wizard: fix regression: allow passphrase for some '2fa' seeds

fixes https://github.com/spesmilo/electrum/issues/9088

electrum/mnemonic.py

@@ -276,6 +276,23 @@ def seed_type(x: str) -> str:
     return ''
 
 
+def can_seed_have_passphrase(seed: str) -> bool:
+    stype = seed_type(seed)
+    if not stype:
+        raise Exception(f'unexpected seed type: {stype!r}')
+    if stype == 'old':
+        return False
+    if stype == '2fa':
+        # post-version-2.7 2fa seeds can have passphrase, but older ones cannot
+        num_words = len(seed.split())
+        if num_words == 12:
+            return True
+        else:
+            return False
+    # all other types can have a seed extension/passphrase
+    return True
+
+
 def is_seed(x: str) -> bool:
     return bool(seed_type(x))
 

electrum/wizard.py

@@ -13,7 +13,7 @@ from electrum.storage import WalletStorage, StorageEncryptionVersion
 from electrum.wallet_db import WalletDB
 from electrum.bip32 import normalize_bip32_derivation, xpub_type
 from electrum import keystore, mnemonic, bitcoin
-from electrum.mnemonic import is_any_2fa_seed_type
+from electrum.mnemonic import is_any_2fa_seed_type, can_seed_have_passphrase
 
 if TYPE_CHECKING:
     from electrum.daemon import Daemon
@@ -492,8 +492,7 @@ class NewWalletWizard(AbstractWizard):
             seed_type = mnemonic.seed_type(seed)
             if seed_type != '':
                 seed_valid = True
-            if seed_type in ['old', '2fa']:
-                can_passphrase = False
+                can_passphrase = can_seed_have_passphrase(seed)
         elif seed_variant == 'bip39':
             is_checksum, is_wordlist = keystore.bip39_is_checksum_valid(seed)
             validation_message = ('' if is_checksum else _('BIP39 checksum failed')) if is_wordlist else _('Unknown BIP39 wordlist')

tests/test_mnemonic.py

@@ -7,7 +7,7 @@ from electrum import mnemonic
 from electrum import slip39
 from electrum import old_mnemonic
 from electrum.util import bfh
-from electrum.mnemonic import is_new_seed, is_old_seed, seed_type, is_matching_seed
+from electrum.mnemonic import is_new_seed, is_old_seed, seed_type, is_matching_seed, can_seed_have_passphrase
 from electrum.version import SEED_PREFIX_SW, SEED_PREFIX
 
 from . import ElectrumTestCase
@@ -244,6 +244,25 @@ class Test_seeds(ElectrumTestCase):
         self.assertFalse(is_matching_seed(seed="when blade focus", seed_again="when bl4de focus"))
         self.assertFalse(is_matching_seed(seed="when blade focus", seed_again="when bla4de focus"))
 
+    def test_can_seed_have_passphrase(self):
+        seed_invalid = 'xxx'
+        with self.assertRaises(Exception):
+            self.assertFalse(can_seed_have_passphrase(seed_invalid))
+        seed_old = 'cell dumb heartbeat north boom tease ship baby bright kingdom rare squeeze'
+        self.assertFalse(can_seed_have_passphrase(seed_old))
+        seed_standard = 'cram swing cover prefer miss modify ritual silly deliver chunk behind inform able'
+        self.assertTrue(can_seed_have_passphrase(seed_standard))
+        seed_segwit = 'frost pig brisk excite novel report camera enlist axis nation novel desert'
+        self.assertTrue(can_seed_have_passphrase(seed_segwit))
+        seed_2fa_12 = 'science dawn member doll dutch real can brick knife deny drive list'
+        self.assertTrue(can_seed_have_passphrase(seed_2fa_12))
+        seed_2fa_24 = 'sibling leg cable timber patient foot occur plate travel finger chef scale radio citizen promote immune must chef fluid sea sphere common acid lab'
+        self.assertFalse(can_seed_have_passphrase(seed_2fa_24))
+        seed_2fa_25 = 'bind clever room kidney crucial sausage spy edit canvas soul liquid ribbon slam open alpha suffer gate relax voice carpet law hill woman tonight abstract'
+        self.assertFalse(can_seed_have_passphrase(seed_2fa_25))
+        seed_2fa_segwit = 'agree install'
+        self.assertTrue(can_seed_have_passphrase(seed_2fa_segwit))
+
 
 class Test_slip39(ElectrumTestCase):
     """ Test SLIP39 test vectors. """