wdiff draft-ietf-ecrit-trustworthy-location-04.txt draft-ietf-ecrit-trustworthy-location-05.txt

ECRIT Working Group H. Tschofenig
INTERNET-DRAFT Nokia Siemens Networks
Category: Informational H. Schulzrinne
Expires: April 22, September 12, 2013 Columbia University
B. Aboba (ed.)
Microsoft Corporation
22 October 2012
13 March 2013

Trustworthy Location
draft-ietf-ecrit-trustworthy-location-04.txt
draft-ietf-ecrit-trustworthy-location-05.txt

Abstract

For some location-based applications, such as emergency calling or
roadside assistance, the trustworthiness of location information is
critically important.

This document describes how to convey location in a manner that is
inherently secure and reliable. It also provides guidelines for
assessing the problem trustworthiness of "trustworthy location" as well
as potential solutions. location information.

Status of This Memo

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provisions of BCP 78 and BCP 79.

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This Internet-Draft will expire on April 22, September 12, 2013.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Emergency Services Architecture . . . . . . . . . . . . . . . 4
3.
2. Threats . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. 5
2.1. Location Spoofing . . . . . . . . . . . . . . . . . . . . 6
3.2.
2.2. Identity Spoofing . . . . . . . . . . . . . . . . . . . . 7
4. Solution Proposals
3. Solutions . . . . . . . . . . . . . . . . . . . . . . 8
4.1. Location Signing . . . . 7
3.1. Signed Location by Value . . . . . . . . . . . . . . . . . 8
4.2.
3.2. Location by Reference . . . . . . . . . . . . . . . . . . 10
4.3.
3.3. Proxy Adding Location . . . . . . . . . . . . . . . . . . 11
5. Operational Considerations . . . . . . . . . . . . . . . . . . 12
5.1. Attribution to a Specific Trusted Source . . . . . . . . . 12
5.2. Application to a Specific Point in Time . . . . 13
4. Location Trust Assessment . . . . . 16
5.3. Linkage to a Specific Endpoint . . . . . . . . . . . . . . 17
6. 15
5. Security Considerations . . . . . . . . . . . . . . . . . . . 17
7.
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
8. Acknowledgments 19
7. References . . . . . . . . . . . . . . . . . . . . . . . . 18
9. References . . 19
7.1. Informative references . . . . . . . . . . . . . . . . . . 19
Acknowledgments . . . . . . . 18
9.1. Informative references . . . . . . . . . . . . . . . . . . 18 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21 22

1. Introduction

Several public and commercial services depend upon location
information in their operations. This includes emergency services
(such as fire, ambulance and police) as well as commercial services
such as food delivery and roadside assistance.

Services that depend on accurate location commonly experience security issues
today. While prank calls have been a problem for emergency services
dating back to the time of street corner call boxes, a recent increase in with the frequency and sophistication of move to
IP-based emergency services, the ability to launch automated attacks
has lead increased. As the European Emergency Number Association (EENA)
has noted [EENA]: "False emergency calls divert emergency services
away from people who may be in life-threatening situations and who
need urgent help. This can mean the difference between life and
death for someone in trouble."

EENA [EENA] has attempted to define terminology and describe best
current practices for dealing with false emergency calls, which in
certain European countries can constitute as much as 70% of all
emergency calls. Reducing the FBI issuing number of prank calls represents a warning [Swatting].
challenge, since emergency services authorities in most countries are
required to answer every call (whenever possible). Where the caller
cannot be identified, the ability to prosecute is limited.

Since prank emergency calls can endanger bystanders or emergency
services personnel, or divert resources away from legitimate
emergencies, they can be life threatening.

It should be kept in mind that issues of location trust and
attribution are closely linked. In situations where tracing A particularly dangerous
form of prank call is "swatting" - an prank emergency call back to the originator is more difficult, experience
has shown that the frequency of nuisance calls can rise dramatically.
For example, where emergency calls have been allowed draws
a response from handsets
lacking law enforcement (e.g. a SIM card, or where ownership fake hostage situation that
results in dispatching of a "Special Weapons And Tactics" (SWAT)
team). In 2008 the SIM card cannot be
determined, FBI issued a warning [Swatting] about an increase
in the frequency and sophistication of nuisance calls has often been
unacceptably high [TASMANIA][UK][SA].

Conversely, where these attacks.

Many documented cases of "swatting" involve not only the ability exists enable faking of an investigator to
determine
emergency, but also the originator absence of a prank emergency call after the fact, accurate caller identification and
the trustworthiness delivery of misleading location data. Today these attacks are
often carried out by providing false caller identification, since for
circuit-switched calls from landlines, location provided to the PSAP
is likely determined from a lookup using the calling telephone number. With
IP-based emergency services, in addition to improve, even without the introduction of measures potential for false
caller identification, it is also possible to limit attach misleading
location spoofing. Under a
court order, an investigator can have access to additional information beyond the messages conveyed in to the emergency call. For
example, in such

Ideally, a situation, audit logs will often call taker at a PSAP should be made available
and put in addition, information relating the position to
assess, in real-time, the owner level of an unlinked
pseudonym could trust that can be placed on the
information provided within a call. This includes automated location
conveyed along with the call and location information communicated by
the caller, as well as identity information about the caller. Where
real-time assessment is not possible, it is important to investigators, enabling them be able to
unravel
determine the chain source of events that lead to the attack. call in a post-mortem, so as to be able
to enforce accountability.

This document reviews defines terminology (including the emergency services architecture meaning of
"trustworthy location") in Section
2, 1.1, investigates security threats
in Section 3, and 2, outlines potential solutions in Section 4. Operational considerations are provided 3, covers trust
assessment in Section 5 4 and discusses security considerations are discussed in
Section 6. 5.

1.1. 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 [RFC2119].

This document uses terms

The definition for "Target" is taken from [RFC5012] Section 3.

2. Emergency Services Architecture

Users of "Geopriv Requirements"
[RFC3693].

The term "location determination method" refers to the telephone network can summon emergency services such as
ambulance, fire and police using mechanism used
to determine the location of a well-known emergency service
number (e.g., 9-1-1 in North America, 1-1-2 in Europe). Location Target. This may be something
employed by a location information is server (LIS), or by the Target
itself. It specifically does not refer to the location configuration
protocol (LCP) used to route emergency calls deliver location information either to the appropriate
regional Public Safety Answering Point (PSAP) that serves
Target or the caller Recipient. This term is re-used from "GEOPRIV PIDF-LO
Usage Clarification, Considerations, and Recommendations" [RFC5491].

The term "source" is used to dispatch first-level responders refer to the emergency site.

In emergency services deployments utilizing voice over IP, many of
the assumptions of LIS, node, or device from
which a Recipient (Target or Third-Party) obtains location
information.

Additionally, the Plain Old Telephone Service (POTS) and public
land mobile network (PLMN) no longer hold. While both POTS terms Location-by-Value (LbyV), Location-by-
Reference (LbyR), Location Configuration Protocol, Location
Dereference Protocol, and PLMN
service providers often both physical access as well as phone
service, with Voice over IP (VoIP) there Location URI are re-used from "Requirements
for a Location-by-Reference Mechanism" [RFC5808].

"Trustworthy Location" is defined as location information that can be
attributed to a split between the role
of the Access Infrastructure Provider (AIP), trusted source, has been protected against
modification in transmit, and has been assessed as trustworthy.

"Location Trust Assessment" refers to the Application
(Voice) Service Provider (VSP). The VSP may be located far away from process by which the AIP and may either
reliability of location information can be assessed. This topic is
discussed in Section 4.

2. Threats

While previous IETF documents have no business relationship with analyzed aspects of the AIP security
of emergency services or
may be a competitor. It is also likely that threats to geographic location privacy,
those documents do not cover the VSP will have no
relationship with threats arising from unreliable
location information.

A threat analysis of the PSAP.

In some situations it emergency services system is possible provided in
"Security Threats and Requirements for Emergency Call Marking and
Mapping" [RFC5069]. RFC 5069 describes attacks on the end host to determine its
own location using technology emergency
services system, such as the Global Positioning System
(GPS). Where the end host cannot determine location on its own,
mechanisms have been standardized attempting to make civic deny system services to all
users in a given area, to gain fraudulent use of services and geodetic location
available to the end host,
divert emergency calls to non-emergency sites. [RFC5069] also
describes attacks against individuals, including LLDP-MED [LLDP-MED], DHCP
extensions [RFC4776][RFC6225], HELD [RFC5985], attempts to prevent
an individual from receiving aid, or link-layer
specifications such as [IEEE-802.11y]. The server offering this to gain information is known as a Location Information Server (LIS). The LIS
may be deployed by about an AIP, or it may be run by a Location Service
Provider (LSP) which may have no relationship with the AIP, the VSP
or
emergency. "Threat Analysis of the PSAP. The Geopriv Protocol" [RFC3694]
describes threats against geographic location information, provided by reference or by
value, is then conveyed to privacy, including
protocol threats, threats resulting from the service-providing entities, i.e. storage of geographic
location recipients, via application protocols, such as HTTP, SIP or
XMPP.

Where data, and threats posed by the end host does not provide location, or is not trusted to do
so, it is possible for an intermediary to retrieve abuse of information.

This document focuses on threats from attackers providing false
location information within emergency calls. Since we do not focus
on behalf attackers gaining control of infrastructure elements (e.g.,
location servers, call route servers) or the emergency services IP
network, the endpoint.

3. Threats

This section focuses on threats deriving are derived from the introduction of
untrustworthy location information, regardless of whether this occurs
intentionally or unintentionally. information by end hosts. In addition to
threats arising from the intentional forging of location information,
end hosts may be induced to provide untrustworthy location
information. For example, end hosts may obtain location from
civilian GPS, which is vulnerable to spoofing [GPSCounter] or from
third party Location Service Providers (LSPs) which may be vulnerable
to attack or may not warrant the use of their services for emergency
purposes.

Emergency services have three finite resources subject to denial of
service attacks: the network and server infrastructure, call takers
and dispatchers, and the first responders, such as fire fighters and
police officers. Protecting the network infrastructure is similar to
protecting other high-value service providers, except that location
information may be used to filter call setup requests, to weed out
requests that are out of area. PSAPs even for large cities may only
have a handful of PSAP call takers on duty, so even if they can, by
questioning the caller, eliminate a lot of prank calls, they are
quickly overwhelmed by even a small-scale attack. Finally, first
responder resources are scarce, particularly during mass-casualty
events.

Legacy emergency services rely on the ability to identify callers, as
well as on the difficulty of location spoofing for normal users to
limit prank calls. The ability to ascertain identity is important,
since the threat of severe punishments reduces prank calls.
Mechanically placing a large number of emergency calls that appear to
come from different locations is difficult. Calls from pay phones
are subject to greater scrutiny by the call taker. In the current
system, it would be very difficult for an attacker from country 'Foo'
to attack the emergency services infrastructure located in country
'Bar'.

One of the main motivations of an adversary in the emergency services
context is to prevent callers from utilizing emergency service
support. This can be done by a variety of means, such as
impersonating a PSAP or directory servers, attacking SIP signaling
elements and location servers.

Attackers may want to modify, prevent or delay emergency calls. In
some cases, this will lead the PSAP to dispatch emergency personnel
to an emergency that does not exist and, hence, the personnel might
not be available to other callers. It might also be possible for an
attacker to impede the users from reaching an appropriate PSAP by
modifying the location of an end host or the information returned
from the mapping protocol. In some countries, regulators may not
require the authenticated identity of the emergency caller, as is
true for PSTN-based emergency calls placed from pay phones or SIM-
less cell phones today. Furthermore, if identities can easily be
crafted (as it is the case with many VoIP offerings today), then the
value of emergency caller authentication itself might be limited. As
a consequence, an attacker can forge emergency call information
without the chance of being held accountable for its own actions.

The above-mentioned attacks are mostly targeting individual emergency
callers or a very small fraction of them. If attacks are, however,
launched against the mapping architecture (see [RFC5582] or against
the emergency services IP network (including PSAPs), a larger region
and a large number of potential emergency callers are affected. The
call takers themselves are a particularly scarce resource and if
human interaction by these call takers is required then this can very
quickly have severe consequences.

To provide a structured analysis we distinguish between three
adversary models:

External adversary model: The end host, e.g., an emergency caller
whose location is going to be communicated, is honest and the
adversary may be located between the end host and the location
server or between the end host and the PSAP. None of the
emergency service infrastructure elements act maliciously.

Malicious infrastructure adversary model: The emergency call routing
elements, such as the LIS, the LoST infrastructure, used for
mapping locations to PSAP address, or call routing elements, may
act maliciously.

Malicious end host adversary model: The end host itself acts
maliciously, whether the owner is aware of this or whether it is
acting as a bot.

In this document, we focus only on the malicious end host adversary
model.

3.1.

2.1. Location Spoofing

An adversary can provide false location information in an emergency
call in order to misdirect emergency resources. For calls
originating within the PSTN, this attack can be carried out via
caller-id spoofing. Where location is attached to the emergency call
by an end host, several avenues are available to provide false
location information:

1. The end host could fabricate a PIDF-LO and convey it within an
emergency call;

2. The VSP (and indirectly a LIS) could be fooled into using the
wrong identity (such as an IP address) for location lookup,
thereby providing the end host with misleading location
information;

3. Inaccurate or out-of-date information (such spoofed GPS
signals, a stale wiremap or an inaccurate access point location
database) could be utilized by the LIS or the endhost end host in its
location determination, thereby leading to an inaccurate
determination of location.

By analysis of the SIP headers, it may be possible to flag situations
where the conveyed location is suspect (e.g. potentially wrong city,
state, country or continent). However, in other situations only
entities close to the caller may be able to verify the correctness of
location information.

The following list presents threats specific to location information
handling:

Place shifting: Trudy, the adversary, pretends to be at an arbitrary
location. In some cases, place shifting can be limited in range,
e.g., to the coverage area of a particular cell tower.

Time shifting: Trudy pretends to be at a location she was a while
ago.

Location theft: Trudy observes Alice's location and replays it as
her own.

Location swapping: Trudy and Malory, located in different locations,
can collude and swap location information and pretend to be in
each other's location.

3.2.

2.2. Identity Spoofing

With calls originating on an IP network, at least two forms of
identity are relevant, with the distinction created by the split
between the AIP and the VSP:

(a) network access identity such as might be determined via
authentication (e.g., using the Extensible Authentication Protocol
(EAP) [RFC3748]);

(b) caller identity, such as might be determined from authentication
of the emergency caller at the VoIP application layer.

If the adversary did not authenticate itself to the VSP, then
accountability may depend on verification of the network access
identity. However, this also may not have been authenticated, such
as in the case where an open IEEE 802.11 Access Point is used to
initiate a nuisance emergency call. Although endpoint information
such as the IP or MAC address may have been logged, tying this back
to the device owner may be challenging.

Unlike the existing telephone system, VoIP emergency calls could
require strong identity, which need not necessarily be coupled to a
business relationship with the AIP, ISP or VSP. However, due to the
time-critical nature of emergency calls, multi-layer authentication
is undesirable, so that in most cases, only the device placing the
call will be able to be identified, making the system vulnerable to
bot-net attacks. Furthermore, deploying additional credentials for
emergency service purposes (such as certificates) increases costs,
introduces a significant administrative overhead and is only useful
if widely deployed.

4. Solution Proposals

3. Solutions

This section presents three potential solutions mechanisms which can be used to the described
threats: convey
location: signed location signing by value (Section 4.1), 3.1), location by
reference (Section 4.2) 3.2) and proxy added location (Section 4.3).

4.1. Location Signing

One way 3.3).

In order for to avoid provide authentication and integrity protection for
the SIP messages conveying location, several security approaches are
available. While it is possible for proxies to use security
mechanisms such as SIP Identity [RFC4474] to ensure that
modifications to the location spoofing in transit can be detected by the
location recipient (e.g., the PSAP), compatibility with Session
Border Controllers (SBCs) that modify integrity-protected headers has
proven to be an issue in practice. As a result, the use of SIP over
TLS is at present a more likely mechanism to let provide per-message
authentication and integrity protection.

3.1. Signed Location by Value

With location signing, a trusted location server sign signs the location
information before it is sent to the end host, i.e., the (the entity subject to
the location determination process. process).

The signed location information is then verified by the location
recipient and not by the target. Figure 1 shows the communication
model with the target requesting signed location in step (a), the
location server returns it in step (b) and it is then conveyed to the
location recipient in step (c) who verifies it. For SIP, the
procedures described in "Location Conveyance for the Session
Initiation Protocol" [RFC6442] are applicable for location
conveyance.

+-----------+ +-----------+
| | | Location |
| LIS | | Recipient |
| | | |
+-+-------+-+ +----+------+
^ | --^
| | --
Geopriv |Req. | --
Location |Signed |Signed -- Geopriv
Configuration |Loc. |Loc. -- Using Protocol
Protocol |(a) |(b) -- (e.g., SIP)
| v -- (c)
+-+-------+-+ --
| Target / | --
| End Host +
| |
+-----------+

Figure 1: Location Signing

Additional

In order to limit replay attacks, additional information, such as
timestamps or expiration times, has to be included together with the
signed location to limit replay
attacks. location. If the location is retrieved from a location
server, even a stationary end host has to periodically obtain a fresh
signed location, or incur the additional delay of querying during the
emergency call. Bot nets

While bot-nets are also unlikely to be deterred by location signing. However, signing,
accurate location information would limit the usable subset of the bot net, bot-net
that could be used for an attack, as only hosts within the PSAP
serving area would be useful in placing emergency calls.

To prevent location-swapping attacks it is necessary to include some
some target specific target-specific identity information. The included required information
depends on whether the purpose, namely either goal is real-time verification by the location
recipient or for the purpose of a post-mortem analysis when (where the location recipient wants to determine goal is determination of
the legal entity behind the
target responsible for prosecution (if this is possible). the attack). As argued in Section 6
the operational considerations make a
4, real-time verification
difficult. A strawman proposal for location is not always possible.

Location signing is provided by
[I-D.thomson-geopriv-location-dependability].

Still, for large-scale unlikely to deter attacks launched by bot nets, this is unlikely bot-nets,
since the work required to be helpful. verify the location signature is
considerable. Location signing is also difficult when the host
provides its own
obtains location via mechanisms such as GPS, which is likely to be a common
occurrence for mobile devices. Trusted unless trusted computing
approaches, with tamper-proof GPS modules, may can be needed in that case. After all, a
device applied.
Otherwise, an end host can always pretend to have a GPS device device, and the
recipient has
no way of verifying this or forcing disclosure will need to rely on its ability to assess the level of non-GPS-derived
trust that should be placed in the end host location information. claim.

A straw-man proposal for location signing is provided in [I-
D.thomson-geopriv-location-dependability], and [NENA-i2] Section 3.7
includes operational recommendations relating to location signing:

Location verification may be most useful if it determination is used out of scope for NENA, but we can offer
guidance on what should be considered when designing mechanisms to
report location:

1. The location object should be digitally signed.

2. The certificate for the signer (LIS operator) should be
rooted in conjunction
with other mechanisms. VESA. For example, this purpose, VPC and ERDB operators
should issue certs to LIS operators.

3. The signature should include a call taker can verify that timestamp.

4. Where possible, the
region that corresponds Location Object should be refreshed
periodically, with the signature (and thus the timestamp)
being refreshed as a consequence.

5. Anti-spoofing mechanisms should be applied to the IP address Location
Reporting method.

[Note: The term Valid Emergency Services Authority (VESA) refers
to the root certificate authority.]

As noted above, signing of location objects implies the media stream roughly
corresponds development
of a trust hierarchy that would enable a certificate chain provided
by the LIS operator to be verified by the location information reported PSAP. Rooting the trust
hierarchy in VESA can be accomplished either by having the caller. To
make VESA
directly sign the use LIS certificates, or by the creation of bot nets more difficult, a CAPTCHA-style test may be
applied
intermediate CAs certified by the VESA, which will then issue
certificates to suspicious calls, although this idea the LIS. In terms of the workload imposed on the
VESA, the latter approach is quite
controversial for emergency services, at highly preferable. However, this raises
the danger question of delaying or
even rejecting valid calls.

4.2. who would operate the intermediate CAs and what the
expectations would be.

In particular, the question arises as to the requirements for LIS
certificate issuance, and whether they are significantly different
from say, requirements for issuance of an SSL/TLS web certificate.

3.2. Location by Reference

The location-by-reference concept

Location-by-reference was developed so that end hosts
could can avoid
having to periodically query the location server for up- to-date
location information in a mobile environment. Additionally, if
operators do not want to disclose location information to the end
host without charging them, location-by-reference provides a
reasonable alternative. As noted in "A Location Dereference Protocol
Using HTTP-Enabled Location Delivery (HELD)" [RFC6753], a location
reference can be obtained via HTTP-Enabled Location Delivery (HELD)
[RFC5985] or the Dynamic Host Configuration Protocol (DHCP) location
URI option [DHCP-URI-OPT].

Figure 2 shows the communication model with the target requesting a
location reference in step (a), the location server returns the
reference in step (b), and it is then conveyed to the location
recipient in step (c). The location recipient needs to resolve the
reference with a request in step (d). Finally, location information
is returned to the Location Recipient afterwards. For location
conveyance in SIP, the procedures described in [I-D.ietf-sip-
location-conveyance] [RFC6442] are
applicable.

Figure 2: Location by Reference

Where location by reference is provided, the recipient needs to
deference the LbyR in order to obtain location. The details for the
dereferencing operations vary with the type of reference, such as a
HTTP, HTTPS, SIP, SIPS URI or a SIP presence URI. HTTP-Enabled Location Delivery (HELD) [RFC5985] is an example
of a protocol that is able to return such references.

For location-by-reference, the location server needs to maintain one
or several URIs for each target, timing out these URIs after a
certain amount of time. References need to expire to prevent the
recipient of such a URL from being able to permanently track a host
and to offer garbage collection functionality for the location
server.

Off-path adversaries must be prevented from obtaining the target's
location. The reference contains a randomized component that
prevents third parties from guessing it. When the location recipient
fetches up-to-date location information from the location server, it
can also be assured that the location information is fresh and not
replayed. However, this does not address location swapping.

However, location-by-reference does not offer significant

With respect to the security
benefits if of the de-reference operation, [RFC6753]
Section 6 states:

TLS MUST be used for dereferencing location URIs unless
confidentiality and integrity are provided by some other
mechanism, as discussed in Section 3. Location Recipients MUST
authenticate the end host uses GPS to determine its location. At
best, identity using the domain name included in
the location URI, using the procedure described in Section 3.1 of
[RFC2818]. Local policy determines what a network provider can use cell tower Location Recipient does
if authentication fails or triangulation
information cannot be attempted.

The authorization by possession model (Section 4.1) further relies
on TLS when transmitting the location URI to limit protect the secrecy
of the URI. Possession of such a URI implies the same privacy
considerations as possession of the PIDF-LO document that the URI
references.

Location URIs MUST only be disclosed to authorized Location
Recipients. The GEOPRIV architecture [RFC6280] designates the
Rule Maker to authorize disclosure of the inaccuracy URI.

Protection of user-provided the location URI is necessary, since the policy
attached to such a location URI permits anyone who has the URI to
view the associated location information.

4.3. Proxy Adding Location

Instead This aspect of security
is covered in more detail in the specification of making location information available
conveyance protocols, such as [RFC6442].

For authorizing access to location-by-reference, two authorization
models were developed: "Authorization by Possession" and
"Authorization via Access Control Lists". With respect to
"Authorization by Possession" [RFC6753] Section 4.1 notes:

In this model, possession -- or knowledge -- of the location URI
is used to control access to location information. A location URI
might be constructed such that it is hard to guess (see C8 of
[RFC5808]), and the end host, set of entities that it is possible disclosed to allow can be
limited. The only authentication this would require by the LS is
evidence of possession of the URI. The LS could immediately
authorize any request that indicates this URI.

Authorization by possession does not require direct interaction
with Rule Maker; it is assumed that the Rule Maker is able to
exert control over the distribution of the location URI.
Therefore, the LIS can operate with limited policy input from a
Rule Maker.

Limited disclosure is an entity in important aspect of this authorization
model. The location URI is a secret; therefore, ensuring that
adversaries are not able to acquire this information is paramount.
Encryption, such as might be offered by TLS [RFC5246] or S/MIME
[RFC5751], protects the AIP, information from eavesdroppers.

Using possession as a basis for authorization means that, once
granted, authorization cannot be easily revoked. Cancellation of
a location URI ensures that legitimate users are also affected;
application of additional policy is theoretically possible but
could be technically infeasible. Expiration of location URIs
limits the usable time for a location URI, requiring that an
attacker continue o learn new location URIs to retain access to
current location information.

In situations where "Authorization by Possession" is not suitable
(such as where location hiding [RFC6444] is required), the
"Authorization via Access Control Lists" model may be preferred.

Without the introduction of hierarchy, it would be necessary for the
PSAP to obtain client certificates or associated Digest credentials for all the
LISes in its coverage area, to enable it to successfully dereference
LbyRs. In situations with more than a few LISes per PSAP, this would
present operational challenges.

A certificate hierarchy providing PSAPs with client certificates
chaining to the
AIP, VESA could be used to retrieve enable the LIS to authenticate
and authorize PSAPs for dereferencing. Note that unlike PIDF-LO
signing (which mitigates against modification of PIDF-LOs), this
merely provides the PSAP with access to a (potentially unsigned)
PIDF-LO, albeit over a protected TLS channel.

Another approach would be for the local LIS to upload location
information on behalf to a location aggregation point who would in turn manage
the relationships with the PSAP. This would shift the management
burden from the PSAPs to the location aggregation points.

3.3. Proxy Adding Location

Instead of relying upon the end point.
This solution host to provide location, is possible when the application layer messages are
routed through an entity with
for a proxy that has the ability to determine the location
information of the end point, for example
point (e.g., based on the end host's host IP or MAC address.

When address) to retrieve and
add or override location information.

The use of proxy-added location is primarily applicable in scenarios
where the untrustworthy end host does not have the ability to access
location information, it cannot modify it either. Proxies can use
various authentication security techniques, including provide location. As noted in [RFC6442]
Section 4.1:

A SIP Identity
[RFC4474], intermediary SHOULD NOT add location to ensure a SIP request that modifications
already contains location. This will quite often lead to the
confusion within LRs. However, if a SIP intermediary adds
location, even if location was not previously present in transit
can be detected by a SIP
request, that SIP intermediary is fully responsible for addressing
the concerns of any 424 (Bad Location Information) SIP response it
receives about this location recipient (e.g., addition and MUST NOT pass on
(upstream) the PSAP). 424 response. A SIP intermediary that adds a
locationValue MUST position the new locationValue as the last
locationValue within the Geolocation header field of the SIP
request.

A SIP intermediary MAY add a Geolocation header field if one is
not present -- for example, when a user agent does not support the
Geolocation mechanism but their outbound proxy does and knows the
Target's location, or any of a number of other use cases (see
Section 3).

As noted
above, in [RFC6442] Section 3.3:

This document takes a "you break it, you bought it" approach to
dealing with second locations placed into a SIP request by an
intermediary entity. That entity becomes completely responsible
for all location within that SIP request (more on this in Section
4).

While it is unlikely possible for the proxy to work override location included by
the end host, [RFC6442] Section 3.4 notes the operational
limitations:

Overriding location information provided by the user requires a
deployment where an intermediary necessarily knows better than an
end user -- after all, it could be that Alice has an on-board GPS,
and the SIP intermediary only knows her nearest cell tower. Which
is more accurate location information? Currently, there is no way
to tell which entity is more accurate or which is wrong, for GPS-based that
matter. This document will not specify how to indicate which
location determination
techniques. is more accurate than another.

The obvious disadvantage of this approach is that there is a the need to deploy application
layer entities, such as SIP proxies, at AIPs or associated with AIPs.
This requires a standardized VoIP profile to be deployed at every end
device and at every AIP, for example, based
on SIP. AIP. This might impose a certain interoperability challenge.
challenges.

Additionally, the AIP more or less takes the needs to take responsibility for emergency
calls, even for customers they have no direct or indirect
relationship with. To provide identity information about the
emergency caller from the VSP it would be necessary to let the AIP
and the VSP to interact for authentication (see, for example,
[RFC4740]). This interaction along the Authentication, Authorization
and Accounting infrastructure (see ) is often based on business
relationships between the involved entities. The AIP and the VSP are
very likely to have no such business relationship, particularly when
talking about an arbitrary VSP somewhere on the Internet. In case
that the interaction between the AIP and the VSP fails due to the
lack of a business relationship then typically a fall-back would be
provided where no emergency caller identity information is made
available to the PSAP and the emergency call still has to be
completed.

5. Operational Considerations

5.1. Attribution

4. Location Trust Assessment

The ability to a Specific Trusted Source

[NENA-i2] Section 3.7 describes some of assess the aspects level of attribution as
follows:

The i2 solution proposes a Location Information Server (LIS) be
the source for distributing trustworthiness of conveyed
location information within an access
network. Furthermore the validity, integrity and authenticity of is important, since this information are directly attributed makes it possible to the LIS operator.

Section 5.1.1 describes the issues that arise in ensuring the
validity of
understand how much value should be placed on location information provided by the LIS operator.
Section 5.1.2 and Section 5.1.3 describe operational issues that
arise in ensuring the integrity and authenticity information,
as part of location
information provided by the LIS operator.

5.1.1. Validity

In existing networks where decision making process. As an example, if automated
location information is both determined by
the access/voice service provider as well as communicated by the AIP/
VSP, responsibility for location validity can be attributed entirely understood to be highly suspect, a single party, namely the AIP/VSP.

However, on the Internet, not only may the AIP and VSP represent
different parties, but call taker
can put more effort into obtaining location determination may depend on information contributed by parties trusted by neither the AIP nor
VSP, or even from the operator
caller.

Caller accountability is another important aspect of trust
assessment. Can the Location Information Server (LIS).
In such circumstances, mechanisms for enhancing individual purchasing the integrity device or
authenticity of location data contribute little toward ensuring the
validity of that data.

It should activating
service be understood that identified or did the means by which location is
determined may not necessarily relate call originate from a non-service
initialized (NSI) device whose owner cannot be determined? Prior to
the means by which the
endpoint communicates with call, was the LIS. Just because a Location
Configuration Protocol (LCP) operates caller authenticated at a particular layer does not
imply that the location data communicated by that protocol is derived
solely based on information obtained at that layer. network or application
layer? In some
circumstances, LCP implementations may base their location
determination on information gathered from a variety of sources which
may merit varying levels of trust, such as information obtained from the calling endpoint, event of a prank call, can audit logs be made
available to an investigator, or wiremap can information that is time consuming relating to verify or may rapidly go out of date.

For example, consider the case of a Location Information Server (LIS)
that utilizes LLDP-MED [LLDP-MED] endpoint move detection
notifications in determining calling endpoint location. Regardless
owner of whether the LIS implementation utilizes an LCP operating above the
link layer (such as an application layer protocol such as HELD
[RFC5985]), the validity of the location information conveyed would unlinked pseudonym be dependent on provided, enabling investigators to
unravel the security properties chain of LLDP-MED.

[LLDP-MED] Section 13.3 defines the endpoint move detection
notification as follows:

lldpXMedTopologyChangeDetected NOTIFICATION-TYPE
OBJECTS { lldpRemChassisIdSubtype,
lldpRemChassisId,
lldpXMedRemDeviceClass
}
STATUS current
DESCRIPTION
"A notification generated by events that lead to the local device
sensing a change in attack? In practice,
the topology that
indicates a new remote device attached ability to identify a
local port, or a remote device disconnected
or moved from one port to another."
::= { lldpXMedNotifications 1 }

Figure 3: Interworking Architecture

As noted in Section 7.4 of [LLDP-MED], caller may decrease the lldpRemChassisIdSubtype,
lldpRemChassisId and lldpXMedRemDeviceClass variables are determined likelihood of
caller misbehavior. For example, where emergency calls have been
allowed from the Chassis ID (1) and LLDP-MED Device Type Type-Length-Value
(TLV) tuples provided within the LLDP advertisement handsets lacking a SIM card, or where ownership of the calling
device. As noted in [LLDP-MED] Section 9.2.3, all Endpoint Devices
use the Network address ID subtype (5) by default. In order to
provide topology change notifications in a timely way, it
SIM card cannot
necessarily be assumed that a Network Connectivity devices will
validate determined, the network address prior to transmission frequency of the move
detection notification. As a result, there is no guarantee that the
network address reported by the endpoint will correspond to nuisance calls has
often been unacceptably high [TASMANIA][UK][SA].

Note that
utilized by the device.

The discrepancy need not be due to nefarious reasons. For example,
an IPv6-capable endpoint may utilize multiple IPv6 addresses.
Similarly, an IPv4-capable endpoint may initially utilize a Link-
Local IPv4 address [RFC3927] and then may subsequently acquire a
DHCP-assigned routable address. All addresses utilized by location trust assessment has value regardless of whether
the
endpoint device may not be advertised in LLDP, location has been conveyed securely (via signed location,
location-by-reference or even if they are,
endpoint move detection notification may not be triggered, either
because no LinkUp/LinkDown notifications occur (e.g. the host adds proxy-added location) or
changes an address not (via location-
by-value without rebooting) or because these notifications
were location signing), since secure conveyance does not detectable by the Network Connectivity device (the endpoint
device was connected to a hub rather than directly to a switch).

Similar issues may arise in situations where the LIS utilizes DHCP
lease data
provide assurance relating to obtain location information. Where the endpoint
address was not obtained via DHCP (such as via manual assignment,
stateless auto-configuration [RFC4862] validity or Link-Local IPv4 self-
assignment), no lease information will be available to enable
determination provenance of device location. This situation should be expected
to become increasingly common as IPv6-capable endpoints are deployed,
and Location Configuration Protocol (LCP) interactions occur over
IPv6.

Even in scenarios in which the LIS relies on location data obtained
from the IP MIB [RFC4293] and
data.

In practice, the Bridge MIB [RFC4188], availability source of the location determination information data is not assured. In important for
location trust assessment. For example, location provided by a
Location Information Server (LIS) whose administrator has an
enterprise scale network, maintenance
established history of current meeting emergency location accuracy
requirements (e.g. Phase II) may be considered more reliable than
location information
depends on the ability provided by a third party Location Service
Provider (LSP) that disclaims use of the management station location information for
emergency purposes.

However, even where an LSP does not attempt to retrieve data via
polling of network devices. As meet the number of devices increases,
constraints of network latency and packet loss may make accuracy
requirements for emergency location, it
increasingly difficult still may be able to ensure that all devices are polled on a
sufficiently frequent interval. In addition, provide
information useful in large networks, it assessing about how reliable location
information is likely that tables will be large so that when UDP transport is
used, query responses will fragment, resulting in increasing packet
loss or even difficulties in firewall or NAT traversal.

Furthermore, even in situations where the location data can be
presumed to exist and be valid, there may be issues with the
integrity of the retrieval process. be. For example, where was location determined
based on the LIS
depends nearest cell tower or 802.11 Access Point (AP), or was a
triangulation method used? If based on cell tower or AP location
data, was the information obtained from a MIB notification or
query, unless SNMPv3 [RFC3411] is used, data integrity and
authenticity is not assured in transit between an authoritative source (e.g.

the network
connectivity device tower or AP owner) and when was the LIS.

From these examples, it should be clear last time that the availability or
validity of location data is a property of the LIS system design and
implementation rather than an inherent property
of the LCP. As a
result, mechanisms utilized to protect tower or access point was verified?

For real-time validation, information in the integrity signaling and authenticity
of location data do not necessarily provide assurances relating to
the validity or provenance of that data.

5.1.2. Location Signing

[NENA-i2] Section 3.7 includes recommendations relating to location
signing:

Location determination is out of scope for NENA, but we media
packets can offer
guidance on what should be considered when designing mechanisms to
report location:

1. The cross checked against location object should be digitally signed.

2. The certificate for the signer (LIS operator) should be
rooted in VESA. information. For this purpose, VPC and ERDB operators
should issue certs
example, it may be possible to LIS operators.

3. The signature should include a timestamp.

4. Where possible, determine the Location Object should be refreshed
periodically, region associated with
the signature (and thus IP address included within SIP Via: or Contact: headers, or the timestamp)
being refreshed as
media source address, and compare this against the location
information reported by the caller or conveyed in the PIDF-LO. While
a consequence.

5. Anti-spoofing mechanisms should CAPTCHA-style test may be applied to the Location
Reporting method.

[Note: The term Valid Emergency Services Authority (VESA) refers suspicious calls to lower the root certificate authority.]

Signing of location objects implies
risk from bot-nets, this is quite controversial for emergency
services, due to the development risk of a trust
hierarchy that would enable a certificate chain provided by the LIS
operator to delaying or rejecting valid calls.

Although privacy-preserving procedures may be verified disabled for emergency
calls, by design, PIDF-LO objects limit the PSAP. Rooting the trust hierarchy information available for
real-time attribution. As noted in
VESA can be accomplished either by having the VESA directly sign the [RFC5985] Section 6.6:

The LIS certificates, or by the creation of intermediate CAs certified by
the VESA, which will then issue certificates to the LIS. In terms MUST NOT include any means of identifying the workload imposed on the VESA, Device in
the latter approach PIDF-LO unless it is highly
preferable. However, this raises able to verify that the question identifier is
correct and inclusion of who would operate identity is expressly permitted by a Rule
Maker. Therefore, PIDF parameters that contain identity are
either omitted or contain unlinked pseudonyms [RFC3693]. A
unique, unlinked presentity URI SHOULD be generated by the intermediate CAs and what LIS for
the expectations would be.

In particular, mandatory presence "entity" attribute of the question arises PIDF document.
Optional parameters such as to the requirements for LIS
certificate issuance, "contact" and whether they "deviceID" elements
[RFC4479] are significantly different
from say, requirements for issuance of an SSL/TLS web certificate.

5.1.3. Location by Reference

Where location by reference is provided, not used.

Also, the recipient needs device referred to
deference the LbyR in order to obtain location. With the
introduction of location by reference concept two authorization
models were developed, see [I-D.ietf-geopriv-deref-protocol], namely PIDF-LO may not necessarily be
the "Authorization by Possession" and "Authorization via Access
Control Lists" model. With same entity conveying the "Authorization by Possession" model
everyone PIDF-LO to the PSAP. As noted in possession of
[RFC6442] Section 1:

In no way does this document assume that the reference SIP user agent client
that sends a request containing a location object is able to obtain necessarily
the
corresponding Target. The location information. This might, however, be
incompatible with other requirements of a Target conveyed within SIP
typically imposed by AIPs, such
as location hiding (see [RFC6444]). As such, the "Authorization via
Access Control Lists" model is likely corresponds to be the preferred model for
many AIPs and subject for discussion in the subsequent paragraphs.

Just as with PIDF-LO signing, that of a device controlled by the operational considerations in
managing credentials
Target, for use in LbyR dereferencing example, a mobile phone, but such devices can be
considerable without the introduction of
separated from their owners, and moreover, in some kind of hierarchy. It
does not seem reasonable for a PSAP to manage client certificates or
Digest credentials for all cases, the LISes in user
agent may not know its coverage area, so as own location.

Due to
enable these design choices, it is possible for an attacker to successfully dereference LbyRs. In some respects, cut
and paste a PIDF-LO obtained by a different device or user into a SIP
INVITE and send this
issue is even more formidable than to the validation of signed PIDF-
LOs. PSAP. While PIDF-LO signing credentials are provided to the LIS
operator, in the case would
prevent modification of de-referencing, the PSAP needs to be obtain
credentials compatible with the LIS configuration, a potentially more
complex operational problem.

As with PIDF-LO signing, the operational issues or invention of LbyR can be
addressed to some extent by introduction one out of hierarchy. Rather than
requiring the PSAP to obtain credentials for accessing each LIS, the
local LIS could be required to upload location information to
location aggregation points who whole
cloth, it would not prevent this cut and paste attack. Neither would
implementation of "Enhancements for Authenticated Identity Management
in turn manage the
relationships with Session Initiation Protocol (SIP)" [RFC4474], allowing the PSAP. This would shift
recipient to verify the management burden
from identity assertion in the PSAPs From: header.
However, while it might not be possible to detect the location aggregation points.

5.2. Application to a Specific Point cut and paste
in Time real-time, examination of the audit logs might provide enough
information to enable events to be reconstructed.

Real-time validation of the timestamp contained within PIDF-LO
objects contain a timestamp, which reflects (reflecting the time at which the location was determined. determined) is
also challenging. Even if the PIDF-LO is signed, signed the timestamp only
represents an assertion by the LIS, which may or may not be
trustworthy. For example, the recipient of the signed PIDF-LO may
not know whether the LIS supports time synchronization, or whether it
is possible to reset the LIS clock manually without detection. Even
if the timestamp was valid at the time location was determined, a
time period may elapse between when the PIDF-LO was provided and when
it is conveyed to the recipient. Periodically refreshing location
information to renew the timestamp even though the location
information itself is unchanged puts additional load on LISes. As a
result, recipients need to validate the timestamp in order to
determine whether it is credible.

5.3. Linkage to a Specific Endpoint

As noted in

While this document focuses on the "HTTP Enabled Location Delivery (HELD)" [RFC5985]
Section 6.6:

The LIS MUST NOT include any means discussion of identifying real-time
determination of suspicious emergency calls, the Device use of audit logs
may help in enforcing accountability among emergency callers. For
example, in the PIDF-LO unless it is able event of a prank call, information relating to verify that the identifier is
correct and inclusion
owner of identity is expressly permitted by a Rule
Maker. Therefore, PIDF parameters that contain identity are
either omitted or contain unlinked pseudonyms [RFC3693]. A
unique, the unlinked presentity URI SHOULD pseudonym could be generated by the LIS for provided to investigators,
enabling them to unravel the mandatory presence "entity" attribute chain of events that lead to the PIDF document.
Optional parameters such as the "contact" element and attack.
However, while auditability is an important deterrent, it is likely
to be of most benefit in situations where attacks on the
"deviceID" element [RFC4479] emergency
services system are not used.

Given likely to be relatively infrequent, since the restrictions
resources required to pursue an investigation are likely to be
considerable. However, although real-time validation based on inclusion PIDF-
LO elements is challenging, where LIS audit logs are available (such
as where a law enforcement agency can present a subpoena), linking of identification information
within
a pseudonym to the PIDF-LO, device obtaining location can be accomplished in a
post-mortem.

Where attacks are frequent and continuous, automated mechanisms are
required. For example, it may not might be possible for valuable to develop mechanisms to
exchange audit trails information in a recipient standardized format between
ISPs and PSAPs / VSPs and PSAPs or heuristics to verify distinguish
potentially fraudulent emergency calls from real emergencies.

5. Security Considerations

IP-based emergency services face a number of security threats that do
not exist within the entity legacy system. In order to limit prank calls,
legacy emergency services rely on whose behalf location was determined represents the same entity conveying location ability to identify callers, as
well as on the recipient.

Where "Enhancements difficulty of location spoofing for Authenticated Identity Management in the
Session Initiation Protocol (SIP)" [RFC4474] is used, it normal users. The
ability to ascertain identity is possible
for important, since the recipient threat of
punishment reduces prank calls; as an example, calls from pay phones
are subject to verify greater scrutiny by the identity assertion call taker.

Mechanically placing a large number of emergency calls that appear to
come from different locations is difficult in a legacy environment.
Also, in the From:
header. However, if PIDF parameters that contain identity are
omitted or contain an unlinked pseudonym, then current system, it may not would be possible very difficult for the recipient to verify whether the conveyed location actually
relates an
attacker from country 'Foo' to attack the entity identified emergency services
infrastructure located in the From: header.

This lack country 'Bar'.

However, within an IP-based emergency services a number of binding between the entity obtaining these
attacks become much easier to mount. Emergency services have three
finite resources subject to denial of service attacks: the PIDF-LO network
and server infrastructure, call takers and dispatchers, and the
entity conveying first
responders, such as fire fighters and police officers. Protecting
the PIDF-LO network infrastructure is similar to the recipient enables cut and paste
attacks which would enable an attacker protecting other high-value
service providers, except that location information may be used to assert
filter call setup requests, to weed out requests that are out of
area. PSAPs even for large cities may only have a bogus location, handful of PSAP
call takers on duty, so even where both if they can, by questioning the SIP message and PIDF-LO are signed. As caller,
eliminate a result,
even implementation lot of both [RFC4474] and location signing does not
guarantee that location can be tied to prank calls, they are quickly overwhelmed by even
a specific endpoint.

6. Security Considerations

IP-based small-scale attack. Finally, first responder resources are scarce,
particularly during mass-casualty events.

Attackers may want to modify, prevent or delay emergency services face many security threats. "Security
Threats and Requirements for Emergency Call Marking and Mapping"
[RFC5069] describes attacks on calls. In
some cases, this will lead the PSAP to dispatch emergency services system, such as
attempting personnel
to deny system services an emergency that does not exist and, hence, the personnel might
not be available to all users in a given area, other callers. It might also be possible for an
attacker to
gain fraudulent use impede the users from reaching an appropriate PSAP by
modifying the location of services and to divert an end host or the information returned
from the mapping protocol. In some countries, regulators may not
require the authenticated identity of the emergency caller, as is
true for PSTN-based emergency calls to non- placed from pay phones or SIM-
less cell phones today. Furthermore, if identities can easily be
crafted (as it is the case with many VoIP offerings today), then the
value of emergency sites. [RFC5069] also describes attacks against
individuals, including attempts to prevent caller authentication itself might be limited. As
a consequence, an attacker can forge emergency call information
without the chance of being held accountable for its own actions.

The above-mentioned attacks are mostly targeting individual from
receiving aid, emergency
callers or to gain information about an emergency.

"Threat Analysis a very small fraction of them. If attacks are, however,
launched against the Geopriv Protocol" [RFC3694] describes threats mapping architecture (see [RFC5582] or against geographic location privacy, including protocol threats,
threats resulting from
the storage emergency services IP network (including PSAPs), a larger region
and a large number of geographic location data, potential emergency callers are affected. The
call takers themselves are a particularly scarce resource and
threats posed if
human interaction by the abuse of information. these call takers is required then this can very
quickly have severe consequences.

Although it is important to ensure that location information cannot
be faked there will be many GPS-enabled devices that will find it
difficult to utilize any of the security mechanisms solutions described in Section 5. 3. It
is also unlikely that users will be willing to upload their location
information for "verification" to a nearby location server located in
the access network.

While auditability is an important deterrent, it is likely to be of
most benefit in situations where attacks on the emergency services
system are likely to be relatively infrequent, since the resources
required to pursue an investigation are likely to be considerable.

Where attacks are frequent and continuous, automated mechanisms are
required. For example, mechanisms to exchange audit trails
information in a standardized format between ISPs and PSAPs / VSPs
and PSAPs or heuristics to distinguish potentially fraudulent
emergency calls from real emergencies might be valuable.

6. IANA Considerations

This document does not require actions by IANA.

8. Acknowledgments

We would like to thank the members of the IETF ECRIT and the IETF
GEOPRIV working group for their input to the discussions related to
this topic. We would also like to thank Andrew Newton, Murugaraj
Shanmugam, Richard Barnes and Matt Lepinski for their feedback to
previous versions of this document. Martin Thomson provided valuable
input to version -02 of this document.

7. References

9.1.

7.1. Informative References

[DHCP-URI-OPT]
Polk, J., "Dynamic Host Configuration Protocol (DHCP) IPv4 and
IPv6 Option for a Location Uniform Resource Identifier (URI)",
Internet draft (work in progress), draft-ietf-geopriv-dhcp-
lbyr-uri-option-19, February 2013.

[EENA] EENA, "False Emergency Calls", EENA Operations Document,
Version 1.0, March 2011,
http://www.eena.org/ressource/static/files/
2011_03_15_3.1.2.fc_v1.0.pdf

[GPSCounter]
Warner, J. S. and R. G. Johnston, "GPS Spoofing
Countermeasures", Los Alamos research paper LAUR-03-6163,
December 2003.

[I-D.thomson-geopriv-location-dependability]
Thomson, M. and J. Winterbottom, "Digital Signature Methods
for Location Dependability", draft-thomson-geopriv-location-
dependability-07 (work in progress), March 2011.

[I-D.ietf-geopriv-deref-protocol]
Winterbottom, J., Tschofenig, H., Schulzrinne, H. and M.
Thomson, "A Location Dereferencing Protocol Using HELD",
draft-ietf-geopriv-deref-protocol-07 (work in progress), July
2012.

[IEEE-802.11y]
Information technology - Telecommunications and information
exchange between systems - Local and metropolitan area
networks - Specific requirements - Part 11: Wireless LAN
Medium Access Control (MAC) and Physical Layer (PHY)
specifications Amendment 3: 3650-3700 MHz Operation in USA,
November 2008.

[LLDP-MED]
"Telecommunications: IP Telephony Infrastructure: Link Layer
Discovery Protocol for Media Endpoint Devices, ANSI/
TIA-1057-2006", April 2006.

[NENA-i2] "08-001 NENA Interim VoIP Architecture for Enhanced 9-1-1
Services (i2)", December 2005.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[RFC3411] Harrington, D., Presuhn, R., and B. Wijnen, "An Architecture
for Describing Simple Network Management Protocol (SNMP)
Management Frameworks", STD 62,

[RFC2818] Rescorla, E., "HTTP over TLS", RFC 3411, December 2002. 2818, May 2000.

[RFC3693] Cuellar, J., Morris, J., Mulligan, D., Peterson, J., and J.
Polk, "Geopriv Requirements", RFC 3693, February 2004.

[RFC3694] Danley, M., Mulligan, D., Morris, J. and J. Peterson, "Threat
Analysis of the Geopriv Protocol", RFC 3694, February 2004.

[RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
Levkowetz, "Extensible Authentication Protocol (EAP)", RFC
3748, June 2004.

[RFC3927] Cheshire, S., Aboba, B., and E. Guttman, "Dynamic
Configuration of IPv4 Link-Local Addresses", RFC 3927, May
2005.

[RFC4188] Norseth, K. and E. Bell, "Definitions of Managed Objects for
Bridges", RFC 4188, September 2005.

[RFC4293] Routhier, S., "Management Information Base for the Internet
Protocol (IP)", RFC 4293, April 2006.

[RFC4474] Peterson, J. and C. Jennings, "Enhancements for Authenticated
Identity Management in the Session Initiation Protocol (SIP)",
RFC 4474, August 2006.

[RFC4479] Rosenberg, J., "A Data Model for Presence", RFC 4479, July
2006.

[RFC4740] Garcia-Martin, M., Belinchon, M., Pallares-Lopez, M., Canales-
Valenzuela, C., and K. Tammi, "Diameter Session Initiation
Protocol (SIP) Application", RFC 4740, November 2006.

[RFC4776] Schulzrinne, H., "Dynamic Host Configuration Protocol (DHCPv4
and DHCPv6) Option for Civic Addresses Configuration
Information", RFC 4776, November 2006.

[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862, September 2007.

[RFC5012] Schulzrinne, H. and R. Marshall, "Requirements for Emergency
Context Resolution with Internet Technologies", RFC 5012,
January 2008.

[RFC5069] Taylor, T., Tschofenig, H., Schulzrinne, H. and M. Shanmugam,
"Security Threats and Requirements for Emergency Call Marking
and Mapping", RFC 5069, January 2008.

[RFC5246] Dierks, T. and E. Rescorla, "The Transport Level Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.

[RFC5491] Winterbottom, J., Thomson, M. and H. Tschofenig, "GEOPRIV
Presence Information Data Format Location Object (PIDF-LO)
Usage Clarification, Considerations, and Recommendations", RFC
5491, March 2009.

[RFC5582] Schulzrinne, H., "Location-to-URL Mapping Architecture and
Framework", RFC 5582, September 2009.

[RFC5751] Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet Mail
Extensions (S/MIME) Version 3.2 Message Specification", RFC
5751, January 2010.

[RFC5808] Marshall, R., "Requirements for a Location-by-Reference
Mechanism", RFC 5808, May 2010.

[RFC5985] Barnes, M., "HTTP Enabled Location Delivery (HELD)", RFC 5985,
September 2010.

[RFC6225] Polk, J., Linsner, M., Thomson, M. and B. Aboba, "Dynamic Host
Configuration Protocol Options

[RFC6280] Barnes, R., et. al, "An Architecture for Coordinate-based Location
Configuration Information", and Location
Privacy in Internet Applications", RFC 6225, 6280, July 2011.

[RFC6442] Polk, J., Rosen, B. and J. Peterson, "Location Conveyance for
the Session Initiation Protocol", RFC 6442, December 2011.

[RFC6444] Schulzrinne, H., Liess, L., Tschofenig, H., Stark, B., and A.
Kuett, "Location Hiding: Problem Statement and Requirements",
RFC 6444, January 2012.

[RFC6753] Winterbottom, J., Tschofenig. H., Schulzrinne, H. and M.
Thomson, "A Location Dereference Protocol Using HTTP-Enabled
Location Delivery (HELD)", RFC 6753, October 2012.

[SA] "Saudi Arabia - Illegal sale of SIMs blamed for surge in prank
calls", Arab News, May 4, 2010,
http://www.menafn.com/qn_news_story_s.asp?StoryId=1093319384

[Swatting]
"Don't Make the Call: The New Phenomenon of 'Swatting',
Federal Bureau of Investigation, February 4, 2008,
http://www.fbi.gov/news/stories/2008/february/swatting020408

[TASMANIA]
"Emergency services seek SIM-less calls block", ABC News
Online, August 18, 2006,
http://www.abc.net.au/news/newsitems/200608/s1717956.htm

[UK] "Rapper makes thousands of prank 999 emergency calls to UK
police", Digital Journal, June 24, 2010,
http://www.digitaljournal.com/article/293796?tp=1

Acknowledgments

We would like to thank the members of the IETF ECRIT working group,
including Marc Linsner, Henning Schulzrinne and Brian Rosen, for
their input at IETF 85 that helped get this documented pointed in the
right direction. We would also like to thank members of the IETF
GEOPRIV WG, including Andrew Newton, Murugaraj Shanmugam, Martin
Thomson, Richard Barnes and Matt Lepinski for their feedback to
previous versions of this document.

Authors' Addresses

Hannes Tschofenig
Nokia Siemens Networks
Linnoitustie 6
Espoo 02600
Finland

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

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

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

Bernard Aboba
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
US

Email: bernard_aboba@hotmail.com