SOFTWARE PROTECTION SYSTEM

摘要

PROBLEM TO BE SOLVED: To ensure the security of a key for deciphering software to be sent and to protect the software to be broadcasted to many unspecified persons. SOLUTION: A content deciphering key ciphering part 13 takes the content deciphering key of requested contents out of a content deciphering key storage part 11, generates key information by ciphering the key with a variation key which is generated by a variation key generation part 12 and varies periodically in value, and sends it to a receiving device 14. A content key deciphering part 17 deciphers the key information received from the deciphering key generating device 10 with a variation key obtained from a variation key generation part 16 which generates the variation key having the same value in synchronism with the variation key generation part 12 to obtain a deciphering key. A reproduction part 18 deciphers the ciphered contents with the ciphering key and outputs the contents.