VICE CITY FM

Walkthrough

Challenge

The player receives playlist.m3u. The audio files are missing, but every playlist entry still contains an unusual duration.

Solution

M3U metadata stores a track duration after #EXTINF:. In this playlist, every duration is the decimal ASCII value of one flag character.

For example:

#EXTINF:83,Vice City Track 00

The duration 83 is ASCII S. Extract every duration in order and convert the numbers to bytes.

python3 solver.py

Output:

Securinets{th3_pl4yl1st_w4s_th3_l34k}

Run python3 make.py whenever the flag changes.

Reference solver

The reference solver supplied with the writeup:

#!/usr/bin/env python3

import re


text = open("playlist.m3u", encoding="utf-8").read()
flag = bytes(map(int, re.findall(r"#EXTINF:(\d+),", text)))
print(flag.decode())

Flag

Securinets{th3_pl4yl1st_w4s_th3_l34k}