The Security Analysis Of Block Cipher SMS4

WAPI (WLAN Authentication and Privacy Infrastructure) is a technical standard for wireless LAN security, which is developed by Chinese and has independent intellectual property rights. The Elliptic Curve Cryptosystem algorithm and block cipher SMS4 which are approved by the office of state commercial cipher administration are adopt in WAPI, and SMS4 is the first commercial block cipher published by Chinese government. How to make a new security evaluation for these algorithms is one of the present research hotspots.An in-depth study for the security of SMS4 will be described in the paper. Square attack is one of the classical attacks and its main idea is to observe and track the active bytes or the active words to search a balanced byte or a balanced word.A certain plaintext is chosen to built a set that contains three active words. Being based on the character of the diversification of the active words in the round structure of SMS4, a balance word is found in the ninth round by observing the spread path of the balance words, therefore a new 12-round distinguisher is constructed, and by using which a 14-round square attack is made on SMS4; according to the characters of round structure and the analysis of transfer process of cipher text's differences in the first 12 rounds of SMS4,a contradiction is found that the first byte in the eighth round are not equal while encrypting and decrypting, and then a 11-round distinguisher can be constructed to attack 12-round SMS4 with related-key impossible differential attack.