Patent ID: 7401232

Claim:
A content playback apparatus comprising: a storing unit that has a secret key stored therein; a key information decrypting unit configured to (i) obtain encrypted key information that has been encrypted by a first secret-key encrypting method, and (ii) decrypt the encrypted key information into key information using the stored secret key, the key information being either a decryption key used for decrypting a content key or key-updating information used for updating the secret key; a content playback unit configured to, when the decrypted key information is the decryption key, (i) decrypt an encrypted content key that has been encrypted by a second secret-key encrypting method, using the decryption key, (ii) descramble a scrambled content that has been scrambled by a scramble encrypting method, using the decrypted content key, and (iii) play back the descrambled content; and an updating unit configured to, when the decrypted key information is the key-updating information, update the secret key according to the key-updating information.