Touch ID and the Secure Enclave ⇥ securosis.com

Instead of speculative bullshit, you may enjoy facts and research from Rich Mogull:

Apple may have some dedicated resources embedded in the A7 for handling Touch ID and passcodes, which would be consistent with their statements and diagrams. Secure operations probably still run on the main A7 processor, in restricted Secure mode so regular user processes (apps) cannot access the Secure Enclave. That is how TrustZone handles secure and non-secure functions sharing the same hardware.