A student team from the Department of Computer and Information Engineering at The Catholic University of Korea has advanced to the finals of ‘DEF CON CTF,’ a world-renowned hacking competition. How did they manage to reach this global stage, where top talent from around the world competes? We sat down with students Yoon Tae-ho, Kim Min-jae, and Kim Hyun-ju to hear about their preparation process, the challenges they faced along the way, and their future goals.

Q1. Could you please introduce yourselves? Please share your major, student cohort (year of entry), name, and the activities you are currently involved in.

Yoon Tae-ho (Dept. of Computer and Information Engineering, Class of ’22) | I focus on web security within CAT-CERT. My work involves identifying vulnerabilities in web systems, as well as studying penetration techniques and defense mechanisms against attacks.

Kim Min-jae (Dept. of Computer and Information Engineering, Class of ’22) | I specialize in system hacking within CAT-CERT.

Kim Hyun-ju (Dept. of Computer and Information Engineering, Class of ’24) | I focus primarily on reverse engineering and participate in various security projects within the club, including penetration testing (mock hacking).

Q2. Many students might not be familiar with DEF CON CTF. From your perspective as participants, could you explain what this competition is about in a way that someone outside the field could understand?

Most standard hacking competitions involve solving a series of given problems. DEF CON CTF, however, is unique: beyond just solving problems, you must actively attack the systems of other teams while simultaneously defending your own.

In the competition, every team is provided with systems under identical conditions. Participants analyze systems to identify vulnerabilities, which they then use to launch attacks against other teams. Conversely, if they discover a vulnerability in their own team’s system, they must take steps—such as modifying the code—to block incoming attacks.

For instance, if a website stores personal information, an attacker might exploit a security flaw to gain access to that data, while a defender works to locate and patch that same flaw. In short, it is a competition that involves both attacking and defending simultaneously.

Q3. What motivated you to participate in this year’s DEF CON CTF? Could you also explain how the joint team ‘D0kdo’—comprising various hackers from Korea—was formed?

CAT-CERT regularly participates in security competitions held both domestically and internationally. Our participation in this year’s DEF CON CTF was part of that ongoing activity.

The team ‘D0kdo’ came together through our consistent networking with Catholic University of Korea alumni and professionals currently working in the field of information security. During our conversations, the idea arose to form a joint team of Koreans for the competition. Consequently, we brought together alumni, industry professionals, their respective acquaintances, and others who were studying security elsewhere to form the team.

Therefore, D0kdo is not composed solely of CAT-CERT members; it is a coalition of participants with diverse backgrounds.

Q4. I understand that the finals followed an ‘Attack & Defense’ format, where teams had to attack the services of their opponents while simultaneously defending their own. How exactly do these attacks and defenses play out during the competition?

This format is known as ‘Attack & Defense.’ In this particular competition, 12 teams vied against one another, with scores tallied every five minutes.

Each team earns points by identifying and exploiting vulnerabilities in the systems of other teams. At the same time, because opponents are also targeting your own systems, you must identify and patch vulnerabilities to prevent losing points.

Since scores are calculated at short, frequent intervals, rapid response is crucial. It’s not enough to simply discover a vulnerability; you must also execute an actual attack while simultaneously taking measures to block incoming attacks from your opponents.

Q5. What specific roles did each of you take on during the main competition? Could you elaborate on the tasks you were responsible for?

Yoon Tae-ho | I primarily focused on the offensive side. My role involved identifying and analyzing system vulnerabilities, then writing code to carry out actual attacks. If an opposing team discovered a vulnerability and patched it, I would check whether the existing exploit still worked. If it was blocked, I would analyze potential workarounds and adjust our strategy accordingly. I also developed tools to automate repetitive attack tasks; since scores were tallied every five minutes, automation allowed us to execute attacks much faster and more efficiently than doing everything manually.

Kim Min-jae | Before the competition, I worked on building tools for both offense and defense. During the event itself, I handled a specific category called "King of the Hill." In this category, success isn't just about finding a single "correct" answer; it’s about achieving the best possible outcome within a given environment. You have to identify superior solutions among various options, and your ranking and score are determined by the quality of those results.

Kim Hyun-ju | I also contributed to developing tools for the competition and solving challenges within the "King of the Hill" category. Additionally, I built a dashboard-style tool to assist with our offensive and defensive operations. It allowed us to monitor the situation in real-time and automate tasks that would otherwise be too time-consuming to handle manually, enabling a more efficient response. Essentially, I created tools to help us quickly access the necessary information and execute tasks within the tight timeframe of the competition.

Q6. Could you share any particularly memorable moments or unexpected challenges you encountered during the final competition?

Kim Min-jae | D0kdo was a newly formed team that year, and most of us were participating in the DEF CON CTF for the first time. Although we had anticipated various scenarios, discussed response strategies, and prepared tools beforehand, the actual competition brought about unexpected variables. There were situations that couldn’t be resolved solely through the plans we had already established. Going through that process, I realized just how crucial it is for team members to maintain constant communication and work together to find solutions.

Additionally, it was quite impressive to see products from various security firms and startups on-site. Exploring the booths set up at the convention center allowed me to encounter software and innovative ideas that I hadn’t come across while studying in Korea. Observing how these companies develop products to address specific problems—and how they articulate and promote their unique strengths—gave me a fresh perspective that extended beyond the purely technical aspects.

Kim Hyun-ju | The rules for the DEF CON CTF tend to shift slightly each year, and this time, they were announced just one day before the competition began. As a result, we had to modify some of the features in the tools we had prepared. Furthermore, DEF CON is a massive event that encompasses not only the CTF competition but also a conference and various corporate exhibitions. We faced some hurdles, such as unstable network conditions and difficulties in communicating among team members at the venue. What stands out to me is that, beyond preparing for the competition itself, you also have to be ready to handle unforeseen variables that arise on-site.

Q7. I understand that CAT-CERT works to ensure information security at The Catholic University of Korea—preventing security-related incidents within the campus network and responding swiftly when they occur. Could you tell us more about the specific activities you carry out?

One of our primary activities at CAT-CERT is the regular assessment of the university’s information systems. Twice a year, we conduct penetration testing (mock hacking) on key information assets, such as the university website, to identify any existing vulnerabilities.

When we discover a vulnerability, we analyze how it could be exploited, the potential damage it might cause if left unaddressed, and how it should be patched. We then compile our findings into a report and submit it to the Information and Communications Center, ensuring that the vulnerabilities are addressed and resolved.

This work is significant because it allows us to identify and remediate potential issues before an actual attack can take place. Furthermore, in the event of an actual security incident on campus, we investigate the root cause, trace the attack path, identify the vulnerable points, and propose the necessary response measures.

Q8. What motivated each of you to join CAT-CERT?

Kim Hyun-ju | CAT-CERT was known as a club that required a significant investment of time and effort. To me, however, that sounded intriguing. Just as I had dedicated myself to my studies in high school, I wanted to engage in meaningful activities during my university years, which is why I joined. I also appreciated that, as a junior (new) member, I could start by learning the fundamentals, such as programming languages. I realized it would be a great way to build the essential skills needed for software development before diving deeper into the field of security.

Yoon Tae-ho | I became interested after hearing some upperclassmen promote the club right before one of my classes began. I was particularly impressed by the materials showcasing CAT-CERT’s activities and the club’s track record in various competitions. Seeing that made me want to join the club myself.

Kim Min-jae | I wasn’t necessarily interested in information security from the very beginning. I first learned about CAT-CERT when some upperclassmen promoted the club during class. The activities sounded really interesting, so I decided to join.

Q9. Could you share some experiences of working together as a team within CAT-CERT? Also, what led the three of you to participate in this competition together?

CAT-CERT is a club that stays active not just during the semester, but throughout the breaks as well. During the semester, we meet three times a week, which gives us plenty of opportunities to study and collaborate together.

We didn’t just come together as strangers for this competition; we were already familiar with each other’s working styles through our regular club activities, and we had plenty of experience solving problems as a team. That background proved very helpful in preparing for this competition and working together effectively.

Q10. How did your experiences in CAT-CERT help you in preparing for this year’s DEF CON?

At CAT-CERT, we frequently form teams to participate in various security competitions and contests. Because of this, we’re well-accustomed to dividing roles, handling individual tasks, and collaborating to solve complex problems.

Participating in the DEF CON CTF requires more than just security knowledge—it also demands the ability to develop your own tools. Beyond analyzing system vulnerabilities and executing attacks or defenses, it’s crucial to be able to build tools that make these processes more efficient. The security studies, vulnerability analysis, development projects, and group study sessions I’ve consistently engaged in at CAT-CERT served as the foundation for this preparation. The technical expertise I built within the club, combined with the experience of collaborating as part of a team, proved invaluable both in preparing for the competition and participating in the finals.

Q11. Having gained new experiences through your participation in DEF CON and your activities with CAT-CERT, what are some new challenges you’d like to take on in the future?

Kim Hyun-ju | I’d like to participate in DEF CON again next year. I believe there’s a distinct difference between traveling abroad for leisure and traveling to compete in a major international event. This was my first time participating in an overseas competition; being in a new environment and encountering such a diverse range of experiences has motivated me to study even harder moving forward.

I owe these opportunities to my time with CAT-CERT and the connections I’ve made with alumni. I want to help future members of the club have similar experiences. Another goal is to successfully host a competition that we at CAT-CERT are currently organizing. We’re preparing a new type of CTF (Capture The Flag) event, slated for January 2027, and I’m determined to see this project through to a successful conclusion.

Kim Min-jae | Since we made it to the finals of the DEF CON CTF this time, my goal is to reach the finals again next year. I competed as part of a team formed with other participants, and if the opportunity arises, I’d love to participate again—perhaps with a new group of teammates.

Yoon Tae-ho | What struck me most about this competition was the chance to collaborate with professionals working across various fields. Exchanging ideas on how to solve problems and discussing different approaches provided me with a great deal of inspiration and new insights. It was a meaningful experience, as I was able to learn firsthand about the perspectives and problem-solving approaches of professionals currently working in the field.

Furthermore, I would like to share this experience with other students. At CAT-CERT, we are preparing an event called "Holy Shield," which we aim to host in January 2027. Our goal is to create a space where not only students from The Catholic University of Korea who are interested in cybersecurity, but also middle and high school students and students from other universities, can come together to interact and share their experiences.

● Text/Photos: External Relations Team, Job Interns Seong Hyeon-seo and Yang Yu-jin