--- 1/draft-ietf-ace-oscore-profile-11.txt 2020-09-21 07:14:07.211436215 -0700 +++ 2/draft-ietf-ace-oscore-profile-12.txt 2020-09-21 07:14:07.279437937 -0700 @@ -1,50 +1,49 @@ ACE Working Group F. Palombini Internet-Draft Ericsson AB Intended status: Standards Track L. Seitz -Expires: December 20, 2020 Combitech +Expires: March 25, 2021 Combitech G. Selander Ericsson AB M. Gunnarsson RISE - June 18, 2020 + September 21, 2020 - OSCORE profile of the Authentication and Authorization for Constrained + OSCORE Profile of the Authentication and Authorization for Constrained Environments Framework - draft-ietf-ace-oscore-profile-11 + draft-ietf-ace-oscore-profile-12 Abstract This memo 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, server authentication, - and proof-of-possession for a key owned by the client and bound to an - OAuth 2.0 access token. + (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 Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." - This Internet-Draft will expire on December 20, 2020. + This Internet-Draft will expire on March 25, 2021. Copyright Notice Copyright (c) 2020 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents @@ -55,62 +54,62 @@ described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 4 3. Client-AS Communication . . . . . . . . . . . . . . . . . . . 6 3.1. C-to-AS: POST to token endpoint . . . . . . . . . . . . . 6 3.2. AS-to-C: Access Token . . . . . . . . . . . . . . . . . . 8 - 3.2.1. OSCORE_Security_Context Object . . . . . . . . . . . 13 - 4. Client-RS Communication . . . . . . . . . . . . . . . . . . . 17 - 4.1. C-to-RS: POST to authz-info endpoint . . . . . . . . . . 18 - 4.1.1. The Nonce 1 Parameter . . . . . . . . . . . . . . . . 19 - 4.2. RS-to-C: 2.01 (Created) . . . . . . . . . . . . . . . . . 19 - 4.2.1. The Nonce 2 Parameter . . . . . . . . . . . . . . . . 21 - 4.3. OSCORE Setup . . . . . . . . . . . . . . . . . . . . . . 21 + 3.2.1. The OSCORE_Input_Material . . . . . . . . . . . . . . 13 + 4. Client-RS Communication . . . . . . . . . . . . . . . . . . . 16 + 4.1. C-to-RS: POST to authz-info endpoint . . . . . . . . . . 17 + 4.1.1. The Nonce 1 Parameter . . . . . . . . . . . . . . . . 18 + 4.2. RS-to-C: 2.01 (Created) . . . . . . . . . . . . . . . . . 18 + 4.2.1. The Nonce 2 Parameter . . . . . . . . . . . . . . . . 20 + 4.3. OSCORE Setup . . . . . . . . . . . . . . . . . . . . . . 20 4.4. Access rights verification . . . . . . . . . . . . . . . 22 5. Secure Communication with AS . . . . . . . . . . . . . . . . 22 6. Discarding the Security Context . . . . . . . . . . . . . . . 23 7. Security Considerations . . . . . . . . . . . . . . . . . . . 24 8. Privacy Considerations . . . . . . . . . . . . . . . . . . . 25 - 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25 - 9.1. ACE OAuth Profile Registry . . . . . . . . . . . . . . . 25 + 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26 + 9.1. ACE Profile Registry . . . . . . . . . . . . . . . . . . 26 9.2. OAuth Parameters Registry . . . . . . . . . . . . . . . . 26 9.3. OAuth Parameters CBOR Mappings Registry . . . . . . . . . 26 - 9.4. OSCORE Security Context Parameters Registry . . . . . . . 26 - 9.5. CWT Confirmation Methods Registry . . . . . . . . . . . . 27 + 9.4. OSCORE Security Context Parameters Registry . . . . . . . 27 + 9.5. CWT Confirmation Methods Registry . . . . . . . . . . . . 28 9.6. JWT Confirmation Methods Registry . . . . . . . . . . . . 28 9.7. Expert Review Instructions . . . . . . . . . . . . . . . 28 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 29 10.1. Normative References . . . . . . . . . . . . . . . . . . 29 10.2. Informative References . . . . . . . . . . . . . . . . . 30 - Appendix A. Profile Requirements . . . . . . . . . . . . . . . . 30 + Appendix A. Profile Requirements . . . . . . . . . . . . . . . . 31 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 31 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 31 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 32 1. Introduction This memo specifies a profile of the ACE framework [I-D.ietf-ace-oauth-authz]. In this profile, a client and a resource - server use CoAP [RFC7252] to communicate. The client uses an access - token, bound to a key (the proof-of-possession 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, proof of possession, and server - authentication the client and resource server use Object Security for - Constrained RESTful Environments (OSCORE) [RFC8613]. Note that the - proof of possession is not done by a dedicated protocol element, but - rather occurs implicitly, based on knowledge of the security keying - material. + server use the Constrained Application Protocol (CoAP) [RFC7252] to + communicate. The client uses an access token, bound to a symmetric + key (the proof-of-possession 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 proof of possession, the client and resource server use + Object Security for Constrained RESTful Environments (OSCORE) + [RFC8613]. Note that the proof of possession is not done by a + dedicated protocol element, but rather occurs after the first OSCORE + exchange. OSCORE specifies how to use CBOR Object Signing and Encryption (COSE) [RFC8152] 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 communication protocol, could be specified analogously to this one. 1.1. Terminology @@ -124,137 +123,140 @@ "authorization", "confidentiality", "(data) integrity", "message authentication code", and "verify" are taken from [RFC4949]. RESTful terminology follows HTTP [RFC7231]. Terminology for entities in the architecture is defined in OAuth 2.0 [RFC6749], 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 Data Definition Language (CDDL) [RFC8610] is used in this - specification. + Concise Binary Object Representation (CBOR) [I-D.ietf-cbor-7049bis] + and Concise Data Definition Language (CDDL) [RFC8610] are used in + this specification. CDDL predefined type names, especially bstr for + CBOR byte strings and tstr for CBOR text strings, are used + extensively in the document. Note that the term "endpoint" is used here, as in [I-D.ietf-ace-oauth-authz], 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 [RFC7252] definition, which is "An entity participating in the CoAP protocol" is not used in this memo. 2. Protocol Overview - This section gives an overview on how to use the ACE Framework + This section gives an overview of how to use the ACE Framework [I-D.ietf-ace-oauth-authz] to secure the communication between a client and a resource server using OSCORE [RFC8613]. The parameters needed by the client to negotiate the use of this profile with the - authorization server, as well as OSCORE setup process, are described - in detail in the following sections. + authorization server, 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's used as input to processing requests from those + 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 a RS, using the token - endpoint, as specified in section 5.6 of [I-D.ietf-ace-oauth-authz]. - To determine the AS in charge of a resource hosted at the RS, the - client C MAY send an initial Unauthorized Resource Request message to - the RS. The RS then denies the request and sends the address of its - AS back to the client C as specified in section 5.1 of + AS for the resource it wants to access on an RS, by sending an access + token request to the token endpoint, as specified in section 5.6 of [I-D.ietf-ace-oauth-authz]. The access token request and response MUST be confidentiality-protected and ensure authenticity. This profile RECOMMENDS the use of OSCORE between client and AS, but other protocols (such as TLS or DTLS) can be used as well. Once the client has retrieved the access token, it generates a nonce N1 and posts both the token and N1 to the RS using the authz-info endpoint and mechanisms specified in section 5.8 of [I-D.ietf-ace-oauth-authz] and Content-Format = application/ace+cbor. - Note that, as specified in the ACE framework, the authz-info endpoint - is not a protected resource, so there is no cryptographic protection - to this request. + When using this profile, the communication with the authz-info + endpoint is not protected, except for 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 in a CBOR map. Moreover, the server - concatenates the input salt, N1, and N2 to obtain the Master Salt of - the OSCORE Security Context (see section 3 of [RFC8613]). The RS - then derives the complete Security Context associated with the - received token from it plus the parameters received in the access - token from the AS, following section 3.2 of [RFC8613]. + concatenates the input salt received in the token, N1, and N2 to + obtain the Master Salt of the OSCORE Security Context (see section 3 + of [RFC8613]). The RS then derives the complete Security Context + associated with the received token from it plus the parameters + received in the access token from the AS, following section 3.2 of + [RFC8613]. - After receiving the nonce N2, the client concatenates the input salt, - N1 and N2 to obtain the Master Salt of the OSCORE Security Context - (see section 3 of [RFC8613]). The client then derives the complete - Security Context from the nonces plus the parameters received from - the AS. + After receiving the nonce N2, the client concatenates the input salt + (received from the AS), N1 and N2 to obtain the Master Salt of the + OSCORE Security Context (see section 3 of [RFC8613]). The client + then derives the complete Security Context from the nonces plus the + parameters received from the AS. Finally, the client sends a request protected with OSCORE to the RS. If the request verifies, 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 expiration. This Security Context is discarded when a token (whether the same or different) is used to successfully derive a new Security Context for that client. The use of random nonces during the exchange prevents the reuse of an - AEAD nonces/key pair for two different messages. This situation - might occur when client and RS derive a new Security Context from an - existing (non-expired) access token, as might occur when either party - has just rebooted. Instead, by using random nonces 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 - Section 3.2.1 of [RFC8613]). Therefore, the main requirement for the - nonces is that they have a good amount of randomness. If random - nonces were not used, a node re-using a non-expired old token would - be susceptible to on-path attackers provoking the creation of OSCORE - messages using old AEAD keys and nonces. + Authenticated Encryption with Associated Data (AEAD) nonces/key pair + for two different messages. Two-time pad might otherwise occur when + client and RS derive a new Security Context from an existing (non- + expired) access token, as might occur when either party has just + rebooted. Instead, by using random nonces 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 Section 3.2.1 of + [RFC8613]). Therefore, the main requirement for the nonces is that + they have a good amount of randomness. If random nonces were not + used, a node re-using a non-expired old token would be susceptible to + on-path attackers provoking the creation of OSCORE messages using old + AEAD keys and nonces. 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 security material it has previously shared with the Client. This specific identifier, which [I-D.ietf-ace-oauth-authz] encodes as a bstr, is formatted to include two OSCORE identifiers, namely ID context and - client ID, that are necessary to determine the correct OSCORE - Security Context. + client ID, that are necessary to determine the correct OSCORE Input + material. An overview of the profile flow for the OSCORE profile is given in - Figure 1. + Figure 1. The names of messages coincide with those of + [I-D.ietf-ace-oauth-authz] when applicable. C RS AS - | [-- Resource Request --->] | | - | | | - | [<---- AS Request ------] | | - | Creation Hints | | | | | | ----- POST /token ----------------------------> | | | | | <---------------------------- Access Token ----- | | + Access Information | | ---- POST /authz-info ---> | | | (access_token, N1) | | | | | | <--- 2.01 Created (N2) --- | | | | | /Sec Context /Sec Context | - Derivation/ Derivation/ | + derivation/ derivation/ | | | | | ---- OSCORE Request -----> | | | | | + | /proof-of-possession | + | Sec Context storage/ | + | | | | <--- OSCORE Response ----- | | | | | + /proof-of-possession | | + Sec Context storage/ | | + | | | | ---- OSCORE Request -----> | | | | | | <--- OSCORE Response ----- | | | ... | | Figure 1: Protocol Overview 3. Client-AS Communication The following subsections describe the details of the POST request @@ -293,33 +295,34 @@ bound to a symmetric key. If the client wants to update its access rights without changing an existing OSCORE Security Context, it MUST include in its POST request to the token endpoint a req_cnf object. The req_cnf MUST include a kid field carrying a bstr-wrapped CBOR array object containing the client's identifier (assigned as discussed in Section 3.2) and the context identifier (if assigned as discussed in Section 3.2). The CBOR array is defined in Figure 3, and follows the notation of [RFC8610]. These identifiers, together with other information such - as audience, can be used by the AS to determine the shared secret - bound to the proof-of-possession token and therefore 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 Section 5.6.3 of + as audience (see Section 5.6.1 of [I-D.ietf-ace-oauth-authz]), can be + used by the AS to determine the shared secret bound to the proof-of- + possession token and therefore 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 Section 5.6.3 of [I-D.ietf-ace-oauth-authz]. kid_arr = [ clientId, - ?IdContext + ?ContextId ] kid = bstr .cbor kid_arr Figure 3: CDDL Notation of kid for Update of Access Rights An example of such a request, with payload in CBOR diagnostic notation without the tag and value abbreviations is reported in Figure 4 @@ -364,126 +367,134 @@ o a client identifier Additionally, the AS MAY send the following data, in the same response. o a context identifier o an AEAD algorithm - o an HKDF algorithm + o an HMAC-based key derivation function (HKDF) algorithm o a salt o the OSCORE version number - The OSCORE_Security_Context is a CBOR map object, defined in - Section 3.2.1. This object is transported in the 'cnf' parameter of - the access token response as defined in Section 3.2 of - [I-D.ietf-ace-oauth-params], as the value of a field named 'osc', - registered in Section 9.5 and Section 9.6. The master secret MUST be - communicated as the 'ms' field in the 'osc' field in the 'cnf' - parameter of the access token response as defined in Section 3.2 of - [I-D.ietf-ace-oauth-params]. The AEAD algorithm may be included as - the 'alg' parameter in the OSCORE_Security_Context; the HKDF - algorithm may be included as the 'hkdf' parameter of the - OSCORE_Security_Context, a salt may be included as the 'salt' - parameter of the OSCORE_Security_Context, and the OSCORE version - number may be included as the 'version' parameter of the - OSCORE_Security_Context. + This data is transported in the the OSCORE_Input_Material. The + OSCORE_Input_Material is a CBOR map object, defined in Section 3.2.1. + This object is transported in the 'cnf' parameter of the access token + response as defined in Section 3.2 of [I-D.ietf-ace-oauth-params], as + the value of a field named 'osc', registered in Section 9.5 and + Section 9.6. - The same parameters MUST be included as part of the access token. - This profile RECOMMENDS the use of CBOR web token (CWT) as specified - in [RFC8392]. If the token is a CWT, the same - OSCORE_Security_Context structure defined above MUST be placed in the - 'osc' field of the 'cnf' claim of this token. The access token MUST - be encrypted, since it will be transferred from the client to the RS - over an unprotected channel. + The AS MUST assign an identifier to the RS (server identifier), and + to the client (client identifier), and MAY assign an identifier to + the context (context identifier). These identifiers are then used as + Sender ID, Recipient ID and ID Context in the OSCORE context as + described in section 3.1 of [RFC8613]: specifically, the server + identifier is used as Sender ID of the node acting as RS in this + profile, and the client identifier is used as Sender ID of the node + acting as ACE client. These parameters are sent as clientId, + serverId and (when assigned) contextId in the OSCORE_Input_Material. + ClientId and serverId MUST be included in the OSCORE_Input_Material, + contextId MUST be included when assigned. The applications need to + consider that these identifiers are sent in the clear and may reveal + information about the endpoints, as mentioned in section 12.8 of + [RFC8613]. The pair (client identifier, context identifier) MUST be + unique in the set of all clients for a single RS. - The AS MUST also assign an identifier to the RS (serverId), and to - the client (clientId), and MAY assign an identifier to the context - (contextId). These identifiers are then used as Sender ID, Recipient - ID and ID Context in the OSCORE context as described in section 3.1 - of [RFC8613]. Applications need to consider that these identifiers - are sent in the clear and may reveal information about the endpoints, - as mentioned in section 12.8 of [RFC8613]. The pair (client - identifier, context identifier) MUST be unique in the set of all - clients for a single RS. Moreover, clientId, serverId and (when - assigned) contextId MUST be included in the OSCORE_Security_Context, - as defined in Section 3.2.1. + The master secret MUST be communicated as the 'ms' field in the 'osc' + field in the 'cnf' parameter of the access token response. If + included, the AEAD algorithm is sent 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. - We assume in this document that a resource is associated to one - single AS, which makes it possible for the AS to enforce uniqueness - of identifiers for each client requesting a particular resource to a - RS. If this is not the case, collisions of identifiers may occur at - the RS, in which case the RS needs to have a mechanism in place to - disambiguate identifiers or mitigate the effect of the collisions. + The same parameters MUST be included in the claims associated with + the access token. This profile RECOMMENDS the use of CBOR web token + (CWT) as specified in [RFC8392]. 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. + + We assume in this document that an RS is associated to one single AS, + which makes it possible for the AS to enforce uniqueness of + identifiers for each client sending requests to an RS. If this is + not the case, collisions of identifiers may occur at the RS, in which + case the RS needs to have a mechanism in place to disambiguate + identifiers or mitigate the effect of the collisions. Moreover, implementers of this specification need to be aware that if other authentication mechanisms are used to set up OSCORE between the same client and RS, that do not rely on AS assigning identifiers, collisions may happen and need to be mitigated. A mitigation example would be to use distinct namespaces of identifiers for different authentication mechanisms. + The AS MUST send different OSCORE_Input_Material (and therefore + different access tokens) to different authorized clients, in order + for the RS to differentiate between clients. + Note that in Section 4.3 C sets the Sender ID of its Security Context to the clientId value received and the Recipient ID to the serverId value, and RS does the opposite. Figure 5 shows an example of an AS response, with payload in CBOR diagnostic notation without the tag and value abbreviations. The access token has been truncated for readability. Header: Created (Code=2.01) Content-Type: "application/ace+cbor" Payload: { - "access_token" : h'a5037674656d7053656e73 ... + "access_token" : h'8343a1010aa2044c53 ... (remainder of access token (CWT) omitted for brevity)', "profile" : "coap_oscore", "expires_in" : "3600", "cnf" : { "osc" : { "alg" : "AES-CCM-16-64-128", "clientId" : h'00', "serverId" : h'01', "ms" : h'f9af838368e353e78888e1426bd94e6f' } } } Figure 5: Example AS-to-C Access Token response with OSCORE profile. - Figure 6 shows an example CWT, containing the necessary OSCORE - parameters in the 'cnf' claim, in CBOR diagnostic notation without - tag and value abbreviations. + Figure 6 shows an example CWT Claims Set, including the relevant + OSCORE parameters in the 'cnf' claim, in CBOR diagnostic notation + without tag and value abbreviations. { "aud" : "tempSensorInLivingRoom", "iat" : "1360189224", "exp" : "1360289224", "scope" : "temperature_g firmware_p", "cnf" : { "osc" : { "alg" : "AES-CCM-16-64-128", "clientId" : h'00', "serverId" : h'01', "ms" : h'f9af838368e353e78888e1426bd94e6f' } } - Figure 6: Example CWT with OSCORE parameters. + Figure 6: Example CWT Claims Set with OSCORE parameters. - The same CWT token as in Figure 6, using the value abbreviations + The same CWT Claims Set as in Figure 6, using the value abbreviations defined in [I-D.ietf-ace-oauth-authz] and [RFC8747] and encoded in - CBOR is shown in Figure 7. + CBOR is shown in Figure 7. 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. NOTE TO THE RFC EDITOR: before publishing, it should be checked (and in case fixed) that the values used below (which are not yet registered) are the final values registered in IANA. A5 # map(5) 03 # unsigned(3) 76 # text(22) 74656D7053656E736F72496E4C6976696E67526F6F6D # "tempSensorInLivingRoom" @@ -506,132 +517,137 @@ 636C69656E74 # "client" 03 # unsigned(3) 46 # bytes(6) 736572766572 # "server" 01 # unsigned(1) 50 # bytes(16) F9AF838368E353E78888E1426BD94E6F # "\xF9\xAF\x83\x83h\xE3S\xE7 \x88\x88\xE1Bk\xD9No" - Figure 7: Example CWT with OSCORE parameters. + Figure 7: Example CWT Claims Set with OSCORE parameters, CBOR + encoded. 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 client identifier and the context identifier (if it was set and included in the initial access token response by the AS) in the 'kid' field in the 'cnf' parameter of the token, with the same structure defined in Figure 3. These identifiers need to be included in the token in order for the RS to identify the previously generated Security Context. Figure 8 shows an example of such an AS response, with payload in CBOR diagnostic notation without the tag and value abbreviations. The access token has been truncated for readability. Header: Created (Code=2.01) Content-Type: "application/ace+cbor" Payload: { - "access_token" : h'a5037674656d7053656e73 ... + "access_token" : h'8343a1010aa2044c53 ... (remainder of access token (CWT) omitted for brevity)', "profile" : "coap_oscore", "expires_in" : "3600" } Figure 8: Example AS-to-C Access Token response with OSCORE profile, for update of access rights. - Figure 9 shows an example CWT, containing the necessary OSCORE - parameters in the 'cnf' claim for update of access rights, in CBOR - diagnostic notation without tag and value abbreviations. + Figure 9 shows an example CWT Claims Set, containing the necessary + OSCORE parameters in the 'cnf' claim for update of access rights, in + CBOR diagnostic notation without tag and value abbreviations. { "aud" : "tempSensorInLivingRoom", "iat" : "1360189224", "exp" : "1360289224", "scope" : "temperature_h", "cnf" : { "kid" : h'43814100' } } - Figure 9: Example CWT with OSCORE parameters for update of access - rights. + Figure 9: Example CWT Claims Set with OSCORE parameters for update of + access rights. -3.2.1. OSCORE_Security_Context Object +3.2.1. The OSCORE_Input_Material - An OSCORE_Security_Context is an object that represents part or all - of an OSCORE Security Context, i.e., the local set of information - elements necessary to carry out the cryptographic operations in - OSCORE (Section 3.1 of [RFC8613]). In particular, the - OSCORE_Security_Context object is defined to be serialized and - transported between nodes, as specified by this document, but can - also be used by other specifications if needed. The - OSCORE_Security_Context object can either be encoded as a JSON object - or as a CBOR map. The set of common parameters that can appear in an - OSCORE_Security_Context object can be found in the IANA "OSCORE - Security Context Parameters" registry (Section 9.4), defined for - extensibility, and is specified below. All parameters are optional. - Table 1 provides a summary of the OSCORE_Security_Context parameters - defined in this section. + 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 (Section 3.1 of [RFC8613]). In particular, the + OSCORE_Input_Material is defined to be serialized and transported + between nodes, as specified by this document, but can also be used by + other specifications if needed. The OSCORE_Input_Material can either + be encoded as a JSON object or as 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 + (Section 9.4), defined for extensibility, and is specified below. + All parameters are optional. Table 1 provides a summary of the + OSCORE_Input_Material parameters defined in this section. - +-----------+-------+----------------+--------------+---------------+ + +-----------+-------+-------------+-------------------+-------------+ | name | CBOR | CBOR type | registry | description | | | label | | | | - +-----------+-------+----------------+--------------+---------------+ - | version | 0 | int | | OSCORE | - | | | | | Version | + +-----------+-------+-------------+-------------------+-------------+ + | version | 0 | unsigned | | OSCORE | + | | | integer | | Version | | | | | | | - | ms | 1 | bstr | | OSCORE Master | - | | | | | Secret value | + | ms | 1 | byte string | | OSCORE | + | | | | | Master | + | | | | | Secret | + | | | | | value | | | | | | | - | clientId | 2 | bstr | | OSCORE Sender | - | | | | | ID value of | + | clientId | 2 | byte string | | OSCORE | + | | | | | Sender ID | + | | | | | value of | | | | | | the client, | | | | | | OSCORE | - | | | | | Recipient ID | - | | | | | value of the | - | | | | | server | - | | | | | | - | serverId | 3 | bstr | | OSCORE Sender | + | | | | | Recipient | | | | | | ID value of | + | | | | | the server | + | | | | | | + | serverId | 3 | byte string | | OSCORE | + | | | | | Sender ID | + | | | | | value of | | | | | | the server, | | | | | | OSCORE | - | | | | | Recipient ID | - | | | | | value of the | - | | | | | client | + | | | | | Recipient | + | | | | | ID value of | + | | | | | the client | | | | | | | - | hkdf | 4 | tstr / int | COSE | OSCORE HKDF | - | | | | Algorithm | value | - | | | | Values | | - | | | | (HMAC-based) | | + | hkdf | 4 | text string | [COSE.Algorithms] | OSCORE HKDF | + | | | / integer | Values (HMAC- | value | + | | | | based) | | | | | | | | - | alg | 5 | tstr / int | COSE | OSCORE AEAD | - | | | | Algorithm | Algorithm | - | | | | Values | value | - | | | | (AEAD) | | + | alg | 5 | text string | [COSE.Algorithms] | OSCORE AEAD | + | | | / integer | Values (AEAD) | Algorithm | + | | | | | value | | | | | | | - | salt | 6 | bstr | | OSCORE Master | - | | | | | Salt value | + | salt | 6 | byte string | | an input to | + | | | | | OSCORE | + | | | | | Master Salt | + | | | | | value | | | | | | | - | contextId | 7 | bstr | | OSCORE ID | - | | | | | Context value | - +-----------+-------+----------------+--------------+---------------+ + | contextId | 7 | byte string | | OSCORE ID | + | | | | | Context | + | | | | | value | + +-----------+-------+-------------+-------------------+-------------+ - Table 1: OSCORE_Security_Context Parameters + Table 1: OSCORE_Input_Material Parameters version: This parameter identifies the OSCORE Version number, which - is an int. For more information about this field, see section 5.4 - of [RFC8613]. In JSON, the "version" value is an integer. In - CBOR, the "version" type is int, and has label 0. + is an unsigned integer. For more information about this field, + see section 5.4 of [RFC8613]. In JSON, the "version" value is an + integer. In CBOR, the "version" type is int, and has label 0. ms: This parameter identifies the OSCORE Master Secret value, which is a byte string. For more information about this field, see section 3.1 of [RFC8613]. In JSON, the "ms" value is a Base64 encoded byte string. In CBOR, the "ms" type is bstr, and has label 1. clientId: This parameter identifies a client identifier as a byte string. This identifier is used as OSCORE Sender ID in the client and OSCORE Recipient ID in the server. For more information about @@ -642,118 +658,119 @@ serverId: This parameter identifies a server identifier as a byte string. This identifier is used as OSCORE Sender ID in the server and OSCORE Recipient ID in the client. For more information about this field, see section 3.1 of [RFC8613]. In JSON, the "serverId" value is a Base64 encoded byte string. In CBOR, the "serverId" type is bstr, and has label 3. hkdf: This parameter identifies the OSCORE HKDF Algorithm. For more information about this field, see section 3.1 of [RFC8613]. The values used MUST be registered in the IANA "COSE Algorithms" - registry and MUST be HMAC-based HKDF algorithms. The value can - either be 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 tstr or int, and has label 4. + registry (see [COSE.Algorithms]) and MUST be HMAC-based HKDF + algorithms. The value can either be 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 + tstr or int, and has label 4. alg: This parameter identifies the OSCORE AEAD Algorithm. For more information about this field, see section 3.1 of [RFC8613] The values used MUST be registered in the IANA "COSE Algorithms" - registry and MUST be AEAD algorithms. The value can either be 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 tstr or int, and has label 5. + registry (see [COSE.Algorithms]) and MUST be AEAD algorithms. The + value can either be 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 tstr or int, and has label 5. - salt: This parameter identifies the OSCORE Master Salt value, which - is a byte string. For more information about this field, see - section 3.1 of [RFC8613]. In JSON, the "salt" value is a Base64 - encoded byte string. In CBOR, the "salt" type is bstr, and has - label 6. + salt: This parameter identifies an input to the OSCORE Master Salt + value, which is a byte string. For more information about this + field, see section 3.1 of [RFC8613]. In JSON, the "salt" value is + a Base64 encoded byte string. In CBOR, the "salt" type is bstr, + and has label 6. 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 section 3.1 of [RFC8613]. In JSON, the "contextID" value is a Base64 encoded byte string. In CBOR, the "contextID" type is bstr, and has label 7. - An example of JSON OSCORE_Security_Context is given in Figure 10. + An example of JSON OSCORE_Input_Material is given in Figure 10. "osc" : { "alg" : "AES-CCM-16-64-128", "clientId" : b64'AA', "serverId" : b64'AQ', "ms" : b64'+a+Dg2jjU+eIiOFCa9lObw' } - Figure 10: Example JSON OSCORE_Security_Context object + Figure 10: Example JSON OSCORE_Input_Material - The CDDL grammar describing the CBOR OSCORE_Security_Context object - is: + The CDDL grammar describing the CBOR OSCORE_Input_Material is: - OSCORE_Security_Context = { + OSCORE_Input_Material = { ? 0 => int, ; version ? 1 => bstr, ; ms ? 2 => bstr, ; clientId ? 3 => bstr, ; serverId ? 4 => tstr / int, ; hkdf ? 5 => tstr / int, ; alg ? 6 => bstr, ; salt ? 7 => bstr, ; contextId * int / tstr => any } 4. Client-RS Communication The following subsections describe the details of the POST request and response to the authz-info endpoint between client and RS. The client generates a nonce N1, and posts it 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 uses Section 3.2 of [RFC8613] to derive a security context based on a shared master secret and the two nonces, established between client - and server. The nonces are encoded as CBOR bstr if CBOR is used, and - as Base64 string if JSON is used. This security context is used to + and server. The nonces are encoded as bstr if CBOR is used, and as + Base64 string if JSON is used. This security context is used to protect all future communication between client and RS using OSCORE, as long as the access token is valid. Note that the RS and client authenticates themselves by generating the shared OSCORE Security Context using the pop-key as master secret. An attacker posting a valid token to the RS will not be able to generate a valid OSCORE context and thus not be able to prove - possession of the pop-key. + possession of the pop-key. Additionally, the mutual authentication + is only achieved after the client has successfully verified the + response from the RS. 4.1. C-to-RS: POST to authz-info endpoint The client MUST generate a nonce value very unlikely to have been previously used with the same input keying material. This profile RECOMMENDS to use a 64-bit long random number as nonce's value. 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. The client MUST use CoAP and the Authorization Information resource as described in section 5.8.1 of [I-D.ietf-ace-oauth-authz] to transport the token and N1 to the RS. Note that the use of the payload and the Content-Format is different - from what described in section 5.8.1 of [I-D.ietf-ace-oauth-authz], - which only transports the token without any CBOR wrapping. In this - profile, the client MUST wrap the token and N1 in a CBOR map. The - client MUST use the Content-Format "application/ace+cbor" defined in - section 8.14 of [I-D.ietf-ace-oauth-authz]. The client MUST include - the access token using the "access_token" parameter and N1 using the - 'nonce1' parameter defined in Section 4.1.1. - - The authz-info endpoint is not protected, nor are the responses from - this resource. + from what is described in section 5.8.1 of + [I-D.ietf-ace-oauth-authz], which only transports the token without + any CBOR wrapping. In this profile, the client MUST wrap the token + and N1 in a CBOR map. The client MUST use the Content-Format + "application/ace+cbor" defined in section 8.14 of + [I-D.ietf-ace-oauth-authz]. The client MUST include the access token + using the "access_token" parameter and N1 using the 'nonce1' + parameter defined in Section 4.1.1. - The access token MUST be encrypted, since it is transferred from the - client to the RS over an unprotected channel. + 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 re-POST 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 nonces will be used. @@ -761,21 +778,21 @@ RS, with payload in CBOR diagnostic notation without the tag and value abbreviations. The access token has been truncated for readability. Header: POST (Code=0.02) Uri-Host: "rs.example.com" Uri-Path: "authz-info" Content-Format: "application/ace+cbor" Payload: { - "access_token": h'a5037674656d7053656e73 ... + "access_token": h'8343a1010aa2044c53 ... (remainder of access token (CWT) omitted for brevity)', "nonce1": h'018a278f7faab55a' } Figure 11: Example C-to-RS POST /authz-info request using CWT 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 @@ -800,22 +817,23 @@ [I-D.ietf-ace-oauth-authz]: 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 in the 'osc' is missing (e.g., any of the mandatory parameters from the AS), or if any parameters received in the 'osc' is 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 to validate the token before responding to - the POST request to the authz-info endpoint. + an introspection request (see Section 5.7.1 of + [I-D.ietf-ace-oauth-authz]) to validate the token before responding + to the POST request to the authz-info endpoint. Additionally, the RS MUST generate a nonce N2 very unlikely to have been previously used with the same input keying material, and send it 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 Section 4.2.1, set to N2. This profile RECOMMENDS to use a 64-bit long random number as nonce's value. The RS MUST use the Content-Format "application/ace+cbor" defined in section 8.14 of [I-D.ietf-ace-oauth-authz]. @@ -835,118 +853,159 @@ As specified in section 5.8.3 of [I-D.ietf-ace-oauth-authz], 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 a OSCORE protected message, it means that the client is requesting an update of access rights. The RS MUST discard any nonce in the request, if any was sent. The RS MUST check that the "kid" of the "cnf" parameter of the new access token matches the OSCORE Security Context used to protect the message. If - that's the case, the RS MUST discard the old token and associate the - new token to the Security Context identified by "kid". 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. + that is the case, the RS MUST discard the old token and associate the + new token to the Security Context identified by the "kid" value in + the "cnf" parameter. 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 section 5.8.1 of [I-D.ietf-ace-oauth-authz], when receiving an updated access token with updated authorization information from the client (see Section 3.1), 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 for the RS to keep track of authorization information - for a given client. + This simplifies the process needed by the RS to keep track of + authorization information for a given client. 4.2.1. The Nonce 2 Parameter This parameter MUST be sent from the RS to the Client if the ace profile used is coap_oscore. 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 - Section 9.2 + Section 9.2. 4.3. OSCORE Setup Once receiving the 2.01 (Created) response from the RS, following the - POST request to authz-info endpoint, the client MUST extract the CBOR - 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 + 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, where salt - was received from the AS in Section 3.2, and where N1 and N2 are the - two nonces encoded as CBOR bstr. The client MUST set the Master - Secret, Sender ID and Recipient ID from the parameters received from - the AS in Section 3.2. The client MUST set the AEAD Algorithm, ID - Context, HKDF, and OSCORE Version from the parameters received from - the AS in Section 3.2, if present. In case these parameters are - omitted, the default values are used as described in sections 3.2 and - 5.4 of [RFC8613]. After that, the client MUST derive the complete - Security Context following section 3.2.1 of [RFC8613]. 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. + is the CBOR byte string received from the AS in Section 3.2, and + where N1 and N2 are the two nonces encoded as CBOR byte strings. An + example of Master Salt construction using CBOR encoding is given in + Figure 13. + +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 + + Figure 13: Example of Master Salt construction using CBOR encoding + + 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 Figure 14. + +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=' + + Figure 14: Example of Master Salt construction using Base64 encoding + + The client MUST set the Master Secret, Sender ID and Recipient ID + from the parameters received from the AS in Section 3.2. The client + MUST set the AEAD Algorithm, ID Context, HKDF, and OSCORE Version + from the parameters received from the AS in Section 3.2, if present. + In case an optional parameter is omitted, the default value SHALL be + used as described in sections 3.2 and 5.4 of [RFC8613]. After that, + the client MUST derive the complete Security Context following + section 3.2.1 of [RFC8613]. 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 is missing (e.g., any of the mandatory parameters from the AS, 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 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 this order: Master Salt - = salt | N1 | N2, where | denotes byte string concatenation, where - salt was received from the AS in Section 4.2, and where N1 and N2 are - the two nonces encoded as CBOR bstr. The RS MUST set the Master - Secret, Sender ID and Recipient ID from the parameters, received from + 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 Figure 13 and using Base64 encoding is given in Figure 14. + The RS MUST set the Master Secret, Sender ID and Recipient ID from + the parameters, received from the AS and forwarded by the client in + the access token in Section 4.1 after validation of the token as + specified in Section 4.2. 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 Section 4.1 - after validation of the token as specified in Section 4.2. 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 Section 4.1 after validation of the token as - specified in Section 4.2, if present. In case these parameters are - omitted, the default values are used as described in sections 3.2 and - 5.4 of [RFC8613]. After that, the RS MUST derive the complete - Security Context following section 3.2.1 of [RFC8613], and MUST - associate this Security Context with the authorization information - from the access token. + after validation of the token as specified in Section 4.2, if + present. In case an optional parameter is omitted, the default value + SHALL be used as described in sections 3.2 and 5.4 of [RFC8613]. + After that, the RS MUST derive the complete Security Context + following section 3.2.1 of [RFC8613], 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 C using OSCORE. If OSCORE verification fails, error responses are used, as specified in section 8 of [RFC8613]. Additionally, if OSCORE verification succeeds, the verification of access rights is performed as described in section Section 4.4. The RS MUST NOT use the Security Context after the related token has expired, and MUST respond with a 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, client and RS can update their ID + Context by running a mechanism such as the one defined in + Appendix B.2 of [RFC8613] if they support it. In that case, the ID + Context in the OSCORE Security Context will not match the "contextId" + parameter of the corresponding OSCORE_Input_Material. That is fine, + as long as the nodes store and use the "contextId" value to identify + the correct OSCORE_Input_Material at the AS. + 4.4. Access rights verification The RS MUST follow the procedures defined in section 5.8.2 of [I-D.ietf-ace-oauth-authz]: if an RS receives an OSCORE-protected request from a client, then the RS processes it according to [RFC8613]. 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. - The response code must be 4.01 (Unauthorized) in case the client has - a valid token associated with that Security Context, but the Security - Context has not been used before, as the proof-of-possession in this - profile is performed by both parties verifying that they have - established the same Security Context. - 5. Secure Communication with AS As specified in the ACE framework (section 5.7 of [I-D.ietf-ace-oauth-authz]), the requesting entity (RS and/or client) and the AS communicates via the introspection or token endpoint. The use of CoAP and OSCORE ([RFC8613]) for this communication is RECOMMENDED in this profile, other protocols (such as HTTP and DTLS or TLS) MAY be used instead. If OSCORE is used, the requesting entity and the AS are expected to @@ -1006,20 +1064,27 @@ 7. Security Considerations This document specifies a profile for the Authentication and Authorization for Constrained Environments (ACE) framework [I-D.ietf-ace-oauth-authz]. Thus the general security considerations from the framework also apply to this profile. Furthermore the general security considerations of OSCORE [RFC8613] 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 Section 4.3, which means that + both the OSCORE request and OSCORE pass verification. RS + authentication requires both that the client trusts the AS and that + the OSCORE response from the RS pass 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 usecase corresponds to the expected use of OSCORE, to prevent weakening the security assurances provided by OSCORE. Since the use of nonces in the exchange guarantees uniqueness of AEAD keys and nonces, it is REQUIRED that nonces are not reused with the @@ -1032,112 +1097,122 @@ of state on either node does not provoke re-use. If that is not guaranteed, nodes are susceptible to re-use of AEAD (nonces, keys) pairs, especially since an on-path attacker can cause the client to use an arbitrary nonce for Security Context establishment by replaying client-to-server messages. This profile recommends that the RS maintains a single access token for a 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 a client. + If a single OSCORE_Input_Material is used with multiple RSs, the RSs + can impersonate C to one of the other RS, and impersonate another RS + to the client. If a master secret is used with several clients, the + Cs can impersonate RS to one of the other C. 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 RS. If the token key is used for any other + communication between the RSs and AS, the RSs can impersonate each + other to the AS. + 8. Privacy Considerations This document specifies a profile for the Authentication and Authorization for Constrained Environments (ACE) framework [I-D.ietf-ace-oauth-authz]. Thus the general privacy considerations from the framework also apply to this profile. As this document uses OSCORE, thus the privacy considerations from [RFC8613] 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. - Although encrypted, 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. + 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, that might leak some information about the client). - The AS is the party tasked of assigning the identifiers used in + The AS is the party tasked with assigning the identifiers used in OSCORE, which are privacy sensitive (see Section 12.8 of [RFC8613]), and which could reveal information about the client, or 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. 9. IANA Considerations Note to RFC Editor: Please replace all occurrences of "[[this specification]]" with the RFC number of this specification and delete this paragraph. -9.1. ACE OAuth Profile Registry +9.1. ACE Profile Registry - The following registration is done for the ACE OAuth Profile Registry - following the procedure specified in section 8.7 of + The following registration is done for the ACE Profile Registry + following the procedure specified in section 8.8 of [I-D.ietf-ace-oauth-authz]: - o Profile name: coap_oscore - o Profile Description: Profile for using OSCORE to secure - communication between constrained nodes using the Authentication - and Authorization for Constrained Environments framework. - o Profile ID: TBD (value between 1 and 255) - o Change Controller: IESG - o Specification Document(s): [[this specification]] + o Name: coap_oscore + o Description: Profile for using OSCORE to secure communication + between constrained nodes using the Authentication and + Authorization for Constrained Environments framework. + o CBOR Value: TBD (value between 1 and 255) + o Reference: [[this specification]] 9.2. OAuth Parameters Registry The following registrations are done for the OAuth Parameters Registry following the procedure specified in section 11.2 of [RFC6749]: o Parameter name: nonce1 - o Parameter usage location: token request + o Parameter usage location: client-rs request o Change Controller: IESG o Specification Document(s): [[this specification]] o Parameter name: nonce2 - o Parameter usage location: token response + o Parameter usage location: rs-client response o Change Controller: IESG o Specification Document(s): [[this specification]] 9.3. OAuth Parameters CBOR Mappings Registry The following registrations are done for the OAuth Parameters CBOR - Mappings Registry following the procedure specified in section 8.9 of - [I-D.ietf-ace-oauth-authz]: + Mappings Registry following the procedure specified in section 8.10 + of [I-D.ietf-ace-oauth-authz]: o Name: nonce1 o CBOR Key: TBD1 o Value Type: bstr o Reference: [[this specification]] o Name: nonce2 o CBOR Key: TBD2 - o Value Type: IESG + o Value Type: bstr o Reference: [[this specification]] 9.4. OSCORE Security Context Parameters Registry It is requested that IANA create a new registry entitled "OSCORE Security Context Parameters" registry. The registry is to be created as Expert Review Required. Guidelines for the experts is provided Section 9.7. It should be noted that in addition to the expert review, some portions of the registry require a specification, potentially on standards track, be supplied as well. @@ -1171,36 +1246,36 @@ The specification column for all of these entries will be this document and [RFC8613]. 9.5. CWT Confirmation Methods Registry The following registration is done for the CWT Confirmation Methods Registry following the procedure specified in section 7.2.1 of [RFC8747]: o Confirmation Method Name: "osc" - o Confirmation Method Description: OSCORE_Security_Context carrying + o Confirmation Method Description: OSCORE_Input_Material carrying the parameters for using OSCORE per-message security with implicit key confirmation o Confirmation Key: TBD (value between 4 and 255) o Confirmation Value Type(s): map o Change Controller: IESG o Specification Document(s): Section 3.2.1 of [[this specification]] 9.6. JWT Confirmation Methods Registry The following registration is done for the JWT Confirmation Methods Registry following the procedure specified in section 6.2.1 of [RFC7800]: o Confirmation Method Value: "osc" - o Confirmation Method Description: OSCORE_Security_Context carrying + o Confirmation Method Description: OSCORE_Input_Material carrying the parameters for using OSCORE per-message security with implicit key confirmation o Change Controller: IESG o Specification Document(s): Section 3.2.1 of [[this specification]] 9.7. 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 @@ -1231,32 +1306,42 @@ document cannot have points assigned outside of that range. The length of the encoded value should be weighed against how many code points of that length are left, the size of device it will be used on, and the number of code points left that encode to that size. 10. References 10.1. Normative References + [COSE.Algorithms] + IANA, "COSE Algorithms", + . + [I-D.ietf-ace-oauth-authz] Seitz, L., Selander, G., Wahlstroem, E., Erdtman, S., and H. Tschofenig, "Authentication and Authorization for Constrained Environments (ACE) using the OAuth 2.0 - Framework (ACE-OAuth)", draft-ietf-ace-oauth-authz-33 - (work in progress), February 2020. + Framework (ACE-OAuth)", draft-ietf-ace-oauth-authz-35 + (work in progress), June 2020. [I-D.ietf-ace-oauth-params] Seitz, L., "Additional OAuth Parameters for Authorization in Constrained Environments (ACE)", draft-ietf-ace-oauth- params-13 (work in progress), April 2020. + [I-D.ietf-cbor-7049bis] + Bormann, C. and P. Hoffman, "Concise Binary Object + Representation (CBOR)", draft-ietf-cbor-7049bis-14 (work + in progress), June 2020. + [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained Application Protocol (CoAP)", RFC 7252, DOI 10.17487/RFC7252, June 2014, . @@ -1318,27 +1403,29 @@ necessary permissions and AS for accessing a resource, different from the one proposed in: Not specified o Optionally specify new grant types: Not specified o Optionally define the use of client certificates as client credential type: Not specified o Specify the communication protocol the client and RS the must use: CoAP o Specify the security protocol the client and RS must use to protect their communication: OSCORE o Specify how the client and the RS mutually authenticate: - Implicitly by possession of a common OSCORE security context + 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. o 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; pre-established symmetric keys - o Specify a unique ace_profile identifier: coap_oscore o If introspection is supported: Specify the communication and security protocol for introspection: HTTP/CoAP (+ TLS/DTLS/OSCORE) o Specify the communication and security protocol for interactions between client and AS: HTTP/CoAP (+ TLS/DTLS/OSCORE) o Specify how/if the authz-info endpoint is protected, including how error responses are protected: Not protected. o Optionally define other methods of token transport than the authz- info endpoint: Not defined