Opening the vault threw java.lang.SecurityException: USE_BIOMETRIC is not in
Delphi default permission list, and CanAuthenticate raises instead of
answering false. So the fault showed up neither at compile time nor at
startup, but on the first unlock - after the cache had already been written
under an auth-protected key.
The permission is the shallow half. The deep half is that SaveVault was
called with a hard-coded True: we asked for a key guarded by a prompt that
could not be shown, producing a file that was unreadable forever. It now
receives BiometricAvailable, evaluated on the main thread before the worker
starts.
BiometricAvailable and AuthenticateThen also swallow what comes up from the
Java layer and map it to boUnavailable. The caller has a path for every
TBioOutcome and none for an exception.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
The Keystore key now requires authentication, valid for 30 s afterwards - short enough that an unattended phone is not exploitable, long enough to decrypt and display. Time-bound rather than a per-use CryptoObject: BiometricPrompt's callback would need a Java class compiled into a jar, while FMX already bridges it.
Two aliases, because the auth constraint is fixed when the key is created and cannot be added later. The file header records which key wrote it, so a read knows whether to authenticate first.
A device with neither fingerprint nor lock screen cannot hold such a key, so SaveVault falls back to the plain key rather than giving up the cache. And a failed authentication no longer wipes the cache: the vault is intact, it is the user who cancelled - erasing it would cost a download and 4 s of derivation for a dismissed prompt.
r-zakarya