Contents management method, contents management apparatus, and recording medium

摘要

When the total number of copies of requested content does not exceed its upper limit value, and when bilateral authentication with a partner to be communicated is successful, encrypted content (Kc[C]) and information (KT1[Kc]) used for decrypting the encrypted contents, which are encrypted using first shared information (KT1) generated by bilateral authentication, are transferred to the partner, thus updating the total number of copies of the transferred content. First data, used to erase information (KT1, Kc, C) that is recorded on the recording medium and is used for decrypting content which is recorded on the recording medium and is requested to erase, is encrypted using second shared information (KT3) generated by bilateral authentication, and the encrypted first data is transferred to the partner. When second data, which is encrypted using third shared information (KT4) generated by another bilateral authentication and is used in rewrite in the partner, is transferred from the partner, the transferred second data is decrypted using the third shared information, and the decrypted second data is compared with the first data (r1) to confirm if the information used for decrypting the content recorded on the recording medium has been erased, thus updating the total number of copies of content which is requested to erase.