news item on GPS hacking

[frankly frankie]

http://news.bbc.co.uk/1/hi/sci/tech/8533157.stm

"Low-power, hand-held [jamming devices] that cost less than £100 can run for
hours on a battery and confuse sat-nav receivers tens of kilometres
away.

"You can now buy a low-cost simulator and link it to Google Earth, put
on a route and it will simulate that route to the timing that you
specify," said Professor Last.

"A GPS receiver overcome by it will behave as if you're travelling
along that route."

... jamming and spoofing, Professor Last said, were irresistible to
the hacker type who did it for fun.

"You can consider GPS a little like computers before the first virus -
if I had stood here before then and cried about the risks, you
would've asked 'why would anyone bother?'.

"It's the same market as the hackers."

[mrcharly-YHT]

"It's the same market as the hackers."

Yes and no.

Hacking & viruses didn't become a serious problem until the criminal element came along.

Apart for Somali pirates, I'm not sure I can see criminals being interested in messing with someone's gps track.

[JonBuoy]

I know that this is a real minority sport but cross-country gliding competitions are totally dependent on gps to prove that course points have been rounded, airspace has not been penetrated, etc, etc.  If GPS position becomes hackable the whole system is compromised.  I am not sure whether any other sports use similar validation technology.

[andygates]

AFAIK, we're talking about local Zones of Confusion [tm], nothing more; the "tens of kilometres" sounds a lot like an absolute max based on line of sight, etc.  Most users will pass through and think they've just dropped signal for a while. 

More useful to the crims is this sort of thing: Car Thieves Use GPS Jammers to Make a Clean Getaway | Gadget Lab | Wired.com

Block the GPS so the car can't report where it is.  Then have one at the chop shop to keep it under a cloud too.

Feeding a false signal is a lot more sophisticated at this point.  It'll be commodity in a week, sure... but wouldn't the fix be to use a more directional antenna that mostly looks up?  That's not hard to do.

[frankly frankie]

The GPS signals are so weak though.  Down at homeopathy levels really. 

The receivers we know are already slightly less than omnidirectional - the Etrex is known to work best when held horizontal, the 60 series is known to work best when held vertical walkie-talkie style.  They presumably need decent reception over a possible 180-degree sky view, in order to get whatever's up there, wherever it is, so that angle is bound to include any source of interference.

[andygates]

Aren't they as dim as a night-light, or something daft?  25 watts, it's a miracle they're visible at all.

What do you reckon then, a new era of localism with villagers jamming satnav so their villages are less fun to drive through for HGVs?   

[simonp]

Making people drive off cliffs. Oh the larks!

[frankly frankie]

Maybe some cyclists carry their own jammers.

I experimented last night with an old GPS (weak signal - on windowsill) and in very close proximity, 2 different 3W LED lights (Fenix and Topeak), in steady and flashing modes, and 2 mobile phones, logging on and off.
Some visible effects but nothing serious enough to compromise GPS reception.

[TimO]

Maybe some cyclists carry their own jammers.

I experimented last night with an old GPS (weak signal - on windowsill) and in very close proximity, 2 different 3W LED lights (Fenix and Topeak), in steady and flashing modes, and 2 mobile phones, logging on and off.
Some visible effects but nothing serious enough to compromise GPS reception.

My Satmap Active 10 sits three or four inches from my Exposure lights, and I've never noticed any issues.  Exposure do say (like other bright LED manufacturers) that their lights can interfere with wireless computers, but that will be broad spectrum noise interfering with a not very robust link (which is not the case with GPS).

The GPS power is pretty low (down below the noise) but is received using a spread-spectrum technique.  This in effect brings the power level up above the noise within the receiver, and a jamming signal won't gain the same advantage, since it won't use a gold code.

A spoofing signal will gain the advantage, and it wouldn't be difficult to generate a signal to do this, but as others have said, on most occasions it wouldn't be useful.

You could possibly limit it's effectiveness by using a electronically steerable antenna, but currently the technology would likely make that heavy, power hungry, and expensive.  You wouldn't so much steer the antenna onto the satellites, as null out the interfering signal.  It's a perfectly well understood mechanism, since the military will use it to avoid jamming.

[alexb]

I presume this is why the military use terrain following techniques to guide nuclear enabled cruise misslies rather than GPS.
TERCOM - Wikipedia, the free encyclopedia

[andygates]

I thought cruise predated GPS.  Moving way too fast to do it without a DEM of its own in-brain, anyway.

Plenty of military kit uses GPS.  There's a special channel and everything (encryption, one presumes, ensuring that it's spoof-proof).  Lots of military kit also sucks, though, so you'll see a lot of Garmins in military use too.

[TimO]

The military use the P(Y) code instead of C/A code.  It uses two frequencies to help compensating for ionospheric effects, and the spreading function runs at about ten times the speed, so you get much better accuracy.

Since the spreading function is essentially a key-variable generator (ie a cryptologically secure sequence), and has a period which is much much much longer than the gold codes used for the C/A code (iirc tens of years vs about one second!), it's going to be pretty much damned impossible to spoof it, and hence any interference will in effect just be "noise", so will be automatically ignored.

Having said that, they probably do include mechanisms to null out jamming as well, depending on the type of receiver.  A handheld receiver can't really do much of that sort of things, but something mounted on a ship or aircraft has more room for complicated antennas, and the power to drive such a system.

Things like PGMs and Cruise Missiles will use combinations of TFR, GPS, laser illumination, inertial guidance etc.  You use multiple sources to improve the overall system accuracy, and minimise the effects of any counter measures.