Information recording/reproducing apparatus and method

An information playback apparatus for playing back data stored in a storage medium, comprising:

• storage means storing a device node key (DNK) set including leaf keys and node keys uniquely assigned to leaves and nodes, respectively, of a hierarchical tree structure, said leaves being assigned to respective different information playback apparatuses;
• and
• cryptographic means for decrypting the data stored in the storage medium,
• wherein the cryptographic means performs processing including:
• acquiring, by means of decrypting-an enabling key block (EKB) using the device node key (DNK) set, one of keys, which are members of the heretical tree structure and which are stored in the enabling key block (EKB) stored in the storage medium, said keys in the enabling key block (EKB) being encrypted in such a manner that each key at a level in the hierarchical tree structure is encrypted using at least a node key at a lower level or a leaf key;
• acquiring an encryption key (Kcon) by decrypting encrypted key data using said one of keys, which are members of the hierarchical tree structure and which are stored in the storage medium;
• and
• producing a decryption key (Kst) to be applied to the data stored in the storage medium by encrypting a value uniquely assigned to the information playback apparatus and then decrypting encrypted data Enc(Kst, DATA) stored in the storage medium using the decryption key (Kst).

An information recording method for an information recording apparatus to record information into a recording medium, said information recording apparatus including:

• storage means storing a device node key (DNK) set including leaf keys and node keys uniquely assigned to leaves and nodes, respectively, of a hierarchical tree structure, said leaves being assigned to respective different information recording apparatuses;
• and cryptographic means for encrypting data to be stored into the storage medium, said information recording method comprising the steps of:
• producing an encryption key (Kst) to be applied to the data to be stored, by encrypting, using an encryption key (Kcon), a value uniquely assigned to a specific data playback apparatus which will play back the data stored in the storage medium;
• producing encrypted data Enc(Kst, DATA), by encrypting the data to be stored using the encryption key (Kst);
• producing encrypted key data by encrypting the encryption key (Kcon) used in the encryption of the uniquely assigned value, using one of keys, which are members of the hierarchical tree structure and which are stored in an enabling key block (EKB), said keys in the enabling key block (EKB) being encrypted in such a manner that each key at a level in the hierarchical tree structure is encrypted using at least a node key at a lower level or a leaf key;
• storing a data file including the encrypted data and the encrypted key data together with the enabling key block (EKB) into the storage medium.

An information playback method for an information playback apparatus to play back data stored in a storage medium, said information playback apparatus including storage means storing a device node key (DNK) set including leaf keys and node keys uniquely assigned to leaves and nodes, respectively, of a hierarchical tree structure, said leaves being assigned to respective different information playback apparatuses;

• and cryptographic means for decrypting the data stored in the storage medium, the information playback method comprising the steps of:
• by means of decrypting an enabling key block (EKB) using the device node key (DNK) set, acquiring one of keys, which are members of the heretical tree structure and which are stored in the enabling key block (EKB) stored in the storage medium, said keys in the enabling key block (EKB) being encrypted in such a manner that each key at a level in the hierarchical tree structure is encrypted using at least a node key at a lower level or a leaf key;
• acquiring an encryption key (Kcon) by decrypting encrypted key data using said one of keys, which are members of the hierarchical tree structure and which are stored in the storage medium;
• and
• producing a decryption key (Kst) to be applied to the data stored in the storage medium by encrypting a value uniquely assigned to the information playback apparatus and then decrypting encrypted data Enc(Kst, DATA) stored in the storage medium using the decryption key (Kst).

A program for causing a computer system to execute an information recording process in an information recording apparatus to store information into a storage medium, said information recording apparatus including storage means storing a device node key (DNK) set including leaf keys and node keys uniquely assigned to leaves and nodes, respectively, of a hierarchical tree structure, said leaves being assigned to respective different information recording apparatuses;

• and cryptographic means for encrypting data to be stored into the storage medium, said program comprising the steps of:
• producing an encryption key (Kst) to be applied to the data to be stored, by encrypting, using an encryption key (Kcon), a value uniquely assigned to a specific data playback apparatus which will play back the data stored in the storage medium;
• producing encrypted data Enc(Kst, DATA), by encrypting the data to be stored using the encryption key (Kst);
• producing encrypted key data by encrypting the encryption key (Kcon) used in the encryption of the uniquely assigned value, using one of keys, which are members of the hierarchical tree structure and which are stored in an enabling key block (EKB), said keys in the enabling key block (EKB) being encrypted in such a manner that each key at a level in the hierarchical tree structure is encrypted using at least a node key at a lower level or a leaf key;
• and
• storing a data file including the encrypted data and the encrypted key data together with the enabling key block (EKB) into the storage medium.

A program for causing a computer system to execute a playback process in an information playback apparatus to play back data stored in a storage medium, said information playback apparatus including storage means storing a device node key (DNK) set including leaf keys and node keys uniquely assigned to leaves and nodes, respectively, of a hierarchical tree structure, said leaves being assigned to respective different information playback apparatuses;

• and cryptographic means for decrypting the data stored in the storage medium, the program comprising the steps of:
• by means of decrypting an enabling key block (EKB) using the device node key (DNK) set, acquiring one of keys, which are members of the heretical tree structure and which are stored in the enabling key block (EKB) stored in the storage medium, said keys in the enabling key block (EKB) being encrypted in such a manner that each key at a level in the hierarchical tree structure is encrypted using at least a node key at a lower level or a leaf key;
• acquiring an encryption key (Kcon) by decrypting encrypted key data using said one of keys, which are members of the hierarchical tree structure and which are stored in the storage medium;
• and
• producing a decryption key (Kst) to be applied to the data stored in the storage medium by encrypting a value uniquely assigned to the information playback apparatus and then decrypting encrypted data Enc(Kst, DATA) stored in the storage medium using the decryption key (Kst).