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Simplify musig2 nonce generation API (no functional changes) #161

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sstone merged 1 commit into from
Sep 18, 2025
Merged

Simplify musig2 nonce generation API (no functional changes) #161

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52 changes: 45 additions & 7 deletions src/commonMain/kotlin/fr/acinq/bitcoin/crypto/musig2/Musig2.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -136,22 +136,45 @@ public data class SecretNonce(internal val data: ByteVector) {
* All optional arguments exist to enrich the quality of the randomness used, which is critical for security.
*
* @param sessionId unique session ID.
* @param privateKey (optional) signer's private key.
* @param publicKey signer's public key.
* @param signingKey signer's private key or public key.
* @param message (optional) message that will be signed, if already known.
* @param keyAggCache (optional) key aggregation cache data from the signing session.
* @param extraInput (optional) additional random data.
* @return secret nonce and the corresponding public nonce.
*/
@JvmStatic
public fun generate(sessionId: ByteVector32, privateKey: PrivateKey?, publicKey: PublicKey, message: ByteVector32?, keyAggCache: KeyAggCache?, extraInput: ByteVector32?): Pair<SecretNonce, IndividualNonce> {
privateKey?.let { require(it.publicKey() == publicKey) { "if the private key is provided, it must match the public key" } }
public fun generate(sessionId: ByteVector32, signingKey: Either<PrivateKey, PublicKey>, message: ByteVector32?, keyAggCache: KeyAggCache?, extraInput: ByteVector32?): Pair<SecretNonce, IndividualNonce> {
val (privateKey, publicKey) = when (signingKey) {
is Either.Left -> Pair(signingKey.value, signingKey.value.publicKey())
is Either.Right -> Pair(null, signingKey.value)
}
val nonce = Secp256k1.musigNonceGen(sessionId.toByteArray(), privateKey?.value?.toByteArray(), publicKey.value.toByteArray(), message?.toByteArray(), keyAggCache?.toByteArray(), extraInput?.toByteArray())
val secretNonce = SecretNonce(nonce.copyOfRange(0, Secp256k1.MUSIG2_SECRET_NONCE_SIZE))
val publicNonce = IndividualNonce(nonce.copyOfRange(Secp256k1.MUSIG2_SECRET_NONCE_SIZE, Secp256k1.MUSIG2_SECRET_NONCE_SIZE + Secp256k1.MUSIG2_PUBLIC_NONCE_SIZE))
return Pair(secretNonce, publicNonce)
}

/**
* Generate a secret nonce to be used in a musig2 signing session.
* This nonce must never be persisted or reused across signing sessions.
* All optional arguments exist to enrich the quality of the randomness used, which is critical for security.
*
* @param sessionId unique session ID.
* @param privateKey (optional) signer's private key.
* @param publicKey signer's public key.
* @param message (optional) message that will be signed, if already known.
* @param keyAggCache (optional) key aggregation cache data from the signing session.
* @param extraInput (optional) additional random data.
* @return secret nonce and the corresponding public nonce.
*/
@Deprecated("Use generate() with an Either<PrivateKey, PublicKey> instead", ReplaceWith("generate()"), DeprecationLevel.WARNING)
@JvmStatic
public fun generate(sessionId: ByteVector32, privateKey: PrivateKey?, publicKey: PublicKey, message: ByteVector32?, keyAggCache: KeyAggCache?, extraInput: ByteVector32?): Pair<SecretNonce, IndividualNonce> {
privateKey?.let { require(it.publicKey() == publicKey) { "if the private key is provided, it must match the public key" } }
val signingKey = privateKey?.let { Either.Left(it) } ?: Either.Right(publicKey)
return generate(sessionId, signingKey, message, keyAggCache, extraInput)
}

/**
* Alternative counter-based method for generating nonce.
* This nonce must never be persisted or reused across signing sessions.
Expand Down Expand Up @@ -236,7 +259,20 @@ public object Musig2 {
*/
@JvmStatic
public fun aggregateKeys(publicKeys: List<PublicKey>): XonlyPublicKey = KeyAggCache.create(publicKeys).first


/**
* @param sessionId a random, unique session ID.
* @param signingKey signer's private key or public key
* @param publicKeys public keys of all participants: callers must verify that all public keys are valid.
* @param message (optional) message that will be signed, if already known.
* @param extraInput (optional) additional random data.
*/
@JvmStatic
public fun generateNonce(sessionId: ByteVector32, signingKey: Either<PrivateKey, PublicKey>, publicKeys: List<PublicKey>, message: ByteVector32?, extraInput: ByteVector32?): Pair<SecretNonce, IndividualNonce> {
val (_, keyAggCache) = KeyAggCache.create(publicKeys)
return SecretNonce.generate(sessionId, signingKey, message, keyAggCache, extraInput)
}

/**
* @param sessionId a random, unique session ID.
* @param privateKey signer's private key
Expand All @@ -245,10 +281,12 @@ public object Musig2 {
* @param message (optional) message that will be signed, if already known.
* @param extraInput (optional) additional random data.
*/
@Deprecated("Use generateNonce() with an Either<PrivateKey, PublicKey> instead", ReplaceWith("generateNonce()"), DeprecationLevel.WARNING)
@JvmStatic
public fun generateNonce(sessionId: ByteVector32, privateKey: PrivateKey?, publicKey: PublicKey, publicKeys: List<PublicKey>, message: ByteVector32?, extraInput: ByteVector32?): Pair<SecretNonce, IndividualNonce> {
val (_, keyAggCache) = KeyAggCache.create(publicKeys)
return SecretNonce.generate(sessionId, privateKey, publicKey, message, keyAggCache, extraInput)
privateKey?.let { require(it.publicKey() == publicKey) { "if the private key is provided, it must match the public key" } }
val signingKey = privateKey?.let { Either.Left(it) } ?: Either.Right(publicKey)
return generateNonce(sessionId, signingKey, publicKeys, message, extraInput)
}

/**
Expand Down
17 changes: 9 additions & 8 deletions src/commonTest/kotlin/fr/acinq/bitcoin/crypto/musig2/Musig2TestsCommon.kt
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Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
package fr.acinq.bitcoin.crypto.musig2

import fr.acinq.bitcoin.*
import fr.acinq.bitcoin.utils.Either
import fr.acinq.secp256k1.Hex
import kotlinx.serialization.json.*
import kotlin.random.Random
Expand Down Expand Up @@ -76,7 +77,7 @@ class Musig2TestsCommon {
val expectedPubnonce = IndividualNonce(it.jsonObject["expected_pubnonce"]!!.jsonPrimitive.content)
// secp256k1 only supports signing 32-byte messages (when provided), which excludes some of the test vectors.
if (msg == null || msg.size == 32) {
val (secnonce, pubnonce) = SecretNonce.generate(randprime, sk, pk, msg?.byteVector32(), keyagg, extraInput?.byteVector32())
val (secnonce, pubnonce) = SecretNonce.generate(randprime, sk?.let { Either.Left(it) } ?: Either.Right(pk), msg?.byteVector32(), keyagg, extraInput?.byteVector32())
assertEquals(expectedPubnonce, pubnonce)
assertEquals(expectedSecnonce, secnonce)
}
Expand Down Expand Up @@ -278,7 +279,7 @@ class Musig2TestsCommon {
}

// Generate secret nonces for each participant.
val nonces = privkeys.map { SecretNonce.generate(Random.Default.nextBytes(32).byteVector32(), it, it.publicKey(), message = null, keyAggCache, extraInput = null) }
val nonces = privkeys.map { SecretNonce.generate(Random.Default.nextBytes(32).byteVector32(), Either.Left(it), message = null, keyAggCache, extraInput = null) }
val secnonces = nonces.map { it.first }
val pubnonces = nonces.map { it.second }

Expand Down Expand Up @@ -316,8 +317,8 @@ class Musig2TestsCommon {

// The first step of a musig2 signing session is to exchange nonces.
// If participants are disconnected before the end of the signing session, they must start again with fresh nonces.
val aliceNonce = Musig2.generateNonce(Random.Default.nextBytes(32).byteVector32(), alicePrivKey, alicePrivKey.publicKey(), listOf(alicePubKey, bobPubKey), null, null)
val bobNonce = Musig2.generateNonce(Random.Default.nextBytes(32).byteVector32(), bobPrivKey, bobPrivKey.publicKey(), listOf(alicePubKey, bobPubKey), null, null)
val aliceNonce = Musig2.generateNonce(Random.Default.nextBytes(32).byteVector32(), Either.Left(alicePrivKey), listOf(alicePubKey, bobPubKey), null, null)
val bobNonce = Musig2.generateNonce(Random.Default.nextBytes(32).byteVector32(), Either.Left(bobPrivKey), listOf(alicePubKey, bobPubKey), null, null)

// Once they have each other's public nonce, they can produce partial signatures.
val publicNonces = listOf(aliceNonce.second, bobNonce.second)
Expand Down Expand Up @@ -354,8 +355,8 @@ class Musig2TestsCommon {
val tx = Transaction(2, listOf(), listOf(TxOut(10_000.sat(), Script.pay2tr(commonPubKey))), 0)
val spendingTx = Transaction(2, listOf(TxIn(OutPoint(tx, 0), sequence = 0)), listOf(TxOut(10_000.sat(), Script.pay2wpkh(alicePubKey))), 0)

val aliceNonce = Musig2.generateNonce(Random.Default.nextBytes(32).byteVector32(), alicePrivKey, alicePrivKey.publicKey(),listOf(alicePubKey, bobPubKey), null, null)
val bobNonce = Musig2.generateNonce(Random.Default.nextBytes(32).byteVector32(), bobPrivKey, bobPrivKey.publicKey(), listOf(alicePubKey, bobPubKey), null, null)
val aliceNonce = Musig2.generateNonce(Random.Default.nextBytes(32).byteVector32(), Either.Left(alicePrivKey), listOf(alicePubKey, bobPubKey), null, null)
val bobNonce = Musig2.generateNonce(Random.Default.nextBytes(32).byteVector32(), Either.Left(bobPrivKey), listOf(alicePubKey, bobPubKey), null, null)
val publicNonces = listOf(aliceNonce.second, bobNonce.second)

val aliceSig = Musig2.signTaprootInput(alicePrivKey, spendingTx, 0, listOf(tx.txOut[0]), listOf(alicePubKey, bobPubKey), aliceNonce.first, publicNonces, scriptTree = null).right
Expand Down Expand Up @@ -411,8 +412,8 @@ class Musig2TestsCommon {
)
// The first step of a musig2 signing session is to exchange nonces.
// If participants are disconnected before the end of the signing session, they must start again with fresh nonces.
val userNonce = Musig2.generateNonce(Random.Default.nextBytes(32).byteVector32(), userPrivateKey, userPrivateKey.publicKey(), listOf(userPublicKey, serverPublicKey), null, null)
val serverNonce = Musig2.generateNonce(Random.Default.nextBytes(32).byteVector32(), serverPrivateKey, serverPrivateKey.publicKey(), listOf(userPublicKey, serverPublicKey), null, null)
val userNonce = Musig2.generateNonce(Random.Default.nextBytes(32).byteVector32(), Either.Left(userPrivateKey), listOf(userPublicKey, serverPublicKey), null, null)
val serverNonce = Musig2.generateNonce(Random.Default.nextBytes(32).byteVector32(), Either.Left(serverPrivateKey), listOf(userPublicKey, serverPublicKey), null, null)

// Once they have each other's public nonce, they can produce partial signatures.
val publicNonces = listOf(userNonce.second, serverNonce.second)
Expand Down