Hide files in PNG
Using this script you can hide any file in a PNG image. The script creates a fake chunk and add the file to that chunk which is ignored by PNG processing tools but it can be retrived later.
Requirement
Only python 2.7 is required, you can use python3 also just change those "print" statements.
Usage
png_hiding.py input.png payload_file output.png
Ex:
python png_hiding.py sample.png png_hiding.py out.png Start: 16 Count: 1266 [*] Header: IHDR Length: 13 Read_CRC: aa6971de Calc_CRC aa6971de [*] Header: bKGD Length: 6 Read_CRC: a0bda793 Calc_CRC a0bda793 [*] Header: pHYs Length: 9 Read_CRC: 009a9c18 Calc_CRC 009a9c18 [*] Header: tIME Length: 7 Read_CRC: 71e7cf0a Calc_CRC 71e7cf0a [*] Header: tEXt Length: 25 Read_CRC: 57810e17 Calc_CRC 57810e17 [*] Header: IDAT Length: 395 Read_CRC: 5130624e Calc_CRC 5130624e [*] Header: IEND Length: 0 Read_CRC: ae426082 Calc_CRC ae426082
We get information like Start and Count which is offset at which our payload is written and no of bytes that are written respectively.
You can retrive the content via several method:
For the above example using values Start: 16 and Count: 1266 on the out.png file.
- Using 'dd'
dd if=out.png of=recovered_file.py bs=1 skip=16 count=1266
- Using python
You can use this one liner to recover the above file, replace start and Count values to recover your file.
python -c "open('recovered_file.py','wb').write(open('out.png','rb').read()[16 : 16+1266])"
You can also use language specific codes to recover the file, just google it for your language.
Final Note
This script can be used to fix invalid CRC error of a PNG which you can encounter in CTFs competitions or you can use it to explore different chunks present in a PNG file (just comment out the file writing part).
For increased security you can encrypt file before adding it to the PNG and then decrypt it after recovering.
If any suggestions or request mail me or open a issue.
Author
Arun Kumar Shreevastava