Cellular Automata in Stream Ciphers

TL;DR

This paper demonstrates that certain nonlinear stream cipher generators can be modeled using linear cellular automata, enabling new cryptanalytic methods and simplifying analysis of keystream generators.

Contribution

It introduces a simple algorithm to convert clock-controlled shrinking generators into linear cellular automata models, facilitating cryptanalysis.

Findings

Clock-controlled generators can be represented by linear automata

Linear models enable effective cryptanalytic approaches

Automata-based modeling simplifies analysis of keystream generators

Abstract

A wide family of nonlinear sequence generators, the so-called clock-controlled shrinking generators, has been analyzed and identified with a subset of linear cellular automata. The algorithm that converts the given generator into a linear model based on automata is very simple and can be applied in a range of practical interest. Due to the linearity of these automata as well as the characteristics of this class of generators, a cryptanalytic approach can be proposed. Linear cellular structures easily model keystream generators with application in stream cipher cryptography.