| 摘要 |
Reduces message length of encrypted message to be transmitted selectively to plurality of decrypting devices. An encrypting device includes a generating unit for generating node associating information configured to associate respective terminal nodes in a tree structure with each decrypting device in relation to a group of decrypting devices enabled for decryption, a extracting unit for extracting a decryption enabled node containing decrypting devices in descendant terminal nodes and not containing a decrypting device with decryption disabled in any of the descendant terminal nodes, and a unit for encrypting the message by use of a node encryption key for the decryption enabled node. Decrypting devices include specifying unit for specifying terminal node associated with decrypting device based on node associating information, and a decrypting unit for decrypting encrypted message using a node decryption key for any decryption enabled nodes ranging from terminal node to root node thereof.
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