MIP6 Working Group                                              Rajeev Koodli
INTERNET DRAFT                                          Nokia Research Center
23 October 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


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
      2.3. Problem Scope . . . . . . . . . . . . . . . . . . . . . .     3

 3.  Problem Illustration                                                    3

 4.  Conclusion                                                                5

 5.  IANA Considerations                                                5                                                      6

 6.  Security Considerations                                            5                                                 6

 7.  Acknowledgment                                                           6

 8.  Author's Address                                                         6

 A.  Background                                                         6                                                                7

Intellectual Property Statement                                             7

Disclaimer of Validity                                                 7                                                       8

Copyright Statement                                                    7                                                          8

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.

    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 context of IP Mobility, as applied to Mobile IPv6.  It does not address the overall profiling privacy
    problem.  Specifically,  For instance, it does not
   concern itself with MAC addresses.  Some other work may address privacy issues related to
    MAC addresses or the
   problem relationship of profiling IP and MAC identifiers (see for instance [1]). addresses [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).

    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).

    2.3. Problem Scope

    With existing Mobile IPv6 solutions, there is some protection against
    location privacy.  If a Mobile Node uses reverse tunneling with ESP
    encryption, then the HoA is not revealed on the MN - HA path.  So,
    eavesdroppers on the MN - HA path cannot determine roaming.  They
    could, however, still profile fields in the ESP header; however, this
    problem is not specific to Mobile IPv6 location privacy.

    When a MN uses reverse tunneling (regardless of ESP encryption),
    the correspondent does not have access to the CoA. Hence, it cannot
    determine that the MN has roamed.

    Hence, the location privacy problem is particularly applicable when
    Mobile IPv6 route optimization is used or when reverse tunneling is
    used without protecting the inner IP packet containing the HoA.

    3. Problem Illustration

    This section is intended to provide an illustration of the overall scope under which problem
    defined in the
   above problems are applicable. previous section.

    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 similar, although there are differences, 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
   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 (without ESP encryption), its Home Address is revealed in
    data packets.  When equipped with an ability to inspect packets ``on
    the wire'', an on-looker on the MN - HA path 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 statically allocated 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 information.

    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

    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.  Solutions should be careful in considering the cost of
    change of either CoA or HoA on signaling.  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 These issues should be
    addressed in the solutions.

    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
    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 discussed the IP Location Privacy location privacy problem
   in the presence of
    as applicable to 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  We have seen that
    bidirectional tunneling allows a MN to this problem are
   expected protect its CoA to specifically address the use of Mobile IPv6 addresses, CN, and not other identifiers (such
    together with ESP encryption allows the MN to protect its HoA from
    the on-lookers on the MN - HA path.

    However, with route optimization, the MN will reveal its CoA to the
    CN. Moreover, the HoA is revealed to on-lookers in the data packets
    as MAC addresses). well as in Mobile IPv6 signaling messages.  The solutions to the location privacy problem described in this
    problem 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.

    7. Acknowledgment

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


    [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].

    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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