Fold sign_holder_commitment_htlc_transactions into sign_holder_commitment

Signing the commitment transaction is almost always followed by signing the attached HTLC transactions, so fold the signing operations into a single method.

Author: devrandom

lightning/src/chain/keysinterface.rs

@@ -239,7 +239,7 @@ pub trait ChannelKeys : Send+Clone {
 	/// An external signer implementation should check that the commitment has not been revoked.
 	//
 	// TODO: Document the things someone using this interface should enforce before signing.
-	fn sign_holder_commitment<T: secp256k1::Signing + secp256k1::Verification>(&self, commitment_tx: &HolderCommitmentTransaction, secp_ctx: &Secp256k1<T>) -> Result<Signature, ()>;
+	fn sign_holder_commitment<T: secp256k1::Signing + secp256k1::Verification>(&self, commitment_tx: &HolderCommitmentTransaction, secp_ctx: &Secp256k1<T>) -> Result<(Signature, Vec<Signature>), ()>;
 
 	/// Same as sign_holder_commitment, but exists only for tests to get access to holder commitment
 	/// transactions which will be broadcasted later, after the channel has moved on to a newer
@@ -248,18 +248,6 @@ pub trait ChannelKeys : Send+Clone {
 	#[cfg(any(test,feature = "unsafe_revoked_tx_signing"))]
 	fn unsafe_sign_holder_commitment<T: secp256k1::Signing + secp256k1::Verification>(&self, commitment_tx: &HolderCommitmentTransaction, secp_ctx: &Secp256k1<T>) -> Result<Signature, ()>;
 
-	/// Create a signature for each HTLC transaction spending a holder's commitment transaction.
-	///
-	/// Unlike sign_holder_commitment, this may be called multiple times with *different*
-	/// commitment_tx values. While this will never be called with a revoked
-	/// commitment_tx, it is possible that it is called with the second-latest
-	/// commitment_tx (only if we haven't yet revoked it) if some watchtower/secondary
-	/// ChannelMonitor decided to broadcast before it had been updated to the latest.
-	///
-	/// Either an Err should be returned, or a Vec with one entry for each HTLC which exists in
-	/// commitment_tx.
-	fn sign_holder_commitment_htlc_transactions<T: secp256k1::Signing + secp256k1::Verification>(&self, commitment_tx: &HolderCommitmentTransaction, secp_ctx: &Secp256k1<T>) -> Result<Vec<Signature>, ()>;
-
 	/// Create a signature for the given input in a transaction spending an HTLC or commitment
 	/// transaction output when our counterparty broadcasts an old state.
 	///
@@ -492,11 +480,14 @@ impl ChannelKeys for InMemoryChannelKeys {
 		Ok((commitment_sig, htlc_sigs))
 	}
 
-	fn sign_holder_commitment<T: secp256k1::Signing + secp256k1::Verification>(&self, commitment_tx: &HolderCommitmentTransaction, secp_ctx: &Secp256k1<T>) -> Result<Signature, ()> {
+	fn sign_holder_commitment<T: secp256k1::Signing + secp256k1::Verification>(&self, commitment_tx: &HolderCommitmentTransaction, secp_ctx: &Secp256k1<T>) -> Result<(Signature, Vec<Signature>), ()> {
 		let funding_pubkey = PublicKey::from_secret_key(secp_ctx, &self.funding_key);
 		let funding_redeemscript = make_funding_redeemscript(&funding_pubkey, &self.counterparty_pubkeys().funding_pubkey);
 		let sig = commitment_tx.trust().built_transaction().sign(&self.funding_key, &funding_redeemscript, self.channel_value_satoshis, secp_ctx);
-		Ok(sig)
+		let channel_parameters = self.get_channel_parameters();
+		let trusted_tx = commitment_tx.trust();
+		let htlc_sigs = trusted_tx.get_htlc_sigs(&self.htlc_base_key, &channel_parameters.as_holder_broadcastable(), secp_ctx)?;
+		Ok((sig, htlc_sigs))
 	}
 
 	#[cfg(any(test,feature = "unsafe_revoked_tx_signing"))]
@@ -506,12 +497,6 @@ impl ChannelKeys for InMemoryChannelKeys {
 		Ok(commitment_tx.trust().built_transaction().sign(&self.funding_key, &channel_funding_redeemscript, self.channel_value_satoshis, secp_ctx))
 	}
 
-	fn sign_holder_commitment_htlc_transactions<T: secp256k1::Signing + secp256k1::Verification>(&self, commitment_tx: &HolderCommitmentTransaction, secp_ctx: &Secp256k1<T>) -> Result<Vec<Signature>, ()> {
-		let channel_parameters = self.get_channel_parameters();
-		let trusted_tx = commitment_tx.trust();
-		trusted_tx.get_htlc_sigs(&self.htlc_base_key, &channel_parameters.as_holder_broadcastable(), secp_ctx)
-	}
-
 	fn sign_justice_transaction<T: secp256k1::Signing + secp256k1::Verification>(&self, justice_tx: &Transaction, input: usize, amount: u64, per_commitment_key: &SecretKey, htlc: &Option<HTLCOutputInCommitment>, secp_ctx: &Secp256k1<T>) -> Result<Signature, ()> {
 		let revocation_key = match chan_utils::derive_private_revocation_key(&secp_ctx, &per_commitment_key, &self.revocation_base_key) {
 			Ok(revocation_key) => revocation_key,

lightning/src/ln/channel.rs

@@ -4723,15 +4723,13 @@ mod tests {
 					&chan.holder_keys.pubkeys().funding_pubkey,
 					chan.counterparty_funding_pubkey()
 				);
-				let holder_sig = chan_keys.sign_holder_commitment(&holder_commitment_tx, &secp_ctx).unwrap();
+				let (holder_sig, htlc_sigs) = chan_keys.sign_holder_commitment(&holder_commitment_tx, &secp_ctx).unwrap();
 				assert_eq!(Signature::from_der(&hex::decode($sig_hex).unwrap()[..]).unwrap(), holder_sig, "holder_sig");
 
 				let funding_redeemscript = chan.get_funding_redeemscript();
 				let tx = holder_commitment_tx.add_holder_sig(&funding_redeemscript, holder_sig);
 				assert_eq!(serialize(&tx)[..], hex::decode($tx_hex).unwrap()[..], "tx");
 
-				let htlc_sigs = chan_keys.sign_holder_commitment_htlc_transactions(&holder_commitment_tx, &secp_ctx).unwrap();
-
 				// ((htlc, counterparty_sig), (index, holder_sig))
 				let mut htlc_sig_iter = holder_commitment_tx.htlcs().iter().zip(&holder_commitment_tx.counterparty_htlc_sigs).zip(htlc_sigs.iter().enumerate());
 

lightning/src/ln/onchaintx.rs

@@ -890,20 +890,29 @@ impl<ChanSigner: ChannelKeys> OnchainTxHandler<ChanSigner> {
 
 	pub(crate) fn provide_latest_holder_tx(&mut self, tx: HolderCommitmentTransaction) {
 		self.prev_holder_commitment = self.holder_commitment.take();
+		self.holder_htlc_sigs = None;
 		self.holder_commitment = Some(tx);
 	}
 
+	// Normally holder HTLCs are signed at the same time as the holder commitment tx.  However,
+	// in some configurations, the holder commitment tx has been signed and broadcast by a replica of
+	// the ChannelMonitor, so we handle that case here.
 	fn sign_latest_holder_htlcs(&mut self) {
-		if let Some(ref holder_commitment) = self.holder_commitment {
-			if let Ok(sigs) = self.key_storage.sign_holder_commitment_htlc_transactions(holder_commitment, &self.secp_ctx) {
+		if self.holder_htlc_sigs.is_none() {
+			if let Some(ref holder_commitment) = self.holder_commitment {
+				let (_sig, sigs) = self.key_storage.sign_holder_commitment(holder_commitment, &self.secp_ctx).expect("sign holder commitment");
 				self.holder_htlc_sigs = Some(Self::extract_holder_sigs(holder_commitment, sigs));
 			}
 		}
 	}
 
+	// Normally only the latest commitment tx and HTLCs need to be signed.  However, in some
+	// configurations we may have updated our holder commtiment but a replica of the ChannelMonitor
+	// broadcast the previous one before we sync with it.  We handle that case here.
 	fn sign_prev_holder_htlcs(&mut self) {
-		if let Some(ref holder_commitment) = self.prev_holder_commitment {
-			if let Ok(sigs) = self.key_storage.sign_holder_commitment_htlc_transactions(holder_commitment, &self.secp_ctx) {
+		if self.prev_holder_htlc_sigs.is_none() {
+			if let Some(ref holder_commitment) = self.prev_holder_commitment {
+				let (_sig, sigs) = self.key_storage.sign_holder_commitment(holder_commitment, &self.secp_ctx).expect("sign previous holder commitment");
 				self.prev_holder_htlc_sigs = Some(Self::extract_holder_sigs(holder_commitment, sigs));
 			}
 		}
@@ -925,8 +934,9 @@ impl<ChanSigner: ChannelKeys> OnchainTxHandler<ChanSigner> {
 	// to monitor before.
 	pub(crate) fn get_fully_signed_holder_tx(&mut self, funding_redeemscript: &Script) -> Option<Transaction> {
 		if let Some(ref mut holder_commitment) = self.holder_commitment {
-			match self.key_storage.sign_holder_commitment(&holder_commitment, &self.secp_ctx) {
-				Ok(sig) => {
+			match self.key_storage.sign_holder_commitment(holder_commitment, &self.secp_ctx) {
+				Ok((sig, htlc_sigs)) => {
+					self.holder_htlc_sigs = Some(Self::extract_holder_sigs(holder_commitment, htlc_sigs));
 					Some(holder_commitment.add_holder_sig(funding_redeemscript, sig))
 				},
 				Err(_) => return None,
@@ -940,7 +950,8 @@ impl<ChanSigner: ChannelKeys> OnchainTxHandler<ChanSigner> {
 	pub(crate) fn get_fully_signed_copy_holder_tx(&mut self, funding_redeemscript: &Script) -> Option<Transaction> {
 		if let Some(ref mut holder_commitment) = self.holder_commitment {
 			match self.key_storage.sign_holder_commitment(holder_commitment, &self.secp_ctx) {
-				Ok(sig) => {
+				Ok((sig, htlc_sigs)) => {
+					self.holder_htlc_sigs = Some(Self::extract_holder_sigs(holder_commitment, htlc_sigs));
 					Some(holder_commitment.add_holder_sig(funding_redeemscript, sig))
 				},
 				Err(_) => return None,
@@ -966,7 +977,7 @@ impl<ChanSigner: ChannelKeys> OnchainTxHandler<ChanSigner> {
 				}
 			}
 		}
-		if self.prev_holder_commitment.is_some() {
+		if htlc_tx.is_none() && self.prev_holder_commitment.is_some() {
 			let commitment_txid = self.prev_holder_commitment.as_ref().unwrap().trust().txid();
 			if commitment_txid == outp.txid {
 				self.sign_prev_holder_htlcs();

lightning/src/util/enforcing_trait_impls.rs

@@ -8,14 +8,13 @@
 // licenses.
 
 use ln::chan_utils::{HTLCOutputInCommitment, ChannelPublicKeys, HolderCommitmentTransaction, CommitmentTransaction, ChannelTransactionParameters, TrustedCommitmentTransaction};
-use ln::{chan_utils, msgs};
+use ln::msgs;
 use chain::keysinterface::{ChannelKeys, InMemoryChannelKeys};
 
 use std::cmp;
 use std::sync::{Mutex, Arc};
 
-use bitcoin::blockdata::transaction::{Transaction, SigHashType};
-use bitcoin::util::bip143;
+use bitcoin::blockdata::transaction::Transaction;
 
 use bitcoin::secp256k1;
 use bitcoin::secp256k1::key::{SecretKey, PublicKey};
@@ -72,7 +71,7 @@ impl ChannelKeys for EnforcingChannelKeys {
 		Ok(self.inner.sign_counterparty_commitment(commitment_tx, secp_ctx).unwrap())
 	}
 
-	fn sign_holder_commitment<T: secp256k1::Signing + secp256k1::Verification>(&self, commitment_tx: &HolderCommitmentTransaction, secp_ctx: &Secp256k1<T>) -> Result<Signature, ()> {
+	fn sign_holder_commitment<T: secp256k1::Signing + secp256k1::Verification>(&self, commitment_tx: &HolderCommitmentTransaction, secp_ctx: &Secp256k1<T>) -> Result<(Signature, Vec<Signature>), ()> {
 		self.verify_holder_commitment_tx(commitment_tx, secp_ctx);
 
 		// TODO: enforce the ChannelKeys contract - error if this commitment was already revoked
@@ -85,25 +84,6 @@ impl ChannelKeys for EnforcingChannelKeys {
 		Ok(self.inner.unsafe_sign_holder_commitment(commitment_tx, secp_ctx).unwrap())
 	}
 
-	fn sign_holder_commitment_htlc_transactions<T: secp256k1::Signing + secp256k1::Verification>(&self, commitment_tx: &HolderCommitmentTransaction, secp_ctx: &Secp256k1<T>) -> Result<Vec<Signature>, ()> {
-		let trusted_tx = self.verify_holder_commitment_tx(commitment_tx, secp_ctx);
-		let commitment_txid = trusted_tx.txid();
-		let holder_csv = self.inner.counterparty_selected_contest_delay();
-
-		for (this_htlc, sig) in trusted_tx.htlcs().iter().zip(&commitment_tx.counterparty_htlc_sigs) {
-			assert!(this_htlc.transaction_output_index.is_some());
-			let keys = trusted_tx.keys();
-			let htlc_tx = chan_utils::build_htlc_transaction(&commitment_txid, trusted_tx.feerate_per_kw(), holder_csv, &this_htlc, &keys.broadcaster_delayed_payment_key, &keys.revocation_key);
-
-			let htlc_redeemscript = chan_utils::get_htlc_redeemscript(&this_htlc, &keys);
-
-			let sighash = hash_to_message!(&bip143::SigHashCache::new(&htlc_tx).signature_hash(0, &htlc_redeemscript, this_htlc.amount_msat / 1000, SigHashType::All)[..]);
-			secp_ctx.verify(&sighash, sig, &keys.countersignatory_htlc_key).unwrap();
-		}
-
-		Ok(self.inner.sign_holder_commitment_htlc_transactions(commitment_tx, secp_ctx).unwrap())
-	}
-
 	fn sign_justice_transaction<T: secp256k1::Signing + secp256k1::Verification>(&self, justice_tx: &Transaction, input: usize, amount: u64, per_commitment_key: &SecretKey, htlc: &Option<HTLCOutputInCommitment>, secp_ctx: &Secp256k1<T>) -> Result<Signature, ()> {
 		Ok(self.inner.sign_justice_transaction(justice_tx, input, amount, per_commitment_key, htlc, secp_ctx).unwrap())
 	}