DOCUMENT-PLAIN TEXT SPACE MAPPING DEVICE, PLAIN TEXT SPACE-DOCUMENT MAPPING DEVICE, METHOD AND PROGRAM

PROBLEM TO BE SOLVED: To provide a mapping technology capable of mapping efficiently into a plain text space, when encrypting an optional plain text by using a public key, and restoring efficiently a plain text from the plain text space. SOLUTION: An encryption processing device 100 performs division and padding to a bit string when encrypting an optional bit string, and thereby maps into the plain text space on torus of a prime number order in a 6-th order extension field. A decoding processing device 200 determines whether padding is performed correctly or not relative to a bit string wherein a cipher text is decoded and mapped and compressed into a compressed expression of the torus in the 6-th order extension field, and bonds each bit string acquired by performing un-padding corresponding to a determination result. COPYRIGHT: (C)2010,JPO&INPIT