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1try {
2    KeyStore keyStore = KeyStore.getInstance("AndroidKeyStore");
3    keyStore.load(null);
4
5    SecretKey secretKey = 
6        (SecretKey) keyStore.getKey(SecurityConstants.KEY_AES, null);
7    Cipher cipher = Cipher.getInstance("AES/CBC/PKCS7Padding");
8
9    // The next line may throw a UserNotAuthenticatedException and
10    // we need to prompt the user to authenticate again
11    cipher.init(Cipher.DECRYPT_MODE, secretKey, new IvParameterSpec(iv));
12    byte[] decryptedBytes = cipher.doFinal(cipherBytes);
13
14} catch (UserNotAuthenticatedException e) {
15    // User is not authenticated, let's authenticate with
16    // device credentials!
17    showAuthenticationScreen();
18    return;
19} catch { … }