> No amount of encryption prevents relay attacks.
Encryption + timestamp + message that expires after MAX_DISTANCE/c seems like it would be pretty foolproof. There are of course some challenges in having enough precision in the clocks, though.
Encryption + timestamp + message that expires after MAX_DISTANCE/c seems like it would be pretty foolproof. There are of course some challenges in having enough precision in the clocks, though.
- Relay attacks can theoretically be solved with high precision clocks, but will affect price and reliability in a negative way
This obviously depends a bit on the situation, but most relay attacks happen within reasonable proximity. Most attacks happen to a car parked in front of a house, since the attacker knows that the keyfob is likely to be within the house. The distance here is often less than 20m. To get reasonably reliable relay detection on these kinds of distances, you'll need very precise clocks, which will make the keyfobs expensive and still increases the risk of false positives on relay detection.
What's the point (to the customer) if the expensive ULTRA SECURE (tm) keyless entry system is 10x the price, and still less reliable than the keyless entry system om their 20 year old Toyota?
Imagine your engine shutting off on the highway, and your steering wheel locks, just because the car briefly looses response from the keyfob...
Also, just about every keyless entry systems have a physical backup key, to start and drive the car in case the battery in the keyfob is empty. A periodical re-authentication would make this impossible.
Stuck in the middle of the desert with a perfectly good car, but an empty keyfob battery? Well, sucks to be you, you'll likely die, but at least your car won't be vulnerable to relay attacks!
Additionally, the highway scenario could also be mitigated with a warning and a grace period. The desert scenario can be mitigated with having a fallback such as having the contactless system double as a smartcard you can put into a reader or by wireless power transfer. Plus, if your contactless system fails in the desert you're screwed anyway as soon as you turn off the engine once.
Right, stop once for a traffic jam, car loses sync with keyfob, and you'll become a stationary target on a highway.
Better swap out those batteries in your keyfob real quick before that 18-wheeler smashes into your car with kids in the backseat!
But hey, at least your car won't be stolen!
> Problem solved.
I guess this proves my point I was trying to make in my original post. Every xx months a sensation article like this comes out, and suddenly everyone, even on HN, becomes an expert that will 'just' solve the issue with a naive solution.
Car manufacturers, hire smart engineers. If the solution was simple, they would have fixed it already. Cars are always a trade-off between safety, security, reliability, affordability and practicality.
Great that your solution makes car theft resistant, but if also kills people, it's not such a great sell...
I doubt Tesla would want to include a motion sensor on the dumb card that fits in a wallet.