Crypto challenge solved by checking that C is a perfect square.

Full writeup: [https://ctf.rip/write-ups/rev/crypto/lactf-2023/#guessbit](https://ctf.rip/write-ups/rev/crypto/lactf-2023/#guessbit)

Original writeup (https://ctf.rip/write-ups/rev/crypto/lactf-2023/#guessbit).