Preimage Attack on ARIRANG

The hash function ARIRANG is one of the 1st round SHA-3 candidates. In this paper, we present preimage attacks on ARIRANG with step-reduced compression functions. We consider two step-reduced variants of the compression function. First one uses the same feedforward1 as the original algorithm, and the other one has the feedforward1 working at the output of the half steps. Our attack finds a preimage of the 33-step OFF(Original FeedForward1)-variants of ARIRANG-256 and ARIRANG-512 from Step 1 to Step 33, and a preimage of the 31-step MFF(Middle FeedForward1)-variants of ARIRANG-256 and ARIRANG512 from Step 3 to Step 33.