KEY-GENERATING METHOD, CONTENT-PROVIDING METHOD, CIPHERED CONTENT DECIPHERING METHOD, PIRATE USER IDENTIFYING METHOD, CONTENT PROVIDER SIDE SYSTEM, USER SIDE SYSTEM, TRACE SYSTEM, CIPHERING APPARATUS, DECIPHERING APPARATUS, AND PROGRAM

摘要

PROBLEM TO BE SOLVED: To content providing system for efficiently attaining both transmission overhead and black box trace, in a broadcast content distribution.

SOLUTION: All user aggregations are divided into sub-groups, and a decipher key is generated by using key generation polynomials which are different for each sub-group. Next, a session key, i.e., a decipher key for ciphered data is distributed so as to be deciphered with the decipher key for each user. Meanwhile, in this key distribution, decipher keys of the arbitrary number of users can be revoked. Against a pirate version deciphering device, black box tracing is performed by assuming users subject to revocation to be suspects. A tracer assumes suspects, and investigates the suspects n number of times (n represents all the number of users), to identify all members in a coalition.

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