APPARATUS FOR PARTIAL ENCRYPTION AND DECRYPTION, ITS METHOD, AND PROGRAM

PROBLEM TO BE SOLVED: To preferentially select and encrypt data having a high use value in partial encryption. SOLUTION: In a partial encryption apparatus 100, an encryption condition determiner 130 determines whether the next data is to be encrypted in response to a fluctuation of a value of preceding data, with respect to map data stored in a data memory 110 which is a target for encryption, and an encryption part 160 performs partial encryption based on the results. The encrypted data is similarly decrypted by a partial decryption apparatus 200. It is determined that a portion with a large fluctuation of target data is data having a high use value, and this data is encrypted preferentially. Further, it is determined whether encryption is required from the preceding data, whereby it is possible to prevent size increase in an encrypted text obtained. COPYRIGHT: (C)2009,JPO&INPIT