--- 1/draft-ietf-ace-oscore-profile-05.txt 2019-01-03 03:13:22.325751336 -0800 +++ 2/draft-ietf-ace-oscore-profile-06.txt 2019-01-03 03:13:22.381752694 -0800 @@ -1,24 +1,24 @@ ACE Working Group F. Palombini Internet-Draft Ericsson AB Intended status: Standards Track L. Seitz -Expires: May 11, 2019 RISE SICS AB +Expires: July 7, 2019 RISE SICS AB G. Selander Ericsson AB M. Gunnarsson RISE SICS AB - November 7, 2018 + January 3, 2019 OSCORE profile of the Authentication and Authorization for Constrained Environments Framework - draft-ietf-ace-oscore-profile-05 + draft-ietf-ace-oscore-profile-06 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. @@ -30,67 +30,67 @@ 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 May 11, 2019. + This Internet-Draft will expire on July 7, 2019. Copyright Notice - Copyright (c) 2018 IETF Trust and the persons identified as the + Copyright (c) 2019 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 3 3. Client-AS Communication . . . . . . . . . . . . . . . . . . . 5 3.1. C-to-AS: POST to token endpoint . . . . . . . . . . . . . 6 3.2. AS-to-C: Access Token . . . . . . . . . . . . . . . . . . 7 - 3.2.1. OSCORE_Security_Context Object . . . . . . . . . . . 10 - 4. Client-RS Communication . . . . . . . . . . . . . . . . . . . 13 - 4.1. C-to-RS: POST to authz-info endpoint . . . . . . . . . . 13 - 4.2. RS-to-C: 2.01 (Created) . . . . . . . . . . . . . . . . . 14 - 4.3. OSCORE Setup . . . . . . . . . . . . . . . . . . . . . . 15 - 4.4. Access rights verification . . . . . . . . . . . . . . . 16 - 5. Secure Communication with AS . . . . . . . . . . . . . . . . 17 - 6. Discarding the Security Context . . . . . . . . . . . . . . . 17 - 7. Security Considerations . . . . . . . . . . . . . . . . . . . 18 - 8. Privacy Considerations . . . . . . . . . . . . . . . . . . . 18 - 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 - 9.1. ACE OAuth Profile Registry . . . . . . . . . . . . . . . 19 - 9.2. OSCORE Security Context Parameters Registry . . . . . . . 19 - 9.3. CWT Confirmation Methods Registry . . . . . . . . . . . . 20 - 9.4. JWT Confirmation Methods Registry . . . . . . . . . . . . 20 - 9.5. Expert Review Instructions . . . . . . . . . . . . . . . 20 - 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 21 - 10.1. Normative References . . . . . . . . . . . . . . . . . . 21 - 10.2. Informative References . . . . . . . . . . . . . . . . . 22 - Appendix A. Profile Requirements . . . . . . . . . . . . . . . . 23 - Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 23 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23 + 3.2.1. OSCORE_Security_Context Object . . . . . . . . . . . 11 + 4. Client-RS Communication . . . . . . . . . . . . . . . . . . . 14 + 4.1. C-to-RS: POST to authz-info endpoint . . . . . . . . . . 15 + 4.2. RS-to-C: 2.01 (Created) . . . . . . . . . . . . . . . . . 16 + 4.3. OSCORE Setup . . . . . . . . . . . . . . . . . . . . . . 17 + 4.4. Access rights verification . . . . . . . . . . . . . . . 18 + 5. Secure Communication with AS . . . . . . . . . . . . . . . . 19 + 6. Discarding the Security Context . . . . . . . . . . . . . . . 19 + 7. Security Considerations . . . . . . . . . . . . . . . . . . . 20 + 8. Privacy Considerations . . . . . . . . . . . . . . . . . . . 21 + 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21 + 9.1. ACE OAuth Profile Registry . . . . . . . . . . . . . . . 21 + 9.2. OSCORE Security Context Parameters Registry . . . . . . . 22 + 9.3. CWT Confirmation Methods Registry . . . . . . . . . . . . 22 + 9.4. JWT Confirmation Methods Registry . . . . . . . . . . . . 23 + 9.5. Expert Review Instructions . . . . . . . . . . . . . . . 23 + 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 24 + 10.1. Normative References . . . . . . . . . . . . . . . . . . 24 + 10.2. Informative References . . . . . . . . . . . . . . . . . 24 + Appendix A. Profile Requirements . . . . . . . . . . . . . . . . 25 + Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 26 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 26 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. In order to provide communication security, proof of possession, and server authentication they use Object Security for Constrained RESTful Environments (OSCORE) @@ -144,44 +144,49 @@ 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 [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 TLS or DTLS MAY be used additionally or instead. - Once the client has retrieved the access token, it posts it to the RS - using the authz-info endpoint and mechanisms specified in section 5.8 - of [I-D.ietf-ace-oauth-authz]. If the access token is valid, the RS - replies to this request with a 2.01 (Created) response, which - contains a nonce N1. + 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. - After receiving the nonce N1, the client generates a nonce N2, - concatenates it with N1 and sets the ID Context in its Security + 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 N1 with N2 and sets the ID Context in the Security Context (see section 3 of [I-D.ietf-core-object-security]) to N1 - concatenated with N2. The client then derives the complete Security - Context from the ID Context plus the parameters received from the AS. + concatenated with N2. The RS then derives the complete Security + Context associated with the received token from it plus the + parameters received in the AS, following section 3.2 of + [I-D.ietf-core-object-security]. + + After receiving the nonce N2, the client concatenates it with N1 and + sets the ID Context in its Security Context (see section 3 of + [I-D.ietf-core-object-security]) to N1 concatenated with N2. The + client then derives the complete Security Context from the ID Context + plus the parameters received from the AS. Finally, the client sends a request protected with OSCORE to the RS. - This message contains the ID Context value. When receiving this - request after the 2.01 (Created) response, the server extract the ID - Context from it, verifies that the first part is equal to the nonce - N1 it previously sent, and if so, sets its own ID Context and derives - the complete Security Context from it plus the parameters received in - the AS, following section 3.2 of [I-D.ietf-core-object-security]. If - the request verifies, then this Security Context is stored in the - server, and used in the response, and in further communications with - the client, until token expiration. Once the client receives a valid - response, it does not continue to include the ID Context value in - further requests. + This message may contain the ID Context value. If the request + verifies, then this Security Context is stored in the server, and + used in the response, and in further communications with the client, + until token expiration. This Security Context is discarded if the + same token is re-used to successfully derive a new Security Context. + Once the client receives a valid response, it does not continue to + include the ID Context value in further requests. The use of random nonces during the exchange prevents the reuse of AEAD nonces and keys with different messages, in case of re- derivation of the Security Context both for Clients and Resource Servers from an old non-expired access token, e.g. in case of re-boot of either the client or RS. In fact, by using random nonces as ID Context, the request to the authz-info endpoint posting the same token results in a different Security Context, since Master Secret, Sender ID and Recipient ID are the same but ID Context is different. Therefore, the main requirement for the nonces is that they have a @@ -196,29 +201,29 @@ C RS AS | [-- Resource Request --->] | | | | | | [<----- AS Information --] | | | | | | ----- POST /token ----------------------------> | | | | | <---------------------------- Access Token ----- | | + RS Information | | ---- POST /authz-info ---> | | + | (access_token, N1) | | | | | - | <--- 2.01 Created (N1) --- | | + | <--- 2.01 Created (N2) --- | | | | | - /Sec Context Derivation/ | | + /Sec Context /Sec Context | + Derivation/ Derivation/ | | | | | ---- OSCORE Request -----> | | - | (N1, N2) | | - | | | - | /Sec Context Derivation/ | + | ?(N1, N2) | | | | | | <--- OSCORE Response ----- | | | | | | ---- OSCORE Request -----> | | | | | | <--- OSCORE Response ----- | | | ... | | Figure 1: Protocol Overview @@ -244,22 +249,20 @@ An example of such a request, in CBOR diagnostic notation without the tag and value abbreviations is reported in Figure 2 Header: POST (Code=0.02) Uri-Host: "as.example.com" Uri-Path: "token" Content-Format: "application/ace+cbor" Payload: { - "grant_type" : "client_credentials", - "client_id" : "myclient", "req_aud" : "tempSensor4711", "scope" : "read" } Figure 2: Example C-to-AS POST /token request for an access token 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 carrying the client's @@ -275,201 +278,242 @@ Section 5.6.3 of [I-D.ietf-ace-oauth-authz]. An example of such a request, in CBOR diagnostic notation without the tag and value abbreviations is reported in Figure 3 Header: POST (Code=0.02) Uri-Host: "as.example.com" Uri-Path: "token" Content-Format: "application/ace+cbor" Payload: { - "grant_type" : "client_credentials", - "client_id" : "myclient", "req_aud" : "tempSensor4711", "scope" : "write", "req_cnf" : { - "kid" : b64'Qg' + "kid" : "myclient" } Figure 3: Example C-to-AS POST /token request for updating rights to an access token bound to a symmetric key. 3.2. 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 section 5.6.2 of [I-D.ietf-ace-oauth-authz]. If the client request was invalid, or not authorized, the AS returns an error response as described in section 5.6.3 of [I-D.ietf-ace-oauth-authz]. - The AS signals that the use of OSCORE is REQUIRED for a specific + The AS can signal that the use of OSCORE is REQUIRED for a specific access token by including the "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 Section 4.3 to derive the security - context to run OSCORE. + context to run OSCORE. Usually it is assumed that constrained + devices will be pre-configured with the necessary profile, so that + this kind of profile negotiation can be omitted. Moreover, the AS MUST provision the following data: o a master secret - o a client identifier - o a server identifier Additionally, the AS MAY provision the following data, in the same response. + o a client identifier + o an AEAD algorithm o an HKDF algorithm o a salt o a replay window type and size The master secret MUST be communicated as the 'ms' field in the OSCORE_Security_Context in the 'cnf' parameter of the access token response as defined in Section 3.2 of [I-D.ietf-ace-oauth-params]. The OSCORE_Security_Context is a CBOR map object, defined in Section 3.2.1. 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, the salt MAY be included as the 'salt' parameter of the - COSCORE_Security_Context and the replay window type and size MAY be + COSCORE_Security_Context, and the replay window type and size MAY be included as the 'rpl' of the OSCORE_Security_Context, as defined in Section 3.2.1. The same parameters MUST be included as metadata 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 'cnf' claim of this token. - The AS MUST also assign identifiers to both client and RS, which are - then used as Sender ID and Recipient ID in the OSCORE context as - described in section 3.1 of [I-D.ietf-core-object-security]. The - client identifiers MUST be unique in the set of all clients on a - single RS, and RS identifiers MUST be unique in the set of all RS for - any given client. Moreover, these MUST be included in the - OSCORE_Security_Context, as defined in Section 3.2.1. + The AS MUST also assign an identifier to the RS, and MAY assign an + identifier to the client. These identifiers are then used as Sender + ID and Recipient ID in the OSCORE context as described in section 3.1 + of [I-D.ietf-core-object-security]. The client identifiers MUST be + unique in the set of all clients on a single RS, and RS identifiers + MUST be unique in the set of all RS for any given client. Moreover, + when assigned, these MUST be included in the OSCORE_Security_Context, + as defined in Section 3.2.1. We assume in this document that a resource is associated to one single AS, which makes it possible to assume unique identifiers for each client requesting a particular resource to a RS. If this is not the case, collisions of identifiers may appear in the RS, in which case the RS needs to have a mechanism in place to disambiguate identifiers or mitigate their effect. 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 4 shows an example of such an AS response, in CBOR diagnostic notation without the tag and value abbreviations. Header: Created (Code=2.01) - Content-Type: "application/cose+cbor" + Content-Type: "application/ace+cbor" Payload: { - "access_token" : b64'SlAV32hkKG ... + "access_token" : h'a5037674656d7053656e73 ...' (remainder of access token omitted for brevity)', "profile" : "coap_oscore", "expires_in" : "3600", "cnf" : { "OSCORE_Security_Context" : { "alg" : "AES-CCM-16-64-128", "clientId" : b64'qA', "serverId" : b64'Qg', - "ms" : b64'+a+Dg2jjU+eIiOFCa9lObw' + "ms" : h'f9af838368e353e78888e1426bd94e6f' } } } Figure 4: Example AS-to-C Access Token response with OSCORE profile. Figure 5 shows an example CWT, containing the necessary 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" : { "OSCORE_Security_Context" : { "alg" : "AES-CCM-16-64-128", - "clientId" : b64'Qg', - "serverId" : b64'qA', - "ms" : b64'+a+Dg2jjU+eIiOFCa9lObw' + "clientId" : "client", + "serverId" : "server", + "ms" : h'f9af838368e353e78888e1426bd94e6f' } } Figure 5: Example CWT with OSCORE parameters. + The same CWT token as in Figure 5, using the value abbreviations + defined in [I-D.ietf-ace-oauth-authz] and + [I-D.ietf-ace-cwt-proof-of-possession] and encoded in CBOR is shown + in Figure 6. + + 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" + 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) + A4 # map(4) + 05 # unsigned(5) + 0A # unsigned(10) + 02 # unsigned(2) + 66 # text(6) + 636C69656E74 # "client" + 03 # unsigned(3) + 66 # text(6) + 736572766572 # "server" + 01 # unsigned(1) + 50 # bytes(16) + F9AF838368E353E78888E1426BD94E6F + + Figure 6: Example CWT with OSCORE parameters. + 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 in the 'kid' field in the 'cnf' parameter of the token. The client identifier needs to be provisioned, in order for the RS to identify the previously generated Security Context. - Figure 6 shows an example of such an AS response, in CBOR diagnostic + Figure 7 shows an example of such an AS response, in CBOR diagnostic notation without the tag and value abbreviations. Header: Created (Code=2.01) - Content-Type: "application/cose+cbor" + Content-Type: "application/ace+cbor" Payload: { - "access_token" : b64'SlAV32hkKG ... + "access_token" : h'a5037674656d7053656e73 ...' (remainder of access token omitted for brevity)', "profile" : "coap_oscore", "expires_in" : "3600" } - Figure 6: Example AS-to-C Access Token response with OSCORE profile, + Figure 7: Example AS-to-C Access Token response with OSCORE profile, for update of access rights. - Figure 7 shows an example CWT, containing the necessary OSCORE + Figure 8 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. { "aud" : "tempSensorInLivingRoom", "iat" : "1360189224", "exp" : "1360289224", "scope" : "temperature_h", "cnf" : { "kid" : b64'Qg' } } - Figure 7: Example CWT with OSCORE parameters for update of access + Figure 8: Example CWT with OSCORE parameters for update of access rights. 3.2.1. OSCORE_Security_Context Object An OSCORE_Security_Context is an object that represents part or all of an OSCORE Security Context (Section 3.1 of [I-D.ietf-core-object-security]). The OSCORE_Security_Context object can either be encoded as JSON or as CBOR. In both cases, 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 Section 9.2) and is defined below. All parameters are optional. Table 1 provides a summary of the OSCORE_Security_Context parameters defined in this section. - +----------+-------+----------------+--------------+----------------+ + +-----------+-------+----------------+--------------+---------------+ | name | CBOR | CBOR type | registry | description | | | label | | | | - +----------+-------+----------------+--------------+----------------+ + +-----------+-------+----------------+--------------+---------------+ | ms | 1 | bstr | | OSCORE Master | | | | | | Secret value | | | | | | | | clientId | 2 | bstr | | OSCORE Sender | | | | | | ID value of | | | | | | the client, | | | | | | OSCORE | | | | | | Recipient ID | | | | | | value of the | | | | | | server | @@ -488,46 +532,49 @@ | | | | (HMAC-based) | | | | | | | | | alg | 5 | tstr / int | COSE | OSCORE AEAD | | | | | Algorithm | Algorithm | | | | | Values | value | | | | | (AEAD) | | | | | | | | | salt | 6 | bstr | | OSCORE Master | | | | | | Salt value | | | | | | | - | rpl | 7 | bstr / int | | OSCORE Replay | + | contextId | 7 | bstr | | OSCORE ID | + | | | | | Context value | + | | | | | | + | rpl | 8 | bstr / int | | OSCORE Replay | | | | | | Window Type | | | | | | and Size | - +----------+-------+----------------+--------------+----------------+ + +-----------+-------+----------------+--------------+---------------+ Table 1: OSCORE_Security_Context Parameters 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 [I-D.ietf-core-object-security]. 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 this field, see section 3.1 of [I-D.ietf-core-object-security]. - In JSON, the "clientID" value is a Base64 encoded byte string. In - CBOR, the "clientID" type is bstr, and has label 2. + In JSON, the "clientId" value is a Base64 encoded byte string. In + CBOR, the "clientId" type is bstr, and has label 2. serverId: This parameter identifies a server 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 this field, see section 3.1 of [I-D.ietf-core-object-security]. - In JSON, the "serverID" value is a Base64 encoded byte string. In - CBOR, the "serverID" type is bstr, and has label 3. + 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 [I-D.ietf-core-object-security]. 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. @@ -541,204 +588,244 @@ 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 [I-D.ietf-core-object-security]. 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 + [I-D.ietf-core-object-security]. In JSON, the "contextID" value + is a Base64 encoded byte string. In CBOR, the "contextID" type is + bstr, and has label 7. + repl: This parameter is used to carry the OSCORE value, encoded as a bstr. This parameter identifies the OSCORE Replay Window Size and Type value, which is a byte string. For more information about this field, see section 3.1 of [I-D.ietf-core-object-security]. In JSON, the "repl" value is a Base64 encoded byte string. In - CBOR, the "repl" type is bstr, and has label 7. + CBOR, the "repl" type is bstr, and has label 8. - An example of JSON OSCORE_Security_Context is given in Figure 8. + An example of JSON OSCORE_Security_Context is given in Figure 9. "OSCORE_Security_Context" : { "alg" : "AES-CCM-16-64-128", "clientId" : b64'qA', "serverId" : b64'Qg', "ms" : b64'+a+Dg2jjU+eIiOFCa9lObw' } - Figure 8: Example JSON OSCORE_Security_Context object + Figure 9: Example JSON OSCORE_Security_Context object The CDDL grammar describing the CBOR OSCORE_Security_Context object is: OSCORE_Security_Context = { ? 1 => bstr, ; ms ? 2 => bstr, ; clientId ? 3 => bstr, ; serverId ? 4 => tstr / int, ; hkdf ? 5 => tstr / int, ; alg ? 6 => bstr, ; salt - ? 7 => bstr / tstr ; rpl + ? 7 => bstr, ; contextId + ? 8 => bstr / tstr, ; rpl + * 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 posts the token that includes the materials provisioned by the - AS to the RS, which can then use Section 3.2 of + client generates a nonce N1 and posts it together with the token that + includes the materials provisioned by the AS to the RS. The RS then + derives a nonce N2 and use Section 3.2 of [I-D.ietf-core-object-security] to derive a security context based on - a shared master secret and a set of other parameters, established - between client and server. + a shared master secret and the two nonces, established between client + and server. Note that the proof-of-possession required to bind the access token to the client is implicitly performed by generating the shared OSCORE Security Context using the pop-key as master secret, for both client and RS. An attacker using a stolen token will not be able to generate a valid OSCORE context and thus not be able to prove possession of the pop-key. 4.1. C-to-RS: POST to authz-info endpoint - 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 to the RS. + The client MUST generate a nonce N1 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. The client + MUST store this nonce 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. 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 correct CBOR label (e.g., "cwt" for CWT, "jwt" for JWT) and + N1 using the 'nonce' parameter defined in section 5.1.2 of + [I-D.ietf-ace-oauth-authz]. The authz-info endpoint is not protected, nor are the responses from this resource. The access token MUST be encrypted, since it is transferred from the client to the RS over an unprotected channel. Note that a client may be required to re-POST the access token, since an RS may delete a stored access token, due to lack of memory. - Figure 9 shows an example of the request sent from the client to the - RS. + Figure 10 shows an example of the request sent from the client to the + RS, in CBOR diagnostic notation without the tag and value + abbreviations. Header: POST (Code=0.02) Uri-Host: "rs.example.com" Uri-Path: "authz-info" - Content-Format: "application/cwt" + Content-Format: "application/ace+cbor" Payload: - b64'SlAV32hkKG ... + { + "access_token": h'a5037674656d7053656e73 ...' (remainder of access token omitted for brevity)', + "nonce": h'018a278f7faab55a' + } - Figure 9: Example C-to-RS POST /authz-info request using CWT + Figure 10: Example C-to-RS POST /authz-info request using CWT 4.2. RS-to-C: 2.01 (Created) The RS MUST follow the procedures defined in section 5.8.1 of [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) the RS + to claims that the RS cannot process (e.g., an unknown scope), or if + any of the expected parameters in the OSCORE_Security_Context is + missing (e.g. any of the mandatory parameters from the AS), the RS MUST respond with a response code equivalent to the CoAP code 4.00 (Bad Request). In the latter case 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. - Additionally, the RS MUST generate a nonce (N1) with a good amount of - randomness, and include it in the payload of the 2.01 (Created) - response as a CBOR byte string. This profile RECOMMENDS to use a - nonce of 64 bits. The RS MUST store this nonce as long as the access - token related to it is still valid. - - Note that, when using this profile, an identifier of the token (e.g., - the cti for a CWT) is not transported in the payload of this request, - as section 5.8.1 of [I-D.ietf-ace-oauth-authz] allows. + 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 'nonce' + parameter defined in section 5.1.2 of [I-D.ietf-ace-oauth-authz], set + to N2. This profile RECOMMENDS to use a 64-bit long random number as + nonce. Moreover, if the OSCORE_Security_Context in the token did not + contain a 'clientId' parameter, the RS MUST generate an identifier, + unique in the set of all its existing client identifiers, and send it + in a 'clientId' parameter in the CBOR map as a CBOR bstr. The RS MAY + generate and send a 'ClientId' identifier even though the + OSCORE_Security_Context contained such a parameter, in order to + guarantee the uniqueness of the client identifier. The RS MUST use + the Content-Format "application/ace+cbor" defined in section 8.14 of + [I-D.ietf-ace-oauth-authz]. - Figure 10 shows an example of the response sent from the RS to the - client. + Figure 11 shows an example of the response sent from the RS to the + client, in CBOR diagnostic notation without the tag and value + abbreviations. Header: Created (Code=2.01) - Content-Format: "application/cbor" + Content-Format: "application/ace+cbor" Payload: - h'018a278f7faab55a', + { + "nonce": h'25a8991cd700ac01' + } - Figure 10: Example RS-to-C 2.01 (Created) response + Figure 11: Example RS-to-C 2.01 (Created) response When receiving an updated access token with updated authorization information from the client (see section 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. 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. 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 - nonce N1 from the CBOR byte string in the payload of the response. - The client MUST generate itself a nonce (N2) with a good amount of - randomness. This profile RECOMMENDS to use a nonce of 64 bits. - Then, the client MUST set the ID Context of the Security Context - created to communicate with the RS to the concatenation of N1 and N2, - in this order: ID Context = N1 | N2, where | denotes byte string - concatenation. 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, Master Salt, HKDF and Replay + nonce N2 from the 'nonce' parameter and the client identifier from + the 'clientId' in the CBOR map in the payload of the response. Then, + the client MUST set the ID Context of the Security Context created to + communicate with the RS to the concatenation of N1 and N2, in this + order: ID Context = N1 | N2, where | denotes byte string + concatenation. The client MUST set the Master Secret and Recipient + ID from the parameters received from the AS in Section 3.2. The + client MUST set the AEAD Algorithm, Master Salt, HKDF, and Replay Window 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 section 3.2 of - [I-D.ietf-core-object-security]. After that, the client MUST derive - the complete Security Context following section 3.2.1 of + [I-D.ietf-core-object-security]. The client MUST set the Sender ID + from the 'clientId in the 2.01 (Created) response, if present; + otherwise, the client MUST set the Sender ID from the parameters + received from the AS in Section 3.2. After that, the client MUST + derive the complete Security Context following section 3.2.1 of [I-D.ietf-core-object-security]. 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, or the 'clientId', either received + from the AS or in the 2.01 (Created) response from the RS), 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. In the first request sent to the RS, the client MUST + using OSCORE. In the first request sent to the RS, the client MAY include the kid context, with value ID Context, i.e. N1 concatenated - with N2. The client needs to make sure the RS receives the kid - context, possibly adding the kid context to later requests, until it - receives a valid OSCORE response from the RS using the same Security - Context. + with N2. - When the RS receives this first OSCORE-protected request, it MUST - extract the kid context from the message first. Then, it needs to - verify that the first part of the kid context corresponds to the - nonce N1 it previously sent, and that it is followed by a non-zero- - length byte string. If that is verified, the RS MUST set the ID - Context to the kid context value. Then, the RS MUST set the Master - Secret, Sender ID and Recipient ID from the parameters received from - the client in the access token in Section 4.1. The RS MUST set the - AEAD Algorithm, Master Salt, HKDF and Replay Window from the + After sending the 2.01 (Created) response, the RS MUST set the ID + Context of the Security Context created to communicate with the + client to the concatenation of N1 and N2, in this order: ID Context = + N1 | N2, where | denotes byte string concatenation. The RS MUST set + the Master Secret, Sender ID and Recipient ID from the parameters, + received from 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, Master Salt, HKDF, and Replay Window from the parameters received from the client in the access token in - Section 4.1, if present. In case these parameters are omitted, the + 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 section 3.2 of [I-D.ietf-core-object-security]. After that, the RS MUST derive the complete Security Context following section 3.2.1 of [I-D.ietf-core-object-security], and MUST associate this Security Context with the authorization information from the access token. - Then, the RS MUST delete the nonce N1 from memory. The RS then uses this Security Context to verify the request and send responses to RS using OSCORE. If OSCORE verification fails, error responses are used, as specified in section 8 of [I-D.ietf-core-object-security]. 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. 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 it processes according to + request from a client, then the RS processes it according to [I-D.ietf-core-object-security]. If OSCORE verification succeeds, and the target resource requires authorization, the RS retrieves the authorization information from 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 not used the Security Context associated with the access token, or if RS has no valid access token for the client. If RS has an access token for the client but not for the resource that was requested, RS @@ -774,23 +861,24 @@ an RS when: o the Sequence Number space ends. o the access token associated with the context expires. o 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. - o the client receives a new nonce in the 2.01 Created response (see - Section 4.2) to a POST request to the authz-info endpoint, when - re-posting a non-expired token associated to the existing context. + o the client receives a new nonce in the 2.01 (Created) response + (see Section 4.2) to a POST request to the authz-info endpoint, + when re-posting a non-expired token associated to the existing + context. The RS MUST discard the current security context associated with a client when: o Sequence Number space ends. o Access token associated with the context expires. 7. Security Considerations @@ -805,24 +893,28 @@ 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 even in case of re-boots, a good amount of randomness - is required. If that is not guaranteed, nodes are still susceptible - to re-using nonces and keys, in case the Security Context is lost, - and on-path attacker replaying messages. + keys and nonces, it is REQUIRED that nonces are not reused with the + same input keying material even in case of re-boots. This document + RECOMMENDS the use of 64 bit random nonces to guarantee non-reuse; if + applications use something else, such as a counter, they need to + guarantee that reboot and lost of state on either node does not + provoke re-use. If that is not guaranteed, nodes are still + susceptible to re-using AEAD nonces and keys, in case the Security + Context is lost, and on-path attacker replay messages. This profiles 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 may contradict each other which 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. @@ -866,28 +958,33 @@ 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]] 9.2. 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 9.5. It should be noted that in additional to the expert + Section 9.5. It should be noted that in addition to the expert review, some portions of the registry require a specification, potentially on standards track, be supplied as well. The columns of the registry are: - name This is a descriptive name that enables easier reference to the - item. It is not used in the CBOR encoding. + name The JSON name requested (e.g., "ms"). Because a core goal of + this specification 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 state 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 algorithm. Key map labels MUST be unique. The label can be a positive integer, a negative integer or a string. Integer values between 0 and 255 and strings of length 1 are designated as Standards Track Document required. Integer values from 256 to 65535 and strings of length 2 are designated as Specification Required. Integer values of 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. @@ -962,27 +1059,27 @@ size. 10. References 10.1. Normative References [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-16 - (work in progress), October 2018. + Framework (ACE-OAuth)", draft-ietf-ace-oauth-authz-17 + (work in progress), November 2018. [I-D.ietf-ace-oauth-params] Seitz, L., "Additional OAuth Parameters for Authorization in Constrained Environments (ACE)", draft-ietf-ace-oauth- - params-00 (work in progress), September 2018. + params-01 (work in progress), November 2018. [I-D.ietf-core-object-security] Selander, G., Mattsson, J., Palombini, F., and L. Seitz, "Object Security for Constrained RESTful Environments (OSCORE)", draft-ietf-core-object-security-15 (work in progress), August 2018. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, @@ -1000,21 +1097,21 @@ [RFC8392] Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig, "CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392, May 2018, . 10.2. Informative References [I-D.ietf-ace-cwt-proof-of-possession] Jones, M., Seitz, L., Selander, G., Erdtman, S., and H. Tschofenig, "Proof-of-Possession Key Semantics for CBOR Web Tokens (CWTs)", draft-ietf-ace-cwt-proof-of- - possession-04 (work in progress), November 2018. + possession-05 (work in progress), November 2018. [RFC4949] Shirey, R., "Internet Security Glossary, Version 2", FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007, . [RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework", RFC 6749, DOI 10.17487/RFC6749, October 2012, . [RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer @@ -1032,21 +1129,21 @@ This section lists the specifications on this profile based on the requirements on the framework, as requested in Appendix C of [I-D.ietf-ace-oauth-authz]. o (Optional) discovery process of how the client finds the right AS for an RS it wants to send a request to: Not specified o communication protocol the client and the RS must use: CoAP o security protocol the client and RS must use: OSCORE o how the client and the RS mutually authenticate: Implicitly by possession of a common OSCORE security context - o Content-format of the protocol messages: "application/cose+cbor" + o Content-format of the protocol messages: "application/ace+cbor" o proof-of-possession protocol(s) and how to select one; which key types (e.g. symmetric/asymmetric) supported: OSCORE algorithms; pre-established symmetric keys o profile identifier: coap_oscore o (Optional) how the RS talks to the AS for introspection: HTTP/CoAP (+ TLS/DTLS/OSCORE) o how the client talks to the AS for requesting a token: HTTP/CoAP (+ TLS/DTLS/OSCORE) o how/if the authz-info endpoint is protected: Security protocol above