I'm currently researching into CAN security for in-vehicle communication. I would like to know if anyone knows a reason why the CAN payloads of an ECU communication (between CAN nodes) should be encrypted when integrity, authenticity and protection against replay attacks are guaranteed.
In case of key exchange messages or other security protocol related messages that need protection against eavesdroppers encryption is undoubtedly necessary. Same goes for privacy critical data like GPS output.
However, I'm wondering why some researchers suggest encryption of any CAN payload. Is there anything useful an adversary could learn by sniffing CAN pakets which neither can be replayed nor manipulated?