In this writeup I will show you how I solved the Signals challenge from HackTheBox. The challenge is an easy hardware challenge. Let’s start!
Initial Analysis #
After downloading and unzipping the file we can see that it is a .wav file. Since this is a really common file type I decided to open it with VLC to hear what it sounds like, but I didn’t hear anything familiar. Maybe the author encoded text in the audio waveforms? So i decided to test this first option, so I’ve used Audacity that is an open-source audio file and waveform-viewing tool, but nothing. I was going in the wrong direction. So I read the challenge description again and I found out that the challenge again, and the phrase similarities with signals transmitted by the ISS hooked me. So I started googling to find something about ISS and img related article, and I found out about the SSTV. Finally I found the right tool to decode the file after I read this super interesting article. So i decided to use mmstv to decode the file.
mmstv #
This is a really cool tool that can decode SSTV images. When you open the program this is what you see.
Now we have to set up vlc in a way that will send the sound directly to our program, because if we will use the mic as input source in mmsstv the image that we will get will be distorted.
I’ve used this article to understand how to connect a digital cable between the vlc and mmsstv. After I’ve connected the cable I opened the file in vlc and I’ve started the program in mmsstv. After we press the play button in vlc we will see that the image is slowly appearing on the RX tab in mmsstv, and this time is not distorted. After we finished playing the file this is the image that we got.
As you can see we have a flag.
