| 摘要 |
PROBLEM TO BE SOLVED: To facilitate contents management at distributing of contents, which are classified into a plurality of steps of grades and to which an option is attached to a client. SOLUTION: The contents are divided into parts A, B and C, and each part is enciphered with different cryptographic keys key1, key2 or key3 and distributed to all clients. Only the cryptographic key key1 for restoring the part A is distributed to the client of a lowest grade 3, the cryptographic keys key1 and key2 for restoring the parts A and B are distributed to the client of a grade 2, and all the cryptographic keys key1, key2 and key3 are distributed to the client of the highest grade 1. Thus, client obtains the contents of a corresponding grade on the basis of a restored part. |
