Efficient software implementation of LFSR and boolean function and its application in nonlinear combiner model

Abstract

Here we present an efficient implementation strategy and some general design criteria for the standard nonlinear combiner model. This model combines the output sequences of several independent Linear Feedback Shift Registers (LFSRs) using a Boolean function to produce the running key sequence. The model is well studied and a standard target for many cryptanalytic attacks. The naive bitwise software implementation of the LFSRs is not efficient. In this paper we explore an efficient block oriented software implementation technique to make it competitive with the recently proposed fast stream ciphers. Our proposed specifications on this model can resist the fast correlation attacks. To evaluate our design criteria and implementation techniques, we carry out the security and performance analysis considering a specific scheme based on this model. © Springer-Verlag Berlin Heidelberg 2003.