Integral and impossible‐differential attacks on the reduced‐round Lesamnta‐LW‐BC

Abstract

Abstract Lesamnta‐LW‐BC is the internal block cipher of the Lesamnta‐LW lightweight hash function, specified in ISO/IEC 29192‐5:2016. It is based on the unbalanced Feistel network and Advanced Encryption Standard round function. In this study, the security of Lesamnta‐LW‐BC against integral and impossible‐differential attacks is evaluated. Specifically, the authors searched for the integral distinguishers and impossible differentials with Mixed‐Integer Linear Programming‐based methods. As a result, the discovered impossible differential can reach up to 21 rounds, while three integral distinguishers reaching 18, 19 and 25 rounds are obtained, respectively. Moreover, it is also feasible to construct a 47‐round integral distinguisher in the known‐key setting. Finally, a 20‐round key‐recovery attack is proposed based on the discovered 18‐round integral distinguisher and a 19‐round key‐recovery attack using a 17‐round impossible differential. To the best of the authors' knowledge, this is the first third‐party cryptanalysis of Lesamnta‐LW‐BC.

Keywords

• integer programming
• linear programming