| Internet-Draft | EDHOC and OSCORE profile of ACE | March 2024 |
| Selander, et al. | Expires 5 September 2024 | [Page] |
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 ACE-OAuth Client and Resource Server, and it binds an authentication credential of the Client to an ACE-OAuth 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. This profile can be used to delegate management of authorization information from a resource-constrained server to a trusted host with less severe limitations regarding processing power and memory.¶
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This document defines the "coap_edhoc_oscore" profile of the ACE-OAuth framework [RFC9200]. This profile addresses a "zero-touch" constrained setting where authenticated and authorized 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, but this profile uses the Ephemeral Diffie-Hellman Over COSE (EDHOC) protocol [I-D.ietf-lake-edhoc] to establish the OSCORE Security Context. 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 the OSCORE Security Context. As recommended in [RFC9200], this document recommends the use of CBOR Web Tokens (CWTs) [RFC8392] as access tokens.¶
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 that C makes to AS.¶
The establishment of an association between RS and AS in an ACE ecosystem is out of scope, but one solution is to build on the same primitives as used in this document, i.e., EDHOC for authentication and OSCORE for communication security, using for example [I-D.ietf-lake-authz] for onboarding RS with AS, and [I-D.ietf-ace-coap-est-oscore] for establishing a trust anchor in RS. A similar procedure can also be applied between C and AS for registering a client and for the establishment of a trust anchor.¶
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].¶
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.¶
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.¶
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, the client (C) and the 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 with OSCORE Security Contexts and with 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 RS, by sending an access token request to the /token endpoint, as specified in Section 5.8 of [RFC9200].¶
This profile also supports the alternative workflow where AS uploads the access token to RS, as defined in [I-D.ietf-ace-workflow-and-params].¶
If C has retrieved an access token, there are two options for C to upload it to RS, as further detailed in this document.¶
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 replies to the request with a 2.01 (Created) response, after which C initiates the EDHOC protocol with RS. The communication with the /authz-info endpoint is typically not protected, except for the update of access rights (see Section 4.5).¶
C initiates the EDHOC protocol and includes the access token as External Authorization Data (EAD), see Section 3.8 of [I-D.ietf-lake-edhoc]. In this case, the access token is validated in parallel with the EDHOC session. This option cannot be used for the update of access rights.¶
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 session successfully, they are mutually authenticated and they derive an OSCORE Security Context as per Appendix A.1 of [I-D.ietf-lake-edhoc].¶
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 there is a valid access token. 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 a "session identifier" (see Section 3.4) provided by AS in the initial request, which allows AS to find the data it has previously shared with C. The session identifier is assigned by AS and used to identify a series of access tokens, called a "token series" (see Section 3.2). Upon a successful update of access rights (see Section 4.5), the new issued access token becomes the latest in its token series, but the session identifier remains the same. When the latest access token of a token series becomes invalid (e.g., when it expires or gets revoked), that token series ends.¶
When RS receives a request from C protected with an OSCORE Security Context derived from an EDHOC session implementing this profile, then the associated session identifier, together with the authentication credential of C used in the EDHOC session, enables the RS to look up the unique access token determining the access rights of C.¶
An overview of the profile flow for the "coap_edhoc_oscore" profile in case of option 1 above is given in Figure 1. The names of messages coincide with those of [RFC9200] when applicable.¶
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.¶
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 containing information related to an EDHOC session, in particular the identifier "session_id", see Section 3.4. This object is transported in the "edhoc_info" parameter registered in Section 10.2 and Section 10.3.¶
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). This document describes the use of CoAP, EDHOC and OSCORE to reduce the number of libraries that C has to support.¶
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 a previous client registration process or 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'
}
}
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. The EDHOC_Information MUST include the "session_id" field. This POST request MUST omit the "req_cnf" parameter. An example of such a request is shown in Figure 3.¶
The identifier "session_id" 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 session_id 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 "session_id" identifies a token series to which a still valid access token issued for C and RS belongs. 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].¶
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" : {
"session_id" : h'01'
}
}
This document refers to "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 associated with the same authentication credential of C¶
issued for the same RS, identified by the same authentication credential¶
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., due to its expiration or revocation), the token series it belongs to ends.¶
The general token series concept is defined in [I-D.ietf-ace-workflow-and-params]. In this profile, a token series is characterized by access tokens used between a given pair (C, RS) having the same "session_id" in the EDHOC_Information, see Section 3.4.¶
AS assigns the "session_id" to the EDHOC_Information when issuing the first access token of a new series and that "session_id" remains fixed throughout the series lifetime. When assigning the identifier, AS MUST ensure that it was not used in a previous series whose access tokens share the following properties with the access tokens of the new series:¶
i) issued for the same RS; and¶
ii) bound to the same authentication credential AUTH_CRED_C of the requesting client (irrespectively of how the AUTH_CRED_C is identified in the access tokens).¶
In case the access token is issued for a group-audience (see Section 6.9 of [RFC9200]), what is defined above applies, with the difference that the token series is associated with all the RSs in the group-audience, as indicated by their respective AUTH_CRED_RS.¶
After verifying the POST request to the /token endpoint and that C is authorized to access, AS responds as defined in Section 5.8.2 of [RFC9200], with potential modifications as detailed below. If the request from C was invalid, or not authorized, AS returns an error response as described in Section 5.8.3 of [RFC9200].¶
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 4.4. 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.¶
The access token may be sent in the access token response to C for subsequent provisioning to RS, or the access token may be uploaded by AS directly to RS, as specified in [I-D.ietf-ace-workflow-and-params].¶
In the former case, AS provides the access token to C, by specifying it in the "access_token" parameter of the access token response.¶
In the latter case, AS uploads the access token to the /authz-info endpoint at RS, similarly to what is defined for C in Section 4.1 and Section 4.2. In case of successful token upload, the access token response to C does not include the parameter "access_token", and includes the parameter "token_uploaded" encoding the CBOR simple value "true" (0xf5). An example is given in Appendix A.3.¶
When issuing any access token, AS MUST send the following data in the response to C.¶
The "session_id" field of EDHOC_Information, which is the identifier of the token series which the issued access token belongs to.¶
When issuing the first access token of a token series, AS MUST send the following data in the response to C.¶
A unique identification of the authentication credential of RS, 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 may include AUTH_CRED_RS by value.¶
When later issuing further access tokens to the same pair (C, RS) using the same AUTH_CRED_RS, it is expected that the response to C includes AUTH_CRED_RS by reference.¶
When issuing the first access token of a token series, AS MAY send EDHOC_Information related to RS, see Section 3.4, in corresponding fields of the response to C. This information is based on knowledge that AS have about RS, e.g., from a previous onboarding process, with particular reference to what RS supports as EDHOC peer.¶
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-Format: 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" : {
"session_id" : h'01',
"methods" : [0, 1, 2, 3],
"cipher_suites": 0
}
}
When issuing any access token of a token series, AS MUST specify the following data in the claims associated with the access token.¶
The "session_id" field of EDHOC_Information, with the same value specified in the response to C from the /token endpoint.¶
The authentication credential that C specified in its POST request to the /token endpoint (see Section 3.1), 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 uniquely 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 included by value.¶
When later issuing further access tokens to the same pair (C, RS) using the same AUTH_CRED_C, it is expected that AUTH_CRED_C is identified by reference.¶
When issuing the first access token of a token series, AS MAY specify the following EDHOC_Information (see Section 3.4) 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 with the same values in the access token.¶
osc_ms_len: The size of the OSCORE Master Secret. If it is not included, the default value from Appendix A.1 of [I-D.ietf-lake-edhoc] is assumed.¶
osc_salt_len: The size of the OSCORE Master Salt. If it is not included, the default value from Appendix A.1 of [I-D.ietf-lake-edhoc] is assumed.¶
osc_version: The OSCORE version. If it is not included, the default value of 1 (see Section 5.4 of [RFC8613]) is assumed.¶
When CWTs are used as access tokens, EDHOC_Information MUST be transported in the "edhoc_info" claim, defined in Section 10.5.¶
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 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/...
(remainder of the access credential omitted for brevity)/'
}
"edhoc_info" : {
"session_id" : h'01',
"methods" : [0, 1, 2, 3],
"cipher_suites": 0
}
}
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, either using the "rs_cnf" parameter or some other trusted source. 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.¶
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 "session_id" field.¶
The EDHOC_Information in the access token MUST include only the "session_id" field. In particular, if the access token is a CWT, the "edhoc_info" claim MUST include only the "session_id" field.¶
The "session_id" 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.¶
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 be encoded either 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 10.9), 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.¶
+---------------+-------+----------+----------------+-----------------+ | Name | CBOR | CBOR | Registry | Description | | | label | type | | | +---------------+-------+----------+----------------+-----------------+ | session_id | 0 | bstr | | Identifier of | | | | | | a session | +---------------+-------+----------+----------------+-----------------+ | methods | 1 | int / | EDHOC Method | Set of | | | | array | Type Registry | supported | | | | | | EDHOC methods | +---------------+-------+----------+----------------+-----------------+ | cipher_suites | 2 | int / | EDHOC Cipher | Set of | | | | array | Suites | supported EDHOC | | | | | Registry | cipher suites | +---------------+-------+----------+----------------+-----------------+ | message_4 | 3 | simple | | Support for | | | | value | | EDHOC message_4 | | | | "true" / | | | | | | simple | | | | | | value | | | | | | "false" | | | +---------------+-------+----------+----------------+-----------------+ | comb_req | 4 | simple | | Support for the | | | | value | | EDHOC + OSCORE | | | | "true" / | | combined | | | | simple | | request | | | | value | | | | | | "false" | | | +---------------+-------+----------+----------------+-----------------+ | uri_path | 5 | tstr | | URI-path of the | | | | | | EDHOC resource | +---------------+-------+----------+----------------+-----------------+ | osc_ms_len | 6 | uint | | Length in bytes | | | | | | of the OSCORE | | | | | | Master Secret | | | | | | to derive | +---------------+-------+----------+----------------+-----------------+ | osc_salt_len | 7 | uint | | Length in bytes | | | | | | of the OSCORE | | | | | | Master Salt to | | | | | | derive | +---------------+-------+----------+----------------+-----------------+ | osc_version | 8 | uint | | OSCORE version | | | | | | number to use | +---------------+-------+----------+----------------+-----------------+ | cred_types | 9 | int / | EDHOC | Set of | | | | array | Authentication | supported | | | | | Credential | types of | | | | | Types Registry | authentication | | | | | | credentials | | | | | | for EDHOC | +---------------+-------+----------+----------------+-----------------+ | id_cred_types | 10 | int / | COSE Header | Set of | | | | tstr / | Parameters | supported | | | | array | Registry | types of | | | | | | authentication | | | | | | credential | | | | | | identifiers for | | | | | | EDHOC | +---------------+-------+----------+----------------+-----------------+ | eads | 11 | uint / | EDHOC External | Set of | | | | array | Authorization | supported EDHOC | | | | | Data Registry | External | | | | | | Authorization | | | | | | Data (EAD) | | | | | | items | +---------------+-------+----------+----------------+-----------------+ | initiator | 12 | simple | | Support for the | | | | value | | EDHOC Initiator | | | | "true" / | | role | | | | simple | | | | | | value | | | | | | "false" | | | +---------------+-------+----------+----------------+-----------------+ | responder | 13 | simple | | Support for the | | | | value | | EDHOC Responder | | | | "true" / | | role | | | | simple | | | | | | value | | | | | | "false" | | | +---------------+-------+----------+----------------+-----------------+
session_id: This parameter identifies a 'session' which the EDHOC information is associated with, but does not necessarily identify a specific EDHOC session. In this document, "session_id" identifies a token series. In JSON, the "session_id" value is a Base64 encoded byte string. In CBOR, the "session_id" type is a byte string, and has label 0.¶
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 a 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 session, 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 session, 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.¶
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.¶
cred_types: This parameter specifies a set of supported types of authentication credentials for EDHOC (see Section 3.5.2 of [I-D.ietf-lake-edhoc]). If the set is composed of a single type of authentication credential, this is encoded as an integer. Otherwise, the set is encoded as an array of integers, where each array element encodes one type of authentication credential. In JSON, the "cred_types" value is an integer or an array of integers. In CBOR, "cred_types" is an integer or an array of integers, and has label 9. The integer values are taken from the "EDHOC Authentication Credential Types" registry defined in [I-D.ietf-core-oscore-edhoc].¶
id_cred_types: This parameter specifies a set of supported types of authentication credential identifiers for EDHOC (see Section 3.5.3 of [I-D.ietf-lake-edhoc]). If the set is composed of a single type of authentication credential identifier, this is encoded as an integer or a text string. Otherwise, the set is encoded as an array, where each array element encodes one type of authentication credential identifier, as an integer or a text string. In JSON, the "id_cred_types" value is an integer, or a text string, or an array of integers and text strings. In CBOR, "id_cred_types" is an integer or a text string, or an array of integers and text strings, and has label 10. The integer or text string values are taken from the 'Label' column of the "COSE Header Parameters" registry [COSE.Header.Parameters].¶
eads: This parameter specifies a set of supported EDHOC External Authorization Data (EAD) items, identified by their ead_label (see Section 3.8 of [I-D.ietf-lake-edhoc]). If the set is composed of a single ead_label, this is encoded as an unsigned integer. Otherwise, the set is encoded as an array of unsigned integers, where each array element encodes one ead_label. In JSON, the "eads" value is an unsigned integer or an array of unsigned integers. In CBOR, "eads" is an unsigned integer or an array of unsigned integers, and has label 11. The unsigned integer values are taken from the 'Label' column of the "EDHOC External Authorization Data" registry defined in [I-D.ietf-lake-edhoc].¶
initiator: This parameter specifies whether the EDHOC Initiator role is supported. In JSON, the "initiator" value is a boolean. In CBOR, "initiator" is the simple value "true" (0xf5) or "false" (0xf4), and has label 12.¶
responder: This parameter specifies whether the EDHOC Responder role is supported. In JSON, the "responder" value is a boolean. In CBOR, "responder" is the simple value "true" (0xf5) or "false" (0xf4), and has label 13.¶
An example of JSON EDHOC_Information is given in Figure 7.¶
"edhoc_info" : {
"session_id" : b64'AQ==',
"methods" : 1,
"cipher_suites" : 0
}
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
? 9 => int / array, ; cred_types
? 10 => int / tstr / array, ; id_cred_types
? 11 => uint / array, ; eads
? 12 => true / false, ; initiator
? 13 => true / false, ; responder
* int / tstr => any
}
¶
This section describes the exchanges between C and RS, which comprise the token uploading to RS, and the execution of the EDHOC protocol. Note that AS may have uploaded the access token directly to RS (see Section 3.3).¶
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 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 an EAD field of an EDHOC message sent to RS. This is further discussed in Section 4.3 and Section 4.4, and shown by the example in Appendix A.2.¶
In either case, C and RS run the EDHOC protocol by exchanging POST requests and related responses to a dedicated EDHOC resource at RS (see Section 4.4). Once completed the EDHOC session, 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 4.4). 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 4.8).¶
C and RS are mutually authenticated once they have successfully completed the EDHOC protocol. RS gets key confirmation of PRK_out by C at the end of the successful EDHOC session. Conversely, C get key confirmation of PRK_out by RS 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.¶
The access token can be uploaded to RS by using the /authz-info endpoint at RS. To this end, C uses 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 (see Section 4.5).¶
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, AUTH_CRED_C, specified in the "cnf" claim of the access token by value or by reference. If not, RS retrieves AUTH_CRED_C, either using the "cnf" claim or some other trusted source.¶
If RS fails to find or validate AUTH_CRED_C, 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.¶
If, instead, the access token is valid but 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 "session_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.¶
If all validations are successful, RS MUST reply to the POST request with a 2.01 (Created) response. The access token is stored such that it is possible to retrieve it based on "session_id" and AUTH_CRED_C.¶
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].¶
Instead of uploading the access token to the /authz-info endpoint at RS as described in Section 4.1, C MAY include the access token in EDHOC message_3 by making use of the External Authorization Data field EAD_3 (see Section 3.8 of [I-D.ietf-lake-edhoc]), see example in Appendix A.2. In this case, the access token is encrypted between C and RS enabling protection of potential sensitive information.¶
This document defines the EAD item EAD_ACCESS_TOKEN = (ead_label, ead_value), where:¶
ead_label is the integer value TBD registered in Section 10.8 and¶
ead_value is a CBOR byte string, with value the binary serialization of a CBOR map. The CBOR map includes one field, whose label is a CBOR unsigned integer with value either 0 or 1, and whose value is a CBOR byte string:¶
For label 0, ead_value = { 0 : access_token }, where access_token is a CBOR byte string equal to the value of the "access_token" field of the access token response from AS, see Section 3.3.¶
For label 1, ead_value = { 1 : session_id }, where session_id is a CBOR byte string equal to the value of the "session_id" field of the access token response from AS, see Section 3.2.¶
This EAD item, which is used in EAD_3, is critical, i.e., it is used only with the negative value of its ead_label, indicating that the receiving RS must either process the access token or abort the EDHOC session (see Section 3.8 of [I-D.ietf-lake-edhoc]). A Client or Resource Server supporting the profile of ACE defined in this document MUST support this EAD item. When EDHOC is used with this profile, this EAD item is included in EAD_3, see Section 4.4.3.¶
Access tokens are transported in EAD fields only for the first access token of a token series, and not for the update of access rights, see Section 4.5.¶
In order to mutually authenticate and establish secure communication for authorized access according to the profile described in this document, C and RS run the EDHOC protocol [I-D.ietf-lake-edhoc] with C as EDHOC Initiator and RS as EDHOC Responder. When a new EDHOC session is established, previous EDHOC sessions associated with the same access token and the same pair (session_id, AUTH_CRED_C) are deleted, see Section 4.4.3. The OSCORE Security Contexts derived from those EDHOC sessions are also deleted.¶
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. RS sends EDHOC message_2 and (optionally) EDHOC message_4 as 2.04 (Changed) CoAP responses. C MUST target the EDHOC resource at RS with the URI path specified in the "uri_path" field of the EDHOC_Information in the access token response received from AS (see Section 3.1), if present.¶
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.¶
The processing of EDHOC message_1 is specified in Section 5.2 of [I-D.ietf-lake-edhoc]. Additionally, the following applies:¶
The EDHOC method MUST be one of the EDHOC methods specified in the "methods" field (if present) in the EDHOC_Information of the access token response to C.¶
The selected cipher suite MUST be an EDHOC cipher suite specified in the "cipher_suites" field (if present) in the EDHOC_Information of the access token response to C.¶
The processing of EDHOC message_2 is specified in Section 5.3 of [I-D.ietf-lake-edhoc] with the following additions:¶
The authentication credential CRED_R indicated by the message field ID_CRED_R is AUTH_CRED_RS.¶
The processing of EDHOC message_3 is specified in Section 5.4 of [I-D.ietf-lake-edhoc] with the following additions:¶
The authentication credential CRED_I indicated by the message field ID_CRED_I is AUTH_CRED_C.¶
The EAD item EAD_ACCESS_TOKEN = (-ead_label, ead_value) MUST be included in the EAD_3 field. If the access token is provisioned with EDHOC message_3 as specified in Section 4.3, then ead_value = { 0 : access_token}, otherwise ead_value = { 1 : session_id}, where session_id is equal to the value of the "session_id" field of the access token response from AS, see Section 3.2.¶
The RS MUST ensure that the access token is valid, potentially first retrieving it using session_id and AUTH_CRED_C, the validation follows the procedure 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 abort the EDHOC session. RS MUST have successfully validated the processing of the access token before completing the EDHOC session. If completed successfully, then the EDHOC session is associated with both the access token and the pair (session_id, AUTH_CRED_C). Any old existing EDHOC session associated with the same access token and with the same pair (session_id, AUTH_CRED_C) MUST be deleted, together with the OSCORE Security Context derived from the EDHOC session.¶
Editor's note: Instead of ERR_CODE = 1, consider to use ERR_CODE = 3 "Access Denied" defined in draft-ietf-lake-authz¶
Once successfully completed the EDHOC session, 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.¶
The length in bytes of the OSCORE Master Secret (i.e., the oscore_key_length parameter, see Appendix A.1 of [I-D.ietf-lake-edhoc]) MUST be the value specified in the "osc_ms_size" field (if present) in the EDHOC_Information of the access token response to C, and of the access token provisioned to RS, respectively.¶
The length in bytes of the OSCORE Master Salt (i.e., the oscore_salt_length parameter, see Appendix A.1 of [I-D.ietf-lake-edhoc]) MUST be the value specified in the "osc_salt_size" field (if present) in the EDHOC_Information of the access token response to C, and of the access token provisioned to RS, respectively.¶
C and RS MUST use the OSCORE version specified in the "osc_version" field (if present) in the EDHOC_Information of the access token response to C, and of the access token provisioned to RS, respectively.¶
RS associates the latest EDHOC session and the derived OSCORE Security Context with the stored access token, which is bound to the authentication credential (AUTH_CRED_C = CRED_I) used in the EDHOC session and with the session_id identifying the token series to which the access token belongs.¶
If supported by C, C MAY use the EDHOC + OSCORE combined request defined in [I-D.ietf-core-oscore-edhoc], unless the "comb_req" field of the EDHOC_Information was present in the access token response and set to the CBOR simple value "false" (0xf4). In the combined request, both EDHOC message_3 and the first OSCORE-protected application request are combined together in a single OSCORE-protected CoAP request, thus saving one round trip. For an example, see Appendix A.2. This requires C to derive the OSCORE Security Context with RS already after having successfully processed the received EDHOC message_2 and before sending EDHOC message_3.¶
If C has already established access rights and an OSCORE Security Context with RS, then C can update its access rights 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). 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.¶
Editor's note: Add description about the alternative when the AS uploads the new access token to RS.¶
If RS receives an access token in an OSCORE protected request, it means that C is requesting an update of access rights. In this case, RS MUST check the following conditions:¶
RS checks whether it stores an access token T_OLD, such that the "session_id" field of EDHOC_Information matches the "session_id" field of EDHOC_Information 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.¶
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 is exhausted.¶
The access token associated with the OSCORE Security Context becomes invalid, for example due to expiration or revocation.¶
C receives a number of unprotected 4.01 (Unauthorized) responses to OSCORE-protected requests, which are 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. This may for example happen due to lack of storage in RS, which then sends the "AS Request Creation Hints" message (see Section 5.3 of [RFC9200]).¶
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 session 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 is 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 session to establish the OSCORE Security Context.¶
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.¶
The procedure of provisioning a new access token to RS specified in this section applies to various cases when an OSCORE Security Context shared between C and RS has been deleted, for example as described in Section 4.6.¶
Another 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 C 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. Unless C and RS re-run the EDHOC protocol, they preserve their OSCORE identifiers, i.e., the OSCORE Sender/Recipient IDs.¶
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, which 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.¶
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 [RFC9147] or TLS [RFC8446]) MAY be used instead.¶
If OSCORE is used, the requesting entity and AS need to have an OSCORE Security Context in place. While this can be pre-installed, the requesting entity and AS can establish such an OSCORE Security 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.¶
Furthermore, as discussed in Section 3.3 and shown by the example in Appendix A.3, AS may upload an access token directly to the /authz-info endpoint at RS. Unless encryption is applied, that exchange between AS and RS discloses the plain text token, just like when C uses the /authz-info endpoint at RS to upload a first token in a series.¶
Editor's note: Elaborate on how to encrypt the token from AS to RS, since there is a pre-established security context.¶
This document defines a number of new CWT confirmation methods (see Section 10.7). The semantics of each confirmation method is defined below.¶
The confirmation method "x5chain" specifies an ordered array of X.509 certificates [RFC5280]. The semantics of "x5chain" is like that of the "x5chain" COSE Header Parameter specified in [RFC9360].¶
The confirmation method "x5bag" specifies a bag of X.509 certificates [RFC5280]. The semantics of "x5bag" is like that of the "x5bag" COSE Header Parameter specified in [RFC9360].¶
The confirmation method "x5t" specifies the hash value of the end-entity X.509 certificate [RFC5280]. The semantics of "x5t" is like that of the "x5t" COSE Header Parameter specified in [RFC9360].¶
The confirmation method "x5u" specifies the URI [RFC3986] of an ordered chain of X.509 certificates [RFC5280]. The semantics of "x5u" is like that of the "x5u" COSE Header Parameter specified in [RFC9360].¶
The confirmation method "c5c" specifies an ordered array of C509 certificates [I-D.ietf-cose-cbor-encoded-cert]. The semantics of "c5c" is like that of the "c5c" COSE Header Parameter specified in [I-D.ietf-cose-cbor-encoded-cert].¶
The confirmation method "c5b" specifies a bag of C509 certificates [I-D.ietf-cose-cbor-encoded-cert]. The semantics of "c5b" is like that of the "c5b" COSE Header Parameter specified in [I-D.ietf-cose-cbor-encoded-cert].¶
The confirmation method "c5t" specifies the hash value of the end-entity C509 certificate [I-D.ietf-cose-cbor-encoded-cert]. The semantics of "c5t" is like that of the "c5t" COSE Header Parameter specified in [I-D.ietf-cose-cbor-encoded-cert].¶
The confirmation method "c5u" specifies the URI [RFC3986] of a COSE_C509 containing an ordered chain of C509 certificates [I-D.ietf-cose-cbor-encoded-cert]. COSE_C509 is defined in [I-D.ietf-cose-cbor-encoded-cert]. The semantics of "c5u" is like that of the "c5u" COSE Header Parameter specified in [I-D.ietf-cose-cbor-encoded-cert].¶
The confirmation method "kcwt" specifies a CBOR Web Token (CWT) [RFC8392] containing a COSE_Key [RFC9053] in a 'cnf' claim and possibly other claims. The semantics of "kcwt" is like that of the "kcwt" COSE Header Parameter specified in [I-D.ietf-lake-edhoc].¶
The confirmation method "kccs" specifies a CWT Claims Set (CCS) [RFC8392] containing a COSE_Key [RFC9053] in a 'cnf' claim and possibly other claims. The semantics of "kccs" is like that of the "kccs" COSE Header Parameter specified in [I-D.ietf-lake-edhoc].¶
This document defines a number of new JWT confirmation methods (see Section 10.6). The semantics of each confirmation method is defined below.¶
The confirmation method "x5c" specifies an ordered array of X.509 certificates [RFC5280]. The semantics of "x5c" is like that of the "x5c" JSON Web Signature and Encryption Header Parameter specified in [RFC7515], with the following difference. The public key contained in the first certificate is the proof-of-possession key and does not have to correspond to a key used to digitally sign the JWS.¶
The confirmation method "x5b" specifies a bag of X.509 certificates [RFC5280]. The semantics of the "x5b" is like that of the "x5c" JWT confirmation method defined in Section 7.1, with the following differences. First, the set of certificates is unordered and may contain self-signed certificates. Second, the composition and processing of "x5b" are like for the "x5bag" COSE Header Parameter defined in [RFC9360].¶
The confirmation method "x5t" specifies the hash value of the end-entity X.509 certificate [RFC5280]. The semantics of "x5t" is like that of the "x5t" JSON Web Signature and Encryption Header Parameter specified in [RFC7515].¶
The confirmation method "x5u" specifies the URI [RFC3986] of an ordered chain of X.509 certificates [RFC5280]. The semantics of "x5u" is like that of the "x5u" COSE Header Parameter specified in [RFC9360], with the following difference. The public key contained in the first certificate is the proof-of-possession key and does not have to correspond to a key used to digitally sign the JWS.¶
The confirmation method "c5c" specifies an ordered array of C509 certificates [I-D.ietf-cose-cbor-encoded-cert]. The semantics of "c5c" is like that of the "x5c" JWT confirmation method defined in Section 7.1, with the following difference. Each string in the JSON array is a base64-encoded (Section 4 of [RFC4648] - not base64url-encoded) C509 certificate.¶
The confirmation method "c5b" specifies a bag of C509 certificates [I-D.ietf-cose-cbor-encoded-cert]. The semantics of "c5b" is like that of the "c5c" JWT confirmation method defined in Section 7.5, with the following differences. First, the set of certificates is unordered and may contain self-signed certificates. Second, the composition and processing of "c5b" is like for the "c5b" COSE Header Parameter defined in [I-D.ietf-cose-cbor-encoded-cert].¶
The confirmation method "c5t" specifies the hash value of the end-entity C509 certificate [I-D.ietf-cose-cbor-encoded-cert]. The semantics of "c5t" is like that of the "x5t" JWT confirmation method defined in Section 7.3, with the following differences. First, the base64url-encoded SHA-1 thumbprint is computed over the C509 certificate. Second, the public key contained in the C509 certificate does not have to correspond to a key used to digitally sign the JWS.¶
The confirmation method "c5u" specifies the URI [RFC3986] of COSE_C509 containing an ordered chain of C509 certificates [I-D.ietf-cose-cbor-encoded-cert]. COSE_C509 is defined in [I-D.ietf-cose-cbor-encoded-cert]. The semantics of "c5u" is like that of the "x5u" JWT confirmation method defined in Section 7.4, with the following differences. First, the URI refers to a resource for the C509 certificate chain. Second, the public key contained in one of the C509 certificates and acting as proof-of-possession key does not have to correspond to a key used to digitally sign the JWS.¶
The confirmation method "kcwt" specifies a CBOR Web Token (CWT) [RFC8392] containing a COSE_Key [RFC9053] in a 'cnf' claim and possibly other claims. The format of "kcwt" is the base64url-encoded serialization of the CWT.¶
The confirmation method "kccs" specifies a CWT Claims Set (CCS) [RFC8392] containing a COSE_Key [RFC9053] in a 'cnf' claim and possibly other claims. The format of "kcwt" is the base64url-encoded serialization of the CWT.¶
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 session, C and RS are mutually authenticated through their respective authentication credentials, whose retrieval has been facilitated by AS. Also once completed the EDHOC session, 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 session. 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.¶
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).¶
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 session. 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].¶
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.¶
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]¶
IANA is asked to add the following entries to the "OAuth Parameters" registry.¶
IANA is asked to add the following entries to the "OAuth Parameters CBOR Mappings" following the procedure specified in [RFC9200].¶
IANA is asked to add the following entries to the "JSON Web Token Claims" registry following the procedure specified in [RFC7519].¶
IANA is asked to add the following entries to the "CBOR Web Token Claims" registry following the procedure specified in [RFC8392].¶
IANA is asked to add the following entries to the "JWT Confirmation Methods" registry following the procedure specified in [RFC7800].¶
Confirmation Method Value: "x5c"¶
Confirmation Method Description: An ordered chain of X.509 certificates¶
Change Controller: IESG¶
Specification Document(s): Section 7.1 of [RFC-XXXX]¶
Confirmation Method Value: "x5b"¶
Confirmation Method Description: An unordered bag of X.509 certificates¶
Change Controller: IESG¶
Specification Document(s): Section 7.2 of [RFC-XXXX]¶
Confirmation Method Value: "x5t"¶
Confirmation Method Description: Hash of an X.509 certificate¶
Change Controller: IESG¶
Specification Document(s): Section 7.3 of [RFC-XXXX]¶
Confirmation Method Value: "x5u"¶
Confirmation Method Description: URI pointing to an ordered chain of X.509 certificates¶
Change Controller: IESG¶
Specification Document(s): Section 7.4 of [RFC-XXXX]¶
Confirmation Method Value: "c5c"¶
Confirmation Method Description: An ordered chain of C509 certificates¶
Change Controller: IESG¶
Specification Document(s): Section 7.5 of [RFC-XXXX]¶
Confirmation Method Value: "c5b"¶
Confirmation Method Description: An unordered bag of C509 certificates¶
Change Controller: IESG¶
Specification Document(s): Section 7.6 of [RFC-XXXX]¶
Confirmation Method Value: "c5t"¶
Confirmation Method Description: Hash of a C509 certificate¶
Change Controller: IESG¶
Specification Document(s): Section 7.7 of [RFC-XXXX]¶
Confirmation Method Value: "c5u"¶
Confirmation Method Description: URI pointing to a COSE_C509 containing an ordered chain of C509 certificates¶
Change Controller: IESG¶
Specification Document(s): Section 7.8 of [RFC-XXXX]¶
Confirmation Method Value: "kcwt"¶
Confirmation Method Description: A CBOR Web Token (CWT) containing a COSE_Key in a 'cnf' claim and possibly other claims¶
Change Controller: IESG¶
Specification Document(s): Section 7.9 of [RFC-XXXX]¶
Confirmation Method Value: "kccs"¶
Confirmation Method Description: A CWT Claims Set (CCS) containing a COSE_Key in a 'cnf' claim and possibly other claims¶
Change Controller: IESG¶
Specification Document(s): Section 7.10 of [RFC-XXXX]¶
IANA is asked to add the following entries to the "CWT Confirmation Methods" registry following the procedure specified in [RFC8747].¶
Confirmation Method Name: x5chain¶
Confirmation Method Description: An ordered chain of X.509 certificates¶
JWT Confirmation Method Name: "x5c"¶
Confirmation Key: TBD¶
Confirmation Value Type(s): COSE_X509¶
Change Controller: IESG¶
Specification Document(s): Section 6.1 of [RFC-XXXX]¶
Confirmation Method Name: x5bag¶
Confirmation Method Description: An unordered bag of X.509 certificates¶
JWT Confirmation Method Name: "x5b"¶
Confirmation Key: TBD¶
Confirmation Value Type(s): COSE_X509¶
Change Controller: IESG¶
Specification Document(s): Section 6.2 of [RFC-XXXX]¶
Confirmation Method Name: x5t¶
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): Section 6.3 of [RFC-XXXX]¶
Confirmation Method Name: x5u¶
Confirmation Method Description: URI pointing to an ordered chain of X.509 certificates¶
JWT Confirmation Method Name: "x5u"¶
Confirmation Key: TBD¶
Confirmation Value Type(s): uri¶
Change Controller: IESG¶
Specification Document(s): Section 6.4 of [RFC-XXXX]¶
Confirmation Method Name: c5c¶
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): Section 6.5 of [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): Section 6.6 of [RFC-XXXX]¶
Confirmation Method Name: c5t¶
Confirmation Method Description: Hash of a C509 certificate¶
JWT Confirmation Method Name: "c5t"¶
Confirmation Key: TBD¶
Confirmation Value Type(s): COSE_CertHash¶
Change Controller: IESG¶
Specification Document(s): Section 6.7 of [RFC-XXXX]¶
Confirmation Method Name: c5u¶
Confirmation Method Description: URI pointing to a COSE_C509 containing an ordered chain of C509 certificates¶
JWT Confirmation Method Name: "c5u"¶
Confirmation Key: TBD¶
Confirmation Value Type(s): uri¶
Change Controller: IESG¶
Specification Document(s): Section 6.8 of [RFC-XXXX]¶
Confirmation Method Name: kcwt¶
Confirmation Method Description: A CBOR Web Token (CWT) containing a COSE_Key in a 'cnf' claim and possibly other claims¶
JWT Confirmation Method Name: "kcwt"¶
Confirmation Key: TBD¶
Confirmation Value Type(s): COSE_Messages¶
Change Controller: IESG¶
Specification Document(s): Section 6.9 of [RFC-XXXX]¶
Confirmation Method Name: kccs¶
Confirmation Method Description: A CWT Claims Set (CCS) containing a COSE_Key in a 'cnf' claim and possibly other claims¶
JWT Confirmation Method Name: "kccs"¶
Confirmation Key: TBD¶
Confirmation Value Type(s): map / #6(map)¶
Change Controller: IESG¶
Specification Document(s): Section 6.10 of [RFC-XXXX]¶
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].¶
The ead_label = TBD and the ead_value defines an access token in EAD_3, with processing specified in Section 4.3.¶
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 10.10. 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 label: 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].¶
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.¶
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.¶
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.¶
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.¶
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.¶
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_3 field of EDHOC message_3 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.¶
The example below builds on the example in Appendix A.2, but assumes that AS is uploading the access token to RS as specified in [I-D.ietf-ace-workflow-and-params].¶
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 RS mutually authenticate: Explicitly, by successfully executing the EDHOC protocol, after which a common OSCORE Security Context is exported from the EDHOC session. 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.¶
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 session 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 session 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 session 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_3 field of EDHOC message_3 (see Section 4.4).¶
RFC EDITOR: PLEASE REMOVE THIS SECTION.¶
Restructured presentation of content.¶
Simplified description of the use of EDHOC_Information.¶
Merged the concepts of EDHOC "session_id" and identifier of token series.¶
Enabled the transport of the access token also in EDHOC EAD_3.¶
Defined semantics of the newly defined CWT/JWT Confirmation Methods.¶
Clarifications and editorial improvements.¶
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.¶
Updated references.¶
Clarifications and editorial improvements.¶
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).¶