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