Key Providing System, Key Providing Apparatus, Terminal Device, Key Providing Method, and Key Generation Method

摘要

A key providing apparatus for providing a key used for encryption or decryption of data to a predetermined terminal device is provided. The key providing apparatus includes an acquiring unit for acquiring a digraph formed by arranging at least one directional branch connecting the coordinate points on a coordinate axis having a plurality of coordinate points each corresponded with a subset representing a combination of a plurality of terminal devices, an extracting unit for extracting information of all the directional branches contained in the directional path connecting a starting point of the digraph and a predetermined coordinate point, and a key generation unit for generating a key corresponded to a subset to which a predetermined terminal deice belongs based on the digraph, where the information of the directional branch is provided to the predetermined terminal device.