A semiconductor device includes a memory, a random number generation circuit, and a control circuit. The memory stores key information, and the random number generation circuit generates first and second random number signals. The control circuit generates sixth and seventh random number signals from the first random number signal and the key information, generates encrypted update data from update data using the seventh random number signal, transmits the first and second random number signals as request signals to an external terminal device, receives, from the external device, first and second response signals as response signals in response to the request signals, generates an eighth random number signal using the first response signal, the second and the sixth random number signals as input signals, and provides the encrypted update data for the external terminal device when the second response signal coincides with the eighth random number signal.