Paper 2024/351 Original: eprint.iacr.org/2024/351 ↗

Improved Differential Meet-In-The-Middle Cryptanalysis

Abstract

In this paper, we extend the applicability of differential meet- in-the-middle attacks, proposed at Crypto 2023, to truncated differen- tials, and in addition, we introduce three new ideas to improve this type of attack: we show how to add longer structures than the original pa- per, we show how to improve the key recovery steps by introducing some probability in them, and we combine this type of attacks with the state- test technique, that was introduced in the context of impossible differ- ential attacks. Furthermore, we have developed a MILP-based tool to automate the search for a truncated differential-MITM attack with op- timized overall complexity, incorporating some of the proposed improve- ments. Thanks to this, we can build the best known attacks on the cipher CRAFT, reaching 23 rounds against 21 previously; we provide a new at- tack on 23-round SKINNY-64-192, and we improve the best attacks on SKINNY-128-384.