| 摘要 |
PROBLEM TO BE SOLVED: To enhance the security of viewing data and audience rating data in a sum-up center or the like. SOLUTION: When the viewing data is transmitted from an IRD to the sum-up center, dialing is performed (step A1), a host identification number is transmitted (step A2), and then a key for ciphering is received from the sum-up center (step A3). Then, the viewing data ciphered by using the received key are transmitted (step A4). Since the viewing data are ciphered by the key specified on the side of the sum-up center, as compared to the case of ciphering them by the key fixedly possessed by the IRD, the confidentiality of the viewing data and the audience rating data is increased.
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