A system comprising an electronic control unit of a vehicle and a data processing device, the electronic control unit comprising: a storage unit adapted to store therein control data of a control target device mounted on a vehicle, the electronic control unit being adapted to rewrite the control data stored therein to a control data transmitted from the data processing device outside the vehicle; and a central processing unit having: a hash code generation unit adapted to generate a unique code corresponding to the control data that is rewritten, when the control data stored in the storage unit is rewritten; a hash code recording unit adapted to record the generated hash code therein by adding the generated hash code to codes already recorded therein, when the code is newly generated; and a device control unit adapted to generate a signal to control the control target device by using the rewritten control data stored in the storage unit; the data processing device comprising a control-data storage unit, a hash-code output unit, a hash-code storage unit and a hash-code comparison unit, the data processing device being configured to transmit a control program update from the control-data storage unit to the storage unit of the electronic control unit, the hash-code output unit being adapted to generate a hash code from the control program transmitted to the electronic control unit, the hash-code storage unit being adapted to store the generated hash-code after existing hash-codes without replacing the existing hash-codes, and the hash-code comparison unit being configured to compare the data stored in the hash-code storage unit and the hash code stored in the hash-code recording unit. a storage unit adapted to store therein control data of a control target device mounted on a vehicle, the electronic control unit being adapted to rewrite the control data stored therein to a control data transmitted from the data processing device outside the vehicle; and a central processing unit having: a hash code generation unit adapted to generate a unique code corresponding to the control data that is rewritten, when the control data stored in the storage unit is rewritten; a hash code recording unit adapted to record the generated hash code therein by adding the generated hash code to codes already recorded therein, when the code is newly generated; and a device control unit adapted to generate a signal to control the control target device by using the rewritten control data stored in the storage unit; the data processing device comprising a control-data storage unit, a hash-code output unit, a hash-code storage unit and a hash-code comparison unit, the data processing device being configured to transmit a control program update from the control-data storage unit to the storage unit of the electronic control unit, the hash-code output unit being adapted to generate a hash code from the control program transmitted to the electronic control unit, the hash-code storage unit being adapted to store the generated hash-code after existing hash-codes without replacing the existing hash-codes, and the hash-code comparison unit being configured to compare the data stored in the hash-code storage unit and the hash code stored in the hash-code recording unit. a hash code generation unit adapted to generate a unique code corresponding to the control data that is rewritten, when the control data stored in the storage unit is rewritten; a hash code recording unit adapted to record the generated hash code therein by adding the generated hash code to codes already recorded therein, when the code is newly generated; and a device control unit adapted to generate a signal to control the control target device by using the rewritten control data stored in the storage unit; the data processing device comprising a control-data storage unit, a hash-code output unit, a hash-code storage unit and a hash-code comparison unit, the data processing device being configured to transmit a control program update from the control-data storage unit to the storage unit of the electronic control unit, the hash-code output unit being adapted to generate a hash code from the control program transmitted to the electronic control unit, the hash-code storage unit being adapted to store the generated hash-code after existing hash-codes without replacing the existing hash-codes, and the hash-code comparison unit being configured to compare the data stored in the hash-code storage unit and the hash code stored in the hash-code recording unit.