Merge branch 'master' into 'preference-switches'

# Conflicts:
#   briar-android/src/main/java/org/briarproject/briar/android/settings/SettingsFragment.java

briar-android/src/main/java/org/briarproject/briar/android/AndroidComponent.java

@@ -28,6 +28,7 @@ import org.briarproject.briar.android.login.SignInReminderReceiver;
 import org.briarproject.briar.android.reporting.BriarReportSender;
 import org.briarproject.briar.api.android.AndroidNotificationManager;
 import org.briarproject.briar.api.android.DozeWatchdog;
+import org.briarproject.briar.api.android.LockManager;
 import org.briarproject.briar.api.android.ScreenFilterMonitor;
 import org.briarproject.briar.api.blog.BlogManager;
 import org.briarproject.briar.api.blog.BlogPostFactory;
@@ -146,6 +147,8 @@ public interface AndroidComponent
 
 	AccountManager accountManager();
 
+	LockManager lockManager();
+
 	void inject(SignInReminderReceiver briarService);
 
 	void inject(BriarService briarService);

briar-android/src/main/java/org/briarproject/briar/android/AndroidNotificationManagerImpl.java

@@ -2,6 +2,7 @@ package org.briarproject.briar.android;
 
 import android.annotation.TargetApi;
 import android.app.Application;
+import android.app.Notification;
 import android.app.NotificationChannel;
 import android.app.NotificationManager;
 import android.app.PendingIntent;
@@ -12,7 +13,6 @@ import android.support.annotation.StringRes;
 import android.support.annotation.UiThread;
 import android.support.v4.app.NotificationCompat;
 import android.support.v4.app.TaskStackBuilder;
-import android.support.v4.content.ContextCompat;
 
 import org.briarproject.bramble.api.Multiset;
 import org.briarproject.bramble.api.contact.ContactId;
@@ -65,7 +65,6 @@ import javax.inject.Inject;
 import static android.app.Notification.DEFAULT_LIGHTS;
 import static android.app.Notification.DEFAULT_SOUND;
 import static android.app.Notification.DEFAULT_VIBRATE;
-import static android.app.Notification.VISIBILITY_SECRET;
 import static android.app.NotificationManager.IMPORTANCE_DEFAULT;
 import static android.app.NotificationManager.IMPORTANCE_LOW;
 import static android.content.Context.NOTIFICATION_SERVICE;
@@ -73,8 +72,12 @@ import static android.content.Intent.FLAG_ACTIVITY_CLEAR_TOP;
 import static android.content.Intent.FLAG_ACTIVITY_NEW_TASK;
 import static android.os.Build.VERSION.SDK_INT;
 import static android.support.v4.app.NotificationCompat.CATEGORY_MESSAGE;
+import static android.support.v4.app.NotificationCompat.CATEGORY_SERVICE;
 import static android.support.v4.app.NotificationCompat.CATEGORY_SOCIAL;
 import static android.support.v4.app.NotificationCompat.PRIORITY_LOW;
+import static android.support.v4.app.NotificationCompat.PRIORITY_MIN;
+import static android.support.v4.app.NotificationCompat.VISIBILITY_SECRET;
+import static android.support.v4.content.ContextCompat.getColor;
 import static java.util.logging.Level.WARNING;
 import static org.briarproject.bramble.util.LogUtils.logException;
 import static org.briarproject.briar.android.activity.BriarActivity.GROUP_ID;
@@ -173,8 +176,7 @@ class AndroidNotificationManagerImpl implements AndroidNotificationManager,
 		nc.setLockscreenVisibility(VISIBILITY_SECRET);
 		nc.enableVibration(true);
 		nc.enableLights(true);
-		nc.setLightColor(
-				ContextCompat.getColor(appContext, R.color.briar_green_light));
+		nc.setLightColor(getColor(appContext, R.color.briar_green_light));
 		notificationManager.createNotificationChannel(nc);
 	}
 
@@ -271,6 +273,47 @@ class AndroidNotificationManagerImpl implements AndroidNotificationManager,
 		});
 	}
 
+	@UiThread
+	@Override
+	public Notification getForegroundNotification() {
+		return getForegroundNotification(false);
+	}
+
+	@UiThread
+	private Notification getForegroundNotification(boolean locked) {
+		int title = locked ? R.string.lock_is_locked :
+				R.string.ongoing_notification_title;
+		int text = locked ? R.string.lock_tap_to_unlock :
+				R.string.ongoing_notification_text;
+		int icon = locked ? R.drawable.startup_lock :
+				R.drawable.notification_ongoing;
+		// Ongoing foreground notification that shows BriarService is running
+		NotificationCompat.Builder b =
+				new NotificationCompat.Builder(appContext, ONGOING_CHANNEL_ID);
+		b.setSmallIcon(icon);
+		b.setColor(getColor(appContext, R.color.briar_primary));
+		b.setContentTitle(appContext.getText(title));
+		b.setContentText(appContext.getText(text));
+		b.setWhen(0); // Don't show the time
+		b.setOngoing(true);
+		Intent i = new Intent(appContext, NavDrawerActivity.class);
+		i.setFlags(FLAG_ACTIVITY_NEW_TASK | FLAG_ACTIVITY_CLEAR_TOP);
+		b.setContentIntent(PendingIntent.getActivity(appContext, 0, i, 0));
+		if (SDK_INT >= 21) {
+			b.setCategory(CATEGORY_SERVICE);
+			b.setVisibility(VISIBILITY_SECRET);
+		}
+		b.setPriority(PRIORITY_MIN);
+		return b.build();
+	}
+
+	@UiThread
+	@Override
+	public void updateForegroundNotification(boolean locked) {
+		Notification n = getForegroundNotification(locked);
+		notificationManager.notify(ONGOING_NOTIFICATION_ID, n);
+	}
+
 	private void showContactNotification(ContactId c) {
 		androidExecutor.runOnUiThread(() -> {
 			if (blockContacts) return;
@@ -636,7 +679,7 @@ class AndroidNotificationManagerImpl implements AndroidNotificationManager,
 		NotificationCompat.Builder b =
 				new NotificationCompat.Builder(appContext, REMINDER_CHANNEL_ID);
 		b.setSmallIcon(R.drawable.ic_signout);
-		b.setColor(ContextCompat.getColor(appContext, R.color.briar_primary));
+		b.setColor(getColor(appContext, R.color.briar_primary));
 		b.setContentTitle(
 				appContext.getText(R.string.reminder_notification_title));
 		b.setContentText(

briar-android/src/main/java/org/briarproject/briar/android/AppModule.java

@@ -29,8 +29,10 @@ import org.briarproject.bramble.plugin.tor.AndroidTorPluginFactory;
 import org.briarproject.bramble.plugin.tor.CircumventionProvider;
 import org.briarproject.bramble.util.AndroidUtils;
 import org.briarproject.bramble.util.StringUtils;
+import org.briarproject.briar.android.account.LockManagerImpl;
 import org.briarproject.briar.api.android.AndroidNotificationManager;
 import org.briarproject.briar.api.android.DozeWatchdog;
+import org.briarproject.briar.api.android.LockManager;
 import org.briarproject.briar.api.android.ScreenFilterMonitor;
 
 import java.io.File;
@@ -200,4 +202,13 @@ public class AppModule {
 		return dozeWatchdog;
 	}
 
+	@Provides
+	@Singleton
+	LockManager provideLockManager(LifecycleManager lifecycleManager,
+			EventBus eventBus, LockManagerImpl lockManager) {
+		lifecycleManager.registerService(lockManager);
+		eventBus.addListener(lockManager);
+		return lockManager;
+	}
+
 }

briar-android/src/main/java/org/briarproject/briar/android/BriarService.java

@@ -2,6 +2,7 @@ package org.briarproject.briar.android;
 
 import android.app.ActivityManager;
 import android.app.ActivityManager.RunningAppProcessInfo;
+import android.app.Notification;
 import android.app.NotificationChannel;
 import android.app.NotificationManager;
 import android.app.PendingIntent;
@@ -15,7 +16,6 @@ import android.content.ServiceConnection;
 import android.os.Binder;
 import android.os.IBinder;
 import android.support.v4.app.NotificationCompat;
-import android.support.v4.content.ContextCompat;
 
 import org.briarproject.bramble.api.account.AccountManager;
 import org.briarproject.bramble.api.crypto.SecretKey;
@@ -25,6 +25,7 @@ import org.briarproject.bramble.api.system.AndroidExecutor;
 import org.briarproject.briar.R;
 import org.briarproject.briar.android.logout.HideUiActivity;
 import org.briarproject.briar.android.navdrawer.NavDrawerActivity;
+import org.briarproject.briar.api.android.AndroidNotificationManager;
 
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.atomic.AtomicBoolean;
@@ -44,8 +45,6 @@ import static android.content.Intent.FLAG_ACTIVITY_EXCLUDE_FROM_RECENTS;
 import static android.content.Intent.FLAG_ACTIVITY_NEW_TASK;
 import static android.content.Intent.FLAG_ACTIVITY_NO_ANIMATION;
 import static android.os.Build.VERSION.SDK_INT;
-import static android.support.v4.app.NotificationCompat.CATEGORY_SERVICE;
-import static android.support.v4.app.NotificationCompat.PRIORITY_MIN;
 import static android.support.v4.app.NotificationCompat.VISIBILITY_SECRET;
 import static java.util.logging.Level.INFO;
 import static java.util.logging.Level.WARNING;
@@ -74,6 +73,8 @@ public class BriarService extends Service {
 	@Nullable
 	private BroadcastReceiver receiver = null;
 
+	@Inject
+	AndroidNotificationManager notificationManager;
 	@Inject
 	AccountManager accountManager;
 
@@ -121,24 +122,9 @@ public class BriarService extends Service {
 			failureChannel.setLockscreenVisibility(VISIBILITY_SECRET);
 			nm.createNotificationChannel(failureChannel);
 		}
-		// Show an ongoing notification that the service is running
-		NotificationCompat.Builder b =
-				new NotificationCompat.Builder(this, ONGOING_CHANNEL_ID);
-		b.setSmallIcon(R.drawable.notification_ongoing);
-		b.setColor(ContextCompat.getColor(this, R.color.briar_primary));
-		b.setContentTitle(getText(R.string.ongoing_notification_title));
-		b.setContentText(getText(R.string.ongoing_notification_text));
-		b.setWhen(0); // Don't show the time
-		b.setOngoing(true);
-		Intent i = new Intent(this, NavDrawerActivity.class);
-		i.setFlags(FLAG_ACTIVITY_NEW_TASK | FLAG_ACTIVITY_CLEAR_TOP);
-		b.setContentIntent(PendingIntent.getActivity(this, 0, i, 0));
-		if (SDK_INT >= 21) {
-			b.setCategory(CATEGORY_SERVICE);
-			b.setVisibility(VISIBILITY_SECRET);
-		}
-		b.setPriority(PRIORITY_MIN);
-		startForeground(ONGOING_NOTIFICATION_ID, b.build());
+		Notification foregroundNotification =
+				notificationManager.getForegroundNotification();
+		startForeground(ONGOING_NOTIFICATION_ID, foregroundNotification);
 		// Start the services in a background thread
 		new Thread(() -> {
 			StartResult result = lifecycleManager.startServices(dbKey);

briar-android/src/main/java/org/briarproject/briar/android/TestingConstants.java

@@ -40,4 +40,9 @@ public interface TestingConstants {
 	 * Feature flag for enabling the sign-in reminder in release builds.
 	 */
 	boolean FEATURE_FLAG_SIGN_IN_REMINDER = IS_DEBUG_BUILD;
+
+	/**
+	 * Feature flag for enabling the PIN lock in release builds.
+	 */
+	boolean FEATURE_FLAG_PIN_LOCK = IS_DEBUG_BUILD;
 }

briar-android/src/main/java/org/briarproject/briar/android/account/LockManagerImpl.java

@@ -0,0 +1,132 @@
+package org.briarproject.briar.android.account;
+
+import android.app.Application;
+import android.arch.lifecycle.LiveData;
+import android.arch.lifecycle.MutableLiveData;
+import android.content.Context;
+import android.support.annotation.UiThread;
+
+import org.briarproject.bramble.api.db.DatabaseExecutor;
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.event.Event;
+import org.briarproject.bramble.api.event.EventListener;
+import org.briarproject.bramble.api.lifecycle.Service;
+import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
+import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
+import org.briarproject.bramble.api.settings.Settings;
+import org.briarproject.bramble.api.settings.SettingsManager;
+import org.briarproject.bramble.api.settings.event.SettingsUpdatedEvent;
+import org.briarproject.briar.api.android.AndroidNotificationManager;
+import org.briarproject.briar.api.android.LockManager;
+
+import java.util.concurrent.Executor;
+import java.util.logging.Logger;
+
+import javax.annotation.concurrent.ThreadSafe;
+import javax.inject.Inject;
+
+import static java.util.logging.Level.WARNING;
+import static org.briarproject.bramble.util.LogUtils.logException;
+import static org.briarproject.briar.android.settings.SettingsFragment.PREF_SCREEN_LOCK;
+import static org.briarproject.briar.android.settings.SettingsFragment.SETTINGS_NAMESPACE;
+import static org.briarproject.briar.android.util.UiUtils.hasScreenLock;
+
+@ThreadSafe
+@MethodsNotNullByDefault
+@ParametersNotNullByDefault
+public class LockManagerImpl implements LockManager, Service, EventListener {
+
+	private static final Logger LOG =
+			Logger.getLogger(LockManagerImpl.class.getName());
+
+	private final Context appContext;
+	private final SettingsManager settingsManager;
+	private final AndroidNotificationManager notificationManager;
+	@DatabaseExecutor
+	private final Executor dbExecutor;
+
+	private volatile boolean locked = false;
+	private volatile boolean lockableSetting = false;
+	private final MutableLiveData<Boolean> lockable = new MutableLiveData<>();
+
+	@Inject
+	public LockManagerImpl(Application app, SettingsManager settingsManager,
+			AndroidNotificationManager notificationManager,
+			@DatabaseExecutor Executor dbExecutor) {
+		this.appContext = app.getApplicationContext();
+		this.settingsManager = settingsManager;
+		this.notificationManager = notificationManager;
+		this.dbExecutor = dbExecutor;
+
+		// setting this in the constructor makes #getValue() @NonNull
+		this.lockable.setValue(false);
+	}
+
+	@Override
+	public void startService() {
+		// only load the setting here, because database isn't open before
+		loadLockableSetting();
+	}
+
+	@Override
+	public void stopService() {
+	}
+
+	@Override
+	public LiveData<Boolean> isLockable() {
+		return lockable;
+	}
+
+	@UiThread
+	@Override
+	public void checkIfLockable() {
+		boolean oldValue = lockable.getValue();
+		boolean newValue = hasScreenLock(appContext) && lockableSetting;
+		if (oldValue != newValue) {
+			this.lockable.setValue(newValue);
+		}
+	}
+
+	@Override
+	public boolean isLocked() {
+		if (locked && !hasScreenLock(appContext)) {
+			lockable.postValue(false);
+			locked = false;
+		}
+		return locked;
+	}
+
+	@Override
+	public void setLocked(boolean locked) {
+		this.locked = locked;
+		notificationManager.updateForegroundNotification(locked);
+	}
+
+	@Override
+	public void eventOccurred(Event event) {
+		if (event instanceof SettingsUpdatedEvent) {
+			SettingsUpdatedEvent e = (SettingsUpdatedEvent) event;
+			String namespace = e.getNamespace();
+			if (namespace.equals(SETTINGS_NAMESPACE)) {
+				loadLockableSetting();
+			}
+		}
+	}
+
+	private void loadLockableSetting() {
+		dbExecutor.execute(() -> {
+			try {
+				Settings settings =
+						settingsManager.getSettings(SETTINGS_NAMESPACE);
+				lockableSetting = settings.getBoolean(PREF_SCREEN_LOCK, false);
+				boolean newValue = hasScreenLock(appContext) && lockableSetting;
+				lockable.postValue(newValue);
+			} catch (DbException e) {
+				logException(LOG, WARNING, e);
+				lockableSetting = false;
+				lockable.postValue(false);
+			}
+		});
+	}
+
+}

briar-android/src/main/java/org/briarproject/briar/android/activity/ActivityComponent.java

@@ -37,6 +37,7 @@ import org.briarproject.briar.android.login.OpenDatabaseActivity;
 import org.briarproject.briar.android.login.PasswordActivity;
 import org.briarproject.briar.android.login.PasswordFragment;
 import org.briarproject.briar.android.login.SetupActivity;
+import org.briarproject.briar.android.login.UnlockActivity;
 import org.briarproject.briar.android.navdrawer.NavDrawerActivity;
 import org.briarproject.briar.android.panic.PanicPreferencesActivity;
 import org.briarproject.briar.android.panic.PanicResponderActivity;
@@ -163,6 +164,8 @@ public interface ActivityComponent {
 
 	void inject(StartupFailureActivity activity);
 
+	void inject(UnlockActivity activity);
+
 	// Fragments
 	void inject(AuthorNameFragment fragment);
 

briar-android/src/main/java/org/briarproject/briar/android/activity/BriarActivity.java

@@ -16,7 +16,9 @@ import org.briarproject.briar.android.controller.BriarController;
 import org.briarproject.briar.android.controller.DbController;
 import org.briarproject.briar.android.controller.handler.UiResultHandler;
 import org.briarproject.briar.android.login.PasswordActivity;
+import org.briarproject.briar.android.login.UnlockActivity;
 import org.briarproject.briar.android.logout.ExitActivity;
+import org.briarproject.briar.api.android.LockManager;
 
 import java.util.logging.Logger;
 
@@ -30,6 +32,7 @@ import static android.content.Intent.FLAG_ACTIVITY_NO_ANIMATION;
 import static android.os.Build.VERSION.SDK_INT;
 import static org.briarproject.briar.android.activity.RequestCodes.REQUEST_DOZE_WHITELISTING;
 import static org.briarproject.briar.android.activity.RequestCodes.REQUEST_PASSWORD;
+import static org.briarproject.briar.android.activity.RequestCodes.REQUEST_UNLOCK;
 import static org.briarproject.briar.android.util.UiUtils.getDozeWhitelistingIntent;
 import static org.briarproject.briar.android.util.UiUtils.isSamsung7;
 
@@ -44,26 +47,43 @@ public abstract class BriarActivity extends BaseActivity {
 
 	@Inject
 	BriarController briarController;
-
 	@Deprecated
 	@Inject
 	DbController dbController;
+	@Inject
+	protected LockManager lockManager;
 
 	@Override
 	protected void onActivityResult(int request, int result, Intent data) {
 		super.onActivityResult(request, result, data);
-		if (request == REQUEST_PASSWORD) {
-			if (result == RESULT_OK) briarController.startAndBindService();
-			else supportFinishAfterTransition();
+		if (request == REQUEST_PASSWORD && result == RESULT_OK) {
+			// PasswordActivity finishes when password was entered correctly.
+			// When back button is pressed there, it will bring itself back,
+			// so that we never arrive here with a result that is not OK.
+			briarController.startAndBindService();
+		} else if (request == REQUEST_UNLOCK && result != RESULT_OK) {
+			// We arrive here, if the user presses 'back'
+			// in the Keyguard unlock screen, because UnlockActivity finishes.
+			// If we don't finish here, isFinishing will be false in onResume()
+			// and we launch a new UnlockActivity causing a loop.
+			supportFinishAfterTransition();
+			// If the result is OK, we don't need to do anything here
+			// and can resume normally.
 		}
 	}
 
 	@Override
-	public void onStart() {
-		super.onStart();
-		if (!briarController.accountSignedIn() && !isFinishing()) {
+	public void onResume() {
+		super.onResume();
+		if (!briarController.accountSignedIn()) {
 			Intent i = new Intent(this, PasswordActivity.class);
 			startActivityForResult(i, REQUEST_PASSWORD);
+		} else if (lockManager.isLocked() && !isFinishing()) {
+			// Also check that the activity isn't finishing already.
+			// This is possible if finishing in onActivityResult().
+			// Failure to do this check would cause an UnlockActivity loop.
+			Intent i = new Intent(this, UnlockActivity.class);
+			startActivityForResult(i, REQUEST_UNLOCK);
 		} else if (SDK_INT >= 23) {
 			briarController.hasDozed(new UiResultHandler<Boolean>(this) {
 				@Override

briar-android/src/main/java/org/briarproject/briar/android/activity/RequestCodes.java

@@ -12,5 +12,7 @@ public interface RequestCodes {
 	int REQUEST_PERMISSION_CAMERA = 8;
 	int REQUEST_DOZE_WHITELISTING = 9;
 	int REQUEST_ENABLE_BLUETOOTH = 10;
+	int REQUEST_UNLOCK = 11;
+	int REQUEST_KEYGUARD_UNLOCK = 12;
 
 }

briar-android/src/main/java/org/briarproject/briar/android/login/PasswordActivity.java

@@ -23,8 +23,6 @@ import org.briarproject.briar.api.android.AndroidNotificationManager;
 
 import javax.inject.Inject;
 
-import static android.content.Intent.ACTION_MAIN;
-import static android.content.Intent.CATEGORY_HOME;
 import static android.content.Intent.FLAG_ACTIVITY_CLEAR_TASK;
 import static android.content.Intent.FLAG_ACTIVITY_NEW_TASK;
 import static android.view.View.INVISIBLE;
@@ -109,10 +107,9 @@ public class PasswordActivity extends BaseActivity {
 
 	@Override
 	public void onBackPressed() {
-		// Show the home screen rather than another password prompt
-		Intent intent = new Intent(ACTION_MAIN);
-		intent.addCategory(CATEGORY_HOME);
-		startActivity(intent);
+		// Move task and activity to the background instead of showing another
+		// password prompt. onActivityResult() won't be called in BriarActivity
+		moveTaskToBack(true);
 	}
 
 	private void deleteAccount() {

briar-android/src/main/java/org/briarproject/briar/android/login/UnlockActivity.java

@@ -0,0 +1,123 @@
+package org.briarproject.briar.android.login;
+
+import android.app.KeyguardManager;
+import android.content.Intent;
+import android.os.Bundle;
+import android.support.annotation.Nullable;
+import android.support.annotation.RequiresApi;
+import android.widget.Button;
+
+import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
+import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
+import org.briarproject.briar.R;
+import org.briarproject.briar.android.activity.ActivityComponent;
+import org.briarproject.briar.android.activity.BaseActivity;
+import org.briarproject.briar.api.android.LockManager;
+
+import java.util.logging.Logger;
+
+import javax.inject.Inject;
+
+import static android.os.Build.VERSION.SDK_INT;
+import static org.briarproject.briar.android.activity.RequestCodes.REQUEST_KEYGUARD_UNLOCK;
+
+@RequiresApi(21)
+@MethodsNotNullByDefault
+@ParametersNotNullByDefault
+public class UnlockActivity extends BaseActivity {
+
+	private static final Logger LOG =
+			Logger.getLogger(UnlockActivity.class.getName());
+	private static final String KEYGUARD_SHOWN = "keyguardShown";
+
+	@Inject
+	LockManager lockManager;
+
+	private boolean keyguardShown = false;
+
+	@Override
+	public void injectActivity(ActivityComponent component) {
+		component.inject(this);
+	}
+
+	public void onCreate(@Nullable Bundle state) {
+		super.onCreate(state);
+		overridePendingTransition(0, 0);
+		setContentView(R.layout.activity_unlock);
+
+		Button button = findViewById(R.id.unlock);
+		button.setOnClickListener(view -> requestKeyguardUnlock());
+
+		keyguardShown = state != null && state.getBoolean(KEYGUARD_SHOWN);
+	}
+
+	@Override
+	protected void onSaveInstanceState(Bundle outState) {
+		super.onSaveInstanceState(outState);
+		// Saving whether we've shown the keyguard already is necessary
+		// for Android 6 when this activity gets destroyed.
+		//
+		// This will not help Android 5.
+		// There the system will show the keyguard once again.
+		// So if this activity was destroyed, the user needs to enter PIN twice.
+		outState.putBoolean(KEYGUARD_SHOWN, keyguardShown);
+	}
+
+	@Override
+	protected void onActivityResult(int requestCode, int resultCode,
+			Intent data) {
+		super.onActivityResult(requestCode, resultCode, data);
+		if (requestCode == REQUEST_KEYGUARD_UNLOCK) {
+			if (resultCode == RESULT_OK) unlock();
+			else {
+				finish();
+				overridePendingTransition(0, 0);
+			}
+		}
+	}
+
+	@Override
+	protected void onResume() {
+		super.onResume();
+		// Show keyguard after onActivityResult() as been called.
+		// Check if app is still locked, lockable
+		// and not finishing (which is possible if recreated)
+		if (!keyguardShown && lockManager.isLocked() && !isFinishing()) {
+			requestKeyguardUnlock();
+		} else if (!lockManager.isLocked()) {
+			setResult(RESULT_OK);
+			finish();
+		}
+	}
+
+	@Override
+	public void onBackPressed() {
+		moveTaskToBack(true);
+	}
+
+	private void requestKeyguardUnlock() {
+		KeyguardManager keyguardManager =
+				(KeyguardManager) getSystemService(KEYGUARD_SERVICE);
+		if (keyguardManager == null) throw new AssertionError();
+		Intent intent = keyguardManager.createConfirmDeviceCredentialIntent(
+				SDK_INT < 23 ? getString(R.string.lock_unlock_verbose) :
+						getString(R.string.lock_unlock), null);
+		if (intent == null) {
+			// the user must have removed the screen lock since locked
+			LOG.warning("Unlocking without keyguard");
+			unlock();
+		} else {
+			keyguardShown = true;
+			startActivityForResult(intent, REQUEST_KEYGUARD_UNLOCK);
+			overridePendingTransition(0, 0);
+		}
+	}
+
+	private void unlock() {
+		lockManager.setLocked(false);
+		setResult(RESULT_OK);
+		finish();
+		overridePendingTransition(0, 0);
+	}
+
+}

briar-android/src/main/java/org/briarproject/briar/android/navdrawer/NavDrawerActivity.java

@@ -7,6 +7,7 @@ import android.os.Bundle;
 import android.support.annotation.NonNull;
 import android.support.design.widget.NavigationView;
 import android.support.design.widget.NavigationView.OnNavigationItemSelectedListener;
+import android.support.v4.app.ActivityCompat;
 import android.support.v4.app.FragmentManager;
 import android.support.v4.app.FragmentTransaction;
 import android.support.v4.content.ContextCompat;
@@ -136,6 +137,8 @@ public class NavDrawerActivity extends BriarActivity implements
 		initializeTransports(getLayoutInflater());
 		transportsView.setAdapter(transportsAdapter);
 
+		lockManager.isLockable().observe(this, this::setLockVisible);
+
 		if (lifecycleManager.getLifecycleState().isAfter(RUNNING)) {
 			showSignOutFragment();
 		} else if (state == null) {
@@ -152,6 +155,7 @@ public class NavDrawerActivity extends BriarActivity implements
 	public void onStart() {
 		super.onStart();
 		updateTransports();
+		lockManager.checkIfLockable();
 		controller.showExpiryWarning(new UiResultHandler<ExpiryWarning>(this) {
 			@Override
 			public void onResultUi(ExpiryWarning expiry) {
@@ -213,9 +217,15 @@ public class NavDrawerActivity extends BriarActivity implements
 	public boolean onNavigationItemSelected(@NonNull MenuItem item) {
 		drawerLayout.closeDrawer(START);
 		clearBackStack();
-		loadFragment(item.getItemId());
-		// Don't display the Settings item as checked
-		return item.getItemId() != R.id.nav_btn_settings;
+		if (item.getItemId() == R.id.nav_btn_lock) {
+			lockManager.setLocked(true);
+			ActivityCompat.finishAfterTransition(this);
+			return false;
+		} else {
+			loadFragment(item.getItemId());
+			// Don't display the Settings item as checked
+			return item.getItemId() != R.id.nav_btn_settings;
+		}
 	}
 
 	@Override
@@ -301,6 +311,11 @@ public class NavDrawerActivity extends BriarActivity implements
 		// Do nothing for now
 	}
 
+	private void setLockVisible(boolean visible) {
+		MenuItem item = navigation.getMenu().findItem(R.id.nav_btn_lock);
+		if (item != null) item.setVisible(visible);
+	}
+
 	@SuppressWarnings("ConstantConditions")
 	private void showExpiryWarning(ExpiryWarning expiry) {
 		int daysUntilExpiry = getDaysUntilExpiry();

briar-android/src/main/java/org/briarproject/briar/android/settings/SettingsFragment.java

@@ -82,10 +82,12 @@ import static org.briarproject.bramble.util.LogUtils.logException;
 import static org.briarproject.bramble.util.LogUtils.now;
 import static org.briarproject.bramble.util.StringUtils.join;
 import static org.briarproject.briar.android.TestingConstants.FEATURE_FLAG_DARK_THEME;
+import static org.briarproject.briar.android.TestingConstants.FEATURE_FLAG_PIN_LOCK;
 import static org.briarproject.briar.android.TestingConstants.FEATURE_FLAG_SIGN_IN_REMINDER;
 import static org.briarproject.briar.android.TestingConstants.IS_DEBUG_BUILD;
 import static org.briarproject.briar.android.activity.RequestCodes.REQUEST_RINGTONE;
 import static org.briarproject.briar.android.navdrawer.NavDrawerActivity.INTENT_SIGN_OUT;
+import static org.briarproject.briar.android.util.UiUtils.hasScreenLock;
 import static org.briarproject.briar.api.android.AndroidNotificationManager.BLOG_CHANNEL_ID;
 import static org.briarproject.briar.api.android.AndroidNotificationManager.CONTACT_CHANNEL_ID;
 import static org.briarproject.briar.api.android.AndroidNotificationManager.FORUM_CHANNEL_ID;
@@ -109,6 +111,7 @@ public class SettingsFragment extends PreferenceFragmentCompat
 	public static final String BT_NAMESPACE = BluetoothConstants.ID.getString();
 	public static final String TOR_NAMESPACE = TorConstants.ID.getString();
 	public static final String LANGUAGE = "pref_key_language";
+	public static final String PREF_SCREEN_LOCK = "pref_key_lock";
 	public static final String NOTIFY_SIGN_IN = "pref_key_notify_sign_in";
 	public static final String TOR_LOCATION = "pref_key_tor_location";
 
@@ -120,13 +123,13 @@ public class SettingsFragment extends PreferenceFragmentCompat
 	private ListPreference enableBluetooth;
 	private ListPreference torNetwork;
 	private SwitchPreference torBlocked;
+	private SwitchPreference screenLock;
 	private SwitchPreference notifyPrivateMessages;
 	private SwitchPreference notifyGroupMessages;
 	private SwitchPreference notifyForumPosts;
 	private SwitchPreference notifyBlogPosts;
 	private SwitchPreference notifyVibration;
 	private SwitchPreference notifyLockscreen;
-
 	private Preference notifySound;
 
 	// Fields that are accessed from background threads must be volatile
@@ -162,6 +165,7 @@ public class SettingsFragment extends PreferenceFragmentCompat
 		setBlockedCountries();
 		SwitchPreference notifySignIn =
 				(SwitchPreference) findPreference(NOTIFY_SIGN_IN);
+		screenLock = (SwitchPreference) findPreference(PREF_SCREEN_LOCK);
 		notifyPrivateMessages = (SwitchPreference) findPreference(
 				"pref_key_notify_private_messages");
 		notifyGroupMessages = (SwitchPreference) findPreference(
@@ -176,8 +180,6 @@ public class SettingsFragment extends PreferenceFragmentCompat
 				"pref_key_notify_lock_screen");
 		notifySound = findPreference("pref_key_notify_sound");
 
-		setSettingsEnabled(false);
-
 		language.setOnPreferenceChangeListener(this);
 		theme.setOnPreferenceChangeListener((preference, newValue) -> {
 			if (getActivity() != null) {
@@ -200,6 +202,7 @@ public class SettingsFragment extends PreferenceFragmentCompat
 		enableBluetooth.setOnPreferenceChangeListener(this);
 		torNetwork.setOnPreferenceChangeListener(this);
 		torBlocked.setOnPreferenceChangeListener(this);
+		screenLock.setOnPreferenceChangeListener(this);
 		if (SDK_INT >= 21) {
 			notifyLockscreen.setVisible(true);
 			notifyLockscreen.setOnPreferenceChangeListener(this);
@@ -220,6 +223,7 @@ public class SettingsFragment extends PreferenceFragmentCompat
 		} else {
 			theme.setVisible(FEATURE_FLAG_DARK_THEME);
 			notifySignIn.setVisible(FEATURE_FLAG_SIGN_IN_REMINDER);
+			screenLock.setVisible(FEATURE_FLAG_PIN_LOCK);
 
 			findPreference("pref_key_explode").setVisible(false);
 			findPreference("pref_key_test_data").setVisible(false);
@@ -229,7 +233,6 @@ public class SettingsFragment extends PreferenceFragmentCompat
 			testing.setVisible(false);
 		}
 
-		loadSettings();
 	}
 
 	@Override
@@ -246,6 +249,8 @@ public class SettingsFragment extends PreferenceFragmentCompat
 	public void onStart() {
 		super.onStart();
 		eventBus.addListener(this);
+		setSettingsEnabled(false);
+		loadSettings();
 	}
 
 	@Override
@@ -354,6 +359,7 @@ public class SettingsFragment extends PreferenceFragmentCompat
 			enableBluetooth.setValue(Boolean.toString(btSetting));
 			torNetwork.setValue(Integer.toString(torNetworkSetting));
 			torBlocked.setChecked(torBlockedSetting);
+			displayScreenLockSetting();
 
 			if (SDK_INT < 26) {
 				notifyPrivateMessages.setChecked(settings.getBoolean(
@@ -411,9 +417,12 @@ public class SettingsFragment extends PreferenceFragmentCompat
 		// preferences not needed here, because handled by SharedPreferences:
 		// - pref_key_theme
 		// - pref_key_notify_sign_in
+		// preferences partly needed here, because they have their own logic
+		// - pref_key_lock (screenLock -> displayScreenLockSetting())
 		enableBluetooth.setEnabled(enabled);
 		torNetwork.setEnabled(enabled);
 		torBlocked.setEnabled(enabled);
+		if (!enabled) screenLock.setEnabled(false);
 		notifyPrivateMessages.setEnabled(enabled);
 		notifyGroupMessages.setEnabled(enabled);
 		notifyForumPosts.setEnabled(enabled);
@@ -423,6 +432,23 @@ public class SettingsFragment extends PreferenceFragmentCompat
 		notifySound.setEnabled(enabled);
 	}
 
+	private void displayScreenLockSetting() {
+		if (SDK_INT < 21) {
+			screenLock.setVisible(false);
+		} else {
+			if (getActivity() != null && hasScreenLock(getActivity())) {
+				screenLock.setEnabled(true);
+				screenLock.setChecked(
+						settings.getBoolean(PREF_SCREEN_LOCK, false));
+				screenLock.setSummary(R.string.pref_lock_summary);
+			} else {
+				screenLock.setEnabled(false);
+				screenLock.setChecked(false);
+				screenLock.setSummary(R.string.pref_lock_disabled_summary);
+			}
+		}
+	}
+
 	@TargetApi(26)
 	private void setupNotificationPreference(SwitchPreference pref,
 			String channelId, @StringRes int summary) {
@@ -478,6 +504,10 @@ public class SettingsFragment extends PreferenceFragmentCompat
 		} else if (preference == torBlocked) {
 			boolean torBlockedSetting = (Boolean) newValue;
 			storeTorBlockedSetting(torBlockedSetting);
+		} else if (preference == screenLock) {
+			Settings s = new Settings();
+			s.putBoolean(PREF_SCREEN_LOCK, (Boolean) newValue);
+			storeSettings(s);
 		} else if (preference == notifyPrivateMessages) {
 			Settings s = new Settings();
 			s.putBoolean(PREF_NOTIFY_PRIVATE, (Boolean) newValue);

briar-android/src/main/java/org/briarproject/briar/android/splash/SplashScreenActivity.java

@@ -14,6 +14,8 @@ import org.briarproject.briar.android.activity.ActivityComponent;
 import org.briarproject.briar.android.activity.BaseActivity;
 import org.briarproject.briar.android.login.OpenDatabaseActivity;
 import org.briarproject.briar.android.login.SetupActivity;
+import org.briarproject.briar.android.navdrawer.NavDrawerActivity;
+import org.briarproject.briar.api.android.LockManager;
 
 import java.util.logging.Logger;
 
@@ -29,6 +31,8 @@ public class SplashScreenActivity extends BaseActivity {
 	@Inject
 	protected AccountManager accountManager;
 	@Inject
+	protected LockManager lockManager;
+	@Inject
 	protected AndroidExecutor androidExecutor;
 
 	@Override
@@ -44,7 +48,16 @@ public class SplashScreenActivity extends BaseActivity {
 		setContentView(R.layout.splash);
 
 		if (accountManager.hasDatabaseKey()) {
-			startActivity(new Intent(this, OpenDatabaseActivity.class));
+			Intent i;
+			if (lockManager.isLocked()) {
+				// The database needs to be opened for the app to be locked.
+				// Start main activity right away. It will open UnlockActivity.
+				// Otherwise, we would end up with two screen unlock inputs.
+				i = new Intent(this, NavDrawerActivity.class);
+			} else {
+				i = new Intent(this, OpenDatabaseActivity.class);
+			}
+			startActivity(i);
 			finish();
 		} else {
 			new Handler().postDelayed(() -> {

briar-android/src/main/java/org/briarproject/briar/android/util/UiUtils.java

@@ -2,6 +2,7 @@ package org.briarproject.briar.android.util;
 
 import android.annotation.SuppressLint;
 import android.annotation.TargetApi;
+import android.app.KeyguardManager;
 import android.content.Context;
 import android.content.DialogInterface.OnClickListener;
 import android.content.Intent;
@@ -36,6 +37,7 @@ import org.briarproject.briar.android.widget.LinkDialogFragment;
 
 import javax.annotation.Nullable;
 
+import static android.content.Context.KEYGUARD_SERVICE;
 import static android.content.Context.POWER_SERVICE;
 import static android.content.Intent.CATEGORY_DEFAULT;
 import static android.content.Intent.FLAG_ACTIVITY_NEW_TASK;
@@ -229,4 +231,15 @@ public class UiUtils {
 		return ContextCompat.getColor(ctx, color);
 	}
 
+	public static boolean hasScreenLock(Context ctx) {
+		if (SDK_INT < 21) return false;
+		KeyguardManager keyguardManager =
+				(KeyguardManager) ctx.getSystemService(KEYGUARD_SERVICE);
+		if (keyguardManager == null) return false;
+		// check if there's a lock mechanism we can use
+		// first one is true if SIM card is locked, so use second if available
+		return (SDK_INT < 23 && keyguardManager.isKeyguardSecure()) ||
+				(SDK_INT >= 23 && keyguardManager.isDeviceSecure());
+	}
+
 }

briar-android/src/main/java/org/briarproject/briar/api/android/AndroidNotificationManager.java

@@ -1,5 +1,7 @@
 package org.briarproject.briar.api.android;
 
+import android.app.Notification;
+
 import org.briarproject.bramble.api.contact.ContactId;
 import org.briarproject.bramble.api.sync.GroupId;
 
@@ -52,6 +54,10 @@ public interface AndroidNotificationManager {
 	// Actions for pending intents
 	String ACTION_DISMISS_REMINDER = "dismissReminder";
 
+	Notification getForegroundNotification();
+
+	void updateForegroundNotification(boolean locked);
+
 	void clearContactNotification(ContactId c);
 
 	void clearAllContactNotifications();

briar-android/src/main/java/org/briarproject/briar/api/android/LockManager.java

@@ -0,0 +1,33 @@
+package org.briarproject.briar.api.android;
+
+import android.arch.lifecycle.LiveData;
+import android.support.annotation.UiThread;
+
+public interface LockManager {
+
+	/**
+	 * Returns an observable LiveData to indicate whether the app can be locked.
+	 */
+	LiveData<Boolean> isLockable();
+
+	/**
+	 * Updates the LiveData returned by {@link #isLockable()}.
+	 * It checks whether a device screen lock is available and
+	 * whether the app setting is checked.
+	 */
+	@UiThread
+	void checkIfLockable();
+
+	/**
+	 * Returns true if app is currently locked, false otherwise.
+	 * If the device's screen lock was removed while the app was locked,
+	 * calling this will unlock the app automatically.
+	 */
+	boolean isLocked();
+
+	/**
+	 * Locks the app if true is passed, otherwise unlocks the app.
+	 */
+	void setLocked(boolean locked);
+
+}