An information processing system and method are disclosed in which information
processing is performed in a highly efficient manner using an enabling key block
(EKB) on the basis of a tree structure including category subtrees. A key tree
is formed so as to include a plurality of subtrees serving as category trees categorized
in accordance with categories and managed by category entities. An EKB including
data produced by selecting a path in a tree and encrypting a higher-level key in
the selected path using a lower-level key in the selected path. The resultant EKB
is provided to a device. Distribution of EKB's is managed on the basis of an EKB
type definition list representing the correspondence between an EKB type identifier
and one or more identification data identifying one or more category trees that
can process an EKB of an EKB type specified by the EKB type identifier.
