Yes, communication is already encrypted or "protected" in almost all modern cars. New interfaces like FlexRay offer true cryptographic protection (albeit usuall

Yes, communication is already encrypted or "protected" in almost all modern cars. New interfaces like FlexRay offer true cryptographic protection (albeit usually weak - things like AES with a universally shared key/IV across a whole model line are common), but even older systems have "protection" in the form of obfuscation, XOR and transformation based challenge-response algorithms (the one in VW cars runs a cute bytecode script against the challenge to yield the appropriate response), serial-number validation, and so on. For example, most modern VW AG cars have all of their core modules protected by Component Protection, a system where the identities of the modules are synchronized together as a (somewhat successful, actually) anti-theft measure. If modules are "mixed and matched" (for example, a used head unit is installed in a different car), they don't function. Private shops can subscribe to a service to reprogram this protection (GeKo) at a cost of around $1000 USD/year. By and large these systems are usually reverse engineered over time as the protection is usually not very good, but the overall ability to add additional hardware is, indeed, getting more challenging.