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0 pointsNelsonMinar14y ago0 comments

This attack is what Iran says they did to capture the US drone a few months ago. It's pretty crazy that GPS signals include no cryptographic authentication, even for military use.

I'm not so worried about this kind of attack on civilian aviation. It would be a directed attack: potentially deadly but rare and focussed. I'm much more worried about the casual disruption to GPS from truck drivers spending $99 on a grey market device.

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zbowling14y ago· 4 in thread

There is cryptographic hash so that you can't send false data, but replaying the existing data but time delayed is still possible. The timing is how the triangulation fix is done. More sources of data, the harder it is to spoof. If you only have 3 or 4 fixed points, it's easy to spoof. 6 to 10 and it becomes extremely difficult.

Also military GPS is far more accurate than civilian GPS by a factor of 10x.

cheald14y ago

I'm speaking out of ignorance here, but why couldn't you just use a quantitized time value (to account for transmission lag) as a part of the data that's hashed? It works great to prevent replay attacks with OAuth.

zbowling14y ago

nope. it's time that is the factor for triangulation. you always take the first time you received from the one source and you can discard certainly something way out side of what you expect. It's how you defeat the concreate canyon effect in big cities where signals are bouncing off everything.

However if you have a low strength signal from one source and you receive a frame that is a second or a two off, it can cause you to think you are miles away from where you think you supposed to be.

ghshephard14y ago

"military GPS is far more accurate than civilian GPS" - is this still true? I don't know how my iPhone GPS triangulates me, but it usually has me located to within 3-5' at all times when I'm walking home.

zbowling14y ago

yep. the reason why your iPhone is fast has to do more with AGPS and that it can use wifi access points as references points as well.

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