To provide a cable television network system by which security on a cable television network can be improved by updating a key for keeping information secret.
In the cable network system in which center equipment is connected with home equipment through the cable television network system, key information on a key used in the case of cipher communication is written in the format of a broadcasting signal from the center equipment and sent to each home equipment. Each home equipment extracts the key of its own home equipment based on information in an IC card inserted to the equipment, and the key is stored in the equipment. This key is updated periodically and when a new key is sent from the center equipment, the key stored in the home equipment is updated to a new one.
TADAUCHI MITSUHARU
ITO SUSUMU
HITACHI LTD
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