diff --git a/apps/twofactor_backupcodes/appinfo/routes.php b/apps/twofactor_backupcodes/appinfo/routes.php
index 8adc9c3901e..243ffb1d1f8 100644
--- a/apps/twofactor_backupcodes/appinfo/routes.php
+++ b/apps/twofactor_backupcodes/appinfo/routes.php
@@ -1,4 +1,7 @@
 <?php
+
+declare(strict_types=1);
+
 /**
  *
  *
diff --git a/apps/twofactor_backupcodes/lib/Activity/Provider.php b/apps/twofactor_backupcodes/lib/Activity/Provider.php
index 12c71f68d1c..37122c33e1b 100644
--- a/apps/twofactor_backupcodes/lib/Activity/Provider.php
+++ b/apps/twofactor_backupcodes/lib/Activity/Provider.php
@@ -1,4 +1,7 @@
 <?php
+
+declare(strict_types=1);
+
 /**
  * @copyright Copyright (c) 2016 Christoph Wurst <christoph@winzerhof-wurst.at>
  *
@@ -53,7 +56,7 @@ class Provider implements IProvider {
 		$this->l10n = $l10n;
 	}
 
-	public function parse($language, IEvent $event, IEvent $previousEvent = null) {
+	public function parse($language, IEvent $event, IEvent $previousEvent = null): IEvent {
 		if ($event->getApp() !== 'twofactor_backupcodes') {
 			throw new InvalidArgumentException();
 		}
diff --git a/apps/twofactor_backupcodes/lib/Controller/SettingsController.php b/apps/twofactor_backupcodes/lib/Controller/SettingsController.php
index 04ec2e19e95..432a89bd25a 100644
--- a/apps/twofactor_backupcodes/lib/Controller/SettingsController.php
+++ b/apps/twofactor_backupcodes/lib/Controller/SettingsController.php
@@ -1,4 +1,7 @@
 <?php
+
+declare(strict_types=1);
+
 /**
  *
  *
@@ -56,7 +59,7 @@ class SettingsController extends Controller {
 	 *
 	 * @return JSONResponse
 	 */
-	public function createCodes() {
+	public function createCodes(): JSONResponse {
 		$user = $this->userSession->getUser();
 		$codes = $this->storage->createCodes($user);
 		return new JSONResponse([
diff --git a/apps/twofactor_backupcodes/lib/Db/BackupCode.php b/apps/twofactor_backupcodes/lib/Db/BackupCode.php
index 8b173890e3c..645c246ec6d 100644
--- a/apps/twofactor_backupcodes/lib/Db/BackupCode.php
+++ b/apps/twofactor_backupcodes/lib/Db/BackupCode.php
@@ -1,4 +1,7 @@
 <?php
+
+declare(strict_types=1);
+
 /**
  *
  *
diff --git a/apps/twofactor_backupcodes/lib/Db/BackupCodeMapper.php b/apps/twofactor_backupcodes/lib/Db/BackupCodeMapper.php
index 84972a5171a..9912f6770e3 100644
--- a/apps/twofactor_backupcodes/lib/Db/BackupCodeMapper.php
+++ b/apps/twofactor_backupcodes/lib/Db/BackupCodeMapper.php
@@ -1,4 +1,7 @@
 <?php
+
+declare(strict_types=1);
+
 /**
  *
  *
@@ -42,7 +45,7 @@ class BackupCodeMapper extends QBMapper {
 	 * @param IUser $user
 	 * @return BackupCode[]
 	 */
-	public function getBackupCodes(IUser $user) {
+	public function getBackupCodes(IUser $user): array {
 		/* @var IQueryBuilder $qb */
 		$qb = $this->db->getQueryBuilder();
 
@@ -56,14 +59,14 @@ class BackupCodeMapper extends QBMapper {
 	/**
 	 * @param IUser $user
 	 */
-	public function deleteCodes(IUser $user) {
+	public function deleteCodes(IUser $user): void {
 		$this->deleteCodesByUserId($user->getUID());
 	}
 
 	/**
 	 * @param string $uid
 	 */
-	public function deleteCodesByUserId($uid) {
+	public function deleteCodesByUserId(string $uid): void {
 		/* @var IQueryBuilder $qb */
 		$qb = $this->db->getQueryBuilder();
 
diff --git a/apps/twofactor_backupcodes/lib/Migration/Version1002Date20170607104347.php b/apps/twofactor_backupcodes/lib/Migration/Version1002Date20170607104347.php
index 68f0d5b3421..ffbb8023007 100644
--- a/apps/twofactor_backupcodes/lib/Migration/Version1002Date20170607104347.php
+++ b/apps/twofactor_backupcodes/lib/Migration/Version1002Date20170607104347.php
@@ -1,4 +1,7 @@
 <?php
+
+declare(strict_types=1);
+
 /**
  * @copyright Copyright (c) 2017 Joas Schilling <coding@schilljs.com>
  *
diff --git a/apps/twofactor_backupcodes/lib/Migration/Version1002Date20170607113030.php b/apps/twofactor_backupcodes/lib/Migration/Version1002Date20170607113030.php
index 771c74853d1..cfd76fefd00 100644
--- a/apps/twofactor_backupcodes/lib/Migration/Version1002Date20170607113030.php
+++ b/apps/twofactor_backupcodes/lib/Migration/Version1002Date20170607113030.php
@@ -1,4 +1,7 @@
 <?php
+
+declare(strict_types=1);
+
 /**
  * @copyright Copyright (c) 2017 Joas Schilling <coding@schilljs.com>
  *
diff --git a/apps/twofactor_backupcodes/lib/Migration/Version1002Date20170919123342.php b/apps/twofactor_backupcodes/lib/Migration/Version1002Date20170919123342.php
index dc42ad2545c..97863583ad2 100644
--- a/apps/twofactor_backupcodes/lib/Migration/Version1002Date20170919123342.php
+++ b/apps/twofactor_backupcodes/lib/Migration/Version1002Date20170919123342.php
@@ -1,4 +1,7 @@
 <?php
+
+declare(strict_types=1);
+
 /**
  * @copyright Copyright (c) 2017 Joas Schilling <coding@schilljs.com>
  *
diff --git a/apps/twofactor_backupcodes/lib/Migration/Version1002Date20170926101419.php b/apps/twofactor_backupcodes/lib/Migration/Version1002Date20170926101419.php
index f8df9e69844..12854f6ff0b 100644
--- a/apps/twofactor_backupcodes/lib/Migration/Version1002Date20170926101419.php
+++ b/apps/twofactor_backupcodes/lib/Migration/Version1002Date20170926101419.php
@@ -1,4 +1,7 @@
 <?php
+
+declare(strict_types=1);
+
 /**
  *
  *
diff --git a/apps/twofactor_backupcodes/lib/Service/BackupCodeStorage.php b/apps/twofactor_backupcodes/lib/Service/BackupCodeStorage.php
index d85e00c0a8c..e9ec187c360 100644
--- a/apps/twofactor_backupcodes/lib/Service/BackupCodeStorage.php
+++ b/apps/twofactor_backupcodes/lib/Service/BackupCodeStorage.php
@@ -1,4 +1,7 @@
 <?php
+
+declare(strict_types=1);
+
 /**
  *
  *
@@ -60,9 +63,10 @@ class BackupCodeStorage {
 
 	/**
 	 * @param IUser $user
+	 * @param int $number
 	 * @return string[]
 	 */
-	public function createCodes(IUser $user, $number = 10) {
+	public function createCodes(IUser $user, int $number = 10): array {
 		$result = [];
 
 		// Delete existing ones
@@ -90,7 +94,7 @@ class BackupCodeStorage {
 	 * @param IUser $user
 	 * @return bool
 	 */
-	public function hasBackupCodes(IUser $user) {
+	public function hasBackupCodes(IUser $user): bool {
 		$codes = $this->mapper->getBackupCodes($user);
 		return count($codes) > 0;
 	}
@@ -99,7 +103,7 @@ class BackupCodeStorage {
 	 * @param IUser $user
 	 * @return array
 	 */
-	public function getBackupCodesState(IUser $user) {
+	public function getBackupCodesState(IUser $user): array {
 		$codes = $this->mapper->getBackupCodes($user);
 		$total = count($codes);
 		$used = 0;
@@ -120,7 +124,7 @@ class BackupCodeStorage {
 	 * @param string $code
 	 * @return bool
 	 */
-	public function validateCode(IUser $user, $code) {
+	public function validateCode(IUser $user, string $code): bool {
 		$dbCodes = $this->mapper->getBackupCodes($user);
 
 		foreach ($dbCodes as $dbCode) {
diff --git a/apps/twofactor_backupcodes/templates/challenge.php b/apps/twofactor_backupcodes/templates/challenge.php
index d269fb4b47e..e4792c8256a 100644
--- a/apps/twofactor_backupcodes/templates/challenge.php
+++ b/apps/twofactor_backupcodes/templates/challenge.php
@@ -1,4 +1,7 @@
 <?php
+
+declare(strict_types=1);
+
 style('twofactor_backupcodes', 'style');
 ?>
 
diff --git a/apps/twofactor_backupcodes/templates/personal.php b/apps/twofactor_backupcodes/templates/personal.php
index c57a589a26a..12def69bbed 100644
--- a/apps/twofactor_backupcodes/templates/personal.php
+++ b/apps/twofactor_backupcodes/templates/personal.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 script('twofactor_backupcodes', 'settings');
 
 ?>
diff --git a/apps/twofactor_backupcodes/tests/Db/BackupCodeMapperTest.php b/apps/twofactor_backupcodes/tests/Db/BackupCodeMapperTest.php
index 17155c266de..5617138f7b1 100644
--- a/apps/twofactor_backupcodes/tests/Db/BackupCodeMapperTest.php
+++ b/apps/twofactor_backupcodes/tests/Db/BackupCodeMapperTest.php
@@ -1,4 +1,7 @@
 <?php
+
+declare(strict_types=1);
+
 /**
  *
  *
diff --git a/apps/twofactor_backupcodes/tests/Service/BackupCodeStorageTest.php b/apps/twofactor_backupcodes/tests/Service/BackupCodeStorageTest.php
index 8aadacec767..264dc822ab8 100644
--- a/apps/twofactor_backupcodes/tests/Service/BackupCodeStorageTest.php
+++ b/apps/twofactor_backupcodes/tests/Service/BackupCodeStorageTest.php
@@ -1,4 +1,7 @@
 <?php
+
+declare(strict_types=1);
+
 /**
  *
  *
diff --git a/apps/twofactor_backupcodes/tests/Unit/Activity/ProviderTest.php b/apps/twofactor_backupcodes/tests/Unit/Activity/ProviderTest.php
index fce23f2ada5..85923bfe0df 100644
--- a/apps/twofactor_backupcodes/tests/Unit/Activity/ProviderTest.php
+++ b/apps/twofactor_backupcodes/tests/Unit/Activity/ProviderTest.php
@@ -1,4 +1,7 @@
 <?php
+
+declare(strict_types=1);
+
 /**
  * @copyright Copyright (c) 2017 Christoph Wurst <christoph@winzerhof-wurst.at>
  *
diff --git a/apps/twofactor_backupcodes/tests/Unit/Controller/SettingsControllerTest.php b/apps/twofactor_backupcodes/tests/Unit/Controller/SettingsControllerTest.php
index fc085472529..a9cb7b8b2dd 100644
--- a/apps/twofactor_backupcodes/tests/Unit/Controller/SettingsControllerTest.php
+++ b/apps/twofactor_backupcodes/tests/Unit/Controller/SettingsControllerTest.php
@@ -1,4 +1,7 @@
 <?php
+
+declare(strict_types=1);
+
 /**
  *
  *
diff --git a/apps/twofactor_backupcodes/tests/Unit/Provider/BackupCodesProviderTest.php b/apps/twofactor_backupcodes/tests/Unit/Provider/BackupCodesProviderTest.php
index 683a196bf86..1b5b2c307a8 100644
--- a/apps/twofactor_backupcodes/tests/Unit/Provider/BackupCodesProviderTest.php
+++ b/apps/twofactor_backupcodes/tests/Unit/Provider/BackupCodesProviderTest.php
@@ -1,4 +1,7 @@
 <?php
+
+declare(strict_types=1);
+
 /**
  *
  *
diff --git a/apps/twofactor_backupcodes/tests/Unit/Service/BackupCodeStorageTest.php b/apps/twofactor_backupcodes/tests/Unit/Service/BackupCodeStorageTest.php
index 74dfa80a30f..a4c29ca5ecc 100644
--- a/apps/twofactor_backupcodes/tests/Unit/Service/BackupCodeStorageTest.php
+++ b/apps/twofactor_backupcodes/tests/Unit/Service/BackupCodeStorageTest.php
@@ -1,4 +1,7 @@
 <?php
+
+declare(strict_types=1);
+
 /**
  *
  *