The long-lived secret for TouchID is generated in the SEP, using the UID of the SoC (a secret known only to the SoC) and the serial number of the respective sen

The long-lived secret for TouchID is generated in the SEP, using the UID of the SoC (a secret known only to the SoC) and the serial number of the respective sensor. That key is then keywrapped with a (symmetric) key known to all TouchID sensors and sent to the fingerprint sensor. It unwraps and verifies the key and burns it into fuses. That key is then used for establishing a session key in the field. The session key uses entropy from both the SEP TRNG and the TouchID TRNG. So an 'evil' Apple couldn't crack the session key unless it had been evil all along and storing the generated keywrapped blobs. In which case you're sorta screwed no matter which way you slice it.