Concatenated automata in cryptanalysis of stream ciphers

Abstract

This work shows that sequences generated by a class of linear cellular automata equal output sequences of certain nonlinear sequence generators. A simple modelling process for obtaining the automata from a partial description of such generators is here described. Furthermore, a method that uses the linearity of these cellular models for reconstructing some deterministic bits of the keystream sequence is presented. © Springer-Verlag Berlin Heidelberg 2006.