SMS4 Algorithm Analysis And Its Application In 3G Communication System

Data confidentiality algorithm F8 and integrity algorithm F9 have been defined by 3 GPP to protect the security of 3G communication systems. They are based on the same block cipher as core algorithm. From the security point of view, China should design a block cipher as core algorithm of F8 and F9. From the following aspects, this paper studies the feasibility of making SMS4 as core algorithm of F8 and F9.Security, the ability for SMS4 to resist linear attack and differential attack is analyzed. A linear bias probability relationship between SMS4 and its round function is established theoretically by using the similar method used to analyze Feistel structure. Owing to one round SP structure of round function, another linear bias probability relationship between SMS4 and S-box is established theoretically. Then one linear bias probability upper bound of 32-round SMS4 is deduced by the latter relationship. Similarly, one differential characteristic probability upper bound of 32-round SMS4 is deduced. Based on two upper bound, corresponding security evaluation is made according to Knudsen's security standard. The results show that 32-round SMS4 has a strong ability to resist linear and differential attack. So SMS4 meets the security requirement of 3 GPP.Randomness, keystreams generated by F8 with SMS4 as core algorithm are tested in randomness. First of all, the F8 is realized by C language, and generates 100 groups 20000-bit keystreams using 100 different cipher keys. Then randomness of the keystreams is tested by FIPS 140-2 standard. The results show that keystreams generated by the F8 behave excellent performance of randomness. So SMS4 meets the randomness requirement of 3GPP. Efficiency, encryption speed of F8 with SMS4 as core algorithm is tested when realized in software. First of all, the F8 generates 6-group keystreams. With these keystreams, six groups time of same plaintext encrypted by 1000 times are recorded respectively. According to the size of plaintext, six groups time are changed into encryption speeds. The result shows that average speed of the F8 in software reaches to 1.924 Mbps. So SMS4 meets approximatively the efficiency requirement of 3 GPP.