CryptoCTF 2023 Writeup
Welcome!! (23 points, 663 solves) Difficulty: Warm-up We surely did get warmed up this CTF, as we came second, even beating the Cryptohackers (merge) team! Well done to everyone who participated 馃挏 Did it! (33 points, 220 solves) Difficulty: Easy The parameters $n = 127$ and $\ell = 20$ is fixed. A hidden subset of $\ell$ numbers $S \subseteq \{0, 1, \cdots, n - 1\}$ with $|S| \leq \ell$ is chosen, and we are given $13$ calls to the following oracle: Given a set $T \subseteq {0, 1, \cdots, n - 1}$ also with $|T| \leq \ell$, the server computes $T \setminus S$ and outputs $\{(u^2 + \varepsilon) \pmod{n} : u \in T \setminus S, \varepsilon \in \{0, 1\}\}$....