Physics allows a method to measure distance in a way that can't be faked... Simply do a challenge-response query between key and car and time how long to get t

Physics allows a method to measure distance in a way that can't be faked... Simply do a challenge-response query between key and car and time how long to get the (correct) response back... If it takes more than 10 nanoseconds, then the key is more than 10 feet away. No attacker can break the laws of physics. Obviously doing much crypto in 10 nanoseconds is a problem, but it turns out the crypto can be calculated ahead of time, effectively letting you just boil the whole thing down to a non-fakable ping.