Stream ciphers for GSM networks

With the advance of wireless communications technology, mobile 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. In this paper, we focus on the security of transferring voice message on the Global System for Mobile communication (GSM) networks. Stream cipher is recommended for message encryption and decryption. First, a key generator is presented. Then, on the basis of the key generator, stream ciphers are designed with respect to different levels of securities of GSM networks. Simulation results indicate that the key generator always produces key strings of evenly distributed 0's and 1's and with a very long period; i.e. it is very unlikely that repeated patterns will appear. Cryptanalysis and operational analysis show that the proposed stream ciphers are secure and efficient; consequently, they provide a comprehensive set of message encryption/decryption algorithms for GSM networks.