The strict avalanche criterion(SAC)is one of the most important cryptographic criteria for substitution boxes(S-boxes)used in many symmetric encryption systems.However,there are few constructive methods for S-boxes fulfilling the SAC until now.In this paper,to construct S-boxes satisfying the SAC directly,we generalize the concatenation techniques of Boolean functions to S-boxes.Using the idea of concatenating small variable S-boxes,we present a simple yet effective construction method of S-boxes satisfying the SAC.Finally,a simple example on how to construct SAC S-boxes with large input variables by small variables SAC S-boxes is given.
