What is Capture The Flag?
CTF (Capture The Flag) competitions are cybersecurity challenges where players solve puzzles, break codes, and exploit vulnerabilities to find hidden "flags"— secret strings that prove you've solved the challenge.
Think of it as a digital treasure hunt
In CTF competitions, you'll encounter various cybersecurity challenges designed to test your skills in different areas. Each challenge contains a hidden "flag"—typically a string like SDG{you_found_it!}.
Your goal is to use your hacking skills, creativity, and problem-solving abilities to discover these flags. The more challenges you solve, the more points you earn—and the higher you climb on the leaderboard!
CTFs are one of the best ways to learn cybersecurity hands-on. They're used by universities, companies, and security researchers worldwide to train and identify talent.
def decode_secret(data):
# The flag is hidden somewhere...
key = "sustainability"
decoded = xor_decrypt(data, key)
return decoded
# Can you find it?
encrypted = b'\x13\x05\x17...'
flag = decode_secret(encrypted)
print(flag)
# Output: SDG{crypto_master_2026}
Types of Challenges
CTF challenges come in many flavors. Here are the main categories you'll encounter.
Web Exploitation
Find vulnerabilities in web applications like SQL injection, XSS, CSRF, and more.
Cryptography
Break encryption, decode ciphers, and understand the mathematics behind security.
Forensics
Analyze files, memory dumps, and network captures to find hidden information.
Reverse Engineering
Understand how software works by analyzing compiled code and binaries.
Binary Exploitation
Exploit vulnerabilities in compiled programs like buffer overflows.
Miscellaneous
Creative challenges that don't fit other categories—expect the unexpected!
How SDG CTF Works
Getting started is easy. Here's how to jump into your first competition.
Register & Join
Create your free account and join or create a team.
Choose a Contest
Browse active competitions or practice with archived challenges anytime.
Solve Challenges
Read the problem, analyze clues, exploit vulnerabilities, and find the flag.
Submit Flags
Enter the flag (usually in format SDG{...}) to earn points for your team.
Climb the Leaderboard
Compete against teams worldwide and track your progress in real-time.
Monthly UN SDG Themes
What makes SDG CTF unique? Every month, we theme our challenges around one of the 17 United Nations Sustainable Development Goals. Learn cybersecurity while raising awareness about global issues.
This Month: January 2026
SDG 9: Industry, Innovation & Infrastructure
Our January challenges focus on securing critical infrastructure, promoting responsible innovation, and building resilient systems. Expect challenges involving industrial control systems, API security, and innovation in tech.
Why SDG CTF?
Learn By Doing
Hands-on challenges teach real-world cybersecurity skills
Global Impact
Connect cybersecurity learning with real-world global issues
Team-Based
Collaborate with teammates and learn from each other
Compete & Win
Test your skills against players worldwide