| 摘要 |
A communication device is provided. A receiving unit (12) of a communication device (10) receives communication data from another communication device. When the receiving unit receives the communication data from the other communication device, an updating unit (22) updates a counter to match the value of a counter of the other communication device. A code generating unit (16) generates a message authentication code on the basis of the communication data received by the receiving unit, the counter, and a common key. A determining unit (18) determines whether the message authentication code generated by the code generating unit matches a message authentication code set in the communication data received by the receiving unit. If the determining unit determines successively, a number of times, that the message authentication codes do not match, and the number of times reaches or exceeds a prescribed successive non-matching number of times, then the transmitting unit (14) transmits a synchronization request causing the counter values to be matched to one another. |
