A data provision system includes a data provision device and a data security device installed in a vehicle. The data provision device includes a vehicle interface configured to transmit data to and receive data from the vehicle and an expected value calculation unit configured to calculate an expected value of application data to be applied to an in-vehicle computer installed in the vehicle. The application data and the expected value are transmitted to the vehicle through the vehicle interface. The data security device includes an interface unit configured to transmit data to and receive data from a device outside the data security device and a measurement unit configured to calculate a measurement value of the application data received from the data provision device through the interface unit and verify the measurement value on the basis of the expected value received from the data provision device through the interface unit.