Patent ID: 7664262

Claim:
A playback apparatus configured to play back digital content stored in a storage medium, the digital content comprising an encrypted video object and an encrypted resource file for interactively playing back the video object, the playback apparatus comprising: a memory comprising a file cache area configured to temporarily store the resource file read out of the storage medium; a first process module configured to decrypt the video object read out of the storage medium; a playback process module configured to play back the decrypted video object and to output a resource file request for requesting the resource file during the playback of the video object; a second process module configured to determine, in response to the resource file request, whether the resource file stored in the file cache area is decrypted, by referring to management information which is stored in the memory and is indicative of whether the resource file stored in the memory is decrypted or not configured to decrypt the resource file if the resource file is not decrypted, configured to write the decrypted resource file over the encrypted resource file, configured to update the management information to a value indicative of completion of decryption, and configured to send the decrypted resource file from the file cache area to the playback process module; and a third process module configured to determine, in response to generation of a copy request for instructing storage of a copy of the resource file in a storage device, whether the resource file stored in the file cache area is decrypted, by referring to the management information, configured to encrypt the decrypted resource file if the resource file is decrypted successfully, configured to write the encrypted resource file over the decrypted resource file, configured to update the management information to a value indicative of non-completion of decryption, and configured to send the encrypted resource file from the file cache area to the storage device wherein the resource file is encrypted by specific key information, the second process module is configured to generate the key information by decrypting a content encryption key stored in the storage medium corresponding to the resource file, to decrypt the resource file by the generated key information, and to store the generated key information in the memory, and the third process module is configured to encrypt the decrypted resource file with the generated key information stored in the memory if the resource file stored in the file cache area is decrypted successfully.