| 摘要 |
PROBLEM TO BE SOLVED: To provide a configuration wherein a quantity of information to be stored in an apparatus to perform decryption of an encrypted sentence thereon can be reduced in an encrypted sentence providing configuration to which a tree structure is applied. SOLUTION: When setting a node key corresponding to each of nodes comprising a hierarchical tree, a value of a higher node key is set to a value that can be calculated by applying a unidirectional function F to a value of a lower node key. To a receiver corresponding to a terminal node of the hierarchical tree, minimum node keys, other than a node key that can be calculated on the basis of the unidirectional function F, in node keys of nodes included in a path from a receiver corresponding node to a route as a most significant node, are provided. If an applied node key of an encrypted sentence as a processing target is not a hold node key, the receiver applies the unidirectional function F to the hold node key, thereby calculating the applied node key of the encrypted sentence. COPYRIGHT: (C)2005,JPO&NCIPI
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