Apple's Face ID is a make-or-break feature for the upcoming iPhone X. It completely replaces Touch ID and should be more accurate and tougher to crack, but up until now we did not know the details of how Face ID works.
Today, Apple has published a six-page whitepaper that explains the ins and outs of Face ID. The tech paper is published on Apple's new privacy and security portal, and the first thing it does is confirm that your face data is only stored on the device and not in the cloud. The Face ID system will read your face and save a partial data for your face that even if somehow extracted from the iPhone X, will not be sufficient for a full face reconstruction of that person.
But what is more curious is the way Face ID stays relevant over time and updates its face models.
And as to all of those concerns that Face ID might be used by others to unlock your phone against your will? Well, the paper says you need to open your eyes and look directly in the phone, but Face ID is so quick that even a glance might be sufficient, so there really are no guarantees. As a safety measure, you can click the side buttons to put the phone in shutdown mode, which disables Face ID.
And this is important also when you use Apple Pay. You will not send a payment by simply looking at your phone, but you will also need to double click the power key before you use the phone at a terminal.
You can read the full paper with all the details right below.
source: Apple Face ID White Paper (PDF)