< draft-ietf-lpwan-coap-static-context-hc-14.txt		draft-ietf-lpwan-coap-static-context-hc-15.txt >
	lpwan Working Group A. Minaburo		lpwan Working Group A. Minaburo
	Internet-Draft Acklio		Internet-Draft Acklio
	Intended status: Standards Track L. Toutain		Intended status: Standards Track L. Toutain
	Expires: November 27, 2020 Institut MINES TELECOM; IMT Atlantique		Expires: January 4, 2021 Institut MINES TELECOM; IMT Atlantique
	R. Andreasen		R. Andreasen
	Universidad de Buenos Aires		Universidad de Buenos Aires
	May 26, 2020		July 03, 2020
	LPWAN Static Context Header Compression (SCHC) for CoAP		LPWAN Static Context Header Compression (SCHC) for CoAP
	draft-ietf-lpwan-coap-static-context-hc-14		draft-ietf-lpwan-coap-static-context-hc-15
	Abstract		Abstract
	This draft defines the way Static Context Header Compression (SCHC)		This draft defines the way Static Context Header Compression (SCHC)
	header compression can be applied to the Constrained Application		header compression can be applied to the Constrained Application
	Protocol (CoAP). SCHC is a header compression mechanism adapted for		Protocol (CoAP). SCHC is a header compression mechanism adapted for
	constrained devices. SCHC uses a static description of the header to		constrained devices. SCHC uses a static description of the header to
	reduce the redundancy and the size of the information in the header.		reduce the redundancy and the size of the information in the header.
	While [rfc8724] describes the SCHC compression and fragmentation		While [rfc8724] describes the SCHC compression and fragmentation
	framework, and its application for IPv6/UDP headers, this document		framework, and its application for IPv6/UDP headers, this document
	skipping to change at page 1, line 47 ¶		skipping to change at page 1, line 47 ¶
	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-
	Drafts is at https://datatracker.ietf.org/drafts/current/.		Drafts is at https://datatracker.ietf.org/drafts/current/.
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
	time. It is inappropriate to use Internet-Drafts as reference		time. It is inappropriate to use Internet-Drafts as reference
	material or to cite them other than as "work in progress."		material or to cite them other than as "work in progress."
	This Internet-Draft will expire on November 27, 2020.		This Internet-Draft will expire on January 4, 2021.
	Copyright Notice		Copyright Notice
	Copyright (c) 2020 IETF Trust and the persons identified as the		Copyright (c) 2020 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
	This document is subject to BCP 78 and the IETF Trust's Legal		This document is subject to BCP 78 and the IETF Trust's Legal
	Provisions Relating to IETF Documents		Provisions Relating to IETF Documents
	(https://trustee.ietf.org/license-info) in effect on the date of		(https://trustee.ietf.org/license-info) in effect on the date of
	publication of this document. Please review these documents		publication of this document. Please review these documents
	skipping to change at page 2, line 25 ¶		skipping to change at page 2, line 25 ¶
	to this document. Code Components extracted from this document must		to this document. Code Components extracted from this document must
	include Simplified BSD License text as described in Section 4.e of		include Simplified BSD License text as described in Section 4.e of
	the Trust Legal Provisions and are provided without warranty as		the Trust Legal Provisions and are provided without warranty as
	described in the Simplified BSD License.		described in the Simplified BSD License.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
	1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4		1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
	2. Applying SCHC to CoAP headers . . . . . . . . . . . . . . . . 4		2. Applying SCHC to CoAP headers . . . . . . . . . . . . . . . . 4
	3. CoAP Headers compressed with SCHC . . . . . . . . . . . . . . 5		3. CoAP Headers compressed with SCHC . . . . . . . . . . . . . . 6
	3.1. Differences between CoAP and UDP/IP Compression . . . . . 5		3.1. Differences between CoAP and UDP/IP Compression . . . . . 7
	4. Compression of CoAP header fields . . . . . . . . . . . . . . 6		4. Compression of CoAP header fields . . . . . . . . . . . . . . 8
	4.1. CoAP version field . . . . . . . . . . . . . . . . . . . 7		4.1. CoAP version field . . . . . . . . . . . . . . . . . . . 8
	4.2. CoAP type field . . . . . . . . . . . . . . . . . . . . . 7		4.2. CoAP type field . . . . . . . . . . . . . . . . . . . . . 8
	4.3. CoAP code field . . . . . . . . . . . . . . . . . . . . . 7		4.3. CoAP code field . . . . . . . . . . . . . . . . . . . . . 8
	4.4. CoAP Message ID field . . . . . . . . . . . . . . . . . . 7		4.4. CoAP Message ID field . . . . . . . . . . . . . . . . . . 9
	4.5. CoAP Token fields . . . . . . . . . . . . . . . . . . . . 7		4.5. CoAP Token fields . . . . . . . . . . . . . . . . . . . . 9
	5. CoAP options . . . . . . . . . . . . . . . . . . . . . . . . 8		5. CoAP options . . . . . . . . . . . . . . . . . . . . . . . . 9
	5.1. CoAP Content and Accept options. . . . . . . . . . . . . 8		5.1. CoAP Content and Accept options. . . . . . . . . . . . . 10
	5.2. CoAP option Max-Age, Uri-Host and Uri-Port fields . . . . 8		5.2. CoAP option Max-Age, Uri-Host and Uri-Port fields . . . . 10
	5.3. CoAP option Uri-Path and Uri-Query fields . . . . . . . . 9		5.3. CoAP option Uri-Path and Uri-Query fields . . . . . . . . 10
	5.3.1. Variable length Uri-Path and Uri-Query . . . . . . . 9		5.3.1. Variable length Uri-Path and Uri-Query . . . . . . . 11
	5.3.2. Variable number of path or query elements . . . . . . 10		5.3.2. Variable number of path or query elements . . . . . . 11
	5.4. CoAP option Size1, Size2, Proxy-URI and Proxy-Scheme		5.4. CoAP option Size1, Size2, Proxy-URI and Proxy-Scheme
	fields . . . . . . . . . . . . . . . . . . . . . . . . . 10		fields . . . . . . . . . . . . . . . . . . . . . . . . . 11
	5.5. CoAP option ETag, If-Match, If-None-Match, Location-Path		5.5. CoAP option ETag, If-Match, If-None-Match, Location-Path
	and Location-Query fields . . . . . . . . . . . . . . . . 10		and Location-Query fields . . . . . . . . . . . . . . . . 12
	6. SCHC compression of CoAP extension RFCs . . . . . . . . . . . 11		6. SCHC compression of CoAP extension RFCs . . . . . . . . . . . 12
	6.1. Block . . . . . . . . . . . . . . . . . . . . . . . . . . 11		6.1. Block . . . . . . . . . . . . . . . . . . . . . . . . . . 12
	6.2. Observe . . . . . . . . . . . . . . . . . . . . . . . . . 11		6.2. Observe . . . . . . . . . . . . . . . . . . . . . . . . . 12
	6.3. No-Response . . . . . . . . . . . . . . . . . . . . . . . 11		6.3. No-Response . . . . . . . . . . . . . . . . . . . . . . . 12
	6.4. OSCORE . . . . . . . . . . . . . . . . . . . . . . . . . 11		6.4. OSCORE . . . . . . . . . . . . . . . . . . . . . . . . . 12
	7. Examples of CoAP header compression . . . . . . . . . . . . . 13		7. Examples of CoAP header compression . . . . . . . . . . . . . 14
	7.1. Mandatory header with CON message . . . . . . . . . . . . 13		7.1. Mandatory header with CON message . . . . . . . . . . . . 14
	7.2. OSCORE Compression . . . . . . . . . . . . . . . . . . . 14		7.2. OSCORE Compression . . . . . . . . . . . . . . . . . . . 15
	7.3. Example OSCORE Compression . . . . . . . . . . . . . . . 17		7.3. Example OSCORE Compression . . . . . . . . . . . . . . . 18
	8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27		8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28
	9. Security considerations . . . . . . . . . . . . . . . . . . . 27		9. Security considerations . . . . . . . . . . . . . . . . . . . 28
	10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 28		10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 29
	11. Normative References . . . . . . . . . . . . . . . . . . . . 28		11. Normative References . . . . . . . . . . . . . . . . . . . . 29
	Appendix A. Extension to the RFC8724 Annex D. . . . . . . . . . 29		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 30
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 29
	1. Introduction		1. Introduction
	CoAP [rfc7252] is designed to easily interop with HTTP (Hypertext		CoAP [rfc7252] is designed to easily interop with HTTP (Hypertext
	Transfer Protocol) and is optimized for REST-based (Representational		Transfer Protocol) and is optimized for REST-based (Representational
	state transfer) services. Although CoAP was designed for constrained		state transfer) services. Although CoAP was designed for constrained
	devices, the size of a CoAP header still is too large for the		devices, the size of a CoAP header still is too large for the
	constraints of LPWAN (Low Power Wide Area Networks) and some		constraints of LPWAN (Low Power Wide Area Networks) and some
	compression is needed to reduce the header size.		compression is needed to reduce the header size.
	The [rfc8724] defines SCHC, a header compression mechanism for LPWAN		The [rfc8724] defines SCHC, a header compression mechanism for LPWAN
	network based on a static context. The section 5 of the [rfc8724]		network based on a static context. Section 5 of the [rfc8724]
	explains the architecture where compression and decompression are		explains the architecture where compression and decompression are
	done. The context is known by both ends before transmission. The		done. The context is known by both ends before transmission. The
	way the context is configured, provisioned or exchanged is out of the		way the context is configured, provisioned or exchanged is out of the
	scope of this document.		scope of this document.
			CoAP is an End-to-End protocol at the application level, so CoAP
			compression requires to install common Rules between two hosts and IP
			Routing may be needed to allow End-to-End communication. Therefore,
			SCHC compression may apply at two different levels, one to compress
			IP and UDP as described in [rfc8724] in the LPWAN network and another
			at the application level. These two compressions may be independent.
			The Compression Rules can be set up by two independent entities and
			are out of the scope of this document. In both cases, SCHC mechanism
			remains the same.
	SCHC compresses and decompresses headers based on shared contexts		SCHC compresses and decompresses headers based on shared contexts
	between devices. Each context consists of multiple Rules. Each Rule		between devices. Each context consists of multiple Rules. Each Rule
	can match header fields and specific values or ranges of values. If		can match header fields and specific values or ranges of values. If
	a Rule matches, the matched header fields are substituted by the		a Rule matches, the matched header fields are substituted by the
	RuleID and optionally some residual bits. Thus, different Rules may		RuleID and optionally some residual bits. Thus, different Rules may
	correspond to different types of packets that a device expects to		correspond to different types of packets that a device expects to
	send or receive.		send or receive.
	A Rule describes the complete header of the packet with an ordered		A Rule describes the complete header of the packet with an ordered
	list of fields descriptions, see section 7 of [rfc8724], thereby each		list of fields descriptions, see section 7 of [rfc8724], thereby each
	skipping to change at page 4, line 29 ¶		skipping to change at page 4, line 40 ¶
	"OPTIONAL" in this document are to be interpreted as described in BCP		"OPTIONAL" in this document are to be interpreted as described in BCP
	14 [RFC2119][rfc8174] when, and only when, they appear in all		14 [RFC2119][rfc8174] when, and only when, they appear in all
	capitals, as shown here.		capitals, as shown here.
	2. Applying SCHC to CoAP headers		2. Applying SCHC to CoAP headers
	The SCHC Compression Rules can be applied to CoAP headers. SCHC		The SCHC Compression Rules can be applied to CoAP headers. SCHC
	Compression of the CoAP header MAY be done in conjunction with the		Compression of the CoAP header MAY be done in conjunction with the
	lower layers (IPv6/UDP) or independently. The SCHC adaptation layers		lower layers (IPv6/UDP) or independently. The SCHC adaptation layers
	as described in Section 5 of [rfc8724] and may be used as shown in		as described in Section 5 of [rfc8724] and may be used as shown in
	Figure 1.		Figure 1, Figure 2 and Figure 3.
	^ +------------+ ^ +------------+ ^ +------------+		In the first example Figure 1, a Rule compresses the complete header
	| | CoAP | | | CoAP | inner | | CoAP |		stack from IPv6 to CoAP. In this case, SCHC C/D (Static Context
	| +------------+ v +------------+ x | OSCORE |		Header Compression Compressor/Decompressor) is performed at the
	| | UDP | | DTLS | outer | +------------+		Sender and at the Receiver. The host communicating with the device
	| +------------+ +------------+ | | UDP |		do not implement SCHC C/D.
	| | IPv6 | | UDP | | +------------+
	v +------------+ +------------+ | | IPv6 |
	| IPv6 | v +------------+
	+------------+
	Figure 1: Rule scope for CoAP		(device) (NGW) (internet) (App)
	Figure 1 shows some examples for CoAP protocol stacks and the SCHC		+--------+ +--------+
	Rule's scope.		| CoAP | | CoAP |
			+--------+ +--------+
			| UDP | | UDP |
			+--------+ +----------------+ +--------+
			| IPv6 | | IPv6 | | IPv6 |
			+--------+ +--------+-------+ +--------+
			| SCHC | | SCHC | | | |
			+--------+ +--------+ + + +
			| LPWAN | | LPWAN | | | |
			+--------+ +--------+-------+ +--------+
			((((((())))))) ----- ------ ------ -----
	In the first example, a Rule compresses the complete header stack		Figure 1: Compression/decompression at the LPWAN bondary
	from IPv6 to CoAP. In this case, SCHC C/D (Static Context Header
	Compression Compressor/Decompressor) is performed at the Sender and
	at the Receiver.
	In the second example, the SCHC compression is applied in the CoAP		In the second example, Figure 2, the SCHC compression is applied in
	layer, compressing the CoAP header independently of the other layers.		the CoAP layer, compressing the CoAP header independently of the
	The RuleID and the Compression Residue are encrypted using a		other layers. The RuleID and the Compression Residue are encrypted
	mechanism such as DTLS. Only the other end can decipher the		using a mechanism such as DTLS. Only the other end can decipher the
	information. If needed, layers below use SCHC to compress the header		information. If needed, layers below use SCHC to compress the header
	as defined in [rfc8724] document. This use case realizes an End-to-		as defined in [rfc8724] document. This use case realizes an End-to-
	End context initialization between the sender and the receiver, see		End context initialization between the sender and the receiver and is
	Appendix A.		out-of-scope of this document.
	In the third example, the Object Security for Constrained RESTful		(device) (NGW) (internet) (App)
	Environments (OSCORE) [rfc8613] is used. In this case, two rulesets
	are used to compress the CoAP message. A first ruleset focused on		+--------+ +--------+
	the inner header and is applied end to end by both ends. A second		| CoAP | | CoAP |
	ruleset compresses the outer header and the layers below and is done		+--------+ +--------+
	between the Sender and the Receiver.		| SCHC | | SCHC |
			+--------+ +--------+
			| DTLS | | DTLS |
			+--------+ +--------+
			. udp . . udp .
			.......... .................. ..........
			. ipv6 . . ipv6 . . ipv6 .
			.......... .................. ..........
			. schc . . schc . . . .
			.......... .......... . . .
			. lpwan . . lpwan . . . .
			.......... .................. ..........
			((((((())))))) ----- ------ ------ -----
			Figure 2: Standalone CoAP ene-to-end compression/decompression
			In the third example, Figure 3 the Object Security for Constrained
			RESTful Environments (OSCORE) [rfc8613] is used. In this case, two
			rulesets are used to compress the CoAP message. A first ruleset
			focused on the inner header and is applied end to end by both ends.
			A second ruleset compresses the outer header and the layers below and
			is done between the Sender and the Receiver.
			(device) (NGW) (internet) (App)
			+--------+ +--------+
			| CoAP | | CoAP |
			| inner | | inner |
			+--------+ +--------+
			| SCHC | | SCHC |
			+--------+ +--------+
			| CoAP | | CoAP |
			| outer | | outer |
			+--------+ +--------+
			. udp . . udp .
			.......... .................. ..........
			. ipv6 . . ipv6 . . ipv6 .
			.......... .................. ..........
			. schc . . schc . . . .
			.......... .......... . . .
			. lpwan . . lpwan . . . .
			.......... .................. ..........
			((((((())))))) ----- ------ ------ -----
			Figure 3: OSCORE compression/decompression.
			In case of 2 rule-sets, as shown in Figure 2 and Figure 3, they may
			come from different provisioning domains, and that they do not
			include the cryptography part that is done in between the two SCHC
			activities. This document focuses on CoAP compression represented in
			the dashed boxes in the previous figures.
	3. CoAP Headers compressed with SCHC		3. CoAP Headers compressed with SCHC
	The use of SCHC over the CoAP header uses the same description and		The use of SCHC over the CoAP header uses the same description and
	compression/decompression techniques as the one for IP and UDP		compression/decompression techniques as the one for IP and UDP
	explained in the [rfc8724]. For CoAP, SCHC Rules description uses		explained in the [rfc8724]. For CoAP, SCHC Rules description uses
	the direction information to optimize the compression by reducing the		the direction information to optimize the compression by reducing the
	number of Rules needed to compress headers. The field description		number of Rules needed to compress headers. The field description
	MAY define both request/response headers and target values in the		MAY define both request/response headers and target values in the
	same Rule, using the DI (direction indicator) to make the difference.		same Rule, using the DI (direction indicator) to make the difference.
	skipping to change at page 8, line 26 ¶		skipping to change at page 9, line 46 ¶
	the format Delta-Type (D-T), Length (L), Value (V). When applying		the format Delta-Type (D-T), Length (L), Value (V). When applying
	SCHC compression to the Option, the D-T, L, and V format serves to		SCHC compression to the Option, the D-T, L, and V format serves to
	make the Rule description of the Option. The SCHC compression builds		make the Rule description of the Option. The SCHC compression builds
	the description of the Option by using in the Field ID the Option		the description of the Option by using in the Field ID the Option
	Number built from D-T; in TV, the Option Value; and the Option Length		Number built from D-T; in TV, the Option Value; and the Option Length
	uses section 7.4 of RFC8724. When the Option Length has a wellknown		uses section 7.4 of RFC8724. When the Option Length has a wellknown
	size it can be stored in the Rule. Therefore, SCHC compression does		size it can be stored in the Rule. Therefore, SCHC compression does
	not send it. Otherwise, SCHC Compression carries the length of the		not send it. Otherwise, SCHC Compression carries the length of the
	Compression Residue in addition to the Compression Residue value.		Compression Residue in addition to the Compression Residue value.
			CoAP request and response do not include the same options. So
			Compression Rules may reflect these assymetry by tagging the
			direction indicator.
	Note that length coding differs between CoAP options and SCHC		Note that length coding differs between CoAP options and SCHC
	variable size Compression Residue.		variable size Compression Residue.
	The following sections present how SCHC compresses some specific CoAP		The following sections present how SCHC compresses some specific CoAP
	Options.		Options.
	5.1. CoAP Content and Accept options.		5.1. CoAP Content and Accept options.
	These fields are both unidirectional and MUST NOT be set to
	bidirectional in a Rule entry.
	If a single value is expected by the client, it can be stored in the		If a single value is expected by the client, it can be stored in the
	TV and elided during the transmission. Otherwise, if several		TV and elided during the transmission. Otherwise, if several
	possible values are expected by the client, a matching-list SHOULD be		possible values are expected by the client, a matching-list SHOULD be
	used to limit the size of the Compression Residue. Otherwise, the		used to limit the size of the Compression Residue. Otherwise, the
	value has to be sent as a Compression Residue (fixed or variable		value has to be sent as a Compression Residue (fixed or variable
	length).		length).
	5.2. CoAP option Max-Age, Uri-Host and Uri-Port fields		5.2. CoAP option Max-Age, Uri-Host and Uri-Port fields
	These fields are unidirectional and MUST NOT be set to bidirectional
	in a Rule DI entry, see section 7.1 of [rfc8724]. They are used only
	by the server to inform of the caching duration and is never found in
	client requests.
	If the duration is known by both ends, the value can be elided.		If the duration is known by both ends, the value can be elided.
	A matching list can be used if some well-known values are defined.		A matching list can be used if some well-known values are defined.
	Otherwise these options can be sent as a Compression Residue (fixed		Otherwise these options can be sent as a Compression Residue (fixed
	or variable length).		or variable length).
	5.3. CoAP option Uri-Path and Uri-Query fields		5.3. CoAP option Uri-Path and Uri-Query fields
	These fields are unidirectional and MUST NOT be set to bidirectional
	in a Rule entry. They are used only by the client to access a
	specific resource and are never found in server responses.
	Uri-Path and Uri-Query elements are a repeatable options, the Field		Uri-Path and Uri-Query elements are a repeatable options, the Field
	Position (FP) gives the position in the path.		Position (FP) gives the position in the path.
	A Mapping list can be used to reduce the size of variable Paths or		A Mapping list can be used to reduce the size of variable Paths or
	Queries. In that case, to optimize the compression, several elements		Queries. In that case, to optimize the compression, several elements
	can be regrouped into a single entry. Numbering of elements do not		can be regrouped into a single entry. Numbering of elements do not
	change, MO comparison is set with the first element of the matching.		change, MO comparison is set with the first element of the matching.
	+-------------+---+--+--+--------+---------+-------------+		+-------------+---+--+--+--------+---------+-------------+
	| Field |FL |FP|DI| Target | Match | CDA |		| Field |FL |FP|DI| Target | Match | CDA |
	| | | | | Value | Opera. | |		| | | | | Value | Opera. | |
	+-------------+---+--+--+--------+---------+-------------+		+-------------+---+--+--+--------+---------+-------------+
	|URI-Path | | 1|up|["/a/b",|equal |not-sent |		|URI-Path | | 1|up|["/a/b",|equal |not-sent |
	| | | | |"/c/d"] | | |		| | | | |"/c/d"] | | |
	|URI-Path |var| 3|up| |ignore |value-sent |		|URI-Path |var| 3|up| |ignore |value-sent |
	+-------------+---+--+--+--------+---------+-------------+		+-------------+---+--+--+--------+---------+-------------+
	Figure 2: complex path example		Figure 4: complex path example
	In Figure 2 a single bit residue can be used to code one of the 2		In Figure 4 a single bit residue can be used to code one of the 2
	paths. If regrouping were not allowed, a 2 bits residue would be		paths. If regrouping were not allowed, a 2 bits residue would be
	needed. The third path element is sent as a variable size residue.		needed. The third path element is sent as a variable size residue.
	5.3.1. Variable length Uri-Path and Uri-Query		5.3.1. Variable length Uri-Path and Uri-Query
	When the length is not known at the Rule creation, the Field Length		When the length is not known at the Rule creation, the Field Length
	MUST be set to variable, and the unit is set to bytes.		MUST be set to variable, and the unit is set to bytes.
	The MSB MO can be applied to a Uri-Path or Uri-Query element. Since		The MSB MO can be applied to a Uri-Path or Uri-Query element. Since
	MSB value is given in bit, the size MUST always be a multiple of 8		MSB value is given in bit, the size MUST always be a multiple of 8
	skipping to change at page 10, line 17 ¶		skipping to change at page 11, line 29 ¶
	+-------------+---+--+--+--------+---------+-------------+		+-------------+---+--+--+--------+---------+-------------+
	| Field |FL |FP|DI| Target | Match | CDA |		| Field |FL |FP|DI| Target | Match | CDA |
	| | | | | Value | Opera. | |		| | | | | Value | Opera. | |
	+-------------+---+--+--+--------+---------+-------------+		+-------------+---+--+--+--------+---------+-------------+
	|URI-Path | 8| 1|up|"c" |equal |not-sent |		|URI-Path | 8| 1|up|"c" |equal |not-sent |
	|URI-Path |var| 2|up| |ignore |value-sent |		|URI-Path |var| 2|up| |ignore |value-sent |
	|URI-Query |var| 1|up|"k=" |MSB(16) |LSB |		|URI-Query |var| 1|up|"k=" |MSB(16) |LSB |
	+-------------+---+--+--+--------+---------+-------------+		+-------------+---+--+--+--------+---------+-------------+
	Figure 3: CORECONF URI compression		Figure 5: CORECONF URI compression
	Figure 3 shows the parsing and the compression of the URI, where c is		Figure 5 shows the parsing and the compression of the URI, where c is
	not sent. The second element is sent with the length (i.e. 0x2 X 6)		not sent. The second element is sent with the length (i.e. 0x2 X 6)
	followed by the query option (i.e. 0x05 "eth0").		followed by the query option (i.e. 0x05 "eth0").
	5.3.2. Variable number of path or query elements		5.3.2. Variable number of path or query elements
	The number of Uri-path or Uri-Query elements in a Rule is fixed at		The number of Uri-path or Uri-Query elements in a Rule is fixed at
	the Rule creation time. If the number varies, several Rules SHOULD		the Rule creation time. If the number varies, several Rules SHOULD
	be created to cover all the possibilities. Another possibility is to		be created to cover all the possibilities. Another possibility is to
	define the length of Uri-Path to variable and send a Compression		define the length of Uri-Path to variable and send a Compression
	Residue with a length of 0 to indicate that this Uri-Path is empty.		Residue with a length of 0 to indicate that this Uri-Path is empty.
	This adds 4 bits to the variable Residue size. See section 7.5.2		This adds 4 bits to the variable Residue size. See section 7.5.2
	[rfc8724]		[rfc8724]
	5.4. CoAP option Size1, Size2, Proxy-URI and Proxy-Scheme fields		5.4. CoAP option Size1, Size2, Proxy-URI and Proxy-Scheme fields
	These fields are unidirectional and MUST NOT be set to bidirectional
	in a Rule DI entry, see section 7.1 of the [rfc8724]. They are used
	only by the client to access a specific resource and are never found
	in server response.
	If the field value has to be sent, TV is not set, MO is set to		If the field value has to be sent, TV is not set, MO is set to
	"ignore" and CDA is set to "value-sent". A mapping MAY also be used.		"ignore" and CDA is set to "value-sent". A mapping MAY also be used.
	Otherwise, the TV is set to the value, MO is set to "equal" and CDA		Otherwise, the TV is set to the value, MO is set to "equal" and CDA
	is set to "not-sent".		is set to "not-sent".
	5.5. CoAP option ETag, If-Match, If-None-Match, Location-Path and		5.5. CoAP option ETag, If-Match, If-None-Match, Location-Path and
	Location-Query fields		Location-Query fields
	These fields are unidirectional.
	These fields values cannot be stored in a Rule entry. They MUST		These fields values cannot be stored in a Rule entry. They MUST
	always be sent with the Compression Residues.		always be sent with the Compression Residues.
	6. SCHC compression of CoAP extension RFCs		6. SCHC compression of CoAP extension RFCs
	6.1. Block		6.1. Block
	Block [rfc7959] allows a fragmentation at the CoAP level. SCHC also		Block [rfc7959] allows a fragmentation at the CoAP level. SCHC also
	includes a fragmentation protocol. They can be both used. If a		includes a fragmentation protocol. They can be both used. If a
	block option is used, its content MUST be sent as a Compression		block option is used, its content MUST be sent as a Compression
	skipping to change at page 12, line 20 ¶		skipping to change at page 13, line 20 ¶
	|<-- CoAP -->|<------ CoAP OSCORE_piv ------> |		|<-- CoAP -->|<------ CoAP OSCORE_piv ------> |
	OSCORE_flags		OSCORE_flags
	<- 1 byte -> <------ s bytes ----->		<- 1 byte -> <------ s bytes ----->
	+------------+----------------------+-----------------------+		+------------+----------------------+-----------------------+
	| s (if any) | kid context (if any) | kid (if any) ... |		| s (if any) | kid context (if any) | kid (if any) ... |
	+------------+----------------------+-----------------------+		+------------+----------------------+-----------------------+
	| | |		| | |
	| <------ CoAP OSCORE_kidctxt ----->|<-- CoAP OSCORE_kid -->|		| <------ CoAP OSCORE_kidctxt ----->|<-- CoAP OSCORE_kid -->|
	Figure 4: OSCORE Option		Figure 6: OSCORE Option
	The encoding of the OSCORE Option Value defined in Section 6.1 of		The encoding of the OSCORE Option Value defined in Section 6.1 of
	[rfc8613] is repeated in Figure 4.		[rfc8613] is repeated in Figure 6.
	The first byte specifies the content of the OSCORE options using		The first byte specifies the content of the OSCORE options using
	flags. The three most significant bits of this byte are reserved and		flags. The three most significant bits of this byte are reserved and
	always set to 0. Bit h, when set, indicates the presence of the kid		always set to 0. Bit h, when set, indicates the presence of the kid
	context field in the option. Bit k, when set, indicates the presence		context field in the option. Bit k, when set, indicates the presence
	of a kid field. The three least significant bits n indicate the		of a kid field. The three least significant bits n indicate the
	length of the piv (Partial Initialization Vector) field in bytes.		length of the piv (Partial Initialization Vector) field in bytes.
	When n = 0, no piv is present.		When n = 0, no piv is present.
	The flag byte is followed by the piv field, kid context field, and		The flag byte is followed by the piv field, kid context field, and
	skipping to change at page 13, line 6 ¶		skipping to change at page 14, line 6 ¶
	o CoAP OSCORE_flags,		o CoAP OSCORE_flags,
	o CoAP OSCORE_piv,		o CoAP OSCORE_piv,
	o CoAP OSCORE_kidctxt,		o CoAP OSCORE_kidctxt,
	o CoAP OSCORE_kid.		o CoAP OSCORE_kid.
	The OSCORE Option shows superimposed these four fields using the		The OSCORE Option shows superimposed these four fields using the
	format Figure 4, the CoAP OSCORE_kidctxt field includes the size bits		format Figure 6, the CoAP OSCORE_kidctxt field includes the size bits
	s.		s.
	7. Examples of CoAP header compression		7. Examples of CoAP header compression
	7.1. Mandatory header with CON message		7.1. Mandatory header with CON message
	In this first scenario, the LPWAN Compressor at the Network Gateway		In this first scenario, the LPWAN Compressor at the Network Gateway
	side receives from an Internet client a POST message, which is		side receives from an Internet client a POST message, which is
	immediately acknowledged by the Device. For this simple scenario,		immediately acknowledged by the Device. For this simple scenario,
	the Rules are described Figure 5.		the Rules are described Figure 7.
	RuleID 1		RuleID 1
	+-------------+--+--+--+------+---------+-------------++------------+		+-------------+--+--+--+------+---------+-------------++------------+
	| Field |FL|FP|DI|Target| Match | CDA || Sent |		| Field |FL|FP|DI|Target| Match | CDA || Sent |
	| | | | |Value | Opera. | || [bits] |		| | | | |Value | Opera. | || [bits] |
	+-------------+--+--+--+------+---------+-------------++------------+		+-------------+--+--+--+------+---------+-------------++------------+
	|CoAP version | | |bi| 01 |equal |not-sent || |		|CoAP version | | |bi| 01 |equal |not-sent || |
	|CoAP Type | | |dw| CON |equal |not-sent || |		|CoAP Type | | |dw| CON |equal |not-sent || |
	|CoAP Type | | |up|[ACK, | | || |		|CoAP Type | | |up|[ACK, | | || |
	| | | | | RST] |match-map|matching-sent|| T |		| | | | | RST] |match-map|matching-sent|| T |
	|CoAP TKL | | |bi| 0 |equal |not-sent || |		|CoAP TKL | | |bi| 0 |equal |not-sent || |
	|CoAP Code | | |bi|[0.00,| | || |		|CoAP Code | | |bi|[0.00,| | || |
	| | | | | ... | | || |		| | | | | ... | | || |
	| | | | | 5.05]|match-map|matching-sent|| CC CCC |		| | | | | 5.05]|match-map|matching-sent|| CC CCC |
	|CoAP MID | | |bi| 0000 |MSB(7 ) |LSB || M-ID|		|CoAP MID | | |bi| 0000 |MSB(7 ) |LSB || M-ID|
	|CoAP Uri-Path| | |dw| path |equal 1 |not-sent || |		|CoAP Uri-Path| | |dw| path |equal 1 |not-sent || |
	+-------------+--+--+--+------+---------+-------------++------------+		+-------------+--+--+--+------+---------+-------------++------------+
	Figure 5: CoAP Context to compress header without token		Figure 7: CoAP Context to compress header without token
	The version and Token Length fields are elided. The 26 method and		The version and Token Length fields are elided. The 26 method and
	response codes defined in [rfc7252] has been shrunk to 5 bits using a		response codes defined in [rfc7252] has been shrunk to 5 bits using a
	matching list. Uri-Path contains a single element indicated in the		matching list. Uri-Path contains a single element indicated in the
	matching operator.		matching operator.
	SCHC Compression reduces the header sending only the Type, a mapped		SCHC Compression reduces the header sending only the Type, a mapped
	code and the least significant bits of Message ID (9 bits in the		code and the least significant bits of Message ID (9 bits in the
	example above).		example above).
	skipping to change at page 14, line 18 ¶		skipping to change at page 15, line 18 ¶
	messages. The goal, therefore, is to hide as much of the message as		messages. The goal, therefore, is to hide as much of the message as
	possible while still enabling proxy operation.		possible while still enabling proxy operation.
	Conceptually this is achieved by splitting the CoAP message into an		Conceptually this is achieved by splitting the CoAP message into an
	Inner Plaintext and Outer OSCORE Message. The Inner Plaintext		Inner Plaintext and Outer OSCORE Message. The Inner Plaintext
	contains sensitive information which is not necessary for proxy		contains sensitive information which is not necessary for proxy
	operation. This, in turn, is the part of the message which can be		operation. This, in turn, is the part of the message which can be
	encrypted until it reaches its end destination. The Outer Message		encrypted until it reaches its end destination. The Outer Message
	acts as a shell matching the format of a regular CoAP message, and		acts as a shell matching the format of a regular CoAP message, and
	includes all Options and information needed for proxy operation and		includes all Options and information needed for proxy operation and
	caching. This decomposition is illustrated in Figure 6.		caching. This decomposition is illustrated in Figure 8.
	CoAP options are sorted into one of 3 classes, each granted a		CoAP options are sorted into one of 3 classes, each granted a
	specific type of protection by the protocol:		specific type of protection by the protocol:
	o Class E: Encrypted options moved to the Inner Plaintext,		o Class E: Encrypted options moved to the Inner Plaintext,
	o Class I: Integrity-protected options included in the AAD for the		o Class I: Integrity-protected options included in the AAD for the
	encryption of the Plaintext but otherwise left untouched in the		encryption of the Plaintext but otherwise left untouched in the
	Outer Message,		Outer Message,
	skipping to change at page 15, line 38 ¶		skipping to change at page 16, line 38 ¶
	+-+-+---+--------+---------------+....+ +-------+-----......+		+-+-+---+--------+---------------+....+ +-------+-----......+
	| Token | | Options (E) |		| Token | | Options (E) |
	+--------------------------------.....+ +-------+------.....+		+--------------------------------.....+ +-------+------.....+
	| Options (IU) | | OxFF |		| Options (IU) | | OxFF |
	. . +-------+-----------+		. . +-------+-----------+
	. OSCORE Option . | |		. OSCORE Option . | |
	+------+-------------------+ | Payload |		+------+-------------------+ | Payload |
	| 0xFF | | |		| 0xFF | | |
	+------+ +-------------------+		+------+ +-------------------+
	Figure 6: A CoAP message is split into an OSCORE outer and plaintext		Figure 8: A CoAP message is split into an OSCORE outer and plaintext
	Figure 6 shows the message format for the OSCORE Message and		Figure 8 shows the message format for the OSCORE Message and
	Plaintext.		Plaintext.
	In the Outer Header, the original message code is hidden and replaced		In the Outer Header, the original message code is hidden and replaced
	by a default dummy value. As seen in Sections 4.1.3.5 and 4.2 of the		by a default dummy value. As seen in Sections 4.1.3.5 and 4.2 of the
	[rfc8613], the message code is replaced by POST for requests and		[rfc8613], the message code is replaced by POST for requests and
	Changed for responses when Observe is not used. If Observe is used,		Changed for responses when Observe is not used. If Observe is used,
	the message code is replaced by FETCH for requests and Content for		the message code is replaced by FETCH for requests and Content for
	responses.		responses.
	The original message code is put into the first byte of the		The original message code is put into the first byte of the
	Plaintext. Following the message code, the class E options comes and		Plaintext. Following the message code, the class E options comes and
	if present the original message Payload is preceded by its payload		if present the original message Payload is preceded by its payload
	marker.		marker.
	The Plaintext is now encrypted by an AEAD algorithm which integrity		The Plaintext is now encrypted by an AEAD algorithm which integrity
	protects Security Context parameters and eventually any class I		protects Security Context parameters and eventually any class I
	options from the Outer Header. Currently no CoAP options are marked		options from the Outer Header. Currently no CoAP options are marked
	class I. The resulting Ciphertext becomes the new Payload of the		class I. The resulting Ciphertext becomes the new Payload of the
	OSCORE message, as illustrated in Figure 7.		OSCORE message, as illustrated in Figure 9.
	This Ciphertext is, as defined in RFC 5116, the concatenation of the		This Ciphertext is, as defined in RFC 5116, the concatenation of the
	encrypted Plaintext and its authentication tag. Note that Inner		encrypted Plaintext and its authentication tag. Note that Inner
	Compression only affects the Plaintext before encryption, thus we can		Compression only affects the Plaintext before encryption, thus we can
	only aim to reduce this first, variable length component of the		only aim to reduce this first, variable length component of the
	Ciphertext. The authentication tag is fixed in length and considered		Ciphertext. The authentication tag is fixed in length and considered
	part of the cost of protection.		part of the cost of protection.
	Outer Header		Outer Header
	+-+-+---+--------+---------------+		+-+-+---+--------+---------------+
	skipping to change at page 16, line 39 ¶		skipping to change at page 17, line 39 ¶
	+------+-------------------+		+------+-------------------+
	| 0xFF |		| 0xFF |
	+------+---------------------------+		+------+---------------------------+
	| |		| |
	| Ciphertext: Encrypted Inner |		| Ciphertext: Encrypted Inner |
	| Header and Payload |		| Header and Payload |
	| + Authentication Tag |		| + Authentication Tag |
	| |		| |
	+----------------------------------+		+----------------------------------+
	Figure 7: OSCORE message		Figure 9: OSCORE message
	The SCHC Compression scheme consists of compressing both the		The SCHC Compression scheme consists of compressing both the
	Plaintext before encryption and the resulting OSCORE message after		Plaintext before encryption and the resulting OSCORE message after
	encryption, see Figure 8.		encryption, see Figure 10.
	This translates into a segmented process where SCHC compression is		This translates into a segmented process where SCHC compression is
	applied independently in 2 stages, each with its corresponding set of		applied independently in 2 stages, each with its corresponding set of
	Rules, with the Inner SCHC Rules and the Outer SCHC Rules. This way		Rules, with the Inner SCHC Rules and the Outer SCHC Rules. This way
	compression is applied to all fields of the original CoAP message.		compression is applied to all fields of the original CoAP message.
	Note that since the Inner part of the message can only be decrypted		Note that since the Inner part of the message can only be decrypted
	by the corresponding end-point, this end-point will also have to		by the corresponding end-point, this end-point will also have to
	implement Inner SCHC Compression/Decompression.		implement Inner SCHC Compression/Decompression.
	skipping to change at page 17, line 41 ¶		skipping to change at page 18, line 41 ¶
	v | +-------+--+		v | +-------+--+
	+--------+ +------------+ | Residue |		+--------+ +------------+ | Residue |
	|RuleID' | | Encryption | <--- +----------+--------+		|RuleID' | | Encryption | <--- +----------+--------+
	+--------+--+ +------------+ | |		+--------+--+ +------------+ | |
	| Residue' | | Payload |		| Residue' | | Payload |
	+-----------+-------+ | |		+-----------+-------+ | |
	| Ciphertext | +-------------------+		| Ciphertext | +-------------------+
	| |		| |
	+-------------------+		+-------------------+
	Figure 8: OSCORE Compression Diagram		Figure 10: OSCORE Compression Diagram
	7.3. Example OSCORE Compression		7.3. Example OSCORE Compression
	An example is given with a GET Request and its consequent Content		An example is given with a GET Request and its consequent Content
	Response from a device-based CoAP client to a cloud-based CoAP		Response from a device-based CoAP client to a cloud-based CoAP
	server. A possible set of Rules for the Inner and Outer SCHC		server. A possible set of Rules for the Inner and Outer SCHC
	Compression is shown. A dump of the results and a contrast between		Compression is shown. A dump of the results and a contrast between
	SCHC + OSCORE performance with SCHC + COAP performance is also		SCHC + OSCORE performance with SCHC + COAP performance is also
	listed. This gives an approximation to the cost of security with		listed. This gives an approximation to the cost of security with
	SCHC-OSCORE.		SCHC-OSCORE.
	Our first example CoAP message is the GET Request in Figure 9		Our first example CoAP message is the GET Request in Figure 11
	Original message:		Original message:
	=================		=================
	0x4101000182bb74656d7065726174757265		0x4101000182bb74656d7065726174757265
	Header:		Header:
	0x4101		0x4101
	01 Ver		01 Ver
	00 CON		00 CON
	0001 tkl		0001 tkl
	skipping to change at page 18, line 28 ¶		skipping to change at page 19, line 28 ¶
	0x0001 = mid		0x0001 = mid
	0x82 = token		0x82 = token
	Options:		Options:
	0xbb74656d7065726174757265		0xbb74656d7065726174757265
	Option 11: URI_PATH		Option 11: URI_PATH
	Value = temperature		Value = temperature
	Original msg length: 17 bytes.		Original msg length: 17 bytes.
	Figure 9: CoAP GET Request		Figure 11: CoAP GET Request
	Its corresponding response is the CONTENT Response in Figure 10.		Its corresponding response is the CONTENT Response in Figure 12.
	Original message:		Original message:
	=================		=================
	0x6145000182ff32332043		0x6145000182ff32332043
	Header:		Header:
	0x6145		0x6145
	01 Ver		01 Ver
	10 ACK		10 ACK
	0001 tkl		0001 tkl
	skipping to change at page 18, line 52 ¶		skipping to change at page 19, line 52 ¶
	0x0001 = mid		0x0001 = mid
	0x82 = token		0x82 = token
	0xFF Payload marker		0xFF Payload marker
	Payload:		Payload:
	0x32332043		0x32332043
	Original msg length: 10		Original msg length: 10
	Figure 10: CoAP CONTENT Response		Figure 12: CoAP CONTENT Response
	The SCHC Rules for the Inner Compression include all fields that are		The SCHC Rules for the Inner Compression include all fields that are
	already present in a regular CoAP message. The methods described in		already present in a regular CoAP message. The methods described in
	Section 4 applies to these fields. As an example, see Figure 11.		Section 4 applies to these fields. As an example, see Figure 13.
	RuleID 0		RuleID 0
	+---------------+--+--+-----------+-----------+-----------++------+		+---------------+--+--+-----------+-----------+-----------++------+
	| Field |FP|DI| Target | MO | CDA || Sent |		| Field |FP|DI| Target | MO | CDA || Sent |
	| | | | Value | | ||[bits]|		| | | | Value | | ||[bits]|
	+---------------+--+--+-----------+-----------+-----------++------+		+---------------+--+--+-----------+-----------+-----------++------+
	|CoAP Code | |up| 1 | equal |not-sent || |		|CoAP Code | |up| 1 | equal |not-sent || |
	|CoAP Code | |dw|[69,132] | match-map |match-sent || c |		|CoAP Code | |dw|[69,132] | match-map |match-sent || c |
	|CoAP Uri-Path | |up|temperature| equal |not-sent || |		|CoAP Uri-Path | |up|temperature| equal |not-sent || |
	|COAP Option-End| |dw| 0xFF | equal |not-sent || |		|COAP Option-End| |dw| 0xFF | equal |not-sent || |
	+---------------+--+--+-----------+-----------+-----------++------+		+---------------+--+--+-----------+-----------+-----------++------+
	Figure 11: Inner SCHC Rules		Figure 13: Inner SCHC Rules
	Figure 12 shows the Plaintext obtained for our example GET Request		Figure 14 shows the Plaintext obtained for our example GET Request
	and follows the process of Inner Compression and Encryption until we		and follows the process of Inner Compression and Encryption until we
	end up with the Payload to be added in the outer OSCORE Message.		end up with the Payload to be added in the outer OSCORE Message.
	In this case the original message has no payload and its resulting		In this case the original message has no payload and its resulting
	Plaintext can be compressed up to only 1 byte (size of the RuleID).		Plaintext can be compressed up to only 1 byte (size of the RuleID).
	The AEAD algorithm preserves this length in its first output, but		The AEAD algorithm preserves this length in its first output, but
	also yields a fixed-size tag which cannot be compressed and has to be		also yields a fixed-size tag which cannot be compressed and has to be
	included in the OSCORE message. This translates into an overhead in		included in the OSCORE message. This translates into an overhead in
	total message length, which limits the amount of compression that can		total message length, which limits the amount of compression that can
	be achieved and plays into the cost of adding security to the		be achieved and plays into the cost of adding security to the
	skipping to change at page 20, line 44 ¶		skipping to change at page 21, line 44 ¶
	| (piv = 0x04)		| (piv = 0x04)
	v		v
	_________________________________________________		_________________________________________________
	| |		| |
	| encrypted_plaintext = 0xa2 (1 byte) |		| encrypted_plaintext = 0xa2 (1 byte) |
	| tag = 0xc54fe1b434297b62 (8 bytes) |		| tag = 0xc54fe1b434297b62 (8 bytes) |
	| |		| |
	| ciphertext = 0xa2c54fe1b434297b62 (9 bytes) |		| ciphertext = 0xa2c54fe1b434297b62 (9 bytes) |
	|_________________________________________________|		|_________________________________________________|
	Figure 12: Plaintext compression and encryption for GET Request		Figure 14: Plaintext compression and encryption for GET Request
	In Figure 13 the process is repeated for the example CONTENT		In Figure 15 the process is repeated for the example CONTENT
	Response. The residue is 1 bit long. Note that since SCHC adds		Response. The residue is 1 bit long. Note that since SCHC adds
	padding after the payload, this misalignment causes the hexadecimal		padding after the payload, this misalignment causes the hexadecimal
	code from the payload to differ from the original, even though it has		code from the payload to differ from the original, even though it has
	not been compressed.		not been compressed.
	On top of this, the overhead from the tag bytes is incurred as		On top of this, the overhead from the tag bytes is incurred as
	before.		before.
	________________________________________________________		________________________________________________________
	| |		| |
	skipping to change at page 21, line 51 ¶		skipping to change at page 22, line 51 ¶
	| (piv = 0x04)		| (piv = 0x04)
	v		v
	_________________________________________________________		_________________________________________________________
	| |		| |
	| encrypted_plaintext = 0x10c6d7c26cc1 (6 bytes) |		| encrypted_plaintext = 0x10c6d7c26cc1 (6 bytes) |
	| tag = 0xe9aef3f2461e0c29 (8 bytes) |		| tag = 0xe9aef3f2461e0c29 (8 bytes) |
	| |		| |
	| ciphertext = 0x10c6d7c26cc1e9aef3f2461e0c29 (14 bytes) |		| ciphertext = 0x10c6d7c26cc1e9aef3f2461e0c29 (14 bytes) |
	|_________________________________________________________|		|_________________________________________________________|
	Figure 13: Plaintext compression and encryption for CONTENT Response		Figure 15: Plaintext compression and encryption for CONTENT Response
	The Outer SCHC Rules (Figure 16) must process the OSCORE Options		The Outer SCHC Rules (Figure 18) must process the OSCORE Options
	fields. In Figure 14 and Figure 15 we show a dump of the OSCORE		fields. In Figure 16 and Figure 17 we show a dump of the OSCORE
	Messages generated from our example messages once they have been		Messages generated from our example messages once they have been
	provided with the Inner Compressed Ciphertext in the payload. These		provided with the Inner Compressed Ciphertext in the payload. These
	are the messages that have to be compressed by the Outer SCHC		are the messages that have to be compressed by the Outer SCHC
	Compression.		Compression.
	Protected message:		Protected message:
	==================		==================
	0x4102000182d8080904636c69656e74ffa2c54fe1b434297b62		0x4102000182d8080904636c69656e74ffa2c54fe1b434297b62
	(25 bytes)		(25 bytes)
	skipping to change at page 22, line 39 ¶		skipping to change at page 23, line 39 ¶
	Value = 0x0904636c69656e74		Value = 0x0904636c69656e74
	09 = 000 0 1 001 Flag byte		09 = 000 0 1 001 Flag byte
	h k n		h k n
	04 piv		04 piv
	636c69656e74 kid		636c69656e74 kid
	0xFF Payload marker		0xFF Payload marker
	Payload:		Payload:
	0xa2c54fe1b434297b62 (9 bytes)		0xa2c54fe1b434297b62 (9 bytes)
	Figure 14: Protected and Inner SCHC Compressed GET Request		Figure 16: Protected and Inner SCHC Compressed GET Request
	Protected message:		Protected message:
	==================		==================
	0x6144000182d008ff10c6d7c26cc1e9aef3f2461e0c29		0x6144000182d008ff10c6d7c26cc1e9aef3f2461e0c29
	(22 bytes)		(22 bytes)
	Header:		Header:
	0x6144		0x6144
	01 Ver		01 Ver
	10 ACK		10 ACK
	skipping to change at page 23, line 29 ¶		skipping to change at page 24, line 29 ¶
	Options:		Options:
	0xd008 (2 bytes)		0xd008 (2 bytes)
	Option 21: OBJECT_SECURITY		Option 21: OBJECT_SECURITY
	Value = b''		Value = b''
	0xFF Payload marker		0xFF Payload marker
	Payload:		Payload:
	0x10c6d7c26cc1e9aef3f2461e0c29 (14 bytes)		0x10c6d7c26cc1e9aef3f2461e0c29 (14 bytes)
	Figure 15: Protected and Inner SCHC Compressed CONTENT Response		Figure 17: Protected and Inner SCHC Compressed CONTENT Response
	For the flag bits, a number of compression methods has been shown to		For the flag bits, a number of compression methods has been shown to
	be useful depending on the application. The simplest alternative is		be useful depending on the application. The simplest alternative is
	to provide a fixed value for the flags, combining MO equal and CDA		to provide a fixed value for the flags, combining MO equal and CDA
	not- sent. This saves most bits but could prevent flexibility.		not- sent. This saves most bits but could prevent flexibility.
	Otherwise, match-mapping could be used to choose from an interested		Otherwise, match-mapping could be used to choose from an interested
	number of configurations to the exchange. Otherwise, MSB could be		number of configurations to the exchange. Otherwise, MSB could be
	used to mask off the 3 hard-coded most significant bits.		used to mask off the 3 hard-coded most significant bits.
	Note that fixing a flag bit will limit the choice of CoAP Options		Note that fixing a flag bit will limit the choice of CoAP Options
	skipping to change at page 24, line 7 ¶		skipping to change at page 25, line 7 ¶
	Note that compressing the sequence numbers effectively reduces the		Note that compressing the sequence numbers effectively reduces the
	maximum amount of sequence numbers that can be used in an exchange.		maximum amount of sequence numbers that can be used in an exchange.
	Once this amount is exceeded, the OSCORE keys need to be re-		Once this amount is exceeded, the OSCORE keys need to be re-
	established.		established.
	The size s included in the kid context field MAY be masked off with		The size s included in the kid context field MAY be masked off with
	CDA MSB. The rest of the field could have additional bits masked		CDA MSB. The rest of the field could have additional bits masked
	off, or have the whole field be fixed with MO equal and CDA not-sent.		off, or have the whole field be fixed with MO equal and CDA not-sent.
	The same holds for the kid field.		The same holds for the kid field.
	Figure 16 shows a possible set of Outer Rules to compress the Outer		Figure 18 shows a possible set of Outer Rules to compress the Outer
	Header.		Header.
	RuleID 0		RuleID 0
	+-------------------+--+--+--------------+--------+---------++------+		+-------------------+--+--+--------------+--------+---------++------+
	| Field |FP|DI| Target | MO | CDA || Sent |		| Field |FP|DI| Target | MO | CDA || Sent |
	| | | | Value | | ||[bits]|		| | | | Value | | ||[bits]|
	+-------------------+--+--+--------------+--------+---------++------+		+-------------------+--+--+--------------+--------+---------++------+
	|CoAP version | |bi| 01 |equal |not-sent || |		|CoAP version | |bi| 01 |equal |not-sent || |
	|CoAP Type | |up| 0 |equal |not-sent || |		|CoAP Type | |up| 0 |equal |not-sent || |
	|CoAP Type | |dw| 2 |equal |not-sent || |		|CoAP Type | |dw| 2 |equal |not-sent || |
	skipping to change at page 24, line 33 ¶		skipping to change at page 25, line 33 ¶
	|CoAP OSCORE_flags | |up| 0x09 |equal |not-sent || |		|CoAP OSCORE_flags | |up| 0x09 |equal |not-sent || |
	|CoAP OSCORE_piv | |up| 0x00 |MSB(4) |LSB ||PPPP |		|CoAP OSCORE_piv | |up| 0x00 |MSB(4) |LSB ||PPPP |
	|COAP OSCORE_kid | |up|0x636c69656e70|MSB(52) |LSB ||KKKK |		|COAP OSCORE_kid | |up|0x636c69656e70|MSB(52) |LSB ||KKKK |
	|COAP OSCORE_kidctxt| |bi| b'' |equal |not-sent || |		|COAP OSCORE_kidctxt| |bi| b'' |equal |not-sent || |
	|CoAP OSCORE_flags | |dw| b'' |equal |not-sent || |		|CoAP OSCORE_flags | |dw| b'' |equal |not-sent || |
	|CoAP OSCORE_piv | |dw| b'' |equal |not-sent || |		|CoAP OSCORE_piv | |dw| b'' |equal |not-sent || |
	|CoAP OSCORE_kid | |dw| b'' |equal |not-sent || |		|CoAP OSCORE_kid | |dw| b'' |equal |not-sent || |
	|COAP Option-End | |dw| 0xFF |equal |not-sent || |		|COAP Option-End | |dw| 0xFF |equal |not-sent || |
	+-------------------+--+--+--------------+--------+---------++------+		+-------------------+--+--+--------------+--------+---------++------+
	Figure 16: Outer SCHC Rules		Figure 18: Outer SCHC Rules
	These Outer Rules are applied to the example GET Request and CONTENT		These Outer Rules are applied to the example GET Request and CONTENT
	Response. The resulting messages are shown in Figure 17 and		Response. The resulting messages are shown in Figure 19 and
	Figure 18.		Figure 20.
	Compressed message:		Compressed message:
	==================		==================
	0x001489458a9fc3686852f6c4 (12 bytes)		0x001489458a9fc3686852f6c4 (12 bytes)
	0x00 RuleID		0x00 RuleID
	1489 Compression Residue		1489 Compression Residue
	458a9fc3686852f6c4 Padded payload		458a9fc3686852f6c4 Padded payload
	Compression Residue:		Compression Residue:
	0b 0001 010 0100 0100 (15 bits -> 2 bytes with padding)		0b 0001 010 0100 0100 (15 bits -> 2 bytes with padding)
	mid tkn piv kid		mid tkn piv kid
	Payload		Payload
	0xa2c54fe1b434297b62 (9 bytes)		0xa2c54fe1b434297b62 (9 bytes)
	Compressed message length: 12 bytes		Compressed message length: 12 bytes
	Figure 17: SCHC-OSCORE Compressed GET Request		Figure 19: SCHC-OSCORE Compressed GET Request
	Compressed message:		Compressed message:
	==================		==================
	0x0014218daf84d983d35de7e48c3c1852 (16 bytes)		0x0014218daf84d983d35de7e48c3c1852 (16 bytes)
	0x00 RuleID		0x00 RuleID
	14 Compression Residue		14 Compression Residue
	218daf84d983d35de7e48c3c1852 Padded payload		218daf84d983d35de7e48c3c1852 Padded payload
	Compression Residue:		Compression Residue:
	0b0001 010 (7 bits -> 1 byte with padding)		0b0001 010 (7 bits -> 1 byte with padding)
	mid tkn		mid tkn
	Payload		Payload
	0x10c6d7c26cc1e9aef3f2461e0c29 (14 bytes)		0x10c6d7c26cc1e9aef3f2461e0c29 (14 bytes)
	Compressed msg length: 16 bytes		Compressed msg length: 16 bytes
	Figure 18: SCHC-OSCORE Compressed CONTENT Response		Figure 20: SCHC-OSCORE Compressed CONTENT Response
	For contrast, we compare these results with what would be obtained by		For contrast, we compare these results with what would be obtained by
	SCHC compressing the original CoAP messages without protecting them		SCHC compressing the original CoAP messages without protecting them
	with OSCORE. To do this, we compress the CoAP messages according to		with OSCORE. To do this, we compress the CoAP messages according to
	the SCHC Rules in Figure 19.		the SCHC Rules in Figure 21.
	RuleID 1		RuleID 1
	+---------------+--+--+-----------+---------+-----------++--------+		+---------------+--+--+-----------+---------+-----------++--------+
	| Field |FP|DI| Target | MO | CDA || Sent |		| Field |FP|DI| Target | MO | CDA || Sent |
	| | | | Value | | || [bits] |		| | | | Value | | || [bits] |
	+---------------+--+--+-----------+---------+-----------++--------+		+---------------+--+--+-----------+---------+-----------++--------+
	|CoAP version | |bi| 01 |equal |not-sent || |		|CoAP version | |bi| 01 |equal |not-sent || |
	|CoAP Type | |up| 0 |equal |not-sent || |		|CoAP Type | |up| 0 |equal |not-sent || |
	|CoAP Type | |dw| 2 |equal |not-sent || |		|CoAP Type | |dw| 2 |equal |not-sent || |
	|CoAP TKL | |bi| 1 |equal |not-sent || |		|CoAP TKL | |bi| 1 |equal |not-sent || |
	|CoAP Code | |up| 2 |equal |not-sent || |		|CoAP Code | |up| 2 |equal |not-sent || |
	|CoAP Code | |dw| [69,132] |match-map|map-sent ||C |		|CoAP Code | |dw| [69,132] |match-map|map-sent ||C |
	|CoAP MID | |bi| 0000 |MSB(12) |LSB ||MMMM |		|CoAP MID | |bi| 0000 |MSB(12) |LSB ||MMMM |
	|CoAP Token | |bi| 0x80 |MSB(5) |LSB ||TTT |		|CoAP Token | |bi| 0x80 |MSB(5) |LSB ||TTT |
	|CoAP Uri-Path | |up|temperature|equal |not-sent || |		|CoAP Uri-Path | |up|temperature|equal |not-sent || |
	|COAP Option-End| |dw| 0xFF |equal |not-sent || |		|COAP Option-End| |dw| 0xFF |equal |not-sent || |
	+---------------+--+--+-----------+---------+-----------++--------+		+---------------+--+--+-----------+---------+-----------++--------+
	Figure 19: SCHC-CoAP Rules (No OSCORE)		Figure 21: SCHC-CoAP Rules (No OSCORE)
	This yields the results in Figure 20 for the Request, and Figure 21		This yields the results in Figure 22 for the Request, and Figure 23
	for the Response.		for the Response.
	Compressed message:		Compressed message:
	==================		==================
	0x0114		0x0114
	0x01 = RuleID		0x01 = RuleID
	Compression Residue:		Compression Residue:
	0b00010100 (1 byte)		0b00010100 (1 byte)
	Compressed msg length: 2		Compressed msg length: 2
	Figure 20: CoAP GET Compressed without OSCORE		Figure 22: CoAP GET Compressed without OSCORE
	Compressed message:		Compressed message:
	==================		==================
	0x010a32332043		0x010a32332043
	0x01 = RuleID		0x01 = RuleID
	Compression Residue:		Compression Residue:
	0b00001010 (1 byte)		0b00001010 (1 byte)
	Payload		Payload
	0x32332043		0x32332043
	Compressed msg length: 6		Compressed msg length: 6
	Figure 21: CoAP CONTENT Compressed without OSCORE		Figure 23: CoAP CONTENT Compressed without OSCORE
	As can be seen, the difference between applying SCHC + OSCORE as		As can be seen, the difference between applying SCHC + OSCORE as
	compared to regular SCHC + COAP is about 10 bytes of cost.		compared to regular SCHC + COAP is about 10 bytes of cost.
	8. IANA Considerations		8. IANA Considerations
	This document has no request to IANA.		This document has no request to IANA.
	9. Security considerations		9. Security considerations
	The Security Considerations of SCHC header compression RFC8724 are		When applied to LPWAN, the Security Considerations of SCHC header
	valid for SCHC CoAP header compression. When CoAP uses OSCORE, the		compression [rfc8724] are valid for SCHC CoAP header compression.
	security considerations defined in RFC8613 does not change when SCHC		When CoAP uses OSCORE, the security considerations defined in
	header compression is applied.		[rfc8613] does not change when SCHC header compression is applied.
	The definition of SCHC over CoAP header fields permits the		The definition of SCHC over CoAP header fields permits the
	compression of header information only. The SCHC header compression		compression of header information only. The SCHC header compression
	itself does not increase or reduce the level of security in the		itself does not increase or reduce the level of security in the
	communication. When the communication does not use any security		communication. When the connection does not use any security
	protocol as OSCORE, DTLS, or other. It is highly necessary to use a		protocol as OSCORE, DTLS, or other, it is highly necessary to use a
	layer two security.		layer two security.
	DoS attacks are possible if an intruder can introduce a compressed		DoS attacks are possible if an intruder can introduce a compressed
	SCHC corrupted packet onto the link and cause a compression		SCHC corrupted packet onto the link and cause a compression
	efficiency reduction. However, an intruder having the ability to add		efficiency reduction. However, an intruder having the ability to add
	corrupted packets at the link layer raises additional security issues		corrupted packets at the link layer raises additional security issues
	than those related to the use of header compression.		than those related to the use of header compression.
	SCHC compression returns variable-length Residues for some CoAP		SCHC compression returns variable-length Residues for some CoAP
	fields. In the compressed header, the length sent is not the		fields. In the compressed header, the length sent is not the
	original header field length but the length of the Residue. So if a		original header field length but the length of the Residue. So if a
	corrupted packet comes to the decompressor with a longer or shorter		corrupted packet comes to the decompressor with a longer or shorter
	length than the one in the original header, SCHC decompression will		length than the one in the original header, SCHC decompression will
	detect an error and drops the packet.		detect an error and drops the packet.
	OSCORE compression is also based on the same compression method		OSCORE compression is also based on the same compression method
	described in [rfc8724]. The size of the Initialisation Vector (IV)		described in [rfc8724]. The size of the Initialisation Vector (IV)
	residue size must be considered carefully. A too large value has an		residue must be considered carefully. A residue size obtained with
	impact on the compression efficiency and a too small value will force		LSB CDA over the IV has an impact on the compression efficiency and
	the device to renew its key more often. This operation may be long		the frequency the device will renew its key. This operation requires
	and energy consuming. The size of the compressed IV MUST be choosen		several exchanges and is energy-consuming.
	regarding the highest expected traffic from the device.
	SCHC header and compression Rules MUST remain tightly coupled.		SCHC header and compression Rules MUST remain tightly coupled.
	Otherwise, an encrypted residue may be decompressed in a different		Otherwise, an encrypted residue may be decompressed differently by
	way by the receiver. To avoid this situation, if the Rule is		the receiver. To avoid this situation, if the Rule is modified in
	modified in one location, the OSCORE keys MUST be re-established.		one location, the OSCORE keys MUST be re-established.
	10. Acknowledgements		10. Acknowledgements
	The authors would like to thank (in alphabetic order): Christian		The authors would like to thank (in alphabetic order): Christian
	Amsuss, Dominique Barthel, Carsten Bormann, Theresa Enghardt, Thomas		Amsuss, Dominique Barthel, Carsten Bormann, Theresa Enghardt, Thomas
	Fossati, Klaus Hartke, Francesca Palombini, Alexander Pelov and Goran		Fossati, Klaus Hartke, Francesca Palombini, Alexander Pelov and Goran
	Selander.		Selander.
	11. Normative References		11. Normative References
	skipping to change at page 29, line 25 ¶		skipping to change at page 30, line 20 ¶
	"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>.
	[rfc8724] Minaburo, A., Toutain, L., Gomez, C., Barthel, D., and JC.		[rfc8724] Minaburo, A., Toutain, L., Gomez, C., Barthel, D., and JC.
	Zuniga, "SCHC: Generic Framework for Static Context Header		Zuniga, "SCHC: Generic Framework for Static Context Header
	Compression and Fragmentation", RFC 8724,		Compression and Fragmentation", RFC 8724,
	DOI 10.17487/RFC8724, April 2020,		DOI 10.17487/RFC8724, April 2020,
	<https://www.rfc-editor.org/info/rfc8724>.		<https://www.rfc-editor.org/info/rfc8724>.
	Appendix A. Extension to the RFC8724 Annex D.
	This section extends the RFC8724 Annex D list.
	o How to establish the End-to-End context initialization using SCHC
	for CoAP header only.
	Authors' Addresses		Authors' Addresses
	Ana Minaburo		Ana Minaburo
	Acklio		Acklio
	1137A avenue des Champs Blancs		1137A avenue des Champs Blancs
	35510 Cesson-Sevigne Cedex		35510 Cesson-Sevigne Cedex
	France		France
	Email: ana@ackl.io		Email: ana@ackl.io
End of changes. 66 change blocks.
	146 lines changed or deleted		185 lines changed or added
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