METHOD AND DEVICE AND RECORDING MEDIUM FOR HIERARCHICAL ENCIPHERING/DECODING

摘要

PROBLEM TO BE SOLVED: To encipher a plurality of hierarchical plaintext data maintaining the hierarchy and to decode, with a single decoding key set for each hierarchy, enciphered data belonging to the hierarchy and to each of the lower hierarchies. SOLUTION: The device for hierarchical enciphering and decoding is provided with a plaintext input means 1 to input a plaintext to be enciphered, a field dividing means 2 to divide the plaintext into a plurality of fields, a hierarchy generating means 3 to carry out grouping of a first hierarchy which contains all the fields between each field and a plurality of field groups contained according to a plurality of containment relations defined between each field contained in the first hierarchy into the hierarchical groups lower than the first hierarchy, and enciphering means 4A, 4B which enciphers the hierarchized fields to make plaintext data into enciphered data and generates a decoding key for each hierarchy. Each key decodes the enciphered data belonging to the corresponding hierarchy and to the lower hierarchies among the enciphered data.