| 摘要 |
After an encryption key creating unit creates/updates an encryption key, an encryption key update timing control unit monitors whether or not the elapsed time since this time has reached the shortest holding time or longest holding time. If the shortest holding time has elapsed, the encryption key update timing control unit monitors whether or not wireless communication is being executed by a wireless unit. If a state wherein no wireless communication is being executed is detected, the encryption key creating unit is caused to create/update an encryption key at this timing. When the longest holding time has elapsed while this state is not detected, the encryption key update timing control unit gives a wireless unit an instruction to temporarily interrupt the wireless communication, and causes the encryption key creating unit to create/update an encryption key during interruption of wireless communication.
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