Table of Contents

rating: Beginner
points: 140pt

description:

I, the codebreaker, have broken the QR code!

Approach
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First I noticed that it was png, so I did the standard steg things like

file *.png
exiftools *.png
strings *.png
binwalk *.png

but I didn’t get any results.

In the first CTF I ever did, NahamCon2024, there was a challenge where he gave a rectangular QR code, and the only way to read it was with the Denso Wave QR code reader app. (Denso were the original creators of the QR code I think). I tried with the app too, but no luck.

I began searching for ways to read partial QR Codes and came across a fantastic article

In the article the author mentioned QRazyBox, so I decided to use that. I recreated the amount of the QR that I could see in QRazyBox, and then scanned it. This gave us the flag.

I highly recommend reading the article, he goes into a lot of depth on QR codes, and from that I realised that the QR code we were given offers the highest possible error tolerance which was why we could scan it even with so many missing data pieces.