add comments about xpub encryption

electrum/lnworker.py

@@ -3610,6 +3610,20 @@ class LNWallet(Logger):
         )
 
     def export_channel_backup(self, channel_id):
+        """Historically, we allowed watching-only wallets and hardware wallets
+        to have lightning channels.  Since these wallets do not have
+        private keys, we use their master public key to encrypt
+        channel backups. This allows users to import channel backups
+        in these wallets. Note that these are static backups: they
+        only allow to request a force close (and, in some scenarios,
+        to sweep funds after a channel has been force closed).
+
+        The creation of lightning channels in watching-only wallets
+        has been disabled for anchor channels. Note that it is still
+        possible to create non-anchor channels, see
+        config.ENABLE_ANCHOR_CHANNELS.
+
+        """
         xpub = self.wallet.get_fingerprint()
         backup_bytes = self.create_channel_backup(channel_id).to_bytes()
         assert backup_bytes == ImportedChannelBackupStorage.from_bytes(backup_bytes).to_bytes(), "roundtrip failed"

electrum/plugins/labels/labels.py

@@ -212,6 +212,10 @@ class LabelsPlugin(BasePlugin):
         return asyncio.run_coroutine_threadsafe(self.push_thread(wallet), wallet.network.asyncio_loop).result()
 
     def start_wallet(self, wallet: 'Abstract_Wallet'):
+        """Labels have the same level of privacy as the wallet transaction
+        history. Since the wallet master public key(s) give access to
+        the transaction history, we also use it to encrypt labels.
+        """
         if not wallet.network:
             return  # 'offline' mode
         mpk = wallet.get_fingerprint()

electrum/wallet.py

@@ -548,6 +548,9 @@ class Abstract_Wallet(ABC, Logger, EventListener):
             ln_xprv = self.keystore.get_lightning_xprv(password)
             self.db.put('lightning_xprv', ln_xprv)
         else:
+            # bip39 seeds and imported zprv.
+            # also, watching-only and hw wallets, if the user disables anchors.
+            # todo: we should kill that branch, it is a footgun.
             seed = os.urandom(32)
             node = BIP32Node.from_rootseed(seed, xtype='standard')
             ln_xprv = node.to_xprv()