| 摘要 |
PROBLEM TO BE SOLVED: To safely and efficiently communicate, even when a cryptographic key of any terminal device is invalidated because of any reason, with each of terminal devices belonging to the same group as that terminal device in a system for distributing cryptographic keys, which are managed in a tree structure, to a plurality of terminal device grouped in accordance with the same tree structure. SOLUTION: Terminal devices 300 from A1 to A8 are made correspond to terminal nodes in a binary tree structure. When A6 is invalidated, for example, for each of partial trees formed by excluding a terminal node corresponding to A6 and an ascendance node of the relevant terminal node from the tree structure, a specific group information generating part 402 specifies a terminal device 300 corresponding to a terminal node included in the same partial tree as a valid terminal. For each group (each of three groups A1-A4/A5/A7, A8) of terminal devices 300 constituted of the relevant valid terminal, a group-by-group information transmitting part 403 collectively transmits to the terminal devices 300 cipher text generated using the common cryptographic key. COPYRIGHT: (C)2010,JPO&INPIT
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