Description:

New Avenger | Stego 300 pts

The Avengers are scouting for a new member. They have travelled all around the world, looking for suitable candidates for the new position.
Finally, they have found the perfect candidate. But, they are in a bad situation. They do not know who the guy is behind the mask.
Can you help the Avengers to uncover the identity of the person behind the mask ?

avengers.gif

Megabeets$ binwalk avengers.gif

DECIMAL         HEX             DESCRIPTION
-------------------------------------------------------------------------------------------------------
0               0x0             GIF image data, version 8"9a", 500 x 272
885278          0xD821E         Zip archive data, at least v2.0 to extract, compressed size: 13422, uncompressed size: 13780, name: "1_image.jpg"
898769          0xDB6D1         Zip archive data, at least v1.0 to extract, compressed size: 1796904, uncompressed size: 1796904, name: "image_2.zip"

Megabeets$ unzip ./avengers.gif
Archive:  avengers.gif
warning [avengers.gif]:  885278 extra bytes at beginning or within zipfile
  (attempting to process anyway)
  inflating: 1_image.jpg
 extracting: image_2.zip

Megabeets$ unzip ./image_2.zip
Archive:  image_2.zip
[image_2.zip] 2_image.jpg password:

Megabeets$ unzip ./image_2.zip
Archive:  image_2.zip
[image_2.zip] 2_image.jpg password: <em>sgtgFhswhfrighaulmvCavmpsb</em>
  inflating: 2_image.jpg
 extracting: image_3.zip

from zipfile import ZipFile
import string

# list storing the passwords, it might help 
passwords =[]
i = 1

while True:
    # read the last line of the file
    f = reversed(open("%s_image.jpg"%i).readlines())
    passw = f.next()
    try:
        # extract the password from the last line, if failed - it's the last zip.
        passw = passw[passw.index(':- ')+3:passw.index(' \n')]
    except:
        break
    # extract the zip file using the password
    with ZipFile('image_%s.zip'%(i+1)) as zf:
        zf.extractall(pwd=passw)
    i+=1    # add the password to the list of passwords
    passwords.append(passw)

lol.

So now we have 15 passwords, each contains 26 characters:

sgtgFhswhfrighaulmvCavmpsb
lppujmioEaynaqrctesAnztgib
lrphntGpzjhkswskepnilrwwjm
hmohAmgcomgpjjhLnqpkepuazi
qjqxzuSkiyjzazwwsqchiqvgoQ
ujinpqyghiulozjnyprZpnswnp
tsquviQwxtgpgarlxelvakaOpo
jljykvfZSycpvscqvzjwelKhok
cqjausmhroogiuabcbpRmsyzpo
qakrlxrGswfovmxhxpjzfyfrie
jyxbLszctbveelbgxtilzfbQng
heojthirkakqvvmxjgAWzuekcp
nkpbhyUmiabnymvzmcppejiisy
mIsmsmsmxpfvkolTbnkafkgvgx
tsYinxviqeykguqznjscomgqbh

The password looks like garbage, it’s not Base64 or some known encoding. The first thing to pop up is the capital letter inside each password. Every password contains one or two capital letters. I know that the English alphabet contains 26 letters, so maybe I can map the location of each capital to the matching letter in the alphabet. i.e, if ‘F’ is in passw[4] i’ll take alphabet[4] which is ‘e’ and so on. I added this code to my script:

locations = []
for p in passwords:
    for c in range(26):
        if p[c] in string.uppercase:
            locations.append(c)

map_result = ''
for l in locations:
    map_result += string.lowercase[l]

print "Result: ", map_result
#Result:  etitgepgztgxhiwthexstgbpc

I ran the script and got meaningless string: “etitgepgztgxhiwthexstgbpc”. Damn! I was so sure that the mapping is the solution, how can’t it be?! All the facts point towards mapping the alphabet. I decided not to give up and ran Caesar Cipher on the string:

YAY! I was so happy to find Spidey is the new Avenger!

Here’s the full script:

The flag was: pragyanctf{peterparkeristhespiderman}

Description:

Lost Friends | Stego 300

Moana and her friends were out on a sea voyage, spending their summer joyously.
Unfortnately, they came across Charybdis, the sea monster. Charybdis, furious over having
unknown visitors, wreaked havoc on their ship. The ship was lost.

Luckily, Moana survived, and she was swept to a nearby island. But, since then, she has not seen her
friends. Moana has come to you for help. She believes that her friends are still alive, and that you are the
only one who can help her find them

lost_friends.png

Moana has lost her friends and we need to help her find them. We are given with an image which is absolutely blank. I opened it in Photoshop and saw that it’s completely transparent. So I grabbed python and Pillow and canceled the alpha channel (which is responsible for transparency).

from PIL import Image
# convert from RGBA to RGB will cancel transparency
Image.open('lost_friends.png').convert('RGB').save('output.png')

I got this image:

Wooho, Chipmunks! It seems like every chipmunk is on another channel, lets split the channels:

import cv2
import numpy as n
img = cv2.imread('lost_friends.png',cv2.IMREAD_UNCHANGED)
b,g,r = cv2.split(img)
cv2.imwrite('b.png',b)
cv2.imwrite('g.png',g)
cv2.imwrite('r.png',r)

Now we have three images of chipmunks:

I played with them, trying to find the flag but found nothing. So I got back to the original image and opened it with Hex Editor. At the bottom of the file I found this hint: “Psssst, Director, maybe ??”. So the flag is probably the name of the director of chipmunks. According to Wikipedia, Chipmunks has 4 movies, I tried to submit with each director and found that the director of the third movie is the flag.

The flag was praganctf{MikeMitchell}