Between a data recording/playback device and a data storage device, CBC-mode encryption processing is executed which encrypts a plurality of encryption keys of content which correspond to sectors. The encrypted data is stored in a header corresponding to the content. The CBC-mode encryption processing is executed by using a storage key unique to media in which the content is stored. For using the content, only by decrypting the key data in media in which mutual authentication is established, the content can be used, so that highly-secure key storage is implemented.