What is a SDR Capture The Flag (CTF)?

There are several riddles about digital signals, modulations and other systems to analyze with different difficulties. A CTF is one of the best possibilities to learn a lot in a short time. To be suitable for beginners and more experienced people there is an introductory part about the most important concepts of digital signal processing, gnuradio and software defined radio. The focus is on trying out things yourself than downloading a tool that does everything for you.

So simply register an account for yourself and begin. :-)


To encourage you to learn interesting things about digital signal processing and SDR.


During rC3 - remote Chaos Experience from 27.12. - 30.12.2020. rC3 is over now, but you can still continue the challenges until mid of january 2021!

Do I need a rC3 ticket?

No. Just create an account here and play. :-)

What software do I need?

Gnuradio is recommended. 3.7.x or 3.8. doesn´t make a big difference, but a recent version ist recommended. (Version has some bugs in the UI but even this version will work.)

I think I found a bug in a challenge!

There are probably many. Please contact me at sdrctf_rc3 [at] tildepipe [dot] org

Is there a meeting point to get in touch with other players?

You can try IRC #rC3-SDRCTF @hackint or - for rC3 participants with ticket - the Jitsi Room in the TMS Assembly of rC3.world. If somebody asks please help them back on track but please DON´T SPOILER solutions. (https://webirc.hackint.org/)

Why are the challenge groups in the wrong order?

Because the used software uses a "modern" web architecture and cannot be modified in an easy way. It is recommended to start always with challenges in the groups with the lowest number. Sorry for that.

Do I need special hardware (e.g. RTL-SDR)?

No, the challenges are provided as downloadable data files.

Why can´t I download the flowgraphs?

At the moment gnuradio 3.7 and 3.8 are both in use. The data format of 3.8 cannot be read from 3.7. Besides the compatiblity issues you learn much more while creating your own programs.

Can I win a prize?

Maybe honor and glory but there are a lot interesting things to learn about digital signals and SDR!

I cannot solve everything.

Don´t worry. Join IRC #rC3-SDRCTF @hackint and ask for help. (https://webirc.hackint.org/)

Can I help?

Please recommend this CTF to your friends. :-) Please use hastag #sdrctf for tweeting.

Why do I need an email address?

Because this software cannot be configured to set it optional. Email is used for password recovery and maybe later to announce the solutions.

Who did all the work?

reald of TMS Assembly


You can contact me at sdrctf_rc3 [at] tildepipe [dot] org

Can I donate something?

This is already financed. If you want to donate something support your local animal shelter or adopt a pet. =^..^=

Can I send you vouchers for upcoming events?

Yes, please. ;-)