【Python】HD walletの親鍵/子鍵とchaincodeの概要

子の秘密鍵は、親のchaincdeと[親の公開鍵+index]をhmac_sha512でハッシュ化して作成している。

### マスター秘密鍵、公開鍵

import os
import binascii
import hmac
import hashlib
import ecdsa

seed = os.urandom(32)
root_key = b"Bitcoin seed"

def hmac_sha512(data, key_message):
    hash = hmac.new(data, key_message, hashlib.sha512).digest()
    return hash

def create_pubkey(private_key):
    publickey = ecdsa.SigningKey.from_string(private_key, curve=ecdsa.SECP256k1).verifying_key.to_string()
    return publickey

master = hmac_sha512(seed, root_key)

master_secretkey = master[:32]
master_chaincode = master[32:]

master_publickey = create_pubkey(master_secretkey)
master_publickey_integer = int.from_bytes(master_publickey[32:], byteorder="big")

if master_publickey_integer %2 == 0:
    master_publickey_x = b"\x02" + master_publickey[:32]
else:
    master_publickey_x = b"\x03" + master_publickey[:32]

print(binascii.hexlify(master_secretkey))
print(binascii.hexlify(master_chaincode))
print(binascii.hexlify(master_publickey_x))

$ python3 master_key.py
b’8a6dbaaff700682778dcbae2bc8718452fe5ed80fc9026a9b564420f8d5b0d80′
b’4ce8b10cc0c0874467d8f438c412fdbf21fba51517e668dbc4bd105af6861dec’
b’03cb15210804ca8f0d45b620832be935e2f90c3830f13f04c4bd6e8b4648f27817′
(secretkey, chaincode, pubkey)

### 子秘密鍵、子公開鍵

index = 0
index_bytes = index.to_bytes(8, "big")

data = master_publickey_x + index_bytes

result_hmac512 = hmac_sha512(data, master_chaincode)
sum_integer = int.from_bytes(master_secretkey,"big") + int.from_bytes(result_hmac512[:32],"big")

p = 2 ** 256 - 2**32 - 2**9 - 2**8 - 2**7 - 2**6 - 2**4 - 1
child_secretkey = (sum_integer % p).to_bytes(32,"big")

child_chaincode = result_hmac512[32:]

child_publickey = create_pubkey(child_secretkey)
child_publickey_integer = int.from_bytes(child_publickey[32:], byteorder="big")

if child_publickey_integer %2 == 0:
    child_publickey_x = b"\x02" + child_publickey[:32]
else:
    child_publickey_x = b"\x03" + child_publickey[:32]

print(binascii.hexlify(child_secretkey))
print(binascii.hexlify(child_chaincode))
print(binascii.hexlify(child_publickey_x))

b’5ff011a3e9cd672aaf0dc9fd52cb3172ac2815cb270f919135e6b0f0e6e03d54′
b’15f4d148b2d7730076d5e670249649ea8f0fd8572dad3818680e347196149dda’
b’03480a1dbb4a87d867bee3d364b608e21d685af271876707b9f9d5b75c6df6fde7′
—
b’23faf6fad81cd93e12c003c944ba3ef215dae714c638756386b6b9404da5aac9′
b’e3563dc6891e238cd0d8ebf99e65ebfc67cecf42364de9756b89859bbd049b62′
b’02039253af3e828bfbf1e560fe0e923a144fc4496ded3b6bbfa0d568cf7177d1c3′

なるほど、一見複雑そうに見えるが、なかなか面白いね