Paper 2025/792

Scrutinizing the Security of AES-based Hashing and One-way Functions

Abstract

AES has cemented its position as the primary symmetric-key primitive for a wide range of cryptographic applications, which motivates the analysis on the concrete security of AES in practical instantiations, for instance, the collision resistance of AES-based hashing, the key commitment security of AES-based authenticated encryption schemes, and the one-wayness of AES-based one-way functions in MPC/ZK protocols. In this work, we further advance the meet-in-the-middle (MITM) attack framework on AES-like constructions. We introduce single-color initial structure (SCIS), which leverages new structural insights to reduce the complexity of neutral word generation, a critical bottleneck in MITM attacks. As a result, we yield a series of improved results on AES over the state-of-the-art, including the first classical one-block collision attack on 7-round AES-MMO/MP, marking the first round advancement in over a decade and matching the best attack round in the quantum setting, as well as the first one-block collision attack on 4-round AES-128-DM, bridging the gap highlighted by Taiyama et al. at Asiacrypt 2024 from a non-differential-based approach. Additionally, we provide a comprehensive list of new results on the security margins of AES-192, AES-256, Rijndael-192, and Rijndael-256 in multiple attack settings.