Preimage Analysis of the Maelstrom-0 Hash Function.

Maelstrom-0 is the second member of a family of AES-based hash functions whose designs are pioneered by Paulo Baretto and Vincent Rijmen. According to its designers, the function is designed to be an evolutionary lightweight alternative to the ISO standard Whirlpool. In this paper, we study the preimage resistance of the Maelstrom-0 hash function using its proposed 3CM chaining construction. More precisely, we apply a meet-in-the-middle preimage attack on the compression function and combine it with a guess and determine approach which allows us to obtain a 6-round pseudo preimage for a given compression function output with time complexity of 2496 and memory complexity of 2112. Then, we propose a four stage attack in which we adopt another meet-in-the-middle attack and a 2-block multicollision approach to defeat the two additional checksum chains and turn the pseudo preimage attack on the compression function into a preimage attack on the hash function. Using our approach, preimages of the 6-round reduced Maelstrom-0 hash function are generated with time complexity of 2505 and memory complexity of 2112.