Find the Flag
Let’s start by listening to the given audio file. You will notice something strange around the 37 second mark.
Language Arts – DEF CON 27- The Official Soundtrack – 02 Luckiness (Kilmanjaro Remix).wav
We will come back to this in a moment. Instead, let’s answer the first question in the room;
Who remixed the song?
It is always a good idea to start with exiftool to look for any details about the file you are working with.
You can see who remixed this song in the Title from the exiftool output. You can also see this information in the filename, but it’s a good idea to check exiftool anyway.
What link is hiding in the music?
Let’s see if we can find anything hidden in the file using sonic-visualiser. We are going to look for something around the time we heard the strange noise. Adjust your time scale so that you can see this section of the waveform in detail.
After adding a spectrogram layer we can see that a QR code is embedded here; how do we scan it?
Scanning a QR code requires high contrast, and the default spectrogram color and scale doesn’t generate a high enough contrast for us to scan. Change the Color to White on Black and adjust the threshold and gain until you are able to scan the code. After you have scanned the code, you should have the link we are looking for.
Go to the link and listen to the file. You will also need to download the file found here.
What does the found audio convert to?
This is very clearly morse code. You can decode this message manually by interpreting it aurally, or visually by viewing the waveform in sonic-visualiser. Compare what you hear (or see) against a morse code chart (http://www.learnmorsecode.com/) to decode the message.
You can also use an online tool to decode it for you (https://morsecode.world/international/decoder/audio-decoder-adaptive.html). Whichever way you decide, you should end up with another URL, so let’s check it out.
What was the found password?
Following that URL will lead you to a password; what is it for?
Using steghide to extract something from our original audio file yields a passphrase prompt. Let’s use this password we found and see if it works.
What is the final flag?
For the final flag, read the contents of the file named secret.