Patent ID: 7167564

Claim:
An information processing system, comprising: a plurality of category entities; a key tree including a plurality of leaves, a root, a plurality of nodes existing in paths from the plurality of leaves to the root, and a plurality of subtrees serving as category trees grouped in accordance with categories and managed by the plurality of category entities; a plurality of devices assigned to at least some of the leaves; a plurality of keys assigned to the root, to at least some of the leaves and to at least some of the nodes; an enabling key block (EKB) including encrypted data, the encrypted data being produced by selecting one of the paths in the key tree and encrypting an upper-level key in the selected path using a lower-level key in the selected path such that the encrypted data can be decrypted only by a selected one of the plurality of devices which can use a node key set corresponding to the selected path, the EKB being provided to the selected device and being capable of being decrypted in common in at least one of the category trees; and a key distribution center (KDC) adapted to produce and issue the EKB, the KDC having an EKB type definition list representing a correspondence between an EKB type identifier and identification data for identifying at least one of the category trees that can process EKB having a particular EKB type identified by the EKB type identifier; wherein the KDC is operable to send a notification of a change in state of a selected one of the category trees which is capable of processing the particular EKB to a selected one of the category entities that uses the particular EKB.