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/commands.py

@@ -469,10 +469,10 @@ class Commands:
         return tx.serialize()
 
     @command('wp')
-    async def signtransaction(self, tx, password=None, wallet: Abstract_Wallet = None):
+    async def signtransaction(self, tx, password=None, wallet: Abstract_Wallet = None, iknowwhatimdoing: bool=False):
         """Sign a transaction. The wallet keys will be used to sign the transaction."""
         tx = tx_from_any(tx)
-        wallet.sign_transaction(tx, password)
+        wallet.sign_transaction(tx, password, ignore_warnings=iknowwhatimdoing)
         return tx.serialize()
 
     @command('')

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))

electrum/gui/qt/main_window.py

@@ -1270,7 +1270,8 @@ class ElectrumWindow(QMainWindow, MessageBoxMixin, Logger, QtEventListener):
             # can sign directly
             task = partial(tx.sign, external_keypairs)
         else:
-            task = partial(self.wallet.sign_transaction, tx, password)
+            # ignore_warnings=True, because UI checks and asks user confirmation itself
+            task = partial(self.wallet.sign_transaction, tx, password, ignore_warnings=True)
         msg = _('Signing transaction...')
         WaitingDialog(self, msg, task, on_success, on_failure)
 

electrum/gui/qt/transaction_dialog.py

@@ -50,8 +50,7 @@ from electrum.bitcoin import base_encode, NLOCKTIME_BLOCKHEIGHT_MAX, DummyAddres
 from electrum.i18n import _
 from electrum.plugin import run_hook
 from electrum import simple_config
-from electrum.transaction import SerializationError, Transaction, PartialTransaction, PartialTxInput, TxOutpoint
-from electrum.transaction import TxinDataFetchProgress
+from electrum.transaction import SerializationError, Transaction, PartialTransaction, TxOutpoint, TxinDataFetchProgress
 from electrum.logging import get_logger
 from electrum.util import ShortID, get_asyncio_loop
 from electrum.network import Network
@@ -77,15 +76,16 @@ _logger = get_logger(__name__)
 dialogs = []  # Otherwise python randomly garbage collects the dialogs...
 
 
-
 class TxSizeLabel(QLabel):
     def setAmount(self, byte_size):
         self.setText(('x   %s bytes   =' % byte_size) if byte_size else '')
 
+
 class TxFiatLabel(QLabel):
     def setAmount(self, fiat_fee):
         self.setText(('≈  %s' % fiat_fee) if fiat_fee else '')
 
+
 class QTextBrowserWithDefaultSize(QTextBrowser):
     def __init__(self, width: int = 0, height: int = 0):
         self._width = width
@@ -96,8 +96,8 @@ class QTextBrowserWithDefaultSize(QTextBrowser):
     def sizeHint(self):
         return QSize(self._width, self._height)
 
-class TxInOutWidget(QWidget):
 
+class TxInOutWidget(QWidget):
     def __init__(self, main_window: 'ElectrumWindow', wallet: 'Abstract_Wallet'):
         QWidget.__init__(self)
 
@@ -113,9 +113,24 @@ class TxInOutWidget(QWidget):
         self.inputs_textedit.setContextMenuPolicy(Qt.CustomContextMenu)
         self.inputs_textedit.customContextMenuRequested.connect(self.on_context_menu_for_inputs)
 
+        self.sighash_label = QLabel()
+        self.sighash_label.setStyleSheet('font-weight: bold')
+        self.sighash_confirm = False
+        self.sighash_reject = False
+        self.sighash_message = ''
+        self.inputs_warning_icon = QLabel()
+        pixmap = QPixmap(icon_path("warning"))
+        pixmap_size = round(2 * char_width_in_lineedit())
+        pixmap = pixmap.scaled(pixmap_size, pixmap_size, Qt.KeepAspectRatio, Qt.SmoothTransformation)
+        self.inputs_warning_icon.setPixmap(pixmap)
+        self.inputs_warning_icon.setVisible(False)
+
         self.inheader_hbox = QHBoxLayout()
         self.inheader_hbox.setContentsMargins(0, 0, 0, 0)
         self.inheader_hbox.addWidget(self.inputs_header)
+        self.inheader_hbox.addStretch(2)
+        self.inheader_hbox.addWidget(self.sighash_label)
+        self.inheader_hbox.addWidget(self.inputs_warning_icon)
 
         self.txo_color_recv = TxOutputColoring(
             legend=_("Wallet Address"), color=ColorScheme.GREEN, tooltip=_("Wallet receiving address"))
@@ -246,6 +261,13 @@ class TxInOutWidget(QWidget):
                 short_id=str(txin.short_id), addr=addr, value=txin_value,
             )
 
+        if isinstance(self.tx, PartialTransaction):
+            self.sighash_confirm, self.sighash_reject, self.sighash_message = self.wallet.check_sighash(self.tx)
+            if self.sighash_message:
+                self.sighash_label.setText(_('Danger! This transaction is non-standard!'))
+                self.inputs_warning_icon.setVisible(True)
+                self.inputs_warning_icon.setToolTip(self.sighash_message)
+
         self.outputs_header.setText(_("Outputs") + ' (%d)'%len(self.tx.outputs()))
         o_text = self.outputs_textedit
         o_text.clear()
@@ -645,6 +667,14 @@ class TxDialog(QDialog, MessageBoxMixin):
             self.update()
             self.main_window.pop_top_level_window(self)
 
+        if self.io_widget.sighash_confirm:
+            if not self.question('\n'.join([
+                _('Danger! This transaction is non-standard!'),
+                self.io_widget.sighash_message,
+                '',
+                _('Are you sure you want to sign this transaction?')
+            ])):
+                return
         self.sign_button.setDisabled(True)
         self.main_window.push_top_level_window(self)
         self.main_window.sign_tx(self.tx, callback=sign_done, external_keypairs=self.external_keypairs)
@@ -771,7 +801,8 @@ class TxDialog(QDialog, MessageBoxMixin):
         self.broadcast_button.setEnabled(tx_details.can_broadcast)
         can_sign = not self.tx.is_complete() and \
             (self.wallet.can_sign(self.tx) or bool(self.external_keypairs))
-        self.sign_button.setEnabled(can_sign)
+        self.sign_button.setEnabled(can_sign and not self.io_widget.sighash_reject)
+        self.sign_button.setToolTip(self.io_widget.sighash_message)
         if tx_details.txid:
             self.tx_hash_e.setText(tx_details.txid)
         else:

electrum/tests/test_wallet_vertical.py

@@ -12,12 +12,10 @@ from electrum import SimpleConfig
 from electrum import util
 from electrum.address_synchronizer import TX_HEIGHT_UNCONFIRMED, TX_HEIGHT_UNCONF_PARENT
 from electrum.wallet import (sweep, Multisig_Wallet, Standard_Wallet, Imported_Wallet,
-                             restore_wallet_from_text, Abstract_Wallet, CannotBumpFee, BumpFeeStrategy)
-from electrum.util import (
-    bfh, NotEnoughFunds, UnrelatedTransactionException,
-    UserFacingException)
-from electrum.transaction import (TxOutput, Transaction, PartialTransaction, PartialTxOutput,
-                                  PartialTxInput, tx_from_any, TxOutpoint)
+                             restore_wallet_from_text, Abstract_Wallet, CannotBumpFee, BumpFeeStrategy,
+                             TransactionPotentiallyDangerousException, TransactionDangerousException)
+from electrum.util import bfh, NotEnoughFunds, UnrelatedTransactionException, UserFacingException
+from electrum.transaction import Transaction, PartialTxOutput, tx_from_any
 from electrum.mnemonic import seed_type
 from electrum.network import Network
 
@@ -2963,13 +2961,23 @@ class TestWalletSending(ElectrumTestCase):
                                              partial_tx)
                         # load tx into cosignerB's offline wallet
                         tx = tx_from_any(partial_tx)
-                        wallet1b_offline.sign_transaction(tx, password=None)
+                        wallet1b_offline.sign_transaction(tx, password=None, ignore_warnings=True)
 
                         self.assertEqual('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',
                                          str(tx))
                         self.assertEqual('d6823918ff82ed240995e9e6f02e0d2f3f15e0b942616ab34481ce8a3399dc72', tx.txid())
                         self.assertEqual('d6823918ff82ed240995e9e6f02e0d2f3f15e0b942616ab34481ce8a3399dc72', tx.wtxid())
 
+                        # again, but raise on warnings (here: signing non-segwit inputs is risky)
+                        tx = tx_from_any(partial_tx)
+                        try:
+                            wallet1b_offline.sign_transaction(tx, password=None)
+                            self.assertFalse(uses_qr_code2)
+                        except TransactionDangerousException:
+                            raise
+                        except TransactionPotentiallyDangerousException:
+                            self.assertTrue(uses_qr_code2)
+
     @mock.patch.object(wallet.Abstract_Wallet, 'save_db')
     async def test_we_dont_sign_tx_including_dummy_address(self, mock_save_db):
         wallet1 = self.create_standard_wallet_from_seed('bitter grass shiver impose acquire brush forget axis eager alone wine silver')
@@ -3095,7 +3103,7 @@ class TestWalletOfflineSigning(ElectrumTestCase):
                 self.assertEqual(tx.txid(), tx_copy.txid())
 
                 # sign tx
-                tx = wallet_offline.sign_transaction(tx_copy, password=None)
+                tx = wallet_offline.sign_transaction(tx_copy, password=None, ignore_warnings=True)
                 self.assertTrue(tx.is_complete())
                 self.assertFalse(tx.is_segwit())
                 self.assertEqual('d9c21696eca80321933e7444ca928aaf25eeda81aaa2f4e5c085d4d0a9cf7aa7', tx.txid())

electrum/transaction.py

@@ -42,6 +42,7 @@ import copy
 
 from . import ecc, bitcoin, constants, segwit_addr, bip32
 from .bip32 import BIP32Node
+from .i18n import _
 from .util import profiler, to_bytes, bfh, chunks, is_hex_str, parse_max_spend
 from .bitcoin import (TYPE_ADDRESS, TYPE_SCRIPT, hash_160,
                       hash160_to_p2sh, hash160_to_p2pkh, hash_to_segwit_addr,

electrum/wallet.py

@@ -71,7 +71,7 @@ from .storage import StorageEncryptionVersion, WalletStorage
 from .wallet_db import WalletDB
 from . import transaction, bitcoin, coinchooser, paymentrequest, ecc, bip32
 from .transaction import (Transaction, TxInput, UnknownTxinType, TxOutput,
-                          PartialTransaction, PartialTxInput, PartialTxOutput, TxOutpoint)
+                          PartialTransaction, PartialTxInput, PartialTxOutput, TxOutpoint, Sighash)
 from .plugin import run_hook
 from .address_synchronizer import (AddressSynchronizer, TX_HEIGHT_LOCAL,
                                    TX_HEIGHT_UNCONF_PARENT, TX_HEIGHT_UNCONFIRMED, TX_HEIGHT_FUTURE, TX_TIMESTAMP_INF)
@@ -233,20 +233,29 @@ class CannotBumpFee(CannotRBFTx):
     def __str__(self):
         return _('Cannot bump fee') + ':\n\n' + Exception.__str__(self)
 
+
 class CannotDoubleSpendTx(CannotRBFTx):
     def __str__(self):
         return _('Cannot cancel transaction') + ':\n\n' + Exception.__str__(self)
 
+
 class CannotCPFP(Exception):
     def __str__(self):
         return _('Cannot create child transaction') + ':\n\n' + Exception.__str__(self)
 
+
 class InternalAddressCorruption(Exception):
     def __str__(self):
         return _("Wallet file corruption detected. "
                  "Please restore your wallet from seed, and compare the addresses in both files")
 
 
+class TransactionPotentiallyDangerousException(Exception): pass
+
+
+class TransactionDangerousException(TransactionPotentiallyDangerousException): pass
+
+
 class BumpFeeStrategy(enum.Enum):
     PRESERVE_PAYMENT = enum.auto()
     DECREASE_PAYMENT = enum.auto()
@@ -2454,7 +2463,7 @@ class Abstract_Wallet(ABC, Logger, EventListener):
         txout.is_change = self.is_change(address)
         self._add_txinout_derivation_info(txout, address, only_der_suffix=only_der_suffix)
 
-    def sign_transaction(self, tx: Transaction, password) -> Optional[PartialTransaction]:
+    def sign_transaction(self, tx: Transaction, password, *, ignore_warnings: bool = False) -> Optional[PartialTransaction]:
         """ returns tx if successful else None """
         if self.is_watching_only():
             return
@@ -2467,6 +2476,24 @@ class Abstract_Wallet(ABC, Logger, EventListener):
         if swap:
             self.lnworker.swap_manager.sign_tx(tx, swap)
             return tx
+
+        # check if signing is dangerous
+        should_confirm, should_reject, message = self.check_sighash(tx)
+        if should_reject:
+            raise TransactionDangerousException('Not signing transaction:\n' + message)
+        if not ignore_warnings:
+            if should_confirm:
+                message = '\n'.join([_('Danger! This transaction is non-standard!'), message])
+            fee = self.get_wallet_delta(tx).fee
+            risk_of_burning_coins = (fee is not None
+                                     and self.get_warning_for_risk_of_burning_coins_as_fees(tx))
+            if risk_of_burning_coins:
+                should_confirm = True
+                message = '\n'.join([message, risk_of_burning_coins])
+
+            if should_confirm:
+                raise TransactionPotentiallyDangerousException('Not signing transaction:\n' + message)
+
         # add info to a temporary tx copy; including xpubs
         # and full derivation paths as hw keystores might want them
         tmp_tx = copy.deepcopy(tx)
@@ -3041,6 +3068,36 @@ class Abstract_Wallet(ABC, Logger, EventListener):
                     "do not accept to sign it more than once,\n"
                     "otherwise you could end up paying a different fee."))
 
+    def check_sighash(self, tx: 'PartialTransaction') -> (bool, bool, str):
+        """Checks the Sighash for my inputs and return hints in the form
+        (confirm, reject, message), where confirm indicates the user should explicitly confirm,
+        reject indicates the transaction should be rejected (unless overruled in e.g. a config property),
+        and message containing a user-facing message describing the context"""
+        hintmap = dict([
+            (0, (False, False, None)),
+            (Sighash.NONE, (True, True, _('Input {} is marked SIGHASH_NONE.'))),
+            (Sighash.SINGLE, (True, False, _('Input {} is marked SIGHASH_SINGLE.'))),
+            (Sighash.ALL, (False, False, None)),
+            (Sighash.ANYONECANPAY, (True, False, _('Input {} is marked SIGHASH_ANYONECANPAY.')))
+        ])
+        confirm = False
+        reject = False
+        messages = []
+        for txin_idx, txin in enumerate(tx.inputs()):
+            if txin.sighash and txin.sighash != Sighash.ALL:  # non-standard
+                addr = self.adb.get_txin_address(txin)
+                if self.adb.is_mine(addr):
+                    sh_out = txin.sighash & (Sighash.ANYONECANPAY ^ 0xff)
+                    sh_in = txin.sighash & Sighash.ANYONECANPAY
+                    confirm |= hintmap[sh_out][0] | hintmap[sh_in][0]
+                    reject |= hintmap[sh_out][1] | hintmap[sh_in][1]
+                    for sh in [sh_out, sh_in]:
+                        msg = hintmap[sh][2]
+                        if msg:
+                            messages.append('%s: %s' % (_('Fatal') if hintmap[sh][1] else _('Warning'),
+                                                        msg.format(txin_idx)))
+        return confirm, reject, '\n'.join(messages)
+
     def get_tx_fee_warning(
             self, *,
             invoice_amt: int,