Capture the Signal!

Capture the Signal (CTS) is a new challenge-based CTF that focuses exclusively on the reverse engineering of radio signals. This activity is also known as “blind signal analysis” as the signals’ specification are unknown to the attacker.

This contest is organized by renowned community radio-hackers for researchers, hackers, and practitioners in the field!


We have been invited to join HARDWEAR.IO USA 2020. We will run a virtual-only contest on April 30th (10AM-2PM PDT) and May 1st (10AM-12:30PM PDT). Registration is required. All information on the contest webpage.

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How does it Work?

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 final, exit signal.

The game is hosted on site at conferences world-wide. 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. We use GNURadio for that.

GNURadio natively supports the tunneling of signals via ZeroMQ, so that the players can focus on the real challenge: reverse engineer the protocols without bothering the distribution of the signals. For the same reason, we provide ready-to-use scripts to remotely access the radio streams, as setting up the GNURadio toolchain is time consuming and is not relevant to the core of the challenge.

We also provide a VM image with all needed software to reverse engineer the signals. Of course, participants are welcome in using their own setup.

Each radio signal corresponds to a challenge. The challenges are sorted by difficulty, and each solved challenge gives you access to the next one. In other words, the flag contained in each signal represents the clue to the next radio signal.

Participants are also welcome to use Software Defined Radio (SDR) equipment to interact directly with RF signals over-the-air.