Secure group communication for CoAP
draft-tiloca-core-multicast-oscoap-01
The information below is for an old version of the document.
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| Authors | Marco Tiloca , Göran Selander , Francesca Palombini | ||
| Last updated | 2017-03-13 | ||
| Replaced by | draft-ietf-core-oscore-groupcomm, draft-ietf-core-oscore-groupcomm, draft-ietf-core-oscore-groupcomm | ||
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draft-tiloca-core-multicast-oscoap-01
CoRE Working Group M. Tiloca
Internet-Draft RISE SICS AB
Intended status: Standards Track G. Selander
Expires: September 14, 2017 F. Palombini
Ericsson AB
March 13, 2017
Secure group communication for CoAP
draft-tiloca-core-multicast-oscoap-01
Abstract
This document describes a method for application layer protection of
messages exchanged with the Constrained Application Protocol (CoAP)
in a group communication context. The proposed approach relies on
Object Security of CoAP (OSCOAP) and the CBOR Object Signing and
Encryption (COSE) format. All security requirements fulfilled by
OSCOAP are maintained for multicast CoAP request messages and related
unicast CoAP response messages. Source authentication of all
messages exchanged within the group is ensured, by means of digital
signatures produced through asymmetric private keys of sender devices
and embedded in the protected CoAP messages.
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 September 14, 2017.
Copyright Notice
Copyright (c) 2017 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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(http://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
include Simplified BSD License text as described in Section 4.e of
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 . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Scope Description . . . . . . . . . . . . . . . . . . . . . . 7
4. Security Context . . . . . . . . . . . . . . . . . . . . . . 8
5. The COSE Object . . . . . . . . . . . . . . . . . . . . . . . 9
6. Message Processing . . . . . . . . . . . . . . . . . . . . . 10
6.1. Protecting the Request . . . . . . . . . . . . . . . . . 10
6.2. Verifying the Request . . . . . . . . . . . . . . . . . . 10
6.3. Protecting the Response . . . . . . . . . . . . . . . . . 11
6.4. Verifying the Response . . . . . . . . . . . . . . . . . 11
7. Security Considerations . . . . . . . . . . . . . . . . . . . 12
7.1. Group-level Security . . . . . . . . . . . . . . . . . . 12
7.2. Management of Group Keying Material . . . . . . . . . . . 12
7.3. Late Joining Endpoints . . . . . . . . . . . . . . . . . 13
7.4. Provisioning of Public Keys . . . . . . . . . . . . . . . 13
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
10.1. Normative References . . . . . . . . . . . . . . . . . . 14
10.2. Informative References . . . . . . . . . . . . . . . . . 15
Appendix A. Group Joining Based on the ACE Framework . . . . . . 16
Appendix B. List of Use Cases . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
1. Introduction
The Constrained Application Protocol (CoAP) [RFC7252] is a web
transfer protocol specifically designed for constrained devices and
networks.
[RFC7390] enables group communication for CoAP, addressing use cases
where deployed devices benefit from a group communication model for
example to limit latencies and improve performance. Use cases
include lighting control, integrated building control, software and
firmware updates, parameter and configuration updates, commissioning
of constrained networks, and emergency multicast. [RFC7390]
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recognizes the importance to introduce a secure mode for CoAP group
communication. This specification defines such a mode.
Object Security of CoAP (OSCOAP)[I-D.ietf-core-object-security]
describes a security protocol based on the exchange of protected CoAP
messages. OSCOAP builds on CBOR Object Signing and Encryption (COSE)
[I-D.ietf-cose-msg] and provides end-to-end encryption, integrity,
and replay protection across intermediate modes. To this end, a CoAP
message is protected by including payload (if any), certain options,
and header fields in a COSE object, which finally replaces the
authenticated and encrypted fields in the protected message.
This document describes multicast OSCOAP, providing end-to-end
security of CoAP messages exchanged between members of a multicast
group. In particular, the described approach defines how OSCOAP
should be used in a group communication context, while fulfilling the
same security requirements. That is, end-to-end security is assured
for multicast CoAP requests sent by multicaster nodes to the group
and for related unicast CoAP responses sent as reply by multiple
listener nodes. Multicast OSCOAP provides source authentication of
all CoAP messages exchanged within the group, by means of digital
signatures produced through asymmetric private keys of sender devices
and embedded in the protected CoAP messages. As in OSCOAP, it is
still possible to simultaneously rely on DTLS to protect hop-by-hop
communication between a multicaster node and a proxy (and vice
versa), and between a proxy and a listener node (and vice versa).
1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. These
words may also appear in this document in lowercase, absent their
normative meanings.
Readers are expected to be familiar with the terms and concepts
described in [RFC7252], [RFC7390] and [RFC7641].
Terminology for constrained environments, such as "constrained
device", "constrained-node network", is defined in [RFC7228].
Terminology for protection and processing of CoAP messages through
OSCOAP, such as "Security Context", "Master Secret", "Master Salt",
is defined in [I-D.ietf-core-object-security].
This document refers also to the following terminology.
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o Keying material: data that is necessary to establish and maintain
secure communication among member of a multicast group. This
includes, for instance, keys, key pairs, and IVs [RFC4949].
o Group Manager (GM): entity responsible for creating a multicast
group, establishing and provisioning security contexts among
authorized group members, and managing the joining of new group
members. A GM can be responsible for multiple multicast groups,
while it is not required to be an actual group member and to take
part in the group communication. The GM may also be responsible
for renewing/updating security contexts and related keying
material. Any message exchange with the GM MUST be secured and
based on different secure channels for different endpoints.
o Multicaster: member of a multicast group that sends multicast CoAP
messagges intended for all members of the group. In a 1-to-N
multicast group, only a single multicaster transmits data to the
group; in an M-to-N multicast group (where M and N do not
necessarily have the same value), M group members are
multicasters.
o Listener: member of a multicast group that receives multicast CoAP
messages when listening to the multicast IP address associated to
the multicast group. A listener MAY reply back, by sending a
unicast response message to the multicaster which has sent the
multicast message.
o Group request: multicast CoAP request message sent by a
multicaster in the group to all listeners in the group through
multicast IP.
o Group response: unicast CoAP response message sent back by a
listener in the group as a response to a group request received
from a multicaster.
o Source authentication: evidence that a received message in the
group originated from a specifically identified group member.
This also provides assurances that the message was not tampered
with by any other group member or an adversary outside the group.
2. Requirements
The following security requirements are out of the scope of this
document and are assumed to be already fulfilled.
o Establishment and management of a security context: a security
context must be established among the group members by the Group
Manager which manages the multicast group. A secure mechanism
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must be used to generate, revoke and (re-)distribute keying
material, multicast security policies and security parameters in
the multicast group. The actual establishment and management of
the security context is out of the scope of this document, and it
is anticipated that an activity in IETF dedicated to the design of
a generic key management scheme will include this feature,
preferably based on [RFC3740][RFC4046][RFC4535].
o Multicast data security ciphersuite: all group members MUST agree
on a ciphersuite to provide authenticity, integrity and
confidentiality of messages in the multicast group. The
ciphersuite is specified as part of the security context.
o Backward security: a new device joining the multicast group should
not have access to any old security contexts used before its
joining. This ensures that a new group member is not able to
decrypt confidential data sent before it has joined the group.
The adopted key management scheme should ensure that the security
context is updated to ensure backward confidentiality. The actual
mechanism to update the security context and renew the group
keying material upon a group member's joining has to be defined as
part of the group key management scheme.
o Forward security: entities that leave the multicast group should
not have access to any future security contexts or message
exchanged within the group after their leaving. This ensures that
a former group member is not able to decrypt confidential data
sent within the group anymore. Also, it ensures that a former
member is not able to send encrypted and/or integrity protected
messages to the group anymore. The actual mechanism to update the
security context and renew the group keying material upon a group
member's leaving has to be defined as part of the group key
management scheme.
The following security requirements need to be fulfilled by the
approach described in this document:
o Multicast communication topology: this document considers both
1-to-N (one multicaster and multiple listeners) and M-to-N
(multiple multicasters and multiple listeners) communication
topologies. The 1-to-N communication topology is the simplest
group communication scenario that would serve the needs of a
typical LLN. For instance, in the lighting control use case,
switches are the only entities responsible for sending commands to
a group of lighting devices. In more advanced lighting control
use cases, a M-to-N communication topology would be required, for
instance in case multiple sensors (presence or day-light) are
responsible to trigger events to a group of lighting devices.
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o Multicast group size: security solutions for group communication
SHOULD be able to adequately support different, possibly large,
group sizes. Group size is the combination of the number of
multicasters and listeners in a multicast group, with possible
overlap (i.e. a multicaster MAY also be a listener at the same
time). In the use cases mentioned in this document, the number of
multicasters (normally the controlling devices) is expected to be
much smaller than the number of listeners (i.e. the controlled
devices). A security solution for group communication that
supports 1 to 50 multicasters would be able to properly cover the
group sizes required for most use cases that are relevant for this
document. The total number of group members is expected to be in
the range of 2 to 100 devices. Groups larger than that SHOULD be
divided into smaller independent multicast groups, e.g. by
grouping lights in a building on a per floor basis.
o Data replay protection: it MUST NOT be possible to replay a group
request message or a group response message, which would disrupt
the correct communication in the group and the activity of group
members.
o Group-level data confidentiality: messages sent within the
multicast group SHALL be encrypted. In fact, some control
commands and/or associated responses could pose unforeseen
security and privacy risks to the system users, when sent as
plaintext. In particular, data confidentiality MAY be required if
privacy sensitive data is exchanged in the group. This document
considers group-level data confidentiality since messages are
encrypted at a group level, i.e. in such a way that they can be
decrypted by any member of the multicast group, but not by an
external adversary or other external entities.
o Source authentication: messages sent within the multicast group
SHALL be authenticated. That is, it is essential to ensure that a
message is originated by a member of the group in the first place
(group authentication), and in particular by a specific member of
the group (source authentication). The approach proposed in this
document provides both group authentication and source
authentication, both for group requests originated by multicasters
and group responses originated by listeners. In order to provide
source authentication, outgoing messages are signed by the
respective originator group member by means of its own asymmetric
private key. The resulting signature is included in the COSE
object.
o Message integrity: messages sent within the multicast group SHOULD
be integrity protected. That is, it is essential to ensure that a
message has not been tampered with by an external adversary or
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other external entities which are not group members. Message
integrity is provided through the same means used to provide
source authentication.
3. Scope Description
An endpoint joins a multicast group by explicitly interacting with
the responsible Group Manager. The actual join process MAY be based
on the ACE framework [I-D.ietf-ace-oauth-authz] and the OSCOAP
profile of ACE [I-D.seitz-ace-oscoap-profile], as discussed in
Appendix A.
An endpoint registered as member of a group can behave as a
multicaster and/or as a listener. As a multicaster, it can transmit
multicast request messages to the group. As a listener, it receives
multicast request messages from any multicaster in the group, and
possibly replies by transmitting unicast response messages. A number
of use cases that benefit from secure group communication are
discussed in Appendix B. Upon joining the group, endpoints are not
required to know how many and what endpoints are active in the same
group.
An endpoint which is registered as member of a group is identified by
an endpoint ID, which is not necessarily related to any protocol-
relevant identifiers, such as IP addresses. The Group Manager
generates and manages endpoint IDs in order to ensure their
uniqueness within a same multicast group. That is, there cannot be
multiple endpoints that belong to the same group and are associated
to a same endpoint ID.
In order to participate in the secure group communication, an
endpoint needs to maintain additional information elements, stored in
its own security context. Those include keying material used to
protect and verify group messages, as well as the public keys of
other endpoints in the groups, in order to verify digital signatures
of secure messages and ensure their source authenticity. These
pieces of information are provided by the Group Manager through out-
of-band means or other pre-established secure channels. Further
details about establishment, revocation and renewal of the security
context and keying material are out of the scope of this document.
According to [RFC7390], any possible proxy entity is supposed to know
about the multicasters in the group and to not perform aggregation of
response messages. Also, every multicaster expects and is able to
handle multiple unicast response messages associated to a given
multicast request message.
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4. Security Context
To support multicast communication secured with OSCOAP, each endpoint
registered as member of a multicast group maintains a Security
Context as defined in Section 3 of [I-D.ietf-core-object-security].
In particular, each endpoint in a group stores:
1. one Common Context, received from the Group Manager upon joining
the multicast group and shared by all the endpoints in the group.
The Common Context contains the COSE AEAD algorithm, the Master
Secret and, optionally, the Master Salt used to derive endpoint-
based keying material (see Section 3.2 of
[I-D.ietf-core-object-security]). All the endpoints in the group
agree on the same COSE AEAD algorithm. Besides, in addition to
what is defined in [I-D.ietf-core-object-security], the Common
Context stores the following parameters:
* Context Identifier (Cid). Variable length byte string that
identifies the Security Context. The Cid used in a multicast
group is determined by the responsible Group Manager and does
not change over time. A Cid MUST be unique in the sets of all
the multicast groups associated to the same Group Manager.
The choice of the Cid for a given group's Security Context is
application specific, but it is RECOMMENDED to use 64-bit long
pseudo-random Cids, in order to have globally unique Context
Identifiers. It is the role of the application to specify how
to handle possible collisions.
* Counter signature algorithm. Value that identifies the
algorithm used for source authenticating messages sent within
the group. Its value is immutable once the security context
is established. All the endpoints in the group agree on the
same counter signature algorithm.
2. one Sender Context, used to secure outgoing messages. In
particular, the Sender Context is initialized according to
Section 3 of [I-D.ietf-core-object-security], once the endpoint
has joined the multicast group. Besides, in addition to what is
defined in [I-D.ietf-core-object-security], the Sender Context
stores also the endpoint's asymmetric public-private key pair;
3. one Recipient Context for each distinct endpoint from which
messages are received, used to process such incoming secure
messages. The endpoint creates a new Recipient Context upon
receiving an incoming message from another endpoint in the group
for the first time. Besides, in addition to what is defined in
[I-D.ietf-core-object-security], each Recipient Context stores
also the public key of the associated other endpoint from which
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secure messages are received. Possible approaches to provision
and retrieve public keys of group members are discussed in
Section 7.4.
The Sender Key/IV stored in the Sender Context and the Recipient
Keys/IVs stored in the Recipient Contexts are derived according to
the same scheme defined in Section 3.2 of
[I-D.ietf-core-object-security].
The 3-tuple (Cid, Sender ID, Partial IV) is called Transaction
Identifier (Tid), and SHALL be unique for each Master Secret. The
Tid is used as a unique challenge in the COSE object of the protected
CoAP request. The Tid is part of the Additional Authenticated Data
(AAD, see Section of 5.2 of [I-D.ietf-core-object-security]) of the
protected CoAP response message, which is how unicast responses are
bound to multicast requests.
5. The COSE Object
When creating a protected CoAP message, an endpoint in the group
computes the COSE object as defined in Section 5 of
[I-D.ietf-core-object-security], with the following modifications.
1. The value of the "Partial IV" parameter in the "protected" field
is set to the Sequence Number and SHALL be present in both
multicast requests and unicast responses. Specifically, a
multicaster endpoint sets the value of "Partial IV" to the
Sequence Number from its own Sender Context, upon sending a
multicast request message. Similarly, a listener endpoint sets
the value of "Partial IV" to the Sequence Number from its own
Sender Context, upon sending a unicast response message.
2. The value of the "kid" parameter in the "protected" field is set
to the Sender ID of the endpoint and SHALL be present in both
multicast requests and unicast responses.
3. The "protected" field of the "Headers" field SHALL include also
the following parameter:
* gid : its value is set to the Context Identifier (Cid) of the
group's Security Context. This parameter is optional if the
message is a CoAP response.
4. The Additional Authenticated Data (AAD) considered to compute the
COSE object is extended. In particular, the "external_aad"
considered for secure response messages SHALL include also the
following parameter:
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* cid : bstr, contains the Context Idenfier (Cid) of the
Security Context considered to protect the request message
(which is same as the Cid considered to protect the response
message).
5. Before transmitting any secure CoAP message, the sender endpoint
uses its own private key to create a counter signature of the
COSE_Encrypt0 object (Appendix C.4 of [I-D.ietf-cose-msg]).
Then, the counter signature is included in the Header of the COSE
object in its "unprotected" field.
6. Message Processing
Each multicast request message and unicast response message is
protected and processed as specified in
[I-D.ietf-core-object-security], with the modifications described in
the following sections. Furthermore, error handling and processing
of invalid messages are performed according to the same principles
adopted in [I-D.ietf-core-object-security].
6.1. Protecting the Request
A multicaster endpoint transmits a secure multicast request message
as described in Section 7.1 of [I-D.ietf-core-object-security], with
the following modifications:
1. The multicaster endpoint stores the association Token - Cid. That
is, it SHALL be able to find the correct Security Context used to
protect the multicast request and verify the unicast response(s)
by using the CoAP Token considered in the message exchange.
2. The multicaster endpoint computes the COSE object as defined in
Section 5 of this specification.
6.2. Verifying the Request
Upon receiving a secure multicast request message, a listener
endpoint proceeds as described in Section 7.2 of
[I-D.ietf-core-object-security], with the following modifications:
1. The listener endpoint retrieves the Context Identifier from the
"gid" parameter of the received COSE object, and uses it to
identify the correct group's Security Context.
2. The listener endpoint retrieves the Sender ID from the header of
the COSE object. Then, the Sender ID is used to retrieve the
correct Recipient Context associated to the multicaster endpoint
and used to process the request message. When receiving a secure
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multicast CoAP request message from that multicaster endpoint for
the first time, the listener endpoint creates a new Recipient
Context, initializes it according to Section 3 of
[I-D.ietf-core-object-security], and includes the multicaster
endpoint's public key.
3. The listener endpoint retrieves the corresponding public key of
the multicaster endpoint from the associated Recipient Context
and uses it to verify the counter signature, before proceeding
with the verification and decryption of the secure request
message.
6.3. Protecting the Response
A listener endpoint that has received a multicast request message MAY
reply with a secure unicast response message, which is protected as
described in Section 7.3 of [I-D.ietf-core-object-security], with the
following modifications:
1. The listener endpoint considers the Transaction Identifier (Tid)
as defined in Section 4 of this specification.
2. The listener endpoint computes the COSE object as defined in
Section 5 of this specification.
6.4. Verifying the Response
Upon receiving a secure unicast response message, a multicaster
endpoint proceeds as described in Section 7.4 of
[I-D.ietf-core-object-security], with the following modifications:
1. The multicaster endpoint considers the Security Context
identified by the Token of the received response message.
2. The multicaster endpoint retrieves the Sender ID from the header
of the COSE object. Then, the Sender ID is used to retrieve the
correct Recipient Context associated to the listener endpoint and
used to process the response message. When receiving a secure
CoAP response message from that listener endpoint for the first
time, the multicaster endpoint creates a new Recipient Context,
initializes it according to Section 3 of
[I-D.ietf-core-object-security], and includes the listener
endpoint's public key.
3. The multicaster endpoint retrieves the corresponding public key
of the listener endpoint from the associated Recipient Context
and uses it to verify the counter signature, before proceeding
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with the verification and decryption of the secure response
message.
The mapping between unicast response messages from listener endpoints
and the associated multicast request message from a multicaster
endpoint relies on the same principle adopted in
[I-D.ietf-core-object-security]. That is, it is based on the
Transaction Identifier (Tid) associated to the secure multicast
request message, which is considered by listener endpoints as part of
the Additional Authenticated Data when protecting their own response
message.
7. Security Considerations
Specific security aspects to be taken into account are discussed
below.
7.1. Group-level Security
The approach described in this document relies on commonly shared
group keying material to protect communication within a multicast
group. This means that messages are encrypted at a group level
(group-level data confidentiality), i.e. they can be decrypted by any
member of the multicast group, but not by an external adversary or
other external entities.
In addition, it is required that all group members are trusted, i.e.
they do not forward the content of group messages to unauthorized
entities. However, in many use cases, the devices in the multicast
group belong to a common authority and are configured by a
commissioner. For instance, in a professional lighting scenario, the
roles of multicaster and listener are configured by the lighting
commissioner, and devices strictly follow those roles.
Furthermore, the presented approach SHOULD take into consideration
the risk of compromise of group members. Such a risk is reduced when
multicast groups are deployed in physically secured locations, like
lighting inside office buildings. The adoption of key management
schemes for secure revocation and renewal of security contexts group
keying material SHOULD be considered.
7.2. Management of Group Keying Material
As stated in Section 2, it is important to adopt a group key
management scheme that SHOULD update the security context and keying
material in the group, before a new endpoint joins the group or after
a currently present endpoint leaves the group. This is necessary in
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order to preserve backward confidentiality and forward
confidentiality in the multicast group.
Especially in dynamic, large-scale, multicast groups where endpoints
can join and leave at any time, it is important that the considered
group key management scheme is efficient and highly scalable with the
group size, in order to limit the impact on performance due to the
security context and keying material update.
7.3. Late Joining Endpoints
Upon joining the multicast group when the system is fully operative,
listeners are not aware of the current sequence number values used by
different multicasters to transmit multicast request messages. This
means that, when such listeners receive a secure multicast message
from a multicaster, they are not able to verify if that message is
fresh and has not been replayed.
In order to address this issue, upon receiving a multicast message
from a particular multicaster for the first time, late joining
listeners can initialize their last-seen sequence number in their
Recipient Context associated to that multicaster. However, after
that they drop the message, without delivering it to the application
layer. This provides a reference point to identify if future
multicast messages from the same multicaster are fresher than the
last one seen. As an alternative, a late joining listener can
directly contact the multicaster, and explicitly request a
confirmation of the sequence number in the first received multicast
message.
A possible different approach considers the GM as an additional
listener in the multicast group. Then, the GM can maintain the
sequence number values of each multicaster in the group. When late
joiners send a request to the GM to join the group, the GM can
provide them with the list of sequence number values to be stored in
the Recipient Contexts associated to the appropriate multicasters.
7.4. Provisioning of Public Keys
Upon receiving a secure CoAP message, a recipient endpoint relies on
the sender endpoint's public key, in order to verify the counter
signature conveyed in the COSE Object.
If not already stored in the Recipient Context associated to the
sender endpoint, the recipient endpoint retrieves the public key from
a trusted key repository. In such a case, the correct binding
between the sender endpoint and the retrieved public key MUST be
assured, for instance by means of public key certificates. Further
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details about how this requirement can be fulfilled are out of the
scope of this document.
Alternatively, the Group Manager can be configured to store public
keys of group members and provide them upon request. In such a case,
upon joining a multicast group, an endpoint provides the Group
Manager with its own public key, by means of the same secure channel
used to carry out the join procedure. After that, the Group Manager
MUST perform a proof-of-possession challenge-response with the
joining endpoint, in order to verify that it actually owns the
associated private key. In case of success, the Group Manager stores
the received public key as associated to the joining endpoint and its
endpoint ID. From then on, that public key will be available for
secure and trusted delivery to other endpoints in the multicast
group.
Note that in simple, less dynamic, multicast groups, it can be
convenient for the Group Manager to provide an endpoint upon its
joining with the public keys associated to all endpoints currently
present in the group.
8. IANA Considerations
This document has no actions for IANA.
9. Acknowledgments
The authors sincerely thank Rolf Blom, Carsten Bormann, John Mattsson
and Jim Schaad for their feedback and comments.
10. References
10.1. Normative References
[I-D.ietf-core-object-security]
Selander, G., Mattsson, J., Palombini, F., and L. Seitz,
"Object Security of CoAP (OSCOAP)", draft-ietf-core-
object-security-01 (work in progress), December 2016.
[I-D.ietf-cose-msg]
Schaad, J., "CBOR Object Signing and Encryption (COSE)",
draft-ietf-cose-msg-24 (work in progress), November 2016.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
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[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<http://www.rfc-editor.org/info/rfc7252>.
[RFC7641] Hartke, K., "Observing Resources in the Constrained
Application Protocol (CoAP)", RFC 7641,
DOI 10.17487/RFC7641, September 2015,
<http://www.rfc-editor.org/info/rfc7641>.
10.2. 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)", draft-ietf-ace-oauth-
authz-05 (work in progress), February 2017.
[I-D.seitz-ace-oscoap-profile]
Seitz, L. and F. Palombini, "OSCOAP profile of ACE",
draft-seitz-ace-oscoap-profile-01 (work in progress),
October 2016.
[I-D.selander-ace-cose-ecdhe]
Selander, G., Mattsson, J., and F. Palombini, "Ephemeral
Diffie-Hellman Over COSE (EDHOC)", draft-selander-ace-
cose-ecdhe-04 (work in progress), October 2016.
[RFC3740] Hardjono, T. and B. Weis, "The Multicast Group Security
Architecture", RFC 3740, DOI 10.17487/RFC3740, March 2004,
<http://www.rfc-editor.org/info/rfc3740>.
[RFC4046] Baugher, M., Canetti, R., Dondeti, L., and F. Lindholm,
"Multicast Security (MSEC) Group Key Management
Architecture", RFC 4046, DOI 10.17487/RFC4046, April 2005,
<http://www.rfc-editor.org/info/rfc4046>.
[RFC4535] Harney, H., Meth, U., Colegrove, A., and G. Gross,
"GSAKMP: Group Secure Association Key Management
Protocol", RFC 4535, DOI 10.17487/RFC4535, June 2006,
<http://www.rfc-editor.org/info/rfc4535>.
[RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
"Transmission of IPv6 Packets over IEEE 802.15.4
Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007,
<http://www.rfc-editor.org/info/rfc4944>.
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[RFC4949] Shirey, R., "Internet Security Glossary, Version 2",
FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007,
<http://www.rfc-editor.org/info/rfc4949>.
[RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6
Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
DOI 10.17487/RFC6282, September 2011,
<http://www.rfc-editor.org/info/rfc6282>.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <http://www.rfc-editor.org/info/rfc6347>.
[RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
RFC 6749, DOI 10.17487/RFC6749, October 2012,
<http://www.rfc-editor.org/info/rfc6749>.
[RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for
Constrained-Node Networks", RFC 7228,
DOI 10.17487/RFC7228, May 2014,
<http://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,
<http://www.rfc-editor.org/info/rfc7390>.
Appendix A. Group Joining Based on the ACE Framework
The join process to register an endpoint as a new member of a
multicast group MAY be based on the ACE framework
[I-D.ietf-ace-oauth-authz] and the OSCOAP profile of ACE
[I-D.seitz-ace-oscoap-profile]. With reference to the terminology
defined in OAuth 2.0 [RFC6749]:
o The joining endpoint acts as Client;
o The Group Manager acts as Resource Server, exporting one join-
resource for each multicast group it is responsible for;
o An Authorization Server enables and enforces authorized access of
the joining endpoint to the Group Manager and its join-resources.
Then, in accordance with [I-D.seitz-ace-oscoap-profile], the joining
endpoint and the Group Manager rely on OSCOAP
[I-D.ietf-core-object-security] for secure communication and consider
Ephemeral Diffie-Hellman Over COSE (EDHOC)
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[I-D.selander-ace-cose-ecdhe] as a possible method to establish key
material.
The joining endpoint sends to the Group Manager an OSCOAP request to
access the join-resource associated to the multicast group to join.
The Group Manager replies with an OSCOAP response including the
Common Context associated to that group (see Section 4). In case the
Group Manager is configured to store the public keys of group
members, the joining endpoint additionally provides the Group Manager
with its own public key, and MAY request from the Group Manager the
public keys of the endpoints currently present in the group (see
Section 7.4).
Both the joining endpoint and the Group Manager MUST adopt secure
communication also for any message exchange with the Authorization
Server. To this end, different alternatives are possible, including
OSCOAP and DTLS [RFC6347].
Appendix B. List of Use Cases
Group Communication for CoAP [RFC7390] provides the necessary
background for multicast-based CoAP communication, with particular
reference to low-power and lossy networks (LLNs) and resource
constrained environments. The interested reader is encouraged to
first read [RFC7390] to understand the non-security related details.
This section discusses a number of use cases that benefit from secure
group communication. Specific security requirements for these use
cases are discussed in Section 2.
o Lighting control: consider a building equipped with IP-connected
lighting devices, switches, and border routers. The devices are
organized into groups according to their physical location in the
building. For instance, lighting devices and switches in a room
or corridor can be configured as members of a single multicast
group. Switches are then used to control the lighting devices by
sending on/off/dimming commands to all lighting devices in a
group, while border routers connected to an IP network backbone
(which is also multicast-enabled) can be used to interconnect
routers in the building. Consequently, this would also enable
logical multicast groups to be formed even if devices in the
lighting group may be physically in different subnets (e.g. on
wired and wireless networks). Connectivity between ligthing
devices may be realized, for instance, by means of IPv6 and
(border) routers supporting 6LoWPAN [RFC4944][RFC6282]. Group
communication enables synchronous operation of a group of
connected lights, ensuring that the light preset (e.g. dimming
level or color) of a large group of luminaires are changed at the
same perceived time. This is especially useful for providing a
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visual synchronicity of light effects to the user. Devices may
reply back to the switches that issue on/off/dimming commands, in
order to report about the execution of the requested operation
(e.g. OK, failure, error) and their current operational status.
o Integrated building control: enabling Building Automation and
Control Systems (BACSs) to control multiple heating, ventilation
and air-conditioning units to pre-defined presets. Controlled
units can be organized into multicast groups in order to reflect
their physical position in the building, e.g. devices in the same
room can be configured as members of a single multicast group.
Furthermore, controlled units are expected to possibly reply back
to the BACS issuing control commands, in order to report about the
execution of the requested operation (e.g. OK, failure, error)
and their current operational status.
o Software and firmware updates: software and firmware updates often
comprise quite a large amount of data. Therefore, it can overload
a LLN that is otherwise typically used to deal with only small
amounts of data, on an infrequent base. Rather than sending
software and firmware updates as unicast messages to each
individual device, multicasting such updated data to a larger
group of devices at once displays a number of benefits. For
instance, it can significantly reduce the network load and
decrease the overall time latency for propagating this data to all
devices. Even if the complete whole update process itself is
secured, securing the individual messages is important, in case
updates consist of relatively large amounts of data. In fact,
checking individual received data piecemeal for tampering avoids
that devices store large amounts of partially corrupted data and
that they detect tampering hereof only after all data has been
received. Devices receiving software and firmware updates are
expected to possibly reply back, in order to provide a feedback
about the execution of the update operation (e.g. OK, failure,
error) and their current operational status.
o Parameter and configuration update: by means of multicast
communication, it is possible to update the settings of a group of
similar devices, both simultaneously and efficiently. Possible
parameters are related, for instance, to network load management
or network access controls. Devices receiving parameter and
configuration updates are expected to possibly reply back, to
provide a feedback about the execution of the update operation
(e.g. OK, failure, error) and their current operational status.
o Commissioning of LLNs systems: a commissioning device is
responsible for querying all devices in the local network or a
selected subset of them, in order to discover their presence, and
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be aware of their capabilities, default configuration, and
operating conditions. Queried devices displaying similarities in
their capabilities and features, or sharing a common physical
location can be configured as members of a single multicast group.
Queried devices are expected to reply back to the commissioning
device, in order to notify their presence, and provide the
requested information and their current operational status.
o Emergency multicast: a particular emergency related information
(e.g. natural disaster) is generated and multicast by an emergency
notifier, and relayed to multiple devices. The latters may reply
back to the emergency notifier, in order to provide their feedback
and local information related to the ongoing emergency.
Authors' Addresses
Marco Tiloca
RISE SICS AB
Isafjordsgatan 22
Kista SE-16440 Stockholm
Sweden
Email: marco.tiloca@ri.se
Goeran Selander
Ericsson AB
Farogatan 6
Kista SE-16480 Stockholm
Sweden
Email: goran.selander@ericsson.com
Francesca Palombini
Ericsson AB
Farogatan 6
Kista SE-16480 Stockholm
Sweden
Email: francesca.palombini@ericsson.com
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