Custom implementation of BIP 39.

bitcoin_bip_0039.py

import sys
import binascii
import hashlib
import random
import hmac
import pbkdf2

PBKDF2_ROUNDS = 2048

# Custom implementation of BIP 39: https://github.com/bitcoin/bips/blob/master/bip-0039.mediawiki

RADIX = 2048
MAP_MS_CS = dict([(12, 4), (15, 5), (18, 6), (21, 7), (24, 8)])
MAP_ENT_CS = dict([(128, 4), (160, 5), (192, 6), (224, 7), (256, 8)])
MAP_ENT_MS = dict([(128, 12), (160, 15), (192, 18), (224, 21), (256, 24)])

def LoadWords(words_file_path):
   with open(words_file_path, "r") as f:
      words = [w.strip() for w in f.readlines()]
   if len(words) != RADIX:
      raise ValueError("Word list must contain %d words, however it contains %d words." % (RADIX, len(words)))
   return words

def PrefixChoice(words, prefix):
   if not isinstance(words, list):
      raise ValueError("Error. Word list must be provided as a list data type.")
   if len(words) != RADIX:
      raise ValueError("Error. Word list must contain %d words, however it contains %d words." % (RADIX, len(words)))
   return [word for word in words if word.startswith(prefix)]

def CalcChecksum(entropy):
   CS = len(entropy) // 32
   checksum_hash = hashlib.sha256(binascii.unhexlify(hex(int(entropy, 2))[2:])).hexdigest()
   return bin(int(checksum_hash, 16))[2:].zfill(256)[:CS]

def EntropyToMnemonic(words, entropy):
   if not isinstance(words, list):
      raise ValueError("Error. Word list must be provided as a list data type.")
   if len(words) != RADIX:
      raise ValueError("Error. Word list must contain %d words, however it contains %d words." % (RADIX, len(words)))
   if len(entropy) not in [128, 160, 192, 224, 256]:
      raise ValueError("Error. Incorrect entropy input length.")
   b = entropy + CalcChecksum(entropy)
   result = []
   for i in range(len(b) // 11):
      idx = int(b[i * 11:(i + 1) * 11], 2)
      result.append(words[idx])
   if len(result) not in [12, 15, 18, 21, 24]:
      raise ValueError("Error. Incorrect word sentence output length.")
   return result
   
def MnemonicToEntropy(words, mnemonic):
   if not isinstance(words, list):
      raise ValueError("Error. Word list must be provided as a list data type.")
   if len(words) != RADIX:
      raise ValueError("Error. Word list must contain %d words, however it contains %d words." % (RADIX, len(words)))
   if not isinstance(mnemonic, list):
      mnemonic = mnemonic.split()
   if len(mnemonic) not in [12, 15, 18, 21, 24]:
      raise ValueError("Error. Incorrect word senence input length.")
   bit_string = ""
   for word in mnemonic:
      i = words.index(word)
      for j in range(11):
         if (i & (1 << (10 - j))) == 0:
            bit_string = bit_string + "0"
         else:
            bit_string = bit_string + "1"
   bit_check_string = bit_string[-MAP_MS_CS[len(mnemonic)]:]
   entropy = bit_string[:-MAP_MS_CS[len(mnemonic)]]
   if bit_check_string != CalcChecksum(entropy):
      raise ValueError("Error. Incorrect checksum.")
   return entropy

def MakeSeed(mnemonic, passphrase = ""):
   if isinstance(mnemonic, list):
      mnemonic = " ".join(mnemonic)
   return pbkdf2.PBKDF2(mnemonic, "mnemonic" + passphrase, iterations = PBKDF2_ROUNDS, macmodule = hmac, digestmodule = hashlib.sha512).read(64)

if __name__ == "__main__":
   test = False
   generate = False

   for arg in sys.argv:
      if arg == "-t":
         test = True
      if arg == "-g":
         generate = True

   if test == True:
      device = LoadWords("english.txt")
      subset = PrefixChoice(device, "an")
      assert subset[0] == "analyst", "Test failed. Invalid prefix option."
      assert subset[1] == "anchor", "Test failed. Invalid prefix option."

      entropy = bin(int("68a79eaca2324873eacc50cb9c6eca8cc68ea5d936f98787c60c7ebc74e6ce7c", 16))[2:].zfill(256)
      sentence = EntropyToMnemonic(device, entropy)
      expected = "hamster diagram private dutch cause delay private meat slide toddler razor book happy fancy gospel tennis maple dilemma loan word shrug inflict delay length".split()
      assert sentence == expected, "Test failed. Invalid sentence."

      entropy_from_sentence = MnemonicToEntropy(device, sentence)
      assert entropy_from_sentence == entropy, "Test failed. Incorrect entropy."

      MakeSeed(sentence, passphrase = "KALPANA")

      print("Tests passed.")

   if generate == True:
      device = LoadWords("english.txt")
      weak_private_key = "".join(random.choice("0123456789abcdef") for n in range(64))
      entropy = bin(int(weak_private_key, 16))[2:].zfill(256)
      sentence = EntropyToMnemonic(device, entropy)
      print("Weak private key: " + weak_private_key)
      print("Mnemonic: " + " ".join(sentence))