Abstract In CRYPTO 2019, Gohr built a bridge between machine learning and differential cryptanalysis, which show that machine learning-aided methods have advantages over classical differential cryptanalysis. Yet, for linear cryptanalysis, there is lack of effective works showing that machine learning-aided cryptanalysis can reach the benchmark of traditional counterparts and also lack of an effective universal framework using machine learning to assist linear cryptanalysis. In this paper, we mainly focus on machine learning-aided linear cryptanalysis and application to Des. First, we propose a machine learning-aided model to distinguish different Bernoulli distributions and demonstrate the validity of the model through experiments and theoretical analysis. Based on the model, we propose a new machine learning-aided linear cryptanalysis framework, which can be applied to one bit and multiple bits key-recovery attacks. As applications, we perform one bit attacks on 3-, 4-, 5-, 6-round Des and multiple bits attack on 8-round Des. Compared with the previous works about machine learning-aided linear cryptanalysis, the results improve the success rate and the complexity. Most importantly, more rounds are covered in our work. Besides, the work indicates that machine learning-aided cryptanalysis can achieve the same or marginally better performance than classical methods.

Abstract At CRYPTO’19, Gohr built a bridge between deep learning and cryptanalysis. Based on deep neural networks, he trained neural distinguishers of SPECK32/64. Besides, with the help of neural distinguishers, he attacked 11-round SPECK32/64 using Bayesian optimization. Compared with the traditional attack, its complexity was reduced. Although his work opened a new direction of machine learning aided cryptanalysis, there are still two research gaps that researchers are eager to fill in. (i) Can the attack using neural distinguishers be used to other block ciphers? (ii) Are there effective key recovery attacks on large-size block ciphers adopting neural distinguishers? In this paper, our core target is to propose an effective neural-aided key recovery policy to attack large-size block ciphers. For large-size block ciphers, it costs too much time in pre-computation, especially in wrong key response profile, which is the main reason why there are almost no neural aided attacks on large-size block ciphers. Fortunately, we find that there is a fatal flaw in the wrong key profile. In the some experiments of SIMON32/64 and SIMON48/96, there is a regular of change in response profiles, which implies that we can use partial response instead of the complete response. Based on this, we propose a generic key recovery attack scheme which can attack large-size block ciphers. As an application, we perform a key recovery attack on 13-round SIMON64/128, which is the first practical attack using neural distinguishers to large-size ciphers. In addition, we also attack 13-round SIMON32/64 and SIMON48/96, which also shows that the neural distinguishers can be used to other block ciphers.

Abstract KATAN ciphers are block ciphers using non‐linear feedback shift registers. In this study, the authors improve the results of conditional differential analysis on KATAN by using deep learning. Multi‐differential neural distinguishers are built to improve the accuracy of the neural distinguishers and increase the number of its rounds. Moreover, a conditional differential analysis framework is proposed based on deep learning with the multi‐differential neural distinguishers, resulting in a significant improvement than the previous. We present a practical key recovery attack on the 97‐round KATAN32 with 2 15.5 data complexity and 2 20.5 time complexity. The attack of the 82‐round KATAN48 and 70‐round KATAN64 are also presented as the best known practical results.