iDecrypt is a GUI front-end for VFDecrypt for Windows/Mac OS X that is used to decrypt .DMG files, such as the rootfs of an IPSW file. This new version of iDecrypt is faster and more efficient, with a better UI and less processing power needed.
A free app for Mac, by Apalon
A free program for Mac, by Pocket Bits LLC.
The code-reading utility app