A content playback apparatus for obtaining encrypted sub-content, decrypting the obtained encrypted sub-content, and playing main content and the decrypted sub-content, the encrypted sub-content being generated by encrypting the sub-content based on a first key, the sub-content being related to the main content, characterized by the first key being generated by applying a predetermined operation to key generation information based on a disc key, the main content, a key management information list, and an encrypted disc key are recorded on a recording medium, the key management information list including encrypted key management information, the encrypted key management information generated by encrypting key management information based on a third key, the key management information including one of a second key and information that shows that the content playback apparatus is revoked, the encrypted disc key generated by encrypting the disc key by using the second key, the content playback apparatus comprising: a key storage unit operable to store the third key which has been pre-assigned to the content playback apparatus; an information reading unit operable to read the main content, the encrypted key management information included in the key management information list and the encrypted disc key from the recording medium; a key obtaining unit operable to decrypt the encrypted key management information based on the third key, to obtain the one of the second key and the information that shows that the content playback apparatus is revoked; a disk key generating unit operable to, when the key obtaining unit has obtained the second key, obtain the second key from the key obtaining unit, and decrypt the read encrypted disc key using the second key, thereby obtaining the disc key; an information obtaining unit operable to obtain the encrypted sub-content and the key generation information from an information source other than the recording medium; a content key generation unit operable to apply the predetermined operation to the obtained key generation information, based on the disc key obtained by the disk key generating unit, thereby generating a first key; a decryption unit operable to decrypt the encrypted sub-content based on the generated first key; and a playback unit operable to generate signals from the main content and the sub-content. a key storage unit operable to store the third key which has been pre-assigned to the content playback apparatus; an information reading unit operable to read the main content, the encrypted key management information included in the key management information list and the encrypted disc key from the recording medium; a key obtaining unit operable to decrypt the encrypted key management information based on the third key, to obtain the one of the second key and the information that shows that the content playback apparatus is revoked; a disk key generating unit operable to, when the key obtaining unit has obtained the second key, obtain the second key from the key obtaining unit, and decrypt the read encrypted disc key using the second key, thereby obtaining the disc key; an information obtaining unit operable to obtain the encrypted sub-content and the key generation information from an information source other than the recording medium; a content key generation unit operable to apply the predetermined operation to the obtained key generation information, based on the disc key obtained by the disk key generating unit, thereby generating a first key; a decryption unit operable to decrypt the encrypted sub-content based on the generated first key; and a playback unit operable to generate signals from the main content and the sub-content.