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When I first experienced this I ignored it. But after some days I noticed that I had to unlock it by pattern lock or password everytime I restart the phone and after unlocking by pattern/password, I was able to use fingerprint.

Why is this so? I am not sure that every Android device has the same issue. Is this a security feature? If yes, why? I mean if this is a security feature the phone must be unlocked by fingerprint, as pattern or password can be guessed after some attempts (especially patterns).

There are some threads (see this and this), but they doesn't seem to be very informative.

daya
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  • To my knowledge, all androids have this restriction. I've heard its not only to decrypt the biometric data, but its so if it gets taken off you and turned on, they can't force it out of you without the password/pin that you know. I've also heard that in the US police officers can force your finger against the reader but if theres a password then its protected by the 5th amendment. I cannot personally say this is the case, only that I have _read it_ online (https://www.reddit.com/r/technology/comments/9tiyiv/passcodes_are_protected_by_fifth_amendment_says/e8wp5ra/) – QuickishFM Dec 27 '19 at 22:43
  • Whether or not protection from being compelled to use biometrics (or passwords) to access a device is a 5th amendment right is still up for debate, IIRC. With the current US Supreme Court it's likely to not be considered protected when a case finally gets before them. – Monica Apologists Get Out Jan 06 '20 at 14:58

2 Answers2

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There is a secure enclave that stores your biometric data. It has to be given your passcode in order to decrypt your biometric data on reboot.

Monica Apologists Get Out
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You have the exact same feature on an iPhone - which is a good indication that it is not some Android limitation but absolutely intentional.

And it is intentional. It means that if someone somehow manages to add their fingerprint to your phone, they will be locked out after some time. Same in case of the one-in-thousands chance that a thief's fingers match your fingerprint. At some point they will lose access without the passcode.

I don't know the exact Android rules. An iPhone requires the passcode after a reboot, after a certain number of failed attempts to unlock with finger print, and after a certain number of days without unlocking by passcode.

gnasher729
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