An Improved Algorithm for Fast Correlation Attack on Stream Ciphers

Fast Correlation Attack on binary linear feedback shift registers (LFSR) in Stream generators for stream ciphers applications are very paramount cryptanalytic techniques which are based on the idea from iterative probabilistic decoding procedures for binary symmetric channels (BSC). This paper presents an efficient correlation attack on stream ciphers, which is equivalent to solve the problem of recovering the LFSR's initial state (u(1), u(2), ... , u(n)) from the observed output sequence z. I consider the problem as a decoding problem for a linear [N,L] code. In order to enhance the speed of correlation attack, the Walsh transform is used, in addition, I adopt the multi-thread method to deal with the parity checks. The novel scheme provides better performance and lower complicity, improves the efficiency of fast correlation attack.