picoCTF 2023 – HideToSee
28 March 2023 – Written by Valentin Huber – in crypto, ctf, forensics, python, steg, and steghide
Challenge
How about some hide and seek heh? Look at this image here.
Solution
The image seems to show a crypto system, but we don’t have any encrypted data. So I checked if there was some data hidden using steganography:
steghide extract -sf HideToSee.jpg -p "" # no password since we don't have anything
Which returned the following: krxlXGU{zgyzhs_xizxp_xz00558y}
. This seemed like an encrypted flag. I couldn’t be bothered to manually decrypt it using the system in the picture, so I wrote a short python script to do it:
import string
input = "krxlXGU{zgyzhs_xizxp_vx4zyz61}"
def swap(a:chr)->str:
if a not in string.ascii_letters:
return a
elif ord(a) <= ord('_'):
return chr(ord('Z')-ord(a)+ord('A'))
else:
return chr(ord('z')-ord(a)+ord('a'))
res = ''
for e in input:
res += swap(e)
print(res)
Et voilà: picoCTF{atbash_crack_ec4aba61}
.