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GPS security a concern for university expert

July 26, 2012 // Rick Merritt

GPS security a concern for university expert

After testifying before Congress about security vulnerabilities in civil GPS systems last week, Todd Humphreys is convinced the industry needs a new approach to plugging holes in what he calls “the most popular unauthenticated protocol in the world.”


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Theres a way to add backward-compatible authentication like digital watermarks to GPS signals, and last week I had my best shot at convincing lawmakers to fix the problem at the signal source, said Humphreys who directs the Radionavigation Laboratory at the University of Texas at Austin.

I dont think I will even pursue that anymore because I got a strong sense it is a non-starter, Humphreys. No one wants to touch the signals broadcast from the satellites even though all we are asking is to define a new message, he added.

Only 15 of the 62 possible GPS messages are currently defined. Humphreys and other GPS security experts recommend defining two messages that could automatically authenticate GPS signals.

Even if the U.S. government had the will to make the technical changes, it could take more than five years to implement, Humphreys said. Thats too late given a Congressional mandate opening up the use of civilian drones in the U.S. in 2015.

Humphreys went to Washington DC hoping lawmakers would embrace the cryptographic solution developed in his lab. We spent two years writing that paper and wanted to hand it to lawmakers as a template free of charge to implement--it will work fairly well, he said.

The problem is that hackers can readily spoof civil GPS signals. Humphreys lab has shown how hackers can use faked GPS signals to take over operation of a drone aircraft, a power grid or a cellular network.

I dont want to be an alarmist, but to me it defies reason that we would continue to develop around unauthenticated civilian GPS protocols, he said. It seems to be a fairly significant vulnerability like leaving the back door to your house openthe odds are nothing will happen, but you wont feel good about it, he said.

With the door to authenticated civilian GPS effectively closed, Humphreys and other researchers are turning their attention to a grassroots campaign. Theres a laundry list of defenses--detailed in his testimony last week--that can be implemented by GPS receivers.

The first thing engineers can do is pay attention to auto gain controls in receiver front ends that can tell you the power levels of the incoming GPS signals, said Humphreys.

GPS signals are very weak. Hackers trying to create fake signals to control a system are most likely to use readily available GPS test systems that emit significantly more powerful signals.

An op amp responsible for auto gain control could deliver a GPS signal voltage readout to a baseband chip. The baseband could then do a relatively straightforward calculation to determine whether the signal was coming from a tester or a satellite.

The measure would not detect a more sophisticated GPS spoofer such as the units the Austin lab has developed using software radios based on Texas Instruments DSPs.

So far only one company supports auto gain control, but it is too coarse to detect GPS tester signals, he said.

Several other fixes could be implemented at the receiver, such as using multiple antennas. But most of them are not suitable for mobile systems because they require too much physical space.

The fixes do not appear to be on the radar screen for consumer GPS chip makers such as Broadcom and Qualcomm. They are probably aware of it but they have taken no steps as far as I can tell, Humphreys said.

Ostensibly, the threat to consumer gadgets such as smartphones and car navigation devices is relatively low. Hackers likely would not be motivated to get the average driver lost on the way to his hotel or weekend party.

However, a GPS hack potentially could be used to compromise other aspects of a device. For example, at the Black Hat conference this week, one security expert will show how hackers could spoof near-field communications signals to access data on a smartphone.

The bigger threat is to critical national infrastructure gear that typically uses higher end chips that still are not protected, many of them supplied by NovAtel of Calgary, Canada, he said.

If you could just build some paranoia using these receiver techniques, we would be leagues ahead of where we are today, he said.

The Texas lab got interested in the drone problem after Iran broadcast pictures of a U.S. drone spy plane it captured last December. Iranians claimed they used a spoofing attack to capture the drone.

The lab was able to secure fundingand use of a White Sands, New Mexico facility-- from the U.S. Department of Homeland Security to determine the level of vulnerability of civilian drones.

It was months of hard work, said Humphreys. We showed these drones nav systems are hackable by their exposed GPS stream, and once you spoof it, you can have your way with a drone, he said.

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