What is sekaictf-2026?

This repository holds the official challenge source code and solution writeups from SekaiCTF 2026, a Capture The Flag competition. A CTF is a security competition where participants solve puzzles that involve finding and exploiting flaws in code, cryptography, or systems, each puzzle rewarding a hidden text string called a flag once solved. The challenges are organized into categories familiar to security competitions: Blockchains, Cryptography, Miscellaneous, Binary Exploitation, Reverse Engineering, and Web. Each challenge folder contains the actual source code contestants were given, and each is listed with its author, a difficulty rating from Easy to Master, and how many teams solved it during the event. Some challenges were also tied to cash bounties, which stayed available for certain unsolved problems even after the competition ended. This is not a tool or application that gets installed and run for a general purpose. It is a reference archive for people who want to study how these particular security puzzles were built, attempt to solve them after the fact, or read the accompanying writeups that explain the intended solutions. Because the challenges span so many categories, the repository as a whole touches many languages and technologies, including Solidity for the blockchain challenges, alongside whatever tools each individual challenge author used. The repository's own program and source code is licensed under the GNU Affero General Public License version 3, while non-code material such as writeups is covered separately under a Creative Commons Attribution NonCommercial ShareAlike license. Anyone interested can browse the linked CTFTime event page, official website, Discord server, and social accounts for more background on SekaiCTF itself.