This is yet another xor encryption, a single byte encryption then a multi byte encryption. Once the player figures out the first key, he can find out the second set of keys and that will retrieve the flag.
The first key is
0x1b and the second set of keys are
[0x4c, 0x3a, 0x25, 0x1a] where second set of keys are xored according to their indexes, for all index which is divisble by 4
0x4c is used, and so on.
Here is the python solver for the challenge