Hallo?

The flag is exactly as decoded. No curly brackets.

NOTE: keep the pound symbols as pound symbols!

Files

• hmm.mp3

Solution

We are given a mp3 file which on playing sounded like key-presses(DTMF) sounds. Convert mp3 file to wav file using ffmpeg and use a DTMF decoder from https://github.com/ribt/dtmf-decoder to decode the keypresses with:

ffmpeg -i hmm.mp3 hmm.wav
dtmf hmm.wav

to get the following output:

7774222228333#99933338#386333#8662666337777#

Decoding this based on the old mobile phone keypad like:

777 - r
4 - g
22 - b
222 - c
8 - t
333 - f
...
..

and so on we get the full flag.