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move bolt-04 onion stuff to its own module

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SomberNight
2018-07-25 18:43:20 +02:00
committed by ThomasV
parent 9247da5203
commit 5a05a92b3d
4 changed files with 305 additions and 288 deletions
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electrum/lnonion.py Normal file
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# -*- coding: utf-8 -*-
#
# Electrum - lightweight Bitcoin client
# Copyright (C) 2018 The Electrum developers
#
# Permission is hereby granted, free of charge, to any person
# obtaining a copy of this software and associated documentation files
# (the "Software"), to deal in the Software without restriction,
# including without limitation the rights to use, copy, modify, merge,
# publish, distribute, sublicense, and/or sell copies of the Software,
# and to permit persons to whom the Software is furnished to do so,
# subject to the following conditions:
#
# The above copyright notice and this permission notice shall be
# included in all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
# BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
# ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
# CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.
import hashlib
import hmac
from collections import namedtuple
from typing import Sequence
from cryptography.hazmat.primitives.ciphers import Cipher, algorithms
from cryptography.hazmat.backends import default_backend
from . import ecc
from .crypto import sha256
from .util import bh2u, profiler, xor_bytes, bfh
from .lnutil import get_ecdh
NUM_MAX_HOPS_IN_PATH = 20
HOPS_DATA_SIZE = 1300 # also sometimes called routingInfoSize in bolt-04
PER_HOP_FULL_SIZE = 65 # HOPS_DATA_SIZE / 20
NUM_STREAM_BYTES = HOPS_DATA_SIZE + PER_HOP_FULL_SIZE
PER_HOP_HMAC_SIZE = 32
class UnsupportedOnionPacketVersion(Exception): pass
class InvalidOnionMac(Exception): pass
class OnionPerHop:
def __init__(self, short_channel_id: bytes, amt_to_forward: bytes, outgoing_cltv_value: bytes):
self.short_channel_id = short_channel_id
self.amt_to_forward = amt_to_forward
self.outgoing_cltv_value = outgoing_cltv_value
def to_bytes(self) -> bytes:
ret = self.short_channel_id
ret += self.amt_to_forward
ret += self.outgoing_cltv_value
ret += bytes(12) # padding
if len(ret) != 32:
raise Exception('unexpected length {}'.format(len(ret)))
return ret
@classmethod
def from_bytes(cls, b: bytes):
if len(b) != 32:
raise Exception('unexpected length {}'.format(len(b)))
return OnionPerHop(
short_channel_id=b[:8],
amt_to_forward=b[8:16],
outgoing_cltv_value=b[16:20]
)
class OnionHopsDataSingle: # called HopData in lnd
def __init__(self, per_hop: OnionPerHop = None):
self.realm = 0
self.per_hop = per_hop
self.hmac = None
def to_bytes(self) -> bytes:
ret = bytes([self.realm])
ret += self.per_hop.to_bytes()
ret += self.hmac if self.hmac is not None else bytes(PER_HOP_HMAC_SIZE)
if len(ret) != PER_HOP_FULL_SIZE:
raise Exception('unexpected length {}'.format(len(ret)))
return ret
@classmethod
def from_bytes(cls, b: bytes):
if len(b) != PER_HOP_FULL_SIZE:
raise Exception('unexpected length {}'.format(len(b)))
ret = OnionHopsDataSingle()
ret.realm = b[0]
if ret.realm != 0:
raise Exception('only realm 0 is supported')
ret.per_hop = OnionPerHop.from_bytes(b[1:33])
ret.hmac = b[33:]
return ret
class OnionPacket:
def __init__(self, public_key: bytes, hops_data: bytes, hmac: bytes):
self.version = 0
self.public_key = public_key
self.hops_data = hops_data # also called RoutingInfo in bolt-04
self.hmac = hmac
def to_bytes(self) -> bytes:
ret = bytes([self.version])
ret += self.public_key
ret += self.hops_data
ret += self.hmac
if len(ret) != 1366:
raise Exception('unexpected length {}'.format(len(ret)))
return ret
@classmethod
def from_bytes(cls, b: bytes):
if len(b) != 1366:
raise Exception('unexpected length {}'.format(len(b)))
version = b[0]
if version != 0:
raise UnsupportedOnionPacketVersion('version {} is not supported'.format(version))
return OnionPacket(
public_key=b[1:34],
hops_data=b[34:1334],
hmac=b[1334:]
)
def get_bolt04_onion_key(key_type: bytes, secret: bytes) -> bytes:
if key_type not in (b'rho', b'mu', b'um', b'ammag'):
raise Exception('invalid key_type {}'.format(key_type))
key = hmac.new(key_type, msg=secret, digestmod=hashlib.sha256).digest()
return key
def get_shared_secrets_along_route(payment_path_pubkeys: Sequence[bytes],
session_key: bytes) -> Sequence[bytes]:
num_hops = len(payment_path_pubkeys)
hop_shared_secrets = num_hops * [b'']
ephemeral_key = session_key
# compute shared key for each hop
for i in range(0, num_hops):
hop_shared_secrets[i] = get_ecdh(ephemeral_key, payment_path_pubkeys[i])
ephemeral_pubkey = ecc.ECPrivkey(ephemeral_key).get_public_key_bytes()
blinding_factor = sha256(ephemeral_pubkey + hop_shared_secrets[i])
blinding_factor_int = int.from_bytes(blinding_factor, byteorder="big")
ephemeral_key_int = int.from_bytes(ephemeral_key, byteorder="big")
ephemeral_key_int = ephemeral_key_int * blinding_factor_int % ecc.CURVE_ORDER
ephemeral_key = ephemeral_key_int.to_bytes(32, byteorder="big")
return hop_shared_secrets
def new_onion_packet(payment_path_pubkeys: Sequence[bytes], session_key: bytes,
hops_data: Sequence[OnionHopsDataSingle], associated_data: bytes) -> OnionPacket:
num_hops = len(payment_path_pubkeys)
hop_shared_secrets = get_shared_secrets_along_route(payment_path_pubkeys, session_key)
filler = generate_filler(b'rho', num_hops, PER_HOP_FULL_SIZE, hop_shared_secrets)
mix_header = bytes(HOPS_DATA_SIZE)
next_hmac = bytes(PER_HOP_HMAC_SIZE)
# compute routing info and MAC for each hop
for i in range(num_hops-1, -1, -1):
rho_key = get_bolt04_onion_key(b'rho', hop_shared_secrets[i])
mu_key = get_bolt04_onion_key(b'mu', hop_shared_secrets[i])
hops_data[i].hmac = next_hmac
stream_bytes = generate_cipher_stream(rho_key, NUM_STREAM_BYTES)
mix_header = mix_header[:-PER_HOP_FULL_SIZE]
mix_header = hops_data[i].to_bytes() + mix_header
mix_header = xor_bytes(mix_header, stream_bytes)
if i == num_hops - 1 and len(filler) != 0:
mix_header = mix_header[:-len(filler)] + filler
packet = mix_header + associated_data
next_hmac = hmac.new(mu_key, msg=packet, digestmod=hashlib.sha256).digest()
return OnionPacket(
public_key=ecc.ECPrivkey(session_key).get_public_key_bytes(),
hops_data=mix_header,
hmac=next_hmac)
def generate_filler(key_type: bytes, num_hops: int, hop_size: int,
shared_secrets: Sequence[bytes]) -> bytes:
filler_size = (NUM_MAX_HOPS_IN_PATH + 1) * hop_size
filler = bytearray(filler_size)
for i in range(0, num_hops-1): # -1, as last hop does not obfuscate
filler = filler[hop_size:]
filler += bytearray(hop_size)
stream_key = get_bolt04_onion_key(key_type, shared_secrets[i])
stream_bytes = generate_cipher_stream(stream_key, filler_size)
filler = xor_bytes(filler, stream_bytes)
return filler[(NUM_MAX_HOPS_IN_PATH-num_hops+2)*hop_size:]
def generate_cipher_stream(stream_key: bytes, num_bytes: int) -> bytes:
algo = algorithms.ChaCha20(stream_key, nonce=bytes(16))
cipher = Cipher(algo, mode=None, backend=default_backend())
encryptor = cipher.encryptor()
return encryptor.update(bytes(num_bytes))
ProcessedOnionPacket = namedtuple("ProcessedOnionPacket", ["are_we_final", "hop_data", "next_packet"])
# TODO replay protection
def process_onion_packet(onion_packet: OnionPacket, associated_data: bytes,
our_onion_private_key: bytes) -> ProcessedOnionPacket:
shared_secret = get_ecdh(our_onion_private_key, onion_packet.public_key)
# check message integrity
mu_key = get_bolt04_onion_key(b'mu', shared_secret)
calculated_mac = hmac.new(mu_key, msg=onion_packet.hops_data+associated_data,
digestmod=hashlib.sha256).digest()
if onion_packet.hmac != calculated_mac:
raise InvalidOnionMac()
# peel an onion layer off
rho_key = get_bolt04_onion_key(b'rho', shared_secret)
stream_bytes = generate_cipher_stream(rho_key, NUM_STREAM_BYTES)
padded_header = onion_packet.hops_data + bytes(PER_HOP_FULL_SIZE)
next_hops_data = xor_bytes(padded_header, stream_bytes)
# calc next ephemeral key
blinding_factor = sha256(onion_packet.public_key + shared_secret)
blinding_factor_int = int.from_bytes(blinding_factor, byteorder="big")
next_public_key_int = ecc.ECPubkey(onion_packet.public_key) * blinding_factor_int
next_public_key = next_public_key_int.get_public_key_bytes()
hop_data = OnionHopsDataSingle.from_bytes(next_hops_data[:PER_HOP_FULL_SIZE])
next_onion_packet = OnionPacket(
public_key=next_public_key,
hops_data=next_hops_data[PER_HOP_FULL_SIZE:],
hmac=hop_data.hmac
)
if hop_data.hmac == bytes(PER_HOP_HMAC_SIZE):
# we are the destination / exit node
are_we_final = True
else:
# we are an intermediate node; forwarding
are_we_final = False
return ProcessedOnionPacket(are_we_final, hop_data, next_onion_packet)
class FailedToDecodeOnionError(Exception): pass
class OnionRoutingFailureMessage:
def __init__(self, code: int, data: bytes):
self.code = code
self.data = data
def __repr__(self):
return repr((self.code, self.data))
def _decode_onion_error(error_packet: bytes, payment_path_pubkeys: Sequence[bytes],
session_key: bytes) -> (bytes, int):
"""Returns the decoded error bytes, and the index of the sender of the error."""
num_hops = len(payment_path_pubkeys)
hop_shared_secrets = get_shared_secrets_along_route(payment_path_pubkeys, session_key)
for i in range(num_hops):
ammag_key = get_bolt04_onion_key(b'ammag', hop_shared_secrets[i])
um_key = get_bolt04_onion_key(b'um', hop_shared_secrets[i])
stream_bytes = generate_cipher_stream(ammag_key, len(error_packet))
error_packet = xor_bytes(error_packet, stream_bytes)
hmac_computed = hmac.new(um_key, msg=error_packet[32:], digestmod=hashlib.sha256).digest()
hmac_found = error_packet[:32]
if hmac_computed == hmac_found:
return error_packet, i
raise FailedToDecodeOnionError()
def decode_onion_error(error_packet: bytes, payment_path_pubkeys: Sequence[bytes],
session_key: bytes) -> (OnionRoutingFailureMessage, int):
"""Returns the failure message, and the index of the sender of the error."""
decrypted_error, sender_index = _decode_onion_error(error_packet, payment_path_pubkeys, session_key)
failure_msg = get_failure_msg_from_onion_error(decrypted_error)
return failure_msg, sender_index
def get_failure_msg_from_onion_error(decrypted_error_packet: bytes) -> OnionRoutingFailureMessage:
# get failure_msg bytes from error packet
failure_len = int.from_bytes(decrypted_error_packet[32:34], byteorder='big')
failure_msg = decrypted_error_packet[34:34+failure_len]
# create failure message object
failure_code = int.from_bytes(failure_msg[:2], byteorder='big')
failure_data = failure_msg[2:]
return OnionRoutingFailureMessage(failure_code, failure_data)