Mobile devices used to access corporate networks send business data over a wide variety of links. From 3G wireless to WiMAX, hotel broadband to Wi-Fi hot spot, every public network interface poses some business risk. With the increase in wireless communication technology, encryption of information sent has become a major concern. GSM standard hardware level encryption uses the A5/1 algorithm. The circuitry for this is embedded into the Mobile Equipment as well as at base station for secure communication. A5/1 algorithm uses LFSR to generate key stream. A5/1 stream cipher generates key which encrypts the information transmitted between subscriber’s mobile and the base station. It is a strong encryption algorithm among all the cryptographic algorithms used in GSM. But, recent research studies have shown that A5/1 cipher is crypt analyzed by a number of attacks. It has feeble clocking mechanism and output bit sequence of A5/1 has low rate of linear complexity. To overcome these problems we introduce the feedback tap mechanism enhanced by variable taps and four nonlinear combination functions. It has been mathematically proved that proposed algorithm is having high algebraic degree correlation immunity against correlation attack, algebraic attack, linear approximation attack and bereleykamp-Massey attack. The A5/1 algorithm is coded in VHDL and synthesized on FPGA-SPARTAN6 device. NIST Statistical test package is will be used to measure the linear complexity of output key stream.