wallet: fix is_mine/can_sign. don't just rely on ks, also check script

Previously a standard (single-sig) wallet would consider a multisig txin as is_mine
(if the keystore found its pubkey in the txin).

fixes #5948

electrum/keystore.py

@@ -33,7 +33,7 @@ from abc import ABC, abstractmethod
 
 from . import bitcoin, ecc, constants, bip32
 from .bitcoin import deserialize_privkey, serialize_privkey
-from .transaction import Transaction, PartialTransaction, PartialTxInput, PartialTxOutput
+from .transaction import Transaction, PartialTransaction, PartialTxInput, PartialTxOutput, TxInput
 from .bip32 import (convert_bip32_path_to_list_of_uint32, BIP32_PRIME,
                     is_xpub, is_xprv, BIP32Node, normalize_bip32_derivation,
                     convert_bip32_intpath_to_strpath)
@@ -78,16 +78,21 @@ class KeyStore(Logger, ABC):
     def _get_tx_derivations(self, tx: 'PartialTransaction') -> Dict[str, Union[Sequence[int], str]]:
         keypairs = {}
         for txin in tx.inputs():
-            if txin.is_complete():
+            keypairs.update(self._get_txin_derivations(txin))
+        return keypairs
+
+    def _get_txin_derivations(self, txin: 'PartialTxInput') -> Dict[str, Union[Sequence[int], str]]:
+        if txin.is_complete():
+            return {}
+        keypairs = {}
+        for pubkey in txin.pubkeys:
+            if pubkey in txin.part_sigs:
+                # this pubkey already signed
+                continue
+            derivation = self.get_pubkey_derivation(pubkey, txin)
+            if not derivation:
                 continue
-            for pubkey in txin.pubkeys:
-                if pubkey in txin.part_sigs:
-                    # this pubkey already signed
-                    continue
-                derivation = self.get_pubkey_derivation(pubkey, txin)
-                if not derivation:
-                    continue
-                keypairs[pubkey.hex()] = derivation
+            keypairs[pubkey.hex()] = derivation
         return keypairs
 
     def can_sign(self, tx: 'Transaction', *, ignore_watching_only=False) -> bool:
@@ -98,6 +103,14 @@ class KeyStore(Logger, ABC):
             return False
         return bool(self._get_tx_derivations(tx))
 
+    def can_sign_txin(self, txin: 'TxInput', *, ignore_watching_only=False) -> bool:
+        """Returns whether this keystore could sign this txin."""
+        if not ignore_watching_only and self.is_watching_only():
+            return False
+        if not isinstance(txin, PartialTxInput):
+            return False
+        return bool(self._get_txin_derivations(txin))
+
     def ready_to_sign(self) -> bool:
         return not self.is_watching_only()
 

electrum/tests/test_wallet_vertical.py

@@ -1478,6 +1478,58 @@ class TestWalletSending(TestCaseForTestnet):
         self.assertEqual((0, 10995000, 0), wallet1.get_balance())
         self.assertEqual((0, 10495000, 0), wallet2.get_balance())
 
+    @mock.patch.object(wallet.Abstract_Wallet, 'save_db')
+    def test_standard_wallet_cannot_sign_multisig_input_even_if_cosigner(self, mock_save_db):
+        """Just because our keystore recognizes the pubkeys in a txin, if the prevout does not belong to the wallet,
+        then wallet.is_mine and wallet.can_sign should return False (e.g. multisig input for single-sig wallet).
+        (see issue #5948)
+        """
+        wallet_2of2 = WalletIntegrityHelper.create_multisig_wallet(
+            [
+                # seed: frost repair depend effort salon ring foam oak cancel receive save usage
+                # convert_xkey(wallet.get_master_public_key(), "p2wsh")
+                keystore.from_xpub('Vpub5gqF73Wpbp9ThwEgZKHLjBDthsatXjajYvrN8CVnkdBYeTR1M1sfZFQqQ5wpKHGhnwKhzgMhaWrtgKG2LthCzxjd653KqKVUAw7UrwYnbKQ'),
+                # seed: bitter grass shiver impose acquire brush forget axis eager alone wine silver
+                # convert_xkey(wallet.get_master_public_key(), "p2wsh")
+                keystore.from_xpub('Vpub5gSKXzxK7FeKNi2WPNW9iuA48SbJRZvKFBwtgucpegMWPdohQPeK2DoR6XFtC7BBLsHhfWDAPKaiecqJ7jTzYSfeg5YATowmPcgCWxARabT')
+            ],
+            '2of2', gap_limit=2,
+            config=self.config
+        )
+        wallet_frost = self.create_standard_wallet_from_seed('frost repair depend effort salon ring foam oak cancel receive save usage')
+
+        # bootstrap wallet_2of2
+        funding_tx = Transaction('020000000001018ed0132bb5f35d097572081524cd5e847c895e765b93d5af46b8a8bef621244a0100000000fdffffff0220a1070000000000220020302981db44eb5dad0dab3987134a985b360ae2227a7e7a10cfe8cffd23bacdc9b07912000000000016001442b423aab2aa803f957084832b10359beaa2469002473044022065c5e28900b4706487223357e8539e176552e3560e2081ac18de7c26e8e420ba02202755c7fc8177ff502634104c090e3fd4c4252bfa8566d4eb6605bb9e236e7839012103b63bbf85ec9e5e312e4d7a2b45e690f48b916a442e787a47a6092d6c052394c5966a1900')
+        funding_txid = funding_tx.txid()
+        self.assertEqual('0c2f5981981a6cb69d7b729feceb55be7962b16dc41e8aaf64e5203f7cb604d0', funding_txid)
+        wallet_2of2.receive_tx_callback(funding_txid, funding_tx, TX_HEIGHT_UNCONFIRMED)
+
+        # create tx
+        outputs = [PartialTxOutput.from_address_and_value('tb1qfrlx5pza9vmez6vpx7swt8yp0nmgz3qa7jjkuf', 100_000)]
+        coins = wallet_2of2.get_spendable_coins(domain=None)
+        tx = wallet_2of2.make_unsigned_transaction(coins=coins, outputs=outputs, fee=5000)
+        tx.set_rbf(True)
+        tx.locktime = 1665628
+
+        partial_tx = tx.serialize_as_bytes().hex()
+        self.assertEqual("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",
+                         partial_tx)
+        tx = tx_from_any(partial_tx)  # simulates moving partial txn between cosigners
+
+        self.assertFalse(tx.is_complete())
+        self.assertTrue(tx.is_segwit())
+        self.assertEqual('652c1a903a659c9fabb9caf4a2281a9fbcc59cd598bf6edc88cd60f940c2352c', tx.txid())
+
+        self.assertEqual('tb1qxq5crk6yadw66rdt8xr3xj5ctvmq4c3z0fl85yx0ar8l6ga6ehysk0rjrk', tx.inputs()[0].address)
+        self.assertEqual('tb1qfrlx5pza9vmez6vpx7swt8yp0nmgz3qa7jjkuf',                     tx.outputs()[0].address)
+        self.assertEqual('tb1qadpg5z77egkpkde34mdcrsz3s3tgwk5ew4w3wlfqf4j3dk8kkvrs3t3mn0', tx.outputs()[1].address)
+
+        # check that wallet_frost does not mistakenly think tx is related to it in any way
+        tx.add_info_from_wallet(wallet_frost)
+        self.assertFalse(wallet_frost.can_sign(tx))
+        self.assertFalse(any([wallet_frost.is_mine(txin.address) for txin in tx.inputs()]))
+        self.assertFalse(any([wallet_frost.is_mine(txout.address) for txout in tx.outputs()]))
+
 
 class TestWalletOfflineSigning(TestCaseForTestnet):
 

electrum/wallet.py

@@ -1372,9 +1372,15 @@ class Abstract_Wallet(AddressSynchronizer, ABC):
             return False
         # add info to inputs if we can; otherwise we might return a false negative:
         tx.add_info_from_wallet(self)
-        for k in self.get_keystores():
-            if k.can_sign(tx):
-                return True
+        for txin in tx.inputs():
+            # note: is_mine check needed to avoid false positives.
+            #       just because keystore could sign, txin does not necessarily belong to wallet.
+            #       Example: we have p2pkh-like addresses and txin is a multisig that involves our pubkey.
+            if not self.is_mine(txin.address):
+                continue
+            for k in self.get_keystores():
+                if k.can_sign_txin(txin):
+                    return True
         return False
 
     def get_input_tx(self, tx_hash, *, ignore_network_issues=False) -> Optional[Transaction]:
@@ -2218,8 +2224,13 @@ class Deterministic_Wallet(Abstract_Wallet):
         for ks in self.get_keystores():
             pubkey, der_suffix = ks.find_my_pubkey_in_txinout(txinout, only_der_suffix=True)
             if der_suffix is not None:
-                self._ephemeral_addr_to_addr_index[address] = list(der_suffix)
-                return True
+                # note: we already know the pubkey belongs to the keystore,
+                #       but the script template might be different
+                if len(der_suffix) != 2: continue
+                my_address = self.derive_address(*der_suffix)
+                if my_address == address:
+                    self._ephemeral_addr_to_addr_index[address] = list(der_suffix)
+                    return True
         return False
 
     def get_master_public_keys(self):