt=brski, without the wildcard character.) This is shown in the
below example. The Pledge requests only the BRSKI root resource of
type rt=brski to check if short names are supported or not. In this
case, the Pledge is not interested to check what voucher request
formats, or status telemetry formats -- other than the mandatory
default formats -- are supported. The compact response then shows
that the Registrar indeed supports a short-name BRSKI resource at /b:
REQ: GET /.well-known/core?rt=brski
RES: 2.05 Content
Content-Format: 40
Payload:
</b>;rt=brski
In above example, the well-known resource present under /.well-known/
brski is not returned because this is assumed to be well-known to the
Pledge and would not require discovery anyway. Effectively, the
client is guided to preferably use the short names under resource /b
instead.
Without discovery, a Pledge can only use the longer well-known URI
for its voucher request, such as:
REQ: GET /.well-known/brski/rv
while with discovery of shorter URLs, a request such as:
REQ: GET /b/rv
is possible.
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The return of multiple content-types in the "ct" attribute allows the
Pledge to choose the most appropriate one for a particular operation,
and allows extension with new voucher (request) formats. Note that
only Content-Format 836 ("application/voucher-cose+cbor") is defined
in this document for the voucher request resource (/rv).
Content-Format 836 MUST be supported by the Registrar for the /rv
resource. If the "ct" attribute is not indicated for the /rv
resource in the link format description, this implies that at least
format 836 is supported.
Note that this specification allows for voucher-cose+cbor format
requests and vouchers to be transmitted over HTTPS, as well as for
voucher-cms+json and other formats yet to be defined over CoAP. The
burden for this flexibility is placed upon the Registrar. A Pledge
on constrained hardware is expected to support a single format only.
The Pledge and MASA need to support one or more formats (at least
format 836) for the voucher and for the voucher request. The MASA
needs to support all formats that the Pledge supports.
Section 11 details how the Pledge discovers the Registrar and Join
Proxy in different deployment scenarios.
6.2.1. RFC8995 Telemetry Returns
[RFC8995] defines two telemetry returns from the Pledge which are
sent to the Registrar. These are the BRSKI Status Telemetry
[RFC8995], Section 5.7 and the Enrollment Status Telemetry [RFC8995],
Section 5.9.4. These are two POST operations made the by Pledge at
two key steps in the process.
[RFC8995] defines the content of these POST operations in CDDL, which
are serialized as JSON. This document extends the list of acceptable
formats to CBOR as well as JSON, using the rules from [RFC8610].
The existing JSON format is described as CoAP Content-Format 50
("application/json"), and it MAY be supported. The new CBOR format
described as CoAP Content-Format 60 ("application/cbor"), MUST be
supported by the Registrar for both the /vs and /es resources.
6.3. Join Proxy options
[I-D.ietf-anima-constrained-join-proxy] specifies the details for a
stateful and stateless constrained Join Proxy which is equivalent to
[RFC8995], Section 4.
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6.4. Extensions to BRSKI
The following section explains extension within the BRSKI/CoAP
connection itself. Section 10 explains ways in which a pledge may
discover the capability to use constrained vouchers, and to use the
CoAPS transport.
6.4.1. CoAP EST Resource Discovery and BRSKI
Once the Pledge discovers an IP address and port number that connects
to the Registrar (probably via a Join Proxy), and it establishes a
DTLS connection.
No further discovery of hosts or port numbers is required, but a
pledge that can do more than one kind of enrollment (future work
offers protocols other than [RFC9148]), then a pledge may need to use
CoAP Discovery to determine what other protocols are available.
A Pledge that only supports the EST-coaps enrollment method SHOULD
NOT use CoAP discovery for BRSKI/EST resources. It is more efficient
to just try the supported enrollment method via the well-known BRSKI/
EST-coaps resources. This also avoids the Pledge having to do any
CoRE Link Format parsing, which is specified in [RFC9148],
Section 4.1.
The Registrar MUST support all of the EST resources at their default
".well-known" locations (on the specified port) as well as any
server-specific shorter form that might also be supported.
However, if discovery is done by the Pledge, it is possible for the
Registrar to return references to resources which are on different
port numbers. The Registrar SHOULD NOT use different ports numbers
by default, because a Pledge that is connected via a Join Proxy can
only access a single UDP port.
A Pledge that receives different port numbers or names SHOULD ignore
those port numbers and continue to use the DTLS connection that it
has already created. Or it MAY fail the entire transaction and look
for another Join Proxy/Registrar to do onboarding with. (If the
resources without the port numbers do not work, then the Pledge will
fail anyway)
A Registrar configured to never use Join Proxies MAY be configured to
use multiple port numbers. Therefore a Registrar MUST host all
discoverable BRSKI resources on the same (UDP) server port that the
Pledge's DTLS connection is using. However, using the same UDP
server port for all resources allows the Pledge to continue via the
same DTLS connection which is more efficient.
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6.4.2. CoAP responses
[RFC8995], Section 5 defines a number of HTTP response codes that the
Registrar is to return when certain conditions occur.
The 401, 403, 404, 406 and 415 response codes map directly to CoAP
codes 4.01, 4.03, 4.04, 4.06 and 4.15.
The 202 Retry process which occurs in the voucher request, is to be
handled in the same way as Section 5.7 of [RFC9148] process for
Delayed Responses.
6.5. Extensions to EST-coaps
This document extends [RFC9148], and it inherits the functions
described in that document: specifically, the mandatory Simple
(Re-)Enrollment (/sen and /sren) and Certification Authority
certificates request (/crts). Support for CSR Attributes Request
(/att) and server-side key generation (/skg, /skc) remains optional
for the EST server.
Collecting the resource definitions from both [RFC8995], [RFC7030],
and [RFC9148] results in the following shorter forms of URI paths for
the commonly used resources:
+=================+=========================+===============+
| BRSKI + EST | Constrained BRSKI + EST | Well-known |
| | | URI namespace |
+=================+=========================+===============+
| /requestvoucher | /rv | brski |
+-----------------+-------------------------+---------------+
| /voucher_status | /vs | brski |
+-----------------+-------------------------+---------------+
| /csrattrs | /att | est |
+-----------------+-------------------------+---------------+
| /simpleenroll | /sen | est |
+-----------------+-------------------------+---------------+
| /cacerts | /crts | est |
+-----------------+-------------------------+---------------+
| /enrollstatus | /es | brski |
+-----------------+-------------------------+---------------+
| /simplereenroll | /sren | est |
+-----------------+-------------------------+---------------+
Table 2: BRSKI/EST URI paths mapping to Constrained
BRSKI/EST short URI paths
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6.5.1. Pledge Extensions
This section defines extensions to the BRSKI Pledge, which are
applicable during the BRSKI bootstrap procedure. A Pledge which only
supports the EST-coaps enrollment method, SHOULD NOT use discovery
for EST-coaps resources, because it is more efficient to enroll (e.g.
/sen) via the well-known EST resource on the current DTLS connection.
This avoids an additional round-trip of packets and avoids the Pledge
having to unnecessarily implement CoRE Link Format parsing.
A constrained Pledge SHOULD NOT perform the optional EST "CSR
attributes request" (/att) to minimize network traffic. The Pledge
selects which attributes to include in the CSR.
One or more Subject Distinguished Name fields MUST be included. If
the Pledge has no specific information on what attributes/fields are
desired in the CSR, it MUST use the Subject Distinguished Name fields
from its IDevID unmodified. The Pledge can receive such information
via the voucher (encoded in a vendor-specific way) or via some other,
out-of-band means.
A constrained Pledge MAY use the following optimized EST-coaps
procedure to minimize network traffic.
1. if the voucher, that validates the current Registrar, contains a
single pinned domain CA certificate, the Pledge provisionally
considers this certificate as the EST trust anchor, as if it were
the result of "CA certificates request" (/crts) to the Registrar.
2. Using this CA certificate as trust anchor it proceeds with EST
simple enrollment (/sen) to obtain its provisionally trusted
LDevID certificate.
3. If the Pledge validates that the trust anchor CA was used to sign
its LDevID certificate, the Pledge accepts the pinned domain CA
certificate as the legitimate trust anchor CA for the Registrar's
domain and accepts the associated LDevID certificate.
4. If the trust anchor CA was NOT used to sign its LDevID
certificate, the Pledge MUST perform an actual "CA certificates
request" (/crts) to the EST server to obtain the EST CA trust
anchor(s) since these can differ from the (temporary) pinned
domain CA.
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5. When doing this /crts request, the Pledge MAY use a CoAP Accept
Option with value 287 ("application/pkix-cert") to limit the
number of returned EST CA trust anchors to only one. A
constrained Pledge MAY support only this format in a /crts
response, per Section 5.3 of [RFC9148].
6. If the Pledge cannot obtain the single CA certificate or the
finally validated CA certificate cannot be chained to the LDevID
certificate, then the Pledge MUST abort the enrollment process
and report the error using the enrollment status telemetry (/es).
Note that even though the Pledge may avoid performing any /crts
request using the above EST-coaps procedure during bootstrap, it
SHOULD support retrieval of the trust anchor CA periodically as
detailed in the next section.
6.5.2. EST-client Extensions
This section defines extensions to EST-coaps clients, used after the
BRSKI bootstrap procedure is completed. (Note that such client is
not called "Pledge" in this section, since it is already enrolled
into the domain.) A constrained EST-coaps client MAY support only
the Content-Format 287 ("application/pkix-cert") in a /crts response,
per Section 5.3 of [RFC9148]. In this case, it can only store one
trust anchor of the domain.
An EST-coaps client that has an idea of the current time (internally,
or via NTP) SHOULD consider the validity time of the trust anchor CA,
and MAY begin requesting a new trust anchor CA using the /crts
request when the CA has 50% of it's validity time (notAfter -
notBefore) left. A client without access to the current time cannot
decide if the trust anchor CA has expired, and SHOULD poll
periodically for a new trust anchor using the /crts request at an
interval of approximately 1 month. An EST-coaps server SHOULD
include the CoAP ETag Option in every response to a /crts request, to
enable clients to perform low-overhead validation whether their trust
anchor CA is still valid. The EST-coaps client SHOULD store the ETag
resulting from a /crts response in memory and SHOULD use this value
in an ETag Option in its next GET /crts request.
The above-mentioned limitation that an EST-coaps client may support
only one trust anchor CA is not an issue in case the domain trust
anchor remains stable. However, special consideration is needed for
cases where the domain trust anchor can change over time. Such a
change may happen due to relocation of the client device to a new
domain, or due to key update of the trust anchor as described in
[RFC4210], Section 4.4.
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From the client's viewpoint, a trust anchor change typically happens
during EST re-enrollment: a change of domain CA requires all devices
operating under the old domain CA to acquire a new LDevID issued by
the new domain CA. A client's re-enrollment may be triggered by
various events, such as an instruction to re-enroll sent by a domain
entity, or an imminent expiry of its LDevID certificate. How the re-
enrollment is explicitly triggered on the client by a domain entity,
such as a commissioner or a Registrar, is out of scope of this
specification.
The mechanism described in [RFC4210], Section 4.4 for Root CA key
update requires four certificates: OldWithOld, OldWithNew,
NewWithOld, and NewWithNew. The OldWithOld certificate is already
stored in the EST client's trust store. The NewWithNew certificate
will be distributed as the single certificate in a /crts response,
during EST re-enrollment. Since the EST client can only accept a
single certificate in a /crts response it implies that the EST client
cannot obtain the certificates OldWithNew and NewWithOld in this way,
to perform the complete verification of the new domain CA. Instead,
the client only verifies the EST-coaps server using its old domain CA
certificate in its trust store as detailed below, and based on this
trust in the active and valid DTLS connection it automatically trusts
the new (NewWithNew) domain CA certificate that the EST-coaps server
provides in the /crts response.
In this manner, even during rollover of trust anchors, it is possible
to have only a single trust anchor provided in a /crts response.
During the period of the certificate renewal, it is not possible to
create new communication channels between devices with NewCA
certificates devices with OldCA certificates. One option is that
devices should avoid restarting existing DTLS or OSCORE connections
during this interval that new certificates are being deployed. The
recommended period for certificate renewal is 24 hours. For re-
enrollment, the constrained EST-coaps client MUST support the
following EST-coaps procedure, where optional re-enrollment to a new
domain is under control of the EST-coaps server:
1. The client connects with DTLS to the EST-coaps server, and
authenticates with its present domain certificate (LDevID
certificate) as usual. The EST-coaps server authenticates itself
with its domain certificate that is trusted by the client, i.e.
it chains to the single trust anchor that the client has stored.
This is the "old" trust anchor, the one that will be eventually
replaced in case the server decides to re-enroll the client into
a new domain. The client also checks that the server is a
Registration Authority (RA) of the domain as required by
Section 3.6.1 of [RFC7030].
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2. The client performs the simple re-enrollment request (/sren) and
upon success it obtains a new LDevID.
3. The client verifies the new LDevID against its (single) existing
domain trust anchor. If it chains successfully, this means the
trust anchor did not change and the client MAY skip retrieving
the current CA certificate using the "CA certificates request"
(/crts). If it does not chain successfully, this means the trust
anchor was changed/updated and the client then MUST retrieve the
new domain trust anchor using the "CA certificates request"
(/crts).
4. If the client retrieved a new trust anchor in step 3, then it
MUST verify that the new trust anchor chains with the new LDevID
certificate it obtained in step 2. If it chains successfully,
the client stores both, accepts the new LDevID certificate and
stops using it prior LDevID certificate. If it does not chain
successfully, the client MUST NOT update its LDevID certificate,
it MUST NOT update its (single) domain trust anchor, and the
client MUST abort the enrollment process and MUST attempt to
report the error to the EST-coaps server using enrollment status
telemetry (/es).
Note that even though the EST-coaps client may skip the /crts request
in step 3, it SHOULD support retrieval of the trust anchor CA
periodically as detailed earlier in this section.
Note that an EST-coaps server that is also a Registrar will already
support the enrollment status telemetry resource (/es) in step 4,
while an EST-coaps server that purely implements [RFC9148], and not
the present specification, will not support this resource.
6.5.3. Registrar Extensions
A Registrar SHOULD host any discoverable EST-coaps resources on the
same (UDP) server port that the Pledge's DTLS initial connection is
using. This avoids the overhead of the Pledge reconnecting using
DTLS, when it performs EST enrollment after the BRSKI voucher
request.
The Content-Format 50 (application/json) MUST be supported and 60
(application/cbor) MUST be supported by the Registrar for the /vs and
/es resources.
Content-Format 836 MUST be supported by the Registrar for the /rv
resource.
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When a Registrar receives a "CA certificates request" (/crts) request
with a CoAP Accept Option with value 287 ("application/pkix-cert") it
SHOULD return only the single CA certificate that is the envisioned
or actual authority for the current, authenticated Pledge making the
request.
If the Pledge included in its request an Accept Option for only the
287 ("application/pkix-cert") Content Format, but the domain has been
configured to operate with multiple CA trust anchors only, then the
Registrar returns a 4.06 Not Acceptable error to signal that the
Pledge needs to use the Content Format 281 ("application/pkcs7-mime;
smime-type=certs-only") to retrieve all the certificates.
If the current authenticated client is an EST-coaps client that was
already enrolled in the domain, and the Registrar is configured to
assign this client to a new domain CA trust anchor during the next
EST re-enrollment procedure, then the Registrar MUST respond with the
new domain CA certificate in case the client performs the "CA
Certificates request" (/crts) with an Accept Option for 287 only.
This signals the client that a new domain is assigned to it. The
client follows the procedure as defined in Section 6.5.2.
7. BRSKI-MASA Protocol
This section describes extensions to and clarifications of the BRSKI-
MASA protocol between Registrar and MASA.
7.1. Protocol and Formats
Section 5.4 of [RFC8995] describes a connection between the Registrar
and the MASA as being a normal TLS connection using HTTPS. This
document does not change that. The Registrar MUST use the format
"application/voucher-cose+cbor" in its voucher request to MASA, when
the Pledge uses this format in its request to the Registrar
[RFC8995].
The MASA only needs to support formats for which it has constructed
Pledges that use that format.
The Registrar MUST use the same format for the RVR as the Pledge used
for its PVR.
The Registrar indicates the voucher format it wants to receive from
MASA using the HTTP Accept header. This format MUST be the same as
the format of the PVR, so that the Pledge can parse it.
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At the moment of writing the creation of coaps based MASAs is deemed
unrealistic. The use of CoAP for the BRSKI-MASA connection can be
the subject of another document. Some consideration was made to
specify CoAP support for consistency, but:
* the Registrar is not expected to be so constrained that it cannot
support HTTPS client connections.
* the technology and experience to build Internet-scale HTTPS
responders (which the MASA is) is common, while the experience
doing the same for CoAP is much less common.
* a Registrar is likely to provide onboarding services to both
constrained and non-constrained devices. Such a Registrar would
need to speak HTTPS anyway.
* a manufacturer is likely to offer both constrained and non-
constrained devices, so there may in practice be no situation in
which the MASA could be CoAP-only. Additionally, as the MASA is
intended to be a function that can easily be oursourced to a
third-party service provider, reducing the complexity would also
seem to reduce the cost of that function.
* security-related considerations: see Section 15.6.
7.2. Registrar Voucher Request
If the PVR contains a proximity assertion, the Registrar MUST
propagate this assertion into the RVR by including the "assertion"
field with the value "proximity". This conforms to the example in
Section 3.3 of [RFC8995] of carrying the assertion forward.
7.3. MASA and the Server Name Indicator (SNI)
A TLS/HTTPS connection is established between the Registrar and MASA.
Section 5.4 of [RFC8995] explains this process, and there are no
externally visible changes. A MASA that supports the unconstrained
voucher formats should be able to support constrained voucher formats
equally well.
There is no requirement that a single MASA be used for both
constrained and unconstrained voucher requests: the choice of MASA is
determined by the id-mod-MASAURLExtn2016 extension contained in the
IDevID.
The Registrar MUST do DNS-ID checks ([I-D.ietf-uta-rfc6125bis]) on
the contents of the certificate provided by the MASA.
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In constrast to the Pledge/Registrar situation, the Registrar always
knows the name of the MASA, and MUST always include an [RFC6066]
Server Name Indicator. The SNI is optional in TLS1.2, but common.
The SNI it considered mandatory with TLS1.3.
The presence of the SNI is needed by the MASA, in order for the
MASA's server to host multiple tenants (for different customers).
The Registrar SHOULD use a TLS Client Certificate to authenticate to
the MASA per Section 5.4.1 of [RFC8995]. If the certificate that the
Registrar uses is marked as a id-kp-cmcRA certificate, via Extended
Key Usage, then it MUST also have the id-kp-clientAuth EKU attribute
set.
7.3.1. Registrar Certificate Requirement
In summary for typical Registrar use, where a single Registrar
certificate is used, then the certificate MUST have EKU of: id-kp-
cmcRA, id-kp-serverAuth, id-kp-clientAuth.
8. Pinning in Voucher Artifacts
The voucher is a statement by the MASA for use by the Pledge that
provides the identity of the Pledge's owner. This section describes
how the owner's identity is determined and how it is specified within
the voucher.
8.1. Registrar Identity Selection and Encoding
Section 5.5 of [RFC8995] describes BRSKI policies for selection of
the owner identity. It indicates some of the flexibility that is
possible for the Registrar, and recommends the Registrar to include
only certificates in the voucher request (CMS) signing structure that
participate in the certificate chain that is to be pinned.
The MASA is expected to evaluate the certificates included by the
Registrar in its voucher request, forming them into a chain with the
Registrar's (signing) identity on one end. Then, it pins a
certificate selected from the chain. For instance, for a domain with
a two-level certification authority (see Figure 1), where the voucher
request has been signed by "Registrar", its signing structure
includes two additional CA certificates. The arrows in the figure
indicate the issuing of a certificate, i.e. author of (1) issued (2)
and author of (2) issued (3).
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.------------------.
| domain CA (1) |
| trust anchor |
'------------------'
|
v
.------------.
| domain (2) |
| Sub-CA |
'------------'
|
|
v
.----------------.
| domain |
| Registrar (3) |
| EE certificate |
'----------------'
Figure 1: Two-Level CA PKI
When the Registrar is using a COSE-signed constrained voucher request
towards MASA, instead of a regular CMS-signed voucher request, the
COSE_Sign1 object contains a protected and an unprotected header.
The Registrar MUST place all the certificates needed to validate the
signature chain from the Registrar on the RVR in an "x5bag" attribute
in the unprotected header [I-D.ietf-cose-x509].
The "x5bag" attribute is very important as it provides the required
signals from the Registrar to control what identity is pinned in the
resulting voucher. This is explained in the next section.
8.2. MASA Pinning Policy
The MASA, having assembled and verified the chain in the signing
structure of the voucher request needs to select a certificate to
pin. (For the case that only the Registrar's End-Entity certificate
is included, only this certificate can be selected and this section
does not apply.) The BRSKI policy for pinning by the MASA as
described in Section 5.5.2 of [RFC8995] leaves much flexibility to
the manufacturer.
The present document adds the following rules to the MASA pinning
policy to reduce the network load:
1. for a voucher containing a nonce, it SHOULD select the most
specific (lowest-level) CA certificate in the chain.
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2. for a nonceless voucher, it SHOULD select the least-specific
(highest-level) CA certificate in the chain that is allowed under
the MASA's policy for this specific domain.
The rationale for 1. is that in case of a voucher with nonce, the
voucher is valid only in scope of the present DTLS connection between
Pledge and Registrar anyway, so there is no benefit to pin a higher-
level CA. By pinning the most specific CA the constrained Pledge can
validate its DTLS connection using less crypto operations. The
rationale for pinning a CA instead of the Registrar's End-Entity
certificate directly is based on the following benefit on constrained
networks: the pinned certificate in the voucher can in common cases
be re-used as a Domain CA trust anchor during the EST enrollment and
during the operational phase that follows after EST enrollment, as
explained in Section 6.5.1.
The rationale for 2. follows from the flexible BRSKI trust model for,
and purpose of, nonceless vouchers (Sections 5.5.* and 7.4.1 of
[RFC8995]).
Refering to Figure 1 of a domain with a two-level certification
authority, the most specific CA ("Sub-CA") is the identity that is
pinned by MASA in a nonced voucher. A Registrar that wished to have
only the Registrar's End-Entity certificate pinned would omit the
"domain CA" and "Sub-CA" certificates from the voucher request.
In case of a nonceless voucher, depending on the trust level, the
MASA pins the "Registrar" certificate (low trust in customer), or the
"Sub-CA" certificate (in case of medium trust, implying that any
Registrar of that sub-domain is acceptable), or even the "domain CA"
certificate (in case of high trust in the customer, and possibly a
pre-agreed need of the customer to obtain flexible long-lived
vouchers).
8.3. Pinning of Raw Public Keys
Specifically for constrained use cases, the pinning of the raw public
key (RPK) of the Registrar is also supported in the constrained
voucher, instead of a PKIX certificate. If an RPK is pinned it MUST
be the RPK of the Registrar.
When the Pledge is known by MASA to support RPK but not PKIX
certificate operations, the voucher produced by the MASA pins the RPK
of the Registrar in either the "pinned-domain-pubk" or "pinned-
domain-pubk-sha256" field of a voucher. This is described in more
detail in [RFC8366bis] and Section 13. A Pledge that does not
support PKIX certificates cannot use EST to enroll; it has to use
another method for enrollment without certificates and the Registrar
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has to support this method also. It is possible that the Pledge will
not enroll, but instead only a network join operation will occur (See
[RFC9031]). How the Pledge discovers this method and details of the
enrollment method are out of scope of this document.
When the Pledge is known by MASA to support PKIX format certificates,
the "pinned-domain-cert" field present in a voucher typically pins a
domain certificate. That can be either the End-Entity certificate of
the Registrar, or the certificate of a domain CA of the Registrar's
domain as specified in Section 8.2. However, if the Pledge is known
to also support RPK pinning and the MASA intends to identify the
Registrar in the voucher (not the CA), then MASA MUST pin the RPK
(RPK3 in Figure 2) of the Registrar instead of the Registrar's End-
Entity certificate to save space in the voucher.
.------------.
| pub-CA (1) |
'------------'
|
v
.------------.
| sub-CA (2) |
'------------'
|
v
.--------------.
| Registrar(3) |
| RPK3 |
'--------------'
Figure 2: Raw Public Key (RPK) pinning
8.4. Considerations for use of IDevID-Issuer
[RFC8366] and [RFC8995] define the idevid-issuer attribute for
voucher and voucher-request (respectively), but they summarily
explain when to use it.
The use of idevid-issuer is provided so that the serial-number to
which the issued voucher pertains can be relative to the entity that
issued the devices' IDevID. In most cases there is a one to one
relationship between the trust anchor that signs vouchers (and is
trusted by the pledge), and the Certification Authority that signs
the IDevID. In that case, the serial-number in the voucher must
refer to the same device as the serial-number that is in IDevID
certificate.
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However, there situations where the one to one relationship may be
broken. This occurs whenever a manufacturer has a common MASA, but
different products (on different assembly lines) are produced with
identical serial numbers. A system of serial numbers which is just a
simple counter is a good example of this. A system of serial numbers
where there is some prefix relating the product type does not fit
into this, even if the lower digits are a counter.
It is not possible for the Pledge or the Registrar to know which
situation applies. The question to be answered is whether or not to
include the idevid-issuer in the PVR and the RVR. A second question
arisews as to what the format of the idevid-issuer contents are.
Analysis of the situation shows that the pledge never needs to
include the idevid-issuer in it's PVR, because the pledge's IDevID
certificate is available to the Registrar, and the Authority Key
Identifier is contained within that. The pledge therefore has no
need to repeat this.
For the RVR, the Registrar has to examine the pledge's IDevID
certificate to discover the serial number for the Registrar's Voucher
Request (RVR). This is clear in Section 5.5 of [RFC8995]. That
section also clarifies that the idevid-issuer is to be included in
the RVR.
Concerning the Authority Key Identifier, [RFC8366] specifies that the
entire object i.e. the extnValue OCTET STRING is to be included:
comprising the AuthorityKeyIdentifier, SEQUENCE, Choice as well as
the OCTET STRING that is the keyIdentifier.
9. Artifacts
There are significant changes to the voucher and voucher request
artifacts from [RFC8366] and [RFC8995] which are required for this
specification. The YANG ([RFC7950]) module changes and CBOR
serialization changes are described in [RFC8366bis]. That document
also assigns SID values to YANG elements in accordance with
[I-D.ietf-core-sid]. The present section provides some examples of
these artifacts and defines a new signature format for these, using
COSE.
The constrained voucher request adds the following fields: proximity-
registrar-pubk, proximity-registrar-pubk-sha256, proximity-registrar-
cert, and prior-signed-voucher-request.
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prior-signed-voucher-request is only used between the Registrar and
the MASA. proximity-registrar-pubk or proximity-registrar-pubk-sha256
optionally replaces proximity-registrar-cert for the most constrained
cases where RPK is used by the Pledge.
The constrained voucher adds the fields pinned-domain-pubk and
pinned-domain-pubk-sha256.
9.1. Example Artifacts
9.1.1. Example Pledge voucher request (PVR) artifact
Below, an example constrained voucher request (PVR) from a Pledge to
a Registrar is shown in CBOR diagnostic notation. Long CBOR byte
strings have been shortened (with "....") for readability. The enum
value of the assertion field is 2 for the "proximity" assertion as
defined in Section 6.3 of [RFC8366bis].
{
2501: { / SID=2501, ietf-voucher-request:voucher|voucher /
1: 2, / SID=2502, assertion 2 = "proximity"/
7: h'831D5198A6CA2C7F', / SID=2508, nonce /
12: h'30593013....D29A54', / SID=2513, proximity-registrar-pubk /
13: "JADA123456789" / SID=2514, serial-number /
}
}
The Pledge has included the item proximity-registrar-pubk which
carries the public key of the Registrar, instead of including the
full Registrar certificate in a proximity-registrar-cert item. This
is done to reduce the size of the PVR. Also note that the Pledge did
not include the created-on field since it lacks an internal real-time
clock and has no knowledge of the current time at the moment of
performing the bootstrapping.
9.1.2. Example Registrar voucher request (RVR) artifact
Next, an example constrained voucher request (RVR) from a Registrar
to a MASA is shown in CBOR diagnostic notation. The Registrar has
created this request triggered by the reception of the Pledge voucher
request (PVR) of the previous example. Again, long CBOR byte strings
have been shortened for readability.
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{
"ietf-request-voucher:voucher": {
"assertion": 2,
"created-on": "2022-12-05T19:19:19.536Z",
"nonce": h'831D5198A6CA2C7F',
"idevid-issuer": h'04183016....1736C3E0',
"serial-number": "JADA123456789",
"prior-signed-voucher-request": h'A11909....373839'
}
}
Note that the Registrar uses here the string data type for all key
names, instead of the more compact SID integer keys. This is fine
for any use cases where the network between Registrar and MASA is an
unconstrained network where data size is not critical. The
constrained voucher request format supports both the string and SID
key types.
9.1.3. Example voucher artifacts
Below, an example constrained voucher is shown in CBOR diagnostic
notation. It was created by a MASA in response to receiving the
Registrar Voucher Request (RVR) shown in Section 9.1.2. The enum
value of the assertion field is set to 2, to acknowledge to both the
Pledge and the Registrar that the proximity of the Pledge to the
Registrar is considered proven.
{
2451: { / SID = 2451, ietf-voucher:voucher|voucher /
1: 2, / SID = 2452, assertion "proximity" /
2: "2022-12-05T19:19:23Z", / SID = 2453, created-on /
3: false, / SID = 2454, domain-cert-revocation-checks /
7: h'831D5198A6CA2C7F', / SID = 2508, nonce /
8: h'308201F8....8CFF', / SID = 2459, pinned-domain-cert /
11: "JADA123456789" / SID = 2462, serial-number /
}
}
While the above example voucher includes the nonce from the PVR, the
next example is a nonce-less voucher. Instead of a nonce, it
includes an expires-on field with the date and time on which the
voucher expires. Because the MASA did not verify the proximity of
the Pledge and Registrar in this case, the assertion field contains a
weaker assertion of "verified" (0). This indicates that the MASA
verified the domain's ownership of the Pledge via some other means.
The enum value of the assertion field for "verified" is calculated to
be 0 by following the algorithm described in section 9.6.4.2 of
[RFC7950].
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{
2451: { / SID = 2451, ietf-voucher:voucher|voucher /
1: 0, / SID = 2452, assertion "verified" /
2: "2022-12-06T10:15:32Z", / SID = 2453, created-on /
3: false, / SID = 2454, domain-cert-revocation-checks /
4: "2022-12-13T10:15:32Z", / SID = 2455, expires-on /
8: h'308201F8....8CFF', / SID = 2459, pinned-domain-cert /
11: "JADA123456789" / SID = 2462, serial-number /
}
}
The voucher is valid for one week. To verify the voucher's validity,
the Pledge would either need an internal real-time clock or some
external means of obtaining the current time, such as Network Time
Protocol (NTP) or a radio time signal receiver.
9.2. Signing voucher and voucher request artifacts with COSE
The COSE_Sign1 structure is discussed in Section 4.2 of [RFC9052].
The CBOR object that carries the body, the signature, and the
information about the body and signature is called the COSE_Sign1
structure. It is used when only one signature is used on the body.
Support for ECDSA with SHA2-256 using curve secp256r1 (aka
prime256k1) is RECOMMENDED. Most current low power hardware has
support for acceleration of this algorithm. Future hardware designs
could omit this in favour of a newer algorithms. This is the ES256
keytype from Table 1 of [RFC9053]. Support for curve secp256k1 is
OPTIONAL.
Support for EdDSA using Curve 25519 is RECOMMENDED in new designs if
hardware support is available. This is keytype EDDSA (-8) from
Table 2 of [RFC9053]. A "crv" parameter is necessary to specify the
Curve, which from Table 18. The 'kty' field MUST be present, and it
MUST be 'OKP'. (Table 17)
A transition towards EdDSA is occurring in the industry. Some
hardware can accelerate only some algorithms with specific curves,
other hardware can accelerate any curve, and still other kinds of
hardware provide a tool kit for acceleration of any eliptic curve
algorithm.
In general, the Pledge is expected to support only a single
algorithm, while the Registrar, usually not constrained, is expected
to support a wide variety of algorithms: both legacy ones and up-and-
coming ones via regular software updates.
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An example of the supported COSE_Sign1 object structure containing a
Pledge Voucher Request (PVR) is shown in Figure 3.
18( / tag for COSE_Sign1 /
[
h'A10126', / protected COSE header encoding: {1: -7} /
/ which means { "alg": ES256 } /
{}, / unprotected COSE header parameters /
h'A119....3839', / voucher-request binary content (in CBOR) /
h'4567....1234' / voucher-request binary Sign1 signature /
]
)
Figure 3: COSE_Sign1 PVR example in CBOR diagnostic notation
The [COSE-registry] specifies the integers/encoding for the "alg"
field in Figure 3. The "alg" field restricts the key usage for
verification of this COSE object to a particular cryptographic
algorithm.
9.2.1. Signing of Registrar Voucher Request (RVR)
A Registrar MUST include a COSE "x5bag" structure in the RVR as
explained in Section 8.1. Figure 4 shows an example Registrar
Voucher Request (RVR) that includes the x5bag as an unprotected
header parameter (32). The bag contains two certificates in this
case.
18( / tag for COSE_Sign1 /
[
h'A10126', / protected COSE header encoding: {1: -7} /
/ which means { "alg": ES256 } /
{
32: [h'308202....9420AE', h'308201....E08CFF'] / x5bag /
},
h'A178....7FED', / voucher-request binary content (in CBOR) /
h'E1B7....2925' / voucher-request binary Sign1 signature /
]
)
Figure 4: COSE_Sign1 RVR example in CBOR diagnostic notation
A "kid" (key ID) field is optionally present in the unprotected COSE
header parameters map of a COSE object. If present, it identifies
the public key of the key pair that was used to sign the COSE
message. The value of the key identifier "kid" parameter may be in
any format agreed between signer and verifier. Usually a hash of the
public key is used to identify the public key; but the choice of key
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identifier method is vendor-specific. If "kid" is not present, then
a verifying party needs to use other context information to retrieve
the right public key to verify the COSE_Sign1 object against.
By default, a Registrar does not include a "kid" parameter in the RVR
since the signing key is already identified by the signing
certificates included in the COSE "x5bag" structure. A Registrar
nevertheless MAY use a "kid" parameter in its RVR to identify its
signing key/identity.
The method of generating such "kid" value is vendor-specific and
SHOULD be configurable in the Registrar to support commonly used
methods. In order to support future business cases and supply chain
integrations, a Registrar using the "kid" field MUST be configurable,
on a per-manufacturer basis, to select a particular method for
generating the "kid" value such that it is compatible with the method
that the manufacturer. Both binary and string values MUST be
supported per [RFC9052], respectively encoded in the "kid" field
using a CBOR byte string (bstr) or text string (tstr).
9.2.2. Signing of Pledge Voucher Request (PVR)
Like in the RVR, a "kid" (key ID) field is also optionally present in
the PVR. It can be used to identify the signing key/identity to the
MASA.
A Pledge by default SHOULD NOT use a "kid" parameter in its PVR,
because its signing key is already identified by the Pledge's unique
serial number that is included in the PVR and (by the Registrar) in
the RVR. This achieves the smallest possible PVR data size while
still enabling the MASA to verify the PVR. Still, when required the
Pledge MAY use a "kid" parameter in its PVR to help the MASA identify
the right public key to verify against. This can occur for example
if a Pledge has multiple IDevID identities. The "kid" parameter in
this case may be a simple integer identifying one out of N identities
present, or it may be a hash of the public key, or anything else the
Pledge vendor decides. A Registrar normally SHOULD ignore a "kid"
parameter used in a received PVR, as this information is intended for
the MASA. In other words, there is no need for the Registrar to
verify the contents of this field, but it may include it in an audit
log.
The example in Figure 5 shows a PVR with the "kid" parameter present.
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18( / tag for COSE_Sign1 /
[
h'A10126', / protected COSE header encoding: {1: -7} /
/ which means { "alg": ES256 } /
{
4: h'59AB3E' / COSE "kid" header parameter /
},
h'A119....3839', / voucher-request binary content (in CBOR) /
h'5678....7890' / voucher-request binary Sign1 signature /
]
)
Figure 5: COSE_Sign1 PVR example with "kid" field present
The Pledge SHOULD NOT use the "x5bag" structure in the PVR. A
Registrar that processes a PVR with an "x5bag" structure MUST ignore
it, and MUST use only the TLS Client Certificate extension for
authentication of the Pledge.
A situation where the Pledge MAY use the x5bag structure is for
communication of certificate chains to the MASA. This would arise in
some vendor- specific situations involving outsourcing of MASA
functionality, or rekeying of the IDevID certification authority.
In Appendix C further examples of signed PVRs are shown.
9.2.3. Signing of voucher by MASA
The MASA SHOULD NOT use a "kid" parameter in the voucher response,
because the MASA's signing key is already known to the Pledge.
Still, where needed the MASA MAY use a "kid" parameter in the voucher
response to help the Pledge identify the right MASA public key to
verify against. This can occur for example if a Pledge has multiple
IDevID identities.
The MASA SHOULD NOT include an x5bag attribute in the voucher
response - the exception is if the MASA knows that the Pledge doesn't
pre-store the signing public key and certificate, and thus the MASA
needs to provide a cert or cert chain that will enable linking the
signing identity to the pre-stored Trust Anchor (CA) in the Pledge.
This approach is not recommended, because including certificates in
the x5bag attribute will significantly increase the size of the
voucher which impacts operations on constrained networks.
If the MASA signing key is based upon a PKI (see
[I-D.richardson-anima-masa-considerations] Section 2.3), and the
Pledge only pre-stores a manufacturer (root) CA identity in its Trust
Store which is not the identity that signs the voucher, then a
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certificate chain needs to be included with the voucher in order for
the Pledge to validate the MASA signing CA's signature by validating
the chain up to the CA in its Trust Store.
In BRSKI CMS signed vouchers [RFC8995], the CMS structure has a place
for such certificates. In the COSE-signed constrained vouchers
described in this document, the x5bag attribute [I-D.ietf-cose-x509]
is used to contain the needed certificates to form the chain. A
Registrar MUST NOT remove the x5bag attribute from the unprotected
COSE header parameters when sending the voucher back to the Pledge.
In Figure 6 an example is shown of a COSE-signed voucher. This
example shows the common case where the "x5bag" attribute is not
used.
18( / tag for COSE_Sign1 /
[
h'A10126', / protected COSE header encoding: {1: -7} /
/ which means { "alg": ES256 } /
{}, / unprotected COSE header parameters /
h'A119....3839', / voucher binary content (in CBOR) /
h'2A2C....7FBF' / voucher binary Sign1 signature by MASA /
]
)
Figure 6: COSE_Sign1 signed voucher in CBOR diagnostic notation
10. Extensions to Discovery
It is assumed that a Join Proxy as defined in
[I-D.ietf-anima-constrained-join-proxy] seamlessly provides a
(relayed) DTLS connection between the Pledge and the Registrar. To
use a Join Proxy, a Pledge needs to discover it. For Pledge
discovery of a Join Proxy, this section extends Section 4.1 of
[RFC8995] for the constrained BRSKI case.
In general, the Pledge may be one or more hops away from the
Registrar, where one hop means the Registrar is a direct link-local
neighbor of the Pledge. The case of one hop away can be considered
as a degenerate case, because a Join Proxy is not really needed then.
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The degenerate case would be unusual in constrained wireless network
deployments, because a Registrar would typically not have a wireless
network interface of the type used for constrained devices. Rather,
it would have a high-speed network interface. Nevertheless, the
situation where the Registrar is one hop away from the Pledge could
occur in various cases like wired IoT networks or in wireless
constrained networks where the Pledge is in radio range of a 6LoWPAN
Border Router (6LBR) and the 6LBR happens to host a Registrar.
In order to support the degenerate case, the Registrar SHOULD
announce itself as if it were a Join Proxy -- though it would
actually announce its real (stateful) Registrar CoAPS endpoint. No
actual Join Proxy functionality is then required on the Registrar.
So, a Pledge only needs to discover a Join Proxy, regardless of
whether it is one or more than one hop away from a relevant
Registrar. It first discovers the link-local address and the join-
port of a Join Proxy. The Pledge then follows the constrained BRSKI
procedure of initiating a DTLS connection using the link-local
address and join-port of the Join Proxy.
Once enrolled, a Pledge itself may function as a Join Proxy. The
decision whether or not to provide this functionality depends upon
many factors and is out of scope for this document. Such a decision
might depend upon the amount of energy available to the device, the
network bandwidth available, as well CPU and memory availability.
The process by which a Pledge discovers the Join Proxy, and how a
Join Proxy discovers the location of the Registrar, are the subject
of the remainder of this section. Further details on both these
topics are provided in [I-D.ietf-anima-constrained-join-proxy].
10.1. Discovery operations by Pledge
The Pledge must discover the address/port and protocol with which to
communicate. The present document only defines coaps (CoAP over
DTLS) as a protocol.
Note that the identifying the format of the voucher request and the
voucher is not a required part of the Pledge's discovery operation.
It is assumed that all Registrars support all relevant voucher(-
request) formats, while the Pledge only supports a single format. A
Pledge that makes a voucher request to a Registrar that does not
support that format will receive a CoAP 4.06 Not Acceptable status
code and the bootstrap attempt will fail.
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10.1.1. 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, using DTLS.
[M_FLOOD, 12340815, h'fe800000000000000000000000000001', 180000,
[["AN_Proxy", 4, 1, "DTLS"],
[O_IPv6_LOCATOR,
h'fe800000000000000000000000000001', IPPROTO_UDP, 5684]]]
Figure 7: Example of Join Proxy announcement message
Note that a Join Proxy that supports also supports RFC8995 onboarding
using HTTPS may announce more than one objective. Objectives with an
empty objective-value (whether CBOR NULL or an empty string) refer to
[RFC8995] defaults.
Here is an example of an announcement that offers both constrained
and unconstrained onboarding:
[M_FLOOD, 12340851, h'fe800000000000000000000000000001', 180000,
[["AN_Proxy", 4, 1, ""],
[O_IPv6_LOCATOR,
h'fe800000000000000000000000000001', IPPROTO_TCP, 4443],
["AN_Proxy", 4, 1, "DTLS"],
[O_IPv6_LOCATOR,
h'fe800000000000000000000000000001', IPPROTO_UDP, 5684]]
Figure 8: Example of Join Proxy announcing two bootstrap methods
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10.1.2. CoAP Discovery
The details on CoAP discovery of a Join Proxy by a Pledge are
provided in Section 5.2.1 of [I-D.ietf-anima-constrained-join-proxy].
In this section some examples of CoAP discovery interactions are
given.
Below, a typical example is provided showing the Pledge's CoAP
request and the Join Proxy's CoAP response. The Join Proxy responds
with a link-local source address, which is the same address as
indicated in the URI-reference element ([RFC6690]) in the discovery
response payload. The Join Proxy has a dedicated port 8485 opened
for DTLS connections of Pledges.
REQ: GET coap://[ff02::fd]/.well-known/core?rt=brski.jp
RES: 2.05 Content
<coaps://[fe80::c78:e3c4:58a0:a4ad]:8485>;rt=brski.jp
The next example shows a Join Proxy that uses the default CoAPS port
5684 for DTLS connections of Pledges. In this case, the Join Proxy
host is not using port 5684 for any other purposes.
REQ: GET coap://[ff02::fd]/.well-known/core?rt=brski.jp
RES: 2.05 Content
<coaps://[fe80::c78:e3c4:58a0:a4ad]>;rt=brski.jp
In the following example, two Join Proxies respond to the multicast
query. The Join Proxies use a slightly different CoRE Link Format
encoding. While the first encoding is more compact, both encodings
are allowed per [RFC6690]. The Pledge may now select one of the two
Join Proxies for initiating its DTLS connection.
REQ: GET coap://[ff02::fd]/.well-known/core?rt=brski*
RES: 2.05 Content
<coaps://[fe80::c78:e3c4:58a0:a4ad]:8485>;rt=brski.jp
RES: 2.05 Content
<coaps://[fe80::d359:3813:f382:3b23]:63245>;rt="brski.jp"
10.2. Discovery operations by Join Proxy
The Join Proxy needs to discover a Registrar, at the moment it needs
to relay data towards the Registrar or prior to that moment.
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10.2.1. GRASP Discovery
This section is normative for uses with an ANIMA ACP. In the context
of autonomic networks, the Registrar announces itself to a stateful
Join Proxy using ACP instance of GRASP using M_FLOOD messages.
Section 4.3 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_join_registrar, identical to [RFC8995].
* the objective name is "BRSKI_JP".
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 Registrar on example port
5684, which is the standard CoAPS port number.
[M_FLOOD, 51804321, h'fda379a6f6ee00000200000064000001', 180000,
[["AN_join_registrar", 4, 255, "BRSKI_JP"],
[O_IPv6_LOCATOR,
h'fda379a6f6ee00000200000064000001', IPPROTO_UDP, 5684]]]
Figure 9: Example of Registrar announcement message
The Registrar uses a routable address that can be used by enrolled
constrained Join Proxies. The address will typically be a Unique
Local Address (ULA) as in the example, but could also be a Global
Unicast Address (GUA).
10.2.2. CoAP discovery
Further details on CoAP discovery of the Registrar by a Join Proxy
are provided in Section 5.1.1 of
[I-D.ietf-anima-constrained-join-proxy].
11. Deployment-specific Discovery Considerations
This section details how discovery is done in specific deployment
scenarios.
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11.1. 6TSCH Deployments
In 6TISCH networks, the Constrained Join Proxy (CoJP) mechanism is
described in [RFC9031]. Such networks are expected to use a
[I-D.ietf-lake-edhoc] to do key management. This is the subject of
future work. The Enhanced Beacon has been extended in [RFC9032] to
allow for discovery of the Join Proxy.
11.2. Generic networks using GRASP
[RFC8995] defines a mechanism for the Pledge to discover a Join Proxy
by listening for [RFC8990] GRASP messages. This mechanism can be
used on any network which does not have another more specific
mechanism. This mechanism supports mesh networks, and can also be
used over unencrypted WIFI.
11.3. Generic networks using mDNS
[RFC8995] also defines a non-normative mechanism for the Pledge to
discover a Join Proxy by doing mDNS queries. This mechanism can be
used on any network which does not have another recommended
mechanism. This mechanism does not easily support mesh networks. It
can be used over unencrypted WIFI.
11.4. Thread networks using Mesh Link Establishment (MLE)
Thread [Thread] is a wireless mesh network protocol based on 6LoWPAN
[RFC6282] and other IETF protocols. In Thread, a new device
discovers potential Thread networks and Thread routers to join by
using the Mesh Link Establishment (MLE)
[I-D.ietf-6lo-mesh-link-establishment] protocol. MLE uses the UDP
port number 19788. The new device sends discovery requests on
different IEEE 802.15.4 radio channels, to which routers (if any
present) respond with a discovery response containing information
about their respective network. Once a suitable router is selected
the new device initiates a DTLS transport-layer secured connection to
the network's commissioning application, over a link-local single
radio hop to the selected Thread router. This link is not yet
secured at the radio level: link-layer security will be set up once
the new device is approved by the commissioning application to join
the Thread network, and it gets provisioned with network access
credentials.
The Thread router acts here as a Join Proxy. The MLE discovery
response message contains UDP port information to signal the new
device which port to use for its DTLS connection.
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12. Design Considerations
The design considerations for the CBOR encoding of vouchers are much
the same as for JSON vouchers in [RFC8366]. One key difference is
that the names of the leaves in the YANG definition do not affect the
size of the resulting CBOR, as the SID ([I-D.ietf-core-sid])
translation process assigns integers to the names.
Any POST request to the Registrar with resource /vs or /es returns a
2.04 Changed response with empty payload. The client should be aware
that the server may use a piggybacked CoAP response (ACK, 2.04) but
may also respond with a separate CoAP response, i.e. first an (ACK,
0.0) that is an acknowledgement of the request reception followed by
a (CON, 2.04) response in a separate CoAP message.
13. Raw Public Key Use Considerations
This section explains techniques to reduce the data volume and
complexity of the BRSKI bootstrap. The use of a raw public key (RPK)
in the pinning process can significantly reduce the number of bytes
sent over the wire and round trips, and reduce the code footprint in
a Pledge, but it comes with a few significant operational
limitations.
13.1. The Registrar Trust Anchor
When the Pledge first connects to the Registrar, the connection to
the Registrar is provisional, as explained in Section 5.6.2 of
[RFC8995]. The Registrar normally provides its public key in a
TLSServerCertificate, and the Pledge uses that to validate that
integrity of the (D)TLS connection, but it does not validate the
identity of the provided certificate.
As the TLSServerCertificate object is never verified directly by the
Pledge, sending it can be considered superfluous. So instead of
using a (TLSServer)Certificate of type X509 (see section 4.4.2 of
[RFC8446]), a RawPublicKey object (as defined by [RFC7250]) is used.
A Registrar operating in a mixed environment can determine whether to
send a Certificate or a Raw Public Key to the Pledge: this is
signaled by the Pledge. In the case it needs an RPK, it includes the
server_certificate_type of RawPublicKey. This is shown in section 5
of [RFC7250].
The Pledge always sends a client_certificate_type of X509 (not an
RPK), so that the Registrar can properly identify the Pledge and
distill the MASA URI information from its IDevID certificate.
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13.2. The Pledge Voucher Request
The Pledge puts the Registrar's public key into the proximity-
registrar-pubk field of the Pledge Voucher Request (PVR). (The
proximity-registrar-pubk-sha256 can also be used for efficiency, if
the 32-bytes of a SHA256 hash turns out to be smaller than a typical
ECDSA key.)
As the format of this pubk field is identical to the TLS RawPublicKey
data object, no manipulation at all is needed to insert this into the
PVR.
13.3. The Voucher Response
A returned voucher will have a pinned-domain-pubk field with the
identical key as was found in the proximity-registrar-pubk field
above, as well as being identical to the Registrar's RPK in the
currently active DTLS connection.
Validation of this key by the Pledge is what takes the DTLS
connection out of the provisional state; see Section 5.6.2 of
[RFC8995] for more details.
The voucher needs to be validated first by the Pledge. The Pledge
needs to have a public key to validate the signature from the MASA on
the voucher.
The MASA's public key counterpart of the (private) MASA signing key
MUST be already installed in the Pledge at manufacturing time.
Otherwise, the Pledge cannot validate the voucher's signature.
14. Use of constrained vouchers with HTTPS
This specification contains two extensions to [RFC8995]: a
constrained voucher format (COSE), and a constrained transfer
protocol (CoAP).
On constrained networks with constrained devices, it make senses to
use both together. However, this document does not mandate that this
be the only way.
A given constrained device design and software may be re-used for
multiple device models, such as a model having only an IEEE 802.15.4
radio, or a model having only an IEEE 802.11 (Wi-Fi) radio, or a
model having both these radios. A manufacturer of such device models
may wish to have code only for the use of the constrained voucher
format (COSE), and use it on all supported radios including the IEEE
802.11 radio. For this radio, the software stack to support HTTP/TLS
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may be already integrated into the radio module hence it is
attractive for the manufacturer to reuse this. This type of approach
is supported by this document. In the case that HTTPS is used, the
regular long [RFC8995] resource names are used, together with the new
"application/voucher-cose+cbor" media type described in this
document. For status telemetry requests, the Pledge may use either
one or both of the formats defined in Section 6.2.1. A Registrar
MUST support both formats.
Other combinations are possible, but they are not enumerated here.
New work such as [I-D.ietf-anima-jws-voucher] provides new formats
that may be useable over a number of different transports. In
general, sending larger payloads over constrained networks makes less
sense, while sending smaller payloads over unconstrained networks is
perfectly acceptable.
The Pledge will in most cases support a single voucher format, which
it uses without negotiation i.e. without discovery of formats
supported. The Registrar, being unconstrained, is expected to
support all voucher formats. There will be cases where a Registrar
does not support a new format that a new Pledge uses, and this is an
unfortunate situation that will result in lack of interoperation.
The responsability for supporting new formats is on the Registrar.
15. Security Considerations
15.1. Duplicate serial-numbers
In the absense of correct use of idevid-issuer by the Registrar as
detailed in Section 8.4, it would be possible for a malicious
Registrar to use an unauthorized voucher for a device. This would
apply only to the case where a Manufacturer Authorized Signing
Authority (MASA) is trusted by different products from the same
manufacturer, and the manufacturer has duplicated serial numbers as a
result of a merge, acquisition or mis-management.
For example, imagine the same manufacturer makes light bulbs as well
as gas centrifuges, and said manufacturer does not uniquely allocate
product serial numbers. This attack only works for nonceless
vouchers. The attacker has obtained a light bulb which happens to
have the same serial-number as a gas centrofuge which it wishes to
obtain access. The attacker performs a normal BRSKI onboarding for
the light bulb, but then uses the resulting voucher to onboard the
gas centrofuge. The attack requires that the gas centrofuge be
returned to a state where it is willing to perform a new onboarding
operation.
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This attack is prevented by the mechanism of having the Registrar
include the idevid-issuer in the RVR, and the MASA including it in
the resulting voucher. The idevid-issuer is not included by default:
a MASA needs to be aware if there are parts of the organization which
duplicates serial numbers, and if so, include it.
15.2. IDevID security in Pledge
The security of this protocol depends upon the Pledge identifying
itself to the Registrar using it's manufacturer installed
certificate: the IDevID certificate. Associated with this
certificate is the IDevID private key, known only to the Pledge.
Disclosure of this private key to an attacker would permit the
attacker to impersonate the Pledge towards the Registrar, probably
gaining access credentials to that Registrar's network.
If the IDevID private key disclosure is known to the manufacturer,
there is little recourse other than recall of the relevant part
numbers. The process for communicating this recall would be within
the BRSKI-MASA protocol. Neither this specification nor [RFC8995]
provides for consultation of a Certification Revocation List (CRL) or
Open Certificate Status Protocol (OCSP) by a Registrar when
evaluating an IDevID certificate. However, the BRSKI-MASA protocol
submits the IDevID from the Registrar to the manufacturer's MASA and
a manufacturer would have an opportunity to decline to issue a
voucher for a device which they believe has become compromised.
It may be difficult for a manufacturer to determine when an IDevID
private key has been disclosed. Two situations present themselves:
in the first situation a compromised private key might be reused in a
counterfeit device, which is sold to another customer. This would
present itself as an onboarding of the same device in two different
networks. The manufacturer may become suspicious seeing two voucher
requests for the same device from different Registrars. Such
activity could be indistinguishable from a device which has been
resold from one operator to another, or re-deployed by an operator
from one location to another.
In the second situation, an attacker having compromised the IDevID
private key of a device might then install malware into the same
device and attempt to return it to service. The device, now blank,
would go through a second onboarding process with the original
Registrar. Such a Registrar could notice that the device has been
"factory reset" and alert the operator to this situation. One remedy
against the presence of malware is through the use of Remote
Attestation such as described in [I-D.ietf-rats-architecture].
Future work will need to specify a background-check Attestation flow
as part of the voucher-request/voucher-response process. Attestation
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may still require access to a private key (e.g. IDevID private key)
in order to sign Evidence, so a primary goal should be to keep any
private key safe within the Pledge.
In larger, more expensive, systems there is budget (power, space, and
bill of materials) to include more specific defenses for a private
key. For instance, this includes putting the IDevID private key in a
Trusted Platform Module (TPM), or use of Trusted Execution
Environments (TEE) for access to the key. On smaller IoT devices,
the cost and power budget for an extra part is often prohibitive.
It is becoming more and more common for CPUs to have an internal set
of one-time fuses that can be programmed (often they are "burnt" by a
laser) at the factory. This section of memory is only accessible in
some priviledged CPU state. The use of this kind of CPU is
appropriate as it provides significant resistance against key
disclosure even when the device can be disassembled by an attacker.
In a number of industry verticals, there is increasing concern about
counterfeit parts. These may be look-alike parts created in a
different factory, or parts which are created in the same factory
during an illegal night-shift, but which are not subject to the
appropriate level of quality control. The use of a manufacturer-
signed IDevID certificate provides for discovery of the pedigree of
each part, and this often justifies the cost of the security measures
associated with storing the private key.
15.3. Security of CoAP and UDP protocols
Section 7.1 explains that no CoAPS version of the BRSKI-MASA protocol
is proposed. The connection from the Registrar to the MASA continues
to be HTTPS as in [RFC8995]. This has been done to simplify the MASA
deployment for the manufacturer, because no new protocol needs to be
enabled on the server.
The use of UDP protocols across the open Internet is sometimes
fraught with security challenges. Denial-of-service attacks against
UDP based protocols are trivial as there is no three-way handshake as
done for TCP. The three-way handshake of TCP guarantees that the
node sending the connection request is reachable using the origin IP
address. While DTLS contains an option to do a stateless challenge
-- a process actually stronger than that done by TCP -- it is not yet
common for this mechanism to be available in hardware at multigigabit
speeds. It is for this reason that this document defines using HTTPS
for the Registrar to MASA connection.
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15.4. Registrar Certificate may be self-signed
The provisional (D)TLS connection formed by the Pledge with the
Registrar does not authenticate the Registrar's identity. This
Registrar's identity is validated by the [RFC8366bis] voucher that is
issued by the MASA, signed with an anchor that was built-in to the
Pledge.
The Registrar may therefore use any certificate, including a self-
signed one. The only restrictions on the certificate is that it MUST
have EKU bits set as detailed in Section 7.3.1.
15.5. Use of RPK alternatives to proximity-registrar-cert
In [RFC8366bis], Part voucher-request-artifact two compact
alternative fields for proximity-registrar-cert are defined that
include an RPK: proximity-registrar-pubk and proximity-registrar-
pubk-sha256. The Pledge can use these fields in its PVR to identify
the Registrar based on its public key only. Since the full
certificate of the proximate Registrar is not included, use of these
fields by a Pledge implies that a Registrar could insert another
certificate with the same public key identity into the RVR. For
example, an older or a newer version of its certificate. The MASA
will not be able to detect such act by the Registrar. But since any
'other' certificate the Registrar could insert in this way still
encodes its identity the additional risk of using the RPK
alternatives is neglible.
When a Registrar sees a PVR that uses one of proximity-registrar-pubk
or proximity-registrar-pubk-sha256 fields, this implies the Registrar
must include the certificate identified by these fields into its RVR.
Otherwise, the MASA is unable to verify proximity. This requirement
is already implied by the "MUST" requirement in Section 8.1.
15.6. MASA support of CoAPS
The use of CoAP for the BRSKI-MASA connection is not in scope of the
current document. The following security considerations have led to
this choice of scope:
* the technology and experience to build secure Internet-scale HTTPS
responders (which the MASA is) is common, while the experience in
doing the same for CoAP is much less common.
* in many enterprise networks, outgoing UDP connections are often
treated as suspicious, which could effectively block CoAP
connections for some firewall configurations.
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* reducing the complexity of MASA (i.e. less protocols supported)
would also reduce its potential attack surface, which is relevant
since the MASA is 24/7 exposed on the Internet and accepting
(untrusted) incoming connections.
16. IANA Considerations
16.1. GRASP Discovery Registry
IANA is asked to extend the registration of the "AN_Proxy" (without
quotes) in the "GRASP Objective Names" table in the Grasp Parameter
registry. This document should also be cited for this existing
registration, because Section 10.1.1 defines the new protocol value
IPPROTO_UDP for the objective.
IANA is asked to extend the registration of the "AN_join_registrar"
(without quotes) in the "GRASP Objective Names" table in the Grasp
Parameter registry. This document should also be cited for this
existing registration, because Section 10.2.1 adds the objective
value "BRSKI_JP" to the objective.
16.2. Resource Type Registry
Additions to the sub-registry "Resource Type Link Target Attribute
Values", within the "CoRE Parameters" IANA registry are specified
below.
Reference: [This RFC]
+===========+==========================================+
| Attribute | Description |
+===========+==========================================+
| brski | Root path of Bootstrapping Remote Secure |
| | Key Infrastructure (BRSKI) resources |
+-----------+------------------------------------------+
| brski.rv | BRSKI request voucher resource |
+-----------+------------------------------------------+
| brski.vs | BRSKI voucher status telemetry resource |
+-----------+------------------------------------------+
| brski.es | BRSKI enrollment status telemetry |
| | resource |
+-----------+------------------------------------------+
Table 3: Resource Type (rt) link target attribute
values for IANA registration
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16.3. Media Types Registry
This section registers the 'application/voucher-cose+cbor' in the
IANA "Media Types" registry. This media type is used to indicate
that the content is a CBOR voucher or voucher request signed with a
COSE_Sign1 structure [RFC9052].
16.3.1. application/voucher-cose+cbor
Type name: application
Subtype name: voucher-cose+cbor
Required parameters: N/A
Optional parameters: N/A
Encoding considerations: binary (CBOR)
Security considerations: Security Considerations of [This RFC].
Interoperability considerations: The format is designed to be
broadly interoperable.
Published specification: [This RFC]
Applications that use this media type: ANIMA, 6tisch, and other
zero-touch onboarding systems
Fragment identifier considerations: The syntax and semantics of
fragment identifiers specified for application/voucher-cose+cbor
are as specified for application/cbor. (At publication of this
document, there is no fragment identification syntax defined for
application/cbor.)
Additional information:
Deprecated alias names for this type: N/A
Magic number(s): N/A
File extension(s): .vch
Macintosh file type code(s): N/A
Person & email address to contact for further information: IETF
ANIMA Working Group (anima@ietf.org) or IETF Operations and
Management Area Working Group (opsawg@ietf.org)
Intended usage: COMMON
Restrictions on usage: N/A
Author: ANIMA WG
Change controller: IETF
Provisional registration? (standards tree only): NO
16.4. CoAP Content-Format Registry
IANA has allocated ID 836 from the sub-registry "CoAP Content-
Formats".
Media type Encoding ID Reference
----------------------------- --------- ---- ----------
application/voucher-cose+cbor - 836 [This RFC]
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16.5. Update to BRSKI Parameters Registry
This section updates the BRSKI Well-Known URIs sub-registry of the
IANA Bootstrapping Remote Secure Key Infrastructures (BRSKI)
Parameters Registry by adding a new column "Short URI". The contents
of this field MUST be specified for any newly registered URI as
follows:
Short URI: A short name for the "URI" resource that can be used by a
Constrained BRSKI Pledge in a CoAP request to the Registrar. In case
the "URI" resource is only used between Registrar and MASA, the value
"--" is registered denoting that a short name is not applicable.
The initial contents of the sub-registry including the new column are
as follows:
+=================+=======+=======================+============+
| URI | Short | Description | Reference |
| | URI | | |
+=================+=======+=======================+============+
| requestvoucher | rv | Request voucher: | [RFC8995], |
| | | Pledge to Registrar, | [This RFC] |
| | | and Registrar to MASA | |
+-----------------+-------+-----------------------+------------+
| voucher_status | vs | Voucher status | [RFC8995], |
| | | telemetry: Pledge to | [This RFC] |
| | | Registrar | |
+-----------------+-------+-----------------------+------------+
| requestauditlog | -- | Request audit log: | [RFC8995] |
| | | Registrar to MASA | |
+-----------------+-------+-----------------------+------------+
| enrollstatus | es | Enrollment status | [RFC8995], |
| | | telemetry: Pledge to | [This RFC] |
| | | Registrar | |
+-----------------+-------+-----------------------+------------+
Table 4: Update of the BRSKI Well-Known URI Sub-Registry
17. Acknowledgements
We are very grateful to Jim Schaad for explaining COSE/CMS choices
and for correcting early versions of the COSE_Sign1 objects.
Michel Veillette did extensive work on _pyang_ to extend it to
support the SID allocation process, and this document was among its
first users.
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Russ Housley , Daniel Franke and Henk Birkholtz provided review
feedback.
The BRSKI design team has met on many Tuesdays and Thursdays for
document review. The team includes: Aurelio Schellenbaum , David von
Oheimb , Steffen Fries , Thomas Werner and Toerless Eckert .
18. Changelog
-11 to -20 (For change details see GitHub issues https://github.com/
anima-wg/constrained-voucher/issues and related Pull Requests.)
-10 Design considerations extended Examples made consistent
-08 Examples for cose_sign1 are completed and improved.
-06 New SID values assigned; regenerated examples
-04 voucher and request-voucher MUST be signed examples for signed
request are added in appendix IANA SID registration is updated SID
values in examples are aligned signed cms examples aligned with new
SIDs
-03
Examples are inverted.
-02
Example of requestvoucher with unsigned appllication/cbor is added
attributes of voucher "refined" to optional
CBOR serialization of vouchers improved
Discovery port numbers are specified
-01
application/json is optional, application/cbor is compulsory
Cms and cose mediatypes are introduced
19. References
19.1. Normative References
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[I-D.ietf-cose-x509]
Schaad, J., "CBOR Object Signing and Encryption (COSE):
Header Parameters for Carrying and Referencing X.509
Certificates", Work in Progress, Internet-Draft, draft-
ietf-cose-x509-09, 13 October 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-cose-
x509-09>.
[I-D.ietf-uta-rfc6125bis]
Saint-Andre, P. and R. Salz, "Service Identity in TLS",
Work in Progress, Internet-Draft, draft-ietf-uta-
rfc6125bis-11, 2 March 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-uta-
rfc6125bis-11>.
[ieee802-1AR]
IEEE Standard, "IEEE 802.1AR Secure Device Identifier",
2009, <http://standards.ieee.org/findstds/
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>.
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005,
<https://www.rfc-editor.org/info/rfc4193>.
[RFC4210] Adams, C., Farrell, S., Kause, T., and T. Mononen,
"Internet X.509 Public Key Infrastructure Certificate
Management Protocol (CMP)", RFC 4210,
DOI 10.17487/RFC4210, September 2005,
<https://www.rfc-editor.org/info/rfc4210>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/info/rfc5280>.
[RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
RFC 5652, DOI 10.17487/RFC5652, September 2009,
<https://www.rfc-editor.org/info/rfc5652>.
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[RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS)
Extensions: Extension Definitions", RFC 6066,
DOI 10.17487/RFC6066, January 2011,
<https://www.rfc-editor.org/info/rfc6066>.
[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>.
[RFC7250] Wouters, P., Ed., Tschofenig, H., Ed., Gilmore, J.,
Weiler, S., and T. Kivinen, "Using Raw Public Keys in
Transport Layer Security (TLS) and Datagram Transport
Layer Security (DTLS)", RFC 7250, DOI 10.17487/RFC7250,
June 2014, <https://www.rfc-editor.org/info/rfc7250>.
[RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
RFC 7950, DOI 10.17487/RFC7950, August 2016,
<https://www.rfc-editor.org/info/rfc7950>.
[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>.
[RFC8366bis]
Watsen, K., Richardson, M., Pritikin, M., Eckert, T. T.,
and Q. Ma, "A Voucher Artifact for Bootstrapping
Protocols", Work in Progress, Internet-Draft, draft-ietf-
anima-rfc8366bis-07, 7 February 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-anima-
rfc8366bis-07>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
[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>.
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[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>.
[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>.
[RFC9031] Vučinić, M., Ed., Simon, J., Pister, K., and M.
Richardson, "Constrained Join Protocol (CoJP) for 6TiSCH",
RFC 9031, DOI 10.17487/RFC9031, May 2021,
<https://www.rfc-editor.org/info/rfc9031>.
[RFC9032] Dujovne, D., Ed. and M. Richardson, "Encapsulation of
6TiSCH Join and Enrollment Information Elements",
RFC 9032, DOI 10.17487/RFC9032, May 2021,
<https://www.rfc-editor.org/info/rfc9032>.
[RFC9052] Schaad, J., "CBOR Object Signing and Encryption (COSE):
Structures and Process", STD 96, RFC 9052,
DOI 10.17487/RFC9052, August 2022,
<https://www.rfc-editor.org/info/rfc9052>.
[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>.
19.2. Informative References
[COSE-registry]
IANA, "CBOR Object Signing and Encryption (COSE)
registry", 2017,
<https://www.iana.org/assignments/cose/cose.xhtml>.
[I-D.ietf-6lo-mesh-link-establishment]
Kelsey, R., "Mesh Link Establishment", Work in Progress,
Internet-Draft, draft-ietf-6lo-mesh-link-establishment-00,
1 December 2015, <https://datatracker.ietf.org/doc/html/
draft-ietf-6lo-mesh-link-establishment-00>.
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[I-D.ietf-anima-constrained-join-proxy]
Richardson, M., Van der Stok, P., and P. Kampanakis,
"Constrained Join Proxy for Bootstrapping Protocols", Work
in Progress, Internet-Draft, draft-ietf-anima-constrained-
join-proxy-13, 23 October 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-anima-
constrained-join-proxy-13>.
[I-D.ietf-anima-jws-voucher]
Werner, T. and M. Richardson, "JWS signed Voucher
Artifacts for Bootstrapping Protocols", Work in Progress,
Internet-Draft, draft-ietf-anima-jws-voucher-06, 22
February 2023, <https://datatracker.ietf.org/doc/html/
draft-ietf-anima-jws-voucher-06>.
[I-D.ietf-core-sid]
Veillette, M., Pelov, A., Petrov, I., Bormann, C., and M.
Richardson, "YANG Schema Item iDentifier (YANG SID)", Work
in Progress, Internet-Draft, draft-ietf-core-sid-20, 1
March 2023, <https://datatracker.ietf.org/doc/html/draft-
ietf-core-sid-20>.
[I-D.ietf-lake-edhoc]
Selander, G., Mattsson, J. P., and F. Palombini,
"Ephemeral Diffie-Hellman Over COSE (EDHOC)", Work in
Progress, Internet-Draft, draft-ietf-lake-edhoc-19, 3
February 2023, <https://datatracker.ietf.org/doc/html/
draft-ietf-lake-edhoc-19>.
[I-D.ietf-rats-architecture]
Birkholz, H., Thaler, D., Richardson, M., Smith, N., and
W. Pan, "Remote ATtestation procedureS (RATS)
Architecture", Work in Progress, Internet-Draft, draft-
ietf-rats-architecture-22, 28 September 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-rats-
architecture-22>.
[I-D.kuehlewind-update-tag]
Kühlewind, M. and S. Krishnan, "Definition of new tags for
relations between RFCs", Work in Progress, Internet-Draft,
draft-kuehlewind-update-tag-04, 12 July 2021,
<https://datatracker.ietf.org/doc/html/draft-kuehlewind-
update-tag-04>.
[I-D.richardson-anima-masa-considerations]
Richardson, M. and W. Pan, "Operatonal Considerations for
Voucher infrastructure for BRSKI MASA", Work in Progress,
Internet-Draft, draft-richardson-anima-masa-
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considerations-07, 11 July 2022,
<https://datatracker.ietf.org/doc/html/draft-richardson-
anima-masa-considerations-07>.
[RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet
Control Message Protocol (ICMPv6) for the Internet
Protocol Version 6 (IPv6) Specification", STD 89,
RFC 4443, DOI 10.17487/RFC4443, March 2006,
<https://www.rfc-editor.org/info/rfc4443>.
[RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6
Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
DOI 10.17487/RFC6282, September 2011,
<https://www.rfc-editor.org/info/rfc6282>.
[RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link
Format", RFC 6690, DOI 10.17487/RFC6690, August 2012,
<https://www.rfc-editor.org/info/rfc6690>.
[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>.
[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>.
[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>.
[RFC9053] Schaad, J., "CBOR Object Signing and Encryption (COSE):
Initial Algorithms", RFC 9053, DOI 10.17487/RFC9053,
August 2022, <https://www.rfc-editor.org/info/rfc9053>.
[Thread] Thread Group, Inc, "Thread support page, White Papers",
November 2022,
<https://www.threadgroup.org/support#Whitepapers>.
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Appendix A. Library Support for BRSKI
For the implementation of BRSKI, the use of a software library to
manipulate certificates and use crypto algorithms is often
beneficial. Two C-based examples are OpenSSL and mbedtls. Others
more targeted to specific platforms or languages exist. It is
important to realize that the library interfaces differ significantly
between libraries.
Libraries do not support all known crypto algorithms. Before
deciding on a library, it is important to look at their supported
crypto algorithms and the roadmap for future support. Apart from
availability, the library footprint, and the required execution
cycles should be investigated beforehand.
The handling of certificates usually includes the checking of a
certificate chain. In some libraries, chains are constructed and
verified on the basis of a set of certificates, the trust anchor
(usually self signed root CA), and the target certificate. In other
libraries, the chain must be constructed beforehand and obey order
criteria. Verification always includes the checking of the
signatures. Less frequent is the checking the validity of the dates
or checking the existence of a revoked certificate in the chain
against a set of revoked certificates. Checking the chain on the
consistency of the certificate extensions which specify the use of
the certificate usually needs to be programmed explicitly.
A libary can be used to construct a (D)TLS connection. It is useful
to realize that differences beetween (D)TLS implementations will
occur due to the differences in the certicate checks supported by the
library. On top of that, checks between client and server
certificates enforced by (D)TLS are not always helpful for a BRSKI
implementation. For example, the certificates of Pledge and
Registrar are usually not related when the BRSKI protocol is started.
It must be verified that checks on the relation between client and
server certificates do not hamper a succeful DTLS connection
establishment.
A.1. OpensSSL
From openssl's apps/verify.c :
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<CODE BEGINS>
X509 *x = NULL;
int i = 0, ret = 0;
X509_STORE_CTX *csc;
STACK_OF(X509) *chain = NULL;
int num_untrusted;
x = load_cert(file, "certificate file");
if (x == NULL)
goto end;
csc = X509_STORE_CTX_new();
if (csc == NULL) {
BIO_printf(bio_err, "error %s: X.509 store context"
"allocation failed\n",
(file == NULL) ? "stdin" : file);
goto end;
}
X509_STORE_set_flags(ctx, vflags);
if (!X509_STORE_CTX_init(csc, ctx, x, uchain)) {
X509_STORE_CTX_free(csc);
BIO_printf(bio_err,
"error %s: X.509 store context"
"initialization failed\n",
(file == NULL) ? "stdin" : file);
goto end;
}
if (tchain != NULL)
X509_STORE_CTX_set0_trusted_stack(csc, tchain);
if (crls != NULL)
X509_STORE_CTX_set0_crls(csc, crls);
i = X509_verify_cert(csc);
X509_STORE_CTX_free(csc);
<CODE ENDS>
A.2. mbedTLS
<CODE BEGINS>
mbedtls_x509_crt cert;
mbedtls_x509_crt caCert;
uint32_t certVerifyResultFlags;
...
int result = mbedtls_x509_crt_verify(&cert, &caCert, NULL, NULL,
&certVerifyResultFlags, NULL, NULL);
<CODE ENDS>
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Appendix B. Constrained BRSKI-EST Message Examples
This appendix extends the message examples from Appendix A of
[RFC9148] with constrained BRSKI messages. The CoAP headers are only
fully worked out for the first example, enrollstatus.
B.1. enrollstatus
A coaps enrollstatus message from Pledge to Registrar can be as
follows:
REQ: POST coaps://192.0.2.1:8085/b/es
Content-Format: 60
Payload: <binary CBOR encoding of an enrollstatus map>
The corresponding CoAP header fields for this request are shown
below.
Ver = 1
T = 0 (CON)
TKL = 1
Code = 0x02 (0.02 is POST method)
Message ID = 0xab0f
Token = 0x4d
Options
Option (Uri-Path)
Option Delta = 0xb (option nr = 11)
Option Length = 0x1
Option Value = "b"
Option (Uri-Path)
Option Delta = 0x0 (option nr = 11)
Option Length = 0x2
Option Value = "es"
Option (Content-Format)
Option Delta = 0x1 (option nr = 12)
Option Length = 0x1
Option Value = 60 (application/cbor)
Payload Marker = 0xFF
Payload = A26776657273696F6E0166737461747573F5 (18 bytes binary)
The Uri-Host and Uri-Port Options are omitted because they coincide
with the transport protocol (UDP) destination address and port
respectively.
The above binary CBOR enrollstatus payload looks as follows in CBOR
diagnostic notation, for the case of enrollment success:
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{
"version": 1,
"status": true
}
Alternatively the payload could look as follows in case of enrollment
failure, using the reason field to describe the failure:
Payload = A36776657273696F6E0166737461747573F466726561736F6E782A3C
496E666F726D61746976652068756D616E207265616461626C652065
72726F72206D6573736167653E (69 bytes binary)
{
"version": 1,
"status": false,
"reason": "<Informative human readable error message>"
}
To indicate successful reception of the enrollmentstatus telemetry
report, a response from the Registrar may then be:
2.04 Changed
Which in case of a piggybacked response has the following CoAP header
fields:
Ver=1
T=2 (ACK)
TKL=1
Code = 0x44 (2.04 Changed)
Message ID = 0xab0f
Token = 0x4d
B.2. voucher_status
A coaps voucher_status message from Pledge to Registrar can be as
follows:
REQ: POST coaps://[2001:db8::2:1]/.well-known/brski/vs
Content-Format: 60 (application/cbor)
Payload =
A46776657273696F6E0166737461747573F466726561736F6E7828496E66
6F726D61746976652068756D616E2D7265616461626C65206572726F7220
6D6573736167656E726561736F6E2D636F6E74657874A100764164646974
696F6E616C20696E666F726D6174696F6E
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The request payload above is binary CBOR but represented here in
hexadecimal for readability. Below is the equivalent CBOR diagnostic
format.
{
"version": 1,
"status": false,
"reason": "Informative human-readable error message",
"reason-context": { 0: "Additional information" }
}
A success response without payload will then be sent by the Registrar
back to the Pledge to indicate reception of the telemetry report:
2.04 Changed
Appendix C. COSE-signed Voucher (Request) Examples
This appendix provides examples of COSE-signed voucher requests and
vouchers. First, the used test keys and certificates are described,
followed by examples of a constrained PVR, RVR and voucher.
C.1. Pledge, Registrar and MASA Keys
This section documents the public and private keys used for all
examples in this appendix. These keys are not used in any production
system, and must only be used for testing purposes.
C.1.1. Pledge IDevID private key
<CODE BEGINS>
-----BEGIN EC PRIVATE KEY-----
MHcCAQEEIMv+C4dbzeyrEH20qkpFlWIH2FFACGZv9kW7rNWtSlYtoAoGCCqGSM49
AwEHoUQDQgAESH6OUiYFRhfIgWl4GG8jHoj8a+8rf6t5s1mZ/4SePlKom39GQ34p
VYryJ9aHmboLLfz69bzICQFKbkoQ5oaiew==
-----END EC PRIVATE KEY-----
<CODE ENDS>
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<CODE BEGINS>
Private-Key: (256 bit)
priv:
cb:fe:0b:87:5b:cd:ec:ab:10:7d:b4:aa:4a:45:95:
62:07:d8:51:40:08:66:6f:f6:45:bb:ac:d5:ad:4a:
56:2d
pub:
04:48:7e:8e:52:26:05:46:17:c8:81:69:78:18:6f:
23:1e:88:fc:6b:ef:2b:7f:ab:79:b3:59:99:ff:84:
9e:3e:52:a8:9b:7f:46:43:7e:29:55:8a:f2:27:d6:
87:99:ba:0b:2d:fc:fa:f5:bc:c8:09:01:4a:6e:4a:
10:e6:86:a2:7b
ASN1 OID: prime256v1
NIST CURVE: P-256
<CODE ENDS>
C.1.2. Registrar private key
<CODE BEGINS>
-----BEGIN PRIVATE KEY-----
MIGHAgEAMBMGByqGSM49AgEGCCqGSM49AwEHBG0wawIBAQQgYJ/MP0dWA9BkYd4W
s6oRY62hDddaEmrAVm5dtAXE/UGhRANCAAQgMIVb6EaRCz7LFcr4Vy0+tWW9xlSh
Xvr27euqi54WCMXJEMk6IIaPyFBNNw8bJvqXWfZ5g7t4hj7amsvqUST2
-----END PRIVATE KEY-----
<CODE ENDS>
<CODE BEGINS>
Private-Key: (256 bit)
priv:
60:9f:cc:3f:47:56:03:d0:64:61:de:16:b3:aa:11:
63:ad:a1:0d:d7:5a:12:6a:c0:56:6e:5d:b4:05:c4:
fd:41
pub:
04:20:30:85:5b:e8:46:91:0b:3e:cb:15:ca:f8:57:
2d:3e:b5:65:bd:c6:54:a1:5e:fa:f6:ed:eb:aa:8b:
9e:16:08:c5:c9:10:c9:3a:20:86:8f:c8:50:4d:37:
0f:1b:26:fa:97:59:f6:79:83:bb:78:86:3e:da:9a:
cb:ea:51:24:f6
ASN1 OID: prime256v1
NIST CURVE: P-256
<CODE ENDS>
C.1.3. MASA private key
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<CODE BEGINS>
-----BEGIN PRIVATE KEY-----
MIGHAgEAMBMGByqGSM49AgEGCCqGSM49AwEHBG0wawIBAQQgrbJ1oU+HIJ2SWYAk
DkBTL+YNPxQG+gwsMsZB94N8mZ2hRANCAASS9NVlWJdztwNY81yPlH2UODYWhlYA
ZfsqnEPSFZKnq8mq8gF78ZVbYi6q2FEg8kkORY/rpIU/X7SQsRuD+wMW
-----END PRIVATE KEY-----
<CODE ENDS>
<CODE BEGINS>
Private-Key: (256 bit)
priv:
ad:b2:75:a1:4f:87:20:9d:92:59:80:24:0e:40:53:
2f:e6:0d:3f:14:06:fa:0c:2c:32:c6:41:f7:83:7c:
99:9d
pub:
04:92:f4:d5:65:58:97:73:b7:03:58:f3:5c:8f:94:
7d:94:38:36:16:86:56:00:65:fb:2a:9c:43:d2:15:
92:a7:ab:c9:aa:f2:01:7b:f1:95:5b:62:2e:aa:d8:
51:20:f2:49:0e:45:8f:eb:a4:85:3f:5f:b4:90:b1:
1b:83:fb:03:16
ASN1 OID: prime256v1
NIST CURVE: P-256
<CODE ENDS>
C.2. Pledge, Registrar, Domain CA and MASA Certificates
All keys and certificates used for the examples have been generated
with OpenSSL - see Appendix D for more details on certificate
generation. Below the certificates are listed that accompany the
keys shown above. Each certificate description is followed by the
hexadecimal representation of the X.509 ASN.1 DER encoded
certificate. This representation can be for example decoded using an
online ASN.1 decoder.
C.2.1. Pledge IDevID Certificate
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<CODE BEGINS>
Certificate:
Data:
Version: 3 (0x2)
Serial Number: 32429 (0x7ead)
Signature Algorithm: ecdsa-with-SHA256
Issuer: CN = masa.stok.nl, O = vanderstok, L = Helmond,
C = NL
Validity
Not Before: Dec 9 12:50:47 2022 GMT
Not After : Dec 31 12:50:47 9999 GMT
Subject: CN = Stok IoT sensor Y-42, serialNumber = JADA123456789
Subject Public Key Info:
Public Key Algorithm: id-ecPublicKey
Public-Key: (256 bit)
pub:
04:48:7e:8e:52:26:05:46:17:c8:81:69:78:18:6f:
23:1e:88:fc:6b:ef:2b:7f:ab:79:b3:59:99:ff:84:
9e:3e:52:a8:9b:7f:46:43:7e:29:55:8a:f2:27:d6:
87:99:ba:0b:2d:fc:fa:f5:bc:c8:09:01:4a:6e:4a:
10:e6:86:a2:7b
ASN1 OID: prime256v1
NIST CURVE: P-256
X509v3 extensions:
X509v3 Key Usage: critical
Digital Signature, Non Repudiation, Key Encipherment,
Data Encipherment
X509v3 Basic Constraints:
CA:FALSE
X509v3 Authority Key Identifier:
CB:8D:98:CA:74:C5:1B:58:DD:E7:AC:EF:86:9A:94:43:A8:D6:66:A6
1.3.6.1.5.5.7.1.32:
hl=2 l= 12 prim: IA5STRING :masa.stok.nl
Signature Algorithm: ecdsa-with-SHA256
Signature Value:
30:45:02:20:4d:89:90:7e:03:fb:52:56:42:0c:3f:c1:b1:f1:
47:b5:b3:93:65:45:2e:be:50:db:67:85:8f:23:89:a2:3f:9e:
02:21:00:95:33:69:d1:c6:db:f0:f1:f6:52:24:59:d3:0a:95:
4e:b2:f4:96:a1:31:3c:7b:d9:2f:28:b3:29:71:bb:60:df
<CODE ENDS>
Below is the hexadecimal representation of the binary X.509 DER-
encoded certificate:
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<CODE BEGINS>
308201CE30820174A00302010202027EAD300A06082A8648CE3D040302304B31
15301306035504030C0C6D6173612E73746F6B2E6E6C31133011060355040A0C
0A76616E64657273746F6B3110300E06035504070C0748656C6D6F6E64310B30
09060355040613024E4C3020170D3232313230393132353034375A180F393939
39313233313132353034375A3037311D301B06035504030C1453746F6B20496F
542073656E736F7220592D3432311630140603550405130D4A41444131323334
35363738393059301306072A8648CE3D020106082A8648CE3D03010703420004
487E8E5226054617C8816978186F231E88FC6BEF2B7FAB79B35999FF849E3E52
A89B7F46437E29558AF227D68799BA0B2DFCFAF5BCC809014A6E4A10E686A27B
A35A3058300E0603551D0F0101FF0404030204F030090603551D130402300030
1F0603551D23041830168014CB8D98CA74C51B58DDE7ACEF869A9443A8D666A6
301A06082B06010505070120040E160C6D6173612E73746F6B2E6E6C300A0608
2A8648CE3D040302034800304502204D89907E03FB5256420C3FC1B1F147B5B3
9365452EBE50DB67858F2389A23F9E022100953369D1C6DBF0F1F6522459D30A
954EB2F496A1313C7BD92F28B32971BB60DF
<CODE ENDS>
C.2.2. Registrar Certificate
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<CODE BEGINS>
Certificate:
Data:
Version: 3 (0x2)
Serial Number:
c3:f6:21:49:b2:e3:0e:3e
Signature Algorithm: ecdsa-with-SHA256
Issuer: CN = Custom-ER Global CA, OU = IT, O = "Custom-ER, Inc.",
L = San Jose, ST = CA, C = US
Validity
Not Before: Dec 9 12:50:47 2022 GMT
Not After : Dec 8 12:50:47 2025 GMT
Subject: CN = Custom-ER Registrar, OU = Office dept, O = "Custom-ER,
Inc.", L = Ottowa, ST = ON, C = CA
Subject Public Key Info:
Public Key Algorithm: id-ecPublicKey
Public-Key: (256 bit)
pub:
04:20:30:85:5b:e8:46:91:0b:3e:cb:15:ca:f8:57:
2d:3e:b5:65:bd:c6:54:a1:5e:fa:f6:ed:eb:aa:8b:
9e:16:08:c5:c9:10:c9:3a:20:86:8f:c8:50:4d:37:
0f:1b:26:fa:97:59:f6:79:83:bb:78:86:3e:da:9a:
cb:ea:51:24:f6
ASN1 OID: prime256v1
NIST CURVE: P-256
X509v3 extensions:
X509v3 Key Usage: critical
Digital Signature, Non Repudiation, Key Encipherment,
Data Encipherment
X509v3 Basic Constraints:
CA:FALSE
X509v3 Subject Key Identifier:
C9:08:0B:38:7D:8D:D8:5B:3A:59:E7:EC:10:0B:86:63:93:A9:CA:4C
X509v3 Authority Key Identifier:
92:EA:76:40:40:4A:8F:AB:4F:27:0B:F3:BC:37:9D:86:CD:72:80:F8
X509v3 Extended Key Usage: critical
CMC Registration Authority, TLS Web Server Authentication,
TLS Web Client Authentication
Signature Algorithm: ecdsa-with-SHA256
Signature Value:
30:45:02:21:00:d8:4a:7c:69:2f:f9:58:6e:82:22:87:18:f6:
3b:c3:05:f0:ae:b8:ae:ec:42:78:82:38:79:81:2a:5d:15:61:
64:02:20:08:f2:3c:13:69:13:b0:2c:e2:63:09:d5:99:4f:eb:
75:70:af:af:ed:98:cd:f1:12:11:c0:37:f7:18:4d:c1:9d
<CODE ENDS>
Richardson, et al. Expires 14 September 2023 [Page 64]
Internet-Draft Constrained BRSKI March 2023
Below is the hexadecimal representation of the binary X.509 DER-
encoded certificate:
<CODE BEGINS>
3082026D30820213A003020102020900C3F62149B2E30E3E300A06082A8648CE
3D0403023072311C301A06035504030C13437573746F6D2D455220476C6F6261
6C204341310B3009060355040B0C02495431183016060355040A0C0F43757374
6F6D2D45522C20496E632E3111300F06035504070C0853616E204A6F7365310B
300906035504080C024341310B3009060355040613025553301E170D32323132
30393132353034375A170D3235313230383132353034375A3079311C301A0603
5504030C13437573746F6D2D4552205265676973747261723114301206035504
0B0C0B4F6666696365206465707431183016060355040A0C0F437573746F6D2D
45522C20496E632E310F300D06035504070C064F74746F7761310B3009060355
04080C024F4E310B30090603550406130243413059301306072A8648CE3D0201
06082A8648CE3D030107034200042030855BE846910B3ECB15CAF8572D3EB565
BDC654A15EFAF6EDEBAA8B9E1608C5C910C93A20868FC8504D370F1B26FA9759
F67983BB78863EDA9ACBEA5124F6A3818A308187300E0603551D0F0101FF0404
030204F030090603551D1304023000301D0603551D0E04160414C9080B387D8D
D85B3A59E7EC100B866393A9CA4C301F0603551D2304183016801492EA764040
4A8FAB4F270BF3BC379D86CD7280F8302A0603551D250101FF0420301E06082B
0601050507031C06082B0601050507030106082B06010505070302300A06082A
8648CE3D0403020348003045022100D84A7C692FF9586E82228718F63BC305F0
AEB8AEEC4278823879812A5D156164022008F23C136913B02CE26309D5994FEB
7570AFAFED98CDF11211C037F7184DC19D
<CODE ENDS>
C.2.3. Domain CA Certificate
The Domain CA certificate is the CA of the customer's domain. It has
signed the Registrar (RA) certificate.
Richardson, et al. Expires 14 September 2023 [Page 65]
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<CODE BEGINS>
Certificate:
Data:
Version: 3 (0x2)
Serial Number: 3092288576548618702 (0x2aea0413a42dc1ce)
Signature Algorithm: ecdsa-with-SHA256
Issuer: CN = Custom-ER Global CA, OU = IT, O = "Custom-ER, Inc.",
L = San Jose, ST = CA, C = US
Validity
Not Before: Dec 9 12:50:47 2022 GMT
Not After : Dec 6 12:50:47 2032 GMT
Subject: CN = Custom-ER Global CA, OU = IT, O = "Custom-ER, Inc.",
L = San Jose, ST = CA, C = US
Subject Public Key Info:
Public Key Algorithm: id-ecPublicKey
Public-Key: (256 bit)
pub:
04:97:b1:ed:96:91:64:93:09:85:bb:b8:ac:9a:2a:
f9:45:5c:df:ee:a4:b1:1d:e2:e7:9d:06:8b:fa:80:
39:26:b4:00:52:51:b3:4f:1c:08:15:a4:cb:e0:3f:
bd:1b:bc:b6:35:f6:43:1a:22:de:78:65:3b:87:b9:
95:37:ec:e1:6c
ASN1 OID: prime256v1
NIST CURVE: P-256
X509v3 extensions:
X509v3 Subject Alternative Name:
email:help@custom-er.example.com
X509v3 Key Usage: critical
Digital Signature, Certificate Sign, CRL Sign
X509v3 Basic Constraints: critical
CA:TRUE
X509v3 Subject Key Identifier:
92:EA:76:40:40:4A:8F:AB:4F:27:0B:F3:BC:37:9D:86:CD:72:80:F8
Signature Algorithm: ecdsa-with-SHA256
Signature Value:
30:44:02:20:66:15:df:c3:70:11:f6:73:78:d8:fd:1c:2a:3f:
bd:d1:3f:51:f6:b6:6f:2d:7c:e2:7a:13:18:21:bb:70:f0:c0:
02:20:69:86:d8:d2:28:b2:92:6e:23:9e:19:0b:8f:18:25:c9:
c1:4c:67:95:ff:a0:b3:24:bd:4d:ac:2e:cb:68:d7:13
<CODE ENDS>
Below is the hexadecimal representation of the binary X.509 DER-
encoded certificate:
Richardson, et al. Expires 14 September 2023 [Page 66]
Internet-Draft Constrained BRSKI March 2023
<CODE BEGINS>
30820242308201E9A00302010202082AEA0413A42DC1CE300A06082A8648CE3D
0403023072311C301A06035504030C13437573746F6D2D455220476C6F62616C
204341310B3009060355040B0C02495431183016060355040A0C0F437573746F
6D2D45522C20496E632E3111300F06035504070C0853616E204A6F7365310B30
0906035504080C024341310B3009060355040613025553301E170D3232313230
393132353034375A170D3332313230363132353034375A3072311C301A060355
04030C13437573746F6D2D455220476C6F62616C204341310B3009060355040B
0C02495431183016060355040A0C0F437573746F6D2D45522C20496E632E3111
300F06035504070C0853616E204A6F7365310B300906035504080C024341310B
30090603550406130255533059301306072A8648CE3D020106082A8648CE3D03
01070342000497B1ED969164930985BBB8AC9A2AF9455CDFEEA4B11DE2E79D06
8BFA803926B4005251B34F1C0815A4CBE03FBD1BBCB635F6431A22DE78653B87
B99537ECE16CA369306730250603551D11041E301C811A68656C704063757374
6F6D2D65722E6578616D706C652E636F6D300E0603551D0F0101FF0404030201
86300F0603551D130101FF040530030101FF301D0603551D0E0416041492EA76
40404A8FAB4F270BF3BC379D86CD7280F8300A06082A8648CE3D040302034700
304402206615DFC37011F67378D8FD1C2A3FBDD13F51F6B66F2D7CE27A131821
BB70F0C002206986D8D228B2926E239E190B8F1825C9C14C6795FFA0B324BD4D
AC2ECB68D713
<CODE ENDS>
C.2.4. MASA Certificate
The MASA CA certificate is the CA that signed the Pledge's IDevID
certificate.
Richardson, et al. Expires 14 September 2023 [Page 67]
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<CODE BEGINS>
Certificate:
Data:
Version: 3 (0x2)
Serial Number:
e3:9c:da:17:e1:38:6a:0a
Signature Algorithm: ecdsa-with-SHA256
Issuer: CN = masa.stok.nl, O = vanderstok, L = Helmond,
C = NL
Validity
Not Before: Dec 9 12:50:47 2022 GMT
Not After : Dec 6 12:50:47 2032 GMT
Subject: CN = masa.stok.nl, O = vanderstok, L = Helmond,
C = NL
Subject Public Key Info:
Public Key Algorithm: id-ecPublicKey
Public-Key: (256 bit)
pub:
04:92:f4:d5:65:58:97:73:b7:03:58:f3:5c:8f:94:
7d:94:38:36:16:86:56:00:65:fb:2a:9c:43:d2:15:
92:a7:ab:c9:aa:f2:01:7b:f1:95:5b:62:2e:aa:d8:
51:20:f2:49:0e:45:8f:eb:a4:85:3f:5f:b4:90:b1:
1b:83:fb:03:16
ASN1 OID: prime256v1
NIST CURVE: P-256
X509v3 extensions:
X509v3 Subject Alternative Name:
email:info@masa.stok.nl
X509v3 Key Usage: critical
Digital Signature, Certificate Sign, CRL Sign
X509v3 Basic Constraints: critical
CA:TRUE, pathlen:3
X509v3 Subject Key Identifier:
CB:8D:98:CA:74:C5:1B:58:DD:E7:AC:EF:86:9A:94:43:A8:D6:66:A6
Signature Algorithm: ecdsa-with-SHA256
Signature Value:
30:46:02:21:00:94:3f:a5:26:51:68:16:38:5b:78:9a:d8:c3:
af:8e:49:28:22:60:56:26:43:4a:14:98:3e:e1:e4:81:ad:ca:
1b:02:21:00:ba:4d:aa:fd:fa:68:42:74:03:2b:a8:41:6b:e2:
90:0c:9e:7b:b8:c0:9c:f7:0e:3f:b4:36:8a:b3:9c:3e:31:0e
<CODE ENDS>
Below is the hexadecimal representation of the binary X.509 DER-
encoded certificate:
Richardson, et al. Expires 14 September 2023 [Page 68]
Internet-Draft Constrained BRSKI March 2023
<CODE BEGINS>
308201F130820196A003020102020900E39CDA17E1386A0A300A06082A8648CE
3D040302304B3115301306035504030C0C6D6173612E73746F6B2E6E6C311330
11060355040A0C0A76616E64657273746F6B3110300E06035504070C0748656C
6D6F6E64310B3009060355040613024E4C301E170D3232313230393132353034
375A170D3332313230363132353034375A304B3115301306035504030C0C6D61
73612E73746F6B2E6E6C31133011060355040A0C0A76616E64657273746F6B31
10300E06035504070C0748656C6D6F6E64310B3009060355040613024E4C3059
301306072A8648CE3D020106082A8648CE3D0301070342000492F4D565589773
B70358F35C8F947D9438361686560065FB2A9C43D21592A7ABC9AAF2017BF195
5B622EAAD85120F2490E458FEBA4853F5FB490B11B83FB0316A3633061301C06
03551D11041530138111696E666F406D6173612E73746F6B2E6E6C300E060355
1D0F0101FF04040302018630120603551D130101FF040830060101FF02010330
1D0603551D0E04160414CB8D98CA74C51B58DDE7ACEF869A9443A8D666A6300A
06082A8648CE3D0403020349003046022100943FA526516816385B789AD8C3AF
8E492822605626434A14983EE1E481ADCA1B022100BA4DAAFDFA684274032BA8
416BE2900C9E7BB8C09CF70E3FB4368AB39C3E310E
<CODE ENDS>
C.3. COSE-signed Pledge Voucher Request (PVR)
In this example, the voucher request (PVR) has been signed by the
Pledge using the IDevID private key of Appendix C.1.1, and has been
sent to the link-local constrained Join Proxy (JP) over CoAPS to the
JP's join port. The join port happens to use the default CoAPS UDP
port 5684.
REQ: POST coaps://[JP-link-local-address]/b/rv
Content-Format: 836
Payload: <signed_pvr>
When the Join Proxy receives the DTLS handshake messages from the
Pledge, it will relay these messages to the Registrar. The payload
signed_voucher_request is shown as hexadecimal dump (with lf added)
below:
<CODE BEGINS>
D28443A10126A0587EA11909C5A40102074823BFBBC9C2BCF2130C585B305930
1306072A8648CE3D020106082A8648CE3D030107034200042030855BE846910B
3ECB15CAF8572D3EB565BDC654A15EFAF6EDEBAA8B9E1608C5C910C93A20868F
C8504D370F1B26FA9759F67983BB78863EDA9ACBEA5124F60D6D4A4144413132
33343536373839584068987DE8B007F4E9416610BBE2D48E1D7EA1032092B8BF
CE611421950F45B22F17E214820C07E777ADF86175E25D3205568404C25FCEEC
1B817C7861A6104B3D
<CODE ENDS>
Richardson, et al. Expires 14 September 2023 [Page 69]
Internet-Draft Constrained BRSKI March 2023
The representiation of signed_pvr in CBOR diagnostic format (with lf
added) is:
<CODE BEGINS>
18([h'A10126', {}, h'A11909C5A40102074823BFBBC9C2BCF2130C585B3059301
306072A8648CE3D020106082A8648CE3D030107034200042030855BE846910B3ECB1
5CAF8572D3EB565BDC654A15EFAF6EDEBAA8B9E1608C5C910C93A20868FC8504D370
F1B26FA9759F67983BB78863EDA9ACBEA5124F60D6D4A41444131323334353637383
9', h'68987DE8B007F4E9416610BBE2D48E1D7EA1032092B8BFCE611421950F45B2
2F17E214820C07E777ADF86175E25D3205568404C25FCEEC1B817C7861A6104B3D']
)
<CODE ENDS>
The COSE payload is the PVR, encoded as a CBOR byte string. The
diagnostic representation of it is shown below:
<CODE BEGINS>
{2501: {1: 2, 7: h'23BFBBC9C2BCF213', 12: h'3059301306072A8648CE3D02
0106082A8648CE3D030107034200042030855BE846910B3ECB15CAF8572D3EB565BD
C654A15EFAF6EDEBAA8B9E1608C5C910C93A20868FC8504D370F1B26FA9759F67983
BB78863EDA9ACBEA5124F6', 13: "JADA123456789"}}
<CODE ENDS>
The Pledge uses the "proximity" (key '1', SID 2502, enum value 2)
assertion together with an included proximity-registrar-pubk field
(key '12', SID 2513) to inform MASA about its proximity to the
specific Registrar.
C.4. COSE-signed Registrar Voucher Request (RVR)
In this example the Registrar's voucher request has been signed by
the JRC (Registrar) using the private key from Appendix C.1.2.
Contained within this voucher request is the voucher request PVR that
was made by the Pledge to JRC. Note that the RVR uses the HTTPS
protocol (not CoAP) and corresponding long URI path names as defined
in [RFC8995]. The Content-Type and Accept headers indicate the
constrained voucher format that is defined in the present document.
Because the Pledge used this format in the PVR, the JRC must also use
this format in the RVR.
REQ: POST https://masa.stok.nl/.well-known/brski/requestvoucher
Content-Type: application/voucher-cose+cbor
Accept: application/voucher-cose+cbor
Body: <signed_rvr>
The payload signed_rvr is shown as hexadecimal dump (with lf added):
Richardson, et al. Expires 14 September 2023 [Page 70]
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<CODE BEGINS>
D28443A10126A11820825902843082028030820225A003020102020900C3F621
49B2E30E3E300A06082A8648CE3D0403023072311C301A06035504030C134375
73746F6D2D455220476C6F62616C204341310B3009060355040B0C0249543118
3016060355040A0C0F437573746F6D2D45522C20496E632E3111300F06035504
070C0853616E204A6F7365310B300906035504080C024341310B300906035504
0613025553301E170D3232313230363131333735395A170D3235313230353131
333735395A30818D3131302F06035504030C28437573746F6D2D455220436F6D
6D65726369616C204275696C64696E6773205265676973747261723113301106
0355040B0C0A4F6666696365206F707331183016060355040A0C0F437573746F
6D2D45522C20496E632E310F300D06035504070C064F74746F7761310B300906
035504080C024F4E310B30090603550406130243413059301306072A8648CE3D
020106082A8648CE3D030107034200042030855BE846910B3ECB15CAF8572D3E
B565BDC654A15EFAF6EDEBAA8B9E1608C5C910C93A20868FC8504D370F1B26FA
9759F67983BB78863EDA9ACBEA5124F6A3818730818430090603551D13040230
00300B0603551D0F0404030204F0301D0603551D0E04160414C9080B387D8DD8
5B3A59E7EC100B866393A9CA4C301F0603551D2304183016801492EA7640404A
8FAB4F270BF3BC379D86CD7280F8302A0603551D250101FF0420301E06082B06
01050507031C06082B0601050507030106082B06010505070302300A06082A86
48CE3D040302034900304602210091A2033692EB81503D53505FFC8DA326B1EE
7DEA96F29174F0B3341A07812201022100FF7339288108B712F418530A18025A
895408CC45E0BB678B46FBAB37DDB4D36B59024730820243308201E9A0030201
0202082AEA0413A42DC1CE300A06082A8648CE3D0403023072311C301A060355
04030C13437573746F6D2D455220476C6F62616C204341310B3009060355040B
0C02495431183016060355040A0C0F437573746F6D2D45522C20496E632E3111
300F06035504070C0853616E204A6F7365310B300906035504080C024341310B
3009060355040613025553301E170D3232313230363131333735395A170D3332
313230333131333735395A3072311C301A06035504030C13437573746F6D2D45
5220476C6F62616C204341310B3009060355040B0C0249543118301606035504
0A0C0F437573746F6D2D45522C20496E632E3111300F06035504070C0853616E
204A6F7365310B300906035504080C024341310B300906035504061302555330
59301306072A8648CE3D020106082A8648CE3D0301070342000497B1ED969164
930985BBB8AC9A2AF9455CDFEEA4B11DE2E79D068BFA803926B4005251B34F1C
0815A4CBE03FBD1BBCB635F6431A22DE78653B87B99537ECE16CA3693067300F
0603551D130101FF040530030101FF30250603551D11041E301C811A68656C70
40637573746F6D2D65722E6578616D706C652E636F6D300E0603551D0F0101FF
040403020186301D0603551D0E0416041492EA7640404A8FAB4F270BF3BC379D
86CD7280F8300A06082A8648CE3D0403020348003045022100D6D813B390BD3A
7B4E85424BCB1ED933AD1E981F2817B59083DD6EC1C5E3FADF02202CEE440619
2BC767E98D7CFAE044C6807481AD8564A7D569DCA3D1CDF1E5E843590124A119
09C5A60102027818323032322D31322D30365432303A30343A31352E3735345A
05581A041830168014CB8D98CA74C51B58DDE7ACEF869A9443A8D666A6074823
BFBBC9C2BCF2130958C9D28443A10126A0587EA11909C5A40102074823BFBBC9
C2BCF2130C585B3059301306072A8648CE3D020106082A8648CE3D0301070342
00042030855BE846910B3ECB15CAF8572D3EB565BDC654A15EFAF6EDEBAA8B9E
1608C5C910C93A20868FC8504D370F1B26FA9759F67983BB78863EDA9ACBEA51
24F60D6D4A414441313233343536373839584068987DE8B007F4E9416610BBE2
D48E1D7EA1032092B8BFCE611421950F45B22F17E214820C07E777ADF86175E2
Richardson, et al. Expires 14 September 2023 [Page 71]
Internet-Draft Constrained BRSKI March 2023
5D3205568404C25FCEEC1B817C7861A6104B3D0D6D4A41444131323334353637
38395840B1DD40B10787437588AEAC9036899191C16CCDBECA31C197855CCB6B
BA142D709FE329CBC3F76297D6063ACB6759EAB98E96EA4C4AA2135AA48A247B
AC1D6A3F
<CODE ENDS>
The representiation of signed_rvr in CBOR diagnostic format (with lf
added) is:
<CODE BEGINS>
18([h'A10126', {32: [h'3082028030820225A003020102020900C3F62149B2E30
E3E300A06082A8648CE3D0403023072311C301A06035504030C13437573746F6D2D4
55220476C6F62616C204341310B3009060355040B0C02495431183016060355040A0
C0F437573746F6D2D45522C20496E632E3111300F06035504070C0853616E204A6F7
365310B300906035504080C024341310B3009060355040613025553301E170D32323
13230363131333735395A170D3235313230353131333735395A30818D3131302F060
35504030C28437573746F6D2D455220436F6D6D65726369616C204275696C64696E6
7732052656769737472617231133011060355040B0C0A4F6666696365206F7073311
83016060355040A0C0F437573746F6D2D45522C20496E632E310F300D06035504070
C064F74746F7761310B300906035504080C024F4E310B30090603550406130243413
059301306072A8648CE3D020106082A8648CE3D030107034200042030855BE846910
B3ECB15CAF8572D3EB565BDC654A15EFAF6EDEBAA8B9E1608C5C910C93A20868FC85
04D370F1B26FA9759F67983BB78863EDA9ACBEA5124F6A3818730818430090603551
D1304023000300B0603551D0F0404030204F0301D0603551D0E04160414C9080B387
D8DD85B3A59E7EC100B866393A9CA4C301F0603551D2304183016801492EA7640404
A8FAB4F270BF3BC379D86CD7280F8302A0603551D250101FF0420301E06082B06010
50507031C06082B0601050507030106082B06010505070302300A06082A8648CE3D0
40302034900304602210091A2033692EB81503D53505FFC8DA326B1EE7DEA96F2917
4F0B3341A07812201022100FF7339288108B712F418530A18025A895408CC45E0BB6
78B46FBAB37DDB4D36B', h'30820243308201E9A00302010202082AEA0413A42DC1
CE300A06082A8648CE3D0403023072311C301A06035504030C13437573746F6D2D45
5220476C6F62616C204341310B3009060355040B0C02495431183016060355040A0C
0F437573746F6D2D45522C20496E632E3111300F06035504070C0853616E204A6F73
65310B300906035504080C024341310B3009060355040613025553301E170D323231
3230363131333735395A170D3332313230333131333735395A3072311C301A060355
04030C13437573746F6D2D455220476C6F62616C204341310B3009060355040B0C02
495431183016060355040A0C0F437573746F6D2D45522C20496E632E3111300F0603
5504070C0853616E204A6F7365310B300906035504080C024341310B300906035504
06130255533059301306072A8648CE3D020106082A8648CE3D0301070342000497B1
ED969164930985BBB8AC9A2AF9455CDFEEA4B11DE2E79D068BFA803926B4005251B3
4F1C0815A4CBE03FBD1BBCB635F6431A22DE78653B87B99537ECE16CA3693067300F
0603551D130101FF040530030101FF30250603551D11041E301C811A68656C704063
7573746F6D2D65722E6578616D706C652E636F6D300E0603551D0F0101FF04040302
0186301D0603551D0E0416041492EA7640404A8FAB4F270BF3BC379D86CD7280F830
0A06082A8648CE3D0403020348003045022100D6D813B390BD3A7B4E85424BCB1ED9
33AD1E981F2817B59083DD6EC1C5E3FADF02202CEE4406192BC767E98D7CFAE044C6
807481AD8564A7D569DCA3D1CDF1E5E843']}, h'A11909C5A601020278183230323
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22D31322D30365432303A30343A31352E3735345A05581A041830168014CB8D98CA7
4C51B58DDE7ACEF869A9443A8D666A6074823BFBBC9C2BCF2130958C9D28443A1012
6A0587EA11909C5A40102074823BFBBC9C2BCF2130C585B3059301306072A8648CE3
D020106082A8648CE3D030107034200042030855BE846910B3ECB15CAF8572D3EB56
5BDC654A15EFAF6EDEBAA8B9E1608C5C910C93A20868FC8504D370F1B26FA9759F67
983BB78863EDA9ACBEA5124F60D6D4A414441313233343536373839584068987DE8B
007F4E9416610BBE2D48E1D7EA1032092B8BFCE611421950F45B22F17E214820C07E
777ADF86175E25D3205568404C25FCEEC1B817C7861A6104B3D0D6D4A41444131323
3343536373839', h'B1DD40B10787437588AEAC9036899191C16CCDBECA31C19785
5CCB6BBA142D709FE329CBC3F76297D6063ACB6759EAB98E96EA4C4AA2135AA48A24
7BAC1D6A3F'])
<CODE ENDS>
C.5. COSE-signed Voucher from MASA
The resulting voucher is created by the MASA and returned to the
Registrar:
RES: 200 OK
Content-Type: application/voucher-cose+cbor
Body: <signed_voucher>
The Registrar then returns the voucher to the Pledge:
RES: 2.04 Changed
Content-Format: 836
Body: <signed_voucher>
It is signed by the MASA's private key (see Appendix C.1.3) and can
be verified by the Pledge using the MASA's public key that it stores.
Below is the binary signed_voucher, encoded in hexadecimal (with lf
added):
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<CODE BEGINS>
D28443A10126A0590288A1190993A60102027818323032322D31322D30365432
303A32333A33302E3730385A03F4074857EED786AD4049070859024730820243
308201E9A00302010202082AEA0413A42DC1CE300A06082A8648CE3D04030230
72311C301A06035504030C13437573746F6D2D455220476C6F62616C20434131
0B3009060355040B0C02495431183016060355040A0C0F437573746F6D2D4552
2C20496E632E3111300F06035504070C0853616E204A6F7365310B3009060355
04080C024341310B3009060355040613025553301E170D323231323036313133
3735395A170D3332313230333131333735395A3072311C301A06035504030C13
437573746F6D2D455220476C6F62616C204341310B3009060355040B0C024954
31183016060355040A0C0F437573746F6D2D45522C20496E632E3111300F0603
5504070C0853616E204A6F7365310B300906035504080C024341310B30090603
550406130255533059301306072A8648CE3D020106082A8648CE3D0301070342
000497B1ED969164930985BBB8AC9A2AF9455CDFEEA4B11DE2E79D068BFA8039
26B4005251B34F1C0815A4CBE03FBD1BBCB635F6431A22DE78653B87B99537EC
E16CA3693067300F0603551D130101FF040530030101FF30250603551D11041E
301C811A68656C7040637573746F6D2D65722E6578616D706C652E636F6D300E
0603551D0F0101FF040403020186301D0603551D0E0416041492EA7640404A8F
AB4F270BF3BC379D86CD7280F8300A06082A8648CE3D04030203480030450221
00D6D813B390BD3A7B4E85424BCB1ED933AD1E981F2817B59083DD6EC1C5E3FA
DF02202CEE4406192BC767E98D7CFAE044C6807481AD8564A7D569DCA3D1CDF1
E5E8430B6D4A4144413132333435363738395840DF31B21A6AD3F5AC7F4C8B02
6F551BD28FBCE62330D3E262AC170F6BFEDDBA5F2E8FBAA2CAACFED9E8614EAC
5BF2450DADC53AC29DFA30E8787A1400B2E7C832
<CODE ENDS>
The representiation of signed_voucher in CBOR diagnostic format (with
lf added) is:
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<CODE BEGINS>
18([h'A10126', {}, h'A1190993A60102027818323032322D31322D30365432303
A32333A33302E3730385A03F4074857EED786AD4049070859024730820243308201E
9A00302010202082AEA0413A42DC1CE300A06082A8648CE3D0403023072311C301A0
6035504030C13437573746F6D2D455220476C6F62616C204341310B3009060355040
B0C02495431183016060355040A0C0F437573746F6D2D45522C20496E632E3111300
F06035504070C0853616E204A6F7365310B300906035504080C024341310B3009060
355040613025553301E170D3232313230363131333735395A170D333231323033313
1333735395A3072311C301A06035504030C13437573746F6D2D455220476C6F62616
C204341310B3009060355040B0C02495431183016060355040A0C0F437573746F6D2
D45522C20496E632E3111300F06035504070C0853616E204A6F7365310B300906035
504080C024341310B30090603550406130255533059301306072A8648CE3D0201060
82A8648CE3D0301070342000497B1ED969164930985BBB8AC9A2AF9455CDFEEA4B11
DE2E79D068BFA803926B4005251B34F1C0815A4CBE03FBD1BBCB635F6431A22DE786
53B87B99537ECE16CA3693067300F0603551D130101FF040530030101FF302506035
51D11041E301C811A68656C7040637573746F6D2D65722E6578616D706C652E636F6
D300E0603551D0F0101FF040403020186301D0603551D0E0416041492EA7640404A8
FAB4F270BF3BC379D86CD7280F8300A06082A8648CE3D0403020348003045022100D
6D813B390BD3A7B4E85424BCB1ED933AD1E981F2817B59083DD6EC1C5E3FADF02202
CEE4406192BC767E98D7CFAE044C6807481AD8564A7D569DCA3D1CDF1E5E8430B6D4
A414441313233343536373839', h'DF31B21A6AD3F5AC7F4C8B026F551BD28FBCE6
2330D3E262AC170F6BFEDDBA5F2E8FBAA2CAACFED9E8614EAC5BF2450DADC53AC29D
FA30E8787A1400B2E7C832'])
<CODE ENDS>
In the above, the third element in the array is the plain CBOR
voucher encoded as a CBOR byte string. When decoded, it can be
represented by the following CBOR diagnostic notation:
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<CODE BEGINS>
{2451: {1: 2, 2: "2022-12-06T20:23:30.708Z", 3: false, 7: h'57EED786
AD404907', 8: h'30820243308201E9A00302010202082AEA0413A42DC1CE300A06
082A8648CE3D0403023072311C301A06035504030C13437573746F6D2D455220476C
6F62616C204341310B3009060355040B0C02495431183016060355040A0C0F437573
746F6D2D45522C20496E632E3111300F06035504070C0853616E204A6F7365310B30
0906035504080C024341310B3009060355040613025553301E170D32323132303631
31333735395A170D3332313230333131333735395A3072311C301A06035504030C13
437573746F6D2D455220476C6F62616C204341310B3009060355040B0C0249543118
3016060355040A0C0F437573746F6D2D45522C20496E632E3111300F06035504070C
0853616E204A6F7365310B300906035504080C024341310B30090603550406130255
533059301306072A8648CE3D020106082A8648CE3D0301070342000497B1ED969164
930985BBB8AC9A2AF9455CDFEEA4B11DE2E79D068BFA803926B4005251B34F1C0815
A4CBE03FBD1BBCB635F6431A22DE78653B87B99537ECE16CA3693067300F0603551D
130101FF040530030101FF30250603551D11041E301C811A68656C7040637573746F
6D2D65722E6578616D706C652E636F6D300E0603551D0F0101FF040403020186301D
0603551D0E0416041492EA7640404A8FAB4F270BF3BC379D86CD7280F8300A06082A
8648CE3D0403020348003045022100D6D813B390BD3A7B4E85424BCB1ED933AD1E98
1F2817B59083DD6EC1C5E3FADF02202CEE4406192BC767E98D7CFAE044C6807481AD
8564A7D569DCA3D1CDF1E5E843', 11: "JADA123456789"}}
<CODE ENDS>
The largest element in the voucher is identified by key 8, which
decodes to SID 2459 (pinned-domain-cert). It contains the complete
DER-encoded X.509 certificate of the Registrar's domain CA. This
certificate is shown in Appendix C.2.3.
Appendix D. Generating Certificates with OpenSSL
This informative appendix shows example Bash shell scripts to
generate test certificates for the Pledge IDevID, the Registrar and
the MASA. The shell scripts cannot be run stand-alone because they
depend on input files which are not all included in this appendix.
Nevertheless, these scripts may provide guidance on how OpenSSL can
be configured for generating Constrained BRSKI certificates.
The scripts were tested with OpenSSL 3.0.2. Older versions may not
work -- OpenSSL 1.1.1 for example does not support all extensions
used.
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<CODE BEGINS>
#!/bin/bash
# File: create-cert-Pledge.sh
# Create new cert for: Pledge IDevID
# days certificate is valid - try to get close to the 802.1AR
# specified 9999-12-31 end date.
SECONDS1=`date +%s` # time now
SECONDS2=`date --date="9999-12-31 23:59:59Z" +%s` # target end time
let VALIDITY="(${SECONDS2}-${SECONDS1})/(24*3600)"
echo "Using validity param -days ${VALIDITY}"
NAME=pledge
# create csr for device
# conform to 802.1AR guidelines, using only CN + serialNumber when
# manufacturer is already present as CA.
# CN is not even mandatory, but just good practice.
openssl req -new -key keys/privkey_pledge.pem -out $NAME.csr -subj \
"/CN=Stok IoT sensor Y-42/serialNumber=JADA123456789"
# sign csr
openssl x509 -set_serial 32429 -CAform PEM -CA output/masa_ca.pem \
-CAkey keys/privkey_masa_ca.pem -extfile x509v3.ext -extensions \
pledge_ext -req -in $NAME.csr -out output/$NAME.pem \
-days $VALIDITY -sha256
# delete temp files
rm -f $NAME.csr
# convert to .der format
openssl x509 -in output/$NAME.pem -inform PEM -out output/$NAME.der \
-outform DER
<CODE ENDS>
<CODE BEGINS>
# File: x509v3.ext
# This file contains all X509v3 extension definitions for OpenSSL
# certificate generation. Each certificate has its own _ext
# section below.
[ req ]
prompt = no
[ masa_ca_ext ]
subjectAltName=email:info@masa.stok.nl
keyUsage = critical,digitalSignature, keyCertSign, cRLSign
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basicConstraints = critical,CA:TRUE,pathlen:3
subjectKeyIdentifier=hash
authorityKeyIdentifier=keyid
[ pledge_ext ]
keyUsage = critical,digitalSignature, nonRepudiation, \
keyEncipherment, dataEncipherment
# basicConstraints for a non-CA cert MAY be marked either
# non-critical or critical.
basicConstraints = CA:FALSE
# Don't include subjectKeyIdentifier (SKI) - see 802.1AR-2018
subjectKeyIdentifier = none
authorityKeyIdentifier=keyid
# Include the MASA URI
1.3.6.1.5.5.7.1.32 = ASN1:IA5STRING:masa.stok.nl
[ domain_ca_ext ]
subjectAltName=email:help@custom-er.example.com
keyUsage = critical, keyCertSign, digitalSignature, cRLSign
basicConstraints=critical,CA:TRUE
# RFC 5280 4.2.1.1 : AKI MAY be omitted, and MUST be non-critical;
# SKI MUST be non-critical
subjectKeyIdentifier=hash
[ registrar_ext ]
keyUsage = critical, digitalSignature, nonRepudiation, \
keyEncipherment, dataEncipherment
basicConstraints=CA:FALSE
subjectKeyIdentifier=hash
authorityKeyIdentifier=keyid
# Set Registrar 'RA' flag along with TLS client/server usage
# see draft-ietf-anima-constrained-voucher#section-7.3
# see tools.ietf.org/html/rfc6402#section-2.10
# see www.openssl.org/docs/man1.1.1/man5/x509v3_config.html
extendedKeyUsage = critical,1.3.6.1.5.5.7.3.28, serverAuth, \
clientAuth
<CODE ENDS>
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<CODE BEGINS>
#!/bin/bash
# File: create-cert-Registrar.sh
# Create new cert for: Registrar in a company domain
# days certificate is valid
VALIDITY=1095
# cert filename
NAME=registrar
# create csr
openssl req -new -key keys/privkey_registrar.pem -out $NAME.csr \
-subj "/CN=Custom-ER Registrar/OU=Office dept/O=Custom-ER, Inc./\
L=Ottowa/ST=ON/C=CA"
# sign csr
openssl x509 -set_serial 0xC3F62149B2E30E3E -CAform PEM -CA \
output/domain_ca.pem -extfile x509v3.ext -extensions registrar_ext \
-req -in $NAME.csr -CAkey keys/privkey_domain_ca.pem \
-out output/$NAME.pem -days $VALIDITY -sha256
# delete temp files
rm -f $NAME.csr
# convert to .der format
openssl x509 -in output/$NAME.pem -inform PEM -out output/$NAME.der \
-outform DER
<CODE ENDS>
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<CODE BEGINS>
#!/bin/bash
# File: create-cert-MASA.sh
# Create new cert for: MASA CA, self-signed CA certificate
# days certificate is valid
VALIDITY=3650
NAME=masa_ca
# create csr
openssl req -new -key keys/privkey_masa_ca.pem -out $NAME.csr \
-subj "/CN=masa.stok.nl/O=vanderstok/L=Helmond/C=NL"
# sign csr
mkdir output >& /dev/null
openssl x509 -set_serial 0xE39CDA17E1386A0A -extfile x509v3.ext \
-extensions masa_ca_ext -req -in $NAME.csr \
-signkey keys/privkey_masa_ca.pem -out output/$NAME.pem \
-days $VALIDITY -sha256
# delete temp files
rm -f $NAME.csr
# convert to .der format
openssl x509 -in output/$NAME.pem -inform PEM -out output/$NAME.der \
-outform DER
<CODE ENDS>
Appendix E. Pledge Device Class Profiles
This specification allows implementers to select between various
functional options for the Pledge, yielding different code size
footprints and different requirements on Pledge hardware. Thus for
each product an optimal trade-off between functionality, development/
maintenance cost and hardware cost can be made.
This appendix illustrates different selection outcomes by means of
defining different example "profiles" of constrained Pledges. In the
following subsections, these profiles are defined and a comparison is
provided.
E.1. Minimal Pledge
The Minimal Pledge profile (Min) aims to reduce code size and
hardware cost to a minimum. This comes with some severe functional
restrictions, in particular:
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* No support for EST re-enrollment: whenever this would be needed, a
factory reset followed by a new bootstrap process is required.
* No support for change of Registrar: for this case, a factory reset
followed by a new bootstrap process is required.
This profile would be appropriate for single-use devices which must
be replaced rather than re-deployed. That might include medical
devices, but also sensors used during construction, such as concrete
temperature sensors.
E.2. Typical Pledge
The Typical Pledge profile (Typ) aims to support a typical
Constrained BRSKI feature set including EST re-enrollment support and
Registrar changes.
E.3. Full-featured Pledge
The Full-featured Pledge profile (Full) illustrates a Pledge category
that supports multiple bootstrap methods, hardware real-time clock,
BRSKI/EST resource discovery, and CSR Attributes request/response.
It also supports most of the optional features defined in this
specification.
E.4. Comparison Chart of Pledge Classes
The below table specifies the functions implemented in the three
example Pledge classes Min, Typ and Full.
+==============================================+=======+=====+======+
| Function |====================| Profiles -> | Min | Typ | Full |
+==============================================+=======+=====+======+
| *General* | === | === | ==== |
+----------------------------------------------+-------+-----+------+
| Support Constrained BRSKI bootstrap | Y | Y | Y |
+----------------------------------------------+-------+-----+------+
| Support other bootstrap method(s) | - | - | Y |
+----------------------------------------------+-------+-----+------+
| Real-time clock and cert time checks | - | - | Y |
+----------------------------------------------+-------+-----+------+
| *Constrained BRSKI* | === | === | ==== |
+----------------------------------------------+-------+-----+------+
| Discovery for rt=brski* | - | - | Y |
+----------------------------------------------+-------+-----+------+
| Support pinned Registrar public key (RPK) | Y | - | Y |
+----------------------------------------------+-------+-----+------+
| Support pinned Registrar certificate | - | Y | Y |
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+----------------------------------------------+-------+-----+------+
| Support pinned Domain CA | - | Y | Y |
+----------------------------------------------+-------+-----+------+
| *Constrained EST* | === | === | ==== |
+----------------------------------------------+-------+-----+------+
| Discovery for rt=ace.est* | - | - | Y |
+----------------------------------------------+-------+-----+------+
| GET /att and response parsing | - | - | Y |
+----------------------------------------------+-------+-----+------+
| GET /crts format 281 (multiple CA certs) | - | - | Y |
+----------------------------------------------+-------+-----+------+
| GET /crts only format 287 (one CA cert only) | Y | Y | - |
+----------------------------------------------+-------+-----+------+
| ETag handling support for GET /crts | - | Y | Y |
+----------------------------------------------+-------+-----+------+
| Re-enrollment supported | - | Y | Y |
| | (1) | | |
+----------------------------------------------+-------+-----+------+
| 6.6.1 optimized procedure | Y | Y | - |
+----------------------------------------------+-------+-----+------+
| Pro-active cert re-enrollment at own | N/A | - | Y |
| initiative | | | |
+----------------------------------------------+-------+-----+------+
| Periodic trust anchor retrieval GET /crts | - | Y | Y |
| | (1) | | |
+----------------------------------------------+-------+-----+------+
| Supports change of Registrar identity | - | Y | Y |
| | (1) | | |
+----------------------------------------------+-------+-----+------+
Table 5
Notes: (1) is possible only by doing a factory-reset followed by a
new bootstrap procedure.
Authors' Addresses
Michael Richardson
Sandelman Software Works
Email: mcr+ietf@sandelman.ca
Peter van der Stok
vanderstok consultancy
Email: stokcons@bbhmail.nl
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Panos Kampanakis
Cisco Systems
Email: pkampana@cisco.com
Esko Dijk
IoTconsultancy.nl
Email: esko.dijk@iotconsultancy.nl
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