(Not a guru) I think the main challenges are deciding how to manage the brute force effort. You can precompute a lot of hashes, and then search them on the co

(Not a guru) I think the main challenges are deciding how to manage the brute force effort. You can precompute a lot of hashes, and then search them on the contest day. Or you can run it only during the 24H of the contest, and only store the result which is nearest. And the second issue: how much resources to invest. A high CPU on EC2 is $20 for the day. Another doubles the price, and doubles the number of hashes you can check. EDIT: The restrictions they place on the input makes rainbow tables kind of pointless. Just partition the search space (i.e. the permutations) pick a piece of it at random, and send it to your brute forcers. EDIT2: Back of the envelope: you will be able to try about 100million hashes for $20.