< draft-dfranke-ntp-data-minimization-01.txt		draft-dfranke-ntp-data-minimization-02.txt >
	Network Working Group D. Franke		Network Working Group D. Franke
	Internet-Draft Akamai		Internet-Draft Akamai
	Updates: 5905 (if approved) A. Malhotra		Updates: 5905 (if approved) A. Malhotra
	Intended status: Standards Track Boston University		Intended status: Standards Track Boston University
	Expires: May 2, 2017 October 29, 2016		Expires: September 28, 2017 March 27, 2017
	NTP Client Data Minimization		NTP Client Data Minimization
	draft-dfranke-ntp-data-minimization-01		draft-dfranke-ntp-data-minimization-02
	Abstract		Abstract
	This memo proposes backward-compatible updates to the Network Time		This memo proposes backward-compatible updates to the Network Time
	Protocol to strip unnecessary identifying information from client		Protocol to strip unnecessary identifying information from client
	requests and to improve resilience against blind spoofing of		requests and to improve resilience against blind spoofing of
	unauthenticated server responses.		unauthenticated server responses.
	Status of This Memo		Status of This Memo
	skipping to change at page 1, line 34 ¶		skipping to change at page 1, line 34 ¶
	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 http://datatracker.ietf.org/drafts/current/.		Drafts is at http://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 2, 2017.		This Internet-Draft will expire on September 28, 2017.
	Copyright Notice		Copyright Notice
	Copyright (c) 2016 IETF Trust and the persons identified as the		Copyright (c) 2017 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
	(http://trustee.ietf.org/license-info) in effect on the date of		(http://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
	carefully, as they describe your rights and restrictions with respect		carefully, as they describe your rights and restrictions with respect
	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 . . . . . . . . . . . . . . . . . . . . . . . . 2		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
	2. Requirements Language . . . . . . . . . . . . . . . . . . . . 2		2. Requirements Language . . . . . . . . . . . . . . . . . . . . 2
	3. Client Packet Format . . . . . . . . . . . . . . . . . . . . 2		3. Client Packet Format . . . . . . . . . . . . . . . . . . . . 2
	4. Security and Privacy Considerations . . . . . . . . . . . . . 3		4. Security and Privacy Considerations . . . . . . . . . . . . . 3
	4.1. Data Minimization . . . . . . . . . . . . . . . . . . . . 3		4.1. Data Minimization . . . . . . . . . . . . . . . . . . . . 3
	4.2. Transmit Timestamp Randomization . . . . . . . . . . . . 3		4.2. Transmit Timestamp Randomization . . . . . . . . . . . . 4
	5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4		5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
	6. References . . . . . . . . . . . . . . . . . . . . . . . . . 4		6. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
	6.1. Normative References . . . . . . . . . . . . . . . . . . 4		6.1. Normative References . . . . . . . . . . . . . . . . . . 4
	6.2. Informative References . . . . . . . . . . . . . . . . . 4		6.2. Informative References . . . . . . . . . . . . . . . . . 5
	Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 5		Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 5
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
	1. Introduction		1. Introduction
	Network Time Protocol (NTP) packets, as specified by RFC 5905		Network Time Protocol (NTP) packets, as specified by RFC 5905
	[RFC5905], carry a great deal of information about the state of the		[RFC5905], carry a great deal of information about the state of the
	NTP daemon which transmitted them. In the case of mode 4 packets		NTP daemon which transmitted them. In the case of mode 4 packets
	(responses sent from server to client), as well as in broadcast (mode		(responses sent from server to client), as well as in broadcast (mode
	5) and symmetric peering modes (mode 1/2), most of this information		5) and symmetric peering modes (mode 1/2), most of this information
	skipping to change at page 3, line 6 ¶		skipping to change at page 3, line 6 ¶
	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",		The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
	"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this		"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
	document are to be interpreted as described in RFC 2119 [RFC2119].		document are to be interpreted as described in RFC 2119 [RFC2119].
	3. Client Packet Format		3. Client Packet Format
	In every client-mode packet sent by a Network Time Protocol [RFC5905]		In every client-mode packet sent by a Network Time Protocol [RFC5905]
	implementation:		implementation:
	The first octet, which contains the leap indicator, version		The first octet, which contains the leap indicator, version
	number, and mode fields, SHALL be set to 0x23 (LI = 0, VN = 4,		number, and mode fields, SHOULD be set to 0x23 (LI = 0, VN = 4,
	Mode = 3).		Mode = 3).
	The Transmit Timestamp field SHALL be set uniformly at random,		The Transmit Timestamp field SHOULD be set uniformly at random,
	generated by a mechanism suitable for cryptographic purposes.		generated by a mechanism suitable for cryptographic purposes.
	[RFC4086] provides guidance on the generation of random values.		[RFC4086] provides guidance on the generation of random values.
	The Poll field MAY be set to the actual polling interval as		The Poll field MAY be set to the actual polling interval as
	specified by RFC 5905, or else MAY be set to zero.		specified by RFC 5905, or else MAY be set to zero.
	All other header fields, specifically the Stratum, Precision, Root		All other header fields, specifically the Stratum, Precision, Root
	Delay, Root Dispersion, Reference ID, Reference Timestamp, Origin		Delay, Root Dispersion, Reference ID, Reference Timestamp, Origin
	Timestamp, and Receive Timestamp, SHALL be set to zero.		Timestamp, and Receive Timestamp, SHOULD be set to zero.
			Servers MUST allow client packets to conform to the above
			recommendations. This requirement shall not be construed so as to
			prohibit servers from rejecting conforming packets for unrelated
			reasons, such as access control or rate limiting.
	4. Security and Privacy Considerations		4. Security and Privacy Considerations
	4.1. Data Minimization		4.1. Data Minimization
	Zeroing out unused fields in client requests prevents disclosure of		Zeroing out unused fields in client requests prevents disclosure of
	information that can be used for fingerprinting [RFC6973].		information that can be used for fingerprinting [RFC6973].
	While populating any of these fields with authentic data reveals at		While populating any of these fields with authentic data reveals at
	least some identifying information about the client, the Origin		least some identifying information about the client, the Origin
	skipping to change at page 3, line 40 ¶		skipping to change at page 3, line 45 ¶
	severe information leak. RFC 5905 calls for clients to copy the		severe information leak. RFC 5905 calls for clients to copy the
	transmit timestamp and destination timestamp of the server's most		transmit timestamp and destination timestamp of the server's most
	recent response into the origin timestamp and receive timestamp		recent response into the origin timestamp and receive timestamp
	(respectively) of their next request to that server. Therefore, when		(respectively) of their next request to that server. Therefore, when
	a client moves between networks, a passive observer of both network		a client moves between networks, a passive observer of both network
	paths can determine with high confidence that the old and new IP		paths can determine with high confidence that the old and new IP
	addresses belong to the same system by noticing that the transmit		addresses belong to the same system by noticing that the transmit
	timestamp of a response sent to the old IP matches the origin		timestamp of a response sent to the old IP matches the origin
	timestamp of a request sent from the new one.		timestamp of a request sent from the new one.
	Zeroing the poll field is made optional because this field conveys no		Zeroing the poll field is made optional (MAY rather than SHOULD) so
	information that an observer could not otherwise obtain simply by		as not to preclude future development of schemes wherein the server
	observing the actual interval between requests. Since in the NTP		uses information about the client's current poll interval in order to
	reference implementation servers copy the poll field from the		recommend adjustments back to the client. Putting accurate
	client's request into their response, if clients rely on the value of		information into this field has no significant impact on privacy
	the poll field in the response then zeroing the poll field of the		since an observer can already obtain this information simply by
	request may result in adverse behavior.		observing the actual interval between requests.
	4.2. Transmit Timestamp Randomization		4.2. Transmit Timestamp Randomization
	While this memo calls for most fields in client packets to be set to		While this memo calls for most fields in client packets to be set to
	zero, the transmit timestamp is randomized. This decision is		zero, the transmit timestamp is randomized. This decision is
	motivated by security as well as privacy.		motivated by security as well as privacy.
	NTP servers copy the transmit timestamp from the client's request		NTP servers copy the transmit timestamp from the client's request
	into the origin timestamp of the response; this memo calls for no		into the origin timestamp of the response; this memo calls for no
	change in this behavior. Clients discard any response whose origin		change in this behavior. Clients discard any response whose origin
End of changes. 10 change blocks.
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