content: /*
   * Copyright (C) 2017 The Android Open Source Project
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package android.security.keystore.recovery;
  
  import android.annotation.NonNull;
  import android.annotation.Nullable;
  import android.annotation.RequiresPermission;
  import android.annotation.SystemApi;
  import android.app.KeyguardManager;
  import android.app.PendingIntent;
  import android.content.Context;
  import android.os.RemoteException;
  import android.os.ServiceManager;
  import android.os.ServiceSpecificException;
  import android.security.KeyStore;
  import android.security.keystore.AndroidKeyStoreProvider;
  import android.security.keystore.KeyPermanentlyInvalidatedException;
  
  import com.android.internal.widget.ILockSettings;
  
  import java.security.Key;
  import java.security.UnrecoverableKeyException;
  import java.security.cert.CertPath;
  import java.security.cert.CertificateException;
  import java.security.cert.X509Certificate;
  import java.util.ArrayList;
  import java.util.List;
  import java.util.Map;
  
  /**
   * Backs up cryptographic keys to remote secure hardware, encrypted with the user's lock screen.
   *
   * <p>A system app with the {@code android.permission.RECOVER_KEYSTORE} permission may generate or
   * import recoverable keys using this class. To generate a key, the app must call
   * {@link #generateKey(String)} with the desired alias for the key. This returns an AndroidKeyStore
   * reference to a 256-bit {@link javax.crypto.SecretKey}, which can be used for AES/GCM/NoPadding.
   * In order to get the same key again at a later time, the app can call {@link #getKey(String)} with
   * the same alias. If a key is generated in this way the key's raw material is never directly
   * exposed to the calling app. The system app may also import key material using
   * {@link #importKey(String, byte[])}. The app may only generate and import keys for its own
   * {@code uid}.
   *
   * <p>The same system app must also register a Recovery Agent to manage syncing recoverable keys to
   * remote secure hardware. The Recovery Agent is a service that registers itself with the controller
   * as follows:
   *
   * <ul>
   *     <li>Invokes {@link #initRecoveryService(String, byte[], byte[])}
   *     <ul>
   *         <li>The first argument is the alias of the root certificate used to verify trusted
   *         hardware modules. Each trusted hardware module must have a public key signed with this
   *         root of trust. Roots of trust must be shipped with the framework. The app can list all
   *         valid roots of trust by calling {@link #getRootCertificates()}.
   *         <li>The second argument is the UTF-8 bytes of the XML listing file. It lists the X509
   *         certificates containing the public keys of all available remote trusted hardware modules.
   *         Each of the X509 certificates can be validated against the chosen root of trust.
   *         <li>The third argument is the UTF-8 bytes of the XML signing file. The file contains a
   *         signature of the XML listing file. The signature can be validated against the chosen root
   *         of trust.
   *     </ul>
   *     <p>This will cause the controller to choose a random public key from the list. From then
   *     on the controller will attempt to sync the key chain with the trusted hardware module to whom
   *     that key belongs.
   *     <li>Invokes {@link #setServerParams(byte[])} with a byte string that identifies the device
   *     to a remote server. This server may act as the front-end to the trusted hardware modules. It
   *     is up to the Recovery Agent to decide how best to identify devices, but this could be, e.g.,
   *     based on the <a href="https://developers.google.com/instance-id/">Instance ID</a> of the
   *     system app.
   *     <li>Invokes {@link #setRecoverySecretTypes(int[])} with a list of types of secret used to
   *     secure the recoverable key chain. For now only
   *     {@link KeyChainProtectionParams#TYPE_LOCKSCREEN} is supported.
   *     <li>Invokes {@link #setSnapshotCreatedPendingIntent(PendingIntent)} with a
   *     {@link PendingIntent} that is to be invoked whenever a new snapshot is created. Although the
   *     controller can create snapshots without the Recovery Agent registering this intent, it is a
   *     good idea to register the intent so that the Recovery Agent is able to sync this snapshot to
   *     the trusted hardware module as soon as it is available.
   * </ul>
   *
   * <p>The trusted hardware module's public key MUST be generated on secure hardware with protections
   * equivalent to those described in the
   * <a href="https://developer.android.com/preview/features/security/ckv-whitepaper.html">Google
   * Cloud Key Vault Service whitepaper</a>. The trusted hardware module itself must protect the key
   * chain from brute-forcing using the methods also described in the whitepaper: i.e., it should
   * limit the number of allowed attempts to enter the lock screen. If the number of attempts is
   * exceeded the key material must no longer be recoverable.
   *
   * <p>A recoverable key chain snapshot is considered pending if any of the following conditions
   * are met:
   *
   * <ul>
   *     <li>The system app mutates the key chain. i.e., generates, imports, or removes a key.
   *     <li>The user changes their lock screen.
   * </ul>
   *
   * <p>Whenever the user unlocks their device, if a snapshot is pending, the Recovery Controller
   * generates a new snapshot. It follows these steps to do so:
   *
   * <ul>
   *     <li>Generates a 256-bit AES key using {@link java.security.SecureRandom}. This is the
   *     Recovery Key.
   *     <li>Wraps the key material of all keys in the recoverable key chain with the Recovery Key.
   *     <li>Encrypts the Recovery Key with both the public key of the trusted hardware module and a
   *     symmetric key derived from the user's lock screen.
   * </ul>
   *
   * <p>The controller then writes this snapshot to disk, and uses the {@link PendingIntent} that was
   * set by the Recovery Agent during initialization to inform it that a new snapshot is available.
   * The snapshot only contains keys for that Recovery Agent's {@code uid} - i.e., keys the agent's
   * app itself generated. If multiple Recovery Agents exist on the device, each will be notified of
   * their new snapshots, and each snapshots' keys will be only those belonging to the same
   * {@code uid}.
   *
   * <p>The Recovery Agent retrieves its most recent snapshot by calling
   * {@link #getKeyChainSnapshot()}. It syncs the snapshot to the remote server. The snapshot contains
   * the public key used for encryption, which the server uses to forward the encrypted recovery key
   * to the correct trusted hardware module. The snapshot also contains the server params, which are
   * used to identify this device to the server.
   *
   * <p>The client uses the server params to identify a device whose key chain it wishes to restore.
   * This may be on a different device to the device that originally synced the key chain. The client
   * sends the server params identifying the previous device to the server. The server returns the
   * X509 certificate identifying the trusted hardware module in which the encrypted Recovery Key is
   * stored. It also returns some vault parameters identifying that particular Recovery Key to the
   * trusted hardware module. And it also returns a vault challenge, which is used as part of the
   * vault opening protocol to ensure the recovery claim is fresh. See the whitepaper for more
   * details.
   *
   * <p>The key chain is recovered via a {@link RecoverySession}. A Recovery Agent creates one by
   * invoking {@link #createRecoverySession()}. It then invokes
   * {@link RecoverySession#start(String, CertPath, byte[], byte[], List)} with these arguments:
   *
   * <ul>
   *     <li>The alias of the root of trust used to verify the trusted hardware module.
   *     <li>The X509 certificate of the trusted hardware module.
   *     <li>The vault parameters used to identify the Recovery Key to the trusted hardware module.
   *     <li>The vault challenge, as issued by the trusted hardware module.
   *     <li>A list of secrets, corresponding to the secrets used to protect the key chain. At the
   *     moment this is a single {@link KeyChainProtectionParams} containing the lock screen of the
   *     device whose key chain is to be recovered.
   * </ul>
   *
   * <p>This method returns a byte array containing the Recovery Claim, which can be issued to the
   * remote trusted hardware module. It is encrypted with the trusted hardware module's public key
   * (which has itself been certified with the root of trust). It also contains an ephemeral symmetric
   * key generated for this recovery session, which the remote trusted hardware module uses to encrypt
   * its responses. This is the Session Key.
   *
   * <p>If the lock screen provided is correct, the remote trusted hardware module decrypts one of the
   * layers of lock-screen encryption from the Recovery Key. It then returns this key, encrypted with
   * the Session Key to the Recovery Agent. As the Recovery Agent does not know the Session Key, it
   * must then invoke {@link RecoverySession#recoverKeyChainSnapshot(byte[], List)} with the encrypted
   * Recovery Key and the list of wrapped application keys. The controller then decrypts the layer of
   * encryption provided by the Session Key, and uses the lock screen to decrypt the final layer of
   * encryption. It then uses the Recovery Key to decrypt all of the wrapped application keys, and
   * imports them into its own KeyStore. The Recovery Agent's app may then access these keys by
   * calling {@link #getKey(String)}. Only this app's {@code uid} may access the keys that have been
   * recovered.
   *
   * @hide
   */
  @SystemApi
  public class RecoveryController {
      private static final String TAG = "RecoveryController";
  
      /** Key has been successfully synced. */
      public static final int RECOVERY_STATUS_SYNCED = 0;
      /** Waiting for recovery agent to sync the key. */
      public static final int RECOVERY_STATUS_SYNC_IN_PROGRESS = 1;
      /** Key cannot be synced. */
      public static final int RECOVERY_STATUS_PERMANENT_FAILURE = 3;
  
      /**
       * Failed because no snapshot is yet pending to be synced for the user.
       *
       * @hide
       */
      public static final int ERROR_NO_SNAPSHOT_PENDING = 21;
  
      /**
       * Failed due to an error internal to the recovery service. This is unexpected and indicates
       * either a problem with the logic in the service, or a problem with a dependency of the
       * service (such as AndroidKeyStore).
       *
       * @hide
       */
      public static final int ERROR_SERVICE_INTERNAL_ERROR = 22;
  
      /**
       * Failed because the user does not have a lock screen set.
       *
       * @hide
       */
      public static final int ERROR_INSECURE_USER = 23;
  
      /**
       * Error thrown when attempting to use a recovery session that has since been closed.
       *
       * @hide
       */
      public static final int ERROR_SESSION_EXPIRED = 24;
  
      /**
       * Failed because the format of the provided certificate is incorrect, e.g., cannot be decoded
       * properly or misses necessary fields.
       *
       * <p>Note that this is different from {@link #ERROR_INVALID_CERTIFICATE}, which implies the
       * certificate has a correct format but cannot be validated.
       *
       * @hide
       */
      public static final int ERROR_BAD_CERTIFICATE_FORMAT = 25;
  
      /**
       * Error thrown if decryption failed. This might be because the tag is wrong, the key is wrong,
       * the data has become corrupted, the data has been tampered with, etc.
       *
       * @hide
       */
      public static final int ERROR_DECRYPTION_FAILED = 26;
  
      /**
       * Error thrown if the format of a given key is invalid. This might be because the key has a
       * wrong length, invalid content, etc.
       *
       * @hide
       */
      public static final int ERROR_INVALID_KEY_FORMAT = 27;
  
      /**
       * Failed because the provided certificate cannot be validated, e.g., is expired or has invalid
       * signatures.
       *
       * <p>Note that this is different from {@link #ERROR_BAD_CERTIFICATE_FORMAT}, which denotes
       * incorrect certificate formats, e.g., due to wrong encoding or structure.
       *
       * @hide
       */
      public static final int ERROR_INVALID_CERTIFICATE = 28;
  
  
      /**
       * Failed because the provided certificate contained serial version which is lower that the
       * version device is already initialized with. It is not possible to downgrade serial version of
       * the provided certificate.
       *
       * @hide
       */
      public static final int ERROR_DOWNGRADE_CERTIFICATE = 29;
  
      private final ILockSettings mBinder;
      private final KeyStore mKeyStore;
  
      private RecoveryController(ILockSettings binder, KeyStore keystore) {
          mBinder = binder;
          mKeyStore = keystore;
      }
  
      /**
       * Internal method used by {@code RecoverySession}.
       *
       * @hide
       */
      ILockSettings getBinder() {
          return mBinder;
      }
  
      /**
       * Gets a new instance of the class.
       */
      @RequiresPermission(android.Manifest.permission.RECOVER_KEYSTORE)
      @NonNull public static RecoveryController getInstance(@NonNull Context context) {
          // lockSettings may be null.
          ILockSettings lockSettings =
                  ILockSettings.Stub.asInterface(ServiceManager.getService("lock_settings"));
          return new RecoveryController(lockSettings, KeyStore.getInstance());
      }
  
      /**
       * Checks whether the recoverable key store is currently available.
       *
       * <p>If it returns true, the device must currently be using a screen lock that is supported for
       * use with the recoverable key store, i.e. AOSP PIN, pattern or password.
       */
      @RequiresPermission(android.Manifest.permission.RECOVER_KEYSTORE)
      public static boolean isRecoverableKeyStoreEnabled(@NonNull Context context) {
          KeyguardManager keyguardManager = context.getSystemService(KeyguardManager.class);
          return keyguardManager != null && keyguardManager.isDeviceSecure();
      }
  
      /**
       * Initializes the recovery service for the calling application. The detailed steps should be:
       * <ol>
       *     <li>Parse {@code signatureFile} to get relevant information.
       *     <li>Validate the signer's X509 certificate, contained in {@code signatureFile}, against
       *         the root certificate pre-installed in the OS and chosen by {@code
       *         rootCertificateAlias}.
       *     <li>Verify the public-key signature, contained in {@code signatureFile}, and verify it
       *         against the entire {@code certificateFile}.
       *     <li>Parse {@code certificateFile} to get relevant information.
       *     <li>Check the serial number, contained in {@code certificateFile}, and skip the following
       *         steps if the serial number is not larger than the one previously stored.
       *     <li>Randomly choose a X509 certificate from the endpoint X509 certificates, contained in
       *         {@code certificateFile}, and validate it against the root certificate pre-installed
       *         in the OS and chosen by {@code rootCertificateAlias}.
       *     <li>Store the chosen X509 certificate and the serial in local database for later use.
       * </ol>
       *
       * @param rootCertificateAlias the alias of a root certificate pre-installed in the OS
       * @param certificateFile the binary content of the XML file containing a list of recovery
       *     service X509 certificates, and other metadata including the serial number
       * @param signatureFile the binary content of the XML file containing the public-key signature
       *     of the entire certificate file, and a signer's X509 certificate
       * @throws CertificateException if the given certificate files cannot be parsed or validated
       * @throws InternalRecoveryServiceException if an unexpected error occurred in the recovery
       *     service.
       */
      @RequiresPermission(android.Manifest.permission.RECOVER_KEYSTORE)
      public void initRecoveryService(
              @NonNull String rootCertificateAlias, @NonNull byte[] certificateFile,
              @NonNull byte[] signatureFile)
              throws CertificateException, InternalRecoveryServiceException {
          try {
              mBinder.initRecoveryServiceWithSigFile(
                      rootCertificateAlias, certificateFile, signatureFile);
          } catch (RemoteException e) {
              throw e.rethrowFromSystemServer();
          } catch (ServiceSpecificException e) {
              if (e.errorCode == ERROR_BAD_CERTIFICATE_FORMAT
                      || e.errorCode == ERROR_INVALID_CERTIFICATE) {
                  throw new CertificateException("Invalid certificate for recovery service", e);
              }
              if (e.errorCode == ERROR_DOWNGRADE_CERTIFICATE) {
                  throw new CertificateException(
                          "Downgrading certificate serial version isn't supported.", e);
              }
              throw wrapUnexpectedServiceSpecificException(e);
          }
      }
  
      /**
       * Returns data necessary to store all recoverable keys. Key material is
       * encrypted with user secret and recovery public key.
       *
       * @return Data necessary to recover keystore or {@code null} if snapshot is not available.
       * @throws InternalRecoveryServiceException if an unexpected error occurred in the recovery
       *     service.
       */
      @RequiresPermission(android.Manifest.permission.RECOVER_KEYSTORE)
      public @Nullable KeyChainSnapshot getKeyChainSnapshot()
              throws InternalRecoveryServiceException {
          try {
              return mBinder.getKeyChainSnapshot();
          } catch (RemoteException e) {
              throw e.rethrowFromSystemServer();
          } catch (ServiceSpecificException e) {
              if (e.errorCode == ERROR_NO_SNAPSHOT_PENDING) {
                  return null;
              }
              throw wrapUnexpectedServiceSpecificException(e);
          }
      }
  
      /**
       * Sets a listener which notifies recovery agent that new recovery snapshot is available. {@link
       * #getKeyChainSnapshot} can be used to get the snapshot. Note that every recovery agent can
       * have at most one registered listener at any time.
       *
       * @param intent triggered when new snapshot is available. Unregisters listener if the value is
       *     {@code null}.
       * @throws InternalRecoveryServiceException if an unexpected error occurred in the recovery
       *     service.
       */
      @RequiresPermission(android.Manifest.permission.RECOVER_KEYSTORE)
      public void setSnapshotCreatedPendingIntent(@Nullable PendingIntent intent)
              throws InternalRecoveryServiceException {
          try {
              mBinder.setSnapshotCreatedPendingIntent(intent);
          } catch (RemoteException e) {
              throw e.rethrowFromSystemServer();
          } catch (ServiceSpecificException e) {
              throw wrapUnexpectedServiceSpecificException(e);
          }
      }
  
      /**
       * Server parameters used to generate new recovery key blobs. This value will be included in
       * {@code KeyChainSnapshot.getEncryptedRecoveryKeyBlob()}. The same value must be included
       * in vaultParams {@link RecoverySession#start(CertPath, byte[], byte[], List)}.
       *
       * @param serverParams included in recovery key blob.
       * @see #getKeyChainSnapshot
       * @throws InternalRecoveryServiceException if an unexpected error occurred in the recovery
       *     service.
       */
      @RequiresPermission(android.Manifest.permission.RECOVER_KEYSTORE)
      public void setServerParams(@NonNull byte[] serverParams)
              throws InternalRecoveryServiceException {
          try {
              mBinder.setServerParams(serverParams);
          } catch (RemoteException e) {
              throw e.rethrowFromSystemServer();
          } catch (ServiceSpecificException e) {
              throw wrapUnexpectedServiceSpecificException(e);
          }
      }
  
      /**
       * Returns a list of aliases of keys belonging to the application.
       */
      @RequiresPermission(android.Manifest.permission.RECOVER_KEYSTORE)
      public @NonNull List<String> getAliases() throws InternalRecoveryServiceException {
          try {
              Map<String, Integer> allStatuses = mBinder.getRecoveryStatus();
              return new ArrayList<>(allStatuses.keySet());
          } catch (RemoteException e) {
              throw e.rethrowFromSystemServer();
          } catch (ServiceSpecificException e) {
              throw wrapUnexpectedServiceSpecificException(e);
          }
      }
  
      /**
       * Sets the recovery status for given key. It is used to notify the keystore that the key was
       * successfully stored on the server or that there was an error. An application can check this
       * value using {@link #getRecoveryStatus(String, String)}.
       *
       * @param alias The alias of the key whose status to set.
       * @param status The status of the key. One of {@link #RECOVERY_STATUS_SYNCED},
       *     {@link #RECOVERY_STATUS_SYNC_IN_PROGRESS} or {@link #RECOVERY_STATUS_PERMANENT_FAILURE}.
       * @throws InternalRecoveryServiceException if an unexpected error occurred in the recovery
       *     service.
       */
      @RequiresPermission(android.Manifest.permission.RECOVER_KEYSTORE)
      public void setRecoveryStatus(@NonNull String alias, int status)
              throws InternalRecoveryServiceException {
          try {
              mBinder.setRecoveryStatus(alias, status);
          } catch (RemoteException e) {
              throw e.rethrowFromSystemServer();
          } catch (ServiceSpecificException e) {
              throw wrapUnexpectedServiceSpecificException(e);
          }
      }
  
      /**
       * Returns the recovery status for the key with the given {@code alias}.
       *
       * <ul>
       *   <li>{@link #RECOVERY_STATUS_SYNCED}
       *   <li>{@link #RECOVERY_STATUS_SYNC_IN_PROGRESS}
       *   <li>{@link #RECOVERY_STATUS_PERMANENT_FAILURE}
       * </ul>
       *
       * @see #setRecoveryStatus(String, int)
       * @throws InternalRecoveryServiceException if an unexpected error occurred in the recovery
       *     service.
       */
      @RequiresPermission(android.Manifest.permission.RECOVER_KEYSTORE)
      public int getRecoveryStatus(@NonNull String alias) throws InternalRecoveryServiceException {
          try {
              Map<String, Integer> allStatuses = mBinder.getRecoveryStatus();
              Integer status = allStatuses.get(alias);
              if (status == null) {
                  return RecoveryController.RECOVERY_STATUS_PERMANENT_FAILURE;
              } else {
                  return status;
              }
          } catch (RemoteException e) {
              throw e.rethrowFromSystemServer();
          } catch (ServiceSpecificException e) {
              throw wrapUnexpectedServiceSpecificException(e);
          }
      }
  
      /**
       * Specifies a set of secret types used for end-to-end keystore encryption. Knowing all of them
       * is necessary to recover data.
       *
       * @param secretTypes {@link KeyChainProtectionParams#TYPE_LOCKSCREEN}
       * @throws InternalRecoveryServiceException if an unexpected error occurred in the recovery
       *     service.
       */
      @RequiresPermission(android.Manifest.permission.RECOVER_KEYSTORE)
      public void setRecoverySecretTypes(
              @NonNull @KeyChainProtectionParams.UserSecretType int[] secretTypes)
              throws InternalRecoveryServiceException {
          try {
              mBinder.setRecoverySecretTypes(secretTypes);
          } catch (RemoteException e) {
              throw e.rethrowFromSystemServer();
          } catch (ServiceSpecificException e) {
              throw wrapUnexpectedServiceSpecificException(e);
          }
      }
  
      /**
       * Defines a set of secret types used for end-to-end keystore encryption. Knowing all of them is
       * necessary to generate KeyChainSnapshot.
       *
       * @return list of recovery secret types
       * @see KeyChainSnapshot
       * @throws InternalRecoveryServiceException if an unexpected error occurred in the recovery
       *     service.
       */
      @RequiresPermission(android.Manifest.permission.RECOVER_KEYSTORE)
      public @NonNull @KeyChainProtectionParams.UserSecretType int[] getRecoverySecretTypes()
              throws InternalRecoveryServiceException {
          try {
              return mBinder.getRecoverySecretTypes();
          } catch (RemoteException e) {
              throw e.rethrowFromSystemServer();
          } catch (ServiceSpecificException e) {
              throw wrapUnexpectedServiceSpecificException(e);
          }
      }
  
      /**
       * Generates a recoverable key with the given {@code alias}.
       *
       * @throws InternalRecoveryServiceException if an unexpected error occurred in the recovery
       *     service.
       * @throws LockScreenRequiredException if the user does not have a lock screen set. A lock
       *     screen is required to generate recoverable keys.
       *
       * @deprecated Use the method {@link #generateKey(String, byte[])} instead.
       */
      @Deprecated
      @RequiresPermission(android.Manifest.permission.RECOVER_KEYSTORE)
      public @NonNull Key generateKey(@NonNull String alias) throws InternalRecoveryServiceException,
              LockScreenRequiredException {
          try {
              String grantAlias = mBinder.generateKey(alias);
              if (grantAlias == null) {
                  throw new InternalRecoveryServiceException("null grant alias");
              }
              return getKeyFromGrant(grantAlias);
          } catch (RemoteException e) {
              throw e.rethrowFromSystemServer();
          } catch (KeyPermanentlyInvalidatedException | UnrecoverableKeyException e) {
              throw new InternalRecoveryServiceException("Failed to get key from keystore", e);
          } catch (ServiceSpecificException e) {
              if (e.errorCode == ERROR_INSECURE_USER) {
                  throw new LockScreenRequiredException(e.getMessage());
              }
              throw wrapUnexpectedServiceSpecificException(e);
          }
      }
  
      /**
       * Generates a recoverable key with the given {@code alias} and {@code metadata}.
       *
       * <p>The metadata should contain any data that needs to be cryptographically bound to the
       * generated key, but does not need to be encrypted by the key. For example, the metadata can
       * be a byte string describing the algorithms and non-secret parameters to be used with the
       * key. The supplied metadata can later be obtained via
       * {@link WrappedApplicationKey#getMetadata()}.
       *
       * <p>During the key recovery process, the same metadata has to be supplied via
       * {@link WrappedApplicationKey.Builder#setMetadata(byte[])}; otherwise, the recovery process
       * will fail due to the checking of the cryptographic binding. This can help prevent
       * potential attacks that try to swap key materials on the backup server and trick the
       * application to use keys with different algorithms or parameters.
       *
       * @throws InternalRecoveryServiceException if an unexpected error occurred in the recovery
       *     service.
       * @throws LockScreenRequiredException if the user does not have a lock screen set. A lock
       *     screen is required to generate recoverable keys.
       */
      @RequiresPermission(android.Manifest.permission.RECOVER_KEYSTORE)
      public @NonNull Key generateKey(@NonNull String alias, @Nullable byte[] metadata)
              throws InternalRecoveryServiceException, LockScreenRequiredException {
          try {
              String grantAlias = mBinder.generateKeyWithMetadata(alias, metadata);
              if (grantAlias == null) {
                  throw new InternalRecoveryServiceException("null grant alias");
              }
              return getKeyFromGrant(grantAlias);
          } catch (RemoteException e) {
              throw e.rethrowFromSystemServer();
          } catch (KeyPermanentlyInvalidatedException | UnrecoverableKeyException  e) {
              throw new InternalRecoveryServiceException("Failed to get key from keystore", e);
          } catch (ServiceSpecificException e) {
              if (e.errorCode == ERROR_INSECURE_USER) {
                  throw new LockScreenRequiredException(e.getMessage());
              }
              throw wrapUnexpectedServiceSpecificException(e);
          }
      }
  
      /**
       * Imports a 256-bit recoverable AES key with the given {@code alias} and the raw bytes {@code
       * keyBytes}.
       *
       * @throws InternalRecoveryServiceException if an unexpected error occurred in the recovery
       *     service.
       * @throws LockScreenRequiredException if the user does not have a lock screen set. A lock
       *     screen is required to generate recoverable keys.
       *
       * @deprecated Use the method {@link #importKey(String, byte[], byte[])} instead.
       */
      @Deprecated
      @RequiresPermission(android.Manifest.permission.RECOVER_KEYSTORE)
      public @NonNull Key importKey(@NonNull String alias, @NonNull byte[] keyBytes)
              throws InternalRecoveryServiceException, LockScreenRequiredException {
          try {
              String grantAlias = mBinder.importKey(alias, keyBytes);
              if (grantAlias == null) {
                  throw new InternalRecoveryServiceException("Null grant alias");
              }
              return getKeyFromGrant(grantAlias);
          } catch (RemoteException e) {
              throw e.rethrowFromSystemServer();
          } catch (KeyPermanentlyInvalidatedException | UnrecoverableKeyException e) {
              throw new InternalRecoveryServiceException("Failed to get key from keystore", e);
          } catch (ServiceSpecificException e) {
              if (e.errorCode == ERROR_INSECURE_USER) {
                  throw new LockScreenRequiredException(e.getMessage());
              }
              throw wrapUnexpectedServiceSpecificException(e);
          }
      }
  
      /**
       * Imports a recoverable 256-bit AES key with the given {@code alias}, the raw bytes {@code
       * keyBytes}, and the {@code metadata}.
       *
       * <p>The metadata should contain any data that needs to be cryptographically bound to the
       * imported key, but does not need to be encrypted by the key. For example, the metadata can
       * be a byte string describing the algorithms and non-secret parameters to be used with the
       * key. The supplied metadata can later be obtained via
       * {@link WrappedApplicationKey#getMetadata()}.
       *
       * <p>During the key recovery process, the same metadata has to be supplied via
       * {@link WrappedApplicationKey.Builder#setMetadata(byte[])}; otherwise, the recovery process
       * will fail due to the checking of the cryptographic binding. This can help prevent
       * potential attacks that try to swap key materials on the backup server and trick the
       * application to use keys with different algorithms or parameters.
       *
       * @throws InternalRecoveryServiceException if an unexpected error occurred in the recovery
       *     service.
       * @throws LockScreenRequiredException if the user does not have a lock screen set. A lock
       *     screen is required to generate recoverable keys.
       */
      @RequiresPermission(android.Manifest.permission.RECOVER_KEYSTORE)
      public @NonNull Key importKey(@NonNull String alias, @NonNull byte[] keyBytes,
              @Nullable byte[] metadata)
              throws InternalRecoveryServiceException, LockScreenRequiredException {
          try {
              String grantAlias = mBinder.importKeyWithMetadata(alias, keyBytes, metadata);
              if (grantAlias == null) {
                  throw new InternalRecoveryServiceException("Null grant alias");
              }
              return getKeyFromGrant(grantAlias);
          } catch (RemoteException e) {
              throw e.rethrowFromSystemServer();
          } catch (KeyPermanentlyInvalidatedException | UnrecoverableKeyException e) {
              throw new InternalRecoveryServiceException("Failed to get key from keystore", e);
          } catch (ServiceSpecificException e) {
              if (e.errorCode == ERROR_INSECURE_USER) {
                  throw new LockScreenRequiredException(e.getMessage());
              }
              throw wrapUnexpectedServiceSpecificException(e);
          }
      }
  
      /**
       * Gets a key called {@code alias} from the recoverable key store.
       *
       * @param alias The key alias.
       * @return The key.
       * @throws InternalRecoveryServiceException if an unexpected error occurred in the recovery
       *     service.
       * @throws UnrecoverableKeyException if key is permanently invalidated or not found.
       */
      @RequiresPermission(android.Manifest.permission.RECOVER_KEYSTORE)
      public @Nullable Key getKey(@NonNull String alias)
              throws InternalRecoveryServiceException, UnrecoverableKeyException {
          try {
              String grantAlias = mBinder.getKey(alias);
              if (grantAlias == null || "".equals(grantAlias)) {
                  return null;
              }
              return getKeyFromGrant(grantAlias);
          } catch (RemoteException e) {
              throw e.rethrowFromSystemServer();
          } catch (KeyPermanentlyInvalidatedException | UnrecoverableKeyException e) {
              throw new UnrecoverableKeyException(e.getMessage());
          } catch (ServiceSpecificException e) {
              throw wrapUnexpectedServiceSpecificException(e);
          }
      }
  
      /**
       * Returns the key with the given {@code grantAlias}.
       */
      @NonNull Key getKeyFromGrant(@NonNull String grantAlias)
              throws UnrecoverableKeyException, KeyPermanentlyInvalidatedException {
          return AndroidKeyStoreProvider.loadAndroidKeyStoreKeyFromKeystore(
                  mKeyStore,
                  grantAlias,
                  KeyStore.UID_SELF);
      }
  
      /**
       * Removes a key called {@code alias} from the recoverable key store.
       *
       * @param alias The key alias.
       * @throws InternalRecoveryServiceException if an unexpected error occurred in the recovery
       *     service.
       */
      @RequiresPermission(android.Manifest.permission.RECOVER_KEYSTORE)
      public void removeKey(@NonNull String alias) throws InternalRecoveryServiceException {
          try {
              mBinder.removeKey(alias);
          } catch (RemoteException e) {
              throw e.rethrowFromSystemServer();
          } catch (ServiceSpecificException e) {
              throw wrapUnexpectedServiceSpecificException(e);
          }
      }
  
      /**
       * Returns a new {@link RecoverySession}.
       *
       * <p>A recovery session is required to restore keys from a remote store.
       */
      @RequiresPermission(android.Manifest.permission.RECOVER_KEYSTORE)
      public @NonNull RecoverySession createRecoverySession() {
          return RecoverySession.newInstance(this);
      }
  
      @RequiresPermission(android.Manifest.permission.RECOVER_KEYSTORE)
      public @NonNull Map<String, X509Certificate> getRootCertificates() {
          return TrustedRootCertificates.getRootCertificates();
      }
  
      InternalRecoveryServiceException wrapUnexpectedServiceSpecificException(
              ServiceSpecificException e) {
          if (e.errorCode == ERROR_SERVICE_INTERNAL_ERROR) {
              return new InternalRecoveryServiceException(e.getMessage());
          }
  
          // Should never happen. If it does, it's a bug, and we need to update how the method that
          // called this throws its exceptions.
          return new InternalRecoveryServiceException("Unexpected error code for method: "
                  + e.errorCode, e);
      }
  }
  