Lillie ΘΔ (@hytracer)

CTF 101 - Introduction to capture-the-flag competitions

Capture the Flag (CTF) competitions are cybersecurity challenges where participants solve a series of puzzles or challenges to find “flags” hidden in various systems or services. These flags typically take the form of a string of text or a file that needs to be extracted.

CTFs can vary in difficulty and format. Some are designed for beginners and focus on basic concepts such as cryptography and web exploitation, while others are more advanced and require knowledge of topics such as binary exploitation and reverse engineering. CTFs can also take place in-person or online, and can be hosted by companies, universities, or groups.

Why participate in CTFs?

CTFs are a great way to improve your computer skills and learn new techniques in a fun and competitive environment. They offer a hands-on way to learn about various topics in cybersecurity, such as cryptography, reverse engineering, web exploitation, and more!!

Participating in CTFs can also help you build a network of like-minded individuals and potentially lead to career opportunities in the cybersecurity field. Employers often look for people who have experience with CTFs, as it shows that they have a passion for learning and a willingness to take on challenges.

How to get started?

You’ll need some basic knowledge of computers. Some good resources to learn from include:

There are many online CTF platforms, such as:

You should refer to CTFTime as it is the biggest hub for CTF competitions.
These platforms offer a variety of challenges for participants of all skill levels. Some offer rankings and prizes for top performers.

It’s also worth noting that many universities and hacker groups host CTFs. These events can be a great way to meet other cybersecurity enthusiasts and learn from experts in the field.

Different Fields of Challenges

CTFs can be divided into different fields of challenges based on the type of skill set required to solve them. Here are some examples:


Cryptography challenges involve cracking codes and ciphers to reveal hidden messages. Participants may need to use frequency analysis, substitution ciphers, or other techniques to solve these challenges.

Web Exploitation

Web exploitation challenges involve finding vulnerabilities in web applications or websites. Participants may need to use techniques such as SQL injection, cross-site scripting, or command injection to exploit these vulnerabilities and retrieve flags.

Reverse Engineering

Reverse engineering challenges involve analyzing software or hardware to determine how it works and find vulnerabilities. Participants may need to use disassemblers, debuggers, or other tools to reverse engineer programs and extract flags.

Binary Exploitation

Binary exploitation challenges involve finding vulnerabilities in binary files, such as executables or shared libraries. Participants may need to use techniques such as buffer overflows, format string exploits, or return-oriented programming to exploit these vulnerabilities and retrieve flags.

Different Types of CTFs

CTFs can also be divided into different types based on the format and rules of the competition. Here are some examples:


Jeopardy-style CTFs are the most common type of CTF. They consist of a set of challenges across different categories, and participants must solve as many challenges as possible within a set amount of time. Points are awarded for each challenge solved, and the team with the most points at the end of the competition wins.


Attack-defense CTFs are more complex than Jeopardy-style CTFs. Participants are given a virtual machine with vulnerable services running, and must both defend their own services from attacks and attack the services of other teams to retrieve flags. Points are awarded for flags retrieved and for defending services from attacks.


King-of-the-Hill CTFs are similar to Attack-defense CTFs, but instead of teams defending their own services, there is a central “king” service that teams must attack and defend. Points are awarded for controlling the king service, defending the king service, and attacking other teams’ services.


CTFs are a fun and engaging way to learn about cybersecurity and improve your skills. With a little practice and perseverance, anyone can become a proficient CTF player. Remember to always prioritize learning and ethical behavior when participating in these competitions, and have fun! Good luck and happy hacking!