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SEMINAR REPORT
ON
WIRELESS LAN SECURITY
I. Introduction
a. The 802.11 Wireless LAN Standard
In 1997, the IEE ratified the 802.11 Wireless LAN standards,
establishing a global standard for implementing and deploying Wireless
LANS. The throughput for 802.11 is 2Mbps, which was well below the IEE
802.3 Ethernet counterpart. Late in 1999, the IEE ratified the 802.11b
standard extension, which raised the throughput to 11 Mbps, making this
extension more comparable to the wired equivalent. The 802.11b also
supports the 2 Mbps data rate and operates on the 2.4GHz band in radio
frequency for high-speed data communications
As with any of the other 802 networking standards (Ethernet, Token
Ring, etc.), the 802.11 specification affects the lower layers of the
OSI reference model, the Physical and Data Link layers.
The Physical Layer defines how data is transmitted over the physical
medium. The IEE assigned 802.11 two transmission methods for radio
frequency (RF) and one for Infrared. The two RF methods are frequency
hopping spread-spectrum (FHSS) and direct sequence spread-spectrum
(DSS). These transmission methods operate within the ISM (Industrial,
Scientific, and Medical) 2.4 GHz band for unlicensed use. Other devices
that operate on this band include remote phones, microwave ovens, and
baby monitors.
FHSS and DSS are different techniques to transmit data over radio
waves. FHSS uses a simple frequency hopping technique to navigate the
2.4GHz band which is divided into 75 sub-channels 1MHz each. The sender
and receiver negotiate a sequence pattern over the sub-channels.
DSS, however, utilizes the same channel for the duration of the
transmission by dividing the 2.4 GHz band into 14 channels at 22MHz
each with 11 channels overlapping the adjacent ones and three non-
overlapping channels. To compensate for noise and interference, DSS
uses a technique called "chipping", where each data bit is converted
into redundant patterns called "chips".
The Data Link layer is made up of two sub-layers, the Media Access
Control (MAC) layer and the Logical Link Control (LLC) layer. The Data
Link layer determines how transmitted data is packaged, addressed and
managed within the network. The LLC layer uses the identical 48-bit
addressing found in other 802 LAN networks like Ethernet where the MAC
layer uses a unique mechanism called carrier sense multiple access,
collision avoidance (CSMA/CA). This mechanism is similar to the carrier
sense multiple access collision detect (CSMA/CD) used in Ethernet, with
a few major differences. Opposed to Ethernet, which sends out a signal
until a collision is detected before a resend, CSMA/CA senses the
airwaves for activity and sends out a signal when the airwaves are
free. If the sender detects conflicting signals, it will wait for a
random period before retrying. This technique is called "listening
before talking" (LBT) and probably would be effective if applied to
verbal communications also.
To minimize the risk of transmission collisions, the 802.11 committee
decided a mechanism called Request-To-Send / Clear-To-Send (RTS/CTS).
An example of this would be when an AP accepts data transmitted from a
wireless station; the AP would send a RTS frame to the wireless station
that requests a specific amount of time that the station has to deliver
data to it. The wireless station would then send an CTS frame
acknowledging that it will wait to send any communications until the AP
completes sending data. All the other wireless stations will hear the
transmission as well and wait before sending data. Due to the fragile
nature of wireless transmission compared to wired transfers, the
acknowledgement model (ACK) is employed on both ends to ensure that
data does not get lost in the airwaves.
b. 802.11 Extensions
Several extensions to the 802.11 standard have been either ratified or
are in progress by their respective task group committees. Below are
three current task group activities that affect WLAN users most
directly:
802.11a
The 802.11a ("another band") extension operates on a different physical
layer specification than the 802.11 standard at 2.4GHz. 802.11a
operates at 5GHz and supports date rates up to 54Mbps. The FCC has
allocated 300Mz of RF spectrum for unlicensed operation in the 5GHz
range. Although 802.11a supports much higher data rates, the effective
distance of transmission is much shorter than 802.11b and is not
compatible with 802.11b equipment and in its current state is usable
only in the US. However, several vendors have embraced the 802.11a
standard and some have dual band support AP devices and network cards.
802.11b
The 802.11b ("baseline") is currently the de facto standard for
Wireless LANs. As discussed earlier, the 802.11b extension raised the
data rate bar from 2Mbps to 11Mbps, even though the actual throughput
is much less. The original method employed by the 802.11 committee for
chipping data transmissions was the 11-bit chipping encoding technique
called the "Barker Sequence". The increased data rate from 2Mbps to
11Mbps was achieved by utilizing an advanced encoding technique called
Complementary Code Keying (CCK). The CCK uses Quadrature Phase Shift
Keying (QPSK) for modulation to achieve the higher data rates.
802.11g
The 802.11g ("going beyond b") task group, like 802.11a is focusing on
raising the data transmission rate up to 54Mbps, but on the 2.4MHz
band. The specification was approved by the IEE in 2001 and is
expected to be ratified in the second half of 2002. It is an attractive
alternative to the 802.11a extension due to its backward compatibility
to 802.11b, which preserves previous infrastructure investments.
The other task groups are making enhancements to specific aspects of
the 802.11 standard. These enhancements do not affect the data rates.
These extensions are below:
802.11d
This group is focusing on extending the technology to countries that
are not covered by the IEE.
802.11e
This group is focusing on improving multi-media transmission quality of
service.
802.11f
This group is focusing on enhancing roaming between APs and
interoperability between vendors.
802.11h
This group is addressing concerns on the frequency selection and power
control mechanisms on the 5GHz band in some European countries.
802.11i
This group is focusing on enhancing wireless lan security and
authentication for 802.11 that include incorporating Remote Access
Dialing User Service (RADIUS), Kerberos and the network port
authentication (IEE 802.1X). 802.1X has already been implemented by
some AP vendors.
c. 802.11 Security Flaws
802.11 wireless LAN security or lack of it remains at the top of most
LAN administrators list of worries. The security for 802.11 is provided
by the Wired Equivalency Policy (WEP) at the MAC layer for
authentication and encryption The original goals of IEE in defining
WEP was to provide the equivalent security of an "unencrypted" wired
network. The difference is the wired networks are somewhat protected by
physical buildings they are housed in. On the wireless side, the same
physical layer is open in the airwaves.
WEP provides authentication to the network and encryption of
transmitted data across the network. WEP can be set either to either an
open network or utilizing a shared key system. The shared key system
used with WEP as well as the WEP encryption algorithm are the most
widely discussed vulnerabilities of WEP. Several manufacturers'
implementations introduce additional vulnerabilities to the already
beleaguered standard.
WEP uses the RC4 algorithm known as a stream cipher for encrypting
data. Several manufacturers tout larger 128-bit keys, the actual size
available is 104 bits. The problem with the key is not the length, but
lies within the actual design of WEP that allows secret identification.
A paper written by Jesse Walker, "Unsafe at any key length" provides
insight to the specifics of the design vulnerabilities and explains the
exploitation of WEP.
The following steps explain the process of how a wireless station
associates to an AP using shared key authentication.
1) The wireless station begins the process by sending an authentication
frame to the AP it is trying to associate with.
2) The receiving AP sends a reply to the wireless station with its own
authentication frame containing 128 octets of challenge text.
3) The wireless station then encrypts the challenge text with the
shared key and sends the result back to the AP.
4) The AP then decrypts the encrypted challenge using the same shared
key and compares it to the original challenge text. If the there is a
match, an ACK is sent back to the wireless station, otherwise a
notification is sent back rejecting the authentication.
It is important to note that this authentication process simply
acknowledges that the wireless station knows the shared key and does
not authenticate against resources behind the AP. Upon authenticating
with the AP, the wireless station gains access to any resources the AP
is connected to.
This is what keeps LAN and security managers up at night. If WEP is the
only and last layer of defense used in a Wireless LAN, intruders that
have compromised WEP, have access to the corporate network. Most APs
are deployed behind the corporate firewall and in most cases
unknowingly are connected to critical down-line systems that were
locked down before APs were invented. There are a number of papers and
technical articles on the vulnerabilities of WEP that are listed in the
Reference section.
II. Wireless LAN Deployment
The biggest difference in deployment of Wireless LANs over their wired
counterpart are due to the physical layer operates in the airwaves and
is affected by transmission and reception factors such as attenuation,
radio frequency (RF) noise and interference, and building and
structural interference.
a. Antenna Primer
Antenna technology plays a significant role in the deployment,
resulting performance of a Wireless LAN, and enhancing security.
Properly planned placement can reduce stray RF signal making
eavesdropping more difficult.
Common terms that are used in describing performance of antenna
technology are as follows:
Isotropic Radiator - An antenna that radiates equally in all directions
in a three dimensional sphere is considered an "isotropic radiator".
Decibel (dB) - Describes loss or gain between two communicating devices
that is expressed in watts as a unit of measure.
dBi value - Describes the ratio of an antenna's gain when compared to
that of an Isotropic Radiator antenna. The higher the value, the
greater the gain.
Attenuation - Describes the reduction of signal strength over distance.
Several factors can affect attenuation including absorption
(obstructions such as trees that absorb radio waves), diffraction
(signal bending around obstructions with reflective qualities),
reflection (signal bounces off a reflective surface such as water), and
refraction (signal bends due to atmospheric conditions such as marine
fog).
Gain - Describes RF concentration over that of an Isotropic Radiator
antenna and is measured in dB.
Azimuth - Describes the axis for which RF is radiated.
Antennas come in all shapes and sizes including the home-made versions
using common kitchen cupboard cans to deliver specific performance
variations. Following are some commonly deployed antenna types.
Dipole Antenna:
This is the most commonly used antenna that is designed into most
Access Points. The antenna itself is usually removable and radiating
element is in the one inch length range. This type of antenna functions
similar to a television "rabbit ears" antenna. As the frequency gets to
the 2.4GHz range, the antenna required gets smaller than that of a
100Mz television. The Dipole antenna radiates equally in all directions
around its Azimuth but does not cover the length of the diagonal giving
a donut-like radiation pattern. Since the Dipole radiates in this
pattern, a fraction of radiation is vertical and bleeds across floors
in a multi-story building and have typical ranges up to 100 feet at
11Mbps.
Directional Antennas:
Directional antennas are designed to be used as a bridge antenna
between two networks or for point-to-point communications. Yagi and
Parabolic antennas are used for these purposes as well as others.
Directional antennas can reduce unwanted spill-over as they concentrate
radiation in one direction.
With the popularity of "war driving" (driving around in a car and
discovering unprotected WLANs) there is continuing research done on
enhancing distances and reducing spill-over by commercial and
underground groups. Advanced antennas like the "Slotted Waveguide" by
Trevor Marshal, utilizes multiple dipoles, one above the other, to
cause the signal radiation to be in phase so that the concentration is
along the axis of the dipoles.
b. Deployment Best Practices
Planning a Wireless LAN requires consideration for factors that affect
attenuation discussed earlier. Indoor and multi-story deployments have
different challenges than outdoor deployments. Attenuation affects
antenna cabling from the radio device to the actual antenna also. The
radio wave actually begins at the radio device and induces voltage as
it travels down the antenna cable and loses strength.
Multi-path distortion occurs in outdoor deployments where a signal
traveling to the receiver arrives from more than one path. This can
occur when the radio wave traverses over water or any other smooth
surface that causes the signal to reflect off the surface and arrive at
a different time than the intended signal does.
Structural issues must also be considered that can affect the
transmission performance through path fading or propagation loss. The
greater the density of the structural obstruction, the slower the radio
wave is propagated through it. When a radio wave is sent from a
transmitter and is obstructed by a structural object, the signal can
penetrate through the object, reflect off it, or be absorbed by it.
A critical step in deploying the WLAN is performing a wireless site
survey prior to the deployment. The survey will help determine the
number of APs to deploy and their optimum placement for performance
with regards to obstacles that affect radio waves as well as business
and security related issues.
Complete understanding of the infrastructure and environment with
respect to network media, operating systems, protocols, hubs, switches,
routers and bridges as well as power supply is necessary to maximize
performance and reduce network problems.
II. Wireless LAN Security Overview
As new deployments of Wireless LANs proliferate, security flaws are
being identified and new techniques to exploit them are freely
available over the Internet.
Sophisticated hackers use long-range antennas that are either
commercially available or built easily with cans or cylinders found in
a kitchen cupboard and can pick up 802.11b signals from up to 2,000
feet away. The intruders can be in the parking lot or completely out of
site. Simply monitoring the adjacent parking lots for suspicious
activity is far from solving the security issues around WLANs.
Many manufacturers ship APs with WEP disabled by default and are never
changed before deployment. In an article by Kevin Poulsen titled "War
driving by the Bay", he and Peter Shipley drove through San Francisco
rush hour traffic and with an external antenna attached to their car
and some custom sniffing software, and within an hour discovered close
to eighty (80) wide open networks. Some of the APs even beacon the
company name into the airwaves as the SSID.
a. Authentication and Encryption
Since the security provided by WEP alone including the new 802.1x Port
Based IEE standard is extremely vulnerable, stronger authentication
and encryption methods should be deployed such as Wireless VPNs using
Remote Authentication Dial-In User Service (RADIUS) servers.
The VPN layer employs strong authentication and encryption mechanisms
between the wireless access points and the network, but do impact
performance, a VPN (IPSec) client over a wireless connection could
degrade performance up to 25%. RADIUS systems are used to manage
authentication, accounting and access to network resources.
While VPNs are being represented as a secure solution for wireless
LANs, one-way authentication VPNs are still vulnerable to exploitation.
In large organizations that deploy dial-up VPNs by distributing client
software to the masses, incorrect configurations can make VPNs more
vulnerable to "session hi-jacking". There are a number of known attacks
to one-way authentication VPNs and RADIUS systems behind them that can
be exploited by attackers. Mutual authentication wireless VPNs offer
strong authentication and overcome weaknesses in WEP.
b. Attacking Wireless LANs
With the popularity of Wireless LANs growing, so is the popularity of
hacking them. It is important to realize that new attacks are being
developed based on old wired network methods. Strategies that worked on
securing wired resources before deploying APs need to be reviewed to
address new vulnerabilities.
These attacks provide the ability to:
Monitor and manipulate traffic between two wired hosts behind a
firewall
Monitor and manipulate traffic between a wired host and a
wireless host
Compromise roaming wireless clients attached to different
Access Points
Monitor and manipulate traffic between two wireless clients
Below are some known attacks to wireless LANs that can be applied to
VPNs and RADIUS systems:
Session Hijacking
Session hijacking can be accomplished by monitoring a valid wireless
station successfully complete authenticating to the network with a
protocol analyzer. Then the attacker will send a spoofed disassociate
message from the AP causing the wireless station to disconnect. When
WEP is not used the attacker has use of the connection until the next
time out Session hijacking can occur due to vulnerabilities in 802.11
and 802.1x state machines. The wireless station and AP are not
synchronized allowing the attacker to disassociate the wireless station
while the AP is unaware that the original wireless station is not
connected.
Man-in-the-middle
The man-in-the-middle attack works because 802.1x uses only one-way
authentication. In this case, the attacker acts as an AP to the user
and as a user to the AP. There are proprietary extensions that enhance
802.1x to defeat this vulnerability from some vendors.
RADIUS Attacks
The XForce at Internet Security Systems published vulnerability
findings in multiple vendors RADIUS offerings. Multiple buffer overflow
vulnerabilities exist in the authentication routines of various RADIUS
implementations. These routines require user-supplied information.
Adequate bounds checking measures are not taken when parsing user-
supplied strings. Generally, the "radiusd" daemon (the RADIUS listener)
runs with super user privilege. Attackers may use knowledge of these
vulnerabilities to launch a Denial of Service (DoS) attack against the
RADIUS server or execute arbitrary code on the RADIUS server. If an
attacker can gain control of the RADIUS server, he may have the ability
to control access to all networked devices served by RADIUS, as well as
gather login and password information for these devices.
An Analysis of the RADIUS Authentication Protocol is listed below:
Response Authenticator Based Shared Secret Attack User-
Password Attribute Cipher Design Comments
User-Password Attribute Based Shared Secret Attack
User-Password Based Password Attack
Request Authenticator Based Attacks
Passive User-Password Compromise Through Repeated Request
Authenticators
Active User-Password Compromise through Repeated Request
Authenticators
Replay of Server Responses through Repeated Request
Authenticators
DOS Arising from the Prediction of the Request Authenticator
IV. Protecting Wireless LANS
As discussed above, there are numerous methods available to exploit the
security of wired networks via wireless LANs. Layered security and well
thought out strategy are necessary steps to locking down the network.
Applying best practices for wireless LAN security does not alert the
security manager or network administrator when the security has been
compromised.
Intrusion Detection Systems (IDS) are deployed on wired networks even
with the security provided with VPNs and firewalls. However, wire-based
IDS can only analyze network traffic once it is on the wire.
Unfortunately, wireless LANs are attacked before entering the wired
network and by the time attackers exploit the security deployed, they
are entering the network as valid users.
For IDS to be effective against wireless LAN attacks, it first MUST be
able to monitor the airwaves to recognize and prevent attacks before
the hacker authenticates to the AP.
a. Principles of Intrusion Detection
Intrusion Detection is the art of detecting inappropriate, incorrect,
or anomalous activity and responding to external attacks as well as
internal misuse of computer systems. Generally speaking, Intrusion
Detection Systems (IDS) are comprised of three functional areas:
A stream source that provides chronological event information
An analysis mechanism to determine potential or actual
intrusions
A response mechanism that takes action on the output of the
analysis mechanism.
In the wireless LAN space, the stream source would be a remote sensor
that promiscuously monitors the airwaves and generates a stream of
802.11 frame data to the analysis mechanism. Since attacks in wireless
occur before data is on the wired network, it is important for the
source of the event stream to have access to the airwaves before the AP
receives the data.
The analysis mechanism can consist of one or more components based on
any of several intrusion detection models. False positives, where the
IDS generated an alarm when the threat did not actually exist, severely
hamper the credibility of the IDS. In the same light, false negatives,
where the IDS did not generate an alarm and a threat did exist, degrade
the reliability of the IDS.
Signature-based techniques produce accurate results but can be limited
to historical attack patterns. Relying solely on manual signature-based
techniques would only be as good as the latest known attack signature
until the next signature update. Anomaly techniques can detect unknown
attacks by analyzing normal traffic patterns of the network but are
less accurate than the signature-based techniques. A multi-dimensional
intrusion detection approach integrates intrusion detection models that
combine anomaly and signature-based techniques with policy deviation
and state analysis.
b. Vulnerability Assessment
Vulnerability assessment is the process of identifying known
vulnerabilities in the network. Wireless scanning tools give a snapshot
of activity and identify devices on each of the 802.11b channels and
perform trend analysis to identify vulnerabilities. A wireless IDS
should be able to provide scanning functionality for persistent
monitoring of activity to identify weaknesses in the network.
The first step in identifying weakness in a Wireless LAN deployment is
to discover all Access Points in the network. Obtaining or determining
each one's MAC address, Extended Service Set name, manufacturer,
supported transmission rates, authentication modes, and whether or not
it is configured to run WEP and wireless administrative management. In
addition, identify every workstation equipped with a wireless network
interface card, recording the MAC address of each device.
The information collected will be the baseline for the IDS to protect.
The IDS should be able to determine rogue AP's and identify wireless
stations by vendor fingerprints that will alert to devices that have
been overlooked in the deployment process or not meant to be deployed
at all.
Radio Frequency (RF) bleed can give hackers unnecessary opportunities
to associate to an AP. RF bleed should be minimized where possible
through the use of directional antennas discussed above or by placing
Access Points closer to the middle of buildings as opposed to the
outside perimeter.
c. Defining Wireless LAN Security Policies
Security policies must be defined to set thresholds for acceptable
network operations and performance. For example, a security policy
could be defined to ensure that Access Points do not broadcast its
Service Set Identifier (SSID). If an Access Point is deployed or
reconfigured and broadcasts the SSID, the IDS should generate an alarm.
Defining security policies gives the security or network administrator
a map of the network security model for effectively managing network
security.
With the introduction of Access Points into the network, security
policies need to be set for Access Point and Wireless Station
configuration thresholds. Policies should be defined for authorized
Access Points and their respective configuration parameters such as
Vendor ID, authentication modes, and allowed WEP modes. Allowable
channels of operation and normal activity hours of operation should be
defined for each AP. Performance thresholds should be defined for
minimum signal strength from a wireless station associating with an AP
to identify potential attacks from outside the building.
The defined security policies form the baseline for how the wireless
network should operate. The thresholds and configuration parameters
should be adjusted over time to tighten or loosen the security baseline
to meet real-world requirements. For example, normal activity hours for
a particular AP could be scaled back due to working hour changes. The
security policy should also be changed to reflect the new hours of
operation.
No one security policy fits all environments or situations. There are
always trade offs between security, usability and implementing new
technologies.
d.State-Analysis
Maintaining state between the wireless stations and their interactions
with Access Points is required for Intrusion Detection to be effective.
The three basic states for the 802.11 model are idle, authentication,
and association. In the idle state, the wireless station has either not
attempted authentication or has disconnected or disassociated. In the
authentication state, the wireless station attempts to authenticate to
the AP or in mutual authentication models such as the Cisco LEAP
implementation, the wireless station also authenticates the AP. The
final state is the association state, where the wireless station makes
the connection to the network via the AP.
Following is an example of the process of maintaining state for a
wireless station:
1. A sensor in promiscuous mode detects a wireless station trying to
authenticate with an AP
2. A state-machine logs the wireless stations MAC address, wireless
card vendor and AP the wireless station is trying to associate to by
reading 802.11b frames, stripping headers and populating a data
structure usually stored in a database
3. A state-machine logs the wireless station's successful association
to the AP
State Analysis looks at the behavioral patterns of the wireless station
and determines whether the activity deviates from the normal state
behavior. For example, if the wireless station was broadcasting
disassociate messages, that behavior would violate the 802.11 state
model and should generate an alarm.
e. Multi-Dimensional Intrusion Detection
The very natures of Wireless LANs intrinsically have more
vulnerabilities than their wired counterparts. Standard wire-line
intrusion detection techniques are not sufficient to protect the
network. The 802.11b protocol itself is vulnerable to attack. A multi-
dimensional approach is required because no single technique can detect
all intrusions that can occur on a wireless LAN. A successful multi-
dimensional intrusion detection approach integrates multiple intrusion
detection models that combine quantitative and statistical measurements
specific to the OSI Layer 1 and 2 as well as policy deviation and
performance thresholds.
Quantitative techniques include signature recognition and policy
deviation. Signature recognition interrogates packets to find pattern
matches in a signature database similar to anti-virus software.
Policies are set to define acceptable thresholds of network operation
and performance. For example, policy deviation analysis would generate
an alarm due to an improper setting in a deployed Access Point. Attacks
that exploit WLAN protocols require protocol analysis to ensure the
protocols used in WLANS have not been compromised. And finally,
statistical anomaly analysis can detect patterns of behavior that
deviate from the norm.
Signature Detection
A signature detection or recognition engine analyzes traffic to find
pattern matches manually against signatures stored in a database or
automatically by learning based on traffic pattern analysis. Manual
signature detection works on the same model as most virus protection
systems where the signature database is updated automatically as new
signatures are discovered. Automatic signature learning systems require
extensive logging of complex network activity and historic data mining
and can impact performance.
For wireless LANs, pattern signatures must include 802.11 protocol
specific attacks. To be effective against these attacks, the signature
detection engine must be able to process frames in the airwaves before
they are on the wire.
Policy Deviation
Security policies define acceptable network activity and performance
thresholds. A policy deviation engine generates alarms when these pre-
set policy or performance thresholds are violated and aids in wireless
LAN management. For example, a constant problem for security and
network administrators are rogue Access Points. With the ability for
employees to purchase and deploy wireless LAN hardware, it is difficult
to know when and where they have been deployed unless you manually
survey the site with a wireless sniffer or scanner.
Policy deviation engines should be able to alarm as soon as a rogue
access point has been deployed. To be effective for a wireless LAN, a
policy deviation engine requires access to wireless frame data from the
airwaves.
Protocol Analysis
Protocol analysis monitors the 802.11 MAC protocols for deviations from
the standards. Real-time monitoring and historical trending provide
intrusion detection and network troubleshooting.
Session hijacking and DoS attacks are examples of a protocol attack.
Maintaining state is crucial to detecting attacks that break the
protocol spec.
V .Wireless LAN Security Summary
Wireless LANs provide new challenges to security and network
administrators that are outside of the wired network. The inherent
nature of wireless transmission and the availability of published
attack tools downloaded from the Internet, security threats must be
taken seriously. Best practices dictate a well thought out layered
approach to WLAN security. Access point configuration, firewalls, and
VPNs should be considered. Security policies should be defined for
acceptable network thresholds and performance. Wireless LAN intrusion
detection systems complement a layered approach and provide
vulnerability assessment, network security management, and ensure that
what you think you are securing is actually secured.
Reference:
iee.org
cse.org
computer networks by Andrew S Tanenbaum
irda.com
Contents:
I. Introduction 1
II. Wireless LAN Deployment 7
II. Wireless LAN Security Overview 10
IV. Protecting Wireless LANs ..13
V. Wireless LAN Security Summary 18
SEMINAR REPORT
ON
WIRELESS LAN SECURITY
I. Introduction
a. The 802.11 Wireless LAN Standard
In 1997, the IEE ratified the 802.11 Wireless LAN standards,
establishing a global standard for implementing and deploying Wireless
LANS. The throughput for 802.11 is 2Mbps, which was well below the IEE
802.3 Ethernet counterpart. Late in 1999, the IEE ratified the 802.11b
standard extension, which raised the throughput to 11 Mbps, making this
extension more comparable to the wired equivalent. The 802.11b also
supports the 2 Mbps data rate and operates on the 2.4GHz band in radio
frequency for high-speed data communications
As with any of the other 802 networking standards (Ethernet, Token
Ring, etc.), the 802.11 specification affects the lower layers of the
OSI reference model, the Physical and Data Link layers.
The Physical Layer defines how data is transmitted over the physical
medium. The IEE assigned 802.11 two transmission methods for radio
frequency (RF) and one for Infrared. The two RF methods are frequency
hopping spread-spectrum (FHSS) and direct sequence spread-spectrum
(DSS). These transmission methods operate within the ISM (Industrial,
Scientific, and Medical) 2.4 GHz band for unlicensed use. Other devices
that operate on this band include remote phones, microwave ovens, and
baby monitors.
FHSS and DSS are different techniques to transmit data over radio
waves. FHSS uses a simple frequency hopping technique to navigate the
2.4GHz band which is divided into 75 sub-channels 1MHz each. The sender
and receiver negotiate a sequence pattern over the sub-channels.
DSS, however, utilizes the same channel for the duration of the
transmission by dividing the 2.4 GHz band into 14 channels at 22MHz
each with 11 channels overlapping the adjacent ones and three non-
overlapping channels. To compensate for noise and interference, DSS
uses a technique called "chipping", where each data bit is converted
into redundant patterns called "chips".
The Data Link layer is made up of two sub-layers, the Media Access
Control (MAC) layer and the Logical Link Control (LLC) layer. The Data
Link layer determines how transmitted data is packaged, addressed and
managed within the network. The LLC layer uses the identical 48-bit
addressing found in other 802 LAN networks like Ethernet where the MAC
layer uses a unique mechanism called carrier sense multiple access,
collision avoidance (CSMA/CA). This mechanism is similar to the carrier
sense multiple access collision detect (CSMA/CD) used in Ethernet, with
a few major differences. Opposed to Ethernet, which sends out a signal
until a collision is detected before a resend, CSMA/CA senses the
airwaves for activity and sends out a signal when the airwaves are
free. If the sender detects conflicting signals, it will wait for a
random period before retrying. This technique is called "listening
before talking" (LBT) and probably would be effective if applied to
verbal communications also.
To minimize the risk of transmission collisions, the 802.11 committee
decided a mechanism called Request-To-Send / Clear-To-Send (RTS/CTS).
An example of this would be when an AP accepts data transmitted from a
wireless station; the AP would send a RTS frame to the wireless station
that requests a specific amount of time that the station has to deliver
data to it. The wireless station would then send an CTS frame
acknowledging that it will wait to send any communications until the AP
completes sending data. All the other wireless stations will hear the
transmission as well and wait before sending data. Due to the fragile
nature of wireless transmission compared to wired transfers, the
acknowledgement model (ACK) is employed on both ends to ensure that
data does not get lost in the airwaves.
b. 802.11 Extensions
Several extensions to the 802.11 standard have been either ratified or
are in progress by their respective task group committees. Below are
three current task group activities that affect WLAN users most
directly:
802.11a
The 802.11a ("another band") extension operates on a different physical
layer specification than the 802.11 standard at 2.4GHz. 802.11a
operates at 5GHz and supports date rates up to 54Mbps. The FCC has
allocated 300Mz of RF spectrum for unlicensed operation in the 5GHz
range. Although 802.11a supports much higher data rates, the effective
distance of transmission is much shorter than 802.11b and is not
compatible with 802.11b equipment and in its current state is usable
only in the US. However, several vendors have embraced the 802.11a
standard and some have dual band support AP devices and network cards.
802.11b
The 802.11b ("baseline") is currently the de facto standard for
Wireless LANs. As discussed earlier, the 802.11b extension raised the
data rate bar from 2Mbps to 11Mbps, even though the actual throughput
is much less. The original method employed by the 802.11 committee for
chipping data transmissions was the 11-bit chipping encoding technique
called the "Barker Sequence". The increased data rate from 2Mbps to
11Mbps was achieved by utilizing an advanced encoding technique called
Complementary Code Keying (CCK). The CCK uses Quadrature Phase Shift
Keying (QPSK) for modulation to achieve the higher data rates.
802.11g
The 802.11g ("going beyond b") task group, like 802.11a is focusing on
raising the data transmission rate up to 54Mbps, but on the 2.4MHz
band. The specification was approved by the IEE in 2001 and is
expected to be ratified in the second half of 2002. It is an attractive
alternative to the 802.11a extension due to its backward compatibility
to 802.11b, which preserves previous infrastructure investments.
The other task groups are making enhancements to specific aspects of
the 802.11 standard. These enhancements do not affect the data rates.
These extensions are below:
802.11d
This group is focusing on extending the technology to countries that
are not covered by the IEE.
802.11e
This group is focusing on improving multi-media transmission quality of
service.
802.11f
This group is focusing on enhancing roaming between APs and
interoperability between vendors.
802.11h
This group is addressing concerns on the frequency selection and power
control mechanisms on the 5GHz band in some European countries.
802.11i
This group is focusing on enhancing wireless lan security and
authentication for 802.11 that include incorporating Remote Access
Dialing User Service (RADIUS), Kerberos and the network port
authentication (IEE 802.1X). 802.1X has already been implemented by
some AP vendors.
c. 802.11 Security Flaws
802.11 wireless LAN security or lack of it remains at the top of most
LAN administrators list of worries. The security for 802.11 is provided
by the Wired Equivalency Policy (WEP) at the MAC layer for
authentication and encryption The original goals of IEE in defining
WEP was to provide the equivalent security of an "unencrypted" wired
network. The difference is the wired networks are somewhat protected by
physical buildings they are housed in. On the wireless side, the same
physical layer is open in the airwaves.
WEP provides authentication to the network and encryption of
transmitted data across the network. WEP can be set either to either an
open network or utilizing a shared key system. The shared key system
used with WEP as well as the WEP encryption algorithm are the most
widely discussed vulnerabilities of WEP. Several manufacturers'
implementations introduce additional vulnerabilities to the already
beleaguered standard.
WEP uses the RC4 algorithm known as a stream cipher for encrypting
data. Several manufacturers tout larger 128-bit keys, the actual size
available is 104 bits. The problem with the key is not the length, but
lies within the actual design of WEP that allows secret identification.
A paper written by Jesse Walker, "Unsafe at any key length" provides
insight to the specifics of the design vulnerabilities and explains the
exploitation of WEP.
The following steps explain the process of how a wireless station
associates to an AP using shared key authentication.
1) The wireless station begins the process by sending an authentication
frame to the AP it is trying to associate with.
2) The receiving AP sends a reply to the wireless station with its own
authentication frame containing 128 octets of challenge text.
3) The wireless station then encrypts the challenge text with the
shared key and sends the result back to the AP.
4) The AP then decrypts the encrypted challenge using the same shared
key and compares it to the original challenge text. If the there is a
match, an ACK is sent back to the wireless station, otherwise a
notification is sent back rejecting the authentication.
It is important to note that this authentication process simply
acknowledges that the wireless station knows the shared key and does
not authenticate against resources behind the AP. Upon authenticating
with the AP, the wireless station gains access to any resources the AP
is connected to.
This is what keeps LAN and security managers up at night. If WEP is the
only and last layer of defense used in a Wireless LAN, intruders that
have compromised WEP, have access to the corporate network. Most APs
are deployed behind the corporate firewall and in most cases
unknowingly are connected to critical down-line systems that were
locked down before APs were invented. There are a number of papers and
technical articles on the vulnerabilities of WEP that are listed in the
Reference section.
II. Wireless LAN Deployment
The biggest difference in deployment of Wireless LANs over their wired
counterpart are due to the physical layer operates in the airwaves and
is affected by transmission and reception factors such as attenuation,
radio frequency (RF) noise and interference, and building and
structural interference.
a. Antenna Primer
Antenna technology plays a significant role in the deployment,
resulting performance of a Wireless LAN, and enhancing security.
Properly planned placement can reduce stray RF signal making
eavesdropping more difficult.
Common terms that are used in describing performance of antenna
technology are as follows:
Isotropic Radiator - An antenna that radiates equally in all directions
in a three dimensional sphere is considered an "isotropic radiator".
Decibel (dB) - Describes loss or gain between two communicating devices
that is expressed in watts as a unit of measure.
dBi value - Describes the ratio of an antenna's gain when compared to
that of an Isotropic Radiator antenna. The higher the value, the
greater the gain.
Attenuation - Describes the reduction of signal strength over distance.
Several factors can affect attenuation including absorption
(obstructions such as trees that absorb radio waves), diffraction
(signal bending around obstructions with reflective qualities),
reflection (signal bounces off a reflective surface such as water), and
refraction (signal bends due to atmospheric conditions such as marine
fog).
Gain - Describes RF concentration over that of an Isotropic Radiator
antenna and is measured in dB.
Azimuth - Describes the axis for which RF is radiated.
Antennas come in all shapes and sizes including the home-made versions
using common kitchen cupboard cans to deliver specific performance
variations. Following are some commonly deployed antenna types.
Dipole Antenna:
This is the most commonly used antenna that is designed into most
Access Points. The antenna itself is usually removable and radiating
element is in the one inch length range. This type of antenna functions
similar to a television "rabbit ears" antenna. As the frequency gets to
the 2.4GHz range, the antenna required gets smaller than that of a
100Mz television. The Dipole antenna radiates equally in all directions
around its Azimuth but does not cover the length of the diagonal giving
a donut-like radiation pattern. Since the Dipole radiates in this
pattern, a fraction of radiation is vertical and bleeds across floors
in a multi-story building and have typical ranges up to 100 feet at
11Mbps.
Directional Antennas:
Directional antennas are designed to be used as a bridge antenna
between two networks or for point-to-point communications. Yagi and
Parabolic antennas are used for these purposes as well as others.
Directional antennas can reduce unwanted spill-over as they concentrate
radiation in one direction.
With the popularity of "war driving" (driving around in a car and
discovering unprotected WLANs) there is continuing research done on
enhancing distances and reducing spill-over by commercial and
underground groups. Advanced antennas like the "Slotted Waveguide" by
Trevor Marshal, utilizes multiple dipoles, one above the other, to
cause the signal radiation to be in phase so that the concentration is
along the axis of the dipoles.
b. Deployment Best Practices
Planning a Wireless LAN requires consideration for factors that affect
attenuation discussed earlier. Indoor and multi-story deployments have
different challenges than outdoor deployments. Attenuation affects
antenna cabling from the radio device to the actual antenna also. The
radio wave actually begins at the radio device and induces voltage as
it travels down the antenna cable and loses strength.
Multi-path distortion occurs in outdoor deployments where a signal
traveling to the receiver arrives from more than one path. This can
occur when the radio wave traverses over water or any other smooth
surface that causes the signal to reflect off the surface and arrive at
a different time than the intended signal does.
Structural issues must also be considered that can affect the
transmission performance through path fading or propagation loss. The
greater the density of the structural obstruction, the slower the radio
wave is propagated through it. When a radio wave is sent from a
transmitter and is obstructed by a structural object, the signal can
penetrate through the object, reflect off it, or be absorbed by it.
A critical step in deploying the WLAN is performing a wireless site
survey prior to the deployment. The survey will help determine the
number of APs to deploy and their optimum placement for performance
with regards to obstacles that affect radio waves as well as business
and security related issues.
Complete understanding of the infrastructure and environment with
respect to network media, operating systems, protocols, hubs, switches,
routers and bridges as well as power supply is necessary to maximize
performance and reduce network problems.
II. Wireless LAN Security Overview
As new deployments of Wireless LANs proliferate, security flaws are
being identified and new techniques to exploit them are freely
available over the Internet.
Sophisticated hackers use long-range antennas that are either
commercially available or built easily with cans or cylinders found in
a kitchen cupboard and can pick up 802.11b signals from up to 2,000
feet away. The intruders can be in the parking lot or completely out of
site. Simply monitoring the adjacent parking lots for suspicious
activity is far from solving the security issues around WLANs.
Many manufacturers ship APs with WEP disabled by default and are never
changed before deployment. In an article by Kevin Poulsen titled "War
driving by the Bay", he and Peter Shipley drove through San Francisco
rush hour traffic and with an external antenna attached to their car
and some custom sniffing software, and within an hour discovered close
to eighty (80) wide open networks. Some of the APs even beacon the
company name into the airwaves as the SSID.
a. Authentication and Encryption
Since the security provided by WEP alone including the new 802.1x Port
Based IEE standard is extremely vulnerable, stronger authentication
and encryption methods should be deployed such as Wireless VPNs using
Remote Authentication Dial-In User Service (RADIUS) servers.
The VPN layer employs strong authentication and encryption mechanisms
between the wireless access points and the network, but do impact
performance, a VPN (IPSec) client over a wireless connection could
degrade performance up to 25%. RADIUS systems are used to manage
authentication, accounting and access to network resources.
While VPNs are being represented as a secure solution for wireless
LANs, one-way authentication VPNs are still vulnerable to exploitation.
In large organizations that deploy dial-up VPNs by distributing client
software to the masses, incorrect configurations can make VPNs more
vulnerable to "session hi-jacking". There are a number of known attacks
to one-way authentication VPNs and RADIUS systems behind them that can
be exploited by attackers. Mutual authentication wireless VPNs offer
strong authentication and overcome weaknesses in WEP.
b. Attacking Wireless LANs
With the popularity of Wireless LANs growing, so is the popularity of
hacking them. It is important to realize that new attacks are being
developed based on old wired network methods. Strategies that worked on
securing wired resources before deploying APs need to be reviewed to
address new vulnerabilities.
These attacks provide the ability to:
Monitor and manipulate traffic between two wired hosts behind a
firewall
Monitor and manipulate traffic between a wired host and a
wireless host
Compromise roaming wireless clients attached to different
Access Points
Monitor and manipulate traffic between two wireless clients
Below are some known attacks to wireless LANs that can be applied to
VPNs and RADIUS systems:
Session Hijacking
Session hijacking can be accomplished by monitoring a valid wireless
station successfully complete authenticating to the network with a
protocol analyzer. Then the attacker will send a spoofed disassociate
message from the AP causing the wireless station to disconnect. When
WEP is not used the attacker has use of the connection until the next
time out Session hijacking can occur due to vulnerabilities in 802.11
and 802.1x state machines. The wireless station and AP are not
synchronized allowing the attacker to disassociate the wireless station
while the AP is unaware that the original wireless station is not
connected.
Man-in-the-middle
The man-in-the-middle attack works because 802.1x uses only one-way
authentication. In this case, the attacker acts as an AP to the user
and as a user to the AP. There are proprietary extensions that enhance
802.1x to defeat this vulnerability from some vendors.
RADIUS Attacks
The XForce at Internet Security Systems published vulnerability
findings in multiple vendors RADIUS offerings. Multiple buffer overflow
vulnerabilities exist in the authentication routines of various RADIUS
implementations. These routines require user-supplied information.
Adequate bounds checking measures are not taken when parsing user-
supplied strings. Generally, the "radiusd" daemon (the RADIUS listener)
runs with super user privilege. Attackers may use knowledge of these
vulnerabilities to launch a Denial of Service (DoS) attack against the
RADIUS server or execute arbitrary code on the RADIUS server. If an
attacker can gain control of the RADIUS server, he may have the ability
to control access to all networked devices served by RADIUS, as well as
gather login and password information for these devices.
An Analysis of the RADIUS Authentication Protocol is listed below:
Response Authenticator Based Shared Secret Attack User-
Password Attribute Cipher Design Comments
User-Password Attribute Based Shared Secret Attack
User-Password Based Password Attack
Request Authenticator Based Attacks
Passive User-Password Compromise Through Repeated Request
Authenticators
Active User-Password Compromise through Repeated Request
Authenticators
Replay of Server Responses through Repeated Request
Authenticators
DOS Arising from the Prediction of the Request Authenticator
IV. Protecting Wireless LANS
As discussed above, there are numerous methods available to exploit the
security of wired networks via wireless LANs. Layered security and well
thought out strategy are necessary steps to locking down the network.
Applying best practices for wireless LAN security does not alert the
security manager or network administrator when the security has been
compromised.
Intrusion Detection Systems (IDS) are deployed on wired networks even
with the security provided with VPNs and firewalls. However, wire-based
IDS can only analyze network traffic once it is on the wire.
Unfortunately, wireless LANs are attacked before entering the wired
network and by the time attackers exploit the security deployed, they
are entering the network as valid users.
For IDS to be effective against wireless LAN attacks, it first MUST be
able to monitor the airwaves to recognize and prevent attacks before
the hacker authenticates to the AP.
a. Principles of Intrusion Detection
Intrusion Detection is the art of detecting inappropriate, incorrect,
or anomalous activity and responding to external attacks as well as
internal misuse of computer systems. Generally speaking, Intrusion
Detection Systems (IDS) are comprised of three functional areas:
A stream source that provides chronological event information
An analysis mechanism to determine potential or actual
intrusions
A response mechanism that takes action on the output of the
analysis mechanism.
In the wireless LAN space, the stream source would be a remote sensor
that promiscuously monitors the airwaves and generates a stream of
802.11 frame data to the analysis mechanism. Since attacks in wireless
occur before data is on the wired network, it is important for the
source of the event stream to have access to the airwaves before the AP
receives the data.
The analysis mechanism can consist of one or more components based on
any of several intrusion detection models. False positives, where the
IDS generated an alarm when the threat did not actually exist, severely
hamper the credibility of the IDS. In the same light, false negatives,
where the IDS did not generate an alarm and a threat did exist, degrade
the reliability of the IDS.
Signature-based techniques produce accurate results but can be limited
to historical attack patterns. Relying solely on manual signature-based
techniques would only be as good as the latest known attack signature
until the next signature update. Anomaly techniques can detect unknown
attacks by analyzing normal traffic patterns of the network but are
less accurate than the signature-based techniques. A multi-dimensional
intrusion detection approach integrates intrusion detection models that
combine anomaly and signature-based techniques with policy deviation
and state analysis.
b. Vulnerability Assessment
Vulnerability assessment is the process of identifying known
vulnerabilities in the network. Wireless scanning tools give a snapshot
of activity and identify devices on each of the 802.11b channels and
perform trend analysis to identify vulnerabilities. A wireless IDS
should be able to provide scanning functionality for persistent
monitoring of activity to identify weaknesses in the network.
The first step in identifying weakness in a Wireless LAN deployment is
to discover all Access Points in the network. Obtaining or determining
each one's MAC address, Extended Service Set name, manufacturer,
supported transmission rates, authentication modes, and whether or not
it is configured to run WEP and wireless administrative management. In
addition, identify every workstation equipped with a wireless network
interface card, recording the MAC address of each device.
The information collected will be the baseline for the IDS to protect.
The IDS should be able to determine rogue AP's and identify wireless
stations by vendor fingerprints that will alert to devices that have
been overlooked in the deployment process or not meant to be deployed
at all.
Radio Frequency (RF) bleed can give hackers unnecessary opportunities
to associate to an AP. RF bleed should be minimized where possible
through the use of directional antennas discussed above or by placing
Access Points closer to the middle of buildings as opposed to the
outside perimeter.
c. Defining Wireless LAN Security Policies
Security policies must be defined to set thresholds for acceptable
network operations and performance. For example, a security policy
could be defined to ensure that Access Points do not broadcast its
Service Set Identifier (SSID). If an Access Point is deployed or
reconfigured and broadcasts the SSID, the IDS should generate an alarm.
Defining security policies gives the security or network administrator
a map of the network security model for effectively managing network
security.
With the introduction of Access Points into the network, security
policies need to be set for Access Point and Wireless Station
configuration thresholds. Policies should be defined for authorized
Access Points and their respective configuration parameters such as
Vendor ID, authentication modes, and allowed WEP modes. Allowable
channels of operation and normal activity hours of operation should be
defined for each AP. Performance thresholds should be defined for
minimum signal strength from a wireless station associating with an AP
to identify potential attacks from outside the building.
The defined security policies form the baseline for how the wireless
network should operate. The thresholds and configuration parameters
should be adjusted over time to tighten or loosen the security baseline
to meet real-world requirements. For example, normal activity hours for
a particular AP could be scaled back due to working hour changes. The
security policy should also be changed to reflect the new hours of
operation.
No one security policy fits all environments or situations. There are
always trade offs between security, usability and implementing new
technologies.
d.State-Analysis
Maintaining state between the wireless stations and their interactions
with Access Points is required for Intrusion Detection to be effective.
The three basic states for the 802.11 model are idle, authentication,
and association. In the idle state, the wireless station has either not
attempted authentication or has disconnected or disassociated. In the
authentication state, the wireless station attempts to authenticate to
the AP or in mutual authentication models such as the Cisco LEAP
implementation, the wireless station also authenticates the AP. The
final state is the association state, where the wireless station makes
the connection to the network via the AP.
Following is an example of the process of maintaining state for a
wireless station:
1. A sensor in promiscuous mode detects a wireless station trying to
authenticate with an AP
2. A state-machine logs the wireless stations MAC address, wireless
card vendor and AP the wireless station is trying to associate to by
reading 802.11b frames, stripping headers and populating a data
structure usually stored in a database
3. A state-machine logs the wireless station's successful association
to the AP
State Analysis looks at the behavioral patterns of the wireless station
and determines whether the activity deviates from the normal state
behavior. For example, if the wireless station was broadcasting
disassociate messages, that behavior would violate the 802.11 state
model and should generate an alarm.
e. Multi-Dimensional Intrusion Detection
The very natures of Wireless LANs intrinsically have more
vulnerabilities than their wired counterparts. Standard wire-line
intrusion detection techniques are not sufficient to protect the
network. The 802.11b protocol itself is vulnerable to attack. A multi-
dimensional approach is required because no single technique can detect
all intrusions that can occur on a wireless LAN. A successful multi-
dimensional intrusion detection approach integrates multiple intrusion
detection models that combine quantitative and statistical measurements
specific to the OSI Layer 1 and 2 as well as policy deviation and
performance thresholds.
Quantitative techniques include signature recognition and policy
deviation. Signature recognition interrogates packets to find pattern
matches in a signature database similar to anti-virus software.
Policies are set to define acceptable thresholds of network operation
and performance. For example, policy deviation analysis would generate
an alarm due to an improper setting in a deployed Access Point. Attacks
that exploit WLAN protocols require protocol analysis to ensure the
protocols used in WLANS have not been compromised. And finally,
statistical anomaly analysis can detect patterns of behavior that
deviate from the norm.
Signature Detection
A signature detection or recognition engine analyzes traffic to find
pattern matches manually against signatures stored in a database or
automatically by learning based on traffic pattern analysis. Manual
signature detection works on the same model as most virus protection
systems where the signature database is updated automatically as new
signatures are discovered. Automatic signature learning systems require
extensive logging of complex network activity and historic data mining
and can impact performance.
For wireless LANs, pattern signatures must include 802.11 protocol
specific attacks. To be effective against these attacks, the signature
detection engine must be able to process frames in the airwaves before
they are on the wire.
Policy Deviation
Security policies define acceptable network activity and performance
thresholds. A policy deviation engine generates alarms when these pre-
set policy or performance thresholds are violated and aids in wireless
LAN management. For example, a constant problem for security and
network administrators are rogue Access Points. With the ability for
employees to purchase and deploy wireless LAN hardware, it is difficult
to know when and where they have been deployed unless you manually
survey the site with a wireless sniffer or scanner.
Policy deviation engines should be able to alarm as soon as a rogue
access point has been deployed. To be effective for a wireless LAN, a
policy deviation engine requires access to wireless frame data from the
airwaves.
Protocol Analysis
Protocol analysis monitors the 802.11 MAC protocols for deviations from
the standards. Real-time monitoring and historical trending provide
intrusion detection and network troubleshooting.
Session hijacking and DoS attacks are examples of a protocol attack.
Maintaining state is crucial to detecting attacks that break the
protocol spec.
V .Wireless LAN Security Summary
Wireless LANs provide new challenges to security and network
administrators that are outside of the wired network. The inherent
nature of wireless transmission and the availability of published
attack tools downloaded from the Internet, security threats must be
taken seriously. Best practices dictate a well thought out layered
approach to WLAN security. Access point configuration, firewalls, and
VPNs should be considered. Security policies should be defined for
acceptable network thresholds and performance. Wireless LAN intrusion
detection systems complement a layered approach and provide
vulnerability assessment, network security management, and ensure that
what you think you are securing is actually secured.
Reference:
iee.org
cse.org
computer networks by Andrew S Tanenbaum
irda.com
Contents:
I. Introduction 1
II. Wireless LAN Deployment 7
II. Wireless LAN Security Overview 10
IV. Protecting Wireless LANs ..13
V. Wireless LAN Security Summary 18