Patent ID: 8055896

Claim:
A tag generation method for generating tags used in a broadcast encryption system which has a layered structure and which includes a plurality of node groups each consisting of a predetermined number of nodes, the method comprising: detecting at least two revoked leaf nodes; setting a node identification (ID) assigned to at least one node among nodes assigned node IDs at a layer 0 and to which the at least two revoked leaf nodes are subordinate, to a node path identification (NPID) of the at least two revoked leaf nodes at the layer 0 ; generating, by a server device, a tag list in the layer 0 by combining the NPID of each of the at least two revoked leaf nodes at the layer 0 in incrementing order of node IDs of the corresponding at least two revoked leaf nodes; and generating a tag list in layers below the layer 0 by performing the setting operation in each layer below the layer 0 and generating a tag list for each layer below the layer 0 by combining the NPID of each of the at least two revoked leaf nodes at each layer below the layer 0 in incrementing order of node IDs of the corresponding at least two revoked leaf nodes; wherein the tag list generated in each layer includes all of the combined NPID's for a single layer and the tag list generated at each layer is a sequential combination of NPIDs of the layer in which each NPID is a hexadecimal representation of a node to which at least two revoked leaf nodes are subordinate, and the number of NPIDs of the tag list at each layer is equivalent to the number of revoked leaf nodes.