> There is very little cryptography involved

Wha? That may have been true about twenty years ago, but not now. BMW was using 256-bit RSA keys to validate ECU firmware and authenticate privileged access in the early 2000s (they're up to 1024-bit keys now) and write-once memory in their instrument clusters for about as long. Other (Euro) car makers using the same vendors offer similar features.

Once you have physical access all bets are off though. That's why the thieves cut the alarm sensors.