SECUINSIDE CTF Quals 2014 – Reversing 100 yayaya

Thu 05 June 2014 CTF

This task contains an SWF file with Crossbridge emdedded. Additionally there is an ELF file inside that SWF. At the first look I thought that this is really an RE job. But I was wrong (thanks to nurfed - it's his solution). There is no RE, and even Flash decompiler was not needed. The entire work comprises capturing Flash movie frames with random color blocks.

Some random frame from Flash movie:

These color blocks appeared with some interval, and the solution was to capture these frames and then combine them together. For screen capture I chose pyscreenshot.

import pyscreenshot as ImageGrab
import time

print 'z'
for z in range(2000):
    im = ImageGrab.grab(bbox=(269, 100, 469, 300))
    im.save('e:\sc\im_{}.png'.format(z))
    time.sleep(0.1)

I decided to use PIL to combine screenshots, but nurfed (thanks again) chose an easy way: ImageMagick. So simple:

convert -evaluate-sequence add "e:\sc\im_*.png" out.png

And we get the final image:

Flag is GANADAHAAH.