Practical Preimage Attack on 5-Round Keccak[r=640, c=160]

Internal differential cryptanalysis has recently yielded a series of new results in the preimage cryptanalysis of round-reduced Keccak. While these existing attacks share a similar high-level framework, they differ in their technical details. This paper provides a comparative analysis of these prior approaches and introduces a variant framework specifically suitable for 5-round Keccak[r=640, c=160]. This technique integrates certain advantages from prior works, so that the complexity of matching the all-zero initial value and the digest can be separated while the period still remains only one-quarter of the lane size, which avoids the need for a complex Forward-TIDA. Although this technique only provides a constrained application scope, we successfully give the practical preimage attack on 5-round Keccak[r=640, c=160] with the complexity of around 259.7, which firstly solve a 5-round pre-image challenge of the Crunchy Contest.