NCS 2021 Writeup

My writeup for the National Cyber Scholarship Competition 2021

Project maintained by codekrafter Hosted on GitHub Pages — Theme by mattgraham

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CM01

Briefing

Download the file and find a way to get the flag.

Contents: code.png, frame.png

Walkthrough

This challenge has two files, code.png and frame.png. frame.png is a valid QR code:

frame.png

When scanned it has the following text:

Hey, I’ve put the flag into the other file using the same trick we always use. You know what to do. :)

code.png looks like some sort of distorted QR code:

code.png

My first thought was that they had to be combined in some way. Combining them through AND would definitely not create a valid QR code as they have some anchor points that are filled in on both images, and combining them through OR (by layering them in GIMP) just created a more distorted code, so I figured I would try using xor. I used G’MIC with the following command to XOR them together:

$ gmic code.png frame.png -blend xor -o result.png

which results in the following image:

result.png

which when scanned(I used zbarimg but you can also just scan it with your phone) reveals the following text:

FLAG: A_Code_For_A_Code