PNG Punked

Inject arbitrary data into PNGs, without breaking the PNG spec.

For technical details on how this works, and outdated Python 2 code, read this blogpost.

original from 2016

How to use

Listing PNG chunks

~ ./punk.py list source.png
Chunk IHDR, 13 bytes
Chunk IDAT, 226876 bytes
Chunk IEND, 0 bytes

Injecting data

~ ./punk.py inject source.png output.png mydata
Chunk IHDR, 13 bytes
Chunk IDAT, 226876 bytes
Chunk IEND, 0 bytes
Injecting puNk chunk 0.007944389275074478 kb
Chunk CRC 43b7dda3
Chunk injected!

~ ./punk.py list output.png
Chunk IHDR, 13 bytes
Chunk IDAT, 226876 bytes
Chunk puNk, 16 bytes
Chunk IEND, 0 bytes

Extracting data

~ ./punk.py extract output.png mydata.txt
Attempting to extract punked data from output.png
Found a punk chunk worth 16 bytes

~ cat mydata.txt 
Attack at dawn!!%

Examples?

The /examples directory contains three files:

hide-this, the content we want to hide
source.png, the image want to use as a source PNG.
output.png, source.png, with the new puNk chunk.

You can verify the contents of output.png by running

~ ./punk.py list example/output.png 
Chunk IHDR, 13 bytes
Chunk IDAT, 226876 bytes
Chunk puNk, 603 bytes
Chunk IEND, 0 bytes

~ stat --format="%s" example/hide-this 
603