Proposal for an Encryption Method Based on Reconfiguration of a Nonlinear Transformation Table and Its Security Assessment

摘要

In recent years, various common-key encryption schemes have been proposed. Among these are schemes that have provable security against both differential and linear cryptanalyses. Upper bounds on the probability that a differential or a linear cryptanalysis has occurred have been derived mathematically, and practical ways to increase security have been outlined that involve changing the key before the occurrence of such attacks. However, when such encryption systems are put into practice, the cycle of key changes must be long. In this article, we propose a system design that moves encryption security closer to the goal of providing provably secure encryption by allowing key-dependent changes in the S-box within the encryption. When the user can reconfigure the S-box, standard cryptanalysis becomes difficult. However, when the changes in the S-box are random, there is a risk of making it vulnerable to differential and linear attack. To remedy this, we propose a scheduling method that makes the S-box resistant to these attacks. The structure of our S-box is based on power-law operations and affine transformations. The user modifies the S-box by altering the affine transformation part. This variable affine transformation incorporates both permutation processing and a triangular matrix into its structure. In the last section of the article, we assess the security and computational cost of our method. We conclude that, despite a slight increase in the computational cost compared to standard methods, secure encryption is obtained.