Microscope - 488 Points (17 solvers) http://microscope01.3dsctf.org:8011/ Author: @atcasanova

The site contain a one gif(http://microscope01.3dsctf.org:8011/gif.gif). So lets to down it with:

wget http://microscope01.3dsctf.org:8011/gif.gif

Convert all the frames to png with:

convert gif.gif gif.png

There are 108900 images, each one has a unique color, if Title Chall name is Microscope and the frames are only one color, i presuppose that the images are pixels of a 330x330, because sqrt(108900) = 330.

Verifing the frames, they are only 2 colors: green and yellow

I'll to use ppm format to manipulate all the frames for a single image.

Obs: before begin, lets rename and enum the files that start with zeros to better the implementation:

mkdir zeros
mv gif_0* zeros/
cd zeros
ls | cat -n | while read n f; do mv "$f" "$n.png"; done
mv * ../

Ppm files have as header: Format(P3), Resolution(330x330), Color max value(255), next comes values RGB for each pixel

output = open("flag.ppm", "w")
output.write("P3\n330 330\n255\n")

Use 'mogrify' to transform the png frame to ppm, after convert P6 to P3 with 'convert'

yellow = "255 225 0 "
green = "1 127 2 "
white = "255 255 255 "
black = "0 0 0 "
i = 0
count = 0
while (i<=329):
    j = 0
    while(j<=329):
        pixel_name_png = "gif_"+str(count)+".png"
        pixel_name_ppm = "gif_"+str(count)+".ppm"
        os.system("mogrify -format ppm "+pixel_name_png)
        os.system("convert "+pixel_name_ppm+" -compress none "+pixel_name_ppm)

After open the frame, compare the Green value to check if the pixel is green or yellow, more than 200 is yellow, bellow is green, if the frame is yellow, print white("255 255 255 ") on output, else, black("0 0 0 ")

        with open(pixel_name_ppm, 'r') as arquivo:
            run = 1
            printed = False
            for linha in arquivo:
                for numero in linha.split():
                    if run <=5:
                        run+=1
                        continue
                    else:
                        if numero >=200:
                            output.write(white)
                        else:
                            output.write(black)
                        printed = True
                        break

After the code execution, we have a QRCODE image, scan it and get the flag!

By: Kali K4L1 Nathalie | FireShell