When I was writing the original edition of Upgrading and Repairing PCs back in the 1980s, the hackers’ favorite way of trying to get into a network without authorization was discovering the telephone number of a modem on the network, dialing in with a computer, and guessing the password—as in the movie War Games. Today, war driving has largely replaced this pastime as a popular hacker sport. War driving is the popular name for driving around neighborhoods with a laptop computer equipped with a wireless network card on the lookout for unsecured networks. They’re all too easy to find, and after someone gets onto your network, all the secrets in your computer can be theirs for the taking.
Because wireless networks can be accessed by anyone within signal range who has a NIC matching the same IEEE standard of that wireless network, wireless NICs and access points provide for encryption options. Most access points (even cheaper SOHO models) also provide the capability to limit connections to the access point by using a list of authorized MAC numbers (each NIC has a unique MAC). MAC address filtering is designed to limit access to authorized devices only.
Although MAC address filtering can be helpful in stopping bandwidth borrowing by your neighbors, it cannot stop attacks because the MAC address can easily be “spoofed” or faked. Consequently, you need to look at other security features included in wireless networks, such as encryption.
All Wi-Fi products support at least 40-bit encryption through the wired equivalent privacy (WEP) specification, but the minimum standard on recent 802.11g products is 64-bit WEP encryption. Many vendors offer 128-bit or 256-bit encryption on their products. However, the 128-bit and stronger encryption feature is more common among enterprise products than SOHO-oriented products. Unfortunately, the WEP specification at any encryption strength has been shown to be notoriously insecure against determined hacking. Enabling WEP keeps a casual snooper at bay, but someone who wants to get into your wireless network won’t have much trouble breaking WEP. For that reason, all wireless network products introduced after 2003 incorporate a different security standard known as Wi-Fi Protected Access (WPA). WPA is derived from the developing IEEE 802.11i security standard. WPA-enabled hardware works with existing WEP-compliant devices, and software upgrades are often available for existing devices to make them WPA capable. The most recent 802.11g and all 802.11n devices also support WPA2, an updated version of WPA that uses a stronger encryption method. (WPA uses TKIP or AES; WPA2 uses AES.) The newer 802.11ac standard does not support WEP.
Upgrading to WPA or WPA2 also can require updates to your OS, especially if you are using an older version of Windows or Linux. For example, Windows XP Service Pack 2 includes support for WPA encryption. However, to use WPA2 with Windows XP Service Pack 2, you must also download the Wireless Client Update for Windows XP with Service Pack 2 or install Service Pack 3. At the http://support.microsoft.com website, look up Knowledge Base article 917021.
Most Linux distros use wpa_supplicant. If your distro does not include wpa_supplicant, or if you need to configure it, see the website URL http://w1.fi/wpa_supplicant/.
Your network will not function if different encryption levels and types are used on its wireless hardware. Use the best available encryption level and encryption type available on both the access points and the NICs for best security. Remember that if some of your network supports WPA but other parts support only WEP, your network must use the lesser of the two security standards (WEP). If you want to use the more robust WPA or WPA2 security, you must ensure that all the devices on your wireless network support WPA. Because WEP is easily broken and the specific WEP implementations vary among manufacturers, I recommend using only devices that support WPA or WPA2.