tx dialog: show various warnings if input amounts cannot be verified (#6217)

see #5749

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

@@ -132,9 +132,10 @@ class TxDialog(Factory.Popup):
         self.tx = tx  # type: Transaction
         self._action_button_fn = lambda btn: None
 
-        # if the wallet can populate the inputs with more info, do it now.
-        # as a result, e.g. we might learn an imported address tx is segwit,
-        # or that a beyond-gap-limit address is is_mine
+        # If the wallet can populate the inputs with more info, do it now.
+        # As a result, e.g. we might learn an imported address tx is segwit,
+        # or that a beyond-gap-limit address is is_mine.
+        # note: this might fetch prev txs over the network.
         tx.add_info_from_wallet(self.wallet)
 
     def on_open(self):
@@ -173,7 +174,7 @@ class TxDialog(Factory.Popup):
         risk_of_burning_coins = (isinstance(self.tx, PartialTransaction)
                                  and self.can_sign
                                  and fee is not None
-                                 and self.tx.is_there_risk_of_burning_coins_as_fees())
+                                 and bool(self.wallet.get_warning_for_risk_of_burning_coins_as_fees(self.tx)))
         if fee is not None and not risk_of_burning_coins:
             self.fee_str = format_amount(fee)
             fee_per_kb = fee / self.tx.estimated_size() * 1000

electrum/gui/qt/transaction_dialog.py

@@ -211,9 +211,10 @@ class BaseTxDialog(QDialog, MessageBoxMixin):
             self.tx.deserialize()
         except BaseException as e:
             raise SerializationError(e)
-        # if the wallet can populate the inputs with more info, do it now.
-        # as a result, e.g. we might learn an imported address tx is segwit,
-        # or that a beyond-gap-limit address is is_mine
+        # If the wallet can populate the inputs with more info, do it now.
+        # As a result, e.g. we might learn an imported address tx is segwit,
+        # or that a beyond-gap-limit address is is_mine.
+        # note: this might fetch prev txs over the network.
         tx.add_info_from_wallet(self.wallet)
 
     def do_broadcast(self):
@@ -479,8 +480,9 @@ class BaseTxDialog(QDialog, MessageBoxMixin):
                 fee_str += ' - ' + _('Warning') + ': ' + _("high fee") + '!'
         if isinstance(self.tx, PartialTransaction):
             risk_of_burning_coins = (can_sign and fee is not None
-                                     and self.tx.is_there_risk_of_burning_coins_as_fees())
-            self.fee_warning_icon.setVisible(risk_of_burning_coins)
+                                     and self.wallet.get_warning_for_risk_of_burning_coins_as_fees(self.tx))
+            self.fee_warning_icon.setToolTip(str(risk_of_burning_coins))
+            self.fee_warning_icon.setVisible(bool(risk_of_burning_coins))
         self.fee_label.setText(fee_str)
         self.size_label.setText(size_str)
         if ln_amount is None:
@@ -596,10 +598,6 @@ class BaseTxDialog(QDialog, MessageBoxMixin):
         pixmap_size = round(2 * char_width_in_lineedit())
         pixmap = pixmap.scaled(pixmap_size, pixmap_size, Qt.KeepAspectRatio, Qt.SmoothTransformation)
         self.fee_warning_icon.setPixmap(pixmap)
-        self.fee_warning_icon.setToolTip(_("Warning") + ": "
-                                         + _("The fee could not be verified. Signing non-segwit inputs is risky:\n"
-                                             "if this transaction was maliciously modified before you sign,\n"
-                                             "you might end up paying a higher mining fee than displayed."))
         self.fee_warning_icon.setVisible(False)
         fee_hbox.addWidget(self.fee_warning_icon)
         fee_hbox.addStretch(1)

electrum/transaction.py

@@ -1953,25 +1953,6 @@ class PartialTransaction(Transaction):
         for txin in self.inputs():
             txin.convert_utxo_to_witness_utxo()
 
-    def is_there_risk_of_burning_coins_as_fees(self) -> bool:
-        """Returns whether there is risk of burning coins as fees if we sign.
-
-        Note:
-            - legacy sighash does not commit to any input amounts
-            - BIP-0143 sighash only commits to the *corresponding* input amount
-            - BIP-taproot sighash commits to *all* input amounts
-        """
-        for txin in self.inputs():
-            # if we have full previous tx, we *know* the input amount
-            if txin.utxo:
-                continue
-            # if we have just the previous output, we only have guarantees if
-            # the sighash commits to this data
-            if txin.witness_utxo and Transaction.is_segwit_input(txin):
-                continue
-            return True
-        return False
-
     def remove_signatures(self):
         for txin in self.inputs():
             txin.part_sigs = {}

electrum/wallet.py

@@ -2023,6 +2023,40 @@ class Abstract_Wallet(AddressSynchronizer, ABC):
             self.sign_transaction(tx, password)
         return tx
 
+    def get_warning_for_risk_of_burning_coins_as_fees(self, tx: 'PartialTransaction') -> Optional[str]:
+        """Returns a warning message if there is risk of burning coins as fees if we sign.
+        Note that if not all inputs are ismine, e.g. coinjoin, the risk is not just about fees.
+
+        Note:
+            - legacy sighash does not commit to any input amounts
+            - BIP-0143 sighash only commits to the *corresponding* input amount
+            - BIP-taproot sighash commits to *all* input amounts
+        """
+        assert isinstance(tx, PartialTransaction)
+        # if we have all full previous txs, we *know* all the input amounts -> fine
+        if all([txin.utxo for txin in tx.inputs()]):
+            return None
+        # a single segwit input -> fine
+        if len(tx.inputs()) == 1 and Transaction.is_segwit_input(tx.inputs()[0]) and tx.inputs()[0].witness_utxo:
+            return None
+        # coinjoin or similar
+        if any([not self.is_mine(txin.address) for txin in tx.inputs()]):
+            return (_("Warning") + ": "
+                    + _("The input amounts could not be verified as the previous transactions are missing.\n"
+                        "The amount of money being spent CANNOT be verified."))
+        # some inputs are legacy
+        if any([not Transaction.is_segwit_input(txin) for txin in tx.inputs()]):
+            return (_("Warning") + ": "
+                    + _("The fee could not be verified. Signing non-segwit inputs is risky:\n"
+                        "if this transaction was maliciously modified before you sign,\n"
+                        "you might end up paying a higher mining fee than displayed."))
+        # all inputs are segwit
+        # https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2017-August/014843.html
+        return (_("Warning") + ": "
+                + _("If you received this transaction from an untrusted device, "
+                    "do not accept to sign it more than once,\n"
+                    "otherwise you could end up paying a different fee."))
+
 
 class Simple_Wallet(Abstract_Wallet):
     # wallet with a single keystore