]> RISE AB

Isafjordsgatan 22 Kista 16440 Stockholm Sweden marco.tiloca@ri.se

RISE AB

Isafjordsgatan 22 Kista 16440 Stockholm Sweden rikard.hoglund@ri.se

Combitech

Djäknegatan 31 Malmö 21135 Malmö Sweden ludwig.seitz@combitech.com

Ericsson AB

Torshamnsgatan 23 Kista 16440 Stockholm Sweden francesca.palombini@ericsson.com

Security ACE Working Group Internet-Draft This document specifies a profile for the Authentication and Authorization for Constrained Environments (ACE) framework. The profile uses Group Object Security for Constrained RESTful Environments (Group OSCORE) to provide communication security between a Client and one or multiple Resource Servers that are members of an OSCORE group. The profile securely binds an OAuth 2.0 Access Token to the public key of the Client associated with the private key used by that Client in the OSCORE group. The profile uses Group OSCORE to achieve server authentication, as well as proof-of-possession for the Client's public key. Also, it provides proof of the Client's membership to the OSCORE group by binding the Access Token to information from the Group OSCORE Security Context, thus allowing the Resource Server(s) to verify the Client's membership upon receiving a message protected with Group OSCORE from the Client. Effectively, the profile enables fine-grained access control paired with secure group communication, in accordance with the Zero Trust principles. Discussion Venues Discussion of this document takes place on the Constrained RESTful Environments Working Group mailing list (ace@ietf.org), which is archived at . Source for this draft and an issue tracker can be found at .

Introduction A number of applications rely on a group communication model where a Client can access a resource shared by multiple Resource Servers at once, e.g., over IP multicast. Typical examples are switching of luminaries, actuators control, and distribution of software updates. Secure communication in the group can be achieved by sharing a set of keying material, which is typically provided upon joining the group. For some of such applications, it may be just fine to enforce access control in a straightforward fashion. That is, any Client authorized to join the group, hence to obtain the group keying material, can be also implicitly authorized to perform any action at any resource of any Server in the group. An example of application where such implicit authorization might be used is a simple lighting scenario, where the lightbulbs are the Servers, while the user account on an app on the user's phone is the Client. In this case, it might be fine to not require additional authorization evidence from any user account, if it is acceptable that any current group member is also authorized to switch on and off any light, or to check their status. However, in different instances of such applications, the approach above is not desirable, as different group members are intended to have different access rights to resources of other group members. For instance, enforcing access control in accordance with a more fine-grained approach is required in the two following use cases. As a first case, an application provides control of smart locks acting as Servers in the group, where: a first type of Client, e.g., a user account of a child, is allowed to only query the status of the smart locks; while a second type of Client, e.g., a user account of a parent, is allowed to both query and change the status of the smart locks. Further similar applications concern the enforcement of different sets of permissions in groups with sensor/actuator devices, e.g., thermostats acting as Servers. Also, some group members may even be intended as Servers only. Hence, they must be prevented from acting as Clients altogether and from accessing resources at other Servers, especially when attempting to perform non-safe operations. As a second case, building automation scenarios often rely on Servers that, under different circumstances, enforce different level of priority for processing received commands. For instance, BACnet deployments consider multiple classes of Clients, e.g., a normal light switch (C1) and an emergency fire panel (C2). Then, a C1 Client is not allowed to override a command from a C2 Client, until the latter relinquishes control at its higher priority. That is: i) only C2 Clients should be able to adjust the minimum required level of priority on the Servers, so rightly locking out C1 Clients if needed; and ii) when a Server is set to accept only high-priority commands, only C2 Clients should be able to perform such commands otherwise allowed also to C1 Clients. Given the different maximum authority of different Clients, fine-grained access control would effectively limit the execution of high- and emergency-priority commands only to devices that are in fact authorized to do so. Besides, it would prevent a misconfigured or compromised device from initiating a high-priority command and lock out normal control. In the cases above, being a legitimate group member and storing the group keying material is not supposed to imply any particular access rights. Instead, access control to the secure group communication channel and access control to the resource space provided by Servers in the group should remain logically separated domains. This is aligned with the Zero Trust paradigm , which focuses on resource protection and builds on the premise that trust is never granted implicitly, but must be continually evaluated. In particular, Zero Trust protections involve "minimizing access to resources (such as data and compute resources and applications/services) to only those subjects and assets identified as needing access as well as continually authenticating and authorizing the identity and security posture of each access request." Furthermore, highlights how the Zero Trust goal is to "prevent unauthorized access to data and services coupled with making the access control enforcement as granular as possible", to "enforce least privileges needed to perform the action in the request." As a step in this direction, one can be tempted to introduce a different security group for each different set of access rights. However, this inconveniently results in additional keying material to distribute and manage. In particular, if the access rights for a single node change, this requires to evict that node from the current group, followed by that node joining a different group aligned with its new access rights. Moreover, the keying material of both groups would have to be renewed for their current members. Overall, this would have a non negligible impact on operations and performance. Instead, a fine-grained yet flexible access control model can be enforced within the same group, by using the Authentication and Authorization for Constrained Environments (ACE) framework . That is, a Client has to first obtain authorization credentials in the form of an Access Token, and post it to the Resource Server(s) in the group before accessing the intended resources. The ACE framework delegates to separate profile documents how to secure communications between the Client and the Resource Servers. However each of the current profiles of ACE defined in relies on a security protocol that cannot be used to protect one-to-many group messages, for example sent over IP multicast. This document specifies the "coap_group_oscore" profile of the ACE framework, where a Client uses the Constrained Application Protocol (CoAP) to communicate with one or multiple Resource Servers that are members of an application group and share a common set of resources. This profile uses Group Object Security for Constrained RESTful Environments (Group OSCORE) as the security protocol to protect messages exchanged between the Client and the Resource Servers. Hence, it requires that both the Client and the Resource Servers have previously joined the same OSCORE group. That is, this profile describes how access control is enforced for a Client after it has joined an OSCORE group, to access resources at other members in that group. The process for joining the OSCORE group through the respective Group Manager as defined in takes place before the process described in this document, and is out of the scope of this profile. The Client proves its access to be authorized to the Resource Server(s) by using an Access Token bound to a key (the proof-of-possession key). This profile uses Group OSCORE to achieve server authentication and proof-of-possession for the Client's public key used in the OSCORE group in question. Note that proof-of-possession is not achieved through a dedicated protocol element, but instead after the first message exchange protected with Group OSCORE. Furthermore, this profile provides proof of the Client's membership to the OSCORE group, by binding the Access Token to the Client's authentication credential used in the group and including the Client's public key, as well as to information from the pre-established Group OSCORE Security Context. This allows the Resource Server(s) to verify the Client's group membership upon reception of a message protected with Group OSCORE from that Client. OSCORE specifies how to use COSE to secure CoAP messages. Group OSCORE builds on OSCORE to provide secure group communication, and ensures source authentication: by means of digital signatures embedded in the protected message (when using the group mode); or by protecting a message with pairwise keying material derived from the asymmetric keys of the two peers exchanging the message (when using the pairwise mode).

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 when, and only when, they appear in all capitals, as shown here. Readers are expected to be familiar with the terms and concepts related to CBOR , COSE , CoAP , OSCORE , and Group OSCORE . These especially include:

• Group Manager, as the entity responsible for a set of groups where communications among members are secured with Group OSCORE.
• Authentication credential, as the set of information associated with an entity, including that entity's public key and parameters associated with the public key. Examples of authentication credentials are CBOR Web Tokens (CWTs) and CWT Claims Sets (CCSs) , X.509 certificates and C509 certificates . Members of an OSCORE group have an associated authentication credential in the format used in the group. As per , an authentication credential provides the public key as well as the comprehensive set of information related to the public key algorithm, including, e.g., the used elliptic curve (when applicable).

Readers are expected to be familiar with the terms and concepts described in the ACE framework for authentication and authorization , as well as in the OSCORE profile of ACE . The terminology for entities in the considered architecture is defined in OAuth 2.0 . In particular, this includes Client (C), Resource Server (RS), and Authorization Server (AS). Note that, unless otherwise indicated, the term "endpoint" is used here following its OAuth definition, aimed at denoting resources such as /token and /introspect at the AS, and /authz-info at the RS. This document does not use the CoAP definition of "endpoint", which is "An entity participating in the CoAP protocol". Additionally, this document makes use of the following terminology.

• Pairwise-only group: an OSCORE group that uses only the pairwise mode of Group OSCORE (see ).

Examples throughout this document are expressed in CBOR diagnostic notation, without the tag and value abbreviations.

Protocol Overview This section provides an overview of this profile, i.e., of how to use the ACE framework for authentication and authorization to secure communications between a Client and one or more Resource Servers using Group OSCORE . Note that this profile of ACE describes how access control can be enforced for a node after it has joined an OSCORE group, to access resources at other members in that group. In particular, the process of joining the OSCORE group through the respective Group Manager as defined in must take place before the process described in this document, and is out of the scope of this profile. An overview of the protocol flow for this profile is shown in , where it is assumed that both the Resource Servers RS1 and RS2 are associated with the same Authorization Server AS. It is also assumed that the Client C, as well as RS1 and RS2 have previously joined an OSCORE group with Group Identifier (gid) 0xabcd0000, and that they got assigned Sender ID (sid) 0x00, 0x01 and 0x02 in the group, respectively. The names of messages coincide with those of when applicable.

Protocol Overview. ] | | | | | | | | [<----- AS Request -------] | | | | Creation Hints | | | | | | | |-------- POST /token ----------------------------------------------->| | (aud: "RS1", sid: 0x00, | | | | gid: 0xabcd0000, ...) | | | | | | | | | | | |<---------------------------------------------- Access Token T1 -----| | | + Access Information | | | | | |---- POST /authz-info ------>| | | | (access_token T1) | | | | | | | |<------ 2.01 Created --------| | | | | | | |-------- POST /token ----------------------------------------------->| | (aud: "RS2", sid: 0x00, | | | | gid: 0xabcd0000, ...) | | | | | | | | | | | |<---------------------------------------------- Access Token T2 -----| | | + Access Information | | | | | |----- POST /authz-info ------------------>| | | (access_token T2) | | | | | | | | | | | |<------ 2.01 Created ---------------------| | | | | | |-- Group OSCORE Request -+-->| | | | (kid: 0x00, \ | | | | gid: 0xabcd0000) \------------->| | | | | | | /proof-of-possession/ | | | | | | | | | |<-- Group OSCORE Response ---| | | | (kid: 0x01) | | | | | | | /proof-of-possession/ | | | | | | | /Mutual authentication | | | between C and RS1/ | | | | | | | | | | | |<-- Group OSCORE Response ----------------| | | (kid: 0x02) | | | | | | | /proof-of-possession/ | | | | | | | /Mutual authentication | | | between C and RS2/ | | | | | | | | ... | | | ]]>

Pre-Conditions Using Group OSCORE and this profile requires that both the Client and the Resource Servers have previously joined the same OSCORE group. This especially includes the derivation of the Group OSCORE Security Context and the assignment of unique Sender IDs to use in the group. Nodes can join the OSCORE group through the respective Group Manager by using the approach defined in , which is also based on ACE. After the Client and Resource Servers have joined the group, this profile provides access control for accessing resources on those Resource Servers, by securely communicating with Group OSCORE. As a pre-requisite for this profile, the Client has to have successfully joined the OSCORE group where also the Resource Servers (RSs) are members. Depending on the limited information initially available, the Client may have to first discover the exact OSCORE group used by the RSs for the resources of interest, e.g., by using the approach defined in .

Access Token Retrieval This profile requires that the Client retrieves an Access Token from the AS for the resource(s) that it wants to access at the RS(s), by using the /token endpoint as specified in . In general, different RSs can be associated with different ASs, even if the RSs are members of the same OSCORE group. However, assuming proper configurations and trust relations, it is possible for multiple RSs associated with the same AS to be part of a single audience (i.e., a group-audience, see ). In such a case, the Client can request a single Access Token intended to the group-audience, hence to all the RSs included therein. A particular group-audience might be defined as including all the RSs in the OSCORE group. In the Access Token request to the AS, the Client MUST include the Group Identifier of the OSCORE group and its own Sender ID in that group. The AS MUST specify these pieces of information in the Access Token, included in the Access Token response to the Client. Furthermore, in the Access Token request to the AS, the Client MUST also include: its own authentication credential used in the OSCORE group; and a proof-of-possession (PoP) evidence to prove possession of the corresponding private key. The PoP evidence is computed over a PoP input uniquely related to the secure communication association between the Client and the AS. The AS MUST include also the authentication credential indicated by the Client in the Access Token. The Access Token request and response MUST be confidentiality-protected and ensure authenticity. In this profile, it is RECOMMENDED to use OSCORE between the Client and the AS, to reduce the number of libraries the client has to support. Other protocols fulfilling the security requirements defined in Sections and of MAY alternatively be used, such as TLS or DTLS .

Access Token Posting After having retrieved the Access Token from the AS, the Client posts the Access Token to the RS, using the /authz-info endpoint and the mechanisms specified in . When using this profile, the communication with the /authz-info endpoint is not protected. If the Access Token is valid, the RS replies to this POST request with a 2.01 (Created) response. Also, the RS associates the received Access Token with the Group OSCORE Security Context identified by the Group Identifier specified in the Access Token, following . In practice, the RS maintains a collection of Security Contexts with associated authorization information, for all the clients that it is currently communicating with. The authorization information is a policy that is used as input when processing requests from those clients. Finally, the RS stores the association between i) the authorization information from the Access Token; and ii) the Group Identifier of the OSCORE group together with the Sender ID and the authentication credential of the Client in that group. This binds the Access Token to the Group OSCORE Security Context of the OSCORE group. Finally, when the Client communicates with the RS using the Group OSCORE Security Context, the RS verifies that the Client is a legitimate member of the OSCORE group and especially the exact group member with the same Sender ID associated with the Access Token. This occurs when verifying a request protected with Group OSCORE, since the request includes the Client's Sender ID and either it embeds a signature computed also over that Sender ID (if protected with the group mode), or it is protected by means of pairwise symmetric keying material derived from the asymmetric keys of the two peers (if protected with the pairwise mode). The above has considered an Access Token intended to a single RS. However, as discussed in , an Access Token can be intended to a group-audience including multiple RSs in the OSCORE group. In such a case, the Client could efficiently post the Access Token to many or all of those RSs at once (e.g., over IP multicast), after which each RS individually performs the same steps described above.

Secure Communication The Client can send a request protected with Group OSCORE to the RS. This can be a unicast request addressed to the RS, or a one-to-many group request (e.g., over IP multicast) addressed to the OSCORE group where the RS is also a member. To this end, the Client uses the Group OSCORE Security Context already established upon joining the OSCORE group, e.g., by using the approach defined in . The RS may send a response back to the Client, protecting it by means of the same Group OSCORE Security Context.

Client-AS Communication This section details the Access Token POST Request that the Client sends to the /token endpoint of the AS, as well as the related Access Token response. The Access Token MUST be bound to the public key of the Client as proof-of-possession key (pop-key), which is included in the Client's authentication credential specified in the 'cnf' claim of the Access Token.

C-to-AS: POST to Token Endpoint The Client-to-AS request is specified in . The Client MUST send this POST request to the /token endpoint over a secure channel that guarantees authentication, message integrity and confidentiality. The POST request is formatted as the analogous Client-to-AS request in the OSCORE profile of ACE (see ), with the following additional parameters that MUST be included in the payload.

• 'context_id', defined in of this document. This parameter specifies the Group Identifier (GID), i.e., the ID Context of an OSCORE group that includes as members both the Client and the RS(s) in the audience for which the Access Token is asked to be issued. In particular, the Client wishes to communicate with the RS(s) in that audience using the Group OSCORE Security Context associated with that OSCORE group.
• 'salt_input', defined in of this document. This parameter includes the Sender ID that the Client has in the OSCORE group whose GID is specified in the 'context_id' parameter above.
• 'req_cnf', defined in . This parameter follows the syntax from , and its inner confirmation value specifies the authentication credential that the Client uses in the OSCORE group. The public key included in the authentication credential will be used as the pop-key bound to the Access Token. At the time of writing this specification, acceptable formats of authentication credentials in Group OSCORE are CBOR Web Tokens (CWTs) and CWT Claims Sets (CCSs) , X.509 certificates , and C509 certificates . Further formats may be available in the future, and would be acceptable to use as long as they comply with the criteria compiled in . In particular, an authentication credential has to explicitly include the public key as well as the comprehensive set of information related to the public key algorithm, including, e.g., the used elliptic curve (when applicable). [ As to CWTs and CCSs, the CWT Confirmation Methods 'kcwt' and 'kccs' are under pending registration requested by draft-ietf-ace-edhoc-oscore-profile. ] [ As to X.509 certificates, the CWT Confirmation Methods 'x5bag' and '5chain' are under pending registration requested by draft-ietf-ace-edhoc-oscore-profile. ] [ As to C509 certificates, the CWT Confirmation Methods 'c5b'and 'c5c' are under pending registration requested by draft-ietf-ace-edhoc-oscore-profile. ]

In addition, the Client computes its proof-of-possession (PoP) evidence, in order to prove to the AS the possession of its own private key used in the OSCORE group. This allows the AS to verify that the Client indeed owns the private key associated with the public key of the authentication credential that the Client allegedly uses in the OSCORE group. To this end, the Client MUST use as PoP input the byte representation of an information that uniquely represents the secure communication association between the Client and the AS. It is RECOMMENDED that the Client considers the following as PoP input.

• If the Client and the AS communicate over (D)TLS, the PoP input is an exporter value computed as defined in . In particular, the exporter label MUST be 'EXPORTER-ACE-Sign-Challenge-Client-AS' defined in of this document, together with an empty 'context_value', and 32 bytes as 'key_length'.
• If the Client and the AS communicate over OSCORE, the PoP input is the output PRK of a HKDF-Extract step , i.e., PRK = HMAC-Hash(salt, IKM). In particular, 'salt' takes (x1 | x2), where x1 is the ID Context of the OSCORE Security Context between the Client and the AS, x2 is the Sender ID of the Client in that Security Context, and | denotes byte string concatenation. Also, 'IKM' is the OSCORE Master Secret of the OSCORE Security Context between the Client and the AS. The HKDF MUST be one of the HMAC-based HKDF algorithms defined for COSE . The Client and AS may agree on the HKDF algorithm to use during the Client's registration at the AS. HKDF SHA-256 is mandatory to implement.

Then, the Client computes the PoP evidence as follows.

• If the OSCORE group is not a pairwise-only group, the PoP evidence MUST be a signature. The Client computes the signature by using the same private key and signature algorithm it uses for signing messages in the OSCORE group. The Client's private key is the one associated with the Client's authentication credential used in the OSCORE group and specified in the 'req_cnf' parameter above.
• If the OSCORE group is a pairwise-only group, the PoP evidence MUST be a MAC computed as follows, by using the HKDF Algorithm HKDF SHA-256, which consists of composing the HKDF-Extract and HKDF-Expand steps . MAC = HKDF(salt, IKM, info, L) The input parameters of HKDF are as follows.
  • salt takes as value the empty byte string.
  • IKM is computed as a cofactor Diffie-Hellman shared secret (see Section 5.7.1.2 of ), using an ECDH algorithm pre-agreed between Client and AS. The Client uses its own Diffie-Hellman private key and the Diffie-Hellman public key of the AS. For X25519 and X448, the procedure is described in . The Client's private key is the one associated with the Client's authentication credential used in the OSCORE group and specified in the 'req_cnf' parameter above. The Client may obtain the Diffie-Hellman public key of the AS during its registration process at the AS. The Client and AS may agree on the ECDH algorithm to use during the Client's registration at the AS. The ECDH-SS + HKDF-256 algorithm specified in is mandatory to implement.
  • info takes as value the PoP input.
  • L is equal to 8, i.e., the size of the MAC, in bytes.

Finally, the Client MUST include one of the two following parameters in the payload of the POST request to the AS.

• 'client_cred_verify', defined in of this document, specifying the Client's PoP evidence as a signature, which is computed as defined above. This parameter MUST be included if and only if the OSCORE group is not a pairwise-only group.
• 'client_cred_verify_mac', defined in of this document, specifying the Client's PoP evidence as a MAC, which is computed as defined above. This parameter MUST be included if and only if the OSCORE group is a pairwise-only group.

An example of such a request is shown in .

Example C-to-AS POST /token request for an Access Token bound to an asymmetric key.

In the example above, the Client specifies that its authentication credential in the OSCORE group is the CCS shown in .

Example of Client Authentication Credential as CWT Claims Set (CCS).

'context_id' Parameter The 'context_id' parameter is an OPTIONAL parameter of the Access Token request message defined in . This parameter provides a value that the Client wishes to use with the RS as a hint for a security context. Its exact content is profile specific.

'salt_input' Parameter The 'salt_input' parameter is an OPTIONAL parameter of the Access Token request message defined in . This parameter provides a value that the Client wishes to use as part of a salt with the RS, for deriving cryptographic keying material. Its exact content is profile specific.

'client_cred_verify' Parameter The 'client_cred_verify' parameter is an OPTIONAL parameter of the Access Token request message defined in . This parameter provides a signature computed by the Client to prove the possession of its own private key.

'client_cred_verify_mac' Parameter The 'client_cred_verify_mac' parameter is an OPTIONAL parameter of the Access Token request message defined in . This parameter provides a Message Authentication Code (MAC) computed by the Client to prove the possession of its own private key.

AS-to-C: Access Token After having verified the POST request to the /token endpoint and that the Client is authorized to obtain an Access Token corresponding to its Access Token request, the AS MUST verify the proof-of-possession (PoP) evidence. In particular, the AS proceeds as follows.

• As PoP input, the AS uses the same value considered by the Client in .
• As public key of the Client, the AS uses the one included in the authentication credential specified in the 'req_cnf' parameter of the Access Token request.
• If the Access Token request includes the 'client_cred_verify' parameter, this specifies the PoP evidence as a signature. Then, the AS verifies the signature by using the public key of the Client.
• If the Access Token request includes the 'client_cred_verify_mac' parameter, this specifies the PoP evidence as a Message Authentication Code (MAC). Then, the AS recomputes the MAC through the same process taken by the Client when preparing the value of the 'client_cred_verify_mac' parameter for the Access Token (see ), with the difference that the AS uses its own Diffie-Hellman private key and the Diffie-Hellman public key of the Client. The verification succeeds if and only if the recomputed MAC is equal to the MAC conveyed as PoP evidence in the Access Token request.

If both the 'client_cred_verify' and 'client_cred_verify_mac' parameters are present, or if the verification of the PoP evidence fails, the AS considers the Client request invalid. If the Client request was invalid, or not authorized, the AS returns an error response as described in . If all verifications are successful, the AS responds as defined in . In particular:

• The AS can signal that the use of Group OSCORE is REQUIRED for a specific Access Token by including the 'ace_profile' parameter with the value "coap_group_oscore" in the Access Token response. The Client MUST use Group OSCORE towards all the Resource Servers for which this Access Token is valid. Usually, it is assumed that constrained devices will be pre-configured with the necessary profile, so that this kind of profile signaling can be omitted.
• The AS MUST NOT include the 'rs_cnf' parameter defined in . In general, the AS may not be aware of the authentication credentials (and public keys included thereof) that the RSs use in the OSCORE group. Also, the Client is able to retrieve the authentication credentials of other group members from the responsible Group Manager, both upon joining the group or later on as a group member, as defined in .

The AS MUST include the following information as metadata of the issued Access Token. The use of CBOR web tokens (CWT) as specified in is RECOMMENDED.

• The profile "coap_group_oscore". If the Access Token is a CWT, this is placed in the 'ace_profile' claim of the Access Token, as per .
• The salt input specified in the 'salt_input' parameter of the Token Request. If the Access Token is a CWT, the content of the 'salt_input' parameter MUST be placed in the 'salt_input' claim of the Access Token, defined in of this document.
• The Context Id input specified in the 'context_id' parameter of the Token Request. If the Access Token is a CWT, the content of the 'context_id' parameter MUST be placed in the 'contextId_input' claim of the Access Token, defined in of this document.
• The authentication credential that the client uses in the OSCORE group and specified in the 'req_cnf' parameter of the Token request. If the Access Token is a CWT, the Client's authentication credential MUST be specified in the 'cnf' claim, which follows the syntax from . In particular, the 'cnf' claim includes the same authentication credential specified in the 'req_cnf' parameter of the Token Request (see ).

shows an example of such an AS response. The access token has been truncated for readability.

Example AS-to-C Access Token response with the Group OSCORE profile.

shows an example CWT Claims Set, containing the Client's public key in the group (as pop-key), as specified by the inner confirmation value in the 'cnf' claim.

Example CWT Claims Set with OSCORE parameters.

The same CWT Claims Set as in and encoded in CBOR is shown in , using the value abbreviations defined in and . The bytes in hexadecimal are reported in the first column, while their corresponding CBOR meaning is reported after the "#" sign on the second column, for easiness of readability. Editor's note: it should be checked (and in case fixed) that the values used below (which are not yet registered) are the final values registered by IANA.

Example CWT Claims Set with OSCORE parameters, CBOR encoded.

Salt Input Claim The 'salt_input' claim provides a value that the Client requesting the Access Token wishes to use as a part of a salt with the RS, e.g., for deriving cryptographic material. This parameter specifies the value of the salt input, encoded as a CBOR byte string.

Context ID Input Claim The 'contextId_input' claim provides a value that the Client requesting the Access Token wishes to use with the RS, as a hint for a security context. This parameter specifies the value of the Context ID input, encoded as a CBOR byte string.

Client-RS Communication This section details the POST request and response to the /authz-info endpoint between the Client and the RS. The proof-of-possession required to bind the Access Token to the Client is explicitly performed when the RS receives and verifies a request from the Client protected with Group OSCORE, either with the group mode (see ) or with the pairwise mode (see ). In particular, the RS uses the Client's public key bound to the Access Token, either when verifying the signature of the request (if protected with the group mode), or when verifying the request as integrity-protected with pairwise keying material derived from the two peers' authentication credentials and asymmetric keys (if protected with the pairwise mode). In either case, the RS also authenticates the Client. Similarly, when receiving a protected response from the RS, the Client uses the RS's public key either when verifying the signature of the response (if protected with the group mode), or when verifying the response as integrity-protected with pairwise keying material derived from the two peers' authentication credentials and asymmetric keys (if protected with the pairwise mode). In either case, the Client also authenticates the RS. Mutual authentication is only achieved after the client has successfully verified the protected response from the RS. Therefore, an attacker using a stolen Access Token cannot generate a valid Group OSCORE message as protected through the Client's private key, and thus cannot prove possession of the pop-key bound to the Access Token. Also, if a Client legitimately owns an Access Token but has not joined the OSCORE group, it cannot generate a valid Group OSCORE message, as it does not store the necessary keying material shared among the group members. Furthermore, a Client C1 is supposed to obtain a valid Access Token from the AS, as specifying the Client's authentication credential (and the public key included thereof) associated with the Client's private key used in the OSCORE group, together with its own Sender ID in that OSCORE group (see ). This allows the RS receiving the Access Token to verify with the Group Manager of that OSCORE group whether such a Client indeed has that Sender ID and uses that authentication credential in the OSCORE group. As a consequence, a different Client C2, also member of the same OSCORE group, is not able to impersonate C1, by: i) getting a valid Access Token, specifying the Sender ID of C1 and a different (made-up) authentication credential; ii) successfully posting the Access Token to the RS; and then iii) attempting to communicate using Group OSCORE impersonating C1, while blaming C1 for the consequences.

C-to-RS POST to authz-info Endpoint The Client posts the Access Token to the /authz-info endpoint of the RS, as defined in .

RS-to-C: 2.01 (Created) The RS MUST verify the validity of the Access Token as defined in , with the following additions.

• The RS MUST check that the claims 'salt_input', 'contextId_input', and 'cnf' are included in the Access Token.
• The RS considers: the content of the 'contextId_input' claim as the GID of the OSCORE group; the content of the 'salt_input' claim as the Sender ID that the Client has in the group; and the inner confirmation value of 'cnf' claim as the authentication credential that the Client uses in the group. The RS MUST check whether it already stores the authentication credential specified in the inner confirmation value of the 'cnf' claim as associated with the pair (GID, Sender ID) above. If this is not the case, the RS MUST request the Client's authentication credential to the Group Manager of the OSCORE group as described in , specifying the Client's Sender ID in the OSCORE group, i.e., the value of the 'salt_input' claim. Then, the RS performs the following actions.
  • The RS MUST check whether the Client's authentication credential retrieved from the Group Manager matches the one retrieved from the inner confirmation value of the 'cnf' claim of the Access Token.
  • The RS MUST check whether the Client's Sender ID provided by the Group Manager together with the Client's authentication credential matches the one retrieved from the 'salt_input' claim of the Access Token.

If any of the checks above fails, the RS MUST consider the Access Token non valid, and MUST respond to the Client with an error response code equivalent to the CoAP code 4.00 (Bad Request). If the Access Token is valid and further checks on its content are successful, the RS associates the authorization information from the Access Token with the Group OSCORE Security Context. In particular, the RS associates the authorization information from the Access Token with the triple (GID, SaltInput, AuthCred), where GID is the Group Identifier of the OSCORE group, while SaltInput and AuthCred are the Sender ID and the authentication credential that the Client uses in that OSCORE group, respectively. The RS MUST keep this association up-to-date over time, as the triple (GID, SaltInput, AuthCred) associated with the Access Token might change. In particular:

• If the OSCORE group is rekeyed (see and ), the Group Identifier also changes in the group, and the new one replaces the current 'GID' value in the triple (GID, SaltInput, AuthCred).
• If the Client requests and obtains a new OSCORE Sender ID from the Group Manager (see and ), the new Sender ID replaces the current 'SaltInput' value in the triple (GID, SaltInput, AuthCred).

Finally, the RS MUST send a 2.01 (Created) response to the Client, as defined in .

Client-RS Secure Communication When previously joining the OSCORE group, both the Client and RS have already established the related Group OSCORE Security Context to communicate as group members. Therefore, they can simply start to securely communicate using Group OSCORE, without deriving any additional keying material or security association.

Client Side After having received the 2.01 (Created) response from the RS, following the POST request to the /authz-info endpoint, the Client starts the communication with the RS, by sending a request protected with Group OSCORE using the Group OSCORE Security Context . When communicating with the RS to access the resources as specified by the authorization information, the Client MUST use the Group OSCORE Security Context of the OSCORE group, whose GID was specified in the 'context_id' parameter of the Access Token request.

Resource Server Side After successful validation of the Access Token as defined in and after having sent the 2.01 (Created) response, the RS can start to communicate with the Client using Group OSCORE . When processing an incoming request protected with Group OSCORE, the RS MUST consider as valid Client's authentication credential only the one associated with the stored Access Token. As defined in , a possible change of authentication credential requires the Client to upload to the RS a new Access Token bound to the new authentication credential. Additionally, for every incoming request, if Group OSCORE verification succeeds, the verification of access rights is performed as described in . After the expiration of the Access Token related to a Group OSCORE Security Context, if the Client uses the Group OSCORE Security Context to send a request for any resource intended for OSCORE group members and that requires an active Access Token, the RS MUST respond with a 4.01 (Unauthorized) error message protected with the Group OSCORE Security Context.

Access Rights Verification The RS MUST follow the procedures defined in . If an RS receives a request protected with Group OSCORE from a Client, the RS processes the request according to . If the Group OSCORE verification succeeds, and the target resource requires authorization, the RS retrieves the authorization information from the Access Token associated with the Group OSCORE Security Context. Then, the RS MUST verify that the action requested on the resource is authorized. The response code MUST be 4.01 (Unauthorized) if the RS has no valid Access Token for the Client. If the RS has an Access Token for the Client but no actions are authorized on the target resource, the RS MUST reject the request and MUST respond to the Client with a 4.03 (Forbidden) response. If the RS has an Access Token for the Client but the requested action is not authorized, the RS MUST reject the request and MUST respond to the Client with a 4.05 (Method Not Allowed) response.

Change of Client's Authentication Credential in the Group During its membership in the OSCORE group, the Client might change the authentication credential that it uses in the group. When this happens, the Client uploads the new authentication credential to the Group Manager, as defined in . After that, and in order to continue communicating with the RS, the Client MUST perform the following actions.

1. The Client requests a new Access Token to the AS, as defined in . In particular, when sending the POST request as defined in , the Client indicates:
   • The current Group Identifier of the OSCORE group, as value of the 'context_id' parameter.
   • The current Sender ID it has in the OSCORE group, as value of the 'salt_input' parameter.
   • The new authentication credential it uses in the OSCORE group, as inner confirmation value of the 'req_cnf' parameter.
   • The proof-of-possession (PoP) evidence corresponding to the public key of the new authentication credential, as value of the 'client_cred_verify' or 'client_cred_verify_mac' parameter.
2. After receiving the response from the AS (see ), the Client performs the same exchanges with the RS as defined in .

When receiving the new Access Token, the RS performs the same steps defined in , with the following addition in case the new Access Token is successfully verified and stored. The RS also deletes the old Access Token, i.e., the one whose associated triple (GID, SaltInput, AuthCred) has the same GID and SaltInput values as in the triple including the new authentication credential of the Client and associated with the new Access Token.

Secure Communication with the AS As specified in the ACE framework (see Sections and of ), the requesting entity (RS and/or Client) and the AS communicate via the /token or /introspection endpoint. The use of CoAP and OSCORE for this communication is RECOMMENDED in this profile. Other protocols fulfilling the security requirements defined in Sections and of (such as HTTP and DTLS or TLS) MAY be used instead. If OSCORE is used, the requesting entity and the AS are expected to have a pre-established Security Context in place. How this Security Context is established is out of the scope of this profile. Furthermore, the requesting entity and the AS communicate using OSCORE through the /introspection endpoint as specified in , and through the /token endpoint as specified in .

Discarding the Security Context As members of an OSCORE group, the Client and the RS may independently leave the group or be forced to, e.g., if compromised or suspected so. Upon leaving the OSCORE group, the Client or RS also discards the Group OSCORE Security Context, which may anyway be renewed by the Group Manager through a group rekeying process (see ). The Client or RS can acquire a new Group OSCORE Security Context, by re-joining the OSCORE group, e.g., by using the approach defined in . In such a case, the Client SHOULD request a new Access Token and post it to the RS.

CBOR Mappings The new parameters defined in this document MUST be mapped to CBOR types as specified in , using the given integer abbreviation for the map key.

CBOR mappings for new parameters.

The new claims defined in this document MUST be mapped to CBOR types as specified in , using the given integer abbreviation for the map key.

CBOR mappings for new claims.

Security Considerations This document specifies a profile for the Authentication and Authorization for Constrained Environments (ACE) framework . Thus, the general security considerations from the ACE framework also apply to this profile. The proof-of-possession (PoP) key bound to an Access Token is always an asymmetric key, i.e., the public key included in the authentication credential that the Client uses in the OSCORE group. This means that there is never a same shared secret used as PoP key with possible multiple RSs. Therefore, it is possible and safe for the AS to issue an Access Token for an audience that includes multiple RSs (i.e., a group-audience, see ). In such a case, as per , the AS has to ensure the integrity protection of the Access Token by protecting it through an asymmetric signature. In addition, the used group-audience has to correctly identify all the RSs that are intended recipients of the Access Token, and for which the single scope specified in the Access Token applies. As a particular case, the audience can be the name of the OSCORE group, if the Access Token is intended to all the RSs in that group. Furthermore, this document inherits the general security considerations about Group OSCORE , as to the specific use of Group OSCORE according to this profile. Group OSCORE is designed to secure point-to-point as well as point-to-multipoint communications, providing a secure binding between a single request and multiple corresponding responses. In particular, Group OSCORE fulfills the same security requirements of OSCORE. Group OSCORE ensures source authentication of messages both in group mode (see ) and in pairwise mode (see ). When protecting an outgoing message in group mode, the sender uses its private key to compute a digital signature, which is embedded in the protected message. The group mode can be used to protect messages sent to multiple recipients (e.g., over IP multicast) or to a single recipient. When protecting an outgoing message in pairwise mode, the sender uses a pairwise symmetric key, as derived from the asymmetric keys of the two peers exchanging the message. The pairwise mode can be used to protect only messages intended to a single recipient.

Privacy Considerations This document specifies a profile for the Authentication and Authorization for Constrained Environments (ACE) framework . Thus the general privacy considerations from the ACE framework also apply to this profile. As this profile uses Group OSCORE, the privacy considerations from apply to this document as well. An unprotected response to an unauthorized request may disclose information about the RS and/or its existing relationship with the Client. It is advisable to include as little information as possible in an unencrypted response. However, since both the Client and the RS share a Group OSCORE Security Context, unauthorized, yet protected requests are followed by protected responses, which can thus include more detailed information. Although it may be encrypted, the Access Token is sent in the clear to the /authz-info endpoint at the RS. Thus, if the Client uses the same single Access Token from multiple locations with multiple Resource Servers, it can risk being tracked through the Access Token's value. Note that, even though communications are protected with Group OSCORE, some information might still leak, due to the observable size, source address, and destination address of exchanged messages.

IANA Considerations This document has the following actions for IANA. Note to RFC Editor: Please replace "[RFC-XXXX]" with the RFC number of this document and delete this paragraph.

ACE Profile Registry IANA is asked to add the following entry to the "ACE Profile" registry within the "Authentication and Authorization for Constrained Environments (ACE)" registry group, following the procedure specified in .

• Name: coap_group_oscore
• Description: Profile to secure communications between constrained nodes using the Authentication and Authorization for Constrained Environments framework, by enabling authentication and fine-grained authorization of members of an OSCORE group, that use a pre-established Group OSCORE Security Context to communicate with Group OSCORE.
• CBOR Value: TBD (value between 1 and 255)
• Reference: [RFC-XXXX]

OAuth Parameters Registry IANA is asked to add the following entries to the "OAuth Parameters" registry, following the procedure specified in .

• Name: "context_id"
• Parameter Usage Location: token request
• Change Controller: IESG
• Specification Document(s): of [RFC-XXXX]

 

• Name: "salt_input"
• Parameter Usage Location: token request
• Change Controller: IESG
• Specification Document(s): of [RFC-XXXX]

 

• Name: "client_cred_verify"
• Parameter Usage Location: token request
• Change Controller: IESG
• Specification Document(s): of [RFC-XXXX]

 

• Name: "client_cred_verify_mac"
• Parameter Usage Location: token request
• Change Controller: IESG
• Specification Document(s): of [RFC-XXXX]

OAuth Parameters CBOR Mappings Registry IANA is asked to add the following entries to the "OAuth Parameters CBOR Mappings" registry within the "Authentication and Authorization for Constrained Environments (ACE)" registry group, following the procedure specified in .

• Name: "context_id"
• CBOR Key: TBD
• Value Type: bstr
• Reference: of [RFC-XXXX]

 

• Name: "salt_input"
• CBOR Key: TBD
• Value Type: bstr
• Reference: of [RFC-XXXX]

 

• Name: "client_cred_verify"
• CBOR Key: TBD
• Value Type: bstr
• Reference: of [RFC-XXXX]

 

• Name: "client_cred_verify_mac"
• CBOR Key: TBD
• Value Type: bstr
• Reference: of [RFC-XXXX]

CBOR Web Token (CWT) Claims Registry IANA is asked to add the following entries to the "CBOR Web Token (CWT) Claims" registry, following the procedure specified in .

• Claim Name: "salt_input"
• Claim Description: Client provided salt input
• JWT Claim Name: "N/A"
• Claim Key: TBD
• Claim Value Type(s): bstr
• Change Controller: IESG
• Specification Document(s): of [RFC-XXXX]

 

• Claim Name: "contextId_input"
• Claim Description: Client context id input
• JWT Claim Name: "N/A"
• Claim Key: TBD
• Claim Value Type(s): bstr
• Change Controller: IESG
• Specification Document(s): of [RFC-XXXX]

TLS Exporter Label Registry IANA is asked to add the following entry to the "TLS Exporter Label" registry within the "Transport Layer Security (TLS) Parameters" registry group, following the procedure specified in and updated in .

• Value: EXPORTER-ACE-Sign-Challenge-Client-AS
• DTLS-OK: Y
• Recommended: N
• Reference: of [RFC-XXXX]

References Normative References IoTconsultancy.nl InterDigital RISE AB This document specifies the use of the Constrained Application Protocol (CoAP) for group communication, including the use of UDP/IP multicast as the default underlying data transport. Both unsecured and secured CoAP group communication are specified. Security is achieved by use of the Group Object Security for Constrained RESTful Environments (Group OSCORE) protocol. The target application area of this specification is any group communication use cases that involve resource-constrained devices or networks that support CoAP. This document replaces RFC 7390, while it updates RFC 7252 and RFC 7641. RISE AB Ericsson AB Ericsson AB Ericsson AB Universitaet Duisburg-Essen This document defines the security protocol Group Object Security for Constrained RESTful Environments (Group OSCORE), providing end-to-end security of CoAP messages exchanged between members of a group, e.g., sent over IP multicast. In particular, the described protocol defines how OSCORE is used in a group communication setting to provide source authentication for CoAP group requests, sent by a client to multiple servers, and for protection of the corresponding CoAP responses. Group OSCORE also defines a pairwise mode where each member of the group can efficiently derive a symmetric pairwise key with any other member of the group for pairwise OSCORE communication. Group OSCORE can be used between endpoints communicating with CoAP or CoAP-mappable HTTP. RISE AB Universitaet Duisburg-Essen Ericsson AB This document defines an application profile of the ACE framework for Authentication and Authorization, to request and provision keying material in group communication scenarios that are based on CoAP and are secured with Group Object Security for Constrained RESTful Environments (Group OSCORE). This application profile delegates the authentication and authorization of Clients, that join an OSCORE group through a Resource Server acting as Group Manager for that group. This application profile leverages protocol-specific transport profiles of ACE to achieve communication security, server authentication and proof-of-possession for a key owned by the Client and bound to an OAuth 2.0 Access Token. In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. A number of protocols wish to leverage Transport Layer Security (TLS) to perform key establishment but then use some of the keying material for their own purposes. This document describes a general mechanism for allowing that. [STANDARDS-TRACK] This document specifies a simple Hashed Message Authentication Code (HMAC)-based key derivation function (HKDF), which can be used as a building block in various protocols and applications. The key derivation function (KDF) is intended to support a wide range of applications and requirements, and is conservative in its use of cryptographic hash functions. This document is not an Internet Standards Track specification; it is published for informational purposes. The OAuth 2.0 authorization framework enables a third-party application to obtain limited access to an HTTP service, either on behalf of a resource owner by orchestrating an approval interaction between the resource owner and the HTTP service, or by allowing the third-party application to obtain access on its own behalf. This specification replaces and obsoletes the OAuth 1.0 protocol described in RFC 5849. [STANDARDS-TRACK] The Constrained Application Protocol (CoAP) is a specialized web transfer protocol for use with constrained nodes and constrained (e.g., low-power, lossy) networks. The nodes often have 8-bit microcontrollers with small amounts of ROM and RAM, while constrained networks such as IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs) often have high packet error rates and a typical throughput of 10s of kbit/s. The protocol is designed for machine- to-machine (M2M) applications such as smart energy and building automation. CoAP provides a request/response interaction model between application endpoints, supports built-in discovery of services and resources, and includes key concepts of the Web such as URIs and Internet media types. CoAP is designed to easily interface with HTTP for integration with the Web while meeting specialized requirements such as multicast support, very low overhead, and simplicity for constrained environments. This memo specifies two elliptic curves over prime fields that offer a high level of practical security in cryptographic applications, including Transport Layer Security (TLS). These curves are intended to operate at the ~128-bit and ~224-bit security level, respectively, and are generated deterministically based on a list of required properties. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. CBOR Web Token (CWT) is a compact means of representing claims to be transferred between two parties. The claims in a CWT are encoded in the Concise Binary Object Representation (CBOR), and CBOR Object Signing and Encryption (COSE) is used for added application-layer security protection. A claim is a piece of information asserted about a subject and is represented as a name/value pair consisting of a claim name and a claim value. CWT is derived from JSON Web Token (JWT) but uses CBOR rather than JSON. This document defines Object Security for Constrained RESTful Environments (OSCORE), a method for application-layer protection of the Constrained Application Protocol (CoAP), using CBOR Object Signing and Encryption (COSE). OSCORE provides end-to-end protection between endpoints communicating using CoAP or CoAP-mappable HTTP. OSCORE is designed for constrained nodes and networks supporting a range of proxy operations, including translation between different transport protocols. Although an optional functionality of CoAP, OSCORE alters CoAP options processing and IANA registration. Therefore, this document updates RFC 7252. This document describes a number of changes to TLS and DTLS IANA registries that range from adding notes to the registry all the way to changing the registration policy. These changes were mostly motivated by WG review of the TLS- and DTLS-related registries undertaken as part of the TLS 1.3 development process. This document updates the following RFCs: 3749, 5077, 4680, 5246, 5705, 5878, 6520, and 7301. This specification describes how to declare in a CBOR Web Token (CWT) (which is defined by RFC 8392) that the presenter of the CWT possesses a particular proof-of-possession key. Being able to prove possession of a key is also sometimes described as being the holder-of-key. This specification provides equivalent functionality to "Proof-of-Possession Key Semantics for JSON Web Tokens (JWTs)" (RFC 7800) but using Concise Binary Object Representation (CBOR) and CWTs rather than JavaScript Object Notation (JSON) and JSON Web Tokens (JWTs). The Concise Binary Object Representation (CBOR) is a data format whose design goals include the possibility of extremely small code size, fairly small message size, and extensibility without the need for version negotiation. These design goals make it different from earlier binary serializations such as ASN.1 and MessagePack. This document obsoletes RFC 7049, providing editorial improvements, new details, and errata fixes while keeping full compatibility with the interchange format of RFC 7049. It does not create a new version of the format. Concise Binary Object Representation (CBOR) is a data format designed for small code size and small message size. There is a need to be able to define basic security services for this data format. This document defines the CBOR Object Signing and Encryption (COSE) protocol. This specification describes how to create and process signatures, message authentication codes, and encryption using CBOR for serialization. This specification additionally describes how to represent cryptographic keys using CBOR. This document, along with RFC 9053, obsoletes RFC 8152. Concise Binary Object Representation (CBOR) is a data format designed for small code size and small message size. There is a need to be able to define basic security services for this data format. This document defines a set of algorithms that can be used with the CBOR Object Signing and Encryption (COSE) protocol (RFC 9052). This document, along with RFC 9052, obsoletes RFC 8152. This specification defines a framework for authentication and authorization in Internet of Things (IoT) environments called ACE-OAuth. The framework is based on a set of building blocks including OAuth 2.0 and the Constrained Application Protocol (CoAP), thus transforming a well-known and widely used authorization solution into a form suitable for IoT devices. Existing specifications are used where possible, but extensions are added and profiles are defined to better serve the IoT use cases. This specification defines new parameters and encodings for the OAuth 2.0 token and introspection endpoints when used with the framework for Authentication and Authorization for Constrained Environments (ACE). These are used to express the proof-of-possession (PoP) key the client wishes to use, the PoP key that the authorization server has selected, and the PoP key the resource server uses to authenticate to the client. This document specifies a profile for the Authentication and Authorization for Constrained Environments (ACE) framework. It utilizes Object Security for Constrained RESTful Environments (OSCORE) to provide communication security and proof-of-possession for a key owned by the client and bound to an OAuth 2.0 access token. Informative References RISE AB Consultant Group communication over the Constrained Application Protocol (CoAP) can be secured by means of Group Object Security for Constrained RESTful Environments (Group OSCORE). At deployment time, devices may not know the exact security groups to join, the respective Group Manager, or other information required to perform the joining process. This document describes how a CoAP endpoint can use descriptions and links of resources registered at the CoRE Resource Directory to discover security groups and to acquire information for joining them through the respective Group Manager. A given security group may protect multiple application groups, which are separately announced in the Resource Directory as sets of endpoints sharing a pool of resources. This approach is consistent with, but not limited to, the joining of security groups based on the ACE framework for Authentication and Authorization in constrained environments. Brunel University Oxbotica This document specifies a profile for the ACE (Authentication and Authorization for Constrained Environments) framework to enable authorization in a Message Queuing Telemetry Transport (MQTT)-based publish-subscribe messaging system. Proof-of-possession keys, bound to OAuth2.0 access tokens, are used to authenticate and authorize MQTT Clients. The protocol relies on TLS for confidentiality and MQTT server (Broker) authentication. Ericsson AB Ericsson AB RISE AB RISE AB Nexus Group This document specifies a CBOR encoding of X.509 certificates. The resulting certificates are called C509 Certificates. The CBOR encoding supports a large subset of RFC 5280 and all certificates compatible with the RFC 7925, IEEE 802.1AR (DevID), CNSA, RPKI, GSMA eUICC, and CA/Browser Forum Baseline Requirements profiles. When used to re-encode DER encoded X.509 certificates, the CBOR encoding can in many cases reduce the size of RFC 7925 profiled certificates with over 50%. The CBOR encoded structure can alternatively be signed directly ("natively signed"), which does not require re- encoding for the signature to be verified. The document also specifies C509 COSE headers, a C509 TLS certificate type, and a C509 file format. A common design pattern in Internet of Things (IoT) deployments is the use of a constrained device that collects data via sensors or controls actuators for use in home automation, industrial control systems, smart cities, and other IoT deployments. This document defines a Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS) 1.2 profile that offers communications security for this data exchange thereby preventing eavesdropping, tampering, and message forgery. The lack of communication security is a common vulnerability in IoT products that can easily be solved by using these well-researched and widely deployed Internet security protocols. This document specifies version 1.3 of the Transport Layer Security (TLS) protocol. TLS allows client/server applications to communicate over the Internet in a way that is designed to prevent eavesdropping, tampering, and message forgery. This document updates RFCs 5705 and 6066, and obsoletes RFCs 5077, 5246, and 6961. This document also specifies new requirements for TLS 1.2 implementations. This document specifies version 1.3 of the Datagram Transport Layer Security (DTLS) protocol. DTLS 1.3 allows client/server applications to communicate over the Internet in a way that is designed to prevent eavesdropping, tampering, and message forgery. The DTLS 1.3 protocol is based on the Transport Layer Security (TLS) 1.3 protocol and provides equivalent security guarantees with the exception of order protection / non-replayability. Datagram semantics of the underlying transport are preserved by the DTLS protocol. This document obsoletes RFC 6347. This specification defines a profile of the Authentication and Authorization for Constrained Environments (ACE) framework that allows constrained servers to delegate client authentication and authorization. The protocol relies on DTLS version 1.2 or later for communication security between entities in a constrained network using either raw public keys or pre-shared keys. A resource-constrained server can use this protocol to delegate management of authorization information to a trusted host with less-severe limitations regarding processing power and memory.

Profile Requirements This appendix lists the specifications of this profile based on the requirements of the ACE framework, as requested in .

• Optionally, define new methods for the Client to discover the necessary permissions and AS for accessing a resource, different from the one proposed in : Not specified.
• Optionally, specify new grant types: Not specified.
• Optionally, define the use of client certificates as client credential type: Not specified.
• Specify the communication protocol the Client and RS must use: CoAP.
• Specify the security protocol the Client and RS must use to protect their communication: Group OSCORE, by using a pre-established Group OSCORE Security Context.
• Specify how the Client and the RS mutually authenticate: Explicitly, by possession of a common Group OSCORE Security Context, and by either: usage of digital signatures embedded in messages, if protected with the group mode of Group OSCORE; or protection of messages with the pairwise mode of Group OSCORE, by using pairwise symmetric keys derived from the asymmetric keys of the two peers exchanging the message. Note that mutual authentication is not completed before the Client has verified a Group OSCORE response using the corresponding Group OSCORE Security Context.
• Specify the proof-of-possession protocol(s) and how to select one, if several are available. Also specify which key types (e.g., symmetric/asymmetric) are supported by a specific proof-of- possession protocol: Group OSCORE algorithms; asymmetric keys verified and distributed by a Group Manager.
• Specify a unique ace_profile identifier: coap_group_oscore.
• If introspection is supported, specify the communication and security protocol for introspection: HTTP/CoAP (+ TLS/DTLS/OSCORE).
• Specify the communication and security protocol for interactions between client and AS: HTTP/CoAP (+ TLS/DTLS/OSCORE).
• Specify if/how the authz-info endpoint is protected, including how error responses are protected: Not protected.
• Optionally, define other methods of token transport than the authz-info endpoint: Not defined.

Acknowledgments The authors sincerely thank , , , , , and for their comments and feedback. The work on this document has been partly supported by VINNOVA and the Celtic-Next project CRITISEC; and by the H2020 project SIFIS-Home (Grant agreement 952652).