Discovery of OSCORE Groups with the CoRE Resource Directory
draft-tiloca-core-oscore-discovery-04
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| Last updated | 2019-11-04 (Latest revision 2019-07-05) | ||
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draft-tiloca-core-oscore-discovery-04
CoRE Working Group M. Tiloca
Internet-Draft RISE AB
Intended status: Standards Track C. Amsuess
Expires: May 7, 2020
P. van der Stok
Consultant
November 04, 2019
Discovery of OSCORE Groups with the CoRE Resource Directory
draft-tiloca-core-oscore-discovery-04
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 OSCORE 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 OSCORE groups and to acquire information for
joining them through the respective Group Manager. A given OSCORE
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 OSCORE groups based on the ACE framework for
Authentication and Authorization in constrained environments.
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
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 7, 2020.
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Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Registration Resource for Group Managers . . . . . . . . . . 5
3. Registration of Group Manager Endpoints . . . . . . . . . . . 6
4. Addition and Update of OSCORE Groups . . . . . . . . . . . . 8
5. Discovery of OSCORE Groups . . . . . . . . . . . . . . . . . 9
5.1. Discovery Example #1 . . . . . . . . . . . . . . . . . . 10
5.2. Discovery Example #2 . . . . . . . . . . . . . . . . . . 11
6. Use Case Example With Full Discovery . . . . . . . . . . . . 13
7. Security Considerations . . . . . . . . . . . . . . . . . . . 17
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
8.1. Resource Types . . . . . . . . . . . . . . . . . . . . . 17
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
9.1. Normative References . . . . . . . . . . . . . . . . . . 18
9.2. Informative References . . . . . . . . . . . . . . . . . 19
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20
1. Introduction
A set of CoAP endpoints constitutes an application group by sharing a
common pool of resources. The members of an application group may be
members of a given security group, by sharing a common set of keying
material to secure group communication.
The Constrained Application Protocol (CoAP) [RFC7252] supports group
communication over IP multicast
[RFC7390][I-D.dijk-core-groupcomm-bis] to improve efficiency and
latency of communication and reduce bandwidth requirements. The
document Object Security for Constrained RESTful Environments
(OSCORE) [RFC8613] describes how to achieve end-to-end security for
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CoAP messages through CBOR Object Signing and Encryption (COSE)
[RFC8152].
In particular, [I-D.ietf-core-oscore-groupcomm] specifies how Group
OSCORE protects CoAP messages in group communication contexts, so
enabling OSCORE groups as security groups. Typically, one
application group relies on exactly one OSCORE group, while a same
OSCORE group may be used by multiple application groups at the same
time.
A CoAP endpoint joins an OSCORE group via a Group Manager (GM), in
order to get the necessary group keying material. As in
[I-D.ietf-ace-key-groupcomm-oscore], the joining process can be based
on the ACE framework for Authentication and Authorization in
constrained environments [I-D.ietf-ace-oauth-authz], 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 associated with the OSCORE group to join and
exported by the GM.
Typically, devices are equipped with a static X509 IDevID certificate
installed at manufacturing time. This certificate is used at
deployment time during an enrollment process that provides the device
with an Operational Certificate, possibly updated during the device
lifetime. In the presence of secure group communication for CoAP,
such an Operational Certificate may be accompanied by information
required to join OSCORE groups. This especially includes a reference
to the group-membership resources to access at the respective GMs.
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 OSCORE
group(s) to join and the responsible GM(s) are generally unknown at
manufacturing time; (2) an OSCORE group of interest is created, or
the responsible GM is deployed, only after the device is enrolled and
fully operative in the network; and (3) information related to
existing OSCORE groups or to their GMs has been changed. This
requires a method for CoAP endpoints to dynamically discover OSCORE
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, in order to discover OSCORE groups and
to retrieve the information required for joining them. With the
discovery process of OSCORE groups expressed in terms of links to
resources, the remaining problem is thus the discovery of those
links. The CoRE Resource Directory (RD)
[I-D.ietf-core-resource-directory] provides such discovery in an
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efficient way, and it is expected to be used in many setups that
would benefit of OSCORE group discovery.
This specification builds on this approach and describes how CoAP
endpoints can use the RD to carry out the necessary link discovery
steps, in order to discover OSCORE groups of interest and retrieve
the information required to join them through their GM. In
principle, the GM registers as an endpoint with the RD. The
corresponding registration resource includes one link for each OSCORE
group under that GM, specifying the path to the related group-
membership resource to access for joining that group.
More information about the OSCORE group is stored in the target
attributes of the respective link. This especially includes the
identifiers of the application groups which use that OSCORE group.
This enables a lookup of those application groups at the Resource
Directory, where they are separately announced by a Commissioning
Tool (see Appendix A of [I-D.ietf-core-resource-directory]).
When querying the RD for OSCORE groups, a CoAP endpoint can further
benefit of the CoAP Observe Option [RFC7641]. This enables the
reception of notifications about the creation of new OSCORE groups or
the updates concerning existing groups. Thus, it facilitates the
early deployment of CoAP endpoints, i.e. even before the GM is
deployed and OSCORE groups are created.
The approach in this document is consistent with, but not limited to,
the joining of OSCORE groups 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.
This specification requires readers to be familiar with the terms and
concepts discussed in [I-D.ietf-core-resource-directory] and
[RFC6690]. Readers should also be familiar with the terms and
concepts discussed in [RFC7252], [I-D.ietf-core-oscore-groupcomm] and
[I-D.ietf-ace-key-groupcomm-oscore].
Terminology for constrained environments, such as "constrained
device" and "constrained-node network", is defined in [RFC7228].
This document also refers to the following terminology.
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o OSCORE group: a set of CoAP endpoints that share one OSCORE Common
Security Context to protect group communication as described in
[I-D.ietf-core-oscore-groupcomm]. Consequently, an OSCORE group
acts as security group for all its members.
o Application group: a set of CoAP endpoints that share a set of
common resources. Application groups are announced in the RD by a
Commissioning Tool, according to the RD-Groups usage pattern (see
Appendix A of [I-D.ietf-core-resource-directory]). An application
group can be associated with a single OSCORE group, while multiple
application groups can use the same OSCORE group. Application
groups share resources by definition. Any two application groups
associated to the same OSCORE group do not share any same
resource.
2. Registration Resource for Group Managers
With reference to Figure 3 of [I-D.ietf-core-resource-directory], a
Group Manager (GM) registers as an endpoint with the CoRE Resource
Directory (RD). The registration includes the links to the group-
membership resources located at the GM, and associated to the OSCORE
groups administrated by that GM.
In particular, each link to a group-membership resource includes:
o "target": URI of the group-membership resource at the GM.
o target attributes, including:
* Resource Type (rt) with the value "core.osc.mbr" defined in
Section 8.1 of this specification.
* The name of the OSCORE group, as defined in
[I-D.ietf-ace-key-groupcomm-oscore].
* One target attribute for each application group associated with
the OSCORE group, specifying the name of that application
group.
* The algorithm used to countersign messages in the OSCORE group.
* The elliptic curve (if applicable) for the algorithm used to
countersign messages in the OSCORE group.
* The key type of countersignature keys used to countersign
messages in the OSCORE group.
* The encoding of public keys used in the OSCORE group.
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* The AEAD algorithm used in the OSCORE group.
* The HKDF algorithm used in the OSCORE group.
3. Registration of Group Manager Endpoints
During deployment, a GM finds the RD as described in Section 4 of
[I-D.ietf-core-resource-directory]. Afterwards, the GM registers as
an endpoint with the RD, as described in Section 5 of
[I-D.ietf-core-resource-directory].
When doing so, the GM also registers all the group-membership
resources it has at that point in time, i.e. one for each of its
OSCORE groups.
For each registered group-membership resource, the GM includes the
following parameters in the payload of the registration request.
o 'rt' = "core.osc.mbr" (see Section 8.1).
o 'sec-gp', specifying the name of the OSCORE group of interest.
This parameter MUST specify a single value.
o 'app-gp', specifying the name(s) of the application group(s)
associated to the OSCORE group of interest indicated by 'sec-gp'.
This parameter MAY be included multiple times, and each occurrence
MUST specify the name of one application group. A same
application group MUST NOT be specified multiple times.
Also, for each registered group-membership resource, the GM may
additionally include the following parameters in the payload of the
registration request.
o 'cs_alg', specifying the algorithm used to countersign messages in
the OSCORE group. If present, this parameter MUST specify a
single value encoded as a text string, which is taken from the
'Value' column of the "COSE Algorithms" Registry defined in
[RFC8152].
o 'cs_crv', specifying the elliptic curve (if applicable) for the
algorithm used to countersign messages in the OSCORE group. If
present, this parameter MUST specify a single value encoded as a
text string, which is taken from the 'Value' column of the "COSE
Elliptic Curve" Registry defined in [RFC8152].
o 'cs_kty', specifying the key type of countersignature keys used to
countersign messages in the OSCORE group. If present, this
parameter MUST specify a single value encoded as a text string,
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which is taken from the 'Value' column of the "COSE Key Types"
Registry defined in [RFC8152].
o 'cs_kenc', specifying the encoding of the public keys used in the
OSCORE group. If present, this parameter MUST specify a single
value encoded as a text string. This specification explicitly
admits the signaling of COSE Keys [RFC8152] as encoding for public
keys, which is indicated with "1", as taken from the 'Confirmation
Key' column of the "CWT Confirmation Method" Registry defined in
[I-D.ietf-ace-cwt-proof-of-possession]. Future specifications may
define additional values for this parameter.
o 'alg', specifying the AEAD algorithm used in the OSCORE group. If
present, this parameter MUST specify a single value encoded as a
text string, which is taken from the 'Value' column of the "COSE
Algorithms" Registry defined in [RFC8152].
o 'hkdf', specifying the HKDF algorithm used in the OSCORE group.
If present, this parameter MUST specify a single value encoded as
a text string, which is taken from the 'Value' column of the "COSE
Algorithms" Registry defined in [RFC8152].
Values registered as a string that looks like an integer are not
supported by this approach. Therefore, they MUST NOT be advertised
through the corresponding parameters above.
A CoAP endpoint that queries the RD to discover OSCORE groups and
their group-membership resource to access (see Section 5) would
benefit from the information above as follows.
o The values of 'cs_alg', 'cs_crv', 'cs_kty' and 'cs_kenc' related
to a group-membership resource provide an early knowledge of the
format and encoding of public keys used in the OSCORE 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 exchange with the GM. Hence, the
CoAP endpoint is able to provide the GM with its own public key in
the correct expected format and encoding at the very first step of
the joining process.
o The values of 'cs_alg', 'alg' and 'hkdf' related to a group-
membership resource provide an early knowledge of the algorithms
used in the OSCORE 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.
The GM SHOULD NOT use the Simple Registration approach described in
Section 5.1 of [I-D.ietf-core-resource-directory].
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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 OSCORE group with name
"feedca570000" and used by the application group with name "group1"
specified with the value of the 'app-gp' parameter. The
countersignature algorithm used in the OSCORE group is EdDSA, with
elliptic curve Ed25519 and keys of type OKP. Public keys used in the
OSCORE group are encoded as COSE Keys [RFC8152].
Request: GM -> RD
Req: POST coap://rd.example.com/rd?ep=gm1
Content-Format: 40
Payload:
</group-oscore/feedca570000>;ct=41;rt="core.osc.mbr";
sec-gp="feedca570000";app-gp="group1";
cs_alg="-8";cs_crv="6";cs_kty="1";
cs_kenc="1"
Response: RD -> GM
Res: 2.01 Created
Location-Path: /rd/4521
4. Addition and Update of OSCORE 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
[I-D.ietf-core-resource-directory], and has to change the content of
the registration when a group-membership resource is added/removed or
if its target attributes have to be changed, such as in the following
cases.
o The GM creates a new OSCORE group and starts exporting the related
group-membership resource.
o The GM dismisses an OSCORE group and stops exporting the related
group-membership resource.
o Information related to an existing OSCORE 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 with their target attributes.
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The example below shows how the GM from Section 3 re-registers with
the RD. When doing so, it specifies:
o The same previous group-membership resource associated to the
OSCORE group with name "feedca570000".
o An additional group-membership resource associated to the OSCORE
group with name "ech0ech00000" and used by the application group
"group2".
o A third group-membership resource associated with the OSCORE group
with name "abcdef120000" and used by two application groups,
namely "group3" and "group4".
Request: GM -> RD
Req: POST coap://rd.example.com/rd?ep=gm1
Content-Format: 40
Payload:
</group-oscore/feedca570000>;ct=41;rt="core.osc.mbr";
sec-gp="feedca570000";app-gp="group1";
cs_alg="-8";cs_crv="6";cs_kty="1";
cs_kenc="1",
</group-oscore/ech0ech00000>;ct=41;rt="core.osc.mbr";
sec-gp="ech0ech00000";app-gp="group2";
cs_alg="-8";cs_crv="6";cs_kty="1";
cs_kenc="1",
</group-oscore/abcdef120000>;ct=41;rt="core.osc.mbr";
sec-gp="abcdef120000";app-gp="group3";
app-gp="group4";cs_alg="-8";
cs_crv="6";cs_kty="1";cs_kenc="1"
Response: RD -> GM
Res: 2.04 Changed
Location-Path: /rd/4521
Alternatively, the GM can perform a PATCH/iPATCH [RFC8132] request to
the RD, as per Section 5.3.3 of [I-D.ietf-core-resource-directory].
This requires new media-types to be defined in future standards, to
apply a link-format document as a patch to an existing stored
document.
5. Discovery of OSCORE Groups
A CoAP endpoint that wants to join an OSCORE group, hereafter called
the joining node, might not have all the necessary information at
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deployment time. Also, it might want to know about possible new
OSCORE 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 [I-D.ietf-core-resource-directory], to retrieve
the missing pieces of information needed to join the OSCORE group(s)
of interest. The joining node can find the RD as described in
Section 4 of [I-D.ietf-core-resource-directory].
The joining node uses the following parameter value for the lookup
filtering.
o 'rt' = "core.osc.mbr" (see Section 8.1).
The joining node may additionally consider the following parameters
for the lookup filtering, depending on the information it has already
available.
o 'sec-gp', specifying the name of the OSCORE group of interest.
This parameter MUST specify a single value.
o 'ep', specifying the registered endpoint of the GM.
o 'app-gp', specifying the name(s) of the application group(s)
associated with the OSCORE group of interest. This parameter MAY
be included multiple times, and each occurrence MUST specify the
name of one application group. A same application group MUST NOT
be specified multiple times.
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.
5.1. Discovery Example #1
Consistently with the examples in Section 3 and Section 4, the
example below considers a joining node that wants to join the OSCORE
group associated with the application group "group1", but that does
not know the name of the OSCORE group, the responsible GM and the
group-membership resource to access.
Request: Joining node -> RD
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Req: GET coap://rd.example.com/rd-lookup/res
?rt=core.osc.mbr&app-gp=group1
Response: RD -> Joining node
Res: 2.05 Content
Payload:
<coap://[2001:db8::ab]/group-oscore/feedca570000>;rt="core.osc.mbr";
sec-gp="feedca570000";app-gp="group1";
cs_alg="-8";cs_crv="6";cs_kty="1";
cs_kenc="1";anchor="coap://[2001:db8::ab]"
To retrieve the multicast IP address used in "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 [I-D.ietf-core-resource-directory],
with ff35:30:2001:db8::23 as associated multicast IP address.
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]"
5.2. Discovery Example #2
Consistently with the examples in Section 3 and Section 4, the
example below considers a joining node that wants to join the OSCORE
group with name "feedca570000", but that does not know the
responsible GM, the group-membership resource to access, and the
associated application groups.
The example also shows how the joining node uses CoAP observation
[RFC7641], in order to be notified of possible changes to the target
attributes of the group-membership resource. This is also useful to
handle the case where the OSCORE group of interest has not been
created yet, so that the joining node can receive the requested
information when it becomes available.
Request: Joining node -> RD
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Req: GET coap://rd.example.com/rd-lookup/res
?rt=core.osc.mbr&sec-gp=feedca570000
Observe: 0
Response: RD -> Joining node
Res: 2.05 Content
Observe: 24
Payload:
<coap://[2001:db8::ab]/group-oscore/feedca570000>;rt="core.osc.mbr";
sec-gp="feedca570000";app-gp="group1";
cs_alg="-8";cs_crv="6";cs_kty="1";
cs_kenc="1";anchor="coap://[2001:db8::ab]"
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.mbr
Response: RD -> Joining node
Res: 2.05 Content
Payload:
<coap://[2001:db8::ab]/group-oscore/feedca570000>;rt="core.osc.mbr";
sec-gp="feedca570000";app-gp="group1";
cs_alg="-8";cs_crv="6";cs_kty="1";
cs_kenc="1";anchor="coap://[2001:db8::ab]",
<coap://[2001:db8::ab]/group-oscore/ech0ech00000>;rt="core.osc.mbr";
sec-gp="ech0ech00000";app-gp="group2";
cs_alg="-8";cs_crv="6";cs_kty="1";
cs_kenc="1";anchor="coap://[2001:db8::ab]",
<coap://[2001:db8::ab]/group-oscore/abcdef120000>;rt="core.osc.mbr";
sec-gp="abcdef120000";app-gp="group3";
app-gp="group4";cs_alg="-8";cs_crv="6";
cs_kty="1";cs_kenc="1";anchor="coap://[2001:db8::ab]"
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.
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6. 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.
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 to a different
security group and uses 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.
Section 7.3 of [I-D.ietf-core-resource-directory] describes how the
Commissioning Tool (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 CT defines the application group "grp_R2-4-015", with resource
/light and base address [ff05::5:1], as follows.
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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]
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]
Payload:
</schedule>;rt="oic.r.time.period"
Response: RD -> CT
Res: 2.01 Created
Location-Path: /rd/502
*** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
Consecutively, the CT registers the four devices in the RD (IP
address: 2001:db8:4::ff), with their endpoint names and application
groups.
For the application group "grp_R2-4-015", four endpoints are
specified as follows, with x = 4, 5, 6, 7.
Request: CT -> RD
Req: POST coap://[2001:db8:4::ff]/rd
?ep=ACME-123x&base=coap://[2001:db8:4::x]&app-gp=grp_R2-4-015
Payload:
</light>;rt="oic.d.light"
Response: RD -> CT
Res: 2.01 Created
Location-Path: /rd/452x
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For the application group "grp_schedule", four other endpoints are
specified as follows, with x = 4, 5, 6, 7.
Request: CT -> RD
Req: POST coap://[2001:db8:4::ff]/rd
?ep=ACME-123x&base=coap://[2001:db8:4::x]&app-gp=grp_schedule
Payload:
</schedule>;rt="oic.r.time.period"
Response: RD -> CT
Res: 2.01 Created
Location-Path: /rd/456x
*** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
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
Req: POST coap://[2001:db8:4::ff]/rd?ep=gm1&base=coap://[2001:db8::ab]
Payload:
</group-oscore/feedca570000>;ct=41;rt="core.osc.mbr";
sec-gp="feedca570000";app-gp="grp_R2-4-015",
</group-oscore/feedsc590000>;ct=41;rt="core.osc.mbr";
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 consequently learn the
groups to which it belongs. In particular, it first does an ep
lookup to the RD to learn the application groups to which it belongs.
Request: Joining node -> RD
Req: GET coap://[2001:db8:4::ff]/rd-lookup/ep
?base=coap://[2001:db8:4::x]
Response: RD -> Joining node
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Res: 2.05 Content
Payload:
<rd/452x>;base=coap://[2001:db8:4::x]&ep=ACME-123x&\
app-gp=grp_R2-4-015,
<rd/456x>;base=coap://[2001:db8:4::x]&ep=ACME-123x&\
app-gp=grp_schedule
To retrieve the multicast IP address used in "grp_R2-4-015", 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_R2-4-015
Response: RD -> Joining node
Res: 2.05 Content
Payload:
</rd/501>;ep="grp_R2-4-015";et="core.rd-group";
base="coap://[ff05::5:1]"
Similarly, to retrieve the multicast IP address used in
"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
Res: 2.05 Content
Payload:
</rd/502>;ep="grp_schedule";et="core.rd-group";
base="coap://[ff05::5:2]"
*** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
Having learnt the application groups to which the device belongs, the
device learns the security groups to which it belongs. 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.mbr&app-gp=grp_R2-4-015
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Response: RD -> Joining Node
Res: 2.05 Content
Payload:
<coap://[2001:db8::ab]/group-oscore/feedca570000>;
rt="core.osc.mbr";sec-gp="feedca570000";
app-gp="grp_R2-4-015";anchor="coap://[2001:db8::ab]"
Similarly, the device does the following for app-gp="grp_schedule".
Req: GET coap://[2001:db8:4::ff]/rd-lookup/res
?rt=core.osc.mbr&app-gp=grp_schedule
Response: RD -> Joining Node
Res: 2.05 Content
Payload:
<coap://[2001:db8::ab]/group-oscore/feedsc590000>;
rt="core.osc.mbr";sec-gp="feedsc590000";
app-gp="grp_schedule";anchor="coap://[2001:db8::ab]"
*** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
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].
7. Security Considerations
The security considerations as described in Section 8 of
[I-D.ietf-core-resource-directory] apply here as well.
8. IANA Considerations
This document has the following actions for IANA.
8.1. Resource Types
IANA is asked to enter the following value into the Resource Type
(rt=) Link Target Attribute Values subregistry within the Constrained
Restful Environments (CoRE) Parameters registry defined in [RFC6690].
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+--------------+----------------------------+-------------------+
| Value | Description | Reference |
+--------------+----------------------------+-------------------+
| | | |
| core.osc.mbr | Group-membership resource | [[this document]] |
| | of an OSCORE Group Manager | |
| | | |
+--------------+----------------------------+-------------------|
9. References
9.1. Normative References
[I-D.ietf-ace-cwt-proof-of-possession]
Jones, M., Seitz, L., Selander, G., Erdtman, S., and H.
Tschofenig, "Proof-of-Possession Key Semantics for CBOR
Web Tokens (CWTs)", draft-ietf-ace-cwt-proof-of-
possession-11 (work in progress), October 2019.
[I-D.ietf-ace-key-groupcomm-oscore]
Tiloca, M., Park, J., and F. Palombini, "Key Management
for OSCORE Groups in ACE", draft-ietf-ace-key-groupcomm-
oscore-03 (work in progress), November 2019.
[I-D.ietf-core-oscore-groupcomm]
Tiloca, M., Selander, G., Palombini, F., and J. Park,
"Group OSCORE - Secure Group Communication for CoAP",
draft-ietf-core-oscore-groupcomm-06 (work in progress),
November 2019.
[I-D.ietf-core-resource-directory]
Shelby, Z., Koster, M., Bormann, C., Stok, P., and C.
Amsuess, "CoRE Resource Directory", draft-ietf-core-
resource-directory-23 (work in progress), July 2019.
[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>.
[RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link
Format", RFC 6690, DOI 10.17487/RFC6690, August 2012,
<https://www.rfc-editor.org/info/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/info/rfc7252>.
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[RFC8152] Schaad, J., "CBOR Object Signing and Encryption (COSE)",
RFC 8152, DOI 10.17487/RFC8152, July 2017,
<https://www.rfc-editor.org/info/rfc8152>.
[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>.
9.2. Informative References
[Fairhair]
FairHair Alliance, "Security Architecture for the Internet
of Things (IoT) in Commercial Buildings", White Paper, ed.
Piotr Polak , March 2018, <https://www.fairhair-
alliance.org/data/downloadables/1/9/
fairhair_security_wp_march-2018.pdf>.
[I-D.dijk-core-groupcomm-bis]
Dijk, E., Wang, C., and M. Tiloca, "Group Communication
for the Constrained Application Protocol (CoAP)", draft-
dijk-core-groupcomm-bis-01 (work in progress), July 2019.
[I-D.ietf-ace-oauth-authz]
Seitz, L., Selander, G., Wahlstroem, E., Erdtman, S., and
H. Tschofenig, "Authentication and Authorization for
Constrained Environments (ACE) using the OAuth 2.0
Framework (ACE-OAuth)", draft-ietf-ace-oauth-authz-25
(work in progress), October 2019.
[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>.
[RFC7390] Rahman, A., Ed. and E. Dijk, Ed., "Group Communication for
the Constrained Application Protocol (CoAP)", RFC 7390,
DOI 10.17487/RFC7390, October 2014,
<https://www.rfc-editor.org/info/rfc7390>.
[RFC7641] Hartke, K., "Observing Resources in the Constrained
Application Protocol (CoAP)", RFC 7641,
DOI 10.17487/RFC7641, September 2015,
<https://www.rfc-editor.org/info/rfc7641>.
[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/info/rfc8132>.
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[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/info/rfc8613>.
Acknowledgments
The authors sincerely thank Carsten Bormann, Klaus Hartke, 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, and by the EIT-Digital High Impact
Initiative ACTIVE.
Authors' Addresses
Marco Tiloca
RISE AB
Isafjordsgatan 22
Kista SE-16440 Stockholm
Sweden
Email: marco.tiloca@ri.se
Christian Amsuess
Hollandstr. 12/4
Vienna 1020
Austria
Email: christian@amsuess.com
Peter van der Stok
Consultant
Phone: +31-492474673 (Netherlands), +33-966015248 (France)
Email: consultancy@vanderstok.org
URI: www.vanderstok.org
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