From 9285a7198ee1f19571d10453db1b708fc6306e9a Mon Sep 17 00:00:00 2001
From: ThomasV <thomasv@electrum.org>
Date: Thu, 20 Oct 2016 10:22:17 +0200
Subject: [PATCH] Revert "remove custom entropy option; nobody uses it"

This reverts commit e0c38b31b40b42138527e9fd3f4bad78e0b12802.
---
 lib/commands.py | 12 ++++++++++--
 lib/mnemonic.py | 14 +++++++++++---
 2 files changed, 21 insertions(+), 5 deletions(-)

diff --git a/lib/commands.py b/lib/commands.py
index ba29b30ba..068949d63 100644
--- a/lib/commands.py
+++ b/lib/commands.py
@@ -143,12 +143,18 @@ class Commands:
         return True
 
     @command('')
-    def make_seed(self, nbits=128, language=None):
+    def make_seed(self, nbits=128, entropy=1, language=None):
         """Create a seed"""
         from mnemonic import Mnemonic
-        s = Mnemonic(language).make_seed(nbits)
+        s = Mnemonic(language).make_seed(nbits, custom_entropy=entropy)
         return s.encode('utf8')
 
+    @command('')
+    def check_seed(self, seed, entropy=1, language=None):
+        """Check that a seed was generated with given entropy"""
+        from mnemonic import Mnemonic
+        return Mnemonic(language).check_seed(seed, entropy)
+
     @command('n')
     def getaddresshistory(self, address):
         """Return the transaction history of any address. Note: This is a
@@ -656,6 +662,7 @@ command_options = {
     'from_addr':   ("-F", "--from",        "Source address. If it isn't in the wallet, it will ask for the private key unless supplied in the format public_key:private_key. It's not saved in the wallet."),
     'change_addr': ("-c", "--change",      "Change address. Default is a spare address, or the source address if it's not in the wallet"),
     'nbits':       (None, "--nbits",       "Number of bits of entropy"),
+    'entropy':     (None, "--entropy",     "Custom entropy"),
     'language':    ("-L", "--lang",        "Default language for wordlist"),
     'gap_limit':   ("-G", "--gap",         "Gap limit"),
     'privkey':     (None, "--privkey",     "Private key. Set to '?' to get a prompt."),
@@ -679,6 +686,7 @@ arg_types = {
     'num': int,
     'nbits': int,
     'imax': int,
+    'entropy': long,
     'tx': tx_from_str,
     'pubkeys': json_loads,
     'jsontx': json_loads,
diff --git a/lib/mnemonic.py b/lib/mnemonic.py
index 1203166fb..8e0f788af 100644
--- a/lib/mnemonic.py
+++ b/lib/mnemonic.py
@@ -154,16 +154,24 @@ class Mnemonic(object):
             i = i*n + k
         return i
 
-    def make_seed(self, num_bits=128, prefix=version.SEED_PREFIX):
+    def check_seed(self, seed, custom_entropy):
+        assert is_new_seed(seed)
+        i = self.mnemonic_decode(seed)
+        return i % custom_entropy == 0
+
+    def make_seed(self, num_bits=128, prefix=version.SEED_PREFIX, custom_entropy=1):
         # increase num_bits in order to obtain a uniform distibution for the last word
         bpw = math.log(len(self.wordlist), 2)
-        n = int(math.ceil(num_bits/bpw)) * bpw
+        num_bits = int(math.ceil(num_bits/bpw)) * bpw
+        # handle custom entropy; make sure we add at least 16 bits
+        n_custom = int(math.ceil(math.log(custom_entropy, 2)))
+        n = max(16, num_bits - n_custom)
         print_error("make_seed", prefix, "adding %d bits"%n)
         my_entropy = ecdsa.util.randrange(pow(2, n))
         nonce = 0
         while True:
             nonce += 1
-            i = my_entropy + nonce
+            i = custom_entropy * (my_entropy + nonce)
             seed = self.mnemonic_encode(i)
             assert i == self.mnemonic_decode(seed)
             if is_old_seed(seed):