draft-ietf-dnsop-server-cookies-01.txt		draft-ietf-dnsop-server-cookies-02.txt
	DNSOP Working Group O. Sury		DNSOP Working Group O. Sury
	Internet-Draft Internet Systems Consortium		Internet-Draft Internet Systems Consortium
	Updates: 7873 (if approved) W. Toorop		Updates: 7873 (if approved) W. Toorop
	Intended status: Standards Track NLnet Labs		Intended status: Standards Track NLnet Labs
	Expires: May 7, 2020 D. Eastlake 3rd		Expires: May 21, 2020 D. Eastlake 3rd
	Futurewei Technologies		Futurewei Technologies
	M. Andrews		M. Andrews
	Internet Systems Consortium		Internet Systems Consortium
	November 4, 2019		November 18, 2019
	Interoperable Domain Name System (DNS) Server Cookies		Interoperable Domain Name System (DNS) Server Cookies
	draft-ietf-dnsop-server-cookies-01		draft-ietf-dnsop-server-cookies-02
	Abstract		Abstract
	DNS cookies, as specified in RFC 7873, are a lightweight DNS		DNS cookies, as specified in RFC 7873, are a lightweight DNS
	transaction security mechanism that provides limited protection to		transaction security mechanism that provides limited protection to
	DNS servers and clients against a variety of denial-of-service and		DNS servers and clients against a variety of denial-of-service and
	amplification, forgery, or cache poisoning attacks by off-path		amplification, forgery, or cache poisoning attacks by off-path
	attackers.		attackers.
	This document provides precise directions for creating Server Cookies		This document provides precise directions for creating Server Cookies
	skipping to change at page 1, line 45 ¶		skipping to change at page 1, line 45 ¶
	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 May 7, 2020.		This Internet-Draft will expire on May 21, 2020.
	Copyright Notice		Copyright Notice
	Copyright (c) 2019 IETF Trust and the persons identified as the		Copyright (c) 2019 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 35 ¶		skipping to change at page 2, line 35 ¶
	2. Changes to [RFC7873] . . . . . . . . . . . . . . . . . . . . 4		2. Changes to [RFC7873] . . . . . . . . . . . . . . . . . . . . 4
	3. Constructing a Client Cookie . . . . . . . . . . . . . . . . 4		3. Constructing a Client Cookie . . . . . . . . . . . . . . . . 4
	4. Constructing a Server Cookie . . . . . . . . . . . . . . . . 5		4. Constructing a Server Cookie . . . . . . . . . . . . . . . . 5
	4.1. The Version Sub-Field . . . . . . . . . . . . . . . . . . 6		4.1. The Version Sub-Field . . . . . . . . . . . . . . . . . . 6
	4.2. The Reserved Sub-Field . . . . . . . . . . . . . . . . . 6		4.2. The Reserved Sub-Field . . . . . . . . . . . . . . . . . 6
	4.3. The Timestamp Sub-Field . . . . . . . . . . . . . . . . . 6		4.3. The Timestamp Sub-Field . . . . . . . . . . . . . . . . . 6
	4.4. The Hash Sub-Field . . . . . . . . . . . . . . . . . . . 6		4.4. The Hash Sub-Field . . . . . . . . . . . . . . . . . . . 6
	5. Updating the Server Secret . . . . . . . . . . . . . . . . . 7		5. Updating the Server Secret . . . . . . . . . . . . . . . . . 7
	6. Cookie Algorithms . . . . . . . . . . . . . . . . . . . . . . 8		6. Cookie Algorithms . . . . . . . . . . . . . . . . . . . . . . 8
	7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8		7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
	8. References . . . . . . . . . . . . . . . . . . . . . . . . . 9		8. Security and Privacy Considerations . . . . . . . . . . . . . 9
	8.1. Normative References . . . . . . . . . . . . . . . . . . 9		9. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
	8.2. Informative References . . . . . . . . . . . . . . . . . 9		9.1. Normative References . . . . . . . . . . . . . . . . . . 10
	Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 10		9.2. Informative References . . . . . . . . . . . . . . . . . 10
	Appendix B. Test vectors . . . . . . . . . . . . . . . . . . . . 10		Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 11
	B.1. Learning a new Server Cookie . . . . . . . . . . . . . . 10		Appendix B. Test vectors . . . . . . . . . . . . . . . . . . . . 11
	B.2. The same client learning a renewed (fresh) Server Cookie 11		B.1. Learning a new Server Cookie . . . . . . . . . . . . . . 11
	B.3. Another client learning a renewed Server Cookie . . . . . 12		B.2. The same client learning a renewed (fresh) Server Cookie 12
	B.4. IPv6 query with rolled over secret . . . . . . . . . . . 13		B.3. Another client learning a renewed Server Cookie . . . . . 13
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14		B.4. IPv6 query with rolled over secret . . . . . . . . . . . 14
			Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15
	1. Introduction		1. Introduction
	DNS cookies, as specified in [RFC7873], are a lightweight DNS		DNS cookies, as specified in [RFC7873], are a lightweight DNS
	transaction security mechanism that provides limited protection to		transaction security mechanism that provides limited protection to
	DNS servers and clients against a variety of denial-of-service and		DNS servers and clients against a variety of denial-of-service and
	amplification, forgery, or cache poisoning attacks by off-path		amplification, forgery, or cache poisoning attacks by off-path
	attackers. This document specifies a means of producing		attackers. This document specifies a means of producing
	interoperable strong cookies so that an anycast server set including		interoperable strong cookies so that an anycast server set including
	diverse implementations can be easily configured to interoperate with		diverse implementations can be easily configured to interoperate with
	skipping to change at page 3, line 49 ¶		skipping to change at page 3, line 50 ¶
	In Section Section 5 instructions on updating Server Secrets are		In Section Section 5 instructions on updating Server Secrets are
	given.		given.
	In Section Section 6 the different hash functions usable for DNS		In Section Section 6 the different hash functions usable for DNS
	Cookie construction are listed. [FNV] and HMAC-SHA-256-64 [RFC6234]		Cookie construction are listed. [FNV] and HMAC-SHA-256-64 [RFC6234]
	are deprecated and [SipHash-2.4] is introduced as a REQUIRED hash		are deprecated and [SipHash-2.4] is introduced as a REQUIRED hash
	function for server side DNS Cookie implementations.		function for server side DNS Cookie implementations.
	IANA considerations are in Section 7.		IANA considerations are in Section 7.
			Privacy and Security Considerations in Section 8.
	Acknowledgements are in Appendix A.		Acknowledgements are in Appendix A.
	Test vectors are in Appendix B.		Test vectors are in Appendix B.
	1.2. Definitions		1.2. Definitions
	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",		"SHOULD", "SHOULD NOT", "RECOMMENDED", "*NOT RECOMMENDED*", "MAY",
	and "OPTIONAL" in this document are to be interpreted as described in		and "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
	skipping to change at page 4, line 35 ¶		skipping to change at page 4, line 39 ¶
	specification in Section 4 of this document, which MUST be used by		specification in Section 4 of this document, which MUST be used by
	Server Cookie implementations.		Server Cookie implementations.
	This document has suggestions on Client Cookie construction in		This document has suggestions on Client Cookie construction in
	Section 3. The previous example in Appendix A.2 of [RFC7873] is NOT		Section 3. The previous example in Appendix A.2 of [RFC7873] is NOT
	RECOMMENDED.		RECOMMENDED.
	3. Constructing a Client Cookie		3. Constructing a Client Cookie
	The Client Cookie is a cryptographic nonce and should be treated as		The Client Cookie is a cryptographic nonce and should be treated as
	such. For simplicity, it can be calculated from Server IP Address,		such. It is RECOMMENDED to create a new Client Cookie for each new
	and a Client Secret known only to the Client that is changed whenever		upstream server a Client connects to. The Client Cookie SHOULD have
	an IP address previously used by the Client is no longer available.		at least 64-bits of entropy.
	The Client Cookie SHOULD have at least 64-bits of entropy.
	Except for when the Client IP address changes, there is no need to		When a Server does not support DNS Cookies, the Client MUST NOT send
	change the Client Secret often if a secure pseudorandom function		the same Client Cookie to that same Server again. Instead, it is
	(like [SipHash-2.4]) is used. It is reasonable to change the Client		recommended that the Client does not send a Client Cookie to that
	secret then only if it has been compromised or after a relatively		Server for a certain period, like for example five minutes, before it
	long period of time such as no longer than a year.		retries with a new Client Cookie.
	It is RECOMMENDED but not required that the following pseudorandom		When a Server does support DNS Cookies, the Client should store the
	function be used to construct the Client Cookie:		Client Cookie alongside the Server Cookie it registered for that
			Server.
	Client-Cookie = MAC_Algorithm(		Except for when the Client IP address changes, there is no need to
	Server IP Address, Client Secret )		change the Client Cookie often. It is reasonable to change the
			Client Cookie then only if it has been compromised or after a
			relatively long period of time such as no longer than a year. Client
			Cookies are not expected to survive a program restart.
			Client-Cookie = 64 bits of entropy
	Previously, the recommended algorithm to compute the Client Cookie		Previously, the recommended algorithm to compute the Client Cookie
	included Client IP Address as an input to the MAC_Algorithm.		included Client IP Address as an input to a hashing function.
	However, when implementing the DNS Cookies, several DNS vendors found		However, when implementing the DNS Cookies, several DNS vendors found
	impractical to include the Client IP as the Client Cookie is		impractical to include the Client IP as the Client Cookie is
	typically computed before the Client IP address is known. Therefore,		typically computed before the Client IP address is known. Therefore,
	the requirement to put Client IP address as input was removed.		the requirement to put Client IP address as input was removed.
	However, for privacy reasons, in order to prevent tracking of devices		However, for privacy reasons, in order to prevent tracking of devices
	across links and to not circumvent IPv6 Privacy Extensions [RFC4941],		across links and to not circumvent IPv6 Privacy Extensions [RFC4941],
	Clients MUST NOT re-use a Client or Server Cookie after the Client IP		Clients MUST NOT re-use a Client or Server Cookie after the Client IP
	address has changed.		address has changed.
	The Client IP address is available on the UDP socket when it receives		One way to track Client IP addresses, is to register the Client IP
	the Server Cookie and should be registered alongside the Server		address alongside the Server Cookie when it receives the Server
	Cookie. In subsequent queries to the Server with that Server Cookie,		Cookie. In subsequent queries to the Server with that Server Cookie,
	the socket MUST be bound to the Client IP address that was also used		the socket MAY be bound to the Client IP address that was also used
	(and registered) when it received the Server Cookie. Failure to bind		(and registered) when it received the Server Cookie. Failure to bind
	must result in a new Client Cookie, which, for the method described		MUST then result in a new Client Cookie.
	in this section means a new Client Secret.
	4. Constructing a Server Cookie		4. Constructing a Server Cookie
	The Server Cookie is effectively a Message Authentication Code (MAC)		The Server Cookie is effectively a Message Authentication Code (MAC)
	and should be treated as such. The Server Cookie is calculated from		and should be treated as such. The Server Cookie is calculated from
	the Client Cookie, a series of Sub-Fields specified below, the Client		the Client Cookie, a series of Sub-Fields specified below, the Client
	IP address, and a Server Secret known only to the servers responding		IP address, and a Server Secret known only to the servers responding
	on the same address in an anycast set.		on the same address in an anycast set.
	Changing the Server Secret regularly is RECOMMENDED but, when a		Changing the Server Secret regularly is RECOMMENDED but, when a
	skipping to change at page 9, line 17 ¶		skipping to change at page 9, line 20 ¶
	+---------+-------+---------------------------------------+		+---------+-------+---------------------------------------+
	| 0 | 8-32 | reserved |		| 0 | 8-32 | reserved |
	| 1 | 8-15 | unassiged |		| 1 | 8-15 | unassiged |
	| 1 | 16 | SipHash-2.4 [this document] Section 4 |		| 1 | 16 | SipHash-2.4 [this document] Section 4 |
	| 1 | 17-32 | unassigned |		| 1 | 17-32 | unassigned |
	| 2-239 | 8-32 | unassigned |		| 2-239 | 8-32 | unassigned |
	| 240-254 | 8-32 | private use |		| 240-254 | 8-32 | private use |
	| 255 | 8-32 | reserved |		| 255 | 8-32 | reserved |
	+---------+-------+---------------------------------------+		+---------+-------+---------------------------------------+
	8. References		8. Security and Privacy Considerations
	8.1. Normative References		DNS Cookies provides limited protection to DNS servers and clients
			against a variety of denial-of-service and amplification/forgery or
			cache poisoning attacks by off-path attackers. They provide no
			protection against on-path adversaries that can observe the plaintext
			DNS traffic. An on-path adversary that can observe a Server Cookie
			for a client and server interaction, can use that Server Cookie for
			amplification and denial-of-service forgery attacks for the lifetime
			of the Server Cookie.
			In [RFC7873] it was RECOMMENDED to construct a Client Cookie by using
			a pseudorandom function of the Client IP Address, the Server IP
			Address, and a secret quantity known only to the client. The Client
			IP Address was included to ensure that a client could not be tracked
			if its IP Address changes due to privacy mechanisms or otherwise.
			In this document, we changed Client Cookie construction to be just 64
			bits of entropy newly created for each new upstream server the client
			connects to. As a consequence additional care needs to be taken to
			prevent tracking of clients. To prevent tracking, a new Client
			Cookie for a server MUST be created whenever the Client IP Address
			changes.
			Unfortunately, tracking Client IP Address Changes is impractical with
			servers that do not support DNS Cookies. To prevent tracking of
			clients with non DNS Cookie supporting servers, a client MUST NOT
			send a previously sent Client Cookie. To prevent the creation of a
			new Client Cookie for each query to an non DNS Cookies supporting
			server, it is RECOMMENDED to not send a Client Cookie to that server
			for a certain period, like for example five minute.
			Summarizing:
			o In order to provide minimal authentication, a client MUST use a
			different Client Cookie for each different Server IP Address.
			o To prevent tracking of clients, a new Client Cookie MUST be
			created when the Client IP Address changes.
			o To prevent tracking of clients for a non DNS Cookie supporting
			server, a client MUST NOT send a previously sent Client Cookie to
			that server, unless it can track Client IP Address changes for
			those servers too.
			Besides the Client Cookie construction, this update on [RFC7873] does
			not introduce any new characteristics to DNS Cookies operations and
			the Security Considerations section of [RFC7873] still applies.
			9. References
			9.1. Normative References
	[RFC1982] Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982,		[RFC1982] Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982,
	DOI 10.17487/RFC1982, August 1996,		DOI 10.17487/RFC1982, August 1996,
	<https://www.rfc-editor.org/info/rfc1982>.		<https://www.rfc-editor.org/info/rfc1982>.
	[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>.
	skipping to change at page 9, line 42 ¶		skipping to change at page 10, line 45 ¶
	<https://www.rfc-editor.org/info/rfc7873>.		<https://www.rfc-editor.org/info/rfc7873>.
	[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>.
	[SipHash-2.4]		[SipHash-2.4]
	Aumasson, J. and D. Bernstein, "SipHash: a fast short-		Aumasson, J. and D. Bernstein, "SipHash: a fast short-
	input PRF", 2012, <https://131002.net/siphash/>.		input PRF", 2012, <https://131002.net/siphash/>.
	8.2. Informative References		9.2. Informative References
	[FNV] Fowler, G., Noll, L., Vo, K., Eastlake, D., and T. Hansen,		[FNV] Fowler, G., Noll, L., Vo, K., Eastlake, D., and T. Hansen,
	"The FNV Non-Cryptographic Hash Algorithm",		"The FNV Non-Cryptographic Hash Algorithm",
	<https://datatracker.ietf.org/doc/draft-eastlake-fnv>.		<https://datatracker.ietf.org/doc/draft-eastlake-fnv>.
	[RFC6234] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms		[RFC6234] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
	(SHA and SHA-based HMAC and HKDF)", RFC 6234,		(SHA and SHA-based HMAC and HKDF)", RFC 6234,
	DOI 10.17487/RFC6234, May 2011,		DOI 10.17487/RFC6234, May 2011,
	<https://www.rfc-editor.org/info/rfc6234>.		<https://www.rfc-editor.org/info/rfc6234>.
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