Paper 2021/820

Further Improving Differential-Linear Attacks: Applications to Chaskey and Serpent

Marek Broll and Federico Canale and Nicolas David and Antonio Florez-Gutierrez and Gregor Leander and María Naya-Plasencia and Yosuke Todo

Abstract

Differential-linear attacks are a cryptanalysis family that has recently benefited from various technical improvements, mainly in the context of ARX constructions. In this paper we push further this refinement, proposing several new improvements. In particular, we develop a better understanding of the related correlations, improve upon the statistics by using the LLR, and finally use ideas from conditional differentials for finding many right pairs. We illustrate the usefulness of these ideas by presenting the first 7.5-round attack on Chaskey. Finally, we present a new competitive attack on 12 rounds of Serpent, and as such the first cryptanalytic progress on Serpent in 10 years.