draft-ietf-cbor-network-addresses-05.txt		draft-ietf-cbor-network-addresses-06.txt
	CBOR Working Group M. Richardson		CBOR Working Group M. Richardson
	Internet-Draft Sandelman Software Works		Internet-Draft Sandelman Software Works
	Intended status: Standards Track C. Bormann		Intended status: Standards Track C. Bormann
	Expires: 13 January 2022 Universität Bremen TZI		Expires: 26 January 2022 Universität Bremen TZI
	12 July 2021		25 July 2021
	CBOR tags for IPv4 and IPv6 addresses and prefixes		CBOR tags for IPv4 and IPv6 addresses and prefixes
	draft-ietf-cbor-network-addresses-05		draft-ietf-cbor-network-addresses-06
	Abstract		Abstract
	This document describes two CBOR Tags to be used with IPv4 and IPv6		This specification describes two CBOR Tags to be used with IPv4 and
	addresses and prefixes.		IPv6 addresses and prefixes.
	RFC-EDITOR-please remove: This work is tracked at https://github.com/		// RFC-EDITOR-please-remove: This work is tracked at
	cbor-wg/cbor-network-address		// https://github.com/cbor-wg/cbor-network-address
	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
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	Copyright Notice		Copyright Notice
	Copyright (c) 2021 IETF Trust and the persons identified as the		Copyright (c) 2021 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
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	license-info) in effect on the date of publication of this document.		license-info) in effect on the date of publication of this document.
	Please review these documents carefully, as they describe your rights		Please review these documents carefully, as they describe your rights
	and restrictions with respect to this document. Code Components		and restrictions with respect to this document. Code Components
	extracted from this document must include Simplified BSD License text		extracted from this document must include Simplified BSD License text
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	provided without warranty as described in the Simplified BSD License.		provided without warranty as described in the Simplified BSD License.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
	2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2		2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
	3. Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . 3		3. Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . 3
	3.1. IPv6 . . . . . . . . . . . . . . . . . . . . . . . . . . 3		3.1. Three Forms . . . . . . . . . . . . . . . . . . . . . . . 3
	3.2. IPv4 . . . . . . . . . . . . . . . . . . . . . . . . . . 3		3.1.1. Addresses . . . . . . . . . . . . . . . . . . . . . . 3
	4. Encoder Consideration for prefixes . . . . . . . . . . . . . 4		3.1.2. Prefixes . . . . . . . . . . . . . . . . . . . . . . 3
	5. Decoder Considerations for prefixes . . . . . . . . . . . . . 5		3.1.3. Interface Definition . . . . . . . . . . . . . . . . 3
	6. CDDL . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5		3.2. IPv6 . . . . . . . . . . . . . . . . . . . . . . . . . . 3
	7. Security Considerations . . . . . . . . . . . . . . . . . . . 6		3.3. IPv4 . . . . . . . . . . . . . . . . . . . . . . . . . . 4
			4. Encoder Considerations for Prefixes . . . . . . . . . . . . . 5
			5. Decoder Considerations for Prefixes . . . . . . . . . . . . . 5
			6. CDDL . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
			7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
	8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7		8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
	8.1. Tag 54 - IPv6 . . . . . . . . . . . . . . . . . . . . . . 7		8.1. Tag 54 - IPv6 . . . . . . . . . . . . . . . . . . . . . . 7
	8.2. Tag 52 - IPv4 . . . . . . . . . . . . . . . . . . . . . . 7		8.2. Tag 52 - IPv4 . . . . . . . . . . . . . . . . . . . . . . 8
	9. Normative References . . . . . . . . . . . . . . . . . . . . 7		9. Normative References . . . . . . . . . . . . . . . . . . . . 8
	Appendix A. Changelog . . . . . . . . . . . . . . . . . . . . . 7		Appendix A. Changelog . . . . . . . . . . . . . . . . . . . . . 8
	Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 8		Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 8
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
	1. Introduction		1. Introduction
	[RFC8949] defines a number of CBOR Tags for common items.		[RFC8949] defines a number of CBOR Tags for common items. Tags 260
			and 261 were later defined through IANA. These tags cover addresses
	Tag 260 and tag 261 was later defined through IANA. These tags cover		(260), and prefixes (261). Tag 260 distinguishes between IPv4, IPv6
	addresses (260), and prefixes (261). Tag 260 distinguishes between		and Ethernet through the length of the byte string only. Tag 261 was
	IPv4, IPv6 and Ethernet through the length of the byte string only.		not documented well enough to be used.
	Tag 261 was not documented well enough to be used.
	The present specification achieves an explicit indication of IPv4 or
	IPv6, and the possibility to omit trailing zeroes.
	This document provides a format for IPv6 and IPv4 addresses,		This specification provides a format for IPv6 and IPv4 addresses,
	prefixes, and addresses with prefixes. Prefixes MUST omit trailing		prefixes, and addresses with prefixes, achieving an explicit
	zeroes in the address. Due to the complexity of testing the value of		indication of IPv4 or IPv6. Prefixes omit trailing zeroes in the
	omitting trailing zeros for addresses was considered non-essential		address. (Due to the complexity of testing, the value of omitting
	and support for that was removed in this specification.		trailing zeros for addresses was considered non-essential and support
			for that was removed in this specification.)
	This document does not deal with 6 or 8-byte Ethernet addressees.		This specification does not deal with 6 or 8-byte Ethernet addresses.
	2. Terminology		2. 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.
	3. Protocol		3. Protocol
	These tags can applied to byte strings to represent a single address.		3.1. Three Forms
			3.1.1. Addresses
			These tags can be applied to byte strings to represent a single
			address.
			This form is called the Address Format.
			3.1.2. Prefixes
	When applied to an array that starts with a number, they represent a		When applied to an array that starts with a number, they represent a
	CIDR-style prefix of that length. When a byte string (without		CIDR-style prefix of that length.
	prefix) appears in a context where a prefix is expected, then it is
	to be assumed that all bits are relevant. That is, for IPv4, a /32		When the Address Format (i.e., without prefix) appears in a context
	is implied, and for IPv6, a /128 is implied.		where a prefix is expected, then it is to be assumed that all bits
			are relevant. That is, for IPv4, a /32 is implied, and for IPv6, a
			/128 is implied.
			This form is called the Prefix Format.
			3.1.3. Interface Definition
	When applied to an array that starts with a byte string, that stands		When applied to an array that starts with a byte string, that stands
	for an IP address, followed by the bit length of a prefix built out		for an IP address, followed by the bit length of a prefix built out
	of the first "length" bits of the address.		of the first "length" bits of the address.
	3.1. IPv6		This form is called the Interface Format.
			3.2. IPv6
	IANA has allocated tag 54 for IPv6 uses. (Note that this is the		IANA has allocated tag 54 for IPv6 uses. (Note that this is the
	ASCII code for '6'.)		ASCII code for '6'.)
	An IPv6 address is to be encoded as a sixteen-byte byte string		An IPv6 address is to be encoded as a sixteen-byte byte string
	(Section 3.1 of [RFC8949], major type 2), enclosed in Tag number 54.		(Section 3.1 of [RFC8949], major type 2), enclosed in Tag number 54.
			For example:
			54(h'20010db81234DEEDBEEFCAFEFACEFEED')
	An IPv6 prefix, such as 2001:db8:1234::/48 is to be encoded as a two		An IPv6 prefix, such as 2001:db8:1234::/48 is to be encoded as a two
	element array, with the length of the prefix first. Trailing zero		element array, with the length of the prefix first. Trailing zero
	bytes MUST be omitted.		bytes MUST be omitted.
	For example:		For example:
	54([ 48, h'20010db81234'])		54([48, h'20010db81234'])
	An IPv6 address combined with a prefix length, such as being used for		An IPv6 address combined with a prefix length, such as being used for
	configuring an interface, is to be encoded as a two element array,		configuring an interface, is to be encoded as a two element array,
	with the (full-length) IPv6 address first and the length of the		with the (full-length) IPv6 address first and the length of the
	associated network the prefix next.		associated network the prefix next.
	For example:		For example:
	54([h'20010db81234DEEDBEEFCAFEFACEFEED', 56])		54([h'20010db81234DEEDBEEFCAFEFACEFEED', 56])
	Note that the address-with-prefix form can be reliably distinguished		Note that the address-with-prefix form can be reliably distinguished
	from the prefix form only in the sequence of the array elements.		from the prefix form only in the sequence of the array elements.
	3.2. IPv4		3.3. IPv4
	IANA has allocated tag 52 for IPv4 uses. (Note that this is the		IANA has allocated tag 52 for IPv4 uses. (Note that this is the
	ASCII code for '4'.)		ASCII code for '4'.)
	An IPv4 address is to be encoded as a four-byte byte string		An IPv4 address is to be encoded as a four-byte byte string
	(Section 3.1 of [RFC8949], major type 2), enclosed in Tag number 52.		(Section 3.1 of [RFC8949], major type 2), enclosed in Tag number 52.
			For example:
			52(h'C0000201')
	An IPv4 prefix, such as 192.0.2.0/24 is to be encoded as a two		An IPv4 prefix, such as 192.0.2.0/24 is to be encoded as a two
	element array, with the length of the prefix first. Trailing zero		element array, with the length of the prefix first. Trailing zero
	bytes MUST be omitted.		bytes MUST be omitted.
	For example:		For example:
	52([ 24, h'C00002'])		52([24, h'C00002'])
	An IPv4 address combined with a prefix length, such as being used for		An IPv4 address combined with a prefix length, such as being used for
	configuring an interface, is to be encoded as a two element array,		configuring an interface, is to be encoded as a two element array,
	with the (full-length) IPv4 address first and the length of the		with the (full-length) IPv4 address first and the length of the
	associated network the prefix next.		associated network the prefix next.
	For example, 192.0.2.1/24 is to be encoded as a two element array,		For example, 192.0.2.1/24 is to be encoded as a two element array,
	with the length of the prefix (implied 192.0.2.0/24) last.		with the length of the prefix (implied 192.0.2.0/24) last.
	52([ h'C0000201', 24])		52([h'C0000201', 24])
	Note that the address-with-prefix form can be reliably distinguished		Note that the address-with-prefix form can be reliably distinguished
	from the prefix form only in the sequence of the array elements.		from the prefix form only in the sequence of the array elements.
	4. Encoder Consideration for prefixes		4. Encoder Considerations for Prefixes
	An encoder may omit as many right-hand (trailing) bytes which are all		For the byte strings used in representing prefixes, an encoder MUST
	zero as it wishes.		omit any right-aligned (trailing) sequence of bytes that are all
			zero.
	There is no relationship between the number of bytes omitted and the		There is no relationship between the number of bytes omitted and the
	prefix length. For instance, the prefix 2001:db8::/64 is optimally		prefix length. For instance, the prefix 2001:db8::/64 is encoded as:
	encoded as:
	54([64, h'20010db8'])		54([64, h'20010db8'])
	An encoder MUST take care to set all trailing bits to zero. While		An encoder MUST take care to set all trailing bits in the final byte
	decoders are expected to ignore them, such garbage entities could be		to zero, if any. While decoders are expected to ignore them, such
	used as a covert channel, or may reveal the state of what would		garbage entities could be used as a covert channel, or may reveal the
	otherewise be private memory contents. So for example,		state of what would otherwise be private memory contents. So for
	2001:db8:1230::/44 MUST be encoded as:		example, "2001:db8:1230::/44" MUST be encoded as:
	52([44, h'20010db81230'])		52([44, h'20010db81230'])
	even though variations like:		even though variations like:
	54([44, h'20010db81233']) WRONG		54([44, h'20010db81233']) WRONG
	54([45, h'20010db8123f']) WRONG		54([45, h'20010db8123f']) WRONG
	would be parsed in the exact same way.		would be parsed in the exact same way.
	The same considerations apply to IPv4 prefixes.		The same considerations apply to IPv4 prefixes.
	5. Decoder Considerations for prefixes		5. Decoder Considerations for Prefixes
	A decoder MUST consider all bits to the right of the prefix length to		A decoder MUST consider all bits to the right of the prefix length to
	be zero.		be zero.
	A decoder MUST handle the case where a prefix length specifies that		A decoder MUST handle the case where a prefix length specifies that
	more bits are relevant than are actually present in the byte-string.		more bits are relevant than are actually present in the byte-string.
	As a pathological case, ::/128 can be encoded as		As a pathological case, ::/128 can be encoded as
	54([128, h''])		54([128, h''])
			A recommendation for implementations is to first create an array of
			16 (or 4) zero bytes.
	A recommendation for implementation is to first create an array of 16		Then taking whichever is smaller between (a) the length of the
	(or 4) bytes in size, set it all to zero.		included byte-string, and (b) the number of bytes covered by the
			prefix-length rounded up to the next multiple of 8: fail if that
			number is greater than 16 (or 4), and then copy that many bytes from
			the byte-string into the array.
	Then looking at the length of the included byte-string, and of the		Finally, looking at the last three bits of the prefix-length in bits
	prefix-length, rounded up to the next multiple of 8, and taking		(that is, the prefix-length modulo 8), use a static array of 8 values
	whichever is smaller, copy that many bytes from the byte-string into		to force the lower, non-relevant bits to zero, or simply:
	the array.
	Finally, looking at the last three bits of the prefix-length (that		unused_bits = (-prefix_length_in_bits) & 7;
	is, the prefix-length modulo 8), use a static array of 8 values to		if (length_in_bytes > 0)
	force the lower bits, non-relevant bits to zero.		address_bytes[length_in_bytes - 1] &= (0xFF << unused_bits);
	A particularly paranoid decoder could examine the lower non-relevant		A particularly paranoid decoder could examine the lower non-relevant
	bits to determine if they are non-zero, and reject the prefix. This		bits to determine if they are non-zero, and reject the prefix. This
	would detect non-compliant encoders, or a possible covert channel.		would detect non-compliant encoders, or a possible covert channel.
			if (length_in_bytes > 0 &&
			(address_bytes[length_in_bytes - 1] & ~(0xFF << unused_bits))
			!= 0)
			fail();
	6. CDDL		6. CDDL
	For use with CDDL [RFC8610], the typenames defined in Figure 1 are		For use with CDDL [RFC8610], the typenames defined in Figure 1 are
	recommended:		recommended:
	ip-address-or-prefix = ipv6-address-or-prefix /		ip-address-or-prefix = ipv6-address-or-prefix /
	ipv4-address-or-prefix		ipv4-address-or-prefix
	ipv6-address-or-prefix = #6.54(ipv6-address /		ipv6-address-or-prefix = #6.54(ipv6-address /
	ipv6-address-with-prefix /		ipv6-address-with-prefix /
	skipping to change at page 6, line 36 ¶		skipping to change at page 7, line 36 ¶
	ipv6-prefix-bytes = bytes .size (uint .le 16)		ipv6-prefix-bytes = bytes .size (uint .le 16)
	ipv4-prefix-bytes = bytes .size (uint .le 4)		ipv4-prefix-bytes = bytes .size (uint .le 4)
	Figure 1		Figure 1
	7. Security Considerations		7. Security Considerations
	Identifying which byte sequences in a protocol are addresses may		Identifying which byte sequences in a protocol are addresses may
	allow an attacker or eavesdropper to better understand what parts of		allow an attacker or eavesdropper to better understand what parts of
	a packet to attack.		a packet to attack. That information, however, is likely to be found
			in the relevant RFCs anyway, so this is not a significant exposure.
	Reading the relevant RFC may provide more information, so it would
	seem that any additional security that was provided by not being able
	to identify what are IP addresses falls into the security by
	obscurity category.
	The right-hand bits of the prefix, after the prefix-length, are		The right-hand bits of the prefix, after the prefix-length, are
	ignored by this protocol. A malicious party could use them to		ignored by this protocol. A malicious party could use them to
	transmit covert data in a way that would not affect the primary use		transmit covert data in a way that would not affect the primary use
	of this encoding. Such abuse would be detected by examination of the		of this encoding. Such abuse would be detected by examination of the
	raw protocol bytes. Users of this encoding should be aware of this		raw protocol bytes. Users of this encoding should be aware of this
	possibility.		possibility.
	8. IANA Considerations		8. IANA Considerations
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