Discovery of OSCORE Groups with the CoRE Resource Directory
draft-tiloca-core-oscore-discovery-02
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| Authors | Marco Tiloca , Christian Amsüss , Peter Van der Stok | ||
| Last updated | 2019-03-11 (Latest revision 2019-01-23) | ||
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draft-tiloca-core-oscore-discovery-02
CoRE Working Group M. Tiloca
Internet-Draft RISE AB
Intended status: Standards Track C. Amsuess
Expires: September 12, 2019
P. van der Stok
Consultant
March 11, 2019
Discovery of OSCORE Groups with the CoRE Resource Directory
draft-tiloca-core-oscore-discovery-02
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 CoAP endpoints can use the CoRE Resource Directory to
discover OSCORE groups and acquire information to join them through
their respective Group Manager. A same 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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 12, 2019.
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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
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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 . . . . . . . . . . . 5
4. Addition and Update of OSCORE Groups . . . . . . . . . . . . 6
5. Discovery of OSCORE Groups . . . . . . . . . . . . . . . . . 7
5.1. Discovery Example #1 . . . . . . . . . . . . . . . . . . 8
5.2. Discovery Example #2 . . . . . . . . . . . . . . . . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
7.1. Resource Types . . . . . . . . . . . . . . . . . . . . . 10
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
8.1. Normative References . . . . . . . . . . . . . . . . . . 11
8.2. Informative References . . . . . . . . . . . . . . . . . 11
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
A set of CoAP endpoints may share a common pool of resources, hence
composing an application group. All the members of an application
group may also be members of a same security group, hence sharing a
common set of keying material to secure group communication.
The Constrained Application Protocol (CoAP) [RFC7252] supports group
communication over IP multicast [RFC7390] to improve efficiency and
latency of communication and reduce bandwidth requirements. The
method Object Security for Constrained RESTful Environments (OSCORE)
[I-D.ietf-core-object-security] enables end-to-end security for CoAP
messages through CBOR Object Signing and Encryption (COSE) [RFC8152].
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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 the responsible 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 as ACE Client and Resource Server, respectively.
That is, the joining endpoint accesses the join resource associated
to 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: the OSCORE
group(s) to join and the responsible GM(s) are generally unknown at
manufacturing time; 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; 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 updated information about those 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 the responsible 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.
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
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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
convenient notifications about the creation of new OSCORE groups or
the updates of information concerning existing ones. Thus, it
facilitates the early deployment of CoAP endpoints, i.e. even before
the GM is deployed and the OSCORE groups of interest 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 a same OSCORE
Common Security Context to protect group communication as
described in [I-D.ietf-core-oscore-groupcomm]. That is, 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 to a single OSCORE group, while different
application groups can rely on the same OSCORE group. Application
groups MAY share resources. Any two application groups associated
to the same OSCORE group do not share any 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
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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 at the GM, associated to the OSCORE groups under 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 7.1 of this specification.
* The zeroed-epoch Group ID of the OSCORE group.
* One target attribute for each application group associated to
the OSCORE group, specifying the name of that application
group.
3. Registration of Group Manager Endpoints
Upon deployment, a GM finds the RD as described in Section 4 of
[I-D.ietf-core-resource-directory]. After that, the GM registers as
an endpoint with the RD, as described in Section 5.3 of
[I-D.ietf-core-resource-directory].
When doing so, the GM MUST also register all the join resources it is
exporting 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 7.1).
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
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of one application group. A same application group MUST NOT be
specified multiple times.
The GM SHOULD NOT use the Simple Registration approach described in
Section 5.3.1 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 link
to one join resource for accessing the OSCORE group with zeroed-epoch
Group ID "feedca570000" and used by one application group with name
"group1".
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"
Response: RD -> GM
Res: 2.01 Created
Location-Path: /rd/4521
4. Addition and Update of OSCORE Groups
The GM is responsible to keep its registration with the RD up to date
with links to all its join resources. This means that the GM has to
update the registration within its lifetime as per Section 5.4.1 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.
In order to perform an update to the set of links in its
registration, the GM can re-register with the RD and fully specify
all links to its join resources and their target attributes in the
payload of the POST request.
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The example below shows the same GM from Section 3 that 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 A second join resource associated to the OSCORE group with zeroed-
epoch Group ID "ech0ech00000" and used by one application group,
namely "group2".
o A third join resource associated to the OSCORE group with zeroed-
epoch Group ID "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:
</join/feedca570000>;ct=41;rt="core.osc.j";
oscore-gid="feedca570000";app-gp="group1",
</join/ech0ech00000>;ct=41;rt="core.osc.j";
oscore-gid="ech0ech00000";app-gp="group2",
</join/abcdef120000>;ct=41;rt="core.osc.j";
oscore-gid="abcdef120000";app-gp="group3";app-gp="group4"
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 5.4.3 of [I-D.ietf-core-resource-directory].
This requires semantics to be defined in future standards, in order
to apply a link-format document as a patch to a different one.
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], in order 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].
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The joining node MUST consider the following search criteria for the
lookup filtering.
o 'rt' = "core.osc.j" (see Section 7.1).
The joining node MAY additionally consider the following search
criteria for the lookup filtering, depending on the information it
has already available.
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 identifier of the GM as endpoint registered
with the RD.
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.
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 to 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/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";
anchor="coap://[2001:db8::ab]"
If it does not know the multicast IP address used in "group1", the
joining node can retrieve it by performing 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.
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Request: Joining node -> RD
Req: GET coap://rd.example.com/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 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 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 available
at a later point in time.
Request: Joining node -> RD
Req: GET coap://rd.example.com/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";
anchor="coap://[2001:db8::ab]"
Depending on the used search criteria, the joining node performing
the resource lookup can get a response whose payload is quite large
in size. This can happen, for instance, in case 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
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Req: GET coap://rd.example.com/lookup/res?rt=osc.j
Response: RD -> Joining node
Res: 2.05 Content
Payload:
<coap://[2001:db8::ab]/join/feedca570000>;rt="osc.j";
oscore-gid="feedca570000";app-gp="group1";
anchor="coap://[2001:db8::ab]",
<coap://[2001:db8::ab]/join/ech0ech00000>;rt="osc.j";
oscore-gid="ech0ech00000";app-gp="group2";
anchor="coap://[2001:db8::ab]",
<coap://[2001:db8::cd]/join/abcdef120000>;rt="osc.j";
oscore-gid="abcdef120000";app-gp="group3";app-gp="group4";
anchor="coap://[2001:db8::cd]"
Therefore, it is RECOMMENDED that a joining node performing a
resource lookup to discover OSCORE groups uses observation only when
including the fine-grained seach criterion 'oscore-gid' in its GET
request sent to the RD.
6. Security Considerations
The security considerations as described in Section 8 of
[I-D.ietf-core-resource-directory] apply here as well.
7. IANA Considerations
This document has the following actions for IANA.
7.1. 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 | |
| | | |
+------------+----------------------+-------------------|
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8. References
8.1. Normative References
[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-01 (work in progress), March 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-04 (work in progress),
March 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-19 (work in progress), January 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>.
[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>.
8.2. Informative References
[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-22
(work in progress), March 2019.
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[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.
[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>.
[RFC8152] Schaad, J., "CBOR Object Signing and Encryption (COSE)",
RFC 8152, DOI 10.17487/RFC8152, July 2017,
<https://www.rfc-editor.org/info/rfc8152>.
Acknowledgments
The authors sincerely thank Carsten Bormann, Francesca Palombini 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
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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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