SYSTEM FOR BROADCASTING DATA SIGNAL WITH SAFE METHOD

摘要

PROBLEM TO BE SOLVED: To revise a 2nd key comparatively quickly without the need for distribution of a huge amount of data by configuring the 2nd key with a combination of a common key in common to all subscribers and the other key that is unique to each genre of programs and encrypting the common key. SOLUTION: A 2nd key P+D consists of a combination of a common key P that is in common to all subscribers in the system and a difference key D that is unique to each genre of programs. A combining device 3E combines the common key P with the difference key D. An encryption device 4E encrypts the difference key D by using a group key G in common to a group of the subscribers. The encrypted difference key D' is also broadcast. Another encryption device 5E encrypts the common key P by using a key H in common to a group whose number of subscribers is substantially more than that of the subscribers having the same group key G. The subscribers using the same key H are called the subscribers of a super-group. The encrypted common key P' is also broadcast.