Deep learning has played an important role in many fields, which shows significant potential for cryptanalysis. Although these existing works opened a new direction of machine learning aided cryptanalysis, there is still a research gap that researchers are eager to fill. How to further improve neural distinguishers? In this paper, we propose a new algorithm and model to improve neural distinguishers in terms of accuracy and the number of rounds. First, we design an algorithm based on SAT to improve neural distinguishers. With the help of SAT/SMT solver, we obtain new effective neural distinguishers of SIMON using the input differences of high-probability differential characteristics. Second, we propose a new neural distinguisher model using multiple output differences. Inspired by the existing works and data augmentation in deep learning, we use the output differences to exploit more derived features and train neural distinguishers, by splicing output differences into a matrix as a sample. Based on the new model, we construct neural distinguishers of SIMON and SPECK with round and accuracy promotion. Utilizing our neural distinguishers, we can distinguish reduced-round SIMON or SPECK from pseudorandom permutation better.
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.
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 215.5 data complexity and 220.5 time complexity. The attack of the 82‐round KATAN48 and 70‐round KATAN64 are also presented as the best known practical results.
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