tldr;- CRC is an affine map: CRC(X) = MX + C0- we can recover M and C0 by querying the oracle- once we have M and C0, we can find a preimage for T with linear algebra: T = MX + C0 => MX = T + C0
[writeup](https://jsur.in/posts/2021-07-19-google-ctf-2021-crypto-writeups#story)