commit 6b90a2d36c52c577a786e8080e3c09531795b16d
parent e5458bb5348be6d73ff834f7db3cd4a993c7ed6a
Author: bitromortac <bitromortac@protonmail.com>
Date: Fri, 18 Dec 2020 11:06:42 +0100
lnpeer: implement upfront shutdown script logic
Upfront shutdown script is a script provided on channel opening,
which will be used by the peer to enforce us closing to this script
on collaborative channel close.
Diffstat:
4 files changed, 110 insertions(+), 7 deletions(-)
diff --git a/electrum/lnchannel.py b/electrum/lnchannel.py
@@ -649,6 +649,9 @@ class Channel(AbstractChannel):
def is_static_remotekey_enabled(self) -> bool:
return bool(self.storage.get('static_remotekey_enabled'))
+ def is_upfront_shutdown_script_enabled(self) -> bool:
+ return bool(self.storage.get('upfront_shutdown_script_enabled'))
+
def get_wallet_addresses_channel_might_want_reserved(self) -> Sequence[str]:
ret = []
if self.is_static_remotekey_enabled():
diff --git a/electrum/lnpeer.py b/electrum/lnpeer.py
@@ -44,7 +44,8 @@ from .lnutil import (Outpoint, LocalConfig, RECEIVED, UpdateAddHtlc,
RemoteMisbehaving,
NBLOCK_OUR_CLTV_EXPIRY_DELTA, format_short_channel_id, ShortChannelID,
IncompatibleLightningFeatures, derive_payment_secret_from_payment_preimage,
- LN_MAX_FUNDING_SAT, calc_fees_for_commitment_tx)
+ LN_MAX_FUNDING_SAT, calc_fees_for_commitment_tx,
+ UpfrontShutdownScriptViolation)
from .lnutil import FeeUpdate, channel_id_from_funding_tx
from .lntransport import LNTransport, LNTransportBase
from .lnmsg import encode_msg, decode_msg
@@ -486,12 +487,33 @@ class Peer(Logger):
def is_static_remotekey(self):
return bool(self.features & LnFeatures.OPTION_STATIC_REMOTEKEY_OPT)
+ def is_upfront_shutdown_script(self):
+ return bool(self.features & LnFeatures.OPTION_UPFRONT_SHUTDOWN_SCRIPT_OPT)
+
+ def upfront_shutdown_script_from_payload(self, payload, msg_identifier: str) -> Optional[bytes]:
+ if msg_identifier not in ['accept', 'open']:
+ raise ValueError("msg_identifier must be either 'accept' or 'open'")
+
+ uss_tlv = payload[msg_identifier + '_channel_tlvs'].get(
+ 'upfront_shutdown_script')
+
+ if uss_tlv and self.is_upfront_shutdown_script():
+ upfront_shutdown_script = uss_tlv['shutdown_scriptpubkey']
+ else:
+ upfront_shutdown_script = b''
+ self.logger.info(f"upfront shutdown script received: {upfront_shutdown_script}")
+ return upfront_shutdown_script
+
def make_local_config(self, funding_sat: int, push_msat: int, initiator: HTLCOwner) -> LocalConfig:
channel_seed = os.urandom(32)
initial_msat = funding_sat * 1000 - push_msat if initiator == LOCAL else push_msat
+
+ static_remotekey = None
+ # sending empty bytes as the upfront_shutdown_script will give us the
+ # flexibility to decide an address at closing time
+ upfront_shutdown_script = b''
+
if self.is_static_remotekey():
- # Note: in the future, if a CSV delay is added,
- # we will want to derive that key
wallet = self.lnworker.wallet
assert wallet.txin_type == 'p2wpkh'
addr = wallet.get_new_sweep_address_for_channel()
@@ -503,6 +525,7 @@ class Peer(Logger):
local_config = LocalConfig.from_seed(
channel_seed=channel_seed,
static_remotekey=static_remotekey,
+ upfront_shutdown_script=upfront_shutdown_script,
to_self_delay=self.network.config.get('lightning_to_self_delay', 7 * 144),
dust_limit_sat=dust_limit_sat,
max_htlc_value_in_flight_msat=funding_sat * 1000,
@@ -546,15 +569,27 @@ class Peer(Logger):
push_msat: int,
temp_channel_id: bytes
) -> Tuple[Channel, 'PartialTransaction']:
+ """Implements the channel opening flow.
+
+ -> open_channel message
+ <- accept_channel message
+ -> funding_created message
+ <- funding_signed message
+
+ Channel configurations are initialized in this method.
+ """
await asyncio.wait_for(self.initialized, LN_P2P_NETWORK_TIMEOUT)
+
feerate = self.lnworker.current_feerate_per_kw()
local_config = self.make_local_config(funding_sat, push_msat, LOCAL)
+
if funding_sat > LN_MAX_FUNDING_SAT:
raise Exception(f"MUST set funding_satoshis to less than 2^24 satoshi. {funding_sat} sat > {LN_MAX_FUNDING_SAT}")
if push_msat > 1000 * funding_sat:
raise Exception(f"MUST set push_msat to equal or less than 1000 * funding_satoshis: {push_msat} msat > {1000 * funding_sat} msat")
if funding_sat < lnutil.MIN_FUNDING_SAT:
raise Exception(f"funding_sat too low: {funding_sat} < {lnutil.MIN_FUNDING_SAT}")
+
# for the first commitment transaction
per_commitment_secret_first = get_per_commitment_secret_from_seed(local_config.per_commitment_secret_seed,
RevocationStore.START_INDEX)
@@ -579,7 +614,13 @@ class Peer(Logger):
channel_flags=0x00, # not willing to announce channel
channel_reserve_satoshis=local_config.reserve_sat,
htlc_minimum_msat=local_config.htlc_minimum_msat,
+ open_channel_tlvs={
+ 'upfront_shutdown_script':
+ {'shutdown_scriptpubkey': local_config.upfront_shutdown_script}
+ }
)
+
+ # <- accept_channel
payload = await self.wait_for_message('accept_channel', temp_channel_id)
remote_per_commitment_point = payload['first_per_commitment_point']
funding_txn_minimum_depth = payload['minimum_depth']
@@ -587,6 +628,10 @@ class Peer(Logger):
raise Exception(f"minimum depth too low, {funding_txn_minimum_depth}")
if funding_txn_minimum_depth > 30:
raise Exception(f"minimum depth too high, {funding_txn_minimum_depth}")
+
+ upfront_shutdown_script = self.upfront_shutdown_script_from_payload(
+ payload, 'accept')
+
remote_config = RemoteConfig(
payment_basepoint=OnlyPubkeyKeypair(payload['payment_basepoint']),
multisig_key=OnlyPubkeyKeypair(payload["funding_pubkey"]),
@@ -602,6 +647,7 @@ class Peer(Logger):
htlc_minimum_msat=payload['htlc_minimum_msat'],
next_per_commitment_point=remote_per_commitment_point,
current_per_commitment_point=None,
+ upfront_shutdown_script=upfront_shutdown_script
)
remote_config.validate_params(funding_sat=funding_sat)
# if channel_reserve_satoshis is less than dust_limit_satoshis within the open_channel message:
@@ -612,6 +658,8 @@ class Peer(Logger):
# MUST reject the channel.
if local_config.reserve_sat < remote_config.dust_limit_sat:
raise Exception("violated constraint: local_config.reserve_sat < remote_config.dust_limit_sat")
+
+ # -> funding created
# replace dummy output in funding tx
redeem_script = funding_output_script(local_config, remote_config)
funding_address = bitcoin.redeem_script_to_address('p2wsh', redeem_script)
@@ -626,7 +674,7 @@ class Peer(Logger):
funding_txid = funding_tx.txid()
assert funding_txid
funding_index = funding_tx.outputs().index(funding_output)
- # remote commitment transaction
+ # build remote commitment transaction
channel_id, funding_txid_bytes = channel_id_from_funding_tx(funding_txid, funding_index)
outpoint = Outpoint(funding_txid, funding_index)
constraints = ChannelConstraints(capacity=funding_sat, is_initiator=True, funding_txn_minimum_depth=funding_txn_minimum_depth)
@@ -640,12 +688,15 @@ class Peer(Logger):
chan.add_or_update_peer_addr(self.transport.peer_addr)
sig_64, _ = chan.sign_next_commitment()
self.temp_id_to_id[temp_channel_id] = channel_id
+
self.send_message("funding_created",
temporary_channel_id=temp_channel_id,
funding_txid=funding_txid_bytes,
funding_output_index=funding_index,
signature=sig_64)
self.funding_created_sent.add(channel_id)
+
+ # <- funding signed
payload = await self.wait_for_message('funding_signed', channel_id)
self.logger.info('received funding_signed')
remote_sig = payload['signature']
@@ -675,6 +726,16 @@ class Peer(Logger):
return StoredDict(chan_dict, None, [])
async def on_open_channel(self, payload):
+ """Implements the channel acceptance flow.
+
+ <- open_channel message
+ -> accept_channel message
+ <- funding_created message
+ -> funding_signed message
+
+ Channel configurations are initialized in this method.
+ """
+ # <- open_channel
if payload['chain_hash'] != constants.net.rev_genesis_bytes():
raise Exception('wrong chain_hash')
funding_sat = payload['funding_satoshis']
@@ -688,6 +749,10 @@ class Peer(Logger):
raise Exception(f"MUST set push_msat to equal or less than 1000 * funding_satoshis: {push_msat} msat > {1000 * funding_sat} msat")
if funding_sat < lnutil.MIN_FUNDING_SAT:
raise Exception(f"funding_sat too low: {funding_sat} < {lnutil.MIN_FUNDING_SAT}")
+
+ upfront_shutdown_script = self.upfront_shutdown_script_from_payload(
+ payload, 'open')
+
remote_config = RemoteConfig(
payment_basepoint=OnlyPubkeyKeypair(payload['payment_basepoint']),
multisig_key=OnlyPubkeyKeypair(payload['funding_pubkey']),
@@ -703,7 +768,9 @@ class Peer(Logger):
htlc_minimum_msat=payload['htlc_minimum_msat'],
next_per_commitment_point=payload['first_per_commitment_point'],
current_per_commitment_point=None,
+ upfront_shutdown_script=upfront_shutdown_script,
)
+
remote_config.validate_params(funding_sat=funding_sat)
# The receiving node MUST fail the channel if:
# the funder's amount for the initial commitment transaction is not sufficient for full fee payment.
@@ -720,12 +787,15 @@ class Peer(Logger):
# note: we ignore payload['channel_flags'], which e.g. contains 'announce_channel'.
# Notably if the remote sets 'announce_channel' to True, we will ignore that too,
# but we will not play along with actually announcing the channel (so we keep it private).
+
+ # -> accept channel
# for the first commitment transaction
per_commitment_secret_first = get_per_commitment_secret_from_seed(local_config.per_commitment_secret_seed,
RevocationStore.START_INDEX)
per_commitment_point_first = secret_to_pubkey(int.from_bytes(per_commitment_secret_first, 'big'))
min_depth = 3
- self.send_message('accept_channel',
+ self.send_message(
+ 'accept_channel',
temporary_channel_id=temp_chan_id,
dust_limit_satoshis=local_config.dust_limit_sat,
max_htlc_value_in_flight_msat=local_config.max_htlc_value_in_flight_msat,
@@ -740,8 +810,16 @@ class Peer(Logger):
delayed_payment_basepoint=local_config.delayed_basepoint.pubkey,
htlc_basepoint=local_config.htlc_basepoint.pubkey,
first_per_commitment_point=per_commitment_point_first,
+ accept_channel_tlvs={
+ 'upfront_shutdown_script':
+ {'shutdown_scriptpubkey': local_config.upfront_shutdown_script}
+ }
)
+
+ # <- funding created
funding_created = await self.wait_for_message('funding_created', temp_chan_id)
+
+ # -> funding signed
funding_idx = funding_created['funding_output_index']
funding_txid = bh2u(funding_created['funding_txid'][::-1])
channel_id, funding_txid_bytes = channel_id_from_funding_tx(funding_txid, funding_idx)
@@ -1407,6 +1485,13 @@ class Peer(Logger):
async def on_shutdown(self, chan: Channel, payload):
their_scriptpubkey = payload['scriptpubkey']
+ their_upfront_scriptpubkey = chan.config[REMOTE].upfront_shutdown_script
+
+ # BOLT-02 check if they use the upfront shutdown script they advertized
+ if their_upfront_scriptpubkey:
+ if not (their_scriptpubkey == their_upfront_scriptpubkey):
+ raise UpfrontShutdownScriptViolation("remote didn't use upfront shutdown script it commited to in channel opening")
+
# BOLT-02 restrict the scriptpubkey to some templates:
if not (match_script_against_template(their_scriptpubkey, transaction.SCRIPTPUBKEY_TEMPLATE_WITNESS_V0)
or match_script_against_template(their_scriptpubkey, transaction.SCRIPTPUBKEY_TEMPLATE_P2SH)
@@ -1433,7 +1518,13 @@ class Peer(Logger):
async def send_shutdown(self, chan: Channel):
if not self.can_send_shutdown(chan):
raise Exception('cannot send shutdown')
- scriptpubkey = bfh(bitcoin.address_to_script(chan.sweep_address))
+
+ if chan.config[LOCAL].upfront_shutdown_script:
+ scriptpubkey = chan.config[LOCAL].upfront_shutdown_script
+ else:
+ scriptpubkey = bfh(bitcoin.address_to_script(chan.sweep_address))
+ assert scriptpubkey
+
# wait until no more pending updates (bolt2)
chan.set_can_send_ctx_updates(False)
while chan.has_pending_changes(REMOTE):
@@ -1452,7 +1543,12 @@ class Peer(Logger):
# if no HTLCs remain, we must not send updates
chan.set_can_send_ctx_updates(False)
their_scriptpubkey = payload['scriptpubkey']
- our_scriptpubkey = bfh(bitcoin.address_to_script(chan.sweep_address))
+ if chan.config[LOCAL].upfront_shutdown_script:
+ our_scriptpubkey = chan.config[LOCAL].upfront_shutdown_script
+ else:
+ our_scriptpubkey = bfh(bitcoin.address_to_script(chan.sweep_address))
+ assert our_scriptpubkey
+
# estimate fee of closing tx
our_sig, closing_tx = chan.make_closing_tx(our_scriptpubkey, their_scriptpubkey, fee_sat=0)
fee_rate = self.network.config.fee_per_kb()
diff --git a/electrum/lnutil.py b/electrum/lnutil.py
@@ -81,6 +81,7 @@ class Config(StoredObject):
initial_msat = attr.ib(type=int)
reserve_sat = attr.ib(type=int) # applies to OTHER ctx
htlc_minimum_msat = attr.ib(type=int) # smallest value for INCOMING htlc
+ upfront_shutdown_script = attr.ib(type=bytes, converter=hex_to_bytes)
def validate_params(self, *, funding_sat: int) -> None:
conf_name = type(self).__name__
@@ -300,6 +301,7 @@ class UnableToDeriveSecret(LightningError): pass
class HandshakeFailed(LightningError): pass
class ConnStringFormatError(LightningError): pass
class RemoteMisbehaving(LightningError): pass
+class UpfrontShutdownScriptViolation(RemoteMisbehaving): pass
class NotFoundChanAnnouncementForUpdate(Exception): pass
diff --git a/electrum/tests/test_lnchannel.py b/electrum/tests/test_lnchannel.py
@@ -69,6 +69,7 @@ def create_channel_state(funding_txid, funding_index, funding_sat, is_initiator,
htlc_minimum_msat=1,
next_per_commitment_point=nex,
current_per_commitment_point=cur,
+ upfront_shutdown_script=b'',
),
"local_config":lnpeer.LocalConfig(
channel_seed = None,
@@ -89,6 +90,7 @@ def create_channel_state(funding_txid, funding_index, funding_sat, is_initiator,
current_commitment_signature=None,
current_htlc_signatures=None,
htlc_minimum_msat=1,
+ upfront_shutdown_script=b'',
),
"constraints":lnpeer.ChannelConstraints(
capacity=funding_sat,
