Move taproot signing helpers to Transaction.kt

This is more consistent with the existing `signInput` helpers.

src/commonMain/kotlin/fr/acinq/bitcoin/Crypto.kt

@@ -197,24 +197,6 @@ public object Crypto {
         return sig
     }
 
-    /** Produce a signature that will be included in the witness of a taproot key path spend. */
-    @JvmStatic
-    public fun signTaprootKeyPath(privateKey: PrivateKey, tx: Transaction, inputIndex: Int, inputs: List<TxOut>, sighashType: Int, scriptTree: ScriptTree?, annex: ByteVector? = null, auxrand32: ByteVector32? = null): ByteVector64 {
-        val data = Transaction.hashForSigningTaprootKeyPath(tx, inputIndex, inputs, sighashType, annex)
-        val tweak = when (scriptTree) {
-            null -> TaprootTweak.NoScriptTweak
-            else -> TaprootTweak.ScriptTweak(scriptTree.hash())
-        }
-        return signSchnorr(data, privateKey, tweak, auxrand32)
-    }
-
-    /** Produce a signature that will be included in the witness of a taproot script path spend. */
-    @JvmStatic
-    public fun signTaprootScriptPath(privateKey: PrivateKey, tx: Transaction, inputIndex: Int, inputs: List<TxOut>, sighashType: Int, tapleaf: ByteVector32, annex: ByteVector? = null, auxrand32: ByteVector32? = null): ByteVector64 {
-        val data = Transaction.hashForSigningTaprootScriptPath(tx, inputIndex, inputs, sighashType, tapleaf, annex)
-        return signSchnorr(data, privateKey, SchnorrTweak.NoTweak, auxrand32)
-    }
-
     @JvmStatic
     public fun verifySignatureSchnorr(data: ByteVector32, signature: ByteVector, publicKey: XonlyPublicKey): Boolean {
         return Secp256k1.verifySchnorr(signature.toByteArray(), data.toByteArray(), publicKey.value.toByteArray())

src/commonMain/kotlin/fr/acinq/bitcoin/Transaction.kt

@@ -798,6 +798,53 @@ public data class Transaction(
             return hashForSigningSchnorr(tx, inputIndex, inputs, sighashType, SigVersion.SIGVERSION_TAPSCRIPT, tapleaf, annex)
         }
 
+        /**
+         * Sign a taproot tx input, using the internal key path.
+         *
+         * @param privateKey private key.
+         * @param tx input transaction.
+         * @param inputIndex index of the tx input that is being signed.
+         * @param inputs list of all UTXOs spent by this transaction.
+         * @param sighashType signature hash type, which will be appended to the signature (if not default).
+         * @param scriptTree tapscript tree of the signed input, if it has script paths.
+         * @return the schnorr signature of this tx for this specific tx input.
+         */
+        @JvmStatic
+        public fun signInputTaprootKeyPath(privateKey: PrivateKey, tx: Transaction, inputIndex: Int, inputs: List<TxOut>, sighashType: Int, scriptTree: ScriptTree?, annex: ByteVector? = null, auxrand32: ByteVector32? = null): ByteVector64 {
+            val data = hashForSigningTaprootKeyPath(tx, inputIndex, inputs, sighashType, annex)
+            val tweak = when (scriptTree) {
+                null -> Crypto.TaprootTweak.NoScriptTweak
+                else -> Crypto.TaprootTweak.ScriptTweak(scriptTree.hash())
+            }
+            return Crypto.signSchnorr(data, privateKey, tweak, auxrand32)
+        }
+
+        /**
+         * Sign a taproot tx input, using one of its script paths.
+         *
+         * @param privateKey private key.
+         * @param tx input transaction.
+         * @param inputIndex index of the tx input that is being signed.
+         * @param inputs list of all UTXOs spent by this transaction.
+         * @param sighashType signature hash type, which will be appended to the signature (if not default).
+         * @param tapleaf tapscript leaf hash of the script that is being spent.
+         * @return the schnorr signature of this tx for this specific tx input and the given script leaf.
+         */
+        @JvmStatic
+        public fun signInputTaprootScriptPath(
+            privateKey: PrivateKey,
+            tx: Transaction,
+            inputIndex: Int,
+            inputs: List<TxOut>,
+            sighashType: Int,
+            tapleaf: ByteVector32,
+            annex: ByteVector? = null,
+            auxrand32: ByteVector32? = null
+        ): ByteVector64 {
+            val data = hashForSigningTaprootScriptPath(tx, inputIndex, inputs, sighashType, tapleaf, annex)
+            return Crypto.signSchnorr(data, privateKey, Crypto.SchnorrTweak.NoTweak, auxrand32)
+        }
+
         @JvmStatic
         public fun correctlySpends(tx: Transaction, previousOutputs: Map<OutPoint, TxOut>, scriptFlags: Int) {
             val prevouts = tx.txIn.map { previousOutputs[it.outPoint]!! }

src/commonTest/kotlin/fr/acinq/bitcoin/TaprootTestsCommon.kt

@@ -95,7 +95,7 @@ class TaprootTestsCommon {
             0
         )
         val sigHashType = 0
-        val sig = Crypto.signTaprootKeyPath(privateKey, tx1, 0, listOf(tx.txOut[1]), sigHashType, scriptTree = null)
+        val sig = Transaction.signInputTaprootKeyPath(privateKey, tx1, 0, listOf(tx.txOut[1]), sigHashType, scriptTree = null)
         val tx2 = tx1.updateWitness(0, Script.witnessKeyPathPay2tr(sig))
         Transaction.correctlySpends(tx2, tx, ScriptFlags.STANDARD_SCRIPT_VERIFY_FLAGS)
     }
@@ -193,7 +193,7 @@ class TaprootTestsCommon {
         )
 
         // compute all 3 signatures
-        val sigs = privs.map { Crypto.signTaprootScriptPath(it, tmp, 0, listOf(fundingTx.txOut[0]), SigHash.SIGHASH_DEFAULT, scriptTree.hash()) }
+        val sigs = privs.map { Transaction.signInputTaprootScriptPath(it, tmp, 0, listOf(fundingTx.txOut[0]), SigHash.SIGHASH_DEFAULT, scriptTree.hash()) }
 
         // one signature is not enough
         val tx = tmp.updateWitness(0, Script.witnessScriptPathPay2tr(internalPubkey, scriptTree, ScriptWitness(listOf(sigs[0], sigs[0], sigs[0])), scriptTree))
@@ -262,7 +262,7 @@ class TaprootTestsCommon {
                 lockTime = 0
             )
             // We still need to provide the tapscript tree because it is used to tweak the private key.
-            val sig = Crypto.signTaprootKeyPath(privs[0], tmp, 0, listOf(fundingTx.txOut[0]), SigHash.SIGHASH_DEFAULT, scriptTree)
+            val sig = Transaction.signInputTaprootKeyPath(privs[0], tmp, 0, listOf(fundingTx.txOut[0]), SigHash.SIGHASH_DEFAULT, scriptTree)
             tmp.updateWitness(0, Script.witnessKeyPathPay2tr(sig))
         }
 
@@ -287,7 +287,7 @@ class TaprootTestsCommon {
                 txOut = listOf(TxOut(fundingTx1.txOut[0].amount - Satoshi(5000), sweepPublicKeyScript)),
                 lockTime = 0
             )
-            val sig = Crypto.signTaprootScriptPath(privs[0], tmp, 0, listOf(fundingTx.txOut[0]), SigHash.SIGHASH_DEFAULT, leaves[0].hash())
+            val sig = Transaction.signInputTaprootScriptPath(privs[0], tmp, 0, listOf(fundingTx.txOut[0]), SigHash.SIGHASH_DEFAULT, leaves[0].hash())
             val witness = Script.witnessScriptPathPay2tr(internalPubkey, leaves[0], ScriptWitness(listOf(sig)), scriptTree)
             tmp.updateWitness(0, witness)
         }
@@ -314,7 +314,7 @@ class TaprootTestsCommon {
                 txOut = listOf(TxOut(fundingTx2.txOut[0].amount - Satoshi(5000), sweepPublicKeyScript)),
                 lockTime = 0
             )
-            val sig = Crypto.signTaprootScriptPath(privs[1], tmp, 0, listOf(fundingTx2.txOut[0]), SigHash.SIGHASH_DEFAULT, leaves[1].hash())
+            val sig = Transaction.signInputTaprootScriptPath(privs[1], tmp, 0, listOf(fundingTx2.txOut[0]), SigHash.SIGHASH_DEFAULT, leaves[1].hash())
             val witness = Script.witnessScriptPathPay2tr(internalPubkey, leaves[1], ScriptWitness(listOf(sig)), scriptTree)
             tmp.updateWitness(0, witness)
         }
@@ -340,7 +340,7 @@ class TaprootTestsCommon {
                 txOut = listOf(TxOut(fundingTx3.txOut[0].amount - Satoshi(5000), addressToPublicKeyScript(blockchain, "tb1qxy9hhxkw7gt76qrm4yzw4j06gkk4evryh8ayp7").right!!)),
                 lockTime = 0
             )
-            val sig = Crypto.signTaprootScriptPath(privs[2], tmp, 0, listOf(fundingTx3.txOut[1]), SigHash.SIGHASH_DEFAULT, leaves[2].hash())
+            val sig = Transaction.signInputTaprootScriptPath(privs[2], tmp, 0, listOf(fundingTx3.txOut[1]), SigHash.SIGHASH_DEFAULT, leaves[2].hash())
             val witness = Script.witnessScriptPathPay2tr(internalPubkey, leaves[2], ScriptWitness(listOf(sig)), scriptTree)
             tmp.updateWitness(0, witness)
         }
@@ -410,7 +410,7 @@ class TaprootTestsCommon {
     fun `parse and validate large ordinals transaction`() {
         val file = resourcesDir().resolve("b5a7e05f28d00e4a791759ad7b6bd6799d856693293ceeaad9b0bb93c8851f7f.bin").openReadableFile()
         val buffer = ByteArray(file.size)
-        file.readBytes(buffer,  0, buffer.size)
+        file.readBytes(buffer, 0, buffer.size)
         file.close()
         val tx = Transaction.read(buffer)
         val parentTx = Transaction.read(

src/commonTest/kotlin/fr/acinq/bitcoin/crypto/musig2/Musig2TestsCommon.kt

@@ -373,7 +373,7 @@ class Musig2TestsCommon {
                 txOut = listOf(TxOut(10_000.sat(), Script.pay2wpkh(userPublicKey))),
                 lockTime = 0
             )
-            val sig = Crypto.signTaprootScriptPath(userRefundPrivateKey, tx, 0, swapInTx.txOut, SigHash.SIGHASH_DEFAULT, scriptTree.hash())
+            val sig = Transaction.signInputTaprootScriptPath(userRefundPrivateKey, tx, 0, swapInTx.txOut, SigHash.SIGHASH_DEFAULT, scriptTree.hash())
             val signedTx = tx.updateWitness(0, Script.witnessScriptPathPay2tr(internalPubKey, scriptTree, ScriptWitness(listOf(sig)), scriptTree))
             Transaction.correctlySpends(signedTx, swapInTx, ScriptFlags.STANDARD_SCRIPT_VERIFY_FLAGS)
         }