Improved Preimage Attacks on 4-Round Keccak-224/256
Keywords:Keccak, SHA-3, Preimage attack, Linear structure
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.
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Copyright (c) 2021 Le He, Xiaoen Lin, Hongbo Yu
This work is licensed under a Creative Commons Attribution 4.0 International License.