| 摘要 |
An apparatus and a method of providing an access control for transmitted stock market data from a central radio station to a plurality of one-way radio receivers. Into each receiver is inputted an access code including a cypher pointer which provides for scrambling of the remainder of the access code which includes the authorized services, the service cutoff date, and the unit serial number which is unique to a particular receiver. The cypher pointer is used to rotate a common map in the receiver used for unscrambling and in the central station used for scrambling. In order to receive service, the permanently stored serial number of the unit must compare with the serial number of the access code, the cutoff date must be greater than the present system date transmitted from the central station, and there must be an authorized service class.
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