CoRE Working Group M. Tiloca
Internet-Draft RISE AB
Intended status: Standards Track C. Amsuess
Expires: January 6, 2020
P. van der Stok
Consultant
July 05, 2019
Discovery of OSCORE Groups with the CoRE Resource Directory
draft-tiloca-core-oscore-discovery-03
Abstract
Group communication over the Constrained Application Protocol (CoAP)
can be secured by means of Object Security for Constrained RESTful
Environments (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 the CoRE Resource Directory to
discover OSCORE groups and acquire information to join 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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material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 6, 2020.
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Copyright Notice
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document authors. All rights reserved.
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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 . . . . . . . . . . . . 12
7. Security Considerations . . . . . . . . . . . . . . . . . . . 17
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
8.1. Resource Types . . . . . . . . . . . . . . . . . . . . . 17
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
9.1. Normative References . . . . . . . . . . . . . . . . . . 17
9.2. Informative References . . . . . . . . . . . . . . . . . 18
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
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) [I-D.ietf-core-object-security] describes how to achieve
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end-to-end security for CoAP messages through CBOR Object Signing and
Encryption (COSE) [RFC8152].
In particular, [I-D.ietf-core-oscore-groupcomm] specifies how 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 join
resource associated with the OSCORE group of interest 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 join 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 valid information about deployed
groups.
This specification describes how CoAP endpoints can use the CoRE
Resource Directory (RD) [I-D.ietf-core-resource-directory] for
discovering an OSCORE group and retrieving the information required
to join that group through a given 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 join resource.
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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.
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
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associated to the same OSCORE group do not share any same
resource.
o Zeroed-epoch Group ID: this refers to the Group ID of an OSCORE
group as stored in the RD. The structure of such a stored Group
ID is as per Appendix C of [I-D.ietf-core-oscore-groupcomm], with
the "Group Epoch" part immutable and set to zero.
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 "join
resources" located at the GM, and associated to the OSCORE groups
administrated by that GM.
In particular, each link to a join resource includes:
o "target": URI of the join resource at the GM.
o target attributes, including:
* Resource Type (rt) with the value "core.osc.j" defined in
Section 8.1 of this specification.
* The zeroed-epoch Group ID of the OSCORE group.
* 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.
* The AEAD algorithm used in the OSCORE group.
* The HKDF algorithm used in the OSCORE group.
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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 MUST also register all the join resources it
has at that point in time, i.e. one for each of its OSCORE groups.
For each registered join resource, the GM MUST specify the following
parameters in the payload of the registration request.
o 'rt' = "core.osc.j" (see Section 8.1).
o 'oscore-gid', specifying the zeroed-epoch Group ID 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. 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 join resource, the GM MAY specify 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, which is taken from the 'Name' 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, which is
taken from the 'Name' 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, which is taken from the
'Name' 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, which is taken from the 'Name' column of Figure 2 in
[I-D.ietf-ace-key-groupcomm-oscore], as registered in the "ACE
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Public Key Encoding" Registry defined in
[I-D.ietf-ace-key-groupcomm].
o 'alg', specifying the AEAD algorithm used in the OSCORE group. If
present, this parameter MUST specify a single value, which is
taken from the 'Name' 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, which is
taken from the 'Name' column of the "COSE Algorithms" Registry
defined in [RFC8152].
A CoAP endpoint that queries the RD to discover OSCORE groups and
their join resource to access (see Section 5) would benefit from the
link target attributes above as follows.
o The values of 'cs_alg', 'cs_crv', 'cs_kty' and 'cs_kenc' related
to a join 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 join 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 join process.
o The values of 'cs_alg', 'alg' and 'hkdf' related to a join
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 join 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].
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 'oscore-gid' parameter for accessing the OSCORE group with
zeroed-epoch Group ID "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
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Req: POST coap://rd.example.com/rd?ep=gm1
Content-Format: 40
Payload:
</join/feedca570000>;ct=41;rt="core.osc.j";oscore-gid="feedca570000";
app-gp="group1";cs_alg="EdDSA";cs_crv="Ed25519";
cs_kty="OKP";cs_kenc="COSE_Key"
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 join
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 join 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
join resource.
o The GM dismisses an OSCORE group and stops exporting the related
join 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 join resources with
their target attributes.
The example below shows how the GM from Section 3 re-registers with
the RD. When doing so, it specifies:
o The same previous join resource associated to the OSCORE group
with zeroed-epoch Group ID "feedca570000".
o An additional join resource associated to the OSCORE group with
zeroed-epoch Group ID "ech0ech00000" and used by the application
group "group2".
o A third join resource associated with the OSCORE group with
zeroed-epoch Group ID "abcdef120000" and used by two application
groups, namely "group3" and "group4".
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Request: GM -> RD
Req: POST coap://rd.example.com/rd?ep=gm1
Content-Format: 40
Payload:
</join/feedca570000>;ct=41;rt="core.osc.j";oscore-gid="feedca570000";
app-gp="group1";cs_alg="EdDSA";cs_crv="Ed25519";
cs_kty="OKP";cs_kenc="COSE_Key",
</join/ech0ech00000>;ct=41;rt="core.osc.j";oscore-gid="ech0ech00000";
app-gp="group2";cs_alg="EdDSA";cs_crv="Ed25519";
cs_kty="OKP";cs_kenc="COSE_Key",
</join/abcdef120000>;ct=41;rt="core.osc.j";oscore-gid="abcdef120000";
app-gp="group3";app-gp="group4";cs_alg="EdDSA";
cs_crv="Ed25519";cs_kty="OKP";cs_kenc="COSE_Key"
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
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 MUST use the following parameter values for the
lookup filtering.
o 'rt' = "core.osc.j" (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.
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o 'oscore-gid', specifying the zeroed-epoch Group ID 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. An application group MUST be
specified only once.
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 zeroed-epoch Group ID of the OSCORE group, the
responsible GM and the join resource to access.
Request: Joining node -> RD
Req: GET coap://rd.example.com/rd-lookup/res
?rt=core.osc.j&app-gp=group1
Response: RD -> Joining node
Res: 2.05 Content
Payload:
<coap://[2001:db8::ab]/join/feedca570000>;rt="core.osc.j";
oscore-gid="feedca570000";app-gp="group1";
cs_alg="EdDSA";cs_crv="Ed25519";cs_kty="OKP";
cs_kenc="COSE_Key";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
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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 zeroed-epoch Group ID "feedca570000", but that does not
know the responsible GM, the join 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 in the join
resource's target attributes. 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
Req: GET coap://rd.example.com/rd-lookup/res
?rt=osc.j&oscore-gid=feedca570000
Observe: 0
Response: RD -> Joining node
Res: 2.05 Content
Observe: 24
Payload:
<coap://[2001:db8::ab]/join/feedca570000>;rt="osc.j";
oscore-gid="feedca570000";app-gp="group1";
cs_alg="EdDSA";cs_crv="Ed25519";cs_kty="OKP";
cs_kenc="COSE_Key";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 join resources at a
specified GM, or all the join 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=osc.j
Response: RD -> Joining node
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Res: 2.05 Content
Payload:
<coap://[2001:db8::ab]/join/feedca570000>;rt="osc.j";
oscore-gid="feedca570000";app-gp="group1";
cs_alg="EdDSA";cs_crv="Ed25519";cs_kty="OKP";
cs_kenc="COSE_Key";anchor="coap://[2001:db8::ab]",
<coap://[2001:db8::ab]/join/ech0ech00000>;rt="osc.j";
oscore-gid="ech0ech00000";app-gp="group2";
cs_alg="EdDSA";cs_crv="Ed25519";cs_kty="OKP";
cs_kenc="COSE_Key";anchor="coap://[2001:db8::ab]",
<coap://[2001:db8::ab]/join/abcdef120000>;rt="osc.j";
oscore-gid="abcdef120000";app-gp="group3";
app-gp="group4";cs_alg="EdDSA";cs_crv="Ed25519";
cs_kty="OKP";cs_kenc="COSE_Key";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 'oscore-gid' in its GET request sent to the RD.
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.
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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)
group "grp_R2-4-015" to the four luminaires; and ii) 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.
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
*** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
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Consecutively, the CT registers the four devices in the RD (IP
address: 2001:db8:4::ff), with their endpoint names and application
groups.
For 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
For 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:
</join/feedca570000>;ct=41;rt="core.osc.j";
oscore-gid="feedca570000";app-gp="grp_R2-4-015",
</join/feedsc590000>;ct=41;rt="core.osc.j";
oscore-gid="feedsc590000";app-gp="grp_schedule"
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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
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
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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.j&app-gp=grp_R2-4-015
Response: RD -> Joining Node
Res: 2.05 Content
Payload:
<coap://[2001:db8::ab]/join/feedca570000>;
rt="core.osc.j";oscore-gid="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.j&app-gp=grp_schedule
Response: RD -> Joining Node
Res: 2.05 Content
Payload:
<coap://[2001:db8::ab]/join/feedsc590000>;
rt="core.osc.j";oscore-gid="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].
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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].
+------------+----------------------+-------------------+
| Value | Description | Reference |
+------------+----------------------+-------------------+
| | | |
| core.osc.j | Join resource of an | [[this document]] |
| | OSCORE Group Manager | |
| | | |
+------------+----------------------+-------------------|
9. References
9.1. Normative References
[I-D.ietf-ace-key-groupcomm]
Palombini, F. and M. Tiloca, "Key Provisioning for Group
Communication using ACE", draft-ietf-ace-key-groupcomm-02
(work in progress), July 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-02 (work in progress), July 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-05 (work in progress),
July 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-22 (work in progress), July 2019.
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[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>.
[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-00 (work in progress), March 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-24
(work in progress), March 2019.
[I-D.ietf-core-object-security]
Selander, G., Mattsson, J., Palombini, F., and L. Seitz,
"Object Security for Constrained RESTful Environments
(OSCORE)", draft-ietf-core-object-security-16 (work in
progress), March 2019.
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[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>.
Acknowledgments
The authors sincerely thank Carsten Bormann, 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
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Peter van der Stok
Consultant
Phone: +31-492474673 (Netherlands), +33-966015248 (France)
Email: consultancy@vanderstok.org
URI: www.vanderstok.org
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