draft-ietf-6man-stable-privacy-addresses-07.txt		draft-ietf-6man-stable-privacy-addresses-08.txt
	IPv6 maintenance Working Group (6man) F. Gont		IPv6 maintenance Working Group (6man) F. Gont
	Internet-Draft SI6 Networks / UTN-FRH		Internet-Draft SI6 Networks / UTN-FRH
	Intended status: Standards Track May 19, 2013		Intended status: Standards Track May 24, 2013
	Expires: November 20, 2013		Expires: November 25, 2013
	A method for Generating Stable Privacy-Enhanced Addresses with IPv6		A method for Generating Stable Privacy-Enhanced Addresses with IPv6
	Stateless Address Autoconfiguration (SLAAC)		Stateless Address Autoconfiguration (SLAAC)
	draft-ietf-6man-stable-privacy-addresses-07		draft-ietf-6man-stable-privacy-addresses-08
	Abstract		Abstract
	This document specifies a method for generating IPv6 Interface		This document specifies a method for generating IPv6 Interface
	Identifiers to be used with IPv6 Stateless Address Autoconfiguration		Identifiers to be used with IPv6 Stateless Address Autoconfiguration
	(SLAAC), such that addresses configured using this method are stable		(SLAAC), such that addresses configured using this method are stable
	within each subnet, but the Interface Identifier changes when hosts		within each subnet, but the Interface Identifier changes when hosts
	move from one network to another. This method is meant to be an		move from one network to another. This method is meant to be an
	alternative to generating Interface Identifiers based on IEEE		alternative to generating Interface Identifiers based on hardware
	identifiers, such that the benefits of stable addresses can be		address (e.g., using IEEE identifiers), such that the benefits of
	achieved without sacrificing the privacy of users.		stable addresses can be achieved without sacrificing the privacy of
			users. The method specified in this document applies to all prefixes
			a host may be employing, including link-local, global, and unique-
			local addresses.
	Status of this Memo		Status of this Memo
	This Internet-Draft is submitted in full conformance with the		This Internet-Draft is submitted in full conformance with the
	provisions of BCP 78 and BCP 79.		provisions of BCP 78 and BCP 79.
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute		Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
	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 November 20, 2013.		This Internet-Draft will expire on November 25, 2013.
	Copyright Notice		Copyright Notice
	Copyright (c) 2013 IETF Trust and the persons identified as the		Copyright (c) 2013 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
	skipping to change at page 2, line 26		skipping to change at page 2, line 29
	6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14		6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
	7. Security Considerations . . . . . . . . . . . . . . . . . . . 15		7. Security Considerations . . . . . . . . . . . . . . . . . . . 15
	8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 17		8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 17
	9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18		9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
	9.1. Normative References . . . . . . . . . . . . . . . . . . . 18		9.1. Normative References . . . . . . . . . . . . . . . . . . . 18
	9.2. Informative References . . . . . . . . . . . . . . . . . . 18		9.2. Informative References . . . . . . . . . . . . . . . . . . 18
	Appendix A. Possible sources for the Net_Iface parameter . . . . 21		Appendix A. Possible sources for the Net_Iface parameter . . . . 21
	A.1. Interface Index . . . . . . . . . . . . . . . . . . . . . 21		A.1. Interface Index . . . . . . . . . . . . . . . . . . . . . 21
	A.2. Interface Name . . . . . . . . . . . . . . . . . . . . . . 21		A.2. Interface Name . . . . . . . . . . . . . . . . . . . . . . 21
	A.3. Link-layer Addresses . . . . . . . . . . . . . . . . . . . 21		A.3. Link-layer Addresses . . . . . . . . . . . . . . . . . . . 21
			A.4. Logical Network Service Identity . . . . . . . . . . . . . 22
	Appendix B. Privacy issues still present when temporary		Appendix B. Privacy issues still present when temporary
	addresses are employed . . . . . . . . . . . . . . . 23		addresses are employed . . . . . . . . . . . . . . . 23
	B.1. Host tracking . . . . . . . . . . . . . . . . . . . . . . 23		B.1. Host tracking . . . . . . . . . . . . . . . . . . . . . . 23
	B.1.1. Tracking hosts across networks #1 . . . . . . . . . . 23		B.1.1. Tracking hosts across networks #1 . . . . . . . . . . 23
	B.1.2. Tracking hosts across networks #2 . . . . . . . . . . 24		B.1.2. Tracking hosts across networks #2 . . . . . . . . . . 24
	B.1.3. Revealing the identity of devices performing		B.1.3. Revealing the identity of devices performing
	server-like functions . . . . . . . . . . . . . . . . 24		server-like functions . . . . . . . . . . . . . . . . 24
	B.2. Address-scanning attacks . . . . . . . . . . . . . . . . . 24		B.2. Address-scanning attacks . . . . . . . . . . . . . . . . . 24
	B.3. Information Leakage . . . . . . . . . . . . . . . . . . . 25		B.3. Information Leakage . . . . . . . . . . . . . . . . . . . 25
	Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 26		Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 26
	1. Introduction		1. Introduction
	[RFC4862] specifies Stateless Address Autoconfiguration (SLAAC) for		[RFC4862] specifies Stateless Address Autoconfiguration (SLAAC) for
	IPv6 [RFC2460], which typically results in hosts configuring one or		IPv6 [RFC2460], which typically results in hosts configuring one or
	more "stable" addresses composed of a network prefix advertised by a		more "stable" addresses composed of a network prefix advertised by a
	local router, and an Interface Identifier (IID) that typically embeds		local router, and an Interface Identifier (IID) that typically embeds
	a hardware address (e.g., using IEEE identifiers) [RFC4291].		a hardware address (e.g., using IEEE identifiers) [RFC4291].
	Cryptograhically Generated Addresses (CGAs) [RFC3972] are yet		Cryptographically Generated Addresses (CGAs) [RFC3972] are yet
	another method for generating Interface Identifiers, which bind a		another method for generating Interface Identifiers, which bind a
	public signature key to an IPv6 address in the SEcure Neighbor		public signature key to an IPv6 address in the SEcure Neighbor
	Discovery (SEND) [RFC3971] protocol.		Discovery (SEND) [RFC3971] protocol.
	Generally, the traditional SLAAC addresses are thought to simplify		Generally, the traditional SLAAC addresses are thought to simplify
	network management, since they simplify Access Control Lists (ACLs)		network management, since they simplify Access Control Lists (ACLs)
	and logging. However, they have a number of drawbacks:		and logging. However, they have a number of drawbacks:
	o since the resulting Interface Identifiers do not vary over time,		o since the resulting Interface Identifiers do not vary over time,
	they allow correlation of node activities within the same network,		they allow correlation of node activities within the same network,
	thus negatively affecting the privacy of users.		thus negatively affecting the privacy of users.
	o since the resulting Interface Identifiers are constant across		o since the resulting Interface Identifiers are constant across
	networks, the resulting IPv6 addresses can be leveraged to track		networks, the resulting IPv6 addresses can be leveraged to track
	and correlate the activity of a node across multiple networks		and correlate the activity of a node across multiple networks
	(e.g. track and correlate the activities of a typical client		(e.g. track and correlate the activities of a typical client
	connecting to the public Internet from different locations), thus		connecting to the public Internet from different locations), thus
	negatively affecting the privacy of users.		negatively affecting the privacy of users.
	o since embedding the underlying link-layer address in the Interface		o since embedding the underlying link-layer address in the Interface
	Identifier results in specific address patterns, such patterns may		Identifier will result in specific address patterns, such patterns
	be leveraged by attackers to reduce the search space when		may be leveraged by attackers to reduce the search space when
	performing address scanning attacks.		performing address scanning attacks. For example, the IPv6
			addresses of all nodes manufactured by the same vendor (at a given
			time frame) will likely contain the same IEEE Organizationally
			Unique Identifier (OUI) in the Interface Identifier.
	o embedding the underlying link-layer address in the Interface		o embedding the underlying link-layer address in the Interface
	Identifier means that changing the interface hardware results in a		Identifier means that replacement of the underlying interface
	different Interface Identifier (and hence different IPv6 address).		hardware will result in a change of the IPv6 address(es) assigned
			to that interface.
	The "Privacy Extensions for Stateless Address Autoconfiguration in		The "Privacy Extensions for Stateless Address Autoconfiguration in
	IPv6" [RFC4941] (henceforth referred to as "temporary addresses")		IPv6" [RFC4941] (henceforth referred to as "temporary addresses")
	were introduced to complicate the task of eavesdroppers and other		were introduced to complicate the task of eavesdroppers and other
	information collectors to correlate the activities of a node, and		information collectors to correlate the activities of a node, and
	basically result in temporary (and random) Interface Identifiers.		basically result in temporary (and random) Interface Identifiers.
	These temporary addresses are generated *in addition* to the		These temporary addresses are generated in addition to the
	traditional IPv6 addresses based on IEEE identifiers, with the		traditional IPv6 addresses based on IEEE identifiers, with the
	"temporary addresses" being employed for "outgoing communications",		"temporary addresses" being employed for "outgoing communications",
	and the traditional SLAAC addresses being employed for "server"		and the traditional SLAAC addresses being employed for "server"
	functions (i.e., receiving incoming connections).		functions (i.e., receiving incoming connections).
	However, even with "temporary addresses" in place, a number of issues		However, even with "temporary addresses" in place, a number of issues
	remain to be mitigated. Namely,		remain to be mitigated. Namely,
	o since "temporary addresses" [RFC4941] do not eliminate the use of		o since "temporary addresses" [RFC4941] do not eliminate the use of
	fixed identifiers for server-like functions, they only *partially*		fixed identifiers for server-like functions, they only partially
	mitigate host-tracking and activity correlation across networks		mitigate host-tracking and activity correlation across networks
	(see Appendix B.1 for some example attacks that are still possible		(see Appendix B.1 for some example attacks that are still possible
	with temporary addresses).		with temporary addresses).
	o since "temporary addresses" [RFC4941] do not replace the		o since "temporary addresses" [RFC4941] do not replace the
	traditional SLAAC addresses, an attacker can still leverage		traditional SLAAC addresses, an attacker can still leverage
	patterns in those addresses to greatly reduce the search space for		patterns in those addresses to greatly reduce the search space for
	"alive" nodes [Gont-DEEPSEC2011] [CPNI-IPv6]		"alive" nodes [Gont-DEEPSEC2011] [CPNI-IPv6]
	[I-D.ietf-opsec-ipv6-host-scanning].		[I-D.ietf-opsec-ipv6-host-scanning].
	skipping to change at page 4, line 43		skipping to change at page 4, line 46
	In scenarios in which temporary addresses are deliberately not used		In scenarios in which temporary addresses are deliberately not used
	(possibly for any of the aforementioned reasons), all a host is left		(possibly for any of the aforementioned reasons), all a host is left
	with is the stable addresses that have been generated using e.g.		with is the stable addresses that have been generated using e.g.
	IEEE identifiers. In such scenarios, it may still be desirable to		IEEE identifiers. In such scenarios, it may still be desirable to
	have addresses that mitigate address scanning attacks, and that at		have addresses that mitigate address scanning attacks, and that at
	the very least do not reveal the node's identity when roaming from		the very least do not reveal the node's identity when roaming from
	one network to another -- without complicating the operation of the		one network to another -- without complicating the operation of the
	corresponding networks.		corresponding networks.
	However, even with temporary addresses [RFC4941] in place,		We note that even with temporary addresses [RFC4941] in place,
	preventing correlation of activities of a node within a network		preventing correlation of activities of a node within a network
	may be difficult (if at all possible) to achieve. As a trivial		may be difficult (if at all possible) to achieve. As a trivial
	example, consider a scenario where there is a single node (or a		example, consider a scenario where there is a single node (or a
	reduced number of nodes) connected to a specific network. An		reduced number of nodes) connected to a specific network. An
	attacker could detect new addresses in use at that network, an		attacker could detect new addresses in use at that network, an
	infer which addresses are being employed by which hosts. This		infer which addresses are being employed by which hosts. This
	task is made particularly easier by the fact that use of		task is made particularly easier by the fact that use of
	"temporary addresses" can be easily inferred (since the follow		"temporary addresses" can be easily inferred (since the follow
	different patterns from that of traditional SLAAC addresses), and		different patterns from that of traditional SLAAC addresses), and
	since they are re-generated periodically (i.e., after a specific		since they are re-generated periodically (i.e., after a specific
	amount of time has elapsed).		amount of time has elapsed).
	This document specifies a method to generate Interface Identifiers		This document specifies a method to generate Interface Identifiers
	that are stable/constant for each network interface within each		that are stable/constant for each network interface within each
	subnet, but that change as hosts move from one network to another,		subnet, but that change as hosts move from one network to another,
	thus keeping the "stability" properties of the Interface Identifiers		thus keeping the "stability" properties of the Interface Identifiers
	specified in [RFC4291], while still mitigating address-scanning		specified in [RFC4291], while still mitigating address-scanning
	attacks and preventing correlation of the activities of a node as it		attacks and preventing correlation of the activities of a node as it
	moves from one network to another.		moves from one network to another.
	For nodes that currently disable "temporary addresses" [RFC4941] for		The method specified in this document is a orthogonal to the use of
	some of the reasons stated above, this mechanism provides stable		"temporary" addresses [RFC4941], since it is meant to improve the
			security and privacy properties of the stable addresses that are
			employed along with the aforementioned "temporary" addresses. In
			scenarios in which "temporary addresses" are employed, implementation
			of the mechanism described in this document (in replacement of stable
			addresses based on e.g. IEEE identifiers) would mitigate address-
			scanning attacks and also mitigate the remaining vectors for
			correlating host activities based on the node's IPv6 addresses. On
			the other hand, for nodes that currently disable "temporary
			addresses" [RFC4941] for some of the reasons described earlier in
			this document, implementation of this mechanism will result in stable
	privacy-enhanced addresses which address some of the concerns related		privacy-enhanced addresses which address some of the concerns related
	to addresses that embed IEEE identifiers [RFC4291]. On the other		to addresses that embed IEEE identifiers [RFC4291], and which
	hand, in scenarios in which "temporary addresses" are employed		mitigate IPv6 address-scanning attacks.
	together with stable addresses such as those based on IEEE
	identifiers, implementation of the mechanism described in this
	document would mitigate address-scanning attacks and also mitigate
	some vectors for correlating host activities that are not mitigated
	by the use of temporary addresses.
	We note that this method is incrementally deployable, since it does		We note that this method is incrementally deployable, since it does
	not pose any interoperability implications when deployed on networks		not pose any interoperability implications when deployed on networks
	where other nodes do not implement or employ it. Additionally, we		where other nodes do not implement or employ it. Additionally, we
	note that this document does not update or modify IPv6 StateLess		note that this document does not update or modify IPv6 StateLess
	Address Auto-Configuration (SLAAC) [RFC4862] itself, but rather only		Address Auto-Configuration (SLAAC) [RFC4862] itself, but rather only
	specifies an alternative algorithm to generate Interface Identifiers.		specifies an alternative algorithm to generate Interface Identifiers.
	Therefore, the usual address lifetime properties (as specified in the		Therefore, the usual address lifetime properties (as specified in the
	corresponding Prefix Information Options) apply when IPv6 addresses		corresponding Prefix Information Options) apply when IPv6 addresses
	are generated as a result of employing the algorithm specified in		are generated as a result of employing the algorithm specified in
	skipping to change at page 6, line 20		skipping to change at page 6, line 20
	o The resulting Interface Identifiers remain constant/stable for		o The resulting Interface Identifiers remain constant/stable for
	each prefix used with SLAAC within each subnet. That is, the		each prefix used with SLAAC within each subnet. That is, the
	algorithm generates the same Interface Identifier when configuring		algorithm generates the same Interface Identifier when configuring
	an address (for the same interface) belonging to the same prefix		an address (for the same interface) belonging to the same prefix
	within the same subnet.		within the same subnet.
	o The resulting Interface Identifiers do change when addresses are		o The resulting Interface Identifiers do change when addresses are
	configured for different prefixes. That is, if different		configured for different prefixes. That is, if different
	autoconfiguration prefixes are used to configure addresses for the		autoconfiguration prefixes are used to configure addresses for the
	same network interface card, the resulting Interface Identifiers		same network interface card, the resulting Interface Identifiers
	must be (statistically) different.		must be (statistically) different. This means that, given two
			addresses produced by the method specified in this document, it
			must be difficult for an attacker tell whether the addresses have
			been generated/used by the same node.
	o It must be difficult for an outsider to predict the Interface		o It must be difficult for an outsider to predict the Interface
	Identifiers that will be generated by the algorithm, even with		Identifiers that will be generated by the algorithm, even with
	knowledge of the Interface Identifiers generated for configuring		knowledge of the Interface Identifiers generated for configuring
	other addresses.		other addresses.
	o Depending on the specific implementation approach (see Section 3		o Depending on the specific implementation approach (see Section 3
	and Appendix A), the resulting Interface Identifiers may be		and Appendix A), the resulting Interface Identifiers may be
	independent of the underlying hardware (e.g. link-layer address).		independent of the underlying hardware (e.g. link-layer address).
	This means that e.g. replacing a Network Interface Card (NIC) will		This means that e.g. replacing a Network Interface Card (NIC) will
	not have the (generally undesirable) effect of changing the IPv6		not have the (generally undesirable) effect of changing the IPv6
	addresses used for that network interface.		addresses used for that network interface.
	o The aforementioned Interface Identifiers are meant to be an		o The method specified in this document is meant to be an
	alternative to those based on e.g. IEEE identifiers, such as		alternative to producing IPv6 addresses based on e.g. IEEE
	those specified in [RFC2464].		identifiers (as specified in [RFC2464]). It is meant to be
			employed for all of the stable (i.e. non-temporary) IPv6 addresses
			configured with SLAAC for a given interface, including global,
			link-local, and unique-local IPv6 addresses.
	We note that of use of the algorithm specified in this document is		We note that of use of the algorithm specified in this document is
	(to a large extent) orthogonal to the use of "temporary addresses"		(to a large extent) orthogonal to the use of "temporary addresses"
	[RFC4941]. Hosts that do not implement/use "temporary addresses"		[RFC4941]. When employed along "temporary addresses", the method
	would have the benefit that they would not be subject to the host-		specified in this document will mitigate address-scanning attacks and
	tracking and address scanning issues discussed in the previous		correlation of node activities across networks (see Appendix B and
	section. On the other hand, in the case of hosts employing		[IAB-PRIVACY]). On the other hand, hosts that do not implement/use
	"temporary addresses", the method specified in this document would		"temporary addresses" but employ the method specified in this
	mitigate address-scanning attacks and correlation of node activities		document would, at the very least, mitigate the host-tracking and
	across networks (see Appendix B and [IAB-PRIVACY]).		address scanning issues discussed in the previous section.
	3. Algorithm specification		3. Algorithm specification
	IPv6 implementations conforming to this specification MUST generate		IPv6 implementations conforming to this specification MUST generate
	Interface Identifiers using the algorithm specified in this section		Interface Identifiers using the algorithm specified in this section
	in replacement of any other algorithms used for generating "stable"		in replacement of any other algorithms used for generating "stable"
	addresses (such as that specified in [RFC2464]). The aforementioned		addresses (such as that specified in [RFC2464]). However,
	algorithm MUST be employed for generating the Interface Identifiers		implementations conforming to this specification MAY employ the
	for all of the IPv6 addresses configured with SLAAC for a given		algorithm specified in [RFC4941] to generate temporary addresses in
	interface, including IPv6 link-local addresses.		addition to the addresses generated with the algorithm specified in
			this document. The method specified in this document MUST be
			employed for generating the Interface Identifiers for all the stable
			addresses of a given interface, including IPv6 global, link-local,
			and unique-local addresses.
	This means that this document does not formally obsolete or		This means that this document does not formally obsolete or
	deprecate any of the existing algorithms to generate Interface		deprecate any of the existing algorithms to generate Interface
	Identifiers (e.g. such as that specified in [RFC2464]). However,		Identifiers (e.g. such as that specified in [RFC2464]). However,
	those IPv6 implementations that employ this specification MUST		those IPv6 implementations that employ this specification MUST
	generate all of their "stable" addresses as specified in this		generate all of their "stable" addresses as specified in this
	document.		document.
	Implementations conforming to this specification SHOULD provide the		Implementations conforming to this specification SHOULD provide the
	means for a system administrator to enable or disable the use of this		means for a system administrator to enable or disable the use of this
	algorithm for generating Interface Identifiers. Implementations		algorithm for generating Interface Identifiers.
	conforming to this specification MAY employ the algorithm specified
	in [RFC4941] to generate temporary addresses in addition to the
	addresses generated with the algorithm specified in this document.
	Unless otherwise noted, all of the parameters included in the		Unless otherwise noted, all of the parameters included in the
	expression below MUST be included when generating an Interface		expression below MUST be included when generating an Interface
	Identifier.		Identifier.
	1. Compute a random (but stable) identifier with the expression:		1. Compute a random (but stable) identifier with the expression:
	RID = F(Prefix, Net_Iface, Network_ID, DAD_Counter, secret_key)		RID = F(Prefix, Net_Iface, Network_ID, DAD_Counter, secret_key)
	Where:		Where:
	RID:		RID:
	Random (but stable) Interface Identifier		Random (but stable) Interface Identifier
	F():		F():
	A pseudorandom function (PRF) that is not computable from the		A pseudorandom function (PRF) that is not computable from the
	outside (without knowledge of the secret key), which		outside (without knowledge of the secret key), which should
	shouldproduce an output of at least 64 bits.The PRF could be		produce an output of at least 64 bits.The PRF could be
	implemented as a cryptographic hash of the concatenation of		implemented as a cryptographic hash of the concatenation of
	each of the function parameters.		each of the function parameters.
	Prefix:		Prefix:
	The prefix to be used for SLAAC, as learned from an ICMPv6		The prefix to be used for SLAAC, as learned from an ICMPv6
	Router Advertisement message.		Router Advertisement message, or the link-local IPv6 unicast
			prefix.
	Net_Iface:		Net_Iface:
	An implementation-dependent stable identifier associated with		An implementation-dependent stable identifier associated with
	the network interface for which the RID is being generated.		the network interface for which the RID is being generated.
	An implementation MAY provide a configuration option to select		An implementation MAY provide a configuration option to select
	the source of the identifier to be used for the Net_Iface		the source of the identifier to be used for the Net_Iface
	parameter. A discussion of possible sources for this value		parameter. A discussion of possible sources for this value
	(along with the corresponding trade-offs) can be found in		(along with the corresponding trade-offs) can be found in
	Appendix A.		Appendix A.
	skipping to change at page 9, line 30		skipping to change at page 9, line 35
	being used by the victim (which we should expect), and the attacker		being used by the victim (which we should expect), and the attacker
	can obtain enough material (i.e. addresses configured by the victim),		can obtain enough material (i.e. addresses configured by the victim),
	the attacker may simply search the entire secret-key space to find		the attacker may simply search the entire secret-key space to find
	matches. To protect against this, the secret key should be of a		matches. To protect against this, the secret key should be of a
	reasonable length. Key lengths of at least 128 bits should be		reasonable length. Key lengths of at least 128 bits should be
	adequate. The secret key is initialized at system installation time		adequate. The secret key is initialized at system installation time
	to a pseudo-random number, thus allowing this mechanism to be		to a pseudo-random number, thus allowing this mechanism to be
	enabled/used automatically, without user intervention.		enabled/used automatically, without user intervention.
	Including the SLAAC prefix in the PRF computation causes the		Including the SLAAC prefix in the PRF computation causes the
	Interface Identifier to vary across networks that employ different		Interface Identifier to vary across each prefix (link-local, global,
	prefixes, thus mitigating host-tracking attacks and any other attacks		etc.) employed by the node and, as consequently, also across
	that benefit from predictable Interface Identifiers (such as address		networks. This mitigates the correlation of activities of multi-
	scanning attacks).		homed nodes (since each of the corresponding addresses will employ a
			different Interface ID), host-tracking (since the network prefix will
			change as the node moves from one network to another), and any other
			attacks that benefit from predictable Interface Identifiers (such as
			address scanning attacks).
	The Net_Iface is a value that identifies the network interface for		The Net_Iface is a value that identifies the network interface for
	which an IPv6 address is being generated. The following properties		which an IPv6 address is being generated. The following properties
	are desirable for the Net_Iface:		are required for the Net_Iface parameter:
	o it MUST be constant across system bootstrap sequences and other		o it MUST be constant across system bootstrap sequences and other
	network events (e.g., bringing another interface up or down)		network events (e.g., bringing another interface up or down)
	o it MUST be different for each network interface		o it MUST be different for each network interface simultaneously in
			use
	Since the stability of the addresses generated with this method		Since the stability of the addresses generated with this method
	relies on the stability of all arguments of F(), it is key that the		relies on the stability of all arguments of F(), it is key that the
	Net_Iface be constant across system bootstrap sequences and other		Net_Iface be constant across system bootstrap sequences and other
	network events. Additionally, the Net_Iface must uniquely identify		network events. Additionally, the Net_Iface must uniquely identify
	an interface within the node, such that two interfaces connecting to		an interface within the node, such that two interfaces connecting to
	the same network do not result in duplicate addresses. Different		the same network do not result in duplicate addresses. Different
	types of operating systems might benefit from different stability		types of operating systems might benefit from different stability
	properties of the Net_Iface parameter. For example, a client-		properties of the Net_Iface parameter. For example, a client-
	oriented operating system might want to employ Net_Iface identifiers		oriented operating system might want to employ Net_Iface identifiers
	that are attached to the underlying network interface card (NIC),		that are attached to the underlying network interface card (NIC),
	such that a removable NIC always gets the same IPv6 address,		such that a removable NIC always gets the same IPv6 address,
	irrespective of the system communications port to which it is		irrespective of the system communications port to which it is
	attached. On the other hand, a server-oriented operating system		attached. On the other hand, a server-oriented operating system
	might prefer Net_Iface identifers that are attached to system slots/		might prefer Net_Iface identifiers that are attached to system slots/
	ports, such that replacement of a network interface card does not		ports, such that replacement of a network interface card does not
	result in an IPv6 address change. Appendix A discusses possible		result in an IPv6 address change. Appendix A discusses possible
	sources for the Net_Iface, along with their pros and cons.		sources for the Net_Iface, along with their pros and cons.
	Including the optional Network_ID parameter when computing the RID		Including the optional Network_ID parameter when computing the RID
	value above would cause the algorithm to produce a different		value above would cause the algorithm to produce a different
	Interface Identifier when connecting to different networks, even when		Interface Identifier when connecting to different networks, even when
	configuring addresses belonging to the same prefix. This means that		configuring addresses belonging to the same prefix. This means that
	a host would employ a different Interface Identifier as it moves from		a host would employ a different Interface Identifier as it moves from
	one network to another even for IPv6 link-local addresses or Unique		one network to another even for IPv6 link-local addresses or Unique
	skipping to change at page 11, line 5		skipping to change at page 11, line 17
	method specified in this document results in random Interface IDs,		method specified in this document results in random Interface IDs,
	the probability of DAD failures is very small.		the probability of DAD failures is very small.
	o Real world data indicates that MAC address reuse is far more		o Real world data indicates that MAC address reuse is far more
	common than assumed [HDMoore]. This means that even IPv6		common than assumed [HDMoore]. This means that even IPv6
	addresses that employ (allegedly) unique identifiers (such as IEEE		addresses that employ (allegedly) unique identifiers (such as IEEE
	identifiers) might result in DAD failures, and hence		identifiers) might result in DAD failures, and hence
	implementations should be prepared to gracefully handle such		implementations should be prepared to gracefully handle such
	occurrences.		occurrences.
	Finally, we note that some popular and widely-deployed operating		o Since some popular and widely-deployed operating systems (such as
	systems (such as Microsoft Windows) do not employ unique identifiers		Microsoft Windows) do not employ unique hardware identifiers for
	for the Interface IDs of their stable addresses. Therefore, such		the Interface IDs of their stable addresses, reliance on such
	implementations would not be affected by the method specified in this		unique identifiers is more reduced in the deployed world (fewer
	document.		deployed systems rely on them for the avoidance of address
			collisions).
	4. Resolving Duplicate Address Detection (DAD) conflicts		4. Resolving Duplicate Address Detection (DAD) conflicts
	If as a result of performing Duplicate Address Detection (DAD)		If as a result of performing Duplicate Address Detection (DAD)
	[RFC4862] a host finds that the tentative address generated with the		[RFC4862] a host finds that the tentative address generated with the
	algorithm specified in Section 3 is a duplicate address, it SHOULD		algorithm specified in Section 3 is a duplicate address, it SHOULD
	resolve the address conflict by trying a new tentative address as		resolve the address conflict by trying a new tentative address as
	follows:		follows:
	o DAD_Counter is incremented by 1.		o DAD_Counter is incremented by 1.
	skipping to change at page 15, line 29		skipping to change at page 15, line 29
	o They mitigate address-scanning techniques which leverage		o They mitigate address-scanning techniques which leverage
	predictable Interface Identifiers (e.g., known Organizationally		predictable Interface Identifiers (e.g., known Organizationally
	Unique Identifiers) [I-D.ietf-opsec-ipv6-host-scanning].		Unique Identifiers) [I-D.ietf-opsec-ipv6-host-scanning].
	o They may result in IPv6 addresses that are independent of the		o They may result in IPv6 addresses that are independent of the
	underlying hardware (i.e. the resulting IPv6 addresses do not		underlying hardware (i.e. the resulting IPv6 addresses do not
	change if a network interface card is replaced) if an appropriate		change if a network interface card is replaced) if an appropriate
	source for Net_Iface (Section 3) is employed.		source for Net_Iface (Section 3) is employed.
			o They prevent the information leakage produced by embedding
			hardware addresses in the Interface Identifier (which could be
			exploited to launch device-specific attacks).
			o Since the method specified in this document will result in
			different Interface Identifiers for each configured address,
			knowledge/leakage of the Interface Identifier employed for one
			stable address of will not negatively affect the security/privacy
			of other stable addresses configured for other prefixes (whether
			at the same time or at some other point in time).
	In scenarios in which an attacker can connect to the same subnet as a		In scenarios in which an attacker can connect to the same subnet as a
	victim node, the attacker might be able to learn the Interface		victim node, the attacker might be able to learn the Interface
	Identifier employed by the victim node for an arbitrary prefix, by		Identifier employed by the victim node for an arbitrary prefix, by
	simply sending a forged Router Advertisement [RFC4861] for that		simply sending a forged Router Advertisement [RFC4861] for that
	prefix, and subsequently learning the corresponding address		prefix, and subsequently learning the corresponding address
	configured by the victim node (either listening to the Duplicate		configured by the victim node (either listening to the Duplicate
	Address Detection packets, or to any other traffic that employs the		Address Detection packets, or to any other traffic that employs the
	newly configued address). We note that a number of factors might		newly configured address). We note that a number of factors might
	limit the ability of an attaker from successfully performing such		limit the ability of an attacker from successfully performing such
	attack:		attack:
	o First-Hop security mechanisms such as RA-Guard [RFC6105]		o First-Hop security mechanisms such as RA-Guard [RFC6105]
	[I-D.ietf-v6ops-ra-guard-implementation] could prevent the forged		[I-D.ietf-v6ops-ra-guard-implementation] could prevent the forged
	Router Advertisement from reaching the victim node		Router Advertisement from reaching the victim node
	o If the victim implementation includes the (optional) Network_ID		o If the victim implementation includes the (optional) Network_ID
	parameter for computing F() (see Section 3), and the Network_ID		parameter for computing F() (see Section 3), and the Network_ID
	employed by the victim for a remote network is unknown to the		employed by the victim for a remote network is unknown to the
	attacker, the Interface Identifier learned by the attacker would		attacker, the Interface Identifier learned by the attacker would
	skipping to change at page 17, line 12		skipping to change at page 17, line 12
	thus possibly offering an interesting trade-off for those scenarios		thus possibly offering an interesting trade-off for those scenarios
	in which the use of temporary addresses is not feasible.		in which the use of temporary addresses is not feasible.
	8. Acknowledgements		8. Acknowledgements
	The algorithm specified in this document has been inspired by Steven		The algorithm specified in this document has been inspired by Steven
	Bellovin's work ([RFC1948]) in the area of TCP sequence numbers.		Bellovin's work ([RFC1948]) in the area of TCP sequence numbers.
	The author would like to thank (in alphabetical order) Ran Atkinson,		The author would like to thank (in alphabetical order) Ran Atkinson,
	Karl Auer, Steven Bellovin, Matthias Bethke, Ben Campbell, Brian		Karl Auer, Steven Bellovin, Matthias Bethke, Ben Campbell, Brian
	Carpenter, Tassos Chatzithomaoglou, Alissa Cooper, Dominik Elsbroek,		Carpenter, Tassos Chatzithomaoglou, Tim Chown, Alissa Cooper, Dominik
	Brian Haberman, Bob Hinden, Christian Huitema, Ray Hunter, Jouni		Elsbroek, Brian Haberman, Bob Hinden, Christian Huitema, Ray Hunter,
	Korhonen, Eliot Lear, Jong-Hyouk Lee, Andrew McGregor, Tom Petch,		Jouni Korhonen, Eliot Lear, Jong-Hyouk Lee, Andrew McGregor, Tom
	Michael Richardson, Mark Smith, Ole Troan, and He Xuan, for providing		Petch, Michael Richardson, Mark Smith, Ole Troan, James Woodyatt, and
	valuable comments on earlier versions of this document.		He Xuan, for providing valuable comments on earlier versions of this
			document.
	This document is based on the technical report "Security Assessment		This document is based on the technical report "Security Assessment
	of the Internet Protocol version 6 (IPv6)" [CPNI-IPv6] authored by		of the Internet Protocol version 6 (IPv6)" [CPNI-IPv6] authored by
	Fernando Gont on behalf of the UK Centre for the Protection of		Fernando Gont on behalf of the UK Centre for the Protection of
	National Infrastructure (CPNI).		National Infrastructure (CPNI).
	Fernando Gont would like to thank CPNI (http://www.cpni.gov.uk) for		Fernando Gont would like to thank CPNI (http://www.cpni.gov.uk) for
	their continued support.		their continued support.
	9. References		9. References
	skipping to change at page 19, line 25		skipping to change at page 19, line 25
	Networks", draft-ietf-opsec-ipv6-host-scanning-01 (work in		Networks", draft-ietf-opsec-ipv6-host-scanning-01 (work in
	progress), April 2013.		progress), April 2013.
	[I-D.ietf-v6ops-ra-guard-implementation]		[I-D.ietf-v6ops-ra-guard-implementation]
	Gont, F., "Implementation Advice for IPv6 Router		Gont, F., "Implementation Advice for IPv6 Router
	Advertisement Guard (RA-Guard)",		Advertisement Guard (RA-Guard)",
	draft-ietf-v6ops-ra-guard-implementation-07 (work in		draft-ietf-v6ops-ra-guard-implementation-07 (work in
	progress), November 2012.		progress), November 2012.
	[HDMoore] HD Moore, "The Wild West", Louisville, Kentucky, U.S.A.		[HDMoore] HD Moore, "The Wild West", Louisville, Kentucky, U.S.A.
	September 25-29, 2012., September 2012,		September 25-29, 2012,
	<https://speakerdeck.com/hdm/derbycon-2012-the-wild-west>.		<https://speakerdeck.com/hdm/derbycon-2012-the-wild-west>.
	[Gont-DEEPSEC2011]		[Gont-DEEPSEC2011]
	Gont, "Results of a Security Assessment of the Internet		Gont, "Results of a Security Assessment of the Internet
	Protocol version 6 (IPv6)", DEEPSEC 2011 Conference,		Protocol version 6 (IPv6)", DEEPSEC 2011 Conference,
	Vienna, Austria, November 2011, <http://		Vienna, Austria, November 2011, <http://
	www.si6networks.com/presentations/deepsec2011/		www.si6networks.com/presentations/deepsec2011/
	fgont-deepsec2011-ipv6-security.pdf>.		fgont-deepsec2011-ipv6-security.pdf>.
	[Gont-BRUCON2012]		[Gont-BRUCON2012]
	skipping to change at page 21, line 20		skipping to change at page 21, line 20
	trade-offs, which may vary from one implementation to another.		trade-offs, which may vary from one implementation to another.
	A.1. Interface Index		A.1. Interface Index
	The Interface Index [RFC3493] [RFC3542] of an interface uniquely		The Interface Index [RFC3493] [RFC3542] of an interface uniquely
	identifies an interface within a node. However, these identifiers		identifies an interface within a node. However, these identifiers
	might or might not have the stability properties required for the		might or might not have the stability properties required for the
	Net_Iface value employed by this method. For example, the Interface		Net_Iface value employed by this method. For example, the Interface
	Index might change upon removal or installation of a network		Index might change upon removal or installation of a network
	interface (typically one with a smaller value for the Interface		interface (typically one with a smaller value for the Interface
	Index, when such a naming scheme is used), or when network interface		Index, when such a naming scheme is used), or when network interfaces
	happen to be initialized in a different order. We note that some		happen to be initialized in a different order. We note that some
	implementations are known to provide configuration knobs to set the		implementations are known to provide configuration knobs to set the
	Interface Index for a given interface. Such configuration knobs		Interface Index for a given interface. Such configuration knobs
	could be employed to prevent the Interface Index from changing (e.g.		could be employed to prevent the Interface Index from changing (e.g.
	as a result of the removal of a network interface).		as a result of the removal of a network interface).
	A.2. Interface Name		A.2. Interface Name
	The Interface Name (e.g., "eth0", "em0", etc) tends to be more stable		The Interface Name (e.g., "eth0", "em0", etc) tends to be more stable
	than the underlying Interface Index, since such stability is		than the underlying Interface Index, since such stability is
	skipping to change at page 21, line 49		skipping to change at page 21, line 49
	from a different vendor.		from a different vendor.
	We note that Interface Names might still change when network		We note that Interface Names might still change when network
	interfaces are added or removed once the system has been bootstrapped		interfaces are added or removed once the system has been bootstrapped
	(for example, consider Universal Serial Bus-based network interface		(for example, consider Universal Serial Bus-based network interface
	cards which might be added or removed once the system has been		cards which might be added or removed once the system has been
	bootstrapped).		bootstrapped).
	A.3. Link-layer Addresses		A.3. Link-layer Addresses
	Link-layer addresses typically provide for unique identfiers for		Link-layer addresses typically provide for unique identifiers for
	network interfaces; although, for obvious reasons, they generally		network interfaces; although, for obvious reasons, they generally
	change when a network interface card is replaced. In scenarios where		change when a network interface card is replaced. In scenarios where
	neither Interface Indexes nor Interface Names have the stability		neither Interface Indexes nor Interface Names have the stability
	properties specified in Section 3 for Net_Iface, an implementation		properties specified in Section 3 for Net_Iface, an implementation
	might want to employ the link-layer address of the interface for the		might want to employ the link-layer address of the interface for the
	Net_Iface parameter, albeit at the expense of making the		Net_Iface parameter, albeit at the expense of making the
	corresponding IPv6 addresses dependent on the underlying network		corresponding IPv6 addresses dependent on the underlying network
	interface card (i.e., the corresponding IPv6 address would typically		interface card (i.e., the corresponding IPv6 address would typically
	change upon replacement of the underlying network interface card).		change upon replacement of the underlying network interface card).
			A.4. Logical Network Service Identity
			Host operating systems with a conception of logical network service
			identity, distinct from network interface identity or index, may keep
			a Universally Unique Identifier (UUID) or similar number with the
			stability properties appropriate for use as the Net_Iface parameter.
	Appendix B. Privacy issues still present when temporary addresses are		Appendix B. Privacy issues still present when temporary addresses are
	employed		employed
	It is not unusual for people to assume or expect that all the		It is not unusual for people to assume or expect that all the
	security/privacy implications of traditional SLAAC addresses to me		security/privacy implications of traditional SLAAC addresses are
	mitigated when "temporary addresses" [RFC4941] are employed.		mitigated when "temporary addresses" [RFC4941] are employed.
	However, as noted in Section 1 of this document and [IAB-PRIVACY],		However, as noted in Section 1 of this document and [IAB-PRIVACY],
	since temporary addresses are employed in addition to (rather than in		since temporary addresses are employed in addition to (rather than in
	replacement of) traditional SLAAC addresses, many of the security/		replacement of) traditional SLAAC addresses, many of the security/
	privacy implications of traditional SLAAC addresses are not mitigated		privacy implications of traditional SLAAC addresses are not mitigated
	by the use of temporary addresses.		by the use of temporary addresses.
	This section discusses a (non-exhaustive) number of scenarios in		This section discusses a (non-exhaustive) number of scenarios in
	which host security/privacy is still negatively affected as a result		which host security/privacy is still negatively affected as a result
	of employing Interface Identifiers that are constant across networks		of employing Interface Identifiers that are constant across networks
	(e.g., those resulting from embedding IEEE identifiers), even when		(e.g., those resulting from embedding IEEE identifiers), even when
	temporary addresses [RFC4941] are employed. It aims to clarify the		temporary addresses [RFC4941] are employed. It aims to clarify the
	motivation of employing the method specified in this document in		motivation of employing the method specified in this document in
	replacement of the traditional SLAAC addresses even when privacy/		replacement of the traditional SLAAC addresses even when privacy/
	temporary addresses [RFC4941] are employed.		temporary addresses [RFC4941] are employed.
	B.1. Host tracking		B.1. Host tracking
	This section describes one possible attack scenario that illustrates		This section describes two attack scenarios which illustrate that
	that host-tracking may still be possible when privacy/temporary		host-tracking may still be possible when privacy/temporary addresses
	addresses [RFC4941] are employed.		[RFC4941] are employed. These examples should remind us that one
			should not disclose more than it is really needed for achieving a
			specific goal (and an Interface Identifier that is constant across
			different networks does exactly that: it discloses more information
			than is needed for providing a stable address).
	B.1.1. Tracking hosts across networks #1		B.1.1. Tracking hosts across networks #1
	A host configures its stable addresses with the constant Interface		A host configures its stable addresses with the constant Interface
	Identifier, and runs any application that needs to perform a server-		Identifier, and runs any application that needs to perform a server-
	like function (e.g. a peer-to-peer application). As a result of		like function (e.g. a peer-to-peer application). As a result of
	that, an attacker/user participating in the same application (e.g.,		that, an attacker/user participating in the same application (e.g.,
	P2P) would learn the constant Interface Identifier used by the host		P2P) would learn the constant Interface Identifier used by the host
	for that network interface.		for that network interface.
	Some time later, the same host moves to a completely different		Some time later, the same host moves to a completely different
	network, and employs the same P2P application, probably even with a		network, and employs the same P2P application. The attacker now
	different username. The attacker now interacts with the same host		interacts with the same host again, and hence can learn its newly-
	again, and hence can learn its newly-configured stable address.		configured stable address. Since the Interface Identifier is the
	Since the Interface Identifier is the same as the one used before,		same as the one used before, the attacker can infer that it is
	the attacker can infer that it is communicating with the same device		communicating with the same device as before.
	as before.
	This is just *one* possible attack scenario, which should remind us
	that one should not disclose more than it is really needed for
	achieving a specific goal (and an Interface Identifier that is
	constant across different networks does exactly that: it discloses
	more information than is needed for providing a stable address).
	B.1.2. Tracking hosts across networks #2		B.1.2. Tracking hosts across networks #2
	Once an attacker learns the constant Interface Identifier employed by		Once an attacker learns the constant Interface Identifier employed by
	the victim host for its stable address, the attacker is able to		the victim host for its stable address, the attacker is able to
	"probe" a network for the presence of such host at any given network.		"probe" a network for the presence of such host at any given network.
	See Appendix B.1.1 for just one example of how an attacker could		See Appendix B.1.1 for just one example of how an attacker could
	learn such value. Other examples include being able to share the		learn such value. Other examples include being able to share the
	same network segment at some point in time (e.g. a conference		same network segment at some point in time (e.g. a conference
	skipping to change at page 25, line 8		skipping to change at page 25, line 7
	While it is usually assumed that IPv6 address-scanning attacks are		While it is usually assumed that IPv6 address-scanning attacks are
	unfeasible, an attacker can leverage address patterns in IPv6		unfeasible, an attacker can leverage address patterns in IPv6
	addresses to greatly reduce the search space		addresses to greatly reduce the search space
	[I-D.ietf-opsec-ipv6-host-scanning] [Gont-BRUCON2012]. Addresses		[I-D.ietf-opsec-ipv6-host-scanning] [Gont-BRUCON2012]. Addresses
	that embed IEEE identifiers result in one of such patterns that could		that embed IEEE identifiers result in one of such patterns that could
	be leveraged to reduce the search space when other nodes employ the		be leveraged to reduce the search space when other nodes employ the
	same IEEE OUI (Organizationally Unique Identifier).		same IEEE OUI (Organizationally Unique Identifier).
	As noted earlier in this document, temporary addresses [RFC4941] do		As noted earlier in this document, temporary addresses [RFC4941] do
	not replace/eliminate the use of IPv6 addresses that embed IEEE		not replace/eliminate the use of IPv6 addresses that embed IEEE
	identifiers (they are employed *in addition* to those), and hence		identifiers (they are employed in addition to those), and hence hosts
	hosts implementing [RFC4941] would still be vulnerable to address-		implementing [RFC4941] would still be vulnerable to address-scanning
	scanning attacks. The method specified in this document is meant as		attacks. The method specified in this document is meant as an
	an alternative to addresses that embed IEEE identifiers, and hence		alternative to addresses that embed IEEE identifiers, and hence
	eliminates such patterns (thus mitigating the aforementioned address-		eliminates such patterns (thus mitigating the aforementioned address-
	scanning attacks).		scanning attacks).
	B.3. Information Leakage		B.3. Information Leakage
	IPv6 addresses embedding IEEE identifiers leak information about the		IPv6 addresses embedding IEEE identifiers leak information about the
	device (Network Interface Card vendor, or even Operating System		device (Network Interface Card vendor, or even Operating System
	and/or software type), which could be leveraged by an attacker with		and/or software type), which could be leveraged by an attacker with
	device/software-specific vulnerabilities knowledge to quickly find		device/software-specific vulnerabilities knowledge to quickly find
	possible targets. Since temporary addresses do not replace the		possible targets. Since temporary addresses do not replace the
	traditional SLAAC addresses that typically embedd IEEE identifiers,		traditional SLAAC addresses that typically embed IEEE identifiers,
	employing temporary addresses does not eliminate this possible		employing temporary addresses does not eliminate this possible
	information leakage.		information leakage.
	Author's Address		Author's Address
	Fernando Gont		Fernando Gont
	SI6 Networks / UTN-FRH		SI6 Networks / UTN-FRH
	Evaristo Carriego 2644		Evaristo Carriego 2644
	Haedo, Provincia de Buenos Aires 1706		Haedo, Provincia de Buenos Aires 1706
	Argentina		Argentina
End of changes. 37 change blocks.
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