Study And Software Implementation Of Variable Coefficient Feedback Shift Register And Its Sequences

Since the security of traditional stream ciphers is very much influenced by more and more attacks, the secure cryptosystems of new types are desired. Many keystream generators using at the present time are usually based on linear feedback shift register (LFSR) and the keystream generated by LFSR can not resist the algebraic attack, Berlekamp - Massey algorithm or rational approximation algorithm. The reason why the keystream can not resist these attacks is that the coefficients of LFSR are specified constants.To solve this problem, a new method which makes the coefficients of generating function changed dynamically, is proposed to improve linear feedback shift register. In this paper, a new keystream generator, called variable coefficient feedback shift register is proposed, whose coefficients of generating function are changed dynamically. Some important cryptological properties have been obtained and these properties are proved in this paper. The corresponding stream cipher cryptosystem has been designed and carried out by software. Compared with those keystream generators based on linear feedback shift register, this new method makes the keystream generator able to resist the algebraic attacks and Berlekamp - Massey algorithm, so that the security problem caused by constant coefficients can be solved, and the primary analysis shows that this new keystream sequences are of high security. Therefore, the variable coefficient feedback shift register has an obvious advantage in the aspect of the security of stream cipher.