WPICTF - CSC The musical

14 Apr 2019

description: […]

category: Steganography

The challenge was providing a link to a web page containing an audio file : theMusical.mp3 Opened with Audacity, we get the following :

When we listen to the sound, we can recognize piano notes. If you have the perfect pitch, you can easily recognize the notes that you are hearing. If not, then you can use any tuner app on your smartphone, just like everyone… At the end you should get the following notes :

E4 F4 D5 E4 F4 D4 E4 E4 E4 E4 D5 G4 E4 C5 D5 E4 C5 D4 E4 B4 E4 E4 A4 G4 E4 C5 A4 E4 A4 C5 E4 C5 A4 E4 B4 D4 D4 C5 G4 E4 B4 B4 E4 C5 B4 D4 C5 B4 E4 B4 E4 E4 A4 G4 E4 A4 E4 D4 C5 E4 E4 D5 B4

We can notice that in most cases, each every 3 notes, we’ve got an “E”. The total amount of notes is 63 and 63 / 3 = 21. So we can think that we have 21 groups of 3 notes.

Now let’s try to put values on them… The lowest note in term of frequency is D4, so let’s consider it as our “base” and assign to it the value 0. In this way, we can increment the value of the following notes and obtain :

Given the previous picture, we can convert our notes to values and then recognize the octal values of ASCII symbols :

oct	127	120	111	173	167	160	151	143	164	146	164	150	063	155	165	065	151	143	141	061	175
ascii	W	P	I	{	w	p	i	c	t	f	t	h	3	m	u	5	i	c	a	1	}

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