International Journal of Engineering and Technology

A stream cipher is a common method to protect confidential information from unauthorized person. This kind of cryptosystem is preferred to block ciphers because its implementation in hardware consumes less power and size. Amidst of different stream ciphers, Non-Linear Feedback Shift Register (NLFSR) based one offers the best trade-off between security and hardware capability. This paper describes the stream cipher that generates 128 bit keystream using only NLFSR element as its main function and XOR operation. Hence, this cryptosystem is named as Exclusive-128 NLFSR stream cipher. This cipher consists of different sizes of NLFSRs both in Galois and Fibonacci configuration which offers better trade-off between the algorithm security and hardware capability. The essential design principles in developing the stream cipher are adopted from the A5/1 and modified A5/1 stream ciphers. The proposed stream cipher provides promising efficiency in hardware costs in reconfigurable Field Programmable Gate Array (FPGA) and Application Specific Integrated Circuits (ASIC) implementations.