Patent ID: 8144869

Claim:
A key data generation apparatus that generates key data such that content can only be used by a valid terminal apparatus, comprising: a processor; a key management unit operable to correspond device keys, which are held by terminal apparatuses, with nodes in a tree structure that defines relations between the device keys shared among the terminal apparatuses and defines whether or not each of the device keys is revoked; a selection unit operable to select, from among device keys held by valid terminal apparatuses, one or more device keys that are corresponded with a node in a highest position in the tree structure; a conversion unit operable to cause the processor to (a) generate conversion information by concatenating pieces of revocation information, each of which relates to a node positioned on a route from a root through to the node with which the selected device key is corresponded, and (b) perform a reversible operation on the generated conversion information and first key data for use in using the content, thereby generating second key data; an encryption unit operable to encrypt the second key data using the selected device key, thereby generating encrypted key data; and an output unit operable to output the encrypted key data and the conversion information.