Research on the Security of Key Generator in Stream Ciphers

Design of key generator is the core process in stream cipher. This paper discusses the security of the LFSR and nonlinear combining functions as two core components of key generator. The models studied in this paper include linear shift register sequence, Geffe sequence, shrinking feedback sequence and widespread to the general nonlinear combining sequence. Improvement advice is proposed for cryptographist after each case of study to obtain stream cipher of higher strength.