Cracking 7z files Using John The Ripper

7z or 7zip it's a compressed archive format that implements AES-256 encryption.  I have an encrypted compressed archive for which I forgot the password.  I decided to guess it using John The Ripper (JTR).

I needed another tool besides JTR. It's a python script called 7z2john.py by PyLZMA Copyright (C) 2004-2010 Joachim Bauch under the GNU LESSER GENERAL PUBLIC LICENSE.  You can Google it: https://www.google.com.co/#q=7z2john.py or clone the repository through git:

• git clone https://bitbucket.org/dhiru/pylzma-ng.git

To extract the hash of the compressed file just execute the python script:

• ./7z2john.py archive.7z > hash.txt

Finally use the output of the python script as a input file for JTR.

This attack is only possible when you have a few list of words and the certainty that they are correct, because the AES encryption used by 7z implements protection against bruteforce attacks.  It's a extremely slow process, in my laptop 193 passwords took it 8 seconds.