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Dec 3: Catch me

Challenge

… if you can

Solution

We get an animated GIF images of a QR code. We see there are 29 frames, each with a small QR code. Manually reading the QR code of the first frame results in the letter ‘H’, so it would appear each frame contains one letter of the nugget.

We extract an read each frame of the gif and read the resulting QR code in python:

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import os, re
from PIL import Image
from qrtools import QR

def extractFrames(giffile, outputdir):
    with Image.open(giffile) as frame:
        nframes = 0
        while frame:
            frame.save( '%s/%s-%s.gif' % (outputdir, os.path.basename(giffile), nframes ) , 'GIF')
            nframes += 1
            try:
                frame.seek( nframes )
            except EOFError:
                break;
        return True


# extract every fram
extractFrames('fast_response_code.gif', 'dec3_frames')

# read qr code in each extracted image
path="./dec3_frames/"

nugget=''
for filename in sorted(os.listdir(path), key=lambda x: int(re.findall(r'\d+', x)[0])):
    myCode = QR(filename=path+filename)
    if myCode.decode():
      nugget+=myCode.data_to_string()

print nugget

Flag

HV15-6Jhd-nWbQ-4dY8-yxH5-vSiA
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