wallet: add sighash check to class Abstract_Wallet

qml: use backend sighash check and add user confirmation path
qt: use backend sighash check and add user confirmation path
qml: include get_warning_for_risk_of_burning_coins_as_fees test in txdetails
qt: add warning icon to sighash warning
add sighash and fee checks to wallet.sign_transaction, making all warnings fatal unless ignore_warnings is set to True
tests: test sign_transaction on both code paths with ignore_warnings True and False,
raise specific exceptions TransactionPotentiallyDangerousException and TransactionDangerousException

electrum/gui/qml/components/TxDetails.qml

@@ -49,6 +49,16 @@ Pane {
                         text: qsTr('On-chain Transaction')
                     }
 
+                    InfoTextArea {
+                        id: warn
+                        Layout.columnSpan: 2
+                        Layout.fillWidth: true
+                        Layout.bottomMargin: constants.paddingLarge
+                        visible: txdetails.warning
+                        text: txdetails.warning
+                        iconStyle: InfoTextArea.IconStyle.Warn
+                    }
+
                     InfoTextArea {
                         id: bumpfeeinfo
                         Layout.columnSpan: 2
@@ -336,7 +346,20 @@ Pane {
                 icon.source: '../../icons/key.png'
                 text: qsTr('Sign')
                 visible: txdetails.canSign
-                onClicked: txdetails.sign()
+                onClicked: {
+                    if (txdetails.shouldConfirm) {
+                        var dialog = app.messageDialog.createObject(app, {
+                            text: qsTr('Confirm signing non-standard transaction?'),
+                            yesno: true
+                        })
+                        dialog.accepted.connect(function() {
+                            txdetails.sign()
+                        })
+                        dialog.open()
+                    } else {
+                        txdetails.sign()
+                    }
+                }
             }
 
             FlatButton {

electrum/gui/qml/qetxdetails.py

@@ -5,7 +5,7 @@ from PyQt6.QtCore import pyqtProperty, pyqtSignal, pyqtSlot, QObject
 from electrum.i18n import _
 from electrum.logging import get_logger
 from electrum.util import format_time, TxMinedInfo
-from electrum.transaction import tx_from_any, Transaction
+from electrum.transaction import tx_from_any, Transaction, PartialTxInput, Sighash, PartialTransaction
 from electrum.network import Network
 from electrum.address_synchronizer import TX_HEIGHT_UNCONF_PARENT, TX_HEIGHT_UNCONFIRMED, TX_HEIGHT_FUTURE
 
@@ -32,6 +32,7 @@ class QETxDetails(QObject, QtEventListener):
         self._txid = ''
         self._rawtx = ''
         self._label = ''
+        self._warning = ''
 
         self._tx = None  # type: Optional[Transaction]
 
@@ -56,6 +57,7 @@ class QETxDetails(QObject, QtEventListener):
         self._is_mined = False
         self._is_final = False
         self._lock_delay = 0
+        self._should_confirm = False
 
         self._mempool_depth = ''
 
@@ -140,6 +142,10 @@ class QETxDetails(QObject, QtEventListener):
     def status(self):
         return self._status
 
+    @pyqtProperty(str, notify=detailsChanged)
+    def warning(self):
+        return self._warning
+
     @pyqtProperty(QEAmount, notify=detailsChanged)
     def amount(self):
         return self._amount
@@ -240,6 +246,10 @@ class QETxDetails(QObject, QtEventListener):
     def lockDelay(self):
         return self._lock_delay
 
+    @pyqtProperty(bool, notify=detailsChanged)
+    def shouldConfirm(self):
+        return self._should_confirm
+
     def update(self, from_txid: bool = False):
         assert self._wallet
 
@@ -284,6 +294,9 @@ class QETxDetails(QObject, QtEventListener):
             fee_per_kb = txinfo.fee / size * 1000
             self._feerate_str = self._wallet.wallet.config.format_fee_rate(fee_per_kb)
 
+        self._should_confirm = False
+        should_reject = False
+
         self._lock_delay = 0
         self._is_mined = False if not txinfo.tx_mined_status else txinfo.tx_mined_status.height > 0
         if self._is_mined:
@@ -293,6 +306,10 @@ class QETxDetails(QObject, QtEventListener):
                 self._mempool_depth = self._wallet.wallet.config.depth_tooltip(txinfo.mempool_depth_bytes)
             elif txinfo.tx_mined_status.height == TX_HEIGHT_FUTURE:
                 self._lock_delay = txinfo.tx_mined_status.wanted_height - self._wallet.wallet.adb.get_local_height()
+            if isinstance(self._tx, PartialTransaction):
+                self._should_confirm, should_reject, message = self._wallet.wallet.check_sighash(self._tx)
+                if message:
+                    self._warning = '\n'.join([_('Danger! This transaction is non-standard!'), message])
 
         if self._wallet.wallet.lnworker:
             # Calling lnworker.get_onchain_history and wallet.get_full_history here
@@ -320,7 +337,13 @@ class QETxDetails(QObject, QtEventListener):
         self._can_cpfp = txinfo.can_cpfp and not txinfo.can_remove
         self._can_save_as_local = txinfo.can_save_as_local and not txinfo.can_remove
         self._can_remove = txinfo.can_remove
-        self._can_sign = not self._is_complete and self._wallet.wallet.can_sign(self._tx)
+        self._can_sign = not self._is_complete and self._wallet.wallet.can_sign(self._tx) and not should_reject
+
+        if isinstance(self._tx, PartialTransaction):
+            risk_of_burning_coins = (self._can_sign and txinfo.fee is not None
+                                     and self._wallet.wallet.get_warning_for_risk_of_burning_coins_as_fees(self._tx))
+            if risk_of_burning_coins:
+                self._warning = '\n'.join([self._warning, risk_of_burning_coins])
 
         self.detailsChanged.emit()
 

electrum/gui/qml/qewallet.py

@@ -512,7 +512,8 @@ class QEWallet(AuthMixin, QObject, QtEventListener):
 
     def do_sign(self, tx, broadcast):
         try:
-            tx = self.wallet.sign_transaction(tx, self.password)
+            # ignore_warnings=True, because UI checks and asks user confirmation itself
+            tx = self.wallet.sign_transaction(tx, self.password, ignore_warnings=True)
         except BaseException as e:
             self._logger.error(f'{e!r}')
             self.signFailed.emit(str(e))