Patent ID: 7181008
Filing Date: 2007-02-20
Classification: G11B

Abstract:
1. A content management method for a content management apparatus for managing an allowable number of recording media, each of the recording media including a first memory area storing at least an encrypted content and a second memory area storing key information item necessary for decrypting the encrypted content, an initial value of the allowable number being a predetermined upper limit, the method including a check out method and a check in method, the check out method comprising: performing first bilateral authentication between the content management apparatus and a recording medium, when the allowable number is more than zero, to obtain a first shared information item that is generated as a result of success in the first bilateral authentication and that is identical to that of the recording medium configured to store the first shared information item generated in the recording medium in the second memory area as the key information item; encrypting a decryption key for decrypting the encrypted content, using the first shared information item, to obtain an encrypted key; transferring the encrypted content and the encrypted key to the recording medium configured to store the encrypted content and the encrypted key in the first memory area; and decreasing the allowable number by one when the encrypted content and the encrypted key are transferred to the recording medium, wherein the check in method comprises: performing second bilateral authentication between the content management apparatus and the recording medium whose first memory area stores the encrypted content and the encrypted key and whose second memory area stores the key information item, to obtain a second shared information item that is identical to that of the recording medium and that is generated as a result of success in the second bilateral authentication; generating a random data item when the second bilateral authentication ends in success; encrypting the random data item using the second shared information item; transferring the encrypted random data item to the recording medium configured to overwrite into the second memory area with the random data item and erase the key information item from the second memory area; performing third bilateral authentication between the content management apparatus and the second recording medium to obtain a third shared information item that is identical to that of the recording medium and that is generated as a result of success in the third bilateral authentication; receiving an encrypted data item that is transferred from the recording medium configured to generate the encrypted data item by encrypting a data item stored in the second memory area using the third shared information item; decrypting the encrypted data item using the third shared information item; determining that the key information item in the second memory area is erased when the decrypted data item is identical to the random data item; and increasing the allowable number by one when the key information item in the second memory area is determined to be erased.