Modified A5 stream cipher using S-boxes

Abstract

With the advance of wireless communications technology, wireless communications has become more convenient than ever. However, because of the openness of wireless communications, how to protect the privacy between communicating parties is becoming a very important issue and the security of wireless communications is necessary to the secure communication. Stream cipher is usually used to protect data in wireless communications. In this paper, we propose a new mechanism to make unsafe A5 algorithm secure, which is a stream cipher in GSM system. New mechanism uses some 4′16 s-boxes only if bit is 0. s-box decision method and s-box row·column method in order to achieve new mechanism. In s-box passing step, new s-box decision method decides to the order of s-box to use among s-boxes. New s-box row·.column method decides certain row and column to use. By analyzing test results, we prove that the proposed model has better randomness and serial correlation characteristic than A5.