Patent ID: 9571213
Date: 2017-02-14
CPC Classifications: H04H,H04L

Claim:
1. 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 one revoked leaf node; 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 one revoked leaf node is subordinate, to a node path identification (NPID) of the at least one revoked leaf node 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 one revoked leaf nodes at the layer 0 in incrementing order of node IDs of the corresponding at least one 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 one revoked leaf nodes at each layer below the layer 0 in incrementing order of node IDs of the corresponding at least one revoked leaf nodes; wherein the tag list generated in each layer includes all of the combined NPID's for a single layer, and wherein, for the tag list in each layer, each NPID is combined with a group ID (GID) of a parent node of a node corresponding to the NPID, the plurality of node groups are circular node groups.