Simple Cryptographic Key Management Scheme of the Electronic Control Unit in the Lifecycle of a Vehicle

Connecting vehicles to various network services increases the risk of in-vehicle cyberattacks. For automotive industries, the supply chain for assembling a vehicle consists of many different organizations such as component suppliers, system suppliers, and car manufacturers (CMs). Moreover, once a vehicle has shipped from the factory of the CM, resellers, dealers, and owners of the vehicle may add and replace the optional authorized and third-party equipment. Such equipment may have serious security vulnerabilities that may be targeted by a malicious attacker. The key management system of a vehicle must be applicable to all use cases.

We propose a novel key management system adaptable to the electronic control unit (ECU) lifecycle of a vehicle. The scope of our system is not only the vehicle product line but also the third-party vendors of automotive accessories and vehicle maintenance facilities, including resellers, dealers, and vehicle users. Our system consists of in-vehicle communication and backend information systems of CMs, ECU manufacturers (EMs), and vehicle maintenance facilities. We introduce an authentication ECU (A-ECU) and apply a one-time pad (OTP) to encrypt pre-shared keys. A pre-shared key ciphered by an OTP is installed in each ECU in an EM. An A-ECU obtains an OTP through the server of the CM from the EM, shares the pre-shared keys with the ECU using the OTP, authenticates the ECU mutually, and generates a session key to communicate with the ECU. When the ECU is replaced in a vehicle maintenance factory, the vehicle maintenance factory obtains the OTP of the replaced ECU from the CM and installs a pre-shared key. With this scheme, there is no critically important information, such as a master key for key generation. In addition, such communications are protected by the public key infrastructure (PKI). If the management of the backend communication is adequately protected, it becomes difficult to crack into the system.

To prove the practicality of the system, we estimate the performance of our protocol in a high-speed controller area network (CAN). The sharing of a pre-shared key costs 10 data frames and, in the best case, takes 1.12 ms.