Automate backups:

- backup wallet file on each channel creation
 - on android, a backup password is entered in settings
 - on desktop, the backup path is in settings

electrum/gui/kivy/main_window.py

@@ -1199,21 +1199,31 @@ class ElectrumWindow(App):
                                    on_success=on_success, on_failure=on_failure, is_change=1)
         self._password_dialog.open()
 
-    def save_backup(self):
+    def change_backup_password(self):
         from .uix.dialogs.password_dialog import PasswordDialog
         from electrum.util import get_backup_dir
+        from electrum.storage import WalletStorage
         if self._password_dialog is None:
             self._password_dialog = PasswordDialog()
         message = _("Create backup.") + '\n' + _("Enter your current PIN:")
         def on_success(old_password, new_password):
-            new_path = os.path.join(get_backup_dir(self.electrum_config), self.wallet.basename() + '.backup')
-            self.wallet.save_backup(new_path, old_password=old_password, new_password=new_password)
-            self.show_info(_("Backup saved:") + f"\n{new_path}")
-        on_failure = lambda: self.show_error(_("PIN codes do not match"))
+            backup_pubkey = WalletStorage.get_eckey_from_password(new_password).get_public_key_hex()
+            # TODO: use a unique PIN for all wallets
+            self.electrum_config.set_key('pin_code', old_password)
+            self.electrum_config.set_key('backup_pubkey', backup_pubkey)
+            self.show_info(_("Backup password set"))
+        on_failure = lambda: self.show_error(_("Passwords do not match"))
         self._password_dialog.init(self, wallet=self.wallet, msg=message,
                                    on_success=on_success, on_failure=on_failure, is_change=1, is_backup=True)
         self._password_dialog.open()
 
+    def save_backup(self):
+        new_path = self.wallet.save_backup()
+        if new_path:
+            self.show_info(_("Backup saved:") + f"\n{new_path}")
+        else:
+            self.show_error(_("Backup directory not configured"))
+
     def export_private_keys(self, pk_label, addr):
         if self.wallet.is_watching_only():
             self.show_info(_('This is a watching-only wallet. It does not contain private keys.'))

electrum/gui/kivy/uix/dialogs/settings.py

@@ -82,6 +82,11 @@ Builder.load_string('''
                     description: _("Send your change to separate addresses.")
                     message: _('Send excess coins to change addresses')
                     action: partial(root.boolean_dialog, 'use_change', _('Use change addresses'), self.message)
+                CardSeparator
+                SettingsItem:
+                    title: _('Backups')
+                    description: _("Set password for encrypted backups.")
+                    action: root.change_backup_password
 
                 # disabled: there is currently only one coin selection policy
                 #CardSeparator
@@ -121,6 +126,9 @@ class SettingsDialog(Factory.Popup):
     def change_password(self, item, dt):
         self.app.change_password(self.update)
 
+    def change_backup_password(self, dt):
+        self.app.change_backup_password()
+
     def language_dialog(self, item, dt):
         if self._language_dialog is None:
             l = self.config.get('language', 'en_UK')

electrum/gui/qt/main_window.py

@@ -562,20 +562,15 @@ class ElectrumWindow(QMainWindow, MessageBoxMixin, Logger):
         self.gui_object.new_window(filename)
 
     def backup_wallet(self):
-        path = self.wallet.storage.path
-        wallet_folder = os.path.dirname(path)
-        filename, __ = QFileDialog.getSaveFileName(self, _('Enter a filename for the copy of your wallet'), wallet_folder)
-        if not filename:
-            return
-        new_path = os.path.join(wallet_folder, filename)
-        if new_path == path:
-            return
         try:
-            self.wallet.save_backup(new_path)
+            new_path = self.wallet.save_backup()
         except BaseException as reason:
             self.show_critical(_("Electrum was unable to copy your wallet file to the specified location.") + "\n" + str(reason), title=_("Unable to create backup"))
             return
+        if new_path:
             self.show_message(_("A copy of your wallet file was created in")+" '%s'" % str(new_path), title=_("Wallet backup created"))
+        else:
+            self.show_message(_("You need to configure a backup directory in your preferences"), title=_("Backup not created"))
 
     def update_recently_visited(self, filename):
         recent = self.config.get('recently_open', [])
@@ -617,7 +612,7 @@ class ElectrumWindow(QMainWindow, MessageBoxMixin, Logger):
         self.recently_visited_menu = file_menu.addMenu(_("&Recently open"))
         file_menu.addAction(_("&Open"), self.open_wallet).setShortcut(QKeySequence.Open)
         file_menu.addAction(_("&New/Restore"), self.new_wallet).setShortcut(QKeySequence.New)
-        file_menu.addAction(_("&Save Copy"), self.backup_wallet).setShortcut(QKeySequence.SaveAs)
+        file_menu.addAction(_("&Save backup"), self.backup_wallet).setShortcut(QKeySequence.SaveAs)
         file_menu.addAction(_("Delete"), self.remove_wallet)
         file_menu.addSeparator()
         file_menu.addAction(_("&Quit"), self.close)

electrum/gui/qt/settings_dialog.py

@@ -145,6 +145,14 @@ class SettingsDialog(WindowModalDialog):
 
         # lightning
         lightning_widgets = []
+
+        backup_help = _("""A backup of your wallet file will be saved to that directory everytime you create a new channel. The backup cannot be used to perform lightning transactions; it may only be used to retrieve the funds in your open channels, using data loss protect (channels will be force closed).""")
+        backup_dir = self.config.get('backup_dir')
+        backup_dir_label = HelpLabel(_('Backup directory') + ':', backup_help)
+        self.backup_dir_e = QPushButton(backup_dir)
+        self.backup_dir_e.clicked.connect(self.select_backup_dir)
+        lightning_widgets.append((backup_dir_label, self.backup_dir_e))
+
         help_persist = _("""If this option is checked, Electrum will persist as a daemon after
 you close all your wallet windows. Your local watchtower will keep
 running, and it will protect your channels even if your wallet is not
@@ -546,6 +554,13 @@ that is always connected to the internet. Configure a port if you want it to be
         if alias:
             self.window.fetch_alias()
 
+    def select_backup_dir(self, b):
+        name = self.config.get('backup_dir', '')
+        dirname = QFileDialog.getExistingDirectory(self, "Select your SSL certificate file", name)
+        if dirname:
+            self.config.set_key('backup_dir', dirname)
+            self.backup_dir_e.setText(dirname)
+
     def select_ssl_certfile(self, b):
         name = self.config.get('ssl_certfile', '')
         filename, __ = QFileDialog.getOpenFileName(self, "Select your SSL certificate file", name)

electrum/lnworker.py

@@ -842,6 +842,7 @@ class LNWallet(LNWorker):
         with self.lock:
             self.channels[chan.channel_id] = chan
         self.lnwatcher.add_channel(chan.funding_outpoint.to_str(), chan.get_funding_address())
+        self.wallet.save_backup()
 
     @log_exceptions
     async def add_peer(self, connect_str: str) -> Peer:

electrum/util.py

@@ -442,7 +442,7 @@ def android_data_dir():
     return PythonActivity.mActivity.getFilesDir().getPath() + '/data'
 
 def get_backup_dir(config):
-    return android_backup_dir() if 'ANDROID_DATA' in os.environ else config.path
+    return android_backup_dir() if 'ANDROID_DATA' in os.environ else config.get('backup_dir')
 
 
 def ensure_sparse_file(filename):

electrum/wallet.py

@@ -51,7 +51,7 @@ from .util import (NotEnoughFunds, UserCancelled, profiler,
                    WalletFileException, BitcoinException, MultipleSpendMaxTxOutputs,
                    InvalidPassword, format_time, timestamp_to_datetime, Satoshis,
                    Fiat, bfh, bh2u, TxMinedInfo, quantize_feerate, create_bip21_uri, OrderedDictWithIndex)
-from .util import PR_TYPE_ONCHAIN, PR_TYPE_LN
+from .util import PR_TYPE_ONCHAIN, PR_TYPE_LN, get_backup_dir
 from .simple_config import SimpleConfig
 from .bitcoin import (COIN, is_address, address_to_script,
                       is_minikey, relayfee, dust_threshold)
@@ -263,15 +263,25 @@ class Abstract_Wallet(AddressSynchronizer, ABC):
         if self.storage:
             self.db.write(self.storage)
 
-    def save_backup(self, path, *, old_password=None, new_password=None):
+    def save_backup(self):
         new_db = WalletDB(self.db.dump(), manual_upgrades=False)
         new_db.put('is_backup', True)
-        new_storage = WalletStorage(path)
-        new_storage._encryption_version = StorageEncryptionVersion.PLAINTEXT
-        w2 = Wallet(new_db, new_storage, config=self.config)
-        if new_password:
-            w2.update_password(old_password, new_password, encrypt_storage=True)
-        w2.save_db()
+        new_path = os.path.join(get_backup_dir(self.config), self.basename() + '.backup')
+        if new_path is None:
+            return
+        new_storage = WalletStorage(new_path)
+        if 'ANDROID_DATA' in os.environ:
+            pin_code = self.config.get('pin_code')
+            w2 = Wallet(new_db, None, config=self.config)
+            w2.update_password(pin_code, None)
+            new_storage._encryption_version = StorageEncryptionVersion.USER_PASSWORD
+            new_storage.pubkey = self.config.get('backup_pubkey')
+        else:
+            new_storage._encryption_version = self.storage._encryption_version
+            new_storage.pubkey = self.storage.pubkey
+        new_db.set_modified(True)
+        new_db.write(new_storage)
+        return new_path
 
     def has_lightning(self):
         return bool(self.lnworker)