The root of the problem isn't encryption or communication but rather than the key fob's location is data in the clear and easily tampered with. That data is the

The root of the problem isn't encryption or communication but rather than the key fob's location is data in the clear and easily tampered with. That data is the signal strength and/or triangulation of the fob's signal. The fob has no knowledge of it's own location, so the car must figure it out on it's own, allowing the attack to occur. If you gave the key fob some way of calculating it's position relative to the car, you may be able to transmit that to the car over the existing communication channel and have the car verify it. The question then becomes: how can one give the tiny computer in a key fob independent access to it's location relative to a car? An inertial navigation system[1] would probably be cheapest and most power-efficient. Though they suffer from inertial drift, that could be mitigated by periodic re-calibration while the car is driving and then parks (and the occasional non-keyless entry). The key fob then only transmits a signal when it detects that it's close enough, and the problem is "solved". Now you just need to replace the batteries on your keys every few weeks... [1]:https://en.wikipedia.org/wiki/Inertial_navigation_system https://en.wikipedia.org/wiki/Inertial_navigation_system