Patent ID: 7707410

Claim:
A method for distributing encrypted message data, the method comprising: using a processor to execute the following: generating an enabling key block (EKB) including a tag and encrypted keys, the encrypted keys including at least one renewed key and the tag including position discrimination data that associates each of the encrypted keys with nodes and leaves of a hierarchical tree structure, the generating step including: forming a simplified tree structure from the hierarchical tree structure by selecting one or more paths between a top node and a terminal node or leaf of the hierarchical tree structure and by not including one or more unnecessary nodes in the selected one or more paths, such that the encrypted keys of the EKB do not include a key corresponding to the one or more unnecessary nodes in the selected one or more paths, generating the encrypted keys such that the encrypted keys comprise only keys corresponding to a node or leaf of the simplified tree structure, and generating the tag such that the position discrimination data indicates whether an encrypted key corresponding to a node is included in the EKB; and generating the encrypted message data using the at least one renewed key for distribution to a device.