| 摘要 |
There is provided an information-processing method for generating a hierarchical tree to be applied to processing to provide decryption apparatus with cryptograms, which can be decrypted only by specifically selected ones of the decryption apparatus excluding revoked decryption apparatus, by adoption of a broadcast encryption method based on a hierarchical tree configuration, the method including: a tree generation step of generating a one-way hierarchical tree as a tree in which a node key assigned to each of nodes composing the one-way hierarchical tree is set at such a value that the node key assigned to a node on a hierarchical layer at a higher level can be computed by applying a one-way function F to at least one of node keys assigned to nodes on a hierarchical layer at a lower level; and a node-key selection step at which, as node keys to be provided to each of the decryption apparatus each serving as a receiver associated with any particular one of terminal nodes on a hierarchical layer at a lowest level of the one-way hierarchical tree, as few node keys as possible are selected among node keys assigned to nodes on a path from the particular lowest-layer terminal node associated with the receiver to a node serving as a root on a hierarchical layer at a highest level of the one-way hierarchical tree except that, as selectable node keys, those of nodes each having a node key computable by applying the one-way function F are excluded.
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