Geopriv H. Tschofenig
Internet-Draft Siemens
Expires: April 5, 2005 F. Adrangi
Intel
A. Lior
M. Jones
Bridgewater
October 5, 2004
Carrying Location Objects in RADIUS
draft-ietf-geopriv-radius-lo-00.txt
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Copyright Notice
Copyright (C) The Internet Society (2004).
Abstract
This document describes RADIUS attributes for conveying the Access
Network's operational ownership and location information based on a
civil and geospatial location location format.
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The distribution of location information is privacy sensitive.
Dealing with mechanisms to preserve the user's privacy is important
and addressed in this document.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Delivery Methods for Location Information . . . . . . . . . . 6
3.1 Authentication/Authorization Phase Delivery . . . . . . . 6
3.2 Mid-session Delivery . . . . . . . . . . . . . . . . . . . 7
4. Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . 9
4.1 Use Case 1 - Use of Location Information in AAA . . . . . 9
4.2 Scenario 2 - Use of Location Information for other
Services . . . . . . . . . . . . . . . . . . . . . . . . . 9
5. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
5.1 Operator-Name Attribute . . . . . . . . . . . . . . . . . 11
5.2 Location-Information Attribute . . . . . . . . . . . . . . 11
5.2.1 Civil Location Information . . . . . . . . . . . . . . 12
5.2.2 Geospatial Location Information . . . . . . . . . . . 14
6. Basic- and Extended-Policy-Rule Attributes . . . . . . . . . . 15
7. Location-Type Attribute . . . . . . . . . . . . . . . . . . . 16
8. Billing-Description Attribute . . . . . . . . . . . . . . . . 17
9. Diameter RADIUS Interoperability . . . . . . . . . . . . . . . 18
10. Attributes . . . . . . . . . . . . . . . . . . . . . . . . . 19
10.1 Operator-Name Attribute . . . . . . . . . . . . . . . . . 19
10.2 Location-Information Attribute . . . . . . . . . . . . . . 19
10.3 Basic Policy Rules Attribute . . . . . . . . . . . . . . . 23
10.4 Extended Policy Rules Attribute . . . . . . . . . . . . . 24
10.5 Location-Type Attribute . . . . . . . . . . . . . . . . . 25
10.6 Billing-Description Attribute . . . . . . . . . . . . . . 25
11. Table of Attributes . . . . . . . . . . . . . . . . . . . . 26
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . 27
13. Matching with Geopriv Requirements . . . . . . . . . . . . . 28
13.1 Distribution of Location Information at the User's
Home Network . . . . . . . . . . . . . . . . . . . . . . . 28
13.2 Distribution of Location Information at the Visited
Network . . . . . . . . . . . . . . . . . . . . . . . . . 29
13.3 Requirements matching . . . . . . . . . . . . . . . . . . 30
14. Example . . . . . . . . . . . . . . . . . . . . . . . . . . 35
15. Privacy Considerations . . . . . . . . . . . . . . . . . . . 36
15.1 Entity in the visited network . . . . . . . . . . . . . . 36
15.2 Entity in the home network . . . . . . . . . . . . . . . . 37
16. Security Considerations . . . . . . . . . . . . . . . . . . 40
17. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 43
18. References . . . . . . . . . . . . . . . . . . . . . . . . . 44
18.1 Normative References . . . . . . . . . . . . . . . . . . . . 44
18.2 Informative References . . . . . . . . . . . . . . . . . . . 44
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Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 46
Intellectual Property and Copyright Statements . . . . . . . . 47
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1. Introduction
Wireless LAN (WLAN) Access Networks (AN) are being deployed in public
places such as airports, hotels, shopping malls, and coffee shops by
a diverse set of incumbent operators such as cellular carriers (GSM
and CDMA), Wireless Internet Service Providers (WISP), and fixed
broadband operators.
When a user executes the network access authentication procedure to
such a network, information about the location and operational
ownership of this network needs to be conveyed to the users's home
network to which the user has a contractal relationship. The main
intent of this document is to enable location aware billing (e.g.,
determine the appropriate tariff and taxation), location aware
subscriber authentication and authorization for roaming environments
and to enable location aware services.
This document describes AAA attributes that are used by a AAA client
or a local AAA server in an access network for conveying
location-related information to the user's home AAA server. This
document defines attributes for RADIUS [1].
Although the proposed attributes in this draft are intended for
wireless LAN deployments, they can also be used in other wireless and
wired networks where location-aware services are required.
Location information needs to be protected against unauthorized
access and distribution to preserve privacy of the owner of the
location information. With [8] requirements for a
protocol-independent model for the access to geographic location
information was defined. The model includes a Location Generator
(LG) that creates Location Information, a Location Server (LS) that
authorizes access to Location Information, a Location Recipient (LR)
that requests and receives information, and a Rule Maker (RM) that
provides authorization policies to the LS which enforce access
control policies on access to a target.
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2. Terminology
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 [2].
RADIUS specific terminology is reused from [1] and [3].
Terminology related to privacy issues, location information and
authorization policy rules are taken from [8].
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3. Delivery Methods for Location Information
Location Infomation Objects defined in this document are transported
over RADIUS protocol from visited access network to the AAA server.
The information can be delivered to the RADIUS server during the
authentication/authorization phase described in Section 3.1, or in
the mid-session using the dynamic authorization protocol framework
described in Section 3.2. This section describes messages flow for
both delivery methods.
3.1 Authentication/Authorization Phase Delivery
Figure 1 shows an example message flow for delivering Location
Information during the network access authentication/authorization
procedure. Upon a network authentication request from an access
network client, the NAS submits a RADIUS Access-Request message which
contains location information attributes among other required
attributes. The authentication and/or authorization procedure is
completed based on a number of criteria, including the newly defined
Location-Information, Operator-Name, Location-Type,
Policy-Information attributes. A RADIUS Accounting Request message
is again allowed to carry location specific attributes.
+---------+ +---------+ +---------+
| Access | | Network | | AAA |
| Network | | Access | | Server |
| Client | | Server | | |
+---------+ +---------+ +---------+
| | |
| Authentication phase | |
| begin | |
|---------------------->| |
| | |
| | |
| | RADIUS |
| | Access-Request |
| | + Location-Information |
| | attributes |
| |----------------------------->|
| | |
: : :
: Multiple Protocol Exchanges to perform :
: Authentication, Key Exchange and Authorization :
: : :
: ...continued... :
: | |
| | RADIUS |
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| | Access-Accept |
| | + Rule set Information |
| |<-----------------------------|
| Authentication | |
| Accept | |
|<----------------------| |
| | |
| | RADIUS |
| | Accounting Request |
| | + Location-Information |
| | attributes |
| |----------------------------->|
| | |
Figure 1: Message Flow: Authentication/Authorization Phase Delivery
3.2 Mid-session Delivery
Mid-session delivery method uses the Change of Authorization (COA)
message as defined in [4]. In accordance to [4], at anytime during
the session the AAA server may send the access network a COA message
containing session identification attributes (see [4] for the
possible options). The COA message may instruct the access network
to generate an Authorize-Only Access-Request (Access-Request with
Service-Type set to "Authorize-Only") in which case it is instructing
the access network to send the location information attributes.
Figure 2 shows the approach graphically.
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Access network AAA server
| |
| COA + Service-Type "Authorize Only" |
|<----------------------------------------------|
| |
| COA NAK + Service-Type "Authorize Only" |
| + Error-Cause "Request Initiated" |
|---------------------------------------------->|
| |
| Access-Request + Service-Type "Authorize Only"|
| + Location Information attributes |
| + Location Information policy |
|---------------------------------------------->|
| |
| Access-Accept |
|<----------------------------------------------|
| |
Figure 2: Message Flow: Mid-session Delivery
Upon receiving the Authorize-Only message from the Access network,
the AAA server MUST respond with either an Access-Accept message or
an Access-Reject message.
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4. Scenarios
In the following subsections we describe two scenarios for use of
location information. The location infomration may refer to network
or user location information which in some cases may be identical.
How the network obtains the user's location information is out of
scope of this document. There are two consumers of the location
information: the AAA servers and other location-based services. The
privacy implications of these scenarios are described in Section 15.
4.1 Use Case 1 - Use of Location Information in AAA
An Operator requires Location Informaion for Authorization and
Billing purposes. The operator may deny service if Location
Information is not available. Or it may offer limited service. The
NAS delivers Location Information to the Home AAA server.
The user's location is transferred from the NAS to the RADIUS server
and the NAS and intermediaries (if any) are not allowed to use that
information other then to forward it to the home network.
The RADIUS server authenticates and authorizes the session. If the
user's location policies are available to the RADIUS server, the
RADIUS server may deliver those policies in an Access Accept. This
information may be needed if intermediaries or other elements want to
act as Location Servers (see Section 4.2). In the absence of
receiving the policies intermediaries MUST NOT divulge the location
information.
Location Information may also be reported in accouning messages.
Accounting messages are generated when the session starts, stops and
periodically. Accounting messages may also be generated when the
user roams during handoff. This information may be needed by the
billing system to calculate the users bill. For example, there may
be different tarrif rates applied based on the location and their
maybe different tax rates applied based on the location. Unless
otherwise specified, location information in the accounting stream
may not be transmitted to third parties.
The location information in the accounting stream MUST only be sent
in the proxy chain to the home network (unless specified otherwise).
4.2 Scenario 2 - Use of Location Information for other Services
Location Servers are entities that receive the user's location
information and transmit it to other entities. For the purpose of
this scenario Location servers are the NAS, and RADIUS servers. The
RADIUS servers are in the home network, in the visited network, or in
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broker networks.
Unless otherwise specified, excluding the proxy chain from the NAS to
the Home RADIUS, the Location Server may not transmit the location
information to other parties.
Upon authentication and authorization, the Home RADIUS may transmit
the Rule set in an Access-Accept to the other Location Server
allowing them to transmit Location Information. Then and only then
they are allowed to share the information.
Note that the NAS is the source of all Location Information that is
disseminated by RADIUS, the NAS could tag the Location Information
with the policy rules or a reference for the policy rules received in
an Access-Accept. All Location Information in the accounting stream
will now be tagged.
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5. Overview
Location Information and operational ownership of the access network
is conveyed in the following RADIUS attributes: Operator-Name,
Location-Information, Location-Type and Billing-Description.
Furthermore, the Basic-Policy-Rules and the Extended-Policy-Rules
attributes are attached to the Location-Information attribute turning
Location Information into a Location Object as defined in [8].
5.1 Operator-Name Attribute
This attribute contains an operator name which uniquely identifies
the ownership of an access network. The Attribute value is a
non-NULL terminated string whose Length MUST NOT exceed 253 bytes.
The attribute value is comprised of the prefix and the identity,
separated by a colon. The prefix identifies the operator type;
example: GSM, CDMA, and REALM. The identity uniquely identifies the
operator name within the scope of the operator type.
As an example consider the string 'GSM:TADIG' where GSM is a prefix
indicating an operator type and TADIC is a unique globally known GSM
operator ID.
This document defines three operator type prefixes which are: GSM,
CDMA, and REALM. The GSM prefix can be used to indicate operator
names based on GSMA TADIG codes. REALM can be used by any domain
name acquired from IANA. Possible forthcoming operator types MUST be
associated with an ogranization responsible for assigning/managing
operator names.
5.2 Location-Information Attribute
This document describes two formats for conveying location
information: civil and geospatial location information. Section
5.2.1 defines the civil location information format. Section 5.2.2
defines the geospatial location information format.
Additionally, a few additional fields provide more details about the
transmitted Location Information.
The 'Precision' field provides information about the accuracy
about the provided Location Information. When the user's home
network receives a Location Object within RADIUS then this field
gives further indication about the accuracy. Location information
can refer to the Access Point, the user, the or the RADIUS server
or the network itself. With large networks the Location
Information of each of these entities might be different. The
'Precision' field allows to give a hint about the precision of the
provided location information.
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The 'Method' field describes the way that the location information
was derived or discovered. Possible values for this field
include, as an example GPS or manual configuration. The inclusion
of this field should help the user's home network deduce further
information about the accuracy and to provide an easier
translation into a Geopriv Location Object for transmission to
third party entities. Note that the values for this field are
reused from [9].
5.2.1 Civil Location Information
Civil location is a popular way to describe the location of an
entity. Using an unstructured (as a text string) or a custom format
for civil location format is dangerous since the automatic processing
capabilities are limited.
For this document we reuse the civil location format defined in [5].
The civil location format includes a number of fields, including the
country (expressed as a two-letter ISO 3166 code) and the
administrative units of [5] A1 through A6. This designation offers
street-level precision.
For completeness we include more detailed information from [5] with
regard to the defined civil location elements (A1 through A6):
+----------------------+----------------------+---------------------+
| Label | Description | Example |
+----------------------+----------------------+---------------------+
| country | The country is | US |
| | identified by the | |
| | two-letter ISO 3166 | |
| | code. | |
| | | |
| A1 | national | New York |
| | subdivisions (state, | |
| | region, province, | |
| | prefecture) | |
| | | |
| A2 | county, parish, gun | King's County |
| | (JP), district (IN) | |
| | | |
| A3 | city, township, shi | New York |
| | (JP) | |
| | | |
| A4 | city division, | Manhattan |
| | borough, city | |
| | district, ward, chou | |
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| | (JP) | |
| | | |
| A5 | neighborhood, block | Morningside Heights |
| | | |
| A6 | street | Broadway |
| | | |
| PRD | Leading street | N, W |
| | direction | |
| | | |
| POD | Trailing street | SW |
| | suffix | |
| | | |
| STS | Street suffix | Avenue, Platz, |
| | | Street |
| | | |
| HNO | House number, | 123 |
| | numeric part only. | |
| | | |
| HNS | House number suffix | A, 1/2 |
| | | |
| LMK | Landmark or vanity | Low Library |
| | address | |
| | | |
| LOC | Additional location | Room 543 |
| | information | |
| | | |
| FLR | Floor | 5 |
| | | |
| NAM | Name (residence, | Joe's Barbershop |
| | business or office | |
| | occupant) | |
| | | |
| PC | Postal code | 10027-0401 |
+----------------------+----------------------+---------------------+
Table 1
Additional CA types are defined in Section 3.4 of [5]. These types
are useful to express further information about the location,
language specific settings via the 'language' item and encoding
information via the 'script' item. Section 14 shows usage examples
of this attribute.
All attributes are optional and can appear in any order. The values
are encoded using UTF-8 [6].
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5.2.2 Geospatial Location Information
This document reusing geospatial location information from [7] which
defines latitude, longitude, and altitude, with resolution indicators
for each. The value in the Altitude field either indicates meters or
floors (via the Altitude Type field). As a coordinate reference
system Section 2.1 of [7] defines (via extensible mechanism using
IANA registration) three values in the Datum field: WGS 84, NAD 83
(with the associated vertical datum for the North American Vertical
Datum of 1988), NAD 83 (with the associated vertical datum for the
Mean Lower Low Water (MLLW). WGS 84 is used by the GPS system.
During a protocol run it is possible to return Location-Information
attributes which provide both location information elements. If only
one location information element is provided then civil location MUST
be included in the request. Additionally, geospatial location MAY be
provided.
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6. Basic- and Extended-Policy-Rule Attributes
In some environments it is possible for the user to attach
information about its privacy preferences. These preferences allow
the visited network, intermediate RADIUS proxies and the home network
to authorize the distribution of the user's location information.
Without the user providing authorization information two approaches
are possible:
o The user hides its location information from the access network
and from intermediate networks using the appropriate network
access authentication mechanism. Section 15 discusses these
issues in more details.
o The access network attaches default authorization policies which
prevents intermediate networks and the home network to distribute
the location information to other entities. Additionally, the
home network might have authorization policies which control
distribution of location information. Users can dynamically
change their policies using the authroization framework defined in
[10] and [11].
With regard to authorization policies this document reuses work done
in [9] and encodes it in an non-XML format. Two fields ('sighting
time' and 'time-to-live') are additionally included in the
Location-Information attribute to conform to the Geopriv Requirements
[8], Section 2.7. Two RADIUS attributes are used for this purpose:
Basic-Policy-Rule and Extended-Policy-Rule attribute; The
Basic-Policy-Rule attribute contains a fixed set of privacy relevant
fields whereas the Extended-Policy-Rule attribute contains a
reference to a more extensive authorization rule set.
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7. Location-Type Attribute
This document defines a separate attribute for the type of the
location. Instead of the values of the 'type-of-place' attribute
defined in Section 4.6 of [12] which is reused by [5] we define our
own list of values for the Location-Type attribute. The reason for
this is given by the size constraints of the attribute, dependence to
other documents and to the location names required for the RADIUS
context. Consequently, CA type '25' which equals the placetype is
not used in the Location-Information attribute as described in
Section 5.2.
0 Reserved
1 Coffee Shop
2 Hotel
3 Airport
4 Mall
5 Restaurant
6 Bus
7 Library
8 Convention Center
9 School
10 Office
11 Airplane
12 Train
13 Ship
14 Educational Institute
15 Public Place
16 Other
Using these attribute types it is possible to describe the area in
more detail.
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8. Billing-Description Attribute
The Billing-Description Attribute contains unstructured text to be
printed on the users bill.
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9. Diameter RADIUS Interoperability
In deployments where both RADIUS clients talking with Diameter
Servers or Diameter Client talking with RADIUS server then a
translation agent will be deployed and operate in accordance to the
NASREQ specification [13].
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10. Attributes
This section defines attributes for access network operational
ownership, Location Name, Location Information and Billing
Description.
10.1 Operator-Name Attribute
Operator-Name Attribute SHOULD be sent in Access-Request, and
Accounting-Request records where the Acc-Status-Type is set to Start,
Interim, or Stop.
A summary of the Operator-Name Attribute is shown below.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Operator-Name ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type:
To Be Assigned by IANA - Operator-Name
Length:
>= 3 Bytes
Operator-Name:
The text field contains an Access Network Operator Name in
prefix-based format as describe above.
Example: REALM:anyisp.com
10.2 Location-Information Attribute
Location-Information attribute SHOULD be sent in Access-Request, and
Accounting-Request records where the Acc-Status-Type is set to Start,
Interim or Stop if available.
The Location-Information Attribute has two variations depending on
civil or geospatial location information. The format is shown below.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Code | Precision |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sighting Time ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sighting Time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time-to-Live ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time-to-Live |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Method | Location-Info ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type (8 bits):
To Be Assigned by IANA - Location-Information
Length (8 bits):
>= 3 Bytes
Code (8 bits):
Describes which location format is carried in this attribute:
(0) describes civil location information
(1) describes geospatial location information
All other bites of the Code field is reserved
and required for alignment.
Precision (8 bits):
Describes which location this attribute refers to:
(0) describes the location of the NAS
(1) describes the location of the AAA server
(2) describes the location of the end host (user)
(3) describes the location of the network
Sighting Time (64 bits):
NTP timestamp for the 'sighting time' field.
Time-to-Live (64 bits):
NTP timestamp for the 'time-to-live' field.
Method (8 bits):
Describes the way that the location information was
derived or discovered. The following values are currently
defined:
(0) Global Positioning System (GPS)
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(1) GPS with assistance (A-GPS)
(2) Manual configured information
(3) Provided by DHCP
(4) Triangulation: triangulated from time-of-arrival,
signal strength or similar measurements
(5) Cell: location of the cellular radio antenna
(6) IEEE 802.11 WLAN access point
Location-Info (variable):
Contains either civil or
geospatial location information attributes.
The following two fields need some explanation:
sighting time: This field indicates when the Location Information was
accurate. The data type of this field is a string and the format
is a 64 bit NTP timestamp [14].
time-to-live: This field gives a hint until when it should be
considered current. Note that the time-to-live field is different
than the 'retention-expires' rule. The data type of this field is
a string and the format is a 64 bit NTP timestamp [14].
For civil location information the Location-Info field in the above
structure is defined as followed:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Countrycode | Civic address elements ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Countrycode (16 bits):
Two-letter ISO 3166 country code in capital ASCII leters.
Civic address elements (variable):
The text field contains location information element.
The format of the civic address elements is described in Section 3.3
of [5] with a TLV pair (whereby the Type and Length fields are
one-octed long). An example is given in Section 14.
For geospatial location information the Location-Info field is
defined as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| LaRes | Latitude +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Latitude | LoRes | Longitude +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Longitude | AT | AltRes | Altitude +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Altitude | Datum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
LaRes (6 bits):
Latitude resolution
Latitude (34 bits)
LoRes (6 bits):
Longitude resolution.
Longitude (34 bits)
Altitude (30 bits)
AltRes (6 bits):
Altitude resolution
AT (4 bits):
Altitude Type for altitude. The following codes are defined:
(1) Meters
(2) Floors
Datum (8 bits):
Coordinate reference system
The following codes for the this field are defined:
(1) WGS 84
(2) NAD 83
(3) NAD 83
The length of the Location-Information Attribute MUST NOT exceed 253
octets. The length of the geospatial location information format is
fixed with 16 bytes plus a four byte header.
The Datum field contains an identifier for the coordinate system used
to interpret the values of Latitude, Longitude and Altitude. The
field with value (2) and the value (3) both represent the NAD 83
coordinate reference system but they differ from each other with
regard to their vertical datum representation as briefly noted in
Section 5.2.2 and described in more detail in [7].
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10.3 Basic Policy Rules Attribute
The Basic-Policy-Rules attribute MUST be sent in Access-Accept,
Access-Challenge, Access-and Access-Reject messages if Location
Information is transmitted with this exchange. If authorization
policy rules are available to the RADIUS client then the
Access-Request MUST carry the Basic-Policy-Rules attribute to to the
RADIUS server.
A summary of the Basic-Policy-Rules attribute is shown below.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |R| Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Retention Expires ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Retention Expires |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Note Well ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type :
To Be Assigned by IANA - Basic-Policy-Rules
Length:
> 3 Bytes
Flag (16 bits)
Only the first bit (R) is defined an corresponds to the
retransmission-allowed field. All other bits are reserved.
Retention Expires (64 bits)
NTP timestamp for the 'retention-expires' field.
Note Well (variable)
Contains a text with human readable privacy instructions.
Its length MUST NOT exceed 64 octets.
For this document we reuse the following fields of the 'usage-rules'
element, described in [9]:
retransmission-allowed: When the value of this element is '0', then
the recipient of this Location Object is not permitted to share
the enclosed Location Information, or the object as a whole, with
other parties. The value of '1' allows to share the Location
Information with other parties by considering the extended policy
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rules.
retention-expires: This field specifies an absolute date at which
time the Recipient is no longer permitted to possess the location
information. The data type of this field is a string and the
format is a 64 bit NTP timestamp [14].
note-well: This field contains a block of text with generic privacy
directives which are human-readable only. This field is useful
when Location Information is distributed to third party entities,
which can include humans in a location based service. RADIUS
entities are not supposed to process this field.
10.4 Extended Policy Rules Attribute
The Extended-Policy-Rules attribute SHOULD be sent in Access-Accept,
Access-Challenge, Access-and Access-Reject messages if Location
Information is transmitted with this exchange. If authorization
policy rules are available to the RADIUS client then the
Access-Request MUST carry the Basic-Policy-Rules attribute to to the
RADIUS server.
This attribute contains a variable length ruleset reference. This
attribute contains a URI that indicates where a fuller ruleset of
policies related to this object can be found. The full ruleset
SHOULD be fetched using Transport Layer Security (TLS). As a
deviation from [9] this field only contains a reference and does not
carry an attached rule set. This modification is motivated by the
size limitations imposed by RADIUS.
A summary of the Extended-Policy-Rules attribute is shown below.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Ruleset reference ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type :
To Be Assigned by IANA - Extended-Policy-Rules
Length:
> 3 Bytes
Ruleset reference:
The text field contains a reference to the policy rules
(see 'usage-rules' field description).
Its length MUST NOT exceed 64 octets.
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10.5 Location-Type Attribute
Location-Type Attribute SHOULD be sent in Access-Request, and
Accounting-Request records where the Acc-Status-Type is set to Start,
Interim, or Stop if available.
A summary of the Location-Type Attribute is shown below.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Loc-Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type (8 bits):
To Be Assigned by IANA - Location-Name
Length (8 bits):
4 Bytes
Loc-Type (16 bits):
The content of this field corresponds to the integer codes for
access network location type.
10.6 Billing-Description Attribute
The Billing-Description attribute contains unstructured text to be
printed on the users bill.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Billing-Text ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type (8 bits):
To Be Assigned by IANA - Billing-Description
Length (8 bits):
>= 3 Bytes
Billing-Text (variable):
The content of this field contains text for billing purpose.
The length of the Billing-Description attribute MUST NOT exceed 32
octets.
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11. Table of Attributes
The following table provides a guide to which attributes may be found
in which kinds of packets, and in what quantity.
Request Accept Reject Challenge Accounting # Attribute
Request
0-1 0 0 0 0-1 TBD Operator-Name
0+ 0 0 0 0+ TBD Location-Information
0-1 0-1 0-1 0-1 0-1 TBD Basic-Policy-Rules
0-1 0-1 0-1 0-1 0-1 TBD Extended-Policy-Rules
0-1 0 0 0 0-1 TBD Location-Type
0-1 0 0 0 0-1 TBD Billing-Description
The Location-Information attribute may appear more than once. This
is useful if the size of one Location-Information attribute exceeds
the maximum size of an AVP. This might happen in case of civil
location which has a variable number of fields. The fields used for
the civil location information format of the Location-Information AVP
(see Section 5.2.1 MUST NOT appear more than once.
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12. IANA Considerations
This document requires the assignment of four new RADIUS attribute
numbers for the following attributes:
Operator-Name
Location-Information
Basic-Policy-Rules
Extended-Policy-Rules
Location-Name
Billing-Description
Please refer to Section 11 for the registered list of numbers.
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13. Matching with Geopriv Requirements
This section compares the Geopriv requirements described in [8] and
the approach of distributing Location Objects with RADIUS.
First, we differentiate between the two scenarios in Section 13.1 and
Section 13.2. These two scenarios focus on the privacy related
aspects descrbed in Section 4. Section 13.3 then matches the Geopriv
requirements against these two scenarios.
13.1 Distribution of Location Information at the User's Home Network
This paragraph focuses on a scenario whereby the RADIUS protocol
transport iocation information from the Location Generator (e.g.,
local AAA server) to the Location Server (e.g., home AAA server). To
use a more generic scenario we assume that the visited AAA and the
home AAA server belong to different administrative domains. The
Location Recipient obtains location information about a particular
Target via protocols specified outside the scope this document (e.g.,
SIP, HTTP or an API).
Please note that the main usage scenario defined in this document
assumes that the Location Server and the Location Recipient are
co-located into a single entity with regard to location based network
access authorization, taxation and billing. The usage of SIP or HTTP
to distribute location information to third party entities is not the
main envised use case. However, the authors are aware of the fact
that the user's location information might be used in a non-intended
way. To reflect the users privacy even in these cases it is
necessary to offer appropriate mechanisms also for this environments.
The Target is the user requesting network access.
The subsequent figure shows the interacting entities graphically.
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visited network | home network
|
| +----------+
| | Rule |
| | Holder |
| | |
| +----+-----+
| |
| rule|interface
| V
+----------+ | +----------+ +----------+
|Location | publication | Location | notification |Location |
|Generator |<------------->| Server |<------------->|Recipient |
| | interface | | interface | |
+----------+ | +----------+ +----------+
|
Local AAA RADIUS Home AAA SIP/HTTP/API/etc.
Server | Server
|
Figure 15: Location Server at the Home Network
13.2 Distribution of Location Information at the Visited Network
This paragraph describes a scenario which might happen during the
deployment but is not within the focus of this document.
In order for this scenario to be applicable a few assumptions must
hold:
o The visited network deploys a Location Server and wants to
distribute Location Objects of a user
o The visited network is able to learn the user identity of the user
The visited network provides location information to a Location
Recipient (e.g., via SIP or HTTP). During the network access
authentication procedure the visited network is able to retrieve
authorization policies of the user via RADIUS from the home AAA
server.
The subsequent figure shows the interacting entities graphically.
The transport of the Location Object is not shown in this figure
since this aspect is already covered in the previous paragraph.
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visited network | home network
|
+----------+ |
|Location | |
|Recipient | |
| | |
+----------+ |
^ | +----------+
| | | Rule |
| | | Holder |
notification | | |
interface | +----+-----+
| | |
| | rule|interface
v | V
+----------+ | +----------+
|Location | Rule Transport| Home AAA |
|Generator |<------------->| Server |
|& Server | RADIUS | |
+----------+ | +----------+
|
Figure 16: Location Server at the Visited Network
13.3 Requirements matching
Section 7.1 of [8] details the requirements of a "Location Object".
There are:
Req. 1. (Location Object generalities):
* Regarding requirement 1.1, the Location Object has to be
understood by the RADIUS server (and possibly a Diameter server
in case of interworking between the two) as defined in this
document. Due to the encoding of the Location Object it is
possible to convert it to the format used in GMLv3. The same
civil location information format is used in PIDF-LO and this
document.
* Regarding requirement 1.2, some fields of the Location Object
defined in this document are optional. See Section 5.2.1 as an
example.
* Regarding requirement 1.3, the inclusion of the Location-Type
attribute which gives a further classification of the location.
This attribute can be seen as an extension.
* Regarding requirement 1.4, the Location Object is extensible in
the same fashion as RADIUS is extensible.
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* Regarding requirement 1.5, the Location Object is useful for
both receiving and sending location information as described in
this document.
* Regarding requirement 1.6, the Location Object contains both,
location information and privacy rules. Location information
is described in Section 5.2 and the corresponding privacy rules
are detailed in Section 10.3 and in Section 10.4.
* Regarding requirement 1.7, the Location Object is usable in a
variety of protocols. The format of the object is reused from
other documents as detailed in the respective sections (see
Section 5.2, Section 10.3 and in Section 10.4).
* Regarding requirement 1.8, the encoding of the Location Object
has an emphasis on a lighweight encoding format. As such it is
useable on constrained devices.
Req. 2. (Location Object fields):
* Regarding requirement 2.1, the Target Identifier is carried
within the network access authentication protocol (e.g., within
the EAP-Identity Response when EAP is used and/or within the
EAP method itself). As described in Section 15 it has a number
of advantages if this identifier is not carried in clear text.
This is possible with cetain EAP methods whereby the identity
in the EAP-Identity Response only contains information relevant
for routing the response to the users home network. The true
user identity is protected by the authentication and key
exchange protocol.
* Regarding requirement 2.2, the Location Recipient Identity is,
in the main scenario the home AAA server. This entity is
located using the structure of the Network Access Identifier.
For a scenario where the Location Recipient is obtaining
Location Information from the Location Server via HTTP or SIP
the respective mechanisms defined in these protocols are used
to identify the recipient. The Location Generator cannot, a
priori, know the recipients if they are not defined in this
protocol.
* Regarding requirement 2.3, the credentials of the Location
Recipient are known to the RADIUS entities based on the
security mechanisms defined in the RADIUS protocol itself.
Section 16 describes these security mechanisms offered by the
RADIUS protocol. The same is true for requirement 2.4.
* Regarding requirement 2.5, Section 5.2 describes the content of
the Location Field. Motion and direction vectors as listed in
requirement 2.6 are not provided as attributes. It is,
however, possible to deduce the motion and direction of an
entity via the Mid-session Delivery mechanism as shown in
Figure 2.
* Regarding requirement 2.6, this document only describes one
Location Data Type for civil and for geospatial location
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information, respectively. No negotiation needs to take place.
* Regarding requirement 2.7, timing information is provided with
'sighting time' and 'time-to-live' field defined in Section
10.3.
* Regarding requirement 2.8, a reference to an external (more
detailed ruleset) is provided with the Section 10.4 attribute.
* Regarding requirement 2.9, security headers and trailers are
provided as part of the RADIUS protocol or even as part of
IPsec.
* Regarding requirement 2.10, a version number in RADIUS is
provided with the IANA registration of the attributes. New
attributes are assigned a new IANA number.
Req. 3. (Location Data Types):
* Regarding requirement 3.1, this document defines two Location
Data Types as described in Section 5.2.
* With the support of civil and geospatial location information
support requirement 3.2 is fullfilled.
* Regarding requirement 3.3, geospatial location information only
supports absolute coordinates rather than a delta. However,
the granuality of the location information can be reduced with
the help of the AltRes, LoRes, LaRes fields described in the
Location-Information attribute (see Section 10.2).
* Regarding requirement 3.4, further Location Data Types can be
added via new coordinate reference systems (CRSs) (see Datum
field in the Location-Information attribut of Section 5.2),
extensions to existing fields (e.g., new location types as
shown in Section 7) or via additional attributes.
Section 7.2 of [8] details the requirements of a "Using Protocol".
There are:
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. This
document requires, that RADIUS entities sending or receiving
location MUST obey such instructions.
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. Section 16 specifies how security mechanisms are
used in RADIUS and how they can be reused to provide security
protection for the Location Object. Additionally, the privacy
considerations (see Section 15) are also applicable for this
discussion.
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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.
The encoding of the Location Object is specifically tailored
towards the inclusion into a single message that even respects the
(Path) MTU size. The concept of a transaction is not immediately
applicable to RADIUS.
Section 7.3 of [8] details the requirements of a "Rule based Location
Data Transfer".
There are:
Req. 7. (LS Rules): With the scenario shown in Figure 15 the
decision of a Location Server to provide a Location Recipient
access to location information is based on Rule Maker-defined
Privacy Rules which are stored at the home network or are
accessible for the home network. With regard to the scenario
shown in Figure 16 the Rule Maker-defined Privacy Rules are sent
from the home network to the visited network as part of the
Policy-Information attribute (see Section 10.3, Section 10.4 and
Section 15 for more details).
Req. 8. (LG Rules): It is possible for the non-initial transmission
(i.e., mid-session delivery) of a Location Object to enforce the
users privacy rules. For the initial transmission of a Location
Object the user would have to use network access authentication
methods which provide user identity confidentiality which would
render the Location Object completely useless for the visited
network. For the scenario shown in Figure 15 the visited network
is already in possession of the users location information prior
to the authentication and authorization of the user (which might
require several roundtrips). A correlation between the location
and the user identity might, however, still not be possible for
the visited network (as explained in Section 15). The visited
network MUST evaluate ruleset provided by the home AAA server as
soon as possible.
Req. 9. (Viewer Rules): The Rule Maker might define (via mechanisms
outside the scope of this document) which policy rules are
disclosed to other entities.
Req. 10. (Full Rule language): Geopriv has defined a rule language
capable of expressing a wide range of privacy rules which is
applicable in this area concerning the distribution of Location
Objects. A basic ruleset is provided with the Basic-Policy-Rules
attribute Section 10.3. A reference to the extended ruleset is
carried in Section 10.4. The format of these rules are described
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in [10] and [11].
Req. 11. (Limited Rule language): A limited (or basic) ruleset is
provided by the Policy-Information attribute Section 10.3 (and as
introduced with PIDF-LO [9]).
Section 7.4 of [8] details the requirements of a "Location Object
Privacy and Security".
There are:
Req. 12 (Identity Protection): Support for unlinkable pseudonyms is
provided by the usage of a corresponding authentication and key
exchange protocol. Such protocols are available, for example,
with the support of EAP as network access authentication methods.
Some EAP methods support passive user identitiy confidentiality
whereas others even support active user identity confidentiality.
This issue is further discussed in Section 16. The importance for
user identity confidentiality and identity protection has already
been recognized (see for example a document on 'EAP Method
Requirements for Wireless LANs' [15]).
Req. 13. (Credential Requirements): As described in Section 16
RADIUS signaling messages can be protected with IPsec. This
allows a number of authentication and key exchange protocols to be
used as part of IKE, IKEv2 or KINK.
Req. 14. (Security Features): Geopriv defines a few security
requirements for the protection of Location Objects such as mutual
end-point authentication, data object integrity, data object
confidentiality and replay protection. As described in Section 16
these requirements are fullfilled with the usage of IPsec if the
mutual authentication refers to the RADIUS entities (acting as
various Geopriv entities) which directly communicate with each
other.
Req. 15. (Minimal Crypto): A minimum of security mechanisms are
mandated by the usage of RADIUS. Security for Location Objects is
provided by the RADIUS protocol (including IPsec and its dynamic
key management framework) rather than on relying on object
security via S/SIME (which is not available with RADIUS). The
handling of emergency calls is not specified as part of the RADIUS
protocol and subject for an architectural investigation. As such
it might not even be applicable to RADIUS itself.
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14. Example
This section provides an example for a civil location information
format within the Location-Information attribute. The size of the
geo-spatial location information object is fixed and well-described
examples can be found in the Appendix of [7].
Due to the size limitations of the RADIUS attributes we give a more
detailed example borrowed from Section 4 of [5].
+-------------+-----------+-------------------+
| Type | Length | Value |
+-------------+-----------+-------------------+
| Type | 8 bits | TBD |
| Length | 8 bits | 43 |
| Code | 16 bits | 1 |
| Precision | 8 bits | 2 |
| Countrycode | 16 bits | DE |
| CAtype | 8 bits | 1 |
| CAlength | 8 bits | 7 |
| CAvalue | 7 bytes | Bavaria |
| CAtype | 8 bits | 3 |
| CAlength | 8 bits | 6 |
| CAvalue | 6 byte | Munich |
| CAtype | 8 bits | 6 |
| CAlength | 8 bits | 11 |
| CAvalue | 11 bytes | Marienplatz |
| CAtype | 8 bits | 19 |
| CAlength | 8 bits | 1 |
| CAvalue | 1 byte | 8 |
| CAtype | 8 bits | 24 |
| CAlength | 8 bits | 5 |
| CAvalue | 5 bytes | 80331 |
+-------------+-----------+-------------------+
The Length element provides the length of the entire payload minus
the length of the initial 'Type', the 'Length' and the 'Code'
attribute. The Precision field has a value of '2' which refers to
the location of the end host (user). The CountryCode is set to 'DE'.
Note that the subsequent attributes are in Type-Length-Value format.
Type '1' indicates the region of 'Bavaria', '3' refers to the city
'Munich', '6' to the street 'Marienplatz', the house number '8' is
indicated by the type '19' and the zip code of '80331' is of type
'24'.
The total sum of these attributes is 46 bytes.
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15. Privacy Considerations
This section discusses privacy implications for the distribution of
location lnformation within RADIUS.
In many cases the location information of the network also reveals
the current location of the user with a certain degree of precision
depending on the mechanism used, the positioning system, update
frequence, where the location was generated, size of the network and
other mechanisms (such as movement traces or interpolation).
Two entities might act as Location Servers as shown in Section 4,
Figure 15 or in Figure 16:
15.1 Entity in the visited network
In this scenario it is be difficult to obtain authorization policies
from the end host (or user) immediately when the user attaches to the
network. In this case we have to assume that the visited network
does not allow unrestricted distribution of location information
other than the intended recipients (e.g, to third party entities)
immediately.
The visited network MUST behave according to the following
guidelines:
o Per default only the home network is allowed to receive location
information. The visited network MUST NOT distribute location
information to third parties without seeing the user's privacy
rule se.
o If the home network provides the Basic-Policy-Rules attribute
either as part of the Access-Accept, the Access-Reject or the
Access-Challenge message then the visited network MUST follow the
guidance given with these rules.
o If the home network provides the Extended-Policy-Rules attributes
either as part of the Access-Accept, the Access-Reject or the
Access-Challenge message then the visited network MUST fetch the
full ruleset at the indicated URL and MUST follow the guidance
given with these rules.
o If the RADIUS client in the visited network learns the basic rule
set or a reference to the extended rule set by means outside the
RADIUS protocol (e.g., provided by the end host) then it MUST
include the Basic-Policy-Rules and the Extended-Policy-Rules
attribute in the Access-Request message towards the home AAA
server. Furthermore, the visited network MUST evaluate these
rules prior to the transmission of Location Information either to
the home network or a third party. The visited network MUST
follow the guidance given with these rules.
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o If the RADIUS client in the visited network received the
Basic-Policy-Rules attribute with Access-Accept or the
Access-Challenge message then the Basic-Policy-Rules MUST be
attach in subsequent RADIUS messages which contain the
Location-Information attribute (such as interim accounting
messages).
o If the RADIUS client in the visited network received the
Extended-Policy-Rules attribute with Access-Accept or the
Access-Challenge message then the Basic-Policy-Rules attribute
MUST be attach in subsequent RADIUS messages which contain the
Location-Information attribute (such as interim accounting
messages).
15.2 Entity in the home network
The AAA server in the home network might be an ideal place for
storing authorization policies. The user typically has a contractual
relationship to his home network and hence the trust relationship
between them are higher. Once the infrastructure is deployed and
useful applications are available there might be a strong desire to
use location information for other purposes as well (such as location
aware applications). Authorization policy rules described in [11]
and in [10] are tailored for this environment. These policies might
be useful for preventing further distribution of the user's location
to other location based services. The home AAA server (or a similar
entity) thereby acts as a location server for access to location
services.
The home network MUST behave according to the following guidelines:
o As a default policy the home network MUST NOT distribute the
user's location information to third party entities.
o If a user provided basic authorization policies then these rules
MUST be returned to the visited network in the Access-Accept, the
Access-Reject or the Access-Challenge message.
o If a user provided basic authorization policies then these rules
MUST be returned to the visited network in the Access-Accept, the
Access-Reject or the Access-Challenge message.
o If a user provided extended authorization policies then they MUST
be accessible for the visited networking using a reference to
these rule set. The Extended-Policy-Rules attribute MUST include
the reference and they MUST be sent to the visited network in the
Access-Accept, the Access-Reject or the Access-Challenge message.
o The home network MUST follow the user provided rule set for both
local storage and for further distribution. With regard to the
usage of these rules the home network MUST ensure that the users
preferences are taken care of within the given boundaries (such as
legal regulations or operational considerations). For example, a
user might not want the home network to store information about
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its Location Information beyond a indicated time frame. However,
a user might on the other hand want to ensure that disputes
concerning the billed amount can be resolved. Location
Information might help to resolve the dispute. The user might,
for example, be able to show that he has never been at the
indicated place.
o If the policy rules provided by the user indicate that location
information must not be distributed at all then the home network
MUST provide the Basic-Policy-Rules to the RADIUS entity in the
visited network via an Access-Accept, the Access-Reject or the
Access-Challenge message. The RADIUS server in the user's home
network would set the 'Retention-Expires' and the
'Retransmission-allowed' field to the user indicated value. and
the Extended-Policy-Rules to particular recipients
For the envisioned usage scenarios the network access authentication
procedure is tighly coupled to the transfer of location information.
If the authentication mechanism allows the visited network or AAA
brokers to learn the user's identity then it is possible to
correleate location information with a particular user. As such, it
allows the visited network and brokers to learn movement patterns of
users.
A scenario where the user is attached to the home network is, from a
privacy point of view, simpler than a scenario where a user roams
into a visited network since the NAS and the home AAA are in the same
administrative domain. No direct relationship between the visited
and the home network operator may be available available and some AAA
brokers need to be consulted. With subscription-based network access
as used today the user has a contractual relationship with the home
network provider which could allow higher privacy considerations to
be applied (including policy rules stored at the home network itself
for the purpose of restricting further distribution).
In many cases it is necessary to secure the transport of location
information along the RADIUS infrastructure. Mechanism to achieve
this functionality are discussed in Section 16.
One way to ensure that the visited network and intermediate networks
are incapable to learn the user identity is to use EAP methods that
hide the user's identity either actively or passively. Some EAP
methods (such as [16]) protect the user's identity against passive
adversaries by utilizing temporal identities. In some cases the
visited network is still able to retrieve the plaintext identity of
the user and user identity confidentiality is only provided against
eavesdroppers at the wireless link. Depending on the movement
patters of the user, the network topology and available roaming
agreements it is possible that a AAA broker is able to see both the
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plaintext user identity and subsequent temporal identities.
Associating location information and the user identity is possible in
these cases.
It is assumed that the true username is not carried within the
initial EAP-Identity Request/Response message exchange. Support for
username privacy is supported with [17].
For stronger security and privacy protection active user identity
confidentiality is highly suggested. EAP methods such as [18] or
[19] provide such a protection.
Unfortunately, most users are not educated about the importance of
user identity confidentiality and many EAP methods do not provide
active user identity confidentiality. User identity confidentiality
is often treated as an exotic features which mainly aims to prevent
eavesdroppers on the wireless link to learn the user identity of the
attached users. Awareness for this threat type does often not exist.
In many cases it is even not possible for users to freely select
their favorite authentication and key exchange protocol (based on
their security requirements). Instead the choice is often
predetermined by a given architecture.
It was noted that different granularity of location information can
be provided to the home network. From a privacy point of view lower
granularity is preferrable. The user, however, has no control over
the granularity and cannot lie about its location.
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16. Security Considerations
Requirements for the security protection of a Location Object is
defined in [8]: Mutual end-point authentication, data object
integrity, data object confidentiality and replay protection. The
distribution of location information can be restricted with the help
of authorization policies. Basic authorization policies are attached
to the location information itself, in the same fashion as described
in [9]. It is possible that the user was already able to transfer
some authorization policies to the access network to restrict the
distribution of location information. This is, however, rather
unlikely in case of roaming users. Hence, it will be primarily the
NAS creating the Location Object which also sets the authorization
policies. If no authorization information is provided by the user
then the visited network MUST set the authorization policies to only
allow the home AAA server to use the provided location information.
Other entities, such as the visited network and possibly AAA brokers
MUST NOT use the location information for a purpose other than
described in this document. More extensible authorization policies
can be stored at the user's home network. These policies are useful
when location information is distributed to other entities in a
location-based service. This scenario is, however, outside the scope
of this document.
It is necessary to use authorization policies to prevent the
unauthorized distribution of location information. The security
requirements which are created based on [8] are inline with threats
which appear in the relationship with disclosure of location
information as described in [20]. [9] proposes S/MIME to protect the
Location Object against modifications and against eavesdropping. To
provide mutual authentication confidentiality protection and a
digital signature is necessary. Furthermore, to offer replay
protection a gurantee of freshness is necessary (for example, based
on timestamps).
The security of S/SIME is based on public key cryptography which
raises performance, deployment and size considerations. Encryption
requires that the local AAA server or the NAS knows the recipient's
public key (e.g., the public key of the home AAA server). Knowing
the final recipient of the location information is in fact impossible
for RADIUS entities. Some sort of public key infrastructure would be
required to obtain the public key and to verify the digital signature
(at the home network). Providing per-object cryptographic protection
is, both at the home and at the visited network, computationally
expensive.
If no authentication, integrity and replay protection between the
participating RADIUS entities is provided then an adversaries can
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spoof and modify transmitted AVPs. Two security mechanisms are
proposed for RADIUS:
o [1] proposes the usage of a static key which might raise some
concerns about the lack dynamic key management.
o RADIUS over IPsec [21] allows to run standard key management
mechanisms, such as KINK [22], IKE and IKEv2 [23], to establish
IPsec security associations. Confidentiality protection MUST be
used to prevent eavesdropper gaining access to location
information. Confidentiality protection is not only a property
required by this document, it is also required for the transport
of keying material in the context of EAP authentication and
authorization. Hence, this requirement is, in many environments,
already fulfilled. Mutual authentication must be provided between
the local AAA server and the home AAA server to prevent
man-in-the-middle attacks. This is another requirement raised in
the area of key transport with RADIUS and does not represent a
deployment obstacle. The performance advantages a superior
compared to the usage of S/MIME and object security since the
expensive authentication and key exchange protocol run needs to be
provided only once (at for a long time). Symmetric channel
security with IPsec is highly efficient. Since IPsec protection
is suggested as a mechanism to protect RAIDUS already no
additional considerations need to be addressed beyond those
described in [21]. Where an untrusted AAA intermediary is
present, the Location Object MUST NOT be provided to the
intermediary.
In case that IPsec protection is not available for some reason and
RADIUS specific security mechanisms have to be used then the
following considerations apply. The Access-Request message is not
integrity protected. This would allow an adversary to change the
contents of the Location Object or to insert and modify attributes
and fields or to delete attributes. To address these problems the
Message-Authenticator (80) can be used to integrity protect the
entire Access-Request packet. The Message-Authenticator (80) is also
required when EAP is used and hence is supported by many modern
RADIUS servers.
Access-Request packets including Location attribute(s) without a
Message-Authenticator(80) attribute SHOULD be silently discarded by
the RADIUS server. A RADIUS server supporting the Location
attributes MUST calculate the correct value of the
Message-Authenticator(80) and MUST silently discard the packet if it
does not match the value sent.
Access-Accept, including Location attribute(s) without a
Message-Authenticator(80) attribute SHOULD be silently discarded by
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the NAS. A NAS supporting the Location attribute MUST calculate the
correct value of a received Message-Authenticator(80) and MUST
silently discard the packet if it does not match the value sent.
RADIUS and DIAMETER make some assumptions about the trust between
traversed AAA entities in sense that object level security is not
provided by neither RADIUS nor DIAMETER. Hence, some trust has to be
placed on the AAA entities to behave according to the defined rules.
Furthermore, the AAA protocols do not involve the user in their
protocol interaction except for tunneling authentication information
(such as EAP messages) through their infrastructure. RADIUS and
DIAMETER have even become a de-facto protocol for key distribution.
Hence, in the past there were some concerns about the trust placed
into the infrastructure particularly from the security area when it
comes to keying. [24] documents this keying infrastructure and the
security implications. The uniqueness of the AAA infrastructure
therefore raises some concerns about the interpretation of the
retention and redistribution restrictions. The privacy guidelines
listed in Section 15 are applicable in this context.
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17. Acknowledgments
The authors would like to thank the following people for their help
with a previous version of this draft and for their input:
Chuck Black
Paul Congdon
Jouni Korhonen
Sami Ala-luukko
Farooq Bari
Ed Van Horne
Mark Grayson
Jukkat Tuomi
Jorge Cuellar
Christian Guenther
Henning Schulzrinne provided the civil location information content
found in this draft. The geospatial location information format is
based on work done by J. Polk, J. Schnizlein and M. Linsner. The
authorization policy format is based on the work done by Jon
Peterson.
The authors would like to thank Victor Lortz, Jose Puthenkulam,
Bernrad Aboba, Jari Arkko, Parviz Yegani, Serge Manning, Kuntal
Chowdury, Pasi Eronen, Blair Bullock and Eugene Chang for their
feedback to an initial version of this draft.
This document is based on the discussions within the IETF GEOPRIV
working group. Therefore, the authors thank Henning Schulzrinne,
James Polk, John Morris, Allison Mankin, Randall Gellens, Andrew
Newton, Ted Hardie, Jon Peterson for their time to discuss a number
of issues with us. We think Stephen Hayes for aligning this work
with 3GPP activities.
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18. References
18.1 Normative References
[1] Rigney, C., Willens, S., Rubens, A. and W. Simpson, "Remote
Authentication Dial In User Service (RADIUS)", RFC 2865, June
2000.
[2] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", March 1997.
[3] Rigney, C., "RADIUS Accounting", RFC 2866, June 2000.
[4] Chiba, M., Dommety, G., Eklund, M., Mitton, D. and B. Aboba,
"Dynamic Authorization Extensions to Remote Authentication Dial
In User Service (RADIUS)", RFC 3576, July 2003.
[5] Schulzrinne, H., "Dynamic Host Configuration Protocol (DHCPv4
and DHCPv6) Option for Civic Addresses",
draft-ietf-geopriv-dhcp-civil-03 (work in progress), July 2004.
[6] Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD
63, RFC 3629, November 2003.
[7] Polk, J., Schnizlein, J. and M. Linsner, "Dynamic Host
Configuration Protocol Option for Coordinate-based Location
Configuration Information", RFC 3825, July 2004.
18.2 Informative References
[8] Cuellar, J., Morris, J., Mulligan, D., Peterson, D. and D.
Polk, "Geopriv Requirements", RFC 3693, February 2004.
[9] Peterson, J., "A Presence-based GEOPRIV Location Object
Format", draft-ietf-geopriv-pidf-lo-03 (work in progress),
September 2004.
[10] Schulzrinne, H., "A Document Format for Expressing Privacy
Preferences", draft-ietf-geopriv-common-policy-01 (work in
progress), July 2004.
[11] Schulzrinne, H., "A Document Format for Expressing Privacy
Preferences for Location Information",
draft-ietf-geopriv-policy-02 (work in progress), July 2004.
[12] Schulzrinne, H., Gurbani, V., Kyzivat, P. and J. Rosenberg,
"RPID: Rich Presence: Extensions to the Presence Information
Data Format (PIDF)", draft-ietf-simple-rpid-03 (work in
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progress), March 2004.
[13] Calhoun, P., Zorn, G., Spence, D. and D. Mitton, "Diameter
Network Access Server Application",
draft-ietf-aaa-diameter-nasreq-17 (work in progress), July
2004.
[14] Mills, D., "Network Time Protocol (Version 3) Specification,
Implementation", RFC 1305, March 1992.
[15] Stanley, D., Walker, J. and B. Aboba, "EAP Method Requirements
for Wireless LANs", draft-walker-ieee802-req-04 (work in
progress), August 2004.
[16] Arkko, J. and H. Haverinen, "EAP AKA Authentication",
draft-arkko-pppext-eap-aka-12 (work in progress), April 2004.
[17] Aboba, B., "The Network Access Identifier",
draft-arkko-roamops-rfc2486bis-02 (work in progress), July
2004.
[18] Josefsson, S., Palekar, A., Simon, D. and G. Zorn, "Protected
EAP Protocol (PEAP) Version 2",
draft-josefsson-pppext-eap-tls-eap-08 (work in progress), July
2004.
[19] Tschofenig, H. and D. Kroeselberg, "EAP IKEv2 Method
(EAP-IKEv2)", draft-tschofenig-eap-ikev2-04 (work in progress),
July 2004.
[20] Danley, M., "Threat Analysis of the Geopriv Protocol", RFC
3694, September 2003, <reference.RFC3694.xml>.
[21] Aboba, B. and P. Calhoun, "RADIUS (Remote Authentication Dial
In User Service) Support For Extensible Authentication Protocol
(EAP)", RFC 3579, September 2003.
[22] Thomas, M. and J. Vilhuber, "Kerberized Internet Negotiation of
Keys (KINK)", draft-ietf-kink-kink-06 (work in progress), July
2004.
[23] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
draft-ietf-ipsec-ikev2-17 (work in progress), October 2004.
[24] Aboba, B., "Extensible Authentication Protocol (EAP) Key
Management Framework", draft-ietf-eap-keying-03 (work in
progress), July 2004.
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[25] Adrangi, F., "Access Network Bandwidth Capability",
draft-adrangi-radius-bandwidth-capability-01 (work in
progress), July 2004.
Authors' Addresses
Hannes Tschofenig
Siemens
Otto-Hahn-Ring 6
Munich, Bayern 81739
Germany
EMail: Hannes.Tschofenig@siemens.com
F. Adrangi
Intel Corporatation
2111 N.E. 25th Avenue
Hillsboro OR
USA
EMail: farid.adrangi@intel.com
Avi Lior
Bridgewater Systems Corporation
303 Terry Fox Drive
Ottawa, Ontario K2K 3J1
CANADA
EMail: avi@bridgewatersystems.com
Mark Jones
Bridgewater Systems Corporation
303 Terry Fox Drive
Ottawa, Ontario K2K 3J1
CANADA
EMail: mark.jones@bridgewatersystems.com
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