draft-palombini-core-oscore-edhoc-01.txt		draft-palombini-core-oscore-edhoc-02.txt
	CoRE Working Group F. Palombini		CoRE Working Group F. Palombini
	Internet-Draft Ericsson		Internet-Draft Ericsson
	Intended status: Standards Track M. Tiloca		Intended status: Standards Track M. Tiloca
	Expires: 6 May 2021 R. Hoeglund		Expires: August 23, 2021 R. Hoeglund
	RISE AB		RISE AB
	S. Hristozov		S. Hristozov
	Fraunhofer AISEC		Fraunhofer AISEC
	G. Selander		G. Selander
	Ericsson		Ericsson
	2 November 2020		February 19, 2021
	Combining EDHOC and OSCORE		Combining EDHOC and OSCORE
	draft-palombini-core-oscore-edhoc-01		draft-palombini-core-oscore-edhoc-02
	Abstract		Abstract
	This document defines possible optimization approaches for combining		This document defines an optimization approach for combining the
	the lightweight authenticated key exchange protocol EDHOC run over		lightweight authenticated key exchange protocol EDHOC run over CoAP
	CoAP with the first subsequent OSCORE transaction. This combination		with the first subsequent OSCORE transaction. This combination
	reduces the number of round trips required to set up an OSCORE		reduces the number of round trips required to set up an OSCORE
	Security Context and complete an OSCORE transaction using that		Security Context and to complete an OSCORE transaction using that
	context.		Security Context.
	Discussion Venues
	This note is to be removed before publishing as an RFC.
	Source for this draft and an issue tracker can be found at
	https://github.com/EricssonResearch/oscore-edhoc
	(https://github.com/EricssonResearch/oscore-edhoc).
	Status of This Memo		Status of This Memo
	This Internet-Draft is submitted in full conformance with the		This Internet-Draft is submitted in full conformance with the
	provisions of BCP 78 and BCP 79.		provisions of BCP 78 and BCP 79.
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute		Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
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	Copyright Notice		Copyright Notice
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	document authors. All rights reserved.		document authors. All rights reserved.
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	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
	1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3		1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
	2. Background . . . . . . . . . . . . . . . . . . . . . . . . . 3		2. Background . . . . . . . . . . . . . . . . . . . . . . . . . 3
	3. EDHOC in OSCORE . . . . . . . . . . . . . . . . . . . . . . . 5		3. EDHOC Option . . . . . . . . . . . . . . . . . . . . . . . . 5
	3.1. Signalling in a New EDHOC Option . . . . . . . . . . . . 6		4. EDHOC Combined with OSCORE . . . . . . . . . . . . . . . . . 6
	3.2. Signalling in the OSCORE Option . . . . . . . . . . . . . 8		4.1. Client Processing . . . . . . . . . . . . . . . . . . . . 6
	4. Security Considerations . . . . . . . . . . . . . . . . . . . 9		4.2. Server Processing . . . . . . . . . . . . . . . . . . . . 7
	5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9		5. Example of EDHOC + OSCORE Request . . . . . . . . . . . . . . 9
	6. Normative References . . . . . . . . . . . . . . . . . . . . 9		6. Security Considerations . . . . . . . . . . . . . . . . . . . 10
	Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 10		7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10		7.1. CoAP Option Numbers Registry . . . . . . . . . . . . . . 10
			8. Normative References . . . . . . . . . . . . . . . . . . . . 10
			Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 11
			Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
	1. Introduction		1. Introduction
	This document presents possible optimization approaches to combine		This document defines an optimization approach to combine the
	the lightweight authenticated key exchange protocol EDHOC		lightweight authenticated key exchange protocol EDHOC
	[I-D.ietf-lake-edhoc], when running over CoAP [RFC7252], with the		[I-D.ietf-lake-edhoc], when running over CoAP [RFC7252], with the
	first subsequent OSCORE [RFC8613] transaction.		first subsequent OSCORE [RFC8613] transaction.
	This allows for a minimum number of round trips necessary to setup		This allows for a minimum number of round trips necessary to setup
	the OSCORE Security Context and complete an OSCORE transaction, for		the OSCORE Security Context and complete an OSCORE transaction, for
	example when an IoT device gets configured in a network for the first		example when an IoT device gets configured in a network for the first
	time.		time.
	The number of protocol round trips impacts the minimum number of		This optimization is desirable, since the number of protocol round
	flights, which can have a substantial impact on performance with		trips impacts the minimum number of flights, which in turn can have a
	certain radio technologies.		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		Without this optimization, it is not possible, not even in theory, to
	achieve the minimum number of flights. This optimization makes it		achieve the minimum number of flights. This optimization makes it
	possible also in practice, since the last message of the EDHOC		possible also in practice, since the last message of the EDHOC
	protocol can be made relatively small (see Section 1 of		protocol can be made relatively small (see Section 1 of
	[I-D.ietf-lake-edhoc]), thus allowing additional OSCORE protected		[I-D.ietf-lake-edhoc]), thus allowing additional OSCORE protected
	CoAP data within target MTU sizes.		CoAP data within target MTU sizes.
	The goal of this document is to provide details on different
	alternatives for transporting and processing the necessary data,
	gather opinions on the different approaches, and select only one of
	those.
	1.1. Terminology		1.1. Terminology
	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",		The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
	"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and		"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
	"OPTIONAL" in this document are to be interpreted as described in		"OPTIONAL" in this document are to be interpreted as described in
	BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all		BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
	capitals, as shown here.		capitals, as shown here.
	The reader is expected to be familiar with terms and concepts defined		The reader is expected to be familiar with terms and concepts defined
	in CoAP [RFC7252], CBOR [I-D.ietf-cbor-7049bis], OSCORE [RFC8613] and		in CoAP [RFC7252], CBOR [RFC8949], CBOR sequences [RFC8742], OSCORE
	EDHOC [I-D.ietf-lake-edhoc].		[RFC8613] and EDHOC [I-D.ietf-lake-edhoc].
	2. Background		2. Background
	EDHOC is a 3-message key exchange protocol. Section 7.1 of		EDHOC is a 3-message key exchange protocol. Section 7.2 of
	[I-D.ietf-lake-edhoc] specifies how to transport EDHOC over CoAP: the		[I-D.ietf-lake-edhoc] specifies how to transport EDHOC over CoAP: the
	EDHOC data (referred to as "EDHOC messages") are transported in the		EDHOC data (referred to as "EDHOC messages") are transported in the
	payload of CoAP requests and responses.		payload of CoAP requests and responses.
	This draft deals with the case of the Initiator acting as CoAP Client		This draft deals with the case of the Initiator acting as CoAP Client
	and the Responder acting as CoAP Server. (The case of the Initiator		and the Responder acting as CoAP Server; instead, the case of the
	acting as CoAP server cannot be optimized in this way.) That is, the		Initiator acting as CoAP Server cannot be optimized by using this
	CoAP Client sends a POST request containing the EDHOC message 1 to a		approach.
	reserved resource at the CoAP Server. This triggers the EDHOC
	exchange on the CoAP Server, which replies with a 2.04 (Changed)		That is, the CoAP Client sends a POST request containing EDHOC
	Response containing the EDHOC message 2. Finally, the EDHOC message		message_1 to a reserved resource at the CoAP Server. This triggers
	3 is sent by the CoAP Client in a CoAP POST request to the same		the EDHOC exchange on the CoAP Server, which replies with a 2.04
	resource used for the EDHOC message 1. The Content-Format of these		(Changed) Response containing EDHOC message_2. Finally, the CoAP
	CoAP messages is set to "application/edhoc".		Client sends EDHOC message_3, as a CoAP POST request to the same
			resource used for EDHOC message_1. The Content-Format of these CoAP
			messages may be set to "application/edhoc".
	After this exchange takes place, and after successful verifications		After this exchange takes place, and after successful verifications
	specified in the EDHOC protocol, the Client and Server derive the		specified in the EDHOC protocol, the Client and Server derive the
	OSCORE Security Context, as specified in Section 7.1.1 of		OSCORE Security Context, as specified in Section 7.2.1 of
	[I-D.ietf-lake-edhoc]. Then, they are ready to use OSCORE.		[I-D.ietf-lake-edhoc]. Then, they are ready to use OSCORE.
	This sequential way of running EDHOC and then OSCORE is specified in		This sequential way of running EDHOC and then OSCORE is specified in
	Figure 1. As shown in the figure, this mechanism is executed in 3		Figure 1. As shown in the figure, this mechanism takes 3 round trips
	round trips.		to complete.
	CoAP Client CoAP Server		CoAP Client CoAP Server
	| ------------- EDHOC message_1 ------------> |		| ------------- EDHOC message_1 ------------> |
	| |		| |
	| <------------ EDHOC message_2 ------------- |		| <------------ EDHOC message_2 ------------- |
	| |		| |
	EDHOC verification |		EDHOC verification |
	| |		| |
	| ------------- EDHOC message_3 ------------> |		| ------------- EDHOC message_3 ------------> |
	| |		| |
	| EDHOC verification		| EDHOC verification
	| |		| +
	OSCORE Sec Ctx OSCORE Sec Ctx		OSCORE Sec Ctx OSCORE Sec Ctx
	Derivation Derivation		Derivation Derivation
	| |		| |
	| -------------- OSCORE Request ------------> |		| ------------- OSCORE Request -------------> |
	| |		| |
	| <------------ OSCORE Response ------------- |		| <------------ OSCORE Response ------------- |
	| |		| |
	Figure 1: EDHOC and OSCORE run sequentially		Figure 1: EDHOC and OSCORE run sequentially
	The number of roundtrips can be minimized: after receiving the EDHOC		The number of roundtrips can be minimized as follows. Already after
	message 2, the CoAP Client has all the information needed to derive		receiving EDHOC message_2 and before sending EDHOC message_3, the
	the OSCORE Security Context before sending the EDHOC message 3.		CoAP Client has all the information needed to derive the OSCORE
			Security Context.
	This means that the Client can potentially send at the same time both		This means that the Client can potentially send at the same time both
	the EDHOC message 3 and the subsequent OSCORE Request. On a semantic		EDHOC message_3 and the subsequent OSCORE Request. On a semantic
	level, this approach practically requires to send two separate REST		level, this approach practically requires to send two separate REST
	requests at the same time.		requests at the same time.
	The high level message flow of running EDHOC and OSCORE combined is		The high level message flow of running EDHOC and OSCORE combined is
	shown in Figure 2.		shown in Figure 2.
	Defining the specific details of how to transport the data and of		Defining the specific details of how to transport the data and of
	their processing order is the goal of this specification.		their processing order is the goal of this specification, as defined
			in Section 4.
	CoAP Client CoAP Server		CoAP Client CoAP Server
	| ------------- EDHOC message_1 ------------> |		| ------------- EDHOC message_1 ------------> |
	| |		| |
	| <------------ EDHOC message_2 ------------- |		| <------------ EDHOC message_2 ------------- |
	| |		| |
	EDHOC verification + |		EDHOC verification |
			+ |
	OSCORE Sec Ctx |		OSCORE Sec Ctx |
	Derivation |		Derivation |
	| |		| |
	| ------------- EDHOC message_3 ------------> |		| ---- EDHOC message_3 + OSCORE Request ----> |
	| + OSCORE Request |
	| |		| |
	| EDHOC verification +		| EDHOC verification
			| +
	| OSCORE Sec Ctx		| OSCORE Sec Ctx
	| Derivation		| Derivation
	| |		| |
	| <------------ OSCORE Response ------------- |		| <------------ OSCORE Response ------------- |
	| |		| |
	Figure 2: EDHOC and OSCORE combined		Figure 2: EDHOC and OSCORE combined
	3. EDHOC in OSCORE		3. EDHOC Option
	This approach consists in sending the EDHOC message 3 inside an		This section defines the EDHOC Option, used in a CoAP request to
	OSCORE message (i.e., an OSCORE protected CoAP message).		signal that the request combines EDHOC message_3 and OSCORE protected
			data.
	The resulting OSCORE + EDHOC request is in practice the OSCORE		The EDHOC Option has the properties summarized in Figure 3, which
	Request from Figure 1, sent to a protected resource and with the		extends Table 4 of [RFC7252]. The option is Critical, Safe-to-
	correct CoAP method and options, with the addition that it also		Forward, and part of the Cache-Key. The option MUST occur at most
	transports the EDHOC message 3.		once and is always empty. If any value is sent, the value is simply
			ignored. The option is intended only for CoAP requests and is of
			Class U for OSCORE [RFC8613].
	As the EDHOC message 3 may be too large to be included in a CoAP		+-------+---+---+---+---+-------+--------+--------+---------+
	Option, e.g. if containing a large public key certificate chain, it		| No. | C | U | N | R | Name | Format | Length | Default |
	would have to be transported in the CoAP payload.		+-------+---+---+---+---+-------+--------+--------+---------+
			| TBD13 | x | | | | EDHOC | Empty | 0 | (none) |
			+-------+---+---+---+---+-------+--------+--------+---------+
			C=Critical, U=Unsafe, N=NoCacheKey, R=Repeatable
	In particular, the payload of the OSCORE + EDHOC request is formatted		Figure 3: The EDHOC Option.
	as a CBOR sequence of two CBOR byte strings: the EDHOC message 3 and
	the OSCORE ciphertext of the original OSCORE Request, in this order,
	both encoded as CBOR byte strings.
	Note that the OSCORE ciphertext is not computed over the EDHOC		The presence of this option means that the message payload contains
	message 3, which is not protected by OSCORE. That is, the client		also EDHOC data, that must be extracted and processed as defined in
	first prepares the OSCORE Request as in Figure 1. Then, it reformats		Section 4.2, before the rest of the message can be processed.
	the payload to include also the EDHOC message 3, as defined above.
	The result is the OSCORE + EDHOC request to send.
	The usage of this approach is indicated by a signalling information		Figure 4 shows the format of a CoAP message containing both the EDHOC
	in the OSCORE + EDHOC request, which can be either a new EDHOC Option		data and the OSCORE ciphertext, using the newly defined EDHOC option
	(see Section 3.1) or the OSCORE Option with a particular Flag Bit set		for signalling.
	(see Section 3.2).
	When receiving such a request, the Server needs to perform the		0 1 2 3
	following processing, in addition to the EDHOC, OSCORE and CoAP		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
	processing:		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
			|Ver| T | TKL | Code | Message ID |
			+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
			| Token (if any, TKL bytes) ...
			+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
			| OSCORE option | EDHOC option | other options (if any) ...
			+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
			|1 1 1 1 1 1 1 1| Payload
			+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	1. Check the signalling information to identify that this is an		Figure 4: CoAP message for EDHOC and OSCORE combined - signalled with
	OSCORE + EDHOC request.		the EDHOC Option
	2. Extract the EDHOC message 3 from the payload of the OSCORE +		4. EDHOC Combined with OSCORE
	EDHOC request, as the value of the first CBOR byte string in the
	CBOR sequence.
	3. Execute the EDHOC processing on the EDHOC message 3, including		The approach defined in this specification consists of sending EDHOC
	verifications and the OSCORE Security Context derivation.		message_3 inside an OSCORE protected CoAP message.
	4. Extract the OSCORE ciphertext from the payload of the OSCORE +		The resulting EDHOC + OSCORE request is in practice the OSCORE
	EDHOC request, as the value of the second CBOR byte string in the		Request from Figure 1, sent to a protected resource and with the
	CBOR sequence. Then, set the CoAP payload of the request to the		correct CoAP method and options, with the addition that it also
	extracted ciphertext.		transports EDHOC message_3.
	5. Decrypt and verify the OSCORE protected CoAP request resulting		Since EDHOC message_3 may be too large to be included in a CoAP
	from step 4, as defined by OSCORE.		Option, e.g. if containing a large public key certificate chain, it
			has to be transported through the CoAP payload.
	6. Process the CoAP request resulting from step 5.		The use of this approach is explicitly signalled by including an
			EDHOC Option (see Section 3) in the EDHOC + OSCORE request.
	The following sections expand on the two ways of signalling that the		4.1. Client Processing
	EDHOC message is transported in the OSCORE message.
	3.1. Signalling in a New EDHOC Option		The Client prepares an EDHOC + OSCORE request as follows.
	One way to signal that the Server has to extract and process the		1. Compose EDHOC message_3 as per Section 5.4.2 of
	EDHOC message 3 before processing the OSCORE protected CoAP request		[I-D.ietf-lake-edhoc].
	is to define a new CoAP Option, called the EDHOC Option.
	The presence of this option means that the message contains EDHOC		Since the Client is the EDHOC Initiator and the used Correlation
	data in the payload, that must be extracted and processed before the		Method is 1 (see Section 3.2.4 of [I-D.ietf-lake-edhoc]), the
	rest of the message can be processed.		EDHOC message_3 always includes the Connection Identifier C_R and
			CIPHERTEXT_3. Note that C_R is the OSCORE Sender ID of the
			Client, encoded as a bstr_identifier (see Section 5.1 of
			[I-D.ietf-lake-edhoc]).
	In particular, the EDHOC message 3 has to be extracted from the CoAP		2. Encrypt the original CoAP request as per Section 8.1 of
	payload, as the first element of a CBOR sequence wrapped in a CBOR		[RFC8613], using the new OSCORE Security Context established
	byte string.		after receiving EDHOC message_2.
	The Option is critical, Safe-to-Forward, and part of the Cache-Key.		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.
	The Option value is always empty. If any value is sent, the value is		3. Build a CBOR sequence [RFC8742] composed of two CBOR byte strings
	simply ignored.		in the following order.
	The Option MUST occur at most once.		* The first CBOR byte string is the CIPHERTEXT_3 of the EDHOC
			message_3 resulting from step 3.
	The Option is of Class U for OSCORE.		* The second CBOR byte string has as value the OSCORE ciphertext
			of the OSCORE protected CoAP request resulting from step 2.
	Figure 3 shows the format for a CoAP message containing both the		4. Compose the EDHOC + OSCORE request, as the OSCORE protected CoAP
	OSCORE ciphertext and EDHOC message 3, using the newly defined EDHOC		request resulting from step 2, where the payload is replaced with
	option for signaling.		the CBOR sequence built at step 3.
	0 1 2 3		5. Signal the usage of this approach within the EDHOC + OSCORE
	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		request, by including the new EDHOC Option defined in Section 3.
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	|Ver| T | TKL | Code | Message ID |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| Token (if any, TKL bytes) ...
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| OSCORE option | EDHOC option | other options (if any) ...
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	|1 1 1 1 1 1 1 1| Payload
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	Figure 3: CoAP message for EDHOC and OSCORE combined - signaled		4.2. Server Processing
	with the EDHOC Option
	An example based on the OSCORE test vector from Appendix C.4 of		When receiving an EDHOC + OSCORE request, the Server performs the
	[RFC8613] and the EDHOC test vector from Appendix B.2 of		following steps.
	[I-D.ietf-lake-edhoc] is given in Figure 4. The example assumes that
	the EDHOC option is registered with CoAP option number 13.
	o OSCORE option value: 0x0914 (2 bytes)		1. Check the presence of the EDHOC option defined in Section 3, to
			determine that the received request is an EDHOC + OSCORE request.
			If this is the case, the Server continues with the steps defined
			below.
	o ciphertext: 0x612f1092f1776f1c1668b3825e (13 bytes)		2. Extract CIPHERTEXT_3 from the payload of the EDHOC + OSCORE
			request, as the first CBOR byte string in the CBOR sequence.
	o EDHOC option value: - (0 bytes)		3. Rebuild EDHOC message_3, as a CBOR sequence composed of two CBOR
			byte strings in the following order.
	o EDHOC message 3: 085253c3991999a5ffb86921e99b607c067770e0		* The first CBOR byte string is the 'kid' of the Client
	(20 bytes)		indicated in the OSCORE option of the EDHOC + OSCORE request,
			encoded as a bstr_identifier (see Section 5.1 of
			[I-D.ietf-lake-edhoc]).
	From there:		* The second CBOR byte string is the CIPHERTEXT_3 retrieved at
			step 2.
	o Protected CoAP request (OSCORE message): 0x44025d1f0000397439		4. Perform the EDHOC processing on the EDHOC message_3 rebuilt at
	6c6f63616c686f737462 0914 04 ff 54085253C3991999A5FFB86921E99		step 3, including verifications, and the OSCORE Security Context
	B607C067770E0 4d612f1092f1776f1c1668b3825e (58 bytes)		derivation, as per Section 5.4.3 and Section 7.2.1 of
			[I-D.ietf-lake-edhoc], respectively.
	Figure 4: CoAP message for EDHOC and OSCORE combined - signaled		5. Extract the OSCORE ciphertext from the payload of the EDHOC +
	with the EDHOC Option		OSCORE request, as the value of the second CBOR byte string in
			the CBOR sequence.
	3.2. Signalling in the OSCORE Option		6. Rebuild the OSCORE protected CoAP request as the EDHOC + OSCORE
			request, where the payload is replaced with the OSCORE ciphertext
			resulting from step 5.
	Another way to signal that the EDHOC message 3 is to be extracted		7. Decrypt and verify the OSCORE protected CoAP request resulting
	from the CoAP payload as the first element of a CBOR sequence wrapped		from step 6, as per Section 8.2 of [RFC8613], by using the new
	in a CBOR byte string, and that the processing defined in Section 3		OSCORE Security Context established at step 4.
	is to be executed, is to use one of the OSCORE Flag Bits of the
	OSCORE Option.
	Bit Position: 1		8. Process the CoAP request resulting from step 7.
	Name: EDHOC		If steps 4 (EDHOC processing) and 7 (OSCORE processing) are both
			successfully completed, the Server MUST reply with an OSCORE
			protected response, in order for the Client to achieve key
			confirmation (see Section 5.4.2 of [I-D.ietf-lake-edhoc]). The usage
			of EDHOC message_4 as defined in Section 7.1 of [I-D.ietf-lake-edhoc]
			is not applicable to the approach defined in this specification.
	Description: Set to 1 if the payload is a sequence of EDHOC message 3		If step 4 (EDHOC processing) fails, the server discontinues the
	and OSCORE ciphertext.		protocol as per Section 5.4.3 of [I-D.ietf-lake-edhoc] and sends an
			EDHOC error message, formatted as defined in Section 6.1 of
			[I-D.ietf-lake-edhoc]. In particular, the CoAP response conveying
			the EDHOC error message:
	Reference: this document		o MUST have Content-Format set to application/edhoc defined in
			Section 9.5 of [I-D.ietf-lake-edhoc].
	The OSCORE Option value with the EDHOC bit set is given in Figure 5.		o MUST specify a CoAP error response code, i.e. 4.00 (Bad Request)
			in case of client error (e.g. due to a malformed EDHOC message_3),
			or 5.00 (Internal Server Error) in case of server error (e.g. due
			to failure in deriving EDHOC key material).
	0 1 2 3 4 5 6 7 <------------- n bytes -------------->		If step 4 (EDHOC processing) is successfully completed but step 7
	+-+-+-+-+-+-+-+-+--------------------------------------		(OSCORE processing) fails, the same OSCORE error handling applies as
	|0|1|0|h|k| n | Partial IV (if any) ...		defined in Section 8.2 of [RFC8613].
	+-+-+-+-+-+-+-+-+--------------------------------------
	<- 1 byte -> <----- s bytes ------>		5. Example of EDHOC + OSCORE Request
	+------------+----------------------+------------------+
	| s (if any) | kid context (if any) | kid (if any) ... |
	+------------+----------------------+------------------+
	Figure 5: The OSCORE Option Value with the EDHOC bit set		An example based on the OSCORE test vector from Appendix C.4 of
			[RFC8613] and the EDHOC test vector from Appendix B.2 of
			[I-D.ietf-lake-edhoc] is given in Figure 5. In particular, the
			example assumes that:
	Figure 6 shows the format for a CoAP message containing both the		o The used OSCORE Partial IV is 0, consistently with the first
	OSCORE ciphertext and EDHOC message 3, using the Flag Bit 1 in the		request protected with the new OSCORE Security Context.
	OSCORE Option for signaling.
	0 1 2 3		o The OSCORE Sender ID of the Client is 0x20. This corresponds to
	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		the EDHOC Connection Identifier C_R, which is encoded as the
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		bstr_identifier 0x08 in EDHOC message_3.
	|Ver| T | TKL | Code | Message ID |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| Token (if any, TKL bytes) ...
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| OSCORE opt (with EDHOC bit set) | other options (if any) ...
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	|1 1 1 1 1 1 1 1| Payload
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	Figure 6: CoAP message for EDHOC and OSCORE combined - signaled
	within the OSCORE option
	An example based on the OSCORE test vector from Appendix C.4 of		o The EDHOC option is registered with CoAP option number 13.
	[RFC8613] and the EDHOC test vector from Appendix B.2 of
	[I-D.ietf-lake-edhoc] is given in Figure 7.
	o OSCORE option value without EDHOC bit set: 0x0914 (2 bytes)		o OSCORE option value: 0x090020 (3 bytes)
	o OSCORE option value with EDHOC bit set: 0x4914 (2 bytes)		o EDHOC option value: - (0 bytes)
	o ciphertext: 0x612f1092f1776f1c1668b3825e (13 bytes)		o C_R: 0x20 (1 byte)
	o EDHOC message 3: 085253c3991999a5ffb86921e99b607c067770e0		o CIPHERTEXT_3: 0x5253c3991999a5ffb86921e99b607c067770e0
			(19 bytes)
			o EDHOC message_3: 0x08 5253c3991999a5ffb86921e99b607c067770e0
	(20 bytes)		(20 bytes)
			o OSCORE ciphertext: 0x612f1092f1776f1c1668b3825e (13 bytes)
	From there:		From there:
	o Protected CoAP request (OSCORE message): 0x44025d1f000039743		o Protected CoAP request (OSCORE message):
	96c6f63616c686f737462 4914 ff 54085253C3991999A5FFB86921E99B
	607C067770E0 4d612f1092f1776f1c1668b3825e (58 bytes)
	Figure 7: CoAP message for EDHOC and OSCORE combined - signaled		0x44025d1f ; CoAP 4-byte header
	within the OSCORE Option		00003974 ; Token
			39 6c6f63616c686f7374 ; Uri-Host Option: "localhost"
			63 090020 ; OSCORE Option
			40 ; EDHOC Option
			ff 5253c3991999a5ffb86921e99b607c067770e0
			4d612f1092f1776f1c1668b3825e
			(57 bytes)
	4. Security Considerations		Figure 5: Example of CoAP message with EDHOC and OSCORE combined
			6. Security Considerations
	The same security considerations from OSCORE [RFC8613] and EDHOC		The same security considerations from OSCORE [RFC8613] and EDHOC
	[I-D.ietf-lake-edhoc] hold for this document.		[I-D.ietf-lake-edhoc] hold for this document.
	TODO (more considerations)		TODO (more considerations)
	5. IANA Considerations		7. IANA Considerations
	Depending on the option chosen, this document will either register a		This document has the following actions for IANA.
	new CoAP Option number to the CoAP Option Number registry, or a new
	bit to the OSCORE Flag Bits registry.
	6. Normative References		7.1. CoAP Option Numbers Registry
	[I-D.ietf-cbor-7049bis]		IANA is asked to enter the following option numbers to the "CoAP
	Bormann, C. and P. Hoffman, "Concise Binary Object		Option Numbers" registry defined in [RFC7252] within the "CoRE
	Representation (CBOR)", Work in Progress, Internet-Draft,		Parameters" registry.
	draft-ietf-cbor-7049bis-16, 30 September 2020,
	<http://www.ietf.org/internet-drafts/draft-ietf-cbor-		[
	7049bis-16.txt>.
			The CoAP option numbers 13 and 21 are both consistent with the
			properties of the EDHOC Option defined in Section 3, and they both
			allow the EDHOC Option to always result in an overall size of 1 byte.
			This is because:
			o The EDHOC option is always empty, i.e. with zero-length value; and
			o Since the OSCORE option with option number 9 is always present in
			the CoAP request, the EDHOC option would be encoded with a maximum
			delta of 4 or 12, depending on its option number being 13 or 21.
			At the time of writing, the CoAP option numbers 13 and 21 are both
			unassigned in the "CoAP Option Numbers" registry, as first available
			and consistent option numbers for the EDHOC option.
			]
			+--------+-------+-------------------+
			| Number | Name | Reference |
			+--------+-------+-------------------+
			| TBD13 | EDHOC | [[this document]] |
			+--------+-------+-------------------+
			8. Normative References
	[I-D.ietf-lake-edhoc]		[I-D.ietf-lake-edhoc]
	Selander, G., Mattsson, J., and F. Palombini, "Ephemeral		Selander, G., Mattsson, J., and F. Palombini, "Ephemeral
	Diffie-Hellman Over COSE (EDHOC)", Work in Progress,		Diffie-Hellman Over COSE (EDHOC)", draft-ietf-lake-
	Internet-Draft, draft-ietf-lake-edhoc-01, 2 August 2020,		edhoc-03 (work in progress), December 2020.
	<http://www.ietf.org/internet-drafts/draft-ietf-lake-
	edhoc-01.txt>.
	[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate		[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
	Requirement Levels", BCP 14, RFC 2119,		Requirement Levels", BCP 14, RFC 2119,
	DOI 10.17487/RFC2119, March 1997,		DOI 10.17487/RFC2119, March 1997,
	<https://www.rfc-editor.org/info/rfc2119>.		<https://www.rfc-editor.org/info/rfc2119>.
	[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained		[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
	Application Protocol (CoAP)", RFC 7252,		Application Protocol (CoAP)", RFC 7252,
	DOI 10.17487/RFC7252, June 2014,		DOI 10.17487/RFC7252, June 2014,
	<https://www.rfc-editor.org/info/rfc7252>.		<https://www.rfc-editor.org/info/rfc7252>.
	[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC		[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
	2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,		2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
	May 2017, <https://www.rfc-editor.org/info/rfc8174>.		May 2017, <https://www.rfc-editor.org/info/rfc8174>.
	[RFC8613] Selander, G., Mattsson, J., Palombini, F., and L. Seitz,		[RFC8613] Selander, G., Mattsson, J., Palombini, F., and L. Seitz,
	"Object Security for Constrained RESTful Environments		"Object Security for Constrained RESTful Environments
	(OSCORE)", RFC 8613, DOI 10.17487/RFC8613, July 2019,		(OSCORE)", RFC 8613, DOI 10.17487/RFC8613, July 2019,
	<https://www.rfc-editor.org/info/rfc8613>.		<https://www.rfc-editor.org/info/rfc8613>.
			[RFC8742] Bormann, C., "Concise Binary Object Representation (CBOR)
			Sequences", RFC 8742, DOI 10.17487/RFC8742, February 2020,
			<https://www.rfc-editor.org/info/rfc8742>.
			[RFC8949] Bormann, C. and P. Hoffman, "Concise Binary Object
			Representation (CBOR)", STD 94, RFC 8949,
			DOI 10.17487/RFC8949, December 2020,
			<https://www.rfc-editor.org/info/rfc8949>.
	Acknowledgments		Acknowledgments
	The authors sincerely thank Christian Amsuess, Klaus Hartke, Jim		The authors sincerely thank Christian Amsuess, Klaus Hartke, Jim
	Schaad and Malisa Vucinic for their feedback and comments in the		Schaad and Malisa Vucinic for their feedback and comments in the
	discussion leading up to this draft.		discussion leading up to this draft.
	The work on this document has been partly supported by VINNOVA and		The work on this document has been partly supported by VINNOVA and
	the Celtic-Next project CRITISEC; and by the H2020 project SIFIS-Home		the Celtic-Next project CRITISEC; and by the H2020 project SIFIS-Home
	(Grant agreement 952652).		(Grant agreement 952652).
	Authors' Addresses		Authors' Addresses
	Francesca Palombini		Francesca Palombini
	Ericsson		Ericsson
	Email: francesca.palombini@ericsson.com		Email: francesca.palombini@ericsson.com
	Marco Tiloca		Marco Tiloca
	RISE AB		RISE AB
	Isafjordsgatan 22		Isafjordsgatan 22
	SE-16440 Stockholm Kista		Kista SE-16440 Stockholm
	Sweden		Sweden
	Email: marco.tiloca@ri.se		Email: marco.tiloca@ri.se
	Rikard Hoeglund		Rikard Hoeglund
	RISE AB		RISE AB
	Isafjordsgatan 22		Isafjordsgatan 22
	SE-16440 Stockholm Kista		Kista SE-16440 Stockholm
	Sweden		Sweden
	Email: rikard.hoglund@ri.se		Email: rikard.hoglund@ri.se
	Stefan Hristozov		Stefan Hristozov
	Fraunhofer AISEC		Fraunhofer AISEC
	Email: stefan.hristozov@aisec.fraunhofer.de		Email: stefan.hristozov@aisec.fraunhofer.de
	Goeran Selander		Goeran Selander
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