| 摘要 |
An information service system including a plurality of receiving stations and information service facilities. The information service facilities include a memory circuit which stores beforehand a distribution destination information set of receiving station identifiers allocated to the receiving stations, distribution destination information set being disposed in a predetermined order within the memory circuit, a memory circuit for storing a plurality of information to be supplied to receiving stations, an enciphering circuit for generating an enciphering key for optical receiving stations within a group which performs broadcast communications, and enciphering the service information with the enciphering key, and a circuit for transmitting the enciphered service information and service destination codes of service destination receiving stations encoded from the distribution destination information set, through broadcast communications. Each receiving station includes a memory circuit for storing beforehand its own identifier and the distribution destination information set of the group which performs broadcast communications, a receiver unit for receiving the enciphered service information and the service destination codes from the information service facilities, and a deciphering circuit for generating a deciphering key corresponding to the distribution destination information set in accordance with the received service destination codes and the corresponding, and previously stored distribution destination information, only when the own identifier of the receiving station is contained in the service destination codes, and the deciphering the enciphered service information with the deciphering key. |
