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Internet Engineering Task Force (IETF)                         R. BarnesRequest for Comments: 6280                                   M. LepinskiBCP: 160                                                BBN TechnologiesUpdates:3693,3694                                            A. CooperCategory: Best Current Practice                                J. MorrisISSN: 2070-1721                        Center for Democracy & Technology                                                           H. Tschofenig                                                  Nokia Siemens Networks                                                          H. Schulzrinne                                                     Columbia University                                                               July 2011An Architecture for Location and Location Privacyin Internet ApplicationsAbstract   Location-based services (such as navigation applications, emergency   services, and 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.Status of This Memo   This memo documents an Internet Best Current Practice.   This document is a product of the Internet Engineering Task Force   (IETF).  It represents the consensus of the IETF community.  It has   received public review and has been approved for publication by the   Internet Engineering Steering Group (IESG).  Further information on   BCPs is available inSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc6280.Barnes, et al.            Best Current Practice                 [Page 1]

RFC 6280             Internet Location Architecture            July 2011Copyright Notice   Copyright (c) 2011 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (http://trustee.ietf.org/license-info) in effect on the date of   publication of this document.  Please review these documents   carefully, as they describe your rights and restrictions with respect   to this document.  Code Components extracted from this document must   include Simplified BSD License text as described in Section 4.e of   the Trust Legal Provisions and are provided without warranty as   described in the Simplified BSD License.Barnes, et al.            Best Current Practice                 [Page 2]

RFC 6280             Internet Location Architecture            July 2011Table of Contents1. Introduction ....................................................31.1. Binding Rules to Data ......................................41.2. Location-Specific Privacy Risks ............................51.3. Privacy Paradigms ..........................................62. Terminology Conventions .........................................73. Overview of the Architecture ....................................73.1. Basic Geopriv Scenario .....................................83.2. Roles and Data Formats ....................................104. The Location Life Cycle ........................................124.1. Positioning ...............................................134.1.1. Determination Mechanisms and Protocols .............144.1.2. Privacy Considerations for Positioning .............164.1.3. Security Considerations for Positioning ............164.2. Location Distribution .....................................174.2.1. Privacy Rules ......................................174.2.2. Location Configuration .............................194.2.3. Location References ................................204.2.4. Privacy Considerations for Distribution ............214.2.5. Security Considerations for Distribution ...........234.3. Location Use ..............................................244.3.1. Privacy Considerations for Use .....................254.3.2. Security Considerations for Use ....................255. Security Considerations ........................................256. Example Scenarios ..............................................286.1. Minimal Scenario ..........................................286.2. Location-Based Web Services ...............................296.3. Emergency Calling .........................................316.4. Combination of Services ...................................327. Glossary .......................................................358. Acknowledgements ...............................................389. References .....................................................389.1. Normative References ......................................389.2. Informative References ....................................381.  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 locationBarnes, et al.            Best Current Practice                 [Page 3]

RFC 6280             Internet Location Architecture            July 2011   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 use by its ultimate recipient(s) --   Geopriv provides mechanisms to secure 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 provides a   general introduction to Geopriv and Internet location-based services,   and is 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 to ensure that entities   that receive location information are informed of how they may use   it.  These rules can convey simple directives ("do not share my   location with others"), or more robust preferences ("allow my spouse   to know my exact location all of the time, but only allow my boss to   know it during work hours").  By creating a structure to convey the   user's preferences along with location information, the likelihood   that those preferences will 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.Barnes, et al.            Best Current Practice                 [Page 4]

RFC 6280             Internet Location Architecture            July 2011   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 [28] 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.   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).  The United States Department of Defense guidelines for   classification [4] provide one example.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 data may be collected everywhere and at any time, often   without user interaction, and it may potentially describe both what a   person is doing and where he or she is doing it.  For example,   location data can reveal the fact that an individual was at a   particular medical clinic at a particular time.  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 is also 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.Barnes, et al.            Best Current Practice                 [Page 5]

RFC 6280             Internet Location Architecture            July 20111.3.  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, and retained as necessary to deliver a particular service   to the data subject, they may not agree about how the data should   otherwise 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 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 information are informed of relevant privacy rules, and are   expected to only use location information in accordance with those   rules.  The distributed nature of the architecture inherently limits   the degree to which compliance can be guaranteed and verified by   technical means.Section 5 describes how some security mechanisms   can address this to a limited extent.Barnes, et al.            Best Current Practice                 [Page 6]

RFC 6280             Internet Location Architecture            July 2011   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   individuals whose location information has been abused.2.  Terminology Conventions   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 inRFC 2119 [1].   Throughout the remainder of this document, capitalized terms defined   inSection 7 refer to Geopriv-specific roles and formats; the same   terms used in all lowercase refer generically to those terms.3.  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 use -- 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).Barnes, et al.            Best Current Practice                 [Page 7]

RFC 6280             Internet Location Architecture            July 2011   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 a 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   creator.3.1.  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), and then it is   transmitted from one host to another (distribution) until finally it   is used by a recipient (use).   For example, suppose Alice is using a mobile device, she learns of   her location from a wireless location service, and she wishes to   share her location privately with her friends by way of a presence   service.  Alice clearly needs to provide the presence server with her   location and rules about which friends can be provided with her   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.Barnes, et al.            Best Current Practice                 [Page 8]

RFC 6280             Internet Location Architecture            July 2011   Some of Alice's friends will be interested in using Alice's location   only for their own purposes, for example, to meet up with her or plot   her location over time.  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.  To operate in a privacy-protective way, 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 information   further, they must go through the same process as Bob.   The whole example is illustrated in the following figure:   +----------+   | Wireless |   | Location |   | Service  |                          Retrieve   +----------+                      Access Control Rules       |                      +--------------------------------+       |                      | +--------------------------+   |    Location                  | |        Access            |   |       |                      | |     Control Rules        v   |       |                      | |                         +-----+       |                      | |                         | Bob |       |                      | |                         |+---+|--> ...       |                      | |                  +----->||PC ||   ...........                v |                  |      ++---++   | +------+|            +----------+             |   | |Mobile|+--Location->| Presence |--Location-->|     +----------+   | |Phone ||            | Server   |             |---->| Friend-1 |   | +------++---Rules--->|          |---Rules---->|     +----------+   |  Alice  |            +----------+             |   |   O     |                                     |   |  /|\    |                                     |     +----------+   |  / \    |                                     +---->| Friend-2 |   `---------'                                           +----------+                     Figure 1: Basic Geopriv ScenarioBarnes, et al.            Best Current Practice                 [Page 9]

RFC 6280             Internet Location Architecture            July 20113.2.  Roles and Data Formats   The above example illustrates the six basic roles in the Geopriv   architecture:   Target:   An individual or other entity whose location is sought in      the Geopriv architecture.  In many cases, the Target will be the      human user of a Device, but it can also be an object such as a      vehicle or shipping container to which a Device is attached.  In      some instances, the Target will be the Device itself.  The Target      is the entity whose privacy Geopriv seeks to protect.  Alice is      the Target in Figure 1.   Device:   The physical device, such as a mobile phone, PC, or      embedded micro-controller, whose location is tracked as a proxy      for the location of a Target.  Alice's mobile phone is the Device      in Figure 1.   Rule Maker (RM):   Performs the role of creating rules governing      access to location information for a Target.  In some cases, the      Target performs the Rule Maker role (as is the case with Alice),      and in other cases they are separate.  For example, a parent may      serve as the Rule Maker when the Target is his child, or a      corporate security officer may serve as the Rule Maker for devices      owned by the corporation but used by employees.  The Rule Maker is      also not necessarily the owner of the Device.  For example, a      corporation may provide a Device to an employee but permit the      employee to serve as the Rule Maker and set her own privacy rules.   Location Generator (LG):   Performs the roles of initially      determining or gathering the location of the Device and providing      it to Location Servers.  Location Generators may be any sort of      software or hardware used to obtain the Device's location.      Examples include Global Positioning System (GPS) chips and      cellular networks.  A Device may even perform the Location      Generator role for itself; Devices capable of unassisted      satellite-based positioning and Devices that accept manually      entered location information are two examples.  The wireless      location service plays the Location Generator role in Figure 1.   Location Server (LS):   Performs the roles of receiving location      information and rules, applying the rules to the location      information to determine what other entities, if any, can receive      location information, and providing the location to Location      Recipients.  Location Servers receive location information from      Location Generators and rules from Rule Makers, and then apply the      rules to the location information.  Location Servers may not      necessarily be "servers" in the colloquial sense of hosts inBarnes, et al.            Best Current Practice                [Page 10]

RFC 6280             Internet Location Architecture            July 2011      remote data centers servicing requests.  Rather, a Location Server      can be any software or hardware component that distributes      location information.  Examples include a server in an access      network, a presence server, or a Web browser or other software      running on a Device.  The above example includes three Location      Servers: Alice's mobile phone, the presence service, and Bob's PC.   Location Recipient (LR):   Performs the role of receiving location      information.  A Location Recipient may ask for a location      explicitly (by sending a query to a Location Server), or it may      receive a location asynchronously.  The presence service, Bob,      Friend-1, and Friend-2 are Location Recipients in Figure 1.   In general, these roles may or may not be performed by physically   separate entities, as demonstrated by the entities in Figure 1, many   of which perform multiple roles.  It is not uncommon for the same   entity to perform both the Location Generator and Location Server   roles, or both the Location Recipient and Location Server roles.  A   single entity may take on multiple roles simply by virtue of its own   capabilities and the permissions provided to it.   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.   There is a close relationship between a Target and its Device.  The   term "Device" is used when discussing protocol interactions, whereas   the term "Target" is used when discussing generically the person or   object being located and its privacy.  While in the example above   there is a one-to-one relationship between the Target and the Device,   Geopriv can also be used to convey location information about a   device that is not directly linked to a single individual or object,   such as a Device shared by multiple individuals.   Two data formats are necessary within this architecture:   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 (see the      considerations in [5] for LOs containing multiple locations).      Location Objects typically include some sort of identifier of the      Target.Barnes, et al.            Best Current Practice                [Page 11]

RFC 6280             Internet Location Architecture            July 2011   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 which entities may obtain location      information in what form (access control rules) and how location      information may be used by an entity (usage rules).   The whole example, using Geopriv roles and formats, is illustrated in   the following figure:   +----+   | LG |   +----+     ^     |   Positioning    Data     |     |    +------------Privacy Rules------------------>+----+     |    |                                      +---->| LR |--> ...     |    |                                      |     | LS |     v    |                                      |     +----+   +-------+                                     |   |Target |                +----+               |     +----+   |Device |--------------->| LR |---------------+---->| LR |   |  RM   |       LO       | LS |       LO      |     +----+   |  LS   |                +----+               |   +-------+                                     |                                                 |     +----+                                                 +---->| LR |                                                       +----+                     Figure 2: Basic Geopriv Scenario4.  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 Device's       location.   2.  Distribution: Location Servers send location information to       Location Recipients, which may in turn act as Location Servers       and further distribute the location to other Location Recipients,       possibly several times.Barnes, et al.            Best Current Practice                [Page 12]

RFC 6280             Internet Location Architecture            July 2011   3.  Use: 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 and security implications.  The   Geopriv roles are mapped onto the location life cycle in the figure   below.                               +----------+                               |  Rule    |+                               |  Maker(s)||   Positioning                 |          ||     Data                      +----------+|       |                        +----------+       |                            | Rules       |                            |       |                            |       V                            V   +----------+                +----------+                +----------+   |Location  |  Location      | Location |+      LO       |Location  |   |Generator |--------------->| Server(s)||-------------->|Recipient |   |          |                |          ||               |          |   +----------+                +----------+|               +----------+                               +----------+   <-------------------------><---------------------------><----------->    Positioning                Distribution                 Use                       Figure 3: Location Life Cycle4.1.  Positioning   Positioning is the process by which the physical location of the   Device is computed, based on some observations about the Device'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 Device, and the   outcome is that the LG knows the location of the Device.   In this section, we give a brief taxonomy of current positioning   systems, their requirements for protocol support, and the privacy and   security requirements for positioning.Barnes, et al.            Best Current Practice                [Page 13]

RFC 6280             Internet Location Architecture            July 20114.1.1.  Determination Mechanisms and Protocols   While the specific positioning mechanisms that can be applied for a   given Device are strongly dependent on the physical situation and   capabilities of the Device, these mechanisms generally fall into the   three categories described in detail below:   o  Device-based   o  Network-based   o  Network-assisted   As suggested by the above names, a positioning scheme can rely on the   Device, 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 Device-based positioning mechanisms, the Device is capable of   determining its location by itself.  This is the case for a manually   entered location or for (unassisted) satellite-based positioning   using a Global Navigation Satellite System (GNSS).  In these cases,   the Device acts as its own LG, and there are no protocols required to   support positioning beyond those that transmit the positioning data   from the satellite to the user.   In network-based positioning schemes, an external LG (an Internet   host other than the Device) has access to sufficient information   about the Device, through out-of-band channels, to establish the   position of the Device.  The most common examples of this type of LG   are entities that have a physical relationship to the Device (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 Device-based, no protocols for   communication between the Device and the LG 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 the Simple Network Management Protocol   (SNMP)) to collect inputs to the positioning process.  Rather, since   these inputs can only be used by certain LGs to determine location,   they are not controlled as private information.  Network-basedBarnes, et al.            Best Current Practice                [Page 14]

RFC 6280             Internet Location Architecture            July 2011   positioning often provides location information to protocols by which   the network informs a Device of its own location.  These are known as   Location Configuration Protocols; seeSection 4.2.2 for further   discussion.   Network-assisted systems account for the greatest number and   diversity of positioning schemes.  In these systems, the work of   positioning is divided between the Device and an external LG via   some communication (possibly over the Internet), typically in one of   two ways:   o  The Device provides measurements to the LG, or   o  The LG provides assistance data to the Device.   "Measurements" are understood to be observations about the Device's   environment, ranging from wireless signal strengths to the Media   Access Control (MAC) address of a first-hop router.  "Assistance" is   the complement to measurement, namely the positioning 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 that   maps 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 Device sends measurements (e.g., MAC addresses and   signal strengths) to an LG, and the LG returns a location to the   client.  In wired networks, the Device can send its MAC address to   the LG, 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 Device   provides the LG with GNSS measurements are measurement-based, while   those in which the assistance server provides ephemeris or almanac   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 Device and the LG requires a protocol over which the information   is carried.  The structure of this protocol will depend on which ofBarnes, et al.            Best Current Practice                [Page 15]

RFC 6280             Internet Location Architecture            July 2011   the two patterns a network-assisted scheme follows.  Conversely, the   structure of the protocol will determine which of the two parties   (the Device, the LG, or both) is aware of the Device's location at   the end of the protocol interaction.4.1.2.  Privacy Considerations for Positioning   Positioning is the first point at which location may be associated   with a particular Device and may be associated with the Target's   identity.  Local identifiers, unlinked pseudonyms, or private   identifiers that are not linked to the real identity of the Target   should be used as forms of identity whenever possible.  This provides   privacy protection by disassociating the location from the Target's   identity before it is distributed.   At the conclusion of the positioning process, the entity acting as   the LG has the Device's location.  If the Device is performing the LG   role, then both the Device and LG have it.  If the entity acting as   the LG also performs the role of LS, the privacy considerations inSection 4.2.4 apply.   In some deployment scenarios, positioning functions and distribution   functions may need to be provided by separate entities, in which case   the LG and LS roles will not be performed by the same entity.  In   this situation, the LG acts as a "dumb", non-privacy-aware   positioning resource, and the LS provides the privacy logic necessary   to support distribution (possibly with multiple LSes using the same   LG).  In order to allow the privacy-unaware LG to distribute location   information to these LSes while maintaining privacy, the relationship   between the LG and its set of LSes MUST be tightly constrained   (effectively "hard-wired").  That is, the LG MUST only provide   location information to a small fixed set of LSes, and each of these   LSes MUST comply with the requirements ofSection 4.2.4.4.1.3.  Security Considerations for Positioning   Manipulation of the positioning process can expose location   information through two mechanisms:   1) A third party could guess or derive measurements about a specific   device and use them to get the location of that Device.  To mitigate   this risk, the LG SHOULD be able to authenticate and authorize   devices providing measurements and, if possible, verify that the   presented measurements are likely to be the actual physical values   measured by that client.  These security procedures rely on the type   of positioning being done, and may not be technically feasible in all   cases.Barnes, et al.            Best Current Practice                [Page 16]

RFC 6280             Internet Location Architecture            July 2011   2) By eavesdropping, a third party may be able to obtain measurements   sent by the Device itself that indicate the rough position of the   Device.  To mitigate this risk, protocols used for positioning MUST   provide confidentiality and integrity protections in order to prevent   observation and modification of transmitted positioning data while en   route between the Target and the LG.   If an LG or a Target chooses to act as an LS, it inherits the   security requirements for an LS, described inSection 4.2.5.4.2.  Location Distribution   When an entity receives location information (from an LG or an LS)   and redistributes it to other entities, it acts as an LS.  Location   Distribution is the process by which one or more LSes provide LOs to   LRs in a privacy-preserving manner.   The role of an LS is thus two-fold: First, it must collect location   information and Rules that control access to that information.  Rules   can be communicated within an LO, within a protocol that carries LOs,   or through a separate protocol that carries Rules.  Second, the LS   must process requests for location information and apply the Rules to   these requests in order to determine whether it is authorized to   fulfill them by returning location information.   An LS thus has at least two types of interactions with other hosts,   namely receiving and sending LOs.  An LS may optionally implement a   third interaction, allowing Rule Makers to provision it with Rules.   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 directly from a Rule Maker has   such a relationship, while an LS that acquires all its Rules through   LOs does not.4.2.1.  Privacy Rules   Privacy Rules are the central mechanism in Geopriv for maintaining a   Target's privacy, because they provide a recipient of an LO (an LS or   LR) with information on how the LO may be used.   Throughout the Geopriv architecture, Privacy Rules are communicated   in rules languages with a defined syntax and semantics.  For example,   the Common Policy rules language has been defined [6] to provide a   framework for broad-based rule specifications.  Geopriv Policy [7]   defines a language for creating location-specific rules.  The XML   Configuration Access Protocol (XCAP) [8] can be used as a protocol to   install rules in both of these formats.Barnes, et al.            Best Current Practice                [Page 17]

RFC 6280             Internet Location Architecture            July 2011   Privacy Rules follow a default-deny pattern: an empty set of Rules   implies that all requests for location information should be denied,   except requests made by the Target itself.  Each Rule adds to the   set, granting a specific permission.  Adding a Rule can only augment   privacy protections because all Rules are positive grants of   permission.   The following are examples of Privacy Rules governing location   distribution:   o  Retransmit location information when requested from example.com.   o  Retransmit only city and country.   o  Retransmit location information with no less than a 100-meter      radius of uncertainty.   o  Retransmit location information only for the next two weeks.   LSes enforce Privacy Rules in two ways: by denying requests for   location information, or by transforming the location information   before retransmitting it.   LSes may also receive Rules governing location retention, such as   "Retain location only for 48 hours".  Such Rules are simply   directives about how long the Target's location information can be   retained.   Privacy Rules can govern the behavior of both LSes and LRs.  Rules   that direct LSes about how to treat a Target's location information   are known as Local Rules.  Local Rules are used internally by the LS   to handle requests from LRs.  They are not distributed to LRs.   Forwarded Rules, on the other hand, travel inside LOs and direct LSes   and LRs about how to 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.Barnes, et al.            Best Current Practice                [Page 18]

RFC 6280             Internet Location Architecture            July 2011   An example can illustrate the interaction between Local Rules and   Forwarded Rules.  Suppose Alice provides the following Local Rules to   an LS:   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 Web site,      which in turn is permitted to retain the location information for      one year and retransmit it to any requesters.   When Steve asks for Alice's location, the LS 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").  An LO may contain a pointer to   more robust Rules, such as those shown in the set of four Rules at   the beginning of this section.4.2.2.  Location Configuration   Some entities performing the LG role are designed only to provide   Targets with their own locations, as opposed to distributing a   Target's location to others.  The process of providing a Target with   its own location is known within Geopriv as Location Configuration.   The term "Location Information Server" (LIS) is often used to   describe the entity that performs this function.  However, a LIS may   also perform other functions, such as providing a Target's location   to other entities.Barnes, et al.            Best Current Practice                [Page 19]

RFC 6280             Internet Location Architecture            July 2011   A Location Configuration Protocol (LCP) [9] is one mechanism that can   be used by a Device to discover its own location from a LIS.  LCPs   provide functions in the way they obtain, transport, and deliver   location requests and responses between a LIS and a Device such that   the LIS can trust that the location requests and responses handled   via the LCP are in fact from/to the Target.  Several LCPs have been   developed within Geopriv [10] [11] [12] [13].   A LIS whose sole purpose is to perform Location Configuration need   only follow a simple privacy-preserving policy: transmit a Target's   location only to the Target itself.  This is known as the "LCP   policy".   Importantly, if an LS is also serving in the role of LG and it has   not been provisioned with Privacy Rules for a particular Target, it   MUST follow the LCP policy, whether it is a LIS or not.  In the   positioning phase, an entity serving the roles of both LG and LS that   has not received Privacy Rules must follow this policy.  The same is   true for any LS in the distribution phase.4.2.3.  Location References   The location distribution process occurs through a series of   transmissions of LOs: 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.).   A location can also be distributed "by reference", where a reference   is represented by a URI that can be dereferenced to obtain the LO.   This document summarizes the properties of location-by-reference that   are discussed at length in [14].   Distribution of location-by-reference (distribution of location URIs)   offers several benefits.  Location URIs are a more compact way of   transmitting location information, since URIs are usually smaller   than LOs.  A recipient of location information can make multiple   requests to a URI over time to receive updated location information   if the URI is configured to provide a fresh location rather than a   single "snapshot".   From a positioning perspective, location-by-reference can offer the   additional benefit of "just in time" positioning.  If a location is   distributed by reference, an entity acting as a combined LG/LS only   needs to perform positioning operations when a recipient dereferences   a previously distributed URI.Barnes, et al.            Best Current Practice                [Page 20]

RFC 6280             Internet Location Architecture            July 2011   From a privacy perspective, distributing a location as a URI instead   of as an LO can help protect privacy by forcing each recipient of the   location to request location information from the referenced LS,   which can then apply access controls individually to each recipient.   But 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 it enforces the   "possession model" defined in [14]), then transmitting a location URI   presents the same privacy risks as transmitting the LO itself.   Moreover, the use of location URIs without access controls can   introduce additional privacy risks: If URIs are predictable, 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 need to be constructed so that   they contain a random component with sufficient entropy to make   guessing infeasible.4.2.4.  Privacy Considerations for Distribution   Location information MUST be accompanied by Rules throughout the   distribution process.  Otherwise, a recipient will not know what uses   are authorized, and will not be able to use the LO.  Consequently,   LOs MUST be able to express Rules that convey appropriate   authorizations.   An LS MUST only accept Rules from authorized Rule Makers.  For an LS   that receives Rules exclusively in LOs and has no direct relationship   with a Rule Maker, this requirement is met by applying the Rules   provided in an LO to the distribution of that LO.  For an LS with a   direct relationship to a Rule Maker, 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 provide 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 information only in ways that are authorized by these Rules.   An LS that receives Rules exclusively through LOs MUST examine the   Rules that accompany a given LO in order to determine how the LS may   use the LO.  If any Rules are included by reference, the LS SHOULD   attempt to download them.  If the LO includes no Rules that allow the   LS to transmit the LO to another entity, then the LS MUST NOT   transmit the LO.  If the LO contains no Rules at all -- for example,Barnes, et al.            Best Current Practice                [Page 21]

RFC 6280             Internet Location Architecture            July 2011   if it is in a format with no Rules syntax -- then the LS MUST delete   it.  Emergency services provide an exception in that Rules can be   implicit; see [15]).  If the LO included Rules by reference, but   these Rules were not obtained for any reason, the LS MUST NOT   transmit the LO and MUST adhere to the provided value in the   retention-expires field.   An LS that receives Rules both directly from one or more Rule Makers   and through LOs MUST combine the Rules in a given LO with Rules it   has received from the RMs.  The strategy the LS 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 are:   Union:   A transmission of location information is authorized if it      is authorized by either a rule in the LO or an RM-provided rule.   Intersection:   A transmission of location information is authorized      if it is authorized by both a rule in the LO and an RM-provided      rule.   RM Override:   A transmission of location information is authorized      if it is authorized by an RM-provided rule, regardless of the LO      Rules.   LO Override:   A transmission of location information is authorized      if it is authorized by an LO-provided rule, regardless of the RM      Rules.   The default combination policy for an LS that receives multiple rule   sets is to combine them according to procedures inSection 10 of   RFC 4745 [6].  Privacy rules always grant access; i.e., the default   is to deny access, and rules specify conditions under which access is   allowed.  Thus, when an LS is provided more than one policy document   that applies to a given LO, it has been instructed to provide access   when any of the rules apply.  That is, the "Union" policy is the   default policy for an LS with multiple sources of policy.  An LS MAY   choose to apply a more restrictive policy by ignoring some of the   grants of permission in the privacy rules provided.  The   "Intersection" policy and both "Override" policies listed above are   of this latter character.   Protocols that are used for managing rules should allow an RM to   retrieve from the LS the set of rules that will ultimately be   applied.  For example, in the basic HTTP-based protocol defined in   [16], an RM can use a GET request to retrieve the policy being   applied by the LS and a PUT request to specify new rules.Barnes, et al.            Best Current Practice                [Page 22]

RFC 6280             Internet Location Architecture            July 2011   Different policies may be applicable in different scenarios.  In   cases where an external RM is more trusted than the source of the LO,   the "RM Override" policy may be suitable (for example, if the   external RM is the Target and the LO is provided by a third party).   Conversely, the "LO Override" policy is better suited to cases where   the LO provider is more trusted than the RM, for example, if the RM   is the user of a mobile device LS and the LO contains Rules from the   RM's parents or corporate security office.  The "Intersection" policy   takes the strictest view of the permission grants, giving equal   weight to all RMs (including the LO creator).   Each of these policies will also have different privacy consequences.   Following the "Intersection" policy ensures that the most privacy-   protective subset of all RMs' rules will be followed.  The "Union"   policy and both "Override" policies may defy the expectations of any   RM (including, potentially, the Target) whose policy is not followed.   For example, if a Target acting as an RM sets Rules and those Rules   are overridden by the application of a more permissive LO Override   policy that has been set by the Target's parent or employer acting as   an RM, the retransmission or retention of the Target's data may come   as a surprise to the Target.  For this reason, it is RECOMMENDED that   LSes provide a way for RMs to be able to find out which policy will   be applied to the distribution of a given LO.4.2.5.  Security Considerations for Distribution   An LS's decisions about how to transmit a location are based on the   identities of entities requesting information and other aspects of   requests for a 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, LSes, and RMs) and other information in the   request.   Protocols to convey LOs and protocols to convey Rules MUST provide   information on the identity of the recipient of location information   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.Barnes, et al.            Best Current Practice                [Page 23]

RFC 6280             Internet Location Architecture            July 2011   As they travel through the Internet, LOs 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 an LO as it travels between   privacy-preserving entities.   Ideally, LOs SHOULD be transmitted with confidentiality protection   end-to-end between an LS that transmits location information and the   LR that receives it.  In some cases, the protocol conveying an LO   provides confidentiality protection as a built-in security solution   for its signaling (and potentially its data traffic).  In this case,   carrying an unprotected LO within such an encrypted channel is   sufficient.  Many protocols, however, are offering communication   modes where messages are either unprotected or protected on a hop-by-   hop basis (for example, between intermediaries in a store-and-forward   protocol).  In such a case, it is RECOMMENDED that the protocol allow   for the use of encrypted LOs, or for the transmission of a reference   to a location in place of an LO [14].4.3.  Location Use   The primary privacy requirement of an LR is to constrain its usage of   location information to the set of uses authorized by the Rules in an   LO.  If an LR only uses an LO in ways that have minimal 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   complete its interaction with the LS -- then no further action is   necessary for the LR to comply with Geopriv requirements.   As an example of this simplest case, if an LR (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 a location, and   promptly then discards the input location, will be in compliance with   any Geopriv Rule set.   LRs that make other uses of an 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   authorized.Barnes, et al.            Best Current Practice                [Page 24]

RFC 6280             Internet Location Architecture            July 20114.3.1.  Privacy Considerations for Use   The principal privacy requirement for LRs is to follow usage rules.   Any LR that wants to retransmit or retain the LO 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.4.3.2.  Security Considerations for Use   Since the LR role does not involve transmission of location   information, there are no protocol security considerations required   to support privacy, other than ensuring that data does not leak   unintentionally due to security breaches.   Aside from privacy, LRs often require some assurance that an 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 "Security Considerations" below.5.  Security Considerations   Security considerations related to the privacy of LOs are discussed   throughout this document.  In this section, we summarize those   concerns and consider security risks not related to privacy.   The life cycle of an LO often consists of a series of location   transmissions.  Protocols that carry location information can provide   strong assurances, but only for a single segment of the LO'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 [17] or Transport Layer Security (TLS) [18].   Additionally, if (1) the protocol provides mutual authentication for   every segment, and (2) every entity in the location distribution   chain exchanges information only with entities with whom it has a   trust relationship, entities can transitively obtain assurances   regarding the origin and ultimate destination of the LO.  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 receives location information from an LS over an   integrity- and confidentiality-protected channel.  The LR knows thatBarnes, et al.            Best Current Practice                [Page 25]

RFC 6280             Internet Location Architecture            July 2011   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 to the   LS (by a previous LS, for example).  Likewise, the LR can verify that   the LO was transmitted by the LS, but cannot verify the origin of the   LO if it did not originate with the LS.   Security mechanisms in protocols are thus unable to provide direct   assurances over multiple transmissions of an LO.  However, the   transmission of a location "by reference" can be used to effectively   turn multi-hop paths into single-hop paths.  If the multiple   transmissions of an LO are replaced by multiple transmissions of a   URI (a multi-hop dissemination channel), the LO need only traverse a   single hop, namely the dereference transaction between the LR and the   dereference server.  The requirements for securing a location passed   by reference [14] are applicable in this case.   The major threats to the security of LOs can be grouped into two   categories.  First, threats against the integrity and authenticity of   LOs can expose entities that rely on LOs.  Second, threats against   the confidentiality of LOs can allow unauthorized access to location   information.   An LO contains four essential types of information: identifiers for   the described Target, location information, timestamps, and Rules.   By grouping values of these various types together within a single   structure, an LO encodes a set of bindings among them.  That is, the   LO 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 that time for the distribution of his   location.  Below, we provide a description of the assurances required   by each party involved in the location distribution in order to   mitigate the possible attacks on these bindings.   Rule Maker:   The Rule Maker is responsible for creating the Target's      Privacy Rules and for uploading them to the LSes.  The primary      assurance required by the Rule Maker is that the Target's Privacy      Rules are correctly associated with the Target's identity when      they are conveyed to each LS that handles the LO.  Ensuring the      integrity of the Privacy Rules distributed to the LSes prevents      rule-tampering attacks.  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 LS.Barnes, et al.            Best Current Practice                [Page 26]

RFC 6280             Internet Location Architecture            July 2011   Location Server:   The Location Server is responsible for enforcing      the Target's Privacy Rules.  The first assurance required by the      LS is that the binding between the Target's Privacy Rules and the      Target's identity is authentic.  Authenticating and authorizing      the Rule Maker who creates, updates, and deletes the Privacy Rules      prevents rule-tampering attacks.  The LS has to ensure that the      authorization policies are not exposed to third parties, if so      desired by the Rule Maker and when the rules themselves are      privacy-sensitive.   Location Recipient:   The Location Recipient is the consumer of the      LO.  The LR 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 helps to      prevent various attacks, such as falsifying the location,      modifying the timestamp, faking the identity, and replaying LOs.   Location Generator:   The primary assurance required by the Location      Generator is that the LS to which the LO is initially published is      one that is trusted to enforce the Target's Privacy Rules.      Authenticating the trusted LS mitigates the risk of server      impersonation attacks.  Additionally, the LG is responsible for      the location determination process, which is also sensible from a      security perspective because wrong input provided by external      entities can lead to undesirable disclosure or access to location      information.   Assurances as to the integrity and confidentiality of a Location   Object can be provided directly through the LO format.RFC 4119 [19]   provides a description for the usage of Secure/Multipurpose Internet   Mail Extensions (S/MIME) to integrity and confidentiality protection.   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 an LO is impractical.   For example, in some deployment scenarios a direct trust relationship   may not exist between the creator of the Location Object and the   recipient.  Additionally, in a scenario where many recipients are   authorized to receive a given LO, the creator of the LO cannot   guarantee end-to-end confidentiality without knowing precisely which   recipient will receive the LO.  Many of these cases can, however, be   addressed by the usage of a location-by-reference mechanism, possibly   combined with an LO.Barnes, et al.            Best Current Practice                [Page 27]

RFC 6280             Internet Location Architecture            July 20116.  Example Scenarios   This section contains a set of examples 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 an LO carries are equivalent to those in a   Presence Information Data Format Location Object (PIDF-LO) [19] --   namely, that the principal Rules that can be set are limits on the   retransmission and retention of the LO.  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 LOs it processes.6.1.  Minimal Scenario   One of the simplest scenarios in the Geopriv architecture is when a   Device determines its own location and uses that LO to request a   service (e.g., by including the LO in an HTTP POST request [20] or   SIP INVITE message [21]), and the server delivers that service   immediately (e.g., in a 200 OK response in HTTP or SIP), without   retaining or retransmitting the Device's location.  The Device acts   as an LG by using a Device-based positioning algorithm (e.g., manual   entry) and as an LS by interpreting the rule and transmitting the LO.   The Target acts as a Rule Maker by specifying that the location   should be sent to the server.  The server acts as an LR by receiving   and using the LO.   In this case, the privacy of location information is maintained in   two steps: The first step is that the location is only transmitted as   directed by the single Rule Maker, namely the Target.  The second   step is simply the fact that the server, as LR, does not do anything   that creates a privacy risk -- it does not retain or retransmit the   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 the location in this   safe manner.   The following outline summarizes this scenario:   o  Positioning: Device-based, Device=LG   o  Distribution hop 1: HTTP User Agent (UA) --> Ephemeral Web      service, privacy via user indicationBarnes, et al.            Best Current Practice                [Page 28]

RFC 6280             Internet Location Architecture            July 2011   o  Use: Ephemeral Web service delivers response without retaining or      retransmitting location   o  Key point:      *  LRs that do not behave in ways that risk privacy are Geopriv-         compliant by default.  No further action is necessary.6.2.  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 Device-based   positioning (manual entry and Global Positioning System (GPS)) and   network-assisted positioning (via Assisted GPS (AGPS), and   multilateration with 802.11 and cellular signals), exposing a   location 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 an LO 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 [22] 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 an LG.   The distribution phase actually occurs entirely within the Target   host.  This phase begins when the positioning server, now acting as   an LS, follows the LCP policy by providing the location only to the   Target.  The next hop in distribution occurs when the browser   extension (an entity under the control of the Target) passes an LO to   the Web page (an entity under the control of its author).  In this   phase, the browser extension acts as an LS, with the Target as the   sole Rule Maker; the user interface for rule-making is effectively aBarnes, et al.            Best Current Practice                [Page 29]

RFC 6280             Internet Location Architecture            July 2011   protocol for conveying Rules, and the extension's API effectively   defines a way to communicate LOs and an LO format.  The Web site acts   as an LR when the Web page accepts the LO.   The use 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   entire Web site as a recipient, rather than a single page, it becomes   clear that sending the LO in an XMLHttpRequest to a back-end server   is 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 the 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 (a map, for instance) from a third-   party site.  In this case, since location information 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, while 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   o  Rule installation: RM (=Target) gives permission to sites and sets      LO Rules   o  Distribution hop 1: positioning server=LS --> Target, privacy via      LCP policy   o  Distribution hop 2: Browser=LS --> Web site=LR, privacy via user      confirmation   o  Use: Back-end server delivers location-relevant information      without further retransmission, then deletes location; privacy via      safe behaviorBarnes, et al.            Best Current Practice                [Page 30]

RFC 6280             Internet Location Architecture            July 2011   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 components that         do not trust each other.      *  Some transmissions of the location are actually internal to         an LR.      *  LRs that do things that might be constrained by Rules need to         verify that these actions are allowed for a particular LO.6.3.  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   [23] [24].  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.  The 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.  The entity doing the positioning, whether the caller or a   proxy, acts as an LS, preserving the privacy of location information   by only including it in emergency calls.   The second step in an emergency call encompasses location   distribution and use.  The entity that is routing the emergency call   sends location information through the Location-to-Service   Translation (LoST) Protocol [15] to a mapping server.  In this role,   the routing entity acts as an LS and the LoST server acts as an LR.   The LO format within LoST does not allow Rules to be sent along with   the location, but because LoST is an application-specific protocol,   the sending of the location within a LoST message authorizes the LoST   server to use the location to complete the protocol, namely to routeBarnes, et al.            Best Current Practice                [Page 31]

RFC 6280             Internet Location Architecture            July 2011   the message as necessary through the LoST mapping architecture [25].   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 use.  The caller, or another entity that inserts the   caller's location, acts as an LS, and the PSAP acts as an LR.  In   this specific example, the caller's location is transmitted either as   a PIDF-LO or as a reference that returns a PIDF-LO, or both; in the   latter case, the reference should be appropriately protected so that   only the PSAP has access.  In any case, the receipt of an 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   o  Distribution/use hop 1: Target=LS --> LoST infrastructure (no      Rules), privacy via authorization implicit in protocol   o  Distribution/use hop 2: Target=LS --> PSAP, privacy via Rules      in LO   o  Use: 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.6.4.  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 LSes.  Here we   consider a more complex example that illustrates this pattern across   multiple logical hops.Barnes, et al.            Best Current Practice                [Page 32]

RFC 6280             Internet Location Architecture            July 2011   Suppose Alice as 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.  This presence provider might use SIP, the Extensible   Messaging and Presence Protocol (XMPP) [26], 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 allow her location to be shared with those services, and that   allow those services to retain and retransmit her location.   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 an 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 to 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 use.   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 the location information to a single   entity to which Alice has delegated privacy responsibilities.Barnes, et al.            Best Current Practice                [Page 33]

RFC 6280             Internet Location Architecture            July 2011   The first distribution hop occurs when the presence server sends the   location to Bob.  In this transaction, the presence server acts as an   LS, Alice acts as an RM, and Bob acts as an LR.  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 acts as an LS, 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 for Bob, since an LO can specify   different Rule sets for different LSes.   Eve is the fourth LS in the chain, and fails to comply with Geopriv   by not checking the Rules in the LO prior to uploading the LO to the   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/use hop 1: Presence server --> Bob, privacy via      Alice's access control rules   o  Distribution/use hop 2: Bob --> photo-sharing site, privacy via      Rules for Bob in LO   o  Distribution/use hop 3: Photo-sharing site --> Eve, privacy via      Rules for site in LO   o  Distribution/use hop 4: Eve --> Social networking site, violates      privacy by retransmitting   o  Use: Social networking site, privacy via checking Rules and      discarding   o  Key points:      *  Privacy can be preserved through multiple hops.      *  An 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.Barnes, et al.            Best Current Practice                [Page 34]

RFC 6280             Internet Location Architecture            July 20117.  Glossary   Various security-related terms not defined here are to be understood   in the sense defined inRFC 4949 [27].   $ Access Control Rule      A rule that describes which entities may receive location      information and in what form.   $ 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, postal code, county, state, and      country.   $ Device      The physical device, such as a mobile phone, PC, or embedded      micro-controller, whose location is tracked as a proxy for the      location of a Target.   $ geodetic location      The geographic position of an entity in a particular coordinate      system, for example, a latitude-longitude pair.   $ Local Rule      A Privacy Rule 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)      Performs the role of initially determining or gathering the      location of a Target.  Location Generators may be any sort of      software or hardware used to obtain a Target's location.  Examples      include GPS chips and cellular networks.Barnes, et al.            Best Current Practice                [Page 35]

RFC 6280             Internet Location Architecture            July 2011   $ 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.   $ 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 (latitude, 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.Barnes, et al.            Best Current Practice                [Page 36]

RFC 6280             Internet Location Architecture            July 2011   $ 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.   $ 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 sought in the      Geopriv architecture.  In many cases, the Target will be the human      user of a Device, or it may be an object such as a vehicle or      shipping container to which a Device is attached.  In some      instances, the Target will be the Device itself.  The Target is      the entity whose privacy Geopriv seeks to protect.Barnes, et al.            Best Current Practice                [Page 37]

RFC 6280             Internet Location Architecture            July 2011   $ Usage Rule      A rule that describes what uses of location information are      authorized.8.  AcknowledgementsSection 5 is largely based on the security investigations conducted   as part of the Geopriv Layer-7 Location Configuration Protocol design   team, which produced [9].  We would like to thank all the members of   the design team.   We would also like to thank Marc Linsner and Martin Thomson for their   contributions regarding terminology and LCPs.9.  References9.1.  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]   Winterbottom, J., Thomson, M., and H. Tschofenig, "GEOPRIV         Presence Information Data Format Location Object (PIDF-LO)         Usage Clarification, Considerations, and Recommendations",RFC 5491, March 2009.   [6]   Schulzrinne, H., Tschofenig, H., Morris, J., Cuellar, J., Polk,         J., and J. Rosenberg, "Common Policy: A Document Format for         Expressing Privacy Preferences",RFC 4745, February 2007.   [7]   Schulzrinne, H., Ed., Tschofenig, H., Ed., Morris, J., Cuellar,         J., and J. Polk, "Geolocation Policy: A Document Format for         Expressing Privacy Preferences for Location Information", Work         in Progress, March 2011.Barnes, et al.            Best Current Practice                [Page 38]

RFC 6280             Internet Location Architecture            July 2011   [8]   Rosenberg, J., "The Extensible Markup Language (XML)         Configuration Access Protocol (XCAP)",RFC 4825, May 2007.   [9]   Tschofenig, H. and H. Schulzrinne, "GEOPRIV Layer 7 Location         Configuration Protocol: Problem Statement and Requirements",RFC 5687, March 2010.   [10]  Polk, J., Schnizlein, J., and M. Linsner, "Dynamic Host         Configuration Protocol Option for Coordinate-based Location         Configuration Information",RFC 3825, July 2004.   [11]  Schulzrinne, H., "Dynamic Host Configuration Protocol (DHCPv4         and DHCPv6) Option for Civic Addresses Configuration         Information",RFC 4776, November 2006.   [12]  Polk, J., "Dynamic Host Configuration Protocol (DHCP) IPv4 and         IPv6 Option for a Location Uniform Resource Identifier (URI)",         Work in Progress, February 2011.   [13]  Barnes, M., Ed., "HTTP-Enabled Location Delivery (HELD)",RFC 5985, September 2010.   [14]  Marshall, R., Ed., "Requirements for a Location-by-Reference         Mechanism",RFC 5808, May 2010.   [15]  Hardie, T., Newton, A., Schulzrinne, H., and H. Tschofenig,         "LoST: A Location-to-Service Translation Protocol",RFC 5222,         August 2008.   [16]  Barnes, R., Thomson, M., Winterbottom, J., and H. Tschofenig,         "Location Configuration Extensions for Policy Management", Work         in Progress, June 2011.   [17]  Kent, S. and K. Seo, "Security Architecture for the Internet         Protocol",RFC 4301, December 2005.   [18]  Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS)         Protocol Version 1.2",RFC 5246, August 2008.   [19]  Peterson, J., "A Presence-based GEOPRIV Location Object         Format",RFC 4119, December 2005.   [20]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L.,         Leach, P., and T. Berners-Lee, "Hypertext Transfer Protocol --         HTTP/1.1",RFC 2616, June 1999.Barnes, et al.            Best Current Practice                [Page 39]

RFC 6280             Internet Location Architecture            July 2011   [21]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,         Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:         Session Initiation Protocol",RFC 3261, June 2002.   [22]  World Wide Web Consortium, "The XMLHttpRequest Object", W3C         documenthttp://www.w3.org/TR/XMLHttpRequest/, August 2010.   [23]  Rosen, B., Schulzrinne, H., Polk, J., and A. Newton, "Framework         for Emergency Calling Using Internet Multimedia", Work         in Progress, October 2010.   [24]  Rosen, B. and J. Polk, "Best Current Practice for         Communications Services in support of Emergency Calling", Work         in Progress, March 2011.   [25]  Schulzrinne, H., "Location-to-URL Mapping Architecture and         Framework",RFC 5582, September 2009.   [26]  Saint-Andre, P., "Extensible Messaging and Presence Protocol         (XMPP): Core",RFC 6120, March 2011.   [27]  Shirey, R., "Internet Security Glossary, Version 2", FYI 36,RFC 4949, August 2007.   [28]  <http://creativecommons.org/>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.comBarnes, et al.            Best Current Practice                [Page 40]

RFC 6280             Internet Location Architecture            July 2011   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   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.eduBarnes, et al.            Best Current Practice                [Page 41]