December 9th: QRgarden

Category

PPC

Hint

Read a lot, and the flag begins with “ADCTF_”.

Challenge

We are given a large image filled with QR codes.

Solution

We use zbar to read QR codes:

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sudo apt-get install zbar-tools

We split the image into the individual qr codes using imagemagick, then read each QR code until we find one starting with ADCTF_

The full image is 8700x8700 pixels, and each qr code is 87x87 pixels. We split this the large image into tiles:

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convert -crop 87x87 qrgarden.png qrcodes/tile_%d.png

Next we read all the images until we find the flag using zbar:

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$ for i in qrcodes/*; do zbarimg $i 2>&1; done |grep ADCTF
QR-Code:ADCTF_re4d1n9_Qrc0de_15_FuN

Flag