Internet DRAFT - draft-tiloca-core-oscore-discovery
draft-tiloca-core-oscore-discovery
CoRE Working Group M. Tiloca
Internet-Draft RISE AB
Intended status: Standards Track C. Amsuess
Expires: 5 September 2024
P. van der Stok
4 March 2024
Discovery of OSCORE Groups with the CoRE Resource Directory
draft-tiloca-core-oscore-discovery-15
Abstract
Group communication over the Constrained Application Protocol (CoAP)
can be secured by means of Group Object Security for Constrained
RESTful Environments (Group OSCORE). At deployment time, devices may
not know the exact security groups to join, the respective Group
Manager, or other information required to perform the joining
process. This document describes how a CoAP endpoint can use
descriptions and links of resources registered at the CoRE Resource
Directory to discover security groups and to acquire information for
joining them through the respective Group Manager. A given security
group may protect multiple application groups, which are separately
announced in the Resource Directory as sets of endpoints sharing a
pool of resources. This approach is consistent with, but not limited
to, the joining of security groups based on the ACE framework for
Authentication and Authorization in constrained environments.
Discussion Venues
This note is to be removed before publishing as an RFC.
Discussion of this document takes place on the Constrained RESTful
Environments Working Group mailing list (core@ietf.org), which is
archived at https://mailarchive.ietf.org/arch/browse/core/.
Source for this draft and an issue tracker can be found at
https://gitlab.com/crimson84/draft-tiloca-core-oscore-discovery.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
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This Internet-Draft will expire on 5 September 2024.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
1.2. Notation and Assumptions in the CoRAL Examples . . . . . 6
2. Registration of Group Manager Endpoints . . . . . . . . . . . 7
2.1. Parameters . . . . . . . . . . . . . . . . . . . . . . . 8
2.2. Relation Link to Authorization Server . . . . . . . . . . 13
2.3. Registration Example . . . . . . . . . . . . . . . . . . 13
2.3.1. Example in Link Format . . . . . . . . . . . . . . . 14
2.3.2. Example in CoRAL . . . . . . . . . . . . . . . . . . 14
3. Addition and Update of Security Groups . . . . . . . . . . . 16
3.1. Addition Example . . . . . . . . . . . . . . . . . . . . 16
3.1.1. Example in Link Format . . . . . . . . . . . . . . . 17
3.1.2. Example in CoRAL . . . . . . . . . . . . . . . . . . 17
4. Discovery of Security Groups . . . . . . . . . . . . . . . . 20
4.1. Discovery Example #1 . . . . . . . . . . . . . . . . . . 21
4.1.1. Example in Link Format . . . . . . . . . . . . . . . 21
4.1.2. Example in CoRAL . . . . . . . . . . . . . . . . . . 23
4.2. Discovery Example #2 . . . . . . . . . . . . . . . . . . 24
4.2.1. Example in Link Format . . . . . . . . . . . . . . . 25
4.2.2. Example in CoRAL . . . . . . . . . . . . . . . . . . 26
5. Use Case Example With Full Discovery . . . . . . . . . . . . 27
6. Security Considerations . . . . . . . . . . . . . . . . . . . 32
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32
7.1. Link Relation Type Registry . . . . . . . . . . . . . . . 32
7.2. Target Attributes Registry . . . . . . . . . . . . . . . 32
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8. References . . . . . . . . . . . . . . . . . . . . . . . . . 34
8.1. Normative References . . . . . . . . . . . . . . . . . . 34
8.2. Informative References . . . . . . . . . . . . . . . . . 37
Appendix A. Use Case Example With Full Discovery (CoRAL) . . . . 39
Appendix B. Shared item tables for Packed CBOR . . . . . . . . . 45
B.1. Compression of CoRAL predicates . . . . . . . . . . . . . 45
B.2. Compression of Values of the rt= Target Attribute . . . . 47
B.3. Compression of Values of the if= Target Attribute . . . . 48
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 48
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 48
1. Introduction
The Constrained Application Protocol (CoAP) [RFC7252] supports group
communication over IP multicast [I-D.ietf-core-groupcomm-bis] to
improve efficiency and latency of communication and reduce bandwidth
requirements. A set of CoAP endpoints constitutes an application
group by sharing a common pool of resources, that can be efficiently
accessed through group communication. The members of an application
group may be members of a security group, thus sharing a common set
of keying material to secure group communication.
The security protocol Group Object Security for Constrained RESTful
Environments (Group OSCORE) [I-D.ietf-core-oscore-groupcomm] builds
on OSCORE [RFC8613] and protects CoAP messages end-to-end in group
communication contexts through CBOR Object Signing and Encryption
(COSE) [RFC9052][RFC9053]. An application group may rely on one or
more security groups, and a same security group may be used by
multiple application groups at the same time.
A CoAP endpoint relies on a Group Manager (GM) to join a security
group and get the group keying material. The joining process in
[I-D.ietf-ace-key-groupcomm-oscore] is based on the ACE framework for
Authentication and Authorization in constrained environments
[RFC9200], with the joining endpoint and the GM acting as ACE Client
and Resource Server, respectively. That is, the joining endpoint
accesses the group-membership resource exported by the GM and
associated with the security group to join.
Typically, devices store a static X509 IDevID certificate installed
at manufacturing time [RFC8995]. This is used at deployment time
during an enrollment process that provides the devices with an
Operational Certificate, possibly updated during the device lifetime.
Operational Certificates may specify information to join security
groups, especially a reference to the group-membership resources to
access at the respective GMs.
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However, it is usually impossible to provide such precise information
to freshly deployed devices, as part of their (early) Operational
Certificate. This can be due to a number of reasons: (1) the
security group(s) to join and the responsible GM(s) are generally
unknown at manufacturing time; (2) a security group of interest is
created, or the responsible GM is deployed, only after the device is
enrolled and fully operative in the network; (3) information related
to existing security groups or to their GMs has changed. This
requires a method for CoAP endpoints to dynamically discover security
groups and their GM, and to retrieve relevant information about
deployed groups.
To this end, CoAP endpoints can use descriptions and links of group-
membership resources at GMs, to discover security groups and retrieve
the information required for joining them. With the discovery
process of security groups expressed in terms of links to resources,
the remaining problem is the discovery of those links. The CoRE
Resource Directory (RD) [RFC9176] allows such discovery in an
efficient way, and it is expected to be used in many setups that
would benefit of security group discovery.
This specification builds on this approach and describes how CoAP
endpoints can use the RD to perform the link discovery steps, in
order to discover security groups and retrieve the information
required to join them through their GM. In short, the GM registers
as an endpoint with the RD. The resulting registration resource
includes one link per security group under that GM, specifying the
path to the related group-membership resource to access for joining
that group.
Additional descriptive information about the security group is stored
with the registered link. In a RD based on Link Format [RFC6690] as
defined in [RFC9176], this information is specified as target
attributes of the registered link, and includes the identifiers of
the application groups which use that security group. This enables a
lookup of those application groups at the RD, where they are
separately announced by a Commissioning Tool (see Appendix A of
[RFC9176]).
When querying the RD for security groups, a CoAP endpoint can use
CoAP observation [RFC7641]. This results in automatic notifications
on the creation of new security groups or the update of existing
groups. Thus, it facilitates the early deployment of CoAP endpoints,
i.e., even before the GM is deployed and security groups are created.
Interaction examples are provided in Link Format, as well as in the
Constrained RESTful Application Language CoRAL [I-D.ietf-core-coral]
with reference to a CoRAL-based RD [I-D.hartke-t2trg-coral-reef].
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The examples in CoRAL are expressed in CBOR diagnostic notation
[RFC8949], and refer to values from external dictionaries using
Packed CBOR [I-D.ietf-cbor-packed]. Section 1.2 introduces the
notation and assumptions used in the CoRAL examples.
The approach in this document is consistent with, but not limited to,
the joining of security groups defined in
[I-D.ietf-ace-key-groupcomm-oscore].
1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
Readers are expected to be familiar with the terms and concepts from
the following specifications.
* Link Format [RFC6690] and the CoRE Resource Directory [RFC9176].
* The Constrained RESTful Application Language (CoRAL)
[I-D.ietf-core-coral] and Constrained Resource Identifiers (CRIs)
[I-D.ietf-core-href].
* CBOR [RFC8949] and Packed CBOR [I-D.ietf-cbor-packed].
* The CoAP protocol [RFC7252], also in group communication scenarios
[I-D.ietf-core-groupcomm-bis].
* The security protocol Group Object Security for Constrained
RESTful Environments (Group OSCORE)
[I-D.ietf-core-oscore-groupcomm], and the joining of security
groups defined in [I-D.ietf-ace-key-groupcomm-oscore].
Consistently with the definitions from Section 2.1 of
[I-D.ietf-core-groupcomm-bis], this document also refers to the
following terminology.
* CoAP group: a set of CoAP endpoints all configured to receive CoAP
multicast messages sent to the group's associated IP multicast
address and UDP port. An endpoint may be a member of multiple
CoAP groups by subscribing to multiple IP multicast addresses.
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* Security group: a set of CoAP endpoints that share the same
security material, and use it to protect and verify exchanged
messages. A CoAP endpoint may be a member of multiple security
groups. There can be a one-to-one or a one-to-many relation
between security groups and CoAP groups.
This document especially considers a security group to be an
OSCORE group, where all members share one OSCORE Security Context
to protect group communication with Group OSCORE
[I-D.ietf-core-oscore-groupcomm]. However, the approach defined
in this document can be used to support the discovery of different
security groups than OSCORE groups.
* Application group: a set of CoAP endpoints that share a common set
of resources. An endpoint may be a member of multiple application
groups. An application group can be associated with one or more
security groups, and multiple application groups can use the same
security group. Application groups are announced in the RD by a
Commissioning Tool, according to the RD-Groups usage pattern (see
Appendix A of [RFC9176]).
Like [I-D.ietf-core-oscore-groupcomm], this document also uses the
following term.
* Authentication credential: set of information associated with an
entity, including that entity's public key and parameters
associated with the public key. Examples of authentication
credentials are CBOR Web Tokens (CWTs) and CWT Claims Sets (CCSs)
[RFC8392], X.509 certificates [RFC5280] and C509 certificates
[I-D.ietf-cose-cbor-encoded-cert].
Terminology for constrained environments, such as "constrained
device" and "constrained-node network", is defined in [RFC7228].
1.2. Notation and Assumptions in the CoRAL Examples
As per Section 2.4 of [I-D.ietf-core-coral], CoRAL expresses Uniform
Resource Identifiers (URIs) [RFC3986] as Constrained Resource
Identifier (CRI) references [I-D.ietf-core-href].
Throughout this document, the examples in CoRAL use the following
notation.
When using the CURIE syntax [CURIE-20101216], the following applies.
* 'linkformat' stands for http://www.iana.org/assignments/
linkformat/
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This URI is to be defined with IANA, together with other URIs that
build on it through further path segments, e.g.,
http://www.iana.org/assignments/linkformat/rt
* 'rel' stands for http://www.iana.org/assignments/relation/
This URI is to be defined with IANA, together with other URIs that
build on it through further path segments, e.g.,
http://www.iana.org/assignments/relation/hosts
* 'reef' stands for http://coreapps.org/reef
When using a URI http://www.iana.org/assignments/linkformat/SEG1/SEG2
* The path segment SEG1 is the name of a web link target attribute.
Names of target attributes used in Link Format [RFC6690] are
expected to be coordinated through the "Target Attributes"
registry [Target.Attributes] defined in
[I-D.ietf-core-target-attr].
* The path segment SEG2 is the value of the target attribute.
When using a URI http://www.iana.org/assignments/relation/SEG , the
path segment SEG denotes a Web Linking relation type [RFC8288].
The application-extension identifier "cri" defined in Appendix C of
[I-D.ietf-core-href] is used to notate a CBOR Extended Diagnostic
Notation (EDN) literal for a CRI or CRI reference. This format is
not expected to be sent over the network.
Packed CBOR [I-D.ietf-cbor-packed] is also used, thus reducing
representation size. The examples especially refer to the values
from the three shared item tables in Appendix B.
Finally, the examples use the CoAP Content-Format ID 65087 for the
media-type application/coral+cbor.
2. Registration of Group Manager Endpoints
During deployment, a Group Manager (GM) can find the CoRE Resource
Directory (RD) as described in Section 4 of [RFC9176].
Afterwards, the GM registers as an endpoint with the RD, as described
in Section 5 of [RFC9176]. The GM SHOULD NOT use the Simple
Registration approach described in Section 5.1 of [RFC9176].
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When registering with the RD, the GM also registers the links to all
the group-membership resources it has at that point in time, i.e.,
one for each of its security groups.
In the registration request, each link to a group-membership resource
has as target the URI of that resource at the GM. Also, it specifies
a number of descriptive parameters as defined in Section 2.1.
Furthermore, the GM MAY additionally register the link to its
resource implementing the ACE authorization information endpoint (see
Section 5.10.1 of [RFC9200]). A joining node can provide the GM with
its own access token by sending it in a request targeting that
resource, thus proving to be authorized to join certain security
groups (see Section 6.1 of [I-D.ietf-ace-key-groupcomm-oscore]). In
such a case, the link MUST include the parameter 'rt' with value
"ace.ai", defined in Section 8.2 of [RFC9200].
2.1. Parameters
For each registered link to a group-membership resource at a GM, the
following parameters are specified together with the link.
In the RD defined in [RFC9176] and based on Link Format, each
parameter is specified in a target attribute with the same name.
In a RD based on CoRAL, such as the one defined in
[I-D.hartke-t2trg-coral-reef], each parameter is specified in a
nested element with the same name.
* 'ct', specifying the content format used with the group-membership
resource at the Group Manager, with the value registered in
Section 11.2 of [I-D.ietf-ace-key-groupcomm] for "application/ace-
groupcomm+cbor".
Note: The examples in this document use the provisional value
65000 from the range "Reserved for Experimental Use" of the "CoAP
Content-Formats" registry, within the "CoRE Parameters" registry.
* 'rt', specifying the resource type of the group-membership
resource at the Group Manager, with value "core.osc.gm" registered
in Section 16.11 of [I-D.ietf-ace-key-groupcomm-oscore].
* 'if', specifying the interface description for accessing the
group-membership resource at the Group Manager, with value
"ace.group" registered in Section 11.5 of
[I-D.ietf-ace-key-groupcomm].
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* 'sec-gp', specifying the name of the security group of interest,
as a stable and invariant identifier, such as the group name used
in [I-D.ietf-ace-key-groupcomm-oscore]. This parameter MUST
specify a single value.
* 'app-gp', specifying the name(s) of the application group(s)
associated with the security group of interest indicated by 'sec-
gp'. This parameter MUST occur once for each application group,
and MUST specify only a single application group.
When a security group is created at the GM, the names of the
application groups using it are also specified as part of the
security group configuration (see [I-D.ietf-ace-oscore-gm-admin][I
-D.ietf-ace-oscore-gm-admin-coral]). Thus, when registering the
links to its group-membership resource, the GM is aware of the
application groups and their names.
If a different entity than the GM registers the security groups to
the RD, e.g., a Commissioning Tool, this entity has to also be
aware of the application groups and their names to specify. To
this end, it can obtain them from the GM or from the Administator
that created the security groups at the GM (see [I-D.ietf-ace-osco
re-gm-admin][I-D.ietf-ace-oscore-gm-admin-coral]).
Optionally, the following parameters can also be specified. If Link
Format is used, the value of each of these parameters is encoded as a
text string.
* 'hkdf', specifying the HKDF algorithm used in the security group,
e.g., aligned with the parameter HKDF Algorithm in the Group
OSCORE Security Context (see Section 2 of
[I-D.ietf-core-oscore-groupcomm]). If present, this parameter
MUST specify a single value, which is taken from the 'Value'
column of the "COSE Algorithms" Registry [COSE.Algorithms].
* 'cred-fmt', specifying the format of the authentication
credentials used in the security group, e.g., aligned with the
parameter Authentication Credential Format in the Group OSCORE
Security Context (see Section 2 of
[I-D.ietf-core-oscore-groupcomm]). If present, this parameter
MUST specify a single value, which is taken from the 'Label'
column of the "COSE Header Parameters" Registry
[COSE.Header.Parameters]. Acceptable values denote a format that
MUST explicitly provide the public key as well as the
comprehensive set of information related to the public key
algorithm, including, e.g., the used elliptic curve (when
applicable).
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At the time of writing this specification, acceptable formats of
authentication credentials are CBOR Web Tokens (CWTs) and CWT
Claim Sets (CCSs) [RFC8392], X.509 certificates [RFC5280] and C509
certificates [I-D.ietf-cose-cbor-encoded-cert]. Further formats
may be available in the future, and would be acceptable to use as
long as they comply with the criteria defined above.
[ As to CWTs and unprotected CWT claim sets, there is a pending
registration requested by draft-ietf-lake-edhoc. ]
[ As to C509 certificates, there is a pending registration
requested by draft-ietf-cose-cbor-encoded-cert. ]
* 'gp-enc-alg', specifying the encryption algorithm used to encrypt
messages in the security group when these are also signed, e.g.,
aligned with the parameter Group Encryption Algorithm in the Group
OSCORE Security Context (see Section 2 of
[I-D.ietf-core-oscore-groupcomm]) to be used with the group mode
of Group OSCORE (see Section 8 of
[I-D.ietf-core-oscore-groupcomm]). If present, this parameter
MUST specify a single value, which is taken from the 'Value'
column of the "COSE Algorithms" Registry [COSE.Algorithms].
* 'sign-alg', specifying the algorithm used to sign messages in the
security group, e.g., aligned with the parameter Signature
Algorithm in the Group OSCORE Security Context (see Section 2 of
[I-D.ietf-core-oscore-groupcomm]) to be used with the group mode
of Group OSCORE (see Section 8 of
[I-D.ietf-core-oscore-groupcomm]). If present, this parameter
MUST specify a single value, which is taken from the 'Value'
column of the "COSE Algorithms" Registry [COSE.Algorithms].
* 'sign-alg-crv', specifying the elliptic curve (if applicable) for
the algorithm used to sign messages in the security group. If
present, this parameter MUST specify a single value, which is
taken from the 'Value' column of the "COSE Elliptic Curves"
Registry [COSE.Elliptic.Curves].
* 'sign-key-kty', specifying the key type of signing keys used to
sign messages in the security group. If present, this parameter
MUST specify a single value, which is taken from the 'Value'
column of the "COSE Key Types" Registry [COSE.Key.Types].
* 'sign-key-crv', specifying the elliptic curve (if applicable) of
signing keys used to sign messages in the security group. If
present, this parameter MUST specify a single value, which is
taken from the 'Value' column of the "COSE Elliptic Curves"
Registry [COSE.Elliptic.Curves].
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* 'alg', specifying the encryption algorithm used to encrypt
messages in the security group when these are encrypted with
pairwise encryption keys, e.g., aligned with the parameter AEAD
Algorithm in the Group OSCORE Security Context (see Section 2 of
[I-D.ietf-core-oscore-groupcomm]) to be used with the pairwise
mode of Group OSCORE (see Section 9 of
[I-D.ietf-core-oscore-groupcomm]). If present, this parameter
MUST specify a single value, which is taken from the 'Value'
column of the "COSE Algorithms" Registry [COSE.Algorithms].
* 'ecdh-alg', specifying the ECDH algorithm used to derive pairwise
encryption keys in the security group, e.g., aligned with the
parameter Pairwise Key Agreement Algorithm in the Group OSCORE
Security Context (see Section 2 of
[I-D.ietf-core-oscore-groupcomm]) to be used with the pairwise
mode of Group OSCORE (see Section 9 of
[I-D.ietf-core-oscore-groupcomm]). If present, this parameter
MUST specify a single value, which is taken from the 'Value'
column of the "COSE Algorithms" Registry [COSE.Algorithms].
* 'ecdh-alg-crv', specifying the elliptic curve for the ECDH
algorithm used to derive pairwise encryption keys in the security
group. If present, this parameter MUST specify a single value,
which is taken from the 'Value' column of the "COSE Elliptic
Curves" Registry [COSE.Elliptic.Curves].
* 'ecdh-key-kty', specifying the key type of keys used with an ECDH
algorithm to derive pairwise encryption keys in the security
group. If present, this parameter MUST specify a single value,
which is taken from the 'Value' column of the "COSE Key Types"
Registry [COSE.Key.Types].
* 'ecdh-key-crv', specifying the elliptic curve of keys used with an
ECDH algorithm to derive pairwise encryption keys in the security
group. If present, this parameter MUST specify a single value,
which is taken from the 'Value' column of the "COSE Elliptic
Curves" Registry [COSE.Elliptic.Curves].
* 'det-hash-alg', specifying the hash algorithm used in the security
group when producing deterministic requests, e.g., as defined in
[I-D.amsuess-core-cachable-oscore]. If present, this parameter
MUST specify a single value, which is taken from the 'Value'
column of the "COSE Algorithms" Registry [COSE.Algorithms]. This
parameter MUST NOT be present if the security group does not use
deterministic requests.
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* 'rekeying-scheme', specifying the rekeying scheme used in the
security group for distributing new group keying meterial to the
group members. If present, this parameter MUST specify a single
value, which is taken from the 'Value' column of the "ACE
Groupcomm Rekeying Schemes" registry defined in Section 11.12 of
[I-D.ietf-ace-key-groupcomm].
If the security group does not recur to message signing, then the
parameters 'gp-enc-alg', 'sign-alg', 'sign-alg-crv', 'sign-key-kty'
and 'sign-key-crv' MUST NOT be present. For instance, this is the
case for a security group that uses Group OSCORE and uses only the
pairwise mode (see Section 9 of [I-D.ietf-core-oscore-groupcomm]).
If the security group does not recur to message encryption through
pairwise encryption keys, then the parameters 'alg', 'ecdh-alg',
'ecdh-alg-crv', 'ecdh-key-kty' and 'ecdh-key-crv' MUST NOT be
present. For instance, this is the case for a security group that
uses Group OSCORE and uses only the group mode see Section 8 of
[I-D.ietf-core-oscore-groupcomm]).
Note that the values registered in the COSE Registries
[COSE.Algorithms][COSE.Elliptic.Curves][COSE.Key.Types] are strongly
typed. On the contrary, Link Format is weakly typed and thus does
not distinguish between, for instance, the string value "-10" and the
integer value -10.
Thus, in RDs that return responses in Link Format, string values
which look like an integer are not supported. Therefore, such values
MUST NOT be advertised through the corresponding parameters above.
A CoAP endpoint that queries the RD to discover security groups and
their group-membership resource to access (see Section 4) would
benefit from the information above as follows.
* The values of 'cred-fmt', 'sign-alg', 'sign-alg-crv', 'sign-key-
kty', 'sign-key-crv', 'ecdh-alg', 'ecdh-alg-crv', 'ecdh-key-kty'
and 'ecdh-key-crv' related to a group-membership resource provide
an early knowledge of the format of authentication credentials as
well as of the type of public keys used in the security group.
Thus, the CoAP endpoint does not need to ask the GM for this
information as a preliminary step before the joining process, or
to perform a trial-and-error joining exchange with the GM. Hence,
at the very first step of the joining process, the CoAP endpoint
is able to provide the GM with its own authentication credential
in the correct expected format and including a public key of the
correct expected type.
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* The values of 'hkdf', 'gp-enc-alg', 'sign-alg', 'alg' and 'ecdh-
alg' related to a group-membership resource provide an early
knowledge of the algorithms used in the security group.
Thus, the CoAP endpoint is able to decide whether to actually
proceed with the joining process, depending on its support for the
indicated algorithms.
2.2. Relation Link to Authorization Server
For each registered link to a group-membership resource, the GM MAY
additionally specify the link to the ACE Authorization Server (AS)
[RFC9200] associated with the GM, and issuing authorization
credentials to join the security group as described in
[I-D.ietf-ace-key-groupcomm-oscore].
The link to the AS has as target the URI of the resource where to
send an authorization request to.
In the RD defined in [RFC9176] and based on Link Format, the link to
the AS is separately registered with the RD, and includes the
following parameters as target attributes.
* 'rel', with value "authorization_server".
* 'anchor', with value the target of the link to the group-
membership resource at the GM.
In a RD based on CoRAL, such as the one defined in
[I-D.hartke-t2trg-coral-reef], this is mapped (as describe there) to
a link from the registration resource to the AS, using the
<http://www.iana.org/assignments/relation/authorization_server> link
relation type.
2.3. Registration Example
The example below shows a GM with endpoint name "gm1" and address
[2001:db8::ab] that registers with the RD.
The GM specifies the value of the 'sec-gp' parameter for accessing
the security group with name "feedca570000", and used by the
application group with name "group1" specified with the value of the
'app-gp' parameter.
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The signature algorithm used in the security group is EdDSA (-8),
with elliptic curve Ed25519 (6). Authentication credentials used in
the security group are X.509 certificates [RFC5280], which is
signaled through the COSE Header Parameter "x5chain" (33). The ECDH
algorithm used in the security group is ECDH-SS + HKDF-256 (-27),
with elliptic curve X25519 (4).
In addition, the GM specifies the link to the ACE Authorization
Server associated with the GM, to which a CoAP endpoint should send
an Authorization Request for joining the corresponding security group
(see [I-D.ietf-ace-key-groupcomm-oscore]).
2.3.1. Example in Link Format
Request: GM -> RD
Req: POST coap://rd.example.com/rd?ep=gm1
Content-Format: 40
Payload:
</ace-group/feedca570000>;ct=65000;rt="core.osc.gm";if="ace.group";
sec-gp="feedca570000";app-gp="group1";
cred-fmt="33";gp-enc-alg="10";
sign-alg="-8";sign-alg-crv="6";
alg="10";ecdh-alg="-27";ecdh-alg-crv="4",
<coap://as.example.com/token>;rel="authorization-server";
anchor="coap://[2001:db8::ab]/ace-group/feedca570000"
Response: RD -> GM
Res: 2.01 Created
Location-Path: /rd/4521
2.3.2. Example in CoRAL
Request: GM -> RD
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Req: POST coap://rd.example.com/rd
Content-Format: 65087 (application/coral+cbor)
Payload:
[
[1, cri'coap://[2001:db8::ab]'],
[2, 6(-22) / item 59 for reef:ep /, "gm1"],
[
2, 6(-20) / item 55 for reef:#rd-item /,
cri'/ace-group/feedca570000',
[
[2, simple(8) / item 8 for linkformat:ct /, 65000],
[
2, simple(6) / item 6 for linkformat:rt /,
6(200) / item 416 for cri'http://www.iana.org/assignments/
linkformat/rt/core.osc.gm' /
],
[
2, simple(7) / item 7 for linkformat:if /,
6(250) / item 516 for cri'http://www.iana.org/assignments/
linkformat/if/ace.group' /
],
[2, 6(-3) / item 21 for linkformat:sec-gp / , "feedca570000"],
[2, 6(3) / item 22 for linkformat:app-gp / , "group1"],
[2, 6(4) / item 24 for linkformat:cred-fmt / , 33],
[2, 6(-5) / item 25 for linkformat:sign-enc-alg / , 10],
[2, 6(5) / item 26 for linkformat:sign-alg / , -8],
[2, 6(-6) / item 27 for linkformat:sign-alg-crv / , 6],
[2, 6(7) / item 30 for linkformat:alg / , 10],
[2, 6(-8) / item 31 for linkformat:ecdh-alg / , -27],
[2, 6(8) / item 32 for linkformat:ecdh-alg-crv / , 4],
[
2, simple(1) / item 1 for rel:authorization-server / ,
cri'coap://as.example.com/token'
]
]
]
]
Response: RD -> GM
Res: 2.01 Created
Location-Path: /rd/4521
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3. Addition and Update of Security Groups
The GM is responsible to refresh the registration of all its group-
membership resources in the RD. This means that the GM has to update
the registration within its lifetime as per Section 5.3.1 of
[RFC9176], and has to change the content of the registration when a
group-membership resource is added/removed, or if its parameters have
to be changed, such as in the following cases.
* The GM creates a new security group and starts exporting the
related group-membership resource.
* The GM dismisses a security group and stops exporting the related
group-membership resource.
* Information related to an existing security group changes, e.g.,
the list of associated application groups.
To perform an update of its registrations, the GM can re-register
with the RD and fully specify all links to its group-membership
resources.
Alternatively, the GM can perform a PATCH/iPATCH [RFC8132] request to
the RD, as per Section 5.3.3 of [RFC9176]. This requires new media-
types to be defined in future standards, to apply a new document as a
patch to an existing stored document.
3.1. Addition Example
The example below shows how the GM from Section 2 re-registers with
the RD. When doing so, it specifies:
* The same previous group-membership resource associated with the
security group with name "feedca570000".
* An additional group-membership resource associated with the
security group with name "ech0ech00000" and used by the
application group "group2".
* A third group-membership resource associated with the security
group with name "abcdef120000" and used by two application groups,
namely "group3" and "group4".
Furthermore, the GM relates the same Authorization Server also to the
security groups "ech0ech00000" and "abcdef120000".
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3.1.1. Example in Link Format
Request: GM -> RD
Req: POST coap://rd.example.com/rd?ep=gm1
Content-Format: 40
Payload:
</ace-group/feedca570000>;ct=65000;rt="core.osc.gm";if="ace.group";
sec-gp="feedca570000";app-gp="group1";
cred-fmt="33";gp-enc-alg="10";
sign-alg="-8";sign-alg-crv="6";
alg="10";ecdh-alg="-27";ecdh-alg-crv="4",
</ace-group/ech0ech00000>;ct=65000;rt="core.osc.gm";if="ace.group";
sec-gp="ech0ech00000";app-gp="group2";
cred-fmt="33";gp-enc-alg="10";
sign-alg="-8";sign-alg-crv="6";
alg="10";ecdh-alg="-27";ecdh-alg-crv="4",
</ace-group/abcdef120000>;ct=65000;rt="core.osc.gm";if="ace.group";
sec-gp="abcdef120000";app-gp="group3";
app-gp="group4";cred-fmt="33";
gp-enc-alg="10";sign-alg="-8";
sign-alg-crv="6";alg="10";ecdh-alg="-27";
ecdh-alg-crv="4",
<coap://as.example.com/token>;rel="authorization-server";
anchor="coap://[2001:db8::ab]/ace-group/feedca570000",
<coap://as.example.com/token>;rel="authorization-server";
anchor="coap://[2001:db8::ab]/ace-group/ech0ech00000",
<coap://as.example.com/token>;rel="authorization-server";
anchor="coap://[2001:db8::ab]/ace-group/abcdef120000"
Response: RD -> GM
Res: 2.04 Changed
Location-Path: /rd/4521
3.1.2. Example in CoRAL
Request: GM -> RD
Req: POST coap://rd.example.com/rd
Content-Format: 65087 (application/coral+cbor)
Payload:
[
[1, cri'coap://[2001:db8::ab]'],
[2, 6(-22) / item 59 for reef:#ep /, "gm1"],
[
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2, 6(-20) / item 55 for reef:#rd-item /,
cri'/ace-group/feedca570000',
[
[2, simple(8) / item 8 for linkformat:ct /, 65000],
[2, simple(6) / item 6 for linkformat:rt /,
6(200) / item 416 for cri'http://www.iana.org/assignments/
linkformat/rt/core.osc.gm' /
],
[2, simple(7) / item 7 for linkformat:if /,
6(250) / item 516 for cri'http://www.iana.org/assignments/
linkformat/if/ace.group' /
],
[2, 6(-3) / item 21 for linkformat:sec-gp / , "feedca570000"],
[2, 6(3) / item 22 for linkformat:app-gp / , "group1"],
[2, 6(4) / item 24 for linkformat:cred_fmt / , 33],
[2, 6(-5) / item 25 for linkformat:sign_enc_alg / , 10],
[2, 6(5) / item 26 for linkformat:sign_alg / , -8],
[2, 6(-6) / item 27 for linkformat:sign_alg_crv / , 6],
[2, 6(7) / item 30 for linkformat:alg / , 10],
[2, 6(-8) / item 31 for linkformat:ecdh_alg / , -27],
[2, 6(8) / item 32 for linkformat:ecdh_alg_crv / , 4],
[
2, simple(1) / item 1 for rel:authorization-server / ,
cri'coap://as.example.com/token'
]
]
],
[
2, 6(-20) / item 55 for reef:#rd-item /,
cri'/ace-group/ech0ech00000',
[
[2, simple(8) / item 8 for linkformat:ct /, 65000],
[
2, simple(6) / item 6 for linkformat:rt /,
6(200) / item 416 for cri'http://www.iana.org/assignments/
linkformat/rt/core.osc.gm' /
],
[
2, simple(7) / item 7 for linkformat:if /,
6(250) / item 516 for cri'http://www.iana.org/assignments/
linkformat/if/ace.group' /
],
[2, 6(-3) / item 21 for linkformat:sec-gp / , "ech0ech00000"],
[2, 6(3) / item 22 for linkformat:app-gp / , "group2"],
[2, 6(4) / item 24 for linkformat:cred_fmt / , 33],
[2, 6(-5) / item 25 for linkformat:sign_enc_alg / , 10],
[2, 6(5) / item 26 for linkformat:sign_alg / , -8],
[2, 6(-6) / item 27 for linkformat:sign_alg_crv / , 6],
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[2, 6(7) / item 30 for linkformat:alg / , 10],
[2, 6(-8) / item 31 for linkformat:ecdh_alg / , -27],
[2, 6(8) / item 32 for linkformat:ecdh_alg_crv / , 4],
[
2, simple(1) / item 1 for rel:authorization-server / ,
cri'coap://as.example.com/token'
]
]
],
[
2, 6(-20) / item 55 for reef:#rd-item /,
cri'/ace-group/abcdef120000',
[
[2, simple(8) / item 8 for linkformat:ct /, 65000],
[2, simple(6) / item 6 for linkformat:rt /,
6(200) / item 416 for cri'http://www.iana.org/assignments/
linkformat/rt/core.osc.gm' /
],
[
2, simple(7) / item 7 for linkformat:if /,
6(250) / item 516 for cri'http://www.iana.org/assignments/
linkformat/if/ace.group' /
],
[2, 6(-3) / item 21 for linkformat:sec-gp / , "abcdef120000"],
[2, 6(3) / item 22 for linkformat:app-gp / , "group3"],
[2, 6(3) / item 22 for linkformat:app-gp / , "group4"],
[2, 6(4) / item 24 for linkformat:cred_fmt / , 33],
[2, 6(-5) / item 25 for linkformat:sign_enc_alg / , 10],
[2, 6(5) / item 26 for linkformat:sign_alg / , -8],
[2, 6(-6) / item 27 for linkformat:sign_alg_crv / , 6],
[2, 6(7) / item 30 for linkformat:alg / , 10],
[2, 6(-8) / item 31 for linkformat:ecdh_alg / , -27],
[2, 6(8) / item 32 for linkformat:ecdh_alg_crv / , 4],
[2, simple(1) / item 1 for rel:authorization-server / ,
cri'coap://as.example.com/token'
]
]
]
]
Response: RD -> GM
Res: 2.04 Changed
Location-Path: /rd/4521
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4. Discovery of Security Groups
A CoAP endpoint that wants to join a security group, hereafter called
the joining node, might not have all the necessary information at
deployment time. Also, it might want to know about possible new
security groups created afterwards by the respective Group Managers.
To this end, the joining node can perform a resource lookup at the RD
as per Section 6.1 of [RFC9176], to retrieve the missing pieces of
information needed to join the security group(s) of interest. The
joining node can find the RD as described in Section 4 of [RFC9176].
The joining node uses the following parameter value for the lookup
filtering.
* 'rt' = "core.osc.gm", specifying the resource type of the group-
membership resource at the Group Manager, with value "core.osc.gm"
registered in Section 16.11 of
[I-D.ietf-ace-key-groupcomm-oscore].
The joining node may additionally consider the following parameters
for the lookup filtering, depending on the information it has already
available.
* 'sec-gp', specifying the name of the security group of interest.
This parameter MUST specify a single value.
* 'ep', specifying the registered endpoint of the GM.
* 'app-gp', specifying the name(s) of the application group(s)
associated with the security group of interest. This parameter
MAY be included multiple times, and each occurrence MUST specify
the name of one application group.
* 'if', specifying the interface description for accessing the
group-membership resource at the Group Manager, with value
"ace.group" registered in Section 11.5 of
[I-D.ietf-ace-key-groupcomm].
The response from the RD may include links to a group-membership
resource specifying multiple application groups, as all using the
same security group. In this case, the joining node is already
expected to know the exact application group of interest.
Furthermore, the response from the RD may include the links to
different group-membership resources, all specifying a same
application group of interest for the joining node, if the
corresponding security groups are all used by that application group.
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In this case, application policies on the joining node should define
how to determine the exact security group to join (see Section 2.1 of
[I-D.ietf-core-groupcomm-bis]). For example, different security
groups can reflect different security algorithms to use. Hence, a
client application can take into account what the joining node
supports and prefers, when selecting one particular security group
among the indicated ones, while a server application would need to
join all of them. Later on, the joining node will be anyway able to
join only security groups for which it is actually authorized to be a
member (see [I-D.ietf-ace-key-groupcomm-oscore]).
Note that, with RD-based discovery, including the 'app-gp' parameter
multiple times would result in finding only the group-membership
resource that serves all the specified application groups, i.e., not
any group-membership resource that serves either. Therefore, a
joining node needs to perform N separate queries with different
values for 'app-gp', in order to safely discover the (different)
group-membership resource(s) serving the N application groups.
The discovery of security groups as defined in this document is
applicable and useful to other CoAP endpoints than the actual joining
nodes. In particular, other entities can be interested to discover
and interact with the group-membership resource at the Group Manager.
These include entities acting as signature checkers, e.g.,
intermediary gateways, that do not join a security group, but can
retrieve authentication credentials of group members from the Group
Manager, in order to verify counter signatures of group messages (see
Section 3.3 of [I-D.ietf-core-oscore-groupcomm]).
4.1. Discovery Example #1
Consistently with the examples in Section 2 and Section 3, the
examples below consider a joining node that wants to join the
security group associated with the application group "group1", but
that does not know the name of the security group, the responsible GM
and the group-membership resource to access.
4.1.1. Example in Link Format
Request: Joining node -> RD
Req: GET coap://rd.example.com/rd-lookup/res
?rt=core.osc.gm&app-gp=group1
Response: RD -> Joining node
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Res: 2.05 Content
Payload:
<coap://[2001:db8::ab]/ace-group/feedca570000>;ct=65000;
rt="core.osc.gm";if="ace.group";sec-gp="feedca570000";
app-gp="group1";cred-fmt="33";gp-enc-alg="10";
sign-alg="-8";sign-alg-crv="6";alg="10";
ecdh-alg="-27";ecdh-alg-crv="4"
By performing the separate resource lookup below, the joining node
can retrieve the link to the ACE Authorization Server associated with
the GM, where to send an Authorization Request for joining the
corresponding security group (see
[I-D.ietf-ace-key-groupcomm-oscore]).
Request: Joining node -> RD
Req: GET coap://rd.example.com/rd-lookup/res
?rel=authorization-server&
anchor=coap://[2001:db8::ab]/ace-group/feedca570000
Response: RD -> Joining node
Res: 2.05 Content
Payload:
<coap://as.example.com/token>;rel=authorization-server;
anchor="coap://[2001:db8::ab]/ace-group/feedca570000"
To retrieve the multicast IP address of the CoAP group used by the
application group "group1", the joining node performs an endpoint
lookup as shown below. The following assumes that the application
group "group1" had been previously registered as per Appendix A of
[RFC9176], with ff35:30:2001:db8::23 as multicast IP address of the
associated CoAP group.
Request: Joining node -> RD
Req: GET coap://rd.example.com/rd-lookup/ep
?et=core.rd-group&ep=group1
Response: RD -> Joining node
Res: 2.05 Content
Payload:
</rd/501>;ep="group1";et="core.rd-group";
base="coap://[ff35:30:2001:db8::23]";rt="core.rd-ep"
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4.1.2. Example in CoRAL
Request: Joining node -> RD
Req: GET coap://rd.example.com/rd-lookup/res
?rt=core.osc.gm&app-gp=group1
Accept: 65087 (application/coral+cbor)
Response: RD -> Joining node
Res: 2.05 Content
Content-Format: 65087 (application/coral+cbor)
Payload:
[
[1, cri'coap://[2001:db8::ab]'],
[
2, 6(-20) / item 55 for reef:#rd-item /,
cri'/ace-group/feedca570000',
[
[2, simple(8) / item 8 for linkformat:ct /, 65000],
[2, simple(6) / item 6 for linkformat:rt /,
6(200) / item 416 for cri'http://www.iana.org/assignments/
linkformat/rt/core.osc.gm' /
],
[2, simple(7) / item 7 for linkformat:if /,
6(250) / item 516 for cri'http://www.iana.org/assignments/
linkformat/if/ace.group' /
],
[2, 6(-3) / item 21 for linkformat:sec-gp / , "feedca570000"],
[2, 6(3) / item 22 for linkformat:app-gp / , "group1"],
[2, 6(4) / item 24 for linkformat:cred_fmt / , 33],
[2, 6(-5) / item 25 for linkformat:sign_enc_alg / , 10],
[2, 6(5) / item 26 for linkformat:sign_alg / , -8],
[2, 6(-6) / item 27 for linkformat:sign_alg_crv / , 6],
[2, 6(7) / item 30 for linkformat:alg / , 10],
[2, 6(-8) / item 31 for linkformat:ecdh_alg / , -27],
[2, 6(8) / item 32 for linkformat:ecdh_alg_crv / , 4],
[2, simple(1) / item 1 for rel:authorization-server / ,
cri'coap://as.example.com/token'
]
]
]
]
To retrieve the multicast IP address of the CoAP group used by the
application group "group1", the joining node performs an endpoint
lookup as shown below. The following assumes that the application
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group "group1" had been previously registered, with
ff35:30:2001:db8::23 as multicast IP address of the associated CoAP
group.
Request: Joining node -> RD
Req: GET coap://rd.example.com/rd-lookup/ep
?et=core.rd-group&ep=group1
Accept: 65087 (application/coral+cbor)
Response: RD -> Joining node
Res: 2.05 Content
Content-Format: 65087 (application/coral+cbor)
Payload:
[
[
2, 6(20) / item 56 for reef:#rd-unit /, cri'/rd/501',
[
[2, 6(-22) / item 59 for reef:#ep /, "group1"],
[2, 6(21) / item 58 for reef:#et /, "core.rd-group"],
[
2, 6(22) / item 60 for reef:#base /,
cri'coap://[ff35:30:2001:db8::23]'
],
[2, 6(-21) / item 57 for reef:#rt /, "core.rd-ep"],
]
]
]
4.2. Discovery Example #2
Consistently with the examples in Section 2 and Section 3, the
examples below consider a joining node that wants to join the
security group with name "feedca570000", but that does not know the
responsible GM, the group-membership resource to access, and the
associated application groups.
The examples also show how the joining node uses CoAP observation
[RFC7641], in order to be notified of possible changes to the
parameters of the group-membership resource. This is also useful to
handle the case where the security group of interest has not been
created yet, so that the joining node can receive the requested
information when it becomes available.
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4.2.1. Example in Link Format
Request: Joining node -> RD
Req: GET coap://rd.example.com/rd-lookup/res
?rt=core.osc.gm&sec-gp=feedca570000
Observe: 0
Response: RD -> Joining node
Res: 2.05 Content
Observe: 24
Payload:
<coap://[2001:db8::ab]/ace-group/feedca570000>;ct=65000;
rt="core.osc.gm";if="ace.group";sec-gp="feedca570000";
app-gp="group1";cred-fmt="33";gp-enc-alg="10";
sign-alg="-8";sign-alg-crv="6";alg="10";
ecdh-alg="-27";ecdh-alg-crv="4"
Depending on the search criteria, the joining node performing the
resource lookup can get large responses. This can happen, for
instance, when the lookup request targets all the group-membership
resources at a specified GM, or all the group-membership resources of
all the registered GMs, as in the example below.
Request: Joining node -> RD
Req: GET coap://rd.example.com/rd-lookup/res?rt=core.osc.gm
Response: RD -> Joining node
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Res: 2.05 Content
Payload:
<coap://[2001:db8::ab]/ace-group/feedca570000>;ct=65000;
rt="core.osc.gm";if="ace.group";sec-gp="feedca570000";
app-gp="group1";cred-fmt="33";gp-enc-alg="10";
sign-alg="-8";sign-alg-crv="6";alg="10";ecdh-alg="-27";
ecdh-alg-crv="4",
<coap://[2001:db8::ab]/ace-group/ech0ech00000>;ct=65000;
rt="core.osc.gm";if="ace.group";sec-gp="ech0ech00000";
app-gp="group2";cred-fmt="33";gp-enc-alg="10";
sign-alg="-8";sign-alg-crv="6";alg="10";ecdh-alg="-27";
ecdh-alg-crv="4",
<coap://[2001:db8::ab]/ace-group/abcdef120000>;ct=65000;
rt="core.osc.gm";if="ace.group";sec-gp="abcdef120000";
app-gp="group3";app-gp="group4";cred-fmt="33";
gp-enc-alg="10";sign-alg="-8";sign-alg-crv="6";alg="10";
ecdh-alg="-27";ecdh-alg-crv="4"
Therefore, it is RECOMMENDED that a joining node which performs a
resource lookup with the CoAP Observe option specifies the value of
the parameter 'sec-gp' in its GET request sent to the RD.
4.2.2. Example in CoRAL
Request: Joining node -> RD
Req: GET coap://rd.example.com/rd-lookup/res
?rt=core.osc.gm&sec-gp=feedca570000
Observe: 0
Accept: 65087 (application/coral+cbor)
Response: RD -> Joining node
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Res: 2.05 Content
Observe: 24
Content-Format: 65087 (application/coral+cbor)
Payload:
[
[1, cri'coap://[2001:db8::ab]'],
[
2, 6(-20) / item 55 for reef:#rd-item /,
cri'/ace-group/feedca570000',
[
[2, simple(8) / item 8 for linkformat:ct /, 65000],
[2, simple(6) / item 6 for linkformat:rt /,
6(200) / item 416 for cri'http://www.iana.org/assignments/
linkformat/rt/core.osc.gm' /
],
[2, simple(7) / item 7 for linkformat:if /,
6(250) / item 516 for cri'http://www.iana.org/assignments/
linkformat/if/ace.group' /
],
[2, 6(-3) / item 21 for linkformat:sec-gp / , "feedca570000"],
[2, 6(3) / item 22 for linkformat:app-gp / , "group1"],
[2, 6(4) / item 24 for linkformat:cred_fmt / , 33],
[2, 6(-5) / item 25 for linkformat:sign_enc_alg / , 10],
[2, 6(5) / item 26 for linkformat:sign_alg / , -8],
[2, 6(-6) / item 27 for linkformat:sign_alg_crv / , 6],
[2, 6(7) / item 30 for linkformat:alg / , 10],
[2, 6(-8) / item 31 for linkformat:ecdh_alg / , -27],
[2, 6(8) / item 32 for linkformat:ecdh_alg_crv / , 4],
[
2, simple(1) / item 1 for rel:authorization-server / ,
cri'coap://as.example.com/token'
]
]
]
]
5. Use Case Example With Full Discovery
In this section, the discovery of security groups is described to
support the installation process of a lighting installation in an
office building. The described process is a simplified version of
one of many processes.
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The process described in this section is intended as an example and
does not have any particular ambition to serve as recommendation or
best practice to adopt. That is, it shows a possible workflow
involving a Commissioning Tool (CT) used in a certain way, while it
is not meant to prescribe how the workflow should necessarily be.
Assume the existence of four luminaires that are members of two
application groups. In the first application group, the four
luminaires receive presence messages and light intensity messages
from sensors or their proxy. In the second application group, the
four luminaires and several other pieces of equipment receive
building state schedules.
Each of the two application groups is associated with a different
security group and to a different CoAP group with its own dedicated
multicast IP address.
The Fairhair Alliance describes how a new device is accepted and
commissioned in the network [Fairhair], by means of its certificate
stored during the manufacturing process. When commissioning the new
device in the installation network, the new device gets a new
identity defined by a newly allocated certificate, following the
BRSKI specification.
Then, consistently with Section 7.1 of [RFC9176], the CT assigns an
endpoint name based on the CN field, (CN=ACME) and the serial number
of the certificate (serial number = 123x, with 3 < x < 8).
Corresponding ep-names ACME-1234, ACME-1235, ACME-1236 and ACME-1237
are also assumed.
It is common practice that locations in the building are specified
according to a coordinate system. After the acceptance of the
luminaires into the installation network, the coordinate of each
device is communicated to the CT. This can be done manually or
automatically.
The mapping between location and ep-name is calculated by the CT.
For instance, on the basis of grouping criteria, the CT assigns: i)
application group "grp_R2-4-015" to the four luminaires; and ii)
application group "grp_schedule" to all schedule requiring devices.
Also, the device with ep name ACME-123x has been assigned IP address:
[2001:db8:4::x]. The RD is assigned IP address: [2001:db8:4:ff].
The used multicast addresses are: [ff05::5:1] and [ff05::5:2].
The following assumes that each device is pre-configured with the
name of the two application groups it belongs to. Additional
mechanisms can be defined in the RD, for supporting devices to
discover the application groups they belong to.
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Appendix A provides this same use case example in CoRAL.
*** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
The CT defines the application group "grp_R2-4-015", with resource
/light and base address [ff05::5:1], as follows.
Request: CT -> RD
Req: POST coap://[2001:db8:4::ff]/rd
?ep=grp_R2-4-015&et=core.rd-group&base=coap://[ff05::5:1]
Content-Format: 40
Payload:
</light>;rt="oic.d.light"
Response: RD -> CT
Res: 2.01 Created
Location-Path: /rd/501
Also, the CT defines a second application group "grp_schedule", with
resource /schedule and base address [ff05::5:2], as follows.
Request: CT -> RD
Req: POST coap://[2001:db8:4::ff]/rd
?ep=grp_schedule&et=core.rd-group&base=coap://[ff05::5:2]
Content-Format: 40
Payload:
</schedule>;rt="oic.r.time.period"
Response: RD -> CT
Res: 2.01 Created
Location-Path: /rd/502
*** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
Finally, the CT defines the corresponding security groups. In
particular, assuming a Group Manager responsible for both security
groups and with address [2001:db8::ab], the CT specifies:
Request: CT -> RD
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Req: POST coap://[2001:db8:4::ff]/rd
?ep=gm1&base=coap://[2001:db8::ab]
Content-Format: 40
Payload:
</ace-group/feedca570000>;ct=65000;rt="core.osc.gm";if="ace.group";
sec-gp="feedca570000";
app-gp="grp_R2-4-015",
</ace-group/feedsc590000>;ct=65000;rt="core.osc.gm";if="ace.group";
sec-gp="feedsc590000";
app-gp="grp_schedule"
Response: RD -> CT
Res: 2.01 Created
Location-Path: /rd/4521
*** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
The device with IP address [2001:db8:4::x] can retrieve the multicast
IP address of the CoAP group used by the application group
"grp_R2-4-015", by performing an endpoint lookup as shown below.
Request: Joining node -> RD
Req: GET coap://[2001:db8:4::ff]/rd-lookup/ep
?et=core.rd-group&ep=grp_R2-4-015
Response: RD -> Joining node
Res: 2.05 Content
Content-Format: 40
Payload:
</rd/501>;ep="grp_R2-4-015";et="core.rd-group";
base="coap://[ff05::5:1]";rt="core.rd-ep"
Similarly, to retrieve the multicast IP address of the CoAP group
used by the application group "grp_schedule", the device performs an
endpoint lookup as shown below.
Request: Joining node -> RD
Req: GET coap://[2001:db8:4::ff]/rd-lookup/ep
?et=core.rd-group&ep=grp_schedule
Response: RD -> Joining node
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Res: 2.05 Content
Content-Format: 40
Payload:
</rd/502>;ep="grp_schedule";et="core.rd-group";
base="coap://[ff05::5:2]";rt="core.rd-ep"
*** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
Consequently, the device learns the security groups it has to join.
In particular, it does the following for app-gp="grp_R2-4-015".
Request: Joining node -> RD
Req: GET coap://[2001:db8:4::ff]/rd-lookup/res
?rt=core.osc.gm&app-gp=grp_R2-4-015
Response: RD -> Joining Node
Res: 2.05 Content
Content-Format: 40
Payload:
<coap://[2001:db8::ab]/ace-group/feedca570000>;ct=65000;
rt="core.osc.gm";if="ace.group";sec-gp="feedca570000";
app-gp="grp_R2-4-015"
Similarly, the device does the following for app-gp="grp_schedule".
Req: GET coap://[2001:db8:4::ff]/rd-lookup/res
?rt=core.osc.gm&app-gp=grp_schedule
Response: RD -> Joining Node
Res: 2.05 Content
Content-Format: 40
Payload:
<coap://[2001:db8::ab]/ace-group/feedsc590000>;ct=65000;
rt="core.osc.gm";if="ace.group";sec-gp="feedsc590000";
app-gp="grp_schedule"
*** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
After this last discovery step, the device can ask permission to join
the security groups, and effectively join them through the Group
Manager, e.g., according to [I-D.ietf-ace-key-groupcomm-oscore].
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6. Security Considerations
The security considerations as described in Section 8 of [RFC9176]
apply here as well.
7. IANA Considerations
This document has the following actions for IANA.
Note to RFC Editor: Please replace all occurrences of "[RFC-XXXX]"
with the RFC number of this specification and delete this paragraph.
7.1. Link Relation Type Registry
IANA is asked to register the following entry in the "Link Relation
Type" registry as per [RFC8288].
Relation Name: authorization-server
Description: Refers to a resource at an Authorization Server
for requesting an authorization credential
to access the link's context
Reference: [RFC-XXXX]
Notes: None
Application Data: None
7.2. Target Attributes Registry
IANA is asked to register the following entries in the "Target
Attributes" registry within the "CoRE Parameters" registry group, as
per [I-D.ietf-core-target-attr].
Attribute Name: sec-gp
Brief Description: Name of the security group that
can be joined through this resource
Change Controller: IETF
Reference: Section 2.1 of [RFC-XXXX]
Attribute Name: app-gp
Brief Description: Name of an application group
associated with a security group
Change Controller: IETF
Reference: Section 2.1 of [RFC-XXXX]
Attribute Name: hkdf
Brief Description: The HKDF algorithm to use
Change Controller: IETF
Reference: Section 2.1 of [RFC-XXXX]
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Attribute Name: cred-fmt
Brief Description: The format of authentication credential to use
Change Controller: IETF
Reference: Section 2.1 of [RFC-XXXX]
Attribute Name: gp-enc-alg
Brief Description: The encryption algorithm to use
for encrypting signed messages
Change Controller: IETF
Reference: Section 2.1 of [RFC-XXXX]
Attribute Name: sign-alg
Brief Description: The signature algorithm to use
Change Controller: IETF
Reference: Section 2.1 of [RFC-XXXX]
Attribute Name: sign-alg-crv
Brief Description: The elliptic curve of the used signature algorithm
Change Controller: IETF
Reference: Section 2.1 of [RFC-XXXX]
Attribute Name: sign-key-kty
Brief Description: The key type of the used signing keys
Change Controller: IETF
Reference: Section 2.1 of [RFC-XXXX]
Attribute Name: sign-key-crv
Brief Description: The curve of the used signing keys
Change Controller: IETF
Reference: Section 2.1 of [RFC-XXXX]
Attribute Name: alg
Brief Description: The encryption algorithm to use
for encrypting non-signed messages
Change Controller: IETF
Reference: Section 2.1 of [RFC-XXXX]
Attribute Name: ecdh-alg
Brief Description: The ECDH algorithm to use
Change Controller: IETF
Reference: Section 2.1 of [RFC-XXXX]
Attribute Name: ecdh-alg-crv
Brief Description: The elliptic curve of the used ECDH algorithm
Change Controller: IETF
Reference: Section 2.1 of [RFC-XXXX]
Attribute Name: ecdh-key-kty
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Brief Description: The key type of the used ECDH keys
Change Controller: IETF
Reference: Section 2.1 of [RFC-XXXX]
Attribute Name: ecdh-key-crv
Brief Description: The curve of the used ECDH keys
Change Controller: IETF
Reference: Section 2.1 of [RFC-XXXX]
Attribute Name: det-hash-alg
Brief Description: The hash algorithm to use
for computing deterministic requests
Change Controller: IETF
Reference: Section 2.1 of [RFC-XXXX]
Attribute Name: rekeying-scheme
Brief Description: The rekeying scheme used
to distribute new keying material
Change Controller: IETF
Reference: Section 2.1 of [RFC-XXXX]
8. References
8.1. Normative References
[COSE.Algorithms]
IANA, "COSE Algorithms",
<https://www.iana.org/assignments/cose/
cose.xhtml#algorithms>.
[COSE.Elliptic.Curves]
IANA, "COSE Elliptic Curves",
<https://www.iana.org/assignments/cose/
cose.xhtml#elliptic-curves>.
[COSE.Header.Parameters]
IANA, "COSE Header Parameters",
<https://www.iana.org/assignments/cose/cose.xhtml#header-
parameters>.
[COSE.Key.Types]
IANA, "COSE Key Types",
<https://www.iana.org/assignments/cose/cose.xhtml#key-
type>.
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[CURIE-20101216]
Birbeck, M. and S. McCarron, "CURIE Syntax 1.0 - A syntax
for expressing Compact URIs - W3C Working Group Note", 16
December 2010,
<http://www.w3.org/TR/2010/NOTE-curie-20101216>.
[I-D.ietf-ace-key-groupcomm-oscore]
Tiloca, M., Park, J., and F. Palombini, "Key Management
for OSCORE Groups in ACE", Work in Progress, Internet-
Draft, draft-ietf-ace-key-groupcomm-oscore-16, 6 March
2023, <https://datatracker.ietf.org/doc/html/draft-ietf-
ace-key-groupcomm-oscore-16>.
[I-D.ietf-cbor-packed]
Bormann, C. and M. Gütschow, "Packed CBOR", Work in
Progress, Internet-Draft, draft-ietf-cbor-packed-12, 2
March 2024, <https://datatracker.ietf.org/doc/html/draft-
ietf-cbor-packed-12>.
[I-D.ietf-core-coral]
Amsüss, C. and T. Fossati, "The Constrained RESTful
Application Language (CoRAL)", Work in Progress, Internet-
Draft, draft-ietf-core-coral-06, 4 March 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-core-
coral-06>.
[I-D.ietf-core-groupcomm-bis]
Dijk, E., Wang, C., and M. Tiloca, "Group Communication
for the Constrained Application Protocol (CoAP)", Work in
Progress, Internet-Draft, draft-ietf-core-groupcomm-bis-
10, 23 October 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-core-
groupcomm-bis-10>.
[I-D.ietf-core-href]
Bormann, C. and H. Birkholz, "Constrained Resource
Identifiers", Work in Progress, Internet-Draft, draft-
ietf-core-href-14, 9 January 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-core-
href-14>.
[I-D.ietf-core-oscore-groupcomm]
Tiloca, M., Selander, G., Palombini, F., Mattsson, J. P.,
and J. Park, "Group Object Security for Constrained
RESTful Environments (Group OSCORE)", Work in Progress,
Internet-Draft, draft-ietf-core-oscore-groupcomm-20, 2
September 2023, <https://datatracker.ietf.org/doc/html/
draft-ietf-core-oscore-groupcomm-20>.
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[I-D.ietf-core-target-attr]
Bormann, C., "CoRE Target Attributes Registry", Work in
Progress, Internet-Draft, draft-ietf-core-target-attr-06,
11 October 2023, <https://datatracker.ietf.org/doc/html/
draft-ietf-core-target-attr-06>.
[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/rfc/rfc2119>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/rfc/rfc3986>.
[RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link
Format", RFC 6690, DOI 10.17487/RFC6690, August 2012,
<https://www.rfc-editor.org/rfc/rfc6690>.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<https://www.rfc-editor.org/rfc/rfc7252>.
[RFC7641] Hartke, K., "Observing Resources in the Constrained
Application Protocol (CoAP)", RFC 7641,
DOI 10.17487/RFC7641, September 2015,
<https://www.rfc-editor.org/rfc/rfc7641>.
[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/rfc/rfc8174>.
[RFC8288] Nottingham, M., "Web Linking", RFC 8288,
DOI 10.17487/RFC8288, October 2017,
<https://www.rfc-editor.org/rfc/rfc8288>.
[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/rfc/rfc8949>.
[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/rfc/rfc9052>.
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[RFC9053] Schaad, J., "CBOR Object Signing and Encryption (COSE):
Initial Algorithms", RFC 9053, DOI 10.17487/RFC9053,
August 2022, <https://www.rfc-editor.org/rfc/rfc9053>.
[RFC9176] Amsüss, C., Ed., Shelby, Z., Koster, M., Bormann, C., and
P. van der Stok, "Constrained RESTful Environments (CoRE)
Resource Directory", RFC 9176, DOI 10.17487/RFC9176, April
2022, <https://www.rfc-editor.org/rfc/rfc9176>.
[RFC9200] Seitz, L., Selander, G., Wahlstroem, E., Erdtman, S., and
H. Tschofenig, "Authentication and Authorization for
Constrained Environments Using the OAuth 2.0 Framework
(ACE-OAuth)", RFC 9200, DOI 10.17487/RFC9200, August 2022,
<https://www.rfc-editor.org/rfc/rfc9200>.
[Target.Attributes]
IANA, "Target Attributes",
<https://www.iana.org/assignments/core-parameters/core-
parameters.xhtml#target-attributes>.
8.2. Informative References
[Fairhair] FairHair Alliance, "Security Architecture for the Internet
of Things (IoT) in Commercial Buildings", White Paper, ed.
Piotr Polak , March 2018, <https://openconnectivity.org/
wp-content/uploads/2019/11/fairhair_security_wp_march-
2018.pdf>.
[I-D.amsuess-core-cachable-oscore]
Amsüss, C. and M. Tiloca, "Cacheable OSCORE", Work in
Progress, Internet-Draft, draft-amsuess-core-cachable-
oscore-08, 10 January 2024,
<https://datatracker.ietf.org/doc/html/draft-amsuess-core-
cachable-oscore-08>.
[I-D.hartke-t2trg-coral-reef]
Hartke, K., "Resource Discovery in Constrained RESTful
Environments (CoRE) using the Constrained RESTful
Application Language (CoRAL)", Work in Progress, Internet-
Draft, draft-hartke-t2trg-coral-reef-04, 9 May 2020,
<https://datatracker.ietf.org/doc/html/draft-hartke-t2trg-
coral-reef-04>.
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[I-D.ietf-ace-key-groupcomm]
Palombini, F. and M. Tiloca, "Key Provisioning for Group
Communication using ACE", Work in Progress, Internet-
Draft, draft-ietf-ace-key-groupcomm-18, 16 January 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-ace-key-
groupcomm-18>.
[I-D.ietf-ace-oscore-gm-admin]
Tiloca, M., Höglund, R., Van der Stok, P., and F.
Palombini, "Admin Interface for the OSCORE Group Manager",
Work in Progress, Internet-Draft, draft-ietf-ace-oscore-
gm-admin-10, 23 October 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-ace-
oscore-gm-admin-10>.
[I-D.ietf-ace-oscore-gm-admin-coral]
Tiloca, M. and R. Höglund, "Using the Constrained RESTful
Application Language (CoRAL) with the Admin Interface for
the OSCORE Group Manager", Work in Progress, Internet-
Draft, draft-ietf-ace-oscore-gm-admin-coral-01, 14 January
2024, <https://datatracker.ietf.org/doc/html/draft-ietf-
ace-oscore-gm-admin-coral-01>.
[I-D.ietf-cose-cbor-encoded-cert]
Mattsson, J. P., Selander, G., Raza, S., Höglund, J., and
M. Furuhed, "CBOR Encoded X.509 Certificates (C509
Certificates)", Work in Progress, Internet-Draft, draft-
ietf-cose-cbor-encoded-cert-09, 4 March 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-cose-
cbor-encoded-cert-09>.
[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/rfc/rfc5280>.
[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/rfc/rfc7228>.
[RFC8132] van der Stok, P., Bormann, C., and A. Sehgal, "PATCH and
FETCH Methods for the Constrained Application Protocol
(CoAP)", RFC 8132, DOI 10.17487/RFC8132, April 2017,
<https://www.rfc-editor.org/rfc/rfc8132>.
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[RFC8392] Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig,
"CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392,
May 2018, <https://www.rfc-editor.org/rfc/rfc8392>.
[RFC8613] Selander, G., Mattsson, J., Palombini, F., and L. Seitz,
"Object Security for Constrained RESTful Environments
(OSCORE)", RFC 8613, DOI 10.17487/RFC8613, July 2019,
<https://www.rfc-editor.org/rfc/rfc8613>.
[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/rfc/rfc8995>.
Appendix A. Use Case Example With Full Discovery (CoRAL)
This section provides the same use case example of Section 5, but
specified in CoRAL [I-D.ietf-core-coral].
*** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
The CT defines the application group "grp_R2-4-015", with resource
/light and base address [ff05::5:1], as follows.
Request: CT -> RD
Req: POST coap://[2001:db8:4::ff]/rd
Content-Format: 65087 (application/coral+cbor)
Payload:
[
[1, cri'coap://[ff05::5:1]'],
[2, 6(-22) / item 59 for reef:#ep /, "grp_R2-4-015"],
[2, 6(21) / item 58 for reef:#et /, "core.rd-group"],
[
2, 6(-20) / item 55 for reef:#rd-item /, cri'/light',
[
2, simple(6) / item 6 for linkformat:rt /,
6(-201) / item 417 for cri'http://www.iana.org/assignments/
linkformat/rt/oic.d.light' /
]
]
]
Response: RD -> CT
Res: 2.01 Created
Location-Path: /rd/501
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Also, the CT defines a second application group "grp_schedule", with
resource /schedule and base address [ff05::5:2], as follows.
Request: CT -> RD
Req: POST coap://[2001:db8:4::ff]/rd
Content-Format: 65087 (application/coral+cbor)
Payload:
[
[1, cri'coap://[ff05::5:2]'],
[2, 6(-22) / item 59 for reef:#ep /, "grp_schedule"],
[2, 6(21) / item 58 for reef:#et /, "core.rd-group"],
[
2, 6(-20) / item 55 for reef:#rd-item /, cri'/schedule',
[
2, simple(6) / item 6 for linkformat:rt /,
6(201) / item 418 for cri'http://www.iana.org/assignments/
linkformat/rt/oic.r.time.period' /
]
]
]
Response: RD -> CT
Res: 2.01 Created
Location-Path: /rd/502
*** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
Finally, the CT defines the corresponding security groups. In
particular, assuming a Group Manager responsible for both security
groups and with address [2001:db8::ab], the CT specifies:
Request: CT -> RD
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Req: POST coap://[2001:db8:4::ff]/rd
Content-Format: 65087 (application/coral+cbor)
Payload:
[
[1, cri'coap://[2001:db8::ab]'],
[2, 6(-22) / item 59 for reef:#ep /, "gm1"],
[
2, 6(-20) / item 55 for reef:#rd-item /,
cri'/ace-group/feedca570000',
[
[2, simple(8) / item 8 for linkformat:ct /, 65000],
[
2, simple(6) / item 6 for linkformat:rt /,
6(200) / item 416 for cri'http://www.iana.org/assignments/
linkformat/rt/core.osc.gm' /
],
[
2, simple(7) / item 7 for linkformat:if /,
6(250) / item 516 for cri'http://www.iana.org/assignments/
linkformat/if/ace.group' /
],
[2, 6(-3) / item 21 for linkformat:sec-gp / , "feedca570000"],
[2, 6(3) / item 22 for linkformat:app-gp / , "grp_R2-4-015"]
]
],
[
2, 6(-20) / item 55 for reef:#rd-item /,
cri'/ace-group/feedsc590000',
[
[2, simple(8) / item 8 for linkformat:ct /, 65000],
[
2, simple(6) / item 6 for linkformat:rt /,
6(200) / item 416 for cri'http://www.iana.org/assignments/
linkformat/rt/core.osc.gm' /
],
[
2, simple(7) / item 7 for linkformat:if /,
6(250) / item 516 for cri'http://www.iana.org/assignments/
linkformat/if/ace.group' /
],
[2, 6(-3) / item 21 for linkformat:sec-gp / , "feedsc590000"],
[2, 6(3) / item 22 for linkformat:app-gp / , "grp_schedule"]
]
]
]
Response: RD -> CT
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Res: 2.01 Created
Location-Path: /rd/4521
*** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
The device with IP address [2001:db8:4::x] can retrieve the multicast
IP address of the CoAP group used by the application group
"grp_R2-4-015", by performing an endpoint lookup as shown below.
Request: Joining node -> RD
Req: GET coap://[2001:db8:4::ff]/rd-lookup/ep
?et=core.rd-group&ep=grp_R2-4-015
Response: RD -> Joining node
Res: 2.05 Content
Content-Format: 65087 (application/coral+cbor)
Payload:
[
[1, cri'coap://[2001:db8:4::ff]/rd'],
[
2, 6(20) / item 56 for reef:#rd-unit /, cri'/501',
[
[2, 6(-22) / item 59 for reef:#ep /, "grp_R2-4-015"],
[2, 6(21) / item 58 for reef:#et /, "core.rd-group"],
[2, 6(22) / item 60 for reef:#base /, cri'coap://[ff05::5:1]/'],
[2, 6(-21) / item 57 for reef:#rt /, "core.rd-ep"],
]
]
]
Similarly, to retrieve the multicast IP address of the CoAP group
used by the application group "grp_schedule", the device performs an
endpoint lookup as shown below.
Request: Joining node -> RD
Req: GET coap://[2001:db8:4::ff]/rd-lookup/ep
?et=core.rd-group&ep=grp_schedule
Response: RD -> Joining node
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Res: 2.05 Content
Content-Format: 65087 (application/coral+cbor)
Payload:
[
[1, cri'coap://[2001:db8:4::ff]/rd'],
[
2, 6(20) / item 56 for reef:#rd-unit /, cri'/502',
[
[2, 6(-22) / item 59 for reef:#ep /, "grp_schedule"],
[2, 6(21) / item 58 for reef:#et /, "core.rd-group"],
[2, 6(22) / item 60 for reef:#base /, cri'coap://[ff05::5:2]/'],
[2, 6(-21) / item 57 for reef:#rt /, "core.rd-ep"],
]
]
]
*** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
Consequently, the device learns the security groups it has to join.
In particular, it does the following for app-gp="grp_R2-4-015".
Request: Joining node -> RD
Req: GET coap://[2001:db8:4::ff]/rd-lookup/res
?rt=core.osc.gm&app-gp=grp_R2-4-015
Response: RD -> Joining Node
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Res: 2.05 Content
Content-Format: 65087 (application/coral+cbor)
Payload:
[
[1, cri'coap://[2001:db8::ab]'],
[
2, 6(-20) / item 55 for reef:#rd-item /,
cri'/ace-group/feedca570000',
[
[2, simple(8) / item 8 for linkformat:ct /, 65000],
[2, simple(6) / item 6 for linkformat:rt /,
6(200) / item 416 for cri'http://www.iana.org/assignments/
linkformat/rt/core.osc.gm' /
],
[2, simple(7) / item 7 for linkformat:if /,
6(250) / item 516 for cri'http://www.iana.org/assignments/
linkformat/if/ace.group' /
],
[2, 6(-3) / item 21 for linkformat:sec-gp / , "feedca570000"],
[2, 6(3) / item 22 for linkformat:app-gp / , "grp_R2-4-015"]
]
]
]
Similarly, the device does the following for app-gp="grp_schedule".
Req: GET coap://[2001:db8:4::ff]/rd-lookup/res
?rt=core.osc.gm&app-gp=grp_schedule
Response: RD -> Joining Node
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Res: 2.05 Content
Content-Format: 65087 (application/coral+cbor)
Payload:
[
[1, cri'coap://[2001:db8::ab]'],
[
2, 6(-20) / item 55 for reef:#rd-item /,
cri'/ace-group/feedsc590000',
[
[2, simple(8) / item 8 for linkformat:ct /, 65000],
[2, simple(6) / item 6 for linkformat:rt /,
6(200) / item 416 for cri'http://www.iana.org/assignments/
linkformat/rt/core.osc.gm' /
],
[2, simple(7) / item 7 for linkformat:if /,
6(250) / item 516 for cri'http://www.iana.org/assignments/
linkformat/if/ace.group' /
],
[2, 6(-3) / item 21 for linkformat:sec-gp / , "feedsc590000"],
[2, 6(3) / item 22 for linkformat:app-gp / , "grp_schedule"]
]
]
]
*** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
After this last discovery step, the device can ask permission to join
the security groups, and effectively join them through the Group
Manager, e.g., according to [I-D.ietf-ace-key-groupcomm-oscore].
Appendix B. Shared item tables for Packed CBOR
This appendix defines the three shared item tables that the examples
in this document refer to for using Packed CBOR
[I-D.ietf-cbor-packed].
The application-extension identifier "cri" defined in Appendix C of
[I-D.ietf-core-href] is used to notate a CBOR Extended Diagnostic
Notation (EDN) literal for a CRI.
B.1. Compression of CoRAL predicates
The following shared item table is used for compressing CoRAL
predicates, as per Section 2.2 of [I-D.ietf-cbor-packed].
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+-------+----------------------------------------------------------+
| Index | Item |
+-------+----------------------------------------------------------+
| 0 | cri'http://www.iana.org/assignments/relation/hosts' |
+-------+----------------------------------------------------------+
| 1 | cri'http://www.iana.org/assignments/relation/ |
| | authorization-server' |
+-------+----------------------------------------------------------+
| 6 | cri'http://www.iana.org/assignments/linkformat/rt' |
+-------+----------------------------------------------------------+
| 7 | cri'http://www.iana.org/assignments/linkformat/if' |
+-------+----------------------------------------------------------+
| 8 | cri'http://www.iana.org/assignments/linkformat/ct' |
+-------+----------------------------------------------------------+
| 9 | cri'http://www.iana.org/assignments/linkformat/anchor' |
+-------+----------------------------------------------------------+
| 10 | cri'http://www.iana.org/assignments/linkformat/rel' |
+-------+----------------------------------------------------------+
| 21 | cri'http://www.iana.org/assignments/linkformat/sec-gp' |
+-------+----------------------------------------------------------+
| 22 | cri'http://www.iana.org/assignments/linkformat/app-gp' |
+-------+----------------------------------------------------------+
| 23 | cri'http://www.iana.org/assignments/linkformat/hkdf' |
+-------+----------------------------------------------------------+
| 24 | cri'http://www.iana.org/assignments/linkformat/cred-fmt' |
+-------+----------------------------------------------------------+
| 25 | cri'http://www.iana.org/assignments/linkformat/ |
| | sign-enc-alg' |
+-------+----------------------------------------------------------+
| 26 | cri'http://www.iana.org/assignments/linkformat/sign-alg' |
+-------+----------------------------------------------------------+
| 27 | cri'http://www.iana.org/assignments/linkformat/ |
| | sign-alg-crv' |
+-------+----------------------------------------------------------+
| 28 | cri'http://www.iana.org/assignments/linkformat/ |
| | sign-key-kty' |
+-------+----------------------------------------------------------+
| 29 | cri'http://www.iana.org/assignments/linkformat/ |
| | sign-key-crv' |
+-------+----------------------------------------------------------+
| 30 | cri'http://www.iana.org/assignments/linkformat/alg' |
+-------+----------------------------------------------------------+
| 31 | cri'http://www.iana.org/assignments/linkformat/ecdh-alg' |
+-------+----------------------------------------------------------+
| 32 | cri'http://www.iana.org/assignments/linkformat/ |
| | ecdh-alg-crv' |
+-------+----------------------------------------------------------+
| 33 | cri'http://www.iana.org/assignments/linkformat/ |
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| | ecdh-key-kty' |
+-------+----------------------------------------------------------+
| 34 | cri'http://www.iana.org/assignments/linkformat/ |
| | ecdh-key-crv' |
+-------+----------------------------------------------------------+
| 35 | cri'http://www.iana.org/assignments/linkformat/ |
| | det-hash-alg' |
+-------+----------------------------------------------------------+
| 36 | cri'http://www.iana.org/assignments/linkformat/ |
| | rekeying-scheme' |
+-------+----------------------------------------------------------+
| 55 | cri'http://coreapps.org/reef#rd-item' |
+-------+----------------------------------------------------------+
| 56 | cri'http://coreapps.org/reef#rd-unit' |
+-------+----------------------------------------------------------+
| 57 | cri'http://coreapps.org/reef#rt' |
+-------+----------------------------------------------------------+
| 58 | cri'http://coreapps.org/reef#et' |
+-------+----------------------------------------------------------+
| 59 | cri'http://coreapps.org/reef#ep' |
+-------+----------------------------------------------------------+
| 60 | cri'http://coreapps.org/reef#base' |
+-------+----------------------------------------------------------+
Figure 1: Shared item table for compressing CoRAL predicates.
B.2. Compression of Values of the rt= Target Attribute
The following shared item table is used for compressing values of the
rt= target attribute, as per Section 2.2 of [I-D.ietf-cbor-packed].
+-------+----------------------------------------------------+
| Index | Item |
+-------+----------------------------------------------------+
| 416 | cri'http://www.iana.org/assignments/linkformat/rt/ |
| | core.osc.gm' |
+-------+----------------------------------------------------+
| 417 | cri'http://www.iana.org/assignments/linkformat/rt/ |
| | oic.d.light' |
+-------+----------------------------------------------------+
| 418 | cri'http://www.iana.org/assignments/linkformat/rt/ |
| | oic.r.time.period' |
+-------+----------------------------------------------------+
Figure 2: Shared item table for compressing values of the rt=
target attribute.
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B.3. Compression of Values of the if= Target Attribute
The following shared item table is used for compressing values of the
if= target attribute, as per Section 2.2 of [I-D.ietf-cbor-packed].
+-------+----------------------------------------------------+
| Index | Item |
+-------+----------------------------------------------------+
| 516 | cri'http://www.iana.org/assignments/linkformat/if/ |
| | ace.group' |
+-------+----------------------------------------------------+
Figure 3: Shared item table for compressing values of the if=
target attribute.
Acknowledgments
The authors sincerely thank Carsten Bormann, Klaus Hartke, Jaime
Jiménez, Francesca Palombini, Dave Robin, and Jim Schaad for their
comments and feedback.
The work on this document has been partly supported by VINNOVA and
the Celtic-Next project CRITISEC; by the H2020 project SIFIS-Home
(Grant agreement 952652); and by the EIT-Digital High Impact
Initiative ACTIVE.
Authors' Addresses
Marco Tiloca
RISE AB
Isafjordsgatan 22
SE-16440 Stockholm Kista
Sweden
Email: marco.tiloca@ri.se
Christian Amsuess
Hollandstr. 12/4
1020 Vienna
Austria
Email: christian@amsuess.com
Peter van der Stok
Email: stokcons@kpnmail.nl
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