These hints were released during the original run of the CTF and you're encouraged to make use of them.
If you're going to log into a company's server, the CEO's first name might be good to know.
The encoding in play doesn't actually use %
AES256 keys are 256 bits long.
ABCDEFGH
0BCDEFGH
00CDEFGH
000DEFGH
0000EFGH
00000FGH
000000GH
0000000H