Ephemeral Diffie-Hellman Over COSE (EDHOC) and Object Security for Constrained Environments (OSCORE) Profile for Authentication and Authorization for Constrained Environments (ACE)
draft-ietf-ace-edhoc-oscore-profile-02
The information below is for an old version of the document.
| Document | Type |
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|---|---|---|---|
| Authors | Göran Selander , John Preuß Mattsson , Marco Tiloca , Rikard Höglund | ||
| Last updated | 2023-07-07 (Latest revision 2023-03-10) | ||
| Replaces | draft-selander-ace-edhoc-oscore-profile | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
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draft-ietf-ace-edhoc-oscore-profile-02
ACE Working Group G. Selander
Internet-Draft J. Preuß Mattsson
Intended status: Standards Track Ericsson
Expires: 8 January 2024 M. Tiloca
R. Höglund
RISE
7 July 2023
Ephemeral Diffie-Hellman Over COSE (EDHOC) and Object Security for
Constrained Environments (OSCORE) Profile for Authentication and
Authorization for Constrained Environments (ACE)
draft-ietf-ace-edhoc-oscore-profile-02
Abstract
This document specifies a profile for the Authentication and
Authorization for Constrained Environments (ACE) framework. It
utilizes Ephemeral Diffie-Hellman Over COSE (EDHOC) for achieving
mutual authentication between an OAuth 2.0 Client and Resource
Server, and it binds an authentication credential of the Client to an
OAuth 2.0 access token. EDHOC also establishes an Object Security
for Constrained RESTful Environments (OSCORE) Security Context, which
is used to secure communications when accessing protected resources
according to the authorization information indicated in the access
token. A resource-constrained server can use this profile to
delegate management of authorization information to a trusted host
with less severe limitations regarding processing power and memory.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 8 January 2024.
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Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 6
3. Client-AS Communication . . . . . . . . . . . . . . . . . . . 8
3.1. C-to-AS: POST to /token endpoint . . . . . . . . . . . . 9
3.2. AS-to-C: Access Token Response . . . . . . . . . . . . . 10
3.3. The EDHOC_Information . . . . . . . . . . . . . . . . . . 17
4. Client-RS Communication . . . . . . . . . . . . . . . . . . . 20
4.1. C-to-RS: POST to /authz-info endpoint . . . . . . . . . . 21
4.2. RS-to-C: 2.01 (Created) . . . . . . . . . . . . . . . . . 23
4.3. EDHOC Execution and Setup of OSCORE Security Context . . 24
4.4. Access Rights Verification . . . . . . . . . . . . . . . 27
5. Secure Communication with AS . . . . . . . . . . . . . . . . 27
6. Discarding the Security Context . . . . . . . . . . . . . . . 28
7. Security Considerations . . . . . . . . . . . . . . . . . . . 29
8. Privacy Considerations . . . . . . . . . . . . . . . . . . . 30
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 31
9.1. ACE OAuth Profile Registry . . . . . . . . . . . . . . . 31
9.2. OAuth Parameters Registry . . . . . . . . . . . . . . . . 31
9.3. OAuth Parameters CBOR Mappings Registry . . . . . . . . . 32
9.4. JSON Web Token Claims Registry . . . . . . . . . . . . . 32
9.5. CBOR Web Token Claims Registry . . . . . . . . . . . . . 32
9.6. JWT Confirmation Methods Registry . . . . . . . . . . . . 33
9.7. CWT Confirmation Methods Registry . . . . . . . . . . . . 35
9.8. EDHOC External Authorization Data Registry . . . . . . . 38
9.9. EDHOC Information Registry . . . . . . . . . . . . . . . 39
9.10. Expert Review Instructions . . . . . . . . . . . . . . . 40
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 40
10.1. Normative References . . . . . . . . . . . . . . . . . . 40
10.2. Informative References . . . . . . . . . . . . . . . . . 43
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 43
A.1. Workflow without Optimizations . . . . . . . . . . . . . 45
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A.2. Workflow with Optimizations . . . . . . . . . . . . . . . 49
A.3. Alternative Workflow (AS token posting) . . . . . . . . . 51
Appendix B. Profile Requirements . . . . . . . . . . . . . . . . 54
Appendix C. Document Updates . . . . . . . . . . . . . . . . . . 55
C.1. Version -00 to -01 . . . . . . . . . . . . . . . . . . . 55
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 56
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 56
1. Introduction
This document defines the "coap_edhoc_oscore" profile of the ACE
framework [RFC9200]. This profile addresses a "zero-touch"
constrained setting where trusted operations can be performed with
low overhead without endpoint specific configurations.
Like in the "coap_oscore" profile [RFC9203], also in this profile a
client (C) and a resource server (RS) use the Constrained Application
Protocol (CoAP) [RFC7252] to communicate, and Object Security for
Constrained RESTful Environments (OSCORE) [RFC8613] to protect their
communications. Also, the processing of requests for specific
protected resources is identical to what is defined in the
"coap_oscore" profile.
When using this profile, C accesses protected resources hosted at RS
with the use of an access token issued by a trusted authorization
server (AS) and bound to an authentication credential of C. This
differs from the "coap_oscore" profile, where the access token is
bound to a symmetric key used to derive OSCORE keying material. As
recommended in [RFC9200], this document recommends the use of CBOR
Web Tokens (CWTs) [RFC8392] as access tokens.
The authentication and authorization processing requires C and RS to
have access to each other's authentication credentials. C can obtain
the authentication credential of RS from AS together with the access
token. RS can obtain the authentication credential of C together
with the associated access token in different ways. If RS
successfully verifies the access token, then C and RS run the
Ephemeral Diffie-Hellman Over COSE (EDHOC) protocol
[I-D.ietf-lake-edhoc] using the authentication credentials.
Once the EDHOC execution is completed, C and RS are mutually
authenticated and can derive an OSCORE Security Context to protect
subsequent communications, over which C can access protected
resources of RS according to the access rights specified in the
access token.
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An authentication credential can be a raw public key, e.g., encoded
as a CWT Claims Set (CCS, [RFC8392]); or a public key certificate,
e.g., encoded as an X.509 certificate [RFC5280] or as a CBOR encoded
X.509 certificate (C509, [I-D.ietf-cose-cbor-encoded-cert]); or a
different type of data structure containing the public key of the
peer in question.
The ACE protocol establishes what those authentication credentials
are, and may transport the actual authentication credentials by value
or uniquely refer to them. If an authentication credential is pre-
provisioned or can be obtained over less constrained links, then it
suffices that ACE provides a unique reference such as a certificate
hash (e.g., by using the COSE header parameter "x5t", see [RFC9360]).
This is in the same spirit as EDHOC, where the authentication
credentials may be transported or referenced in the ID_CRED_x message
fields (see Section 3.5.3 of [I-D.ietf-lake-edhoc]).
In general, AS and RS are likely to have trusted access to each
other's authentication credentials, since AS acts on behalf of RS as
per the trust model of ACE. Also, AS needs to have some information
about C, including the relevant authentication credential, in order
to identify C when it requests an access token and to determine what
access rights it can be granted. However, the authentication
credential of C may potentially be conveyed (or uniquely referred to)
within the request for access which C makes to AS.
1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
Certain security-related terms such as "authentication",
"authorization", "confidentiality", "(data) integrity", "Message
Authentication Code (MAC)", "Hash-based Message Authentication Code
(HMAC)", and "verify" are taken from [RFC4949].
RESTful terminology follows HTTP [RFC9110].
Readers are expected to be familiar with the terms and concepts
defined in CoAP [RFC7252], OSCORE [RFC8613] and EDHOC
[I-D.ietf-lake-edhoc].
Readers are also expected to be familiar with the terms and concepts
of the ACE framework described in [RFC9200] and in [RFC9201].
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Terminology for entities in the architecture is defined in OAuth 2.0
[RFC6749], such as the client (C), the resource server (RS), and the
authorization server (AS). It is assumed in this document that a
given resource on a specific RS is associated with a unique AS.
Note that the term "endpoint" is used here, as in [RFC9200],
following its OAuth definition, which is to denote resources such as
/token and /introspect at AS and /authz-info at RS. The CoAP
[RFC7252] definition, which is "An entity participating in the CoAP
protocol" is not used in this document.
The authorization information (authz-info) resource refers to the
authorization information endpoint as specified in [RFC9200]. The
term "claim" is used in this document with the same semantics as in
[RFC9200], i.e., it denotes information carried in the access token
or returned from introspection.
This document defines "token series" as a series of access tokens
sorted in chronological order as they are released, characterized by
the following properties:
* issued by the same AS
* issued to the same C and for the same RS
* issued together with the same authentication credential of RS
* associated with the same authentication credential of C
When an access token becomes invalid (e.g., due to its expiration or
revocation), the token series it belongs to ends.
Concise Binary Object Representation (CBOR) [RFC8949][RFC8742] and
Concise Data Definition Language (CDDL) [RFC8610] are used in this
document. CDDL predefined type names, especially bstr for CBOR byte
strings and tstr for CBOR text strings, are used extensively in this
document.
Examples throughout this document are expressed in CBOR diagnostic
notation without the tag and value abbreviations.
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2. Protocol Overview
This section gives an overview of how to use the ACE framework
[RFC9200] together with the authenticated key establishment protocol
EDHOC [I-D.ietf-lake-edhoc]. By doing so, a client (C) and a
resource server (RS) generate an OSCORE Security Context [RFC8613]
associated with authorization information, and use that Security
Context to protect their communications. The parameters needed by C
to negotiate the use of this profile with the authorization server
(AS), as well as the OSCORE setup process, are described in detail in
the following sections.
RS maintains a collection of authentication credentials. These are
associated to OSCORE Security Contexts and to authorization
information for all clients that RS is communicating with. The
authorization information is used to enforce polices for processing
requests from those clients.
This profile specifies how C requests an access token from AS for the
resources it wants to access on an RS, by sending an access token
request to the /token endpoint, as specified in Section 5.8 of
[RFC9200]. The access token request and response MUST be
confidentiality protected and ensure authenticity. The use of EDHOC
and OSCORE between C and AS is RECOMMENDED in this profile, in order
to reduce the number of libraries that C has to support. However,
other protocols fulfilling the security requirements defined in
Section 5 of [RFC9200] MAY alternatively be used, such as TLS
[RFC8446] or DTLS [RFC9147].
If C has retrieved an access token, there are two options for C to
upload it to RS, as further detailed in this document.
1. C posts the access token to the /authz-info endpoint by using the
mechanisms specified in Section 5.10 of [RFC9200]. If the access
token is valid, RS responds to the request with a 2.01 (Created)
response, after which C initiates the EDHOC protocol by sending
EDHOC message_1 to RS. The communication with the /authz-info
endpoint is not protected, except for the update of access
rights.
2. C initiates the EDHOC protocol by sending EDHOC message_1 to RS,
specifying the access token as External Authorization Data (EAD)
in the EAD_1 field of EDHOC message_1 (see Section 3.8 of
[I-D.ietf-lake-edhoc]). If the access token is valid and the
processing of EDHOC message_1 is successful, RS responds with
EDHOC message_2, thus continuing the EDHOC protocol. This option
cannot be used for the update of access rights only.
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When running the EDHOC protocol, C uses the authentication credential
of RS specified by AS together with the access token, while RS uses
the authentication credential of C bound to and specified within the
access token. If C and RS complete the EDHOC execution successfully,
they are mutually authenticated and they derive an OSCORE Security
Context as per Appendix A.1 of [I-D.ietf-lake-edhoc]. Also, RS
associates the two used authentication credentials and the completed
EDHOC execution with the derived Security Context. The latter is in
turn associated with the access token and the access rights of C
specified therein.
From then on, C effectively gains authorized and secure access to
protected resources on RS with the established OSCORE Security
Context, for as long as the access token is valid. The Security
Context is discarded when an access token (whether the same or a
different one) is used to successfully derive a new Security Context
for C.
After the whole procedure has completed and while the access token is
valid, C can contact AS to request an update of its access rights, by
sending a similar request to the /token endpoint. This request also
includes an identifier, which allows AS to find the data it has
previously shared with C. This specific identifier, encoded as a
byte string, is assigned by AS to a "token series" (see Section 1.1).
Upon a successful update of access rights, the new issued access
token becomes the latest in its token series. When the latest access
token of a token series becomes invalid (e.g., when it expires or
gets revoked), that token series ends.
An overview of the profile flow for the "coap_edhoc_oscore" profile
is given in Figure 1. The names of messages coincide with those of
[RFC9200] when applicable.
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C RS AS
| | |
| <==== Mutual authentication and secure channel ====> |
| | |
| ------- POST /token ------------------------------> |
| | |
| <-------------------------------- Access Token ----- |
| + Access Information |
| | |
| ---- POST /authz-info ---> | |
| (access_token) | |
| | |
| <----- 2.01 Created ------ | |
| | |
| <========= EDHOC ========> | |
| Mutual authentication | |
| and derivation of an | |
| OSCORE Security Context | |
| | |
| /Proof-of-possession and |
| Security Context storage/ |
| | |
| ---- OSCORE Request -----> | |
| | |
| <--- OSCORE Response ----- | |
| | |
/Proof-of-possession | |
and Security Context | |
storage (latest)/ | |
| | |
| ---- OSCORE Request -----> | |
| | |
| <--- OSCORE Response ----- | |
| | |
| ... | |
Figure 1: Protocol Overview
3. Client-AS Communication
The following subsections describe the details of the POST request
and response to the /token endpoint between C and AS.
In this exchange, AS provides C with the access token, together with
a set of parameters that enable C to run EDHOC with RS. In
particular, these include information about the authorization
credential of RS, AUTH_CRED_RS, transported by value or uniquely
referred to.
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The access token is securely associated with the authentication
credential of C, AUTH_CRED_C, by including it or uniquely referring
to it in the access token.
AUTH_CRED_C is specified in the "req_cnf" parameter defined in
[RFC9201] of the POST request to the /token endpoint from C to AS,
either transported by value or uniquely referred to.
The request to the /token endpoint and the corresponding response can
include EDHOC_Information, which is a CBOR map object defined in
Section 3.3. This object is transported in the "edhoc_info"
parameter registered in Section 9.2 and Section 9.3.
3.1. C-to-AS: POST to /token endpoint
The client-to-AS request is specified in Section 5.8.1 of [RFC9200].
The client must send this POST request to the /token endpoint over a
secure channel that guarantees authentication, message integrity and
confidentiality (see Section 5).
Editor's note: This formulation overlaps with 3rd para in Section 2,
which has normative language. Preferable to keep normative language
here.
An example of such a request is shown in Figure 2. In this example,
C specifies its own authentication credential by reference, as the
hash of an X.509 certificate carried in the "x5t" field of the
"req_cnf" parameter. In fact, it is expected that C can typically
specify its own authentication credential by reference, since AS is
expected to obtain the actual authentication credential during an
early client registration process or during a previous secure
association establishment with C.
Header: POST (Code=0.02)
Uri-Host: "as.example.com"
Uri-Path: "token"
Content-Format: "application/ace+cbor"
Payload:
{
"audience" : "tempSensor4711",
"scope" : "read",
"req_cnf" : {
"x5t" : h'822E4879F2A41B510C1F9B'
}
}
Figure 2: Example of C-to-AS POST /token request for an access token.
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If C wants to update its access rights without changing an existing
OSCORE Security Context, it MUST include EDHOC_Information in its
POST request to the /token endpoint. In turn, EDHOC_Information MUST
include the "id" field, carrying a CBOR byte string containing the
identifier of the token series to which the current, still valid
access token shared with RS belongs to. This POST request MUST omit
the "req_cnf" parameter.
This identifier is assigned by AS as discussed in Section 3.2, and,
together with other information such as audience (see Section 5.8.1
of [RFC9200]), can be used by AS to determine the token series to
which the new requested access token has to be added. Therefore, the
identifier MUST identify the pair (AUTH_CRED_C, AUTH_CRED_RS)
associated with a still valid access token previously issued for C
and RS by AS.
AS MUST verify that the received value identifies a token series to
which a still valid access token issued for C and RS belongs to. If
that is not the case, the Client-to-AS request MUST be declined with
the error code "invalid_request" as defined in Section 5.8.3 of
[RFC9200].
An example of such a request is shown in Figure 3.
Header: POST (Code=0.02)
Uri-Host: "as.example.com"
Uri-Path: "token"
Content-Format: "application/ace+cbor"
Payload:
{
"audience" : "tempSensor4711",
"scope" : "write",
"edhoc_info" : {
"id" : h'01'
}
}
Figure 3: Example of C-to-AS POST /token request for updating
access rights to an access token.
3.2. AS-to-C: Access Token Response
After verifying the POST request to the /token endpoint and that C is
authorized to obtain an access token corresponding to its access
token request, AS responds as defined in Section 5.8.2 of [RFC9200].
If the request from C was invalid, or not authorized, AS returns an
error response as described in Section 5.8.3 of [RFC9200].
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AS can signal that the use of EDHOC and OSCORE as per this profile is
REQUIRED for a specific access token, by including the "ace_profile"
parameter with the value "coap_edhoc_oscore" in the access token
response. This means that C MUST use EDHOC with RS and derive an
OSCORE Security Context, as specified in Section 4.3. After that, C
MUST use the established OSCORE Security Context to protect
communications with RS, when accessing protected resources at RS
according to the authorization information indicated in the access
token. Usually, it is assumed that constrained devices will be pre-
configured with the necessary profile, so that this kind of profile
signaling can be omitted.
When issuing any access token of a token series, AS MUST send the
following data in the response to C.
* The identifier of the token series to which the issued access
token belongs to. This is specified in the "id" field of
EDHOC_Information.
All the access tokens belonging to the same token series are
associated with the same identifier, which does not change
throughout the series lifetime. A token series ends when the
latest issued access token in the series becomes invalid (e.g.,
when it expires or gets revoked).
AS assigns an identifier to a token series when issuing the first
access token T of that series. When assigning the identifier, AS
MUST ensure that this was never used in a previous series of
access tokens such that: i) they were issued for the same RS for
which the access token T is being issued; and ii) they were bound
to the same authentication credential AUTH_CRED_C of the
requesting client to which the access token T is being issued
(irrespectively of the exact way AUTH_CRED_C is specified in such
access tokens).
When issuing the first access token of a token series, AS MUST send
the following data in the response to C.
* The authentication credential of RS, namely AUTH_CRED_RS. This is
specified in the "rs_cnf" parameter defined in [RFC9201].
AUTH_CRED_RS can be transported by value or referred to by means
of an appropriate identifier.
When issuing the first access token ever to a pair (C, RS) using a
pair of corresponding authentication credentials (AUTH_CRED_C,
AUTH_CRED_RS), it is typically expected that the response to C
specifies AUTH_CRED_RS by value.
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When later issuing further access tokens to the same pair (C, RS)
using the same AUTH_CRED_RS, it is typically expected that the
response to C specifies AUTH_CRED_RS by reference.
When issuing the first access token of a token series, AS MAY send
the following data in the response to C. If present, this data MUST
be included in the corresponding fields of EDHOC_Information. Some
of this information takes advantage of the knowledge that AS may have
about C and RS since a previous registration process, with particular
reference to what they support as EDHOC peers.
* The EDHOC methods supported by both C and RS (see Section 3.2 of
[I-D.ietf-lake-edhoc]). This is specified in the "methods" field
of EDHOC_Information.
* The EDHOC cipher suite (see Section 3.6 of [I-D.ietf-lake-edhoc])
to be used by C and RS as selected cipher suite when running
EDHOC. This is specified in the "cipher_suites" field of
EDHOC_Information. If present, this MUST specify the EDHOC cipher
suite which is most preferred by C and at the same time supported
by both C and RS.
* Whether RS supports or not EDHOC message_4 (see Section 5.5 of
[I-D.ietf-lake-edhoc]). This is specified in the "message_4"
field of EDHOC_Information.
* Whether RS supports or not the combined EDHOC + OSCORE request
defined in [I-D.ietf-core-oscore-edhoc]. This is specified in the
"comb_req" field of EDHOC_Information.
* The path component of the URI of the EDHOC resource at RS, where C
is expected to send EDHOC messages as CoAP requests. This is
specified in the "uri_path" field of EDHOC_Information. If not
specified, the URI path "/.well-known/edhoc" defined in
Section 9.7 of [I-D.ietf-lake-edhoc]) is assumed.
* The size in bytes of the OSCORE Master Secret to derive after the
EDHOC execution (see Appendix A.1 of [I-D.ietf-lake-edhoc]) and to
use for establishing an OSCORE Security Context. This is
specified in the "osc_ms_len" field of EDHOC_Information. If not
specified, the default value from Appendix A.1 of
[I-D.ietf-lake-edhoc] is assumed.
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* The size in bytes of the OSCORE Master Salt to derive after the
EDHOC execution (see Appendix A.1 of [I-D.ietf-lake-edhoc]) and to
use for establishing an OSCORE Security Context. This is
specified in the "osc_salt_len" field of EDHOC_Information. If
not specified, the default value from Appendix A.1 of
[I-D.ietf-lake-edhoc] is assumed.
* The OSCORE version to use (see Section 5.4 of [RFC8613]). This is
specified in the "osc_version" field of EDHOC_Information. If
specified, AS MUST indicate the highest OSCORE version supported
by both C and RS. If not specified, the default value of 1 (see
Section 5.4 of [RFC8613]) is assumed.
When issuing any access token of a token series, AS MUST specify the
following data in the claims associated with the access token.
* The identifier of the token series, specified in the "id" field of
EDHOC_Information, and with the same value specified in the
response to C from the /token endpoint.
* The same authentication credential of C that C specified in its
POST request to the /token endpoint (see Section 3.1), namely
AUTH_CRED_C. If the access token is a CWT, this information MUST
be specified in the "cnf" claim.
In the access token, AUTH_CRED_C can be transported by value or
referred to by means of an appropriate identifier, regardless of
how C specified it in the request to the /token endpoint. Thus,
the specific field carried in the access token claim and
specifying AUTH_CRED_C depends on the specific way used by AS.
When issuing the first access token ever to a pair (C, RS) using a
pair of corresponding authentication credentials (AUTH_CRED_C,
AUTH_CRED_RS), it is typically expected that AUTH_CRED_C is
specified by value.
When later issuing further access tokens to the same pair (C, RS)
using the same AUTH_CRED_C, it is typically expected that
AUTH_CRED_C is specified by reference.
When issuing the first access token of a token series, AS MAY specify
the following data in the claims associated with the access token.
If these data are specified in the response to C from the /token
endpoint, they MUST be included in the access token and specify the
same values that they have in the response from the /token endpoint.
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* The size in bytes of the OSCORE Master Secret to derive after the
EDHOC execution and to use for establishing an OSCORE Security
Context. If it is included, it is specified in the "osc_ms_len"
field of EDHOC_Information, and it has the same value that the
"osc_ms_len" field has in the response to C. If it is not
included, the default value from Appendix A.1 of
[I-D.ietf-lake-edhoc] is assumed.
* The size in bytes of the OSCORE Master Salt to derive after the
EDHOC execution (see Appendix A.1 of [I-D.ietf-lake-edhoc]) and to
use for establishing an OSCORE Security Context. If it is
included, it is specified in the "osc_salt_len" field of
EDHOC_Information, and it has the same value that the
"osc_salt_len" field has in the response to C. If it is not
included, the default value from Appendix A.1 of
[I-D.ietf-lake-edhoc] is assumed.
* The OSCORE version to use (see Section 5.4 of [RFC8613]). This is
specified in the "osc_version" field of the "edhoc_info"
parameter. If it is included, it is specified in the
"osc_version" field of EDHOC_Information, and it has the same
value that the "osc_version" field has in the response to C. If
it is not included, the default value of 1 (see Section 5.4 of
[RFC8613]) is assumed.
When issuing the first access token of a token series, AS can take
either of the two possible options.
* AS provides the access token to C, by specifying it in the
"access_token" parameter of the access token response. In such a
case, the access token response MAY include the parameter
"token_uploaded", which MUST encode the CBOR simple value "false"
(0xf4).
* AS does not provide the access token to C. Rather, AS uploads the
access token to the /authz-info endpoint at RS, exactly like C
would do, and as defined in Section 4.1 and Section 4.2. Then,
when replying to C with the access token response as defined
above, the response MUST NOT include the parameter "access_token",
and MUST include the parameter "token_uploaded" encoding the CBOR
simple value "true" (0xf5). This is shown by the example in
Appendix A.3.
Note that, in case C and RS have already completed an EDHOC
execution leveraging a previous access token series, using this
approach implies that C and RS have to re-run the EDHOC protocol.
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When receiving an Access Token response including the "rs_cnf"
parameter, C checks whether it is already storing the authentication
credential of RS, namely AUTH_CRED_RS, specified in "rs_cnf" by value
or reference.
If this is not the case, C retrieves AUTH_CRED_RS, e.g., from the
"rs_cnf" parameter if the authentication credential is specified
therein by value, or from a further trusted source pointed to by the
AUTH_CRED_RS identifier included in the "rs_cnf" parameter. After
that, C validates the actual AUTH_CRED_RS. In case of successful
validation, C stores AUTH_CRED_RS as a valid authentication
credential. Otherwise, C MUST delete the access token.
When CWTs are used as access tokens, EDHOC_Information MUST be
transported in the "edhoc_info" claim, defined in Section 9.5.
Since the access token does not contain secret information, only its
integrity and source authentication are strictly necessary to ensure.
Therefore, AS can protect the access token with either of the means
discussed in Section 6.1 of [RFC9200]. Nevertheless, when using this
profile, it is RECOMMENDED that the access token is a CBOR web token
(CWT) protected with COSE_Encrypt/COSE_Encrypt0 as specified in
[RFC8392].
Figure 4 shows an example of an AS response. The "rs_cnf" parameter
specifies the authentication credential of RS, as an X.509
certificate transported by value in the "x5chain" field. The access
token and the authentication credential of RS have been truncated for
readability.
Header: Created (Code=2.01)
Content-Type: "application/ace+cbor"
Payload:
{
"access_token" : h'8343a1010aa2044c53 ...
(remainder of access token (CWT) omitted for brevity)',
"ace_profile" : "coap_edhoc_oscore",
"expires_in" : "3600",
"rs_cnf" : {
"x5chain" : h'3081ee3081a1a00302 ...'
(remainder of the access credential omitted for brevity)'
}
"edhoc_info" : {
"id" : h'01',
"methods" : [0, 1, 2, 3],
"cipher_suites": 0
}
}
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Figure 4: Example of AS-to-C Access Token response with EDHOC and
OSCORE profile.
Figure 5 shows an example CWT Claims Set, including the relevant
EDHOC parameters in the "edhoc_info" claim. The "cnf" claim
specifies the authentication credential of C, as an X.509 certificate
transported by value in the "x5chain" field. The authentication
credential of C has been truncated for readability.
{
"aud" : "tempSensorInLivingRoom",
"iat" : "1360189224",
"exp" : "1360289224",
"scope" : "temperature_g firmware_p",
"cnf" : {
"x5chain" : h'3081ee3081a1a00302 ...'
}
"edhoc_info" : {
"id" : h'01',
"methods" : [0, 1, 2, 3],
"cipher_suites": 0
}
}
Figure 5: Example of CWT Claims Set with EDHOC parameters.
If C has requested an update to its access rights using the same
OSCORE Security Context, which is valid and authorized, then:
* The response MUST NOT include the "rs_cnf" parameter.
* The EDHOC_Information in the response MUST include only the "id"
field, specifying the identifier of the token series.
* The EDHOC_Information in the access token MUST include only the
"id" field, specifying the identifier of the token series. In
particular, if the access token is a CWT, the "edhoc_info" claim
MUST include only the "id" field.
This identifier of the token series needs to be included in the new
access token in order for RS to identify the old access token to
supersede, as well as the OSCORE Security Context already shared
between C and RS and to be associated with the new access token.
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3.3. The EDHOC_Information
An EDHOC_Information is an object including information that guides
two peers towards executing the EDHOC protocol. In particular, the
EDHOC_Information is defined to be serialized and transported between
nodes, as specified by this document, but it can also be used by
other specifications if needed.
The EDHOC_Information can either be encoded as a JSON object or as a
CBOR map. The set of common fields that can appear in an
EDHOC_Information can be found in the IANA "EDHOC Information"
registry (see Section 9.9), defined for extensibility, and the
initial set of parameters defined in this document is specified
below. All parameters are optional.
Figure 6 provides a summary of the EDHOC_Information parameters
defined in this section.
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+---------------+--------------+------+----------+--------------------+
| Name | CBOR value | CBOR | Registry | Description |
| | | Type | | |
+---------------+--------------+------+----------+--------------------+
| id | bstr | 0 | | Identifier of |
| | | | | EDHOC execution |
+---------------+--------------+------+----------+--------------------+
| methods | int / | | EDHOC | Set of supported |
| | array of int | 1 | Method | EDHOC methods |
| | | | Type | |
| | | | Registry | |
+---------------+--------------+------+----------+--------------------+
| cipher_suites | int / | | EDHOC | Set of supported |
| | array of int | 2 | Cipher | EDHOC cipher |
| | | | Suites | suites |
| | | | Registry | |
+---------------+--------------+------+----------+--------------------+
| message_4 | simple value | | | Support for EDHOC |
| | "true" / | 3 | | message_4 |
| | simple value | | | |
| | "false" | | | |
+---------------+--------------+------+----------+--------------------+
| comb_req | simple value | | | Support for the |
| | "true" / | 4 | | EDHOC + OSCORE |
| | simple value | | | combined request |
| | "false" | | | |
+---------------+--------------+------+----------+--------------------+
| uri_path | tstr | 5 | | URI-path of the |
| | | | | EDHOC resource |
+---------------+--------------+------+----------+--------------------+
| osc_ms_len | uint | | | Length in bytes of |
| | | 6 | | the OSCORE Master |
| | | | | Secret to derive |
+---------------+--------------+------+----------+--------------------+
| osc_salt_len | uint | | | Length in bytes of |
| | | 7 | | the OSCORE Master |
| | | | | Salt to derive |
+---------------+--------------+------+----------+--------------------+
| osc_version | uint | 8 | | OSCORE version |
| | | | | number to use |
+---------------+--------------+------+----------+--------------------+
Figure 6: EDHOC_Information Parameters
* id: This parameter identifies an EDHOC execution and is encoded as
a byte string. In JSON, the "id" value is a Base64 encoded byte
string. In CBOR, the "id" type is a byte string, and has label 0.
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* methods: This parameter specifies a set of supported EDHOC methods
(see Section 3.2 of [I-D.ietf-lake-edhoc]). If the set is
composed of a single EDHOC method, this is encoded as an integer.
Otherwise, the set is encoded as an array of integers, where each
array element encodes one EDHOC method. In JSON, the "methods"
value is an integer or an array of integers. In CBOR, the
"methods" is an integer or an array of integers, and has label 1.
* cipher_suites: This parameter specifies a set of supported EDHOC
cipher suites (see Section 3.6 of [I-D.ietf-lake-edhoc]). If the
set is composed of a single EDHOC cipher suite, this is encoded as
an integer. Otherwise, the set is encoded as an array of
integers, where each array element encodes one EDHOC cipher suite.
In JSON, the "cipher_suites" value is an integer or an array of
integers. In CBOR, the "cipher_suites" is an integer or an array
of integers, and has label 2.
* message_4: This parameter indicates whether the EDHOC message_4
(see Section 5.5 of [I-D.ietf-lake-edhoc]) is supported. In JSON,
the "message_4" value is a boolean. In CBOR, "message_4" is the
simple value "true" or "false", and has label 4.
* comb_req: This parameter indicates whether the combined EDHOC +
OSCORE request defined in [I-D.ietf-core-oscore-edhoc]) is
supported. In JSON, the "comb_req" value is a boolean. In CBOR,
"comb_req" is the simple value "true" or "false", and has label 5.
* uri_path: This parameter specifies the path component of the URI
of the EDHOC resource where EDHOC messages have to be sent as
requests. In JSON, the "uri_path" value is a string. In CBOR,
"uri_path" is text string, and has label 6.
* osc_ms_len: This parameter specifies the size in bytes of the
OSCORE Master Secret to derive after the EDHOC execution, as per
Appendix A.1 of [I-D.ietf-lake-edhoc]. In JSON, the "osc_ms_len"
value is an integer. In CBOR, the "osc_ms_len" type is unsigned
integer, and has label 7.
* osc_salt_len: This parameter specifies the size in bytes of the
OSCORE Master Salt to derive after the EDHOC execution, as per
Appendix A.1 of [I-D.ietf-lake-edhoc]. In JSON, the
"osc_salt_len" value is an integer. In CBOR, the "osc_salt_len"
type is unsigned integer, and has label 8.
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* osc_version: This parameter specifies the OSCORE Version number
that the two EDHOC peers have to use when using OSCORE. For more
information about this parameter, see Section 5.4 of [RFC8613].
In JSON, the "osc_version" value is an integer. In CBOR, the
"osc_version" type is unsigned integer, and has label 9.
An example of JSON EDHOC_Information is given in Figure 7.
"edhoc_info" : {
"id" : b64'AQ==',
"methods" : 1,
"cipher_suites" : 0
}
Figure 7: Example of JSON EDHOC\_Information
The CDDL grammar describing the CBOR EDHOC_Information is:
EDHOC_Information = {
? 0 => bstr, ; id
? 1 => int / array, ; methods
? 2 => int / array, ; cipher_suites
? 3 => true / false, ; message_4
? 4 => true / false, ; comb_req
? 5 => tstr, ; uri_path
? 6 => uint, ; osc_ms_len
? 7 => uint, ; osc_salt_len
? 8 => uint, ; osc_version
* int / tstr => any
}
4. Client-RS Communication
The following subsections describe the exchanges between C and RS,
which comprise the token uploading to RS, and the execution of the
EDHOC protocol. Note that, as defined in Section 3.2, AS may not
have provided C with the access token, and have rather uploaded the
access token to the /authz-info endpoint at RS on behalf of C.
In order to upload the access token to RS, C can send a POST request
to the /authz-info endpoint at RS. This is detailed in Section 4.1
and Section 4.2, and it is shown by the example in Appendix A.1.
Alternatively, C can upload the access token while executing the
EDHOC protocol, by transporting the access token in the EAD_1 field
of the first EDHOC message sent to RS. This is further discussed in
Section 4.3, and it is shown by the example in Appendix A.2.
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In either case, following the uploading of the access token, C and RS
run the EDHOC protocol to completion, by exchanging POST requests and
related responses to a dedicated EDHOC resource at RS (see
Section 4.3). Once completed the EDHOC execution, C and RS have
agreed on a common secret key PRK_out (see Section 4.1.3 of
[I-D.ietf-lake-edhoc]), from which they establish an OSCORE Security
Context (see Section 4.3). After that, C and RS use the established
OSCORE Security Context to protect their communications when
accessing protected resources at RS, as per the access rights
specified in the access token (see Section 4.4).
Note that, by means of the respective authentication credentials, C
and RS are mutually authenticated once they have successfully
completed the execution of the EDHOC protocol.
As to proof-of-possession, RS always gains knowledge that C has
PRK_out at the end of the successful EDHOC execution. Conversely, C
gains knowledge that RS has PRK_out either when receiving and
successfully verifying the optional EDHOC message_4 from RS, or when
successfully verifying a response from RS protected with the
generated OSCORE Security Context.
4.1. C-to-RS: POST to /authz-info endpoint
The access token can be uploaded to RS by using the /authz-info
endpoint at RS. To this end, C MUST use CoAP [RFC7252] and the
Authorization Information endpoint described in Section 5.10.1 of
[RFC9200] in order to transport the access token.
That is, C sends a POST request to the /authz-info endpoint at RS,
with the request payload conveying the access token without any CBOR
wrapping. As per Section 5.10.1 of [RFC9200], the Content-Format of
the POST request has to reflect the format of the transported access
token. In particular, if the access token is a CWT, the content-
format MUST be "application/cwt".
The communication with the /authz-info endpoint is in general not
protected, except in the case of updating the access rights described
below.
The Client provisioning of an initial access token to the RS is
followed by the execution of the EDHOC protocol (or combined using
EAD as described in Section 4.3) and by the derivation of an OSCORE
Security Context, as detailed later in this section.
The same procedure of C provisioning a new access token to RS applies
to other cases when an OSCORE Security Context shared between C and
RS has been deleted, for example:
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* The old access token has expired and thus the token series is
terminated.
* Lack of storage. This situation can be detected by C when it
receives a 4.01 (Unauthorized) response from RS, e.g., as an "AS
Request Creation Hints" message, see Section 5.3 of [RFC9200].
* The EDHOC session from which this OSCORE Security Context was
derived has become invalid, e.g., due to the expiration of an
authentication credential.
* Other security policy.
A different exceptional case is when there is still a valid OSCORE
Security Context but it needs to be updated, e.g., due to a policy
limiting its use in terms of time or amount of processed data, or to
the imminent exhaustion of the OSCORE Sender Sequence Number space.
In this case C and RS SHALL attempt to run the KUDOS key update
protocol [I-D.ietf-core-oscore-key-update] which is a lightweight
alternative independent of ACE and EDHOC that does not require the
posting of an access token. If KUDOS is not supported, then the
Client and RS falls back to EDHOC as outlined above.
In either case, C and RS establish a new OSCORE Security Context that
replaces the old one and will be used for protecting their
communications from then on. In particular, RS MUST associate the
new OSCORE Security Context with the current (potentially re-posted)
access token. Note that, unless C and RS re-run the EDHOC protocol,
they preserve their same OSCORE identifiers, i.e., their OSCORE
Sender/Recipient IDs.
If C has already posted a valid access token, has already established
an OSCORE Security Context with RS, and wants to update its access
rights, then C can do so by posting a new access token to the /authz-
info endpoint. The new access token contains the updated access
rights for C to access protected resources at RS, and C has to obtain
it from AS as a new access token in the same token series of the
current one (see Section 3.1 and Section 3.2). When posting the new
access token to the /authz-info endpoint, C MUST protect the POST
request using the current OSCORE Security Context shared with RS.
After successful verification (see Section 4.2), RS will replace the
old access token with the new one, while preserving the same OSCORE
Security Context. In particular, C and RS do not re-run the EDHOC
protocol and they do not establish a new OSCORE Security Context.
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4.2. RS-to-C: 2.01 (Created)
Upon receiving an access token from C, RS MUST follow the procedures
defined in Section 5.10.1 of [RFC9200]. That is, RS must verify the
validity of the access token. RS may make an introspection request
(see Section 5.9.1 of [RFC9200]) to validate the access token.
If the access token is valid, RS proceeds as follows.
RS checks whether it is already storing the authentication credential
of C, namely AUTH_CRED_C, specified as PoP-key in the access token by
value or reference. In such a case, RS stores the access token and
MUST reply to the POST request with a 2.01 (Created) response.
Otherwise, RS retrieves AUTH_CRED_C, e.g., from the access token if
the authentication credential is specified therein by value, or from
a further trusted source pointed to by the AUTH_CRED_C identifier
included in the access token. After that, RS validates the actual
AUTH_CRED_C. In case of successful validation, RS stores AUTH_CRED_C
as a valid authentication credential. Then, RS stores the access
token and MUST reply to the POST request with a 2.01 (Created)
response.
If RS does not find an already stored AUTH_CRED_C, or fails to
retrieve it or to validate it, then RS MUST respond with an error
response code equivalent to the CoAP code 4.00 (Bad Request). RS may
provide additional information in the payload of the error response,
in order to clarify what went wrong.
Instead, if the access token is valid but it is associated with
claims that RS cannot process (e.g., an unknown scope), or if any of
the expected parameters is missing (e.g., any of the mandatory
parameters from AS or the identifier "id"), or if any parameters
received in the EDHOC_Information is unrecognized, then RS MUST
respond with an error response code equivalent to the CoAP code 4.00
(Bad Request). In the latter two cases, RS may provide additional
information in the payload of the error response, in order to clarify
what went wrong.
When an access token becomes invalid (e.g., due to its expiration or
revocation), RS MUST delete the access token and the associated
OSCORE Security Context, and MUST notify C with an error response
with code 4.01 (Unauthorized) for any long running request, as
specified in Section 5.8.3 of [RFC9200].
If RS receives an access token in an OSCORE protected request, it
means that C is requesting an update of access rights. In such a
case, RS MUST check that both the following conditions hold.
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* RS checks whether it stores an access token T_OLD, such that the
"id" field of EDHOC_Identifier matches the "id" field of
EDHOC_Identifier in the new access token T_NEW.
* RS checks whether the OSCORE Security Context CTX used to protect
the request matches the OSCORE Security Context associated with
the stored access token T_OLD.
If both the conditions above hold, RS MUST replace the old access
token T_OLD with the new access token T_NEW, and associate T_NEW with
the OSCORE Security Context CTX. Then, RS MUST respond with a 2.01
(Created) response protected with the same OSCORE Security Context,
with no payload.
Otherwise, RS MUST respond with a 4.01 (Unauthorized) error response.
RS may provide additional information in the payload of the error
response, in order to clarify what went wrong.
As specified in Section 5.10.1 of [RFC9200], when receiving an
updated access token with updated authorization information from C
(see Section 4.1), it is recommended that RS overwrites the previous
access token. That is, only the latest authorization information in
the access token received by RS is valid. This simplifies the
process needed by RS to keep track of authorization information for a
given client.
4.3. EDHOC Execution and Setup of OSCORE Security Context
In order to mutually authenticate and establish a long-term secret
key PRK_out with forward secrecy, C and RS run the EDHOC protocol
[I-D.ietf-lake-edhoc]. In particular, C acts as EDHOC Initiator thus
sending EDHOC message_1, while RS acts as EDHOC Responder.
As per Appendix A.2 of [I-D.ietf-lake-edhoc], C sends EDHOC message_1
and EDHOC message_3 to an EDHOC resource at RS, as CoAP POST
requests. Also RS sends EDHOC message_2 and (optionally) EDHOC
message_4 as 2.04 (Changed) CoAP responses. If, in the access token
response received from AS (see Section 3.1), the "uri_path" field of
the EDHOC_Information was included, then C MUST target the EDHOC
resource at RS with the URI path specified in the "uri_path" field.
In order to seamlessly run EDHOC, a client does not have to first
upload to RS an access token whose scope explicitly indicates
authorized access to the EDHOC resource. At the same time, RS has to
ensure that attackers cannot perform requests on the EDHOC resource,
other than sending EDHOC messages. Specifically, it SHOULD NOT be
possible to perform anything else than POST on an EDHOC resource.
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When preparing EDHOC message_1, C performs the following steps, in
additions to those defined in Section 5.2.1 of [I-D.ietf-lake-edhoc].
* If, in the access token response received from AS (see
Section 3.1), the "methods" field of the EDHOC_Information was
included, then C MUST specify one of those EDHOC methods in the
METHOD field of EDHOC message_1. That is, one of the EDHOC
methods specified in the "methods" field of EDHOC_Information MUST
be the EDHOC method used when running EDHOC with RS.
* If, in the access token response received from AS (see
Section 3.1), the "cipher_suites" field of the EDHOC_Information
was included, then C MUST specify the EDHOC cipher suite therein
in the SUITES_I field of EDHOC message_1. That is, the EDHOC
cipher suite specified in the "cipher_suites" field of
EDHOC_Information MUST be the selected cipher suite when running
EDHOC with RS.
* Rather than first uploading the access token to the /authz-info
endpoint at RS as described in Section 4.1, C MAY include the
access token in the EAD_1 field of EDHOC message_1 (see
Section 3.8 of [I-D.ietf-lake-edhoc]). This is shown by the
example in Appendix A.2.
In such a case, as per Section 3.8 of [I-D.ietf-lake-edhoc], C
adds the EAD item EAD_ACCESS_TOKEN = (ead_label, ead_value) to the
EAD_1 field. In particular, ead_label is the integer value TBD
registered in Section 9.8 of this document, while ead_value is a
CBOR byte string with value the access token. That is, the CBOR
byte string is equal to the value of the "access_token" field of
the access token response from AS (see Section 3.2).
If EDHOC message_1 includes the EAD item EAD_ACCESS_TOKEN within
the field EAD_1, then RS MUST process the access token carried out
in ead_value as specified in Section 4.2. If such a process
fails, RS MUST reply to C with an EDHOC error message with
ERR_CODE 1 (see Section 6 of [I-D.ietf-lake-edhoc]), and it MUST
discontinue the EDHOC protocol. RS MUST have successfully
completed the processing of the access token before continuing the
EDHOC execution by sending EDHOC message_2.
Note that the EAD_1 field of EDHOC message_1 cannot carry an
access token for the update of access rights, but rather only an
access token issued as the first of a token series.
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In EDHOC message_2, the authentication credential CRED_R indicated by
the message field ID_CRED_R is the authentication credential of RS,
namely AUTH_CRED_RS, that C obtained from AS. The processing of
EDHOC message_2 is defined in detail in Section 5.3 of
[I-D.ietf-lake-edhoc].
In EDHOC message_3, the authentication credential CRED_I indicated by
the message field ID_CRED_I is the authentication credential of C,
namely AUTH_CRED_C, i.e., the PoP key bound to the access token and
specified therein. The processing of EDHOC message_3 is defined in
detail in Section 5.4 of [I-D.ietf-lake-edhoc].
Once successfully completed the EDHOC execution, C and RS have both
derived the long-term secret key PRK_out (see Section 4.1.3 of
[I-D.ietf-lake-edhoc]), from which they both derive the key
PRK_Exporter (see Section 4.2.1 of [I-D.ietf-lake-edhoc]). Then, C
and RS derive an OSCORE Security Context, as defined in Appendix A.1
of [I-D.ietf-lake-edhoc]. In addition, the following applies.
* If, in the access token response received from AS (see
Section 3.1) and in the access token, the "osc_ms_size" field of
the EDHOC_Information was included, then C and RS MUST use the
value specified in the "osc_ms_size" field as length in bytes of
the OSCORE Master Secret. That is, the value of the "osc_ms_size"
field MUST be used as value for the oscore_key_length parameter of
the EDHOC-Exporter function when deriving the OSCORE Master Secret
(see Appendix A.1 of [I-D.ietf-lake-edhoc]).
* If, in the access token response received from AS (see
Section 3.1) and in the access token, the "osc_salt_size" field of
the EDHOC_Information was included, then C and RS MUST use the
value specified in the "osc_salt_size" field as length in bytes of
the OSCORE Master Salt. That is, the value of the "osc_salt_size"
field MUST be used as value for the oscore_salt_length parameter
of the EDHOC-Exporter function when deriving the OSCORE Master
Salt (see Appendix A.1 of [I-D.ietf-lake-edhoc]).
* If, in the access token response received from AS (see
Section 3.1) and in the access token, the "osc_version" field of
the EDHOC_Information was included, then C and RS MUST derive the
OSCORE Security Context, and later use it to protect their
communications, consistently with the OSCORE version specified in
the "osc_version" field.
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* Given AUTH_CRED_C the authentication credential of C used as
CRED_I in the completed EDHOC execution, RS associates the derived
OSCORE Security Context with the stored access token bound to
AUTH_CRED_C as PoP-key (regardless of whether AUTH_CRED_C is
specified by value or by reference in the access token claims).
If C supports it, C MAY use the EDHOC + OSCORE combined request
defined in [I-D.ietf-core-oscore-edhoc], as also shown by the example
in Appendix A.2. In such a case, both EDHOC message_3 and the first
OSCORE-protected application request to a protected resource are sent
to RS as combined together in a single OSCORE-protected CoAP request,
thus saving one round trip. This requires C to derive the OSCORE
Security Context with RS already after having successfully processed
the received EDHOC message_2. If, in the access token response
received from AS (see Section 3.1), the "comb_req" field of the
EDHOC_Information was included and specified the CBOR simple value
"false" (0xf4), then C MUST NOT use the EDHOC + OSCORE combined
request with RS.
4.4. Access Rights Verification
RS MUST follow the procedures defined in Section 5.10.2 of [RFC9200].
That is, if RS receives an OSCORE-protected request targeting a
protected resource from C, then RS processes the request according to
[RFC8613], when Version 1 of OSCORE is used. Future specifications
may define new versions of OSCORE, that AS can indicate C and RS to
use by means of the "osc_version" field of EDHOC_Information (see
Section 3).
If OSCORE verification succeeds and the target resource requires
authorization, RS retrieves the authorization information using the
access token associated with the OSCORE Security Context. Then, RS
must verify that the authorization information covers the target
resource and the action intended by C on it.
5. Secure Communication with AS
As specified in the ACE framework (see Sections 5.8 and 5.9 of
[RFC9200]), the requesting entity (RS and/or C) and AS communicates
via the /token or /introspect endpoint. When using this profile, the
use of CoAP [RFC7252] and OSCORE [RFC8613] for this communication is
RECOMMENDED. Other protocols fulfilling the security requirements
defined in Section 5 of [RFC9200] (such as HTTP and DTLS or TLS) MAY
be used instead.
If OSCORE is used, the requesting entity and AS need to have a OSCORE
Security Context in place. While this can be pre-installed, the
requesting entity and AS can establish such an OSCORE Security
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Context, for example, by running the EDHOC protocol, as shown between
C and AS by the examples in Appendix A.1, Appendix A.2 and
Appendix A.3. The requesting entity and AS communicate through the
/token endpoint as specified in Section 5.8 of [RFC9200] and through
the /introspect endpoint as specified in Section 5.9 of [RFC9200].
Furthermore, as defined in Section 3.2 and shown by the example in
Appendix A.3, AS may upload the access token to the /authz-info
endpoint at RS, on behalf of C. In such a case, that exchange
between AS and RS is not protected, just like when C uploads the
access token to RS by itself.
6. Discarding the Security Context
There are a number of cases where C or RS have to discard the OSCORE
Security Context, and possibly establish a new one.
C MUST discard the current OSCORE Security Context shared with RS
when any of the following occurs.
* The OSCORE Sender Sequence Number space of C gets exhausted.
* The access token associated with the OSCORE Security Context
becomes invalid, for example due to expiration or revocation.
* C receives a number of 4.01 (Unauthorized) responses to OSCORE-
protected requests sent to RS and protected using the same OSCORE
Security Context. The exact number of such received responses
needs to be specified by the application.
* The authentication credential of C (of RS) becomes invalid (e.g.,
due to expiration or revocation), and it was used as CRED_I
(CRED_R) in the EDHOC execution whose PRK_out was used to
establish the OSCORE Security Context.
RS MUST discard the current OSCORE Security Context shared with C
when any of the following occurs:
* The OSCORE Sender Sequence Number space of RS gets exhausted.
* The access token associated with the OSCORE Security Context
becomes invalid, for example due to expiration or revocation.
* The authentication credential of C (of RS) becomes invalid (e.g.,
due to expiration or revocation), and it was used as CRED_I
(CRED_R) in the EDHOC execution whose PRK_out was used to
establish the OSCORE Security Context.
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After a new access token is successfully uploaded to RS, and a new
OSCORE Security Context is established between C and RS, messages
still in transit that were protected with the previous OSCORE
Security Context might not be successfully verified by the recipient,
since the old OSCORE Security Context might have been discarded.
This means that messages sent shortly before C has uploaded the new
access token to RS might not be successfully accepted by the
recipient.
Furthermore, implementations may want to cancel CoAP observations at
RS, if registered before the new OSCORE Security Context has been
established. Alternatively, applications need to implement a
mechanism to ensure that, from then on, messages exchanged within
those observations are going to be protected with the newly derived
OSCORE Security Context.
7. Security Considerations
This document specifies a profile for the Authentication and
Authorization for Constrained Environments (ACE) framework [RFC9200].
Thus, the general security considerations from the ACE framework also
apply to this profile.
Furthermore, the security considerations from OSCORE [RFC8613] and
from EDHOC [I-D.ietf-lake-edhoc] also apply to this specific use of
the OSCORE and EDHOC protocols.
As previously stated, once completed the EDHOC execution, C and RS
are mutually authenticated through their respective authentication
credentials, whose retrieval has been facilitated by AS. Also once
completed the EDHOC execution, C and RS have established a long-term
secret key PRK_out enjoying forward secrecy. This is in turn used by
C and RS to establish an OSCORE Security Context.
Furthermore, RS achieves confirmation that C has PRK_out (proof-of-
possession) when completing the EDHOC execution. Rather, C achieves
confirmation that RS has PRK_out (proof-of-possession) either when
receiving the optional EDHOC message_4 from RS, or when successfully
verifying a response from RS protected with the established OSCORE
Security Context.
OSCORE is designed to secure point-to-point communication, providing
a secure binding between a request and the corresponding response(s).
Thus, the basic OSCORE protocol is not intended for use in point-to-
multipoint communication (e.g., enforced via multicast or a publish-
subscribe model). Implementers of this profile should make sure that
their use case of OSCORE corresponds to the expected one, in order to
prevent weakening the security assurances provided by OSCORE.
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When using this profile, it is RECOMMENDED that RS stores only one
access token per client. The use of multiple access tokens for a
single client increases the strain on RS, since it must consider
every access token associated with the client and calculate the
actual permissions that client has. Also, access tokens indicating
different or disjoint permissions from each other may lead RS to
enforce wrong permissions. If one of the access tokens expires
earlier than others, the resulting permissions may offer insufficient
protection. Developers SHOULD avoid using multiple access tokens for
a same client. Furthermore, RS MUST NOT store more than one access
token per client per PoP-key (i.e., per client's authentication
credential).
8. Privacy Considerations
This document specifies a profile for the Authentication and
Authorization for Constrained Environments (ACE) framework [RFC9200].
Thus, the general privacy considerations from the ACE framework also
apply to this profile.
Furthermore, the privacy considerations from OSCORE [RFC8613] and
from EDHOC [I-D.ietf-lake-edhoc] also apply to this specific use of
the OSCORE and EDHOC protocols.
An unprotected response to an unauthorized request may disclose
information about RS and/or its existing relationship with C. It is
advisable to include as little information as possible in an
unencrypted response. When an OSCORE Security Context already exists
between C and RS, more detailed information may be included.
Except for the case where C attempts to update its access rights, the
(encrypted) access token is sent in an unprotected POST request to
the /authz-info endpoint at RS. Thus, if C uses the same single
access token from multiple locations, it can risk being tracked by
the access token's value even when the access token is encrypted.
The identifiers used in OSCORE, i.e., the OSCORE Sender/Recipient
IDs, are negotiated by C and RS during the EDHOC execution. That is,
the EDHOC Connection Identifier C_I of C is going to be the OSCORE
Recipient ID of C (the OSCORE Sender ID of RS). Conversely, the
EDHOC Connection Identifier C_R of RS is going to be the OSCORE
Recipient ID of RS (the OSCORE Sender ID of C). These OSCORE
identifiers are privacy sensitive (see Section 12.8 of [RFC8613]).
In particular, they could reveal information about C, or may be used
for correlating different requests from C, e.g., across different
networks that C has joined and left over time. This can be mitigated
if C and RS dynamically update their OSCORE identifiers, e.g., by
using the method defined in [I-D.ietf-core-oscore-key-update].
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9. IANA Considerations
This document has the following actions for IANA.
Note to RFC Editor: Please replace all occurrences of "[RFC-XXXX]"
with the RFC number of this specification and delete this paragraph.
9.1. ACE OAuth Profile Registry
IANA is asked to add the following entry to the "ACE OAuth Profile"
Registry following the procedure specified in [RFC9200].
* Profile name: coap_edhoc_oscore
* Profile Description: Profile for delegating client authentication
and authorization in a constrained environment by establishing an
OSCORE Security Context [RFC8613] between resource-constrained
nodes, through the execution of the authenticated key
establishment protocol EDHOC [I-D.ietf-lake-edhoc].
* Profile ID: TBD (value between 1 and 255)
* Change Controller: IESG
* Reference: [RFC-XXXX]
9.2. OAuth Parameters Registry
IANA is asked to add the following entries to the "OAuth Parameters"
registry.
* Name: "edhoc_info"
* Parameter Usage Location: token request, token response
* Change Controller: IESG
* Reference: [RFC-XXXX]
* Name: "token_uploaded"
* Parameter Usage Location: token response
* Change Controller: IESG
* Reference: [RFC-XXXX]
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9.3. OAuth Parameters CBOR Mappings Registry
IANA is asked to add the following entries to the "OAuth Parameters
CBOR Mappings" following the procedure specified in [RFC9200].
* Name: "edhoc_info"
* CBOR Key: TBD
* Value Type: map
* Reference: [RFC-XXXX]
* Name: "token_uploaded"
* CBOR Key: TBD
* Value Type: simple value "true" / simple type "false"
* Reference: [RFC-XXXX]
9.4. JSON Web Token Claims Registry
IANA is asked to add the following entries to the "JSON Web Token
Claims" registry following the procedure specified in [RFC7519].
* Claim Name: "edhoc_info"
* Claim Description: Information for EDHOC execution
* Change Controller: IETF
* Reference: [RFC-XXXX]
9.5. CBOR Web Token Claims Registry
IANA is asked to add the following entries to the "CBOR Web Token
Claims" registry following the procedure specified in [RFC8392].
* Claim Name: "edhoc_info"
* Claim Description: Information for EDHOC execution
* JWT Claim Name: "edhoc_info"
* Claim Key: TBD
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* Claim Value Type(s): map
* Change Controller: IESG
* Specification Document(s): [RFC-XXXX]
9.6. JWT Confirmation Methods Registry
IANA is asked to add the following entries to the "JWT Confirmation
Methods" registry following the procedure specified in [RFC7800].
* Confirmation Method Value: "x5bag"
* Confirmation Method Description: An unordered bag of X.509
certificates
* Change Controller: IESG
* Specification Document(s): [RFC-XXXX]
* Confirmation Method Value: "x5chain"
* Confirmation Method Description: An ordered chain of X.509
certificates
* Change Controller: IESG
* Specification Document(s): [RFC-XXXX]
* Confirmation Method Value: "x5t"
* Confirmation Method Description: Hash of an X.509 certificate
* Change Controller: IESG
* Specification Document(s): [RFC-XXXX]
* Confirmation Method Value: "x5u"
* Confirmation Method Description: URI pointing to an X.509
certificate
* Change Controller: IESG
* Specification Document(s): [RFC-XXXX]
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* Confirmation Method Value: "c5b"
* Confirmation Method Description: An unordered bag of C509
certificates
* Change Controller: IESG
* Specification Document(s): [RFC-XXXX]
* Confirmation Method Value: "c5c"
* Confirmation Method Description: An ordered chain of C509
certificates
* Change Controller: IESG
* Specification Document(s): [RFC-XXXX]
* Confirmation Method Value: "c5t"
* Confirmation Method Description: Hash of an C509 certificate
* Change Controller: IESG
* Specification Document(s): [RFC-XXXX]
* Confirmation Method Value: "c5u"
* Confirmation Method Description: URI pointing to a COSE_C509
containing an ordered chain of certificates
* Change Controller: IESG
* Specification Document(s): [RFC-XXXX]
* Confirmation Method Value: "kcwt"
* Confirmation Method Description: A CBOR Web Token (CWT) containing
a COSE_Key in a 'cnf' claim
* Change Controller: IESG
* Specification Document(s): [RFC-XXXX]
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* Confirmation Method Value: "kccs"
* Confirmation Method Description: A CWT Claims Set (CCS) containing
a COSE_Key in a 'cnf' claim
* Change Controller: IESG
* Specification Document(s): [RFC-XXXX]
9.7. CWT Confirmation Methods Registry
IANA is asked to add the following entries to the "CWT Confirmation
Methods" registry following the procedure specified in [RFC8747].
* Confirmation Method Name: x5bag
* Confirmation Method Description: An unordered bag of X.509
certificates
* JWT Confirmation Method Name: "x5bag"
* Confirmation Key: TBD
* Confirmation Value Type(s): COSE_X509
* Change Controller: IESG
* Specification Document(s): [RFC-XXXX]
* Confirmation Method Name: x5chain
* Confirmation Method Description: An ordered chain of X.509
certificates
* JWT Confirmation Method Name: "x5chain"
* Confirmation Key: TBD
* Confirmation Value Type(s): COSE_X509
* Change Controller: IESG
* Specification Document(s): [RFC-XXXX]
* Confirmation Method Name: x5t
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* Confirmation Method Description: Hash of an X.509 certificate
* JWT Confirmation Method Name: "x5t"
* Confirmation Key: TBD
* Confirmation Value Type(s): COSE_CertHash
* Change Controller: IESG
* Specification Document(s): [RFC-XXXX]
* Confirmation Method Name: x5u
* Confirmation Method Description: URI pointing to an X.509
certificate
* JWT Confirmation Method Name: "x5u"
* Confirmation Key: TBD
* Confirmation Value Type(s): uri
* Change Controller: IESG
* Specification Document(s): [RFC-XXXX]
* Confirmation Method Name: c5b
* Confirmation Method Description: An unordered bag of C509
certificates
* JWT Confirmation Method Name: "c5b"
* Confirmation Key: TBD
* Confirmation Value Type(s): COSE_C509
* Change Controller: IESG
* Specification Document(s): [RFC-XXXX]
* Confirmation Method Name: c5c
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* Confirmation Method Description: An ordered chain of C509
certificates
* JWT Confirmation Method Name: "c5c"
* Confirmation Key: TBD
* Confirmation Value Type(s): COSE_C509
* Change Controller: IESG
* Specification Document(s): [RFC-XXXX]
* Confirmation Method Name: c5t
* Confirmation Method Description: Hash of an C509 certificate
* JWT Confirmation Method Name: "c5t"
* Confirmation Key: TBD
* Confirmation Value Type(s): COSE_CertHash
* Change Controller: IESG
* Specification Document(s): [RFC-XXXX]
* Confirmation Method Name: c5u
* Confirmation Method Description: URI pointing to a COSE_C509
containing an ordered chain of certificates
* JWT Confirmation Method Name: "c5u"
* Confirmation Key: TBD
* Confirmation Value Type(s): uri
* Change Controller: IESG
* Specification Document(s): [RFC-XXXX]
* Confirmation Method Name: kcwt
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* Confirmation Method Description: A CBOR Web Token (CWT) containing
a COSE_Key in a 'cnf' claim
* JWT Confirmation Method Name: "kcwt"
* Confirmation Key: TBD
* Confirmation Value Type(s): COSE_Messages
* Change Controller: IESG
* Specification Document(s): [RFC-XXXX]
* Confirmation Method Name: kccs
* Confirmation Method Description: A CWT Claims Set (CCS) containing
a COSE_Key in a 'cnf' claim
* JWT Confirmation Method Name: "kccs"
* Confirmation Key: TBD
* Confirmation Value Type(s): map / #6(map)
* Change Controller: IESG
* Specification Document(s): [RFC-XXXX]
9.8. EDHOC External Authorization Data Registry
IANA is asked to add the following entry to the "EDHOC External
Authorization Data" registry defined in Section 9.5 of
[I-D.ietf-lake-edhoc].
* Label: TBD
* Message: EDHOC message_1
* Description: "ead_value" specifies an access token
* Reference: [RFC-XXXX]
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9.9. EDHOC Information Registry
It is requested that IANA create a new registry entitled "EDHOC
Information" registry. The registry is to be created with
registration policy Expert Review [RFC8126]. Guidelines for the
experts are provided in Section 9.10. It should be noted that in
addition to the expert review, some portions of the registry require
a specification, potentially on Standards Track, be supplied as well.
The columns of the registry are:
* Name: A descriptive name that enables easier reference to this
item. Because a core goal of this document is for the resulting
representations to be compact, it is RECOMMENDED that the name be
short.
This name is case sensitive. Names may not match other registered
names in a case-insensitive manner unless the Designated Experts
determine that there is a compelling reason to allow an exception.
The name is not used in the CBOR encoding.
* CBOR Value: The value to be used as CBOR abbreviation of the item.
The value MUST be unique. The value can be a positive integer, a
negative integer or a string. Integer values between -256 and 255
and strings of length 1 are to be registered by Standards Track
documents (Standards Action). Integer values from -65536 to -257
and from 256 to 65535 and strings of maximum length 2 are to be
registered by public specifications (Specification Required).
Integer values greater than 65535 and strings of length greater
than 2 are subject to the Expert Review policy. Integer values
less than -65536 are marked as private use.
* CBOR Type: The CBOR type of the item, or a pointer to the registry
that defines its type, when that depends on another item.
* Registry: The registry that values of the item may come from, if
one exists.
* Description: A brief description of this item.
* Specification: A pointer to the public specification for the item,
if one exists.
This registry will be initially populated by the values in Figure 6.
The "Specification" column for all of these entries will be this
document and [I-D.ietf-lake-edhoc].
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9.10. Expert Review Instructions
The IANA registry established in this document is defined to use the
registration policy Expert Review. This section gives some general
guidelines for what the experts should be looking for, but they are
being designated as experts for a reason so they should be given
substantial latitude.
Expert reviewers should take into consideration the following points:
* Point squatting should be discouraged. Reviewers are encouraged
to get sufficient information for registration requests to ensure
that the usage is not going to duplicate one that is already
registered and that the point is likely to be used in deployments.
The zones tagged as private use are intended for testing purposes
and closed environments; code points in other ranges should not be
assigned for testing.
* Specifications are required for the Standards Action range of
point assignment. Specifications should exist for Specification
Required ranges, but early assignment before a specification is
available is considered to be permissible. Specifications are
needed for the first-come, first-serve range if they are expected
to be used outside of closed environments in an interoperable way.
When specifications are not provided, the description provided
needs to have sufficient information to identify what the point is
being used for.
* Experts should take into account the expected usage of fields when
approving point assignment. The fact that there is a range for
Standards Track documents does not mean that a Standards Track
document cannot have points assigned outside of that range. The
length of the encoded value should be weighed against how many
code points of that length are left, the size of device it will be
used on, and the number of code points left that encode to that
size.
10. References
10.1. Normative References
[I-D.ietf-core-oscore-edhoc]
Palombini, F., Tiloca, M., Höglund, R., Hristozov, S., and
G. Selander, "Using EDHOC with CoAP and OSCORE", Work in
Progress, Internet-Draft, draft-ietf-core-oscore-edhoc-07,
13 March 2023, <https://datatracker.ietf.org/doc/html/
draft-ietf-core-oscore-edhoc-07>.
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[I-D.ietf-cose-cbor-encoded-cert]
Mattsson, J. P., Selander, G., Raza, S., Höglund, J., and
M. Furuhed, "CBOR Encoded X.509 Certificates (C509
Certificates)", Work in Progress, Internet-Draft, draft-
ietf-cose-cbor-encoded-cert-05, 10 January 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-cose-
cbor-encoded-cert-05>.
[I-D.ietf-lake-edhoc]
Selander, G., Mattsson, J. P., and F. Palombini,
"Ephemeral Diffie-Hellman Over COSE (EDHOC)", Work in
Progress, Internet-Draft, draft-ietf-lake-edhoc-20, 7 July
2023, <https://datatracker.ietf.org/doc/html/draft-ietf-
lake-edhoc-20>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/rfc/rfc5280>.
[RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
RFC 6749, DOI 10.17487/RFC6749, October 2012,
<https://www.rfc-editor.org/rfc/rfc6749>.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<https://www.rfc-editor.org/rfc/rfc7252>.
[RFC7519] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
(JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
<https://www.rfc-editor.org/rfc/rfc7519>.
[RFC7800] Jones, M., Bradley, J., and H. Tschofenig, "Proof-of-
Possession Key Semantics for JSON Web Tokens (JWTs)",
RFC 7800, DOI 10.17487/RFC7800, April 2016,
<https://www.rfc-editor.org/rfc/rfc7800>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/rfc/rfc8126>.
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[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.
[RFC8392] Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig,
"CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392,
May 2018, <https://www.rfc-editor.org/rfc/rfc8392>.
[RFC8610] Birkholz, H., Vigano, C., and C. Bormann, "Concise Data
Definition Language (CDDL): A Notational Convention to
Express Concise Binary Object Representation (CBOR) and
JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610,
June 2019, <https://www.rfc-editor.org/rfc/rfc8610>.
[RFC8613] Selander, G., Mattsson, J., Palombini, F., and L. Seitz,
"Object Security for Constrained RESTful Environments
(OSCORE)", RFC 8613, DOI 10.17487/RFC8613, July 2019,
<https://www.rfc-editor.org/rfc/rfc8613>.
[RFC8742] Bormann, C., "Concise Binary Object Representation (CBOR)
Sequences", RFC 8742, DOI 10.17487/RFC8742, February 2020,
<https://www.rfc-editor.org/rfc/rfc8742>.
[RFC8747] Jones, M., Seitz, L., Selander, G., Erdtman, S., and H.
Tschofenig, "Proof-of-Possession Key Semantics for CBOR
Web Tokens (CWTs)", RFC 8747, DOI 10.17487/RFC8747, March
2020, <https://www.rfc-editor.org/rfc/rfc8747>.
[RFC8949] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", STD 94, RFC 8949,
DOI 10.17487/RFC8949, December 2020,
<https://www.rfc-editor.org/rfc/rfc8949>.
[RFC9200] Seitz, L., Selander, G., Wahlstroem, E., Erdtman, S., and
H. Tschofenig, "Authentication and Authorization for
Constrained Environments Using the OAuth 2.0 Framework
(ACE-OAuth)", RFC 9200, DOI 10.17487/RFC9200, August 2022,
<https://www.rfc-editor.org/rfc/rfc9200>.
[RFC9201] Seitz, L., "Additional OAuth Parameters for Authentication
and Authorization for Constrained Environments (ACE)",
RFC 9201, DOI 10.17487/RFC9201, August 2022,
<https://www.rfc-editor.org/rfc/rfc9201>.
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[RFC9203] Palombini, F., Seitz, L., Selander, G., and M. Gunnarsson,
"The Object Security for Constrained RESTful Environments
(OSCORE) Profile of the Authentication and Authorization
for Constrained Environments (ACE) Framework", RFC 9203,
DOI 10.17487/RFC9203, August 2022,
<https://www.rfc-editor.org/rfc/rfc9203>.
[RFC9360] Schaad, J., "CBOR Object Signing and Encryption (COSE):
Header Parameters for Carrying and Referencing X.509
Certificates", RFC 9360, DOI 10.17487/RFC9360, February
2023, <https://www.rfc-editor.org/rfc/rfc9360>.
10.2. Informative References
[I-D.ietf-core-oscore-key-update]
Höglund, R. and M. Tiloca, "Key Update for OSCORE
(KUDOS)", Work in Progress, Internet-Draft, draft-ietf-
core-oscore-key-update-04, 13 March 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-core-
oscore-key-update-04>.
[RFC4949] Shirey, R., "Internet Security Glossary, Version 2",
FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007,
<https://www.rfc-editor.org/rfc/rfc4949>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/rfc/rfc8446>.
[RFC9110] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP Semantics", STD 97, RFC 9110,
DOI 10.17487/RFC9110, June 2022,
<https://www.rfc-editor.org/rfc/rfc9110>.
[RFC9147] Rescorla, E., Tschofenig, H., and N. Modadugu, "The
Datagram Transport Layer Security (DTLS) Protocol Version
1.3", RFC 9147, DOI 10.17487/RFC9147, April 2022,
<https://www.rfc-editor.org/rfc/rfc9147>.
Appendix A. Examples
This appendix provides examples where this profile of ACE is used.
In particular:
* Appendix A.1 does not make use of use of any optimization.
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* Appendix A.2 makes use of the optimizations defined in this
specification, hence reducing the roundtrips of the interactions
between the Client and the Resource Server.
* Appendix A.3 considers an alternative workflow where AS uploads
the access token to RS.
All these examples build on the following assumptions, as relying on
expected early procedures performed at AS. These include the
registration of RSs by the respective Resource Owners as well as the
registrations of Clients authorized to request access token for those
RSs.
* AS knows the authentication credential AUTH_CRED_C of the Client
C.
* The Client knows the authentication credential AUTH_CRED_AS of AS.
* AS knows the authentication credential AUTH_CRED_RS of RS.
* RS knows the authentication credential AUTH_CRED_AS of AS.
This is relevant in case AS and RS actually require a secure
association (e.g., for RS to perform token introspection at AS, or
for AS to upload an access token to RS on behalf of the Client).
As a result of the assumptions above, it is possible to limit the
transport of AUTH_CRED_C and AUTH_CRED_RS by value only to the
following two cases, and only when the Client requests an access
token for RS in question for the first time when considering the pair
(AUTH_CRED_C, AUTH_CRED_RS).
* In the Token Response from AS to the Client, where AUTH_CRED_RS is
specified by the 'rs_cnf' parameter.
* In the access token, where AUTH_CRED_C is specified by the 'cnf'
claim.
Note that, even under the circumstances mentioned above, AUTH_CRED_C
might rather be indicated by reference. This is possible if RS can
effectively use such a reference from the access token to retrieve
AUTH_CRED_C (e.g., from a trusted repository of authentication
credentials reachable through a non-constrained link), and if AS is
in turn aware of that.
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In any other case, it is otherwise possible to indicate both
AUTH_CRED_C and AUTH_CRED_RS by reference, when performing the ACE
access control workflow as well as later on when the Client and RS
run EDHOC.
A.1. Workflow without Optimizations
The example below considers the simplest (though least efficient)
interaction between the Client and RS. That is: first C uploads the
access token to RS; then C and RS run EDHOC; and, finally, the Client
accesses the protected resource at RS.
C AS RS
| | |
| EDHOC message_1 to /edhoc | |
M01 |--------------------------------->| |
| | |
| | |
| EDHOC message_2 | |
M02 |<---------------------------------| |
| ID_CRED_R identifies | |
| CRED_R = AUTH_CRED_AS | |
| by reference | |
| | |
| | |
| EDHOC message_3 to /edhoc | |
M03 |--------------------------------->| |
| ID_CRED_I identifies | |
| CRED_I = AUTH_CRED_C | |
| by reference | |
| | |
| | |
| Token request to /token | |
| (OSCORE-protected message) | |
M04 |--------------------------------->| |
| 'req_cnf' identifies | |
| AUTH_CRED_C by reference | |
| | |
| | |
| Token response | |
| (OSCORE-protected message) | |
M05 |<---------------------------------| |
| 'rs_cnf' specifies | |
| AUTH_CRED_RS by value | |
| | |
| 'ace_profile' = | |
| coap_edhoc_oscore | |
| | |
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| 'edhoc_info' specifies: | |
| { | |
| id : h'01', | |
| cipher_suites : 2, | |
| methods : 3 | |
| } | |
| | |
| In the access token: | |
| * the 'cnf' claim specifies | |
| AUTH_CRED_C by value | |
| * the 'edhoc_info' claim | |
| specifies the same as | |
| 'edhoc_info' above | |
| | |
// Possibly after chain verification, the Client adds AUTH_CRED_RS
// to the set of its trusted peer authentication credentials,
// relying on AS as trusted provider
| | |
| Token upload to /authz-info | |
| (unprotected message) | |
M06 |---------------------------------------------------------------->|
| | |
// Possibly after chain verification, RS adds AUTH_CRED_C
// to the set of its trusted peer authentication credentials,
// relying on AS as trusted provider
| | |
| 2.01 (Created) | |
| (unprotected message) | |
M07 |<----------------------------------------------------------------|
| | |
| | |
| EDHOC message_1 to /edhoc | |
| (no access control is enforced) | |
M08 |---------------------------------------------------------------->|
| | |
| | |
| EDHOC message_2 | |
M09 |<----------------------------------------------------------------|
| ID_CRED_R identifies | |
| CRED_R = AUTH_CRED_RS | |
| by reference | |
| | |
| | |
| EDHOC message_3 to /edhoc | |
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| (no access control is enforced) | |
M10 |---------------------------------------------------------------->|
| ID_CRED_I identifies | |
| CRED_I = AUTH_CRED_C | |
| by reference | |
| | |
| | |
| Access to protected resource | |
| (OSCORE-protected message) | |
| (access control is enforced) | |
M11 |---------------------------------------------------------------->|
| | |
| Response | |
| (OSCORE-protected message) | |
M12 |<----------------------------------------------------------------|
| | |
// Later on, the access token expires ...
// - The Client and RS delete their OSCORE Security Context and
// purge the EDHOC session used to derive it (unless the same
// session is also used for other reasons).
// - RS retains AUTH_CRED_C as still valid,
// and AS knows about it.
// - The Client retains AUTH_CRED_RS as still valid,
// and AS knows about it.
| | |
| | |
// Time passes ...
| | |
| | |
// The Client asks for a new access token; now all the
// authentication credentials can be indicated by reference
// The price to pay is on AS, about remembering that at least
// one access token has been issued for the pair (Client, RS)
// and considering the pair (AUTH_CRED_C, AUTH_CRED_RS)
| | |
| Token request to /token | |
| (OSCORE-protected message) | |
M13 |--------------------------------->| |
| 'req_cnf' identifies | |
| CRED_I = AUTH_CRED_C | |
| by reference | |
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| | |
| | |
| Token response | |
| (OSCORE-protected message) | |
M14 |<---------------------------------| |
| 'rs_cnf' identifies | |
| AUTH_CRED_RS by reference | |
| | |
| 'ace_profile' = | |
| coap_edhoc_oscore | |
| | |
| 'edhoc_info' specifies: | |
| { | |
| id : h'05', | |
| cipher_suites : 2, | |
| methods : 3 | |
| } | |
| | |
| In the access token: | |
| * the 'cnf' claim specifies | |
| AUTH_CRED_C by reference | |
| * the 'edhoc_info' claim | |
| specifies the same as | |
| 'edhoc_info' above | |
| | |
| | |
| Token upload to /authz-info | |
| (unprotected message) | |
M15 |---------------------------------------------------------------->|
| | |
| | |
| 2.01 (Created) | |
| (unprotected message) | |
M16 |<----------------------------------------------------------------|
| | |
| | |
| EDHOC message_1 to /edhoc | |
| (no access control is enforced) | |
M17 |---------------------------------------------------------------->|
| | |
| | |
| EDHOC message_2 | |
| (no access control is enforced) | |
M18 |<----------------------------------------------------------------|
| ID_CRED_R specifies | |
| CRED_R = AUTH_CRED_RS | |
| by reference | |
| | |
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| | |
| EDHOC message_3 to /edhoc | |
| (no access control is enforced) | |
M19 |---------------------------------------------------------------->|
| ID_CRED_I identifies | |
| CRED_I = AUTH_CRED_C | |
| by reference | |
| | |
| | |
| Access to protected resource /r | |
| (OSCORE-protected message) | |
| (access control is enforced) | |
M20 |---------------------------------------------------------------->|
| | |
| | |
| Response | |
| (OSCORE-protected message) | |
M21 |<----------------------------------------------------------------|
| | |
A.2. Workflow with Optimizations
The example below builds on the example in Appendix A.1, while
additionally relying on the two following optimizations.
* The access token is not separately uploaded to the /authz-info
endpoint at RS, but rather included in the EAD_1 field of EDHOC
message_1 sent by C to RS.
* The Client uses the EDHOC+OSCORE request defined in
[I-D.ietf-core-oscore-edhoc] is used, when running EDHOC both with
AS and with RS.
These two optimizations used together result in the most efficient
interaction between C and RS, as consisting of only two roundtrips to
upload the access token, run EDHOC and access the protected resource
at RS.
C AS RS
| | |
| EDHOC message_1 to /edhoc | |
M01 |--------------------------------->| |
| | |
| | |
| EDHOC message_2 | |
M02 |<---------------------------------| |
| ID_CRED_R identifies | |
| CRED_R = AUTH_CRED_AS | |
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| by reference | |
| | |
| | |
| EDHOC+OSCORE request to /token | |
M03 |--------------------------------->| |
| * EDHOC message_3 | |
| ID_CRED_I identifies | |
| CRED_I = AUTH_CRED_C | |
| by reference | |
| --- --- --- | |
| * OSCORE-protected part | |
| Token request | |
| 'req_cnf' identifies | |
| AUTH_CRED_C by reference | |
| | |
| | |
| Token response | |
| (OSCORE-protected message) | |
M04 |<---------------------------------| |
| 'rs_cnf' specifies | |
| AUTH_CRED_RS by value | |
| | |
| 'ace_profile' = | |
| coap_edhoc_oscore | |
| | |
| 'edhoc_info' specifies: | |
| { | |
| id : h'01', | |
| cipher_suites : 2, | |
| methods : 3 | |
| } | |
| | |
| In the access token: | |
| * the 'cnf' claim specifies | |
| AUTH_CRED_C by value | |
| * the 'edhoc_info' claim | |
| specifies the same as | |
| 'edhoc_info' above | |
| | |
// Possibly after chain verification, the Client adds AUTH_CRED_RS
// to the set of its trusted peer authentication credentials,
// relying on AS as trusted provider
| | |
| EDHOC message_1 to /edhoc | |
| (no access control is enforced) | |
M05 |---------------------------------------------------------------->|
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| Access token specified in EAD_1 | |
| | |
// Possibly after chain verification, RS adds AUTH_CRED_C
// to the set of its trusted peer authentication credentials,
// relying on AS as trusted provider
| | |
| EDHOC message_2 | |
M06 |<----------------------------------------------------------------|
| ID_CRED_R identifies | |
| CRED_R = AUTH_CRED_RS | |
| by reference | |
| | |
| | |
| EDHOC+OSCORE request to /r | |
M07 |---------------------------------------------------------------->|
| * EDHOC message_3 | |
| ID_CRED_I identifies | |
| CRED_I = AUTH_CRED_C | |
| by reference | |
| --- --- --- | |
| * OSCORE-protected part | |
| Application request to /r | |
| | |
// After the EDHOC processing is completed, access control
// is enforced on the rebuilt OSCORE-protected request,
// like if it had been sent stand-alone
| | |
| Response | |
| (OSCORE-protected message) | |
M08 |<----------------------------------------------------------------|
| | |
A.3. Alternative Workflow (AS token posting)
The example below builds on the example in Appendix A.2, but assumes
that AS is uploading the access token to RS on behalf of C.
C AS RS
| | |
| | |
| | |
| EDHOC message_1 to /edhoc | |
M01 |--------------------------------->| |
| | |
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| | |
| EDHOC message_2 | |
M02 |<---------------------------------| |
| ID_CRED_R identifies | |
| CRED_R = AUTH_CRED_AS | |
| by reference | |
| | |
| | |
| EDHOC+OSCORE request to /token | |
M03 |--------------------------------->| |
| * EDHOC message_3 | |
| ID_CRED_I identifies | |
| CRED_I = AUTH_CRED_C | |
| by reference | |
| --- --- --- | |
| * OSCORE-protected part | |
| Token request | |
| 'req_cnf' identifies | |
| AUTH_CRED_C by reference | |
| | |
| | |
| | Token upload to /authz-info |
M04 | |----------------------------->|
| | In the access token: |
| | * the 'cnf' claim |
| | specifies AUTH_CRED_C |
| | by value |
| | * the 'edhoc_info' |
| | claim specifies |
| | { |
| | id : h'01', |
| | cipher_suites : 2, |
| | methods: 3 |
| | } |
| | |
// Possibly after chain verification, RS adds AUTH_CRED_C
// to the set of its trusted peer authentication credentials,
// relying on AS as trusted provider
| | |
| | 2.01 (Created) |
M05 | |<-----------------------------|
| | |
| | |
| Token response | |
| (OSCORE-protected message) | |
M06 |<---------------------------------| |
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| 'rs_cnf' specifies | |
| AUTH_CRED_RS by value | |
| | |
| 'ace_profile' = | |
| coap_edhoc_oscore | |
| | |
| 'token_uploaded' = true | |
| | |
| 'edhoc_info' specifies: | |
| { | |
| id : h'01', | |
| cipher_suites : 2, | |
| methods : 3 | |
| } | |
| | |
// Possibly after chain verification, the Client adds AUTH_CRED_RS
// to the set of its trusted peer authentication credentials,
// relying on AS as trusted provider
| | |
| EDHOC message_1 to /edhoc | |
| (no access control is enforced) | |
M07 |---------------------------------------------------------------->|
| | |
| | |
| EDHOC message_2 | |
M08 |<----------------------------------------------------------------|
| ID_CRED_R identifies | |
| CRED_R = AUTH_CRED_RS | |
| by reference | |
| | |
| | |
| EDHOC+OSCORE request to /r | |
M09 |---------------------------------------------------------------->|
| * EDHOC message_3 | |
| ID_CRED_I identifies | |
| CRED_I = AUTH_CRED_C | |
| by reference | |
| --- --- --- | |
| * OSCORE-protected part | |
| Application request to /r | |
| | |
// After the EDHOC processing is completed, access control
// is enforced on the rebuilt OSCORE-protected request,
// like if it had been sent stand-alone
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| | |
| Response | |
| (OSCORE-protected message) | |
M10 |<----------------------------------------------------------------|
| | |
Appendix B. Profile Requirements
This section lists the specifications of this profile based on the
requirements of the framework, as requested in Appendix C of
[RFC9200].
* Optionally, define new methods for the client to discover the
necessary permissions and AS for accessing a resource, different
from the one proposed in [RFC9200]: Not specified
* Optionally, specify new grant types: Not specified
* Optionally, define the use of client certificates as client
credential type: C can use authentication credentials of any type
admitted by the EDHOC protocol, including public key certificates
such as X.509 and C509 certificates.
* Specify the communication protocol the client and RS must use:
CoAP
* Specify the security protocol the client and RS must use to
protect their communication: OSCORE
* Specify how the client and the RS mutually authenticate:
Explicitly, by successfully executing the EDHOC protocol, after
which a common OSCORE Security Context is established from the
EDHOC session keying material. As per the EDHOC authentication
method used during the EDHOC session, authentication is provided
by digital signatures, or by Message Authentication Codes (MACs)
computed from an ephemeral-static ECDH shared secret.
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* Specify the proof-of-possession protocol(s) and how to select one,
if several are available. Also specify which key types (e.g.,
symmetric/asymmetric) are supported by a specific proof-of-
possession protocol: proof-of-possession is first achieved by RS
when successfully processing EDHOC message_3 during the EDHOC
execution with C, through EDHOC algorithms and symmetric EDHOC
session keys. Also, proof-of-possession is later achieved by C
when receiving from RS: i) the optional EDHOC message_4 during the
EDHOC execution with RS, through EDHOC algorithms and symmetric
EDHOC session keys; or ii) the first response protected with the
OSCORE Security Context established after the EDHOC execution with
RS, through OSCORE algorithms and OSCORE symmetric keys derived
from the completed EDHOC session.
* Specify a unique ace_profile identifier: coap_edhoc_oscore
* If introspection is supported, specify the communication and
security protocol for introspection: HTTP/CoAP (+ TLS/DTLS/OSCORE)
* Specify the communication and security protocol for interactions
between client and AS: HTTP/CoAP (+ TLS/DTLS/OSCORE)
* Specify if/how the authz-info endpoint is protected, including how
error responses are protected: Not protected
* Optionally, define methods of token transport other than the
authz-info endpoint: C can upload the access token when executing
EDHOC with RS, by including the access token in the EAD_1 field of
EDHOC message_1 (see Section 4.3).
Appendix C. Document Updates
RFC EDITOR: PLEASE REMOVE THIS SECTION.
C.1. Version -00 to -01
* Fixed semantics of the ead_value for transporting an Access Token
in the EAD_1 field.
* Error handling aligned with EDHOC.
* Precise characterization of the EDHOC execution considered for
EDHOC-KeyUpdate.
* Fixed message exchange examples.
* Added appendix with profile requirements.
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* Updated references.
* Clarifications and editorial improvements.
Acknowledgments
The authors sincerely thank Christian Amsüss and Carsten Bormann for
their comments and feedback.
Work on this document has in part been supported by the H2020 project
SIFIS-Home (grant agreement 952652).
Authors' Addresses
Göran Selander
Ericsson
Email: goran.selander@ericsson.com
John Preuß Mattsson
Ericsson
Email: john.mattsson@ericsson.com
Marco Tiloca
RISE
Email: marco.tiloca@ri.se
Rikard Höglund
RISE
Email: rikard.hoglund@ri.se
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