Add low-level taproot helpers (#3086)

We add a new commitment format for simple taproot channels,
and implement creating and verifying musig2 and taproot sigs
for these channels.

Wire format and channel creation/update workflows have not
been modified, this will be done in another PR. This is currently
dead code, but is ready to be used and extensively tested!

Author: sstone

.mvn/checksums/checksums-central.sha256

@@ -169,7 +169,6 @@
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@@ -311,6 +310,7 @@
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@@ -329,7 +329,6 @@
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-45cc11268c1cee5de307595bf2ec2d8a1c17faa794f8e0a8657f74a9f04eb879  fr/acinq/bitcoin/bitcoin-kmp-jvm/0.22.2/bitcoin-kmp-jvm-0.22.2.pom
 46300ff8f2885d679df1d0123c4e575a73c8ed1a87a206751e1bffa2b1d61702  fr/acinq/secp256k1/secp256k1-kmp-jni-common/0.17.3/secp256k1-kmp-jni-common-0.17.3.pom
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@@ -610,7 +609,6 @@
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-86e74b15b39d9b02e8db92129a1de62ccf040997f0b843a29f52408784a8b1bd  fr/acinq/bitcoin-lib_2.13/0.37/bitcoin-lib_2.13-0.37.jar
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@@ -629,6 +627,7 @@
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@@ -752,6 +751,7 @@ a70e1f662fa81b72eb468d28eec72fd7f2b7b49c4b54d1cf1c14ccd197d4eafd  org/apache/mav
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@@ -797,7 +797,6 @@ b1587c577a8f244aff37bc1418443e01ffbf4291536483de6ecd0054aa460679  com/typesafe/a
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-b2176722f4696d151d4bf91860723ca64d10b68154f949ea3b0173f26f1ab330  fr/acinq/bitcoin-lib_2.13/0.37/bitcoin-lib_2.13-0.37.pom
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@@ -993,6 +992,7 @@ e68fc19a48cec582a6732fd0b10dbfe9feca25060963def89e547f8a3759d379  org/apache/apa
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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/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, LegacySimpleTaprootChannelCommitmentFormat, UnsafeLegacyAnchorOutputsCommitmentFormat, ZeroFeeHtlcTxSimpleTaprootChannelCommitmentFormat, ZeroFeeHtlcTxAnchorOutputsCommitmentFormat}
 
 // @formatter:off
 sealed trait ConfirmationPriority extends Ordered[ConfirmationPriority] {
@@ -76,16 +76,16 @@ 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 Transactions.DefaultCommitmentFormat  => networkFeerate * ratioHigh < proposedFeerate
+      case ZeroFeeHtlcTxAnchorOutputsCommitmentFormat | UnsafeLegacyAnchorOutputsCommitmentFormat | LegacySimpleTaprootChannelCommitmentFormat | ZeroFeeHtlcTxSimpleTaprootChannelCommitmentFormat => 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 | LegacySimpleTaprootChannelCommitmentFormat | ZeroFeeHtlcTxSimpleTaprootChannelCommitmentFormat => 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/Commitments.scala

@@ -196,12 +196,14 @@ object LocalCommit {
     val (localCommitTx, htlcTxs) = Commitment.makeLocalTxs(params, commitKeys, localCommitIndex, fundingKey, remoteFundingPubKey, commitInput, spec)
     val remoteCommitSigOk = params.commitmentFormat match {
       case _: SegwitV0CommitmentFormat => localCommitTx.checkRemoteSig(fundingKey.publicKey, remoteFundingPubKey, ChannelSpendSignature.IndividualSignature(commit.signature))
+      case _: SimpleTaprootChannelCommitmentFormat => ???
     }
     if (!remoteCommitSigOk) {
       return Left(InvalidCommitmentSignature(params.channelId, fundingTxId, localCommitIndex, localCommitTx.tx))
     }
     val commitxTxAndRemoteSig = params.commitmentFormat match {
       case _: SegwitV0CommitmentFormat => CommitTxAndRemoteSig(localCommitTx, ChannelSpendSignature.IndividualSignature(commit.signature))
+      case _: SimpleTaprootChannelCommitmentFormat => ???
     }
     val sortedHtlcTxs = htlcTxs.sortBy(_.input.outPoint.index)
     if (commit.htlcSignatures.size != sortedHtlcTxs.size) {
@@ -230,6 +232,7 @@ case class RemoteCommit(index: Long, spec: CommitmentSpec, txid: TxId, remotePer
       case _: SegwitV0CommitmentFormat =>
         val sig = remoteCommitTx.sign(fundingKey, remoteFundingPubKey).sig
         CommitSig(params.channelId, sig, htlcSigs.toList)
+      case _: SimpleTaprootChannelCommitmentFormat => ???
     }
   }
 }
@@ -661,6 +664,7 @@ case class Commitment(fundingTxIndex: Long,
       case _: SegwitV0CommitmentFormat =>
         val sig = remoteCommitTx.sign(fundingKey, remoteFundingPubKey).sig
         CommitSig(params.channelId, sig, htlcSigs.toList, TlvStream(tlvs))
+      case _: SimpleTaprootChannelCommitmentFormat => ???
     }
     val nextRemoteCommit = NextRemoteCommit(commitSig, RemoteCommit(remoteCommit.index + 1, spec, remoteCommitTx.tx.txid, remoteNextPerCommitmentPoint))
     (copy(nextRemoteCommit_opt = Some(nextRemoteCommit)), commitSig)
@@ -1156,11 +1160,7 @@ case class Commitments(params: ChannelParams,
     active.forall { commitment =>
       val localFundingKey = channelKeys.fundingKey(commitment.fundingTxIndex).publicKey
       val remoteFundingKey = commitment.remoteFundingPubKey
-      val redeemInfo = params.commitmentFormat match {
-        case _: SegwitV0CommitmentFormat =>
-          val fundingScript = Script.write(Scripts.multiSig2of2(localFundingKey, remoteFundingKey))
-          RedeemInfo.P2wsh(fundingScript)
-      }
+      val redeemInfo = Helpers.Funding.makeFundingScript(localFundingKey, remoteFundingKey, params.commitmentFormat)
       commitment.commitInput.txOut.publicKeyScript == redeemInfo.pubkeyScript
     }
   }

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

@@ -373,6 +373,7 @@ object Helpers {
     def makeFundingScript(localFundingKey: PublicKey, remoteFundingKey: PublicKey, commitmentFormat: CommitmentFormat): RedeemInfo = {
       commitmentFormat match {
         case _: SegwitV0CommitmentFormat => RedeemInfo.P2wsh(Script.write(multiSig2of2(localFundingKey, remoteFundingKey)))
+        case _: SimpleTaprootChannelCommitmentFormat => RedeemInfo.TaprootKeyPath(Taproot.musig2Aggregate(localFundingKey, remoteFundingKey), None)
       }
     }
 
@@ -676,7 +677,7 @@ 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.
@@ -901,7 +902,7 @@ object Helpers {
 
       def claimAnchor(fundingKey: PrivateKey, commitKeys: LocalCommitmentKeys, commitTx: Transaction, commitmentFormat: CommitmentFormat)(implicit log: LoggingAdapter): Option[ClaimAnchorOutputTx] = {
         withTxGenerationLog("local-anchor") {
-          ClaimAnchorOutputTx.createUnsignedTx(fundingKey, commitKeys.publicKeys, commitTx, commitmentFormat)
+          ClaimAnchorOutputTx.createUnsignedTx(fundingKey, commitKeys, commitTx, commitmentFormat)
         }
       }
 
@@ -1003,7 +1004,7 @@ object Helpers {
 
       def claimAnchor(fundingKey: PrivateKey, commitKeys: RemoteCommitmentKeys, commitTx: Transaction, commitmentFormat: CommitmentFormat)(implicit log: LoggingAdapter): Option[ClaimAnchorOutputTx] = {
         withTxGenerationLog("remote-anchor") {
-          ClaimAnchorOutputTx.createUnsignedTx(fundingKey, commitKeys.publicKeys, commitTx, commitmentFormat)
+          ClaimAnchorOutputTx.createUnsignedTx(fundingKey, commitKeys, commitTx, commitmentFormat)
         }
       }
 
@@ -1014,7 +1015,7 @@ object Helpers {
           case DefaultCommitmentFormat => withTxGenerationLog("remote-main") {
             ClaimP2WPKHOutputTx.createSignedTx(commitKeys, commitTx, params.localParams.dustLimit, finalScriptPubKey, feerate, params.commitmentFormat)
           }
-          case _: AnchorOutputsCommitmentFormat => withTxGenerationLog("remote-main-delayed") {
+          case _: AnchorOutputsCommitmentFormat | _: SimpleTaprootChannelCommitmentFormat => withTxGenerationLog("remote-main-delayed") {
             ClaimRemoteDelayedOutputTx.createSignedTx(commitKeys, commitTx, params.localParams.dustLimit, finalScriptPubKey, feerate, params.commitmentFormat)
           }
         }
@@ -1132,7 +1133,7 @@ object Helpers {
           case DefaultCommitmentFormat => withTxGenerationLog("remote-main") {
             ClaimP2WPKHOutputTx.createSignedTx(commitKeys, commitTx, localParams.dustLimit, finalScriptPubKey, feerateMain, commitmentFormat)
           }
-          case _: AnchorOutputsCommitmentFormat => withTxGenerationLog("remote-main-delayed") {
+          case _: AnchorOutputsCommitmentFormat | _: SimpleTaprootChannelCommitmentFormat => withTxGenerationLog("remote-main-delayed") {
             ClaimRemoteDelayedOutputTx.createSignedTx(commitKeys, commitTx, localParams.dustLimit, finalScriptPubKey, feerateMain, commitmentFormat)
           }
         }

eclair-core/src/main/scala/fr/acinq/eclair/channel/fsm/ChannelOpenSingleFunded.scala

@@ -31,7 +31,7 @@ import fr.acinq.eclair.crypto.ShaChain
 import fr.acinq.eclair.crypto.keymanager.{LocalCommitmentKeys, RemoteCommitmentKeys}
 import fr.acinq.eclair.io.Peer.OpenChannelResponse
 import fr.acinq.eclair.transactions.Scripts
-import fr.acinq.eclair.transactions.Transactions.SegwitV0CommitmentFormat
+import fr.acinq.eclair.transactions.Transactions.{SegwitV0CommitmentFormat, SimpleTaprootChannelCommitmentFormat}
 import fr.acinq.eclair.wire.protocol.{AcceptChannel, AnnouncementSignatures, ChannelReady, ChannelTlv, Error, FundingCreated, FundingSigned, OpenChannel, TlvStream}
 import fr.acinq.eclair.{MilliSatoshiLong, UInt64, randomKey, toLongId}
 import scodec.bits.ByteVector
@@ -218,6 +218,7 @@ trait ChannelOpenSingleFunded extends SingleFundingHandlers with ErrorHandlers {
           require(fundingTx.txOut(fundingTxOutputIndex).publicKeyScript == localCommitTx.input.txOut.publicKeyScript, s"pubkey script mismatch!")
           val localSigOfRemoteTx = params.commitmentFormat match {
             case _: SegwitV0CommitmentFormat => remoteCommitTx.sign(fundingKey, remoteFundingPubKey).sig
+            case _: SimpleTaprootChannelCommitmentFormat => ???
           }
           // signature of their initial commitment tx that pays remote pushMsat
           val fundingCreated = FundingCreated(
@@ -273,6 +274,7 @@ trait ChannelOpenSingleFunded extends SingleFundingHandlers with ErrorHandlers {
             case true =>
               val localSigOfRemoteTx = params.commitmentFormat match {
                 case _: SegwitV0CommitmentFormat => remoteCommitTx.sign(fundingKey, remoteFundingPubKey).sig
+                case _: SimpleTaprootChannelCommitmentFormat => ???
               }
               val channelId = toLongId(fundingTxId, fundingTxOutputIndex)
               val fundingSigned = FundingSigned(

eclair-core/src/main/scala/fr/acinq/eclair/channel/fsm/ErrorHandlers.scala

@@ -277,7 +277,7 @@ trait ErrorHandlers extends CommonHandlers {
               case _ => None
             }
             signedTx_opt.map(tx => PublishFinalTx(tx, tx.fee, Some(commitTx.txid)))
-          case _: Transactions.AnchorOutputsCommitmentFormat =>
+          case _: Transactions.AnchorOutputsCommitmentFormat | _: SimpleTaprootChannelCommitmentFormat =>
             val confirmationTarget = ConfirmationTarget.Absolute(htlcTx.htlcExpiry.blockHeight)
             val replaceableTx_opt = (htlcTx, preimage_opt) match {
               case (htlcTx: HtlcSuccessTx, Some(preimage)) => Some(ReplaceableHtlcSuccess(htlcTx, commitKeys, preimage, remoteSig, commitTx, commitment))