Decrypt Mii QR code data from 3DS / Wii U / Miitomo

mii-qr.py

# Decrypt Mii QR codes from 3DS / Wii U / Miitomo
# Usage: python3 <input file> <output file>
# QR docs: https://www.3dbrew.org/wiki/Mii_Maker

from Crypto.Cipher import AES
from sys import argv

key = bytes([0x59, 0xFC, 0x81, 0x7E, 0x64, 0x46, 0xEA, 0x61, 0x90, 0x34, 0x7B, 0x20, 0xE9, 0xBD, 0xCE, 0x52])

with open(argv[1], "rb") as infile, open(argv[2], "wb") as outfile:
  nonce = infile.read(8)
  cipher = AES.new(key, AES.MODE_CCM, nonce + bytes([0, 0, 0, 0]))
  content = cipher.decrypt(infile.read(0x58))
  result = content[:12] + nonce + content[12:]
  outfile.write(result)