Build witness_script for remote htlc transactions inside

OnchainTxHandler

By moving script generation inside OnchainTxHandler, we may dry-up
further ChannelMonitor in next commits

Author: Antoine Riard

lightning/src/ln/channelmonitor.rs

@@ -430,7 +430,7 @@ pub(crate) enum InputMaterial {
 		amount: u64,
 	},
 	RemoteHTLC {
-		witness_script: Script,
+		per_commitment_point: PublicKey,
 		key: SecretKey,
 		preimage: Option<PaymentPreimage>,
 		amount: u64,
@@ -455,9 +455,9 @@ impl Writeable for InputMaterial  {
 				input_descriptor.write(writer)?;
 				writer.write_all(&byte_utils::be64_to_array(*amount))?;
 			},
-			&InputMaterial::RemoteHTLC { ref witness_script, ref key, ref preimage, ref amount, ref locktime } => {
+			&InputMaterial::RemoteHTLC { ref per_commitment_point, ref key, ref preimage, ref amount, ref locktime } => {
 				writer.write_all(&[1; 1])?;
-				witness_script.write(writer)?;
+				per_commitment_point.write(writer)?;
 				key.write(writer)?;
 				preimage.write(writer)?;
 				writer.write_all(&byte_utils::be64_to_array(*amount))?;
@@ -493,13 +493,13 @@ impl Readable for InputMaterial {
 				}
 			},
 			1 => {
-				let witness_script = Readable::read(reader)?;
+				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 {
-					witness_script,
+					per_commitment_point,
 					key,
 					preimage,
 					amount,
@@ -1592,13 +1592,7 @@ 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 revocation_pubkey = ignore_error!(chan_utils::derive_public_revocation_key(&self.secp_ctx, revocation_point, &self.onchain_detection.keys.pubkeys().revocation_basepoint));
-					let b_htlc_key = ignore_error!(chan_utils::derive_public_key(&self.secp_ctx, revocation_point, &self.onchain_detection.keys.pubkeys().htlc_basepoint));
 					let htlc_privkey = ignore_error!(chan_utils::derive_private_key(&self.secp_ctx, revocation_point, &self.onchain_detection.keys.htlc_base_key()));
-					let a_htlc_key = match self.their_htlc_base_key {
-						None => return (claimable_outpoints, (commitment_txid, watch_outputs)),
-						Some(their_htlc_base_key) => ignore_error!(chan_utils::derive_public_key(&self.secp_ctx, revocation_point, &their_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 = {
@@ -1611,16 +1605,14 @@ impl<ChanSigner: ChannelKeys> ChannelMonitor<ChanSigner> {
 					// Then, try to find htlc outputs
 					for (_, &(ref htlc, _)) in per_commitment_data.iter().enumerate() {
 						if let Some(transaction_output_index) = htlc.transaction_output_index {
-							let expected_script = chan_utils::get_htlc_redeemscript_with_explicit_keys(&htlc, &a_htlc_key, &b_htlc_key, &revocation_pubkey);
 							if transaction_output_index as usize >= tx.output.len() ||
-									tx.output[transaction_output_index as usize].value != htlc.amount_msat / 1000 ||
-									tx.output[transaction_output_index as usize].script_pubkey != expected_script.to_v0_p2wsh() {
+									tx.output[transaction_output_index as usize].value != htlc.amount_msat / 1000 {
 								return (claimable_outpoints, (commitment_txid, watch_outputs)); // Corrupted per_commitment_data, fuck this user
 							}
 							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 { witness_script: expected_script, key: htlc_privkey, preimage, amount: htlc.amount_msat / 1000, locktime: htlc.cltv_expiry };
+								let witness_data = InputMaterial::RemoteHTLC { per_commitment_point: *revocation_point, key: htlc_privkey, 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

@@ -693,20 +693,33 @@ 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 witness_script, ref key, ref preimage, ref amount, ref locktime } => {
-						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]);
+					&InputMaterial::RemoteHTLC { ref per_commitment_point, ref key, 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) {
+								for htlc in htlcs {
+									if htlc.transaction_output_index.unwrap() == outp.vout {
+										this_htlc = Some(htlc);
+									}
+								}
+							}
+							if this_htlc.is_none() { return None; }
+							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());
+							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);
 						}
-						bumped_tx.input[i].witness.push(witness_script.clone().into_bytes());
-						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);
 					},
 					_ => unreachable!()
 				}