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Differences from draft-haddad-momipriv-problem-statement-00.txt
Internet Engineering Task Force Wassim Haddad
Mobility and Multi-homing Privacy Ericsson
Internet Draft Erik Nordmark
Expires July 2005 Sun Microsystems
Francis Dupont
Point6
Marcelo Bagnulo
UC3M
Soohong Daniel Park
Samsung Electronics
Basavaraj Patil
Nokia
February 2005
Privacy for Mobile and Multi-homed Nodes:
MoMiPriv Problem Statement
<draft-haddad-momipriv-problem-statement-01>
Status of this Memo
By submitting this Internet-Draft, I certify that any applicable
patent or other IPR claims of which I am aware have been
disclosed, or will be disclosed, and any of which I become aware
will be disclosed, in accordance with RFC 3668.
This document is an Internet Draft and is in full conformance with
all provisions of Section 10 of RFC 2026.
This document is an Internet-Draft. Internet-Drafts are working
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Distribution of this memo is unlimited
Abstract
This memo describes the privacy in mobility and multi-homing
problem statement.
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Table of Contents
1. Introduction................................................2
2. Glossary....................................................3
3. Problem Statement...........................................6
3.1. Location Privacy vs. Privacy...........................6
3.2. The MAC Layer Problem..................................8
3.3. The IP Layer Problem...................................9
3.4. The Interdependency Problem...........................11
4. Security Considerations....................................11
5. Acknowledgments............................................11
6. References.................................................12
7. Authors' Addresses.........................................13
Intellectual Property Statement...............................15
Disclaimer of Validity........................................15
Copyright Statement...........................................15
1. Introduction
In the near future, mobility and multi-homing functionalities
will coexist in the majority of end hosts, such as terminals,
PDAs, etc. For this purpose, Mobile IPv6 [MIPv6] protocol has
been designed to provide a solution for the mobility at the
network layer while Multi-homing is still an ongoing work.
MIPv6 does not provide any mechanism to protect the mobile
node's privacy when moving across the Internet, while in the
multi-homing area, the privacy may well be supported in any
potential solution but may probably lack some features. This is
mainly due to the fact that the privacy issues are not limited
to the IP layer only.
This memo describes the privacy in mobility and multi-homing
(momipriv) problem statement based on IPv6 only.
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2. Glossary
Anonymity
Anonymity is a property of network security. An entity "A"
in a system has anonymity if no other entity can identify
"A", nor is there any link back to "A" that can be used, nor
any way to verify that any two anonymous acts are performed
by "A".
Anonymity ensures that a user may use a resource or service
without disclosing the user's identity.
Anonymity in wireless networks means that neither the mobile
node nor its system software shall by default expose any
information, that allows any conclusions on the owner or
current use of the node.
Consequently, in scenarios where a device and/or network
identifiers are used (e.g., MAC address, IP address),
neither the communication partner nor any outside attacker
should be able to disclose any possible link between the
respective identifier and the user's identity.
Pseudonymity
Pseudonymity is a weaker property related to anonymity. It
means that one cannot identify an entity, but it may be
possible to prove that two pseudonymous acts were performed
by the same entity.
Pseudonymity ensures that a user may use a resource or
service without disclosing its user identity, but can still
be accountable for that use.
Consequently, a pseudonym is an identifier for a party to a
transaction, which is not in the normal course of events,
sufficient to associate the transaction with a particular
user.
Hence a transaction is pseudonymous in relation to a
particular party if the transaction data contains no direct
identifier for that party, and can only be related to them
in the event that a very specific piece of additional data
is associated with it.
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Unlinkability
Two events are unlinkable if they are no more and no less
related than they are related concerning the a-priori
knowledge.
Unlinkability ensures that a user may make use of resources
or services without others being able to link these two
uses together.
Note that unlinkability is a sufficient condition of
anonymity, but it is not a necessary condition.
Privacy
Privacy is a more general term than anonymity. Privacy is
the claim of individuals, groups and institutions to
determine for themesleves, when, how and to what extent
information about them is communicated to others.
In wireless telecommunications, privacy addresses especially
the protection of the content as well as the context (e.g.,
time, location, type of service, ...) of a communication
event.
Consequently, neither the mobile node nor its system
software shall support the creation of user-related usage
profiles. Such profiles basically comprise of a correlation
of time and location of the node's use, as well as the type
and details of the transaction performed.
Privacy can even be achieved by disconnectivity, i.e., not
being connected to a network.
MAC Address
A MAC Address is a 48 bits unique value associated with a
network adapter. The MAC address uniqueness is by default
global. A MAC Address is also known as the device/hardware
identifier.
Link
A communication facility or medium over which nodes can
communicate at the link layer, such as an Ethernet (simple
or bridged). A link is the layer immediately below IP.
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IPv6 Address
An IP address is a unique 128-bit IP layer identifier for an
interface or a set of interfaces attached to an IP network.
An IPv6 address can be unicast, i.e., identifier for a
single interface, or anycast, i.e., an identifier for a set
of interfaces, and a packet sent to an anycast address is
delivered to only one interface, or multicast, i.e., an
identifier for a set of interfaces and a packet sent to a
multicast address is delivered to all these interfaces.
Interface Identifier
A number used to identify a node's interface on a link. The
interface identifier is the remaining low-order bits in the
node's IP address after the subnet prefix.
Basic Service Set (BSS)
A set of stations controlled by a single coordination
function.
Extended Service Set (ESS)
A set of one or more interconnected basic service set (BSSs)
and integrated local area networks (LANs) that appears as a
single BSS to the logical link control layer at any station
associated with one of those BSSs.
Distribution System (DS)
A system used to interconnect a set of basic service sets
(BSSs) and integrated local area networks (LANs) to create
an extended service set (ESS).
For more literature about the Glossary content, please refer to
[ANON], [ISO99], [Priv-NG], [Freedom] and [ANON-PRIV].
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3. Problem Statement
The growing ability to trace a mobile node by an untrusted
third party, especially in public access networks, is a direct
and serious violation of the mobile user's privacy and can
cause serious damage to its personal, social and professional
life. Privacy becomes a real concern especially when the mobile
node (MN) uses permanent device and/or network identifiers.
Unfortunately, the privacy problem is not limited to a single
layer and should not be solved independantly on one layer.
Protecting the user's privacy can be achieved, in many
scenarios, by providing one or many of the privacy aspects
defined above with regards to the mobile node's requirements
and/or location. For this purpose, we try in the rest of this
document to use the terms defined above, in order to highlight
the issues in a more precise way.
It should be noted that this document focuses only on the
privacy problem for a mobile and multi-homed node only and does
not make any assumption regarding the privacy of a static node,
e.g., static correspondent node (CN). In addition, this
document assumes that the real IPv6 address is not hidden by
default, i.e., any node is always reachable via its real IPv6
address.
The problem statement is divided into three problems. The first
two problems are related to the identifiers associated with a
mobile device, i.e., the MAC address and the IP address, and the
third problem highlights their interdependency. But before
delving into these problems, a quick overview on differences
between location privacy and privacy is provided.
3.1. Location Privacy vs. Privacy
Before describing privacy problems related to the IP and the
link layer, it seems useful to highlight the differences between
the location privacy and privacy, in order to avoid a possible
confusion later.
Location privacy is the ability to prevent other parties from
learning one's current or past location [LOPRIPEC]. In order
to get such ability, the mobile node must conceal any relation
between its location and the personal identifiable information.
Note that in the momipriv context, the mobile node location
refers normally to the topological location and not the
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geographic one. The latter is provided by other means (e.g.,
GPS) than an IPv6 address. But it should be noted that it may
possible sometimes to deduce the geographical location from
the topological one.
However, concealing any relation between the location and the
user's identifier(s) does not guarantee that the identifier(s)
itself will not be disclosed, since it may be possible to hide
the real location alone. But, having at least one user's
identifier disclosed may be enough (e.g., if coupled with prior
knowledge about few possible whereabouts) for other party to
discover the user's current and/or previous location(s).
For example, in a context limited to IP and MAC layers, the
only available identifiers and/or locators are the IP and MAC
addresses, and only the IP address carries information, which
can directly disclose the MN's location (note that mobile IPv6
discloses both the mobile node's home and current locations).
The MAC address alone does not provide any hint regarding the
mobile node current/previous location. But if the other party
has already established the link between the target and its
MAC address and gained knowledge about some of the user's
possible current/future whereabouts, then it will be possible
to locate and even track the target.
On the other side, it should be noted that the two main
privacy aspects, i.e., anonymity and pseudonymity, provide
implicitly the location privacy feature by concealing the
real user's identifiers regardless of his/her location(s).
Actually, in both privacy aspects, real identifiers are
replaced by static or dynamic ones, thus making the other
party no more able to identify its target even at the
correct location, i.e., any past/current location
information becomes practically useless for locating and
tracking purposes.
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3.2. The MAC Layer Problem
The first problem focus on the MAC layer and is raising growing
concerns related to the user's privacy, especially with the
massive ongoing indoor/outdoor deployment of WLAN technologies.
A mobile device attached to a particular link is uniquely
identified on that link by its MAC address, i.e., the device
identifier. In addition, the device identifier is disclosed in
any packet sent by/to the MN when it reaches that particular
link, thus making it a very efficient tool to trace a mobile
user in a shared wireless medium access. Similar problems have
caused bad press for cellular operators.
For example, a malicious node located in one distributed system
(DS) can trace a mobile node via its device identifier while
moving in the entire ESS, and learn enough information about
the user's activities and whereabouts. Having these information
available in the wrong hands, especially with the exact time
when they occur, may have bad consequences on the user.
Another concern on the MAC layer, which can also be exploited
by an eavesdropper to trace its victim, is the sequence number
carried by the frame header. The sequence number is incremented
by 1 for each data frame and allows the bad guy to trace its
targeted node, in addition to the MAC address.
In addition, the sequence number allows also the malicious node
to keep tracing the MN, if/when the real MAC address is replaced
by one or many pseudo-identifier(s) during an ongoing session
[WLAN-IID].
In addition, it should be noted that even if the real MN's device
identifier remains undisclosed during all the session(s), it may
probably not be enough to provide the unlinkability protection
on the MAC layer, between ongoing session(s).
Actually, in a scenario, where the malicious node is located on
the link or in the distributed system, replacing the real MAC
address with a static pseudo-identifier, i.e., to provide
pseudonymity, or with temporary ones, i.e., to provide anonymity,
it will always be possible to break the unlinkability protection
provided by the MAC layer if the MN's IPv6 address remains
unchanged.
Note that in such scenario, even a periodical change of the
sequence number won't prevent the eavesdropper from correlating
ongoing session(s), pseudo-identifiers and the mobile node.
However, it should be mentioned that replacing the real device
identifier with static/dynamic pseudo-identifiers, in order to
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provide anonymity/pseudonymity, during an ongoing session(s),
raises another critical issue on the MAC layer level, which
concerns the uniqueness of these new pseudo-identifier(s).
In fact, any temporary/static identifiers MUST be unique within
the Extended Service Set (ESS) and the distributed system (DS).
3.3. The IP Layer Problem
The second problem focus on the IP layer and analyzes the
privacy problems related to IPv6 only.
A MN can configure its IPv6 address either from a DHCP server
or by itself. The latter scenario is called the stateless
address autoconfiguration [STAT], and discloses the MN MAC
address in the IPv6 address, thus enabling an eavesdropper to
easily learn both addresses in this case.
In order to mitigate the privacy concerns raised from using
the stateless address auto-configuration [PRIV-STAT], [PRIVACY]
introduced a method allowing to periodically change the MN's
interface identifier.
However, being limited to the interface identifier only, such
change discloses the real network identifier, which in turn can
reveal enough information about the topological location, the
user or can even be the exact piece of information needed by the
eavesdropper. Another limitation to its efficiency lays in the
fact that such change cannot occur during an ongoing session.
While using only a different IPv6 address for each new session
may prevent/mitigate the ability to trace a MN on the IP layer
level, it remains always possible to trace it through its device
identifier(s) on the MAC layer level, i.e., when a malicious node
(or another one) is also attached to the same link/DS than its
target. Consequently, it will be possible to learn all IPv6
addresses used by the MN by correlating different sessions, thus
breaking any unlinkability protection provided at the IP layer.
MIPv6 allows an MN to move across the Internet while ensuring
optimal routing (i.e., by using route optimization (RO)) mode
and keeping ongoing session(s) alive. Although these two
features make the RO mode protocol looks efficient, they
disclose the MN's home IPv6 address and its current location,
i.e., care-of address (CoA), in each data packet exchanged
between the MN and the correspondent node (CN).
Furthermore, each time a MN switches to a new network, it has
to send in clear a binding update (BU) message to the CN to
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notify it about its new location.
Consequently, MIPv6 RO mode discloses to a malicious node
located between the MN and the CN, all data required to
identify, locate and trace in real time its mobile target,
once it moves outside its home network(s) [Priv-NG].
MIPv6 defines another mode called the bidirectional tunneling
(BT), which allows the MN to hide its movements and locations
from the CN by sending all data packets through its HA (i.e.,
encapsulated). In such mode, the CN uses only the MN's home
IPv6 address to communicate with the MN.
But if the CN initiates a session with a MN then it has to use
the MN's home IPv6 address. In such scenario, if the MN wants
to keep its movements hidden from the CN, then it has to switch
to the bidirectional tunneling mode.
Consequently, all data packets sent/received by the MN are
exchanged through the MN's HA and the MN needs to update only
its HA with its location.
Although, the bi-directional tunneling mode allows hiding the
MN's care-of address to the CN, it can disclose its real
identity, i.e., IPv6 home address, and current location to a
malicious node located between the HA and the MN (e.g., by
looking to the data packets inner header), unless the HA-MN
tunnel is protected by using ESP.
In addition to mobility, the multi-homing feature allows a
mobile node to belong to different home networks and to switch
between these home networks without interrupting ongoing
session(s) [MULTI].
Although multi-homing can be considered as another aspect of
mobility, switching between different home networks, in addition
to moving between foreign networks, can disclose to a malicious
node well located between the multi-homed MN and the CN, part or
all of the MN's home IPv6 addresses, its device identifiers
(e.g., when stateless address autoconfiguring is used) and its
location(s). Such variety of identifiers can make the malicious
eavesdropper's task easier.
For example, a malicious node located between the MN and the CN
can start tracing its victim based on prior knowledge of one of
its home address or MAC address, and by tracking the BU messages
(e.g., the MN is using the RO mode).
After that, the malicious eavesdropper can correlate between
different signaling messages and possibly data packets to expand
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his knowledge to other victim's home/MAC addresses.
Learning new identifiers offer the eavesdropper additional tools
to detect and track future movements.
3.4. The Interdependency Problem
The MAC and IP layers problems described above highlight another
concern that needs to be addressed in order to protect the MN's
identifiers and/or hiding its locations: any change/update of
the IP address and the pseudo-identifier must be performed in a
synchronized way.
Otherwise, a change/update at the IP layer only, may allow the
eavesdropper to keep tracing the MN via the device identifier
and consequently to learn how/when the MN's identifiers are
modified on the MAC layer, thus making such change(s)
meaningless.
4. Security Considerations
This document is a problem statement, which describes privacy
issues related to a mobile and multi-homed node, and does not
introduce security considerations by itself.
However it should be noted that any potential solution for
the momipriv problem, which allows using temporary device
identifiers, dynamic pseudo-IP addresses and other parameters
during an ongoing session should not allow a malicious
eavesdropper to learn how nor when these identifiers are
updated.
Any potential solution must protect against replaying messages
using old identifiers and/or hijacking an ongoing session
during an update of the identifiers.
Any potential solution should not allow exploiting any aspect
of privacy, in order to gain access to networks.
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5. Acknowledgements
Many Thanks to Hannes Tschofenig for his review and comments on
the draft.
6. References
[ANON] A. Pfitzmann et al. "Anonymity, Unobservability,
Pseudonymity, and Identity Management - A Proposal
for Terminology", Draft v0.21, September, 2004.
[ANON-PRIV] M. Schmidt, "Subscriptionless Mobile Networking:
Anonymity and Privacy Aspects within Personal Area
Networks", IEEE WCNC 2002.
[Freedom] A.F. Westin, "Privacy and Freedom", Atheneum Press,
New York, USA, 1967.
[ISO99] ISO IS 15408, 1999, http://www.commoncriteria.org/.
[LOPRIPEC] A. Beresfold, F. Stajano, "Location Privacy in
Pervasive Computing", IEEE Pervasive Computing,
2(1):46-55, 2003 IEEE.
[MIPv6] D. Johnson, C. Perkins, J. Arkko, "Mobility Support
in IPv6", RFC 3775, June 2004.
[MULTI] N. Montavont, R. Wakikawa, T. Ernst, T. Noel, C. Ng,
"Analysis of Multihoming in Mobile IPv6",
draft-montavont-mobileip-multihoming-pb-statement-03,
January, 2005.
[PRIV-NG] A. Escudero-Pascual, "Privacy in the Next Generation
Internet", December 2002.
[PRIV-STAT] S. Deering, B. Hinden, "Statement on IPv6 Address
Privacy", http://playground.sun.com/pub/ipng/html/
specs/ipv6-address-privacy.html November, 1999.
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[Privacy] T. Narten, R. Draves, S. Krishnan, "Privacy
Extensions for Stateless Address Autoconfiguration
in IPv6", draft-ietf-ipv6-privacy-addrs-v2-02,
December, 2004.
[STAT] S. Thomson, T. Narten, T. Jinmei, "IPv6 Stateless
Address Autoconfiguration",
draft-ietf-ipv6-rfc2462bis-07, December, 2004.
[WLAN-IID] M. Gruteser, D. Grunwald, "Enhancing Location
Privacy in Wireless LAN Through Disposable Interface
Identifiers: A Quantitative Analysis, September
2003", First ACM International Workshop on Wireless
Mobile Applications and Services on WLAN Hotspots,
September 2003.
6. Authors'Addresses
Wassim Haddad
Ericsson Research
8400, Decarie Blvd
Town of Mount Royal
Quebec H4P 2N2
Canada
Phone: +1 514 345 7900
E-Mail: Wassim.Haddad@ericsson.com
Erik Nordmark
Sun Microsystems, Inc.
17 Network Circle
Mountain View, CA
USA
Phone: +1 650 786 2921
Fax: +1 650 786 5896
E-Mail: Erik.Nordmark@sun.com
Francis Dupont
Point6
c/o GET/ENST Bretagne
Campus de Rennes
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2, rue de la Chataigneraie
CS 17607
35576 Cesson-Sevigne Cedex
France
E-Mail: Francis.Dupont@enst-bretagne.fr
Marcelo Bagnulo
Universidad Carlos III de Madrid
Av. Universidad 30
Leganes, Madrid 28911
SPAIN
Phone: 34 91 6249500
E-Mail: Marcelo@it.uc3m.es
URI: http://www.it.uc3m.es/marcelo
Soohong Daniel Park
Samsung Electronics
Mobile Platform Laboratory, Samsung Electronics
416. Maetan-Dong, Yeongtong-Gu, Suwon
Korea
Phone: +81 31 200 4508
E-Mail: soohong.park@samsung.com
Basavaraj Patil
Nokia
6000 Connection Drive
Irving, TX 75039
USA
Phone: +1 972 894-6709
E-Mail: Basavaraj.Patil@nokia.com
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Intellectual Property Statement
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The IETF has been notified of intellectual property rights
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Copyright Statement
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subject to the rights, licenses and restrictions contained in
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