diff --git a/build.gradle.kts b/build.gradle.kts
index 2517e413..46c8eec5 100644
--- a/build.gradle.kts
+++ b/build.gradle.kts
@@ -12,7 +12,7 @@ plugins {
 val currentOs = org.gradle.internal.os.OperatingSystem.current()
 
 group = "fr.acinq.bitcoin"
-version = "0.17.0-SNAPSHOT"
+version = "0.17.0-MUSIG2-SNAPSHOT"
 
 repositories {
     google()
@@ -45,7 +45,7 @@ kotlin {
     }
 
     sourceSets {
-        val secp256k1KmpVersion = "0.13.0"
+        val secp256k1KmpVersion = "0.14.0-MUSIG2-SNAPSHOT"
 
         val commonMain by getting {
             dependencies {
diff --git a/src/commonMain/kotlin/fr/acinq/bitcoin/crypto/musig2/Musig2.kt b/src/commonMain/kotlin/fr/acinq/bitcoin/crypto/musig2/Musig2.kt
new file mode 100644
index 00000000..8402cb75
--- /dev/null
+++ b/src/commonMain/kotlin/fr/acinq/bitcoin/crypto/musig2/Musig2.kt
@@ -0,0 +1,171 @@
+package fr.acinq.bitcoin.crypto.musig2
+
+import fr.acinq.bitcoin.*
+import fr.acinq.secp256k1.Hex
+import fr.acinq.secp256k1.Secp256k1
+import kotlin.jvm.JvmStatic
+
+/**
+ * Musig2 key aggregation cache
+ * Keeps track of an aggregate of public keys, that can optionally be tweaked
+ */
+public data class KeyAggCache(val data: ByteVector) {
+    public constructor(data: ByteArray) : this(data.byteVector())
+
+    init {
+        require(data.size() == Secp256k1.MUSIG2_PUBLIC_KEYAGG_CACHE_SIZE) { "musig2 keyagg cache must be ${Secp256k1.MUSIG2_PUBLIC_KEYAGG_CACHE_SIZE} bytes" }
+    }
+
+    public fun toByteArray(): ByteArray = data.toByteArray()
+
+    /**
+     * @param tweak tweak to apply
+     * @param isXonly true if the tweak is an x-only tweak
+     * @return an updated cache, and the tweaked aggregated public key
+     */
+    public fun tweak(tweak: ByteVector32, isXonly: Boolean): Pair<KeyAggCache, PublicKey> {
+        val localCache = toByteArray()
+        val tweaked = if (isXonly) {
+            Secp256k1.musigPubkeyXonlyTweakAdd(localCache, tweak.toByteArray())
+        } else {
+            Secp256k1.musigPubkeyTweakAdd(localCache, tweak.toByteArray())
+        }
+        return Pair(KeyAggCache(localCache), PublicKey.parse(tweaked))
+    }
+
+    public companion object {
+        /**
+         * @param pubkeys public keys to aggregate
+         * @param cache an optional key aggregation cache
+         * @return a new (if cache was null) or updated cache, and the aggregated public key
+         */
+        @JvmStatic
+        public fun add(pubkeys: List<PublicKey>, cache: KeyAggCache?): Pair<XonlyPublicKey, KeyAggCache> {
+            val localCache = cache?.data?.toByteArray() ?: ByteArray(Secp256k1.MUSIG2_PUBLIC_KEYAGG_CACHE_SIZE)
+            val aggkey = Secp256k1.musigPubkeyAgg(pubkeys.map { it.value.toByteArray() }.toTypedArray(), localCache)
+            return Pair(XonlyPublicKey(aggkey.byteVector32()), KeyAggCache(localCache.byteVector()))
+        }
+    }
+}
+
+/**
+ * Musig2 signing session
+ */
+public data class Session(val data: ByteVector) {
+    init {
+        require(data.size() == Secp256k1.MUSIG2_PUBLIC_SESSION_SIZE) { "musig2 session must be ${Secp256k1.MUSIG2_PUBLIC_SESSION_SIZE} bytes" }
+    }
+
+    public fun toByteArray(): ByteArray = data.toByteArray()
+
+    /**
+     * @param secretNonce secret nonce
+     * @param pk private key
+     * @param aggCache key aggregation cache
+     * @return a Musig2 partial signature
+     */
+    public fun sign(secretNonce: SecretNonce, pk: PrivateKey, aggCache: KeyAggCache): ByteVector32 {
+        return Secp256k1.musigPartialSign(secretNonce.data.toByteArray(), pk.value.toByteArray(), aggCache.data.toByteArray(), toByteArray()).byteVector32()
+    }
+
+    /**
+     * @param psig musig2 partial signature
+     * @param pubnonce public nonce, that must match the secret nonce psig was generated with
+     * @param pubkey public key, that must match the private key psig was generated with
+     * @param cache key aggregation cache
+     * @return true if the partial signature is valid
+     */
+    public fun verify(psig: ByteVector32, pubnonce: IndividualNonce, pubkey: PublicKey, cache: KeyAggCache): Boolean {
+        return Secp256k1.musigPartialSigVerify(psig.toByteArray(), pubnonce.toByteArray(), pubkey.value.toByteArray(), cache.data.toByteArray(), toByteArray()) == 1
+    }
+
+    /**
+     * @param psigs partial signatures
+     * @return the aggregate of all input partial signatures
+     */
+    public fun add(psigs: List<ByteVector32>): ByteVector64 {
+        return Secp256k1.musigPartialSigAgg(toByteArray(), psigs.map { it.toByteArray() }.toTypedArray()).byteVector64()
+    }
+
+    public companion object {
+        /**
+         * @param aggregatedNonce aggregated public nonce
+         * @param msg message to sign
+         * @param cache key aggregation cache
+         * @return a Musig signing session
+         */
+        @JvmStatic
+        public fun build(aggregatedNonce: AggregatedNonce, msg: ByteVector32, cache: KeyAggCache): Session {
+            val session = Secp256k1.musigNonceProcess(aggregatedNonce.toByteArray(), msg.toByteArray(), cache.data.toByteArray())
+            return Session(session.byteVector())
+        }
+    }
+}
+
+/**
+ * Musig2 secret nonce. Not meant to be reused !!
+ */
+public data class SecretNonce(val data: ByteVector) {
+    public constructor(bin: ByteArray) : this(bin.byteVector())
+
+    public constructor(hex: String) : this(Hex.decode(hex))
+
+    init {
+        require(data.size() == Secp256k1.MUSIG2_SECRET_NONCE_SIZE) { "musig2 secret nonce must be ${Secp256k1.MUSIG2_SECRET_NONCE_SIZE} bytes" }
+    }
+
+    public companion object {
+        /**
+         * @param sessionId random session id. Must not be reused !!
+         * @param seckey optional private key
+         * @param pubkey public key
+         * @param msg optional message to sign
+         * @param cache optional key aggregation cache
+         * @param extraInput optional extra input value
+         * @return a (secret nonce, public nonce) tuple
+         */
+        @JvmStatic
+        public fun generate(sessionId: ByteVector32, seckey: PrivateKey?, pubkey: PublicKey, msg: ByteVector32?, cache: KeyAggCache?, extraInput: ByteVector32?): Pair<SecretNonce, IndividualNonce> {
+            val nonce = Secp256k1.musigNonceGen(sessionId.toByteArray(), seckey?.value?.toByteArray(), pubkey.value.toByteArray(), msg?.toByteArray(), cache?.data?.toByteArray(), extraInput?.toByteArray())
+            return Pair(SecretNonce(nonce.copyOfRange(0, Secp256k1.MUSIG2_SECRET_NONCE_SIZE)), IndividualNonce(nonce.copyOfRange(Secp256k1.MUSIG2_SECRET_NONCE_SIZE, Secp256k1.MUSIG2_SECRET_NONCE_SIZE + Secp256k1.MUSIG2_PUBLIC_NONCE_SIZE)))
+        }
+    }
+}
+
+/**
+ * Musig2 public nonce
+ */
+public data class IndividualNonce(val data: ByteVector) {
+    public constructor(bin: ByteArray) : this(bin.byteVector())
+
+    public constructor(hex: String) : this(Hex.decode(hex))
+
+    init {
+        require(data.size() == Secp256k1.MUSIG2_PUBLIC_NONCE_SIZE) { "individual musig2 public nonce must be ${Secp256k1.MUSIG2_PUBLIC_NONCE_SIZE} bytes" }
+    }
+
+    public fun toByteArray(): ByteArray = data.toByteArray()
+
+    public companion object {
+        @JvmStatic
+        public fun aggregate(nonces: List<IndividualNonce>): AggregatedNonce {
+            val agg = Secp256k1.musigNonceAgg(nonces.map { it.toByteArray() }.toTypedArray())
+            return AggregatedNonce(agg)
+        }
+    }
+}
+
+/**
+ * Musig2 aggregated nonce
+ */
+public data class AggregatedNonce(val data: ByteVector) {
+    public constructor(bin: ByteArray) : this(bin.byteVector())
+
+    public constructor(hex: String) : this(Hex.decode(hex))
+
+    init {
+        require(data.size() == Secp256k1.MUSIG2_PUBLIC_NONCE_SIZE) { "aggregated musig2 public nonce must be ${Secp256k1.MUSIG2_PUBLIC_NONCE_SIZE} bytes" }
+    }
+
+    public fun toByteArray(): ByteArray = data.toByteArray()
+}
\ No newline at end of file
diff --git a/src/commonTest/kotlin/fr/acinq/bitcoin/crypto/musig2/Musig2TestsCommon.kt b/src/commonTest/kotlin/fr/acinq/bitcoin/crypto/musig2/Musig2TestsCommon.kt
new file mode 100644
index 00000000..868efef4
--- /dev/null
+++ b/src/commonTest/kotlin/fr/acinq/bitcoin/crypto/musig2/Musig2TestsCommon.kt
@@ -0,0 +1,288 @@
+package fr.acinq.bitcoin.crypto.musig2
+
+import fr.acinq.bitcoin.*
+import fr.acinq.bitcoin.reference.TransactionTestsCommon
+import fr.acinq.secp256k1.Hex
+import kotlinx.serialization.json.*
+import kotlin.random.Random
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertFails
+import kotlin.test.assertTrue
+
+class Musig2TestsCommon {
+    @Test
+    fun `aggregate public keys`() {
+        val tests = TransactionTestsCommon.readData("musig2/key_agg_vectors.json")
+        val pubkeys = tests.jsonObject["pubkeys"]!!.jsonArray.map { PublicKey(ByteVector(it.jsonPrimitive.content)) }
+        val tweaks = tests.jsonObject["tweaks"]!!.jsonArray.map { ByteVector32.fromValidHex(it.jsonPrimitive.content) }
+
+        tests.jsonObject["valid_test_cases"]!!.jsonArray.forEach {
+            val keyIndices = it.jsonObject["key_indices"]!!.jsonArray.map { it.jsonPrimitive.int }
+            val expected = XonlyPublicKey(ByteVector32.fromValidHex(it.jsonObject["expected"]!!.jsonPrimitive.content))
+            val (aggkey, _) = KeyAggCache.add(keyIndices.map { pubkeys[it] }, null)
+            assertEquals(expected, aggkey)
+        }
+        tests.jsonObject["error_test_cases"]!!.jsonArray.forEach {
+            val keyIndices = it.jsonObject["key_indices"]!!.jsonArray.map { it.jsonPrimitive.int }
+            val tweakIndices = it.jsonObject["tweak_indices"]!!.jsonArray.map { it.jsonPrimitive.int }
+            val isXonly = it.jsonObject["is_xonly"]!!.jsonArray.map { it.jsonPrimitive.boolean }
+            assertFails {
+                var (_, cache) = KeyAggCache.add(keyIndices.map { pubkeys[it] }, null)
+                tweakIndices.zip(isXonly).forEach { cache = cache.tweak(tweaks[it.first], it.second).first }
+            }
+        }
+    }
+
+    @Test
+    fun `generate secret nonce`() {
+        val tests = TransactionTestsCommon.readData("musig2/nonce_gen_vectors.json")
+        tests.jsonObject["test_cases"]!!.jsonArray.forEach {
+            val randprime = ByteVector32.fromValidHex(it.jsonObject["rand_"]!!.jsonPrimitive.content)
+            val sk = it.jsonObject["sk"]?.jsonPrimitive?.contentOrNull?.let { PrivateKey.fromHex(it) }
+            val pk = PublicKey.fromHex(it.jsonObject["pk"]!!.jsonPrimitive.content)
+            val aggpk = it.jsonObject["aggpk"]?.jsonPrimitive?.contentOrNull?.let { XonlyPublicKey(ByteVector32.fromValidHex(it)) }
+            val msg = it.jsonObject["msg"]?.jsonPrimitive?.contentOrNull?.let { Hex.decode(it) }
+            val extraInput = it.jsonObject["extra_in"]?.jsonPrimitive?.contentOrNull?.let { Hex.decode(it) }
+            //val expectedSecnonce = SecretNonce(it.jsonObject["expected_secnonce"]!!.jsonPrimitive.content)
+            val expectedPubnonce = IndividualNonce(it.jsonObject["expected_pubnonce"]!!.jsonPrimitive.content)
+            if (aggpk == null) {
+                val (_, pubnonce) = SecretNonce.generate(randprime, sk, pk, msg?.byteVector32(), null, extraInput?.byteVector32())
+                // assertEquals(expectedSecnonce, secnonce)
+                assertEquals(expectedPubnonce, pubnonce)
+            }
+        }
+    }
+
+    @Test
+    fun `aggregate nonces`() {
+        val tests = TransactionTestsCommon.readData("musig2/nonce_agg_vectors.json")
+        val nonces = tests.jsonObject["pnonces"]!!.jsonArray.map { IndividualNonce(it.jsonPrimitive.content) }
+        tests.jsonObject["valid_test_cases"]!!.jsonArray.forEach {
+            val nonceIndices = it.jsonObject["pnonce_indices"]!!.jsonArray.map { it.jsonPrimitive.int }
+            val expected = AggregatedNonce(it.jsonObject["expected"]!!.jsonPrimitive.content)
+            val agg = IndividualNonce.aggregate(nonceIndices.map { nonces[it] })
+            assertEquals(expected, agg)
+        }
+        tests.jsonObject["error_test_cases"]!!.jsonArray.forEach {
+            val nonceIndices = it.jsonObject["pnonce_indices"]!!.jsonArray.map { it.jsonPrimitive.int }
+            assertFails {
+                IndividualNonce.aggregate(nonceIndices.map { nonces[it] })
+            }
+        }
+    }
+
+    @Test
+    fun `aggregate signatures`() {
+        val tests = TransactionTestsCommon.readData("musig2/sig_agg_vectors.json")
+        val pubkeys = tests.jsonObject["pubkeys"]!!.jsonArray.map { PublicKey(ByteVector(it.jsonPrimitive.content)) }
+        val pnonces = tests.jsonObject["pnonces"]!!.jsonArray.map { IndividualNonce(it.jsonPrimitive.content) }
+        val tweaks = tests.jsonObject["tweaks"]!!.jsonArray.map { ByteVector32.fromValidHex(it.jsonPrimitive.content) }
+        val psigs = tests.jsonObject["psigs"]!!.jsonArray.map { ByteVector32.fromValidHex(it.jsonPrimitive.content) }
+        val msg = ByteVector32.fromValidHex(tests.jsonObject["msg"]!!.jsonPrimitive.content)
+
+        tests.jsonObject["valid_test_cases"]!!.jsonArray.forEach {
+            val keyIndices = it.jsonObject["key_indices"]!!.jsonArray.map { it.jsonPrimitive.int }
+            val nonceIndices = it.jsonObject["nonce_indices"]!!.jsonArray.map { it.jsonPrimitive.int }
+            val psigIndices = it.jsonObject["psig_indices"]!!.jsonArray.map { it.jsonPrimitive.int }
+            val expected = ByteVector64.fromValidHex(it.jsonObject["expected"]!!.jsonPrimitive.content)
+            val aggnonce = IndividualNonce.aggregate(nonceIndices.map { pnonces[it] })
+            val tweakIndices = it.jsonObject["tweak_indices"]!!.jsonArray.map { it.jsonPrimitive.int }
+            val isXonly = it.jsonObject["is_xonly"]!!.jsonArray.map { it.jsonPrimitive.boolean }
+            assertEquals(AggregatedNonce(it.jsonObject["aggnonce"]!!.jsonPrimitive.content), aggnonce)
+            val cache = run {
+                var (_, c) = KeyAggCache.add(keyIndices.map { pubkeys[it] }, null)
+                tweakIndices.zip(isXonly).map { tweaks[it.first] to it.second }.forEach { (tweak, isXonly) ->
+                    c = c.tweak(tweak, isXonly).first
+                }
+                c
+            }
+            val session = Session.build(aggnonce, msg, cache)
+            val aggsig = session.add(psigIndices.map { psigs[it] })
+            assertEquals(expected, aggsig)
+        }
+        tests.jsonObject["error_test_cases"]!!.jsonArray.forEach {
+            val keyIndices = it.jsonObject["key_indices"]!!.jsonArray.map { it.jsonPrimitive.int }
+            val nonceIndices = it.jsonObject["nonce_indices"]!!.jsonArray.map { it.jsonPrimitive.int }
+            val psigIndices = it.jsonObject["psig_indices"]!!.jsonArray.map { it.jsonPrimitive.int }
+            val aggnonce = IndividualNonce.aggregate(nonceIndices.map { pnonces[it] })
+            val tweakIndices = it.jsonObject["tweak_indices"]!!.jsonArray.map { it.jsonPrimitive.int }
+            val isXonly = it.jsonObject["is_xonly"]!!.jsonArray.map { it.jsonPrimitive.boolean }
+            assertEquals(AggregatedNonce(it.jsonObject["aggnonce"]!!.jsonPrimitive.content), aggnonce)
+            val cache = run {
+                var (_, c) = KeyAggCache.add(keyIndices.map { pubkeys[it] }, null)
+                tweakIndices.zip(isXonly).map { tweaks[it.first] to it.second }.forEach { (tweak, isXonly) ->
+                    c = c.tweak(tweak, isXonly).first
+                }
+                c
+            }
+            val session = Session.build(aggnonce, msg, cache)
+            assertFails {
+                session.add(psigIndices.map { psigs[it] })
+            }
+        }
+    }
+
+    @Test
+    fun `simple musig2 example`() {
+        val random = Random.Default
+        val msg = random.nextBytes(32).byteVector32()
+
+        val privkeys = listOf(
+            PrivateKey(ByteArray(32) { 1 }),
+            PrivateKey(ByteArray(32) { 2 }),
+            PrivateKey(ByteArray(32) { 3 }),
+        )
+        val pubkeys = privkeys.map { it.publicKey() }
+
+        val plainTweak = ByteVector32("this could be a BIP32 tweak....".encodeToByteArray() + ByteArray(1))
+        val xonlyTweak = ByteVector32("this could be a taproot tweak..".encodeToByteArray() + ByteArray(1))
+
+        val aggsig = run {
+            val nonces = privkeys.map {
+                SecretNonce.generate(random.nextBytes(32).byteVector32(), it, it.publicKey(), null, null, null)
+            }
+            val secnonces = nonces.map { it.first }
+            val pubnonces = nonces.map { it.second }
+
+            // aggregate public nonces
+            val aggnonce = IndividualNonce.aggregate(pubnonces)
+            val cache = run {
+                val (_, c) = KeyAggCache.add(pubkeys, null)
+                val (c1, _) = c.tweak(plainTweak, false)
+                val (c2, _) = c1.tweak(xonlyTweak, true)
+                c2
+            }
+            val session = Session.build(aggnonce, msg, cache)
+            // create partial signatures
+            val psigs = privkeys.indices.map {
+                session.sign(secnonces[it], privkeys[it], cache)
+            }
+
+            // verify partial signatures
+            pubkeys.indices.forEach {
+                assertTrue(session.verify(psigs[it], pubnonces[it], pubkeys[it], cache))
+            }
+
+            // aggregate partial signatures
+            session.add(psigs)
+        }
+
+        // aggregate public keys
+        val aggpub = run {
+            val (_, c) = KeyAggCache.add(pubkeys, null)
+            val (c1, _) = c.tweak(plainTweak, false)
+            val (_, p) = c1.tweak(xonlyTweak, true)
+            p
+        }
+
+        // check that the aggregated signature is a valid, plain Schnorr signature for the aggregated public key
+        assertTrue(Crypto.verifySignatureSchnorr(msg, aggsig, aggpub.xOnly()))
+    }
+
+    @Test
+    fun `use musig2 to replace multisig 2-of-2`() {
+        val alicePrivKey = PrivateKey(ByteArray(32) { 1 })
+        val alicePubKey = alicePrivKey.publicKey()
+        val bobPrivKey = PrivateKey(ByteArray(32) { 2 })
+        val bobPubKey = bobPrivKey.publicKey()
+
+        // Alice and Bob exchange public keys and agree on a common aggregated key
+        val (internalPubKey, cache) = KeyAggCache.add(listOf(alicePubKey, bobPubKey), null)
+        // we use the standard BIP86 tweak
+        val commonPubKey = internalPubKey.outputKey(Crypto.TaprootTweak.NoScriptTweak).first
+
+        // this tx sends to a standard p2tr(commonPubKey) script
+        val tx = Transaction(2, listOf(), listOf(TxOut(Satoshi(10000), Script.pay2tr(commonPubKey))), 0)
+
+        // this is how Alice and Bob would spend that tx
+        val spendingTx = Transaction(2, listOf(TxIn(OutPoint(tx, 0), sequence = 0)), listOf(TxOut(Satoshi(10000), Script.pay2wpkh(alicePubKey))), 0)
+
+        val commonSig = run {
+            val random = kotlin.random.Random.Default
+            val aliceNonce = SecretNonce.generate(random.nextBytes(32).byteVector32(), alicePrivKey, alicePubKey, null, cache, null)
+            val bobNonce = SecretNonce.generate(random.nextBytes(32).byteVector32(), bobPrivKey, bobPubKey, null, null, null)
+
+            val aggnonce = IndividualNonce.aggregate(listOf(aliceNonce.second, bobNonce.second))
+            val msg = Transaction.hashForSigningSchnorr(spendingTx, 0, listOf(tx.txOut[0]), SigHash.SIGHASH_DEFAULT, SigVersion.SIGVERSION_TAPROOT)
+
+            // we use the same ctx for Alice and Bob, they both know all the public keys that are used here
+            val (cache1, _) = cache.tweak(internalPubKey.tweak(Crypto.TaprootTweak.NoScriptTweak), true)
+            val session = Session.build(aggnonce, msg, cache1)
+            val aliceSig = session.sign(aliceNonce.first, alicePrivKey, cache1)
+            val bobSig = session.sign(bobNonce.first, bobPrivKey, cache1)
+            session.add(listOf(aliceSig, bobSig))
+        }
+
+        // this tx looks like any other tx that spends a p2tr output, with a single signature
+        val signedSpendingTx = spendingTx.updateWitness(0, ScriptWitness(listOf(commonSig)))
+        Transaction.correctlySpends(signedSpendingTx, tx, ScriptFlags.STANDARD_SCRIPT_VERIFY_FLAGS)
+    }
+
+    @Test
+    fun `swap-in-potentiam example with musig2 and taproot`() {
+        val userPrivateKey = PrivateKey(ByteArray(32) { 1 })
+        val serverPrivateKey = PrivateKey(ByteArray(32) { 2 })
+        val userRefundPrivateKey = PrivateKey(ByteArray(32) { 3 })
+        val refundDelay = 25920
+
+        val random = Random.Default
+
+        // the redeem script is just the refund script. it is generated from this policy: and_v(v:pk(user),older(refundDelay))
+        // it does not depend upon the user's or server's key, just the user's refund key and the refund delay
+        val redeemScript = listOf(OP_PUSHDATA(userRefundPrivateKey.publicKey().xOnly()), OP_CHECKSIGVERIFY, OP_PUSHDATA(Script.encodeNumber(refundDelay)), OP_CHECKSEQUENCEVERIFY)
+        val scriptTree = ScriptTree.Leaf(0, redeemScript)
+        val merkleRoot = scriptTree.hash()
+
+        // the internal pubkey is the musig2 aggregation of the user's and server's public keys: it does not depend upon the user's refund's key
+        val (internalPubKey, cache) = KeyAggCache.add(listOf(userPrivateKey.publicKey(), serverPrivateKey.publicKey()), null)
+
+        // it is tweaked with the script's merkle root to get the pubkey that will be exposed
+        val pubkeyScript: List<ScriptElt> = Script.pay2tr(internalPubKey, merkleRoot)
+
+        val swapInTx = Transaction(
+            version = 2,
+            txIn = listOf(),
+            txOut = listOf(TxOut(Satoshi(10000), pubkeyScript)),
+            lockTime = 0
+        )
+
+        // The transaction can be spent if the user and the server produce a signature.
+        run {
+            val tx = Transaction(
+                version = 2,
+                txIn = listOf(TxIn(OutPoint(swapInTx, 0), sequence = TxIn.SEQUENCE_FINAL)),
+                txOut = listOf(TxOut(Satoshi(10000), Script.pay2wpkh(userPrivateKey.publicKey()))),
+                lockTime = 0
+            )
+            // this is the beginning of an interactive musig2 signing session. if user and server are disconnected before they have exchanged partial
+            // signatures they will have to start again with fresh nonces
+            val userNonce = SecretNonce.generate(random.nextBytes(32).byteVector32(), userPrivateKey, userPrivateKey.publicKey(), null, cache, null)
+            val serverNonce = SecretNonce.generate(random.nextBytes(32).byteVector32(), serverPrivateKey, serverPrivateKey.publicKey(), null, cache, null)
+
+            val txHash = Transaction.hashForSigningSchnorr(tx, 0, swapInTx.txOut, SigHash.SIGHASH_DEFAULT, SigVersion.SIGVERSION_TAPROOT)
+            val commonNonce = IndividualNonce.aggregate(listOf(userNonce.second, serverNonce.second))
+
+            val (cache1, _) = cache.tweak(internalPubKey.tweak(Crypto.TaprootTweak.ScriptTweak(merkleRoot)), true)
+            val session = Session.build(commonNonce, txHash, cache1)
+            val userSig = session.sign(userNonce.first, userPrivateKey, cache1)
+            val serverSig = session.sign(serverNonce.first, serverPrivateKey, cache1)
+            val commonSig = session.add(listOf(userSig, serverSig))
+            val signedTx = tx.updateWitness(0, ScriptWitness(listOf(commonSig)))
+            Transaction.correctlySpends(signedTx, swapInTx, ScriptFlags.STANDARD_SCRIPT_VERIFY_FLAGS)
+        }
+
+        // Or it can be spent with only the user's signature, after a delay.
+        run {
+            val tx = Transaction(
+                version = 2,
+                txIn = listOf(TxIn(OutPoint(swapInTx, 0), sequence = refundDelay.toLong())),
+                txOut = listOf(TxOut(Satoshi(10000), Script.pay2wpkh(userPrivateKey.publicKey()))),
+                lockTime = 0
+            )
+            val sig = Crypto.signTaprootScriptPath(userRefundPrivateKey, tx, 0, swapInTx.txOut, SigHash.SIGHASH_DEFAULT, merkleRoot)
+            val signedTx = tx.updateWitness(0, Script.witnessScriptPathPay2tr(internalPubKey, scriptTree, ScriptWitness(listOf(sig)), scriptTree))
+            Transaction.correctlySpends(signedTx, swapInTx, ScriptFlags.STANDARD_SCRIPT_VERIFY_FLAGS)
+        }
+    }
+}
\ No newline at end of file