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Key Collisions on AES and Its Applications

Authors:
Kodai Taiyama , University of Hyogo, Kobe, Japan
Kosei Sakamoto , Mitsubishi Electric Corporation, Kamakura, Japan
Ryoma Ito , National Institute of Information and Communications Technology, Koganei, Japan
Kazuma Taka , University of Hyogo, Kobe, Japan
Takanori Isobe , University of Hyogo, Kobe, Japan
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Conference: ASIACRYPT 2024
Abstract: In this paper, we explore a new type of key collisions called target-plaintext key collisions of AES, which emerge as an open problem in the key committing security and are directly converted into single-block collision attacks on Davies-Meyer (DM) hashing mode. For this key collision, a ciphertext collision is uniquely observed when a specific plaintext is encrypted under two distinct keys. We introduce an efficient automatic search tool designed to find target-plaintext key collisions. This tool exploits bit-wise behaviors of differential characteristics and dependencies among operations and internal variables of both data processing and key scheduling parts. This allows us to hierarchically perform rebound-type attacks to identify key collisions. As a result, we demonstrate single-block collision attacks on 2/5/6-round AES-128/192/256-DM and semi-free-start collision attacks on 5/7/9-round AES-128/192/256-DM, respectively. To validate our attacks, we provide an example of fixed-target-plaintext key collision/semi-free-start collisions on 9-round AES-256-DM. Furthermore, by exploiting a specific class of free-start collisions with our tool, we present two-block collision attacks on 3/9-round AES-128/256-DM, respectively.
BibTeX
@inproceedings{asiacrypt-2024-34704,
  title={Key Collisions on AES and Its Applications},
  publisher={Springer-Verlag},
  author={Kodai Taiyama and Kosei Sakamoto and Ryoma Ito and Kazuma Taka and Takanori Isobe},
  year=2024
}