What’s CTF? Capture The Flag Competitions for Cybersecurity

As a technology practitioner, what’s the best way to stay on top of your game? Challenge yourself in real-world settings, of course.

This is especially true in the always-evolving world of cybersecurity. New attack vectors are discovered every day, new TTPs are always being tried. Cybersecurity practitioners must respond with innovative, creative and novel solutions, often proactively. This means that InfoSec experts, security analysts, and developers must always be learning — new tools, methodologies, and practices — to combat these threats.

But how can you expose yourself to these challenges in a controlled environment? Your goal can be two-fold:

• To evaluate and grown your own skills.
• To prepare your team and organization for encounters against real-world threats.

You should understand what you know already and discover what you don't know yet. You should be able to act on your knowledge, develop strategies, and use technology to your advantage.

And what better way to get there than by participating in competitions against other cyber professionals, collaborating with experts, and using new technologies to solve unprecedented cybersecurity challenges.

What are capture the flag competitions?

Capture the Flag (CTF) is a cybersecurity competition. In CTF, participants search for vulnerabilities in technology systems to discover hidden “flags”. Similar to the real-world Capture the Flag game (yes, the one you played outside as a kid), the target may be defended by a counterparty or a competitor.

First introduced at the DEF CON cybersecurity convention in 1996, the game has since been adopted in the cyber industry and academia as means to educate, collaborate, and compete.

Types of CTF competitions

There are different variations of CTFs, let's take a look.

Jeopardy-style

The most popular and common is a Jeopardy-style competition. Here, the challenges are categorized into different domains. Solving a challenge yields a flag that you submit for points, so the more challenges you solv, the better. In these challenges, participants solve tasks related to many topics, including:

• Web security
• Cryptography
• Intrusion
• Digital forensics
• Anomaly detection

The tasks are solved sequentially and each iteration increases in complexity, just like an episode of Jeopardy. A great example of this competition is the DEF CON qualifier.

Attack-defense

Another variation of the CTF is the attack-defense style, just like the one hosted as the DEF CON CTF event. This competition variant is closer to the actual real-world game. It works like this: Participants operate their own networks, which contain vulnerable technologies. They are given a set time to:

• Secure vulnerable systems.
• Develop exploits to target their competitors.

During the competition, participants earn points for defending their services and hacking their opponents.

Get a little IRL experience of CTF compeitions from DEF CON. This video is part of the qualifying rounds from DEF CON 32 in 2024:

How to take part in CTF competitions

CTF competitions are held globally — look up opportunities on the handy CTFtime.org.

• Participants. You can play a CTF solo or find a team on your own.
• Length of competition. CTFs typically last only a few days, often for dedicated conferences and cybersecurity conventions. Some open projects are available year-round.

Getting started

To get started, simply download a Linux distribution. Most competitions require the Kali and Parrot Linux package.

Configure a virtual machine to reach the competition network in a host-only network. This means that data communication only takes place between the connected devices within a virtual CTF network so that your host machine remains secure.

Categories in cyber CTF competitions

Let’s look at some of the popular challenge categories:

Reversing or reverse engineering

In a Reversing CTF, an executable file is provided to verify an input string based on an algorithm. Participants are required to discover the correct key, which also serves as the target flag.

How do they get there?

Any reverse engineering technique may be used, but the general idea is to identify how the algorithm maps an unknown input to the provided output string. The algorithm may be:

• A simple conceptual example of a cryptography algorithm
• A process that applies several distinct transformations to the input

Pwning

In pwning comptitions, participants receive an executable file, an IP address, and the port number of the host server running the program/file.

The goal is to analyze the executable, identify vulnerabilities, and exploit the program to execute arbitrary code remotely on the target server. Successful exploitation often involves reading a specific file (e.g., a "flag file") on the target server.

Common techniques for these exploits include:

• Buffer overflow: overwriting critical areas of the program by manipulating the program’s memory.
• Code injection: inserting and executing malicious code inside the program.
• Other memory corruption techniques, like exploiting flaws such as use-after-free or heap corruption

Cryptography

In a cryptography challenge, a cypher-text is provided and participants attempt to decrypt the text using cryptography algorithms and mathematical techniques. This challenge is on the more difficult side, as it requires domain expertise, especially in cryptography and mathematics for cybersecurity.

Decrypting the ciphertext correctly produces the flag. Participants earn points based on how fast they can decrypt and the difficulty levels involved.

Web security

Participants are provided with a URL to a Web application or a website they can exploit using various techniques such as:

• SQL injection
• Bypassing identity and access controls
• Cross-site scripting (XSS)
• Many more

These challenges are commonly found in attack-defense style CTF competitions. The participants are expected to identify and secure their own web apps while attacking their competitors in a time-trial setting.

Miscellaneous programming

Other challenges may not have a predefined category and can vary on tasks such as:

• Optical Character Recognition (OCR) for captcha
• Maze solving
• Optimization problems

Participants can earn points on pre-determined criteria such as time efficiency, complexity and optimization of the program, and pre-defined tests.

Cyber competition for all, newbs to experts

Once you get started with the CTFs, know that these competitions include both the hobbyists and seasoned experts.

From a business perspective, encouraging participation in such competitions can help identify where your experts rank in this spectrum — and how you need to upskill your workforce with the right talent.