Add high-level helpers for taproot channels

We add a new specific commitment format for taproot channels, and high-level methods for creating and spending taproot channel transactions.

Author: sstone

eclair-core/src/main/scala/fr/acinq/eclair/NodeParams.scala

@@ -134,7 +134,7 @@ case class NodeParams(nodeKeyManager: NodeKeyManager,
       min = (commitmentFeerate * feerateTolerance.ratioLow).max(minimumFeerate),
       max = (commitmentFormat match {
         case Transactions.DefaultCommitmentFormat => commitmentFeerate * feerateTolerance.ratioHigh
-        case _: Transactions.AnchorOutputsCommitmentFormat => (commitmentFeerate * feerateTolerance.ratioHigh).max(feerateTolerance.anchorOutputMaxCommitFeerate)
+        case _: Transactions.AnchorOutputsCommitmentFormat | Transactions.SimpleTaprootChannelCommitmentFormat => (commitmentFeerate * feerateTolerance.ratioHigh).max(feerateTolerance.anchorOutputMaxCommitFeerate)
       }).max(minimumFeerate),
     )
     RecommendedFeerates(chainHash, fundingFeerate, commitmentFeerate, TlvStream(fundingRange, commitmentRange))

eclair-core/src/main/scala/fr/acinq/eclair/SpendFromChannelAddress.scala

@@ -43,7 +43,7 @@ trait SpendFromChannelAddress {
       inputTx <- appKit.wallet.getTransaction(outPoint.txid)
       localFundingPubkey = appKit.nodeParams.channelKeyManager.fundingPublicKey(fundingKeyPath, fundingTxIndex)
       fundingRedeemScript = multiSig2of2(localFundingPubkey.publicKey, remoteFundingPubkey)
-      inputInfo = InputInfo(outPoint, inputTx.txOut(outPoint.index.toInt), fundingRedeemScript)
+      inputInfo = InputInfo.SegwitInput(outPoint, inputTx.txOut(outPoint.index.toInt), fundingRedeemScript)
       localSig = appKit.nodeParams.channelKeyManager.sign(
         Transactions.SpliceTx(inputInfo, unsignedTx), // classify as splice, doesn't really matter
         localFundingPubkey,

eclair-core/src/main/scala/fr/acinq/eclair/blockchain/fee/OnChainFeeConf.scala

@@ -20,7 +20,7 @@ import fr.acinq.bitcoin.scalacompat.Crypto.PublicKey
 import fr.acinq.bitcoin.scalacompat.Satoshi
 import fr.acinq.eclair.BlockHeight
 import fr.acinq.eclair.transactions.Transactions
-import fr.acinq.eclair.transactions.Transactions.{CommitmentFormat, UnsafeLegacyAnchorOutputsCommitmentFormat, ZeroFeeHtlcTxAnchorOutputsCommitmentFormat}
+import fr.acinq.eclair.transactions.Transactions.{CommitmentFormat, SimpleTaprootChannelCommitmentFormat, UnsafeLegacyAnchorOutputsCommitmentFormat, ZeroFeeHtlcTxAnchorOutputsCommitmentFormat}
 
 // @formatter:off
 sealed trait ConfirmationPriority extends Ordered[ConfirmationPriority] {
@@ -77,15 +77,15 @@ case class FeerateTolerance(ratioLow: Double, ratioHigh: Double, anchorOutputMax
   def isProposedFeerateTooHigh(commitmentFormat: CommitmentFormat, networkFeerate: FeeratePerKw, proposedFeerate: FeeratePerKw): Boolean = {
     commitmentFormat match {
       case Transactions.DefaultCommitmentFormat => networkFeerate * ratioHigh < proposedFeerate
-      case ZeroFeeHtlcTxAnchorOutputsCommitmentFormat | UnsafeLegacyAnchorOutputsCommitmentFormat => networkFeerate * ratioHigh < proposedFeerate
+      case ZeroFeeHtlcTxAnchorOutputsCommitmentFormat | UnsafeLegacyAnchorOutputsCommitmentFormat | SimpleTaprootChannelCommitmentFormat => networkFeerate * ratioHigh < proposedFeerate
     }
   }
 
   def isProposedFeerateTooLow(commitmentFormat: CommitmentFormat, networkFeerate: FeeratePerKw, proposedFeerate: FeeratePerKw): Boolean = {
     commitmentFormat match {
       case Transactions.DefaultCommitmentFormat => proposedFeerate < networkFeerate * ratioLow
       // When using anchor outputs, we allow low feerates: fees will be set with CPFP and RBF at broadcast time.
-      case ZeroFeeHtlcTxAnchorOutputsCommitmentFormat | UnsafeLegacyAnchorOutputsCommitmentFormat => false
+      case ZeroFeeHtlcTxAnchorOutputsCommitmentFormat | UnsafeLegacyAnchorOutputsCommitmentFormat | SimpleTaprootChannelCommitmentFormat => false
     }
   }
 }
@@ -121,7 +121,7 @@ case class OnChainFeeConf(feeTargets: FeeTargets,
 
     commitmentFormat match {
       case Transactions.DefaultCommitmentFormat => networkFeerate
-      case _: Transactions.AnchorOutputsCommitmentFormat =>
+      case _: Transactions.AnchorOutputsCommitmentFormat | Transactions.SimpleTaprootChannelCommitmentFormat =>
         val targetFeerate = networkFeerate.min(feerateToleranceFor(remoteNodeId).anchorOutputMaxCommitFeerate)
         // We make sure the feerate is always greater than the propagation threshold.
         targetFeerate.max(networkMinFee * 1.25)

eclair-core/src/main/scala/fr/acinq/eclair/channel/Helpers.scala

@@ -33,6 +33,7 @@ import fr.acinq.eclair.payment.relay.Relayer.RelayFees
 import fr.acinq.eclair.router.Announcements
 import fr.acinq.eclair.transactions.DirectedHtlc._
 import fr.acinq.eclair.transactions.Scripts._
+import fr.acinq.eclair.transactions.Transactions.InputInfo.RedeemPath
 import fr.acinq.eclair.transactions.Transactions._
 import fr.acinq.eclair.transactions._
 import fr.acinq.eclair.wire.protocol._
@@ -275,7 +276,7 @@ object Helpers {
 
     for {
       script_opt <- extractShutdownScript(accept.temporaryChannelId, localFeatures, remoteFeatures, accept.upfrontShutdownScript_opt)
-      fundingScript = Funding.makeFundingPubKeyScript(open.fundingPubkey, accept.fundingPubkey)
+      fundingScript = Funding.makeFundingPubKeyScript(open.fundingPubkey, accept.fundingPubkey, channelType.commitmentFormat)
       liquidityPurchase_opt <- LiquidityAds.validateRemoteFunding(open.requestFunding_opt, remoteNodeId, accept.temporaryChannelId, fundingScript, accept.fundingAmount, open.fundingFeerate, isChannelCreation = true, accept.willFund_opt)
     } yield {
       val channelFeatures = ChannelFeatures(channelType, localFeatures, remoteFeatures, open.channelFlags.announceChannel)
@@ -372,13 +373,20 @@ object Helpers {
   }
 
   object Funding {
+    def makeFundingPubKeyScript(localFundingKey: PublicKey, remoteFundingKey: PublicKey, commitmentFormat: CommitmentFormat): ByteVector = commitmentFormat match {
+      case DefaultCommitmentFormat | _: AnchorOutputsCommitmentFormat => write(pay2wsh(multiSig2of2(localFundingKey, remoteFundingKey)))
+      case SimpleTaprootChannelCommitmentFormat => write(Taproot.musig2FundingScript(localFundingKey, remoteFundingKey))
+    }
 
-    def makeFundingPubKeyScript(localFundingKey: PublicKey, remoteFundingKey: PublicKey): ByteVector = write(pay2wsh(multiSig2of2(localFundingKey, remoteFundingKey)))
-
-    def makeFundingInputInfo(fundingTxId: TxId, fundingTxOutputIndex: Int, fundingSatoshis: Satoshi, fundingPubkey1: PublicKey, fundingPubkey2: PublicKey): InputInfo.SegwitInput = {
-      val fundingScript = multiSig2of2(fundingPubkey1, fundingPubkey2)
-      val fundingTxOut = TxOut(fundingSatoshis, pay2wsh(fundingScript))
-      InputInfo.SegwitInput(OutPoint(fundingTxId, fundingTxOutputIndex), fundingTxOut, write(fundingScript))
+    def makeFundingInputInfo(fundingTxId: TxId, fundingTxOutputIndex: Int, fundingSatoshis: Satoshi, fundingPubkey1: PublicKey, fundingPubkey2: PublicKey, commitmentFormat: CommitmentFormat): InputInfo = commitmentFormat match {
+      case SimpleTaprootChannelCommitmentFormat =>
+        val fundingScript = Taproot.musig2FundingScript(fundingPubkey1, fundingPubkey2)
+        val fundingTxOut = TxOut(fundingSatoshis, fundingScript)
+        InputInfo.TaprootInput(OutPoint(fundingTxId, fundingTxOutputIndex), fundingTxOut, Taproot.musig2Aggregate(fundingPubkey1, fundingPubkey2), RedeemPath.KeyPath(None))
+      case DefaultCommitmentFormat | _: AnchorOutputsCommitmentFormat =>
+        val fundingScript = multiSig2of2(fundingPubkey1, fundingPubkey2)
+        val fundingTxOut = TxOut(fundingSatoshis, pay2wsh(fundingScript))
+        InputInfo.SegwitInput(OutPoint(fundingTxId, fundingTxOutputIndex), fundingTxOut, write(fundingScript))
     }
 
     /**
@@ -441,7 +449,7 @@ object Helpers {
 
       val fundingPubKey = keyManager.fundingPublicKey(localParams.fundingKeyPath, fundingTxIndex)
       val channelKeyPath = keyManager.keyPath(localParams, channelConfig)
-      val commitmentInput = makeFundingInputInfo(fundingTxId, fundingTxOutputIndex, fundingAmount, fundingPubKey.publicKey, remoteFundingPubKey)
+      val commitmentInput = makeFundingInputInfo(fundingTxId, fundingTxOutputIndex, fundingAmount, fundingPubKey.publicKey, remoteFundingPubKey, params.commitmentFormat)
       val localPerCommitmentPoint = keyManager.commitmentPoint(channelKeyPath, localCommitmentIndex)
       val (localCommitTx, _) = Commitment.makeLocalTxs(keyManager, channelConfig, channelFeatures, localCommitmentIndex, localParams, remoteParams, fundingTxIndex, remoteFundingPubKey, commitmentInput, localPerCommitmentPoint, localSpec)
       val (remoteCommitTx, htlcTxs) = Commitment.makeRemoteTxs(keyManager, channelConfig, channelFeatures, remoteCommitmentIndex, localParams, remoteParams, fundingTxIndex, remoteFundingPubKey, commitmentInput, remotePerCommitmentPoint, remoteSpec)
@@ -679,7 +687,7 @@ object Helpers {
           case DefaultCommitmentFormat =>
             // we "MUST set fee_satoshis less than or equal to the base fee of the final commitment transaction"
             requestedFeerate.min(commitment.localCommit.spec.commitTxFeerate)
-          case _: AnchorOutputsCommitmentFormat => requestedFeerate
+          case _: AnchorOutputsCommitmentFormat | SimpleTaprootChannelCommitmentFormat => requestedFeerate
         }
         // NB: we choose a minimum fee that ensures the tx will easily propagate while allowing low fees since we can
         // always use CPFP to speed up confirmation if necessary.
@@ -909,13 +917,25 @@ object Helpers {
 
       def claimAnchors(keyManager: ChannelKeyManager, commitment: FullCommitment, lcp: LocalCommitPublished, confirmationTarget: ConfirmationTarget)(implicit log: LoggingAdapter): LocalCommitPublished = {
         if (shouldUpdateAnchorTxs(lcp.claimAnchorTxs, confirmationTarget)) {
-          val localFundingPubKey = keyManager.fundingPublicKey(commitment.localParams.fundingKeyPath, commitment.fundingTxIndex).publicKey
+          val (localAnchorKey, remoteAnchorKey) = commitment.params.commitmentFormat match {
+            case DefaultCommitmentFormat | _: AnchorOutputsCommitmentFormat =>
+              // The public keys used in this case are the channel funding public keys.
+              val localFundingPubkey = keyManager.fundingPublicKey(commitment.localParams.fundingKeyPath, commitment.fundingTxIndex).publicKey
+              (localFundingPubkey, commitment.remoteFundingPubKey)
+            case SimpleTaprootChannelCommitmentFormat =>
+              // The public keys used in this case are the payment public keys: we don't want to reveal individual
+              // funding public keys since we're using musig2.
+              val channelKeyPath = keyManager.keyPath(commitment.localParams, commitment.params.channelConfig)
+              val localPerCommitmentPoint = keyManager.commitmentPoint(channelKeyPath, commitment.localCommit.index)
+              val localDelayedPaymentPubkey = Generators.derivePubKey(keyManager.delayedPaymentPoint(channelKeyPath).publicKey, localPerCommitmentPoint)
+              (localDelayedPaymentPubkey, commitment.remoteParams.paymentBasepoint)
+          }
           val claimAnchorTxs = List(
             withTxGenerationLog("local-anchor") {
-              Transactions.makeClaimLocalAnchorOutputTx(lcp.commitTx, localFundingPubKey, confirmationTarget)
+              Transactions.makeClaimLocalAnchorOutputTx(lcp.commitTx, localAnchorKey, confirmationTarget)
             },
             withTxGenerationLog("remote-anchor") {
-              Transactions.makeClaimRemoteAnchorOutputTx(lcp.commitTx, commitment.remoteFundingPubKey)
+              Transactions.makeClaimRemoteAnchorOutputTx(lcp.commitTx, remoteAnchorKey)
             }
           ).flatten
           lcp.copy(claimAnchorTxs = claimAnchorTxs)
@@ -1038,13 +1058,23 @@ object Helpers {
 
       def claimAnchors(keyManager: ChannelKeyManager, commitment: FullCommitment, rcp: RemoteCommitPublished, confirmationTarget: ConfirmationTarget)(implicit log: LoggingAdapter): RemoteCommitPublished = {
         if (shouldUpdateAnchorTxs(rcp.claimAnchorTxs, confirmationTarget)) {
-          val localFundingPubkey = keyManager.fundingPublicKey(commitment.localParams.fundingKeyPath, commitment.fundingTxIndex).publicKey
+          val (localAnchorKey, remoteAnchorKey) = commitment.params.commitmentFormat match {
+            case DefaultCommitmentFormat | _: AnchorOutputsCommitmentFormat =>
+              // The public keys used in this case are the channel funding public keys.
+              val localFundingPubkey = keyManager.fundingPublicKey(commitment.localParams.fundingKeyPath, commitment.fundingTxIndex).publicKey
+              (localFundingPubkey, commitment.remoteFundingPubKey)
+            case SimpleTaprootChannelCommitmentFormat =>
+              val channelKeyPath = keyManager.keyPath(commitment.localParams, commitment.params.channelConfig)
+              val localPaymentPubkey = commitment.localParams.walletStaticPaymentBasepoint.getOrElse(keyManager.paymentPoint(channelKeyPath).publicKey)
+              val remoteDelayedPaymentPubkey = Generators.derivePubKey(commitment.remoteParams.delayedPaymentBasepoint, commitment.remoteCommit.remotePerCommitmentPoint)
+              (localPaymentPubkey, remoteDelayedPaymentPubkey)
+          }
           val claimAnchorTxs = List(
             withTxGenerationLog("local-anchor") {
-              Transactions.makeClaimLocalAnchorOutputTx(rcp.commitTx, localFundingPubkey, confirmationTarget)
+              Transactions.makeClaimLocalAnchorOutputTx(rcp.commitTx, localAnchorKey, confirmationTarget)
             },
             withTxGenerationLog("remote-anchor") {
-              Transactions.makeClaimRemoteAnchorOutputTx(rcp.commitTx, commitment.remoteFundingPubKey)
+              Transactions.makeClaimRemoteAnchorOutputTx(rcp.commitTx, remoteAnchorKey)
             }
           ).flatten
           rcp.copy(claimAnchorTxs = claimAnchorTxs)
@@ -1077,7 +1107,7 @@ object Helpers {
                 Transactions.addSigs(claimMain, localPubkey, sig)
               })
             }
-            case _: AnchorOutputsCommitmentFormat => withTxGenerationLog("remote-main-delayed") {
+            case _: AnchorOutputsCommitmentFormat | SimpleTaprootChannelCommitmentFormat => withTxGenerationLog("remote-main-delayed") {
               Transactions.makeClaimRemoteDelayedOutputTx(tx, params.localParams.dustLimit, localPaymentPoint, finalScriptPubKey, feeratePerKwMain).map(claimMain => {
                 val sig = keyManager.sign(claimMain, keyManager.paymentPoint(channelKeyPath), TxOwner.Local, params.commitmentFormat, Map.empty)
                 Transactions.addSigs(claimMain, sig)
@@ -1224,7 +1254,7 @@ object Helpers {
                 Transactions.addSigs(claimMain, localPaymentPubkey, sig)
               })
             }
-            case _: AnchorOutputsCommitmentFormat => withTxGenerationLog("remote-main-delayed") {
+            case _: AnchorOutputsCommitmentFormat | SimpleTaprootChannelCommitmentFormat => withTxGenerationLog("remote-main-delayed") {
               Transactions.makeClaimRemoteDelayedOutputTx(commitTx, localParams.dustLimit, localPaymentPoint, finalScriptPubKey, feerateMain).map(claimMain => {
                 val sig = keyManager.sign(claimMain, keyManager.paymentPoint(channelKeyPath), TxOwner.Local, commitmentFormat, Map.empty)
                 Transactions.addSigs(claimMain, sig)