Key Management for OSCORE Groups in ACE
draft-ietf-ace-key-groupcomm-oscore-03
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| Authors | Marco Tiloca , Jiye Park , Francesca Palombini | ||
| Last updated | 2019-11-04 (Latest revision 2019-07-05) | ||
| Replaces | draft-tiloca-ace-oscoap-joining | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
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draft-ietf-ace-key-groupcomm-oscore-03
ACE Working Group M. Tiloca
Internet-Draft RISE AB
Intended status: Standards Track J. Park
Expires: May 7, 2020 Universitaet Duisburg-Essen
F. Palombini
Ericsson AB
November 04, 2019
Key Management for OSCORE Groups in ACE
draft-ietf-ace-key-groupcomm-oscore-03
Abstract
This document describes a method to request and provision keying
material in group communication scenarios where the group
communication is based on CoAP and secured with Object Security for
Constrained RESTful Environments (OSCORE). The proposed method
delegates the authentication and authorization of new client nodes
that join an OSCORE group through a Group Manager server. This
approach builds on the ACE framework for Authentication and
Authorization, and leverages protocol-specific transport profiles of
ACE to achieve communication security, proof-of-possession and server
authentication.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 7, 2020.
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
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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 . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 5
2.1. Overview of the Joining Process . . . . . . . . . . . . . 7
2.2. Overview of the Group Rekeying Process . . . . . . . . . 8
3. Joining Node to Authorization Server . . . . . . . . . . . . 8
3.1. Authorization Request . . . . . . . . . . . . . . . . . . 9
3.2. Authorization Response . . . . . . . . . . . . . . . . . 9
4. Joining Node to Group Manager . . . . . . . . . . . . . . . . 10
4.1. Token Post . . . . . . . . . . . . . . . . . . . . . . . 10
4.2. Joining Request . . . . . . . . . . . . . . . . . . . . . 12
4.3. Joining Response . . . . . . . . . . . . . . . . . . . . 13
5. Public Keys of Joining Nodes . . . . . . . . . . . . . . . . 17
6. Retrieval of Updated Keying Material . . . . . . . . . . . . 19
7. Retrieval of New Keying Material . . . . . . . . . . . . . . 19
8. Retrieval of Public Keys of Group Members . . . . . . . . . . 20
9. Retrieval of Group Policies . . . . . . . . . . . . . . . . . 20
10. Retrieval of Keying Material Version . . . . . . . . . . . . 21
11. Request to Leave the Group . . . . . . . . . . . . . . . . . 21
12. Removal of a Group Member . . . . . . . . . . . . . . . . . . 21
13. Group Rekeying Process . . . . . . . . . . . . . . . . . . . 22
14. Security Considerations . . . . . . . . . . . . . . . . . . . 23
15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24
15.1. ACE Groupcomm Key Registry . . . . . . . . . . . . . . . 24
15.2. OSCORE Security Context Parameters Registry . . . . . . 24
15.3. ACE Groupcomm Profile Registry . . . . . . . . . . . . . 26
15.4. Sequence Number Synchronization Method Registry . . . . 26
15.5. ACE Groupcomm Parameters Registry . . . . . . . . . . . 27
16. References . . . . . . . . . . . . . . . . . . . . . . . . . 27
16.1. Normative References . . . . . . . . . . . . . . . . . . 27
16.2. Informative References . . . . . . . . . . . . . . . . . 28
Appendix A. Profile Requirements . . . . . . . . . . . . . . . . 29
Appendix B. Document Updates . . . . . . . . . . . . . . . . . . 31
B.1. Version -02 to -03 . . . . . . . . . . . . . . . . . . . 31
B.2. Version -01 to -02 . . . . . . . . . . . . . . . . . . . 32
B.3. Version -00 to -01 . . . . . . . . . . . . . . . . . . . 32
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Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 33
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 33
1. Introduction
Object Security for Constrained RESTful Environments (OSCORE)
[RFC8613] is a method for application-layer protection of the
Constrained Application Protocol (CoAP) [RFC7252], using CBOR Object
Signing and Encryption (COSE) [RFC8152] and enabling end-to-end
security of CoAP payload and options.
As described in [I-D.ietf-core-oscore-groupcomm], Group OSCORE is
used to protect CoAP group communication over IP multicast
[RFC7390][I-D.dijk-core-groupcomm-bis]. This relies on a Group
Manager, which is responsible for managing an OSCORE group, where
members exchange CoAP messages secured with Group OSCORE. The Group
Manager can be responsible for multiple groups, coordinates the
joining process of new group members, and is entrusted with the
distribution and renewal of group keying material.
This specification builds on the ACE framework for Authentication and
Authorization [I-D.ietf-ace-oauth-authz] and defines a method to:
o Authorize a node to join an OSCORE group, and provide it with the
group keying material to communicate with other group members.
o Provide updated keying material to group members upon request.
o Renew the group keying material and distribute it to the OSCORE
group (rekeying) upon changes in the group membership.
A client node joins an OSCORE group through a resource server acting
as Group Manager for that group. The joining process relies on an
Access Token, which is bound to a proof-of-possession key and
authorizes the client to access a specific group-membership resource
at the Group Manager.
Message exchanges among the participants as well as message formats
and processing follow what specified in [I-D.ietf-ace-key-groupcomm]
for provisioning and renewing keying material in group communication
scenarios.
In order to achieve communication security, proof-of-possession and
server authentication, the client and the Group Manager leverage
protocol-specific transport profiles of ACE. These include also
possible forthcoming transport profiles that comply with the
requirements in Appendix C of [I-D.ietf-ace-oauth-authz].
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1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119][RFC8174] when, and only when, they appear in all
capitals, as shown here.
Readers are expected to be familiar with the terms and concepts
described in the ACE framework for authentication and authorization
[I-D.ietf-ace-oauth-authz]. The terminology for entities in the
considered architecture is defined in OAuth 2.0 [RFC6749]. In
particular, this includes Client (C), Resource Server (RS), and
Authorization Server (AS).
Readers are expected to be familiar with the terms and concepts
related to the CoAP protocol described in
[RFC7252][RFC7390][I-D.dijk-core-groupcomm-bis]. Note that, unless
otherwise indicated, the term "endpoint" is used here following its
OAuth definition, aimed at denoting resources such as /token and
/introspect at the AS and /authz-info at the RS. This document does
not use the CoAP definition of "endpoint", which is "An entity
participating in the CoAP protocol".
Readers are expected to be familiar with the terms and concepts for
protection and processing of CoAP messages through OSCORE [RFC8613]
and through Group OSCORE [I-D.ietf-core-oscore-groupcomm] in group
communication scenarios. These include the concept of Group Manager,
as the entity responsible for a set of groups where communications
are secured with Group OSCORE. In this specification, the Group
Manager acts as Resource Server.
This document refers also to the following terminology.
o Joining node: a network node intending to join an OSCORE group,
where communication is based on CoAP
[RFC7390][I-D.dijk-core-groupcomm-bis] and secured with Group
OSCORE as described in [I-D.ietf-core-oscore-groupcomm].
o Joining process: the process through which a joining node becomes
a member of an OSCORE group. The joining process is enforced and
assisted by the Group Manager responsible for that group.
o Group name: stable and invariant identifier of an OSCORE group.
The group name MUST be unique under the same Group Manager, and
MUST include only characters that are valid for a url-path
segment, namely unreserved and pct-encoded characters [RFC3986].
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o Group-membership resource: a resource hosted by the Group Manager,
associated to an OSCORE group under that Group Manager. A group-
membership resource is identifiable with the name of the
respective OSCORE group. A joining node accesses a group-
membership resource to start the joining process and become a
member of that group. The url-path of a group-membership resource
is fixed, and ends with the segments /group-oscore/NAME , where
"NAME" is the name of the associated OSCORE group. This replaces
the url-path /ace-group/gid at the KDC used in
[I-D.ietf-ace-key-groupcomm], with "gid" indicating the group
identifier. The url-path /group-oscore/NAME is a default name:
implementations are not required to use this name, and can define
their own instead.
o Group-membership endpoint: an endpoint at the Group Manager
associated to a group-membership resource.
o Requester: member of an OSCORE group that sends request messages
to other members of the group.
o Responder: member of an OSCORE group that receives request
messages from other members of the group. A responder may reply
back, by sending a response message to the requester which has
sent the request message.
o Monitor: member of an OSCORE group that is configured as responder
and never replies back to requesters after receiving request
messages. This corresponds to the term "silent server" used in
[I-D.ietf-core-oscore-groupcomm].
o Group rekeying process: the process through which the Group
Manager renews the security parameters and group keying material,
and (re-)distributes them to the OSCORE group members.
2. Protocol Overview
Group communication for CoAP over IP multicast has been enabled in
[RFC7390][I-D.dijk-core-groupcomm-bis] and can be secured with Group
Object Security for Constrained RESTful Environments (OSCORE)
[RFC8613] as described in [I-D.ietf-core-oscore-groupcomm]. A
network node joins an OSCORE group by interacting with the
responsible Group Manager. Once registered in the group, the new
node can securely exchange messages with other group members.
This specification describes how to use the ACE framework for
authentication and authorization [I-D.ietf-ace-oauth-authz] to:
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o Enable a node to join an OSCORE group through the Group Manager
and receive the security parameters and keying material to
communicate with the other members of the group.
o Enable members of OSCORE groups to retrieve updated group keying
material and public key of other group members, from the Group
Manager.
o Enable the Group Manager to renew the security parameters and
group keying material, and to (re-)distribute them to the members
of the OSCORE group (rekeying).
With reference to the ACE framework and the terminology defined in
OAuth 2.0 [RFC6749]:
o The Group Manager acts as Resource Server (RS), and hosts one
group-membership resource for each OSCORE group it manages. Each
group-membership resource is exported by a distinct group-
membership endpoint. During the joining process, the Group
Manager provides joining nodes with the parameters and keying
material for taking part to secure communications in the OSCORE
group. The Group Manager also maintains the group keying material
and performs the group rekeying process to distribute updated
keying material to the group members.
o The joining node acts as Client (C), and requests to join an
OSCORE group by accessing the related group-membership endpoint at
the Group Manager.
o The Authorization Server (AS) authorizes joining nodes to join
OSCORE groups under their respective Group Manager. Multiple
Group Managers can be associated to the same AS. The AS MAY
release Access Tokens for other purposes than joining OSCORE
groups under registered Group Managers. For example, the AS may
also release Access Tokens for accessing resources hosted by
members of OSCORE groups.
All communications between the involved entities rely on the CoAP
protocol and MUST be secured.
In particular, communications between the joining node and the Group
Manager leverage protocol-specific transport profiles of ACE to
achieve communication security, proof-of-possession and server
authentication. To this end, the AS MAY signal the specific
transport profile to use, consistently with requirements and
assumptions defined in the ACE framework [I-D.ietf-ace-oauth-authz].
Note that in the commonly referred base-case the transport profile to
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use is pre-configured and well-known to nodes participating in
constrained applications.
With reference to the AS, communications between the joining node and
the AS (/token endpoint) as well as between the Group Manager and the
AS (/introspect endpoint) can be secured by different means, for
instance using DTLS [RFC6347] or OSCORE [RFC8613]. Further details
on how the AS secures communications (with the joining node and the
Group Manager) depend on the specifically used transport profile of
ACE, and are out of the scope of this specification.
2.1. Overview of the Joining Process
A node performs the following steps in order to join an OSCORE group.
The format and processing of messages exchanged among the
participants follow what is defined in [I-D.ietf-ace-key-groupcomm],
and are further specified in Section 3 and Section 4 of this
document. The Group Manager acts as the Key Distribution Center
(KDC) defined in [I-D.ietf-ace-key-groupcomm].
1. The joining node requests an Access Token from the AS, in order
to access a group-membership resource on the Group Manager and
hence join the associated OSCORE group (see Section 3). The
joining node will start or continue using a secure communication
association with the Group Manager, according to the response
from the AS.
2. The joining node transfers authentication and authorization
information to the Group Manager, by posting the obtained Access
Token to the /authz-info endpoint at the Group Manager (see
Section 4). After that, a joining node MUST have a secure
communication association established with the Group Manager,
before starting to join an OSCORE group under that Group Manager
(see Section 4). Possible ways to provide a secure communication
association are DTLS [RFC6347] and OSCORE [RFC8613].
3. The joining node starts the joining process to become a member of
the OSCORE group, by accessing the related group-membership
resource hosted by the Group Manager (see Section 4).
4. At the end of the joining process, the joining node has received
from the Group Manager the parameters and keying material to
securely communicate with the other members of the OSCORE group.
5. The joining node and the Group Manager maintain the secure
association, to support possible future communications. These
especially include key management operations, such as retrieval
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of updated keying material from the Group Manager or
participation to a group rekeying process (see Section 2.2).
All further communications between the joining node and the Group
Manager MUST be secured, for instance with the same secure
association mentioned in step 2.
2.2. Overview of the Group Rekeying Process
If the application requires backward and forward security, the Group
Manager MUST generate new security parameters and group keying
material, and distribute them to the group (rekeying) upon membership
changes.
That is, the group is rekeyed when a node joins the group as a new
member, or after a current member leaves the group. By doing so, a
joining node cannot access communications in the group prior its
joining, while a leaving node cannot access communications in the
group after its leaving.
Parameters and group keying material include a new Group Identifier
(Gid) for the group and a new Master Secret for the OSCORE Common
Security Context of that group (see Section 2 of
[I-D.ietf-core-oscore-groupcomm]). Once completed a group rekeying,
the GM MUST increment the version number of the group keying
material.
The Group Manager MUST support the Group Rekeying Process described
in Section 13. Future application profiles may define alternative
message formats and distribution schemes to perform group rekeying.
3. Joining Node to Authorization Server
This section describes how the joining node interacts with the AS in
order to be authorized to join an OSCORE group under a given Group
Manager. In particular, it considers a joining node that intends to
contact that Group Manager for the first time.
The message exchange between the joining node and the AS consists of
the messages Authorization Request and Authorization Response defined
in Section 3 of [I-D.ietf-ace-key-groupcomm].
In case the specific AS associated to the Group Manager is unknown to
the joining node, the latter can rely on mechanisms like the
Unauthorized Resource Request message described in Section 5.1.1 of
[I-D.ietf-ace-oauth-authz] to discover the correct AS to contact.
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3.1. Authorization Request
The joining node contacts the AS, in order to request an Access Token
for accessing the group-membership resource hosted by the Group
Manager and associated to the OSCORE group. The Access Token request
sent to the /token endpoint follows the format of the Authorization
Request message defined in Section 3.1 of
[I-D.ietf-ace-key-groupcomm]. In particular:
o The 'scope' parameter MUST be present and MUST include:
* in the first element, the name of the OSCORE group to join
under the Group Manager, encoded as a CBOR text string.
* in the second element, the role (encoded as a text string) or
CBOR array of roles that the joining node intends to have in
the group it intends to join. Accepted values of roles are:
"requester", "responder", and "monitor". Possible combinations
are: ["requester" , "responder"]; ["requester" , "monitor"].
o The 'audience' parameter MUST be present and is set to the
identifier of the Group Manager.
3.2. Authorization Response
The AS is responsible for authorizing the joining node to join
specific OSCORE groups, according to join policies enforced on behalf
of the respective Group Manager.
In case of successful authorization, the AS releases an Access Token
bound to a proof-of-possession key associated to the joining node.
Then, the AS provides the joining node with the Access Token as part
of an Access Token response, which follows the format of the
Authorization Response message defined in Section 3.2 of
[I-D.ietf-ace-key-groupcomm].
The AS MUST include the 'exp' parameter in the response to the
joining node. Other means for the AS to specify the lifetime of
Access Tokens are out of the scope of this specification.
The AS must include the 'scope' parameter in the response to the
joining node, when the value included in the Access Token differs
from the one specified by the joining node in the request. In such a
case, the second element of 'scope' MUST be present and includes the
role or CBOR array of roles that the joining node is actually
authorized to take in the group, encoded as specified in Section 3.1
of this document.
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The AS MAY also include the 'profile' parameter in the response to
the joining node, in order to indicate the specific transport profile
of ACE to use for securing communications between the joining node
and the Group Manager (see Section 5.6.4.3 of
[I-D.ietf-ace-oauth-authz]).
In particular, if symmetric keys are used, the AS generates a proof-
of-possession key, binds it to the Access Token, and provides it to
the joining node in the 'cnf' parameter of the Access Token response.
Instead, if asymmetric keys are used, the joining node provides its
own public key to the AS in the 'req_cnf' parameter of the Access
Token request. Then, the AS uses it as proof-of-possession key bound
to the Access Token, and provides the joining node with the Group
Manager's public key in the 'rs_cnf' parameter of the Access Token
response.
4. Joining Node to Group Manager
The following subsections describe the interactions between the
joining node and the Group Manager, i.e. the sending of the Access
Token and the Request-Response exchange to join the OSCORE group.
4.1. Token Post
The joining node posts the Access Token to the /authz-info endpoint
at the Group Manager, according to the Token post defined in
Section 3.3 of [I-D.ietf-ace-key-groupcomm].
At this point in time, the joining node might not have all the
necessary information concerning the public keys in the OSCORE group,
as well as concerning the algorithm and related parameters for
computing countersignatures in the OSCORE group. In such a case, the
joining node MAY use the 'sign_info' and 'pub_key_enc' parameters
defined in Section 3.3 of [I-D.ietf-ace-key-groupcomm] to ask for
such information.
Alternatively, the joining node may retrieve this information by
other means, e.g. by using the approach described in
[I-D.tiloca-core-oscore-discovery].
If the Access Token is valid, the Group Manager responds to the POST
request with a 2.01 (Created) response, according to what is
specified in the signalled transport profile of ACE. The Group
Manager MUST use the Content-Format "application/ace+cbor" defined in
Section 8.14 of [I-D.ietf-ace-oauth-authz].
The payload of the 2.01 (Created) response is a CBOR map, which MUST
include the 'rsnonce' parameter defined in Section 3.3.3 of
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[I-D.ietf-ace-key-groupcomm], and MAY include the 'sign_info'
parameter as well as the 'pub_key_enc' parameter, defined in its
Sections 3.3.1 and 3.3.2, respectively. Note that this deviates from
the default payload format for this response message as defined in
the ACE framework (see Section 5.8.1 of [I-D.ietf-ace-oauth-authz]).
The 'rsnonce' parameter includes a dedicated nonce N_S generated by
the Group Manager. The joining node may use this nonce in order to
prove the possession of its own private key, upon joining the group
(see Section 4.2).
If present in the response:
o 'sign_alg', i.e. the first element of the 'sign_info' parameter,
takes value from Tables 5 and 6 of [RFC8152].
o 'sign_parameters', i.e. the second element of the 'sign_info'
parameter, takes values from the "Counter Signature Parameters"
Registry (see Section 9.1 of [I-D.ietf-core-oscore-groupcomm]).
Its structure depends on the value of 'sign_alg'. If no
parameters of the counter signature algorithm are specified,
'sign_parameters' MUST be encoding the CBOR simple value Null.
o 'sign_key_parameters', i.e. the third element of the 'sign_info'
parameter, takes values from the "Counter Signature Key
Parameters" Registry (see Section 9.2 of
[I-D.ietf-core-oscore-groupcomm]). Its structure depends on the
value of 'sign_alg'. If no parameters of the key used with the
counter signature algorithm are specified, 'sign_key_parameters'
MUST be encoding the CBOR simple value Null.
o 'pub_key_enc' takes value 1 ("COSE_Key") from the 'Confirmation
Key' column of the "CWT Confirmation Method" Registry defined in
[I-D.ietf-ace-cwt-proof-of-possession], so indicating that public
keys in the OSCORE group are encoded as COSE Keys [RFC8152].
Future specifications may define additional values for this
parameter.
The CBOR map specified as payload of the 2.01 (Created) response may
include further parameters, e.g. according to the signalled transport
profile of ACE.
Finally, the joining node establishes a secure channel with the Group
Manager, according to what is specified in the Access Token response
and the signalled transport profile of ACE.
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4.2. Joining Request
Once a secure communication channel with the Group Manager has been
established, the joining node requests to join the OSCORE group, by
sending a Joining Request message to the related group-membership
resource at the Group Manager, as per Section 4.2 of
[I-D.ietf-ace-key-groupcomm].
In particular, the joining node sends a CoAP POST request to the
endpoint /group-oscore/NAME at the Group Manager, where NAME is the
name of the OSCORE group to join. This Joining Request is formatted
as defined in Section 4.1.2.1 of [I-D.ietf-ace-key-groupcomm].
Specifically:
o The 'scope' parameter MUST be present.
o The 'get_pub_keys' parameter is present only if the joining node
wants to retrieve the public keys of the group members from the
Group Manager during the joining process (see Section 5).
Otherwise, this parameter MUST NOT be present.
o The 'client_cred' parameter, if present, includes the public key
of the joining node. In case the joining node knows the encoding
of public keys in the OSCORE group, as well as the
countersignature algorithm and possible associated parameters used
in the OSCORE group, the included public key MUST be compatible
with those criteria. That is, the public key MUST be encoded
according to the encoding of public keys in the OSCORE group, and
MUST be compatible with the countersignature algorithm and
possible associated parameters used in the OSCORE group. This
parameter MAY be omitted if: i) the joining node is asking to
access the group exclusively as monitor; or ii) the Group Manager
already acquired this information, for instance during a past
joining process. In any other case, this parameter MUST be
present.
Furthermore, if the 'client_cred' parameter is present, the CBOR map
specified as payload of the Joining Request MUST also include the
following parameters.
o 'cnonce', as defined in Section 5.1.2 of
[I-D.ietf-ace-oauth-authz], and including a dedicated nonce N_C
generated by the Client.
o The 'client_cred_verify' parameter, including a signature encoded
as a CBOR byte string, computed by the joining node to prove
possession of its own private key. The signature is computed over
N_S concatenated with N_C, where N_S is the nonce received in the
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'rsnonce' parameter of the 2.01 (Created) response to the Token
POST (see Section 4.1), while N_C is the nonce generated by the
Client and specified in the 'cnonce' parameter above. The joining
node computes the signature by using the same private key and
countersignature algorithm it intends to use for signing messages
in the OSCORE group.
4.3. Joining Response
The Group Manager processes the Joining Request as defined in
Section 4.1.2.1 of [I-D.ietf-ace-key-groupcomm]. Also, the Group
Manager MUST return a 4.00 (Bad Request) response in case the Joining
Request includes the 'client_cred' parameter but does not include
both the 'cnonce' and 'client_cred_verify' parameters.
If the request processing yields a positive outcome, the Group
Manager performs the further following checks.
o In case the Joining Request includes the 'client_cred' parameter,
the Group Manager checks that the public key of the joining node
has an accepted format. That is, the public key has to be encoded
as expected in the OSCORE group, and has to be compatible with the
counter signature algorithm and possible associated parameters
used in the OSCORE group. The joining process fails if the public
key of the joining node does not have an accepted format.
o In case the Joining Request does not include the 'client_cred'
parameter, the Group Manager checks whether it is storing a public
key for the joining node, which is compatible with the encoding,
counter signature algorithm and possible associated parameters
used in the OSCORE group. The joining process fails if the Group
Manager either: i) does not store a public key with an accepted
format for the joining node; or ii) stores multiple public keys
with an accepted format for the joining node.
o In case the Joining Request includes the 'client_cred_verify'
parameter, the Group Manager verifies the signature contained in
the parameter. To this end, it considers: i) as signed value, N_S
concatenated with N_C, where N_S is the nonce previously provided
in the 'rsnonce' parameter of the 2.01 (Created) response to the
Token POST (see Section 4.1), while N_C is the nonce provided in
the 'cnonce' parameter of the Joining Request; ii) the
countersignature algorithm used in the OSCORE group, and possible
correponding parameters; and iii) the public key of the joining
node, either retrieved from the 'client_cred' parameter, or
already stored as acquired from previous interactions with the
joining node. The joining process fails if the Group Manager does
not successfully verify the signature.
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If the joining process has failed, the Group Manager MUST reply to
the joining node with a 4.00 (Bad Request) response. The payload of
this response is a CBOR map, which includes a 'sign_info' parameter
and a 'pub_key_enc' parameter, formatted as in the Token POST
response in Section 4.1.
Upon receiving this response, the joining node SHOULD send a new
Joining Request to the Group Manager, which contains:
o The 'client_cred' parameter, including a public key compatible
with the encoding, countersignature algorithm and possible
associated parameters indicated by the Group Manager.
o The 'client_cred_verify' parameter, including a signature computed
as described in Section 4.2, by using the public key indicated in
the current 'client_cred' parameter, with the countersignature
algorithm and possible associated parameters indicated by the
Group Manager.
Otherwise, in case of success, the Group Manager updates the group
membership by registering the joining node as a new member of the
OSCORE group. If the joining node is not exclusively configured as
monitor, the Group Manager performs also the following actions.
o The Group Manager selects an available OSCORE Sender ID in the
OSCORE group, and exclusively assigns it to the joining node.
o If the 'client_cred' parameter was present in the request, the
Group Manager adds the specified public key of the joining node to
the list of public keys of the current group members.
o If the 'client_cred' parameter was not present in the request, the
Group Manager retrieves the already stored public key of the
joining node, as acquired from previous interactions (see also
Section 5). Then, the Group Manager adds the retrieved public key
to the list of public keys of the current group members.
o The Group Manager stores the association between i) the public key
of the joining node; and ii) the Group Identifier (Gid) associated
to the OSCORE group together with the OSCORE Sender ID assigned to
the joining node in the group. The Group Manager MUST keep this
association updated over time.
Then, the Group Manager replies to the joining node providing the
updated security parameters and keying meterial necessary to
participate in the group communication. This success Joining
Response is formatted as defined in Section 4.1.2.1 of
[I-D.ietf-ace-key-groupcomm]. In particular:
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o The 'kty' parameter identifies a key of type
"Group_OSCORE_Security_Context object", defined in Section 15.1 of
this specification.
o The 'key' parameter includes what the joining node needs in order
to set up the OSCORE Security Context as per Section 2 of
[I-D.ietf-core-oscore-groupcomm]. This parameter has as value a
Group_OSCORE_Security_Context object, which is defined in this
specification and extends the OSCORE_Security_Context object
encoded in CBOR as defined in Section 3.2.1 of
[I-D.ietf-ace-oscore-profile]. In particular, it contains the
additional parameters 'cs_alg', 'cs_params', 'cs_key_params' and
'cs_key_enc' defined in Section 15.2 of this specification. More
specifically, the 'key' parameter is composed as follows.
* The 'ms' parameter MUST be present and includes the OSCORE
Master Secret value.
* The 'clientId' parameter, if present, has as value the OSCORE
Sender ID assigned to the joining node by the Group Manager, as
described above. This parameter is not present if the node
joins the group exclusively as monitor, according to what
specified in the Access Token (see Section 3.2). In any other
case, this parameter MUST be present.
* The 'hkdf' parameter, if present, has as value the KDF
algorithm used in the group.
* The 'alg' parameter, if present, has as value the AEAD
algorithm used in the group.
* The 'salt' parameter, if present, has as value the OSCORE
Master Salt.
* The 'contextId' parameter MUST be present and has as value the
Group Identifier (Gid) associated to the OSCORE group.
* The 'rpl' parameter, if present, specifies the OSCORE Replay
Window Size and Type value.
* The 'cs_alg' parameter MUST be present and specifies the
algorithm used to countersign messages in the group. This
parameter takes values from Tables 5 and 6 of [RFC8152].
* The 'cs_params' parameter MAY be present and specifies the
additional parameters for the counter signature algorithm.
This parameter is a CBOR map whose content depends on the
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counter signature algorithm, as specified in Section 2 and
Section 9.1 of [I-D.ietf-core-oscore-groupcomm].
* The 'cs_key_params' parameter MAY be present and specifies the
additional parameters for the key used with the counter
signature algorithm. This parameter is a CBOR map whose
content depends on the counter signature algorithm, as
specified in Section 2 and Section 9.2 of
[I-D.ietf-core-oscore-groupcomm].
* The 'cs_key_enc' parameter MAY be present and specifies the
encoding of the public keys of the group members. This
parameter is a CBOR integer, whose value is 1 ("COSE_Key")
taken from the 'Confirmation Key' column of the "CWT
Confirmation Method" Registry defined in
[I-D.ietf-ace-cwt-proof-of-possession], so indicating that
public keys in the OSCORE group are encoded as COSE Keys
[RFC8152]. Future specifications may define additional values
for this parameter. If this parameter is not present, 1
("COSE_Key") MUST be assumed as default value.
o The 'num' parameter MUST be present and specifies the current
version number of the group keying material.
o The 'profile' parameter MUST be present and has value
coap_group_oscore_app (TBD), which is defined in Section 15.3 of
this specification.
o The 'exp' parameter MUST be present and specifies the expiration
time in seconds after which the OSCORE Security Context derived
from the 'key' parameter is not valid anymore.
o The 'pub_keys' parameter is present only if the 'get_pub_keys'
parameter was present in the Joining Request. If present, this
parameter includes the public keys of the group members that are
relevant to the joining node. That is, it includes: i) the public
keys of the responders currently in the group, in case the joining
node is configured (also) as requester; and ii) the public keys of
the requesters currently in the group, in case the joining node is
configured (also) as responder or monitor. If public keys are
encoded as COSE_Keys, each of them has as 'kid' the Sender ID that
the corresponding owner has in the group, thus used as group
member identifier.
o The 'group_policies' parameter SHOULD be present and includes a
list of parameters indicating particular policies enforced in the
group. In particular, if the field "Sequence Number
Synchronization Method" is present, it indicates the method to
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achieve synchronization of sequence numbers among group members
(see Appendix E of [I-D.ietf-core-oscore-groupcomm]), by
specifying the corresponding value from the "Sequence Number
Synchronization Method" Registry defined in Section 8.6 of
[I-D.ietf-ace-key-groupcomm].
Finally, the joining node uses the information received in the
Joining Response to set up the OSCORE Security Context, as described
in Section 2 of [I-D.ietf-core-oscore-groupcomm]. From then on, the
joining node can exchange group messages secured with Group OSCORE as
described in [I-D.ietf-core-oscore-groupcomm].
If the application requires backward security, the Group Manager MUST
generate updated security parameters and group keying material, and
provide it to all the current group members (see Section 13).
5. Public Keys of Joining Nodes
Source authentication of OSCORE messages exchanged within the group
is ensured by means of digital counter signatures (see Sections 2 and
3 of [I-D.ietf-core-oscore-groupcomm]). Therefore, group members
must be able to retrieve each other's public key from a trusted key
repository, in order to verify source authenticity of incoming group
messages.
As also discussed in [I-D.ietf-core-oscore-groupcomm], the Group
Manager acts as trusted repository of the public keys of the group
members, and provides those public keys to group members if requested
to. Upon joining an OSCORE group, a joining node is thus expected to
provide its own public key to the Group Manager.
In particular, one of the following four cases can occur when a new
node joins an OSCORE group.
o The joining node is going to join the group exclusively as
monitor. That is, it is not going to send messages to the group,
and hence to produce signatures with its own private key. In this
case, the joining node is not required to provide its own public
key to the Group Manager, which thus does not have to perform any
check related to the public key encoding, or to a countersignature
algorithm and possible associated parameters for that joining
node.
o The Group Manager already acquired the public key of the joining
node during a past joining process. In this case, the joining
node MAY choose not to provide again its own public key to the
Group Manager, in order to limit the size of the Joining Request.
The joining node MUST provide its own public key again if it has
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provided the Group Manager with multiple public keys during past
joining processes, intended for different OSCORE groups. If the
joining node provides its own public key, the Group Manager
performs consistency checks as per Section 4.3 and, in case of
success, considers it as the public key associated to the joining
node in the OSCORE group.
o The joining node and the Group Manager use an asymmetric proof-of-
possession key to establish a secure communication channel. Then,
two cases can occur.
1. The proof-of-possession key is compatible with the encoding as
well as with the counter signature algorithm and possible
associated parameters used in the OSCORE group. Then, the
Group Manager considers the proof-of-possession key as the
public key associated to the joining node in the OSCORE group.
If the joining node is aware that the proof-of-possession key
is also valid for the OSCORE group, it MAY not provide it
again as its own public key to the Group Manager. The joining
node MUST provide its own public key again if it has provided
the Group Manager with multiple public keys during past
joining processes, intended for different OSCORE groups. If
the joining node provides its own public key in the
'client_cred' parameter of the Joining Request (see
Section 4.2), the Group Manager performs consistency checks as
per Section 4.3 and, in case of success, considers it as the
public key associated to the joining node in the OSCORE group.
2. The proof-of-possession key is not compatible with the
encoding or with the counter signature algorithm and possible
associated parameters used in the OSCORE group. In this case,
the joining node MUST provide a different compatible public
key to the Group Manager in the 'client_cred' parameter of the
Joining Request (see Section 4.2). Then, the Group Manager
performs consistency checks on this latest provided public key
as per Section 4.3 and, in case of success, considers it as
the public key associated to the joining node in the OSCORE
group.
o The joining node and the Group Manager use a symmetric proof-of-
possession key to establish a secure communication channel. In
this case, upon performing a joining process with that Group
Manager for the first time, the joining node specifies its own
public key in the 'client_cred' parameter of the Joining Request
targeting the group-membership endpoint (see Section 4.2).
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6. Retrieval of Updated Keying Material
At some point, a group member considers the OSCORE Security Context
invalid and to be renewed. This happens, for instance, after a
number of unsuccessful security processing of incoming messages from
other group members, or when the Security Context expires as
specified by the 'exp' parameter of the Joining Response.
When this happens, the group member retrieves updated security
parameters and group keying material, by sending a Key Distribution
Request message to the Group Manager, as per Section 4.3 of
[I-D.ietf-ace-key-groupcomm]. In particular, it sends a CoAP GET
request to the endpoint /group-oscore/NAME at the Group Manager,
where NAME is the name of the OSCORE group. The Key Distribution
Request is formatted as defined in Section 4.1.2.2 of
[I-D.ietf-ace-key-groupcomm].
The Group Manager processes the Key Distribution Request according to
Section 4.1.2.2 of [I-D.ietf-ace-key-groupcomm]. The Key
Distribution Response is formatted as defined in Section 4.1.2.2 of
[I-D.ietf-ace-key-groupcomm].
Upon receiving the Key Distribution Response, the group member
retrieves the updated security parameters and group keying material,
and use them to set up the new OSCORE Security Context as described
in Section 2 of [I-D.ietf-core-oscore-groupcomm].
7. Retrieval of New Keying Material
As discussed in Section 2.2 of [I-D.ietf-core-oscore-groupcomm], a
group member may at some point experience a wrap-around of its own
Sender Sequence Number in the group.
When this happens, the group member MUST send a Key Renewal Request
message to the Group Manager, as per Section 4.4 of
[I-D.ietf-ace-key-groupcomm]. In particular, it sends a CoAP GET
request to the endpoint /group-oscore/NAME/node at the Group Manager,
where NAME is the name of the OSCORE group.
Upon receiving the Key Renewal Request, the Group Manager processes
it as defined in Section 4.1.6.2 of [I-D.ietf-ace-key-groupcomm], and
performs one of the following actions.
1. The Group Manager replies to the group member with a 4.06 (Not
Acceptable) error response, and rekeys the whole OSCORE group as
discussed in Section 13.
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2. The Group Manager generates a new Sender ID for that group member
and replies with a Key Renewal Response, formatted as defined in
Section 4.1.6.2 of [I-D.ietf-ace-key-groupcomm]. In particular,
the CBOR Map in the response payload includes a single parameter
'clientId' defined in Section 15.5 of this document, specifying
the new Sender ID of the group member encoded as a CBOR byte
string.
8. Retrieval of Public Keys of Group Members
A group member may need to retrieve the public keys of other group
members. To this end, the group member sends a Public Key Request
message to the Group Manager, as per Section 4.5 of
[I-D.ietf-ace-key-groupcomm]. In particular, it sends the request to
the endpoint /group-oscore/NAME/pub-key at the Group Manager, where
NAME is the name of the OSCORE group.
If the Public Key Request uses the method POST, the Public Key
Request is formatted as defined in Section 4.1.3.1 of
[I-D.ietf-ace-key-groupcomm]. In particular, each element of the
'get_pub_keys' parameter is a CBOR byte string, which encodes the
Sender ID of the group member for which the associated public key is
requested.
Upon receiving the Public Key Request, the Group Manager processes it
as per Section 4.1.3.1 or 4.1.3.2 of [I-D.ietf-ace-key-groupcomm],
depending on the request method being POST or GET, respectively. If
the Public Key Request uses the method POST, the Group Manager
silently ignores identifiers included in the 'get_pub_keys' parameter
of the request that are not associated to any current group member.
The success Public Key Response is formatted as defined in
Section 4.1.3.1 of [I-D.ietf-ace-key-groupcomm].
9. Retrieval of Group Policies
A group member may request the current policies used in the OSCORE
group. To this end, the group member sends a Policies Request, as
per Section 4.6 of [I-D.ietf-ace-key-groupcomm]. In particular, it
sends a CoAP GET request to the endpoint /group-oscore/NAME/policies
at the Group Manager, where NAME is the name of the OSCORE group.
Upon receiving the Policies Request, the Group Manager processes it
as per Section 4.1.4.1 of [I-D.ietf-ace-key-groupcomm]. The success
Policies Response is formatted as defined in Section 4.1.4.1 of
[I-D.ietf-ace-key-groupcomm].
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10. Retrieval of Keying Material Version
A group member may request the current version of the keying material
used in the OSCORE group. To this end, the group member sends a
Version Request, as per Section 4.7 of [I-D.ietf-ace-key-groupcomm].
In particular, it sends a CoAP GET request to the endpoint /group-
oscore/NAME/ctx-num at the Group Manager, where NAME is the name of
the OSCORE group.
Upon receiving the Version Request, the Group Manager processes it as
per Section 4.1.5.1 of [I-D.ietf-ace-key-groupcomm]. The success
Version Response is formatted as defined in Section 4.1.5.1 of
[I-D.ietf-ace-key-groupcomm].
11. Request to Leave the Group
A group member may request to leave the OSCORE group. To this end,
the group member sends a Group Leaving Request, as per Section 4.8 of
[I-D.ietf-ace-key-groupcomm]. In particular, it sends a CoAP POST
request to the endpoint /group-oscore/NAME/node at the Group Manager,
where NAME is the name of the OSCORE group to leave.
The Leaving Request is formatted as defined in Section 4.1.6.1 of
[I-D.ietf-ace-key-groupcomm], and MUST have an empty CBOR Map as
payload.
Upon receiving the Leaving Request, the Group Manager processes it as
per Section 4.1.6.1 of [I-D.ietf-ace-key-groupcomm].
12. Removal of a Group Member
Other than after a spontaneous request to the Group Manager as
described in Section 11, a node may be forcibly removed from the
OSCORE group, e.g. due to expired or revoked authorization.
In either case, if the leaving node is not configured exclusively as
monitor, the Group Manager performs the following actions.
o The Group Manager frees the OSCORE Sender ID value of the leaving
node, which becomes available for possible upcoming joining nodes.
o The Group Manager cancels the association between, on one hand,
the public key of the leaving node and, on the other hand, the
Group Identifier (Gid) associated to the OSCORE group together
with the freed OSCORE Sender ID value. The Group Manager deletes
the public key of the leaving node, if that public key has no
remaining association with any pair (Group ID, Sender ID).
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If the application requires forward security, the Group Manager MUST
generate updated security parameters and group keying material, and
provide it to the remaining group members (see Section 13). As a
consequence, the leaving node is not able to acquire the new security
parameters and group keying material distributed after its leaving.
Same considerations in Section 5 of [I-D.ietf-ace-key-groupcomm]
apply here as well, considering the Group Manager acting as KDC.
13. Group Rekeying Process
In order to rekey the OSCORE group, the Group Manager distributes a
new Group ID of the group and a new OSCORE Master Secret for that
group. When doing so, the Group Manager MUST increment the version
number of the group keying material. Also, the Group Manager MUST
preserve the same unchanged Sender IDs for all group members. This
avoids affecting the retrieval of public keys from the Group Manager
as well as the verification of message countersignatures.
The Group Manager MUST support at least the following group rekeying
scheme. Future application profiles may define alternative message
formats and distribution schemes.
The Group Manager uses the same format of the Joining Response
message in Section 4.3. In particular:
o Only the parameters 'kty', 'key', 'num', 'profile' and 'exp' are
present.
o The 'ms' parameter of the 'key' parameter specifies the new OSCORE
Master Secret value.
o The 'contextId' parameter of the 'key' parameter specifies the new
Group ID.
The Group Manager separately sends a group rekeying message to each
group member to be rekeyed. Each rekeying message MUST be secured
with the pairwise secure communication channel between the Group
Manager and the group member used during the joining process.
This approach requires group members to act (also) as servers, in
order to correctly handle unsolicited group rekeying messages from
the Group Manager. In particular, if a group member and the Group
Manager use OSCORE [RFC8613] to secure their pairwise communications,
the group member MUST create a Replay Window in its own Recipient
Context upon establishing the OSCORE Security Context with the Group
Manager, e.g. by means of the OSCORE profile of ACE
[I-D.ietf-ace-oscore-profile].
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Group members and the Group Manager SHOULD additionally support
alternative rekeying approaches that do not require group members to
act (also) as servers. A number of such approaches are defined in
Section 4 of [I-D.ietf-ace-key-groupcomm]. In particular, a group
member may subscribe for updates to the group-membership resource of
the group, at the endpoint /group-oscore/NAME of the Group Manager,
where NAME is the name of the OSCORE group. This can rely on CoAP
Observe [RFC7641] or on a full-fledged Pub-Sub model
[I-D.ietf-core-coap-pubsub] with the Group Manager acting as Broker.
14. Security Considerations
The method described in this document leverages the following
management aspects related to OSCORE groups and discussed in the
sections of [I-D.ietf-core-oscore-groupcomm] referred below.
o Management of group keying material (see Section 2.1 of
[I-D.ietf-core-oscore-groupcomm]). The Group Manager is
responsible for the renewal and re-distribution of the keying
material in the groups of its competence (rekeying). According to
the specific application requirements, this can include rekeying
the group upon changes in its membership. In particular, renewing
the group keying material is required upon a new node's joining or
a current node's leaving, in case backward security and forward
security have to be preserved, respectively.
o Provisioning and retrieval of public keys (see Section 2 of
[I-D.ietf-core-oscore-groupcomm]). The Group Manager acts as key
repository of public keys of group members, and provides them upon
request.
o Synchronization of sequence numbers (see Section 5 of
[I-D.ietf-core-oscore-groupcomm]). This concerns how a responder
node that has just joined an OSCORE group can synchronize with the
sequence number of requesters in the same group.
Before sending the Joining Response, the Group Manager MUST verify
that the joining node actually owns the associated private key. To
this end, the Group Manager can rely on the proof-of-possession
challenge-response defined in Section 4. Alternatively, the joining
node can use its own public key as asymmetric proof-of-possession key
to establish a secure channel with the Group Manager, e.g. as in
Section 3.2 of [I-D.ietf-ace-dtls-authorize]. However, this requires
such proof-of-possession key to be compatible with the encoding as
well as with the countersignature algorithm and possible associated
parameters used in the OSCORE group.
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A node may have joined multiple OSCORE groups under different non-
synchronized Group Managers. Therefore, it can happen that those
OSCORE groups have the same Group Identifier (Gid). It follows that,
upon receiving a Group OSCORE message addressed to one of those
groups, the node would have multiple Security Contexts matching with
the Gid in the incoming message. It is up to the application to
decide how to handle such collisions of Group Identifiers, e.g. by
trying to process the incoming message using one Security Context at
the time until the right one is found.
Further security considerations are inherited from
[I-D.ietf-ace-key-groupcomm], the ACE framework for Authentication
and Authorization [I-D.ietf-ace-oauth-authz], and the specific
transport profile of ACE signalled by the AS, such as
[I-D.ietf-ace-dtls-authorize] and [I-D.ietf-ace-oscore-profile].
15. IANA Considerations
Note to RFC Editor: Please replace all occurrences of "[[This
specification]]" with the RFC number of this specification and delete
this paragraph.
This document has the following actions for IANA.
15.1. ACE Groupcomm Key Registry
IANA is asked to register the following entry in the "ACE Groupcomm
Key" Registry defined in Section 8.3 of [I-D.ietf-ace-key-groupcomm].
o Name: Group_OSCORE_Security_Context object
o Key Type Value: TBD
o Profile: "coap_group_oscore_app", defined in Section 15.3 of this
specification.
o Description: A Group_OSCORE_Security_Context object encoded as
described in Section 4.3 of this specification.
o Reference: [[This specification]]
15.2. OSCORE Security Context Parameters Registry
IANA is asked to register the following entries in the "OSCORE
Security Context Parameters" Registry defined in Section 9.2 of
[I-D.ietf-ace-oscore-profile].
o Name: cs_alg
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o CBOR Label: TBD
o CBOR Type: tstr / int
o Registry: COSE Algorithm Values (ECDSA, EdDSA)
o Description: OSCORE Counter Signature Algorithm Value
o Reference: [[This specification]]
o Name: cs_params
o CBOR Label: TBD
o CBOR Type: map
o Registry: Counter Signatures Parameters
o Description: OSCORE Counter Signature Algorithm Additional
Parameters
o Reference: [[This specification]]
o Name: cs_key_params
o CBOR Label: TBD
o CBOR Type: map
o Registry: Counter Signatures Key Parameters
o Description: OSCORE Counter Signature Key Additional Parameters
o Reference: [[This specification]]
o Name: cs_key_enc
o CBOR Label: TBD
o CBOR Type: integer
o Registry: ACE Public Key Encoding
o Description: Encoding of Public Keys to be used with the OSCORE
Counter Signature Algorithm
o Reference: [[This specification]]
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15.3. ACE Groupcomm Profile Registry
IANA is asked to register the following entry in the "ACE Groupcomm
Profile" Registry defined in Section 8.4 of
[I-D.ietf-ace-key-groupcomm].
o Name: coap_group_oscore_app
o Description: Application profile to provision keying material for
participating in group communication protected with Group OSCORE
as per [I-D.ietf-core-oscore-groupcomm].
o CBOR Value: TBD
o Reference: [[This specification]]
15.4. Sequence Number Synchronization Method Registry
IANA is asked to register the following entries in the "Sequence
Number Synchronization Method" Registry defined in Section 8.6 of
[I-D.ietf-ace-key-groupcomm].
o Name: Best effort
o Value: 1
o Description: No action is taken.
o Reference: [I-D.ietf-core-oscore-groupcomm] (Appendix E.1).
o Name: Baseline
o Value: 2
o Description: The first received request sets the baseline
reference point, and is discarded with no delivery to the
application.
o Reference: [I-D.ietf-core-oscore-groupcomm] (Appendix E.2).
o Name: Echo challenge-response
o Value: 3
o Description: Challenge response using the Echo Option for CoAP
from [I-D.ietf-core-echo-request-tag].
o Reference: [I-D.ietf-core-oscore-groupcomm] (Appendix E.3).
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15.5. ACE Groupcomm Parameters Registry
IANA is asked to register the following entry in the "ACE Groupcomm
Parameters" Registry defined in Section 8.2 of
[I-D.ietf-ace-key-groupcomm].
o Name: clientId
o CBOR Key: TBD
o CBOR Type: Byte string
o Reference: [[This document]] (Section 7).
16. References
16.1. Normative References
[I-D.ietf-ace-cwt-proof-of-possession]
Jones, M., Seitz, L., Selander, G., Erdtman, S., and H.
Tschofenig, "Proof-of-Possession Key Semantics for CBOR
Web Tokens (CWTs)", draft-ietf-ace-cwt-proof-of-
possession-11 (work in progress), October 2019.
[I-D.ietf-ace-key-groupcomm]
Palombini, F. and M. Tiloca, "Key Provisioning for Group
Communication using ACE", draft-ietf-ace-key-groupcomm-03
(work in progress), November 2019.
[I-D.ietf-ace-oauth-authz]
Seitz, L., Selander, G., Wahlstroem, E., Erdtman, S., and
H. Tschofenig, "Authentication and Authorization for
Constrained Environments (ACE) using the OAuth 2.0
Framework (ACE-OAuth)", draft-ietf-ace-oauth-authz-25
(work in progress), October 2019.
[I-D.ietf-ace-oscore-profile]
Palombini, F., Seitz, L., Selander, G., and M. Gunnarsson,
"OSCORE profile of the Authentication and Authorization
for Constrained Environments Framework", draft-ietf-ace-
oscore-profile-08 (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.
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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>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>.
[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>.
[RFC8613] Selander, G., Mattsson, J., Palombini, F., and L. Seitz,
"Object Security for Constrained RESTful Environments
(OSCORE)", RFC 8613, DOI 10.17487/RFC8613, July 2019,
<https://www.rfc-editor.org/info/rfc8613>.
16.2. Informative References
[I-D.dijk-core-groupcomm-bis]
Dijk, E., Wang, C., and M. Tiloca, "Group Communication
for the Constrained Application Protocol (CoAP)", draft-
dijk-core-groupcomm-bis-01 (work in progress), July 2019.
[I-D.ietf-ace-dtls-authorize]
Gerdes, S., Bergmann, O., Bormann, C., Selander, G., and
L. Seitz, "Datagram Transport Layer Security (DTLS)
Profile for Authentication and Authorization for
Constrained Environments (ACE)", draft-ietf-ace-dtls-
authorize-08 (work in progress), April 2019.
[I-D.ietf-core-coap-pubsub]
Koster, M., Keranen, A., and J. Jimenez, "Publish-
Subscribe Broker for the Constrained Application Protocol
(CoAP)", draft-ietf-core-coap-pubsub-09 (work in
progress), September 2019.
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[I-D.ietf-core-echo-request-tag]
Amsuess, C., Mattsson, J., and G. Selander, "CoAP: Echo,
Request-Tag, and Token Processing", draft-ietf-core-echo-
request-tag-08 (work in progress), November 2019.
[I-D.tiloca-core-oscore-discovery]
Tiloca, M., Amsuess, C., and P. Stok, "Discovery of OSCORE
Groups with the CoRE Resource Directory", draft-tiloca-
core-oscore-discovery-03 (work in progress), July 2019.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <https://www.rfc-editor.org/info/rfc6347>.
[RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
RFC 6749, DOI 10.17487/RFC6749, October 2012,
<https://www.rfc-editor.org/info/rfc6749>.
[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>.
Appendix A. Profile Requirements
This appendix lists the specifications on this application profile of
ACE, based on the requiremens defined in Appendix A of
[I-D.ietf-ace-key-groupcomm].
o REQ1 - Specify the encoding and value of the identifier of group
of 'scope': see Section 3.1.
o REQ2 - Specify the encoding and value of the identifier of roles
of 'scope': see Section 3.1.
o REQ3 (Optional) - Specify the acceptable values for 'sign_alg':
values from Tables 5 and 6 of [RFC8152].
o REQ4 (Optional) - Specify the acceptable values for
'sign_parameters': values from the "Counter Signature Parameters"
Registry (see Section 9.1 of [I-D.ietf-core-oscore-groupcomm]).
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o REQ5 (Optional) - Specify the acceptable values for
'sign_key_parameters': values from the "Counter Signature Key
Parameters" Registry (see Section 9.2 of
[I-D.ietf-core-oscore-groupcomm]).
o REQ6 (Optional) - Specify the acceptable values for 'pub_key_enc':
1 ("COSE_Key") from the 'Confirmation Key' column of the "CWT
Confirmation Method" Registry defined in
[I-D.ietf-ace-cwt-proof-of-possession]. Future specifications may
define additional values for this parameter.
o REQ7 - Format of the 'key' value: see Section 4.3.
o REQ8 - Acceptable values of 'kty': Group_OSCORE_Security_Context
object (see Section 4.3).
o REQ9: Specify the format of the identifiers of group members: see
Section 4.3 and Section 8.
o REQ10 (Optional) - Specify the format and content of
'group_policies' entries: three values are defined and registered,
as content of the entry "Sequence Number Synchronization Method"
(see Section 15.4).
o REQ11 - Communication protocol that the members of the group must
use: CoAP, possibly over IP multicast.
o REQ12 - Security protocols that the group members must use to
protect their communication: Group OSCORE.
o REQ13 - Profile identifier: coap_group_oscore_app
o REQ14 (Optional) - Specify the encoding of public keys, of
'client_cred', and of 'pub_keys' if COSE_Keys are not used: no.
o REQ15 - Specify policies at the KDC to handle member ids that are
not included in 'get_pub_keys': see Section 8.
o REQ16 - Specify the format and content of 'group_policies': see
Section 4.3.
o REQ17 - Specify the format of newly-generated individual keying
material for group members, or of the information to derive it,
and corresponding CBOR label: see Section 7.
o REQ18 - Specify how the communication is secured between the
Client and KDC: by means of any transport profile of ACE
[I-D.ietf-ace-oauth-authz] between Client and Group Manager that
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complies with the requirements in Appendix C of
[I-D.ietf-ace-oauth-authz].
o OPT1 (Optional) - Specify the encoding of public keys, of
'client_cred', and of 'pub_keys' if COSE_Keys are not used: no.
o OPT2 (Optional) - Specify the negotiation of parameter values for
signature algorithm and signature keys, if 'sign_info' and
'pub_key_enc' are not used: possible early discovery by using the
approach based on the CoRE Resource Directory described in
[I-D.tiloca-core-oscore-discovery].
o OPT3 (Optional) - Specify the format and content of
'mgt_key_material': no.
o OPT4 (Optional) - Specify policies that instruct clients to retain
unsuccessfully decrypted messages and for how long, so that they
can be decrypted after getting updated keying material: no.
Appendix B. Document Updates
RFC EDITOR: PLEASE REMOVE THIS SECTION.
B.1. Version -02 to -03
o New sections, aligned with the interface of ace-key-groupcomm .
o Exchange of information on the countersignature algorithm and
related parameters, during the Token POST (Section 4.1).
o Nonce 'rsnonce' from the Group Manager to the Client
(Section 4.1).
o Client PoP signature in the Key Distribution Request upon joining
(Section 4.2).
o Local actions on the Group Manager, upon a new node's joining
(Section 4.2).
o Local actions on the Group Manager, upon a node's leaving
(Section 12).
o IANA registration in ACE Groupcomm Parameters Registry.
o More fulfilled profile requirements (Appendix A).
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B.2. Version -01 to -02
o Editorial fixes.
o Changed: "listener" to "responder"; "pure listener" to "monitor".
o Changed profile name to "coap_group_oscore_app", to reflect it is
an application profile.
o Added the 'type' parameter for all requests to a Join Resource.
o Added parameters to indicate the encoding of public keys.
o Challenge-response for proof-of-possession of signature keys
(Section 4).
o Renamed 'key_info' parameter to 'sign_info'; updated its format;
extended to include also parameters of the countersignature key
(Section 4.1).
o Code 4.00 (Bad request), in responses to joining nodes providing
an invalid public key (Section 4.3).
o Clarifications on provisioning and checking of public keys
(Sections 4 and 6).
o Extended discussion on group rekeying and possible different
approaches (Section 7).
o Extended security considerations: proof-of-possession of signature
keys; collision of OSCORE Group Identifiers (Section 8).
o Registered three entries in the IANA Registry "Sequence Number
Synchronization Method Registry" (Section 9).
o Registered one public key encoding in the "ACE Public Key
Encoding" IANA Registry (Section 9).
B.3. Version -00 to -01
o Changed name of 'req_aud' to 'audience' in the Authorization
Request (Section 3.1).
o Added negotiation of countersignature algorithm/parameters between
Client and Group Manager (Section 4).
o Updated format of the Key Distribution Response as a whole
(Section 4.3).
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o Added parameter 'cs_params' in the 'key' parameter of the Key
Distribution Response (Section 4.3).
o New IANA registrations in the "ACE Authorization Server Request
Creation Hints" Registry, "ACE Groupcomm Key" Registry, "OSCORE
Security Context Parameters" Registry and "ACE Groupcomm Profile"
Registry (Section 9).
Acknowledgments
The authors sincerely thank Santiago Aragon, Stefan Beck, Carsten
Bormann, Martin Gunnarsson, Rikard Hoeglund, Daniel Migault, Jim
Schaad, Ludwig Seitz, Goeran Selander and Peter van der Stok 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-164 29 Stockholm
Sweden
Email: marco.tiloca@ri.se
Jiye Park
Universitaet Duisburg-Essen
Schuetzenbahn 70
Essen 45127
Germany
Email: ji-ye.park@uni-due.de
Francesca Palombini
Ericsson AB
Torshamnsgatan 23
Kista SE-16440 Stockholm
Sweden
Email: francesca.palombini@ericsson.com
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