source：http://www.ifans.com/forums/threads/decrypt-any-ios-firmware-on-mac-windows-linux.354206/
Decrypting iPhone firmware will allow you to browse the iPhone firmware files and make any changes if you wanted to. Here are the instructions for mac and linux:
Scroll down for the windows version (I haven't tried it) and the gui versions for windows, mac.
There are 2 ways to do this-easy and hard (GUI or Terminal) GUI version is on the bottom
Hard/Terminal code Version
Mac/Linux version
Step 1: Locate your ipsw/firmware to decrypt. and change the file type into .zip and extract it.
Step 2: Download VFDECRYPT for Mac or Linux and extract it.
Step 2: Now start Terminal
Step 3: Open the VFDECRYPT folder and drag the vfdecrypt file into Terminal (Mac) and type in " -i "
Step 4: Drag the largest dmg file into Terminal and type in " -o decrypted_fs.dmg -k "
Step 5: Go to this Link to get the key for your corresponding firmware.
Step 6: Copy the key into Terminal and click enter.
Step 7: After the Terminal is done the file will be called decrypted_fs in your finder - Username.
Simplified Instructions for terminal for Mac or Linux: /vfdecrypt -i <dmg> -o decrypted_fs.dmg -k <key>
Replace “<dmg>” with extracted DMG from the IPSW file. And replace “<key>” with decryption key of your device.
Windows Version
Step 1: Locate your ipsw/firmware to decrypt. and change the file type into .zip and extract it.
Step 2: Download VFDECRYPT for Windows and extract it.
Step 2: Now start Command Prompt or cmd
Step 3: Open the VFDECRYPT folder and type in the vfdecrypt.exe file location into command prompt and add " -i "
Step 4: Type in the largest dmg file location into Command Prompt and add " -o decrypted_fs.dmg -k "
Step 5: Go to this Link to get the key for your corresponding firmware.
Step 6: Copy the key into Command Prompt and click enter.
Step 7: After the Command Prompt is done the file will be called decrypted_fs somewhere on your computer (haven't tried it on windows not sure where it is)
Simplified Instructions for terminal for Windows: vfdecrypt.exe -i <dmg> -o decrypted_fs.dmg -k <key>
Replace “<dmg>” with extracted DMG from the IPSW file. And replace “<key>” with decryption key of your device.
Easy/GUI Version
GUI Version- Windows, Mac
Step 1: Download the firmware that you want to decrypt or view root file system (like after jailbreak).
Step 2: Go to this link for the windows download, this link for the Mac download or from [PIRACY.mf]. Sorry used proxy so couldn't copy direct link.
Step 3: Open the file and locate your ipsw.
Step 4: Click decrypt and let it do it's decoding. Keys should be automatically found, if not go to the link to find your corresponding one.
Step 5: Find you decrypted dmg file and find a way to open it E.g. magiciso...
That’s it! Your iPhone firmware should have been decrypted now. You can mount and browse it and make the changes you want.
You can go into the System/Library/Coreservices/Springboard.app and edit the N__AP.plist. Visit this forum for the master of plist hacks. When you finish your plist editing and other stuff you could just save it and close the dmg file and restore you idevice to make the features appear without jailbreaking if you absolutely hate it.
Have fun!