Coin - 200 (Forensics)

Write-up by Shwinn

Created: 2015-12-08


I'm like 99% sure this is the coin sound.




Except there weren't that many notes...



Find a flag in the notes by removing "filler" notes, converting the remaining notes to ASCII values, and then converting those values to letters.


The problem gives a .png file of a musical piece generated by LilyPond. The picture also has lots of noise and a warped staff towards the bottom. The key to this problem is ignoring these distractors, as the real flag lies in the notes.

First we transcribed the notes of the piece, and noticed a few quick patterns. For one, every note was followed by a quarter rest. After every 2 - 3 notes, the same pattern of 6 notes would repeat (G - C - A - G - E - F). Since there was so much repetition and the hint leads us to believe that there are now excess notes in the piece, we removed all of these "filler" notes.

We removed the repeated G - C - A - G - E - F and the quarter rests but left spaces do denote each division by the pattern. Now we were left with blocks of 2 or 3 notes each. Hmmm ... this looks like if each note was a number we would have the ASCII for each character.

The pattern was that starting with C#, each increase of a musical half-step increases the decimal value by 1. Here is the full pattern:

C# - 0
D - 1
D# - 2
E - 3
F - 4
F# - 5
G# - 6
A - 7
A# - 8
B - 9

Converting each non-filler note to its corresponding ASCII value, and then converting these values to letters gives you the flag: sctf{velatovibratosctf}