Cryptanalysis of Achterbahn-128/80

Abstract

This paper presents two key-recovery attacks against Achterbahn-128/80, the last version of one of the stream cipher proposals in the eSTREAM project. The attack against the 80-bit variant, Achterbahn80, has complexity 261. The attack against Achterbahn-128 requires 280.58 operations and 260 keystream bits. These attacks are based on an improvement of the attack due to Hell and Johansson against Achterbahn version 2. They mainly rely on an algorithm that makes profit of the independence of the constituent registers. © International Association for Cryptologic Research 2007.