Design and implementation of keystream generator with improved security

This paper provides the design of stream ciphers based on hash functions and an alternating step generator based on clock control. The keystream generators used for the design of stream ciphers uses low hardware and low power based circuits called Linear Feedback Shift Register circuits. The first two stream ciphers use toeplitz hash, CRC hash and keystream generation circuits whereas the third one uses clock controlling mechanism. Analysis is made for the generation of keystream for clock controlled generator (CCG). The irregular clocking in clock controlled alternating step generator provides good security against various cryptographic attacks. The parameters like periodicity, attacktime and throughput of stream ciphers are measured and compared. As per the results, the first stream cipher gives high periodicity and low attacktime, second stream cipher gives low periodicity and high attacktime. The alternating step generator provides good periodicity, high attacktime and good amount of security compared to other stream ciphers. MATLAB tool is used to calculate periodicity, attacktime and throughput whereas XILINX FPGA is used for the design and implementation purpose. Design includes synthesis, simulation, mapping, place route, verification, and timing analysis done for all the stream ciphers. FPGA results of stream ciphers and alternating step generator evaluate their hardware efficiencies. In all the three designs keystream generation plays a major role.