Patent ID: 8600052

Claim:
A key generation device characterized by comprising: a tree-structure construction unit that hierarchically constructs a Y-ary tree structure where n reception devices are assigned to leaves, Y is the number of branches, and a height is represented by (log Y n), and forms subgroups constituted by a plurality of leaves existing in a layer lower than intermediate nodes existing between the leaves and a root; a leaf-key assigning unit that assigns leaf keys g y to the individual leaves and the individual intermediate nodes; a parameter assigning unit that assigns different parameters ν x,y (x: layer, y: 1, 2, . . . , Y x ) and node parameters γ x,y (x: layer, y: 1, 2, . . . , Y x ) to the individual intermediate nodes and the root; and a key calculation unit that identifies paths extending from the root to the leaves, and calculates keys on the basis of the leaf keys g y assigned to the intermediate nodes or the leaves existing in the paths and the parameters ν x,y and the node parameters γ x,y assigned to parent nodes of the intermediate nodes or the leaves.