| 摘要 |
PROBLEM TO BE SOLVED: To provide an encryption strength index calculation method that allows derivating a differential path, having characteristic probability near its upper bound and a linear approximation in a symmetric-key block encryption having an SPN-type F function of which the upper bound is derived using a truncated difference path, and to provide an encryption strength evaluating and processing apparatus, and a computer program. SOLUTION: The encryption strength index calculation method and encryption strength evaluating and processing apparatus perform a symmetric-key block encryption algorithm, and calculates a path of probability which is close to the upper bound in the encryption analysis of an encryption processing function comprising a Feistel structure, having a plurality of stages of round functions including a SPN-type F function. A truncated differential path, to which 0 or 1 is allocated, depending on whether a differential value of differential data is 0 or non zero, is inputted. An encryption processing unit is divided into a left chain and a right chain. A differential analysis is performed based on data included in each chain to calculate the difference characteristic probability (DCP), and the difference characteristic probability (DCP) having a highest value is calculated as the maximum difference characteristic probability (MDCPT) of an encryption strength index. COPYRIGHT: (C)2004,JPO
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