rfc9202.original   rfc9202.txt 
ACE Working Group S. Gerdes Internet Engineering Task Force (IETF) S. Gerdes
Internet-Draft O. Bergmann Request for Comments: 9202 O. Bergmann
Intended status: Standards Track C. Bormann Category: Standards Track C. Bormann
Expires: 6 December 2021 Universität Bremen TZI ISSN: 2070-1721 Universität Bremen TZI
G. Selander G. Selander
Ericsson AB Ericsson AB
L. Seitz L. Seitz
Combitech Combitech
4 June 2021 March 2022
Datagram Transport Layer Security (DTLS) Profile for Authentication and Datagram Transport Layer Security (DTLS) Profile for Authentication and
Authorization for Constrained Environments (ACE) Authorization for Constrained Environments (ACE)
draft-ietf-ace-dtls-authorize-18
Abstract Abstract
This specification defines a profile of the ACE framework that allows This specification defines a profile of the Authentication and
constrained servers to delegate client authentication and Authorization for Constrained Environments (ACE) framework that
allows constrained servers to delegate client authentication and
authorization. The protocol relies on DTLS version 1.2 for authorization. The protocol relies on DTLS version 1.2 for
communication security between entities in a constrained network communication security between entities in a constrained network
using either raw public keys or pre-shared keys. A resource- using either raw public keys or pre-shared keys. A resource-
constrained server can use this protocol to delegate management of constrained server can use this protocol to delegate management of
authorization information to a trusted host with less severe authorization information to a trusted host with less-severe
limitations regarding processing power and memory. limitations regarding processing power and memory.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This is an Internet Standards Track document.
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
material or to cite them other than as "work in progress." Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
This Internet-Draft will expire on 6 December 2021. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9202.
Copyright Notice Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Terminology
2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 4 2. Protocol Overview
3. Protocol Flow . . . . . . . . . . . . . . . . . . . . . . . . 6 3. Protocol Flow
3.1. Communication Between the Client and the Authorization 3.1. Communication between the Client and the Authorization
Server . . . . . . . . . . . . . . . . . . . . . . . . . 6 Server
3.2. Raw Public Key Mode . . . . . . . . . . . . . . . . . . . 7 3.2. Raw Public Key Mode
3.2.1. Access Token Retrieval from the Authorization 3.2.1. Access Token Retrieval from the Authorization Server
Server . . . . . . . . . . . . . . . . . . . . . . . 7 3.2.2. DTLS Channel Setup between the Client and Resource
3.2.2. DTLS Channel Setup Between Client and Resource Server
Server . . . . . . . . . . . . . . . . . . . . . . . 9 3.3. PreSharedKey Mode
3.3. PreSharedKey Mode . . . . . . . . . . . . . . . . . . . . 10 3.3.1. Access Token Retrieval from the Authorization Server
3.3.1. Access Token Retrieval from the Authorization 3.3.2. DTLS Channel Setup between the Client and Resource
Server . . . . . . . . . . . . . . . . . . . . . . . 11 Server
3.3.2. DTLS Channel Setup Between Client and Resource 3.4. Resource Access
Server . . . . . . . . . . . . . . . . . . . . . . . 15 4. Dynamic Update of Authorization Information
3.4. Resource Access . . . . . . . . . . . . . . . . . . . . . 17 5. Token Expiration
4. Dynamic Update of Authorization Information . . . . . . . . . 19 6. Secure Communication with an Authorization Server
5. Token Expiration . . . . . . . . . . . . . . . . . . . . . . 20 7. Security Considerations
6. Secure Communication with an Authorization Server . . . . . . 20 7.1. Reuse of Existing Sessions
7. Security Considerations . . . . . . . . . . . . . . . . . . . 21 7.2. Multiple Access Tokens
7.1. Reuse of Existing Sessions . . . . . . . . . . . . . . . 23 7.3. Out-of-Band Configuration
7.2. Multiple Access Tokens . . . . . . . . . . . . . . . . . 23 8. Privacy Considerations
7.3. Out-of-Band Configuration . . . . . . . . . . . . . . . . 23 9. IANA Considerations
8. Privacy Considerations . . . . . . . . . . . . . . . . . . . 24 10. References
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24 10.1. Normative References
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 25 10.2. Informative References
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 25 Acknowledgments
11.1. Normative References . . . . . . . . . . . . . . . . . . 25 Authors' Addresses
11.2. Informative References . . . . . . . . . . . . . . . . . 27
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 28
1. Introduction 1. Introduction
This specification defines a profile of the ACE framework This specification defines a profile of the ACE framework [RFC9200].
[I-D.ietf-ace-oauth-authz]. In this profile, a client and a resource In this profile, a client (C) and a resource server (RS) use the
server use CoAP [RFC7252] over DTLS version 1.2 [RFC6347] to Constrained Application Protocol (CoAP) [RFC7252] over DTLS version
communicate. This specification uses DTLS 1.2 terminology, but later 1.2 [RFC6347] to communicate. This specification uses DTLS 1.2
versions such as DTLS 1.3 can be used instead. The client obtains an terminology, but later versions such as DTLS 1.3 can be used instead.
access token, bound to a key (the proof-of-possession key), from an The client obtains an access token bound to a key (the proof-of-
authorization server to prove its authorization to access protected possession (PoP) key) from an authorization server (AS) to prove its
resources hosted by the resource server. Also, the client and the authorization to access protected resources hosted by the resource
resource server are provided by the authorization server with the server. Also, the client and the resource server are provided by the
necessary keying material to establish a DTLS session. The authorization server with the necessary keying material to establish
communication between client and authorization server may also be a DTLS session. The communication between the client and
secured with DTLS. This specification supports DTLS with Raw Public authorization server may also be secured with DTLS. This
Keys (RPK) [RFC7250] and with Pre-Shared Keys (PSK) [RFC4279]. How specification supports DTLS with raw public keys (RPKs) [RFC7250] and
token introspection [RFC7662] is performed between RS and AS is out with pre-shared keys (PSKs) [RFC4279]. How token introspection
of scope for this specification. [RFC7662] is performed between the RS and AS is out of scope for this
specification.
The ACE framework requires that client and server mutually The ACE framework requires that the client and server mutually
authenticate each other before any application data is exchanged. authenticate each other before any application data is exchanged.
DTLS enables mutual authentication if both client and server prove DTLS enables mutual authentication if both the client and server
their ability to use certain keying material in the DTLS handshake. prove their ability to use certain keying material in the DTLS
The authorization server assists in this process on the server side handshake. The authorization server assists in this process on the
by incorporating keying material (or information about keying server side by incorporating keying material (or information about
material) into the access token, which is considered a "proof of keying material) into the access token, which is considered a "proof-
possession" token. of-possession" token.
In the RPK mode, the client proves that it can use the RPK bound to In the RPK mode, the client proves that it can use the RPK bound to
the token and the server shows that it can use a certain RPK. the token and the server shows that it can use a certain RPK.
The resource server needs access to the token in order to complete The resource server needs access to the token in order to complete
this exchange. For the RPK mode, the client must upload the access this exchange. For the RPK mode, the client must upload the access
token to the resource server before initiating the handshake, as token to the resource server before initiating the handshake, as
described in Section 5.10.1 of the ACE framework described in Section 5.10.1 of the ACE framework [RFC9200].
[I-D.ietf-ace-oauth-authz].
In the PSK mode, client and server show with the DTLS handshake that In the PSK mode, the client and server show with the DTLS handshake
they can use the keying material that is bound to the access token. that they can use the keying material that is bound to the access
To transfer the access token from the client to the resource server, token. To transfer the access token from the client to the resource
the "psk_identity" parameter in the DTLS PSK handshake may be used server, the psk_identity parameter in the DTLS PSK handshake may be
instead of uploading the token prior to the handshake. used instead of uploading the token prior to the handshake.
As recommended in Section 5.8 of [I-D.ietf-ace-oauth-authz], this As recommended in Section 5.8 of [RFC9200], this specification uses
specification uses CBOR web tokens to convey claims within an access Concise Binary Object Representation (CBOR) web tokens to convey
token issued by the server. While other formats could be used as claims within an access token issued by the server. While other
well, those are out of scope for this document. formats could be used as well, those are out of scope for this
document.
1.1. Terminology 1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
Readers are expected to be familiar with the terms and concepts Readers are expected to be familiar with the terms and concepts
described in [I-D.ietf-ace-oauth-authz] and in described in [RFC9200] and [RFC9201].
[I-D.ietf-ace-oauth-params].
The authorization information (authz-info) resource refers to the The authorization information (authz-info) resource refers to the
authorization information endpoint as specified in authorization information endpoint, as specified in [RFC9200]. The
[I-D.ietf-ace-oauth-authz]. The term "claim" is used in this term claim is used in this document with the same semantics as in
document with the same semantics as in [I-D.ietf-ace-oauth-authz], [RFC9200], i.e., it denotes information carried in the access token
i.e., it denotes information carried in the access token or returned or returned from introspection.
from introspection.
2. Protocol Overview 2. Protocol Overview
The CoAP-DTLS profile for ACE specifies the transfer of The CoAP-DTLS profile for ACE specifies the transfer of
authentication information and, if necessary, authorization authentication information and, if necessary, authorization
information between the client (C) and the resource server (RS) information between the client (C) and the resource server (RS)
during setup of a DTLS session for CoAP messaging. It also specifies during setup of a DTLS session for CoAP messaging. It also specifies
how the client can use CoAP over DTLS to retrieve an access token how the client can use CoAP over DTLS to retrieve an access token
from the authorization server (AS) for a protected resource hosted on from the authorization server (AS) for a protected resource hosted on
the resource server. As specified in Section 6.7 of the resource server. As specified in Section 6.7 of [RFC9200], use
[I-D.ietf-ace-oauth-authz], use of DTLS for one or both of these of DTLS for one or both of these interactions is completely
interactions is completely independent. independent.
This profile requires the client to retrieve an access token for This profile requires the client to retrieve an access token for the
protected resource(s) it wants to access on the resource server as protected resource(s) it wants to access on the resource server, as
specified in [I-D.ietf-ace-oauth-authz]. Figure 1 shows the typical specified in [RFC9200]. Figure 1 shows the typical message flow in
message flow in this scenario (messages in square brackets are this scenario (messages in square brackets are optional):
optional):
-->
C RS AS C RS AS
| [---- Resource Request ------>]| | | [---- Resource Request ------>]| |
| | | | | |
| [<-AS Request Creation Hints-] | | | [<-AS Request Creation Hints-] | |
| | | | | |
| ------- Token Request ----------------------------> | | ------- Token Request ----------------------------> |
| | | | | |
| <---------------------------- Access Token --------- | | <---------------------------- Access Token --------- |
| + Access Information | | + Access Information |
Figure 1: Retrieving an Access Token Figure 1: Retrieving an Access Token
To determine the authorization server in charge of a resource hosted To determine the authorization server in charge of a resource hosted
at the resource server, the client can send an initial Unauthorized at the resource server, the client can send an initial Unauthorized
Resource Request message to the resource server. The resource server Resource Request message to the resource server. The resource server
then denies the request and sends an AS Request Creation Hints then denies the request and sends an AS Request Creation Hints
message containing the address of its authorization server back to message containing the address of its authorization server back to
the client as specified in Section 5.3 of [I-D.ietf-ace-oauth-authz]. the client, as specified in Section 5.3 of [RFC9200].
Once the client knows the authorization server's address, it can send Once the client knows the authorization server's address, it can send
an access token request to the token endpoint at the authorization an access token request to the token endpoint at the authorization
server as specified in [I-D.ietf-ace-oauth-authz]. As the access server, as specified in [RFC9200]. As the access token request and
token request as well as the response may contain confidential data, the response may contain confidential data, the communication between
the communication between the client and the authorization server the client and the authorization server must be confidentiality
must be confidentiality-protected and ensure authenticity. The protected and ensure authenticity. The client is expected to have
client is expected to have been registered at the authorization been registered at the authorization server, as outlined in Section 4
server as outlined in Section 4 of [I-D.ietf-ace-oauth-authz]. of [RFC9200].
The access token returned by the authorization server can then be The access token returned by the authorization server can then be
used by the client to establish a new DTLS session with the resource used by the client to establish a new DTLS session with the resource
server. When the client intends to use an asymmetric proof-of- server. When the client intends to use an asymmetric proof-of-
possession key in the DTLS handshake with the resource server, the possession key in the DTLS handshake with the resource server, the
client MUST upload the access token to the authz-info resource, i.e. client MUST upload the access token to the authz-info resource, i.e.,
the authz-info endpoint, on the resource server before starting the the authz-info endpoint, on the resource server before starting the
DTLS handshake, as described in Section 5.10.1 of DTLS handshake, as described in Section 5.10.1 of [RFC9200]. In case
[I-D.ietf-ace-oauth-authz]. In case the client uses a symmetric the client uses a symmetric proof-of-possession key in the DTLS
proof-of-possession key in the DTLS handshake, the procedure as above handshake, the procedure above MAY be used, or alternatively the
MAY be used, or alternatively, the access token MAY instead be access token MAY instead be transferred in the DTLS ClientKeyExchange
transferred in the DTLS ClientKeyExchange message (see message (see Section 3.3.2). In any case, DTLS MUST be used in a
Section 3.3.2). In any case, DTLS MUST be used in a mode that mode that provides replay protection.
provides replay protection.
Figure 2 depicts the common protocol flow for the DTLS profile after Figure 2 depicts the common protocol flow for the DTLS profile after
the client has retrieved the access token from the authorization the client has retrieved the access token from the authorization
server, AS. server (AS).
C RS AS C RS AS
| [--- Access Token ------>] | | | [--- Access Token ------>] | |
| | | | | |
| <== DTLS channel setup ==> | | | <== DTLS channel setup ==> | |
| | | | | |
| == Authorized Request ===> | | | == Authorized Request ===> | |
| | | | | |
| <=== Protected Resource == | | | <=== Protected Resource == | |
Figure 2: Protocol overview Figure 2: Protocol Overview
3. Protocol Flow 3. Protocol Flow
The following sections specify how CoAP is used to interchange The following sections specify how CoAP is used to interchange
access-related data between the resource server, the client and the access-related data between the resource server, the client, and the
authorization server so that the authorization server can provide the authorization server so that the authorization server can provide the
client and the resource server with sufficient information to client and the resource server with sufficient information to
establish a secure channel, and convey authorization information establish a secure channel and convey authorization information
specific for this communication relationship to the resource server. specific for this communication relationship to the resource server.
Section 3.1 describes how the communication between the client (C) Section 3.1 describes how the communication between the client (C)
and the authorization server (AS) must be secured. Depending on the and the authorization server (AS) must be secured. Depending on the
used CoAP security mode (see also Section 9 of [RFC7252], the Client- used CoAP security mode (see also Section 9 of [RFC7252]), the
to-AS request, AS-to-Client response and DTLS session establishment client-to-AS request, AS-to-client response, and DTLS session
carry slightly different information. Section 3.2 addresses the use establishment carry slightly different information. Section 3.2
of raw public keys while Section 3.3 defines how pre-shared keys are addresses the use of raw public keys, while Section 3.3 defines how
used in this profile. pre-shared keys are used in this profile.
3.1. Communication Between the Client and the Authorization Server 3.1. Communication between the Client and the Authorization Server
To retrieve an access token for the resource that the client wants to To retrieve an access token for the resource that the client wants to
access, the client requests an access token from the authorization access, the client requests an access token from the authorization
server. Before the client can request the access token, the client server. Before the client can request the access token, the client
and the authorization server MUST establish a secure communication and the authorization server MUST establish a secure communication
channel. This profile assumes that the keying material to secure channel. This profile assumes that the keying material to secure
this communication channel has securely been obtained either by this communication channel has securely been obtained either by
manual configuration or in an automated provisioning process. The manual configuration or in an automated provisioning process. The
following requirements in alignment with Section 6.5 of following requirements, in alignment with Section 6.5 of [RFC9200],
[I-D.ietf-ace-oauth-authz] therefore must be met: therefore must be met:
* The client MUST securely have obtained keying material to * The client MUST securely have obtained keying material to
communicate with the authorization server. communicate with the authorization server.
* Furthermore, the client MUST verify that the authorization server * Furthermore, the client MUST verify that the authorization server
is authorized to provide access tokens (including authorization is authorized to provide access tokens (including authorization
information) about the resource server to the client, and that information) about the resource server to the client and that this
this authorization information about the authorization server is authorization information about the authorization server is still
still valid. valid.
* Also, the authorization server MUST securely have obtained keying * Also, the authorization server MUST securely have obtained keying
material for the client, and obtained authorization rules approved material for the client and obtained authorization rules approved
by the resource owner (RO) concerning the client and the resource by the resource owner (RO) concerning the client and the resource
server that relate to this keying material. server that relate to this keying material.
The client and the authorization server MUST use their respective The client and the authorization server MUST use their respective
keying material for all exchanged messages. How the security keying material for all exchanged messages. How the security
association between the client and the authorization server is association between the client and the authorization server is
bootstrapped is not part of this document. The client and the bootstrapped is not part of this document. The client and the
authorization server must ensure the confidentiality, integrity and authorization server must ensure the confidentiality, integrity, and
authenticity of all exchanged messages within the ACE protocol. authenticity of all exchanged messages within the ACE protocol.
Section 6 specifies how communication with the authorization server Section 6 specifies how communication with the authorization server
is secured. is secured.
3.2. Raw Public Key Mode 3.2. Raw Public Key Mode
When the client uses raw public key authentication, the procedure is When the client uses raw public key authentication, the procedure is
as described in the following. as described in the following.
3.2.1. Access Token Retrieval from the Authorization Server 3.2.1. Access Token Retrieval from the Authorization Server
After the client and the authorization server mutually authenticated After the client and the authorization server mutually authenticated
each other and validated each other's authorization, the client sends each other and validated each other's authorization, the client sends
a token request to the authorization server's token endpoint. The a token request to the authorization server's token endpoint. The
client MUST add a "req_cnf" object carrying either its raw public key client MUST add a req_cnf object carrying either its raw public key
or a unique identifier for a public key that it has previously made or a unique identifier for a public key that it has previously made
known to the authorization server. It is RECOMMENDED that the client known to the authorization server. It is RECOMMENDED that the client
uses DTLS with the same keying material to secure the communication uses DTLS with the same keying material to secure the communication
with the authorization server, proving possession of the key as part with the authorization server, proving possession of the key as part
of the token request. Other mechanisms for proving possession of the of the token request. Other mechanisms for proving possession of the
key may be defined in the future. key may be defined in the future.
An example access token request from the client to the authorization An example access token request from the client to the authorization
server is depicted in Figure 3. server is depicted in Figure 3.
skipping to change at page 8, line 10 skipping to change at line 324
} }
} }
Figure 3: Access Token Request Example for RPK Mode Figure 3: Access Token Request Example for RPK Mode
The example shows an access token request for the resource identified The example shows an access token request for the resource identified
by the string "tempSensor4711" on the authorization server using a by the string "tempSensor4711" on the authorization server using a
raw public key. raw public key.
The authorization server MUST check if the client that it The authorization server MUST check if the client that it
communicates with is associated with the RPK in the "req_cnf" communicates with is associated with the RPK in the req_cnf parameter
parameter before issuing an access token to it. If the authorization before issuing an access token to it. If the authorization server
server determines that the request is to be authorized according to determines that the request is to be authorized according to the
the respective authorization rules, it generates an access token respective authorization rules, it generates an access token response
response for the client. The access token MUST be bound to the RPK for the client. The access token MUST be bound to the RPK of the
of the client by means of the "cnf" claim. client by means of the cnf claim.
The response MUST contain an "ace_profile" parameter if The response MUST contain an ace_profile parameter if the ace_profile
the"ace_profile" parameter in the request is empty, and MAY contain parameter in the request is empty and MAY contain this parameter
this parameter otherwise (see Section 5.8.2 of otherwise (see Section 5.8.2 of [RFC9200]). This parameter is set to
[I-D.ietf-ace-oauth-authz]). This parameter is set to "coap_dtls" to coap_dtls to indicate that this profile MUST be used for
indicate that this profile MUST be used for communication between the communication between the client and the resource server. The
client and the resource server. The response also contains an access response also contains an access token with information for the
token with information for the resource server about the client's resource server about the client's public key. The authorization
public key. The authorization server MUST return in its response the server MUST return in its response the parameter rs_cnf unless it is
parameter "rs_cnf" unless it is certain that the client already knows certain that the client already knows the public key of the resource
the public key of the resource server. The authorization server MUST server. The authorization server MUST ascertain that the RPK
ascertain that the RPK specified in "rs_cnf" belongs to the resource specified in rs_cnf belongs to the resource server that the client
server that the client wants to communicate with. The authorization wants to communicate with. The authorization server MUST protect the
server MUST protect the integrity of the access token such that the integrity of the access token such that the resource server can
resource server can detect unauthorized changes. If the access token detect unauthorized changes. If the access token contains
contains confidential data, the authorization server MUST also confidential data, the authorization server MUST also protect the
protect the confidentiality of the access token. confidentiality of the access token.
The client MUST ascertain that the access token response belongs to a The client MUST ascertain that the access token response belongs to a
certain previously sent access token request, as the request may certain, previously sent access token request, as the request may
specify the resource server with which the client wants to specify the resource server with which the client wants to
communicate. communicate.
An example access token response from the authorization server to the An example access token response from the authorization server to the
client is depicted in Figure 4. Here, the contents of the client is depicted in Figure 4. Here, the contents of the
"access_token" claim have been truncated to improve readability. The access_token claim have been truncated to improve readability. For
response comprises access information for the client that contains the client, the response comprises Access Information that contains
the server's public key in the "rs_cnf" parameter. Caching proxies the server's public key in the rs_cnf parameter. Caching proxies
process the Max-Age option in the CoAP response which has a default process the Max-Age option in the CoAP response, which has a default
value of 60 seconds (Section 5.6.1 of [RFC7252]). The authorization value of 60 seconds (Section 5.6.1 of [RFC7252]). The authorization
server SHOULD adjust the Max-Age option such that it does not exceed server SHOULD adjust the Max-Age option such that it does not exceed
the "expires_in" parameter to avoid stale responses. the expires_in parameter to avoid stale responses.
2.01 Created 2.01 Created
Content-Format: application/ace+cbor Content-Format: application/ace+cbor
Max-Age: 3560 Max-Age: 3560
Payload: Payload:
{ {
access_token : b64'SlAV32hkKG... access_token : b64'SlAV32hkKG...
(remainder of CWT omitted for brevity; (remainder of CWT omitted for brevity;
CWT contains the client's RPK in the cnf claim)', CWT contains the client's RPK in the cnf claim)',
expires_in : 3600, expires_in : 3600,
skipping to change at page 9, line 26 skipping to change at line 384
kty : EC2, kty : EC2,
crv : P-256, crv : P-256,
x : h'd7cc072de2205bdc1537...', x : h'd7cc072de2205bdc1537...',
y : h'f95e1d4b851a2cc80fff...' y : h'f95e1d4b851a2cc80fff...'
} }
} }
} }
Figure 4: Access Token Response Example for RPK Mode Figure 4: Access Token Response Example for RPK Mode
3.2.2. DTLS Channel Setup Between Client and Resource Server 3.2.2. DTLS Channel Setup between the Client and Resource Server
Before the client initiates the DTLS handshake with the resource Before the client initiates the DTLS handshake with the resource
server, the client MUST send a "POST" request containing the obtained server, the client MUST send a POST request containing the obtained
access token to the authz-info resource hosted by the resource access token to the authz-info resource hosted by the resource
server. After the client receives a confirmation that the resource server. After the client receives a confirmation that the resource
server has accepted the access token, it proceeds to establish a new server has accepted the access token, it proceeds to establish a new
DTLS channel with the resource server. The client MUST use its DTLS channel with the resource server. The client MUST use its
correct public key in the DTLS handshake. If the authorization correct public key in the DTLS handshake. If the authorization
server has specified a "cnf" field in the access token response, the server has specified a cnf field in the access token response, the
client MUST use this key. Otherwise, the client MUST use the public client MUST use this key. Otherwise, the client MUST use the public
key that it specified in the "req_cnf" of the access token request. key that it specified in the req_cnf of the access token request.
The client MUST specify this public key in the SubjectPublicKeyInfo The client MUST specify this public key in the SubjectPublicKeyInfo
structure of the DTLS handshake as described in [RFC7250]. structure of the DTLS handshake, as described in [RFC7250].
If the client does not have the keying material belonging to the If the client does not have the keying material belonging to the
public key, the client MAY try to send an access token request to the public key, the client MAY try to send an access token request to the
AS where it specifies its public key in the "req_cnf" parameter. If AS, where it specifies its public key in the req_cnf parameter. If
the AS still specifies a public key in the response that the client the AS still specifies a public key in the response that the client
does not have, the client SHOULD re-register with the authorization does not have, the client SHOULD re-register with the authorization
server to establish a new client public key. This process is out of server to establish a new client public key. This process is out of
scope for this document. scope for this document.
To be consistent with [RFC7252], which allows for shortened MAC tags To be consistent with [RFC7252], which allows for shortened MAC tags
in constrained environments, an implementation that supports the RPK in constrained environments, an implementation that supports the RPK
mode of this profile MUST at least support the cipher suite mode of this profile MUST at least support the cipher suite
TLS_ECDHE_ECDSA_WITH_AES_128_CCM_8 [RFC7251]. As discussed in TLS_ECDHE_ECDSA_WITH_AES_128_CCM_8 [RFC7251]. As discussed in
[RFC7748], new Elliptic Curve Cryptography (ECC) curves have been
[RFC7748], new ECC curves have been defined recently that are defined recently that are considered superior to the so-called NIST
considered superior to the so-called NIST curves. Implementations of curves. Implementations of this profile MUST therefore implement
this profile therefore MUST implement support for curve25519 (cf. support for curve25519 (cf. [RFC8032], [RFC8422]), as this curve is
[RFC8032], [RFC8422]) as this curve said to be efficient and less said to be efficient and less dangerous, regarding implementation
dangerous regarding implementation errors than the secp256r1 curve errors, than the secp256r1 curve mandated in [RFC7252].
mandated in [RFC7252].
The resource server MUST check if the access token is still valid, if The resource server MUST check if the access token is still valid, if
the resource server is the intended destination (i.e., the audience) the resource server is the intended destination (i.e., the audience)
of the token, and if the token was issued by an authorized of the token, and if the token was issued by an authorized
authorization server (see also section 5.10.1.1 of authorization server (see also Section 5.10.1.1 of [RFC9200]). The
[I-D.ietf-ace-oauth-authz]). The access token is constructed by the access token is constructed by the authorization server such that the
authorization server such that the resource server can associate the resource server can associate the access token with the client's
access token with the Client's public key. The "cnf" claim MUST public key. The cnf claim MUST contain either the client's RPK or,
contain either the client's RPK or, if the key is already known by if the key is already known by the resource server (e.g., from
the resource server (e.g., from previous communication), a reference previous communication), a reference to this key. If the
to this key. If the authorization server has no certain knowledge authorization server has no certain knowledge that the client's key
that the Client's key is already known to the resource server, the is already known to the resource server, the client's public key MUST
Client's public key MUST be included in the access token's "cnf" be included in the access token's cnf parameter. If CBOR web tokens
parameter. If CBOR web tokens [RFC8392] are used (as recommended in [RFC8392] are used (as recommended in [RFC9200]), keys MUST be
[I-D.ietf-ace-oauth-authz]), keys MUST be encoded as specified in encoded, as specified in [RFC8747]. A resource server MUST have the
[RFC8747]. A resource server MUST have the capacity to store one capacity to store one access token for every proof-of-possession key
access token for every proof-of-possession key of every authorized of every authorized client.
client.
The raw public key used in the DTLS handshake with the client MUST The raw public key used in the DTLS handshake with the client MUST
belong to the resource server. If the resource server has several belong to the resource server. If the resource server has several
raw public keys, it needs to determine which key to use. The raw public keys, it needs to determine which key to use. The
authorization server can help with this decision by including a "cnf" authorization server can help with this decision by including a cnf
parameter in the access token that is associated with this parameter in the access token that is associated with this
communication. In this case, the resource server MUST use the communication. In this case, the resource server MUST use the
information from the "cnf" field to select the proper keying information from the cnf field to select the proper keying material.
material.
Thus, the handshake only finishes if the client and the resource Thus, the handshake only finishes if the client and the resource
server are able to use their respective keying material. server are able to use their respective keying material.
3.3. PreSharedKey Mode 3.3. PreSharedKey Mode
When the client uses pre-shared key authentication, the procedure is When the client uses pre-shared key authentication, the procedure is
as described in the following. as described in the following.
3.3.1. Access Token Retrieval from the Authorization Server 3.3.1. Access Token Retrieval from the Authorization Server
To retrieve an access token for the resource that the client wants to To retrieve an access token for the resource that the client wants to
access, the client MAY include a "cnf" object carrying an identifier access, the client MAY include a cnf object carrying an identifier
for a symmetric key in its access token request to the authorization for a symmetric key in its access token request to the authorization
server. This identifier can be used by the authorization server to server. This identifier can be used by the authorization server to
determine the shared secret to construct the proof-of-possession determine the shared secret to construct the proof-of-possession
token. The authorization server MUST check if the identifier refers token. The authorization server MUST check if the identifier refers
to a symmetric key that was previously generated by the authorization to a symmetric key that was previously generated by the authorization
server as a shared secret for the communication between this client server as a shared secret for the communication between this client
and the resource server. If no such symmetric key was found, the and the resource server. If no such symmetric key was found, the
authorization server MUST generate a new symmetric key that is authorization server MUST generate a new symmetric key that is
returned in its response to the client. returned in its response to the client.
The authorization server MUST determine the authorization rules for The authorization server MUST determine the authorization rules for
the client it communicates with as defined by the resource owner and the client it communicates with, as defined by the resource owner,
generate the access token accordingly. If the authorization server and generate the access token accordingly. If the authorization
authorizes the client, it returns an AS-to-Client response. If the server authorizes the client, it returns an AS-to-client response.
"ace_profile" parameter is present, it is set to "coap_dtls". The If the ace_profile parameter is present, it is set to coap_dtls. The
authorization server MUST ascertain that the access token is authorization server MUST ascertain that the access token is
generated for the resource server that the client wants to generated for the resource server that the client wants to
communicate with. Also, the authorization server MUST protect the communicate with. Also, the authorization server MUST protect the
integrity of the access token to ensure that the resource server can integrity of the access token to ensure that the resource server can
detect unauthorized changes. If the token contains confidential data detect unauthorized changes. If the token contains confidential
such as the symmetric key, the confidentiality of the token MUST also data, such as the symmetric key, the confidentiality of the token
be protected. Depending on the requested token type and algorithm in MUST also be protected. Depending on the requested token type and
the access token request, the authorization server adds access algorithm in the access token request, the authorization server adds
Information to the response that provides the client with sufficient Access Information to the response that provides the client with
information to setup a DTLS channel with the resource server. The sufficient information to set up a DTLS channel with the resource
authorization server adds a "cnf" parameter to the access information server. The authorization server adds a cnf parameter to the Access
carrying a "COSE_Key" object that informs the client about the shared Information carrying a COSE_Key object that informs the client about
secret that is to be used between the client and the resource server. the shared secret that is to be used between the client and the
To convey the same secret to the resource server, the authorization resource server. To convey the same secret to the resource server,
server can include it directly in the access token by means of the the authorization server can include it directly in the access token
"cnf" claim or provide sufficient information to enable the resource by means of the cnf claim or provide sufficient information to enable
server to derive the shared secret from the access token. As an the resource server to derive the shared secret from the access
alternative, the resource server MAY use token introspection to token. As an alternative, the resource server MAY use token
retrieve the keying material for this access token directly from the introspection to retrieve the keying material for this access token
authorization server. directly from the authorization server.
An example access token request for an access token with a symmetric An example access token request for an access token with a symmetric
proof-of-possession key is illustrated in Figure 5. proof-of-possession key is illustrated in Figure 5.
POST coaps://as.example.com/token POST coaps://as.example.com/token
Content-Format: application/ace+cbor Content-Format: application/ace+cbor
Payload: Payload:
{ {
audience : "smokeSensor1807", audience : "smokeSensor1807",
} }
Figure 5: Example Access Token Request, (implicit) symmetric PoP-key Figure 5: Example Access Token Request, (Implicit) Symmetric PoP Key
A corresponding example access token response is illustrated in A corresponding example access token response is illustrated in
Figure 6. In this example, the authorization server returns a 2.01 Figure 6. In this example, the authorization server returns a 2.01
response containing a new access token (truncated to improve response containing a new access token (truncated to improve
readability) and information for the client, including the symmetric readability) and information for the client, including the symmetric
key in the cnf claim. The information is transferred as a CBOR data key in the cnf claim. The information is transferred as a CBOR data
structure as specified in [I-D.ietf-ace-oauth-authz]. structure as specified in [RFC9200].
2.01 Created 2.01 Created
Content-Format: application/ace+cbor Content-Format: application/ace+cbor
Max-Age: 85800 Max-Age: 85800
Payload: Payload:
{ {
access_token : h'd08343a10... access_token : h'd08343a10...
(remainder of CWT omitted for brevity) (remainder of CWT omitted for brevity)
token_type : PoP, token_type : PoP,
expires_in : 86400, expires_in : 86400,
profile : coap_dtls, profile : coap_dtls,
cnf : { cnf : {
COSE_Key : { COSE_Key : {
kty : symmetric, kty : symmetric,
kid : h'3d027833fc6267ce', kid : h'3d027833fc6267ce',
k : h'73657373696f6e6b6579' k : h'73657373696f6e6b6579'
} }
} }
} }
Figure 6: Example Access Token Response, symmetric PoP-key Figure 6: Example Access Token Response, Symmetric PoP Key
The access token also comprises a "cnf" claim. This claim usually The access token also comprises a cnf claim. This claim usually
contains a "COSE_Key" object [RFC8152] that carries either the contains a COSE_Key object [RFC8152] that carries either the
symmetric key itself or a key identifier that can be used by the symmetric key itself or a key identifier that can be used by the
resource server to determine the secret key it shares with the resource server to determine the secret key it shares with the
client. If the access token carries a symmetric key, the access client. If the access token carries a symmetric key, the access
token MUST be encrypted using a "COSE_Encrypt0" structure (see token MUST be encrypted using a COSE_Encrypt0 structure (see
section 7.1 of [RFC8392]). The authorization server MUST use the Section 7.1 of [RFC8392]). The authorization server MUST use the
keying material shared with the resource server to encrypt the token. keying material shared with the resource server to encrypt the token.
The "cnf" structure in the access token is provided in Figure 7. The cnf structure in the access token is provided in Figure 7.
cnf : { cnf : {
COSE_Key : { COSE_Key : {
kty : symmetric, kty : symmetric,
kid : h'3d027833fc6267ce' kid : h'3d027833fc6267ce'
} }
} }
Figure 7: Access Token without Keying Material Figure 7: Access Token without Keying Material
A response that declines any operation on the requested resource is A response that declines any operation on the requested resource is
constructed according to Section 5.2 of [RFC6749], (cf. constructed according to Section 5.2 of [RFC6749] (cf. Section 5.8.3
Section 5.8.3. of [I-D.ietf-ace-oauth-authz]). Figure 8 shows an of [RFC9200]). Figure 8 shows an example for a request that has been
example for a request that has been rejected due to invalid request rejected due to invalid request parameters.
parameters.
4.00 Bad Request 4.00 Bad Request
Content-Format: application/ace+cbor Content-Format: application/ace+cbor
Payload: Payload:
{ {
error : invalid_request error : invalid_request
} }
Figure 8: Example Access Token Response With Reject Figure 8: Example Access Token Response with Reject
The method for how the resource server determines the symmetric key The method for how the resource server determines the symmetric key
from an access token containing only a key identifier is application- from an access token containing only a key identifier is application
specific; the remainder of this section provides one example. specific; the remainder of this section provides one example.
The authorization server and the resource server are assumed to share The authorization server and the resource server are assumed to share
a key derivation key used to derive the symmetric key shared with the a key derivation key used to derive the symmetric key shared with the
client from the key identifier in the access token. The key client from the key identifier in the access token. The key
derivation key may be derived from some other secret key shared derivation key may be derived from some other secret key shared
between the authorization server and the resource server. This key between the authorization server and the resource server. This key
needs to be securely stored and processed in the same way as the key needs to be securely stored and processed in the same way as the key
used to protect the communication between the authorization server used to protect the communication between the authorization server
and the resource server. and the resource server.
Knowledge of the symmetric key shared with the client must not reveal Knowledge of the symmetric key shared with the client must not reveal
any information about the key derivation key or other secret keys any information about the key derivation key or other secret keys
shared between the authorization server and resource server. shared between the authorization server and resource server.
In order to generate a new symmetric key to be used by client and In order to generate a new symmetric key to be used by the client and
resource server, the authorization server generates a new key resource server, the authorization server generates a new key
identifier which MUST be unique among all key identifiers used by the identifier that MUST be unique among all key identifiers used by the
authorization server for this resource server. The authorization authorization server for this resource server. The authorization
server then uses the key derivation key shared with the resource server then uses the key derivation key shared with the resource
server to derive the symmetric key as specified below. Instead of server to derive the symmetric key, as specified below. Instead of
providing the keying material in the access token, the authorization providing the keying material in the access token, the authorization
server includes the key identifier in the "kid" parameter, see server includes the key identifier in the kid parameter (see
Figure 7. This key identifier enables the resource server to Figure 7). This key identifier enables the resource server to
calculate the symmetric key used for the communication with the calculate the symmetric key used for the communication with the
client using the key derivation key and a KDF to be defined by the client using the key derivation key and a key derivation function
application, for example HKDF-SHA-256. The key identifier picked by (KDF) to be defined by the application, for example, HKDF-SHA-256.
the authorization server MUST be unique for each access token where a The key identifier picked by the authorization server MUST be unique
unique symmetric key is required. for each access token where a unique symmetric key is required.
In this example, HKDF consists of the composition of the HKDF-Extract In this example, the HMAC-based key derivation function (HKDF)
and HKDF-Expand steps [RFC5869]. The symmetric key is derived from consists of the composition of the HKDF-Extract and HKDF-Expand steps
the key identifier, the key derivation key and other data: [RFC5869]. The symmetric key is derived from the key identifier, the
key derivation key, and other data:
OKM = HKDF(salt, IKM, info, L), OKM = HKDF(salt, IKM, info, L),
where: where:
* OKM, the output keying material, is the derived symmetric key * OKM, the output keying material, is the derived symmetric key
* salt is the empty byte string * salt is the empty byte string
* IKM, the input keying material, is the key derivation key as * IKM, the input keying material, is the key derivation key, as
defined above defined above
* info is the serialization of a CBOR array consisting of * info is the serialization of a CBOR array consisting of [RFC8610]:
([RFC8610]):
info = [ info = [
type : tstr, type : tstr,
L : uint, L : uint,
access_token: bytes access_token: bytes
] ]
where: where:
* type is set to the constant text string "ACE-CoAP-DTLS-key- - type is set to the constant text string "ACE-CoAP-DTLS-key-
derivation", derivation"
* L is the size of the symmetric key in bytes, - L is the size of the symmetric key in bytes
* access_token is the content of the "access_token" field as - access_token is the content of the access_token field, as
transferred from the authorization server to the resource server. transferred from the authorization server to the resource
server.
All CBOR data types are encoded in CBOR using preferred serialization All CBOR data types are encoded in CBOR using preferred serialization
and deterministic encoding as specified in Section 4 of [RFC8949]. and deterministic encoding, as specified in Section 4 of [RFC8949].
This implies in particular that the "type" and "L" components use the In particular, this implies that the type and L components use the
minimum length encoding. The content of the "access_token" field is minimum length encoding. The content of the access_token field is
treated as opaque data for the purpose of key derivation. treated as opaque data for the purpose of key derivation.
Use of a unique (per resource server) "kid" and the use of a key Use of a unique (per-resource-server) kid and the use of a key
derivation IKM that MUST be unique per authorization server/resource derivation IKM that MUST be unique per AS/RS pair, as specified
server pair as specified above will ensure that the derived key is above, will ensure that the derived key is not shared across multiple
not shared across multiple clients. However, to provide variation in clients. However, to provide variation in the derived key across
the derived key across different tokens used by the same client, it different tokens used by the same client, it is additionally
is additionally RECOMMENDED to include the "iat" claim and either the RECOMMENDED to include the "iat" claim and either the "exp" or "exi"
"exp" or "exi" claims in the access token. claims in the access token.
3.3.2. DTLS Channel Setup Between Client and Resource Server 3.3.2. DTLS Channel Setup between the Client and Resource Server
When a client receives an access token response from an authorization When a client receives an access token response from an authorization
server, the client MUST check if the access token response is bound server, the client MUST check if the access token response is bound
to a certain previously sent access token request, as the request may to a certain, previously sent access token request, as the request
specify the resource server with which the client wants to may specify the resource server with which the client wants to
communicate. communicate.
The client checks if the payload of the access token response The client checks if the payload of the access token response
contains an "access_token" parameter and a "cnf" parameter. With contains an access_token parameter and a cnf parameter. With this
this information the client can initiate the establishment of a new information, the client can initiate the establishment of a new DTLS
DTLS channel with a resource server. To use DTLS with pre-shared channel with a resource server. To use DTLS with pre-shared keys,
keys, the client follows the PSK key exchange algorithm specified in the client follows the PSK key exchange algorithm specified in
Section 2 of [RFC4279] using the key conveyed in the "cnf" parameter Section 2 of [RFC4279], using the key conveyed in the cnf parameter
of the AS response as PSK when constructing the premaster secret. To of the AS response as a PSK when constructing the premaster secret.
be consistent with the recommendations in [RFC7252], a client in the To be consistent with the recommendations in [RFC7252], a client in
PSK mode MUST support the cipher suite TLS_PSK_WITH_AES_128_CCM_8 the PSK mode MUST support the cipher suite TLS_PSK_WITH_AES_128_CCM_8
[RFC6655]. [RFC6655].
In PreSharedKey mode, the knowledge of the shared secret by the In PreSharedKey mode, the knowledge of the shared secret by the
client and the resource server is used for mutual authentication client and the resource server is used for mutual authentication
between both peers. Therefore, the resource server must be able to between both peers. Therefore, the resource server must be able to
determine the shared secret from the access token. Following the determine the shared secret from the access token. Following the
general ACE authorization framework, the client can upload the access general ACE authorization framework, the client can upload the access
token to the resource server's authz-info resource before starting token to the resource server's authz-info resource before starting
the DTLS handshake. The client then needs to indicate during the the DTLS handshake. The client then needs to indicate during the
DTLS handshake which previously uploaded access token it intends to DTLS handshake which previously uploaded access token it intends to
use. To do so, it MUST create a "COSE_Key" structure with the "kid" use. To do so, it MUST create a COSE_Key structure with the kid that
that was conveyed in the "rs_cnf" claim in the token response from was conveyed in the rs_cnf claim in the token response from the
the authorization server and the key type "symmetric". This authorization server and the key type symmetric. This structure then
structure then is included as the only element in the "cnf" structure is included as the only element in the cnf structure whose CBOR
whose CBOR serialization is used as value for "psk_identity" as shown serialization is used as value for psk_identity, as shown in
in Figure 9. Figure 9.
{ cnf : { { cnf : {
COSE_Key : { COSE_Key : {
kty: symmetric, kty: symmetric,
kid : h'3d027833fc6267ce' kid : h'3d027833fc6267ce'
} }
} }
} }
Figure 9: Access token containing a single kid parameter Figure 9: Access Token Containing a Single kid Parameter
The actual CBOR serialization for the data structure from Figure 9 as The actual CBOR serialization for the data structure from Figure 9 as
sequence of bytes in hexadecimal notation will be: a sequence of bytes in hexadecimal notation will be:
A1 08 A1 01 A2 01 04 02 48 3D 02 78 33 FC 62 67 CE A1 08 A1 01 A2 01 04 02 48 3D 02 78 33 FC 62 67 CE
As an alternative to the access token upload, the client can provide As an alternative to the access token upload, the client can provide
the most recent access token in the "psk_identity" field of the the most recent access token in the psk_identity field of the
ClientKeyExchange message. To do so, the client MUST treat the ClientKeyExchange message. To do so, the client MUST treat the
contents of the "access_token" field from the AS-to-Client response contents of the access_token field from the AS-to-client response as
as opaque data as specified in Section 4.2 of [RFC7925] and not opaque data, as specified in Section 4.2 of [RFC7925], and not
perform any re-coding. This allows the resource server to retrieve perform any recoding. This allows the resource server to retrieve
the shared secret directly from the "cnf" claim of the access token. the shared secret directly from the cnf claim of the access token.
DTLS 1.3 does not use the ClientKeyExchange message; for DTLS 1.3,
the access token is placed in the identity field of a PSKIdentity
within the PreSharedKeyExtension of the ClientHello.
If a resource server receives a ClientKeyExchange message that If a resource server receives a ClientKeyExchange message that
contains a "psk_identity" with a length greater than zero, it MUST contains a psk_identity with a length greater than zero, it MUST
parse the contents of the "psk_identity" field as CBOR data structure parse the contents of the psk_identity field as a CBOR data structure
and process the contents as following: and process the contents as following:
* If the data contains a "cnf" field with a "COSE_Key" structure * If the data contains a cnf field with a COSE_Key structure with a
with a "kid", the resource server continues the DTLS handshake kid, the resource server continues the DTLS handshake with the
with the associated key that corresponds to this kid. associated key that corresponds to this kid.
* If the data comprises additional CWT information, this information * If the data comprises additional CWT information, this information
must be stored as an access token for this DTLS association before must be stored as an access token for this DTLS association before
continuing with the DTLS handshake. continuing with the DTLS handshake.
If the contents of the "psk_identity" do not yield sufficient If the contents of the psk_identity do not yield sufficient
information to select a valid access token for the requesting client, information to select a valid access token for the requesting client,
the resource server aborts the DTLS handshake with an the resource server aborts the DTLS handshake with an
"illegal_parameter" alert. illegal_parameter alert.
When the resource server receives an access token, it MUST check if When the resource server receives an access token, it MUST check if
the access token is still valid, if the resource server is the the access token is still valid, if the resource server is the
intended destination (i.e., the audience of the token), and if the intended destination (i.e., the audience of the token), and if the
token was issued by an authorized authorization server. This token was issued by an authorized authorization server. This
specification implements access tokens as proof-of-possession tokens. specification implements access tokens as proof-of-possession tokens.
Therefore, the access token is bound to a symmetric PoP key that is Therefore, the access token is bound to a symmetric PoP key that is
used as shared secret between the client and the resource server. A used as a shared secret between the client and the resource server.
resource server MUST have the capacity to store one access token for A resource server MUST have the capacity to store one access token
every proof-of-possession key of every authorized client. The for every proof-of-possession key of every authorized client. The
resource server may use token introspection [RFC7662] on the access resource server may use token introspection [RFC7662] on the access
token to retrieve more information about the specific token. The use token to retrieve more information about the specific token. The use
of introspection is out of scope for this specification. of introspection is out of scope for this specification.
While the client can retrieve the shared secret from the contents of While the client can retrieve the shared secret from the contents of
the "cnf" parameter in the AS-to-Client response, the resource server the cnf parameter in the AS-to-client response, the resource server
uses the information contained in the "cnf" claim of the access token uses the information contained in the cnf claim of the access token
to determine the actual secret when no explicit "kid" was provided in to determine the actual secret when no explicit kid was provided in
the "psk_identity" field. If key derivation is used, the "cnf" claim the psk_identity field. If key derivation is used, the cnf claim
MUST contain a "kid" parameter to be used by the server as the IKM MUST contain a kid parameter to be used by the server as the IKM for
for key derivation as described above. key derivation, as described above.
3.4. Resource Access 3.4. Resource Access
Once a DTLS channel has been established as described in Section 3.2 Once a DTLS channel has been established, as described in Sections
or Section 3.3, respectively, the client is authorized to access 3.2 and 3.3, respectively, the client is authorized to access
resources covered by the access token it has uploaded to the authz- resources covered by the access token it has uploaded to the authz-
info resource hosted by the resource server. info resource that is hosted by the resource server.
With the successful establishment of the DTLS channel, the client and With the successful establishment of the DTLS channel, the client and
the resource server have proven that they can use their respective the resource server have proven that they can use their respective
keying material. An access token that is bound to the client's keying material. An access token that is bound to the client's
keying material is associated with the channel. According to keying material is associated with the channel. According to
Section 5.10.1 of [I-D.ietf-ace-oauth-authz], there should be only Section 5.10.1 of [RFC9200], there should be only one access token
one access token for each client. New access tokens issued by the for each client. New access tokens issued by the authorization
authorization server SHOULD replace previously issued access tokens server SHOULD replace previously issued access tokens for the
for the respective client. The resource server therefore needs a respective client. The resource server therefore needs a common
common understanding with the authorization server how access tokens understanding with the authorization server about how access tokens
are ordered. The authorization server may, e.g., specify a "cti" are ordered. The authorization server may, e.g., specify a cti claim
claim for the access token (see Section 5.9.4 of for the access token (see Section 5.9.4 of [RFC9200]) to employ a
[I-D.ietf-ace-oauth-authz]) to employ a strict order. strict order.
Any request that the resource server receives on a DTLS channel that Any request that the resource server receives on a DTLS channel that
is tied to an access token via its keying material MUST be checked is tied to an access token via its keying material MUST be checked
against the authorization rules that can be determined with the against the authorization rules that can be determined with the
access token. The resource server MUST check for every request if access token. The resource server MUST check for every request if
the access token is still valid. If the token has expired, the the access token is still valid. If the token has expired, the
resource server MUST remove it. Incoming CoAP requests that are not resource server MUST remove it. Incoming CoAP requests that are not
authorized with respect to any access token that is associated with authorized with respect to any access token that is associated with
the client MUST be rejected by the resource server with 4.01 the client MUST be rejected by the resource server with a 4.01
response. The response SHOULD include AS Request Creation Hints as response. The response SHOULD include AS Request Creation Hints, as
described in Section 5.2 of [I-D.ietf-ace-oauth-authz]. described in Section 5.2 of [RFC9200].
The resource server MUST NOT accept an incoming CoAP request as The resource server MUST NOT accept an incoming CoAP request as
authorized if any of the following fails: authorized if any of the following fails:
1. The message was received on a secure channel that has been 1. The message was received on a secure channel that has been
established using the procedure defined in this document. established using the procedure defined in this document.
2. The authorization information tied to the sending client is 2. The authorization information tied to the sending client is
valid. valid.
3. The request is destined for the resource server. 3. The request is destined for the resource server.
4. The resource URI specified in the request is covered by the 4. The resource URI specified in the request is covered by the
authorization information. authorization information.
5. The request method is an authorized action on the resource with 5. The request method is an authorized action on the resource with
respect to the authorization information. respect to the authorization information.
Incoming CoAP requests received on a secure DTLS channel that are not Incoming CoAP requests received on a secure DTLS channel that are not
thus authorized MUST be rejected according to Section 5.10.1.1 of thus authorized MUST be rejected according to Section 5.10.1.1 of
[I-D.ietf-ace-oauth-authz] [RFC9200]:
1. with response code 4.03 (Forbidden) when the resource URI 1. with response code 4.03 (Forbidden) when the resource URI
specified in the request is not covered by the authorization specified in the request is not covered by the authorization
information, and information and
2. with response code 4.05 (Method Not Allowed) when the resource 2. with response code 4.05 (Method Not Allowed) when the resource
URI specified in the request covered by the authorization URI specified in the request is covered by the authorization
information but not the requested action. information but not the requested action.
The client MUST ascertain that its keying material is still valid The client MUST ascertain that its keying material is still valid
before sending a request or processing a response. If the client before sending a request or processing a response. If the client
recently has updated the access token (see Section 4), it must be recently has updated the access token (see Section 4), it must be
prepared that its request is still handled according to the previous prepared that its request is still handled according to the previous
authorization rules as there is no strict ordering between access authorization rules, as there is no strict ordering between access
token uploads and resource access messages. See also Section 7.2 for token uploads and resource access messages. See also Section 7.2 for
a discussion of access token processing. a discussion of access token processing.
If the client gets an error response containing AS Request Creation If the client gets an error response containing AS Request Creation
Hints (cf. Section 5.3 of [I-D.ietf-ace-oauth-authz] as response to Hints (cf. Section 5.3 of [RFC9200]) as a response to its requests,
its requests, it SHOULD request a new access token from the it SHOULD request a new access token from the authorization server in
authorization server in order to continue communication with the order to continue communication with the resource server.
resource server.
Unauthorized requests that have been received over a DTLS session Unauthorized requests that have been received over a DTLS session
SHOULD be treated as non-fatal by the resource server, i.e., the DTLS SHOULD be treated as nonfatal by the resource server, i.e., the DTLS
session SHOULD be kept alive until the associated access token has session SHOULD be kept alive until the associated access token has
expired. expired.
4. Dynamic Update of Authorization Information 4. Dynamic Update of Authorization Information
Resource servers must only use a new access token to update the Resource servers must only use a new access token to update the
authorization information for a DTLS session if the keying material authorization information for a DTLS session if the keying material
that is bound to the token is the same that was used in the DTLS that is bound to the token is the same that was used in the DTLS
handshake. By associating the access tokens with the identifier of handshake. By associating the access tokens with the identifier of
an existing DTLS session, the authorization information can be an existing DTLS session, the authorization information can be
updated without changing the cryptographic keys for the DTLS updated without changing the cryptographic keys for the DTLS
communication between the client and the resource server, i.e. an communication between the client and the resource server, i.e., an
existing session can be used with updated permissions. existing session can be used with updated permissions.
The client can therefore update the authorization information stored The client can therefore update the authorization information stored
at the resource server at any time without changing an established at the resource server at any time without changing an established
DTLS session. To do so, the client requests a new access token from DTLS session. To do so, the client requests a new access token from
the authorization server for the intended action on the respective the authorization server for the intended action on the respective
resource and uploads this access token to the authz-info resource on resource and uploads this access token to the authz-info resource on
the resource server. the resource server.
Figure 10 depicts the message flow where the client requests a new Figure 10 depicts the message flow where the client requests a new
access token after a security association between the client and the access token after a security association between the client and the
resource server has been established using this protocol. If the resource server has been established using this protocol. If the
client wants to update the authorization information, the token client wants to update the authorization information, the token
request MUST specify the key identifier of the proof-of-possession request MUST specify the key identifier of the proof-of-possession
key used for the existing DTLS channel between the client and the key used for the existing DTLS channel between the client and the
resource server in the "kid" parameter of the Client-to-AS request. resource server in the kid parameter of the client-to-AS request.
The authorization server MUST verify that the specified "kid" denotes The authorization server MUST verify that the specified kid denotes a
a valid verifier for a proof-of-possession token that has previously valid verifier for a proof-of-possession token that has previously
been issued to the requesting client. Otherwise, the Client-to-AS been issued to the requesting client. Otherwise, the client-to-AS
request MUST be declined with the error code "unsupported_pop_key" as request MUST be declined with the error code unsupported_pop_key, as
defined in Section 5.8.3 of [I-D.ietf-ace-oauth-authz]. defined in Section 5.8.3 of [RFC9200].
When the authorization server issues a new access token to update When the authorization server issues a new access token to update
existing authorization information, it MUST include the specified existing authorization information, it MUST include the specified kid
"kid" parameter in this access token. A resource server MUST replace parameter in this access token. A resource server MUST replace the
the authorization information of any existing DTLS session that is authorization information of any existing DTLS session that is
identified by this key identifier with the updated authorization identified by this key identifier with the updated authorization
information. information.
C RS AS C RS AS
| <===== DTLS channel =====> | | | <===== DTLS channel =====> | |
| + Access Token | | | + Access Token | |
| | | | | |
| --- Token Request ----------------------------> | | --- Token Request ----------------------------> |
| | | | | |
| <---------------------------- New Access Token - | | <---------------------------- New Access Token - |
skipping to change at page 20, line 26 skipping to change at line 883
| | | | | |
| == Authorized Request ===> | | | == Authorized Request ===> | |
| | | | | |
| <=== Protected Resource == | | | <=== Protected Resource == | |
Figure 10: Overview of Dynamic Update Operation Figure 10: Overview of Dynamic Update Operation
5. Token Expiration 5. Token Expiration
The resource server MUST delete access tokens that are no longer The resource server MUST delete access tokens that are no longer
valid. DTLS associations that have been setup in accordance with valid. DTLS associations that have been set up in accordance with
this profile are always tied to specific tokens (which may be this profile are always tied to specific tokens (which may be
exchanged with a dynamic update as described in Section 4). As exchanged with a dynamic update, as described in Section 4). As
tokens may become invalid at any time (e.g., because they have tokens may become invalid at any time (e.g., because they have
expired), the association may become useless at some point. A expired), the association may become useless at some point. A
resource server therefore MUST terminate existing DTLS association resource server therefore MUST terminate existing DTLS association
after the last access token associated with this association has after the last access token associated with this association has
expired. expired.
As specified in Section 5.10.3 of [I-D.ietf-ace-oauth-authz], the As specified in Section 5.10.3 of [RFC9200], the resource server MUST
resource server MUST notify the client with an error response with notify the client with an error response with code 4.01
code 4.01 (Unauthorized) for any long running request before (Unauthorized) for any long-running request before terminating the
terminating the association. association.
6. Secure Communication with an Authorization Server 6. Secure Communication with an Authorization Server
As specified in the ACE framework (Sections 5.8 and 5.9 of As specified in the ACE framework (Sections 5.8 and 5.9 of
[I-D.ietf-ace-oauth-authz]), the requesting entity (the resource [RFC9200]), the requesting entity (the resource server and/or the
server and/or the client) and the authorization server communicate client) and the authorization server communicate via the token
via the token endpoint or introspection endpoint. The use of CoAP endpoint or introspection endpoint. The use of CoAP and DTLS for
and DTLS for this communication is RECOMMENDED in this profile. this communication is RECOMMENDED in this profile. Other protocols
Other protocols fulfilling the security requirements defined in fulfilling the security requirements defined in Section 5 of
Section 5 of [I-D.ietf-ace-oauth-authz] MAY be used instead. [RFC9200] MAY be used instead.
How credentials (e.g., PSK, RPK, X.509 cert) for using DTLS with the How credentials (e.g., PSK, RPK, X.509 cert) for using DTLS with the
authorization server are established is out of scope for this authorization server are established is out of scope for this
profile. profile.
If other means of securing the communication with the authorization If other means of securing the communication with the authorization
server are used, the communication security requirements from server are used, the communication security requirements from
Section 6.2 of [I-D.ietf-ace-oauth-authz] remain applicable. Section 6.2 of [RFC9200] remain applicable.
7. Security Considerations 7. Security Considerations
This document specifies a profile for the Authentication and This document specifies a profile for the Authentication and
Authorization for Constrained Environments (ACE) framework Authorization for Constrained Environments (ACE) framework [RFC9200].
[I-D.ietf-ace-oauth-authz]. As it follows this framework's general As it follows this framework's general approach, the general security
approach, the general security considerations from Section 6 of considerations from Section 6 of [RFC9200] also apply to this
[I-D.ietf-ace-oauth-authz] also apply to this profile. profile.
The authorization server must ascertain that the keying material for The authorization server must ascertain that the keying material for
the client that it provides to the resource server actually is the client that it provides to the resource server actually is
associated with this client. Malicious clients may hand over access associated with this client. Malicious clients may hand over access
tokens containing their own access permissions to other entities. tokens containing their own access permissions to other entities.
This problem cannot be completely eliminated. Nevertheless, in RPK This problem cannot be completely eliminated. Nevertheless, in RPK
mode it should not be possible for clients to request access tokens mode, it should not be possible for clients to request access tokens
for arbitrary public keys: if the client can cause the authorization for arbitrary public keys; if the client can cause the authorization
server to issue a token for a public key without proving possession server to issue a token for a public key without proving possession
of the corresponding private key, this allows for identity misbinding of the corresponding private key, this allows for identity misbinding
attacks where the issued token is usable by an entity other than the attacks, where the issued token is usable by an entity other than the
intended one. The authorization server therefore at some point needs intended one. At some point, the authorization server therefore
to validate that the client can actually use the private key needs to validate that the client can actually use the private key
corresponding to the client's public key. corresponding to the client's public key.
When using pre-shared keys provisioned by the authorization server, When using pre-shared keys provisioned by the authorization server,
the security level depends on the randomness of PSK, and the security the security level depends on the randomness of PSKs and the security
of the TLS cipher suite and key exchange algorithm. As this of the TLS cipher suite and key exchange algorithm. As this
specification targets at constrained environments, message payloads specification targets constrained environments, message payloads
exchanged between the client and the resource server are expected to exchanged between the client and the resource server are expected to
be small and rare. CoAP [RFC7252] mandates the implementation of be small and rare. CoAP [RFC7252] mandates the implementation of
cipher suites with abbreviated, 8-byte tags for message integrity cipher suites with abbreviated, 8-byte tags for message integrity
protection. For consistency, this profile requires implementation of protection. For consistency, this profile requires implementation of
the same cipher suites. For application scenarios where the cost of the same cipher suites. For application scenarios where the cost of
full-width authentication tags is low compared to the overall amount full-width authentication tags is low compared to the overall amount
of data being transmitted, the use of cipher suites with 16-byte of data being transmitted, the use of cipher suites with 16-byte
integrity protection tags is preferred. integrity protection tags is preferred.
The PSK mode of this profile offers a distribution mechanism to The PSK mode of this profile offers a distribution mechanism to
convey authorization tokens together with a shared secret to a client convey authorization tokens together with a shared secret to a client
and a server. As this specification aims at constrained devices and and a server. As this specification aims at constrained devices and
uses CoAP [RFC7252] as transfer protocol, at least the cipher suite uses CoAP [RFC7252] as the transfer protocol, at least the cipher
TLS_PSK_WITH_AES_128_CCM_8 [RFC6655] should be supported. The access suite TLS_PSK_WITH_AES_128_CCM_8 [RFC6655] should be supported. The
tokens and the corresponding shared secrets generated by the access tokens and the corresponding shared secrets generated by the
authorization server are expected to be sufficiently short-lived to authorization server are expected to be sufficiently short-lived to
provide similar forward-secrecy properties to using ephemeral Diffie- provide similar forward-secrecy properties to using ephemeral Diffie-
Hellman (DHE) key exchange mechanisms. For longer-lived access Hellman (DHE) key exchange mechanisms. For longer-lived access
tokens, DHE cipher suites should be used, i.e., cipher suites of the tokens, DHE cipher suites should be used, i.e., cipher suites of the
form TLS_DHE_PSK_*. form TLS_DHE_PSK_* or TLS_ECDHE_PSK_*.
Constrained devices that use DTLS [RFC6347] are inherently vulnerable Constrained devices that use DTLS [RFC6347] are inherently vulnerable
to Denial of Service (DoS) attacks as the handshake protocol requires to Denial of Service (DoS) attacks, as the handshake protocol
creation of internal state within the device. This is specifically requires creation of an internal state within the device. This is
of concern where an adversary is able to intercept the initial cookie specifically of concern where an adversary is able to intercept the
exchange and interject forged messages with a valid cookie to initial cookie exchange and interject forged messages with a valid
continue with the handshake. A similar issue exists with the cookie to continue with the handshake. A similar issue exists with
unprotected authorization information endpoint when the resource the unprotected authorization information endpoint when the resource
server needs to keep valid access tokens for a long time. server needs to keep valid access tokens for a long time.
Adversaries could fill up the constrained resource server's internal Adversaries could fill up the constrained resource server's internal
storage for a very long time with interjected or otherwise retrieved storage for a very long time with interjected or otherwise retrieved
valid access tokens. To mitigate against this, the resource server valid access tokens. To mitigate against this, the resource server
should set a time boundary until an access token that has not been should set a time boundary until an access token that has not been
used until then will be deleted. used until then will be deleted.
The protection of access tokens that are stored in the authorization The protection of access tokens that are stored in the authorization
information endpoint depends on the keying material that is used information endpoint depends on the keying material that is used
between the authorization server and the resource server: The between the authorization server and the resource server; the
resource server must ensure that it processes only access tokens that resource server must ensure that it processes only access tokens that
are (encrypted and) integrity-protected by an authorization server are (encrypted and) integrity-protected by an authorization server
that is authorized to provide access tokens for the resource server. that is authorized to provide access tokens for the resource server.
7.1. Reuse of Existing Sessions 7.1. Reuse of Existing Sessions
To avoid the overhead of a repeated DTLS handshake, [RFC7925] To avoid the overhead of a repeated DTLS handshake, [RFC7925]
recommends session resumption [RFC8446] to reuse session state from recommends session resumption [RFC8446] to reuse session state from
an earlier DTLS association and thus requires client side an earlier DTLS association and thus requires client-side
implementation. In this specification, the DTLS session is subject implementation. In this specification, the DTLS session is subject
to the authorization rules denoted by the access token that was used to the authorization rules denoted by the access token that was used
for the initial setup of the DTLS association. Enabling session for the initial setup of the DTLS association. Enabling session
resumption would require the server to transfer the authorization resumption would require the server to transfer the authorization
information with the session state in an encrypted SessionTicket to information with the session state in an encrypted SessionTicket to
the client. Assuming that the server uses long-lived keying the client. Assuming that the server uses long-lived keying
material, this could open up attacks due to the lack of forward material, this could open up attacks due to the lack of forward
secrecy. Moreover, using this mechanism, a client can resume a DTLS secrecy. Moreover, using this mechanism, a client can resume a DTLS
session without proving the possession of the PoP key again. session without proving the possession of the PoP key again.
Therefore, session resumption should be used only in combination with Therefore, session resumption should be used only in combination with
reasonably short-lived PoP keys. reasonably short-lived PoP keys.
Since renegotiation of DTLS associations is prone to attacks as well, Since renegotiation of DTLS associations is prone to attacks as well,
[RFC7925] requires clients to decline any renegotiation attempt. A [RFC7925] requires that clients decline any renegotiation attempt. A
server that wants to initiate re-keying therefore SHOULD periodically server that wants to initiate rekeying therefore SHOULD periodically
force a full handshake. force a full handshake.
7.2. Multiple Access Tokens 7.2. Multiple Access Tokens
Developers SHOULD avoid using multiple access tokens for a client Developers SHOULD avoid using multiple access tokens for a client
(see also section 5.10.1 of [I-D.ietf-ace-oauth-authz]). (see also Section 5.10.1 of [RFC9200]).
Even when a single access token per client is used, an attacker could Even when a single access token per client is used, an attacker could
compromise the dynamic update mechanism for existing DTLS connections compromise the dynamic update mechanism for existing DTLS connections
by delaying or reordering packets destined for the authz-info by delaying or reordering packets destined for the authz-info
endpoint. Thus, the order in which operations occur at the resource endpoint. Thus, the order in which operations occur at the resource
server (and thus which authorization info is used to process a given server (and thus which authorization info is used to process a given
client request) cannot be guaranteed. Especially in the presence of client request) cannot be guaranteed. Especially in the presence of
later-issued access tokens that reduce the client's permissions from later-issued access tokens that reduce the client's permissions from
the initial access token, it is impossible to guarantee that the the initial access token, it is impossible to guarantee that the
reduction in authorization will take effect prior to the expiration reduction in authorization will take effect prior to the expiration
of the original token. of the original token.
7.3. Out-of-Band Configuration 7.3. Out-of-Band Configuration
To communicate securely, the authorization server, the client and the To communicate securely, the authorization server, the client, and
resource server require certain information that must be exchanged the resource server require certain information that must be
outside the protocol flow described in this document. The exchanged outside the protocol flow described in this document. The
authorization server must have obtained authorization information authorization server must have obtained authorization information
concerning the client and the resource server that is approved by the concerning the client and the resource server that is approved by the
resource owner as well as corresponding keying material. The resource owner, as well as corresponding keying material. The
resource server must have received authorization information approved resource server must have received authorization information approved
by the resource owner concerning its authorization managers and the by the resource owner concerning its authorization managers and the
respective keying material. The client must have obtained respective keying material. The client must have obtained
authorization information concerning the authorization server authorization information concerning the authorization server
approved by its owner as well as the corresponding keying material. approved by its owner, as well as the corresponding keying material.
Also, the client's owner must have approved of the client's Also, the client's owner must have approved of the client's
communication with the resource server. The client and the communication with the resource server. The client and the
authorization server must have obtained a common understanding how authorization server must have obtained a common understanding about
this resource server is identified to ensure that the client obtains how this resource server is identified to ensure that the client
access token and keying material for the correct resource server. If obtains access tokens and keying material for the correct resource
the client is provided with a raw public key for the resource server, server. If the client is provided with a raw public key for the
it must be ascertained to which resource server (which identifier and resource server, it must be ascertained to which resource server
authorization information) the key is associated. All authorization (which identifier and authorization information) the key is
information and keying material must be kept up to date. associated. All authorization information and keying material must
be kept up to date.
8. Privacy Considerations 8. Privacy Considerations
This privacy considerations from Section 7 of the This privacy considerations from Section 7 of [RFC9200] apply also to
[I-D.ietf-ace-oauth-authz] apply also to this profile. this profile.
An unprotected response to an unauthorized request may disclose An unprotected response to an unauthorized request may disclose
information about the resource server and/or its existing information about the resource server and/or its existing
relationship with the client. It is advisable to include as little relationship with the client. It is advisable to include as little
information as possible in an unencrypted response. When a DTLS information as possible in an unencrypted response. When a DTLS
session between an authenticated client and the resource server session between an authenticated client and the resource server
already exists, more detailed information MAY be included with an already exists, more detailed information MAY be included with an
error response to provide the client with sufficient information to error response to provide the client with sufficient information to
react on that particular error. react on that particular error.
Also, unprotected requests to the resource server may reveal Also, unprotected requests to the resource server may reveal
information about the client, e.g., which resources the client information about the client, e.g., which resources the client
attempts to request or the data that the client wants to provide to attempts to request or the data that the client wants to provide to
the resource server. The client SHOULD NOT send confidential data in the resource server. The client SHOULD NOT send confidential data in
an unprotected request. an unprotected request.
Note that some information might still leak after DTLS session is Note that some information might still leak after the DTLS session is
established, due to observable message sizes, the source, and the established, due to observable message sizes, the source, and the
destination addresses. destination addresses.
9. IANA Considerations 9. IANA Considerations
The following registrations are done for the ACE OAuth Profile The following registration has been made in the "ACE Profiles"
Registry following the procedure specified in registry, following the procedure specified in [RFC9200].
[I-D.ietf-ace-oauth-authz].
Note to RFC Editor: Please replace all occurrences of "[RFC-XXXX]"
with the RFC number of this specification and delete this paragraph.
Profile name: coap_dtls
Profile Description: Profile for delegating client authentication and
authorization in a constrained environment by establishing a Datagram
Transport Layer Security (DTLS) channel between resource-constrained
nodes.
Profile ID: TBD (suggested: 1)
Change Controller: IESG
Reference: [RFC-XXXX]
10. Acknowledgments
Special thanks to Jim Schaad for his contributions and reviews of
this document and to Ben Kaduk for his thorough reviews of this
document. Thanks also to Paul Kyzivat for his review. The authors
also would like to thank Marco Tiloca for his contributions.
Ludwig Seitz worked on this document as part of the CelticNext
projects CyberWI, and CRITISEC with funding from Vinnova.
11. References
11.1. Normative References Name: coap_dtls
Description: Profile for delegating client Authentication and
Authorization for Constrained Environments by establishing a
Datagram Transport Layer Security (DTLS) channel between resource-
constrained nodes.
CBOR Value: 1
Reference: RFC 9202
[I-D.ietf-ace-oauth-authz] 10. References
Seitz, L., Selander, G., Wahlstroem, E., Erdtman, S., and
H. Tschofenig, "Authentication and Authorization for
Constrained Environments (ACE) using the OAuth 2.0
Framework (ACE-OAuth)", Work in Progress, Internet-Draft,
draft-ietf-ace-oauth-authz-41, 6 May 2021,
<https://www.ietf.org/archive/id/draft-ietf-ace-oauth-
authz-41.txt>.
[I-D.ietf-ace-oauth-params] 10.1. Normative References
Seitz, L., "Additional OAuth Parameters for Authorization
in Constrained Environments (ACE)", Work in Progress,
Internet-Draft, draft-ietf-ace-oauth-params-15, 6 May
2021, <https://www.ietf.org/archive/id/draft-ietf-ace-
oauth-params-15.txt>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC4279] Eronen, P., Ed. and H. Tschofenig, Ed., "Pre-Shared Key [RFC4279] Eronen, P., Ed. and H. Tschofenig, Ed., "Pre-Shared Key
Ciphersuites for Transport Layer Security (TLS)", Ciphersuites for Transport Layer Security (TLS)",
RFC 4279, DOI 10.17487/RFC4279, December 2005, RFC 4279, DOI 10.17487/RFC4279, December 2005,
<https://www.rfc-editor.org/info/rfc4279>. <https://www.rfc-editor.org/info/rfc4279>.
skipping to change at page 27, line 21 skipping to change at line 1154
[RFC8747] Jones, M., Seitz, L., Selander, G., Erdtman, S., and H. [RFC8747] Jones, M., Seitz, L., Selander, G., Erdtman, S., and H.
Tschofenig, "Proof-of-Possession Key Semantics for CBOR Tschofenig, "Proof-of-Possession Key Semantics for CBOR
Web Tokens (CWTs)", RFC 8747, DOI 10.17487/RFC8747, March Web Tokens (CWTs)", RFC 8747, DOI 10.17487/RFC8747, March
2020, <https://www.rfc-editor.org/info/rfc8747>. 2020, <https://www.rfc-editor.org/info/rfc8747>.
[RFC8949] Bormann, C. and P. Hoffman, "Concise Binary Object [RFC8949] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", STD 94, RFC 8949, Representation (CBOR)", STD 94, RFC 8949,
DOI 10.17487/RFC8949, December 2020, DOI 10.17487/RFC8949, December 2020,
<https://www.rfc-editor.org/info/rfc8949>. <https://www.rfc-editor.org/info/rfc8949>.
11.2. Informative References [RFC9200] Seitz, L., Selander, G., Wahlstroem, E., Erdtman, S., and
H. Tschofenig, "Authentication and Authorization for
Constrained Environments (ACE) Using the OAuth 2.0
Framework (ACE-OAuth)", RFC 9200, DOI 10.17487/RFC9200,
March 2022, <https://www.rfc-editor.org/info/rfc9200>.
[RFC9201] Seitz, L., "Additional OAuth Parameters for Authentication
and Authorization for Constrained Environments (ACE)",
RFC 9201, DOI 10.17487/RFC9201, March 2022,
<https://www.rfc-editor.org/info/rfc9201>.
10.2. Informative References
[RFC5869] Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand [RFC5869] Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand
Key Derivation Function (HKDF)", RFC 5869, Key Derivation Function (HKDF)", RFC 5869,
DOI 10.17487/RFC5869, May 2010, DOI 10.17487/RFC5869, May 2010,
<https://www.rfc-editor.org/info/rfc5869>. <https://www.rfc-editor.org/info/rfc5869>.
[RFC6655] McGrew, D. and D. Bailey, "AES-CCM Cipher Suites for [RFC6655] McGrew, D. and D. Bailey, "AES-CCM Cipher Suites for
Transport Layer Security (TLS)", RFC 6655, Transport Layer Security (TLS)", RFC 6655,
DOI 10.17487/RFC6655, July 2012, DOI 10.17487/RFC6655, July 2012,
<https://www.rfc-editor.org/info/rfc6655>. <https://www.rfc-editor.org/info/rfc6655>.
skipping to change at page 28, line 11 skipping to change at line 1200
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>. <https://www.rfc-editor.org/info/rfc8446>.
[RFC8610] Birkholz, H., Vigano, C., and C. Bormann, "Concise Data [RFC8610] Birkholz, H., Vigano, C., and C. Bormann, "Concise Data
Definition Language (CDDL): A Notational Convention to Definition Language (CDDL): A Notational Convention to
Express Concise Binary Object Representation (CBOR) and Express Concise Binary Object Representation (CBOR) and
JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610, JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610,
June 2019, <https://www.rfc-editor.org/info/rfc8610>. June 2019, <https://www.rfc-editor.org/info/rfc8610>.
Acknowledgments
Special thanks to Jim Schaad for his contributions and reviews of
this document and to Ben Kaduk for his thorough reviews of this
document. Thanks also to Paul Kyzivat for his review. The authors
also would like to thank Marco Tiloca for his contributions.
Ludwig Seitz worked on this document as part of the CelticNext
projects CyberWI and CRITISEC with funding from Vinnova.
Authors' Addresses Authors' Addresses
Stefanie Gerdes Stefanie Gerdes
Universität Bremen TZI Universität Bremen TZI
Postfach 330440 Postfach 330440
D-28359 Bremen D-28359 Bremen
Germany Germany
Phone: +49-421-218-63906 Phone: +49-421-218-63906
Email: gerdes@tzi.org Email: gerdes@tzi.org
Olaf Bergmann Olaf Bergmann
Universität Bremen TZI Universität Bremen TZI
Postfach 330440 Postfach 330440
D-28359 Bremen D-28359 Bremen
Germany Germany
Phone: +49-421-218-63904 Phone: +49-421-218-63904
Email: bergmann@tzi.org Email: bergmann@tzi.org
Carsten Bormann Carsten Bormann
Universität Bremen TZI Universität Bremen TZI
Postfach 330440 Postfach 330440
D-28359 Bremen D-28359 Bremen
Germany Germany
Phone: +49-421-218-63921 Phone: +49-421-218-63921
Email: cabo@tzi.org Email: cabo@tzi.org
Göran Selander Göran Selander
Ericsson AB Ericsson AB
Email: goran.selander@ericsson.com Email: goran.selander@ericsson.com
Ludwig Seitz Ludwig Seitz
Combitech Combitech
Djäknegatan 31 Djäknegatan 31
SE-211 35 Malmö SE-211 35 Malmö
Sweden Sweden
Email: ludwig.seitz@combitech.com Email: ludwig.seitz@combitech.com
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