diff --git a/lib/src/utils/crypto/encrypted_file.dart b/lib/src/utils/crypto/encrypted_file.dart
index 847bf616..754e5ced 100644
--- a/lib/src/utils/crypto/encrypted_file.dart
+++ b/lib/src/utils/crypto/encrypted_file.dart
@@ -1,4 +1,3 @@
-// @dart=2.9
 /*
  *   Famedly Matrix SDK
  *   Copyright (C) 2019, 2020, 2021 Famedly GmbH
@@ -23,10 +22,10 @@ import 'crypto.dart';
 
 class EncryptedFile {
   EncryptedFile({
-    this.data,
-    this.k,
-    this.iv,
-    this.sha256,
+    required this.data,
+    required this.k,
+    required this.iv,
+    required this.sha256,
   });
   Uint8List data;
   String k;
@@ -47,7 +46,7 @@ Future<EncryptedFile> encryptFile(Uint8List input) async {
   );
 }
 
-Future<Uint8List> decryptFile(EncryptedFile input) async {
+Future<Uint8List?> decryptFile(EncryptedFile input) async {
   if (base64.encode(await sha256(input.data)) !=
       base64.normalize(input.sha256)) {
     return null;
diff --git a/lib/src/utils/crypto/js.dart b/lib/src/utils/crypto/js.dart
index 56099614..aeb72996 100644
--- a/lib/src/utils/crypto/js.dart
+++ b/lib/src/utils/crypto/js.dart
@@ -1,10 +1,11 @@
-// @dart=2.9
 // Copyright (c) 2020 Famedly GmbH
 // SPDX-License-Identifier: AGPL-3.0-or-later
 
 import 'dart:typed_data';
 
+// ignore: import_of_legacy_library_into_null_safe
 import 'subtle.dart';
+// ignore: import_of_legacy_library_into_null_safe
 import 'subtle.dart' as subtle;
 
 abstract class Hash {
diff --git a/lib/src/utils/crypto/subtle.dart b/lib/src/utils/crypto/subtle.dart
index 6216c639..a850344e 100644
--- a/lib/src/utils/crypto/subtle.dart
+++ b/lib/src/utils/crypto/subtle.dart
@@ -1,4 +1,3 @@
-// @dart=2.9
 // Copyright (c) 2020 Famedly GmbH
 // SPDX-License-Identifier: AGPL-3.0-or-later
 
@@ -16,21 +15,29 @@ class CryptoKey {}
 @JS()
 @anonymous
 class Pbkdf2Params {
-  external factory Pbkdf2Params(
-      {String name, String hash, Uint8List salt, int iterations});
-  String name;
-  String hash;
-  Uint8List salt;
-  int iterations;
+  external factory Pbkdf2Params({
+    String name,
+    String hash,
+    Uint8List salt,
+    int iterations,
+  });
+  String? name;
+  String? hash;
+  Uint8List? salt;
+  int? iterations;
 }
 
 @JS()
 @anonymous
 class AesCtrParams {
-  external factory AesCtrParams({String name, Uint8List counter, int length});
-  String name;
-  Uint8List counter;
-  int length;
+  external factory AesCtrParams({
+    String name,
+    Uint8List counter,
+    int length,
+  });
+  String? name;
+  Uint8List? counter;
+  int? length;
 }
 
 @JS('crypto.subtle.encrypt')