GenPass

GenPass generates the VFDecrypt keys for the filesystem image of an iDevice. It requires either a decrypted restore or update ramdisk.

Note: in the firmwares, the decryption happens in /usr/sbin/asr, which can be found on the ramdisk.

NOTE: I've experienced that running genpass after you've mounted the decrypted ramdisk causes genpass to give a false key.

GenPass Usage
./genpass Platform is the applications processor (i.e.- S5L8900x, S5L8720x, S5L8920x, S5L8922x, S5L8930x)

Source
http://github.com/posixninja/genpass