Patent ID: 7991155

Claim:
A backup system comprising: a recording/playback device storing and playing back a content; and a backup device managing a backup of the content and storing the backup of the content, wherein the recording/playback device includes: a storage hardware unit that stores the content; a secure storage hardware unit that stores playback right information showing a right to play back the content only when the content is stored in the storage hardware unit; an acquisition hardware unit that acquires an instruction to delete the content so as to be restorable; and a deletion hardware unit that keeps, when the instruction to delete the content so as to be restorable is acquired, the playback right information stored in the secure storage hardware unit, that keeps the backup stored in the backup device, and that deletes the content from the recording/playback device, wherein the backup includes: an encrypted work generated by encrypting a digital work using an encryption key; and an encrypted key generated by encrypting the encryption key using a specific key that is specific to the recording/playback device, wherein the backup system further comprises a request device, wherein the request device stores a secret key for decrypting the encryption key encrypted using a public key, and transmits a transfer request of the backup to the recording/playback device, wherein the recording/playback device further includes: a transfer request receiving hardware unit that receives the transfer request from the request device; an encrypted key request hardware unit that transmits, when the transfer request is received, a transmission request of the encrypted key included in the backup to the backup device; an encrypted key receiving hardware unit that receives the encrypted key, as a response to the transmission request, from the backup device; a re-encrypted key generation hardware unit that stores beforehand the specific key and the public key, that decrypts the received encrypted key using the specific key to generate the encryption key, and that encrypts the generated encryption key using the public key to generate a re-encrypted key; a transmission hardware unit that transmits, to the backup device, a rewriting request including the generated re-encrypted key and for instructing to rewrite the encrypted key included in the backup as the generated re-encrypted key; and a playback right information deletion hardware unit that deletes the playback right information from the secure storage hardware unit, and wherein the backup device includes: an encrypted key request receiving hardware unit that receives the transmission request; an encrypted key transmission hardware unit that transmits, when the transmission request is received, the encrypted key included in the backup to the recording/playback device; a rewriting request receiving hardware unit that receives the rewriting request; and a rewriting hardware unit that rewrites the encrypted key included in the backup as the re-encrypted key included in the received rewriting request.