Let's say they encrypted
the challenge with AES. What are we supposed to do with it? Bruteforce?
If they would have encrypted it with AES, that would've been much more fun to solve, especially since a reverse key analysis still takes months using smart guesses on the
round modifier on a small supercomputer. And it would take even longer if the
S-box (Rijndael S-Box) wasn't derived from a
matrix multiplication for fast encryption.