BDD-based cryptanalysis of stream cipher: a practical approach

Binary decision diagram (BDD) is a state-of-the-art data structure for representing and manipulating Boolean functions. In 2002, Krause proposed theoretical framework for BDD-based cryptanalysis of stream ciphers. Since then not much work have been reported in this area. In this study, the authors propose a practical approach for cryptanalysis of stream cipher using reduced ordered BDD (ROBDD). They propose various methods for ANDing operation on ROBDDs, required during process of cryptanalysis. Out of these proposed methods, ‘recursive symmetric ANDing’ gives optimal order of ANDing. They use their approach to demonstrate cryptanalysis of E 0 stream cipher. They also discuss some implementation results. The attack can recover 39 unknown key bits in 5 s on regular personal computer. BuDDy-2.4 library is used for performing operations on BDDs.