This is a stripped down version of xpwntool from xwpn. We ripped out a lot of stuff that is not required for simple xpwntool usage in order to decrypt IMG3 files that ship with iOS firmwares.
The source is released under the terms of the GNU General Public License version 3. The full text of the license can be found in the file LICENSE. The original source code this code is based on can be found at: http://github.com/planetbeing/xpwn