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trezor-firmware/trezorlib/ckd_public.py
2016-05-20 13:46:51 +02:00

126 lines
3.6 KiB
Python

import struct
import hmac
import hashlib
import ecdsa
from ecdsa.util import string_to_number, number_to_string
from ecdsa.curves import SECP256k1
from ecdsa.ellipticcurve import Point, INFINITY
from . import tools
from . import types_pb2 as proto_types
PRIME_DERIVATION_FLAG = 0x80000000
def point_to_pubkey(point):
order = SECP256k1.order
x_str = number_to_string(point.x(), order)
y_str = number_to_string(point.y(), order)
vk = x_str + y_str
return chr((ord(vk[63]) & 1) + 2) + vk[0:32] # To compressed key
def sec_to_public_pair(pubkey):
"""Convert a public key in sec binary format to a public pair."""
x = string_to_number(pubkey[1:33])
sec0 = pubkey[:1]
if sec0 not in (b'\2', b'\3'):
raise Exception("Compressed pubkey expected")
def public_pair_for_x(generator, x, is_even):
curve = generator.curve()
p = curve.p()
alpha = (pow(x, 3, p) + curve.a() * x + curve.b()) % p
beta = ecdsa.numbertheory.square_root_mod_prime(alpha, p)
if is_even == bool(beta & 1):
return (x, p - beta)
return (x, beta)
return public_pair_for_x(ecdsa.ecdsa.generator_secp256k1, x, is_even=(sec0 == b'\2'))
def is_prime(n):
return (bool)(n & PRIME_DERIVATION_FLAG)
def fingerprint(pubkey):
return string_to_number(tools.hash_160(pubkey)[:4])
def get_address(public_node, address_type):
return tools.public_key_to_bc_address(public_node.public_key, address_type)
def public_ckd(public_node, n):
if not isinstance(n, list):
raise Exception('Parameter must be a list')
node = proto_types.HDNodeType()
node.CopyFrom(public_node)
for i in n:
node.CopyFrom(get_subnode(node, i))
return node
def get_subnode(node, i):
# Public Child key derivation (CKD) algorithm of BIP32
i_as_bytes = struct.pack(">L", i)
if is_prime(i):
raise Exception("Prime derivation not supported")
# Public derivation
data = node.public_key + i_as_bytes
I64 = hmac.HMAC(key=node.chain_code, msg=data, digestmod=hashlib.sha512).digest()
I_left_as_exponent = string_to_number(I64[:32])
node_out = proto_types.HDNodeType()
node_out.depth = node.depth + 1
node_out.child_num = i
node_out.chain_code = I64[32:]
node_out.fingerprint = fingerprint(node.public_key)
# BIP32 magic converts old public key to new public point
x, y = sec_to_public_pair(node.public_key)
point = I_left_as_exponent * SECP256k1.generator + \
Point(SECP256k1.curve, x, y, SECP256k1.order)
if point == INFINITY:
raise Exception("Point cannot be INFINITY")
# Convert public point to compressed public key
node_out.public_key = point_to_pubkey(point)
return node_out
def serialize(node, version=0x0488B21E):
s = ''
s += struct.pack('>I', version)
s += struct.pack('>B', node.depth)
s += struct.pack('>I', node.fingerprint)
s += struct.pack('>I', node.child_num)
s += node.chain_code
if node.private_key:
s += '\x00' + node.private_key
else :
s += node.public_key
s += tools.Hash(s)[:4]
return tools.b58encode(s)
def deserialize(xpub):
data = tools.b58decode(xpub, None)
if tools.Hash(data[:-4])[:4] != data[-4:]:
raise Exception("Checksum failed")
node = proto_types.HDNodeType()
node.depth = struct.unpack('>B', data[4:5])[0]
node.fingerprint = struct.unpack('>I', data[5:9])[0]
node.child_num = struct.unpack('>I', data[9:13])[0]
node.chain_code = data[13:45]
key = data[45:-4]
if key[0] == '\x00':
node.private_key = key[1:]
else:
node.public_key = key
return node