Randomness evaluation of stream cipher for secure mobile communication

Information Security over mobile communication networks is important for secure communication. In GSM mobile standard, A5/1 stream cipher is used to provide security over-the-air voice transmissions. It is strong encryption algorithm among the cryptographic algorithms used in GSM. However, it is cryptanalized by a number of attacks. Recent studies show that it has serious security weaknesses in its architecture. In this paper, an enhanced version of A5/1 stream cipher to improve the security of A5/1 scheme is presented. Enhancements are made in clocking mechanism and combining function of the cipher. The proposed scheme is coded in VHDL. NIST Statistical test package is used to evaluate the randomness performance of output bit-streams of two ciphers. The randomness results show that the output bit-stream generated by the proposed stream cipher has better randomness performance.