Differences of stream cipher implementations based on LFSR multiplication circuits and division circuits

Stream cipher is the classical cryptography in ensuring information security. Pseudo-random sequence generator is of vital importance in stream ciphers, where the linear feedback shift registers (LFSR) play an important role. In this paper, differences in analysis of LFSR implementations based on multiplication circuits and division circuits are researched. Then an idea that transforms division circuits into multiplication circuits is proposed. Inputs of feed-function in the feed-forward model based on division circuits are expressed by linear combination of continuous fragments from a tap sequence, so as to be processed with the method that fit for multiplication circuits. And finally a concrete expressing form is given.