Wi-Fi Planet: How to locate network intruders

Lisa Phifer works for Core Competence Inc., an IT security consultancy in Philadelphia, a company that presumably knows a thing or two about encryption algorithms, public key infrastructure, and other technology designed to keep networks protected. But Phifer also knows that something has been left out of the dialogue surrounding wireless network security: location.

“Location really is the missing link,” she said, pointing out that it’s all well and good to keep access controlled via encryption, and to be able to say there’s an intruder on the network. But it’s quite another thing to be able to say where that person is.

To fill help that gap in the protection paradigm, Phifer attended a discussion about wireless security at Wi-Fi Planet, a wireless technology conference held in Toronto from March 16 to 18. Here a pair of industry insiders gave conference attendees a tutorial in location-based security measures for wireless LANs (WLANs).

Bob Friday, chief scientist at Airespace Inc., a wireless network provider, said wireless networks are more difficult to lock down than wireline networks are. Wireless ignores barriers like walls, so networks can spill out into streets. And whereas you could track down a rogue user on a wired network by following a cable’s physical path, wireless networks offer no wires to go by.

Still, he said, there are ways to find unwanted network visitors and rogue access points. Location-based security comes in a couple of flavours. There are “time difference of arrival” (TDA) systems that consider the time it takes a signal from a client or network node to reach an access point. Generally one nanosecond equates to one foot. If you catch a client signal with an elapsed time of arrival of, say, 90 nanoseconds, you know the intruder is about 90 feet away.

Friday said TDA systems are easy to set up and require no site survey to do the job. However, they also require custom hardware and quick processing capabilities to detect the tiny difference of one or two nanoseconds. As well, they don’t account for walls, which can hinder a signal by at least a nanosecond and throw off the entire distance calculation.

Another kind of location-based security uses signal strength to decide where an intruder might be. The simplest of this type calculates the closest access point to the questionable signal, while a more sophisticated “fingerprinting” model provides a probability map of where the rogue is hiding. Friday said these systems can pinpoint a client’s location down to one metre, but they require a detailed site survey to work well.

For his part of the seminar, Michael Maggio, president of location-based security solution provider Newbury Networks Inc., presented the U.S. Air Force’s story, which wanted to install WLANs at its bases so mechanics working on planes could access manuals and parts lists via wireless computers, and pilots on the tarmac would be able to download mission instructions from the cockpit.

But the Air Force also did not want to let rogue users and access points connect to the network, and it realized that encryption alone wouldn’t provide the level of protection required.

“I refer to it as ‘the grass hut, steel door model,’” Maggio said, explaining that encryption might protect one part of the network, but with time and covertness on his side, an intruder might find another way into the system.

By deploying location detectors, the Air Force managed to create perimeter security around its WLAN, Maggio said.

Asked if she found the session helpful, Phifer from Core Competence said she did, pointing out that Friday’s breakdown of security methods give her a starting point for putting location back into the security dialogue. “Now I know what to look for.”

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