Writeup for unfairy-ring from SekaiCTF 2025.

Writeups for crypto challenges from SekaiCTF 2025. unfairy-ring will be in a separate post.

之前参加了 imaginaryCTF 的练习赛，解了 Complex Curve Crypto 这道在复数域上的椭圆曲线题，很好玩。 做这道题的时候也学习了一下复数域上的椭圆曲线，所以会顺带介绍一下。

这周跟 Project SEKAI 一起打了 IERAE CTF 2025，比赛的时候基本全花在做 Cubic Math 上了，但没做出来。 赛后看了作者的解释，发现自己只差一步就能做出来了，很气。

Played with Redbud and got third place. The challenges are really difficult and out of my distribution. I solved PRFCasino, LinearCasino, OhMyDH, softHash and hashgame and here’s the writeup.

I played as Twilight Light and solved 3.5 crypto challenges. The crypto is very hard and I can’t fully understand why everything works. So this writeup will mainly focus on how I found these properties heuristically.