Tags: warmup stego 

Rating:

elytra - Beginner (50 pts)

Description

I beat the game! But where's the flag?

Provided files

iwon.txt - a plaintext file [download]

Ideas and observations

  1. googling the task name, elytra are a rare end-game item in the game Minecraft
  2. googling part of the text file, it's the End Poem (found in the Java Edition's client.jar at assets/minecraft/texts/end.txt) a poem penned by Julian Gough that appears to players at the end of a Minecraft playthrough before the credits crawl.
    • the raw text from end.txt has some byte-sequences replaced before the text is displayed to the player, in iwon.txt the PLAYERNAME sequence is replaced with doubledelete, the line begining §2 and §3 are stripped, and the §f§k§a§b§3 denoting scrambled text is replaced with [scrambled]

Notes

  1. comparing the original end.txt with the aforementioned replacements with iwon.txt shows some line-ending differences
  2. not all lines are different, though, some lines in iwon.txt are \r\n terminated, others are \n terminated

Solution script

from Crypto.Util.number import long_to_bytes

text=open('iwon.txt','r', newline='').read()
flag_l = int(''.join(['1' if x[-1] == '\r' else '0' for x in o.split('\n') if len(x) > 0]),2)
print(long_to_bytes(flag_l).decode())

wctf{ggwp}

Original writeup (https://gist.github.com/shinmai/5720d1f0a214d0878cfb530eb975c469#elytra---beginner-50-pts).