Frequently Asked Questions

What is the GRCon26 Capture-the-Flag (CTF)?

The GRCon26 CTF is a collection of signal-focused puzzles that challenge participants to analyze, process, and decode real-world RF signals. Challenges may be simple, involving a single decoding step, or multi-layered, requiring participants to combine several techniques to uncover the solution.

Each challenge ultimately leads to a flag, which is a unique string in the format:

flag{secretwordsandnumbers}

The flag is hidden somewhere within the transmitted data and serves as proof that the challenge has been successfully solved.

Participants are typically provided with one or more of the following:

• A clue describing the challenge or providing background information
• An IQ recording (often in SigMF format)
• Access to a live over-the-air transmission
• Protocol information or partial hints, depending on the challenge design

Solving a challenge may require any combination of:

• Signal detection and identification
• Demodulation
• Decoding digital protocols
• Packet extraction and analysis
• File recovery
• Digital signal processing (DSP)
• Reverse engineering custom formats
• Cryptographic or logic-based puzzle solving

No single technique is required for all challenges; part of the challenge is determining the appropriate approach.

Participation Options

Challenges can be offered in several ways:

On-Site Only: Some challenges require physical presence at the conference because they involve specialized hardware, local RF transmissions, directional antennas, or other equipment that cannot be easily replicated remotely.

On-Site and Virtual: For challenges that do not depend on physical access, participants may be provided with recorded IQ data (typically in SigMF format). This allows both in-person and remote participants to compete using the same underlying signal data.

Who Can Participate?

The CTF is designed for a wide range of experience levels. Some challenges can be solved with basic GNU Radio and SDR knowledge, while others may require advanced RF engineering, DSP, protocol analysis, or software development skills. Participants are encouraged to collaborate, experiment, and learn new techniques throughout the event.

The primary goal is not only to find flags, but also to develop practical skills in signal analysis, wireless communications, and software-defined radio.

Do I need GNU Radio?

Generally, no — GNU Radio is often useful, but participants are free to use any tools they prefer, including GNU Radio, Inspectrum, Universal Radio Hacker (URH), Python, MATLAB, Wireshark, SDRangel, or custom code. The goal is to solve the challenge, not to use a specific tool.