Sisy_B8_Stego_Extra.py

from PIL import Image

fp = "lena.png"

# extrahiere Nachricht vom Bild
extracted_bin = []
with Image.open(fp) as img:
    data = img.tobytes()
    for i in range(0, len(data)//8):
        extracted_bin.append(data[i]&1)

# dekodiere Nachricht (binär zu char via big-endian)
b = bytearray(len(extracted_bin)//8)
for i in range(0, len(extracted_bin)//8, 1):
    for j in range(8):
        b[i] += extracted_bin[i*8+j]<<(7-j)

text = b.decode("ascii",'ignore')

# parse Parameter
length, text = text.split(":",1)
secret = text[:int(length)]

# finde key in Flag
import re
key = re.search(r"\^FLAG\^(.+?)\^FLAG\^", secret)[1]

# dekodiere Key
import base64
print(base64.b64decode(key))