| Internet-Draft | Using EDHOC with CoAP and OSCORE | August 2023 |
| Palombini, et al. | Expires 9 February 2024 | [Page] |
The lightweight authenticated key exchange protocol EDHOC can be run over CoAP and used by two peers to establish an OSCORE Security Context. This document details this use of the EDHOC protocol, by specifying a number of additional and optional mechanisms. These especially include an optimization approach for combining the execution of EDHOC with the first OSCORE transaction. This combination reduces the number of round trips required to set up an OSCORE Security Context and to complete an OSCORE transaction using that Security Context.¶
This note is to be removed before publishing as an RFC.¶
Discussion of this document takes place on the Constrained RESTful Environments Working Group mailing list (core@ietf.org), which is archived at https://mailarchive.ietf.org/arch/browse/core/.¶
Source for this draft and an issue tracker can be found at https://github.com/core-wg/oscore-edhoc.¶
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Ephemeral Diffie-Hellman Over COSE (EDHOC) [I-D.ietf-lake-edhoc] is a lightweight authenticated key exchange protocol, especially intended for use in constrained scenarios. In particular, EDHOC messages can be transported over the Constrained Application Protocol (CoAP) [RFC7252] and used for establishing a Security Context for Object Security for Constrained RESTful Environments (OSCORE) [RFC8613].¶
This document details this use of the EDHOC protocol, and specifies a number of additional and optional mechanisms. These especially include an optimization approach that combines the EDHOC execution with the first OSCORE transaction (see Section 3). This allows for a minimum number of round trips necessary to setup the OSCORE Security Context and complete an OSCORE transaction, e.g., when an IoT device gets configured in a network for the first time.¶
This optimization is desirable, since the number of protocol round trips influences the minimum number of flights, which in turn can have a substantial impact on the latency of conveying the first OSCORE request, when using certain radio technologies.¶
Without this optimization, it is not possible, not even in theory, to achieve the minimum number of flights. This optimization makes it possible also in practice, since the last message of the EDHOC protocol can be made relatively small (see Section 1.2 of [I-D.ietf-lake-edhoc]), thus allowing additional OSCORE-protected CoAP data within target MTU sizes.¶
Furthermore, this document defines a number of parameters corresponding to different information elements of an EDHOC application profile (see Section 6). These can be specified as target attributes in the link to an EDHOC resource associated with that application profile, thus enabling an enhanced discovery of such a resource for CoAP clients.¶
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶
The reader is expected to be familiar with terms and concepts defined in CoAP [RFC7252], CBOR [RFC8949], OSCORE [RFC8613], and EDHOC [I-D.ietf-lake-edhoc].¶
This section is not normative and summarizes what is specified in [I-D.ietf-lake-edhoc], in particular its Appendix A.2. Thus, it provides a baseline for the enhancements in the subsequent sections.¶
The EDHOC protocol specified in [I-D.ietf-lake-edhoc] allows two peers to agree on a cryptographic secret, in a mutually-authenticated way and by using Diffie-Hellman ephemeral keys to achieve forward secrecy. The two peers are denoted as Initiator and Responder, as the one sending or receiving the initial EDHOC message_1, respectively.¶
After successful processing of EDHOC message_3, both peers agree on a cryptographic secret that can be used to derive further security material, and especially to establish an OSCORE Security Context [RFC8613]. The Responder can also send an optional EDHOC message_4 to achieve key confirmation, e.g., in deployments where no protected application message is sent from the Responder to the Initiator.¶
Appendix A.2 of [I-D.ietf-lake-edhoc] specifies how to transfer EDHOC over CoAP. That is, the EDHOC data (referred to as "EDHOC messages") are transported in the payload of CoAP requests and responses. The default, forward message flow of EDHOC consists in the CoAP client acting as Initiator and the CoAP server acting as Responder. Alternatively, the two roles can be reversed, as per the reverse message flow of EDHOC. In the rest of this document, EDHOC messages are considered to be transferred over CoAP.¶
Figure 1 shows a CoAP client and a CoAP server running EDHOC as Initiator and Responder, respectively. That is, the client sends a POST request to a reserved EDHOC resource at the server, by default at the Uri-Path "/.well-known/edhoc". The request payload consists of the CBOR simple value "true" (0xf5) concatenated with EDHOC message_1, which also includes the EDHOC connection identifier C_I of the client encoded as per Section 3.3 of [I-D.ietf-lake-edhoc]. The Content-Format of the request can be set to application/cid-edhoc+cbor-seq.¶
This triggers the EDHOC execution at the server, which replies with a 2.04 (Changed) response. The response payload consists of EDHOC message_2, which also includes the EDHOC connection identifier C_R of the server encoded as per Section 3.3 of [I-D.ietf-lake-edhoc]. The Content-Format of the response can be set to application/edhoc+cbor-seq.¶
Finally, the client sends a POST request to the same EDHOC resource used earlier to send EDHOC message_1. The request payload consists of the EDHOC connection identifier C_R encoded as per Section 3.3 of [I-D.ietf-lake-edhoc], concatenated with EDHOC message_3. The Content-Format of the request can be set to application/cid-edhoc+cbor-seq.¶
After this exchange takes place, and after successful verifications as specified in the EDHOC protocol, the client and server can derive an OSCORE Security Context, as defined in Appendix A.1 of [I-D.ietf-lake-edhoc]. After that, they can use OSCORE to protect their communications as per [RFC8613].¶
The client and server are required to agree in advance on certain information and parameters describing how they should use EDHOC. These are specified in an application profile associated with the EDHOC resource addressed (see Section 3.9 of [I-D.ietf-lake-edhoc].¶
As shown in Figure 1, this purely-sequential flow where EDHOC is run first and then OSCORE is used takes three round trips to complete.¶
Section 3 defines an optimization for combining EDHOC with the first OSCORE transaction. This reduces the number of round trips required to set up an OSCORE Security Context and to complete an OSCORE transaction using that Security Context.¶
This section defines an optimization for combining the EDHOC message exchange with the first OSCORE transaction, thus minimizing the number of round trips between the two peers.¶
This approach can be used only if the default, forward message flow of EDHOC is used, i.e., when the client acts as Initiator and the server acts as Responder. That is, it cannot be used in the case with reversed roles as per the reverse message flow of EDHOC.¶
When running the purely-sequential flow of Section 2, the client has all the information to derive the OSCORE Security Context already after receiving EDHOC message_2 and before sending EDHOC message_3.¶
Hence, the client can potentially send both EDHOC message_3 and the subsequent OSCORE Request at the same time. On a semantic level, this requires sending two REST requests at once, as in Figure 2.¶
To this end, the specific approach defined in this section consists of sending a single EDHOC + OSCORE request, which conveys the pair (C_R, EDHOC message_3) within an OSCORE-protected CoAP message.¶
That is, the EDHOC + OSCORE request is composed of the following two parts combined together in a single CoAP message:¶
EDHOC data consisting of the pair (C_R, EDHOC message_3) required for completing the EDHOC session. Note that, as specified in Section 3.2, C_R is transported in the OSCORE Option of the OSCORE Request rather than in the CoAP payload of the EDHOC + OSCORE request.¶
Since EDHOC message_3 may be too large to be included in a CoAP Option, e.g., if conveying a large public key certificate chain as ID_CRED_I (see Section 3.5.3 of [I-D.ietf-lake-edhoc]) or if conveying large External Authorization Data as EAD_3 (see Section 3.8 of [I-D.ietf-lake-edhoc]), EDHOC message_3 has instead to be transported in the CoAP payload of the EDHOC + OSCORE request, as prepended to the payload of the OSCORE Request.¶
The rest of this section specifies how to transport the data in the EDHOC + OSCORE request and their processing order. In particular, the use of this approach is explicitly signalled by including an EDHOC Option (see Section 3.1) in the EDHOC + OSCORE request. The processing of the EDHOC + OSCORE request is specified in Section 3.2 for the client side and in Section 3.3 for the server side.¶
This section defines the EDHOC Option. The option is used in a CoAP request, to signal that the request payload conveys both an EDHOC message_3 and OSCORE-protected data, combined together.¶
The EDHOC Option has the properties summarized in Table 1, which extends Table 4 of [RFC7252]. The option is Critical, Safe-to-Forward, and part of the Cache-Key. The option MUST occur at most once and MUST be empty. If any value is sent, the recipient MUST ignore it. (Future documents may update the definition of the option, by expanding its semantics and specifying admitted values.) The option is intended only for CoAP requests and is of Class U for OSCORE [RFC8613].¶
| No. | C | U | N | R | Name | Format | Length | Default |
|---|---|---|---|---|---|---|---|---|
| TBD21 | x | EDHOC | Empty | 0 | (none) |
Note to RFC Editor: Following the registration of the CoAP Option Number 21 as per Section 8.1, please replace "TBD21" with "21" in the figure above. Then, please delete this paragraph.¶
The presence of this option means that the message payload also contains EDHOC data, which must be extracted and processed as defined in Section 3.3, before the rest of the message can be processed.¶
Figure 3 shows an example of a CoAP message transported over UDP and containing both the EDHOC data and the OSCORE ciphertext, using the newly defined EDHOC option for signalling.¶
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Ver| T | TKL | Code | Message ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Token (if any, TKL bytes) ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Observe Option| OSCORE Option ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | EDHOC Option | Other Options (if any) ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |1 1 1 1 1 1 1 1| Payload ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The client prepares an EDHOC + OSCORE request as follows.¶
Establish the new OSCORE Security Context and use it to encrypt the original CoAP request as per Section 8.1 of [RFC8613].¶
Note that the OSCORE ciphertext is not computed over EDHOC message_3, which is not protected by OSCORE. That is, the result of this step is the OSCORE Request as in Figure 1.¶
Build COMB_PAYLOAD as the concatenation of EDHOC_MSG_3 and OSCORE_PAYLOAD in this order: COMB_PAYLOAD = EDHOC_MSG_3 | OSCORE_PAYLOAD, where | denotes byte string concatenation and:¶
Compose the EDHOC + OSCORE request, as the OSCORE-protected CoAP request resulting from step 2, where the payload is replaced with COMB_PAYLOAD built at step 3.¶
Note that the new payload includes EDHOC message_3, but it does not include the EDHOC connection identifier C_R. As the client is the EDHOC Initiator, C_R is the OSCORE Sender ID of the client, which is already specified as 'kid' in the OSCORE Option of the request from step 2, hence of the EDHOC + OSCORE request.¶
Signal the usage of this approach, by including the new EDHOC Option defined in Section 3.1 into the EDHOC + OSCORE request.¶
The application/cid-edhoc+cbor-seq media type does not apply to this message, whose media type is unnamed.¶
With the same server, the client SHOULD NOT have multiple simultaneous outstanding interactions (see Section 4.7 of [RFC7252]) such that: they consist of an EDHOC + OSCORE request; and their EDHOC data pertain to the EDHOC session with the same connection identifier C_R.¶
(An exception might apply for clients that operate under particular time constraints over particularly unreliable networks, thus raising the chances to promptly complete the EDHOC execution with the server through multiple, simultaneous EDHOC + OSCORE requests. As discussed in Section 7, this does not have any impact in terms of security.)¶
If Block-wise [RFC7959] is supported, the client may fragment the first application CoAP request before protecting it as an original message with OSCORE, as defined in Section 4.1.3.4.1 of [RFC8613].¶
In such a case, the OSCORE processing in step 2 of Section 3.2 is performed on each inner block of the first application CoAP request, and the following also applies.¶
The client takes the additional following step between steps 2 and 3 of Section 3.2.¶
A. If the OSCORE-protected request from step 2 conveys a non-first inner block of the first application CoAP request (i.e., the Block1 Option processed at step 2 had NUM different than 0), then the client skips the following steps and sends the OSCORE-protected request to the server. In particular, the client MUST NOT include the EDHOC Option in the OSCORE-protected request.¶
The client takes the additional following step between steps 3 and 4 of Section 3.2.¶
B. If the size of COMB_PAYLOAD exceeds MAX_UNFRAGMENTED_SIZE (see Section 4.1.3.4.2 of [RFC8613]), the client MUST stop processing the request and MUST abandon the Block-wise transfer. Then, the client can continue by switching to the purely sequential workflow shown in Figure 1. That is, the client first sends EDHOC message_3 prepended by the EDHOC Connection Identifier C_R encoded as per Section 3.3 of [I-D.ietf-lake-edhoc], and then sends the OSCORE-protected CoAP request once the EDHOC execution is completed.¶
The performance advantage of using the EDHOC + OSCORE request can be lost when used in combination with Block-wise transfers that rely on specific parameter values and block sizes.¶
In order to process a request containing the EDHOC option, i.e., an EDHOC + OSCORE request, the server MUST perform the following steps.¶
Retrieve the correct EDHOC session by using the connection identifier C_R from step 3.¶
If the application profile used in the EDHOC session specifies that EDHOC message_4 shall be sent, the server MUST stop the EDHOC processing and consider it failed, as due to a client error.¶
Otherwise, perform the EDHOC processing on the EDHOC message_3 extracted at step 2 as per Section 5.4.3 of [I-D.ietf-lake-edhoc], based on the protocol state of the retrieved EDHOC session.¶
The application profile used in the EDHOC session is the same one associated with the EDHOC resource where the server received the request conveying EDHOC message_1 that started the session. This is relevant in case the server provides multiple EDHOC resources, which may generally refer to different application profiles.¶
Decrypt and verify the OSCORE-protected CoAP request rebuilt at step 7, as per Section 8.2 of [RFC8613], by using the OSCORE Security Context established at step 5.¶
When the decrypted request is checked for any critical CoAP options (as it is during regular CoAP processing), the presence of an EDHOC option MUST be regarded as an unprocessed critical option, unless it is processed by some further mechanism.¶
If steps 4 (EDHOC processing) and 8 (OSCORE processing) are both successfully completed, the server MUST reply with an OSCORE-protected response (see Section 5.4.3 of [I-D.ietf-lake-edhoc]). The usage of EDHOC message_4 as defined in Section 5.5 of [I-D.ietf-lake-edhoc] is not applicable to the approach defined in this document.¶
If step 4 (EDHOC processing) fails, the server discontinues the protocol as per Section 5.4.3 of [I-D.ietf-lake-edhoc] and responds with an EDHOC error message with error code 1, formatted as defined in Section 6.2 of [I-D.ietf-lake-edhoc]. The server MUST NOT establish a new OSCORE Security Context from the present EDHOC session with the client, hence the CoAP response conveying the EDHOC error message is not protected with OSCORE. As per Section 8.5 of [I-D.ietf-lake-edhoc], the server has to make sure that the error message does not reveal sensitive information. The CoAP response conveying the EDHOC error message MUST have Content-Format set to application/edhoc+cbor-seq defined in Section 9.9 of [I-D.ietf-lake-edhoc].¶
If step 4 (EDHOC processing) is successfully completed but step 8 (OSCORE processing) fails, the same OSCORE error handling as defined in Section 8.2 of [RFC8613] applies.¶
If Block-wise [RFC7959] is supported, the server takes the additional following step before any other in Section 3.3.¶
A. If Block-wise is present in the request, then process the Outer Block options according to [RFC7959], until all blocks of the request have been received (see Section 4.1.3.4 of [RFC8613]).¶
Figure 4 shows an example of EDHOC + OSCORE Request transported over UDP. In particular, the example assumes that:¶
The OSCORE Sender ID of the client is 0x01.¶
As per Section 3.3.3 of [I-D.ietf-lake-edhoc], this straightforwardly corresponds to the EDHOC connection identifier C_R 0x01.¶
As per Section 3.3.2 of [I-D.ietf-lake-edhoc], when using the purely-sequential flow shown in Figure 1, the same C_R with value 0x01 would be encoded on the wire as the CBOR integer 1 (0x01 in CBOR encoding), and prepended to EDHOC message_3 in the payload of the second EDHOC request.¶
Note to RFC Editor: Please delete the last bullet point in the previous list, since, at the time of publication, the CoAP option number will be in fact registered.¶
This results in the following components shown in Figure 4:¶
Protected CoAP request (OSCORE message):
0x44025d1f ; CoAP 4-byte header
00003974 ; Token
93 090001 ; OSCORE Option
c0 ; EDHOC Option
ff 52d5535f3147e85f1cfacd9e78abf9e0a81bbf
612f1092f1776f1c1668b3825e
(46 bytes)
Section 3.3.3 of [I-D.ietf-lake-edhoc] defines the straightforward mapping from an EDHOC connection identifier to an OSCORE Sender/Recipient ID. That is, an EDHOC identifier and the corresponding OSCORE Sender/Recipient ID are both byte strings with the same value.¶
Therefore, the conversion from an OSCORE Sender/Recipient ID to an EDHOC identifier is equally straightforward. In particular, at step 3 of Section 3.3, the value of 'kid' in the OSCORE Option of the EDHOC + OSCORE request is both the server's Recipient ID (i.e., the client's Sender ID) and the EDHOC Connection Identifier C_R of the server.¶
When using EDHOC to establish an OSCORE Security Context, the client and server MUST perform the following additional steps during an EDHOC execution, thus extending Section 5 of [I-D.ietf-lake-edhoc].¶
The Initiator selects an EDHOC Connection Identifier C_I as follows.¶
The Initiator MUST choose a C_I that is neither used in any current EDHOC session as this peer's EDHOC Connection Identifier, nor the Recipient ID in a current OSCORE Security Context where the ID Context is not present.¶
The chosen C_I SHOULD NOT be the Recipient ID of any current OSCORE Security Context. Note that, unless the two peers concurrently use alternative methods to establish OSCORE Security Contexts, this allows the Responder to always omit the 'kid context' in the OSCORE Option of its messages sent to the Initiator, when protecting those with an OSCORE Security Context where C_I is the Responder's OSCORE Sender ID (see Section 6.1 of [RFC8613]).¶
The Responder selects an EDHOC Connection Identifier C_R as follows.¶
The Responder MUST choose a C_R that is neither used in any current EDHOC session as this peer's EDHOC Connection Identifier, nor is equal to the EDHOC Connection Identifier C_I specified in the EDHOC message_1 of the present EDHOC session (i.e., after its decoding as per Section 3.3 of [I-D.ietf-lake-edhoc]), nor is the Recipient ID in a current OSCORE Security Context where the ID Context is not present.¶
The chosen C_R SHOULD NOT be the Recipient ID of any current OSCORE Security Context. Note that, for a reason analogous to the one given above with C_I, this allows the Initiator to always omit the 'kid context' in the OSCORE Option of its messages sent to the Responder, when protecting those with an OSCORE Security Context where C_R is the Initiator's OSCORE Sender ID (see Section 6.1 of [RFC8613]).¶
If the following condition holds, the Initiator MUST discontinue the protocol and reply with an EDHOC error message with error code 1, formatted as defined in Section 6.2 of [I-D.ietf-lake-edhoc].¶
The application profile referred by the client and server can include the information below, according to the specified consistency rules.¶
If the server supports the EDHOC + OSCORE request within an EDHOC execution started at a certain EDHOC resource, then the application profile associated with that resource SHOULD explicitly specify support for the EDHOC + OSCORE request.¶
In case the application profile indicates that the server supports the optional EDHOC message_4 (see Section 5.5 of [I-D.ietf-lake-edhoc]), the client has to bear in mind that the usage of EDHOC message_4 is not applicable to the optimized workflow based on the EDHOC + OSCORE request (see Section 3.3).¶
Section 9.10 of [I-D.ietf-lake-edhoc] registers the resource type "core.edhoc", which can be used as target attribute in a web link [RFC8288] to an EDHOC resource, e.g., using a link-format document [RFC6690]. This enables clients to discover the presence of EDHOC resources at a server, possibly using the resource type as filter criterion.¶
At the same time, the application profile associated with an EDHOC resource provides information describing how the EDHOC protocol can be used through that resource. While a client may become aware of the application profile through several means, it would be convenient to obtain its information elements upon discovering the EDHOC resources at the server. This might aim at discovering especially the EDHOC resources whose associated application profile denotes a way of using EDHOC which is most suitable to the client, e.g., with EDHOC cipher suites or authentication methods that the client also supports or prefers.¶
That is, it would be convenient that a client discovering an EDHOC resource contextually obtains relevant pieces of information from the application profile associated with that resource. The resource discovery can occur by means of a direct interaction with the server, or instead by means of the CoRE Resource Directory [RFC9176], where the server may have registered the links to its resources.¶
In order to enable the above, this section defines a number of parameters, each of which can be optionally specified as a target attribute with the same name in the link to the respective EDHOC resource, or as filter criteria in a discovery request from the client. When specifying these parameters in a link to an EDHOC resource, the target attribute rt="core.edhoc" MUST be included, and the same consistency rules defined in Section 5 for the corresponding information elements of an application profile MUST be followed.¶
The following parameters are defined.¶
'ed-idcred-t', specifying a type of identifier supported by the server for identifying authentication credentials. This parameter MUST specify a single value, which is taken from the 'Label' column of the "COSE Header Parameters" registry [COSE.Header.Parameters]. This parameter MAY occur multiple times, with each occurrence specifying a type of identifier for authentication credentials.¶
Note that the values in the 'Label' column of the "COSE Header Parameters" registry 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. Thus, if responses in Link Format are returned, string values which look like an integer are not supported. Therefore, such values MUST NOT be used in the 'ed-idcred-t' parameter.¶
(Future documents may update the definition of the parameters 'ed-i', 'ed-r', and 'ed-comb-req', by expanding their semantics and specifying admitted values.)¶
The example in Figure 5 shows how a client discovers one EDHOC resource at a server, obtaining information elements from the respective application profile. The Link Format notation from Section 5 of [RFC6690] is used.¶
REQ: GET /.well-known/core
RES: 2.05 Content
</sensors/temp>;osc,
</sensors/light>;if=sensor,
</.well-known/edhoc>;rt=core.edhoc;ed-csuite=0;ed-csuite=2;
ed-method=0;ed-cred-t=1;ed-cred-t=3;ed-idcred-t=4;
ed-i;ed-r;ed-comb-req
The same security considerations from OSCORE [RFC8613] and EDHOC [I-D.ietf-lake-edhoc] hold for this document. In addition, the following considerations also apply.¶
Section 3.2 specifies that a client SHOULD NOT have multiple outstanding EDHOC + OSCORE requests pertaining to the same EDHOC session. Even if a client did not fulfill this requirement, it would not have any impact in terms of security. That is, the server would still not process different instances of the same EDHOC message_3 more than once in the same EDHOC session (see Section 5.1 of [I-D.ietf-lake-edhoc]), and would still enforce replay protection of the OSCORE-protected request (see Sections 7.4 and 8.2 of [RFC8613]).¶
When using the optimized workflow in Figure 2, a minimum of 128-bit security against online brute force attacks is achieved after the client receives and successfully verifies the first OSCORE-protected response (see Section 8.1 of [I-D.ietf-lake-edhoc]). As an example, if EDHOC is used with method 3 (see Section 3.2 of [I-D.ietf-lake-edhoc]) and cipher suite 2 (see Section 3.6 of [I-D.ietf-lake-edhoc]), then the following holds.¶
With reference to the purely sequential workflow in Figure 1, the OSCORE request might have to undergo access control checks at the server, before being actually executed for accessing the target protected resource. The same MUST hold when the optimized workflow in Figure 2 is used, i.e., when using the EDHOC + OSCORE request.¶
That is, the rebuilt OSCORE-protected application request from step 7 in Section 3.3 MUST undergo the same access control checks that would be performed on a traditional OSCORE-protected application request sent individually as shown in Figure 1.¶
To this end, validated information to perform access control checks (e.g., an access token issued by a trusted party) has to be available at the server before starting to process the rebuilt OSCORE-protected application request. Such information may have been provided to the server separately before starting the EDHOC execution altogether, or instead as External Authorization Data during the EDHOC execution (see Section 3.8 of [I-D.ietf-lake-edhoc]).¶
Thus, a successful completion of the EDHOC protocol and the following derivation of the OSCORE Security Context at the server do not play a role in determining whether the rebuilt OSCORE-protected request is authorized to access the target protected resource at the server.¶
This document has the following actions for IANA.¶
Note to RFC Editor: Please replace all occurrences of "[RFC-XXXX]" with the RFC number of this specification and delete this paragraph.¶
IANA is asked to enter the following option number to the "CoAP Option Numbers" registry within the "CoRE Parameters" registry group.¶
| Number | Name | Reference |
|---|---|---|
| TBD21 | EDHOC | [RFC-XXXX] |
Note to RFC Editor: Following the registration of the CoAP Option Number 21, please replace "TBD21" with "21" in the table above. Then, please delete this paragraph and all the following text within the present Section 8.1.¶
[¶
The CoAP option number 21 is consistent with the properties of the EDHOC Option defined in Section 3.1, and it allows the EDHOC Option to always result in an overall size of 1 byte. This is because:¶
Therefore, this document suggests 21 (TBD21) as option number to be assigned to the new EDHOC Option. Although the currently unassigned option number 13 would also work well for the same reasons in the use case in question, different use cases or protocols may make a better use of the option number 13. Hence the preference for the option number 21, and why it is not necessary to register additional option numbers than 21.¶
]¶
IANA is asked to register the following entries in the "Target Attributes" registry within the "CoRE Parameters" registry group, as per [I-D.ietf-core-target-attr]. For all entries, the Change Controller is IESG, and the reference is [RFC-XXXX].¶
| Attribute Name: | Brief Description: |
|---|---|
| ed-i | Hint: support for the EDHOC Initiator role |
| ed-r | Hint: support for the EDHOC Responder role |
| ed-method | A supported authentication method for EDHOC |
| ed-csuite | A supported cipher suite for EDHOC |
| ed-cred-t | A supported type of authentication credential for EDHOC |
| ed-idcred-t | A supported type of authentication credential identifier for EDHOC |
| ed-ead | A supported External Authorization Data (EAD) item for EDHOC |
| ed-comb-req | Hint: support for the EDHOC+OSCORE request |
IANA is requested to create a new "EDHOC Authentication Credential Types" registry within the "Ephemeral Diffie-Hellman Over COSE (EDHOC)" registry group defined in [I-D.ietf-lake-edhoc].¶
The registry uses the "Expert Review" registration procedure [RFC8126]. Expert Review guidelines are provided in Section 8.4.¶
The columns of this registry are:¶
Value: This field contains the value used to identify the type of authentication credential. These values MUST be unique. The value can be an unsigned integer or a negative integer. Different ranges of values use different registration policies [RFC8126]:¶
Initial entries in this registry are as listed in Table 4.¶
| Value | Description | Reference |
|---|---|---|
| 0 | CBOR Web Token (CWT) containing a COSE_Key in a 'cnf' claim | [RFC8392] |
| 1 | CWT Claims Set (CCS) containing a COSE_Key in a 'cnf' claim | [RFC8392] |
| 2 | X.509 certificate | [RFC5280] |
| 3 | C509 certificate | [I-D.ietf-cose-cbor-encoded-cert] |
The IANA registry established in this document is defined as "Expert Review". This section gives some general guidelines for what the experts should be looking for; but they are being designated as experts for a reason, so they should be given substantial latitude.¶
Expert reviewers should take into consideration the following points:¶
This section is to be removed before publishing as an RFC.¶
The authors sincerely thank Christian Amsüss, Carsten Bormann, Esko Dijk, Klaus Hartke, John Preuß Mattsson, David Navarro, Jim Schaad, and Mališa Vučinić for their feedback and comments.¶
The work on this document has been partly supported by VINNOVA and the Celtic-Next project CRITISEC; and by the H2020 project SIFIS-Home (Grant agreement 952652).¶