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Blue Noise
Blue Noise
The player receives only blue_noise.png. The visible photograph is a distraction; the solve has two layers.
Recover the key from a blue-channel bit plane
Start with structural checks:
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file blue_noise.png
strings blue_noise.png
binwalk blue_noise.png
The image itself does not contain a readable flag. Inspect RGB channels and their bit planes. In blue-channel bit plane 2, the image contains a QR code. Visualizing that plane or extracting the hidden region reveals the QR. Scanning it gives:
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737-ABQ
The key is deliberately in bit plane 2 rather than the obvious LSB.
Find and unlock the appended artifact
The PNG has data after its IEND chunk. binwalk reports a ZIP archive in the suffix. Recover it either with binwalk -e or by locating the ZIP local header and copying from there:
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offset=$(binwalk blue_noise.png | awk '/Zip archive data/ {print $1; exit}')
dd if=blue_noise.png of=hidden.zip bs=1 skip="$offset" status=none
unzip -P 737-ABQ hidden.zip
cat note.txt
The password-protected note.txt contains:
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CYS{BLU3_H1D35_M0R3_TH4N_C0L0R}
The intended chain is therefore: blue bit plane → QR key → trailing ZIP → flag.
Flag
CYS{BLU3_H1D35_M0R3_TH4N_C0L0R}