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Comment by eridius | Hacker News Reader

> The probability of a false match is different for twins and siblings that look like you as well as among children under the age of 13, because their Face ID Security September 2017 2 distinct facial features may not have fully developed. If you're concerned about this, we recommend using a passcode to authenticate.

I was really hoping they'd provide the probability for identical twins, but maybe they don't have enough data to give a specific number on this (I assume most of their data comes from people without identical twins).

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I believe the probability for identical twins is 1 in 1; they mentioned in the keynote that some people will have to stick with passcodes, including those with "evil twins". (Presumably if you trust your identical twin to not be evil, you don't care if they're able to unlock your phone.)

Identical twins aren't identical down to every last detail. What I'm curious about is if Face ID can pick up on any details that are different that humans wouldn't notice.

Also regarding the "evil twin" thing, evil twins came from another dimension so, aside from the goatee, they really were literally identical down to every last detail. It's unclear to me if that joke was meant as "your identical twin will be able to unlock your phone, so hopefully they aren't evil", or was just meant as "someone who looks like you might be able to unlock your phone". Probably a bit of both. But this is why I want to know what the actual probability is that an identical twin can unlock the phone. Maybe it really is 1 : 1, but maybe it's not.

Assuming the hardware isn't being pushed to the accuracy limit for the sake of processing time, perhaps there could be an "enhanced security" mode that requires a more thorough check? I suspect their 1:1,000,000 false-positive number is an extrapolation of the maximum allowable difference in measurement. They probably could have set that "fudge factor" to a value that corresponds to something like 1:1,000,000,000 and increased false negatives to 50%.

Maybe it needs to see more "liveliness" and a few degrees head rotation?

Overall I think with the alertness test, the 48-hour passcode lockout, the "press the lock button 5 times" panic mode, and a limit on all attempts is enough to discourage most three letter agencies. It seems to have been enough with TouchID.

I understood “evil twin” as “twin who happens to be evil”. The example they showed was Spock’s evil twin which would match your interpretation, though.

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