The Contest

IMPORTANT: Each edition of the CTS may have specific rules. Consider this page as a high-level overview of the game overall, and follow the instructions given at the specific edition you’re playing!


Capture the Signal (CTS) is a challenge-based CTF that focuses exclusively on the reverse engineering of radio signals. This activity is also known as “blind signal analysis” as the specifications of the signal are unknown to an attacker. This contest is organized by Trend Micro’s researchers for researchers, hackers, and practitioners in the field!

Contestants should use their RF-hacking kung fu and tools like GNURadio, GQRX, URH, Python, C, black magic, to examine a series of increasingly complex radio signals to extract key information leading them to the next signal.

The game runs virtual. The radio signals will be distributed over IP. The use of IP eliminates the complexity of deploying actual radios and transmitting RF over the air.

GNURadio, for example, supports the tunneling of signals natively (ZeroMQ), so the entry barrier is fairly low and the players could focus on the real challenge. For the same reason, we may provide VMs to support the GNURadio toolchain, as setting it up can be a time consuming process and is not relevant to the core of the challenge. Of course, participants are welcome in using their own setup.

The more challenges you solve, the more points you gain. Points for challenges are statically assigned and are proportional to the difficulty of the challenge. The first participants to solve a challenge will receive a higher number of points.

At the end of the competition, the team with highest total points will be named the winner. In the case of two different teams having the same points, whichever team was quickest to reach this high score will be declared the champion.

Format of the Game

At game start, we will direct the contestants to the so-called entry signal, by supplying the virtual frequency to connect to. The contestants will connect to our infrastructure, in order to receive the RF data for the game.

With reverse engineering this first signal, the successful contestants will obtain the flag to submit to the scoreboard and to use to unlock challenge number 2.

The contest will continue in this fashion with an increasingly difficult set of analog and digital signals to demodulate and decode.

Things to Bring (on-site contest only)


We try hard to keep the competition as free and exciting as possible; however we do require teams to adhere to a few simple rules:

  1. (On-site only) The use of radio equipment is optional. Should anyone, for some reason, decide to use radio equipment, they will do so under their responsibility and must adhere to the local law (regulations) on the matter of RF operations.

  2. Show up on time or you’ll miss the briefing!

  3. No cooperation between teams with independent accounts. Sharing of solutions or providing revealing hints to other teams is cheating: don’t do it!

  4. No attacking the competition infrastructure. If bugs or vulns are found, please alert the competition organizers immediately. Hint: you might get free hints for responsible disclosure. Absolutely no sabotaging of other competing teams using SE or physical attacks, or in any way hindering their independent competition progress.

  5. No brute forcing of challenge flag/ keys against the scoring server.

  6. DoS of the CTF platform or any of the jeopardy challenges services will not be tolerated.

  7. (On-site only) All participants must obey to PIT STOP calls. PIT STOP calls are rest intervals where all the players must leave the CTF area to facilitate for the CTF Crew to perform maintenance work. Teams who don’t adhere to the rules will be penalized or disqualified from the competition.

The organizer reserves the right to dispatch long-term (>1 year) all CTS contest bans.

At all times, the decision of the CTS organizing crew (and host event) is final on any matter in question.