Cryptanalysis of CRUSH hash structure

In this paper, we will present a cryptanalysis of CRUSH hash structure. Surprisingly, our attack could find pre-image for any desired length of internal message. Time complexity of this attack is completely negligible. We will show that the time complexity of finding a pre-image of any length is O(1). In this attack, an adversary could freely find a pre-image with the length of his own choice for any given message digits. We can also find second pre-image, collision, multi-collision in the same complexity with our attack. In this paper, we also introduce a stronger variant of the algorithm, and show that an adversary could still be able to produce collisions for this stronger variant of CRUSH hash structure with a time complexity less than a Birthday attack.