Patent ID: 7362870

Claim:
An information recording apparatus for recording information onto a recording medium, said apparatus comprising: storage means for storing a device node key (DNK) set that includes one or more leaf keys and a plurality of node keys, the one or more leaf keys being associated with one or more leaves such that a unique one of the one or more leaf keys is associated with a particular one of the one or more leaves, the plurality of node keys being associated with a plurality of nodes such that a respective one of the plurality of node keys is associated with a specific one of the plurality of nodes, the plurality of nodes and the one or more leaves being arranged according to a hierarchical tree structure having a plurality of levels, the one or more leaves being further associated with one or more information recording apparatuses such that a given one of the one or more leaves is associated with an individual one of the one or more information recording apparatuses; and cryptographic means for encrypting content data to be stored in the recording medium, said cryptographic means including: means for producing a first encryption key (Kst) by encrypting, using a second encryption key (Kcon), a value uniquely assigned to a specific data playback apparatus that is to play back the content data, means for producing encrypted data Enc(Kst, DATA) by encrypting the content data using the first encryption key (Kst), means for producing encrypted key data by encrypting the second encryption key (Kcon) using a selected one of at least a portion of the plurality of node keys located along at least one path within the hierarchical tree structure, the at least portion of the plurality of node keys being stored in an enabling key block (EKB) and being encrypted such that each one of the at least portion of the plurality of node keys is encrypted using at least another one of the at least portion of the plurality of node keys that is located at a lower level along the at least one path than the one of the at least portion of the plurality of node keys or using one of the one or more leaf keys, and means for storing a data file including the encrypted data, the encrypted key data, and the enabling key block (EKB) into the recording medium.