Music assignment

Overview

• Overall difficulty for me (From 1-10 stars): ★☆☆☆☆☆☆☆☆☆

Background

Find the flag

In this challenge, we can download a file:

┌[siunam♥earth]-(~/ctf/VU-Cyberthon-2023/Steganography/Music-assignment)-[2023.02.25|18:58:17(HKT)]
└> file Music_assignment.zip 
Music_assignment.zip: Zip archive data, at least v2.0 to extract, compression method=deflate
┌[siunam♥earth]-(~/ctf/VU-Cyberthon-2023/Steganography/Music-assignment)-[2023.02.25|18:58:18(HKT)]
└> unzip Music_assignment.zip 
Archive:  Music_assignment.zip
  inflating: VU Cyberthon 2023.html

We can open it in firefox:

┌[siunam♥earth]-(~/ctf/VU-Cyberthon-2023/Steganography/Music-assignment)-[2023.02.25|18:58:21(HKT)]
└> firefox VU\ Cyberthon\ 2023.html

Hmm… Nothing weird?

Let’s view the source page:

<meta property=og:description content="The aim of the VU Cyberthon is to inspire and encourage participants for independent analysis of cyber security problems and security methods, to develop critical thinking and creativity while solving challenges.">
<meta property=og:image content=https://www.cyberthon.lt/img/share.png>
<meta property=og:image content=https://bit.ly/simple-png>
[...]

The bit.ly link looks sussy:

It’s a google drive shared file!

Let’s download it!

┌[siunam♥earth]-(~/ctf/VU-Cyberthon-2023/Steganography/Music-assignment)-[2023.02.25|18:58:32(HKT)]
└> file CT-Instrument-23.wav 
CT-Instrument-23.wav: RIFF (little-endian) data, WAVE audio, Microsoft PCM, 8 bit, mono 11050 Hz

It’s a WAV sound file.

If we open it in Audacity and listen it, you’ll find that it’s a morse code:

We can go to an online tool to decode it:

We found it!

• Flag: VU{CYBERTHON2023}

Conclusion

What we’ve learned:

1. Decoding Morse Code In An Audio File