I’m a security engineer based in Japan. I run this site as a space to document what I learn from CTF challenges — not just the solutions, but the reasoning behind them.
How It Started
My interest in security started with iPhone jailbreaking. Taking apart a locked system to understand how it works — and then making it do something it wasn’t supposed to — turned out to be a pretty direct path into security thinking. From there, CTF challenges were a natural next step: controlled environments where breaking things is the point.
I started competing in 2022 with team HypomaniaOD. Since then we’ve played in events including WaniCTF, SekaiCTF, snakeCTF, and a handful of others across different years. My focus is forensics, though cryptography challenges are what keep me up the longest.
What This Site Is For
Most CTF writeups answer one question: “how do you solve this?” I try to answer a different one: “why does this work, and when would you actually encounter it outside a competition?”
A QR code challenge isn’t just about knowing zbarimg exists. An RSA low-exponent challenge isn’t just about running gmpy2.iroot(). The techniques in these problems show up in real vulnerability research, incident response, and malware analysis. I write about that connection because it’s what makes the challenge worth documenting.
The goal is for this to become a resource that’s useful beyond just “I’m stuck on this picoCTF problem” — something people come back to when they want to understand a concept more deeply.
Tools and Focus Areas
Day-to-day I work as a security engineer. CTF is where I keep the hands-on side sharp. The areas I spend the most time in:
- Forensics — disk images, memory, network captures, steganography
- Cryptography — RSA attacks, hash analysis, encoding/decoding chains
- Web exploitation — source disclosure, injection, authentication bypass
Tools I use regularly: Wireshark, tshark, ffmpeg, Audacity, fdisk, dd, binwalk, zbarimg, pngcheck, gmpy2, pwntools.
Find Me
- X (Twitter): @rudy_candy_
- CTFtime: rudy_candy / HypomaniaOD
- GitHub: rudy-candy
- Writeup repository: picoctf-writeup
- Email: rudy00candy@gmail.com