This is only ElGamal cryptosystem on Rubik Cube.
The order of Rubik Cube Group is `43_252_003_274_489_856_000n` and this is small enough to use Pohlig-Hellman.
So the algorithm is simple:
1. get `g, h, c1, c2`.
2. calculate `y = log_g(c1)` using Pohlig-Hellman.
3. get message cube `m = c2.multiply(invert(pow(h,y)))`.
4. from all cubes, recover flag.