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Wireless LAN Security

Wireless local area networks (WLANs) based on the Wi-Fi (wireless fidelity) standards are one of today's fastest growing technologies in businesses, schools, and homes, for good reasons. They provide mobile access to the Internet and to enterprise networks so users can remain connected away from their desks. These networks can be up and running quickly when there is no available wired Ethernet infrastructure. They can be made to work with a minimum of effort without relying on specialized corporate installers.

Some of the business advantages of WLANs include:
" Mobile workers can be continuously connected to their crucial applications and data;
" New applications based on continuous mobile connectivity can be deployed;
" Intermittently mobile workers can be more productive if they have continuous access to email, instant messaging, and other applications;
" Impromptu interconnections among arbitrary numbers of participants become possible.
" But having provided these attractive benefits, most existing WLANs have not effectively addressed security-related issues.

THREATS TO WLAN ENVIRONMENTS

All wireless computer systems face security threats that can compromise its systems and services. Unlike the wired network, the intruder does not need physical access in order to pose the following security threats:

Eavesdropping

This involves attacks against the confidentiality of the data that is being transmitted across the network. In the wireless network, eavesdropping is the most significant threat because the attacker can intercept the transmission over the air from a distance away from the premise of the company.

Tampering

The attacker can modify the content of the intercepted packets from the wireless network and this results in a loss of data integrity.

Unauthorized access and spoofing

The attacker could gain access to privileged data and resources in the network by assuming the identity of a valid user. This kind of attack is known as spoofing. To overcome this attack, proper authentication and access control mechanisms need to be put up in the wireless network.

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WIRELESS LAN SECURITY

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Introduction

The 802.11 Wireless LAN Standard

In 1997, the IEEE 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 IEEE 802.3 Ethernet counterpart. Late in 1999, the IEEE 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.

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 IEEE 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.

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.

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.

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.

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.

Authentication and Encryption

Since the security provided by WEP alone including the new 802.1x Port Based IEEE 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.

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.