CONTENT PROVISION SIDE SYSTEM, USER SIDE SYSTEM, TRACKING SYSTEM, DEVICE, METHOD, AND PROGRAM

摘要

PROBLEM TO BE SOLVED: To provide a tracking system for performing tracking surely even for a skillful unauthorized decoder during black box tracking, without making the decoder know the intent of input. SOLUTION: A content provision system 1 comprises a content encryption portion 14 for encrypting a content to be offered with a session key in a decoding enable fashion and for obtaining an encrypted content, and a header generation portion 15 for encrypting the session key with each user side system unique decoding key in a decoding enable fashion and for generating a header information including the obtained encrypted session key and a value based on user identification information on at least one user side system out of user side systems allowing decoding of the encrypted session key. The content provision system 1 transmits the encrypted content and the header information to each user side system. Since the header information does not contain the user identification information on the user side system, information on whose decoding key is nullified is not leaked during black box tracking. COPYRIGHT: (C)2005,JPO&NCIPI