Decrypting Firmwares

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

Ramdisks
This section details the decryption of the ramdisks in an IPSW file. The listed console commands are applicable to the IMG2 or IMG3 files under  also.

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 if=ramdisk.dmg of=ramdisk.stripped.dmg bs=512 skip=4 count=37464 conv=sync
 * where ramdisk.dmg is the filename of the restore ramdisk (ex: the iPhone 2G 1.0 firmware (1A543a) would be )
 * 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 - 2.0b3
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  byte (2 kibibytes) header, then open a console and run  []: openssl enc -d -in ramdisk.dmg -out ramdisk.decrypted.dmg -aes-128-cbc -K 188458a6d15034dfe386f23b61d43774 -iv 0
 * where ramdisk.dmg is the filename of the ramdisk you are decrypting (ex: the iPhone 2G 1.1.1 firmware (3A109a) would be either  or  )
 * where ramdisk.decrypted.dmg is the output file name

2.0b4 - 3.0b5
With the fourth beta of 2.0, Apple introduced the IMG3 file format, replacing the broken IMG2 file format. This format was soon reversed and img3decrypt [src] was created by Steven Smith (@stroughtonsmith). His code was later implemented into xpwntool [src]. In order to decrypt the ramdisk, open a console and run one of the commands depending on your program choice: img3decrypt e ramdisk.dmg ramdisk.decrypted.dmg iv key xpwntool ramdisk.dmg ramdisk.decrypted.dmg -k key -iv iv
 * where ramdisk.dmg is the filename of the ramdisk you are decrypting (ex: the iPhone 3G 2.0 firmware (5A347) would be )
 * where ramdisk.decrypted.dmg is the output file name
 * where iv is the initialization vector (IV) of the ramdisk you are decrypting (ex: the iPhone 3G 2.0 firmware (5A347) would be )
 * where key is the key of the ramdisk you are decrypting (ex: the iPhone 3G 2.0 firmware (5A347) would be )

The IV and key for a specified firmware is available through the Firmware Keys page or from the  file underneath PwnageTool's   folder.

3.0GM+
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.

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.