Abstract: An encryption evaluation device 100 is a device evaluating the security of a block cipher encrypting data of a predetermined size for each block by repeatedly executing, a predetermined number of rounds, a round process using a round function converting data based on a key. The encryption evaluation device 100 includes: a structure specification information accepting part 101 configured to accept structure specification information for specifying a structure of the block cipher; and a security index value calculating part 102 configured to specify a non-use number as the number of round functions that are not used in meet-in-the-middle attack, based on the accepted structure specification information, and calculate a security index value indicating a calculation amount required to specify the key by performing the meet-in-the-middle attack, based on the specified non-use number.

Abstract: An encryption/decryption method comprises by using a generalized Feistel structure in which data is divided into n pieces and mixing processing with key data is performed, diffusion processing, in which data transformation via linear operation is executed, is performed at least once between rounds of the generalized Feistel structure, wherein. As the diffusion processing, linear transformation is performed in which each of n pieces of output data is operated on by two or more pieces of input data. The method is adapted for encryption or decryption.

Abstract: An encryption/decryption method comprises by using a generalized Feistel structure in which data is divided into n pieces and mixing processing with key data is performed, diffusion processing, in which data transformation via linear operation is executed, is performed at least once between rounds of the generalized Feistel structure, wherein. As the diffusion processing, linear transformation is performed in which each of n pieces of output data is operated on by two or more pieces of input data. The method is adapted for encryption or decryption.

Abstract: To achieve both information confidentiality management and early discovery of information leak.