MIP6 Working Group                                         Rajeev Koodli
INTERNET DRAFT                                     Nokia Research Center
25 June 2006

    IP Address Location Privacy and Mobile IPv6:  Problem Statement

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   In this document, we discuss Location Privacy as applicable to
   Mobile IPv6.  We document the concerns arising from revealing Home
   Address to an on-looker and from disclosing Care of Address to a

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Abstract                                                               i

 1. Introduction                                                       1

 2. Problem Definition                                                 2
     2.1. Disclosing the Care of Address to the Correspondent Node     2
     2.2. Revealing the Home Address to On-lookers  . . . . . . . .    3

 3. Problem Illustration                                               3

 4. Conclusion                                                         5

 5. IANA Considerations                                                5

 6. Security Considerations                                            5

 7. Acknowledgment                                                     6

 8. Author's Address                                                   6

 A. Background                                                         6

Intellectual Property Statement                                        7

Disclaimer of Validity                                                 7

Copyright Statement                                                    7

Acknowledgment                                                         8

   1. Introduction

   The problems of location privacy, and privacy when using IP for
   communication have become important.  IP privacy is broadly concerned
   with protecting user communication from unwittingly revealing
   information that could be used to analyze and gather sensitive user
   data.  Examples include gathering data at certain vantage points,
   collecting information related to specific traffic, and monitoring
   (perhaps) certain populations of users for activity during specific
   times of the day, etc.  In this document, we refer to this as the
   "profiling" problem.

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   Location privacy is concerned with the problem of revealing roaming,
   which we define here as the process of a Mobile Node moving from one
   network to another with or without on-going sessions.  A constant
   identifier with global scope can reveal roaming.  Such a global scope
   identifier could be a device identifier or a user identifier.  Often,
   a binding between these two identifiers is also available, e.g.,
   through DNS. The location privacy problem is particularly applicable
   to Mobile IP where the Home Address on a visited network can reveal
   device roaming and, together with a user identifier (such as a SIP
   URI), can reveal user roaming.  Even when the binding between a user
   identifier and the Home Address is unavailable, freely available
   tools on the Internet can map the Home Address to the owner of the
   Home Prefix, which can reveal that a user from a particular ISP
   has roamed.  So, the location privacy problem is a subset of the
   profiling problem in which revealing a globally visible identifier
   compromises a user's location privacy.  When location privacy is
   compromised, it could lead to more targetted profiling.

   Furthermore, a user may not wish to reveal roaming to
   correspondent(s).  In Mobile IP, this translates to the use
   of Care of Address.  As with Home Address, the Care of Address can
   also reveal the topological location of the Mobile Node.

   In this document, the concerns arising from the use of a globally
   visible identifier, such as a Home Address, when roaming are
   described.  Similarly, the concerns from revealing a Care of Address
   to a correspondent are also outlined.  The solutions to these
   problems are meant to be specified in a separate document.

   This document is only concerned with IP Address Location Privacy in
   the presence of IP Mobility, as applied to Mobile IPv6.  It does not
   address the overall profiling problem.  Specifically, it does not
   concern itself with MAC addresses.  Some other work may address the
   problem of profiling IP and MAC identifiers (see for instance [1]).

   2. Problem Definition

   2.1. Disclosing the Care of Address to the Correspondent Node

   When a Mobile IP MN roams from its home network to a visited network
   or from one visited network to another, use of Care of Address in
   communication with a correspondent reveals that the MN has roamed.
   This assumes that the correspondent is able to associate the CoA to
   HoA, for instance by inspecting the Binding Cache Entry.  The HoA
   itself is assumed to have been obtained by whatever means (e.g.,
   through DNS lookup).

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   2.2. Revealing the Home Address to On-lookers

   When a Mobile IP MN roams from its home network to a visited network
   or from one visited network to another, use of Home Address in
   communication reveals to an on-looker that the MN has roamed.  When
   a binding of Home Address to a user identifier (such as a SIP
   URI or NAI) is available, the Home Address can be used to also
   determine that the user has roamed.  This problem is independent of
   whether the MN uses Care of Address to communicate directly with the
   correspondent (i.e., uses route optimization), or the MN communicates
   via the Home Agent (i.e., uses reverse tunneling).

   Location privacy may be compromised if an on-looker is present on
   the MN - HA path (when bidirectional tunneling is used), or when the
   on-looker is present on the MN and CN path (when route optimization
   is used).

   3. Problem Illustration

   This section is intended to provide the overall scope under which the
   above problems are applicable.

   Consider a Mobile Node at its home network.  Whenever it is involved
   in IP communication, its correspondents can see an IP address valid
   on the home network.  Elaborating further, the users involved in peer
   - peer communication are likely to see a user-friendly identifier
   such as a SIP URI, and the communication end-points in the IP
   stack will see IP addresses.  Users uninterested in or unaware of
   IP communication details will not see any difference when the MN
   acquires a new IP address.  Of course any user can ``tcpdump'' or
   ``ethereal'' a session, capture IP packets and map the MN's IP
   address to an approximate geo-location.  When this mapping reveals a
   ``home location'' of the user, the correspondent can conclude that
   the user has not roamed.  Assessing the physical location based on
   IP addresses is similar to assessing the geographical location based
   on the area-code of a telephone number.  The granularity of the
   physical area corresponding to an IP address can vary depending on
   how sophisticated the available tools are, how often an ISP conducts
   its network re-numbering, etc.

   When the MN roams to another network, the location privacy problem
   consists of two parts:  revealing information to its correspondents
   and to on-lookers.

   With its correspondents, the MN can either communicate directly or
   reverse tunnel its packets through the Home Agent.  Using reverse
   tunneling does not reveal the new IP address of the MN, although
   end-to-end delay may vary depending on the particular scenario.  The

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   difference in delay may be noticeable enough to serve as a hint to
   the correspondent, but such a hint cannot always be used to infer
   that the MN has roamed.  With those correspondents with which it can
   disclose its new IP address ``on the wire'', the MN has the option
   of using route-optimized communication.  The transport protocol
   still sees the Home Address with route optimization.  Unless the
   correspondent runs some packet capturing utility, the user cannot see
   which mode (reverse tunneling or route optimization) is being used,
   but knows that it is communicating with the same peer whose URI it
   knows.  This is similar to conversing with a roaming cellphone user
   whose phone number, like the URI, remains unchanged.

   Regardless of whether the MN uses route optimization or reverse
   tunneling, its Home Address is revealed in data packets.  When
   equipped with an ability to inspect packets ``on the wire'', an
   on-looker can determine that the MN has roamed and could possibly
   also determine that the user has roamed.  This could compromise
   the location privacy even if the MN took steps to hide its roaming
   information from a correspondent.

   The above description is valid regardless of whether a Home Address
   is static or is dynamically allocated.  In either case, the mapping
   of IP address to geo-location will most likely yield results with
   the same level of granularity.  With the freely available tools on
   the Internet, this granularity is the physical address of the ISP or
   the organization which registers ownership of a prefix chunk.  Since
   an ISP or an organization is not, rightly, required to provide a
   blue-print of its subnets, the granularity remains fairly coarse for
   a mobile wireless network.  However, sophisticated attackers might
   be able to conduct site mapping and obtain more fine-grained subnet

   A compromise in location privacy could lead to more targetted
   profiling of user data.  An eavesdropper may specifically track the
   traffic containing the Home Address, and monitor the movement of the
   Mobile Node with changing Care of Address.  The profiling problem is
   not specific to Mobile IPv6, but could be triggered by a compromise
   in location privacy due to revealing the Home Address.
   A correspondent may take advantage of the knowledge that a user
   has roamed when Care of Address is revealed, and modulate actions
   based on such a knowledge.  Such an information could cause concern
   to a mobile user especially when the correspondent turns out be

   When roaming, a MN may treat its home network nodes as any other
   correspondents.  Reverse tunneling is perhaps sufficient for home
   network communication, since route-optimized communication will
   traverse the identical path.  Hence, a MN can avoid revealing its
   Care of Address to its home network correspondents simply by using

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   reverse tunneling.  The Proxy Neighbor Advertisements from the Home
   Agent could serve as hints to the home network nodes that the Mobile
   Node is away.  However, they won't be able to know the Mobile Node's
   current point of attachment unless the MN uses route optimization
   with them.

   Finally, it is also worthwhile to note that both the Home Address
   and the Care of Address could be subject to profiling, just as
   any other user traffic.  However, applying existing techniques to
   thwart profiling may have implications to Mobile IPv6 signaling
   performance.  For instance, changing the Care of Address often would
   cause additional Return Routability and binding management signaling.
   And, changing the Home Address often has implications on IPSec
   security association management.  These issues need to be addressed
   in the solutions.

   4. Conclusion

   In this document, we have formulated the IP Location Privacy problem
   in the presence of Mobile IPv6.  The problem can be summarized as
   follows:  disclosing Care of Address to a correspondent and revealing
   Home Address to an on-looker can compromise the location privacy of a
   Mobile Node, and hence that of a user.  Solutions to this problem are
   expected to specifically address the use of Mobile IPv6 addresses,
   and not other identifiers (such as MAC addresses).

   The solutions to the location privacy problem described in this
   document are expected to be protocol specifications assuming the
   existing Mobile IPv6 functional entities, namely, the Mobile Node,
   its Home Agent and the Correspondent Node.

   5. IANA Considerations

   There are no IANA considerations introduced by this draft.

   6. Security Considerations

   This document discusses location privacy because of IP mobility.
   Solutions to provide location privacy, especially any signaling over
   the Internet, must be secure in order to be effective.  Individual
   solutions must describe the security implications.

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   7. Acknowledgment

   Thanks to Jari Arkko, James Kempf, Qiu Ying and Sam Xia for the
   review and feedback.  Thanks to Kilian Weniger for the last call
   review and for suggesting improvements.


   [1] W. Haddad and et al.  Privacy for Mobile and Multi-homed Nodes:
       MoMiPriv Problem Statement (work in progress).  Internet Draft,
       Internet Engineering Task Force, October 2004.

   [2] J. Polk, J. Schnizlein, and M. Linsner.  DHCP Option for
       Coordinate-based Location Configuration Information.  Request for
       Comments 3825, Internet Engineering Task Force, July 2004.

   8. Author's Address

     Rajeev Koodli
     Nokia Research Center
     313 Fairchild Drive
     Mountain View, CA 94043 USA
     Phone: +1 650 625 2359
     Fax: +1 650 625 2502
     E-Mail: Rajeev.Koodli@nokia.com

   A. Background

   The location privacy topic is broad and often has different
   connotations.  It also spans multiple layers in the OSI reference
   model.  Besides, there are attributes beyond an IP address alone
   that can reveal hints about location.  For instance, even if a
   correspondent is communicating with the same end-point it is used
   to, the ``time of the day'' attribute can reveal a hint to the
   user.  Some roaming cellphone users may have noticed that their SMS
   messages carry a timestamp of their ``home network'' timezone (for
   location privacy or otherwise) which can reveal that the user is in
   a different timezone when messages are sent during ``normal'' time
   of the day.  Furthermore, tools exist on the Internet which can map
   an IP address to the physical address of an ISP or the organization
   which owns the prefix chunk.  Taking this to another step, with
   in-built GPS receivers on IP hosts, applications can be devised
   to map geo-locations to IP network information.  Even without GPS
   receivers, geo-location can also be obtained in environments where
   [Geopriv] is supported, for instance as a DHCP option [2].

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   In summary, a user's physical location can be determined or guessed
   with some certainty and with varying levels of granularity by
   different means even though IP addresses themselves do not inherently
   provide any geo-location information.  It is perhaps useful to bear
   this broad scope in mind as the problem of IP address location
   privacy in the presence of IP Mobility is addressed.

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   Copyright Statement

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