Patent ID: 8150040

Claim:
A key providing system configured by a plurality of terminal devices, and an information processing device for providing a key used in encryption or decryption of data to a predetermined terminal device, wherein the information processing device includes, a tree setting unit configured to generate a logical binary tree; a coordinate axis setting unit configured to generate a plurality of horizontal coordinate axes based on the binary tree for forming a predetermined digraph; a digraph generation unit configured to generate the predetermined digraph by arranging directional branches connecting coordinate points on each horizontal coordinate axis including a plurality of coordinate points each corresponding with a set representing a combination of the plurality of terminal devices, the directional branches including arch-shaped curves and horizontally extending lines; a selecting unit for selecting the set representing some or all of the plurality of terminal devices, a key generation unit for generating the key corresponding to the selected set based on the predetermined digraph, and a providing unit for providing the generated key and information related to the selected set to the plurality of terminal devices; and the terminal device includes, an acquiring unit for acquiring the generated key and the information related to the selected set, a digraph generation unit for generating the directional branch for generating the key corresponding to the selected set to which it belongs of the directional branches forming the predetermined digraph, and a key generation unit for generating the key corresponding to the selected set to which it belongs based on a digraph formed by the generated directional branch.