The fact that a majority of this year’s graduates from USAF basic pilot training are assigned to drone squadrons has got quite a bit of play in the blogosphere. Here, via Jamie Kenny, John Robb (who may still be burying money for fear of Obama or may not) argues that the reason they still do an initial flight training course is so that the pilot-heavy USAF hierarchy can maintain its hold on the institution. He instead wants to recruit South Korean gamers, in his usual faintly trendy dad way. Jamie adds the snark and suggests setting up a call centre in Salford.
On the other hand, before Christmas, the Iranians caught an RQ-170 intelligence/reconnaissance drone. Although the RQ-170 is reportedly meant to be at least partly stealthy, numerous reports suggest that the CIA was using it among other things to get live video of suspected nuclear sites. This seems to be a very common use case for drones, which usually have a long endurance in the air and can be risked remaining over the target for hours on end, if the surveillance doesn’t have to be covert.
Obviously, live video means that a radio transmitter has to be active 100% of the time. It’s also been reported that one of the RQ-170’s main sensors is a synthetic-aperture radar. Just as obviously, using radar involves transmitting lots of radio energy.
It is possible to make a radio transmitter less obvious, for example by saving up information and sending it in infrequent bursts, and by making the transmissions as directional as possible, which also requires less power and reduces the zone in which it is possible to detect the transmission. However, the nature of the message governs its form. Live video can’t be burst-transmitted because it wouldn’t be live. Similarly, real-time control signalling for the drone itself has to be instant, although engineering telemetry and the like could be saved and sent later, or only sent on request. And the need to keep a directional antenna pointing precisely at the satellite sets limits on the drone’s manoeuvring. None of this really works for a mapping radar, though, which by definition needs to sweep a radio beam across its field of view.
Even if it was difficult to acquire it on radar, then, it would have been very possible to detect and track the RQ-170 passively, by listening to its radio emissions. And it would have been much easier to get a radar detection with the advantage of knowing where to look.
There has been a lot of speculation about how they then attacked it. The most likely scenario suggests that they jammed the command link, forcing the drone to follow a pre-programmed routine for what to do if the link is lost. It might, for example, be required to circle a given location and wait for instructions, or even to set a course for somewhere near home, hold, and wait for the ground station to acquire them in line-of-sight mode.
Either way, it would use GPS to find its way, and it seems likely that the Iranians broadcast a fake GPS signal for it. Clive “Scary Commenter” Robinson explains how to go about spoofing GPS in some detail in Bruce Schneier’s comments, and points out that the hardware involved is cheap and available.
Although the military version would require you to break the encryption in order to prepare your own GPS signal, it’s possible that the Iranians either jammed it and forced the drone to fall back on the civilian GPS signal, and spoofed that, or else picked up the real signal at the location they wanted to spoof and re-broadcast it somewhere else, an attack known as “meaconing” during the second world war when the RAF Y-Service did it to German radio navigation. We would now call it a replay attack with a fairly small time window. (In fact, it’s still called meaconing.) Because GPS is based on timing, there would be a limit to how far off course they could put it this way without either producing impossible data or messages that failed the crypto validation, but this is a question of degree.
It’s been suggested that Russian hackers have a valid exploit of the RSA cipher, although the credibility of this suggestion is unknown.
The last link is from Charlie Stross, who basically outlined a conceptual GPS-spoofing attack in my old Enetation comments back in 2006, as a way of subverting Alistair Darling’s national road-pricing scheme.
Anyway, whether they cracked the RSA key or forced a roll-back to the cleartext GPS signal or replayed the real GPS signal from somewhere else, I think we can all agree it was a pretty neat trick. But what is the upshot? In the next post, I’m going to have a go at that…