Ericsson AB

francesca.palombini@ericsson.com

Combitech

Djäknegatan 31 Malmö 211 35 Sweden ludwig.seitz@combitech.com

Ericsson AB

goran.selander@ericsson.com

RISE

Scheelevägen 17 Lund 22370 Sweden martin.gunnarsson@ri.se

Security ACE CoAP OAuth 2.0 Access Control Authorization Internet of Things 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.

Status of This Memo This is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at .

Copyright Notice Copyright (c) 2022 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents () in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License.

Table of Contents

• .  Introduction
  • .  Terminology
• .  Protocol Overview
• .  Client-AS Communication
  • .  C-to-AS: POST to Token Endpoint
  • .  AS-to-C: Access Token
    • .  The OSCORE_Input_Material
• .  Client-RS Communication
  • .  C-to-RS: POST to authz-info Endpoint
    • .  The Nonce 1 Parameter
    • .  The ace_client_recipientid Parameter
  • .  RS-to-C: 2.01 (Created)
    • .  The Nonce 2 Parameter
    • .  The ace_server_recipientid Parameter
  • .  OSCORE Setup
  • .  Access Rights Verification
• .  Secure Communication with AS
• .  Discarding the Security Context
• .  Security Considerations
• .  Privacy Considerations
• .  IANA Considerations
  • .  ACE Profile Registry
  • .  OAuth Parameters Registry
  • .  OAuth Parameters CBOR Mappings Registry
  • .  OSCORE Security Context Parameters Registry
  • .  CWT Confirmation Methods Registry
  • .  JWT Confirmation Methods Registry
  • .  Expert Review Instructions
• . References
  • .  Normative References
  • .  Informative References
• .  Profile Requirements
• Acknowledgments
• Authors' Addresses

Introduction This document specifies the coap_oscore profile of the ACE framework . In this profile, a client (C) and a resource server (RS) use the Constrained Application Protocol (CoAP) to communicate. The client uses an access token, bound to a symmetric key (the proof-of-possession (PoP) key) to authorize its access to the resource server. Note that this profile uses a symmetric-crypto-based scheme, where the symmetric secret is used as input material for keying material derivation. In order to provide communication security and PoP, the client and resource server use Object Security for Constrained RESTful Environments (OSCORE) as defined in . Note that the PoP is not achieved through a dedicated protocol element but rather occurs after the first message exchange using OSCORE. OSCORE specifies how to use CBOR Object Signing and Encryption (COSE) to secure CoAP messages. Note that OSCORE can be used to secure CoAP messages, as well as HTTP and combinations of HTTP and CoAP; a profile of ACE similar to the one described in this document, with the difference of using HTTP instead of CoAP as the communication protocol, could be specified analogously to this one.

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. 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 . RESTful terminology follows HTTP . Readers are expected to be familiar with the terms and concepts defined in OSCORE , such as "security context" and "Recipient ID". Terminology for entities in the architecture is defined in OAuth 2.0 , such as client (C), resource server (RS), and authorization server (AS). It is assumed in this document that a given resource on a specific RS is associated to a unique AS. Concise Binary Object Representation (CBOR) and Concise Data Definition Language (CDDL) 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. Note that the term "endpoint" is used as in , following its OAuth definition, which is to denote resources such as token and introspect at the AS and authz-info at the RS. The CoAP definition, which is "[a]n entity participating in the CoAP protocol" , is not used in this document. Throughout this document, examples for CBOR data items are expressed in CBOR extended diagnostic notation as defined in and ("diagnostic notation"), unless noted otherwise. We often use diagnostic notation comments to provide a textual representation of the numeric parameter names and values. In this document, the term "base64-encoded" refers to URL-Safe base64 encoding (see ) without padding.

Protocol Overview This section gives an overview of how to use the ACE Framework to secure the communication between a client and a resource server using OSCORE . The parameters needed by the client to negotiate the use of this profile with the AS, as well as the OSCORE setup process, are described in detail in the following sections. The RS maintains a collection of OSCORE security contexts with associated authorization information for all the clients that it is communicating with. The authorization information is maintained as policy that is used as input to processing requests from those clients. This profile requires a client to retrieve an access token from the AS for the resource it wants to access on an RS, by sending an access token request to the token endpoint, as specified in . The access token request and response MUST be confidentiality protected and ensure authenticity. The use of OSCORE between the client and AS is RECOMMENDED in this profile, to reduce the number of libraries the client has to support, but other protocols fulfilling the security requirements defined in MAY alternatively be used, such as TLS or DTLS . Once the client has retrieved the access token, it generates a nonce N1, as defined in this document (see ). The client also generates its own OSCORE Recipient ID, ID1 (see ), for use with the keying material associated to the RS. The client posts the token, N1, and its Recipient ID to the RS using the authz-info endpoint and mechanisms specified in and Content-Format = application/ace+cbor. When using this profile, the communication with the authz-info endpoint is not protected, except for the update of access rights. If the access token is valid, the RS replies to this request with a 2.01 (Created) response with Content-Format = application/ace+cbor, which contains a nonce N2 and its newly generated OSCORE Recipient ID, ID2, for use with the keying material associated to the client. Moreover, the server concatenates the input salt received in the token, N1, and N2 to obtain the Master Salt of the OSCORE security context (see ). The RS then derives the complete security context associated with the received token from the Master Salt; the OSCORE Recipient ID generated by the client (set as its OSCORE Sender ID); its own OSCORE Recipient ID; plus the parameters received in the access token from the AS, following . In a similar way, after receiving the nonce N2, the client concatenates the input salt, N1, and N2 to obtain the Master Salt of the OSCORE security context. The client then derives the complete security context from the Master Salt; the OSCORE Recipient ID generated by the RS (set as its OSCORE Sender ID); its own OSCORE Recipient ID; plus the parameters received from the AS. Finally, the client starts the communication with the RS by sending a request protected with OSCORE to the RS. If the request is successfully verified, the server stores the complete security context state that is ready for use in protecting messages and uses it in the response, and in further communications with the client, until token deletion due to, for example, expiration. This security context is discarded when a token (whether the same or a different one) is used to successfully derive a new security context for that client. The use of nonces N1 and N2 during the exchange prevents the reuse of an Authenticated Encryption with Associated Data (AEAD) nonce/key pair for two different messages. Reuse might otherwise occur when the client and RS derive a new security context from an existing (non-expired) access token, as might occur when either party has just rebooted, and that might lead to loss of both confidentiality and integrity. Instead, by using the exchanged nonces N1 and N2 as part of the Master Salt, the request to the authz-info endpoint posting the same token results in a different security context, by OSCORE construction, since even though the Master Secret, Sender ID, and Recipient ID are the same, the Master Salt is different (see ). If the exchanged nonces were reused, a node reusing a non-expired old token would be susceptible to on-path attackers provoking the creation of an OSCORE message using an old AEAD key and nonce. After the whole message exchange has taken place, the client can contact the AS to request an update of its access rights, sending a similar request to the token endpoint that also includes an identifier so that the AS can find the correct OSCORE Input Material it has previously shared with the client. This specific identifier, encoded as a byte string, is assigned by the AS to be unique in the sets of its OSCORE Input Materials, and it is not used as input material to derive the full OSCORE security context. An overview of the profile flow for the OSCORE profile is given in . The names of messages coincide with those of when applicable.

Protocol Overview C RS AS | | | | ----- POST /token ----------------------------> | | | | | <---------------------------- Access Token ----- | | + Access Information | | ---- POST /authz-info ---> | | | (access_token, N1, ID1) | | | | | | <- 2.01 Created (N2, ID2)- | | | | | /Sec Context /Sec Context | derivation/ derivation/ | | | | | ---- OSCORE Request -----> | | | | | | /proof-of-possession | | Sec Context storage/ | | | | | <--- OSCORE Response ----- | | | | | /proof-of-possession | | Sec Context storage/ | | | | | | ---- OSCORE Request -----> | | | | | | <--- OSCORE Response ----- | | | | | | ... | |

Client-AS Communication The following subsections describe the details of the POST request and response to the token endpoint between the client and AS. defines how to derive a security context based on a shared Master Secret and a set of other parameters, established between the client and server, which the client receives from the AS in this exchange. The PoP key included in the response from the AS MUST be used as a Master Secret in OSCORE.

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 (see ). An example of such a request is shown in .

Example C-to-AS POST /token Request for an Access Token Bound to a Symmetric Key Header: POST (Code=0.02) Uri-Host: "as.example.com" Uri-Path: "token" Content-Format: application/ace+cbor Payload: { / audience / 5 : "tempSensor4711", / scope / 9 : "read" }

If the client wants to update its access rights without changing an existing OSCORE security context, it MUST include a req_cnf object in its POST request to the token endpoint, with the kid field carrying a CBOR byte string containing the OSCORE Input Material identifier (assigned as discussed in ). This identifier, together with other information such as audience (see ), can be used by the AS to determine the shared secret bound to the proof-of-possession token; therefore, it MUST identify a symmetric key that was previously generated by the AS as a shared secret for the communication between the client and the RS. The AS MUST verify that the received value identifies a proof-of-possession key that has previously been issued to the requesting client. If that is not the case, the client-to-AS request MUST be declined with the error code invalid_request as defined in . An example of such a request is shown in .

Example C-to-AS POST /token Request for Updating Rights to an Access Token Bound to a Symmetric Key Header: POST (Code=0.02) Uri-Host: "as.example.com" Uri-Path: "token" Content-Format: application/ace+cbor Payload: { / audience / 5 : "tempSensor4711", / scope / 9 : "write", / req_cnf / 4 : { / kid / 3 : h'01' } }

AS-to-C: Access Token After verifying 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 responds as defined in . If the client request was invalid, or not authorized, the AS returns an error response as described in . The AS can signal that the use of OSCORE is REQUIRED for a specific access token by including the ace_profile parameter with the value coap_oscore in the access token response. This means that the client MUST use OSCORE towards all resource servers for which this access token is valid, and follow to derive the security context to run OSCORE. Usually, it is assumed that constrained devices will be preconfigured with the necessary profile, so that this kind of profile signaling can be omitted. Moreover, the AS MUST send the following data:

• a Master Secret
• an identifier of the OSCORE Input Material

Additionally, the AS MAY send the following data, in the same response.

• a context identifier
• an AEAD algorithm
• an HMAC-based key derivation function (HKDF) algorithm . It is specified by the HMAC algorithm value; see .
• a salt
• the OSCORE version number

This data is transported in the OSCORE_Input_Material. The OSCORE_Input_Material is a CBOR map object, defined in . This object is transported in the cnf parameter of the access token response, as defined in , as the value of a field named osc, which is registered in Sections and . The AS MAY assign an identifier to the context (context identifier). This identifier is used as ID Context in the OSCORE context as described in . If assigned, these parameters MUST be communicated as the contextId field in the OSCORE_Input_Material. The application needs to consider that this identifier is sent in the clear and may reveal information about the endpoints, as mentioned in . The Master Secret and the identifier of the OSCORE_Input_Material MUST be communicated as the ms and id field in the osc field in the cnf parameter of the access token response. If included, the following are sent: the AEAD algorithm in the alg parameter in the OSCORE_Input_Material; the HKDF algorithm in the hkdf parameter of the OSCORE_Input_Material; a salt in the salt parameter of the OSCORE_Input_Material; and the OSCORE version in the version parameter of the OSCORE_Input_Material. The same parameters MUST be included in the claims associated with the access token. The OSCORE Master Secret MUST be encrypted by the authorization server so that only the resource server can decrypt it (see ). The use of a CBOR Web Token (CWT) protected with COSE_Encrypt/COSE_Encrypt0 as specified in is RECOMMENDED in this profile. If the token is a CWT, the same OSCORE_Input_Material structure defined above MUST be placed in the osc field of the cnf claim of this token. The AS MUST send a different OSCORE_Input_Material (and therefore different access tokens) to different authorized clients, in order for the RS to differentiate between clients. shows an example of an AS response. The access token has been truncated for readability.

Example AS-to-C Access Token Response with an OSCORE Profile Header: Created (Code=2.01) Content-Type: application/ace+cbor Payload: { / access_token / 1 : h'8343a1010aa2044c53/... (remainder of access token (CWT) omitted for brevity)/', / ace_profile / 38 : / coap_oscore / 2, / expires_in / 2 : 3600, / cnf / 8 : { / osc / 4 : { / id / 0 : h'01', / ms / 2 : h'f9af838368e353e78888e1426bd94e6f' } } }

shows an example CWT Claims Set, including the relevant OSCORE parameters in the cnf claim.

Example CWT Claims Set with OSCORE Parameters { / aud / 3 : "tempSensorInLivingRoom", / iat / 6 : 1360189224, / exp / 4 : 1360289224, / scope / 9 : "temperature_g firmware_p", / cnf / 8 : { / osc / 4 : { / id / 0 : h'01', / ms / 2 : h'f9af838368e353e78888e1426bd94e6f' } } }

The same CWT Claims Set as in , using the value abbreviations defined in and and encoded in CBOR, is shown in . 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 readability.

Example CWT Claims Set with OSCORE Parameters Using CBOR Encoding A5 # map(5) 03 # unsigned(3) 76 # text(22) 74656D7053656E736F72496E4C6976696E67526F6F6D # "tempSensorInLivingRoom" 06 # unsigned(6) 1A 5112D728 # unsigned(1360189224) 04 # unsigned(4) 1A 51145DC8 # unsigned(1360289224) 09 # unsigned(9) 78 18 # text(24) 74656D70657261747572655F67206669726D776172655F70 # "temperature_g firmware_p" 08 # unsigned(8) A1 # map(1) 04 # unsigned(4) A2 # map(2) 00 # unsigned(0) 41 # bytes(1) 01 02 # unsigned(2) 50 # bytes(16) F9AF838368E353E78888E1426BD94E6F

If the client has requested an update to its access rights using the same OSCORE security context, which is valid and authorized, the AS MUST omit the cnf parameter in the response and MUST carry the OSCORE Input Material identifier in the kid field in the cnf claim of the token. This identifier needs to be included in the token in order for the RS to identify the correct OSCORE Input Material. shows an example of such an AS response. The access token has been truncated for readability.

Example AS-to-C Access Token Response with an OSCORE Profile for the Update of Access Rights Header: Created (Code=2.01) Content-Type: application/ace+cbor Payload: { / access_token / 1 : h'8343a1010aa2044c53/ ... (remainder of access token (CWT) omitted for brevity)/', / ace_profile / 38 : / coap_oscore / 2, / expires_in / 2 : 3600 }

shows an example CWT Claims Set that contains the necessary OSCORE parameters in the cnf claim for the update of access rights.

Example CWT Claims Set with OSCORE Parameters for the Update of Access Rights { / aud / 3 : "tempSensorInLivingRoom", / iat / 6 : 1360189224, / exp / 4 : 1360289224, / scope / 9 : "temperature_h", / cnf / 8 : { / kid / 3 : h'01' } }

The OSCORE_Input_Material An OSCORE_Input_Material is an object that represents the input material to derive an OSCORE security context, i.e., the local set of information elements necessary to carry out the cryptographic operations in OSCORE (). In particular, the OSCORE_Input_Material 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 OSCORE_Input_Material can be encoded as either a JSON object or a CBOR map. The set of common parameters that can appear in an OSCORE_Input_Material can be found in the IANA "OSCORE Security Context Parameters" registry (), defined for extensibility, and the initial set of parameters defined in this document is specified below. All parameters are optional. provides a summary of the OSCORE_Input_Material parameters defined in this section. OSCORE_Input_Material Parameters

name	CBOR label	CBOR type	registry	description
id	0	byte string		OSCORE Input Material identifier
version	1	unsigned integer		OSCORE version
ms	2	byte string		OSCORE Master Secret value
hkdf	3	text string / integer	values (HMAC-based)	OSCORE HKDF value
alg	4	text string / integer	values (AEAD)	OSCORE AEAD Algorithm value
salt	5	byte string		an input to OSCORE Master Salt value
contextId	6	byte string		OSCORE ID Context value

id:

This parameter identifies the OSCORE_Input_Material and is encoded as a byte string. In JSON, the id value is a base64-encoded byte string. In CBOR, the id type is a byte string, and it has label 0.

version:

This parameter identifies the OSCORE version number, which is an unsigned integer. For more information about this field, see . In JSON, the version value is an integer. In CBOR, the version type is an integer, and it has label 1.

ms:

This parameter identifies the OSCORE Master Secret value, which is a byte string. For more information about this field, see . In JSON, the ms value is a base64-encoded byte string. In CBOR, the ms type is byte string, and it has label 2.

hkdf:

This parameter identifies the OSCORE HKDF Algorithm. For more information about this field, see . The values used MUST be registered in the IANA "COSE Algorithms" registry (see ) and MUST be HMAC-based HKDF algorithms (see ). The value can be either the integer or the text-string value of the HMAC-based HKDF algorithm in the "COSE Algorithms" registry. In JSON, the hkdf value is a case-sensitive ASCII string or an integer. In CBOR, the hkdf type is a text string or integer, and it has label 3.

alg:

This parameter identifies the OSCORE AEAD Algorithm. For more information about this field, see . The values used MUST be registered in the IANA "COSE Algorithms" registry (see ) and MUST be AEAD algorithms. The value can be either the integer or the text-string value of the HMAC-based HKDF algorithm in the "COSE Algorithms" registry. In JSON, the alg value is a case-sensitive ASCII string or an integer. In CBOR, the alg type is a text string or integer, and it has label 4.

salt:

This parameter identifies an input to the OSCORE Master Salt value, which is a byte string. For more information about this field, see . In JSON, the salt value is a base64-encoded byte string. In CBOR, the salt type is a byte string, and it has label 5.

contextId:

This parameter identifies the security context as a byte string. This identifier is used as OSCORE ID Context. For more information about this field, see . In JSON, the contextID value is a base64-encoded byte string. In CBOR, the contextID type is a byte string, and it has label 6.

An example of JSON OSCORE_Input_Material is given in .

Example JSON OSCORE_Input_Material "osc" : { "alg" : "AES-CCM-16-64-128", "id" : "AQ", "ms" : "-a-Dg2jjU-eIiOFCa9lObw" }

The CDDL grammar describing the CBOR OSCORE_Input_Material is shown in .

CDDL Grammar of the OSCORE_Input_Material OSCORE_Input_Material = { ? 0 => bstr, ; id ? 1 => int, ; version ? 2 => bstr, ; ms ? 3 => tstr / int, ; hkdf ? 4 => tstr / int, ; alg ? 5 => bstr, ; salt ? 6 => bstr, ; contextId * (int / tstr) => any }

Client-RS Communication The following subsections describe the details of the POST request and response to the authz-info endpoint between the client and RS. The client generates a nonce N1 and an identifier ID1 that is unique in the sets of its own Recipient IDs and posts them together with the token that includes the materials (e.g., OSCORE parameters) received from the AS to the RS. The RS then generates a nonce N2 and an identifier ID2 that is unique in the sets of its own Recipient IDs and uses to derive a security context based on a shared Master Secret, the two exchanged nonces, and the two identifiers, established between the client and server. The exchanged nonces and identifiers are encoded as a CBOR byte string if CBOR is used and as a base64 string if JSON is used. This security context is used to protect all future communication between the client and RS using OSCORE, as long as the access token is valid. Note that the RS and client authenticate each other by generating the shared OSCORE security context using the PoP key as the Master Secret. An attacker posting a valid token to the RS will not be able to generate a valid OSCORE security context and thus will not be able to prove possession of the PoP key. Additionally, the mutual authentication is only achieved after the client has successfully verified a response from the RS protected with the generated OSCORE security context.

C-to-RS: POST to authz-info Endpoint The client MUST generate a nonce value N1 that is very unlikely to have been previously used with the same input keying material. The use of a 64-bit long random number as the nonce's value is RECOMMENDED in this profile. The client MUST store the nonce N1 as long as the response from the RS is not received and the access token related to it is still valid (to the best of the client's knowledge). The client generates its own Recipient ID, ID1, for the OSCORE security context that it is establishing with the RS. By generating its own Recipient ID, the client makes sure that it does not collide with any of its Recipient IDs, nor with any other identifier ID1 if the client is executing this exchange with a different RS at the same time. The client MUST use CoAP and the authorization information resource as described in to transport the token, N1, and ID1 to the RS. Note that the use of the payload and the Content-Format is different from what is described in , which only transports the token without any CBOR wrapping. In this profile, the client MUST wrap the token, N1, and ID1 in a CBOR map. The client MUST use the Content-Format application/ace+cbor defined in . The client MUST include the access token using the access_token parameter; N1 using the nonce1 parameter defined in ; and ID1 using the ace_client_recipientid parameter defined in . The communication with the authz-info endpoint does not have to be protected, except for the update of access rights case described below. Note that a client may be required to repost the access token in order to complete a request, since an RS may delete a stored access token (and associated security context) at any time, for example, due to all storage space being consumed. This situation is detected by the client when it receives an AS Request Creation Hints response. Reposting the same access token will result in deriving a new OSCORE security context to be used with the RS, as different exchanged nonces will be used. The client may also choose to repost the access token in order to update its OSCORE security context. In that case, the client and the RS will exchange newly generated nonces, renegotiate identifiers, and derive new keying material. The client and RS might decide to keep the same identifiers or renew them during the renegotiation. shows an example of the request sent from the client to the RS. The access token has been truncated for readability.

Example C-to-RS POST /authz-info Request Using CWT Header: POST (Code=0.02) Uri-Host: "rs.example.com" Uri-Path: "authz-info" Content-Format: application/ace+cbor Payload: { / access_token / 1 : h'8343a1010aa2044c53/... (remainder of access token (CWT) omitted for brevity)/', / nonce1 / 40 : h'018a278f7faab55a', / ace_client_recipientid / 43 : h'1645' }

If the client has already posted a valid token, has already established a security association with the RS, and wants to update its access rights, the client can do so by posting the new token (retrieved from the AS and containing the update of access rights) to the /authz-info endpoint. The client MUST protect the request using the OSCORE security context established during the first token exchange. The client MUST only send the access_token field in the CBOR map in the payload; no nonce or identifier is sent. After proper verification (see ), the RS will replace the old token with the new one, maintaining the same security context.

The Nonce 1 Parameter The nonce1 parameter MUST be sent from the client to the RS, together with the access token, if the ACE profile used is coap_oscore, and the message is not an update of access rights, protected with an existing OSCORE security context. The parameter is encoded as a byte string for CBOR-based interactions and as a string (base64-encoded binary) for JSON-based interactions. This parameter is registered in .

The ace_client_recipientid Parameter The ace_client_recipientid parameter MUST be sent from the client to the RS, together with the access token, if the ACE profile used is coap_oscore, and the message is not an update of access rights, protected with an existing OSCORE security context. The parameter is encoded as a byte string for CBOR-based interactions and as a string (base64-encoded binary) for JSON-based interactions. This parameter is registered in .

RS-to-C: 2.01 (Created) The RS MUST follow the procedures defined in : the RS must verify the validity of the token. If the token is valid, the RS must respond to the POST request with 2.01 (Created). If the token is valid but is associated to claims that the RS cannot process (e.g., an unknown scope), or if any of the expected parameters are missing (e.g., any of the mandatory parameters from the AS or the identifier ID1), or if any parameters received in the osc field are unrecognized, the RS must respond with an error response code equivalent to the CoAP code 4.00 (Bad Request). In the latter two cases, the RS may provide additional information in the error response, in order to clarify what went wrong. The RS may make an introspection request (see ) to validate the token before responding to the POST request to the authz-info endpoint. Additionally, the RS MUST generate a nonce N2 that is very unlikely to have been previously used with the same input keying material and its own Recipient ID, ID2. The RS makes sure that ID2 does not collide with any of its Recipient IDs. The RS MUST ensure that ID2 is different from the value received in the ace_client_recipientid parameter. The RS sends N2 and ID2 within the 2.01 (Created) response. The payload of the 2.01 (Created) response MUST be a CBOR map containing the nonce2 parameter defined in , set to N2, and the ace_server_recipientid parameter defined in , set to ID2. The use of a 64-bit long random number as the nonce's value is RECOMMENDED in this profile. The RS MUST use the Content-Format application/ace+cbor defined in . shows an example of the response sent from the RS to the client.

Example RS-to-C 2.01 (Created) Response Header: Created (Code=2.01) Content-Format: application/ace+cbor Payload: { / nonce2 / 42 : h'25a8991cd700ac01', / ace_server_recipientid / 44 : h'0000' }

As specified in , the RS must notify the client with an error response with code 4.01 (Unauthorized) for any long running request before terminating the session, when the access token expires. If the RS receives the token in an OSCORE-protected message, it means that the client is requesting an update of access rights. The RS MUST ignore any nonce and identifiers in the request, if any were sent. The RS MUST check that the kid of the cnf claim of the new access token matches the identifier of the OSCORE Input Material of the context used to protect the message. If that is the case, the RS MUST overwrite the old token and associate the new token to the security context identified by the kid value in the cnf claim. The RS MUST respond with a 2.01 (Created) response protected with the same security context, with no payload. If any verification fails, the RS MUST respond with a 4.01 (Unauthorized) error response. As specified in , when receiving an updated access token with updated authorization information from the client (see ), it is recommended that the RS overwrites the previous token; that is, only the latest authorization information in the token received by the RS is valid. This simplifies the process needed by the RS to keep track of authorization information for a given client.

The Nonce 2 Parameter The nonce2 parameter MUST be sent from the RS to the client if the ACE profile used is coap_oscore and the message is not a response to an update of access rights, protected with an existing OSCORE security context. The parameter is encoded as a byte string for CBOR-based interactions and as a string (base64-encoded binary) for JSON-based interactions. This parameter is registered in

The ace_server_recipientid Parameter The ace_server_recipientid parameter MUST be sent from the RS to the client if the ACE profile used is coap_oscore and the message is not a response to an update of access rights, protected with an existing OSCORE security context. The parameter is encoded as a byte string for CBOR-based interactions and as a string (base64-encoded binary) for JSON-based interactions. This parameter is registered in

OSCORE Setup Once the 2.01 (Created) response is received from the RS, following the POST request to authz-info endpoint, the client MUST extract the bstr nonce N2 from the nonce2 parameter in the CBOR map in the payload of the response. Then, the client MUST set the Master Salt of the security context created to communicate with the RS to the concatenation of salt, N1, and N2 in this order: Master Salt = salt | N1 | N2, where | denotes byte string concatenation, salt is the CBOR byte string received from the AS in , and N1 and N2 are the two nonces encoded as CBOR byte strings. An example of Master Salt construction using CBOR encoding is given in .

Example of Master Salt Construction Using CBOR Encoding N1, N2, and input salt expressed in CBOR diagnostic notation: nonce1 = h'018a278f7faab55a' nonce2 = h'25a8991cd700ac01' input salt = h'f9af838368e353e78888e1426bd94e6f' N1, N2, and input salt as CBOR encoded byte strings: nonce1 = 0x48018a278f7faab55a nonce2 = 0x4825a8991cd700ac01 input salt = 0x50f9af838368e353e78888e1426bd94e6f Master Salt = 0x50 f9af838368e353e78888e1426bd94e6f 48 018a278f7faab55a 48 25a8991cd700ac01

If JSON is used instead of CBOR, the Master Salt of the security context is the base64 encoding of the concatenation of the same parameters, each of them prefixed by their size, encoded in 1 byte. When using JSON, the nonces and input salt have a maximum size of 255 bytes. An example of Master Salt construction using base64 encoding is given in .

Example of Master Salt Construction Using Base64 Encoding N1, N2, and input salt values: nonce1 = 0x018a278f7faab55a (8 bytes) nonce2 = 0x25a8991cd700ac01 (8 bytes) input salt = 0xf9af838368e353e78888e1426bd94e6f (16 bytes) Input to base64 encoding: 0x10 f9af838368e353e78888e1426bd94e6f 08 018a278f7faab55a 08 25a8991cd700ac01 Master Salt = b64'EPmvg4No41PniIjhQmvZTm8IAYonj3+qtVoIJaiZHNcArAE='

The client MUST set the Sender ID to the ace_server_recipientid received in and set the Recipient ID to the ace_client_recipientid sent in . The client MUST set the Master Secret from the parameter received from the AS in . The client MUST set the AEAD algorithm, ID Context, HKDF, and OSCORE version from the parameters received from the AS in , if present. In case an optional parameter is omitted, the default value SHALL be used as described in Sections and of . After that, the client MUST derive the complete security context following . From this point on, the client MUST use this security context to communicate with the RS when accessing the resources as specified by the authorization information. If any of the expected parameters are missing (e.g., any of the mandatory parameters from the AS or the RS), or if ace_client_recipientid equals ace_server_recipientid (and as a consequence, the Sender and Recipient Keys derived would be equal; see ), then the client MUST stop the exchange and MUST NOT derive the security context. The client MAY restart the exchange, to get the correct security material. The client then uses this security context to send requests to the RS using OSCORE. After sending the 2.01 (Created) response, the RS MUST set the Master Salt of the security context created to communicate with the client to the concatenation of salt, N1, and N2 in the same way described above. An example of Master Salt construction using CBOR encoding is given in and using base64 encoding is given in . The RS MUST set the Sender ID from the ace_client_recipientid received in and set the Recipient ID from the ace_server_recipientid sent in . The RS MUST set the Master Secret from the parameter received from the AS and forwarded by the client in the access token in after validation of the token as specified in . The RS MUST set the AEAD algorithm, ID Context, HKDF, and OSCORE version from the parameters received from the AS and forwarded by the client in the access token in after validation of the token as specified in , if present. In case an optional parameter is omitted, the default value SHALL be used as described in Sections and of . After that, the RS MUST derive the complete security context following and MUST associate this security context with the authorization information from the access token. The RS then uses this security context to verify requests and send responses to the client using OSCORE. If OSCORE verification fails, error responses are used, as specified in . Additionally, if OSCORE verification succeeds, the verification of access rights is performed as described in . The RS MUST NOT use the security context after the related token has expired and MUST respond with an unprotected 4.01 (Unauthorized) error message to requests received that correspond to a security context with an expired token. Note that the ID Context can be assigned by the AS, communicated and set in both the RS and client after the exchange specified in this profile is executed. Subsequently, the client and RS can update their ID Context by running a mechanism such as the one defined in if they both support it and are configured to do so. In that case, the ID Context in the OSCORE security context will not match the contextId parameter of the corresponding OSCORE_Input_Material. Running Appendix results in the keying material being updated in the security contexts of the client and RS; this same result can also be achieved by the client reposting the access token to the unprotected /authz-info endpoint at the RS, as described in , but without updating the ID Context.

Access Rights Verification The RS MUST follow the procedures defined in : if an RS receives an OSCORE-protected request from a client, then the RS processes it according to . If OSCORE verification succeeds, and the target resource requires authorization, the RS retrieves the authorization information using the access token associated to the security context. The RS then must verify that the authorization information covers the resource and the action requested.

Secure Communication with AS As specified in the ACE framework (), the requesting entity (RS and/or client) and the AS communicates via the introspection or token endpoint. The use of CoAP and OSCORE for this communication is RECOMMENDED in this profile; other protocols fulfilling the security requirements defined in (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 preestablished security contexts in place. How these security contexts are established is out of scope for this profile. Furthermore, the requesting entity and the AS communicate through the introspection endpoint as specified in and through the token endpoint as specified in .

Discarding the Security Context There are a number of scenarios where a client or RS needs to discard the OSCORE security context and acquire a new one. The client MUST discard the current security context associated with an RS when any of the following occurs:

• the sequence number space ends.
• the access token associated with the context becomes invalid due to, for example, expiration.
• the client receives a number of 4.01 Unauthorized responses to OSCORE requests using the same security context. The exact number needs to be specified by the application.
• the client receives a new nonce in the 2.01 (Created) response (see ) to a POST request to the authz-info endpoint, when reposting a (non-expired) token associated to the existing context.

The RS MUST discard the current security context associated with a client when any of the following occurs:

• the sequence number space ends.
• the access token associated with the context expires.
• the client has successfully replaced the current security context with a newer one by posting an access token to the unprotected /authz-info endpoint at the RS, e.g., by reposting the same token, as specified in .

Whenever one more access token is successfully posted to the RS, and a new security context is derived between the client and RS, messages in transit that were protected with the previous security context might not pass verification, as the old context is discarded. That means that messages sent shortly before the client posts one more access tokens to the RS might not successfully reach the destination. Analogously, implementations may want to cancel CoAP observations at the RS registered before the security context is replaced, or conversely, they will need to implement a mechanism to ensure that those observations are to be protected with the newly derived security context.

Security Considerations This document specifies a profile for the ACE framework . Thus, the general security considerations from the framework also apply to this profile. Furthermore, the general security considerations of OSCORE also apply to this specific use of the OSCORE protocol. As previously stated, the proof of possession in this profile is performed by both parties verifying that they have established the same security context, as specified in , which means that both the OSCORE request and the OSCORE response passes verification. RS authentication requires both that the client trusts the AS and that the OSCORE response from the RS passes verification. OSCORE is designed to secure point-to-point communication, providing a secure binding between the request and the response(s). Thus, the basic OSCORE protocol is not intended for use in point-to-multipoint communication (e.g., multicast, publish-subscribe). Implementers of this profile should make sure that their use case corresponds to the expected use of OSCORE, to prevent weakening the security assurances provided by OSCORE. Since the use of nonces N1 and N2 during the exchange guarantees uniqueness of AEAD keys and nonces, it is REQUIRED that the exchanged nonces are not reused with the same input keying material even in case of reboots. The exchange of 64-bit random nonces is RECOMMENDED in this document. Considering the birthday paradox, the average collision for each nonce will happen after 2³² messages, which is considerably more token provisionings than would be expected for intended applications. If applications use something else, such as a counter, they need to guarantee that reboot and loss of state on either node does not provoke reuse. If that is not guaranteed, nodes are susceptible to reuse of AEAD (nonce, key) pairs, especially since an on-path attacker can cause the use of a previously exchanged client nonce N1 for security context establishment by replaying the corresponding client-to-server message. In this profile, it is RECOMMENDED that the RS maintains a single access token for each client. The use of multiple access tokens for a single client increases the strain on the resource server as it must consider every access token and calculate the actual permissions of the client. Also, tokens indicating different or disjoint permissions from each other may lead the server 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 the same client. If a single OSCORE Input Material is used with multiple RSs, the RSs can impersonate the client to one of the other RSs and impersonate another RS to the client. If a Master Secret is used with several clients, the clients can impersonate RS to one of the other clients. Similarly, if symmetric keys are used to integrity protect the token between AS and RS and the token can be used with multiple RSs, the RSs can impersonate AS to one of the other RSs. If the token key is used for any other communication between the RSs and AS, the RSs can impersonate each other to the AS.

Privacy Considerations This document specifies a profile for the ACE framework . Thus, the general privacy considerations from the framework also apply to this profile. As this document uses OSCORE, the privacy considerations from apply here as well. An unprotected response to an unauthorized request may disclose information about the resource server and/or its existing relationship with the client. It is advisable to include as little information as possible in an unencrypted response. When an OSCORE security context already exists between the client and the resource server, more detailed information may be included. The token is sent in the clear to the authz-info endpoint, so if a client uses the same single token from multiple locations with multiple resource servers, it can risk being tracked by the token's value even when the access token is encrypted. The nonces exchanged in the request and response to the authz-info endpoint are also sent in the clear, so using random nonces is best for privacy (as opposed to, e.g., a counter, which might leak some information about the client). The identifiers used in OSCORE, negotiated between the client and RS, are privacy sensitive (see ) and could reveal information about the client, or they may be used for correlating requests from one client. Note that some information might still leak after OSCORE is established, due to observable message sizes, the source, and the destination addresses.

IANA Considerations

ACE Profile Registry The following registration has been made in the "ACE Profiles" registry following the procedure specified in :

Name:

coap_oscore

Description:

Profile for using OSCORE to secure communication between constrained nodes using the Authentication and Authorization for Constrained Environments framework.

CBOR Value:

2

Reference:

RFC 9203

OAuth Parameters Registry The following registrations have been made in the "OAuth Parameters" registry following the procedure specified in :

Parameter name:

nonce1

Parameter usage location:

client-rs request

Change Controller:

IETF

Specification Document(s):

RFC 9203

Parameter name:

nonce2

Parameter usage location:

rs-client response

Change Controller:

IETF

Specification Document(s):

RFC 9203

Parameter name:

ace_client_recipientid

Parameter usage location:

client-rs request

Change Controller:

IETF

Specification Document(s):

RFC 9203

Parameter name:

ace_server_recipientid

Parameter usage location:

rs-client response

Change Controller:

IETF

Specification Document(s):

RFC 9203

OAuth Parameters CBOR Mappings Registry The following registrations have been made in the "OAuth Parameters CBOR Mappings" registry following the procedure specified in :

Name:

nonce1

CBOR Key:

40

Value Type:

bstr

Reference:

RFC 9203

Name:

nonce2

CBOR Key:

42

Value Type:

bstr

Reference:

RFC 9203

Name:

ace_client_recipientid

CBOR Key:

43

Value Type:

bstr

Reference:

RFC 9203

Name:

ace_server_recipientid

CBOR Key:

44

Value Type:

bstr

Reference:

RFC 9203

OSCORE Security Context Parameters Registry IANA has created a new registry entitled "OSCORE Security Context Parameters". The registration procedure depends on the range of CBOR label values, following . Guidelines for the experts are provided in . The columns of the registry are:

Name:

The JSON name requested (e.g., "ms"). 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 to identify this name. Map key labels MUST be unique. The label can be a positive integer, a negative integer, or a string. Integer values between -256 and 255 and strings of length 1 are designated as Standards Track document required. Integer values from -65536 to -257 and from 256 to 65535 and strings of length 2 are designated as Specification Required. Integer values greater than 65535 and strings of length greater than 2 are designated as Expert Review. Integer values less than -65536 are marked as Private Use.

CBOR Type:

This field contains the CBOR type for the field.

Registry:

This field denotes the registry that values may come from, if one exists.

Description:

This field contains a brief description for the field.

Reference:

This contains a pointer to the public specification for the field, if one exists.

This registry has been initially populated by the values in . The Reference column for all of these entries is this document.

CWT Confirmation Methods Registry The following registration has been made in the "CWT Confirmation Methods" registry following the procedure specified in :

Confirmation Method Name:

osc

Confirmation Method Description:

OSCORE_Input_Material carrying the parameters for using OSCORE per-message security with implicit key confirmation

JWT Confirmation Method Name:

osc

Confirmation Key:

4

Confirmation Value Type(s):

map

Change Controller:

IETF

Specification Document(s):

of RFC 9203

JWT Confirmation Methods Registry The following registration has been made in the "JWT Confirmation Methods" registry following the procedure specified in :

Confirmation Method Value:

osc

Confirmation Method Description:

OSCORE_Input_Material carrying the parameters for using OSCORE per-message security with implicit key confirmation

Change Controller:

IETF

Specification Document(s):

of RFC 9203

Expert Review Instructions The IANA registry established in this document is defined to use the Expert Review registration policy. 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 Track 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 Served 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.

References Normative References IANA IANA IANA IANA 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. This document describes the commonly used base 64, base 32, and base 16 encoding schemes. It also discusses the use of line-feeds in encoded data, use of padding in encoded data, use of non-alphabet characters in encoded data, use of different encoding alphabets, and canonical encodings. [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 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. 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 proposes a notational convention to express Concise Binary Object Representation (CBOR) data structures (RFC 7049). Its main goal is to provide an easy and unambiguous way to express structures for protocol messages and data formats that use CBOR or 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. 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. Informative References This Glossary provides definitions, abbreviations, and explanations of terminology for information system security. The 334 pages of entries offer recommendations to improve the comprehensibility of written material that is generated in the Internet Standards Process (RFC 2026). The recommendations follow the principles that such writing should (a) use the same term or definition whenever the same concept is mentioned; (b) use terms in their plainest, dictionary sense; (c) use terms that are already well-established in open publications; and (d) avoid terms that either favor a particular vendor or favor a particular technology or mechanism over other, competing techniques that already exist or could be developed. This memo provides information for the Internet community. 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] This specification describes how to declare in a JSON Web Token (JWT) that the presenter of the JWT possesses a particular proof-of- possession key and how the recipient can cryptographically confirm proof of possession of the key by the presenter. Being able to prove possession of a key is also sometimes described as the presenter being a holder-of-key. Many protocols make use of points of extensibility that use constants to identify various protocol parameters. To ensure that the values in these fields do not have conflicting uses and to promote interoperability, their allocations are often coordinated by a central record keeper. For IETF protocols, that role is filled by the Internet Assigned Numbers Authority (IANA). To make assignments in a given registry prudently, guidance describing the conditions under which new values should be assigned, as well as when and how modifications to existing values can be made, is needed. This document defines a framework for the documentation of these guidelines by specification authors, in order to assure that the provided guidance for the IANA Considerations is clear and addresses the various issues that are likely in the operation of a registry. This is the third edition of this document; it obsoletes RFC 5226. 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 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 Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document describes the overall architecture of HTTP, establishes common terminology, and defines aspects of the protocol that are shared by all versions. In this definition are core protocol elements, extensibility mechanisms, and the "http" and "https" Uniform Resource Identifier (URI) schemes. This document updates RFC 3864 and obsoletes RFCs 2818, 7231, 7232, 7233, 7235, 7538, 7615, 7694, and portions of 7230. 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.

Profile Requirements This section lists the specifications of this profile based on the requirements of the 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: OSCORE
• Specify how the client and the RS mutually authenticate: Implicitly by possession of a common OSCORE security context. Note that the mutual authentication is not completed before the client has verified an OSCORE response using this 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: OSCORE algorithms; preestablished symmetric keys
• Specify a unique ace_profile identifier: coap_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: Not defined

Acknowledgments The authors wish to thank and for the substantial input to this document, as well as , , , , , , , and for their reviews and feedback. Special thanks to the responsible area director for his extensive review and contributed text. worked on this document as part of the CelticNext projects CyberWI and CRITISEC with funding from Vinnova. The work on this document has been partly supported also by the H2020 project SIFIS-Home (Grant agreement 952652).

Authors' Addresses Ericsson AB

francesca.palombini@ericsson.com

Combitech

Djäknegatan 31 Malmö 211 35 Sweden ludwig.seitz@combitech.com

Ericsson AB

goran.selander@ericsson.com

RISE

Scheelevägen 17 Lund 22370 Sweden martin.gunnarsson@ri.se