They would have to be signed including GPS coordinates, otherwise they would be vulnerable to a replay attack. And since GPS is not that precise, you would still be able to, say, take two nearby signs and switch them.
No, those markers work by listening to the GPS signals for an extended period of time and maybe PPK or perhaps an alternative network that's not satellite based.
I think the thrust of GPs argument is "Before they take away the UA string (the one clumsy tool that I can use to half-accomplish my goals) I wish they'd add official APIs to detect these kinds of things".
That's completely unrelated. "GPS" on that sign is shorthand for "navigation map data". Even in populated areas like bay area, there are instances of this all around.
> if the car's local sensors deviate from the gps data significantly, that should throw up a red flag to the car and driver.
This happens too often for benign reasons (and GPS hacking too rare) for it to be useful. The GPS system in my Ford Focus jumps around wildly if I start the car in an enclosed space before it gets a good lock, and it can be thrown-off under bridges and around tall buildings as it doesn't have A-GPS (does any car have A-GPS?). The worst is when a poor signal is combined with road-snapping - I've had a lot of trouble with off-ramps on partially submerged urban highways, the I-5 in downtown Seattle, for example.
We are using a lot of signals too. GPS is the only one we talk about :)
You're right, it is a very delicate line between catching as many cheaters as possible while avoiding false-positives. We like to err on the side of false-negatives as much as possible.
considering that GPS has civilian and military parts of the signal, are the messages not signed by, i don't know, U.S. military or something? how come it is easy to spoof?
Do GPS signals not correlate themselves with a compass reading? I would think that comparing the change in coordinates to the external fact would prevent spoofing.
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