We congratulate Xiaoen Lin, Hongbo Yu, Chongxu Ren, Zhengrong Lu and Yantian Shen of Tsinghua University, Beijing, China, for solving the 4-round pre-image challenge on Keccak[r=240, c=160].

The previous pre-image challenge on the 400-bit version was solved on 3 rounds by Yao Sun and Ting Li in 2017. The solution to the present challenge was obtained using a meet-in-the-middle (MitM) involving symmetric states. The team reports a total complexity of about 2^58.7 4-round Keccak-f calls. It took about 4 days on the Sunway TaihuLight supercomputer using 10 thousand cores!