Support signing to_remote anchors variant for StaticPaymentOutput
authorWilmer Paulino <wilmer@wilmerpaulino.com>
Mon, 25 Sep 2023 23:55:22 +0000 (16:55 -0700)
committerWilmer Paulino <wilmer@wilmerpaulino.com>
Fri, 29 Sep 2023 20:46:59 +0000 (13:46 -0700)
`to_remote` outputs on commitment transactions with anchor outputs have
an additional `1 CSV` constraint on its spending condition,
transitioning away from the previous P2WPKH script to a P2WSH.

Since our `ChannelMonitor` was never updated to track the proper
`to_remote` script on anchor outputs channels, we also missed updating
our signer to handle the new script changes.

lightning/src/chain/channelmonitor.rs
lightning/src/ln/chan_utils.rs
lightning/src/sign/mod.rs

index b535e4b6cad34edbad3121e77f84d0976c3da0ee..95f68ba22f6de4bd870dd04e43da32e1bac5582e 100644 (file)
@@ -4043,6 +4043,7 @@ impl<Signer: WriteableEcdsaChannelSigner> ChannelMonitorImpl<Signer> {
                                        output: outp.clone(),
                                        channel_keys_id: self.channel_keys_id,
                                        channel_value_satoshis: self.channel_value_satoshis,
+                                       channel_transaction_parameters: Some(self.onchain_tx_handler.channel_transaction_parameters.clone()),
                                }));
                        }
                        if self.shutdown_script.as_ref() == Some(&outp.script_pubkey) {
index 6e683b2fb9ecd5654f389889ec336e4902817136..d1489e2716836f928d5bdc04450f3d8722d4fbc9 100644 (file)
@@ -475,7 +475,7 @@ impl_writeable_tlv_based!(TxCreationKeys, {
 });
 
 /// One counterparty's public keys which do not change over the life of a channel.
-#[derive(Clone, Debug, PartialEq, Eq)]
+#[derive(Clone, Debug, Hash, PartialEq, Eq)]
 pub struct ChannelPublicKeys {
        /// The public key which is used to sign all commitment transactions, as it appears in the
        /// on-chain channel lock-in 2-of-2 multisig output.
@@ -863,7 +863,7 @@ pub fn build_anchor_input_witness(funding_key: &PublicKey, funding_sig: &Signatu
 ///
 /// Normally, this is converted to the broadcaster/countersignatory-organized DirectedChannelTransactionParameters
 /// before use, via the as_holder_broadcastable and as_counterparty_broadcastable functions.
-#[derive(Clone, Debug, PartialEq, Eq)]
+#[derive(Clone, Debug, Hash, PartialEq, Eq)]
 pub struct ChannelTransactionParameters {
        /// Holder public keys
        pub holder_pubkeys: ChannelPublicKeys,
@@ -883,7 +883,7 @@ pub struct ChannelTransactionParameters {
 }
 
 /// Late-bound per-channel counterparty data used to build transactions.
-#[derive(Clone, Debug, PartialEq, Eq)]
+#[derive(Clone, Debug, Hash, PartialEq, Eq)]
 pub struct CounterpartyChannelTransactionParameters {
        /// Counter-party public keys
        pub pubkeys: ChannelPublicKeys,
index 5b42796a94f9586fe2dd42fd7210fada4be7297f..04652166f05978b6dd8bb1ab0a4b4c2ed9c37d5f 100644 (file)
@@ -121,20 +121,38 @@ pub struct StaticPaymentOutputDescriptor {
        pub channel_keys_id: [u8; 32],
        /// The value of the channel which this transactions spends.
        pub channel_value_satoshis: u64,
+       /// The necessary channel parameters that need to be provided to the re-derived signer through
+       /// [`ChannelSigner::provide_channel_parameters`].
+       ///
+       /// Added as optional, but always `Some` if the descriptor was produced in v0.0.117 or later.
+       pub channel_transaction_parameters: Option<ChannelTransactionParameters>,
 }
 impl StaticPaymentOutputDescriptor {
        /// The maximum length a well-formed witness spending one of these should have.
        /// Note: If you have the grind_signatures feature enabled, this will be at least 1 byte
        /// shorter.
-       // Calculated as 1 byte legnth + 73 byte signature, 1 byte empty vec push, 1 byte length plus
-       // redeemscript push length.
-       pub const MAX_WITNESS_LENGTH: usize = 1 + 73 + 34;
+       pub fn max_witness_length(&self) -> usize {
+               if self.channel_transaction_parameters.as_ref()
+                       .map(|channel_params| channel_params.channel_type_features.supports_anchors_zero_fee_htlc_tx())
+                       .unwrap_or(false)
+               {
+                       let witness_script_weight = 1 /* pubkey push */ + 33 /* pubkey */ +
+                               1 /* OP_CHECKSIGVERIFY */ + 1 /* OP_1 */ + 1 /* OP_CHECKSEQUENCEVERIFY */;
+                       1 /* num witness items */ + 1 /* sig push */ + 73 /* sig including sighash flag */ +
+                               1 /* witness script push */ + witness_script_weight
+               } else {
+                       // Calculated as 1 byte legnth + 73 byte signature, 1 byte empty vec push, 1 byte length plus
+                       // redeemscript push length.
+                       1 + 73 + 34
+               }
+       }
 }
 impl_writeable_tlv_based!(StaticPaymentOutputDescriptor, {
        (0, outpoint, required),
        (2, output, required),
        (4, channel_keys_id, required),
        (6, channel_value_satoshis, required),
+       (7, channel_transaction_parameters, option),
 });
 
 /// Describes the necessary information to spend a spendable output.
@@ -201,15 +219,23 @@ pub enum SpendableOutputDescriptor {
        /// [`DelayedPaymentOutputDescriptor::to_self_delay`] contained here to
        /// [`chan_utils::get_revokeable_redeemscript`].
        DelayedPaymentOutput(DelayedPaymentOutputDescriptor),
-       /// An output to a P2WPKH, spendable exclusively by our payment key (i.e., the private key
-       /// which corresponds to the `payment_point` in [`ChannelSigner::pubkeys`]). The witness
-       /// in the spending input is, thus, simply:
+       /// An output spendable exclusively by our payment key (i.e., the private key that corresponds
+       /// to the `payment_point` in [`ChannelSigner::pubkeys`]). The output type depends on the
+       /// channel type negotiated.
+       ///
+       /// On an anchor outputs channel, the witness in the spending input is:
+       /// ```bitcoin
+       /// <BIP 143 signature> <witness script>
+       /// ```
+       ///
+       /// Otherwise, it is:
        /// ```bitcoin
        /// <BIP 143 signature> <payment key>
        /// ```
        ///
        /// These are generally the result of our counterparty having broadcast the current state,
-       /// allowing us to claim the non-HTLC-encumbered outputs immediately.
+       /// allowing us to claim the non-HTLC-encumbered outputs immediately, or after one confirmation
+       /// in the case of anchor outputs channels.
        StaticPaymentOutput(StaticPaymentOutputDescriptor),
 }
 
@@ -280,13 +306,22 @@ impl SpendableOutputDescriptor {
                        match outp {
                                SpendableOutputDescriptor::StaticPaymentOutput(descriptor) => {
                                        if !output_set.insert(descriptor.outpoint) { return Err(()); }
+                                       let sequence =
+                                               if descriptor.channel_transaction_parameters.as_ref()
+                                                       .map(|channel_params| channel_params.channel_type_features.supports_anchors_zero_fee_htlc_tx())
+                                                       .unwrap_or(false)
+                                               {
+                                                       Sequence::from_consensus(1)
+                                               } else {
+                                                       Sequence::ZERO
+                                               };
                                        input.push(TxIn {
                                                previous_output: descriptor.outpoint.into_bitcoin_outpoint(),
                                                script_sig: Script::new(),
-                                               sequence: Sequence::ZERO,
+                                               sequence,
                                                witness: Witness::new(),
                                        });
-                                       witness_weight += StaticPaymentOutputDescriptor::MAX_WITNESS_LENGTH;
+                                       witness_weight += descriptor.max_witness_length();
                                        #[cfg(feature = "grind_signatures")]
                                        { witness_weight -= 1; } // Guarantees a low R signature
                                        input_value += descriptor.output.value;
@@ -891,18 +926,30 @@ impl InMemorySigner {
                if !spend_tx.input[input_idx].script_sig.is_empty() { return Err(()); }
                if spend_tx.input[input_idx].previous_output != descriptor.outpoint.into_bitcoin_outpoint() { return Err(()); }
 
-               let remotepubkey = self.pubkeys().payment_point;
-               let witness_script = bitcoin::Address::p2pkh(&::bitcoin::PublicKey{compressed: true, inner: remotepubkey}, Network::Testnet).script_pubkey();
+               let remotepubkey = bitcoin::PublicKey::new(self.pubkeys().payment_point);
+               let witness_script = if self.channel_type_features().supports_anchors_zero_fee_htlc_tx() {
+                       chan_utils::get_to_countersignatory_with_anchors_redeemscript(&remotepubkey.inner)
+               } else {
+                       Script::new_p2pkh(&remotepubkey.pubkey_hash())
+               };
                let sighash = hash_to_message!(&sighash::SighashCache::new(spend_tx).segwit_signature_hash(input_idx, &witness_script, descriptor.output.value, EcdsaSighashType::All).unwrap()[..]);
                let remotesig = sign_with_aux_rand(secp_ctx, &sighash, &self.payment_key, &self);
-               let payment_script = bitcoin::Address::p2wpkh(&::bitcoin::PublicKey{compressed: true, inner: remotepubkey}, Network::Bitcoin).unwrap().script_pubkey();
+               let payment_script = if self.channel_type_features().supports_anchors_zero_fee_htlc_tx() {
+                       witness_script.to_v0_p2wsh()
+               } else {
+                       Script::new_v0_p2wpkh(&remotepubkey.wpubkey_hash().unwrap())
+               };
 
                if payment_script != descriptor.output.script_pubkey { return Err(()); }
 
                let mut witness = Vec::with_capacity(2);
                witness.push(remotesig.serialize_der().to_vec());
                witness[0].push(EcdsaSighashType::All as u8);
-               witness.push(remotepubkey.serialize().to_vec());
+               if self.channel_type_features().supports_anchors_zero_fee_htlc_tx() {
+                       witness.push(witness_script.to_bytes());
+               } else {
+                       witness.push(remotepubkey.to_bytes());
+               }
                Ok(witness)
        }
 
@@ -1353,9 +1400,11 @@ impl KeysManager {
                                SpendableOutputDescriptor::StaticPaymentOutput(descriptor) => {
                                        let input_idx = psbt.unsigned_tx.input.iter().position(|i| i.previous_output == descriptor.outpoint.into_bitcoin_outpoint()).ok_or(())?;
                                        if keys_cache.is_none() || keys_cache.as_ref().unwrap().1 != descriptor.channel_keys_id {
-                                               keys_cache = Some((
-                                                       self.derive_channel_keys(descriptor.channel_value_satoshis, &descriptor.channel_keys_id),
-                                                       descriptor.channel_keys_id));
+                                               let mut signer = self.derive_channel_keys(descriptor.channel_value_satoshis, &descriptor.channel_keys_id);
+                                               if let Some(channel_params) = descriptor.channel_transaction_parameters.as_ref() {
+                                                       signer.provide_channel_parameters(channel_params);
+                                               }
+                                               keys_cache = Some((signer, descriptor.channel_keys_id));
                                        }
                                        let witness = Witness::from_vec(keys_cache.as_ref().unwrap().0.sign_counterparty_payment_input(&psbt.unsigned_tx, input_idx, &descriptor, &secp_ctx)?);
                                        psbt.inputs[input_idx].final_script_witness = Some(witness);