5 ms·

What happens when an untrusted person that uses your PIN on a regular basis for legitimate reasons becomes untrusted? Now you need to reset your PIN and retrain

What happens when an untrusted person that uses your PIN on a regular basis for legitimate reasons becomes untrusted? Now you need to reset your PIN and retrain FaceID? I hope IOS gives a warning when changing the PIN that if you think FaceID has been compromised to retrain FaceID. edit: because the idea that FaceID could be compromised like this is non-obvious

skywhopper 9y ago
Sounds like it will only happen if the faces are similar. So if the threshold for matching is 95% match to the internal model, but the faces are 90% similar, and then the new face enters the correct PIN, then the new face will be used to tweak the model, which will move the error to inbetween the features of both. So if their faces are similar to within twice the margin-of-error of the detection algorithm, then you can probably get this effect. All that said "an untrusted person that uses your PIN" knows your PIN... so they are a trusted person as far as the OS is concerned. There's nothing you can do with FaceID/TouchID that you can't do with the PIN. All FaceID/TouchID do is decrypt the PIN from the secure enclave. So if you've shared your PIN with them, then this is a weird thing, but not actually a security violation.
- dTal 9y ago
  The difference is that it's easy to change a PIN, but hard to retrain FaceID. So sharing a PIN is reasonable in the knowledge that it can be changed, but you might not be aware that it has more ramifications under opaque and unclear circumstances.
  - zwily 9y ago
    Retraining FaceID takes about 20 seconds. How is that hard?
    - ProblemFactory 9y ago
      The hardest part might be noticing in the first place that your FaceID model has drifted away from only your face.
      - ricardobeat 9y ago
        I assume changing the PIN forces a FaceID reset?
      - dpkonofa 9y ago
        That's the thing, though... it would only drift from your face if the face it was drifting too looked similarly enough to your own.

skywhopper 9y ago

Sounds like it will only happen if the faces are similar. So if the threshold for matching is 95% match to the internal model, but the faces are 90% similar, and then the new face enters the correct PIN, then the new face will be used to tweak the model, which will move the error to inbetween the features of both. So if their faces are similar to within twice the margin-of-error of the detection algorithm, then you can probably get this effect. All that said "an untrusted person that uses your PIN" knows your PIN... so they are a trusted person as far as the OS is concerned. There's nothing you can do with FaceID/TouchID that you can't do with the PIN. All FaceID/TouchID do is decrypt the PIN from the secure enclave. So if you've shared your PIN with them, then this is a weird thing, but not actually a security violation.

dTal 9y ago
The difference is that it's easy to change a PIN, but hard to retrain FaceID. So sharing a PIN is reasonable in the knowledge that it can be changed, but you might not be aware that it has more ramifications under opaque and unclear circumstances.
- zwily 9y ago
  Retraining FaceID takes about 20 seconds. How is that hard?
  - ProblemFactory 9y ago
    The hardest part might be noticing in the first place that your FaceID model has drifted away from only your face.
    - ricardobeat 9y ago
      I assume changing the PIN forces a FaceID reset?
    - dpkonofa 9y ago
      That's the thing, though... it would only drift from your face if the face it was drifting too looked similarly enough to your own.