Researcher reveals GPS vulnerabilities

A University of Texas professor successfully spoofed timing signals that control cellular networks and help power smart electric grid.

GPS timing signals that control the base stations in some cellular networks and other gadgets the size of small refrigerators that power the smart electric grid can fall prey to sophisticated spoofing attacks, according to a University of Texas researcher.

Todd Humphreys, an assistant professor at the University of Texas Radionavigation Laboratory, said he successfully spoofed a type of laboratory time reference receiver of the code division multiple access -- network technology Sprint and Verizon use that relies on GPS time -- with a transmitter he built for about $1,000.

Humphreys spoke in Washington last week during a meeting of an advisory board of the multi-agency Space Based Position, Timing and Navigation National Executive Committee.

In an interview, Humphreys said this spoof, which took about an hour, literally dragged the time of the reference receiver backward, inducing a 10-microsecond delay in an hour that could incapacitate the base stations that Sprint and Verizon use.

He also spoofed a type of timing receiver that provides precise signals to synchrophasors, which measure voltages and currents at diverse locations on a power grid so operators can assess the state of the electrical system. Humphreys said in less than an hour he degraded the timing signal so it sent spurious signals.

The North American SynchroPhasor Initiative, a partnership of the Energy Department and the North American Electric Reliability Corp., plans to install synchrophasors in power systems nationwide to help manage the smart grid; in turn the grid will use communications systems to manage distribution of power from generator to home or office.

The CDMA base stations and synchrophasors both use civil GPS timing receivers, which do not have built-in anti-spoofing protection, Humphreys said, noting only the GPS receivers the military uses have the ability to detect and frustrate spoofing attacks.

A spoofing attack against synchrophasors today would not bring down the power system, but Humphreys said, "it would make the smart grid less smart." Attacks against multiple cellular base stations in any city could shut down the network, he added.

Alison Silverstein, project manager for the North American SynchroPhasor Initiative, said her organization was well aware of the vulnerabilities of GPS and has redundant systems in place today, including a supervisory control and a data acquisition system, in case of spoofing attacks. She said her group wants to develop data check and validation methods to ensure the integrity of the information it uses to help run the grid.

"It's not within our capabilities to protect GPS" against spoofing, Silverstein said, adding, "I hope someone is working on it."

Logan Scott, a systems and signal processing consultant in Fort Collins, Colo., said the best way to prevent spoofing is to include data authentication in the civil GPS signal, which requires it be incorporated in satellite signals before they are launched. Scott said this could be done at "almost no cost," and said he suggested that civil signal authentication be incorporated in new GPS satellites in 2006 -- a recommendation that went nowhere.

Humphreys said the need to protect against spoofing becomes more important as the cost of gear drops, making it more attractive to those looking to wreak havoc.