implemented an E2E-encrypted Nextcloud push-v2 notification system with support for RSA decryption and signature verification; introduced an iOS Notification Service Extension and native AppDelegate handlers for Talk actions (inline reply and mark-as-read); replaced the legacy notification registration with a new lifecycle managing app passwords and secure keypair storage; added background message handling with tray synchronization and a test notification utility in the settings.

lib/push/push_decryptor.dart

@@ -0,0 +1,77 @@
+import 'dart:convert';
+import 'dart:typed_data';
+
+import 'package:crypton/crypton.dart';
+import 'package:pointycastle/export.dart' as pc;
+
+import 'push_subject.dart';
+
+/// Verifies and decrypts the encrypted `subject` of a Nextcloud push-v2
+/// notification. Pure crypto, no plugin/platform access, so it runs safely
+/// inside the FCM background isolate.
+///
+/// - Signature: `SHA512withRSA` over the *encrypted* subject bytes, verified
+///   with the per-user server public key returned at registration.
+/// - Encryption: the subject is encrypted with the device public key, so the
+///   device decrypts with its private key. Nextcloud 32 defaults to
+///   OAEP (SHA-1/MGF1-SHA-1); older instances use PKCS#1 v1.5. We try OAEP
+///   first and fall back to PKCS#1.
+class PushDecryptor {
+  final RSAPrivateKey devicePrivateKey;
+
+  /// Per-user server public key (the `publicKey` from the NC registration
+  /// response). When null, signature verification is skipped.
+  final RSAPublicKey? serverPublicKey;
+
+  const PushDecryptor({required this.devicePrivateKey, this.serverPublicKey});
+
+  /// Returns true when [signatureBase64] is a valid server signature over the
+  /// encrypted subject. Returns true when no server key is configured (the
+  /// proxy already verified the signature before forwarding).
+  bool verify(String subjectBase64, String signatureBase64) {
+    final key = serverPublicKey;
+    if (key == null) return true;
+    try {
+      final signed = Uint8List.fromList(base64.decode(subjectBase64));
+      final signature = Uint8List.fromList(base64.decode(signatureBase64));
+      return key.verifySHA512Signature(signed, signature);
+    } on Object {
+      return false;
+    }
+  }
+
+  /// Decrypts the base64 subject into a [PushSubject], or returns null when
+  /// neither padding scheme yields valid JSON.
+  PushSubject? decrypt(String subjectBase64) {
+    final encrypted = Uint8List.fromList(base64.decode(subjectBase64));
+    final plain = _decryptOaep(encrypted) ?? _decryptPkcs1(encrypted);
+    if (plain == null) return null;
+    try {
+      final json = jsonDecode(plain) as Map<String, dynamic>;
+      return PushSubject.fromJson(json);
+    } on Object {
+      return null;
+    }
+  }
+
+  String? _decryptOaep(Uint8List data) =>
+      _tryDecrypt(pc.OAEPEncoding(pc.RSAEngine()), data);
+
+  String? _decryptPkcs1(Uint8List data) =>
+      _tryDecrypt(pc.PKCS1Encoding(pc.RSAEngine()), data);
+
+  String? _tryDecrypt(pc.AsymmetricBlockCipher cipher, Uint8List data) {
+    try {
+      cipher.init(
+        false,
+        pc.PrivateKeyParameter<pc.RSAPrivateKey>(
+          devicePrivateKey.asPointyCastle,
+        ),
+      );
+      final out = cipher.process(data);
+      return utf8.decode(out);
+    } on Object {
+      return null;
+    }
+  }
+}