AUTOSAR Secure Onboard Communication (SecOC): AES-128 CMAC and Truncation Strategies

Unsecured CAN networks are inherently vulnerable to frame injection: any compromised peripheral (e.g., telematics dongle, infotainment head unit) can broadcast spoofed brake or steering commands.

AUTOSAR SecOC (Secure Onboard Communication) resolves this by appending an authentication code to critical PDUs. The sender generates a 128-bit Cipher-based Message Authentication Code (CMAC) using AES-128 over the data payload concatenated with a dynamic Freshness Value. To conserve bus bandwidth, the CMAC is truncated (typically to 24 or 32 bits) and packed alongside the lower bits of the Freshness Value into the CAN-FD frame. The receiving ECU recalculates the CMAC; if the values match, the message is authenticated.