COMMUNICATION TERMINAL AND PROGRAM

The communication terminal includes a communication interface for acquiring external time information from outside and a non-volatile memory and operates as described below. The communication terminal periodically acquires external time information, encrypts the internal time information calibrated based on the acquired external time information and thereafter writes the encrypted internal time information into the non-volatile memory. In an initialization sequence after power-on of the communication terminal, the communication terminal reads and decrypts internal time information that is lastly written to the non-volatile memory before the power-on, newly acquires external time information and verifies validity of the acquired external time information by comparing the acquired external time information with the read internal time information.