Capture the Signal

November 18th & 19th 13:00 - 18:00 (GMT +4)

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, anything, 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.

Brought to you by @embyte, @phretor, @FlUxIuS, @miaoski, JonA & Josiah. 



Links to the Scoreboard and to the Slack workspace can be found through the official contest webpage, which will go live November 1st

Format of the Game

  1. 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.
  2. 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.
  3. The contest will continue in this fashion with an increasingly difficult set of analog and digital signals to demodulate and decode.

Check In

  • You will need to register to our Scoreboard to participate (and to submit the flags)
    • The same Scoreboard contains all the info you need to play, e.g. the tools to access the CTS infrastructure. Please read it carefully.
  • We will use a dedicated Slack workspace during the game. Please remember to join.


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. Show up on time or you’ll miss the briefing
  2. No cooperation between teams with independent accounts. Sharing of solutions or providing revealing hints to other teams is cheating: don’t do it!
  3. No attacking the competition infrastructure. If bugs or vulns are found, please alert the competition organizers immediately. 
  4. Absolutely no sabotaging of other competing teams, or in any way hindering their independent competition progress.
  5. No brute forcing of challenge flags / keys against the scoreboard.
  6. DoSing the CTF platform or any of the jeopardy challenges services is forbidden.


At all times, the decision of the HITB and CTS organizing crew is final on any matter in question.