Cryptanalysing the Shrinking Generator

Abstract In this work, we propose a cryptanalysis of the nonlinear sequence generator called the shrinking generator. The output sequence of this cryptographic generator, the shrunken sequence, can be modelled as one of the output sequences of linear cellular automata (CA). The shrunken sequence and the other sequences generated by the CA can be reduced to a combination of PN-sequences generated by the same characteristic polynomial. Therefore, all these PN-sequences are the same but shifted. We propose an efficient cryptanalysis that takes advantage of the linearity of these PN-sequences and the CA.