feat(push): Optionally use OAEP padding

app/src/gplay/java/com/owncloud/android/services/firebase/NCFirebaseMessagingService.java

@@ -28,6 +28,9 @@
 import androidx.annotation.NonNull;
 import dagger.android.AndroidInjection;
 
+/**
+ * Works only with gplay variant and Google Play Services installed devices.
+ */
 public class NCFirebaseMessagingService extends FirebaseMessagingService {
     @Inject AppPreferences preferences;
     @Inject UserAccountManager accountManager;

app/src/main/java/com/nextcloud/client/jobs/NotificationWork.kt

@@ -55,6 +55,7 @@ import java.io.IOException
 import java.security.GeneralSecurityException
 import java.security.PrivateKey
 import java.security.SecureRandom
+import javax.crypto.BadPaddingException
 import javax.crypto.Cipher
 import javax.inject.Inject
 
@@ -96,9 +97,7 @@ class NotificationWork constructor(
                         base64DecodedSubject
                     )
                     if (signatureVerification != null && signatureVerification.signatureValid) {
-                        val cipher = Cipher.getInstance("RSA/None/PKCS1Padding")
-                        cipher.init(Cipher.DECRYPT_MODE, privateKey)
-                        val decryptedSubject = cipher.doFinal(base64DecodedSubject)
+                        val decryptedSubject = decryptSubject(privateKey, base64DecodedSubject)
                         val gson = Gson()
                         val decryptedPushMessage = gson.fromJson(
                             String(decryptedSubject),
@@ -124,6 +123,17 @@ class NotificationWork constructor(
         return Result.success()
     }
 
+    private fun decryptSubject(privateKey: PrivateKey, base64DecodedSubject: ByteArray): ByteArray = try {
+        val cipher = Cipher.getInstance("RSA/ECB/OAEPWithSHA-1AndMGF1Padding")
+        cipher.init(Cipher.DECRYPT_MODE, privateKey)
+        cipher.doFinal(base64DecodedSubject)
+    } catch (e: BadPaddingException) {
+        Log_OC.e(TAG, "OAEP padding failed, trying PKCS1 for compatibility", e)
+        val cipher = Cipher.getInstance("RSA/None/PKCS1Padding")
+        cipher.init(Cipher.DECRYPT_MODE, privateKey)
+        cipher.doFinal(base64DecodedSubject)
+    }
+
     @Suppress("LongMethod") // legacy code
     private fun sendNotification(notification: Notification, user: User) {
         val randomId = SecureRandom()