CoRE Working Group M. Tiloca Internet-Draft RISE AB Intended status: Standards Track C. Amsuess Expires: January 14, 2021 P. van der Stok Consultant July 13, 2020 Discovery of OSCORE Groups with the CoRE Resource Directory draft-tiloca-core-oscore-discovery-06 Abstract Group communication over the Constrained Application Protocol (CoAP) can be secured by means of Group Object Security for Constrained RESTful Environments (Group OSCORE). At deployment time, devices may not know the exact OSCORE groups to join, the respective Group Manager, or other information required to perform the joining process. This document describes how a CoAP endpoint can use descriptions and links of resources registered at the CoRE Resource Directory to discover OSCORE groups and to acquire information for joining them through the respective Group Manager. A given OSCORE group may protect multiple application groups, which are separately announced in the Resource Directory as sets of endpoints sharing a pool of resources. This approach is consistent with, but not limited to, the joining of OSCORE groups based on the ACE framework for Authentication and Authorization in constrained environments. 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 January 14, 2021. Tiloca, et al. Expires January 14, 2021 [Page 1] Internet-Draft OSCORE group discovery with the CoRE RD July 2020 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 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 . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 2. Registration of Group Manager Endpoints . . . . . . . . . . . 6 2.1. Parameters . . . . . . . . . . . . . . . . . . . . . . . 6 2.2. Relation Link to Authorization Server . . . . . . . . . . 8 2.3. Registration Example . . . . . . . . . . . . . . . . . . 9 2.3.1. Example in Link Format . . . . . . . . . . . . . . . 9 2.3.2. Example in CoRAL . . . . . . . . . . . . . . . . . . 10 3. Addition and Update of Security Groups . . . . . . . . . . . 10 3.1. Addition Example . . . . . . . . . . . . . . . . . . . . 11 3.1.1. Example in Link Format . . . . . . . . . . . . . . . 11 3.1.2. Example in CoRAL . . . . . . . . . . . . . . . . . . 12 4. Discovery of Security Groups . . . . . . . . . . . . . . . . 14 4.1. Discovery Example #1 . . . . . . . . . . . . . . . . . . 15 4.1.1. Example in Link Format . . . . . . . . . . . . . . . 15 4.1.2. Example in CoRAL . . . . . . . . . . . . . . . . . . 16 4.2. Discovery Example #2 . . . . . . . . . . . . . . . . . . 17 4.2.1. Example in Link Format . . . . . . . . . . . . . . . 17 4.2.2. Example in CoRAL . . . . . . . . . . . . . . . . . . 18 5. Use Case Example With Full Discovery . . . . . . . . . . . . 19 6. Security Considerations . . . . . . . . . . . . . . . . . . . 23 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23 7.1. Resource Types . . . . . . . . . . . . . . . . . . . . . 23 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 24 8.1. Normative References . . . . . . . . . . . . . . . . . . 24 8.2. Informative References . . . . . . . . . . . . . . . . . 25 Appendix A. Use Case Example With Full Discovery (CoRAL) . . . . 26 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 30 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 31 Tiloca, et al. Expires January 14, 2021 [Page 2] Internet-Draft OSCORE group discovery with the CoRE RD July 2020 1. Introduction The Constrained Application Protocol (CoAP) [RFC7252] supports group communication over IP multicast [I-D.ietf-core-groupcomm-bis] to improve efficiency and latency of communication and reduce bandwidth requirements. A set of CoAP endpoints constitutes an application group by sharing a common pool of resources, that can be efficiently accessed through group communication. The members of an application group may be members of a security group, thus sharing a common set of keying material to secure group communication. The security protocol Group Object Security for Constrained RESTful Environments (Group OSCORE) [I-D.ietf-core-oscore-groupcomm] builds on OSCORE [RFC8613] and protects CoAP messages end-to-end in group communication contexts through CBOR Object Signing and Encryption (COSE) [I-D.ietf-cose-rfc8152bis-struct][I-D.ietf-cose-rfc8152bis-algs]. An application group may rely on one or more OSCORE groups as security groups, and a same OSCORE group may be used by multiple application groups at the same time. A CoAP endpoint relies on a Group Manager (GM) to join an OSCORE group and get the group keying material. The joining process in [I-D.ietf-ace-key-groupcomm-oscore] is based on the ACE framework for Authentication and Authorization in constrained environments [I-D.ietf-ace-oauth-authz], with the joining endpoint and the GM acting as ACE Client and Resource Server, respectively. That is, the joining endpoint accesses the group-membership resource exported by the GM and associated with the OSCORE group to join. Typically, devices store a static X509 IDevID certificate installed at manufacturing time [I-D.ietf-anima-bootstrapping-keyinfra]. This is used at deployment time during an enrollment process that provides the devices with an Operational Certificate, possibly updated during the device lifetime. Operational Certificates may specify information to join OSCORE groups, especially a reference to the group-membership resources to access at the respective GMs. However, it is usually impossible to provide such precise information to freshly deployed devices, as part of their (early) Operational Certificate. This can be due to a number of reasons: (1) the OSCORE group(s) to join and the responsible GM(s) are generally unknown at manufacturing time; (2) an OSCORE group of interest is created, or the responsible GM is deployed, only after the device is enrolled and fully operative in the network; (3) information related to existing OSCORE groups or to their GMs has changed. This requires a method for CoAP endpoints to dynamically discover OSCORE groups and their GM, and to retrieve relevant information about deployed groups. Tiloca, et al. Expires January 14, 2021 [Page 3] Internet-Draft OSCORE group discovery with the CoRE RD July 2020 To this end, CoAP endpoints can use descriptions and links of group- membership resources at GMs, to discover OSCORE groups and retrieve the information required for joining them. With the discovery process of OSCORE groups expressed in terms of links to resources, the remaining problem is the discovery of those links. The CoRE Resource Directory (RD) [I-D.ietf-core-resource-directory] allows such discovery in an efficient way, and it is expected to be used in many setups that would benefit of OSCORE group discovery. This specification builds on this approach and describes how CoAP endpoints can use the RD to perform the link discovery steps, in order to discover OSCORE groups and retrieve the information required to join them through their GM. In short, the GM registers as an endpoint with the RD. The resulting registration resource includes one link per OSCORE group under that GM, specifying the path to the related group-membership resource to access for joining that group. Additional descriptive information about the OSCORE group is stored with the registered link. In the RD based on Link Format [RFC6690] and defined in [I-D.ietf-core-resource-directory], this information is specified as target attributes of the registered link, and includes the identifiers of the application groups which use that OSCORE group. This enables a lookup of those application groups at the RD, where they are separately announced by a Commissioning Tool (see Appendix A of [I-D.ietf-core-resource-directory]). When querying the RD for OSCORE groups, a CoAP endpoint can use CoAP observation [RFC7641]. This results in automatic notifications on the creation of new OSCORE groups or the update of existing groups. Thus, it facilitates the early deployment of CoAP endpoints, i.e. even before the GM is deployed and OSCORE groups are created. Interaction examples are provided in Link Format, as well as in the Constrained RESTful Application Language CoRAL [I-D.ietf-core-coral] with reference to a CoRAL-based RD [I-D.hartke-t2trg-coral-reef]. While all the CoRAL examples use the CoRAL textual serialization format, the CBOR [RFC7049] or JSON [RFC8259] binary serialization format is used when sending such messages on the wire. The approach in this document is consistent with, but not limited to, the joining of OSCORE groups in [I-D.ietf-ace-key-groupcomm-oscore]. 1.1. Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP Tiloca, et al. Expires January 14, 2021 [Page 4] Internet-Draft OSCORE group discovery with the CoRE RD July 2020 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. This specification requires readers to be familiar with the terms and concepts discussed in [I-D.ietf-core-resource-directory] and [RFC6690], as well as in [I-D.ietf-core-coral]. Readers should also be familiar with the terms and concepts discussed in [RFC7252][I-D.ietf-core-groupcomm-bis], [I-D.ietf-core-oscore-groupcomm] and [I-D.ietf-ace-key-groupcomm-oscore]. Terminology for constrained environments, such as "constrained device" and "constrained-node network", is defined in [RFC7228]. Consistently with the definitions from Section 2.1 of [I-D.ietf-core-groupcomm-bis], this document also refers to the following terminology. o CoAP group: a set of CoAP endpoints all configured to receive CoAP multicast messages sent to the group's associated IP multicast address and UDP port. An endpoint may be a member of multiple CoAP groups by subscribing to multiple IP multicast addresses. o Security group: a set of CoAP endpoints that share the same security material, and use it to protect and verify exchanged messages. A CoAP endpoint may be a member of multiple security groups. There can be a one-to-one or a one-to-many relation between security groups and CoAP groups. This document especially considers a security group to be an OSCORE group, where all members share one OSCORE Security Context to protect group communication with Group OSCORE [I-D.ietf-core-oscore-groupcomm]. However, the approach defined in this document can be used to support the discovery of different security groups than OSCORE groups. o Application group: a set of CoAP endpoints that share a common set of resources. An endpoint may be a member of multiple application groups. An application group can be associated with one or more security groups, and multiple application groups can use the same security group. Application groups are announced in the RD by a Commissioning Tool, according to the RD-Groups usage pattern (see Appendix A of [I-D.ietf-core-resource-directory]). Tiloca, et al. Expires January 14, 2021 [Page 5] Internet-Draft OSCORE group discovery with the CoRE RD July 2020 2. Registration of Group Manager Endpoints During deployment, a Group Manager (GM) can find the CoRE Resource Directory (RD) as described in Section 4 of [I-D.ietf-core-resource-directory]. Afterwards, the GM registers as an endpoint with the RD, as described in Section 5 of [I-D.ietf-core-resource-directory]. The GM SHOULD NOT use the Simple Registration approach described in Section 5.1 of [I-D.ietf-core-resource-directory]. When registering with the RD, the GM also registers the links to all the group-membership resources it has at that point in time, i.e. one for each of its security groups. In the registration request, each link to a group-membership resource has as target the URI of that resource at the GM. Also, it specifies a number of descriptive parameters as defined in Section 2.1. 2.1. Parameters For each registered link to a group-membership resource at a GM, the following parameters are specified together with the link. In the RD defined in [I-D.ietf-core-resource-directory] and based on Link Format, each parameter is specified in a target attribute with the same name. In an RD based on CoRAL, such as the one defined in [I-D.hartke-t2trg-coral-reef], each parameter is specified in a nested element with the same name. o 'rt', with value "core.osc.mbr" (see Section 7.1). o 'sec-gp', specifying the name of the security group of interest, as a stable and invariant identifier, such as the group name used in [I-D.ietf-ace-key-groupcomm-oscore]. This parameter MUST specify a single value. o 'app-gp', specifying the name(s) of the application group(s) associated to the security group of interest indicated by 'sec- gp'. This parameter MUST occur once for each application group, and MUST specify only a single application group. Optionally, the following parameters can also be specified. o 'cs_alg', specifying the algorithm used to countersign messages in the security group. If present, this parameter MUST specify a Tiloca, et al. Expires January 14, 2021 [Page 6] Internet-Draft OSCORE group discovery with the CoRE RD July 2020 single value encoded as a text string, which is taken from the 'Value' column of the "COSE Algorithms" Registry [COSE.Algorithms]. o 'cs_alg_crv', specifying the elliptic curve (if applicable) for the algorithm used to countersign messages in the security group. If present, this parameter MUST specify a single value encoded as a text string, which is taken from the 'Value' column of the "COSE Elliptic Curves" Registry [COSE.Elliptic.Curves]. o 'cs_key_kty', specifying the key type of countersignature keys used to countersign messages in the security group. If present, this parameter MUST specify a single value encoded as a text string, which is taken from the 'Value' column of the "COSE Key Types" Registry [COSE.Key.Types]. o 'cs_key_crv', specifying the elliptic curve (if applicable) of countersignature keys used to countersign messages in the security group. If present, this parameter MUST specify a single value encoded as a text string, which is taken from the 'Value' column of the "COSE Elliptic Curves" Registry defined in [COSE.Elliptic.Curves]. o 'cs_kenc', specifying the encoding of the public keys used in the security group. If present, this parameter MUST specify a single value encoded as a text string. This specification explicitly admits the signaling of COSE Keys [I-D.ietf-cose-rfc8152bis-struct] as encoding for public keys, which is indicated with "1", as taken from the 'Confirmation Key' column of the "CWT Confirmation Method" Registry defined in [RFC8747]. Future specifications may define additional values for this parameter. o 'alg', specifying the AEAD algorithm used in the security group. If present, this parameter MUST specify a single value encoded as a text string, which is taken from the 'Value' column of the "COSE Algorithms" Registry [COSE.Algorithms]. o 'hkdf', specifying the HKDF algorithm used in the security group. If present, this parameter MUST specify a single value encoded as a text string, which is taken from the 'Value' column of the "COSE Algorithms" Registry defined in [COSE.Algorithms]. Note that the values registered in the COSE Registries [COSE.Algorithms][COSE.Elliptic.Curves][COSE.Key.Types] are strongly typed. On the contrary, Link Format is weakly typed and thus does not distinguish between, for instance, the string value "-10" and the integer value -10. Tiloca, et al. Expires January 14, 2021 [Page 7] Internet-Draft OSCORE group discovery with the CoRE RD July 2020 Therefore, in the RD defined in [I-D.ietf-core-resource-directory] and based on Link Format, possible values registered as a string that looks like an integer, e.g. the string "-10" in the 'Value' column of the "COSE Algorithms" Registry [COSE.Algorithms], are not supported by this approach. Therefore, they MUST NOT be advertised through the corresponding parameters above. A CoAP endpoint that queries the RD to discover security groups and their group-membership resource to access (see Section 4) would benefit from the information above as follows. o The values of 'cs_alg', 'cs_alg_crv', 'cs_key_kty', 'cs_key_crv' and 'cs_kenc' related to a group-membership resource provide an early knowledge of the format and encoding of public keys used in the security group. Thus, the CoAP endpoint does not need to ask the GM for this information as a preliminary step before the joining process, or to perform a trial-and-error joining exchange with the GM. Hence, the CoAP endpoint is able to provide the GM with its own public key in the correct expected format and encoding at the very first step of the joining process. o The values of 'cs_alg', 'alg' and 'hkdf' related to a group- membership resource provide an early knowledge of the algorithms used in the security group. Thus, the CoAP endpoint is able to decide whether to actually proceed with the joining process, depending on its support for the indicated algorithms. 2.2. Relation Link to Authorization Server For each registered link to a group-membership resource, the GM MAY additionally specify the link to the ACE Authorization Server (AS) [I-D.ietf-ace-oauth-authz] associated to the GM, and issuing authorization credentials to join the security group as described in [I-D.ietf-ace-key-groupcomm-oscore]. The link to the AS has as target the URI of the resource where to send an authorization request to. In the RD defined in [I-D.ietf-core-resource-directory] and based on Link Format, the link to the AS is separately registered with the RD, and includes the following parameters as target attributes. o 'rel', with value "authorization_server". o 'anchor', with value the target of the link to the group- membership resource at the GM. Tiloca, et al. Expires January 14, 2021 [Page 8] Internet-Draft OSCORE group discovery with the CoRE RD July 2020 In an RD based on CoRAL, such as the one defined in [I-D.hartke-t2trg-coral-reef], this is mapped (as describe there) to a link from the registration resource to the AS, using the link relation type. 2.3. Registration Example The example below shows a GM with endpoint name "gm1" and address 2001:db8::ab that registers with the RD. The GM specifies the value of the 'sec-gp' parameter for accessing the security group with name "feedca570000", and used by the application group with name "group1" specified with the value of the 'app-gp' parameter. The countersignature algorithm used in the security group is EdDSA, with elliptic curve Ed25519 and keys of type OKP. Public keys used in the security group are encoded as COSE Keys [I-D.ietf-cose-rfc8152bis-struct]. In addition, the GM specifies the link to the ACE Authorization Server associated to the GM, to which a CoAP endpoint should send an Authorization Request for joining the corresponding security group [I-D.ietf-ace-key-groupcomm-oscore]. 2.3.1. Example in Link Format Request: GM -> RD Req: POST coap://rd.example.com/rd?ep=gm1 Content-Format: 40 Payload: ;ct=41;rt="core.osc.mbr"; sec-gp="feedca570000";app-gp="group1"; cs_alg="-8";cs_alg_crv="6"; cs_key_kty="1";cs_key_crv=6"; cs_kenc="1", ; rel="authorization-server"; anchor="coap://[2001:db8::ab]/group-oscore/feedca570000" Response: RD -> GM Res: 2.01 Created Location-Path: /rd/4521 Tiloca, et al. Expires January 14, 2021 [Page 9] Internet-Draft OSCORE group discovery with the CoRE RD July 2020 2.3.2. Example in CoRAL Request: GM -> RD Req: POST coap://rd.example.com/rd?ep=gm1 Content-Format: TBD123456 (application/coral+cbor) Payload: #using #using reef = #using iana = #base reef:rd-item { reef:rt "core.osc.mbr" sec-gp "feedca570000" app-gp "group1" cs_alg -8 cs_alg_crv 6 cs_key_kty 1 cs_key_crv 6 cs_kenc 1 iana:authorization-server } Response: RD -> GM Res: 2.01 Created Location-Path: /rd/4521 3. Addition and Update of Security Groups The GM is responsible to refresh the registration of all its group- membership resources in the RD. This means that the GM has to update the registration within its lifetime as per Section 5.3.1 of [I-D.ietf-core-resource-directory], and has to change the content of the registration when a group-membership resource is added/removed, or if its parameters have to be changed, such as in the following cases. o The GM creates a new security group and starts exporting the related group-membership resource. o The GM dismisses an security group and stops exporting the related group-membership resource. o Information related to an existing security group changes, e.g. the list of associated application groups. Tiloca, et al. Expires January 14, 2021 [Page 10] Internet-Draft OSCORE group discovery with the CoRE RD July 2020 To perform an update of its registrations, the GM can re-register with the RD and fully specify all links to its group-membership resources. Alternatively, the GM can perform a PATCH/iPATCH [RFC8132] request to the RD, as per Section 5.3.3 of [I-D.ietf-core-resource-directory]. This requires new media-types to be defined in future standards, to apply a new document as a patch to an existing stored document. 3.1. Addition Example The example below shows how the GM from Section 2 re-registers with the RD. When doing so, it specifies: o The same previous group-membership resource associated to the security group with name "feedca570000". o An additional group-membership resource associated to the security group with name "ech0ech00000" and used by the application group "group2". o A third group-membership resource associated with the security group with name "abcdef120000" and used by two application groups, namely "group3" and "group4". Furthermore, the GM relates the same Authorization Server also to the security groups "ech0ech00000" and "abcdef120000". 3.1.1. Example in Link Format Request: GM -> RD Tiloca, et al. Expires January 14, 2021 [Page 11] Internet-Draft OSCORE group discovery with the CoRE RD July 2020 Req: POST coap://rd.example.com/rd?ep=gm1 Content-Format: 40 Payload: ;ct=41;rt="core.osc.mbr"; sec-gp="feedca570000";app-gp="group1"; cs_alg="-8";cs_alg_crv="6"; cs_key_kty="1";cs_key_crv=6"; cs_kenc="1", ;ct=41;rt="core.osc.mbr"; sec-gp="ech0ech00000";app-gp="group2"; cs_alg="-8";cs_alg_crv="6"; cs_key_kty="1";cs_key_crv=6"; cs_kenc="1", ;ct=41;rt="core.osc.mbr"; sec-gp="abcdef120000";app-gp="group3"; app-gp="group4";cs_alg="-8"; cs_alg_crv="6";cs_key_kty="1"; cs_key_crv=6";cs_kenc="1", ; rel="authorization-server"; anchor="coap://[2001:db8::ab]/group-oscore/feedca570000", ; rel="authorization-server"; anchor="coap://[2001:db8::ab]/group-oscore/ech0ech00000", ; rel="authorization-server"; anchor="coap://[2001:db8::ab]/group-oscore/abcdef120000" Response: RD -> GM Res: 2.04 Changed Location-Path: /rd/4521 3.1.2. Example in CoRAL Request: GM -> RD Tiloca, et al. Expires January 14, 2021 [Page 12] Internet-Draft OSCORE group discovery with the CoRE RD July 2020 Req: POST coap://rd.example.com/rd?ep=gm1 Content-Format: TBD123456 (application/coral+cbor) Payload: #using #using reef = #using iana = #base reef:rd-item { reef:rt "core.osc.mbr" sec-gp "feedca570000" app-gp "group1" cs_alg -8 cs_alg_crv 6 cs_key_kty 1 cs_key_crv 6 cs_kenc 1 iana:authorization-server } reef:rd-item { reef:rt "core.osc.mbr" sec-gp "ech0ech00000" app-gp "group2" cs_alg -8 cs_alg_crv 6 cs_key_kty 1 cs_key_crv 6 cs_kenc 1 iana:authorization-server } reef:rd-item { reef:rt "core.osc.mbr" sec-gp "abcdef120000" app-gp "group3" app-gp "group4" cs_alg -8 cs_alg_crv 6 cs_key_kty 1 cs_key_crv 6 cs_kenc 1 iana:authorization-server } Response: RD -> GM Res: 2.04 Changed Location-Path: /rd/4521 Tiloca, et al. Expires January 14, 2021 [Page 13] Internet-Draft OSCORE group discovery with the CoRE RD July 2020 4. Discovery of Security Groups A CoAP endpoint that wants to join a security group, hereafter called the joining node, might not have all the necessary information at deployment time. Also, it might want to know about possible new security groups created afterwards by the respective Group Managers. To this end, the joining node can perform a resource lookup at the RD as per Section 6.1 of [I-D.ietf-core-resource-directory], to retrieve the missing pieces of information needed to join the security group(s) of interest. The joining node can find the RD as described in Section 4 of [I-D.ietf-core-resource-directory]. The joining node uses the following parameter value for the lookup filtering. o 'rt' = "core.osc.mbr" (see Section 7.1). The joining node may additionally consider the following parameters for the lookup filtering, depending on the information it has already available. o 'sec-gp', specifying the name of the security group of interest. This parameter MUST specify a single value. o 'ep', specifying the registered endpoint of the GM. o 'app-gp', specifying the name(s) of the application group(s) associated with the security group of interest. This parameter MAY be included multiple times, and each occurrence MUST specify the name of one application group. The response from the RD may include links to a group-membership resource specifying multiple application groups, as all using the same security group. In this case, the joining node is already expected to know the exact application group of interest. Furthermore, the response from the RD may include the links to different group-membership resources, all specifying a same application group of interest for the joining node, if the corresponding security groups are all used by that application group. In this case, application policies on the joining node should define how to determine the exact security group to join, depending on what exactly the endpoint is intended to do in the application group of interest. Later on, the joining node will be anyway able to join only security groups for which it is actually authorized to be a member (see [I-D.ietf-ace-key-groupcomm-oscore]). Tiloca, et al. Expires January 14, 2021 [Page 14] Internet-Draft OSCORE group discovery with the CoRE RD July 2020 Note that, with RD-based discovery, including the 'app-gp' parameter multiple times would result in finding only the group-membership resource that serves all the specified application groups, i.e. not any group-membership resource that serves either. Therefore, a joining node needs to perform N separate queries with different values for 'app-gp', in order to safely discover the (different) group-membership resource(s) serving the N application groups. 4.1. Discovery Example #1 Consistently with the examples in Section 2 and Section 3, the examples below consider a joining node that wants to join the security group associated with the application group "group1", but that does not know the name of the security group, the responsible GM and the group-membership resource to access. 4.1.1. Example in Link Format Request: Joining node -> RD Req: GET coap://rd.example.com/rd-lookup/res ?rt=core.osc.mbr&app-gp=group1 Response: RD -> Joining node Res: 2.05 Content Payload: ;rt="core.osc.mbr"; sec-gp="feedca570000";app-gp="group1"; cs_alg="-8";cs_alg_crv="6";cs_key_kty="1"; cs_key_crv=6";cs_kenc="1";anchor="coap://[2001:db8::ab]" To retrieve the multicast IP address of the CoAP group used by the application group "group1", the joining node performs an endpoint lookup as shown below. The following assumes that the application group "group1" had been previously registered as per Appendix A of [I-D.ietf-core-resource-directory], with ff35:30:2001:db8::23 as multicast IP address of the associated CoAP group. Request: Joining node -> RD Req: GET coap://rd.example.com/rd-lookup/ep ?et=core.rd-group&ep=group1 Response: RD -> Joining node Tiloca, et al. Expires January 14, 2021 [Page 15] Internet-Draft OSCORE group discovery with the CoRE RD July 2020 Res: 2.05 Content Payload: ;ep="group1";et="core.rd-group"; base="coap://[ff35:30:2001:db8::23]" 4.1.2. Example in CoRAL Request: Joining node -> RD Req: GET coap://rd.example.com/rd-lookup/res ?rt=core.osc.mbr&app-gp=group1 Accept: TBD123456 (application/coral+cbor) Response: RD -> Joining node Res: 2.05 Content Content-Format: TBD123456 (application/coral+cbor) Payload: #using #using reef = #using iana = #base reef:rd-item { reef:rt "core.osc.mbr" sec-gp "feedca570000" app-gp "group1" cs_alg -8 cs_alg_crv 6 cs_key_kty 1 cs_key_crv 6 cs_kenc 1 iana:authorization-server } To retrieve the multicast IP address of the CoAP group used by the application group "group1", the joining node performs an endpoint lookup as shown below. The following assumes that the application group "group1" had been previously registered, with ff35:30:2001:db8::23 as multicast IP address of the associated CoAP group. Request: Joining node -> RD Req: GET coap://rd.example.com/rd-lookup/ep ?et=core.rd-group&ep=group1 Accept: TBD123456 (application/coral+cbor) Tiloca, et al. Expires January 14, 2021 [Page 16] Internet-Draft OSCORE group discovery with the CoRE RD July 2020 Response: RD -> Joining node Res: 2.05 Content Content-Format: TBD123456 (application/coral+cbor) Payload: #using #using reef = reef:rd-unit <./rd/501> { reef:ep="group1" reef:et="core.rd-group" reef:base } 4.2. Discovery Example #2 Consistently with the examples in Section 2 and Section 3, the examples below consider a joining node that wants to join the security group with name "feedca570000", but that does not know the responsible GM, the group-membership resource to access, and the associated application groups. The examples also show how the joining node uses CoAP observation [RFC7641], in order to be notified of possible changes to the parameters of the group-membership resource. This is also useful to handle the case where the security group of interest has not been created yet, so that the joining node can receive the requested information when it becomes available. 4.2.1. Example in Link Format Request: Joining node -> RD Req: GET coap://rd.example.com/rd-lookup/res ?rt=core.osc.mbr&sec-gp=feedca570000 Observe: 0 Response: RD -> Joining node Res: 2.05 Content Observe: 24 Payload: ;rt="core.osc.mbr"; sec-gp="feedca570000";app-gp="group1"; cs_alg="-8";cs_alg_crv="6";cs_key_kty="1"; cs_key_crv=6";cs_kenc="1";anchor="coap://[2001:db8::ab]" Tiloca, et al. Expires January 14, 2021 [Page 17] Internet-Draft OSCORE group discovery with the CoRE RD July 2020 Depending on the search criteria, the joining node performing the resource lookup can get large responses. This can happen, for instance, when the lookup request targets all the group-membership resources at a specified GM, or all the group-membership resources of all the registered GMs, as in the example below. Request: Joining node -> RD Req: GET coap://rd.example.com/rd-lookup/res?rt=core.osc.mbr Response: RD -> Joining node Res: 2.05 Content Payload: ;rt="core.osc.mbr"; sec-gp="feedca570000";app-gp="group1"; cs_alg="-8";cs_alg_crv="6";cs_key_kty="1"; cs_key_crv=6";cs_kenc="1";anchor="coap://[2001:db8::ab]", ;rt="core.osc.mbr"; sec-gp="ech0ech00000";app-gp="group2"; cs_alg="-8";cs_alg_crv="6";cs_key_kty="1"; cs_key_crv=6";cs_kenc="1";anchor="coap://[2001:db8::ab]", ;rt="core.osc.mbr"; sec-gp="abcdef120000";app-gp="group3"; app-gp="group4";cs_alg="-8";cs_alg_crv="6"; cs_key_kty="1";cs_key_crv=6";cs_kenc="1"; anchor="coap://[2001:db8::ab]" Therefore, it is RECOMMENDED that a joining node which performs a resource lookup with the CoAP Observe option specifies the value of the parameter 'sec-gp' in its GET request sent to the RD. 4.2.2. Example in CoRAL Request: Joining node -> RD Req: GET coap://rd.example.com/rd-lookup/res ?rt=core.osc.mbr&sec-gp=feedca570000 Accept: TBD123456 (application/coral+cbor) Observe: 0 Response: RD -> Joining node Tiloca, et al. Expires January 14, 2021 [Page 18] Internet-Draft OSCORE group discovery with the CoRE RD July 2020 Res: 2.05 Content Observe: 24 Content-Format: TBD123456 (application/coral+cbor) Payload: #using #using reef = #using iana = #base reef:rd-item { reef:rt "core.osc.mbr" sec-gp "feedca570000" app-gp "group1" cs_alg -8 cs_alg_crv 6 cs_key_kty 1 cs_key_crv 6 cs_kenc 1 iana:authorization-server } 5. Use Case Example With Full Discovery In this section, the discovery of security groups is described to support the installation process of a lighting installation in an office building. The described process is a simplified version of one of many processes. The process described in this section is intended as an example and does not have any particular ambition to serve as recommendation or best practice to adopt. That is, it shows a possible workflow involving a Commissioning Tool (CT) used in a certain way, while it is not meant to prescribe how the workflow should necessarily be. Assume the existence of four luminaires that are members of two application groups. In the first application group, the four luminaires receive presence messages and light intensity messages from sensors or their proxy. In the second application group, the four luminaires and several other pieces of equipment receive building state schedules. Each of the two application groups is associated to a different security group and to a different CoAP group with its own dedicated multicast IP address. The Fairhair Alliance describes how a new device is accepted and commissioned in the network [Fairhair], by means of its certificate Tiloca, et al. Expires January 14, 2021 [Page 19] Internet-Draft OSCORE group discovery with the CoRE RD July 2020 stored during the manufacturing process. When commissioning the new device in the installation network, the new device gets a new identity defined by a newly allocated certificate, following the BRSKI specification. Section 7.3 of [I-D.ietf-core-resource-directory] describes how the CT assigns an endpoint name based on the CN field, (CN=ACME) and the serial number of the certificate (serial number = 123x, with 3 < x < 8). Corresponding ep-names ACME-1234, ACME-1235, ACME-1236 and ACME-1237 are also assumed. It is common practice that locations in the building are specified according to a coordinate system. After the acceptance of the luminaires into the installation network, the coordinate of each device is communicated to the CT. This can be done manually or automatically. The mapping between location and ep-name is calculated by the CT. For instance, on the basis of grouping criteria, the CT assigns: i) application group "grp_R2-4-015" to the four luminaires; and ii) application group "grp_schedule" to all schedule requiring devices. Also, the device with ep name ACME-123x has been assigned IP address: [2001:db8:4::x]. The RD is assigned IP address: [2001:db8:4:ff]. The used multicast addresses are: [ff05::5:1] and [ff05::5:2]. The following assumes that each device is pre-configured with the name of the two application groups it belongs to. Additional mechanisms can be defined in the RD, for supporting devices to discover the application groups they belong to. Appendix A provides this same use case example in CoRAL. *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** The CT defines the application group "grp_R2-4-015", with resource /light and base address [ff05::5:1], as follows. Request: CT -> RD Req: POST coap://[2001:db8:4::ff]/rd ?ep=grp_R2-4-015&et=core.rd-group&base=coap://[ff05::5:1] Content-Format: 40 Payload: ;rt="oic.d.light" Response: RD -> CT Tiloca, et al. Expires January 14, 2021 [Page 20] Internet-Draft OSCORE group discovery with the CoRE RD July 2020 Res: 2.01 Created Location-Path: /rd/501 Also, the CT defines a second application group "grp_schedule", with resource /schedule and base address [ff05::5:2], as follows. Request: CT -> RD Req: POST coap://[2001:db8:4::ff]/rd ?ep=grp_schedule&et=core.rd-group&base=coap://[ff05::5:2] Content-Format: 40 Payload: ;rt="oic.r.time.period" Response: RD -> CT Res: 2.01 Created Location-Path: /rd/502 *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** Finally, the CT defines the corresponding security groups. In particular, assuming a Group Manager responsible for both security groups and with address [2001:db8::ab], the CT specifies: Request: CT -> RD Req: POST coap://[2001:db8:4::ff]/rd ?ep=gm1&base=coap://[2001:db8::ab] Content-Format: 40 Payload: ;ct=41;rt="core.osc.mbr"; sec-gp="feedca570000"; app-gp="grp_R2-4-015", ;ct=41;rt="core.osc.mbr"; sec-gp="feedsc590000"; app-gp="grp_schedule" Response: RD -> CT Res: 2.01 Created Location-Path: /rd/4521 *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** The device with IP address [2001:db8:4::x] can retrieve the multicast IP address of the CoAP group used by the application group "grp_R2-4-015", by performing an endpoint lookup as shown below. Tiloca, et al. Expires January 14, 2021 [Page 21] Internet-Draft OSCORE group discovery with the CoRE RD July 2020 Request: Joining node -> RD Req: GET coap://[2001:db8:4::ff]/rd-lookup/ep ?et=core.rd-group&ep=grp_R2-4-015 Response: RD -> Joining node Res: 2.05 Content Content-Format: 40 Payload: ;ep="grp_R2-4-015";et="core.rd-group"; base="coap://[ff05::5:1]" Similarly, to retrieve the multicast IP address of the CoAP group used by the application group "grp_schedule", the device performs an endpoint lookup as shown below. Request: Joining node -> RD Req: GET coap://[2001:db8:4::ff]/rd-lookup/ep ?et=core.rd-group&ep=grp_schedule Response: RD -> Joining node Res: 2.05 Content Content-Format: 40 Payload: ;ep="grp_schedule";et="core.rd-group"; base="coap://[ff05::5:2]" *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** Consequently, the device learns the security groups it has to join. In particular, it does the following for app-gp="grp_R2-4-015". Request: Joining node -> RD Req: GET coap://[2001:db8:4::ff]/rd-lookup/res ?rt=core.osc.mbr&app-gp=grp_R2-4-015 Response: RD -> Joining Node Res: 2.05 Content Content-Format: 40 Payload: ; rt="core.osc.mbr";sec-gp="feedca570000"; app-gp="grp_R2-4-015";anchor="coap://[2001:db8::ab]" Tiloca, et al. Expires January 14, 2021 [Page 22] Internet-Draft OSCORE group discovery with the CoRE RD July 2020 Similarly, the device does the following for app-gp="grp_schedule". Req: GET coap://[2001:db8:4::ff]/rd-lookup/res ?rt=core.osc.mbr&app-gp=grp_schedule Response: RD -> Joining Node Res: 2.05 Content Content-Format: 40 Payload: ; rt="core.osc.mbr";sec-gp="feedsc590000"; app-gp="grp_schedule";anchor="coap://[2001:db8::ab]" *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** After this last discovery step, the device can ask permission to join the security groups, and effectively join them through the Group Manager, e.g. according to [I-D.ietf-ace-key-groupcomm-oscore]. 6. Security Considerations The security considerations as described in Section 8 of [I-D.ietf-core-resource-directory] apply here as well. 7. IANA Considerations This document has the following actions for IANA. 7.1. Resource Types IANA is asked to enter the following value into the Resource Type (rt=) Link Target Attribute Values subregistry within the Constrained Restful Environments (CoRE) Parameters registry defined in [RFC6690]. +--------------+----------------------------+-------------------+ | Value | Description | Reference | +--------------+----------------------------+-------------------+ | | | | | core.osc.mbr | Group-membership resource | [[this document]] | | | of an OSCORE Group Manager | | | | | | +--------------+----------------------------+-------------------+ Tiloca, et al. Expires January 14, 2021 [Page 23] Internet-Draft OSCORE group discovery with the CoRE RD July 2020 8. References 8.1. Normative References [COSE.Algorithms] IANA, "COSE Algorithms", . [COSE.Elliptic.Curves] IANA, "COSE Elliptic Curves", . [COSE.Key.Types] IANA, "COSE Key Types", . [I-D.ietf-core-coral] Hartke, K., "The Constrained RESTful Application Language (CoRAL)", draft-ietf-core-coral-03 (work in progress), March 2020. [I-D.ietf-core-groupcomm-bis] Dijk, E., Wang, C., and M. Tiloca, "Group Communication for the Constrained Application Protocol (CoAP)", draft- ietf-core-groupcomm-bis-00 (work in progress), March 2020. [I-D.ietf-core-oscore-groupcomm] Tiloca, M., Selander, G., Palombini, F., and J. Park, "Group OSCORE - Secure Group Communication for CoAP", draft-ietf-core-oscore-groupcomm-09 (work in progress), June 2020. [I-D.ietf-core-resource-directory] Shelby, Z., Koster, M., Bormann, C., Stok, P., and C. Amsuess, "CoRE Resource Directory", draft-ietf-core- resource-directory-24 (work in progress), March 2020. [I-D.ietf-cose-rfc8152bis-algs] Schaad, J., "CBOR Object Signing and Encryption (COSE): Initial Algorithms", draft-ietf-cose-rfc8152bis-algs-11 (work in progress), July 2020. Tiloca, et al. Expires January 14, 2021 [Page 24] Internet-Draft OSCORE group discovery with the CoRE RD July 2020 [I-D.ietf-cose-rfc8152bis-struct] Schaad, J., "CBOR Object Signing and Encryption (COSE): Structures and Process", draft-ietf-cose-rfc8152bis- struct-11 (work in progress), July 2020. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link Format", RFC 6690, DOI 10.17487/RFC6690, August 2012, . [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained Application Protocol (CoAP)", RFC 7252, DOI 10.17487/RFC7252, June 2014, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8747] Jones, M., Seitz, L., Selander, G., Erdtman, S., and H. Tschofenig, "Proof-of-Possession Key Semantics for CBOR Web Tokens (CWTs)", RFC 8747, DOI 10.17487/RFC8747, March 2020, . 8.2. Informative References [Fairhair] FairHair Alliance, "Security Architecture for the Internet of Things (IoT) in Commercial Buildings", White Paper, ed. Piotr Polak , March 2018, . [I-D.hartke-t2trg-coral-reef] Hartke, K., "Resource Discovery in Constrained RESTful Environments (CoRE) using the Constrained RESTful Application Language (CoRAL)", draft-hartke-t2trg-coral- reef-04 (work in progress), May 2020. [I-D.ietf-ace-key-groupcomm-oscore] Tiloca, M., Park, J., and F. Palombini, "Key Management for OSCORE Groups in ACE", draft-ietf-ace-key-groupcomm- oscore-07 (work in progress), June 2020. Tiloca, et al. Expires January 14, 2021 [Page 25] Internet-Draft OSCORE group discovery with the CoRE RD July 2020 [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-35 (work in progress), June 2020. [I-D.ietf-anima-bootstrapping-keyinfra] Pritikin, M., Richardson, M., Eckert, T., Behringer, M., and K. Watsen, "Bootstrapping Remote Secure Key Infrastructures (BRSKI)", draft-ietf-anima-bootstrapping- keyinfra-41 (work in progress), April 2020. [RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049, October 2013, . [RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for Constrained-Node Networks", RFC 7228, DOI 10.17487/RFC7228, May 2014, . [RFC7641] Hartke, K., "Observing Resources in the Constrained Application Protocol (CoAP)", RFC 7641, DOI 10.17487/RFC7641, September 2015, . [RFC8132] van der Stok, P., Bormann, C., and A. Sehgal, "PATCH and FETCH Methods for the Constrained Application Protocol (CoAP)", RFC 8132, DOI 10.17487/RFC8132, April 2017, . [RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data Interchange Format", STD 90, RFC 8259, DOI 10.17487/RFC8259, December 2017, . [RFC8613] Selander, G., Mattsson, J., Palombini, F., and L. Seitz, "Object Security for Constrained RESTful Environments (OSCORE)", RFC 8613, DOI 10.17487/RFC8613, July 2019, . Appendix A. Use Case Example With Full Discovery (CoRAL) This section provides the same use case example of Section 5, but specified in CoRAL [I-D.ietf-core-coral]. *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** Tiloca, et al. Expires January 14, 2021 [Page 26] Internet-Draft OSCORE group discovery with the CoRE RD July 2020 The CT defines the application group "grp_R2-4-015", with resource /light and base address [ff05::5:1], as follows. Request: CT -> RD Req: POST coap://[2001:db8:4::ff]/rd Content-Format: TBD123456 (application/coral+cbor) Payload: #using reef = #base reef:ep "grp_R2-4-015" reef:et "core.rd-group" reef:rd-item { reef:rt "oic.d.light" } Response: RD -> CT Res: 2.01 Created Location-Path: /rd/501 Also, the CT defines a second application group "grp_schedule", with resource /schedule and base address [ff05::5:2], as follows. Request: CT -> RD Req: POST coap://[2001:db8:4::ff]/rd?ep=grp_schedule&et=core.rd-group Content-Format: TBD123456 (application/coral+cbor) Payload: #using reef = #base reef:rd-item { reef:rt "oic.r.time.period" } Response: RD -> CT Res: 2.01 Created Location-Path: /rd/502 *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** Tiloca, et al. Expires January 14, 2021 [Page 27] Internet-Draft OSCORE group discovery with the CoRE RD July 2020 Finally, the CT defines the corresponding security groups. In particular, assuming a Group Manager responsible for both security groups and with address [2001:db8::ab], the CT specifies: Request: CT -> RD Req: POST coap://[2001:db8:4::ff]/rd?ep=gm1 Content-Format: TBD123456 (application/coral+cbor) Payload: #using #using reef = #base reef:rd-item { reef:ct 41 reef:rt "core.osc.mbr" sec-gp "feedca570000" app-gp "grp_R2-4-015" } reef:rd-item { reef:ct 41 reef:rt "core.osc.mbr" sec-gp "feedsc590000" app-gp "grp_schedule" } Response: RD -> CT Res: 2.01 Created Location-Path: /rd/4521 *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** The device with IP address [2001:db8:4::x] can retrieve the multicast IP address of the CoAP group used by the application group "grp_R2-4-015", by performing an endpoint lookup as shown below. Request: Joining node -> RD Req: GET coap://[2001:db8:4::ff]/rd-lookup/ep ?et=core.rd-group&ep=grp_R2-4-015 Response: RD -> Joining node Tiloca, et al. Expires January 14, 2021 [Page 28] Internet-Draft OSCORE group discovery with the CoRE RD July 2020 Res: 2.05 Content Content-Format: TBD123456 (application/coral+cbor) Payload: #using reef = #base reef:rd-unit <501> { reef:ep "grp_R2-4-015" reef:et "core.rd-group" reef:base } Similarly, to retrieve the multicast IP address of the CoAP group used by the application group "grp_schedule", the device performs an endpoint lookup as shown below. Request: Joining node -> RD Req: GET coap://[2001:db8:4::ff]/rd-lookup/ep ?et=core.rd-group&ep=grp_schedule Response: RD -> Joining node Res: 2.05 Content Content-Format: TBD123456 (application/coral+cbor) Payload: #using reef = #base reef:rd-unit <501> { reef:ep "grp_schedule" reef:et "core.rd-group" reef:base } *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** Consequently, the device learns the security groups it has to join. In particular, it does the following for app-gp="grp_R2-4-015". Request: Joining node -> RD Req: GET coap://[2001:db8:4::ff]/rd-lookup/res ?rt=core.osc.mbr&app-gp=grp_R2-4-015 Response: RD -> Joining Node Tiloca, et al. Expires January 14, 2021 [Page 29] Internet-Draft OSCORE group discovery with the CoRE RD July 2020 Res: 2.05 Content Content-Format: TBD123456 (application/coral+cbor) Payload: #using #using reef = #base reef:rd-item { reef:rt "core.osc.mbr" sec-gp "feedca570000" app-gp "grp_R2-4-015" } Similarly, the device does the following for app-gp="grp_schedule". Req: GET coap://[2001:db8:4::ff]/rd-lookup/res ?rt=core.osc.mbr&app-gp=grp_schedule Response: RD -> Joining Node Res: 2.05 Content Content-Format: TBD123456 (application/coral+cbor) Payload: #using #using reef = #base reef:rd-item { reef:rt "core.osc.mbr" sec-gp "feedsc590000" app-gp "grp_schedule" } *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** After this last discovery step, the device can ask permission to join the security groups, and effectively join them through the Group Manager, e.g. according to [I-D.ietf-ace-key-groupcomm-oscore]. Acknowledgments The authors sincerely thank Carsten Bormann, Klaus Hartke, Jaime Jimenez, Francesca Palombini, Dave Robin and Jim Schaad for their comments and feedback. Tiloca, et al. Expires January 14, 2021 [Page 30] Internet-Draft OSCORE group discovery with the CoRE RD July 2020 The work on this document has been partly supported by VINNOVA and the Celtic-Next project CRITISEC, and by the EIT-Digital High Impact Initiative ACTIVE. Authors' Addresses Marco Tiloca RISE AB Isafjordsgatan 22 Kista SE-16440 Stockholm Sweden Email: marco.tiloca@ri.se Christian Amsuess Hollandstr. 12/4 Vienna 1020 Austria Email: christian@amsuess.com Peter van der Stok Consultant Phone: +31-492474673 (Netherlands), +33-966015248 (France) Email: consultancy@vanderstok.org URI: www.vanderstok.org Tiloca, et al. Expires January 14, 2021 [Page 31]