New Differential‐Based Distinguishers for Ascon via Constraint Programming

Abstract

As the winner of the NIST lightweight cryptography project, Ascon has undergone extensive self‐evaluation and third‐party cryptanalysis. In this paper, we use constraint programming (CP) as a tool to analyze the Ascon permutation and propose several differential‐based distinguishers. We first propose a search methodology for finding truncated differentials for Ascon with CP, the core of which is modeling with the undisturbed bits of the S‐box. By using this method, we find the five‐ and six‐round truncated differentials with a probability of 2−44 and 2−162, respectively. Considering the application of permutation in the context, we also provide the five‐ and six‐round truncated differential distinguishers under the weak‐key setting. Then, inspired by our five‐round truncated differentials, we propose a six‐round boomerang characteristic, and based on this, we obtain the five‐ and six‐round sandwich distinguishers with a complexity of 270 and 2134, respectively. Using the CP tool again and specifying that the “3‐3” differential pattern is satisfied in the middle rounds, we propose a six‐round differential characteristic with a probability of 2−280, which increases the probability by 225 compared to the best known six‐round differential characteristic.