The following excerpt if from iPod hacking Wiki:
the key to the root filesystem of 1.1.1 is:
d45b837ddd85bdae0ec82a033ba00ea03ceb8c827040034f7554c65d6376472844b8dc6a
And should be used as the following:
vfdecrypt -i 022-3642-8.dmg -o decrypted.dmg -k d45b837ddd85bdae0ec82a033ba00ea03ceb8c827040034f7554c65d6376472844b8dc6a