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No one can tell at a glance how similar two people's fingerprints might be, so finding a collision by accident is very hard. Finding similar-looking faces from

No one can tell at a glance how similar two people's fingerprints might be, so finding a collision by accident is very hard. Finding similar-looking faces from a pool of candidates is, in contrast, very easy for humans. It would probably be even easier to find matches if we knew the precise heuristics Apple employs for ignoring glasses, headwear, facial hair, and so on; to be at all practical the feature must have generous degrees of freedom, which in turn reduce discrimination. Finally, as many have observed, there are plenty of situations where humans will be in close physical and social proximity to others with similar faces: twins, siblings, etc. Even if collisions are as infrequent as Apple claims (which I find dubious), face identification is fundamentally a lock that is easier to "pick" than fingerprints. I am forced to conclude that depending on facial recognition is a poor engineering decision motivated by user convenience whose limitations are deliberately mischaracterized by marketing materials.

mikeash 9y ago
The main use case for a phone passcode is keeping your stuff secure in the event that it’s lost or stolen randomly. Both technologies are fairly secure against run-of-the-mill thieves. They’re good enough that the market for stolen phones is probably reduced to breaking them down and selling them for spare parts. If you happen to fall victim to a more sophisticated criminal, Touch ID is going to be way worse. Your phone is covered with the fingerprints needed to unlock it. It will take some sophistication to turn a print into something that can unlock the phone, but it’s doable. There’s no equivalent for Face ID. Most likely the criminal doesn’t know what you look like at all, so they could try five random people and then get locked out with a probability of success of roughly 1 in 200,000. If they know who you are they could try to look you up and find similar looking people, but that’s going to take time and effort and you have to get it done within 48 hours, and the odds of success are still not great. (If it was easy to reliably unlock the phone with a similar-looking person, we would have heard a hundred stories like this by now.) It’s far from perfect but I have no qualms trusting my security to it. It’s better than Touch ID and far better than the 0000 passcode I used before that.

mikeash 9y ago

The main use case for a phone passcode is keeping your stuff secure in the event that it’s lost or stolen randomly. Both technologies are fairly secure against run-of-the-mill thieves. They’re good enough that the market for stolen phones is probably reduced to breaking them down and selling them for spare parts. If you happen to fall victim to a more sophisticated criminal, Touch ID is going to be way worse. Your phone is covered with the fingerprints needed to unlock it. It will take some sophistication to turn a print into something that can unlock the phone, but it’s doable. There’s no equivalent for Face ID. Most likely the criminal doesn’t know what you look like at all, so they could try five random people and then get locked out with a probability of success of roughly 1 in 200,000. If they know who you are they could try to look you up and find similar looking people, but that’s going to take time and effort and you have to get it done within 48 hours, and the odds of success are still not great. (If it was easy to reliably unlock the phone with a similar-looking person, we would have heard a hundred stories like this by now.) It’s far from perfect but I have no qualms trusting my security to it. It’s better than Touch ID and far better than the 0000 passcode I used before that.