CONDITIONAL ACCESS SYSTEM, CONTENT DISTRIBUTION APPARATUS, CONTENT RECEPTION APPARATUS, AND PROGRAM FOR CONTENT DISTRIBUTION APPARATUS AND CONTENT RECEPTION APPARATUS

摘要

PROBLEM TO BE SOLVED: To provide a conditional access system capable of suppressing broadcast band oppression and reducing storage capacity and a calculation cost for an encryption key in a reception apparatus.SOLUTION: An individual public key, secret key, and key restoration individual information of public information in a public key broadcast encryption method are previously distributed to a user. A conditional access system comprises a content distribution apparatus 1 comprising: encryption key generation means 21 for generating an encryption key from the public information; key restoration information generation means 23 for generating key restoration information from the public information and a set of user identifiers; content encryption means 32 for encrypting a content by using the encryption key to generate an encrypted content; and multiplexing means 40 for multiplexing the encrypted content and the key restoration information.