Move remote htlc transaction signature behind ChanSigner

Author: Antoine Riard

lightning/src/chain/keysinterface.rs

@@ -230,6 +230,9 @@ pub trait ChannelKeys : Send+Clone {
 	/// Signs a justice transaction.
 	fn sign_justice_transaction<T: secp256k1::Signing>(&self, bumped_tx: &mut Transaction, input: usize, witness_script: &Script, amount: u64, per_commitment_key: &SecretKey, revocation_pubkey: &PublicKey, is_htlc: bool, secp_ctx: &Secp256k1<T>);
 
+	/// Signs a remote htlc transaction.
+	fn sign_remote_htlc_transaction<T: secp256k1::Signing>(&self, bumped_tx: &mut Transaction, input: usize, witness_script: &Script, amount: u64, per_commitment_point: &PublicKey, preimage: &Option<PaymentPreimage>, secp_ctx: &Secp256k1<T>);
+
 	/// Create a signature for a (proposed) closing transaction.
 	///
 	/// Note that, due to rounding, there may be one "missing" satoshi, and either party may have
@@ -436,6 +439,22 @@ impl ChannelKeys for InMemoryChannelKeys {
 		}
 	}
 
+	fn sign_remote_htlc_transaction<T: secp256k1::Signing>(&self, bumped_tx: &mut Transaction, input: usize, witness_script: &Script, amount: u64, per_commitment_point: &PublicKey, preimage: &Option<PaymentPreimage>, secp_ctx: &Secp256k1<T>) {
+		if let Ok(htlc_key) = chan_utils::derive_private_key(&secp_ctx, &per_commitment_point, &self.htlc_base_key) {
+			let sighash_parts = bip143::SighashComponents::new(&bumped_tx);
+			let sighash = hash_to_message!(&sighash_parts.sighash_all(&bumped_tx.input[input], &witness_script, amount)[..]);
+			let sig = secp_ctx.sign(&sighash, &htlc_key);
+			bumped_tx.input[input].witness.push(sig.serialize_der().to_vec());
+			bumped_tx.input[input].witness[0].push(SigHashType::All as u8);
+			if let &Some(preimage) = preimage {
+				bumped_tx.input[input].witness.push(preimage.0.to_vec());
+			} else {
+				bumped_tx.input[input].witness.push(vec![0]);
+			}
+			bumped_tx.input[input].witness.push(witness_script.clone().into_bytes());
+		}
+	}
+
 	fn sign_closing_transaction<T: secp256k1::Signing>(&self, closing_tx: &Transaction, secp_ctx: &Secp256k1<T>) -> Result<Signature, ()> {
 		if closing_tx.input.len() != 1 { return Err(()); }
 		if closing_tx.input[0].witness.len() != 0 { return Err(()); }

lightning/src/ln/channelmonitor.rs

@@ -431,7 +431,6 @@ pub(crate) enum InputMaterial {
 	},
 	RemoteHTLC {
 		per_commitment_point: PublicKey,
-		key: SecretKey,
 		preimage: Option<PaymentPreimage>,
 		amount: u64,
 		locktime: u32,
@@ -455,10 +454,9 @@ impl Writeable for InputMaterial  {
 				input_descriptor.write(writer)?;
 				writer.write_all(&byte_utils::be64_to_array(*amount))?;
 			},
-			&InputMaterial::RemoteHTLC { ref per_commitment_point, ref key, ref preimage, ref amount, ref locktime } => {
+			&InputMaterial::RemoteHTLC { ref per_commitment_point, ref preimage, ref amount, ref locktime } => {
 				writer.write_all(&[1; 1])?;
 				per_commitment_point.write(writer)?;
-				key.write(writer)?;
 				preimage.write(writer)?;
 				writer.write_all(&byte_utils::be64_to_array(*amount))?;
 				writer.write_all(&byte_utils::be32_to_array(*locktime))?;
@@ -494,13 +492,11 @@ impl Readable for InputMaterial {
 			},
 			1 => {
 				let per_commitment_point = Readable::read(reader)?;
-				let key = Readable::read(reader)?;
 				let preimage = Readable::read(reader)?;
 				let amount = Readable::read(reader)?;
 				let locktime = Readable::read(reader)?;
 				InputMaterial::RemoteHTLC {
 					per_commitment_point,
-					key,
 					preimage,
 					amount,
 					locktime
@@ -1592,7 +1588,6 @@ impl<ChanSigner: ChannelKeys> ChannelMonitor<ChanSigner> {
 						if revocation_points.0 == commitment_number + 1 { Some(point) } else { None }
 					} else { None };
 				if let Some(revocation_point) = revocation_point_option {
-					let htlc_privkey = ignore_error!(chan_utils::derive_private_key(&self.secp_ctx, revocation_point, &self.onchain_detection.keys.htlc_base_key()));
 					let local_payment_key = ignore_error!(chan_utils::derive_private_key(&self.secp_ctx, revocation_point, &self.onchain_detection.keys.payment_base_key()));
 
 					self.broadcasted_remote_payment_script = {
@@ -1612,7 +1607,7 @@ impl<ChanSigner: ChannelKeys> ChannelMonitor<ChanSigner> {
 							let preimage = if htlc.offered { if let Some(p) = self.payment_preimages.get(&htlc.payment_hash) { Some(*p) } else { None } } else { None };
 							let aggregable = if !htlc.offered { false } else { true };
 							if preimage.is_some() || !htlc.offered {
-								let witness_data = InputMaterial::RemoteHTLC { per_commitment_point: *revocation_point, key: htlc_privkey, preimage, amount: htlc.amount_msat / 1000, locktime: htlc.cltv_expiry };
+								let witness_data = InputMaterial::RemoteHTLC { per_commitment_point: *revocation_point, preimage, amount: htlc.amount_msat / 1000, locktime: htlc.cltv_expiry };
 								claimable_outpoints.push(ClaimRequest { absolute_timelock: htlc.cltv_expiry, aggregable, outpoint: BitcoinOutPoint { txid: commitment_txid, vout: transaction_output_index }, witness_data });
 							}
 						}

lightning/src/ln/onchaintx.rs

@@ -3,10 +3,9 @@
 //! OnchainTxHandler objetcs are fully-part of ChannelMonitor and encapsulates all
 //! building, tracking, bumping and notifications functions.
 
-use bitcoin::blockdata::transaction::{Transaction, TxIn, TxOut, SigHashType};
+use bitcoin::blockdata::transaction::{Transaction, TxIn, TxOut};
 use bitcoin::blockdata::transaction::OutPoint as BitcoinOutPoint;
 use bitcoin::blockdata::script::Script;
-use bitcoin::util::bip143;
 
 use bitcoin_hashes::sha256d::Hash as Sha256dHash;
 
@@ -693,7 +692,7 @@ impl<ChanSigner: ChannelKeys> OnchainTxHandler<ChanSigner> {
 							log_trace!(self, "Going to broadcast Penalty Transaction {} claiming revoked {} output {} from {} with new feerate {}...", bumped_tx.txid(), if *input_descriptor == InputDescriptors::RevokedOutput { "to_local" } else if *input_descriptor == InputDescriptors::RevokedOfferedHTLC { "offered" } else if *input_descriptor == InputDescriptors::RevokedReceivedHTLC { "received" } else { "" }, outp.vout, outp.txid, new_feerate);
 						}
 					},
-					&InputMaterial::RemoteHTLC { ref per_commitment_point, ref key, ref preimage, ref amount, ref locktime } => {
+					&InputMaterial::RemoteHTLC { ref per_commitment_point, ref preimage, ref amount, ref locktime } => {
 						if let Ok(chan_keys) = TxCreationKeys::new(&self.secp_ctx, &per_commitment_point, &self.remote_tx_cache.remote_delayed_payment_base_key, &self.remote_tx_cache.remote_htlc_base_key, &self.key_storage.pubkeys().revocation_basepoint, &self.key_storage.pubkeys().payment_basepoint, &self.key_storage.pubkeys().htlc_basepoint) {
 							let mut this_htlc = None;
 							if let Some(htlcs) = self.remote_tx_cache.per_htlc.get(&outp.txid) {
@@ -707,17 +706,7 @@ impl<ChanSigner: ChannelKeys> OnchainTxHandler<ChanSigner> {
 							let witness_script = chan_utils::get_htlc_redeemscript_with_explicit_keys(&this_htlc.unwrap(), &chan_keys.a_htlc_key, &chan_keys.b_htlc_key, &chan_keys.revocation_key);
 
 							if !preimage.is_some() { bumped_tx.lock_time = *locktime }; // Right now we don't aggregate time-locked transaction, if we do we should set lock_time before to avoid breaking hash computation
-							let sighash_parts = bip143::SighashComponents::new(&bumped_tx);
-							let sighash = hash_to_message!(&sighash_parts.sighash_all(&bumped_tx.input[i], &witness_script, *amount)[..]);
-							let sig = self.secp_ctx.sign(&sighash, &key);
-							bumped_tx.input[i].witness.push(sig.serialize_der().to_vec());
-							bumped_tx.input[i].witness[0].push(SigHashType::All as u8);
-							if let &Some(preimage) = preimage {
-								bumped_tx.input[i].witness.push(preimage.clone().0.to_vec());
-							} else {
-								bumped_tx.input[i].witness.push(vec![0]);
-							}
-							bumped_tx.input[i].witness.push(witness_script.clone().into_bytes());
+							self.key_storage.sign_remote_htlc_transaction(&mut bumped_tx, i, &witness_script, *amount, &per_commitment_point, preimage, &self.secp_ctx);
 							log_trace!(self, "Going to broadcast Claim Transaction {} claiming remote {} htlc output {} from {} with new feerate {}...", bumped_tx.txid(), if preimage.is_some() { "offered" } else { "received" }, outp.vout, outp.txid, new_feerate);
 						}
 					},

lightning/src/util/enforcing_trait_impls.rs

@@ -93,6 +93,10 @@ impl ChannelKeys for EnforcingChannelKeys {
 		self.inner.sign_justice_transaction(bumped_tx, input, witness_script, amount, per_commitment_key, revocation_pubkey, is_htlc, secp_ctx);
 	}
 
+	fn sign_remote_htlc_transaction<T: secp256k1::Signing>(&self, bumped_tx: &mut Transaction, input: usize, witness_script: &Script, amount: u64, per_commitment_point: &PublicKey, preimage: &Option<PaymentPreimage>, secp_ctx: &Secp256k1<T>) {
+		self.inner.sign_remote_htlc_transaction(bumped_tx, input, witness_script, amount, per_commitment_point, preimage, secp_ctx);
+	}
+
 	fn sign_closing_transaction<T: secp256k1::Signing>(&self, closing_tx: &Transaction, secp_ctx: &Secp256k1<T>) -> Result<Signature, ()> {
 		Ok(self.inner.sign_closing_transaction(closing_tx, secp_ctx).unwrap())
 	}