Rating:
tldr;
- `m` is odd, so `m//2` becomes `(m-1)/2`
- Franklin-Reiter related-message attack
[writeup](https://jsur.in/posts/2021-03-07-zer0pts-ctf-2021-crypto-writeups#warsamup)
Original writeup (https://jsur.in/posts/2021-03-07-zer0pts-ctf-2021-crypto-writeups#warsamup).
