So the encryption is not solving it then. But I may need to add to my original post:

- 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?

For lots of modern cars, the users phone is a key, and the car itself is connected, so you could also theoretically share and compare gps location during the unlock attempt.

I'm no expert, but I'm pretty sure GPS isn't going to have the accuracy needed to prevent a relay attack.

I think the accuracy should be fine, cell phones typically have a GPS accuracy of 5-10 m. The problem is that you won't be able to rely on it. You probably won't have any GPS signal at all in an underground parking garage, and even in an above ground parking deck you will likely have poor or no signal due to being surrounded by steel and concrete.

It takes a pretty sustained period of polling to get to 5-10m accuracy though right?

Even without measuring the distance you could require periodic re-authentication after entry to keep the car driving. If the attacker did a one-time relay to open the car and start it and then drives away they'd lose contact and thus fail the next challenge-response authentication cycle.

None of the keyless start systems do this, on purpose. Because this may lead to very dangerous situations.

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!

That doesn't mean it's impossible to prevent relay attacks, it's just that people choose not to.

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.

Please don’t. Imagine I am driving and suddenly the car in front of me fails to reauth and suddenly stops in the middle of an intersection. That would be unnecessarily unsafe.

It could just only deactivate the car if the car is stationary. Problem solved.

> It could just only deactivate the car if the car is stationary.

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...

What about making the key only broadcast the unlock signal when it's been moved within the last {X} mins? Sitting in a drawer, not broadcasting and not vulnerable to relay attack. Walking to the car, key activates, driver unlocks like normal.

You have to be able to support “dumb” key fobs/RFID cards as well as phones.

I doubt Tesla would want to include a motion sensor on the dumb card that fits in a wallet.

I imagine that MAX_DISTANCE/c would be tiny compared to the amount of noise involved, to the point where this would be functionally impossible.

I wonder if it would be possible to have a crystal oscillator be that precise and still be robust enough to survive in a car. This method should work. But, if the system can’t survive the external vibration, temperature changes, and weather, it won’t help a car manufacturer.