CTF as a Service: A reproducible and scalable infrastructure for cybersecurity training
This paper presents the design, development, and evaluation of a reproducible and scalable "CTF as a Service" platform built on Proxmox, Terraform, Ansible, and Docker Swarm to automate the deployment of cybersecurity training challenges and overcome the infrastructure barriers that typically limit their adoption in academic settings.
Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
Imagine you are a teacher who wants to run a giant, digital "escape room" for your students. In this escape room, the students aren't trying to find a hidden key in a closet; they are trying to hack into fake websites, crack secret codes, and break into virtual computers to find a "flag" (a secret code) that proves they solved the puzzle. This is called a Capture The Flag (CTF) competition.
The problem? Setting up these escape rooms is a nightmare. Every single puzzle needs its own isolated, secure computer environment. If you have 50 puzzles, you need 50 separate computers. If 100 students show up at the same time, your computers might crash. And if a student breaks one puzzle, you don't want them to accidentally break the teacher's main computer or the other puzzles.
Traditionally, setting this up required a team of super-experts and a lot of expensive hardware. This paper describes a solution built by the Public University of Navarre that makes this process as easy as ordering a pizza.
Here is the story of how they built "CTF as a Service" (CaaS), explained simply:
1. The Big Idea: The "Magic Factory"
Instead of building a new computer for every puzzle by hand, the team built a factory that builds them automatically. They call this "Infrastructure as Code."
Think of it like a Lego instruction manual. Instead of a human spending hours gluing bricks together, you just hand the manual to a robot. The robot reads the instructions and builds the exact same Lego castle every single time, perfectly and instantly.
- The Robot: They used tools called Terraform and Ansible. These are the "robots" that read the instructions and set up the virtual computers.
- The Factory Floor: They used Proxmox, which is like a giant warehouse that can hold hundreds of these virtual computers without needing a physical building for each one.
2. The Puzzle Containers: The "Bubble Wrap"
Each challenge (puzzle) is packed into a Docker container.
- The Analogy: Imagine every puzzle is inside a sealed, transparent bubble wrap. Inside the bubble, the puzzle has everything it needs (the code, the operating system, the tools).
- The Benefit: It doesn't matter if the bubble is sitting on a wooden table, a metal desk, or a spaceship. The puzzle works exactly the same way. If a student breaks the bubble, it doesn't pop the other bubbles or the table. It's perfectly isolated.
3. The Traffic Cop: The "Concierge"
When 500 students log in at once, they all need to find their specific puzzle. If everyone tried to run to the same door, it would get jammed.
- The Solution: They used HAProxy and Docker Swarm.
- The Analogy: Think of HAProxy as a super-efficient Concierge at a hotel. When a student arrives (connects), the Concierge checks their ID (IP address) and says, "Ah, you are here for the 'Crypto' puzzle. Please go to Room 3."
- The Sticky Note: Here is the tricky part. If a student solves half of a puzzle, the computer remembers their progress. If the Concierge sends them to a different room next time, they lose their progress. To fix this, the Concierge uses a Sticky Note (called a "stick-table"). Once a student is assigned to a specific room (a specific computer replica), the Concierge makes sure every time that student comes back, they are sent to that exact same room. This keeps their progress safe.
4. The Assembly Line: The "Git Pipeline"
Usually, if a teacher wants to update a puzzle (fix a bug or add a hint), they have to manually go to every computer and change the files. That's slow and prone to mistakes.
- The Solution: They built a CI/CD Pipeline (Continuous Integration/Continuous Deployment).
- The Analogy: Imagine a conveyor belt. The teacher writes the new puzzle code and drops it into a box at the start of the belt (a Git repository).
- A robot sees the new box.
- It packs the puzzle into a new "bubble" (Docker image).
- It sends the new bubble to the factory floor.
- The old bubble is popped, and the new one takes its place instantly.
- Result: The teacher never has to touch the servers. They just update the code, and the system updates itself.
5. Why This Matters
Before this system, running a CTF was like trying to host a music festival in a backyard with a garden hose and a few extension cords. It was messy, risky, and hard to scale.
With this new system, it's like having a professional concert venue that can instantly expand.
- Scalable: If 10 students show up, the system uses 10 computers. If 1,000 show up, the system can spin up 1,000 more computers automatically (though they are still working on making this fully automatic).
- Reproducible: You can shut down the whole system and turn it back on tomorrow, and it will be exactly the same as before.
- Safe: Because every puzzle is in its own "bubble," a hacker can't jump from one puzzle to the teacher's main computer.
The Bottom Line
The authors built a system that turns the complex, scary job of hosting cybersecurity competitions into a simple, automated process. They used open-source tools to create a "self-healing," "self-building" digital playground.
The Future:
They are now working on making the system even smarter. They want to add:
- A Dashboard: A simple website where teachers can click buttons instead of typing code.
- Auto-Scaling: Making the system add more computers automatically when it gets crowded, like a highway adding extra lanes when traffic gets heavy.
- Better Monitoring: A "health check" system that tells the teachers immediately if a puzzle has stopped working.
In short, they turned a chaotic, manual nightmare into a smooth, automated machine, making it easier for students to learn how to hack (and defend) in a safe, fun environment.
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