| 摘要 |
When a reader/writer 3 is connected to a modem device 1 and makes communication with an authentication server 6 using the Internet line 5 and the like, an ID unique to the modem device 1, which has been written to the modem device 1 when the modem device 1 is manufactured and cannot be rewritten thereafter, is stored in a modem ID memory 13, an authentication is performed using both the ID unique to the modem device 1 and an ID of an IC card 4, and further a response to an authentication request from the authentication server 6 is sent to the authorized modem device 1. With the operation, the modem device 1 which is generally in power-ON state all the time can detect the unauthorized access by receiving the response to the authentication request even when an authentication-request-in-progress flag 14 is OFF.
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