By comparison, Touch ID can store up to five fingerprints, and each of those fingerprints can belong to a different person. This allows a married couple, for example, to be able to securely authenticate a single iPhone.
In an email to a customer, however, Federighi appears to admit that Touch ID's multi-finger support has always been intended for a single iPhone owner to authenticate with a finger or thumb on both the left and right hand if desired.
Federighi added that Face ID could eventually authenticate multiple faces as the system evolves in the future, but his email makes it clear that Apple doesn't have any immediate plans to implement said functionality.
The user who shared this email on Reddit has a good reputation and history on the website, so we're inclined to believe it is authentic. However, we are still waiting to receive full headers of the email to verify its origins.
Apple says Face ID has a one in 1,000,000 chance of being spoofed, compared to one in 50,000 for Touch ID, although the probability of a false match is higher among identical twins, siblings who look alike, and children.
Vietnamese security firm Bkav has also been able to spoof Face ID twice with 3D printed masks, but the steps involved are quite complex and this isn't something the average user should be very concerned about.
In practical, real-world usage, Face ID has proved to be very secure and reliable. But, at least for now, it appears that iPhone X owners won't be able to extend this convenience to their trusted family members or friends.
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