This is the third year I had a writeup on Google CTF (see my writeup in 2020 and 2021). Yet this time it is the official writeup for a challenge - as the challenge author! There are eventually 35 solvers (out of 382 teams) for the challenge. Challenge Summary We are given a public key of Paillier cryptosystem $(n, g)$, and is asked to complete 16 rounds of challenge $\mathcal{C}$. In each round of $\mathcal{C}$:
