Patent ID: 8001370

Claim:
A system including an encrypting device and a decrypting device, comprising: a node associating information generating unit for generating node associating information for associating each of a plurality of first terminal nodes in a first tree structure; a plurality of second terminal nodes in a second tree structure connecting a plurality of nodes with each of a plurality of decrypting devices, wherein the decrypting devices correspond to respective descendant first terminal nodes of a first decryption enabled node and on the device decryption key of a specified decrypting device, on condition that any nodes ranging from a first terminal node associated with the specified decrypting device to a root node of the first tree structure, the second tree structure among a plurality of first nodes in the first tree structure, and the plurality of the second terminal nodes on the second tree structure connecting a plurality of nodes, is the first decryption enabled node, wherein said decrypting devices enabled to decrypt the encrypted message are associated with a descendent first terminal node in the first tree structure and the second tree structure; a node extracting unit for extracting the first decryption enabled node from the first tree structure and a second decryption enabled node from the second tree structure, in which said decryption devices are enabled to decrypt the encrypted message; a message encrypting unit for encrypting the message by use of a first node encryption key associated with the first decryption enabled node, wherein a public key and a secret key are predefined in relation to each of the decrypting devices, and the message encrypting unit further generates the first node encryption key based on the product of the secret keys, said secret keys corresponding to the respective decrypting devices, and said secret keys not being associated with the respective descendant first terminal nodes of the first decryption enabled node.