Improved Preimage Attacks on 3-Round Keccak-224/256

In this paper, we provide an improved method on preimage attacks of standard 3-round Keccak-224/256. Our is based the work by Li and Sun. Their strategy to find a 2-block instead 1-block one constructing first second message blocks in two stages. Under strategy, they design new linear structure for 2-round Keccak-224/256 with 194 degrees freedom left, which able construct block complexity 231/262. However, bottleneck that stage needs much more expense than one. Therefore, improve using techniques. The technique multi-block messages rather one-block stage, can reach better inner state. setting restricting equations efficiently, Keccak-256. As result, finding be decreased from 238/281 232/265.