A Capture the Flag competition, or CTF, is a set of cybersecurity challenges. A challenge gives you a task and an authorized system, program, or file to inspect. When you solve the task, you find a hidden code called a flag.
A typical flag looks similar to OmniCTF{example_flag}. The flag confirms that you found the intended result. You submit it to the competition platform to receive points.
Scope comes first
The competition scope tells you what you can test. It can identify a website, network address, downloadable file, or local program. Test only the items that the rules identify.
Safe practice: A CTF is not permission to test the competition organizer, another participant, the hosting provider, or any unrelated system.
Common challenge categories
- Web security: Inspect how a challenge website handles requests, input, identity, and data.
- Cryptography: Identify how information was transformed and recover the intended message or key.
- Digital forensics: Examine files, metadata, logs, memory, or network captures to find evidence.
- Reverse engineering: Study how a program works without access to its original design notes.
- Binary exploitation: Analyze memory behavior in a purpose-built program and use the behavior to reach the challenge goal.
- Open-source intelligence: Find and connect public information while respecting privacy and challenge rules.
A repeatable challenge process
- Read the full challenge text and the competition rules.
- Write down the target, goal, supplied files, and limits.
- Inspect before you change anything. Record visible facts.
- Create one hypothesis that explains the facts.
- Run the smallest test that can confirm or reject the hypothesis.
- Record the result. Do not rely on memory.
- Repeat until you find the flag or need to change categories.
- Write a short solution after the challenge.
Work as a team
A team can divide work by category or by task. One person can inspect the supplied files. Another person can read documentation. A third person can test a hypothesis. Share findings in a common note so that other team members do not repeat the same test.
When you report a result, include the command or action, the observed output, and what the result means. “It does not work” is not enough information for another person to continue.
Tools for a first event
You need a current web browser, a text editor, a terminal, and a place for team notes. Some challenges require additional tools. Install a tool only when you understand why the challenge needs it.
Use a separate practice environment when possible. Do not store personal passwords, private documents, or work credentials in that environment.
What to do after a challenge
Create a writeup. A writeup records the task, evidence, tests, solution, and lesson. Remove active credentials and private data before you share it. Follow the competition rules about when solutions can become public.
Next, read our writeup guide or select a technical topic from the resource library.