Extract the AES-256-GCM Android Keystore plumbing that `KeystoreCrypto` and
`DatabaseKeyCipher` copy-pasted (~60 lines) into a shared alias-parameterized
base, `AesGcmKeystoreCipher`: the encrypt/decrypt bodies, existing-key lookup /
get-or-create under a lock, key deletion, and the 5 identical GCM constants now
live in ONE place. Each cipher keeps only its delta — the `KeyGenParameterSpec`
(via `keySpecBuilder()`) and, for the auth-bound key, the invalidation handling.
Preserve — deliberately — the two ciphers' different missing-key-on-decrypt
behavior via a `generateKeyOnDecrypt` policy parameter, documented on the base:
- master key (`KeystoreCrypto`, true): auto-generates on a missing alias, correct
for a first-run key with nothing sealed yet.
- auth-bound cache key (`DatabaseKeyCipher`, false): fails fast, because a missing
auth-bound key means it was INVALIDATED and silently regenerating it would
re-arm the lock against a cache that can no longer be decrypted.
Also map the opaque `AEADBadTagException` (thrown when the master path generates a
fresh key then can't decrypt old data) to a clear `GeneralSecurityException`,
while leaving `KeyPermanentlyInvalidatedException` to propagate unwrapped.
Unify the accepted-authenticator policy behind one source of truth,
`AuthenticatorPolicy.ACCEPTED`, mapped into each API's vocabulary
(`AppLockManager.AUTHENTICATORS` for BiometricManager / BiometricPrompt,
`DatabaseKeyCipher.keySpec` for KeyProperties / KeyGenParameterSpec) so the two
can no longer drift — a drift that yields a prompt that succeeds but a key that
throws `UserNotAuthenticatedException` at use.
Add JVM tests for the shared base (both `generateKeyOnDecrypt` modes + the AES-GCM
error mapping) and for the authenticator mapping. #100's seal-exchange and
policy-table safety net stays green.
Closes#102
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
JMR-devandClaude Fable 5