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[Custom Transactions] Commitment Transaction & Channel Refactors #3606

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merged 10 commits into from
Mar 25, 2025
Merged

[Custom Transactions] Commitment Transaction & Channel Refactors #3606

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e58184c
Remove redundant parameters from the `CommitmentTransaction` constructor
tankyleo Feb 26, 2025
0ac188f
Let `CommitmentTransaction` build the `TxCreationKeys` it will cache
tankyleo Feb 26, 2025
9b71c64
Remove some unneeded `Result`'s in `CommitmentTransaction`
tankyleo Mar 5, 2025
1023d0b
Remove explicit per-commitment key derivations from channel objects
tankyleo Feb 26, 2025
592f17d
Remove unnecessary allocation in `send_commitment_no_state_update`
tankyleo Mar 2, 2025
728e7c2
Remove `i64` casts in `ChannelContext::build_commitment_transaction`
tankyleo Feb 26, 2025
22be385
Clean up tautologies in `ChannelContext::build_commitment_transaction`
tankyleo Feb 26, 2025
09422dd
Remove redundant fields in `CommitmentStats`
tankyleo Feb 26, 2025
935a8fd
Reorg return values of `ChannelContext::build_commitment_transaction`
tankyleo Feb 27, 2025
ff259ba
Cover the saturating sub of the fee and anchors from funder's balance
tankyleo Mar 17, 2025
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17 changes: 3 additions & 14 deletions lightning/src/chain/channelmonitor.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -38,7 +38,7 @@ use crate::types::features::ChannelTypeFeatures;
use crate::types::payment::{PaymentHash, PaymentPreimage};
use crate::ln::msgs::DecodeError;
use crate::ln::channel_keys::{DelayedPaymentKey, DelayedPaymentBasepoint, HtlcBasepoint, HtlcKey, RevocationKey, RevocationBasepoint};
use crate::ln::chan_utils::{self,CommitmentTransaction, CounterpartyCommitmentSecrets, HTLCOutputInCommitment, HTLCClaim, ChannelTransactionParameters, HolderCommitmentTransaction, TxCreationKeys};
use crate::ln::chan_utils::{self,CommitmentTransaction, CounterpartyCommitmentSecrets, HTLCOutputInCommitment, HTLCClaim, ChannelTransactionParameters, HolderCommitmentTransaction};
use crate::ln::channelmanager::{HTLCSource, SentHTLCId, PaymentClaimDetails};
use crate::chain;
use crate::chain::{BestBlock, WatchedOutput};
Expand Down Expand Up @@ -3506,20 +3506,9 @@ impl<Signer: EcdsaChannelSigner> ChannelMonitorImpl<Signer> {
to_broadcaster_value: u64, to_countersignatory_value: u64, feerate_per_kw: u32,
mut nondust_htlcs: Vec<(HTLCOutputInCommitment, Option<Box<HTLCSource>>)>
) -> CommitmentTransaction {
let broadcaster_keys =
&self.funding.channel_parameters.counterparty_parameters.as_ref().unwrap().pubkeys;
let countersignatory_keys = &self.funding.channel_parameters.holder_pubkeys;

let broadcaster_funding_key = broadcaster_keys.funding_pubkey;
let countersignatory_funding_key = countersignatory_keys.funding_pubkey;
let keys = TxCreationKeys::from_channel_static_keys(&their_per_commitment_point,
&broadcaster_keys, &countersignatory_keys, &self.onchain_tx_handler.secp_ctx);
let channel_parameters = &self.funding.channel_parameters.as_counterparty_broadcastable();

CommitmentTransaction::new_with_auxiliary_htlc_data(commitment_number,
to_broadcaster_value, to_countersignatory_value, broadcaster_funding_key,
countersignatory_funding_key, keys, feerate_per_kw, &mut nondust_htlcs,
channel_parameters)
CommitmentTransaction::new_with_auxiliary_htlc_data(commitment_number, their_per_commitment_point,
to_broadcaster_value, to_countersignatory_value, feerate_per_kw, &mut nondust_htlcs, channel_parameters, &self.onchain_tx_handler.secp_ctx)
}

fn counterparty_commitment_txs_from_update(&self, update: &ChannelMonitorUpdate) -> Vec<CommitmentTransaction> {
Expand Down
75 changes: 31 additions & 44 deletions lightning/src/ln/chan_utils.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1180,13 +1180,6 @@ impl HolderCommitmentTransaction {
let dummy_key = PublicKey::from_secret_key(&secp_ctx, &SecretKey::from_slice(&[42; 32]).unwrap());
let dummy_sig = sign(&secp_ctx, &secp256k1::Message::from_digest([42; 32]), &SecretKey::from_slice(&[42; 32]).unwrap());

let keys = TxCreationKeys {
per_commitment_point: dummy_key.clone(),
revocation_key: RevocationKey::from_basepoint(&secp_ctx, &RevocationBasepoint::from(dummy_key), &dummy_key),
broadcaster_htlc_key: HtlcKey::from_basepoint(&secp_ctx, &HtlcBasepoint::from(dummy_key), &dummy_key),
countersignatory_htlc_key: HtlcKey::from_basepoint(&secp_ctx, &HtlcBasepoint::from(dummy_key), &dummy_key),
broadcaster_delayed_payment_key: DelayedPaymentKey::from_basepoint(&secp_ctx, &DelayedPaymentBasepoint::from(dummy_key), &dummy_key),
};
let channel_pubkeys = ChannelPublicKeys {
funding_pubkey: dummy_key.clone(),
revocation_basepoint: RevocationBasepoint::from(dummy_key),
Expand All @@ -1208,7 +1201,7 @@ impl HolderCommitmentTransaction {
for _ in 0..htlcs.len() {
counterparty_htlc_sigs.push(dummy_sig);
}
let inner = CommitmentTransaction::new_with_auxiliary_htlc_data(0, 0, 0, dummy_key.clone(), dummy_key.clone(), keys, 0, htlcs, &channel_parameters.as_counterparty_broadcastable());
let inner = CommitmentTransaction::new_with_auxiliary_htlc_data(0, &dummy_key, 0, 0, 0, htlcs, &channel_parameters.as_counterparty_broadcastable(), &secp_ctx);
htlcs.sort_by_key(|htlc| htlc.0.transaction_output_index);
HolderCommitmentTransaction {
inner,
Expand Down Expand Up @@ -1518,12 +1511,13 @@ impl CommitmentTransaction {
/// Only include HTLCs that are above the dust limit for the channel.
///
/// This is not exported to bindings users due to the generic though we likely should expose a version without
pub fn new_with_auxiliary_htlc_data<T>(commitment_number: u64, to_broadcaster_value_sat: u64, to_countersignatory_value_sat: u64, broadcaster_funding_key: PublicKey, countersignatory_funding_key: PublicKey, keys: TxCreationKeys, feerate_per_kw: u32, htlcs_with_aux: &mut Vec<(HTLCOutputInCommitment, T)>, channel_parameters: &DirectedChannelTransactionParameters) -> CommitmentTransaction {
pub fn new_with_auxiliary_htlc_data<T>(commitment_number: u64, per_commitment_point: &PublicKey, to_broadcaster_value_sat: u64, to_countersignatory_value_sat: u64, feerate_per_kw: u32, htlcs_with_aux: &mut Vec<(HTLCOutputInCommitment, T)>, channel_parameters: &DirectedChannelTransactionParameters, secp_ctx: &Secp256k1<secp256k1::All>) -> CommitmentTransaction {
let to_broadcaster_value_sat = Amount::from_sat(to_broadcaster_value_sat);
let to_countersignatory_value_sat = Amount::from_sat(to_countersignatory_value_sat);
let keys = TxCreationKeys::from_channel_static_keys(per_commitment_point, channel_parameters.broadcaster_pubkeys(), channel_parameters.countersignatory_pubkeys(), secp_ctx);

// Sort outputs and populate output indices while keeping track of the auxiliary data
let (outputs, htlcs) = Self::internal_build_outputs(&keys, to_broadcaster_value_sat, to_countersignatory_value_sat, htlcs_with_aux, channel_parameters, &broadcaster_funding_key, &countersignatory_funding_key).unwrap();
let (outputs, htlcs) = Self::internal_build_outputs(&keys, to_broadcaster_value_sat, to_countersignatory_value_sat, htlcs_with_aux, channel_parameters);

let (obscured_commitment_transaction_number, txins) = Self::internal_build_inputs(commitment_number, channel_parameters);
let transaction = Self::make_transaction(obscured_commitment_transaction_number, txins, outputs);
Expand Down Expand Up @@ -1552,19 +1546,19 @@ impl CommitmentTransaction {
self
}

fn internal_rebuild_transaction(&self, keys: &TxCreationKeys, channel_parameters: &DirectedChannelTransactionParameters, broadcaster_funding_key: &PublicKey, countersignatory_funding_key: &PublicKey) -> Result<BuiltCommitmentTransaction, ()> {
fn internal_rebuild_transaction(&self, keys: &TxCreationKeys, channel_parameters: &DirectedChannelTransactionParameters) -> BuiltCommitmentTransaction {
let (obscured_commitment_transaction_number, txins) = Self::internal_build_inputs(self.commitment_number, channel_parameters);

let mut htlcs_with_aux = self.htlcs.iter().map(|h| (h.clone(), ())).collect();
let (outputs, _) = Self::internal_build_outputs(keys, self.to_broadcaster_value_sat, self.to_countersignatory_value_sat, &mut htlcs_with_aux, channel_parameters, broadcaster_funding_key, countersignatory_funding_key)?;
let (outputs, _) = Self::internal_build_outputs(keys, self.to_broadcaster_value_sat, self.to_countersignatory_value_sat, &mut htlcs_with_aux, channel_parameters);

let transaction = Self::make_transaction(obscured_commitment_transaction_number, txins, outputs);
let txid = transaction.compute_txid();
let built_transaction = BuiltCommitmentTransaction {
transaction,
txid
};
Ok(built_transaction)
built_transaction
}

fn make_transaction(obscured_commitment_transaction_number: u64, txins: Vec<TxIn>, outputs: Vec<TxOut>) -> Transaction {
Expand All @@ -1580,17 +1574,20 @@ impl CommitmentTransaction {
// - initial sorting of outputs / HTLCs in the constructor, in which case T is auxiliary data the
// caller needs to have sorted together with the HTLCs so it can keep track of the output index
// - building of a bitcoin transaction during a verify() call, in which case T is just ()
fn internal_build_outputs<T>(keys: &TxCreationKeys, to_broadcaster_value_sat: Amount, to_countersignatory_value_sat: Amount, htlcs_with_aux: &mut Vec<(HTLCOutputInCommitment, T)>, channel_parameters: &DirectedChannelTransactionParameters, broadcaster_funding_key: &PublicKey, countersignatory_funding_key: &PublicKey) -> Result<(Vec<TxOut>, Vec<HTLCOutputInCommitment>), ()> {
let countersignatory_pubkeys = channel_parameters.countersignatory_pubkeys();
fn internal_build_outputs<T>(keys: &TxCreationKeys, to_broadcaster_value_sat: Amount, to_countersignatory_value_sat: Amount, htlcs_with_aux: &mut Vec<(HTLCOutputInCommitment, T)>, channel_parameters: &DirectedChannelTransactionParameters) -> (Vec<TxOut>, Vec<HTLCOutputInCommitment>) {
let countersignatory_payment_point = &channel_parameters.countersignatory_pubkeys().payment_point;
let countersignatory_funding_key = &channel_parameters.countersignatory_pubkeys().funding_pubkey;
let broadcaster_funding_key = &channel_parameters.broadcaster_pubkeys().funding_pubkey;
let channel_type = channel_parameters.channel_type_features();
let contest_delay = channel_parameters.contest_delay();

let mut txouts: Vec<(TxOut, Option<&mut HTLCOutputInCommitment>)> = Vec::new();

if to_countersignatory_value_sat > Amount::ZERO {
let script = if channel_parameters.channel_type_features().supports_anchors_zero_fee_htlc_tx() {
get_to_countersigner_keyed_anchor_redeemscript(&countersignatory_pubkeys.payment_point).to_p2wsh()
let script = if channel_type.supports_anchors_zero_fee_htlc_tx() {
get_to_countersigner_keyed_anchor_redeemscript(countersignatory_payment_point).to_p2wsh()
} else {
ScriptBuf::new_p2wpkh(&Hash160::hash(&countersignatory_pubkeys.payment_point.serialize()).into())
ScriptBuf::new_p2wpkh(&Hash160::hash(&countersignatory_payment_point.serialize()).into())
};
txouts.push((
TxOut {
Expand All @@ -1616,7 +1613,7 @@ impl CommitmentTransaction {
));
}

if channel_parameters.channel_type_features().supports_anchors_zero_fee_htlc_tx() {
if channel_type.supports_anchors_zero_fee_htlc_tx() {
if to_broadcaster_value_sat > Amount::ZERO || !htlcs_with_aux.is_empty() {
let anchor_script = get_keyed_anchor_redeemscript(broadcaster_funding_key);
txouts.push((
Expand All @@ -1642,7 +1639,7 @@ impl CommitmentTransaction {

let mut htlcs = Vec::with_capacity(htlcs_with_aux.len());
for (htlc, _) in htlcs_with_aux {
let script = get_htlc_redeemscript(&htlc, &channel_parameters.channel_type_features(), &keys);
let script = get_htlc_redeemscript(htlc, channel_type, keys);
let txout = TxOut {
script_pubkey: script.to_p2wsh(),
value: htlc.to_bitcoin_amount(),
Expand Down Expand Up @@ -1674,7 +1671,7 @@ impl CommitmentTransaction {
}
outputs.push(out.0);
}
Ok((outputs, htlcs))
(outputs, htlcs)
}

fn internal_build_inputs(commitment_number: u64, channel_parameters: &DirectedChannelTransactionParameters) -> (u64, Vec<TxIn>) {
Expand Down Expand Up @@ -1753,14 +1750,14 @@ impl CommitmentTransaction {
///
/// An external validating signer must call this method before signing
/// or using the built transaction.
pub fn verify<T: secp256k1::Signing + secp256k1::Verification>(&self, channel_parameters: &DirectedChannelTransactionParameters, broadcaster_keys: &ChannelPublicKeys, countersignatory_keys: &ChannelPublicKeys, secp_ctx: &Secp256k1<T>) -> Result<TrustedCommitmentTransaction, ()> {
pub fn verify<T: secp256k1::Signing + secp256k1::Verification>(&self, channel_parameters: &DirectedChannelTransactionParameters, secp_ctx: &Secp256k1<T>) -> Result<TrustedCommitmentTransaction, ()> {
// This is the only field of the key cache that we trust
let per_commitment_point = self.keys.per_commitment_point;
let keys = TxCreationKeys::from_channel_static_keys(&per_commitment_point, broadcaster_keys, countersignatory_keys, secp_ctx);
let per_commitment_point = &self.keys.per_commitment_point;
let keys = TxCreationKeys::from_channel_static_keys(per_commitment_point, channel_parameters.broadcaster_pubkeys(), channel_parameters.countersignatory_pubkeys(), secp_ctx);
if keys != self.keys {
return Err(());
}
let tx = self.internal_rebuild_transaction(&keys, channel_parameters, &broadcaster_keys.funding_pubkey, &countersignatory_keys.funding_pubkey)?;
let tx = self.internal_rebuild_transaction(&keys, channel_parameters);
if self.built.transaction != tx.transaction || self.built.txid != tx.txid {
return Err(());
}
Expand Down Expand Up @@ -1967,8 +1964,8 @@ pub fn get_commitment_transaction_number_obscure_factor(
mod tests {
use super::{CounterpartyCommitmentSecrets, ChannelPublicKeys};
use crate::chain;
use crate::ln::chan_utils::{get_htlc_redeemscript, get_to_countersigner_keyed_anchor_redeemscript, CommitmentTransaction, TxCreationKeys, ChannelTransactionParameters, CounterpartyChannelTransactionParameters, HTLCOutputInCommitment};
use bitcoin::secp256k1::{PublicKey, SecretKey, Secp256k1};
use crate::ln::chan_utils::{get_htlc_redeemscript, get_to_countersigner_keyed_anchor_redeemscript, CommitmentTransaction, ChannelTransactionParameters, CounterpartyChannelTransactionParameters, HTLCOutputInCommitment};
use bitcoin::secp256k1::{self, PublicKey, SecretKey, Secp256k1};
use crate::util::test_utils;
use crate::sign::{ChannelSigner, SignerProvider};
use bitcoin::{Network, Txid, ScriptBuf, CompressedPublicKey};
Expand All @@ -1983,13 +1980,12 @@ mod tests {

struct TestCommitmentTxBuilder {
commitment_number: u64,
holder_funding_pubkey: PublicKey,
counterparty_funding_pubkey: PublicKey,
keys: TxCreationKeys,
per_commitment_point: PublicKey,
feerate_per_kw: u32,
htlcs_with_aux: Vec<(HTLCOutputInCommitment, ())>,
channel_parameters: ChannelTransactionParameters,
counterparty_pubkeys: ChannelPublicKeys,
secp_ctx: Secp256k1::<secp256k1::All>,
}

impl TestCommitmentTxBuilder {
Expand All @@ -2014,32 +2010,23 @@ mod tests {
channel_type_features: ChannelTypeFeatures::only_static_remote_key(),
channel_value_satoshis: 3000,
};
let directed_parameters = channel_parameters.as_holder_broadcastable();
let keys = TxCreationKeys::from_channel_static_keys(
&per_commitment_point, directed_parameters.broadcaster_pubkeys(),
directed_parameters.countersignatory_pubkeys(), &secp_ctx,
);
let htlcs_with_aux = Vec::new();

Self {
commitment_number: 0,
holder_funding_pubkey: holder_pubkeys.funding_pubkey,
counterparty_funding_pubkey: counterparty_pubkeys.funding_pubkey,
keys,
per_commitment_point,
feerate_per_kw: 1,
htlcs_with_aux,
channel_parameters,
counterparty_pubkeys,
secp_ctx,
}
}

fn build(&mut self, to_broadcaster_sats: u64, to_countersignatory_sats: u64) -> CommitmentTransaction {
CommitmentTransaction::new_with_auxiliary_htlc_data(
self.commitment_number, to_broadcaster_sats, to_countersignatory_sats,
self.holder_funding_pubkey.clone(),
self.counterparty_funding_pubkey.clone(),
self.keys.clone(), self.feerate_per_kw,
&mut self.htlcs_with_aux, &self.channel_parameters.as_holder_broadcastable()
self.commitment_number, &self.per_commitment_point, to_broadcaster_sats, to_countersignatory_sats, self.feerate_per_kw,
&mut self.htlcs_with_aux, &self.channel_parameters.as_holder_broadcastable(), &self.secp_ctx
)
}
}
Expand Down Expand Up @@ -2087,7 +2074,7 @@ mod tests {
builder.channel_parameters.channel_type_features = ChannelTypeFeatures::only_static_remote_key();
builder.htlcs_with_aux = vec![(received_htlc.clone(), ()), (offered_htlc.clone(), ())];
let tx = builder.build(3000, 0);
let keys = &builder.keys.clone();
let keys = tx.trust().keys();
assert_eq!(tx.built.transaction.output.len(), 3);
assert_eq!(tx.built.transaction.output[0].script_pubkey, get_htlc_redeemscript(&received_htlc, &ChannelTypeFeatures::only_static_remote_key(), &keys).to_p2wsh());
assert_eq!(tx.built.transaction.output[1].script_pubkey, get_htlc_redeemscript(&offered_htlc, &ChannelTypeFeatures::only_static_remote_key(), &keys).to_p2wsh());
Expand Down
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