An Overview of CTF(Capture The Flag)

An Overview of CTF(Capture The Flag)
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Written by Shuvhojit DebDecember 13, 2021
11 min read
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Shuvhojit Deb

Full Stack Developer

Today we'll know about what CTF is and how to do it.

What is CTF(Capture The Flag)

A Capture the Flag event, or CTF for short, is a gamified exercise designed to test cybersecurity skills. The goal of the game, much like in the live-action, outdoor game many of us remember from childhood, is to get the highest score by capturing the most flags.

The most common formats of cybersecurity CTF events, according to the European Union Agency for Cybersecurity, are Jeopardy and Attack-Defense. Jeopardy challenges are stand-alone, problem-solving challenges that yield one flag for each completed challenge. In Attack-Defense challenges, participants are given a range of targets in the form of vulnerable services, and the goal is to take down as many targets as possible to retrieve as many “flags” as possible. Depending on the CTF, participants may form teams or compete independently.

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The Benefits of CTFs

CTF events can be effective tools for assessing cybersecurity skill level and for teaching new skills in a gamified scenario. CTF creators can design competitions to test a variety of skills at any level. For example, some CTFs may focus on penetration testing and set challenges testing the offensive cybersecurity skills of participants. Other CTFs may be designed to test both offensive and defensive capabilities with teams attempting to reach each other’s networks and protect their own against attacks. CTFs can also have more specific focuses, testing skills in reverse engineering, network traffic analysis, or other subfields within cybersecurity.

Types of Challenges

Challenges are typically divided into 6 categories for CTF, common the types of challenges are:-

1. Web:

This type of challenge focus on finding and exploiting the vulnerabilities in web application. They may be testing the participants’ knowledge on SQL Injection, XSS (Cross-Site Scripting), and many more.

2. Forensics:

Participants need to investigate some sort of data, like do a packet analysis on .pcap file, memory dump analysis, and so on.

3. Cryptography:

Challenges will focus on decrypting encrypted strings from various types of cryptography such as Substitution crypto, Caesar cipher, and many more.

4. Reversing (or Reverse Engineering):

RE usually needs participants to explore a given binary file whether PE file, ELF file, APK, or some types of other executable binary. Participants need to find the key by decompilation, disassemble using static or dynamic analysis, or other reverse engineering tools.

5. OSINT:

The OSINT idea is to see how much information is available to you and understand the underlying hints hidden in the challenges themselves with the help of google and bit problem-solving skills. So more tools like sherlock, and no focus on domain enumeration, etc.

6. Miscellaneous:

Everything not listed else that is still relevant to Information Security is in this category. This need require Google-Fu skill. In short, you can say it can have anything.

Tools To Use

Some tools that can help you often are:-

  • Python: is an extremely useful scripting language, with a rich ecosystem of packages to add functionality. You should develop new code in python3 (python 2.7 is the old version and is no longer supported). Pip is the Python utility to use for installing additional packages.
  • CyberChef: is a Javascript-based website for easily creating recipes, or a series of steps, to decode text or data. There is also a code repository if you want to deploy a standalone instance.
  • Boxentriq: is another website with a solid overview of ciphers and analysis tools.
  • Kali: is a Linux distribution that already includes many tools useful for penetration testing. More tools can be installed with the apt-get utility. You can also run Kali as a virtual machine on another computer.
  • Derb: is a handy tool for scanning directories and files on a web server. Or try Gobuster – a similar tool implemented in the Go language, for improved performance.
  • Metasploit: is a powerful set of exploit tools for penetration testing. A related tool, Msfvenom, can create and encode an exploit payload.
  • Pwntools: is a Python-based framework for CTFs and exploit development.
  • exploit-db: is a useful website for finding proof-of-concept exploit code.
  • IDA: is an interactive disassembler and debugger. The professional version (IDA Pro) is both pricey and powerful. You can get started with the free version from the link above.
  • Ghidra: is a powerful (and free!) set of Java-based tools from the NSA for reverse engineering software. It includes a decompiler to convert binary code to high-level C code.

Tricks to Win CTF

Practice alone

There are tons of ways you can practice for CTF competitions. Many old contests will upload their past flags and solutions. Folks will often also post writeups on their security blogs of particularly interesting challenges and puzzles they’ve solved.

Follow the news

CTFs like to be trendy. Keeping up with what’s going on at other CTFs, security conferences, and the wider cybersecurity community can be important in giving you an idea on how to approach hacks and which vulnerabilities to try and exploit. If you see an interesting proof of concept hack or exploit online that you can replicate in your home lab, take the time to work through it and pick up new skills.

Build a toolkit

Before you even get to a CTF you should know what tools you need to win. As you do practice exercises and go to CTFs, keep a list of tools you find yourself using and keep them stored in one place on your computer. Find an approach that works for you and be sure that you spend the bare minimum time at a CTF downloading and researching tools you’ve used in the past.

Take care of yourself

Like at Hackathons, it’s important at a CTF to keep track of your well-being. If you need to sleep — do so.

Make some friends

Take time to get to know the other teams at the competition. Be friendly and approachable. Reciprocate and be nice to people who approach you but try and keep strategically important information close.

Conclusion

CTFs are a fun way to learn and hone your skills, in the guise of competition. If you have never tried one before, you may realize you have been missing out!

If you are just getting started with CTFs, I recommend checking out the PicoGym practice challenges. You can sign up for free and try your hand at challenges from previous PicoCTF competitions. The practice challenges are available year-round, and the website has resources to get you started in tackling various challenge types. CTF is a great hobby for those interested in problem-solving and/or cyber security. The community is always welcoming and it can be a lot of fun tackling challenges with friends.

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Shuvhojit Deb
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