Security enhancements in GSM cellular standard

GSM is widely used cellular standard in the world. GSM uses A5/x algorithms to secure the information sent over the air interface. A5/1 is a strong encryption algorithm among all A5/x algorithms. However, recent studies show that it has security flaws in its architecture, owing to which it is susceptible to several cryptographic attacks. This paper presents an enhanced scheme of A5/1 algorithm to improve the level of security provided by the GSM. Proposed scheme is analyzed against some cryptographic attacks and it is shown that the scheme provides more security by offering more resistance to correlation attack, algebraic attack and linear approximation attack. Moreover, the linear complexity of the enhanced cipher is quite large and makes the cipher to withstand the Berleykamp-Massey attack. It is also shown that the proposed scheme is little faster with respect to the output rate. Both the designs are coded in VHDL andP synthesized on FPGA device.