Provide warnings about invalid BIP39 checksum in seed dialog

gui/qt/seed_dialog.py

@@ -64,6 +64,7 @@ class SeedLayout(QVBoxLayout):
             def f(b):
                 self.is_seed = (lambda x: bool(x)) if b else self.saved_is_seed
                 self.on_edit()
+                self.is_bip39 = b
                 if b:
                     msg = ' '.join([
                         '<b>' + _('Warning') + ': BIP39 seeds are dangerous!' + '</b><br/><br/>',
@@ -76,7 +77,6 @@ class SeedLayout(QVBoxLayout):
                 else:
                     msg = ''
                 self.seed_warning.setText(msg)
-
             cb_bip39 = QCheckBox(_('BIP39 seed'))
             cb_bip39.toggled.connect(f)
             cb_bip39.setChecked(self.is_bip39)
@@ -130,9 +130,9 @@ class SeedLayout(QVBoxLayout):
             self.addLayout(hbox)
         self.addStretch(1)
         self.seed_warning = WWLabel('')
-        self.addWidget(self.seed_warning)
         if msg:
             self.seed_warning.setText(seed_warning_msg(seed))
+        self.addWidget(self.seed_warning)
 
     def get_seed(self):
         text = unicode(self.seed_e.text())
@@ -146,7 +146,10 @@ class SeedLayout(QVBoxLayout):
             t = seed_type(s)
             label = _('Seed Type') + ': ' + t if t else ''
         else:
-            label = 'BIP39 (checksum disabled)'
+            from electrum.keystore import bip39_is_checksum_valid
+            is_checksum, is_wordlist = bip39_is_checksum_valid(s)
+            status = ('checksum: ' + ('ok' if is_checksum else 'failed')) if is_wordlist else 'unknown wordlist'
+            label = 'BIP39' + ' (%s)'%status
         self.seed_type_label.setText(label)
         self.parent.next_button.setEnabled(b)
 

lib/keystore.py

@@ -24,6 +24,7 @@
 # CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 # SOFTWARE.
 
+import struct
 
 from unicodedata import normalize
 
@@ -35,7 +36,7 @@ from bitcoin import *
 
 from bitcoin import is_old_seed, is_new_seed, is_seed
 from util import PrintError, InvalidPassword
-from mnemonic import Mnemonic
+from mnemonic import Mnemonic, load_wordlist
 
 
 class KeyStore(PrintError):
@@ -555,7 +556,34 @@ def bip39_to_seed(mnemonic, passphrase):
                          iterations = PBKDF2_ROUNDS, macmodule = hmac,
                          digestmodule = hashlib.sha512).read(64)
 
-
+# returns tuple (is_checksum_valid, is_wordlist_valid)
+def bip39_is_checksum_valid(mnemonic):
+    words = [ normalize('NFKD', word) for word in mnemonic.split() ]
+    words_len = len(words)
+    wordlist = load_wordlist("english.txt")
+    n = len(wordlist)
+    checksum_length = 11*words_len//33
+    entropy_length = 32*checksum_length
+    i = 0
+    words.reverse()
+    while words:
+        w = words.pop()
+        try:
+            k = wordlist.index(w)
+        except ValueError:
+            return False, False
+        i = i*n + k
+    if words_len not in [12, 15, 18, 21, 24]:
+        return False, True
+    entropy = i >> checksum_length
+    checksum = i % 2**checksum_length
+    h = '{:x}'.format(entropy)
+    while len(h) < entropy_length/4:
+        h = '0'+h
+    b = bytearray.fromhex(h)
+    hashed = int(hashlib.sha256(b).digest().encode('hex'), 16)
+    calculated_checksum = hashed >> (256 - checksum_length)
+    return checksum == calculated_checksum, True
 
 # extended pubkeys
 

lib/mnemonic.py

@@ -91,6 +91,20 @@ def normalize_text(seed):
     seed = u''.join([seed[i] for i in range(len(seed)) if not (seed[i] in string.whitespace and is_CJK(seed[i-1]) and is_CJK(seed[i+1]))])
     return seed
 
+def load_wordlist(filename):
+    path = os.path.join(os.path.dirname(__file__), 'wordlist', filename)
+    s = open(path,'r').read().strip()
+    s = unicodedata.normalize('NFKD', s.decode('utf8'))
+    lines = s.split('\n')
+    wordlist = []
+    for line in lines:
+        line = line.split('#')[0]
+        line = line.strip(' \r')
+        assert ' ' not in line
+        if line:
+            wordlist.append(line)
+    return wordlist
+
 
 filenames = {
     'en':'english.txt',
@@ -110,17 +124,7 @@ class Mnemonic(object):
         lang = lang or 'en'
         print_error('language', lang)
         filename = filenames.get(lang[0:2], 'english.txt')
-        path = os.path.join(os.path.dirname(__file__), 'wordlist', filename)
-        s = open(path,'r').read().strip()
-        s = unicodedata.normalize('NFKD', s.decode('utf8'))
-        lines = s.split('\n')
-        self.wordlist = []
-        for line in lines:
-            line = line.split('#')[0]
-            line = line.strip(' \r')
-            assert ' ' not in line
-            if line:
-                self.wordlist.append(line)
+        self.wordlist = load_wordlist(filename)
         print_error("wordlist has %d words"%len(self.wordlist))
 
     @classmethod

lib/tests/test_mnemonic.py

@@ -1,4 +1,5 @@
 import unittest
+from lib import keystore
 from lib import mnemonic
 from lib import old_mnemonic
 
@@ -27,3 +28,11 @@ class Test_OldMnemonic(unittest.TestCase):
         words = 'hardly point goal hallway patience key stone difference ready caught listen fact'
         self.assertEquals(result, words.split())
         self.assertEquals(old_mnemonic.mn_decode(result), seed)
+
+class Test_BIP39Checksum(unittest.TestCase):
+
+    def test(self):
+        mnemonic = u'gravity machine north sort system female filter attitude volume fold club stay feature office ecology stable narrow fog'
+        is_checksum_valid, is_wordlist_valid = keystore.bip39_is_checksum_valid(mnemonic)
+        self.assertTrue(is_wordlist_valid)
+        self.assertTrue(is_checksum_valid)