solver.py

from PIL import Image
from struct import pack, unpack
from typing import List, Tuple
import random

with Image.open('out.png') as image:
    seed = b'\xed\xfe\xcb\x10'
    random.seed(seed)
    image = image.convert("RGB")
    pixels = image.load()
    available = image.width * image.height * 3
    size = 34
    valid_spots = []
    for channel in range(3):
        for y in range(image.height):
            for x in range(image.width):
                valid_spots.append((x, y, channel))
    metadata = b"\x90\xbfhttps://github.com/evil-steganography/evil-stego-1" + bytes(seed) + pack("<I", size)
    c = len(metadata)*8
    locations = random.sample(valid_spots[c:], size * 8 + 1)
    c = 0
    flag = ''
    for i in range(size):
        bit_location = locations[c:c+8]
        bit = ''
        for x, y, channel in bit_location:
            orig = list(pixels[x, y])
            bit += str(orig[channel] & 1)
        flag += chr(int(bit, 2))
        c += 8
    print('[+] Flag:', flag)