The Iranian government says it has downed a “stealth” drone, not by shooting at it but by fooling it's GPS system into thinking it was landing at its home base. The story appeared in the Christian Science Monitor, which featured an interview with an Iranian engineer, explaining how they did it.
Senior U.S. officials deny it, but in principle, fooling a GPS signal isn’t that complicated. Global Positioning System signals aren’t very strong -- local television can interfere with them sometimes. According to the Iranian source, if a drone's signal were jammed, the drone would go on autopilot. At that point, the Iranian military could “spoof” the GPS signal, essentially fooling the drone into thinking it was in a different location than it actually was.
There are two GPS signals that go out to drones. One is a military-grade signal that is heavily encrypted. The other is the civilian one that isn’t as secure. By fooling the drone, the Iranians saved themselves the trouble of actually trying to break the encryption on the telemetry from the drone’s base.
The captured drone, called an RQ-170 sentinel, was designed with stealth in mind, which is why it looks rather like a B-2 bomber. It also contains some of the most advanced electronics the military uses.
While this is in principle a simple operation, the devil is in the details. It isn’t clear that the Iranian military could have fooled the drone with enough precision to land it without crashing, and the drone that appears in the Iranian news services’ footage looks to be in remarkably good shape. So there are skeptics out there who think the Iranian government is shooting for a propaganda victory and hasn’t actually managed to take over the drone.
That said, it's also true that drones’ signals aren’t as secure as they might be. In 2009, Iraqi insurgents were able to download the video feeds from U.S. military drones with inexpensive hardware and software.
And on top of that, there’s the possibility of hacking in the other direction. In August, two security researchers demonstrated that a drone built for a few thousand dollars from surplus parts could hack into phone systems and Wi-Fi networks.
The U.S. Air Force has been working on a navigation system that doesn’t depend on GPS for the last two years, so it's certainly aware of the problem.
More than a military setback for the United States, however, this incident might have diplomatic repercussions. The United States was using the drone to monitor Iran’s uranium-enrichment program, which the Iranians say is for energy; the United States has condemned the program as an attempt to build a nuclear weapon. Iran has taken its case to the United Nations, with Iranian television calling the overflights an act of war. If Iran can convince other nations that the United States has acted unlawfully, nations may find it difficult to support additional sanctions.