Tin Cans and Wireless LANs

Did you read the recent British Broadcasting Corporation (BBC) news story about "war-driving"? War-driving is the act of driving around with an antenna trying to detect unprotected wireless networks, and a lot of people have been doing just that ever since wireless LAN (WLAN) equipment made its debut. (See "Hacking with a Pringles tube".)

The story seems to be an attempt to sensationalize the fact that people can make their own antennas with readily available parts, such as standard antenna cable connectors and potato-chip cans, and that those antennas are more sensitive than run-of-the-mill commercial wireless antennas. Because the homemade antennas are more sensitive, they're more capable of finding insecure WLANs that have weaker signals leaking from their various origin points. In addition, you can orient some homemade antennas directionally. The antennas not only pick up signals from and possibly connect to unprotected wireless devices but also help pinpoint where those unsecured LAN devices are relative to the antennas' position. Clearly, intruders might use such antennas to identify and attack companies that don't practice adequate wireless security.

About a month ago, Gregory Rehm updated his Web site with the latest "802.11b Homebrew Antenna Shootout" data. When you visit the Web site, you'll find that reviewers rated several homemade antennas and one commercial antenna during tests. As it turns out, a waveguide antenna got the best reception. The particular waveguide antenna was made from a small piece of copper wire, a standard antenna cable connector, and a metal can that once held Nalley Big Chunk Beef Stew. No, I'm not kidding. That combination is all you need to make a powerful wireless antenna. Constructed from those basic parts, the waveguide antenna demonstrated a tremendous signal gain over off-the-shelf commercial antennas.

So what does this information mean to security administrators? You can use an inexpensive homemade antenna to test the signal leakage parameters of your WLAN and perform leakage tests for others against their WLANs. In addition, if you have LAN-connectivity problems that require wireless equipment to span a distance (e.g., between two buildings), you can build your own antennas and save money. Check out Rehm's Web site, which provides links to information about a half-dozen homemade wireless antennas (including plans) and to Web-based calculators that help you design your own antennas from items such as empty coffee cans from the company break room.

For background information about WLAN security, be sure to read my commentary
"802.11 Wireless Networks: Is Yours Really Safe?".

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