Theres a nifty little program you can use to decrypt and open those pesky little (well, not so little) DMG files inside your ipsw file. In other words, you can get into and view the contents of your iPhone/iPod/iPad’s firmware and I guess extract things you may need, or just view whats inside your IPSW file. Note, you can’t re-encrypt the ipsw in hopes that you can restore your iDevice’s firmware. No, it doesn’t work like that. I just thought it was pretty cool. You can download it here.
You are also going to need the decryption keys for your dmg files, which can found here:
Once you get into that link, just search for your device and iOS version and click it to view the decryption key.
Update (June 15, 2011): Many of you are wondering, why doesn’t vfdecrypt open? It just opens then crashes? Heres the solution. You need to run vfdecrypt via command prompt. I recommend creating a folder in the root of the C:\ drive, and name it “vfdecrypt” so now the file path should be C:\vfdecrypt You should also move the DMG file to that directory. Now go to the Start menu, and click “Run” and type in cmd.exe In the command prompt, type in cd C:\vfdecrypt and here where it gets really… peculiar…
The arguments for this program in the command prompt is: vfdecrypt -i input -p password -o output
For example, the root file system for iOS 4.2.1 for iPod Touch 2G is located in the file: 038-0014-002.dmg, Before you decrypt it, rename it to something shorter because the default file name won’t work. I renamed mine to ios421.dmg so this is how you do it in the command prompt:
vfdecrypt -i ios421.dmg -p (replace this with the dmg decryption key) -o ios421_new.dmg
Press enter, then just wait for the operation to be completed. To open this file, you can just simply open it on Mac OS X. Windows users can download a program called “HFSExplorer”. Its free of course. I hope this article helped shed some light on the usage of vfdecrypt.