The Group Object Security for Constrained RESTful Environments (Group OSCORE) Profile of the Authentication and Authorization for Constrained Environments (ACE) Framework
draft-ietf-ace-group-oscore-profile-03
| Document | Type | Active Internet-Draft (ace WG) | |
|---|---|---|---|
| Authors | Marco Tiloca , Rikard Höglund , Francesca Palombini | ||
| Last updated | 2024-10-21 | ||
| Replaces | draft-tiloca-ace-group-oscore-profile | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | (None) | ||
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draft-ietf-ace-group-oscore-profile-03
ACE Working Group M. Tiloca
Internet-Draft R. Höglund
Intended status: Standards Track RISE AB
Expires: 24 April 2025 F. Palombini
Ericsson AB
21 October 2024
The Group Object Security for Constrained RESTful Environments (Group
OSCORE) Profile of the Authentication and Authorization for Constrained
Environments (ACE) Framework
draft-ietf-ace-group-oscore-profile-03
Abstract
This document specifies a profile for the Authentication and
Authorization for Constrained Environments (ACE) framework. The
profile uses Group Object Security for Constrained RESTful
Environments (Group OSCORE) to provide communication security between
a client and one or multiple resource servers that are members of an
OSCORE group. The profile securely binds an OAuth 2.0 access token
to the public key of the client associated with the private key used
by that client in the OSCORE group. The profile uses Group OSCORE to
achieve server authentication, as well as proof-of-possession for the
client's public key. Also, it provides proof of the client's
membership to the OSCORE group by binding the access token to
information from the Group OSCORE Security Context, thus allowing the
resource server(s) to verify the client's membership upon receiving a
message protected with Group OSCORE from the client. Effectively,
the profile enables fine-grained access control paired with secure
group communication, in accordance with the Zero Trust principles.
Discussion Venues
This note is to be removed before publishing as an RFC.
Discussion of this document takes place on the Authentication and
Authorization for Constrained Environments Working Group mailing list
(ace@ietf.org), which is archived at
https://mailarchive.ietf.org/arch/browse/ace/.
Source for this draft and an issue tracker can be found at
https://github.com/ace-wg/ace-group-oscore-profile.
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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Copyright Notice
Copyright (c) 2024 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
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 7
2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 8
2.1. Pre-Conditions . . . . . . . . . . . . . . . . . . . . . 10
2.2. Requesting an Access Token . . . . . . . . . . . . . . . 10
2.3. Access Token Uploading . . . . . . . . . . . . . . . . . 11
2.4. Secure Communication . . . . . . . . . . . . . . . . . . 12
3. Client-AS Communication . . . . . . . . . . . . . . . . . . . 13
3.1. Preliminary Operations . . . . . . . . . . . . . . . . . 13
3.2. C-to-AS: POST to Token Endpoint . . . . . . . . . . . . . 14
3.2.1. 'context_id' Parameter . . . . . . . . . . . . . . . 20
3.2.2. 'salt_input' Parameter . . . . . . . . . . . . . . . 20
3.2.3. 'client_cred_verify' Parameter . . . . . . . . . . . 20
3.2.4. 'client_cred_verify_mac' Parameter . . . . . . . . . 20
3.3. AS-to-C: Response . . . . . . . . . . . . . . . . . . . . 21
3.3.1. Update of Access Rights . . . . . . . . . . . . . . . 26
3.3.2. 'context_id' Claim . . . . . . . . . . . . . . . . . 27
3.3.3. 'salt_input' Claim . . . . . . . . . . . . . . . . . 27
4. Client-RS Communication . . . . . . . . . . . . . . . . . . . 27
4.1. C-to-RS POST to /authz-info Endpoint . . . . . . . . . . 29
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4.2. RS-to-C: 2.01 (Created) . . . . . . . . . . . . . . . . . 29
4.3. Client-RS Secure Communication . . . . . . . . . . . . . 32
4.3.1. Client Side . . . . . . . . . . . . . . . . . . . . . 32
4.3.2. Resource Server Side . . . . . . . . . . . . . . . . 32
4.4. Update of Access Rights . . . . . . . . . . . . . . . . . 33
4.5. Access Rights Verification . . . . . . . . . . . . . . . 33
4.6. Storing Multiple Access Tokens per PoP Key . . . . . . . 34
5. Change of Client's Authentication Credential in the Group . . 37
6. Secure Communication with the AS . . . . . . . . . . . . . . 38
7. Discarding the Security Context . . . . . . . . . . . . . . . 38
8. Guidelines on Using Multiple Profiles . . . . . . . . . . . . 38
9. CBOR Mappings . . . . . . . . . . . . . . . . . . . . . . . . 40
10. Security Considerations . . . . . . . . . . . . . . . . . . . 41
11. Privacy Considerations . . . . . . . . . . . . . . . . . . . 42
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 42
12.1. ACE Profiles Registry . . . . . . . . . . . . . . . . . 42
12.2. OAuth Parameters Registry . . . . . . . . . . . . . . . 43
12.3. OAuth Parameters CBOR Mappings Registry . . . . . . . . 44
12.4. CBOR Web Token (CWT) Claims Registry . . . . . . . . . . 45
12.5. TLS Exporter Label Registry . . . . . . . . . . . . . . 46
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 46
13.1. Normative References . . . . . . . . . . . . . . . . . . 46
13.2. Informative References . . . . . . . . . . . . . . . . . 49
Appendix A. Profile Requirements . . . . . . . . . . . . . . . . 50
Appendix B. CDDL Model . . . . . . . . . . . . . . . . . . . . . 51
Appendix C. Document Updates . . . . . . . . . . . . . . . . . . 52
C.1. Version -02 to -03 . . . . . . . . . . . . . . . . . . . 52
C.2. Version -01 to -02 . . . . . . . . . . . . . . . . . . . 53
C.3. Version -00 to -01 . . . . . . . . . . . . . . . . . . . 53
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 53
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 54
1. Introduction
A number of applications rely on a group communication model where a
client can access a resource hosted by multiple resource servers at
once, e.g., over IP multicast. Typical examples include switching of
luminaries, actuators control, and distribution of software updates.
Secure communication in the group can be achieved by sharing a set of
keying material, which is typically provided upon joining the group.
For some of such applications, it may be just fine to enforce access
control in a straightforward fashion. That is, any client authorized
to join the group, hence to obtain the group keying material, can be
also implicitly authorized to perform any action at any resource of
any server in the group. An example of application where such
implicit authorization might serve well is a simple lighting
scenario, where the lightbulbs are the servers, while the user
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account on an app on the user's phone is the client. In this case,
it might be fine to not require additional authorization evidence
from any user account, if it is acceptable that any current group
member is also authorized to switch on and off any light, or to check
the status of any light.
However, in different instances of such applications, the approach
above is not desirable, as different group members are intended to
have different access rights to resources of other group members.
For instance, enforcing access control in accordance with a more
fine-grained approach is required in the two following use cases.
As a first case, an application provides control of smart locks
acting as servers in the group, where: a first type of client, e.g.,
a user account of a child, is allowed to only query the status of the
smart locks; while a second type of client, e.g., a user account of a
parent, is allowed to both query and change the status of the smart
locks. Further similar applications concern the enforcement of
different sets of permissions in groups with sensor/actuator devices,
e.g., thermostats acting as servers. Also, some group members may
even be intended as servers only. Hence, they must be prevented from
acting as clients altogether and from accessing resources at other
servers in the group, especially when attempting to perform non-safe
operations.
As a second case, building automation scenarios often rely on servers
that, under different circumstances, enforce different level of
priority for processing received commands. For instance, BACnet
deployments consider multiple classes of clients, e.g., a normal
light switch (C1) and an emergency fire panel (C2). Then, a C1
client is not allowed to override a command from a C2 client, until
the latter relinquishes control at its higher priority. That is: i)
only C2 clients should be able to adjust the minimum required level
of priority on the servers, so rightly locking out C1 clients if
needed; and ii) when a server is set to accept only high-priority
commands, only C2 clients should be able to perform such commands
otherwise allowed also to C1 clients. Given the different maximum
authority of different clients, fine-grained access control would
effectively limit the execution of high- and emergency-priority
commands only to devices that are in fact authorized to perform such
actions. Besides, it would prevent a misconfigured or compromised
device from initiating a high-priority command and lock out normal
control.
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In the cases above, being a legitimate group member and storing the
group keying material is not supposed to imply any particular access
rights. Instead, access control to the secure group communication
channel and access control to the resource space provided by servers
in the group should remain logically separated domains.
This is aligned with the Zero Trust paradigm [NIST-800-207], which
focuses on resource protection and builds on the premise that trust
is never granted implicitly, but must be continually evaluated. In
particular, Zero Trust protections involve "minimizing access to
resources (such as data and compute resources and applications/
services) to only those subjects and assets identified as needing
access as well as continually authenticating and authorizing the
identity and security posture of each access request."
Furthermore, [NIST-800-207] highlights how the Zero Trust goal is to
"prevent unauthorized access to data and services coupled with making
the access control enforcement as granular as possible", to "enforce
least privileges needed to perform the action in the request."
As a step in this direction, one can be tempted to introduce a
different security group for each different set of access rights.
However, this inconveniently results in additional keying material to
distribute and manage. In particular, if the access rights
pertaining to a node change, this requires to evict the node from the
group, after which the node has to join a different group aligned
with its new access rights. Moreover, the keying material of both
groups would have to be renewed for their current members. Overall,
this would have a non negligible impact on operations and
performance.
Instead, a fine-grained yet flexible access control model can be
enforced within the same group, by using the Authentication and
Authorization for Constrained Environments (ACE) framework [RFC9200].
That is, a client has to first obtain authorization credentials in
the form of an access token, and upload it to the intended resource
server(s) in the group before accessing the target resources hosted
therein.
The ACE framework delegates to separate profile documents how to
secure communications between the client and the resource servers.
However each of the current profiles of ACE defined in
[RFC9202][RFC9203][RFC9431][I-D.ietf-ace-edhoc-oscore-profile] relies
on a security protocol that cannot be used to protect one-to-many
group messages, for example sent over IP multicast.
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This document specifies the "coap_group_oscore" profile of the ACE
framework, where a client uses the Constrained Application Protocol
(CoAP) [RFC7252][I-D.ietf-core-groupcomm-bis] to communicate with one
or multiple resource servers that are members of an application group
and share a common set of resources. This profile uses Group Object
Security for Constrained RESTful Environments (Group OSCORE)
[I-D.ietf-core-oscore-groupcomm] as the security protocol to protect
messages exchanged between the client and the resource servers.
Hence, it requires that both the client and the resource servers have
previously joined the same OSCORE group.
That is, this profile describes how access control is enforced for a
client after it has joined an OSCORE group, to access resources
hosted by other members in that group. The process for joining the
OSCORE group through the respective Group Manager as defined in
[I-D.ietf-ace-key-groupcomm-oscore] takes place before the process
described in this document, and is out of the scope of this profile.
The client proves its access to be authorized to the resource
server(s) by using an access token bound to a key (the proof-of-
possession key). This profile uses Group OSCORE to achieve server
authentication and proof-of-possession for the client's public key
used in the OSCORE group in question. Note that proof-of-possession
is not achieved through a dedicated protocol element, but instead
after the first message exchange protected with Group OSCORE.
Furthermore, this profile provides proof of the client's membership
to the OSCORE group, by binding the access token to information from
the pre-established Group OSCORE Security Context, as well as to the
client's authentication credential used in the group and including
the client's public key. This allows the resource server(s) to
verify the client's group membership upon reception of a message
protected with Group OSCORE from that client.
OSCORE [RFC8613] specifies how to use COSE [RFC9052][RFC9053] to
secure CoAP messages. Group OSCORE builds on OSCORE to provide
secure group communication, and ensures source authentication: by
means of digital signatures embedded in the protected message (when
using the group mode); or by protecting a message with pairwise
keying material derived from the asymmetric keys of the two peers
exchanging the message (when using the pairwise mode).
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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
related to CBOR [RFC8949], COSE [RFC9052][RFC9053], CoAP [RFC7252],
OSCORE [RFC8613], and Group OSCORE [I-D.ietf-core-oscore-groupcomm].
These especially include:
* Group Manager, as the entity responsible for a set of groups where
communications among members are secured with Group OSCORE.
* Authentication credential, as the set of information associated
with an entity, including that entity's public key and parameters
associated with the public key. Examples of authentication
credentials are CBOR Web Tokens (CWTs) and CWT Claims Sets (CCSs)
[RFC8392], X.509 certificates [RFC5280], and C509 certificates
[I-D.ietf-cose-cbor-encoded-cert].
Members of an OSCORE group have an associated authentication
credential in the format used within the group. As per
Section 2.4 of [I-D.ietf-core-oscore-groupcomm], an authentication
credential provides the public key as well as the comprehensive
set of information related to the public key algorithm, including,
e.g., the used elliptic curve (when applicable).
Readers are also expected to be familiar with the terms and concepts
described in the ACE framework for authentication and authorization
[RFC9200], as well as in the OSCORE profile of ACE [RFC9203]. 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).
Note that the term "endpoint" is used here following its OAuth
definition [RFC6749], 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".
Additionally, this document makes use of the following terminology.
* Pairwise-only group: an OSCORE group that uses only the pairwise
mode of Group OSCORE (see Section 8 of
[I-D.ietf-core-oscore-groupcomm]).
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Examples throughout this document are expressed in CBOR diagnostic
notation as defined in Section 8 of [RFC8949] and Appendix G of
[RFC8610]. Diagnostic notation comments are often used to provide a
textual representation of the parameters' keys and values.
In the CBOR diagnostic notation used in this document, constructs of
the form e'SOME_NAME' are replaced by the value assigned to SOME_NAME
in the CDDL model shown in Figure 7 of Appendix B. For example,
{e'context_id_param': h'abcd0000', e'salt_input_param': h'00} stands
for {71: h'abcd0000', 72: h'00}.
Note to RFC Editor: Please delete the paragraph immediately preceding
this note. Also, in the CBOR diagnostic notation used in this
document, please replace the constructs of the form e'SOME_NAME' with
the value assigned to SOME_NAME in the CDDL model shown in Figure 7
of Appendix B. Finally, please delete this note.
2. Protocol Overview
This section provides an overview of this profile, i.e., of how to
use the ACE framework for authentication and authorization [RFC9200]
to secure communications between a client and one or more resource
servers using Group OSCORE [I-D.ietf-core-oscore-groupcomm].
Note that this profile of ACE describes how access control can be
enforced for a node after it has joined an OSCORE group, to access
resources hosted by other members in that group.
In particular, the process of joining the OSCORE group through the
respective Group Manager as defined in
[I-D.ietf-ace-key-groupcomm-oscore] must take place before the
process described in this document, and is out of the scope of this
profile.
An overview of the protocol flow for this profile is shown in
Figure 1, where it is assumed that both the resource servers RS1 and
RS2 are associated with the same authorization server AS. It is also
assumed that the client C, as well as RS1 and RS2 have previously
joined an OSCORE group with Group Identifier (gid) 0xabcd0000, and
that they got assigned Sender ID (sid) 0x00, 0x01, and 0x02 in the
group, respectively. The names of messages coincide with those of
[RFC9200] when applicable, and messages in square brackets are
optional.
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C RS1 RS2 AS
| | | |
| [--- Resource Request ---->] | | |
| | | |
| [<------ AS Request -------] | | |
| Creation Hints | | |
| | | |
+-------- POST /token ----------------------------------------------->|
| (aud: "RS1", sid: 0x00, | | |
| gid: 0xabcd0000, ...) | | |
| | | |
|<---------------------------------------------- Access token T1 -----+
| | + Access Information |
| | | |
+----- POST /authz-info ------>| | |
| (access_token: T1) | | |
| | | |
|<------- 2.01 Created --------+ | |
| | | |
+-------- POST /token ----------------------------------------------->|
| (aud: "RS2", sid: 0x00, | | |
| gid: 0xabcd0000, ...) | | |
| | | |
|<---------------------------------------------- Access token T2 -----+
| | + Access Information |
| | | |
+----- POST /authz-info ------------------>| |
| (access_token: T2) | | |
| | | |
|<------ 2.01 Created ---------------------+ |
| | | |
+-- Group OSCORE Request --+-->| | |
| (kid: 0x00, \ | | |
| gid: 0xabcd0000) \ | | |
| `----------->| |
| | | |
| /proof-of-possession/ |
| | | |
|<--- Group OSCORE Response ---+ | |
| (kid: 0x01) | | |
| | | |
/proof-of-possession/ | | |
| | | |
| | | |
/Mutual authentication | | |
between C and RS1/ | | |
| | | |
|<--- Group OSCORE Response ---------------+ |
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| (kid: 0x02) | | |
| | | |
/proof-of-possession/ | | |
| | | |
| | | |
/Mutual authentication | | |
between C and RS2/ | | |
| | | |
| ... | | |
| | | |
Figure 1: Protocol Overview.
2.1. Pre-Conditions
Using Group OSCORE and this profile requires that both the client and
the resource servers have previously joined the same OSCORE group.
This especially includes the derivation of the Group OSCORE Security
Context and the assignment of unique Sender IDs to use in the group.
Nodes can join the OSCORE group through the respective Group Manager
by using the approach defined in [I-D.ietf-ace-key-groupcomm-oscore],
which is also based on ACE.
After the client and resource servers have joined the group, this
profile provides access control for accessing resources on those
resource servers, by securely communicating with Group OSCORE.
As a pre-requisite for this profile, the client has to have
successfully joined the OSCORE group where also the resource servers
(RSs) are members. Depending on the limited information initially
available, the client may have to first discover the exact OSCORE
group used by the RSs for the resources of interest, e.g., by using
the approach defined in [I-D.tiloca-core-oscore-discovery].
2.2. Requesting an Access Token
This profile requires that the client requests an access token from
the AS for the resource(s) that it wants to access at the RS(s), by
using the /token endpoint as specified in Section 5.8 of [RFC9200].
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In general, different RSs can be associated with different ASs, even
if the RSs are members of the same OSCORE group. However, assuming
proper configurations and trust relations, it is possible for
multiple RSs associated with the same AS to be part of a single
audience (i.e., a group-audience, see Section 6.9 of [RFC9200]). In
such a case, the client can request a single access token intended
for the group-audience, hence to all the RSs included therein. A
particular group-audience might be defined as including all the RSs
in the OSCORE group.
In the Access Token Request to the AS, the client MUST include the
Group Identifier of the OSCORE group and its own Sender ID in that
group. The AS MUST specify these pieces of information in the access
token.
Furthermore, in the Access Token Request to the AS, the client MUST
also include: its own authentication credential used in the OSCORE
group; and a proof-of-possession (PoP) evidence to prove possession
of the corresponding private key to the AS. The PoP evidence is
computed over a PoP input uniquely related to the secure
communication association between the client and the AS. The AS MUST
include also the authentication credential specified by the client in
the access token.
If the request from the client is granted, then the AS can send back
the issued access token in the Access Token Response to the client,
or instead upload the access token directly to the RS as described in
the alternative workflow defined in
[I-D.ietf-ace-workflow-and-params]. This document focuses on the
former option (also shown in the example in Figure 1), while the
latter option is not detailed further here.
The Access Token Request and Response exchanged between the client
and the AS MUST be confidentiality-protected and ensure authenticity.
In this profile, it is RECOMMENDED to use OSCORE [RFC8613] between
the client and the AS, to reduce the number of libraries that the
client has to support. Other protocols fulfilling the security
requirements defined in Sections 5 and 6 of [RFC9200] MAY
alternatively be used, such as TLS [RFC8446] or DTLS [RFC9147].
2.3. Access Token Uploading
After having retrieved the access token from the AS, the client
uploads the access token to the RS, by sending a POST request to the
/authz-info endpoint and using the mechanisms specified in
Section 5.10 of [RFC9200]. When using this profile, the
communication that C has with the /authz-info endpoint is not
protected.
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If the access token is valid, the RS replies to the POST request with
a 2.01 (Created) response. Also, the RS associates the received
access token with the Group OSCORE Security Context identified by the
Group Identifier specified in the access token (see Section 2.1.3 of
[I-D.ietf-core-oscore-groupcomm]). In practice, the RS maintains a
collection of Security Contexts with associated authorization
information, for all the clients that it is currently communicating
with. The authorization information is a policy that is used as
input when processing requests from those clients.
Finally, the RS stores the association between i) the authorization
information from the access token; and ii) the Group Identifier of
the OSCORE group together with the Sender ID and the authentication
credential of the client in that group (see Section 2 of
[I-D.ietf-core-oscore-groupcomm]). This binds the access token to
the Group OSCORE Security Context of the OSCORE group.
Finally, when the client communicates with the RS using the Group
OSCORE Security Context, the RS verifies that the client is a
legitimate member of the OSCORE group and especially the exact group
member with the same Sender ID associated with the access token.
This occurs when verifying a request protected with Group OSCORE,
since the request includes the client's Sender ID and either it
embeds a signature computed also over that Sender ID (if protected
with the group mode), or it is protected by means of pairwise
symmetric keying material derived from the asymmetric keys of the two
peers (if protected with the pairwise mode).
The above has considered an access token intended for a single RS.
However, as discussed in Section 2.2, an access token can be intended
for a group-audience including multiple RSs in the OSCORE group. In
such a case, the client could efficiently upload the access token to
many or all of those RSs at once (e.g., over IP multicast), after
which each RS individually performs the same steps described above.
2.4. Secure Communication
The client can send a request protected with Group OSCORE
[I-D.ietf-core-oscore-groupcomm] to the RS. This can be a unicast
request targeting the RS, or a one-to-many group request (e.g., over
IP multicast) targeting the OSCORE group where the RS is also a
member. To this end, the client uses the Group OSCORE Security
Context already established upon joining the OSCORE group, e.g., by
using the approach defined in [I-D.ietf-ace-key-groupcomm-oscore].
The RS may send a response back to the client, protecting it by means
of the same Group OSCORE Security Context.
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3. Client-AS Communication
This section details the Access Token POST Request that the client
sends to the /token endpoint of the AS, as well as the related Access
Token Response.
The access token MUST be bound to the public key of the client as
proof-of-possession key (PoP) key, which is included in the client's
authentication credential specified in the 'cnf' claim of the access
token.
3.1. Preliminary Operations
The following considers a client that is a member of an OSCORE group
G with GID* as current Group Identifier (GID), within which the
client currently has SID* as Sender ID and uses a public
authentication credential AUTH_CRED_C that specifies the PoP key K.
The client MUST perform the following steps, before requesting an
access token to be bound to AUTH_CRED_C (hence to the PoP key K) and
to be associated with the client's membership in group G through the
values GID* and SID*.
1. The client checks whether it is a member of any two OSCORE groups
G1 and G2 such that all the following conditions hold.
* Both groups have GID* as current GID.
* The client uses SID* as Sender ID in both groups.
* The client uses the same AUTH_CRED_C in both groups.
2. If such two groups G1 and G2 are found at Step 2, then the client
moves to Step 3. Otherwise, the client terminates this algorithm
and proceeds with requesting the access token as defined in
Section 3.2.
3. The client can choose to terminate this algorithm and perform it
again later on.
Alternatively, the client can alter its current group
memberships, in order to ensure that two groups like G1 and G2
cannot be determined. To this end, the client has two available
options.
* The client leaves some of the OSCORE groups that could be
determined as groups like G1 and G2 (see Section 9.11 of
[I-D.ietf-ace-key-groupcomm-oscore]).
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* The client obtains a new Sender ID in some of the OSCORE
groups that could be determined as groups like G1 and G2. To
this end, the client can request a new Sender ID in a group to
the Group Manager responsible for that group (see Section 9.2
of [I-D.ietf-ace-key-groupcomm-oscore]), or re-join a group
thereby obtaining a new Sender ID in that group (see Section 6
of [I-D.ietf-ace-key-groupcomm-oscore]).
Finally, the client moves to Step 1.
3.2. C-to-AS: POST to Token Endpoint
The Client-to-AS request is specified in Section 5.8.1 of [RFC9200].
The client MUST send this POST request to the /token endpoint over a
secure channel that guarantees authentication, message integrity, and
confidentiality.
The POST request is formatted as the analogous Client-to-AS request
in the OSCORE profile of ACE (see Section 3.1 of [RFC9203]), with the
following additional parameters that MUST be included in the payload.
* 'context_id', defined in Section 3.2.1 of this document. This
parameter specifies the GID, i.e., the ID Context of an OSCORE
group that includes as members both the client and the RS(s) in
the audience for which the access token is asked to be issued. In
particular, the client wishes to communicate with the RS(s) in
that audience using the Group OSCORE Security Context associated
with that OSCORE group.
* 'salt_input', defined in Section 3.2.2 of this document. This
parameter includes the Sender ID that the client has in the OSCORE
group whose GID is specified in the 'context_id' parameter above.
* 'req_cnf', defined in Section 3.1 of [RFC9201]. This parameter
follows the syntax from Section 3.1 of [RFC8747], and its inner
confirmation value specifies the authentication credential that
the client uses in the OSCORE group. The public key included in
the authentication credential will be used as the PoP key bound to
the access token.
At the time of writing this specification, acceptable formats of
authentication credentials in Group OSCORE are CBOR Web Tokens
(CWTs) and CWT Claims Sets (CCSs) [RFC8392], X.509 certificates
[RFC5280], and C509 certificates
[I-D.ietf-cose-cbor-encoded-cert].
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Further formats may be available in the future, and would be
acceptable to use as long as they comply with the criteria
compiled in Section 2.4 of [I-D.ietf-core-oscore-groupcomm]. In
particular, an authentication credential has to explicitly include
the public key as well as the comprehensive set of information
related to the public key algorithm, including, e.g., the used
elliptic curve (when applicable).
[ As to CWTs and CCSs, the CWT Confirmation Methods 'kcwt' and
'kccs' are under pending registration requested by draft-ietf-ace-
edhoc-oscore-profile. ]
[ As to X.509 certificates, the CWT Confirmation Methods 'x5bag'
and '5chain' are under pending registration requested by draft-
ietf-ace-edhoc-oscore-profile. ]
[ As to C509 certificates, the CWT Confirmation Methods 'c5b'and
'c5c' are under pending registration requested by draft-ietf-ace-
edhoc-oscore-profile. ]
In addition, the client computes its proof-of-possession (PoP)
evidence, in order to prove to the AS the possession of its own
private key used in the OSCORE group. This allows the AS to verify
that the client indeed owns the private key associated with the
public key of the authentication credential that the client allegedly
uses in the OSCORE group.
To this end, the client MUST use as PoP input the byte representation
of an information that uniquely represents the secure communication
association between the client and the AS. It is RECOMMENDED that
the client uses the following as PoP input.
* If the client and the AS communicate over TLS 1.2 [RFC5246] or
DTLS 1.2 [RFC6347], the PoP input is an exporter value computed as
defined in Section 4 of [RFC5705], using the following inputs:
- The exporter label "EXPORTER-ACE-PoP-Input-Client-AS", defined
in Section 12.5 of this document.
- The empty 'context value', i.e., a 'context value' of zero-
length.
- 32 as length value in bytes.
* If the client and the AS communicate over TLS 1.3 [RFC8446] or
DTLS 1.3 [RFC9147], the PoP input is an exporter value computed as
defined in Section 7.5 of [RFC8446], using the following inputs:
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- The exporter label "EXPORTER-ACE-PoP-Input-Client-AS", defined
in Section 12.5 of this document.
- The empty 'context_value', i.e., a 'context_value' of zero-
length.
- 32 as 'key_length' in bytes.
* If the client and the AS communicate over OSCORE [RFC8613], the
PoP input is the output PRK of an HKDF-Extract step [RFC5869],
i.e., PRK = HMAC-Hash(salt, IKM).
In particular, given the OSCORE Security Context CTX shared
between the client and the AS, then the following applies.
- 'salt' takes (x1 | x2), where | denotes byte string
concatenation, while x1 and x2 are defined as follows.
o x1 is the binary representation of a CBOR data item. If CTX
does not specify an OSCORE ID Context, the CBOR data item is
the CBOR simple value null (0xf6). Otherwise, the CBOR data
item is a CBOR byte string, with value the OSCORE ID Context
specified in CTX.
o x2 is the binary representation of a CBOR byte string. The
value of the CBOR byte string is the OSCORE Sender ID of the
client, which the client stores in its Sender Context of CTX
and the AS stores in its Recipient Context of CTX.
- 'IKM' is the OSCORE Master Secret specified in CTX.
- The used HKDF is the HKDF Algorithm specified in CTX.
The following shows an example of input to the HMAC-Hash()
function.
On the client side, the OSCORE Security Context shared with the AS
includes:
ID Context: 0x37cbf3210017a2d3 (8 bytes)
Sender ID: 0x01 (1 byte)
Master Secret: 0x0102030405060708090a0b0c0d0e0f10 (16 bytes)
Then, the following holds.
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x1 (Raw value) (8 bytes)
0x37cbf3210017a2d3
x1 (CBOR Data Item) (9 bytes)
0x4837cbf3210017a2d3
x2 (Raw value) (1 bytes)
0x01
x2 (CBOR Data Item) (2 bytes)
0x4101
salt (11 bytes)
0x4837cbf3210017a2d34101
IKM (16 bytes)
0x0102030405060708090a0b0c0d0e0f10
After that, the client computes the PoP evidence as follows.
* If the OSCORE group is not a pairwise-only group, the PoP evidence
MUST be a signature. The client computes the signature by using
the same private key and signature algorithm it uses for signing
messages in the OSCORE group. The client's private key is the one
associated with the client's authentication credential used in the
OSCORE group and specified in the 'req_cnf' parameter above.
* If the OSCORE group is a pairwise-only group, the PoP evidence
MUST be a MAC computed as follows, by using the HKDF Algorithm
HKDF SHA-256, which consists of composing the HKDF-Extract and
HKDF-Expand steps [RFC5869].
MAC = HKDF(salt, IKM, info, L)
The input parameters of HKDF are as follows.
- salt takes as value the empty byte string.
- IKM is computed as a cofactor Diffie-Hellman shared secret (see
Section 5.7.1.2 of [NIST-800-56A]), using the ECDH algorithm
that is used as Pairwise Key Agreement Algorithm in the OSCORE
group. The client uses its own Diffie-Hellman private key and
the Diffie-Hellman public key of the AS. For X25519 and X448,
the procedure is described in Section 5 of [RFC7748].
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The client's private key is the one associated with the
client's authentication credential used in the OSCORE group and
specified in the 'req_cnf' parameter above. The client may
obtain the Diffie-Hellman public key of the AS during its
registration process at the AS.
- info takes as value the PoP input.
- L is equal to 8, i.e., the size of the MAC, in bytes.
Finally, the client MUST include one of the two following parameters
in the payload of the POST request to the AS.
* 'client_cred_verify', defined in Section 3.2.3 of this document,
specifying the client's PoP evidence as a signature, which is
computed as defined above. This parameter MUST be included if and
only if the OSCORE group is not a pairwise-only group.
* 'client_cred_verify_mac', defined in Section 3.2.4 of this
document, specifying the client's PoP evidence as a MAC, which is
computed as defined above. This parameter MUST be included if and
only if the OSCORE group is a pairwise-only group.
An example of such a request is shown in Figure 2.
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Header: POST (Code=0.02)
Uri-Host: "as.example.com"
Uri-Path: "token"
Content-Format: 19 (application/ace+cbor)
Payload:
{
/ audience / 5 : "tempSensor4711",
/ scope / 9 : "read",
e'context_id_param' : h'abcd0000',
e'salt_input_param' : h'00',
e'client_cred_verify' : h'c5a6...f100' / elided for brevity /,
/ req_cnf / 4 : {
e'kccs' : {
/ sub / 2 : "42-50-31-FF-EF-37-32-39",
/ cnf / 8 : {
/ COSE_Key / 1 : {
/ kty / 1 : 2 / EC2 /,
/ crv / -1 : 1 / P-256 /,
/ x / -2 : h'd7cc072de2205bdc1537a543d53c60a6
acb62eccd890c7fa27c9e354089bbe13',
/ y / -3 : h'f95e1d4b851a2cc80fff87d8e23f22af
b725d535e515d020731e79a3b4e47120'
}
}
}
}
}
Figure 2: Example C-to-AS POST /token Request for an Access Token
Bound to an Asymmetric Key.
In the example above, the client specifies that its authentication
credential in the OSCORE group is the CCS shown in Figure 3.
{
/ sub / 2 : "42-50-31-FF-EF-37-32-39",
/ cnf / 8 : {
/ COSE_Key / 1 : {
/ kty / 1 : 2 / EC2 /,
/ crv / -1 : 1 / P-256 /,
/ x / -2 : h'd7cc072de2205bdc1537a543d53c60a6
acb62eccd890c7fa27c9e354089bbe13',
/ y / -3 : h'f95e1d4b851a2cc80fff87d8e23f22af
b725d535e515d020731e79a3b4e47120'
}
}
}
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Figure 3: Example of client Authentication Credential as CWT
Claims Set (CCS).
[
TODO: Specify how C requests a new access token that dynamically
updates its access rights. (See Section 3.3.1 for pre-requirements
and a high-level direction)
]
3.2.1. 'context_id' Parameter
The 'context_id' parameter is an OPTIONAL parameter of the Access
Token Request message defined in Section 5.8.1 of [RFC9200]. This
parameter provides a value that the client wishes to use with the RS
as a hint for a security context. Its exact content is profile
specific.
3.2.2. 'salt_input' Parameter
The 'salt_input' parameter is an OPTIONAL parameter of the Access
Token Request message defined in Section 5.8.1 of [RFC9200]. This
parameter provides a value that the client wishes to use as part of a
salt with the RS, for deriving cryptographic keying material. Its
exact content is profile specific.
3.2.3. 'client_cred_verify' Parameter
The 'client_cred_verify' parameter is an OPTIONAL parameter of the
Access Token Request message defined in Section 5.8.1. of [RFC9200].
This parameter provides a signature computed by the client to prove
the possession of its own private key.
3.2.4. 'client_cred_verify_mac' Parameter
The 'client_cred_verify_mac' parameter is an OPTIONAL parameter of
the Access Token Request message defined in Section 5.8.1. of
[RFC9200]. This parameter provides a Message Authentication Code
(MAC) computed by the client to prove the possession of its own
private key.
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3.3. AS-to-C: Response
After having verified the POST request to the /token endpoint and
that the client is authorized to obtain an access token corresponding
to its Access Token Request, the AS MUST verify the proof-of-
possession (PoP) evidence. In particular, the AS proceeds as
follows.
* As PoP input, the AS uses the same value used by the client in
Section 3.2.
* As public key of the client, the AS uses the one included in the
authentication credential specified in the 'req_cnf' parameter of
the Access Token Request.
This requires the AS to support the format of the authentication
credential specified in the 'req_cnf' parameter, i.e., the format
of authentication credential that is used in the OSCORE group
where the client uses that authentication credential.
Practically, this is not an issue, since an RS supporting this
profile is expected to be registered only at an AS that supports
the formats of authentication credential that the RS supports.
* If the Access Token Request includes the 'client_cred_verify'
parameter, this specifies the PoP evidence as a signature. Then,
the AS verifies the signature by using the public key of the
client.
This requires the AS to support the signature algorithm and curve
(when applicable) that are used in the OSCORE group where the
client uses the authentication credential specified in the
'req_cnf' parameter of the Access Token Request. Practically,
this is not an issue, since an RS supporting this profile is
expected to be registered only at an AS that supports the
signature algorithms and curves (when applicable) that the RS
supports.
* If the Access Token Request includes the 'client_cred_verify_mac'
parameter, this specifies the PoP evidence as a Message
Authentication Code (MAC).
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Then, the AS recomputes the MAC through the same process taken by
the client when preparing the value of the
'client_cred_verify_mac' parameter for the access token (see
Section 3.2), with the difference that the AS uses its own Diffie-
Hellman private key and the Diffie-Hellman public key of the
client. The verification succeeds if and only if the recomputed
MAC is equal to the MAC conveyed as PoP evidence in the Access
Token Request.
This requires the AS to support the ECDH algorithm that is used as
Pairwise Key Agreement Algorithm in the OSCORE group where the
client uses the authentication credential specified in the
'req_cnf' parameter of the Access Token Request. Practically,
this is not an issue, since an RS supporting this profile is
expected to be registered only at an AS that supports the ECDH
algorithms that the RS supports.
If both the 'client_cred_verify' and 'client_cred_verify_mac'
parameters are present, or if the verification of the PoP evidence
fails, the AS considers the client request invalid.
If the client request was invalid or not authorized, the AS returns
an error response as described in Section 5.8.3 of [RFC9200].
If all verifications are successful, the AS responds as defined in
Section 5.8.2 of [RFC9200]. In particular:
* The AS can signal that the use of Group OSCORE is REQUIRED for a
specific access token by including the 'ace_profile' parameter
with the value "coap_group_oscore" in the Access Token Response.
The client MUST use Group OSCORE towards all the resource servers
for which this access token is valid. Usually, it is assumed that
constrained devices will be pre-configured with the necessary
profile, so that this kind of profile signaling can be omitted.
* The AS MUST NOT include the 'rs_cnf' parameter defined in
[RFC9201]. In general, the AS may not be aware of the
authentication credentials (and public keys included thereof) that
the RSs use in the OSCORE group. Also, the client is able to
retrieve the authentication credentials of other group members
from the responsible Group Manager, both upon joining the group or
later on as a group member, as defined in
[I-D.ietf-ace-key-groupcomm-oscore].
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* According to this document, the AS includes the 'access_token'
parameter specifying the issued access token in the Access Token
Response. An alternative workflow where the access token is
uploaded by the AS directly to the RS is described in
[I-D.ietf-ace-workflow-and-params].
The AS MUST include the following information as metadata of the
issued access token. The use of CBOR web tokens (CWT) as specified
in [RFC8392] is RECOMMENDED.
* The profile "coap_group_oscore". If the access token is a CWT,
this is specified in the 'ace_profile' claim of the access token,
as per Section 5.10 of [RFC9200].
* The salt input specified in the 'salt_input' parameter of the
Access Token Request. If the access token is a CWT, the content
of the 'salt_input' parameter MUST be specified in the
'salt_input' claim of the access token, defined in Section 3.3.3
of this document.
* The Context ID input specified in the 'context_id' parameter of
the Access Token Request. If the access token is a CWT, the
content of the 'context_id' parameter MUST be specified in the
'context_id' claim of the access token, defined in Section 3.3.2
of this document.
* The authentication credential that the client uses in the OSCORE
group and specified in the 'req_cnf' parameter of the Access Token
Request.
If the access token is a CWT, the client's authentication
credential MUST be specified in the 'cnf' claim, which follows the
syntax from Section 3.1 of [RFC8747]. In particular, the 'cnf'
claim includes the same authentication credential specified in the
'req_cnf' parameter of the Access Token Request (see Section 3.2).
Figure 4 shows an example of such an AS response. The access token
has been truncated for readability.
Header: Created (Code=2.01)
Content-Format: 19 (application/ace+cbor)
Payload:
{
/ access_token / 1 : h'8343a1010aa2044c...00', / elided for brevity /
/ ace_profile / 38 : e'coap_group_oscore',
/ expires_in / 2 : 3600
}
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Figure 4: Example AS-to-C Access Token Response with the Group
OSCORE Profile.
Figure 5 shows an example CWT Claims Set, containing the client's
public key in the group (as PoP key), as specified by the inner
confirmation value in the 'cnf' claim.
{
/ aud / 3 : "tempSensorInLivingRoom",
/ iat / 6 : 1719820800,
/ exp / 4 : 2035353600,
/ scope / 9 : "temperature_g firmware_p",
e'context_id_claim' : h'abcd0000',
e'salt_input_claim' : h'00',
/ cnf / 8 : {
e'kccs' : {
/ sub / 2 : "42-50-31-FF-EF-37-32-39",
/ cnf / 8 : {
/ COSE_Key / 1 : {
/ kty / 1 : 2 / EC2 /,
/ crv / -1 : 1 / P-256 /,
/ x / -2 : h'd7cc072de2205bdc1537a543d53c60a6
acb62eccd890c7fa27c9e354089bbe13',
/ y / -3 : h'f95e1d4b851a2cc80fff87d8e23f22af
b725d535e515d020731e79a3b4e47120'
}
}
}
}
}
Figure 5: Example CWT Claims Set.
The same CWT Claims Set as in Figure 5 and encoded in CBOR is shown
in Figure 6, using the value abbreviations defined in [RFC9200] and
[RFC8747]. The bytes in hexadecimal are reported in the first
column, while their corresponding CBOR meaning is reported after the
"#" sign on the second column, for easiness of readability.
Editor's note: it should be checked (and in case fixed) that the
values used below (which are not yet registered) are the final values
registered by IANA.
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A7 # map(7)
03 # unsigned(3)
76 # text(22)
74656D7053656E736F72496E4C6976696E67526F6F6D
# "tempSensorInLivingRoom"
06 # unsigned(6)
1A 66826200 # unsigned(1719820800)
04 # unsigned(4)
1A 79510800 # unsigned(2035353600)
09 # unsigned(9)
78 18 # text(24)
74656D70657261747572655F67206669726D776172655F70
# "temperature_g firmware_p"
18 33 # unsigned(51)
44 # bytes(4)
ABCD0000
18 34 # unsigned(52)
41 # bytes(1)
00
08 # unsigned(8)
A1 # map(1)
0E # unsigned(14)
A2 # map(2)
02 # unsigned(2)
77 # text(23)
34322D35302D33312D46462D45462D33372D33322D3339
# "42-50-31-FF-EF-37-32-39"
08 # unsigned(8)
A1 # map(1)
01 # unsigned(1)
A4 # map(4)
01 # unsigned(1)
02 # unsigned(2)
20 # negative(0)
01 # unsigned(1)
21 # negative(1)
58 20 # bytes(32)
D7CC072DE2205BDC1537A543D53C60A6
ACB62ECCD890C7FA27C9E354089BBE13
22 # negative(2)
58 20 # bytes(32)
F95E1D4B851A2CC80FFF87D8E23F22AF
B725D535E515D020731E79A3B4E47120
Figure 6: Example CWT Claims Set Using CBOR Encoding.
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3.3.1. Update of Access Rights
[
TODO: Specify how the AS issues an access token that dynamically
updates the access rights of C. (See below for pre-requirements and
a high-level direction)
(This should be specified with content in the present section, as
well as in Section 3.2 and Section 4.4).
At the moment, this profile does not support the dynamic update of
access rights for the client like other transport profiles of ACE do.
This can be enabled by building on concepts defined in
[I-D.ietf-ace-workflow-and-params]:
* "Token series" - In this profile, it would be specialized as a set
of consecutive access tokens issued by the AS for the pair (C,
AUD), where C is the client whose public authentication credential
is bound to those access tokens, while AUD is the audience for
which C requests those access tokens.
* "token_series_id" - At the time of writing,
[I-D.ietf-ace-workflow-and-params] describes the intended
direction for defining this new prospective parameter, to be used
in the Access Token Request/Response exchange between C and the
AS.
This parameter is meant to specify the unique identifier of a
token series. In parallel, it is planned to define a new,
corresponding claim to include into access tokens.
At a high-level, the above can enable the dynamic update of access
rights as follows:
* Each access token in a token series includes the claim
"token_series_id", with value the identifier of the token series
that the access token belongs to.
* When issuing the first access token in a token series, the AS
includes the parameter "token_series_id" in the Access Token
Response to the client, with value the identifier of the token
series that the access token belongs to.
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* When C requests from the AS an access token that dynamically
updates its current access rights to access protected resources at
the same audience, C sends to the AS an Access Token Request such
that:
- It includes the parameter "token_series_id", with value the
identifier of the token series for which the new access token
is requested.
- It does _not_ include the parameters "context_id",
"salt_input", and "client_cred_verify" or
"client_cred_verify_mac".
* If the AS issues the new access token that dynamically updated the
access rights of C, then the access token includes the claim
"token_series_id", with value the identifier of the same token
series for which the access token has been issued.
When receiving the new access token, the RS uses the value of the
claim "token_series_id", and identifies the stored old access token
that has to be superseded by the new one, as both belonging to the
same token series.
]
3.3.2. 'context_id' Claim
The 'context_id' claim provides a value that the client requesting
the access token wishes to use with the RS, as a hint for a security
context.
This parameter specifies the value of the Context ID input, encoded
as a CBOR byte string.
3.3.3. 'salt_input' Claim
The 'salt_input' claim provides a value that the client requesting
the access token wishes to use as a part of a salt with the RS, e.g.,
for deriving cryptographic material.
This parameter specifies the value of the salt input, encoded as a
CBOR byte string.
4. Client-RS Communication
This section details the POST request and response to the /authz-info
endpoint between the client and the RS.
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The proof-of-possession required to bind the access token to the
client is explicitly performed when the RS receives and verifies a
request from the client protected with Group OSCORE, either with the
group mode (see Section 7 of [I-D.ietf-core-oscore-groupcomm]) or
with the pairwise mode (see Section 8 of
[I-D.ietf-core-oscore-groupcomm]).
In particular, the RS uses the client's public key bound to the
access token, either when verifying the signature of the request (if
protected with the group mode), or when verifying the request as
integrity-protected with pairwise keying material derived from the
two peers' authentication credentials and asymmetric keys (if
protected with the pairwise mode). In either case, the RS also
authenticates the client.
Similarly, when receiving a protected response from the RS, the
client uses the RS's public key either when verifying the signature
of the response (if protected with the group mode), or when verifying
the response as integrity-protected with pairwise keying material
derived from the two peers' authentication credentials and asymmetric
keys (if protected with the pairwise mode). In either case, the
client also authenticates the RS. Mutual authentication is only
achieved after the client has successfully verified the protected
response from the RS.
Therefore, an attacker using a stolen access token cannot generate a
valid Group OSCORE message as protected through the client's private
key, and thus cannot prove possession of the PoP key bound to the
access token. Also, if a client legitimately owns an access token
but has not joined the OSCORE group, it cannot generate a valid Group
OSCORE message, as it does not store the necessary keying material
shared among the group members.
Furthermore, a client C1 is supposed to obtain a valid access token
from the AS, as specifying its own authentication credential (and the
public key included thereof) associated with its own private key used
in the OSCORE group, together with its own Sender ID in that OSCORE
group (see Section 3.2). This allows the RS receiving the access
token to verify with the Group Manager of that OSCORE group whether
such a client indeed has that Sender ID and uses that authentication
credential in the OSCORE group.
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As a consequence, a different client C2, also member of the same
OSCORE group, is not able to impersonate C1, by: i) getting a valid
access token, specifying the Sender ID of C1 and a different (made-
up) authentication credential; ii) successfully posting the access
token to the RS; and then iii) attempting to communicate using Group
OSCORE and impersonating C1, while also blaming C1 for the
consequences of the interaction with the RS.
4.1. C-to-RS POST to /authz-info Endpoint
The client uploads the access token to the /authz-info endpoint of
the RS, as defined in Section 5.10.1 of [RFC9200].
4.2. RS-to-C: 2.01 (Created)
The RS MUST verify the validity of the access token as defined in
Section 5.10.1 of [RFC9200], with the following additions.
* The RS checks that the claims 'context_id', 'salt_input', and
'cnf' are included in the access token.
If any of these claims are missing or malformed, the RS MUST
consider the access token invalid, and MUST reply to the client
with an error response code equivalent to the CoAP code 4.00 (Bad
Request).
Otherwise, the RS retrieves:
- GID* as the GID of the OSCORE group, specified in the
'context_id' claim.
- SID* as the Sender ID that the client has in the OSCORE group,
specified in the 'salt_input' claim.
- AUTH_CRED_C* as the authentication credential that the client
uses in the OSCORE group, specified in the inner confirmation
value of the 'cnf' claim.
* The RS builds GROUPS as the set of OSCORE groups such that all the
following conditions hold, for each group G in the set.
- The RS is a member of the group G.
- The group G has GID* as current GID.
- The audience targeted by the access token is consistent with
using the group G for accessing protected resources hosted by
the RS.
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If no such group is found, the RS MUST consider the access token
invalid, and MUST reply to the client with an error response code
equivalent to the CoAP code 4.00 (Bad Request).
Otherwise, for each of the N >= 1 groups G in the set GROUPS, the
RS MUST request to the corresponding Group Manager the
authentication credential that the client uses in G, specifying
SID* in the request sent to the Group Manager (see Section 9.3 of
[I-D.ietf-ace-key-groupcomm-oscore]).
When receiving a successful response from each of the Group
Managers, the RS MUST check whether the client's authentication
credential AUTH_CRED_C retrieved from the Group Manager is equal
to AUTH_CRED_C* retrieved from the access token.
If any of the following conditions hold, the RS MUST consider the
access token invalid, and MUST reply to the client with an error
response code equivalent to the CoAP code 5.03 (Service
Unavailable).
- None or more than one of the Group Managers provide the RS with
a successful response where the conveyed AUTH_CRED_C is equal
to AUTH_CRED_C*.
- After having performed a maximum, pre-configured amount of
attempts, or after a maximum, pre-configured amount of time has
elapsed, less than N Group Managers have sent a successful
response to the RS.
The process above is successful if and only if the RS receives a
successful response from all the N Group Managers, and exactly one
of such responses conveys AUTH_CRED_C equal to AUTH_CRED_C*. This
ensures that there is only one OSCORE group G* such that: the
client and the RS are both its members; it has GID* as current
GID; and the client uses SID* as Sender ID in the group. In turn,
this will ensure that the RS can bound the access token to such
single OSCORE group G*.
If the operations above are successful, the access token is valid,
and further checks on its content are successful, then the RS
associates the authorization information from the access token with
the Group OSCORE Security Context of the OSCORE group G*.
In particular, the RS associates the authorization information from
the access token with the quartet (GID, SaltInput, AuthCred,
AuthCredGM), where:
* GID is the Group Identifier of G* (i.e., GID*).
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* SaltInput is the Sender ID that the client uses in G* (i.e.,
SID*).
* AuthCred is the authentication credential that the client uses in
G* (i.e., AUTH_CRED_C*).
* AuthCredGM is the authentication credential of the Group Manager
responsible for G* (see Section 2.1.6 of
[I-D.ietf-core-oscore-groupcomm]).
The RS MUST keep this association up-to-date over time, as the
quartet (GID, SaltInput, AuthCred, AuthCredGM) associated with the
access token might change. In particular:
* If the OSCORE group is rekeyed (see Section 12.2 of
[I-D.ietf-core-oscore-groupcomm] and Section 11 of
[I-D.ietf-ace-key-groupcomm-oscore]), the Group Identifier also
changes in the group, and the new one replaces the current 'GID'
value in the quartet (GID, SaltInput, AuthCred, AuthCredGM).
* If the client requests and obtains a new OSCORE Sender ID from the
Group Manager (see Section 2.6.3.1 of
[I-D.ietf-core-oscore-groupcomm] and Section 9.2 of
[I-D.ietf-ace-key-groupcomm-oscore]), the new Sender ID replaces
the current 'SaltInput' value in the quartet (GID, SaltInput,
AuthCred, AuthCredGM).
* If the Group Manager of the OSCORE group changes its
authentication credential, the new authentication credential of
the Group Manager replaces the current 'AuthCredGM' value in the
quartet (GID, SaltInput, AuthCred, AuthCredGM).
In order to obtain the latest authentication credential of the
Group Manager, the RS can re-join the group (see Section 6 of
[I-D.ietf-ace-key-groupcomm-oscore]) or send a dedicated request
to the Group Manager (see Section 9.3 of
[I-D.ietf-ace-key-groupcomm-oscore]).
As defined in Section 5, a possible change of the client's
authentication credential requires the client to upload to the RS a
new access token bound to the new authentication credential.
Finally, the RS MUST send a 2.01 (Created) response to the client, as
defined in Section 5.10.1 of [RFC9200].
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4.3. Client-RS Secure Communication
When previously joining the OSCORE group, both the client and the RS
have already established the related Group OSCORE Security Context to
communicate as group members. Therefore, they can simply start to
securely communicate using Group OSCORE, without deriving any
additional keying material or security association.
If either of the client or the RS deletes an access token (e.g., when
the access token has expired or has been revoked), it MUST NOT delete
the related Group OSCORE Security Context. The client MAY request a
new access token from the AS, to be uploaded to the RS for re-
enabling access to protected resources for the client.
4.3.1. Client Side
After having received the 2.01 (Created) response from the RS,
following the POST request to the /authz-info endpoint, the client
starts the communication with the RS, by sending a request protected
with Group OSCORE using the Group OSCORE Security Context
[I-D.ietf-core-oscore-groupcomm].
When communicating with the RS to access the resources as specified
by the authorization information, the client MUST use the Group
OSCORE Security Context of the pertinent OSCORE group, whose GID was
specified in the 'context_id' parameter of the Access Token Request.
4.3.2. Resource Server Side
After successful validation of the access token as defined in
Section 4.2 and after having sent the 2.01 (Created) response, the RS
can start to communicate with the client using Group OSCORE
[I-D.ietf-core-oscore-groupcomm].
When processing an incoming request protected with Group OSCORE, the
RS MUST consider as valid client's authentication credential only the
one associated with the stored access token. As defined in
Section 5, a possible change of the client's authentication
credential requires the client to upload to the RS a new access token
bound to the new authentication credential.
For every incoming request, if Group OSCORE verification succeeds,
the verification of access rights is performed as described in
Section 4.5.
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If the RS receives a request protected with a Group OSCORE Security
Context CTX, the target resource requires authorization, and the RS
does not store a valid access token related to CTX, then the RS MUST
reply with a 4.01 (Unauthorized) error response protected with CTX.
4.4. Update of Access Rights
[
TODO: Specify the processing on the RS when receiving an access token
that dynamically updates the access rights of C. (See Section 3.3.1
for pre-requirements and a high-level direction)
]
4.5. Access Rights Verification
The RS MUST follow the procedures defined in Section 5.10.2 of
[RFC9200]. If an RS receives a request protected with Group OSCORE
from a client, the RS processes the request according to
[I-D.ietf-core-oscore-groupcomm].
If the Group OSCORE verification succeeds and the target resource
requires authorization, the RS retrieves the authorization
information from the access token associated with the Group OSCORE
Security Context.
In particular, the RS retrieves the access token associated with the
quartet (GID, SaltInput, AuthCred, AuthCredGM), where:
* GID is the Group Identifier of the OSCORE group, which is
specified in the 'kid context' parameter of the CoAP OSCORE option
in the received request. The RS maintains GID in its Common
Context within the Group OSCORE Security Context associated with
the OSCORE group (see Section 2 of
[I-D.ietf-core-oscore-groupcomm]).
* SaltInput is the Sender ID that the client has in the OSCORE
group, which is specified in the 'kid' parameter of the CoAP
OSCORE option in the received request. The RS maintains SaltInput
in its Recipient Context associated with the client, within the
Group OSCORE Security Context associated with the OSCORE group
(see Section 2 of [I-D.ietf-core-oscore-groupcomm]).
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* AuthCred is the authentication credential that the client uses in
the OSCORE group. The RS maintains AuthCred in its Recipient
Context associated with the client, within the Group OSCORE
Security Context associated with the OSCORE group (see Section 2
of [I-D.ietf-core-oscore-groupcomm]).
* AuthCredGM is the authentication credential of the Group Manager
responsible for the OSCORE group. The RS maintains AuthCredGM in
its Common Context within the Group OSCORE Security Context
associated with the OSCORE group (see Section 2 of
[I-D.ietf-core-oscore-groupcomm]).
Then, the RS MUST verify that the action requested on the resource is
authorized.
If the RS has no valid access token for the client, the RS MUST
reject the request and MUST reply to the client with a 4.01
(Unauthorized) error response.
If the RS has an access token for the client but no actions are
authorized on the target resource, the RS MUST reject the request and
MUST reply to the client with a 4.03 (Forbidden) error response.
If the RS has an access token for the client but the requested action
is not authorized, the RS MUST reject the request and MUST reply to
the client with a 4.05 (Method Not Allowed) error response.
4.6. Storing Multiple Access Tokens per PoP Key
According to Section 5.10.1 of [RFC9200], an RS is recommended to
store only one access token per proof-of-possession (PoP) key, and to
supersede such an access token when receiving and successfully
validating a new one bound to the same PoP key.
However, when using the profile specified in this document, an RS
might practically have to deviate from that recommendation and store
multiple access tokens bound to the same PoP key, i.e., to the same
public authentication credential of a client.
For example, this can occur in the following cases.
* The RS is the single RS associated with an audience AUD1, and also
belongs to a group-audience AUD2 (see Section 6.9 of [RFC9200]).
A client C with public authentication credential AUTH_CRED_C can
request two access tokens T1 and T2 from the AS, such that:
- T1 targets AUD1 and has scope SCOPE1;
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- T2 targets AUD2 and has scope SCOPE2 different from SCOPE1.
Both T1 and T2 are going to be bound to the same PoP key specified
by AUTH_CRED_C.
In fact, if the AS issues access tokens targeting a group-
audience, then the above can possibly be the case when using any
transport profile of ACE that supports asymmetric PoP keys. If
so, the RS should be ready to store at minimum one access token
per PoP key per audience it belongs to.
* The RS is a member of two OSCORE groups G1 and G2. In particular,
the same format of public authentication credentials is used in
both OSCORE groups.
A client C with public authentication credential AUTH_CRED_C of
such format, also member of the two OSCORE group G1 and G2, can
conveniently use AUTH_CRED_C as its public authentication
credential in both those groups. Therefore, C can request two
access tokens T1 and T2 from the AS, such that:
- T1 targets RS and reflects the membership of C in G1, as per
its claims "context_id" and "salt_input";
- T2 targets RS and reflects the membership of C in G2, as per
its claims "context_id" and "salt_input".
Both T1 and T2 are going to be bound to the same PoP key specified
by AUTH_CRED_C.
When using the profile specified in this document, the RS should
be ready to store at minimum one access token per PoP key per
OSCORE group it is a member of (although, per the previous point,
even this can be limiting).
* The RS uses both the profile specified in this document and a
different transport profile of ACE that also relies on asymmetric
PoP keys, e.g., the EDHOC and OSCORE profile defined in
[I-D.ietf-ace-edhoc-oscore-profile].
In such a case, a client C with public authentication credential
AUTH_CRED_C can request two access tokens T1 and T2 from the AS,
such that:
- T1 targets RS and is meant to be used according to the Group
OSCORE profile defined in this document;
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- T2 targets RS and is meant to be used according to the EDHOC
and OSCORE profile defined in
[I-D.ietf-ace-edhoc-oscore-profile].
Both T1 and T2 are going to be bound to the same PoP key specified
by AUTH_CRED_C.
When using multiple transport profiles of ACE that rely on
asymmetric PoP keys, it is reasonable that the RS is capable to
store at minimum one access token per PoP key per used profile
(although, per the previous points, even this can be limiting).
In order to keep the same spirit of the recommendation in
Section 5.10.1 of [RFC9200] without impeding cases such as those
outlined in the examples above, the following defines a more fine-
grained recommendations for the storage of access tokens at an RS
when this profile is used.
* As to access tokens issued in accordance with this profile (i.e.,
specifying the profile "coap_group_oscore"), it is RECOMMENDED
that an RS stores only one access token that:
- is bound to a specific PoP key; and
- targets a specific audience; and
- is related to a specific OSCORE group.
* As to access tokens issued in accordance with a different profile
P that an RS may use in parallel with the profile defined in this
document, it is RECOMMENDED that an RS stores only one access
token that:
- is issued in accordance with the profile P; and
- is bound to a specific PoP key; and
- targets a specific audience; and
- is related to a specific secure association used by the client
to protect communications with the RS.
In accordance with these recommendations, if an access token T_NEW
does not differ in any of the respects above from an existing access
token T_OLD stored at the RS, then T_NEW will supersede T_OLD by
replacing the corresponding authorization information.
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Not complying with these recommendations can additionally complicate
(constrained) implementations of RSs, with respect to required
storage and the validation of a protected request against the
applicable, stored access tokens associated with the same client.
That is, it increases the strain on an RS in determining the actual
permissions of a client, e.g., if access tokens contradict each other
and thus might lead the RS to enforce wrong permissions. Moreover,
if one of the access tokens expires earlier than others, the
resulting permissions may offer insufficient protection.
5. Change of Client's Authentication Credential in the Group
During its membership in the OSCORE group, the client might change
the authentication credential that it uses in the group. When this
happens, the client uploads the new authentication credential to the
Group Manager, as defined in Section 9.4 of
[I-D.ietf-ace-key-groupcomm-oscore].
After that, and in order to continue communicating with the RS, the
client MUST perform the following actions.
1. The client requests a new access token T_NEW to the AS, as
defined in Section 3. In particular, when sending the Access
Token Request as defined in Section 3.2, the client specifies:
* The current Group Identifier of the OSCORE group, as value of
the 'context_id' parameter.
* The current Sender ID that it has in the OSCORE group, as
value of the 'salt_input' parameter.
* The new authentication credential that it uses in the OSCORE
group, as inner confirmation value of the 'req_cnf' parameter.
* The proof-of-possession (PoP) evidence corresponding to the
public key of the new authentication credential, as value of
the 'client_cred_verify' or 'client_cred_verify_mac'
parameter.
2. After receiving the Access Token Response from the AS (see
Section 3.3), the client performs the same exchanges with the RS
as defined in Section 4.
When receiving the new access token T_NEW, the RS performs the same
steps defined in Section 4.2, with the following addition in case the
new access token is successfully verified and stored:
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* The RS deletes any stored access token T_OLD such that the
associated quartet (GID, SaltInput, AuthCred, AuthCredGM) differs
from the same quartet associated with T_NEW only as to the value
of AuthCred.
6. Secure Communication with the AS
As specified in the ACE framework (see Sections 5.8 and 5.9 of
[RFC9200]), the requesting entity (client and/or RS) and the AS
communicate via the /token or /introspect endpoint. The use of CoAP
and OSCORE [RFC8613] for this communication is RECOMMENDED in this
profile. Other protocols fulfilling the security requirements
defined in Sections 5 and 6 of [RFC9200] (such as HTTP and DTLS or
TLS) MAY be used instead.
If OSCORE [RFC8613] is used, the requesting entity and the AS are
expected to have a pre-established Security Context in place. How
this Security Context is established is out of the scope of this
profile. Furthermore, the requesting entity and the AS communicate
using OSCORE through the /token endpoint as specified in Section 5.8
of [RFC9200], and through the /introspect endpoint as specified in
Section 5.9 of [RFC9200].
7. Discarding the Security Context
As members of an OSCORE group, the client and the RS may
independently leave the group or be forced to, e.g., if compromised
or suspected so. Upon leaving the OSCORE group, the client or RS
also discards the Group OSCORE Security Context, which may anyway be
renewed by the Group Manager through a group rekeying process (see
Section 12.2 of [I-D.ietf-core-oscore-groupcomm]).
The client or RS can acquire a new Group OSCORE Security Context, by
re-joining the OSCORE group, e.g., by using the approach defined in
[I-D.ietf-ace-key-groupcomm-oscore]. In such a case, the client
SHOULD request a new access token to be uploaded to the RS.
8. Guidelines on Using Multiple Profiles
When using the profile defined in this document, access tokens are to
be bound to a Group OSCORE Security Context, which is used to protect
communications between the client and the RS(s) in the targeted
audience by using the security protocol Group OSCORE.
After having obtained an access token T1 for this profile and
uploaded it to the RS (RSs) pertaining to the targeted audience, the
client might want to establish a separate, pairwise OSCORE
association with that RS (with one RS among those RSs). In order to
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do that, the client can ask the AS for a different access token T2
intended for that RS (for one RS among those RSs), as per the OSCORE
profile defined in [RFC9203].
Since the ACE framework does not allow the client to negotiate with
the AS the profile to use, the client has instead to choose the use
of the OSCORE profile, and to explicitly indicate it to the AS when
requesting T2.
To this end, the client may indicate its wish for an access token
aligned with the Group OSCORE profile or with the OSCORE profile, by
specifying one of two different audiences in the 'audience' parameter
of the Access Token Request to the AS. Assuming a proper
configuration of the access policies at the AS, this is still
conducive to a consistent evaluation of what is specified in the
'scope' parameter of the Access Token Request against the access
policies at the AS.
For example, an RS registered at the AS can be associated with two
audiences:
* "AUD_GP_OSC", which the client can use to request an access token
for the Group OSCORE profile and targeting (also) that RS. That
is, the client specifies this audience when requesting the access
token T1.
* "AUD_OSC", which the client can use to request an access token for
the OSCORE profile and targeting only that RS. That is, the
client specifies this audience when requesting the access token
T2.
Note that an RS has to be able to store at least one access token per
PoP key. When specifically considering the Group OSCORE profile and
the OSCORE profile, the RS can always store both corresponding access
tokens T1 and T2, since they are always bound to different PoP keys.
That is:
* In the Group OSCORE profile, the PoP key is the client's public
key, which is included in the client's authentication credential
specified in the 'cnf' claim of the access token.
* In the OSCORE profile, the PoP key is fundamentally an OSCORE
Master Secret, which is specified within the OSCORE_Input_Material
object of the 'cnf' claim of the access token.
The same approach discussed above can be used in case the profile
used for the access token T2 is instead the EDHOC and OSCORE profile
defined in [I-D.ietf-ace-edhoc-oscore-profile]. In such a case, the
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same PoP key might be bound to both T1 and T2, i.e., if the client's
public key is included both in the authentication credential that the
client uses in the OSCORE group and in the authentication credential
that the client uses as CRED_I (CRED_R) when running the EDHOC
protocol in the forward (reverse) message flow.
Section 4.6 provides considerations and recommendations on storing
multiple access tokens per PoP key when using the Group OSCORE
profile, also in parallel with alternative profiles.
9. CBOR Mappings
The new parameters defined in this document MUST be mapped to CBOR
types as specified in Table 1, using the given integer abbreviation
for the map key.
+========================+==========+=============+
| Parameter name | CBOR Key | Value Type |
+========================+==========+=============+
| context_id | TBD | byte string |
+------------------------+----------+-------------+
| salt_input | TBD | byte string |
+------------------------+----------+-------------+
| client_cred_verify | TBD | byte string |
+------------------------+----------+-------------+
| client_cred_verify_mac | TBD | byte string |
+------------------------+----------+-------------+
Table 1: CBOR Mappings for New Parameters.
The new claims defined in this document MUST be mapped to CBOR types
as specified in Table 2, using the given integer abbreviation for the
map key.
+============+==========+=============+
| Claim name | CBOR Key | Value Type |
+============+==========+=============+
| context_id | TBD | byte string |
+------------+----------+-------------+
| salt_input | TBD | byte string |
+------------+----------+-------------+
Table 2: CBOR Mappings for New Claims.
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10. Security Considerations
This document specifies a profile for the Authentication and
Authorization for Constrained Environments (ACE) framework [RFC9200].
Thus, the general security considerations from the ACE framework also
apply to this profile.
The proof-of-possession (PoP) key bound to an access token is always
an asymmetric key, i.e., the public key included in the
authentication credential that the client uses in the OSCORE group.
This means that there is never a same shared secret used as PoP key
with possible multiple RSs. Therefore, it is possible and safe for
the AS to issue an access token for an audience that includes
multiple RSs (i.e., a group-audience, see Section 6.9 of [RFC9200]).
In such a case, as per Section 6.1 of [RFC9200], the AS has to ensure
the integrity protection of the access token by protecting it through
an asymmetric signature. In addition, the used group-audience has to
correctly identify all the RSs that are intended recipients of the
access token, and for which the single scope specified in the access
token applies. As a particular case, the audience can be the name of
the OSCORE group, if the access token is intended for all the RSs in
that group.
Furthermore, this document inherits the general security
considerations about Group OSCORE [I-D.ietf-core-oscore-groupcomm],
as to the specific use of Group OSCORE according to this profile.
Group OSCORE is designed to secure point-to-point as well as point-
to-multipoint communications, providing a secure binding between a
single request and multiple corresponding responses. In particular,
Group OSCORE fulfills the same security requirements of OSCORE.
Group OSCORE ensures source authentication of messages both in group
mode (see Section 7 of [I-D.ietf-core-oscore-groupcomm]) and in
pairwise mode (see Section 8 of [I-D.ietf-core-oscore-groupcomm]).
When protecting an outgoing message in group mode, the sender uses
its private key to compute a digital signature, which is embedded in
the protected message. The group mode can be used to protect
messages sent to multiple recipients (e.g., over IP multicast) or to
a single recipient.
When protecting an outgoing message in pairwise mode, the sender uses
a pairwise symmetric key, which is derived from the asymmetric keys
of the two peers exchanging the message. The pairwise mode can be
used to protect only messages intended for a single recipient.
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11. Privacy Considerations
This document specifies a profile for the Authentication and
Authorization for Constrained Environments (ACE) framework [RFC9200].
Thus the general privacy considerations from the ACE framework also
apply to this profile.
As this profile uses Group OSCORE, the privacy considerations from
[I-D.ietf-core-oscore-groupcomm] apply to this document as well.
An unprotected response to an unauthorized request may disclose
information about the RS and/or its existing relationship with the
client. It is advisable to include as little information as possible
in an unencrypted response. However, since both the client and the
RS share a Group OSCORE Security Context, unauthorized, yet protected
requests are followed by protected responses, which can thus include
more detailed information.
Although it may be encrypted, the access token is sent in the clear
to the /authz-info endpoint at the RS. Thus, if the client uses the
same single access token from multiple locations with multiple
resource servers, it can risk being tracked through the access
token's value.
Note that, even though communications are protected with Group
OSCORE, some information might still leak, due to the observable
size, source address, and destination address of exchanged messages.
12. IANA Considerations
This document has the following actions for IANA.
Note to RFC Editor: Please replace "[RFC-XXXX]" with the RFC number
of this document and delete this paragraph.
12.1. ACE Profiles Registry
IANA is asked to add the following entry to the "ACE Profiles"
registry within the "Authentication and Authorization for Constrained
Environments (ACE)" registry group, following the procedure specified
in Section 8.8 of [RFC9200].
* Name: coap_group_oscore
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* Description: Profile to secure communications between constrained
nodes using the Authentication and Authorization for Constrained
Environments framework, by enabling authentication and fine-
grained authorization of members of an OSCORE group that use a
pre-established Group OSCORE Security Context to communicate with
Group OSCORE.
* CBOR Value: TBD (value between 1 and 255)
* Reference: [RFC-XXXX]
12.2. OAuth Parameters Registry
IANA is asked to add the following entries to the "OAuth Parameters"
registry, following the procedure specified in Section 11.2 of
[RFC6749].
* Name: context_id
* Parameter Usage Location: token request
* Change Controller: IETF
* Reference: Section 3.2.1 of [RFC-XXXX]
* Name: salt_input
* Parameter Usage Location: token request
* Change Controller: IETF
* Reference: Section 3.2.2 of [RFC-XXXX]
* Name: client_cred_verify
* Parameter Usage Location: token request
* Change Controller: IETF
* Reference: Section 3.2.3 of [RFC-XXXX]
* Name: client_cred_verify_mac
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* Parameter Usage Location: token request
* Change Controller: IETF
* Reference: Section 3.2.4 of [RFC-XXXX]
12.3. OAuth Parameters CBOR Mappings Registry
IANA is asked to add the following entries to the "OAuth Parameters
CBOR Mappings" registry within the "Authentication and Authorization
for Constrained Environments (ACE)" registry group, following the
procedure specified in Section 8.10 of [RFC9200].
* Name: context_id
* CBOR Key: TBD
* Value Type: byte string
* Reference: Section 3.2.1 of [RFC-XXXX]
* Original Specification: [RFC-XXXX]
* Name: salt_input
* CBOR Key: TBD
* Value Type: byte string
* Reference: Section 3.2.2 of [RFC-XXXX]
* Original Specification: [RFC-XXXX]
* Name: client_cred_verify
* CBOR Key: TBD
* Value Type: byte string
* Reference: Section 3.2.3 of [RFC-XXXX]
* Original Specification: [RFC-XXXX]
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* Name: client_cred_verify_mac
* CBOR Key: TBD
* Value Type: byte string
* Reference: Section 3.2.4 of [RFC-XXXX]
* Original Specification: [RFC-XXXX]
12.4. CBOR Web Token (CWT) Claims Registry
IANA is asked to add the following entries to the "CBOR Web Token
(CWT) Claims" registry, following the procedure specified in
Section 9.1 of [RFC8392].
* Claim Name: context_id
* Claim Description: Client provided Context ID
* JWT Claim Name: N/A
* Claim Key: TBD
* Claim Value Type: byte string
* Change Controller: IETF
* Reference: Section 3.3.2 of [RFC-XXXX]
* Claim Name: salt_input
* Claim Description: Client provided salt input
* JWT Claim Name: N/A
* Claim Key: TBD
* Claim Value Type: byte string
* Change Controller: IETF
* Reference: Section 3.3.3 of [RFC-XXXX]
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12.5. TLS Exporter Label Registry
IANA is asked to add the following entry to the "TLS Exporter Label"
registry within the "Transport Layer Security (TLS) Parameters"
registry group, following the procedure specified in Section 6 of
[RFC5705] and updated in Section 12 of [RFC8447].
* Value: EXPORTER-ACE-PoP-Input-Client-AS
* DTLS-OK: Y
* Recommended: N
* Reference: Section 3.2 of [RFC-XXXX]
13. References
13.1. Normative References
[I-D.ietf-ace-key-groupcomm-oscore]
Tiloca, M., Park, J., and F. Palombini, "Key Management
for OSCORE Groups in ACE", Work in Progress, Internet-
Draft, draft-ietf-ace-key-groupcomm-oscore-16, 6 March
2023, <https://datatracker.ietf.org/doc/html/draft-ietf-
ace-key-groupcomm-oscore-16>.
[I-D.ietf-core-groupcomm-bis]
Dijk, E., Wang, C., and M. Tiloca, "Group Communication
for the Constrained Application Protocol (CoAP)", Work in
Progress, Internet-Draft, draft-ietf-core-groupcomm-bis-
11, 24 April 2024, <https://datatracker.ietf.org/doc/html/
draft-ietf-core-groupcomm-bis-11>.
[I-D.ietf-core-oscore-groupcomm]
Tiloca, M., Selander, G., Palombini, F., Mattsson, J. P.,
and R. Höglund, "Group Object Security for Constrained
RESTful Environments (Group OSCORE)", Work in Progress,
Internet-Draft, draft-ietf-core-oscore-groupcomm-23, 26
September 2024, <https://datatracker.ietf.org/doc/html/
draft-ietf-core-oscore-groupcomm-23>.
[NIST-800-56A]
Barker, E., Chen, L., Roginsky, A., Vassilev, A., and R.
Davis, "Recommendation for Pair-Wise Key-Establishment
Schemes Using Discrete Logarithm Cryptography - NIST
Special Publication 800-56A, Revision 3", April 2018,
<https://nvlpubs.nist.gov/nistpubs/SpecialPublications/
NIST.SP.800-56Ar3.pdf>.
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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/rfc/rfc2119>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<https://www.rfc-editor.org/rfc/rfc5246>.
[RFC5705] Rescorla, E., "Keying Material Exporters for Transport
Layer Security (TLS)", RFC 5705, DOI 10.17487/RFC5705,
March 2010, <https://www.rfc-editor.org/rfc/rfc5705>.
[RFC5869] Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand
Key Derivation Function (HKDF)", RFC 5869,
DOI 10.17487/RFC5869, May 2010,
<https://www.rfc-editor.org/rfc/rfc5869>.
[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/rfc/rfc6347>.
[RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
RFC 6749, DOI 10.17487/RFC6749, October 2012,
<https://www.rfc-editor.org/rfc/rfc6749>.
[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/rfc/rfc7252>.
[RFC7748] Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves
for Security", RFC 7748, DOI 10.17487/RFC7748, January
2016, <https://www.rfc-editor.org/rfc/rfc7748>.
[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/rfc/rfc8174>.
[RFC8392] Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig,
"CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392,
May 2018, <https://www.rfc-editor.org/rfc/rfc8392>.
[RFC8447] Salowey, J. and S. Turner, "IANA Registry Updates for TLS
and DTLS", RFC 8447, DOI 10.17487/RFC8447, August 2018,
<https://www.rfc-editor.org/rfc/rfc8447>.
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[RFC8610] Birkholz, H., Vigano, C., and C. Bormann, "Concise Data
Definition Language (CDDL): A Notational Convention to
Express Concise Binary Object Representation (CBOR) and
JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610,
June 2019, <https://www.rfc-editor.org/rfc/rfc8610>.
[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/rfc/rfc8613>.
[RFC8747] Jones, M., Seitz, L., Selander, G., Erdtman, S., and H.
Tschofenig, "Proof-of-Possession Key Semantics for CBOR
Web Tokens (CWTs)", RFC 8747, DOI 10.17487/RFC8747, March
2020, <https://www.rfc-editor.org/rfc/rfc8747>.
[RFC8949] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", STD 94, RFC 8949,
DOI 10.17487/RFC8949, December 2020,
<https://www.rfc-editor.org/rfc/rfc8949>.
[RFC9052] Schaad, J., "CBOR Object Signing and Encryption (COSE):
Structures and Process", STD 96, RFC 9052,
DOI 10.17487/RFC9052, August 2022,
<https://www.rfc-editor.org/rfc/rfc9052>.
[RFC9053] Schaad, J., "CBOR Object Signing and Encryption (COSE):
Initial Algorithms", RFC 9053, DOI 10.17487/RFC9053,
August 2022, <https://www.rfc-editor.org/rfc/rfc9053>.
[RFC9200] Seitz, L., Selander, G., Wahlstroem, E., Erdtman, S., and
H. Tschofenig, "Authentication and Authorization for
Constrained Environments Using the OAuth 2.0 Framework
(ACE-OAuth)", RFC 9200, DOI 10.17487/RFC9200, August 2022,
<https://www.rfc-editor.org/rfc/rfc9200>.
[RFC9201] Seitz, L., "Additional OAuth Parameters for Authentication
and Authorization for Constrained Environments (ACE)",
RFC 9201, DOI 10.17487/RFC9201, August 2022,
<https://www.rfc-editor.org/rfc/rfc9201>.
[RFC9203] Palombini, F., Seitz, L., Selander, G., and M. Gunnarsson,
"The Object Security for Constrained RESTful Environments
(OSCORE) Profile of the Authentication and Authorization
for Constrained Environments (ACE) Framework", RFC 9203,
DOI 10.17487/RFC9203, August 2022,
<https://www.rfc-editor.org/rfc/rfc9203>.
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13.2. Informative References
[I-D.ietf-ace-edhoc-oscore-profile]
Selander, G., Mattsson, J. P., Tiloca, M., and R. Höglund,
"Ephemeral Diffie-Hellman Over COSE (EDHOC) and Object
Security for Constrained Environments (OSCORE) Profile for
Authentication and Authorization for Constrained
Environments (ACE)", Work in Progress, Internet-Draft,
draft-ietf-ace-edhoc-oscore-profile-06, 21 October 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-ace-
edhoc-oscore-profile-06>.
[I-D.ietf-ace-workflow-and-params]
Tiloca, M. and G. Selander, "Alternative Workflow and
OAuth Parameters for the Authentication and Authorization
for Constrained Environments (ACE) Framework", Work in
Progress, Internet-Draft, draft-ietf-ace-workflow-and-
params-02, 8 July 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-ace-
workflow-and-params-02>.
[I-D.ietf-cose-cbor-encoded-cert]
Mattsson, J. P., Selander, G., Raza, S., Höglund, J., and
M. Furuhed, "CBOR Encoded X.509 Certificates (C509
Certificates)", Work in Progress, Internet-Draft, draft-
ietf-cose-cbor-encoded-cert-11, 8 July 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-cose-
cbor-encoded-cert-11>.
[I-D.tiloca-core-oscore-discovery]
Tiloca, M., Amsüss, C., and P. Van der Stok, "Discovery of
OSCORE Groups with the CoRE Resource Directory", Work in
Progress, Internet-Draft, draft-tiloca-core-oscore-
discovery-16, 4 September 2024,
<https://datatracker.ietf.org/doc/html/draft-tiloca-core-
oscore-discovery-16>.
[NIST-800-207]
Rose, S., Borchert, O., Mitchell, S., and S. Connelly,
"Zero Trust Architecture - NIST Special Publication
800-207", August 2020,
<https://nvlpubs.nist.gov/nistpubs/SpecialPublications/
NIST.SP.800-207.pdf>.
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[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/rfc/rfc5280>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/rfc/rfc8446>.
[RFC9147] Rescorla, E., Tschofenig, H., and N. Modadugu, "The
Datagram Transport Layer Security (DTLS) Protocol Version
1.3", RFC 9147, DOI 10.17487/RFC9147, April 2022,
<https://www.rfc-editor.org/rfc/rfc9147>.
[RFC9202] 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)", RFC 9202,
DOI 10.17487/RFC9202, August 2022,
<https://www.rfc-editor.org/rfc/rfc9202>.
[RFC9431] Sengul, C. and A. Kirby, "Message Queuing Telemetry
Transport (MQTT) and Transport Layer Security (TLS)
Profile of Authentication and Authorization for
Constrained Environments (ACE) Framework", RFC 9431,
DOI 10.17487/RFC9431, July 2023,
<https://www.rfc-editor.org/rfc/rfc9431>.
Appendix A. Profile Requirements
This appendix lists the specifications of this profile based on the
requirements of the ACE framework, as requested in Appendix C of
[RFC9200].
* Optionally, define new methods for the client to discover the
necessary permissions and AS for accessing a resource, different
from the one proposed in [RFC9200]: Not specified.
* Optionally, specify new grant types: Not specified.
* Optionally, define the use of client certificates as client
credential type: Not specified.
* Specify the communication protocol the client and RS must use:
CoAP.
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* Specify the security protocol the client and RS must use to
protect their communication: Group OSCORE, by using a pre-
established Group OSCORE Security Context.
* Specify how the client and the RS mutually authenticate:
Explicitly, by possession of a common Group OSCORE Security
Context, and by either: usage of digital signatures embedded in
messages, if protected with the group mode of Group OSCORE; or
protection of messages with the pairwise mode of Group OSCORE, by
using pairwise symmetric keys derived from the asymmetric keys of
the two peers exchanging the message. Note that mutual
authentication is not completed before the client has verified a
Group OSCORE response using the corresponding Group OSCORE
Security Context.
* Specify the proof-of-possession protocol(s) and how to select one,
if several are available. Also specify which key types (e.g.,
symmetric/asymmetric) are supported by a specific proof-of-
possession protocol: Group OSCORE algorithms; asymmetric keys
verified and distributed by a Group Manager.
* Specify a unique ace_profile identifier: coap_group_oscore.
* If introspection is supported, specify the communication and
security protocol for introspection: HTTP/CoAP (+ TLS/DTLS/
OSCORE).
* Specify the communication and security protocol for interactions
between the client and AS: HTTP/CoAP (+ TLS/DTLS/OSCORE).
* Specify if/how the /authz-info endpoint is protected, including
how error responses are protected: Not protected.
* Optionally, define other methods of token transport than the
/authz-info endpoint: Not defined.
Appendix B. CDDL Model
This section is to be removed before publishing as an RFC.
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; ACE Profiles
coap_group_oscore = 5
; OAuth Parameters CBOR Mappings
context_id_param = 71
salt_input_param = 72
client_cred_verify = 73
client_cred_verify_mac = 74
; CBOR Web Token (CWT) Claims
context_id_claim = 51
salt_input_claim = 52
; CWT Confirmation Methods
kccs = 14
Figure 7: CDDL model
Appendix C. Document Updates
This section is to be removed before publishing as an RFC.
C.1. Version -02 to -03
* Lowercase "client", "resource server", "authorization server", and
"access token".
* Consistent update of section numbers for external references.
* Mentioned that this profile can also use the ACE alternative
workflow.
* Clarified that the client may ask for a new access token after the
old one becomes invalid.
* Enforced uniqueness pre-requirements on the client's group
membership before requesting an access token.
* Added checks on uniqueness of clients' group membership at the RS.
* Clarified the process of access right verification.
* Added fine-grained recommendations on storing multiple access
tokens bound to the same PoP key.
* Added guidelines on using multiple profiles.
* Fixes in the IANA considerations.
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* Editorial fixes and improvements.
C.2. Version -01 to -02
* CBOR diagnostic notation uses placeholders from a CDDL model.
* Renamed the claim 'contextId_input' to 'context_id'.
* Revised examples.
* Placeholders and early direction for dynamic update of access
rights.
* Added text on storing multiple access tokens per PoP key on the
RS.
* Fixes in the IANA considerations.
* Editorial fixes and improvements.
C.3. Version -00 to -01
* Deleting an access token does not delete the Group OSCORE Security
Context.
* Distinct computation of the PoP input when C and the AS use (D)TLS
1.2 or 1.3.
* Revised computation of the PoP input when C and the AS use OSCORE.
* Revised computation of the PoP evidence when the OSCORE group is a
pairwise-only group.
* Clarified requirements on the AS for verifying the PoP evidence.
* Renamed the TLS Exporter Label for computing the PoP input.
* Editorial fixes and improvements.
Acknowledgments
Ludwig Seitz contributed as a co-author of initial versions of this
document.
The authors sincerely thank Christian Amsüss, Tim Hollebeek, Benjamin
Kaduk, John Preuß Mattsson, Dave Robin, Jim Schaad, and Göran
Selander for their comments and feedback.
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The work on this document has been partly supported by the Sweden's
Innovation Agency VINNOVA and the Celtic-Next projects CRITISEC and
CYPRESS; and by the H2020 project SIFIS-Home (Grant agreement
952652).
Authors' Addresses
Marco Tiloca
RISE AB
Isafjordsgatan 22
SE-16440 Stockholm Kista
Sweden
Email: marco.tiloca@ri.se
Rikard Höglund
RISE AB
Isafjordsgatan 22
SE-16440 Stockholm Kista
Sweden
Email: rikard.hoglund@ri.se
Francesca Palombini
Ericsson AB
Torshamnsgatan 23
SE-16440 Stockholm Kista
Sweden
Email: francesca.palombini@ericsson.com
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