Patent ID: 7908479

Claim:
A data transmitting apparatus comprising: a processor configured to generate first authentication data based on shared data shared with a data receiving apparatus; a communication interface configured to transmit a first response request command to said data receiving apparatus, said first response request command including said first authentication data, and receive a first response message to the first response request command from the data receiving apparatus, the response message including second authentication data generated by the data receiving apparatus based on the shared data and a first sequence number included in the first response request command indicating a position of the first response request command in a sequence of response request commands to be transmitted by the communication interface; the communication interface configured to transmit a second response request command to the data receiving apparatus after receiving the first response message from said data receiving apparatus, the second response request command including third authentication data generated based on the shared data, and receive a second response message to the second response request command from the data receiving apparatus, said second response message containing fourth authentication data generated at the data receiving apparatus based on the shared data and a second sequence number included in the second response request command indicating a position of the second response request command in the sequence of response request command to be transmitted by the command transmission unit; and an authentication unit configured to produce an authentication result for said data receiving apparatus based on the fourth authentication data included in the second response message; a measurement unit configured to measure a response time between transmitting the second response request command and receiving the second response message; and a judgment unit configured to judge if a subsequent data transmission to said data receiving apparatus is granted based on the authentication result and the response time.