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make sure seed last word is uniformly distributed. count prefix length as entropy

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This commit is contained in:
ThomasV 2016-09-22 14:37:08 +02:00
parent 7982cadd22
commit 569a3b4fab
1 changed files with 8 additions and 7 deletions
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15
lib/mnemonic.py
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@ -160,13 +160,14 @@ class Mnemonic(object):
return i % custom_entropy == 0 return i % custom_entropy == 0
def make_seed(self, num_bits=128, prefix=version.SEED_PREFIX, custom_entropy=1): def make_seed(self, num_bits=128, prefix=version.SEED_PREFIX, custom_entropy=1):
n = int(math.ceil(math.log(custom_entropy,2))) # increase num_bits in order to obtain a uniform distibution for the last word
# bits of entropy used by the prefix bpw = math.log(len(self.wordlist), 2)
k = len(prefix)*4 num_bits = int(math.ceil(num_bits/bpw)) * bpw
# we add at least 16 bits # handle custom entropy; make sure we add at least 16 bits
n_added = max(16, k + num_bits - n) n_custom = int(math.ceil(math.log(custom_entropy, 2)))
print_error("make_seed", prefix, "adding %d bits"%n_added) n = max(16, num_bits - n_custom)
my_entropy = ecdsa.util.randrange( pow(2, n_added) ) print_error("make_seed", prefix, "adding %d bits"%n)
my_entropy = ecdsa.util.randrange(pow(2, n))
nonce = 0 nonce = 0
while True: while True:
nonce += 1 nonce += 1