There is no perfect system for anything but you can probably take it to the point where an attacker won't profit from his efforts, and I see that as a reasonabl

There is no perfect system for anything but you can probably take it to the point where an attacker won't profit from his efforts, and I see that as a reasonable goal post for a threat model here. I implement a RSA key for each car, signed before it leaves the factory. Each key is housed in memory that is heavily epoxied and very difficult to remove (in a place that you would have to remove the majority of the engine to reach). The cars ignition system requests validation from the on board key on every start (in fact it gets the actual <start car> command from the chip itself). If the key is not present, the car does not start and instead tells you to return it to the dealership. Now you say, I can remove the key and then reverse engineer it. What if I put n keys? How many do I realistically have to add to make it so time and labor intensive for you to remove my little inexpensive keys that you just give up? Probably not that many. Oh and did I mention that all of them are in an array? Better be sure you didn't miss one or it will zero itself out giving you no hope of recovery. (The warranty specifically mentions this as something that will void it) After all that, if you still want to attempt to modify it. Fine. I'll add 1% to the purchase price of the car and reimburse anyone who bought lemons from your little (illegal) scheme.