Practically Secure against Differential Cryptanalysis for Block Cipher SMS4

摘要

SMS4 is a 128-bit block cipher with a 128-bit user key and 32 rounds,which is used in the Chinese National Standard for Wireless LAN WAPI. This paper studies the practical security of SMS4 against differential attack which is evaluated by upper bounds of maximum differential characteristic probability (MLCP). We design a method to calculate the lower bounds on the number of active S-Boxes in some consecutive rounds of SMS4. The results show that SMS4 is practically secure against differential cryptanalysis.