One document matched: draft-ietf-mip6-location-privacy-ps-05.txt
Differences from draft-ietf-mip6-location-privacy-ps-04.txt
MIP6 Working Group Rajeev Koodli
INTERNET DRAFT Nokia Research Center
Informational
2 February 2007
IP Address Location Privacy and Mobile IPv6: Problem Statement
draft-ietf-mip6-location-privacy-ps-05.txt
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Abstract
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
correspondent.
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Contents
Abstract i
1. Introduction 1
2. Definitions 3
3. Problem Definition 4
3.1. Disclosing the Care-of Address to the Correspondent Node 4
3.2. Revealing the Home Address to On-lookers . . . . . . . 4
3.3. Problem Scope . . . . . . . . . . . . . . . . . 4
4. Problem Illustration 5
5. Conclusion 8
6. IANA Considerations 8
7. Security Considerations 8
8. Acknowledgment 9
9. References 9
9.1. Normative References . . . . . . . . . . . . . . 9
9.2. Informative References . . . . . . . . . . . . . 9
10. Author's Address 10
A. Background 11
Intellectual Property Statement 12
Disclaimer of Validity 12
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Copyright Statement 13
Acknowledgment 13
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
(MN) moving from one network to another with or without on-going
sessions. A constant identifier with global scope can reveal
roaming. Examples are a device identifier such as an IP address,
and a user identifier such as a SIP [9] URI [2]. Often, a binding
between these two identifiers is available, e.g., through DNS [5].
Traffic analysis of such IP and Upper Layer Protocol identifiers
on single network can indicate device and user roaming. Roaming
could also be inferred by means of profiling constant fields in IP
communication across multiple network movements. For example, an
Interface Identifier (IID) [10 ] in the IPv6 address that remains
unchanged across networks could suggest roaming. The SPI in the
IPsec [4] header is another field that may be subject to such
profiling and inference. Inferring roaming in this way typically
requires traffic analysis across multiple networks, or colluding
attackers, or both. When location privacy is compromised, it could
lead to more targetted profiling of user communication.
As can be seen, the location privacy problem spans multiple
protocol layers. Nevertheless, it is important to understand and
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specify the problem as applicable to concerned protocols in order
to at least mitigate the effects of the problem. In this context,
it is particularly important to Mobile IP, which defines a global
identifier (Home Address) that can reveal device roaming, and in
conjunction with a corresponding user identifier (such as a SIP
URI), can also reveal user roaming. Furthermore, a user may not
wish to reveal roaming to correspondent(s), which 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.
This document describes the concerns arising from the use of Home
Address from a visited network. This document also outlines the
considerations in disclosing a Care-of Address. This document
is primarily concerned with the vulnerabilities arising from
possible traffic analysis along the MN - CN path and the MN - HA
path, where the disclosure of Mobile IP addresses is sufficient to
reveal roaming. This document does not consider inferring roaming
from profiling fields such as an IID or an SPI for the following
reasons: First, such inference could be done independently, so the
problem is not specific to Mobile IP. Second, with Mobile IP, it
is sufficient to simply monitor the usage of Home Address from a
single visited network in order to deduce roaming. In other words,
the attackers need not conduct traffic profiling across multiple
networks, or collude with each other, or do both in order to infer
roaming when Mobile IP is used. Hence, we limit the scope of this
document to revealing the Mobile IP addresses.
This document is only concerned with IP Address Location Privacy
in the context of Mobile IPv6. It does not address the overall
privacy problem. For instance, it does not address privacy
issues related to MAC addresses or the relationship of IP and MAC
addresses [3], or the Upper Layer Protocol addresses. Solution
to the problem specified here should provide protection against
roaming disclosure due to using Mobile IPv6 addresses from a
visited network.
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This document assumes that the reader is familiar with the basic
operation of Mobile IPv6 [1] and the associated terminology defined
therein. For convenience, we provide some definitions below.
2. Definitions
- Mobile Node (MN): A Mobile IPv6 Mobile Node that freely roams
around networks
- Correspondent Node (CN): A Mobile IPv6 that node corresponds
with a MN
- Home Network: The network where the MN is normally present
when it is not roaming
- Visited Network: A network which a MN uses to access Internet
when it is roaming
- Home Agent: A router on the MN's home network which provides
forwarding support when the MN is roaming
- Home Address (HoA): The MN's unicast IP address valid on its
home network
- Care-of Address (CoA): The MN's unicast IP address valid on the
visited network
- Reverse Tunneling or Bidirectional Tunneling: A mechanism used
for packet forwarding between the MN and its Home Agent
- Route Optimization: A mechanism which allows direct routing
of packets between a roaming MN and its CN, without having to
traverse the home network.
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3. Problem Definition
3.1. 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 Care-of Address to Home Address, for instance by
inspecting the Binding Cache Entry. The Home Address itself is
assumed to have been obtained by whatever means (e.g., through DNS
lookup).
3.2. 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) 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).
3.3. 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 Home Address is not revealed on
the MN - HA path. So, eavesdroppers on the MN - HA path cannot
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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 Care-of Address.
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 Home
Address.
4. Problem Illustration
This section is intended to provide an illustration of the problem
defined in the 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. This mapping may reveal the home location of a
user, but a correspondent cannot ascertain whether the user has
actually roamed or not. Assessing the physical location based on
IP addresses has some similarities 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. And,
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an IP address cannot also guarantee that a peer is at a certain
geographic area due to technologies such as VPN and tunneling.
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 Care-of Address of the MN,
although end-to-end delay may vary depending on the particular
scenario. With those correspondents with which it can disclose its
Care-of 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 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
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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 untrustworthy. For these reasons, appropriate management
interfaces on the MN to guard against the misuse of location
information should be considered.
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 [1] 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 Care-of Address or Home Address on
signaling.
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 [7] from the
Home Agent could serve as hints to the home network nodes that the
Mobile Node is away. However, they will not be able to know the
Mobile Node's current point of attachment unless the MN uses route
optimization with them.
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5. Conclusion
In this document, we have discussed the location privacy problem
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. We have seen
that bidirectional tunneling allows a MN to protect its Care-of
Address to the CN. And, ESP encryption of inner IP packet allows
the MN to protect its Home Address from the on-lookers on the MN -
HA path. However, with route optimization, the MN will reveal its
Care-of Address to the CN. Moreover, route optimization causes the
Home Address to be revealed to on-lookers in the data packets as
well as in Mobile IPv6 signaling messages. The solutions to 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.
6. IANA Considerations
There are no IANA considerations introduced by this draft.
7. Security Considerations
This document discusses the location privacy problem specific to
Mobile IPv6. Any solution must be able to protect (e.g., using
encryption) the Home Address from disclosure to on-lookers in
data packets when using route optimization or reverse tunneling.
In addition, solutions must consider protecting the Mobile IPv6
signaling messages from disclosing the Home Address along the MN -
HA and MN - CN paths.
Disclosing the Care-of Address is inevitable if a MN wishes to
use route optimization. Regardless of whether Care-of Address
is an on-link address of the MN on the visited link or that of
a co-operating proxy, mere presence of Binding Cache entry is
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sufficient for a CN to ascertain roaming. Hence, a MN concerned
with location privacy should exercise prudence in determining
whether to use route optimization with, especially previously
unacquainted, correspondents.
The solutions should also consider the use of temporary addresses
and their implications on Mobile IPv6 signaling as discussed in
Section 4. Use of IP addresses with privacy extensions [6] could
be especially useful for Care-of Addresses if appropriate tradeoffs
with Return Routability signaling are taken into account.
8. Acknowledgment
Thanks to James Kempf, Qiu Ying, Sam Xia and Lakshminath Dondeti
for the review and feedback. Thanks to Jari Arkko and Kilian
Weniger for the last call review and for suggesting improvements
and text.
9. References
9.1. Normative References
[1] D. Johnson, C. Perkins, and J. Arkko. Mobility Support in
IPv6. Request for Comments 3775, Internet Engineering Task
Force, June 2004.
9.2. Informative References
[2] T. Berners-Lee, R. Fielding, and L. Masinter. Uniform Resource
Identifiers (URI): Generic Syntax. Request for Comments (Draft
Standard) 2396, Internet Engineering Task Force, August 1998.
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[3] 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.
[4] S. Kent and K. Seo. Security Architecture for the Internet
Protocol. Request for Comments (Proposed Standard) 4301,
Internet Engineering Task Force, December 2005.
[5] P. V. Mockapetris. Domain names - implementation and
specification. Request for Comments (Standard) 1035, Internet
Engineering Task Force, November 1987.
[6] T. Narten and R. Draves. Privacy Extensions for Stateless
Address Autoconfiguration in IPv6. Request for Comments 3041,
Internet Engineering Task Force, January 2001.
[7] T. Narten, E. Nordmark, and W. Simpson. Neighbor Discovery for
IP Version 6 (IPv6). Request for Comments (Draft Standard)
2461, Internet Engineering Task Force, December 1998.
[8] 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.
[9] J. Rosenberg and et al. SIP: Session Initiation Protocol.
Request for Comments (Proposed Standard) 3261, Internet
Engineering Task Force, June 2002.
[10] S. Thomson and T. Narten. IPv6 Stateless Address
Autoconfiguration. Request for Comments (Draft Standard) 2462,
Internet Engineering Task Force, December 1998.
10. Author's Address
Rajeev Koodli
Nokia Research Center
975 Page Mill Road, 200
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Palo Alto, CA 94034 USA
Phone: +1 408 425 6684
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 [8].
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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This document is subject to the rights, licenses and restrictions
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