Abstract: Updating of a program is realized even with a small-sized temporary storage area. A program update system distributes an update program from an update program distributing unit to a vehicle control device. The update program distributing unit encrypts an update program by a predetermined unit of encryption, and transmits the update program, which has been encrypted, by a predetermined unit of transfer to the vehicle control device to be updated, the vehicle control device decrypts the received update program by the unit of encryption, and stores the update program, which has been decrypted, by a predetermined unit of writing in a program storage unit, and the unit of writing is an integral multiple of the unit of encryption.

Abstract: Provided is a program updating process according to which even when power supply to an electronic control unit stops during program updating, invalid data's remaining in a storage area at completion of program updating is prevented without acquiring a power supply status of a vehicle. An electronic control unit includes a communication interface, a nonvolatile memory, and an arithmetic processing unit that executes a program. The nonvolatile memory includes a program storage area and a data storage area. The program storage area has a program updating process unit that carries out an updating process, and a program updating target unit that stores an updating program. The arithmetic processing unit reads the program updating process unit as the program and executes the program, divides an updating program received by the communication interface into divided updating programs each having a given size, and writes each of the divided updating programs to the program updating target unit.

Abstract: Provided is a vehicle control device that ensures normal control even when a program including an error is distributed. A vehicle control device includes a calculation unit and a memory, and updates software stored in the memory, and the vehicle control device includes a communication unit which receives encrypted software, a decrypting unit which decrypts the encrypted software into a plaintext, a rewriting unit which is set in the memory and stores the decrypted software, and a determination unit which collates first collation information set in advance in the memory, second collation information given to the software, and the first collation information, determines whether or not to store the decrypted software based on a collation result, and selects the decrypted software as software for next activation when the decrypted software is stored.