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Paper: Improved Preimage Attacks on 4-Round Keccak-224/256

Authors:
Le He , Department of Computer Science and Technology, Tsinghua University, Beijing 100084, China
Xiaoen Lin , Department of Computer Science and Technology, Tsinghua University, Beijing 100084, China
Hongbo Yu , Department of Computer Science and Technology, Tsinghua University, Beijing 100084, China
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DOI: 10.46586/tosc.v2021.i1.217-238
URL: https://tosc.iacr.org/index.php/ToSC/article/view/8838
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Abstract: This paper provides an improved preimage attack method on standard 4-round Keccak-224/256. The method is based on the work pioneered by Li and Sun, who design a linear structure of 2-round Keccak-224/256 with 194 degrees of freedom left. By partially linearizing 17 output bits through the last 2 rounds, they finally reach a complexity of 2207/2239 for searching a 4-round preimage. Yet under their strategy, those 17 bits are regarded as independent bits and the linearization costs a great amount of freedom. Inspired by their thoughts, we improve the partial linearization method where multiple output bits can reuse some common degrees of freedom. As a result, the complexity of preimage attack on 4-round Keccak-224/256 can be decreased to 2192/2218, which are both the best known theoretical preimage cryptanalysis so far. To support the theoretical analysis, we apply our strategy to a 64-bit partial preimage attack within practical complexity. It is remarkable that this partial linearization method can be directly applied if a better linear structure with more freedom left is proposed.
BibTeX
@article{tosc-2021-30950,
  title={Improved Preimage Attacks on 4-Round Keccak-224/256},
  journal={IACR Transactions on Symmetric Cryptology},
  publisher={Ruhr-Universit├Ąt Bochum},
  volume={2021, Issue 1},
  pages={217-238},
  url={https://tosc.iacr.org/index.php/ToSC/article/view/8838},
  doi={10.46586/tosc.v2021.i1.217-238},
  author={Le He and Xiaoen Lin and Hongbo Yu},
  year=2021
}