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Network Working Group J. Cuellar
Request for Comments: 3693 Siemens AG
Category: Informational J. Morris
Center for Democracy & Technology
D. Mulligan
Samuelson Law, Technology & Public Policy Clinic
J. Peterson
NeuStar
J. Polk
Cisco
February 2004
Geopriv Requirements
Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
Location-based services, navigation applications, emergency services,
management of equipment in the field, and other location-dependent
services need geographic location information about a Target (such as
a user, resource or other entity). There is a need to securely
gather and transfer location information for location services, while
at the same time protect the privacy of the individuals involved.
This document focuses on the authorization, security and privacy
requirements for such location-dependent services. Specifically, it
describes the requirements for the Geopriv Location Object (LO) and
for the protocols that use this Location Object. This LO is
envisioned to be the primary data structure used in all Geopriv
protocol exchanges to securely transfer location data.
Cuellar, et al. Informational [Page 1]
RFC 3693 Geopriv Requirements February 2004
Table of Contents
1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used in this Document. . . . . . . . . . . . . . . 4
3. Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Primary Geopriv Entities . . . . . . . . . . . . . . . . . . . 6
5. Further Geopriv Terminology. . . . . . . . . . . . . . . . . . 7
5.1. Location Information and Sighting. . . . . . . . . . . . 7
5.2. The Location Object and Using Protocol . . . . . . . . . 9
5.3. Trusted vs. Non-trusted Data Flows . . . . . . . . . . . 10
5.4. Further Geopriv Principals . . . . . . . . . . . . . . . 10
5.5. Privacy Rules. . . . . . . . . . . . . . . . . . . . . . 12
5.6. Identifiers, Authentication and Authorization. . . . . . 13
6. Scenarios and Explanatory Discussion . . . . . . . . . . . . . 15
7. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 19
7.1. Location Object. . . . . . . . . . . . . . . . . . . . . 19
7.2. The Using Protocol . . . . . . . . . . . . . . . . . . . 21
7.3. Rule based Location Data Transfer. . . . . . . . . . . . 21
7.4. Location Object Privacy and Security . . . . . . . . . . 22
7.4.1. Identity Protection. . . . . . . . . . . . . . . 22
7.4.2. Authentication Requirements. . . . . . . . . . . 23
7.4.3. Actions to be secured. . . . . . . . . . . . . . 23
7.5. Non-Requirements . . . . . . . . . . . . . . . . . . . . 24
8. Security Considerations. . . . . . . . . . . . . . . . . . . . 24
8.1. Traffic Analysis . . . . . . . . . . . . . . . . . . . . 24
8.2. Securing the Privacy Rules . . . . . . . . . . . . . . . 24
8.3. Emergency Case . . . . . . . . . . . . . . . . . . . . . 24
8.4. Identities and Anonymity . . . . . . . . . . . . . . . . 25
8.5. Unintended Target. . . . . . . . . . . . . . . . . . . . 26
9. Protocol and LO Issues for later Consideration . . . . . . . . 26
9.1. Multiple Locations in one LO . . . . . . . . . . . . . . 26
9.2. Translation Fields . . . . . . . . . . . . . . . . . . . 26
9.3. Truth Flag . . . . . . . . . . . . . . . . . . . . . . . 27
9.4. Timing Information Format. . . . . . . . . . . . . . . . 27
9.5. The Name Space of Identifiers. . . . . . . . . . . . . . 27
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 28
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 28
11.1. Normative Reference . . . . . . . . . . . . . . . . . . 28
11.2. Informative References . . . . . . . . . . . . . . . . . 28
12. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 29
13. Full Copyright Statement . . . . . . . . . . . . . . . . . . . 30
Cuellar, et al. Informational [Page 2]
RFC 3693 Geopriv Requirements February 2004
1. Overview
Location-based services (applications that require geographic
location information as input) are becoming increasingly common. The
collection and transfer of location information about a particular
Target can have important privacy implications. A key goal of the
protocol described in this document is to facilitate the protection
of privacy pursuant to Privacy Rules set by the "user/owner of the
Target" (or, more precisely in the terminology of this document given
in Section 3 and 5.4 below, the "Rule Maker").
The ability to gather and generate a Target's location, and access to
the derived or computed location, are key elements of the location-
based services privacy equation. Central to a Target's privacy are
(a) the identity of entities that have access to raw location data,
derive or compute location, and/or have access to derived or computed
location information, and (b) whether those entities can be trusted
to know and follow the Privacy Rules of the user.
The main principles guiding the requirements described in this
document are:
1) Security of the transmission of Location Object is essential to
guarantee the integrity and confidentiality of the location
information. This includes authenticating the sender and receiver
of the Location Object, and securing the Location Object itself.
2) A critical role is played by user-controlled Privacy Rules, which
describe the restrictions imposed or permissions given by the
"user" (or, as defined below, the "Rule Maker"). The Privacy
Rules specify the necessary conditions that allow a Location
Server to forward Location Information to a Location Recipient,
and the conditions and purposes for which the Location Information
can be used.
3) One type of Privacy Rules specify how location information should
be filtered, depending on who the recipient is. Filtering is the
process of reducing the precision or resolution of the data. A
typical rule may be of the form: "my location can only be
disclosed to the owner of such credentials in such precision or
resolution" (e.g., "my co-workers can be told the city I am
currently in").
4) The Location Object should be able to carry a limited but core set
of Privacy Rules. The exact form or expressiveness of those Rules
in the core set or in the full set is not further discussed in
this document, but will be discussed more extensively in future
documents produced by this working group.
Cuellar, et al. Informational [Page 3]
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5) Whenever appropriate, the location information should not be
linked to the real identity of the user or a static identifier
easily linked back to the real identity of the user (i.e.,
Personally Identifiable Information such as a name, mailing
address, phone number, social security number, or email address or
username). Rather, the user should be able to specify which local
identifier, unlinked pseudonym, or private identifier is to be
bound to the location information.
6) The user may want to hide the real identities of himself and his
partners, not only to eavesdroppers but also to other entities
participating in the protocol.
Although complete anonymity may not be appropriate for some
applications because of legal constraints or because some location
services may in fact need explicit identifications, most often the
location services only need some type of authorization information
and/or perhaps anonymous identifiers of the entities in question.
2. Conventions Used in this Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
Note that the requirements discussed here are requirements on the
generic Location Object and on using protocols for location services.
Thus, for the most part, the requirements discussed in this document
refer to capabilities that are mandatory-to-implement. For example,
requiring that implementations support integrity is not the same
thing as requiring that all protocol traffic be authenticated. In
contrast, an example of a mandatory-to-use (not just mandatory-to-
implement) requirement might be one that states that the user always
receives a notice when his location data was not authenticated. This
practice is mandatory-to-use, not just to implement.
3. Glossary
For easy reference and readability, below are basic terms that will
be defined more formally and fully later in this document.
Location Generator (LG): The entity that initially determines or
gathers the location of the Target and creates Location Objects
describing the location of the Target.
Cuellar, et al. Informational [Page 4]
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Location Object (LO): An object conveying location information
(and possibly privacy rules) to which Geopriv security
mechanisms and privacy rules are to be applied.
Location Recipient (LR): The entity that receives location
information. It may have asked for this location explicitly
(by sending a query to a location server), or it may receive
this location asynchronously.
Location Server (LS): The entity to which a LG publishes location
objects, the recipient of queries from location receivers, and
the entity that applies rules designed by the rule maker.
Precision: The number of significant digits to which a value has
been reliably measured.
Principal: The holder/subject of the credentials, e.g., a
workstation user or a network server.
Resolution: The fineness of detail that can be distinguished in a
measured area. Applied to Geopriv this means the finite area
within provided and closed borders (ex. Latitude and Longitude
boundaries).
Rule Holder: The entity that provides the rules associated with a
particular target for the distribution of location information.
It may either 'push' rules to a location server, or a location
server may 'pull' rules from the Rule Holder.
Rule Maker: The authority that creates rules governing access to
location information for a target (typically, this it the
target themselves).
Rule, or Privacy Rule: A directive that regulates an entity's
activities with respect to location information, including the
collection, use, disclosure, and retention of location
information.
Target: A person or other entity whose location is communicated by
a Geopriv Location Object.
Using Protocol: A protocol that carries a Location Object.
Viewer: A Principal that consumes location information that is
communicated by a Geopriv Location Object, but does not pass
this information further.
Cuellar, et al. Informational [Page 5]
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Resolution and Precision are very close terms. Either quality can be
'reduced' to coarsen location information: 'resolution' by defining a
off-center perimeter around a user's location or otherwise enlarging
the area in consideration (from state to country, say) and
'precision' by discarding significant digits of positioning
information (rounding off longitude and latitude from seconds to
minutes, say). Another WG document discusses this topic in much more
detail.
4. Primary Geopriv Entities
The following picture shows the primary Geopriv entities in a simple
and basic architecture, without claim of completeness or any
suggestion that the entities identified must in all cases be
physically separate entities.
+----------+
| Rule |
| Holder |
| |
+----+-----+
|
rule|interface
V
+----------+ +----------+ +----------+
|Location | publication | Location | notification |Location |
|Generator +-------------->| Server +-------------->|Recipient |
| | interface | | interface | |
+----------+ +----------+ +----------+
The four primary Entities are described as follows:
Location Generator (LG): The entity that initially determines or
gathers the location of the Target and creates Location Objects
describing that location. LGs publish Location Objects to
Location Servers. The manner in which the Location Generator
learns of Location Information is outside the scope of the
Geopriv Protocol.
Location Server (LS): The LS is an element that receives
publications of Location Objects from Location Generators and
may receive subscriptions from Location Recipients. The LS
applies the rules (which it learns from the Rule Holder) to LOs
it receives from LGs, and then notifies LRs of resulting LOs as
necessary.
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Location Recipient (LR): The LR is an element that receives
notifications of Location Objects from Location Servers. The
LR may render these LOs to a user or automaton in some fashion.
Rule Holder (RH): The RH is an element that houses Privacy Rules
for receiving, filtering and distributing Location Objects for
specific Targets. An LS may query an RH for a set of rules, or
rules may be pushed from the RH to an LS. The rules in the
Rule Holder are populated by the Rule Maker.
Thus Location Generation is the process of gathering Location
Information, perhaps from multiple sources, at an IP-based Geopriv
Entity, the LG, which communicates with other Geopriv Entities.
Rules MUST be authenticated and protected. How this is done and in
particular how to distribute the keys to the RM and other authorities
is outside of the scope of this document. See also Section 8.2,
"Securing the Privacy Rules".
The interfaces between the Geopriv entities are not necessarily
protocol interfaces; they could be internal interfaces within a
single composed device. In some architectures, the Location
Generator, Rule Holder, and Location Server might all be implemented
in the same device. There may be several Rule Holders that enforce
the Privacy Rules at a particular Location Server.
5. Further Geopriv Terminology
The terminology and definitions detailed below include both terms
that, besides the primary Geopriv entities, (1) are used in the
requirements section of this document, and (2) provide additional
detail about the usage model envisioned for the Geopriv Location
Object. These latter terms will be utilized in a separate scenarios
document and elsewhere.
5.1. Location Information and Sighting
The focus of the Geopriv working group is on information about a
Target's location that is NOT based on generally or publicly
available sources, but instead on private information provided or
created by a Target, a Target's Device, or a Target's network or
service provider. Notwithstanding this focus on private location
information, the Geopriv Location Object could certainly be used to
convey location information from publicly available sources.
Location Information: A relatively specific way of describing
where a Device is located.
Cuellar, et al. Informational [Page 7]
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This Location Information may have been determined in many different
ways, including:
(a) derived or computed from information generally not available to
the general public (such as information mainly available to a network
or service provider), (b) determined by a Device that may not be
generally publicly addressable or accessible, or (c) input or
otherwise provided by a Target.
As examples, the Location Information could include (a) information
calculated by triangulating on a wireless signal with respect to cell
phone towers, (b) longitude and latitude information determined by a
Device with GPS (global positioning satellite) capabilities, (c)
information manually entered into a cell phone or laptop by a Target
in response to a query, or (d) automatically delivered by some other
IP protocol, such as at device configuration via DHCP.
Excluded from this definition is the determination of location
information wholly without the knowledge or consent of the Target (or
the Target's network or access service provider), based on generally
available information such as an IP or e-mail address. In some
cases, information like IP address can enable someone to estimate (at
least roughly) a location. Commercial services exist that provide
rough location information based on IP addresses. Currently, this
type of location information is typically less precise than the type
of location information addressed in this document. Although this
type of location computation still raises significant potential
privacy and public privacy concerns, such scenarios are generally
outside the scope of this document.
Within any given location-based transaction, the INITIAL
determination of location (and thus the initial creation of Location
Information) is termed a Sighting:
Sighting:
The initial determination of location based on non-public
information (as discussed in the definition of Location
Information), and the initial creation of Location Information.
Some variant of the sighting information is included in the Location
Object. Abstractly, it consists of two separate data fields:
(Identifier, Location)
Cuellar, et al. Informational [Page 8]
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where Identifier is the identifier assigned to a Target being
sighted, and Location is the current position of that Target being
sighted. Not all entities may have access to exactly the same piece
of sighting information. A sighting may be transformed to a new
sighting pair:
(Identifier-1, Location-1)
before it is provided by a Location Generator or Location Server to
Location Recipient. In this case, Identifier-1 may be a Pseudonym,
and Location-1 may have less precision or resolution than the
original value.
5.2. The Location Object and Using Protocol
A main goal of the Geopriv working group is to define a Location
Object (LO), to be used to convey both Location Information and basic
privacy-protecting instructions:
Location Object (LO): This data contains the Location Information
of the Target, and other fields including an identity or
pseudonym of the Target, time information, core Privacy Rules,
authenticators, etc. Most of the fields are optional,
including the Location Information itself.
Nothing is said about the semantics of a missing field. For
instance, a partially filled object MAY be understood implicitly as a
request to complete it. Or, if no time information is included, this
MAY implicitly mean "at the current time" or "at a very recent time",
but it could be interpreted in a different way, depending on the
context.
The "using protocol" is the protocol that uses (reads or modifies)
the Location Object. A protocol that just transports the LO as a
string of bits, without looking at them (like an IP storage protocol
could do), is not a using protocol, but only a transport protocol.
Nevertheless, the entity or protocol that caused the transport
protocol to move the LO is responsible for the appropriate
distribution, protection, usage, retention, and storage of the LO
based on the rules that apply to that LO.
The security and privacy enhancing mechanisms used to protect the LO
are of two types: First, the Location Object definition MUST include
the fields or mechanisms used to secure the LO as such. The LO MAY
be secured, for example, using cryptographic checksums or encryption
as part of the LO itself. Second, the using protocol may also
provide security mechanisms to securely transport the Location
Object.
Cuellar, et al. Informational [Page 9]
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When defining the LO, the design should observe that the security
mechanisms of the Location Object itself are to be preferred. Thus
the definition of the LO MUST include some minimal crypto
functionality (Req. 14 and 15). Moreover, if the RM specifies the
use of a particular LO security mechanism, it MUST be used (Req. 4).
5.3. Trusted vs. Non-trusted Data Flows
Location information can be used in very different environments. In
some cases, the participants will have longstanding relationships,
while in others the participants may have discrete interactions with
no prior contractual or other contact.
The different relationships raise different concerns for the
implementation of privacy rules, including the need to communicate
Privacy Rules. A public Rule Holder, for example, may be unnecessary
in a trusted environment where more efficient methods of addressing
privacy issues exist. The following terms distinguish between the
two basic types of data flows:
Trusted Data Flow:
A data flow that is governed by a pre-existing contractual
relationship that addresses location privacy.
Non-trusted Data Flow:
The data flow is not governed by a pre-existing contractual
relationship that addresses location privacy.
5.4. Further Geopriv Principals
Target:
The entity whose location is desired by the Location Recipient.
In many cases the Target will be the human "user" of a Device
or an object such as a vehicle or shipping container to which
the Device is attached. In some instances the Target will be
the Device itself.
Device:
The technical device whereby the location is tracked as a proxy
for the location of a Target.
A Device might, for example, be a cell phone, a Global Positioning
Satellite (GPS) receiver, a laptop equipped with a wireless access
Device, or a transmitter that emits a signal that can be tracked or
located. In some situations, such as when a Target manually inputs
location information (perhaps with a web browser), the Target is
effectively performing the function of a Device.
Cuellar, et al. Informational [Page 10]
RFC 3693 Geopriv Requirements February 2004
Rule Maker (RM):
The individual or entity that has the authorization to set the
applicable Privacy Rules for a potential Geopriv Target. In
many cases this will be the owner of the Device, and in other
cases this may be the user who is in possession of the Device.
For example, parents may control what happens to the location
information derived from a child's cell phone. A company, in
contrast, may own and provide a cell phone to an employee but
permit the employee to set the privacy rules.
There are four scenarios in which some form of constraint or
override might be placed on the Privacy Rules of the Rule
Maker:
1. In the case of emergency services (such as E911 within the
United States), local or national laws may require that
accurate location information be transmitted in certain
defined emergency call situations. The Geopriv Working
Group MUST facilitate this situation.
2. In the case of legal interception, the RM may not be aware
of an override directive imposed by a legal authority. It
is not the expectation of the Working Group that a
particular accommodation will be made to facilitate this
situation.
3. In the context of an employment relationship or other
contractual relationship, the owner of a particular location
(such as a corporate campus) may impose constraints on the
use of Privacy Rules by a Rule Maker. It is not the
expectation of the Working Group that a particular
accommodation will be made to facilitate this situation.
4. It is conceivable that a governmental authority may seek to
impose constraints on the use of Privacy Rules by a Rule
Maker in non-emergency situations. It is not the
expectation of the Working Group that a particular
accommodation will be made to facilitate this situation.
Viewer:
An individual or entity who receives location data about a
Target and does not transmit the location information or
information based on the Target's location (such as driving
directions to or from the Target) to any party OTHER than the
Target or the Rule Maker.
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RFC 3693 Geopriv Requirements February 2004
Data Transporter:
An entity or network that receives and forwards data without
processing or altering it. A Data Transporter could
theoretically be involved in almost any transmission between a
Device and a Location Server, a Location Server and a second
Location Server, or a Location Server and a Viewer. Some
location tracking scenarios may not involve a Data Transporter.
Access Provider (AP):
The domain that provides the initial network access or other
data communications services essential for the operation of
communications functions of the Device or computer equipment in
which the Device operates. Often, the AP -- which will be a
wireless carrier, an Internet Service Provider, or an internal
corporate network -- contains the LG. Sometimes the AP has a
"dumb" LG, one that transmits Geopriv LOs but does not use any
part of the Geopriv Location Object. Other cases may not
involve any AP, or the AP may only act as a Data Transporter.
Location Storage:
A Device or entity that stores raw or processed Location
Information, such as a database, for any period of time longer
than the duration necessary to complete an immediate
transaction regarding the Location Information.
The existence and data storage practices of Location Storage is
crucial to privacy considerations, because this may influence what
Location Information could eventually be revealed (through later
distribution, technical breach, or legal processes).
5.5. Privacy Rules
Privacy Rules are rules that regulate an entity's activities with
respect to location and other information, including, but not limited
to, the collection, use, disclosure, and retention of location
information. Such rules are generally based on fair information
practices, as detailed in (for example) the OECD Guidelines on the
Protection of Privacy and Transporter Flows of Personal Data [OECD].
Privacy Rule:
A rule or set of rules that regulate an entity's activities
with respect to location information, including the collection,
use, disclosure, and retention of location information. In
particular, the Rule describes how location information may be
used by an entity and which transformed location information
may be released to which entities under which conditions.
Rules must be obeyed; they are not advisory.
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A full set of Privacy Rules will likely include both rules that have
only one possible technical meaning, and rules that will be affected
by a locality's prevailing laws and customs. For example, a
distribution rule of the form "my location can only be disclosed to
the owner of such credentials and in such precision or resolution"
has clear-cut implications for the protocol that uses the LO. But
other rules, like retention or usage Rules, may have unclear
technical consequences for the protocol or for the involved entities.
For example, the precise scope of a retention rule stating "you may
not store my location for more than 2 days" may in part turn on local
laws or customs.
5.6. Identifiers, Authentication and Authorization
Anonymity is the property of being not identifiable (within a set of
subjects). Anonymity serves as the base case for privacy: without
the ability to remain anonymous, individuals may be unable to control
their own privacy. Unlinkability ensures that a user may make
multiple uses of resources or services without others being able to
link these uses to each other. Unlinkability requires that entities
be unable to determine whether the same user caused certain specific
operations in the system. [ISO99] A pseudonym is simply a bit string
which is unique as an ID and is suitable to be used for end-point
authentication.
Unlinked Pseudonym:
A pseudonym where the linking between the pseudonym and its
holder is, at least initially, not known to anybody with the
possible exception of the holder himself or a trusted server of
the user. See [Pfi01] (there the term is called Initially
Unlinked Pseudonym).
The word authentication is used in different manners. Some require
that authentication associates an entity with a more or less well-
known identity. This basically means that if A authenticates another
entity B as being "id-B", then the label "id-B" is a well-known, or
at least a linkable identity of the entity. In this case, the label
"id-B" is called a publicly known identifier, and the authentication
is "explicit":
Explicit Authentication:
The act of verifying a claimed identity as the sole originator
of a message (message authentication) or as the end-point of a
channel (entity authentication). Moreover, this identity is
easily linked back to the real identity of the entity in
question, for instance being a pre-existing static label from a
predefined name space (telephone number, name, etc.)
Cuellar, et al. Informational [Page 13]
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Authorization:
The act of determining if a particular right, such as access to
some resource, can be granted to the presenter of a particular
credential.
Depending on the type of credential, authorization may or may not
imply Explicit Authentication.
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6. Scenarios and Explanatory Discussion
In this subsection we introduce short scenarios to illustrate how
these terms and attributes describe location information
transactions. Additional illustrative scenarios are discussed in a
separate document.
SCENARIO 1: GPS Device with Internal Computing Power: Closed System
In this example, the Target wishes to know his/her location using the
Global Positioning System (GPS) and the Device is capable of
independently processing the raw data to determine its location. The
location is derived as follows: the Device receives transmissions
from the GPS satellites, internally computes and displays location.
This is a closed system. For the purpose of this and subsequent
examples, it is assumed that the GPS satellite broadcasts some
signal, and has no information about the identity or whereabouts of
Devices using the signal.
GPS Satellite
|
| Sighting (not a Geopriv Interface)
|
|
|
V GPS Device
--------------------------------------------------
/ \
| Location ----- Location ----- Location |
| Generator Server Storage |
\ | /
-------------------------------------------|------
|
| Notification
| Interface
|
------------|------
/ V \
/ Target Location \
| Recipient |
| |
\ Rule Maker /
\ /
-------------------
In this scenario the GPS Device is both the AP and the LG. The
interaction occurs in a Trusted environment because it occurs in the
Rule Maker's Device.
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SCENARIO 2: Cell Phone Roaming
In this example, a cell phone is used outside its home service area
(roaming). Also, the cell phone service provider (cell phone Corp 2)
outsourced the accounting of cell phone usage. The cell phone is not
GPS-enabled. Location is derived by the cell phone network in which
the Target and Device are roaming. When the Target wishes to use the
cell phone, cell phone Corp 1 (AP) provides the roaming service for
the Target, which sends the raw data about usage (e.g., duration of
call, location in the roaming network, etc.) to cell phone Corp 2,
the home service provider. Cell phone Corp 2 submits the raw data to
the accounting company, which processes the raw data for the
accounting statements. Finally, the raw data is sent to a data
warehouse where the raw data is stored in a Location Server (e.g.,
computer server).
Cell Phone Corp 1 Cell Phone Corp 2
----------------- -----------------
Sighting / \ Publish / \
Device ----- | Data Transporter | --------- | Data Transporter |
Target \ / Interface \ /
----------------- / -----------------
/ |
/ | Notification
/ | Interface
----------- |
/ V
------------ / ----------
/ \ / / \
/ Location \ / | Location |
| Storage | Location Info | Storage |
| |<----------------- | |
| Location | | Location |
| Recipient | | Recipient |
\ / \ /
------------- ----------
Here, cell phone Corp 1 is the AP and the LG. In this scenario, Cell
phone Corp 2 is likely to be a Trusted entity, but cell phone Corp 1
may be Non-trusted.
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SCENARIO 3: Mobile Communities and Location-Based Services
The figure below shows a common scenario, where a user wants to find
his friends or colleagues or wants to share his position with them or
with a Location-Based Service Provider. Some of the messages use a
Location Object to carry, for instance, identities or pseudonyms,
credentials and proof-of-possession of them, Rules and Location Data
Information, including Data Types and Precision or Resolution.
Messages that do not use the Location Object and are outside of the
scope of the Geopriv WG, but should be mentioned for
understandability, are shown in the figure as starred arrows
("***>").
+---------+ +------------+
| | | |
| Location|<** | Public |
|Generator| * | Rule Holder|
| | * | |
+---------+\ * +------------+
\ *3 1a* *
\ * * *
\ ** *
\ * * *1a
\* * *
* \ * *
* \ * *
* \4 * *
* \ * V
* \->+-----------+
+----------+ 1 | Location |
| Rule |--------------------->| Server + |
| Maker | | Private |
+----------+ |Rule Holder|
+-----------+
^ |
3| |5
| V
+----------+
| Location |
| Recipient|
+----------+
Assume that the Rule Maker and the Target are registered with the
Location Server. The RM has somehow proven to the LS that he indeed
is the owner of the privacy rights of the Target (the Target is
usually a Device owned by the Rule Maker). The Rule Maker and the
Location Server have agreed on the set of keys or credentials and
cryptographic material that they will use to authenticate each other,
Cuellar, et al. Informational [Page 17]
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and in particular, to authenticate or sign the Rules. How this has
been done is outside of the scope of the document.
1: Rule Transfer:
The Rule Maker sends a Rule to the Location Server. This Rule
may or may not be a field in a Location Object.
1a:Signed Rule:
As an alternative, the Rule Maker may write a Rule and place it
in a Public Rule Holder. The entities access the repository to
read the signed Rules.
2: Location Information Request:
The Location Recipient requests location information for a
Target. In this request, the Location Recipient may select
which location information data type it prefers. One way of
requesting Location Information MAY be sending a partially
filled Location Object, including only the identities of the
Target and Location Recipient and the desired Data Type and
precision or resolution, and providing proof of possession of
the required credentials. But whether or not the using
protocol understands this partially filled object as a request
MAY depend on the using protocol or on the context. The
Location Recipient could also specify the need for periodic
location information updates, but this is probably out of the
scope of Geopriv.
3: Locate:
When a Location Server receives a Location Information Request
for a Target which has no current location information, the
server may ask the Location Generator to locate the Target.
4: Location Information:
The Location Generator sends the "full" location information to
the Location Server. This Location Information may or may not
be embedded in a Location Object.
5: Filtered Location Information:
The Location Server sends the location information to the
Location Recipient. The information may be filtered in the
sense that in general a less precise or a computed version of
the information is being delivered.
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7. Requirements
7.1. Location Object
Remember that this document is primarily specifying requirements on
the definition of the LO. Some Requirements read like this: "The LO
definition MUST contain Field 'A' as an optional field." This
requirement states that
o the document that defines the LO MUST define the LO field 'A',
o the field 'A' MUST be defined as optional to use (an instance of a
LO MAY or may not contain the field 'A').
Some Requirements read like this: "The LO definition MUST contain
Field 'A', which MAY be an optional field." This requirement states
that
o the document that defines the LO MUST define the LO field 'A',
o the field 'A' MAY be defined as optional or not to use. If it is
defined as optional to use, any instance of an LO MAY or may not
contain the field 'A'; if it is not optional, all instances of LOs
MUST contain the field 'A'.
Req. 1. (Location Object generalities)
1.1) Geopriv MUST define one Location Object (LO) -- both in
syntax and semantics -- that must be supported by all Geopriv
entities.
1.2) Some fields of the Location Object MAY be optional. This
means that an instance of a Location Object MAY or may not contain
the fields.
1.3) Some fields of the Location Object MAY be defined as
"extensions". This means that the syntax or semantics of these
fields is not fully defined in the basic Location Object
definition, but their use may be private to one or more of the
using protocols.
1.4) The Location Object MUST be extensible, allowing the
definition of new attributes or fields.
1.5) The object MUST be suitable for requesting and receiving a
location.
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1.6) The object MUST permit (but not require) the Privacy Rules to
be enforced by a third party.
1.7) The object MUST be usable in a variety of protocols, such as
HTTP and SIP, as well as local APIs.
1.8) The object MUST be usable in a secure manner even by
applications on constrained devices.
Req. 2. (Location Object fields) The Location Object definition MUST
contain the following Fields, which MAY be optional to use:
2.1) Target Identifier
2.2) Location Recipient Identity
This identity may be a multicast or group identity, used to
include the Location Object in multicast-based using protocols.
2.3) Location Recipient Credential
2.4) Location Recipient Proof-of-Possession of the Credential
2.5) Location Field
2.5.1) Motion and direction vectors. This field MUST be optional.
2.6) Location Data Type
When transmitting the Location Object, the sender and the receiver
must agree on the data type of the location information. The
using protocol may specify that the data type information is part
of the Location Object or that the sender and receiver have agreed
on it before the actual data transfer.
2.7) Timing information:
(a) When was the Location Information accurate? (sighting time)
(b) Until when considered current? TTL (Time-to-live) (This is
different than a privacy rule setting a limit on data retention)
2.8) Rule Field: this field MAY be a referral to an applicable
Rule (for instance, a URI to a full Rule), or it MAY contain a
Limited Rule (see Req. 11), or both.
2.9) Security-headers and -trailers (for instance encryption
information, hashes, or signatures) (see Req. 14 and 15).
2.10) Version number
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Req. 3. (Location Data Types)
3.1) The Location Object MUST define at least one Location Data
Type to be supported by all Geopriv receivers (entities that
receive LOs).
3.2) The Location Object SHOULD define two Location Data Types:
one for latitude / longitude / altitude coordinates and one for
civil locations (City, Street, Number) supported by all Geopriv
receivers (entities that receive LOs).
3.3) The latitude / longitude / altitude Data Type SHOULD also
support a delta format in addition to an absolute one, used for
the purpose of reducing the size of the packages or the security
and confidentiality needs.
3.4) The Location Object definition SHOULD agree on further
Location Data Types supported by some Geopriv entities and defined
by other organizations.
7.2. The Using Protocol
Req. 4. The using protocol has to obey the privacy and security
instructions coded in the Location Object and in the corresponding
Rules regarding the transmission and storage of the LO.
Req. 5. The using protocol will typically facilitate that the keys
associated with the credentials are transported to the respective
parties, that is, key establishment is the responsibility of the
using protocol.
Req. 6. (Single Message Transfer) In particular, for tracking of
small target devices, the design should allow a single
message/packet transmission of location as a complete transaction.
Other requirements on the using protocol are out of the scope of this
document, but might be the subject of future efforts from this
working group. See also Section 9 (Protocol and LO Issues for later
Consideration).
7.3. Rule based Location Data Transfer
Req. 7. (LS Rules) The decision of a Location Server to provide a
Location Recipient access to Location Information MUST be based on
Rule Maker-defined Privacy Rules.
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It is outside of our scope how Privacy Rules are managed and how a
Location Server has access to the Privacy Rules. Note that it might
be that some rules contain private information not intended for
untrusted parties.
Req. 8. (LG Rules) Even if a Location Generator is unaware of and
lacks access to the full Privacy Rules defined by the Rule Maker,
the Location Generator MUST transmit Location Information in
compliance with instructions set by the Rule Maker. Such
compliance MAY be accomplished by the Location Generator
transmitting the LO only to a URI designated by the Rule Maker.
Req. 9. (Viewer Rules) A Viewer does not need to be aware of the
full Rules defined by the Rule Maker (because a Viewer SHOULD NOT
retransmit Location Information), and thus a Viewer SHOULD receive
only the subset of Privacy Rules necessary for the Viewer to
handle the LO in compliance with the full Privacy Rules (such as,
instruction on the time period for which the LO can be retained).
Req. 10. (Full Rule language) Geopriv MAY specify a Rule language
capable of expressing a wide range of privacy rules concerning
location information. This Rule language MAY be an existing one,
an adaptation of an existing one or a new Rule language, and it
SHOULD be as simple as possible.
Req. 11. (Limited Rule language) Geopriv MUST specify a limited Rule
language capable of expressing a limited set of privacy rules
concerning location information. This Rule language MAY be an
existing one, an adaptation of an existing one or a new Rule
language. The Location Object MUST include sufficient fields and
data to express the limited set of privacy rules.
7.4. Location Object Privacy and Security
7.4.1. Identity Protection
Req. 12. (Identity Protection) The Location Object MUST support use
of Unlinked Pseudonyms in the corresponding identification fields
of Rule Maker, Target, Device, and Location Recipient. Since
Unlinked Pseudonyms are simply bit strings that are not linked
initially to a well-known identity, this requirement boils down to
saying that the name space for Identifiers used in the LO has to
be large enough to contain many unused strings.
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7.4.2. Authentication Requirements
Req. 13. (Credential Requirements) The using protocol and the
Location Object SHOULD allow the use of different credential
types, including privacy-enhancing credentials (for instance those
described in [Bra00] or [Cha85]).
7.4.3. Actions to be secured
Req. 14. (Security Features) The Location Object MUST support fields
suitable for protecting the Object to provide the following
security features:
14.1) Mutual end-point authentication: the using protocol is
able to authenticate both parties in a Location Object
transmission,
14.2) Data object integrity: the LO is secured from
modification by unauthorized entities during transmission and
storage,
14.3) Data object confidentiality: the LO is secured from
eavesdropping (unauthorized reading) during transmission and
storage, and
14.4) Replay protection: an old LO may not be replayed by an
adversary or by the same entity that used the LO itself (except
perhaps during a small window of time that is configurable or
accepted by the Rule Maker).
Req. 15. (Minimal Crypto)
15.1) Geopriv MUST specify a minimum mandatory to implement
Location Object security, including mandatory to implement crypto
algorithms for digital signature algorithms and encryption
algorithms.
15.2) It MAY also define further mandatory to implement
Location Object security mechanisms for message authentication
codes (MACs) or other purposes.
15.3) The protocol SHOULD allow a bypass if authentication
fails in an emergency call.
The issue addressed in the last point is that an emergency call in
some unfavorable situations may not be completed if the minimal
authentication fails. This is probably not what the user would like
to happen. The user may prefer an unauthenticated call to an
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unauthenticated emergency server over no call completion at all, even
at the risk that he is talking to an attacker or that his information
is not secured.
7.5. Non-Requirements
Non-Req. 1. (Bridging to non-IP networks) The Geopriv specification
SHOULD NOT specify the bridging to non-IP networks (PSTN, etc).
8. Security Considerations
The purpose of the Geopriv Location Object and the requirements on
the using protocol are to allow a Privacy Rule-controlled disclosure
of location information for location services.
8.1. Traffic Analysis
The information carried within the Location Object is secured in a
way compliant with the privacy and security Rules of the Rule Maker,
but other information, carried in other objects or headers are in
general not secured in the same way. This means that Geopriv may not
as a general matter, secure the Target against general traffic
analysis attacks or other forms of privacy violations.
8.2. Securing the Privacy Rules
The Privacy Rules of the Rule Maker regarding the location of the
Target may be accessible to a Location Server in a public or non-
public Rule Holder, or they may be carried by the Location Object, or
they may be presented by the Location Recipient as capabilities or
tokens. Each type of Rule has to be secured its own particular way.
The rules in a non-public Rule Holder are typically authenticated
using a MAC (Message Authentication Code) or a signature, depending
on the type of keys used. The rules in a public Rule Holder (one
that in principle may be accessed directly by several entities, for
instance several Location Servers) are typically digitally signed.
Rule Fields in an LO are secured as part of the LO itself. A Geopriv
Token (a token or ticket issued by the Rule Maker to a Location
Recipient, expressing the explicit consent of the Rule Maker to
access his location information) is authenticated or signed.
8.3. Emergency Case
Let us consider the situation where the authentication fails in an
emergency call because the authentication center fails to
authenticate itself. In this case, one way of implementing the
Cuellar, et al. Informational [Page 24]
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authentication bypass for emergency calls (mentioned in Req 15.3) is
to let the user have the choice of writing a Rule that says:
- "If the emergency server does not authenticate itself, send the
location information anyway", or
- "If the emergency server does not authenticate itself, let the
call fail".
Second, in the case where the authentication of the emergency call
fails because the user may not authenticate itself, the question
arises: whose Rule to use? It is reasonable to use a default one:
this location information can only be sent to an emergency center.
The third situation, which should be studied in more detail, is:
what to do if not only the user fails to authenticate itself, but
also the emergency center is not authenticable? It is reasonable to
send the Location Information anyway, but are there any security
threats that must be considered?
8.4. Identities and Anonymity
The use of Unlinked Pseudonyms is necessary to obtain anonymity.
The purpose of the use of Unlinked Pseudonyms is the following: the
using protocol should be able to hide the real identity of the Rule
Maker, the Target, and the Device, from Location Servers or Location
Recipients, if required by the RM. Also, the using protocol SHOULD
be able to hide the real identity of the Location Recipient from the
Location Server.
In this last case, the Target is not concerned about the Server
identifying him and knowing his location, but identifying his
business partners, and therefore his habits, etc. Reasons for hiding
the real identities of the Location Recipients include (a) that this
knowledge may be used to infer the identity of the Target, (b) that
knowledge of the identity of the Location Recipient may embarrass the
Target or breach confidential information, and (c) that the dossier
telling who has obtained a Target's location information over a long
period of time can give information on habits, movements, etc. Even
if the location service providers agree to respect the privacy of the
user, are compelled by laws or regulations to protect the privacy of
the user, and misbehavior or negligence of the Location Server can be
ruled out, there is still risk that personal data may become
available to unauthorized persons through attacks from outsiders,
unauthorized access from insiders, technical or human errors, or
legal processes.
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On some occasions, a Location Server has to know who is supplying the
Privacy Rules for a particular Target, while in other situations it
could be enough to know that the supplier of the Rules is authorized
to do so.
8.5. Unintended Target
An Unintended Target is a person or object tracked by proximity to
the Target. This special case most frequently occurs if the Target
is not a person. For example, the Target may be a rental car
equipped with a GPS Device, used to track car inventory. The rental
company may not care about the driver's location, but the driver's
privacy is implicitly affected.
Geopriv may or may not protect or affect the privacy of Unintended
Targets, but the impact on Unintended Targets should be acknowledged.
9. Protocol and LO Issues for later Consideration
This section briefly discusses issues relating to the Location Object
or the protocol that have emerged during the discussion of earlier
versions of this document.
9.1. Multiple Locations in one LO
A location Field is intended to represent one point or one region in
space (either 1, 2, or 3 dimensionally). The possibility of
inclusion of multiple locations is discussed in another document.
The current rough consensus is the following: the LO definition MAY
allow the Location Field to be optional, to appear exactly one time
or to occur several times. Each Location Field may contain one or
more "Location Representations", each of which is intended to
represent a different measurement or a different formatting of the
same position. But there are other possibilities for using multiple
Location Fields and multiple representations: maybe several Location
Fields would be used to report the same sighting in different
formats, or multiple sightings at different times, or multiple sensor
locations for the same device, or other purposes, which could also
depend on the using protocol. This is all for further discussion.
9.2. Translation Fields
It is possible to include fields to indicate that one of the
locations is a translation of another. If this is done, it is also
possible to have a field to identify the translator, as identity and
method.
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9.3. Truth Flag
Geopriv MUST be silent on the truth or lack-of-truth of the location
information contained in the LO. Thus, the LO MUST NOT provide an
attribute in object saying "I am (or am not) telling you the whole
truth."
9.4. Timing Information Format
The format of timing information is out of the scope of this
document.
9.5. The Name Space of Identifiers
Who defines the Identities: can the using protocol define the
Identifiers or must the using protocol use and authenticate
Pseudonyms proposed by the Rules, chosen independently of the using
protocol? Of course, if the using protocol has an appropriate
namespace, containing many unused names that may be used as
pseudonyms and may be replaced by new ones regularly, then the
Location Object may be able to use the name space. For this purpose,
the user would probably have to write his Rules using this name
space. Note that it is necessary to change the used pseudonyms
regularly, because identifying the user behind an unlinked pseudonym
can be very simple.
There are several advantages in letting the using protocol define the
name space:
o the embedded authentication would be easier, as the using protocol
often already has the credentials for the authentication identity
in place and the "embedded" authentication would be independent on
the form of Identifiers,
o the size of the names would be fixed.
On the other hand, the benefits of the Rule choosing the identifiers
are:
o the user has a control of his anonymity, and
o the interworking of multiple systems with Location object across
protocol boundaries is facilitated.
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10. Acknowledgements
We wish to thank the members of the IETF Geopriv WG for their
comments and suggestions. Aaron Burstein, Mehmet Ersue, Allison
Mankin, Randall Gellens, and the participants of the Geopriv meetings
in San Diego and Yokohama provided detailed comments or text.
11. References
11.1. Normative Reference
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
11.2. Informative References
[Bra00] Stefan A.: Rethinking Public Key Infrastructures and
Digital Certificates : Building in Privacy, MIT Press;
ISBN: 0262024918; 1st edition, August, 2000
[Cha85] Chaum, David: Security without Identification, Card
Computers to make Big Brother Obsolete. Original Version
appeared in: Communications of the ACM, vol. 28 no. 10,
October 1985 pp. 1030-1044. Revised version available at
http://www.chaum.com/articles/
[ISO99] ISO99: ISO IS 15408, 1999, http://www.commoncriteria.org/.
[OECD] OECD Guidelines on the Protection of Privacy and
Transborder Flows of Personal Data, http://www.oecd.org.
[Pfi01] Pfitzmann, Andreas; Koehntopp, Marit: Anonymity,
Unobservability, and Pseudonymity - A Proposal for
Terminology; in: H Federrath (Ed.): Designing Privacy
Enhancing Technologies; Proc. Workshop on Design Issues in
Anonymity and Unobservability; LNCS 2009; 2001; 1-9. Newer
versions available at
http://www.koehntopp.de/marit/pub/anon
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12. Authors' Addresses
Jorge R Cuellar
Siemens AG
Corporate Technology
CT IC 3
81730 Munich, Germany
EMail: Jorge.Cuellar@siemens.com
John B. Morris, Jr.
Director, Internet Standards, Technology & Privacy Project
Center for Democracy & Technology
1634 I Street NW, Suite 1100
Washington, D.C. 20006 USA
EMail: jmorris@cdt.org
URI: http://www.cdt.org
Deirdre K. Mulligan
Samuelson Law, Technology & Public Policy Clinic
Boalt Hall School of Law
University of California
Berkeley, CA 94720 USA
EMail: dmulligan@law.berkeley.edu
URI: http://www.law.berkeley.edu/cenpro/samuelson/
Jon Peterson
NeuStar, Inc.
1800 Sutter St
Suite 5707
Concord, CA 94520 USA
EMail: jon.peterson@neustar.biz
URI: http://www.neustar.biz/
James M. Polk
Cisco Systems
2200 East President George Bush Turnpike
Richardson, Texas 75082 USA
EMail: jmpolk@cisco.com
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13. Full Copyright Statement
Copyright (C) The Internet Society (2004). This document is subject
to the rights, licenses and restrictions contained in BCP 78 and
except as set forth therein, the authors retain all their rights.
This document and the information contained herein are provided on an
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REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE
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Acknowledgement
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Internet Society.
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