Device Password fallback when Touch-ID devices are unavailable

[findus]

Device Password fallback when Touch-ID devices are unavailable

I often use my macbook docked with the lid closed, so I cannot use the fingerprint sensor, and I got rather tired reentering my whole database password every time after unlocking my session.

This change adds the "kSecAccessControlDevicePasscode" flag to the AccessControlFlags, so it is possible to use the device password to unlock the database again.

This feature is disabled by default and can be enabled in the settings menu.

• Fixes Hide option for TouchID when the TouchID scanner/button isn't accessible #8105

Screenshots

poc.mov

• Touch-ID Hardware present, database locked
• Unlock DB with Touch-ID sensor
• Lid gets closed(no hardware available anymore)
• Lock DB again
• Password fallback kicks in after pressing unlock again

Type of change

• ✅ New feature (change that adds functionality)

[droidmonkey]

Oh neat, didn't even know that was an option. I don't think we need a special setting to toggle it though. Recommend removing that part and just making this part of the default security control options.

[findus]

@droidmonkey ok then I'll remove the settings menu entry again.

Having this default fallback, that is available all the time, we could also get rid of the isWatchIDAvailable/isTouchIdAvailable checks altogether.

Doing this TouchID/WatchID unlock would always be possbile, even when you open the database for the first time with no biometric/apple watch hardware present and open the lid later.

[findus]

Oh, its probably saver to keep all checks in place and add another one with https://developer.apple.com/documentation/localauthentication/klapolicydeviceownerauthentication, I'll do that later this day

[findus]

It was not as easy as I thought, the kSecAccessControlBiometryCurrentSet flag is only allowed when TouchID is enrolled, adding the flag while its not enrolled results in an error when trying to save the secret to the keychain.

But it is possible to catch the specific "is not enrolled" error, and only skip adding the flag when this one occurs.

The kSecAccessControlWatch seems to not have this constraint, but I need to test it a little more, same as my current implementation for TouchID.

[findus]

I tested i a little more and it seems to be pretty reliable, the only dangerous path is trying to save the key to the enclave with kSecAccessControlBiometryCurrentSet or kSecAccessControlTouchIDCurrentSet as the saving logic is throwing an error when having no fingers scanned, but that path is covered with the new touchidEnrolled check.

With this new logic it is now possible to:

• Use TouchID in this constellations:
  • Docked Laptop, Lid Closed, no Magic Keyboard with TouchID paired -> Open Database -> Lock DB -> Open Lid -> TouchID available
  • Use WatchID Unlock even if TouchID is disabled
  • Use Password unlock exclusively when no other biometric or companion hardware is present
  • Use WatchID all the time even when pairing/unlocking the watch after unlocking Keepass for the first time

But I dont have an iMac or Mac Mini to test what happens on devices with no integrated TouchID, I tested this constellation in a qemu vm and this case also got handled by the kLAErrorBiometryNotEnrolled error, but I would feel saver if it could get tested with actual imac/mac mini hardware once.

I also could get my hands on a magic keyboard on monday to test that aswell at least once.

[droidmonkey]

Awesome thank you @findus, this will greatly improve usability of quick unlock. Also helps when I finish implementing "remembered" quick unlock.

[findus]

I've set up a Hackintosh yesterday to check what happens on devices with no TouchID present at all, there the "isEnrolled" check does not work because the API returns LAErrorBiometryNotAvailable, which kinda sucks because now this error is used for two states:

• No Hardware present at all (Setkey fails all the time when the TouchID Flag is used)
• Hardware not present because lid closed/magickeyboard unpaired (SetKey only fails when no fingers enrolled)

To "fix" this I just call setKey a second time without the TouchID/Biometrics flag when the first call fails, that makes it a little more robust.