S21SEC [DCS17CTF] – Ucrania

Hi mates,

During my spare time i have tried some tasks from DSC17 CTF by S21sec. I will comment here on those in which I found more difficult or fun. FBCTF was present as platform so from here tasks names will be countries associated.

Ucrania – 450 points 

Initial analisis

Some indicates that is a image ciphered, isn’t it? :P. Need to know what cipher and in case of ECB (assumption) we need resolution, because BMP encodes it on file.

See this previous writeup to better understand: https://github.com/jesstess/tinyctf/blob/master/ecb/ecb.md

Making use of this script (https://github.com/doegox/ElectronicColoringBook/blob/master/ElectronicColoringBook.py) only need to ‘brute’ X resolution, from 800-1200 and wait for a valid image:

for x in {800..1200..100}; do python ElectronicColoringBook.py -x $x image_bffd6d7169826614c3f23cf0a7bdf997.enc ; done

It produces several images but one that we can read.

Flag: USECBC!