It turns out this was the perfect convergence for the synergy needed to allow Apple to move forward with TouchID. Apple has customized a highly optimized version of TrustZone and created what is now known Secure Enclave. - Quora

Impressive technology deserved a decent explanation. It’s amazing how Apple once again turned something complex as finger print authentication into an almost hidden technology.

Its comparable to details like the breathing status led on a sleeping MacBook Pro, and it’s that attention to detail that Apple lost with Forstall and apparently rediscovered with Ive and Federighi.

Federighi is quick to admit that any engineer tasked with such a challenge would be sure to call attention to his brilliant work. "You know, you're going to have some big message saying 'Scanning!' and buzz-buzz-zzz-zzz later it says 'Authenticated,' blink-blink-blink, with 10 seconds of animation," he says, as Ive starts laughing. "Ultimately we realized all that had to disappear," says Federighi. "If it disappears, we know we've done it." - USA Today