extended seed prefix

lib/bitcoin.py

@@ -23,8 +23,8 @@ import re
 import sys
 import hmac
 
+import version
 from util import print_error
-from version import SEED_PREFIX
 
 try:
     import ecdsa
@@ -147,7 +147,10 @@ def Hash(x):
 hash_encode = lambda x: x[::-1].encode('hex')
 hash_decode = lambda x: x.decode('hex')[::-1]
 hmac_sha_512 = lambda x,y: hmac.new(x, y, hashlib.sha512).digest()
-is_new_seed = lambda x: hmac_sha_512("Seed version", x.encode('utf8')).encode('hex')[0:2].startswith(SEED_PREFIX)
+
+def is_new_seed(x, prefix=version.SEED_BIP44):
+    s = hmac_sha_512("Seed version", x.encode('utf8')).encode('hex')
+    return s.startswith(prefix)
 
 
 def is_old_seed(seed):

lib/commands.py

@@ -133,7 +133,7 @@ class Commands:
 
     def make_seed(self, nbits, custom_entropy, language):
         from mnemonic import Mnemonic
-        s = Mnemonic(language).make_seed(nbits, custom_entropy)
+        s = Mnemonic(language).make_seed(nbits, custom_entropy=custom_entropy)
         return s.encode('utf8')
 
     def check_seed(self, seed, custom_entropy, language):

lib/mnemonic.py

@@ -27,7 +27,7 @@ import pbkdf2
 
 from util import print_error
 from bitcoin import is_old_seed, is_new_seed
-
+import version
 
 class Mnemonic(object):
     # Seed derivation follows BIP39
@@ -89,11 +89,13 @@ class Mnemonic(object):
         i = self.mnemonic_decode(seed)
         return i % custom_entropy == 0
 
-    def make_seed(self, num_bits=128, custom_entropy=1):
+    def make_seed(self, num_bits=128, prefix=version.SEED_BIP44, custom_entropy=1):
         n = int(math.ceil(math.log(custom_entropy,2)))
+        # bits of entropy used by the prefix
+        k = len(prefix)*4
         # we add at least 16 bits
-        n_added = max(16, 8 + num_bits - n)
-        print_error("make_seed: adding %d bits"%n_added)
+        n_added = max(16, k + num_bits - n)
+        print_error("make_seed", prefix, "adding %d bits"%n_added)
         my_entropy = ecdsa.util.randrange( pow(2, n_added) )
         nonce = 0
         while True:
@@ -103,8 +105,7 @@ class Mnemonic(object):
             assert i == self.mnemonic_decode(seed)
             if is_old_seed(seed):
                 continue
-            # this removes 8 bits of entropy
-            if is_new_seed(seed):
+            if is_new_seed(seed, prefix):
                 break
         print_error('%d words'%len(seed.split()))
         return seed

lib/version.py

@@ -5,4 +5,5 @@ OLD_SEED_VERSION = 4        # old electrum deterministic generation
 
 
 # The hash of the mnemonic seed must begin with this
-SEED_PREFIX      = '01'     # for BIP44
+SEED_BIP44       = '01'      # BIP44
+SEED_2FA         = '101'     # extended seed for two-factor authentication