unique ID (UID)

A 256-bit AES key that’s burned into each processor at manufacture. It can’t be read by firmware or software, and it’s used only by the processor’s hardware AES Engine. To obtain the actual key, an attacker would have to mount a highly sophisticated and expensive physical attack against the processor’s silicon. The UID isn’t related to any other identifier on the device including, but not limited to, the UDID.