| /* |
| * Copyright (C) 2018 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 com.android.server.backup.encryption.keys; |
| |
| import android.content.Context; |
| import android.content.SharedPreferences; |
| import android.util.Slog; |
| |
| import com.android.internal.annotations.VisibleForTesting; |
| |
| import java.util.Locale; |
| |
| /** |
| * Tracks when a tertiary key rotation is due. |
| * |
| * <p>After a certain number of incremental backups, the device schedules a full backup, which will |
| * generate a new encryption key, effecting a key rotation. We should do this on a regular basis so |
| * that if a key does become compromised it has limited value to the attacker. |
| * |
| * <p>No additional synchronization of this class is provided. Only one instance should be used at |
| * any time. This should be fine as there should be no parallelism in backups. |
| */ |
| public class TertiaryKeyRotationTracker { |
| private static final int MAX_BACKUPS_UNTIL_TERTIARY_KEY_ROTATION = 31; |
| private static final String SHARED_PREFERENCES_NAME = "tertiary_key_rotation_tracker"; |
| |
| private static final String TAG = "TertiaryKeyRotationTracker"; |
| private static final boolean DEBUG = false; |
| |
| /** |
| * A new instance, using {@code context} to commit data to disk via {@link SharedPreferences}. |
| */ |
| public static TertiaryKeyRotationTracker getInstance(Context context) { |
| return new TertiaryKeyRotationTracker( |
| context.getSharedPreferences(SHARED_PREFERENCES_NAME, Context.MODE_PRIVATE)); |
| } |
| |
| private final SharedPreferences mSharedPreferences; |
| |
| /** New instance, storing data in {@code mSharedPreferences}. */ |
| @VisibleForTesting |
| TertiaryKeyRotationTracker(SharedPreferences sharedPreferences) { |
| mSharedPreferences = sharedPreferences; |
| } |
| |
| /** |
| * Returns {@code true} if the given app is due having its key rotated. |
| * |
| * @param packageName The package name of the app. |
| */ |
| public boolean isKeyRotationDue(String packageName) { |
| return getBackupsSinceRotation(packageName) >= MAX_BACKUPS_UNTIL_TERTIARY_KEY_ROTATION; |
| } |
| |
| /** |
| * Records that an incremental backup has occurred. Each incremental backup brings the app |
| * closer to the time when its key should be rotated. |
| * |
| * @param packageName The package name of the app for which the backup occurred. |
| */ |
| public void recordBackup(String packageName) { |
| int backupsSinceRotation = getBackupsSinceRotation(packageName) + 1; |
| mSharedPreferences.edit().putInt(packageName, backupsSinceRotation).apply(); |
| if (DEBUG) { |
| Slog.d( |
| TAG, |
| String.format( |
| Locale.US, |
| "Incremental backup for %s. %d backups until key rotation.", |
| packageName, |
| Math.max( |
| 0, |
| MAX_BACKUPS_UNTIL_TERTIARY_KEY_ROTATION |
| - backupsSinceRotation))); |
| } |
| } |
| |
| /** |
| * Resets the rotation delay for the given app. Should be invoked after a key rotation. |
| * |
| * @param packageName Package name of the app whose key has rotated. |
| */ |
| public void resetCountdown(String packageName) { |
| mSharedPreferences.edit().putInt(packageName, 0).apply(); |
| } |
| |
| /** Marks all enrolled packages for key rotation. */ |
| public void markAllForRotation() { |
| SharedPreferences.Editor editor = mSharedPreferences.edit(); |
| for (String packageName : mSharedPreferences.getAll().keySet()) { |
| editor.putInt(packageName, MAX_BACKUPS_UNTIL_TERTIARY_KEY_ROTATION); |
| } |
| editor.apply(); |
| } |
| |
| private int getBackupsSinceRotation(String packageName) { |
| return mSharedPreferences.getInt(packageName, 0); |
| } |
| } |