Decrypting Firmwares

iOS contains many layers of encryption. This page details how to remove the encryption wrapper around each file in the IPSW file.

1.0.x

With the release of the iPhone, the ramdisks weren't encrypted. So, in order to mount them, all you need to do is remove some data from the beginning. You can either open up a hex editor and remove ##### bytes from the beginning, or open up a console and run dd(1)^[man]:

dd if=ramdisk.dmg of=ramdisk.stripped.dmg bs=512 skip=4 count=37464 conv=sync

where ramdisk.dmg is the file name of the restore ramdisk (ex: the iPhone 2G 1.0 firmware (1A543a) would be 694-5259-38.dmg)

where ramdisk.stripped.dmg is the output file name

Once the data has been stripped, you can then mount ramdisk.stripped.dmg in Finder on OS X, or with any other program. If you encounter errors after mounting the stripped ramdisk, you can safely ignore them.

1.1.x

With the release of the iPod touch, Apple added a layer of encryption around the ramdisks. The decryption key wasn't obscured however, and a simple analysis of iBoot by Zibri revealed the 0x837 key. At first, its purpose wasn't known. After a while, geohot discovered its purpose.

In order to decrypt them, all you need to do is remove the 0x800 byte (2 kibibytes) header, then open a console and run openssl(1)^[man]:

openssl enc -d -in ramdisk.dmg -out ramdisk.decrypted.dmg -aes-128-cbc -K 188458A6D15034DFE386F23B61D43774 -iv 0

where ramdisk.dmg is the file name of the ramdisk you are decrypting (ex: the iPhone 2G 1.1.1 firmware (3A109a) would be either 022-3630-9.dmg or 022-3629-9.dmg)

where ramdisk.decrypted.dmg is the output file name

2.x+

The ramdisks on 2.x and up firmwares is a simple IMG3 file that you can decrypt using img3decrypt[1] or xpwntool[2]. You must download one of these utilities. For easier access, put them in /usr/local/bin on Unix-based and Linux-based machines or wherever on Windows. If you use Windows, you must use the cd command to navigate to the XPwn directory.

If you're using img3decrypt, run this:

img3decrypt e restore_ramdisk.dmg restore_ramdisk_decrypted.dmg "Ramdisk_IV" "Ramdisk_Key"

If you're using xpwntool, run this:

xpwntool restore_ramdisk.dmg restore_ramdisk_decrypted.dmg -k "Ramdisk_Key" -iv "Ramdisk_IV"

Where restore_ramdisk.dmg is image of restore ramdisk and restore_ramdisk_decrypted.dmg is decrypted image, that you can mount and explore from Finder. "Ramdisk_IV" and "Ramdisk_Key" is the decryption keys that you can find at the VFDecrypt Keys page or in the Info.plist from PwnageTool FirmwareBundles folder.

Because of the new HFS Compression used in Snow Leopard and 3.0 DMGs, you may see zero-sized files in the DMG if you don't use Snow Leopard. In order to extract those, check Talk:Decrypting Firmwares.

3.0GM+

S5L8900

To decrypt a firmware file, decrypt the encrypted key and IV in the KBAG using GIDecrypt, or OpenSSL with the key 5F650295E1FFFC97CE77ABD49DD955B3 and the iv 0

S5L8720

Business as usual, but keys and IVs have to be decrypted on the device still, unlike with the new S5L8900 KBAGs. Apple incorrectly assumed that by encrypting iBEC and iBSS they were being sly. They were not. You can decrypt those on a 2.2.1 aes setup no problem whatsoever.

S5L8920

The iPhone 3GS firmware files are interesting. They have two KBAGs, which use AES-256 instead of the S5L8900 and S5L8720 that are using AES-128 still. The first KBAG has an identifier in it's header indicating that it is to be decrypted with the gid key, and the second is not known. For those that don't know how AES256 works, this now means that the first 0x10 bytes are the IV, and the remaining 0x20 bytes (not 0x10 anymore!) are the key.