Content processing apparatus and encryption processing method

An encryption processing method comprising steps of:

• reading out, from a recording medium which records at least one encrypted content and first encrypted key information formed by encrypting first key information containing content keys corresponding to the encrypted contents, the first encrypted key information;
• decrypting the first encrypted key information by using a unique device key and dynamic information to obtain decrypted first key information;
• updating the dynamic information;
• extracting a target content key serving as a content key corresponding to a move target encrypted content from the decrypted first key information;
• generating second key information by removing the target content key from the decrypted first key information;
• encrypting the second key information by using the device key and the updated dynamic information to obtain second encrypted key information;
• generating a shared key;
• encrypting the target content key by using the shared key to obtain an encrypted content key;
• and
• writing the second encrypted key information in the recording medium by overwriting the second encrypted key information on the first encrypted key information and writing the encrypted content key in the recording medium.

A non-transitory computer readable storage medium storing instructions of a computer program which when executed by a computer results in performance of steps comprising:

• reading out, from a recording medium which records at least one encrypted content and first encrypted key information formed by encrypting first key information containing content keys corresponding to the encrypted contents, the first encrypted key information;
• decrypting the first encrypted key information by using a unique device key and dynamic information to obtain decrypted first key information;
• updating the dynamic information;
• extracting a target content key serving as a content key corresponding to a move target encrypted content from the decrypted first key information;
• generating second key information by removing the target content key from the decrypted first key information;
• encrypting the second key information by using the device key and the updated dynamic information to obtain second encrypted key information;
• generating a shared key;
• encrypting the target content key by using the shared key to obtain an encrypted content key;
• and
• writing the second encrypted key information in the recording medium by overwriting the second encrypted key information on the first encrypted key information and writing the encrypted content key in the recording medium.

A content processing apparatus using a recording medium comprising:

• a first storage unit storing a unique device key;
• a second storage unit storing dynamic information;
• and
• a computer programmed to:
• read out from the recording medium recording at least one encrypted content and first encrypted key information formed by encrypting first key information containing content keys corresponding to the encrypted contents;
• decrypt the first encrypted key information by using the device key and the dynamic information to obtain decrypted first key information;
• update the dynamic information stored in the second storage unit to obtain updated dynamic information;
• extract a target content key serving as a content key corresponding to a move target encrypted content from the decrypted first key information, and generate second key information by removing the target content key from the decrypted first key information;
• encrypt the second key information by using the device key and the updated dynamic information to obtain second encrypted key information;
• generate a shared key;
• encrypt the target content key by using the shared key to obtain an encrypted content key;
• and
• write the second encrypted key information in the recording medium by overwriting the second encrypted key information on the first encrypted key information and write the encrypted content key in the recording medium.