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GEOPRIV                                                        R. Barnes
Internet-Draft                                               M. Lepinski
Updates: 3693, 3694                                     BBN Technologies
(if approved)                                                  A. Cooper
Intended status: BCP                                           J. Morris
Expires: September 10, 2009                       Center for Democracy &
                                                              Technology
                                                           H. Tschofenig
                                                  Nokia Siemens Networks
                                                          H. Schulzrinne
                                                     Columbia University
                                                           March 9, 2009


     An Architecture for Location and Location Privacy in Internet
                              Applications
                     draft-barnes-geopriv-lo-sec-05

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
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   This Internet-Draft will expire on September 10, 2009.

Copyright Notice

   Copyright (c) 2009 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents in effect on the date of
   publication of this document (http://trustee.ietf.org/license-info).
   Please review these documents carefully, as they describe your rights
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Abstract

   Location-based services (such as navigation applications, emergency
   services, management of equipment in the field) need geographic
   location information about Internet hosts, their users, and other
   related entities.  These applications need to securely gather and
   transfer location information for location services, and at the same
   time protect the privacy of the individuals involved.  This document
   describes an architecture for privacy-preserving location-based
   services in the Internet, focusing on authorization, security, and
   privacy requirements for the data formats and protocols used by these
   services.


























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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Binding Rules to Data  . . . . . . . . . . . . . . . . . .  4
     1.2.  Location-Specific Privacy Risks  . . . . . . . . . . . . .  5
     1.3.  Privacy Paradigms  . . . . . . . . . . . . . . . . . . . .  6
   2.  Overview of the Architecture . . . . . . . . . . . . . . . . .  8
     2.1.  Basic Geopriv Scenario . . . . . . . . . . . . . . . . . .  9
     2.2.  Roles and Data Formats . . . . . . . . . . . . . . . . . . 10
     2.3.  Relationships Between Geopriv Roles  . . . . . . . . . . . 13
   3.  The Location Life-Cycle  . . . . . . . . . . . . . . . . . . . 14
     3.1.  Positioning  . . . . . . . . . . . . . . . . . . . . . . . 15
       3.1.1.  Determination Mechanisms and Protocols . . . . . . . . 16
       3.1.2.  Privacy Considerations . . . . . . . . . . . . . . . . 18
       3.1.3.  Security Considerations  . . . . . . . . . . . . . . . 20
     3.2.  Location Distribution  . . . . . . . . . . . . . . . . . . 20
       3.2.1.  Privacy Rules  . . . . . . . . . . . . . . . . . . . . 21
       3.2.2.  Location References  . . . . . . . . . . . . . . . . . 24
       3.2.3.  Privacy Considerations . . . . . . . . . . . . . . . . 25
       3.2.4.  Security Considerations  . . . . . . . . . . . . . . . 26
     3.3.  Receipt of Location Information  . . . . . . . . . . . . . 27
       3.3.1.  Privacy Considerations . . . . . . . . . . . . . . . . 28
       3.3.2.  Security Considerations  . . . . . . . . . . . . . . . 28
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . . 28
     4.1.  Threats to Location Objects  . . . . . . . . . . . . . . . 29
       4.1.1.  Threats to Location Integrity and Authenticity . . . . 30
       4.1.2.  Threats to Location Privacy  . . . . . . . . . . . . . 31
     4.2.  Required Assurances  . . . . . . . . . . . . . . . . . . . 31
     4.3.  Protocol mechanisms  . . . . . . . . . . . . . . . . . . . 33
     4.4.  Mechanisms within the Location Object  . . . . . . . . . . 33
   5.  Example Scenarios  . . . . . . . . . . . . . . . . . . . . . . 34
     5.1.  Minimal Scenario . . . . . . . . . . . . . . . . . . . . . 35
     5.2.  Location-based Web Services  . . . . . . . . . . . . . . . 36
     5.3.  Emergency Calling  . . . . . . . . . . . . . . . . . . . . 38
     5.4.  Combination of Services  . . . . . . . . . . . . . . . . . 39
   6.  Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 44
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 45
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 45
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 45
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 45
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 46









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1.  Introduction

   Location-based services (applications that require information about
   the geographic location of an individual or device) are becoming
   increasingly common on the Internet.  Navigation and direction
   services, emergency services, friend finders, management of equipment
   in the field and many other applications require geographic location
   information about Internet hosts, their users, and other related
   entities.  As the accuracy of location information improves and the
   expense of calculating and obtaining it declines, the distribution
   and use of location information in Internet-based services will
   likely become increasingly pervasive.  Ensuring that location
   information is transmitted and accessed in a secure and privacy-
   protective way is essential to the future success of these services,
   as well as the minimization of the privacy harms that could flow from
   their wide deployment and use.

   Standards for communicating location information over the Internet
   have an important role to play in providing a technical basis for
   privacy and security protection.  This document describes a
   standardized privacy- and security-focused architecture for location-
   based services in the Internet: the Geopriv architecture.  The
   central component of the Geopriv architecture is the location object,
   which is used to convey both location information about an individual
   or device and user-specified privacy rules governing that location
   information.  As location information moves through its life cycle --
   positioning, distribution, and finally receipt and use by its
   ultimate recipient(s) -- Geopriv provides mechanisms to guarantee the
   integrity and confidentiality of location objects and to ensure that
   location information is only transmitted in compliance with the
   user's privacy rules.

   The goals of this document are two-fold: First, the architecture
   described revises and expands on the basic Geopriv Requirements
   [2][3], in order to clarify how these privacy concerns and the
   Geopriv architecture apply to use cases that have arisen since the
   publication of those documents.  Second, this document should provide
   a general introduction to Geopriv and Internet location-based
   services, and be useful as a good first document for readers new to
   Geopriv.

1.1.  Binding Rules to Data

   A central feature of the Geopriv architecture is that location
   information is always bound to privacy rules, in order to ensure that
   entities that receive location are informed of how to they may use
   it.  By creating a structure to convey the user's preferences along
   with location information, the likelihood that those preferences will



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   be honored necessarily increases.  In particular, no recipient of the
   location information can disavow knowledge of users' preferences for
   how their location may be used.  The binding of privacy rules to
   location information can convey users' desire for and expectations of
   privacy, which in turn helps to bolster social and legal systems'
   protection of those expectations.

   Binding of usage rules to sensitive information is a common way of
   protecting information.  Several emerging schemes for expressing
   copyright information provide for rules to be transmitted together
   with copyrighted works.  The Creative Commons [21] model is the most
   prominent example, allowing an owner of a work to set four types of
   rules ("Attribution," "Noncommercial," "No Derivative Works" and
   "ShareAlike") governing the subsequent use of the work.  After the
   author sets these rules, the rules are conveyed together with the
   work itself, so that every recipient is aware of the copyright terms
   of the work.

   Classification systems for controlling sensitive documents within an
   organization are another example.  In these systems, when a document
   is created, it is marked with a classification such as "SECRET" or
   "PROPRIETARY."  Each recipient of the document knows from this
   marking that the document should only be shared with other people who
   are authorized to access documents with that marking.  Classification
   markings can also convey other sorts of rules, such as a
   specification for how long the marking is valid (a declassification
   date).  For example, the United States Department of Defense
   guidelines for classification [4] allow the creator of a document to
   mark it with a classification level that restricts access (e.g.,
   "SECRET") and an indication of when the document should be
   declassified or downgraded to a lower classification (e.g.,
   "DECLASSIFY ON December 31, 2011" or "DOWNGRADE TO CONFIDENTIAL ON
   December 31, 2011").

1.2.  Location-Specific Privacy Risks

   While location-based services raise some privacy concerns that are
   common to all forms of personal information, many of them are
   heightened and others are uniquely applicable in the context of
   location information.

   Location information is frequently generated on or by mobile devices.
   Because individuals often carry their mobile devices with them,
   location information may be used to form a comprehensive record of an
   individual's movements and activities.  While other kinds of data
   could arguably be considered more sensitive than location information
   in certain contexts -- an individual's medical records or bank
   statements, for instance -- these kinds of data provide mere



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   snapshots of an individual's activities at discrete moments in time,
   or within discrete aspects of their lives.  Location information, on
   the other hand, may be collected everywhere and at any time, often
   without explicit user interaction, and it may potentially describe
   both what a person is doing and where he or she is doing it.  The
   fact that an individual's mobile device location is obtained when he
   is at the bank can reveal that he was at the bank, when he was there,
   and which branch he uses.  Location-based services may allow for
   amassing such data points about an individual's every movement,
   potentially spurring the creation of richly detailed profiles of
   individual behavior.

   The availability of location information may also allow an
   individual's whereabouts to unwittingly become more public than
   desired, with potentially serious consequences.  Location information
   may reveal the fact that an individual was in a particular medical
   clinic or government building, for example, implying potentially very
   sensitive information about the individual that was not meant to be
   shared.  The ubiquity of location information may also increase the
   risks of stalking and domestic violence if perpetrators are able to
   use (or abuse) location-based services to gain access to location
   information about their victims.  Location information additionally
   raises significant child safety concerns as more and more children
   access location-aware devices.

   Finally, location information is and will continue to be of
   particular interest to governments and law enforcers around the
   world.  The existence of detailed records of individuals' movements
   should not automatically facilitate the ability for governments to
   track their citizens, but in some jurisdictions, laws dictating what
   government agents must do to obtain location data are either non-
   existent or out-of-date.

1.3.  Privacy Paradigms

   Traditionally, the extent to which data about individuals enjoys
   privacy protections on the Internet has largely been decided by the
   recipients of the data.  Internet users may or may not be aware of
   the privacy practices of the entities with whom they share data.
   Even if they are aware, they have generally been limited to making a
   binary choice between sharing data with a particular entity or not
   sharing it.  Internet users have not historically been granted the
   opportunity to express their own privacy preferences to the
   recipients of their data and to have those preferences honored.

   This paradigm is problematic because the interests of data recipients
   are often not aligned with the interests of data subjects.  While
   both parties may agree that data should be collected, used, disclosed



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   and retained as necessary to deliver a particular service to the data
   subject, they may not agree about how the data should otherwised be
   used.  For example, an Internet user may gladly provide his email
   address on a Web site to receive a newsletter, but he may not want
   the Web site to share his email address with marketers, whereas the
   Web site may profit from such sharing.  Neither providing the address
   for both purposes nor deciding not to provide it is an optimal option
   from the Internet user's perspective.

   The Geopriv model departs from this paradigm for privacy protection.
   As explained above, location information can be uniquely sensitive.
   And as siloed location-based services emerge and proliferate, they
   increasingly require standardized protocols for communicating
   location information between services and entities.  Recognizing both
   of these dynamics, Geopriv gives data subjects the ability to express
   their choices with respect to their own location information, rather
   than allowing the recipients of the information to define how it will
   be used.  The combination of heightened privacy risk and the need for
   standardization compelled the Geopriv designers to shift away from
   the prevailing Internet privacy model, instead empowering users to
   express their privacy preferences about the use of their location
   information.

   Geopriv does not, by itself, provide technical means through which it
   can be guaranteed that users' location privacy rules will be honored
   by recipients.  The privacy protections in the Geopriv architecture
   are largely provided by virtue of the fact that recipients of
   location (Location Servers and Location Recipients in the below
   discussion) are informed of relevant privacy rules, and must only use
   location in accordance with those rules.  The distributed nature of
   the architecture inherently limits the degree to which compliance
   privacy controls -- the fact that an entity has not used location in
   an unauthorized way -- can be guaranteed and verified by technical
   means.  (Some security mechanisms can address this problem to a
   limited extent; see Section 4.)

   By binding privacy rules to location information, however, Geopriv
   provides valuable information about users' privacy preferences, so
   that non-technical forces such as legal contracts, governmental
   consumer protection authorities, and marketplace feedback can better
   enforce those privacy preferences.  If a commercial recipient of
   location information, for example, violates the location rules bound
   to the information, the recipient can in a growing number of
   countries be charged with violating consumer or data protection laws.
   In the absence of a binding of rules with location information,
   consumer protection authorities would be less able to protect
   consumers whose location information has been abused.




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2.  Overview of the Architecture

   This section provides an overview of the Geopriv architecture for the
   secure and private distribution of location information on the
   Internet.  We describe the three phases of the "location life cycle"
   -- positioning, distribution and receipt -- and discuss how the
   components of the architecture fit within each phase.  The next
   section provides additional detail about how each phase can be
   achieved in a private and secure manner.

   The risks discussed in the previous section all arise from
   unauthorized disclosure or usage of location information.  Thus, the
   Geopriv architecture has two fundamental privacy goals:

   1.  Ensure that location information is distributed only to
       authorized entities, and

   2.  Provide information to those entities about how they are
       authorized to use the location information.

   If these two goals are met, all parties that receive location
   information will also receive directives about how they can use that
   information.  Privacy-preserving entities will only engage in
   authorized uses, and entities that violate privacy will do so
   knowingly, since they have been informed of what is authorized (and
   thus, implicitly, of what is not).

   Privacy rules and their distribution are thus the central technical
   components of the privacy system, since they inform location
   recipients about how they are authorized to use that information.
   The two goals in the preceding paragraph are enabled by two classes
   of rules:

   1.  Access control rules: Rules that describe which entities may
       receive location information and in what form

   2.  Usage rules: Rules that describe what uses of location
       information are authorized

   Within this framework for privacy, security mechanisms provide
   support for the application of privacy rules.  For example,
   authentication mechanisms validate the identities of entities
   requesting location (so that authorization and access-control
   policies can be applied), and confidentiality mechanisms protect
   location information en route between privacy-preserving entities.
   Security mechanisms can also provide assurances that are outside the
   purview of privacy by, for example, assuring location recipients that
   location information has been faithfully transmitted to them by its



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   creator.

2.1.  Basic Geopriv Scenario

   As location information is transmitted among Internet hosts, it goes
   through a "location life-cycle:" first, the location is computed
   based on some external information (positioning), then it is
   transmitted from one host to another (distribution) until finally it
   is used by a recipient (receipt).

   For example, suppose Alice learns of her location from a wireless
   location service and wishes to share it privately with her friends by
   way of a presence service.  Alice clearly needs to provide the
   presence server with her location and a list of friends to whom the
   server can grant access to the location.  To enable Alice's friends
   to preserve her privacy, they need to be provided with privacy rules.
   Alice may tell some of her friends the rules directly, or she can
   have the presence server provide the rules to her friends when it
   provides them with her location.  In this way, every friend who
   receives Alice's location is authorized by Alice to receive it, and
   every friend who receives it knows the rules.  Good friends will obey
   the rules.  If a bad friend breaks them and Alice finds out, the bad
   friend cannot claim that he was unaware of the rules.

   Some of Alice's friends will be interested in using Alice's location
   only for their own purposes (to meet up with her or plot her location
   over time, for example).  The usage rules that they receive direct
   them as to what they can or cannot do (for example, Alice might not
   want them keeping her location for more than, say, two weeks).

   Consider one friend, Bob, who wants to send Alice's location to some
   of his friends.  Bob needs not only usage rules for himself, but also
   access control rules that describe who he can send information to and
   rules to give to the recipients.  If the rules he received from the
   presence server authorize him to give Alice's location to others, he
   may do so; otherwise, he will require additional rules from Alice
   before he is authorized to distribute her location.  If recipients
   who receive Alice's location from Bob want to distribute the location
   on further, they must go through the same process as Bob.












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   The whole example is illustrated in the following figure:

   +----------+
   | Wireless |
   | Location |
   | Service  |
   +----------+
      |
      |
     Location
      |
      |
      |    +------------More-Rules---------------------->+-----+
      |    |                                       +---->| Bob |--> ...
      |    |                                       |     +-----+
      v    |                                       |
   +-------+            +----------+               |
   |       |--Location->| Presence |--Location-+   |     +----------+
   | Alice |            | Service  |           |---+---->| Friend-1 |
   |       |---Rules--->|          |---Rules---+   |     +----------+
   +-------+            +----------+               |
                                                               |
                                                   |     +----------+
                                                   +---->| Friend-2 |
                                                         +----------+

                     Figure 1: Basic Geopriv Scenario

2.2.  Roles and Data Formats

   The above example illustrates the five basic roles in the Geopriv
   architecture:

   Target:   An individual or other entity whose location is conveyed in
      the Geopriv architecture.  The Target is the entity whose privacy
      Geopriv seeks to protect.  Alice is the Target in the figure
      above.

   Rule Maker (RM):   An individual or entity that creates rules
      governing access to location information for a Target.  In some
      cases the Rule Maker and the Target will be the same individual or
      entity (as is the case with Alice), and in other cases they will
      be separate.  For example, a parent may serve as the Rule Maker
      when the Target is his child, or a corporate security officer may
      be the Rule Maker for devices owned by the corporation but used by
      employees.  The Rule Maker, however, is not necessarily the owner
      of a Target device.  For example, a corporation may provide a
      device to an employee but permit the employee to serve as the Rule



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      Maker and set her own privacy rules.

   Location Generator (LG):   The entity that initially determines or
      gathers the location of the Target.  Location Generators may be
      any sort of software or hardware used to obtain the Target's
      position (examples include GPS chips and cellular networks).  A
      Target may even be its own Location Generator; devices capable of
      unassisted satellite-based positioning and devices that accept
      manually entered location information are two examples.  The
      wireless location service is the Location Generator in the figure
      above.

   Location Server (LS):   An entity that receives both location
      information and rules, and applies the rules to the location
      information to determine what other entities, if any, can receive
      location information.  The first LS in the Geopriv process
      receives location information from Location Generators and rules
      from Rule Makers, and then applies the rules to the location
      information.  Location Servers may not necessarily be "servers" in
      the colloquial sense of hosts in remote data centers servicing
      requests.  Rather, a Location Server can be any software or
      hardware component that receives and distributes location
      information.  Examples include a server in an access network, a
      presence server, or a Web browser or other software running on a
      Target's device.  The above example includes four Location
      Servers: the wireless location service, Alice, the presence
      service and Bob.

   Location Recipient (LR):   The ultimate end point entity to which
      location information is distributed.  A Location Recipient may ask
      for location explicitly (by sending a query to a Location Server),
      or it may receive location asynchronously.  Location Recipients do
      not distribute location information to any other Geopriv entities.
      Friend-1 an Friend-2 are Location Recipients in the figure above.

   In general, these entities may or may not be physically separate from
   each other.

   Within this architecture, entities acting in Geopriv roles
   communicate using three types of protocols, which carry Location
   Objects and Privacy Rules in well-defined data formats:

   Privacy Rule:   A directive that regulates an entity's activities
      with respect to location information, including the collection,
      use, disclosure, and retention of the location information.
      Privacy Rules describe how location information may be used by an
      entity, the level of detail with which location information may be
      described to an entity, and the conditions under which location



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      information may be disclosed to an entity.

   Location Object (LO):   An object used to convey location information
      together with Privacy Rules.  Geopriv supports both geodetic
      location data (latitude/longitude/altitude/etc.) and civic
      location data (street/city/state/etc.).  Either or both types of
      location information may be present in a single LO.  In the
      positioning phase, a LO may contain location information without
      Privacy Rules (which are passed from one entity to another during
      the distribution phase).

   Positioning Protocol:   A protocol used by a Location Generator and a
      source external to the LG (the Target, for example) to exchange
      information necessary to determine the Target's location.  Many
      Positioning Protocols also carry a Location Object representing
      the location derived from this information.

   Conveyance Protocol:   A protocol used by a Location Server to send a
      Location Object to a Location Recipient or another Location
      Server.

   Rules Protocol:   A protocol used by a Rule Maker to provide Privacy
      Rules to a Location Server.




























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   The whole example, using Geopriv roles, objects and protocols, is
   illustrated in the following figure:

   +----+
   | LG |
   +----+
     |
     |
   Positioning (LO w/o Rules)
   Protocol
     |
     |    +------------Rules Protocol------------------->+----+
     |    |            (Privacy Rules)           +---->| LS |--> ...
     |    |                                      |     +----+
     v    |                                      |
   +-------+                                     |
   |Target | Conv. Proto.   +----+ Conv. Proto.  |     +----+
   |  RM   |--------------->| LS |---------------+---->| LR |
   |  LS   | (LO w/ Rules)  +----+ (LO w/ Rules) |     +----+
   +-------+                                     |
                                                 |     +----+
                                                 +---->| LR |
                                                       +----+

                     Figure 2: Basic Geopriv Scenario

2.3.  Relationships Between Geopriv Roles

   Although in the above example there is only a single Location
   Generator and a single Rule Maker, in some cases a Location Server
   may receive Location Objects from multiple Location Generators or
   Rules from multiple Rule Makers.  Likewise, a single Location
   Generator may publish location information to multiple Location
   Servers, and a single Location Recipient may receive Location Objects
   from multiple Location Servers.

   The term "Target" may refer not only to an individual whose location
   is described by a LO, but also to that individual's device, since the
   device engages in protocol interactions, not the individual.  For the
   remainder of this document, the term "Target" refers to the device.
   Geopriv can also be used to convey location information about a
   device that is not directly linked to a single individual, such as a
   package or product containing a location-capable sensor, or a device
   linked to multiple individuals.

   Although a single individual may use multiple devices, the Geopriv
   protocols address one device per individual at a time; it is outside
   the scope of Geopriv to interpolate one individual's location



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   information across multiple devices or to arbitrate between privacy
   preferences that differ across the individual's devices.

   There is also typically a close binding between a Location Generator
   and the first Location Server in the distribution path.  These two
   roles may be played by the same entity, for example, a positioning
   server that can also be queried for location.  While these two roles
   can be played by different entities, the relationship between them
   needs to be closely prescribed in order to preserve privacy, since an
   LS is a privacy-aware entity and an LG may not be.  The specific
   constraints on the relationship between an LG and an LS are described
   in Section 3.1.2.


3.  The Location Life-Cycle

   The previous section gave an example of how an individual's location
   can be distributed through the Internet.  In general, the location
   life-cycle breaks down into three phases:

   1.  Positioning: A Location Generator determines the Target's
       location

   2.  Distribution: Location Servers send location from one Location
       Server to another (possibly several times)

   3.  Receipt: A Location Recipient receives the location and uses it.

   Each of these phases involves a different set of Geopriv roles, and
   each has a different set of privacy implications.  The Geopriv roles
   are mapped onto the location life-cycle in the figure below.




















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   +----------+                +----------+
   |          |                |  Rule    |+
   |  Target  |                |  Maker(s)||
   |          |                |          ||
   +----------+                +----------+|
        ^|                      +----------+
        || Positioning              | Rules
        || Protocol                 | Protocol
        ||                          |
        |V                          V        LO (w/ Rules)
   +----------+                +----------+   Conveyance   +----------+
   |Location  | LO (w/o Rules) | Location |+   Protocol    |Location  |
   |Generator |--------------->| Server(s)||-------+------>|Recipient |
   |          |                |          ||               |          |
   +----------+                +----------+|               +----------+
                               +----------+
   <-----------><-----------------------------------------><----------->
    Positioning                Distribution                 Receipt


                       Figure 3: Location Life-Cycle

3.1.  Positioning

   Positioning is the process by which the physical location of the
   Target is computed, based on some observations about the Target's
   situation in the physical world.  (This process goes by several other
   names, including Location Determination or Sighting.)  The input to
   the positioning process is some information about the Target, and the
   outcome is that the Location Generator knows the location of the
   Target.  Said differently, positioning is the process by which a
   Location Generator generates a Location Object from other information
   about a Target.

   Given that they are situated at the beginning of the life-cycle of
   location information, positioning mechanisms and the protocols that
   support them play a central role in determining who has access to a
   Target's location information.  At the end of the positioning
   process, the Location Generator (which may be the Target itself)
   knows the location of the Target.  The LG, and possibly the Target,
   thus have the capability to distribute the Target's position, and the
   responsibility to do so in a privacy-preserving manner.

   In this section, we give a brief taxonomy of current positioning
   systems, their requirements for protocol support, and the privacy and
   security requirements for these protocols.





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3.1.1.  Determination Mechanisms and Protocols

   While the specific positioning mechanisms that can be applied for a
   given Target are strongly dependent on the physical situation and
   capabilities of the Target, these mechanisms generally fall into the
   three categories described in detail below:

   1.  Target-based

   2.  Network-based

   3.  Network-assisted

   As suggested by the above names, a positioning scheme can rely on the
   Target, an Internet-accessible resource (not necessarily a network
   operator), or a combination of the two.  For a given scheme, the
   nature of this reliance will dictate the protocol mechanisms needed
   to support it.

   With Target-based positioning mechanisms, the Target is capable of
   determining its location by itself.  This is the case for manually-
   entered location or for (unassisted) satellite-based positioning
   (using a Global Navigation Satellite System, or GNSS).  In these
   cases, the Target itself is a Location Generator, and there are no
   protocols required to support positioning (since no information needs
   to be communicated).

   In network-based positioning schemes, a third-party Location
   Generator (i.e., an Internet host other than the Target) has access
   to sufficient information about the Target, through out-of-band
   channels, to establish the position of the Target.  In these cases,
   the Location Generator is the entity that has access to the out-of-
   band information used for positioning.  The most common examples of
   this type of LG are entities that have a physical relationship to the
   Target (such as ISPs).  In wired networks, wiremap-based location is
   a network-based technique; in wireless networks, timing and signal-
   strength based techniques that use measurements from base stations
   are considered to be network-based.  Large-scale IP-to-geo databases
   (for example, those based on WHOIS data or latency measurements) are
   also considered to be network-based positioning mechanisms.

   For network-based positioning as for Target-based, no protocols are
   strictly necessary to support positioning, since positioning
   information is collected outside of the location distribution system
   (at lower layers of the network stack, for example).  This does not
   rule out the use of other Internet protocols (like SNMP) to collect
   inputs to the positioning process; rather, since these inputs can
   only be used by certain Location Generators to determine location,



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   they are not controlled as private information.  (However, when used
   in this way, they are Positioning Protocols.)  Network-based
   positioning often provides location to protocols by which the network
   informs a Target device of its position (Location Configuration
   Protocols [5]).

   Network-assisted systems account for the greatest number and
   diversity of positioning schemes.  In these systems, the work of
   positioning is divided between the Target and an external Location
   Generator via some communication (possibly over the Internet),
   typically in one of two ways:

   1.  The Target provides measurements to the LG

   2.  The LG provides assistance data to the Target

   In this case, "measurements" are understood to be observations about
   the Target's environment, ranging from wireless signal strengths to
   the MAC address of a first-hop router.  "Assistance" is the
   complement to measurement, namely the information that enables the
   computation of location-based on measurements.  A set of wireless
   base station locations (or wireless calibration information) would be
   an assistance datum, as would be a table mapping routers to buildings
   in a corporate campus.

   For example, wireless and wired networks can serve as the basis for
   network-assisted positioning.  In several current 802.11 positioning
   systems, the Target sends measurements (e.g., MAC addresses and
   signal strengths) to a Location Generator, and the Location Generator
   returns a location to the client.  In fixed networks, the Target can
   send its MAC address to the Location Generator, which can query the
   MAC-layer infrastructure to determine the switch and port to which
   that MAC address is connected, then query a wire map to determine the
   location at which the wire connected to that port terminates.

   As an aside, the common phrase "assisted GPS" ("assisted GNSS" more
   broadly) actually encompasses techniques that transmit both
   measurements and assistance data.  Systems in which the Target
   provides the assistance server with data such as pseudo-ranges are
   measurement-based, while those in which the assistance server provide
   ephemeris or alamanac data are assistance-based in the above
   terminology.  (Those familiar with GNSS positioning will note that
   there are of course cases in which both of these interactions occur
   within a single location determination protocol, so the categories
   are not mutually exclusive.)

   Naturally, the exchange of measurement or positioning data between
   the Target and the LG requires a protocol over which the information



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   is carried.  The structure of this protocol will depend on which of
   the two patterns a network-assisted scheme follows.  Conversely, the
   structure of the protocol will determine which of the two parties
   (the Target, the LG, or both) is aware of the Target's location at
   the end of the protocol.

   In summary, the positioning process can involve three Geopriv roles,
   and three protocols:

   Location Generator:  An LG supports the positioning process, and if
      it has applicable Rules may act as a Location Server for Location
      Objects generated through the positioning process.

   Target:  The Target can act as either as an LG (if it receives
      location as a result of positioning) or simply as a source of
      inputs to the positioning process.

   Location Server:  At the end of the positioning process, either the
      Target or an external Location Generator is enabled to act as an
      LS, making it subject to privacy requirements, or the LG transmits
      the information to the first LS (which in this case must obtain
      Rules from a Rule Maker).

   Positioning Protocol:  The protocol used by the Target and a Location
      Generator to exchange measurement and assistance data.

   Rules Protocol:  The protocol used by the a Rule Maker to provide
      privacy rules to a Location Server or Location Generator.

   Conveyance Protocol:  The protocol used by a Location Generator or
      Location Server to send a Location Object to a Location Recipient
      or another Location Server.

3.1.2.  Privacy Considerations

   At the conclusion of the positioning process, either the Target or an
   external LG (or both) has access to the location of the Target, and
   those entities (if they have applicable Rules from the Rule Maker)
   can act as Location Servers, or they will transmit the location to
   the first LS in the Geopriv process.

   If either entity chooses to act as an LS by distributing the Target's
   location, then it must only do so in authorized ways.  This
   requirement means that an LS must be provided with Privacy Rules for
   the Target's location, which dictate where the location may be sent,
   and what Privacy Rules should be sent with it.  If no Rules are
   available to an LS, then it must obey a set of privacy-preserving
   default rules (namely, the LCP policy described below).



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   The simplest case is when the Target acts as the initiating LS, which
   happens with a Target-based positioning scheme or a network-assisted
   scheme that results in the Target knowing its location.  In this
   case, Rules are always available, since the Target (or a user of a
   Target device) can act as a Rule Maker.  This requirement implies
   that software that implements LS functions on a host (i.e., software
   that distributes location) MUST provide interfaces for the user to
   specify both (1) to whom the software may send location information
   and (2) what Rules should be transmitted along with that location.

   When an entity other than the Target acts as an initiating LS, then
   it must follow appropriate Rules to protect the privacy of location
   that it distributes.  If Rules have been provided to it by an
   authorized Rule Maker -- either as part of the Positioning Protocol
   or through another channel, e.g., a Rules Protocol -- then the LG
   (acting as an initial LS) MUST transmit location only as allowed by
   these Rules.  (Note that as for other Location Servers, the decision
   as to which Rule Makers are authorized is a matter of local policy.)
   Where possible, Positioning Protocols SHOULD enable the Target to
   convey Rules to the LG.  If an LG supports Positioning Protocols that
   do not convey Rules and the LG is to serve as an LS, it MUST be able
   to receive Rules via a Rules Protocol.

   If an LS (especially an initiating LS) is not provisioned with
   Privacy Rules that authorize transmission of location information for
   a given Target, then it MUST transmit location only to the Target,
   and consider all other recipients unauthorized.  This default rule is
   known as the "LCP Policy", since it underlies the privacy aspects of
   Location Configuration Protocols (LCPs) [5].

   As an aside: There are several Location Configuration Protocols that
   have been developed within the IETF, both using DHCP [6][7][8] and
   using HTTP [9].  Within the architecture described in this document,
   these protocols are Conveyance Protocols: the Location Information
   Server that provides location through an LCP is a Location Server
   that provides location to the Target, following the LCP policy.

   In some deployment scenarios, positioning functions and distribution
   functions may need to be provided by separate entities.  That is, the
   LG and LS roles may need to be separated, with the LG acting as a
   "dumb," non-privacy-aware positioning resource, and the LS providing
   the privacy logic necessary to support distribution (possibly with
   multiple LSs using the same LG).  In order to allow the privacy-
   unaware LG to distribute location to these LSs while maintaining
   privacy, the relationship between the LG and set of LSs MUST be
   tightly constrained, effectively "hard-wired."  That is, the LG MUST
   provide location only to a small fixed set of LSs, and each of these
   LSs MUST comply with the requirements of this section and those in



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   Section 3.2.

3.1.3.  Security Considerations

   Manipulation of Positioning Protocols can expose location through two
   mechanisms: If a third party can guess measurements that a given
   Target would provide to the LG, and then use them to get the location
   of that Target, or if a third party can obtain assistance data that
   indicate the rough position of the client.  To mitigate this risk, a
   Positioning Protocol SHOULD allow the LG to authenticate Positioning
   Protocol clients (i.e., the Target or other information sources), in
   the sense of verifying that measurements presented by a client are
   likely to be the actual physical values measured by that client (and
   likewise, that the requested assistance data are consistent with the
   client's actual rough position).  These authentication mechanisms
   will necessarily rely on the nature of the positioning being done,
   and may not be technically feasible in all cases.

   In any case, Positioning Protocols MUST provide confidentiality and
   integrity protections in order to prevent observation and
   modification of transmitted positioning data and Location Objects
   while en route between the positioning client and the LG.

   If a Location Generator or a Target choose to act as an initiating
   Location Server, they inherit the security requirements for an LS,
   described in Section 3.2.4.

3.2.  Location Distribution

   When an entity receives location (from an LG or another LS) and
   redistributes it to other entities, it acts as a Location Server.
   Location Distribution is the process by which one or more Location
   Servers move location information from its source (a Location
   Generator) to its destination (a Location Recipient), in a privacy-
   preserving manner.

   The role of a Location Server is thus two-fold: First, it must
   collect location information and Rules that control access to that
   information.  Rules can be communicated within a Location Object,
   within a Conveyance Protocol that carries LOs, or through a separate
   Rules Protocol.  Second, the Location Server must process requests
   for location and apply the Rules to these requests in order to
   determine whether it is authorized to fulfill them by returning
   location information.

   A Location Server thus has at least two types of interactions with
   other hosts, namely receiving and sending Location Objects through a
   Conveyance Protocol.  An LS may optionally implement a third



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   interaction, allowing Rule Makers to provision it with Rules via a
   Rules Protocol.  The distinction between these two cases is important
   in practice, because it determines whether the LS has a direct
   relationship with a Rule Maker: An LS that accepts Rules via a Rules
   Protocol (or via a direct interaction with the Rule Maker) is known
   as an "Authorized LS" (LSa), while an LS that acquires all its Rules
   through a Conveyance Protocol is known as an "Independent LS" (LSi).

   The location distribution process thus involves three roles and three
   protocols:

   Location Servers:   Entities that perform the actual transmissions of
      location, in accordance with available Rules

   Rule Makers:   Entities that set Rules that constrain how location
      information is disseminated

   Location Recipients:   The ultimate destinations for location
      information

   Conveyance Protocols:   Protocols used by an LS to transmit Location
      Objects

   Rules Protocols:   Protocols used by an RM to supply Rules to an LS

   LO Formats:   The structure of a LO, including the available location
      and Rules semantics.

3.2.1.  Privacy Rules

   Privacy Rules are the central mechanism in Geopriv for maintaining a
   Target's privacy, because they provide a recipient of a LO (an LS or
   LR) with information on how the LO may be used.

   Throughout the Geopriv architecture, Privacy Rules are communicated
   in a rules language with a defined syntax and semantics (a Rules
   Format).  For example, the Common Policy rules language has been
   defined [10] to provide a framework for broad-based rule
   specifications.  Geopriv Policy [11] defines a language for creating
   location-specific rules.  XCAP [12] can be used as a Rules Protocol
   to install rules in both of these formats.

   Privacy Rules follow a default-deny pattern: an empty set of Rules
   implies that all requests for location should be denied (other than
   requests made by the Target itself), with each Rule added to the set
   granting a specific permission.  Adding a Rule to a set can never
   reduce existing permissions; it can only augment them.




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   The following are examples of Privacy Rules governing location
   distribution:

   o  Retransmit location when requested from example.com

   o  Retransmit location when requested by a specific group of
      requesters

   o  Retransmit only geodetic location

   o  Retransmit location accurate within 100 meters

   o  Retransmit location only to the first three recipients who request
      it

   o  Retransmit location only before midnight on December 31, 2009

   Location Servers enforce Privacy Rules in two ways: by denying
   requests for location, or by transforming the location information
   before retransmitting it.  Some Rules will only be enforceable
   through denial.  For example, if the entire Rule set for a particular
   Target consisted of the first Rule listed above, then a Location
   Server would be required to deny all requests for the Target's
   location from any recipients other than example.com.  On the other
   hand, the second rule above could be enforced either by rejecting
   requests for civic location or by stripping out all civic location
   from a LO received from an LG before retransmitting the LO to any LR
   that requests it.

   Location Servers may also receive Rules governing location retention,
   such as:

   o  Retain location only for 24 hours

   o  Retain location only until December 31, 2009

   These Rules are simply directives about how long the Target's
   location information can be retained.

   Privacy Rules can govern the behavior of both Location Servers and
   Location Recipients.  Rules that direct Location Servers about how to
   treat a Target's location information are known as Local Rules.
   Local Rules are used internally by the Location Server to handle
   requests from Location Recipients.  They are not distributed to
   Location Recipients.

   Rules that travel inside LOs are known as Forwarded Rules.  Forwarded
   Rules direct Location Servers and Location Recipients about how to



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   handle the location information they receive.  Because the Rules
   themselves may reveal potentially sensitive information about the
   Target, only the minimal subset of Forwarded Rules necessary to
   handle the LO is distributed.

   An example can illustrate the interaction between Local Rules and
   Forwarded Rules.  Suppose Alice provides the following Local Rules to
   a Location Server:

   o  The LS may retain location only for 24 hours

   o  The LS may retransmit Alice's precise location to Bob, who in turn
      is permitted to retain the location information for one month

   o  The LS may retransmit Alice's city, state, and country to Steve,
      who in turn is permitted to retain the location information for
      one hour

   o  The LS may retransmit Alice's country to a photo-sharing website,
      which in turn is permitted to retain the location information
      indefinitely and retransmit it to any requesters

   When Steve asks for Alice's location, the Location Server (assuming
   the request is within the authorized 24-hour window for the LS to
   retain Alice's location) can transmit to Steve the limited location
   information (city, state, and country) along with Forwarded Rules
   instructing Steve to (a) not further retransmit Alice's location
   information, and (b) only retain the location information for one
   hour.  By only sending these specifically applicable Forwarded Rules
   to Steve (as opposed to the full set of Local Rules), the LS is
   protecting Alice's privacy by not disclosing to Steve that (for
   example) Alice allows Bob to obtain more precise location information
   than Alice allows Steve to receive.

   Geopriv is designed to be usable even by devices with constrained
   processing capabilities.  To ensure that Forwarded Rules can be
   processed on constrained devices, LOs are required to carry only a
   limited set of Forwarded Rules, with an option to reference a more
   robust set of external Rules.  The limited Rule set covers two
   privacy aspects: how long the Target's location may be retained
   ("Retention"), and whether or not the Target's location may be
   retransmitted ("Retransmission").  (The latter rule will never grant
   an LR the permission to retransmit, since by definition an LR is a
   final end point for a Target's location, but an LS that receives a LO
   may be granted this permission.)  A LO may contain a pointer to more
   robust Rules, such as those shown in the set of six Rules at the
   beginning of this section.




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3.2.2.  Location References

   The location distribution process occurs through a series of
   transmissions of Location Objects: transmissions of location "by
   value."  Location "by value" can be expressed in terms of geodetic
   location data (latitude/longitude/altitude/etc.) and civic location
   data (street/city/state/etc.).

   Location can also be distributed "by reference."  A Location Object
   is represented by reference when it is represented by a URI that can
   be dereferenced to obtain the LO.  This document summarizes the
   concerns about location by reference that are discussed at length in
   [13].

   Distribution of location by reference (distribution of location URIs)
   offer several benefits.  From a practical perspective, it can make
   location more compact, more recent, and more easily discoverable.
   Location URIs are a more compact way of transmitting location, since
   URIs are usually smaller than LOs.  A recipient of location can make
   multiple requests to a URI over time to receive updated location (if
   the URI is configured to provide fresh location rather than a single
   "snapshot").  Location URIs can serve as an "LS discovery" mechanism,
   in that an entity can provide a location URI to an LS or LR in order
   to inform the recipient about which LS it should query to obtain a
   Location Object.

   From a positioning perspective (i.e., for an LG), location by
   reference can offer the additional benefit of "just in time"
   positioning.  If location is distributed by reference until it is
   needed for consumption, the LG (here acting as the referenced LS)
   only needs to perform positioning operations when a recipient makes a
   request for location.

   From a privacy perspective, distributing location as a URI instead of
   a Location Object can help protect privacy by forcing each recipient
   of the location to request location from the referenced LS, which can
   then apply access controls individually to each recipient.  Note,
   however, that the benefit provided here is contingent on the LS
   applying access controls.  If the LS does not apply an access control
   policy to requests for a location URI (in other words, if enforces
   the "possession model" defined in [13]), then transmitting a location
   URI presents the same privacy risks as transmitting the Object
   itself.  Moreover, the use of location URIs without access controls
   can introduce additional privacy risks: If URIs are more predictable
   than the location (e.g., if they are issued in sequence), then an
   attacker to whom the URI has not been sent may be able to guess the
   URI and use it to obtain the referenced LO.  To mitigate this,
   location URIs without access controls MUST be constructed so that



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   they are unpredictable.

3.2.3.  Privacy Considerations

   Two types of information are distributed in the location distribution
   process: location information and Privacy Rules.  Rules can be
   communicated either independently (through a Rules Protocol) between
   an RM and an LS, or as part of a Location Object carrying location
   information.  Location information, however, MUST always be
   accompanied by Rules -- otherwise, a recipient (whether an LS or an
   LR) will not know what uses are authorized, and will not be able to
   use the LO.  Consequently, LO formats MUST be able to express Rules
   that convey appropriate authorizations.

   An LS MUST only accept Rules from authorized Rule Makers.  For an
   LSi, this requirement is met by applying the Rules provided in a LO
   to the distribution of that LO.  For an LSa, this requirement means
   that the LS MUST be configurable with an RM authorization policy.  An
   LS SHOULD define a prescribed set of RMs that may define Rules for a
   given Target or LO.  For example, an LS may only allow the Target to
   set Rules for itself, or it might allow an RM to set Rules for
   several Targets (e.g., a parent for children, or a corporate security
   officer for employees).

   No matter how Rules are provided to an LS, for each LO it receives,
   it MUST combine all Rules that apply to the LO into a rule set that
   defines which transmissions are authorized, and it MUST transmit
   location only in ways that are authorized by these Rules.

   For an LSi, all Rules are provided in the LO.  When an LSi receives a
   LO, it MUST examine the Rules that accompany that LO in order to
   determine how it may use the LO (if any Rules are included by
   reference, the LSi SHOULD attempt to download them).  If the LO
   includes no Rules that allow the LSi to transmit the LO to another
   entity, then the LSi MUST NOT transmit the LO.  It may, however use
   the LO for other purposes, e.g., logging, if these other actions are
   authorized.  If the LO contains no Rules at all (e.g., if it is in a
   format with no Rules syntax), then the LSi MUST delete it.

   When an LSa receives a LO, it MUST combine the Rules in the LO with
   Rules it has received from RMs.  The strategy the LSa uses to combine
   these sets of Rules is a matter for local policy, depending on the
   relative priority that the LS grants to each source of Rules.  Some
   example policies:







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   Union:   A transmission of location is authorized if it is authorized
      by either a rule in the LO or an RM-provided rule.

   Intersection:   A transmission of location is authorized if it is
      authorized by both a rule in the LO and an RM-provided rule.

   RM Override:   A transmission of location is authorized if it is
      authorized by an RM-provided rule (regardless of the LO Rules)

   LO Override:   A transmission of location is authorized if it is
      authorized by a LO-provided rule (regardless of the RM Rules)

   In general, it is RECOMMENDED that an LSi follow either the
   "Intersection" policy, since it grants equal weight to all RMs
   (including the LO creator).  In cases where an external RM is more
   trusted than the source of the LO, the "Override" policy may be more
   suitable (e.g., if the external RM is the Target, and the LO is
   provided by a third party).  Conversely, the "LO Override" policy is
   best suited to cases where the LO provider is more trused than the RM
   (e.g., if the RM is the user of a mobile device LS and the LO is
   provided with Rules from the RM's parents or corporate security
   office).

3.2.4.  Security Considerations

   An LS's decisions about how to transmit location are based on the
   identities of entities requesting information and other aspects of
   requests for location.  In order to ensure that these decisions are
   made properly, the LS needs assurance of the reliability of
   information on the identities of the entities with which the LS
   interacts (including LRs, LSs, and RMs) and other information in the
   request.

   Conveyance Protocols and Rules Protocols MUST provide information on
   the identity of the recipient of location (an LR or LS) and the
   identity of the RM, respectively.  In order to ensure the validity of
   this information, these protocols MUST allow for mutual
   authentication of both parties, and MUST provide integrity protection
   for protocol messages.  These security features ensure that the LG
   has sufficient information (and sufficiently reliable information) to
   make privacy decisions.

   As they travel through the Internet within a Conveyance Protocol,
   Location Objects necessarily pass through a sequence of
   intermediaries, ranging from layer-2 switches to IP routers to
   application-layer proxies and gateways.  The ability of an LS to
   protect privacy by making access-control decisions is reduced if
   these intermediaries have access to a Location Object as it travels



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   between privacy-preserving entities.

   A Conveyance Protocol MUST provide end-to-end confidentiality between
   an LS that transmits location and the LS or LR that receives it.
   When the protocol itself is protected end-to-end between the LS and
   the recipient, carrying an unprotected Location Object within this
   encrypted channel is sufficient.  When the protocol has a mode in
   which messages are either unprotected or protected on a hop-by-hop
   basis (e.g., between intermediaries in a store-and-forward protocol),
   the protocol SHOULD allow the use of encrypted LOs, or for the
   transmission of a reference to location in place of a LO [13].

   It is RECOMMENDED that Rule Makers, Location Servers, and Location
   Recipients use the security features of Rules Protocols and Coveyance
   Protocols to ensure that Rules are installed and applied properly,
   and that location is protected en route.

3.3.  Receipt of Location Information

   After location information has been distributed via a series of
   Location Servers, it finally comes to rest with a Location Recipient.
   Location Recipients are consumers of location; they do not forward
   location information to other entities.  (Any recipient of location
   information that forwards it to other entities is acting as a
   Location Server in the distribution chain.  The privacy requirements
   for an LS are described in Section 3.2.)

   The primary privacy requirement of an LR is to constrain its usage of
   location to the set of uses authorized by the Rules in an LO.  If an
   LR only uses a LO in ways that do not have a privacy impact --
   specifically, if it does not transmit the LO to any other entity, and
   does not retain the LO for longer than is required to execute the
   Conveyance Protocol -- then no further action is necessary for the LR
   to comply with the requirements of this document.

   As an example of this simplest case, if a Location Recipient (a)
   receives a location, (b) immediately provides to the Target
   information or a service based on the location, (c) does not retain
   the information, and (d) does not retransmit the location to any
   other entity, then the LR will comply with any set of Rules that are
   permissible under Geopriv.  Thus, a service that, for example, only
   provides directions to the closest bookstore in response to an input
   of location, and promptly then discards the input location, will be
   in compliance with any Geopriv rule set.

   LRs that make other uses of a LO (e.g., those that store LOs, or send
   them to other service providers to obtain location-based services)
   MUST meet the requirements below to assure that these uses are



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   authorized.

   The Location Receipt process thus involves one Geopriv role and two
   protocols:

   Location Recipients:   Entities that accept LOs and use them, subject
      to the Privacy Rules they contain

   Conveyance Protocols:   Protocols by which LOs are delivered to
      Location Recipients

   LO Formats:   The structure of a LO, including the available location
      and Rules semantics.

3.3.1.  Privacy Considerations

   The principle privacy requirement for Location Recipients is to
   follow usage rules.  When an LR receives a LO, it is REQUIRED to
   examine the Rules included with that LO.  Any usage the LR makes of
   the LO MUST be explicitly authorized by these Rules.  Since Rules are
   positive grants of permission, any action not explicitly authorized
   is denied by default.

   In particular, given a LO in a particular format, an LR MUST NOT take
   any action that could be authorized by a rule within that format,
   unless such an rule is present in the LO to authorize the action.  If
   such an action were authorized, then the RM would have included a
   rule to express this authorization.  For instance, the PIDF-LO format
   [14] defines a rule that allows an LR to retain the LO for a
   specified amount of time; if an LR receives a LO that does not have
   such a rule, then it MUST NOT retain the location.

3.3.2.  Security Considerations

   Since a Location Recipient does not transmit location, there are no
   protocol security considerations required to support privacy (only
   the LR's compliance with Rules, as described above).

   Aside from privacy, Location Recipients often require some assurance
   that a LO is reliable (assurance of the integrity, authenticity, and
   validity of an LO), since LRs use LOs in order to deliver location-
   based services.  Threats against this reliability and corresponding
   mitigations are discussed in the Security Considerations below.


4.  Security Considerations

   Security considerations related to the privacy of Location Objects



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   are discussed throughout this document.  In this section we summarize
   those concerns and consider security risks not related to privacy.

   The life-cycle of a Location Object often consists of a series of
   location transmissions (see Figure 4).  For example, location might
   initially be published to a location configuration server which then
   transmits the location to the Target.  The Target may then act as a
   Location Server and convey this location to a service provider (who
   acts as Location Recipient in this transmission) to facilitate some
   location-based service.

   (Note that although Figure 4 depicts a single "path", a single
   location server may transmit location to multiple location recipients
   over time; groups of these paths together form a logical distribution
   tree, with the location generator as the root node.)

    +----+    +----+    +----+    +----+    +----+
    | LG |--->| LS |--->| LS |--->| LS |--->| LR |
    +----+    +----+    +----+    +----+    +----+
                |         |         |
              +----+    +----+    +----+
              | RM |    | RM |    | RM |
              +----+    +----+    +----+

                       Figure 4: Location Life-Cycle

   The location life-cycle gives rise to additional security concerns.
   For example, in a scenario where some intermediate location servers
   are untrusted, a location recipient may desire additional assurances
   that the LO was generated by a trusted LG, and not modified by these
   untrusted entities.  In this section, we first consider threats and
   possible attacks against a Location Object throughout its entire life
   cycle.  We then describe the assurances that various parties require
   to mitigate these threats.  Finally, we discuss possible mechanisms
   that protocols or location object formats should make available to
   provide such assurances.

4.1.  Threats to Location Objects

   The major threats to the end-to-end security of Location Objects can
   be grouped into two categories: First, threats against the integrity
   and authenticity of Location Objects can expose entities that rely on
   Location Objects to many types of fraud.  Second, threats against the
   confidentiality of Location Objects can reduce the ability of
   location servers to control access to location.






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4.1.1.  Threats to Location Integrity and Authenticity

   A Location Object contains four essential types of information:
   Identifiers for the described Target, location information, time-
   stamps, and Rules.  By grouping values of these various types
   together within a single structure, a Location Object encodes a set
   of bindings among them.  That is, the Location Object asserts that
   the identified Target was present at the given location at the given
   time; and that the given Rules express the Target's desired policy,
   at the given time, for the distribution of his location.  Below, we
   provide a set of attacks that a malicious party (e.g. an intermediate
   LS, an eavesdropper on the path between LS and LR, or the Target
   himself) might conduct to falsify one or more of the bindings
   asserted by the Location Object.

   Note that in all cases the Target identity provided in a Location
   Object should be based on an authentication between the Target and
   the location generator (e.g. an explicit authentication based on a
   shared secret, or an implicit authentication based on the ability to
   receive a message).  Therefore, the identity binding in a received
   Location Object is only as strong as the authentication between the
   Target and the location generator (that is, the Location Object can
   only attest to the fact that someone at the given location is capable
   of authenticating as the given identity).  It is vital to the
   authenticity of location information that this authentication be as
   strong as is feasible in any deployment scenario.  However,
   mechanisms within a Geopriv Location Object or protocol can provide
   no protection from attacks against this authentication mechanism and
   thus we do not explicitly consider such attacks.

   Place Shifting:  Falsifying the location in an otherwise valid
      Location Object.  For example, Alice pretends to that she is
      currently in a location that she has never previously visited.

   Time Shifting:  Falsifying the time-stamp in an otherwise valid
      Location Object.  For example, Alice pretends that she is
      currently in a location that she has not visited since last year.

   Location Theft:  Falsifying the identity in an otherwise valid
      Location Object.  For example, a malicious intermediary sees a
      valid Location Object for Alice and produces a Location Object
      asserting that Bob is the given location at the given time.

   Location-Identity Theft:  An attacker replays a stale Location Object
      as though it were current.  For example, a malicious intermediary
      sees a valid Location Object for Alice and replays it later to
      make it seem that Alice has not moved.




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   Location Swapping:  Two malicious Targets conspire to produce two
      Location Objects asserting that each Target is at the other's
      location.  For example, Alice pretends that she is at Bob's
      location and Bob pretends that he is at Alice's location.  (Note
      that this attack cannot be prevented if the two attackers are
      willing to exchange authentication credentials.  Because the
      identity assertions in a Location Object are only as strong as the
      Target authentication, the goal of Geopriv protocols is to ensure
      that this attack is not possible unless both Alice and Bob can
      successfully authenticate as the other.)

4.1.2.  Threats to Location Privacy

   In the Geopriv model, the privacy of location information is
   protected by the application of Privacy Rules specified by authorized
   rule makers, and by confidentiality protection en route.  (For more
   information on privacy rule enforcement, see Section 3.2.3).)  Below,
   we provide a set of attacks that a malicious party might conduct to
   allow distribution of a Location Object to unauthorized parties.

   Eavesdropping:  An unauthorized party observes the Location Object in
      transit.  For example, a device on the path between a trusted LS
      and an authorized LR observes a Location Object sent in the clear.

   Rule Tampering:  A malicious party modifies a Target's Privacy Rules
      and thus causes a trusted LS to unknowingly distribute the
      Location Object to unauthorized parties.  For example, a device on
      the path between an LG and a trusted LS deletes the Privacy Rules
      contained in a Location Object and replaces them with a new set of
      Rules authorizing all parties to receive the Location Object.

   Server Impersonation:  A malicious party impersonates a trusted
      location server and then knowingly disregards the Privacy Rules.
      For example, a man-in-the-middle between the LG and the trusted LS
      pretends to be the trusted LS, and then proceeds to distribute the
      Location Object to unauthorized entities.

4.2.  Required Assurances

   We now describe the assurances required by each party involved in
   location distribution in order to mitigate the attacks described in
   the previous two sections:

   Rule Maker:  The rule maker is responsible for distributing the
      Target's Privacy Rules to the location servers.  The primary
      assurance required by the Rule Maker is thus that the binding
      between the Target's Privacy Rules and the Target's identity is
      correctly conveyed to each location server that handles the



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      Location Object.  Ensuring the integrity of the Privacy Rules
      distributed to the location servers prevents rule-tampering
      attacks.  (Note that in many circumstances, the privacy policy of
      the Target may itself be sensitive information, in these cases the
      Rule Maker also requires the assurance that the binding between
      the Target's identity and the Target's Privacy Rules are not
      deducible by anyone other than an authorized location server).

   Location Server:  The Location Server is responsible for enforcing
      the Target's privacy policy.  The first assurance required by the
      location server is that the binding between the Target's Privacy
      Rules and the Target's identity is authentic.  Authenticating the
      rule-maker who created the Privacy Rules prevents rule-tampering
      attacks.  The second assurance required by the location server is
      that the binding between the Target's identity and the Target's
      location are not deducible by any entity except as allowed the
      Target's privacy policy.  Ensuring the confidentiality of these
      bindings prevents eavesdropping attacks.  (Note that ensuring the
      confidentiality of the Location Object also helps to mitigate
      location-theft and location-identity-theft attacks, since it makes
      it more difficult for an attacker to obtain a valid Location
      Object to replay.)

   Location Recipient:  The Location Recipient is the end consumer of
      the Location Object.  The location recipient thus requires
      assurances about the authenticity of the bindings between the
      Target's location, the Target's identity and the time.  Ensuring
      the authenticity of these bindings prevents place-shifting, time-
      shifting, location-theft, and location-identity-theft attacks; and
      mitigates location-swapping attacks to the greatest possible
      extent.

   Location Generator:  The Location Generator shares responsibility for
      ensuring that the Target's privacy policy is enforced.  The
      primary assurance required by the Location Generator is that the
      Location Server to which the Location Object is initially
      published is one that is trusted to enforce the Target's privacy
      policy.  Authenticating the trusted Location Server mitigates the
      risk of server impersonation attacks.  (Additionally, in some
      scenarios, there may be no Location Server which can be trusted to
      sufficiently safe-guard the Target's location information, in
      which case the Location Generator may require assurance that
      intermediate location servers are unable to deduce the binding
      between the Target's identity and the Target's location.)







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4.3.  Protocol mechanisms

   Protocols that carry location can provide strong assurances, but only
   for a single segment of the Location Object's life cycle.  In
   particular, a protocol can provide integrity protection and
   confidentiality for the data exchanged, and mutual authentication of
   the parties involved in the protocol, by using a secure transport
   such as IPsec or TLS.

   Additionally, note that if (1) the protocol provides mutual
   authentication for every segment; and (2) every entity in the
   location distribution exchanges information only with entities with
   whom it has a trust relationship, then entities can transitively
   obtain assurances regarding the origin and ultimate destination of
   the Location Object.  Of course, direct assurances are always
   preferred over assurances requiring transitive trust, since they
   require fewer assumptions.

   Using protocol mechanisms alone, the entities can receive assurances
   only about a single hop in the distribution chain.  For example,
   suppose that an LR retrieves location from an LS over an integrity-
   and confidentiality-protected channel.  The LR knows that the
   transmitted LO has not been modified or observed en route.  However,
   the assurances provided by the protocol do not guarantee that the
   transmitted LO was not corrupted before it was sent (e.g., by a
   previous LS).  Likewise, the LR can verify that the LO was
   transmitted by the LS, but cannot verify the origin of the LO if it
   is different from the LS.

   Security mechanisms in protocols are thus unable to provide direct
   assurances over multiple transmissions of an LO.  However, it should
   be noted that the transmission of location "by reference" can be used
   to effectively turn multi-hop paths into single-hop paths.  If the
   multiple transmissions of a LO are replaced by multiple transmissions
   of an identifier (a multi-hop dissemination channel), then the LO
   need only traverse a single hop, namely the dereference transaction
   between the LR and the dereference server.

4.4.  Mechanisms within the Location Object

   Assurances as to the integrity and confidentiality of a Location
   Object can be provided directly through the Location Object format.
   Additionally, the Location Object format can be used to authenticate
   the originator of a Location Object.  In particular, integrity and
   origin authentication can be assured by signing a Location Object
   (e.g., using S/MIME or XMLSIG), and confidentiality can be assured by
   encrypting the Location Object using a public encryption key
   belonging to the intended recipient (e.g. using S/MIME).  Recipients



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   of Location Objects secured in this fashion can obtain assurance as
   to the integrity and authenticity of the Location Object even after
   it has been handled by untrusted intermediaries.  Similarly, a
   Location Server (or Location Generator) that guarantees
   confidentiality in this fashion can be assured that the Location
   Object is protected from unauthorized viewing even in the presence of
   untrusted intermediaries.

   Although such direct, end-to-end assurances are desirable, and these
   mechanisms should be used whenever possible, there are many
   deployment scenarios where directly securing a Location Object is
   impractical.  In particular, in some deployment scenarios a direct
   trust relationship may not exist between the creator of the Location
   Object and the ultimate recipient.  Additionally, in a scenario where
   many recipients are authorized to receive a given Location Object,
   the creator of the Location Object cannot guarantee end-to-end
   confidentiality without knowing precisely which recipient will
   receive the Location Object.

   An additional challenge in providing end-to-end authenticity
   guarantees by signing the Location Object is that in many deployments
   different entities may assert different bindings within the same
   Location Object.  Consider, for example, a scenario where a Location
   Generator produces a Location Object that asserts a binding between a
   time, a location, and a pseudonym for the Target.  Additionally, a
   Rule Maker creates a binding between a set of Privacy Rules and a
   public Target identity.  A presence server receives the Rules binding
   from Rule Maker and the Location Object from the Location Generator.
   The presence server then generates a new Location Object binding
   together the time, the location, the public Target identity and the
   Privacy Rules.  In such a scenario there is no single entity who can
   directly assert the validity of the entire Location Object.  In such
   a case, a mechanism is needed within the Location Object format that
   allows multiple originators to jointly assert various components of
   the Location Object bindings.


5.  Example Scenarios

   This section contains a set of example of how the Geopriv
   architecture can be deployed in practice.  These examples are meant
   to illustrate key points of the architecture, rather than to form an
   exhaustive set of use cases.

   For convenience and clarity in these examples, we assume that the
   Privacy Rules that a LO carries are equivalent to those in a PIDF-LO
   Location Object (namely, that the principal Rules that can be set are
   limits on the retransmission and retention of the LO).  It should be



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   noted that while these two Rules are the most well-known and
   important examples, the specific types of Rules an LS or LR must
   consider will in general depend on the types of LO it processes.  It
   is possible that in some cases, Geopriv entities will have to
   consider additional Rules and in others, retention and retransmission
   will be unconstrained.  For the rest of this section, however, we
   assume for simplicity that limiting retention and controlling access
   to location are the two primary responsibilities incumbent on a
   recipient of location (an LS or LR).

5.1.  Minimal Scenario

   One of the simplest scenarios in the Geopriv architecture is when a
   Target determines its own location and uses that LO to request a
   service (e.g., by including the LO in an HTTP POST request or SIP
   INVITE message), and the server delivers that service immediately
   (e.g., in a 200 OK response in HTTP or SIP), without retaining or
   retransmitting the Target's location.  The Target acts as an LG by
   using a Target-based positioning algorithm (e.g., manual entry), as a
   Rule Maker by specifying that the location should be sent to the
   server, and as an initial Location Server by interpreting the rule
   and transmitting the LO.  The server acts as a Location Recipient by
   receiving and using the LO.

   In this case, the privacy of location information is maintained in
   two steps: The first step is that location is only transmitted as
   directed by the single Rule Maker, namely the Target.  The second
   step is simply the fact that the server (i.e., the LR) did not do
   anything that created a privacy risk -- it did not retain or
   retransmit location.  Because the server limits its behavior in this
   way, it does not need to read the Rules in the LO (even though they
   were provided) -- no rule would prevent it from using location in
   this safe manner.

   The following outline summarizes this scenario:

   o  Positioning: Target-based, Target=LG=initial LS

   o  Distribution hop 1: HTTP UA --> Ephemeral web service, privacy via
      user indication

   o  Receipt: Ephemeral web service delivers response without retaining
      or retransmitting location

   o  Key points:

      *  LRs that do not behave in ways that risk privacy are Geopriv-
         compliant by default.  No further action is necessary.



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5.2.  Location-based Web Services

   Many location-based services are delivered over the Web, using
   Javascript code to orchestrate a series of HTTP requests for location
   specific information.  To support these applications, browser
   extensions have been developed that support Target-based positioning
   (manual entry and GPS) and network-assisted positioning (via AGPS,
   and multilateration with 802.11 and cellular signals), exposing
   position to web pages through Javascript APIs.

   In this scenario, we consider a Target that uses a browser with a
   network-assisted positioning extension.  When the Target uses this
   browser to request location-based services from a web page, the
   browser prompts the user to grant the page permission to access the
   user's location.  If the user grants permission, the browser
   extension sends 802.11 signal strength measurements to a positioning
   server, which then returns the position of the host.  The extension
   constructs a Location Object with this location and Rules set by the
   user, then passes the LO to the page through its Javascript API.  The
   page then obtains location-relevant information using an
   XMLHttpRequest [15] to a server in the same domain as the page and
   renders this information to the user.

   At first blush, this scenario seems much more complicated than the
   minimal scenario above.  However, most of the privacy considerations
   are actually the same.

   The positioning phase in this scenario begins when the browser
   extension contacts the positioning server.  The positioning server
   acts as a Location Generator, and the protocol that supports this
   interaction is a Positioning Protocol.  The positioning server
   supports the privacy of the location information it provides by
   following the LCP Policy, i.e., by providing location information
   only to the entity being located.

   The distribution phase actually occurs entirely within the Target
   host: The single hop in distribution occurs when the browser
   extension (an entity under the control of the Target) passes a LO to
   the web page (an entity under the control of its author).  In this
   phase, the browser extension acts as the initiating LS, with the
   user/Target as the sole Rule Maker; the user interface for rule-
   making is effectively a Rules Protocol, and the extension's API
   effectively defines a Conveyance Protocol and LO Format.  The web
   site acts as Location Recipient when the web page accepts the LO.

   The receipt phase encompasses the web site's use of the LO.  In this
   context, the phrase "web site" encompasses not only the web page, but
   also the dedicated supporting logic behind it.  Considering the



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   entire web site as a recipient, rather than a single page, it becomes
   clear that by sending the LO in an XMLHttpRequest to a back-end
   server is more like passing it to a separate component of the LR (as
   opposed to retransmitting it to another entity).  Thus, even in this
   case, where location-relevant information is obtained from a back-end
   server, the LR does not retain or retransmit location, so its
   behavior is "privacy-safe" -- it doesn't need to interpret the Rules
   in the LO.

   However, consider a variation on this scenario where the web page
   requests additional information (e.g., a map) from a third-party
   site.  In this case, since location is being transmitted to a third
   party, the web site (either in the web page or in a back-end server)
   would need to verify that this transmission is allowed by the LO's
   Privacy Rules.  Similarly, if the site wanted to log the user's
   location information, then it would need to examine the LO to
   determine how long this information can be retained.  In such a case,
   if the LR needs to do something that is not allowed by the Rules, it
   may have to deny service to the user (hopefully providing a message
   with the reason).  Nonetheless, if the Rules permit retention or
   retransmission (even if this retransmission is limited by access
   control rules), then the LR may do so to the extent the Rules allow.

   The following outline summarizes this scenario:

   o  Positioning: Network-assisted, positioning server=LG, privacy via
      LCP Policy

   o  Rule installation: RM (=Target/user) gives permission to sites and
      sets LO Rules

   o  Distribution hop 1: Browser=LS --> Web site=LR, privacy via user
      confirmation

   o  Receipt: Back-end server delivers location-relevant information
      without further retransmission, then deletes location; privacy via
      safe behavior

   o  Key points:

      *  Privacy in this scenario is provided by a combination of
         explicit user direction and Rules in an LO

      *  Distribution can occur within a host, between mutually
         untrusting components

      *  Some transmissions of location are actually internal to an LR




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      *  LRs that do things that might be constrained by Rules need to
         verify that these actions are allowed for a particular LO

5.3.  Emergency Calling

   Support for emergency calls by Voice-over-IP devices is a critical
   use case for location information about Internet hosts.  The details
   of the Internet architecture for emergency calling are described in
   [16][17].  In this architecture, there are three critical steps in
   the placement of an emergency call, each involving location
   information:

   1.  Determine the location of the caller

   2.  Determine the proper Public Safety Answering Point (PSAP) for the
       caller's location

   3.  Send a SIP INVITE message (including the caller's location) to
       the PSAP

   The first step in an emergency call is to determine the location of
   the caller.  This step is the positioning phase of the location life-
   cycle.  Location is determined by whatever means are available to the
   caller's device, or to the network, if this step is being done by a
   proxy.  Whichever entity does the positioning (either the caller or a
   proxy) acts as the initiating Location Server, preserving the privacy
   of location information by only including it in emergency calls.

   The second step in an emergency call encompasses location
   distribution and receipt.  The entity that is routing the emergency
   call sends location though the LoST protocol [18] to a mapping
   server.  In this role, the routing entity acts as a Location Server,
   LoST acts as a Location Conveyance protocol, and the LoST server acts
   as a Location Recipient.  The LO format within LoST does not allow
   Rules to be sent along with location, but because LoST is an
   application-specific protocol, the sending of location within a LoST
   message authorizes the LoST server to use the location to complete
   the protocol, namely to route the message as necessary through the
   LoST mapping architecture [19].  That is, the LoST server is
   authorized to complete the LoST protocol, but to do nothing else.

   The third step in an emergency call is again a combination of
   distribution and receipt.  The caller (or another entity that inserts
   the caller's location) acts as an LS, SIP acts as a Conveyance
   Protocol [20], and the PSAP acts as a Location Recipient.  In this
   specific example, the caller's location is transmitted either as a
   PIDF-LO object or as a reference that returns a PIDF-LO (or both); in
   the latter case, the reference should be appropriately protected so



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   that only the PSAP has access.  In any case, the receipt of a LO
   implies that the PSAP should obey the Rules in those LOs in order to
   preserve privacy.  Depending on the regulatory environment, the PSAP
   may have the option to ignore those constraints in order to respond
   to an emergency, or it may be bound to respect these Rules (in spite
   of the emergency situation).

   The following outline summarizes this scenario:

   o  Positioning: Any, Target=initial LS

   o  Distribution/receipt hop 1: Target=LS --> LoST infrastructure (no
      Rules), privacy via authorization implicit in protocol

   o  Distribution/receipt hop 2: Target=LS --> PSAP, privacy via Rules
      in LO

   o  Receipt: PSAP uses location to deliver emergency services

   o  Key points:

      *  Privacy in this scenario is provided by a combination of
         explicit user direction, implicit authorization particular to a
         protocol, and Rules in an LO

      *  LRs may be constrained to respect or ignore Privacy Rules by
         local regulation

5.4.  Combination of Services

   In modern Internet applications, users frequently receive information
   via one channel and broadcast it via another.  In this sense, both
   users and channels (e.g., web services) become location servers.
   Here we consider a more complex example that illustrates this pattern
   across multiple logical hops.

   Suppose Alice (the Target) subscribes to a wireless ISP that
   determines her location using a network-based positioning technique
   (e.g., via the location of the base station serving the Target), and
   provides that information directly to a location-enhanced presence
   provider (which might use SIP, XMPP, or another protocol).  The
   location-enhanced presence provider allows Alice to specify Rules for
   how this location is distributed: which friends should receive
   Alice's location and what Rules they should get with it.  Alice uses
   a few other location-enhanced services as well, so she sends Rules
   that allows her location to be shared with those services, and allows
   those services to retain and retransmit her location.




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   Bob is one of Alice's friends, and he receives her location via this
   location-enhanced presence service.  Noting that she's at their
   favorite coffee shop, Bob wants to upload a photo of the two of them
   at the coffee shop to a photo-sharing site, along with a LO that
   marks the location.  Bob checks the Rules in Alice's LO and verifies
   that the photo sharing site is one of the services that Alice
   authorized.  Seeing that Alice has authorized him to give the LO to
   the photo-sharing site, he attaches it to the photo and uploads it.

   Once the geo-tagged photo is uploaded, the photo sharing site reads
   the Rules in the LO and verifies that the site is authorized to store
   the photo and to share it with others.  Since Alice has allowed the
   site the retransmit and retain without any constraints, the site
   fulfills Bob's request to make the geo-tagged photo publicly
   accessible.

   Eve, another user of the photo sharing site, downloads the photo of
   Alice and Bob at the coffee shop and receives Alice's LO along with
   it.  Eve posts the photo and location to her public page on a social
   networking site without checking the Rules, even though the LO
   doesn't allow Eve to send the location anywhere else.  The social
   networking site, however, observes that no retransmission or
   retention are allowed (both of which it needs for a public posting),
   and rejects the upload.

   In terms of the location life-cycle, this scenario consists of a
   positioning step, followed by four distribution hops and receipt.
   Positioning is the simplest step: An LG in Alice's ISP monitors her
   location and transmits it to the presence service, maintaining
   privacy by only transmitting location to a single entity (to which
   privacy responsibilities are delegated).

   The first distribution hop occurs when the presence server sends
   location to Bob. In this transaction, the presence server acts as an
   LS, Alice acts as an RM, and Bob acts as another LS (on the receiving
   side).  The privacy of this transaction is assured by the fact that
   Alice has installed Rules on the presence server that dictate who it
   may allow to access her location.  The second distribution hop is
   when Bob uploads the LO to the photo-sharing site.  Here Bob again
   acts an LS (on the sending side), preserving the privacy of location
   information by verifying that the Rules in the LO allow him to upload
   it.  The third distribution hop is when the photo-sharing site sends
   the LO to Eve, likewise following the Rules -- but a different set of
   Rules than Bob, since a LO can specify different rulesets for
   different Location Servers.

   Eve is the fourth LS in the chain, and fails to comply with Geopriv
   by not checking the rule in the LO prior to uploading it to the



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   social networking site.  The site, however, is a responsible LR -- it
   checks the Rules in the LO, sees that they don't allow it to use the
   location as it needs to, and discards the LO.

   The following outline summarizes this scenario:

   o  Positioning: Network-based, LG in network, privacy via exclusive
      relationship with presence service

   o  Distribution hop 1: Presence server --> Bob, privacy via Alice's
      access control rules (installed via Rules Protocol)

   o  Distribution hop 2: Bob --> photo sharing site, privacy via Rules
      for Bob in LO

   o  Distribution hop 3: Photo sharing site --> Eve, privacy via Rules
      for site in LO

   o  Distribution hop 4: Eve --> Social networking site, violates
      privacy by retransmitting

   o  Recipient: Social networking site, privacy via checking Rules and
      discarding

   o  Key points:

      *  Privacy can be preserved through multiple hops

      *  A LO can specify different Rules for different entities

      *  An LS can still disobey the Rules, but even then, the
         architecture still works in some cases


6.  Glossary

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [1].

   $ Access Control Rule

      A rule that describe which entities may receive location
      information and in what form.







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   $ Authorized Location Server (LSa)

      A Location Server that receives Rules from a Rule Maker (in
      addition to Rules provided in LOs).  An Authorized Location Server
      may receive Location Objects containing Privacy Rules from
      Location Generators and other Location Servers, and it may also
      receive Privacy Rules directly from Rule Makers.

   $ civic location

      The geographic position of an entity in terms of a postal address
      or civic landmark.  Examples of such data are room number, street
      number, street name, city, ZIP code, county, state and country.

   $ geodetic location

      The geographic position of an entity in a particular coordinate
      system (for example, a latitude-longitude pair).

   $ Independent Location Server (LSi)

      A Location Server that has no relationship with a Rule Maker.  An
      Independent Location Server may receive Location Objects
      containing Privacy Rules from Location Generators and other
      Location Servers, but it does not receive Privacy Rules directly
      from Rule Makers.

   $ Local Rule

      A Privacy Rules that directs a Location Server about how to treat
      a Target's location information.  Local Rules are used internally
      by a Location Server to handle requests from Location Recipients.
      They are not distributed to Location Recipients.

   $ Location Generator (LG)

      An entity that initially determines or gathers the location of a
      Target.  Location Generators may be any sort of software or
      hardware used to obtain a Target's position (examples include GPS
      chips and cellular networks).

   $ Location Information Server (LIS)

      An entity responsible for providing devices within an access
      network with information about their own locations.  A Location
      Information Server uses knowledge of the access network and its
      physical topology to generate and distribute location information
      to devices.



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   $ Location Object (LO)

      A data unit that conveys location information together with
      Privacy Rules within the Geopriv architecture.  A Location Object
      may convey geodetic location data (latitiude/longitude/altitude),
      civic location data (street/city/state/etc.), or both.

   $ Location Recipient (LR)

      An ultimate end point entity to which a Location Object is
      distributed.  Location Recipients request location information
      about a particular Target from a Location Server.  If allowed by
      the appropriate Privacy Rules, a Location Recipient will receive
      Location Objects describing the Target's location from the
      Location Server.

   $ Location Server (LS)

      An entity that receives Location Objects from Location Generators,
      Privacy Rules from Rule Makers, and location requests from
      Location Recipients.  A Location Server applies the appropriate
      Privacy Rules to a Location Object received from a Location
      Generator and may disclose the Location Object, in compliance with
      the Rules, to Location Recipients.

      Location Servers may not necessarily be "servers" in the
      colloquial sense of hosts in remote data centers servicing
      requests.  Rather, a Location Server can be any software or
      hardware component that receives and distributes location
      information.  Examples include a positioning server (with a
      location interface) in an access network, a presence server, or a
      Web browser or other software running on a Target's device.

   $ Privacy Rule

      A directive that regulates an entity's activities with respect to
      a Target's location information, including the collection, use,
      disclosure, and retention of the location information.  Privacy
      Rules describe how location information may be used by an entity,
      the level of detail with which location information may be
      described to an entity, and the conditions under which location
      information may be disclosed to an entity.  Privacy Rules are
      communicated from Rule Makers to Location Servers and conveyed in
      Location Objects throughout the Geopriv architecture.







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   $ Rule

      See Privacy Rule.

   $ Rule Maker (RM)

      An individual or entity that is authorized to set Privacy Rules
      for a Target.  In some cases a Rule Maker and a Target will be the
      same individual or entity, and in other cases they will be
      separate.  For example, a parent may serve as the Rule Maker when
      the Target is his child.  The Rule Maker is also not necessarily
      the owner of a Target device.  For example, a corporation may own
      a device that it provides to an employee but permit the employee
      to serve as the Rule Maker and set her own Privacy Rules.  Rule
      Makers provide the Privacy Rules associated with a Target to
      Location Servers.

   $ Forwarded Rule

      A Privacy Rule that travels inside a Location Object.  Forwarded
      Rules direct Location Recipients about how to handle the location
      information they receive.  Because the Forwarded Rules themselves
      may reveal potentially sensitive information about a Target, only
      the minimal subset of Forwarded Rules necessary for a Location
      Recipient to handle a Location Object is distributed to the
      Location Recipient.

   $ Target

      An individual or other entity whose location is described by a
      Location Object.  The Target is the entity whose privacy Geopriv
      seeks to protect.

   $ Usage Rule

      A rule that describe what uses of location information are
      authorized.


7.  Acknowledgements

   This work was largely based on the security investigations conducted
   as part of the Geopriv Layer-7 Location Configuration Protocol design
   team, which produced [5].  We would like to thank all the members of
   the design team.






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8.  IANA Considerations

   This document makes no request of IANA.


9.  References

9.1.  Normative References

   [1]   Bradner, S., "Key words for use in RFCs to Indicate Requirement
         Levels", BCP 14, RFC 2119, March 1997.

9.2.  Informative References

   [2]   Cuellar, J., Morris, J., Mulligan, D., Peterson, J., and J.
         Polk, "Geopriv Requirements", RFC 3693, February 2004.

   [3]   Danley, M., Mulligan, D., Morris, J., and J. Peterson, "Threat
         Analysis of the Geopriv Protocol", RFC 3694, February 2004.

   [4]   U.S. Department of Defense, "National Industrial Security
         Program Operating Manual", DoD 5220-22M, January 1995.

   [5]   Tschofenig, H. and H. Schulzrinne, "GEOPRIV Layer 7 Location
         Configuration Protocol; Problem Statement and  Requirements",
         draft-ietf-geopriv-l7-lcp-ps-09 (work in progress),
         February 2009.

   [6]   Polk, J., Schnizlein, J., and M. Linsner, "Dynamic Host
         Configuration Protocol Option for Coordinate-based Location
         Configuration Information", RFC 3825, July 2004.

   [7]   Schulzrinne, H., "Dynamic Host Configuration Protocol (DHCPv4
         and DHCPv6) Option for Civic Addresses Configuration
         Information", RFC 4776, November 2006.

   [8]   Polk, J., "Dynamic Host Configuration Protocol (DHCP) Option
         for a Location Uniform  Resource Identifier (URI)",
         draft-ietf-geopriv-dhcp-lbyr-uri-option-03 (work in progress),
         November 2008.

   [9]   Barnes, M., Winterbottom, J., Thomson, M., and B. Stark, "HTTP
         Enabled Location Delivery (HELD)",
         draft-ietf-geopriv-http-location-delivery-13 (work in
         progress), February 2009.

   [10]  Schulzrinne, H., Tschofenig, H., Morris, J., Cuellar, J., Polk,
         J., and J. Rosenberg, "Common Policy: A Document Format for



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         Expressing Privacy Preferences", RFC 4745, February 2007.

   [11]  Schulzrinne, H., Tschofenig, H., Morris, J., Cuellar, J., and
         J. Polk, "Geolocation Policy: A Document Format for Expressing
         Privacy Preferences for  Location Information",
         draft-ietf-geopriv-policy-20 (work in progress), February 2009.

   [12]  Rosenberg, J., "The Extensible Markup Language (XML)
         Configuration Access Protocol (XCAP)", RFC 4825, May 2007.

   [13]  Marshall, R., "Requirements for a Location-by-Reference
         Mechanism", draft-ietf-geopriv-lbyr-requirements-07 (work in
         progress), February 2009.

   [14]  Peterson, J., "A Presence-based GEOPRIV Location Object
         Format", RFC 4119, December 2005.

   [15]  World Wide Web Consortium, "The XMLHttpRequest Object", W3C
         document http://www.w3.org/TR/XMLHttpRequest/, April 2008.

   [16]  Rosen, B., Schulzrinne, H., Polk, J., and A. Newton, "Framework
         for Emergency Calling using Internet Multimedia",
         draft-ietf-ecrit-framework-08 (work in progress),
         February 2009.

   [17]  Rosen, B. and J. Polk, "Best Current Practice for
         Communications Services in support of Emergency  Calling",
         draft-ietf-ecrit-phonebcp-08 (work in progress), February 2009.

   [18]  Hardie, T., Newton, A., Schulzrinne, H., and H. Tschofenig,
         "LoST: A Location-to-Service Translation Protocol", RFC 5222,
         August 2008.

   [19]  Schulzrinne, H., "Location-to-URL Mapping Architecture and
         Framework", draft-ietf-ecrit-mapping-arch-04 (work in
         progress), March 2009.

   [20]  Polk, J. and B. Rosen, "Location Conveyance for the Session
         Initiation Protocol", draft-ietf-sip-location-conveyance-12
         (work in progress), November 2008.

URIs

   [21]  <http://creativecommons.org/>







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Authors' Addresses

   Richard Barnes
   BBN Technologies
   9861 Broken Land Pkwy, Suite 400
   Columbia, MD  21046
   USA

   Phone: +1 410 290 6169
   Email: rbarnes@bbn.com


   Matt Lepinski
   BBN Technologies
   10 Moulton St
   Cambridge, MA  02138
   USA

   Phone: +1 617 873 5939
   Email: mlepinski@bbn.com


   Alissa Cooper
   Center for Democracy & Technology
   1634 I Street NW, Suite 1100
   Washington, DC
   USA

   Email: acooper@cdt.org


   John Morris
   Center for Democracy & Technology
   1634 I Street NW, Suite 1100
   Washington, DC
   USA

   Email: jmorris@cdt.org













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   Hannes Tschofenig
   Nokia Siemens Networks
   Linnoitustie 6
   Espoo  02600
   Finland

   Phone: +358 (50) 4871445
   Email: Hannes.Tschofenig@gmx.net
   URI:   http://www.tschofenig.priv.at


   Henning Schulzrinne
   Columbia University
   Department of Computer Science
   450 Computer Science Building
   New York, NY  10027
   US

   Phone: +1 212 939 7004
   Email: hgs@cs.columbia.edu
   URI:   http://www.cs.columbia.edu






























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