Patent ID: 7505599
Filing Date: 2009-03-17
Classification: G06F,G11B,H04L

Abstract:
1. A device for use in an information processing system that distributes encrypted message data, the device comprising: a receiver for receiving the encrypted message data and an enabling key block (EKB), the EKB including encrypted keys and a tag, 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; a memory for storing a key set, the key set including at least one key corresponding to a node or leaf of the hierarchical tree structure; and an encryption processor operable to (a) decrypt the encrypted keys of the received EKB using the stored key set and the position discrimination data of the received EKB to recover the at least one renewed key and (b) decrypt the received encrypted message using the at least one recovered renewed key, the encrypted keys of the EKB including keys corresponding to a simplified tree structure, the simplified tree structure being constructed from the hierarchical tree structure by selecting one or more paths between a top node and an end point node or a leaf of the hierarchical tree structure and not including one or more unnecessary nodes being 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.