Update splicing protocol

The current "simple taproot channels" proposal is not compatible with splices.
Supporting splices means supporting multiple commitment transactions that are valid at the same time, with the same commitment index but with different funding transactions.
We need to extend the taproot proposal to include a list of musig2 nonces (one for each active commitment transaction).
Similar to how commitment points are handled, `firstRemoteNonce` and `secondRemoteNonce` fields have been added to `SpliceInit` and `SpliceAck`, encoded as a list of nonces (instead of 2 expicit nonces)
We also need a  for the new commit tx that is being built, here it has been added to `SpliceInit` and `SpliceAck`.

The funding tx that is being built during the interactive session needs to spend the current funding tx.
For this, we re-use the scheme that we developped for our custome "swaproot" musig swap-ins: we add musig2 nonces to the `TxComplete` message, one nonce for each input that requires one, ordered by serial id.
The life-cycle of these nonces is tied to the life-cycle of the interactive session which is never persisted (nonces here do not have to be deterministic).

Author: sstone

eclair-core/pom.xml

@@ -188,6 +188,21 @@
             <version>4.1.94.Final</version>
         </dependency>
         <!-- BITCOIN -->
+        <dependency>
+            <groupId>fr.acinq.bitcoin</groupId>
+            <artifactId>bitcoin-kmp-jvm</artifactId>
+            <version>0.20.0-SNAPSHOT</version>
+        </dependency>
+        <dependency>
+            <groupId>fr.acinq.secp256k1</groupId>
+            <artifactId>secp256k1-kmp-jvm</artifactId>
+            <version>0.15.0</version>
+        </dependency>
+        <dependency>
+            <groupId>fr.acinq.secp256k1</groupId>
+            <artifactId>secp256k1-kmp-jni-jvm</artifactId>
+            <version>0.15.0</version>
+        </dependency>
         <dependency>
             <groupId>fr.acinq</groupId>
             <artifactId>bitcoin-lib_${scala.version.short}</artifactId>

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

@@ -121,7 +121,7 @@ case class OnChainFeeConf(feeTargets: FeeTargets,
 
     commitmentFormat match {
       case Transactions.DefaultCommitmentFormat => networkFeerate
-      case _: Transactions.AnchorOutputsCommitmentFormat  =>
+      case _: Transactions.AnchorOutputsCommitmentFormat =>
         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/ChannelData.scala

@@ -569,14 +569,15 @@ final case class DATA_WAIT_FOR_DUAL_FUNDING_CREATED(channelId: ByteVector32,
                                                     remotePushAmount: MilliSatoshi,
                                                     txBuilder: typed.ActorRef[InteractiveTxBuilder.Command],
                                                     deferred: Option[CommitSig],
-                                                    remoteNextLocalNonce: Option[IndividualNonce],
+                                                    secondRemoteNonce_opt: Option[IndividualNonce],
                                                     replyTo_opt: Option[akka.actor.typed.ActorRef[Peer.OpenChannelResponse]]) extends TransientChannelData
 final case class DATA_WAIT_FOR_DUAL_FUNDING_SIGNED(channelParams: ChannelParams,
                                                    secondRemotePerCommitmentPoint: PublicKey,
                                                    localPushAmount: MilliSatoshi,
                                                    remotePushAmount: MilliSatoshi,
                                                    signingSession: InteractiveTxSigningSession.WaitingForSigs,
-                                                   remoteChannelData_opt: Option[ByteVector]) extends ChannelDataWithoutCommitments
+                                                   remoteChannelData_opt: Option[ByteVector],
+                                                   secondRemoteNonce_opt: Option[IndividualNonce]) extends ChannelDataWithoutCommitments
 final case class DATA_WAIT_FOR_DUAL_FUNDING_CONFIRMED(commitments: Commitments,
                                                       localPushAmount: MilliSatoshi,
                                                       remotePushAmount: MilliSatoshi,

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

@@ -131,18 +131,16 @@ object ChannelTypes {
     override def commitmentFormat: CommitmentFormat = ZeroFeeHtlcTxAnchorOutputsCommitmentFormat
     override def toString: String = s"anchor_outputs_zero_fee_htlc_tx${if (scidAlias) "+scid_alias" else ""}${if (zeroConf) "+zeroconf" else ""}"
   }
-  case object SimpleTaprootChannelsStaging extends SupportedChannelType {
+  case class SimpleTaprootChannelsStaging(scidAlias: Boolean = false, zeroConf: Boolean = false) extends SupportedChannelType {
     /** Known channel-type features */
     override def features: Set[ChannelTypeFeature] = Set(
+      if (scidAlias) Some(Features.ScidAlias) else None,
+      if (zeroConf) Some(Features.ZeroConf) else None,
       Some(Features.SimpleTaprootStaging)
     ).flatten
-
-        /** True if our main output in the remote commitment is directly sent (without any delay) to one of our wallet addresses. */
     override def paysDirectlyToWallet: Boolean = false
-    /** Format of the channel transactions. */
     override def commitmentFormat: CommitmentFormat = SimpleTaprootChannelsStagingCommitmentFormat
-
-    override def toString: String = "simple_taproot_channel_staging"
+    override def toString: String = s"simple_taproot_channel_staging${if (scidAlias) "+scid_alias" else ""}${if (zeroConf) "+zeroconf" else ""}"
   }
 
   case class UnsupportedChannelType(featureBits: Features[InitFeature]) extends ChannelType {
@@ -168,7 +166,11 @@ object ChannelTypes {
     AnchorOutputsZeroFeeHtlcTx(zeroConf = true),
     AnchorOutputsZeroFeeHtlcTx(scidAlias = true),
     AnchorOutputsZeroFeeHtlcTx(scidAlias = true, zeroConf = true),
-    SimpleTaprootChannelsStaging)
+    SimpleTaprootChannelsStaging(),
+    SimpleTaprootChannelsStaging(zeroConf = true),
+    SimpleTaprootChannelsStaging(scidAlias = true),
+    SimpleTaprootChannelsStaging(scidAlias = true, zeroConf = true),
+  )
     .map(channelType => Features(channelType.features.map(_ -> FeatureSupport.Mandatory).toMap) -> channelType)
     .toMap
 
@@ -184,7 +186,7 @@ object ChannelTypes {
     val scidAlias = canUse(Features.ScidAlias) && !announceChannel // alias feature is incompatible with public channel
     val zeroConf = canUse(Features.ZeroConf)
     if (canUse(Features.SimpleTaprootStaging)) {
-      SimpleTaprootChannelsStaging
+      SimpleTaprootChannelsStaging(scidAlias, zeroConf)
     } else if (canUse(Features.AnchorOutputsZeroFeeHtlcTx)) {
       AnchorOutputsZeroFeeHtlcTx(scidAlias, zeroConf)
     } else if (canUse(Features.AnchorOutputs)) {

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

@@ -1,7 +1,7 @@
 package fr.acinq.eclair.channel
 
-import akka.event.LoggingAdapter
-import fr.acinq.bitcoin.crypto.musig2.IndividualNonce
+import akka.event.{DiagnosticLoggingAdapter, LoggingAdapter}
+import fr.acinq.bitcoin.crypto.musig2.{IndividualNonce, SecretNonce}
 import fr.acinq.bitcoin.scalacompat.Crypto.{PrivateKey, PublicKey}
 import fr.acinq.bitcoin.scalacompat.{ByteVector32, ByteVector64, Crypto, Musig2, Satoshi, SatoshiLong, Script, Transaction, TxId}
 import fr.acinq.eclair.blockchain.fee.{FeeratePerByte, FeeratePerKw, FeeratesPerKw, OnChainFeeConf}
@@ -17,6 +17,7 @@ import fr.acinq.eclair.transactions.Transactions._
 import fr.acinq.eclair.transactions._
 import fr.acinq.eclair.wire.protocol._
 import fr.acinq.eclair.{BlockHeight, CltvExpiry, CltvExpiryDelta, Features, MilliSatoshi, MilliSatoshiLong, payment}
+import grizzled.slf4j.Logging
 import scodec.bits.ByteVector
 
 /** Static channel parameters shared by all commitments. */
@@ -229,11 +230,23 @@ case class LocalCommit(index: Long, spec: CommitmentSpec, commitTxAndRemoteSig:
 object LocalCommit {
   def fromCommitSig(keyManager: ChannelKeyManager, params: ChannelParams, fundingTxId: TxId,
                     fundingTxIndex: Long, remoteFundingPubKey: PublicKey, commitInput: InputInfo,
-                    commit: CommitSig, localCommitIndex: Long, spec: CommitmentSpec, localPerCommitmentPoint: PublicKey): Either[ChannelException, LocalCommit] = {
+                    commit: CommitSig, localCommitIndex: Long, spec: CommitmentSpec, localPerCommitmentPoint: PublicKey, localNonce_opt: Option[(SecretNonce, IndividualNonce)]): Either[ChannelException, LocalCommit] = {
     val (localCommitTx, htlcTxs) = Commitment.makeLocalTxs(keyManager, params.channelConfig, params.channelFeatures, localCommitIndex, params.localParams, params.remoteParams, fundingTxIndex, remoteFundingPubKey, commitInput, localPerCommitmentPoint, spec)
     if (!localCommitTx.checkSig(commit, remoteFundingPubKey, TxOwner.Remote, params.commitmentFormat)) {
       return Left(InvalidCommitmentSignature(params.channelId, fundingTxId, fundingTxIndex, localCommitTx.tx))
     }
+    commit.sigOrPartialSig match {
+      case Left(_) =>
+        if (!localCommitTx.checkSig(commit, remoteFundingPubKey, TxOwner.Remote, params.commitmentFormat)) {
+          return Left(InvalidCommitmentSignature(params.channelId, fundingTxId, fundingTxIndex, localCommitTx.tx))
+        }
+      case Right(psig) =>
+        val fundingPubkey = keyManager.fundingPublicKey(params.localParams.fundingKeyPath, fundingTxIndex).publicKey
+        val Some(localNonce) = localNonce_opt
+        if (!localCommitTx.checkPartialSignature(psig, fundingPubkey, localNonce._2, remoteFundingPubKey)) {
+          return Left(InvalidCommitmentSignature(params.channelId, fundingTxId, fundingTxIndex, localCommitTx.tx))
+        }
+    }
     val sortedHtlcTxs = htlcTxs.sortBy(_.input.outPoint.index)
     if (commit.htlcSignatures.size != sortedHtlcTxs.size) {
       return Left(HtlcSigCountMismatch(params.channelId, sortedHtlcTxs.size, commit.htlcSignatures.size))
@@ -252,7 +265,7 @@ object LocalCommit {
 
 /** The remote commitment maps to a commitment transaction that only our peer can sign and broadcast. */
 case class RemoteCommit(index: Long, spec: CommitmentSpec, txid: TxId, remotePerCommitmentPoint: PublicKey) {
-  def sign(keyManager: ChannelKeyManager, params: ChannelParams, fundingTxIndex: Long, remoteFundingPubKey: PublicKey, commitInput: InputInfo, remoteNonce_opt: Option[IndividualNonce]): CommitSig = {
+  def sign(keyManager: ChannelKeyManager, params: ChannelParams, fundingTxIndex: Long, remoteFundingPubKey: PublicKey, commitInput: InputInfo, remoteNonce_opt: Option[IndividualNonce])(implicit log: LoggingAdapter): CommitSig = {
     val (remoteCommitTx, htlcTxs) = Commitment.makeRemoteTxs(keyManager, params.channelConfig, params.channelFeatures, index, params.localParams, params.remoteParams, fundingTxIndex, remoteFundingPubKey, commitInput, remotePerCommitmentPoint, spec)
     val (sig, tlvStream) = params.commitmentFormat match {
       case SimpleTaprootChannelsStagingCommitmentFormat =>
@@ -653,6 +666,7 @@ case class Commitment(fundingTxIndex: Long,
         val localNonce = keyManager.signingNonce(params.localParams.fundingKeyPath, fundingTxIndex)
         val Some(remoteNonce) = nextRemoteNonce_opt
         val Right(psig) = keyManager.partialSign(remoteCommitTx, keyManager.fundingPublicKey(params.localParams.fundingKeyPath, fundingTxIndex), remoteFundingPubKey, TxOwner.Remote, localNonce, remoteNonce)
+        log.debug(s"sendCommit: creating partial sig $psig for remote commit tx ${remoteCommitTx.tx.txid} with remote nonce $remoteNonce and remoteNextPerCommitmentPoint = $remoteNextPerCommitmentPoint")
         Set(CommitSigTlv.PartialSignatureWithNonceTlv(PartialSignatureWithNonce(psig, localNonce._2)))
       case _ =>
         Set.empty
@@ -668,11 +682,12 @@ case class Commitment(fundingTxIndex: Long,
     val commitSig = CommitSig(params.channelId, sig, htlcSigs.toList, TlvStream(Set(
       if (batchSize > 1) Some(CommitSigTlv.BatchTlv(batchSize)) else None
     ).flatten[CommitSigTlv] ++ partialSig))
+    log.debug(s"sendCommit: setting remoteNextPerCommitmentPoint to $remoteNextPerCommitmentPoint")
     val nextRemoteCommit = NextRemoteCommit(commitSig, RemoteCommit(remoteCommit.index + 1, spec, remoteCommitTx.tx.txid, remoteNextPerCommitmentPoint))
     (copy(nextRemoteCommit_opt = Some(nextRemoteCommit)), commitSig)
   }
 
-  def receiveCommit(keyManager: ChannelKeyManager, params: ChannelParams, changes: CommitmentChanges, localPerCommitmentPoint: PublicKey, commit: CommitSig)(implicit log: LoggingAdapter): Either[ChannelException, Commitment] = {
+  def receiveCommit(keyManager: ChannelKeyManager, params: ChannelParams, changes: CommitmentChanges, localPerCommitmentPoint: PublicKey, commit: CommitSig, localNonce_opt: Option[(SecretNonce, IndividualNonce)])(implicit log: LoggingAdapter): Either[ChannelException, Commitment] = {
     // they sent us a signature for *their* view of *our* next commit tx
     // so in terms of rev.hashes and indexes we have:
     // ourCommit.index -> our current revocation hash, which is about to become our old revocation hash
@@ -683,7 +698,7 @@ case class Commitment(fundingTxIndex: Long,
     // and will increment our index
     val localCommitIndex = localCommit.index + 1
     val spec = CommitmentSpec.reduce(localCommit.spec, changes.localChanges.acked, changes.remoteChanges.proposed)
-    LocalCommit.fromCommitSig(keyManager, params, fundingTxId, fundingTxIndex, remoteFundingPubKey, commitInput, commit, localCommitIndex, spec, localPerCommitmentPoint).map { localCommit1 =>
+    LocalCommit.fromCommitSig(keyManager, params, fundingTxId, fundingTxIndex, remoteFundingPubKey, commitInput, commit, localCommitIndex, spec, localPerCommitmentPoint, localNonce_opt).map { localCommit1 =>
       log.info(s"built local commit number=$localCommitIndex toLocalMsat=${spec.toLocal.toLong} toRemoteMsat=${spec.toRemote.toLong} htlc_in={} htlc_out={} feeratePerKw=${spec.commitTxFeerate} txid=${localCommit1.commitTxAndRemoteSig.commitTx.tx.txid} fundingTxId=$fundingTxId", spec.htlcs.collect(DirectedHtlc.incoming).map(_.id).mkString(","), spec.htlcs.collect(DirectedHtlc.outgoing).map(_.id).mkString(","))
       copy(localCommit = localCommit1)
     }
@@ -698,9 +713,10 @@ case class Commitment(fundingTxIndex: Long,
         addSigs(unsignedCommitTx, keyManager.fundingPublicKey(params.localParams.fundingKeyPath, fundingTxIndex).publicKey, remoteFundingPubKey, localSig, remoteSig)
       case Right(remotePartialSigWithNonce) =>
         val fundingPubKey = keyManager.fundingPublicKey(params.localParams.fundingKeyPath, fundingTxIndex)
-        val localNonce = keyManager.verificationNonce(params.localParams.fundingKeyPath, fundingTxIndex, ChannelKeyManager.keyPath(fundingPubKey.publicKey), localCommit.index)
+        val channelKeyPath = ChannelKeyManager.keyPath(keyManager.fundingPublicKey(params.localParams.fundingKeyPath, fundingTxIndex = 0L))
+        val localNonce = keyManager.verificationNonce(params.localParams.fundingKeyPath, fundingTxIndex, channelKeyPath, localCommit.index)
         val Right(partialSig) = keyManager.partialSign(unsignedCommitTx,
-          keyManager.fundingPublicKey(params.localParams.fundingKeyPath, fundingTxIndex = 0), remoteFundingPubKey,
+          keyManager.fundingPublicKey(params.localParams.fundingKeyPath, fundingTxIndex), remoteFundingPubKey,
           TxOwner.Local,
           localNonce, remotePartialSigWithNonce.nonce)
         val Right(aggSig) = Musig2.aggregateTaprootSignatures(
@@ -1037,11 +1053,17 @@ case class Commitments(params: ChannelParams,
     }
   }
 
-  def sendCommit(keyManager: ChannelKeyManager, nextRemoteNonce_opt: Option[IndividualNonce] = None)(implicit log: LoggingAdapter): Either[ChannelException, (Commitments, Seq[CommitSig])] = {
+  def sendCommit(keyManager: ChannelKeyManager, nextRemoteNonces: List[IndividualNonce] = List.empty)(implicit log: LoggingAdapter): Either[ChannelException, (Commitments, Seq[CommitSig])] = {
     remoteNextCommitInfo match {
       case Right(_) if !changes.localHasChanges => Left(CannotSignWithoutChanges(channelId))
       case Right(remoteNextPerCommitmentPoint) =>
-        val (active1, sigs) = active.map(_.sendCommit(keyManager, params, changes, remoteNextPerCommitmentPoint, active.size, nextRemoteNonce_opt)).unzip
+        val (active1, sigs) = this.params.commitmentFormat match {
+          case SimpleTaprootChannelsStagingCommitmentFormat =>
+            require(active.size <= nextRemoteNonces.size, s"we have ${active.size} commitments but ${nextRemoteNonces.size} remote musig2 nonces")
+            active.zip(nextRemoteNonces).map { case (c, n) => c.sendCommit(keyManager, params, changes, remoteNextPerCommitmentPoint, active.size, Some(n)) } unzip
+          case _ =>
+            active.map(_.sendCommit(keyManager, params, changes, remoteNextPerCommitmentPoint, active.size, None)).unzip
+        }
         val commitments1 = copy(
           changes = changes.copy(
             localChanges = changes.localChanges.copy(proposed = Nil, signed = changes.localChanges.proposed),
@@ -1066,7 +1088,11 @@ case class Commitments(params: ChannelParams,
     val localPerCommitmentPoint = keyManager.commitmentPoint(channelKeyPath, localCommitIndex + 1)
     // Signatures are sent in order (most recent first), calling `zip` will drop trailing sigs that are for deactivated/pruned commitments.
     val active1 = active.zip(commits).map { case (commitment, commit) =>
-      commitment.receiveCommit(keyManager, params, changes, localPerCommitmentPoint, commit) match {
+      val localNonce_opt = params.commitmentFormat match {
+        case SimpleTaprootChannelsStagingCommitmentFormat => Some(keyManager.verificationNonce(params.localParams.fundingKeyPath, commitment.fundingTxIndex, channelKeyPath, localCommitIndex + 1))
+        case _ => None
+      }
+      commitment.receiveCommit(keyManager, params, changes, localPerCommitmentPoint, commit, localNonce_opt) match {
         case Left(f) => return Left(f)
         case Right(commitment1) => commitment1
       }
@@ -1076,9 +1102,12 @@ case class Commitments(params: ChannelParams,
     val localNextPerCommitmentPoint = keyManager.commitmentPoint(channelKeyPath, localCommitIndex + 2)
     val tlvStream: TlvStream[RevokeAndAckTlv] = params.commitmentFormat match {
       case SimpleTaprootChannelsStagingCommitmentFormat =>
-        val (_, nonce) = keyManager.verificationNonce(params.localParams.fundingKeyPath, this.latest.fundingTxIndex, channelKeyPath, localCommitIndex + 2)
-        log.debug("generating our next local nonce with {} {} {} {}", params.localParams.fundingKeyPath, this.latest.fundingTxIndex, channelKeyPath, localCommitIndex + 2)
-        TlvStream(RevokeAndAckTlv.NextLocalNonceTlv(nonce))
+        val nonces = this.active.map(c => {
+          val n = keyManager.verificationNonce(params.localParams.fundingKeyPath, c.fundingTxIndex, channelKeyPath, localCommitIndex + 2)
+          log.debug(s"revokeandack: creating verification nonce ${n._2} fundingIndex = ${c.fundingTxIndex} commit index = ${localCommitIndex + 2}")
+          n
+        })
+        TlvStream(RevokeAndAckTlv.NextLocalNoncesTlv(nonces.map(_._2).toList))
       case _ =>
         TlvStream.empty
     }
@@ -1103,7 +1132,7 @@ case class Commitments(params: ChannelParams,
     remoteNextCommitInfo match {
       case Right(_) => Left(UnexpectedRevocation(channelId))
       case Left(_) if revocation.perCommitmentSecret.publicKey != active.head.remoteCommit.remotePerCommitmentPoint => Left(InvalidRevocation(channelId))
-      case Left(_) if this.params.commitmentFormat == SimpleTaprootChannelsStagingCommitmentFormat && revocation.nexLocalNonce_opt.isEmpty => Left(MissingNextLocalNonce(channelId))
+      case Left(_) if this.params.commitmentFormat == SimpleTaprootChannelsStagingCommitmentFormat && revocation.nexLocalNonces.isEmpty => Left(MissingNextLocalNonce(channelId))
       case Left(_) =>
         // Since htlcs are shared across all commitments, we generate the actions only once based on the first commitment.
         val receivedHtlcs = changes.remoteChanges.signed.collect {