Use ChannelPublicKeys in create_spendable_outputs_psbt to derive the basepoint and the key tweak.

Implement StaticPaymentOutput to PSBT input conversion.

Author: yellowred

lightning/src/chain/channelmonitor.rs

@@ -4255,7 +4255,6 @@ impl<Signer: WriteableEcdsaChannelSigner> ChannelMonitorImpl<Signer> {
 						revocation_pubkey: broadcasted_holder_revokable_script.2,
 						channel_keys_id: self.channel_keys_id,
 						channel_value_satoshis: self.channel_value_satoshis,
-						delayed_payment_basepoint: Some(self.onchain_tx_handler.signer.pubkeys().delayed_payment_basepoint),
 					}));
 				}
 			}

lightning/src/ln/channel_keys.rs

@@ -37,6 +37,19 @@ macro_rules! basepoint_impl {
             pub fn to_public_key(&self) -> PublicKey {
                 self.0
             }
+
+            /// Derives a per-commitment-transaction (eg an htlc key or delayed_payment key) private key addition tweak
+            /// from a basepoint and a per_commitment_point:
+            /// `privkey = basepoint_secret + SHA256(per_commitment_point || basepoint)`
+            pub fn derive_add_tweak(
+                &self,
+                per_commitment_point: &PublicKey,
+            ) -> [u8; 32] {
+                let mut sha = Sha256::engine();
+                sha.input(&per_commitment_point.serialize());
+                sha.input(&self.to_public_key().serialize());
+                Sha256::from_engine(sha).to_byte_array()
+            }
         }
 
         impl From<PublicKey> for $BasepointT {
@@ -226,22 +239,6 @@ impl RevocationKey {
 key_read_write!(RevocationKey);
 
 
-/// Derives a per-commitment-transaction (eg an htlc key or delayed_payment key) private key addition tweak
-/// from a delayed payment basepoint and a per_commitment_point:
-/// `privkey = basepoint_secret + SHA256(per_commitment_point || basepoint)`
-/// TODO(oleg): refactor after migration to LDK v119
-pub fn derive_add_tweak(
-    per_commitment_point: &PublicKey,
-    basepoint: &DelayedPaymentBasepoint,
-) -> Vec<u8> {
-    let mut sha = Sha256::engine();
-    sha.input(&per_commitment_point.serialize());
-    sha.input(&basepoint.to_public_key().serialize());
-    let res = Sha256::from_engine(sha).to_byte_array();
-    res.to_vec()
-}
-
-
 #[cfg(test)]
 mod test {
     use bitcoin::secp256k1::{Secp256k1, SecretKey, PublicKey};

lightning/src/sign/mod.rs

@@ -37,14 +37,14 @@ use bitcoin::secp256k1::ecdsa::{RecoverableSignature, Signature};
 use bitcoin::secp256k1::schnorr;
 use bitcoin::{secp256k1, Sequence, Witness, Txid};
 
+use crate::ln::channel::ANCHOR_OUTPUT_VALUE_SATOSHI;
 use crate::util::transaction_utils;
 use crate::util::crypto::{hkdf_extract_expand_twice, sign, sign_with_aux_rand};
 use crate::util::ser::{Writeable, Writer, Readable, ReadableArgs};
 use crate::chain::transaction::OutPoint;
-use crate::ln::channel::ANCHOR_OUTPUT_VALUE_SATOSHI;
 use crate::ln::{chan_utils, PaymentPreimage};
 use crate::ln::chan_utils::{HTLCOutputInCommitment, make_funding_redeemscript, ChannelPublicKeys, HolderCommitmentTransaction, ChannelTransactionParameters, CommitmentTransaction, ClosingTransaction, get_revokeable_redeemscript};
-use crate::ln::channel_keys::{DelayedPaymentBasepoint, DelayedPaymentKey, HtlcKey, HtlcBasepoint, RevocationKey, RevocationBasepoint, derive_add_tweak};
+use crate::ln::channel_keys::{DelayedPaymentBasepoint, DelayedPaymentKey, HtlcKey, HtlcBasepoint, RevocationKey, RevocationBasepoint, PaymentBasepoint};
 use crate::ln::msgs::{UnsignedChannelAnnouncement, UnsignedGossipMessage};
 #[cfg(taproot)]
 use crate::ln::msgs::PartialSignatureWithNonce;
@@ -103,8 +103,6 @@ pub struct DelayedPaymentOutputDescriptor {
 	pub channel_keys_id: [u8; 32],
 	/// The value of the channel which this output originated from, possibly indirectly.
 	pub channel_value_satoshis: u64,
-	/// Channel base key used to generate a witness data to spend this output.
-	pub delayed_payment_basepoint: Option<DelayedPaymentBasepoint>
 }
 
 impl DelayedPaymentOutputDescriptor {
@@ -124,7 +122,6 @@ impl_writeable_tlv_based!(DelayedPaymentOutputDescriptor, {
 	(8, revocation_pubkey, required),
 	(10, channel_keys_id, required),
 	(12, channel_value_satoshis, required),
-	(14, delayed_payment_basepoint, option),
 });
 
 pub(crate) const P2WPKH_WITNESS_WEIGHT: u64 = 1 /* num stack items */ +
@@ -309,7 +306,7 @@ impl SpendableOutputDescriptor {
 	///
 	/// This is not exported to bindings users as there is no standard serialization for an input.
 	/// See [`Self::create_spendable_outputs_psbt`] instead.
-	pub fn to_psbt_input<T: secp256k1::Signing>(&self, secp_ctx: &Secp256k1<T>) -> bitcoin::psbt::Input {
+	pub fn to_psbt_input<T: secp256k1::Signing>(&self, secp_ctx: &Secp256k1<T>, channel_public_keys: Option<&ChannelPublicKeys>) -> bitcoin::psbt::Input {
 		match self {
 			SpendableOutputDescriptor::StaticOutput { output, .. } => {
 				// Is a standard P2WPKH, no need for witness script
@@ -319,14 +316,18 @@ impl SpendableOutputDescriptor {
 				}
 			},
 			SpendableOutputDescriptor::DelayedPaymentOutput(descriptor) => {
-				let (witness_script, add_tweak) = if let Some(basepoint) = descriptor.delayed_payment_basepoint.as_ref() {
+				let delayed_payment_basepoint = channel_public_keys.map(|keys| DelayedPaymentBasepoint::from(
+					keys.delayed_payment_basepoint,
+				));
+
+				let (witness_script, add_tweak) = if let Some(basepoint) = delayed_payment_basepoint.as_ref() {
 						let payment_key = DelayedPaymentKey::from_basepoint(
 							secp_ctx,
 							basepoint,
 							&descriptor.per_commitment_point,
 						);
 						// Required to derive signing key: privkey = basepoint_secret + SHA256(per_commitment_point || basepoint)
-						let add_tweak = derive_add_tweak(&descriptor.per_commitment_point, basepoint);
+						let add_tweak = basepoint.derive_add_tweak(&descriptor.per_commitment_point);
 						(Some(get_revokeable_redeemscript(
 							&descriptor.revocation_pubkey,
 							descriptor.to_self_delay,
@@ -336,7 +337,6 @@ impl SpendableOutputDescriptor {
 				   (None, None)
 				};
 
-				
 				bitcoin::psbt::Input {
 					witness_utxo: Some(descriptor.output.clone()),
 					witness_script,
@@ -346,15 +346,43 @@ impl SpendableOutputDescriptor {
 							subtype: 0,
 							key: "add_tweak".as_bytes().to_vec(),
 						},
-						add_tweak,
+						add_tweak.to_vec(),
 					)].into_iter().collect()}).unwrap_or_default(),
 					..Default::default()
 				}
 			},
 			SpendableOutputDescriptor::StaticPaymentOutput(descriptor) => {
-				// TODO we could add the witness script as well
+				// Use simplified derivation, assuming `option_static_remotekey` or `option_anchors` is negotiated.
+				// `remote_payment_basepoint` is used to produce add tweak which is needed in order to produce the signing key.
+				let remote_payment_basepoint = channel_public_keys.map(|keys| 
+					PaymentBasepoint::from(keys.payment_point)
+				);
+
+				let witness_script = match remote_payment_basepoint {
+					Some(ref basepoint) => {
+						// We cannot always assume that `channel_parameters` is set, so can't just call
+						// `self.channel_parameters()` or anything that relies on it
+						let supports_anchors_zero_fee_htlc_tx = descriptor.channel_transaction_parameters.as_ref()
+						.map(|features| features.channel_type_features.supports_anchors_zero_fee_htlc_tx())
+						.unwrap_or(false);
+
+						let witness_script = if supports_anchors_zero_fee_htlc_tx {
+							chan_utils::get_to_countersignatory_with_anchors_redeemscript(&basepoint.to_public_key())
+						} else {
+							ScriptBuf::new_p2pkh(&bitcoin::PublicKey::new(basepoint.to_public_key()).pubkey_hash())
+						};
+
+						// With simplified derivation, the private payment key is equal to private payment basepoint, 
+						// so add tweak is not needed.
+						Some(witness_script)
+					},
+					_ => None,
+    			};
+				
+				
 				bitcoin::psbt::Input {
 					witness_utxo: Some(descriptor.output.clone()),
+					witness_script,
 					..Default::default()
 				}
 			},
@@ -378,7 +406,7 @@ impl SpendableOutputDescriptor {
 	/// does not match the one we can spend.
 	///
 	/// We do not enforce that outputs meet the dust limit or that any output scripts are standard.
-	pub fn create_spendable_outputs_psbt(descriptors: &[&SpendableOutputDescriptor], outputs: Vec<TxOut>, change_destination_script: ScriptBuf, feerate_sat_per_1000_weight: u32, locktime: Option<LockTime>) -> Result<(PartiallySignedTransaction, u64), ()> {
+	pub fn create_spendable_outputs_psbt(descriptors: &[&SpendableOutputDescriptor], outputs: Vec<TxOut>, change_destination_script: ScriptBuf, feerate_sat_per_1000_weight: u32, locktime: Option<LockTime>, channel_public_keys: Option<&ChannelPublicKeys>) -> Result<(PartiallySignedTransaction, u64), ()> {
 		let secp_ctx = Secp256k1::new();
 		let mut input = Vec::with_capacity(descriptors.len());
 		let mut input_value = 0;
@@ -446,7 +474,7 @@ impl SpendableOutputDescriptor {
 		let expected_max_weight =
 			transaction_utils::maybe_add_change_output(&mut tx, input_value, witness_weight, feerate_sat_per_1000_weight, change_destination_script)?;
 
-		let psbt_inputs = descriptors.iter().map(|d| d.to_psbt_input(&secp_ctx)).collect::<Vec<_>>();
+		let psbt_inputs = descriptors.iter().map(|d| d.to_psbt_input(&secp_ctx, channel_public_keys)).collect::<Vec<_>>();
 		let psbt = PartiallySignedTransaction {
 			inputs: psbt_inputs,
 			outputs: vec![Default::default(); tx.output.len()],
@@ -1649,7 +1677,8 @@ impl KeysManager {
 	/// May panic if the [`SpendableOutputDescriptor`]s were not generated by channels which used
 	/// this [`KeysManager`] or one of the [`InMemorySigner`] created by this [`KeysManager`].
 	pub fn spend_spendable_outputs<C: Signing>(&self, descriptors: &[&SpendableOutputDescriptor], outputs: Vec<TxOut>, change_destination_script: ScriptBuf, feerate_sat_per_1000_weight: u32, locktime: Option<LockTime>, secp_ctx: &Secp256k1<C>) -> Result<Transaction, ()> {
-		let (mut psbt, expected_max_weight) = SpendableOutputDescriptor::create_spendable_outputs_psbt(descriptors, outputs, change_destination_script, feerate_sat_per_1000_weight, locktime)?;
+		// TODO: provide channel keys to construct witness script
+		let (mut psbt, expected_max_weight) = SpendableOutputDescriptor::create_spendable_outputs_psbt(descriptors, outputs, change_destination_script, feerate_sat_per_1000_weight, locktime, None)?;
 		psbt = self.sign_spendable_outputs_psbt(descriptors, psbt, secp_ctx)?;
 
 		let spend_tx = psbt.extract_tx();