Add API commands to sign & verify arbitrary messages (#1499)

It can be useful to sign arbitrary messages with the key associated with our node_id (to prove ownership of a node).

Adds 2 new API commands:
  eclair-cli signmessage --msg=${message}
  eclair-cli verifymessage --msg=${message} --sig=${signature}

eclair-core/src/main/scala/fr/acinq/eclair/Eclair.scala

@@ -16,13 +16,14 @@
 
 package fr.acinq.eclair
 
+import java.nio.charset.StandardCharsets
 import java.util.UUID
 
 import akka.actor.ActorRef
 import akka.pattern._
 import akka.util.Timeout
 import fr.acinq.bitcoin.Crypto.PublicKey
-import fr.acinq.bitcoin.{ByteVector32, Crypto, Satoshi}
+import fr.acinq.bitcoin.{ByteVector32, ByteVector64, Crypto, Satoshi}
 import fr.acinq.eclair.TimestampQueryFilters._
 import fr.acinq.eclair.blockchain.OnChainBalance
 import fr.acinq.eclair.blockchain.bitcoind.BitcoinCoreWallet
@@ -38,7 +39,7 @@ import fr.acinq.eclair.payment.relay.Relayer.{GetOutgoingChannels, OutgoingChann
 import fr.acinq.eclair.payment.send.PaymentInitiator.{SendPaymentRequest, SendPaymentToRouteRequest, SendPaymentToRouteResponse}
 import fr.acinq.eclair.router.Router._
 import fr.acinq.eclair.router.{NetworkStats, RouteCalculation}
-import fr.acinq.eclair.wire.{ChannelAnnouncement, ChannelUpdate, NodeAddress, NodeAnnouncement, GenericTlv}
+import fr.acinq.eclair.wire._
 import scodec.bits.ByteVector
 
 import scala.concurrent.duration._
@@ -51,6 +52,10 @@ case class AuditResponse(sent: Seq[PaymentSent], received: Seq[PaymentReceived],
 
 case class TimestampQueryFilters(from: Long, to: Long)
 
+case class SignedMessage(nodeId: PublicKey, message: String, signature: ByteVector)
+
+case class VerifiedMessage(valid: Boolean, publicKey: PublicKey)
+
 object TimestampQueryFilters {
   /** We use this in the context of timestamp filtering, when we don't need an upper bound. */
   val MaxEpochMilliseconds = Duration.fromNanos(Long.MaxValue).toMillis
@@ -64,6 +69,11 @@ object TimestampQueryFilters {
   }
 }
 
+object SignedMessage {
+  def signedBytes(message: ByteVector): ByteVector32 =
+    Crypto.hash256(ByteVector("Lightning Signed Message:".getBytes(StandardCharsets.UTF_8)) ++ message)
+}
+
 object ApiTypes {
   type ChannelIdentifier = Either[ByteVector32, ShortChannelId]
 }
@@ -134,6 +144,9 @@ trait Eclair {
 
   def onChainTransactions(count: Int, skip: Int): Future[Iterable[WalletTransaction]]
 
+  def signMessage(message: ByteVector): SignedMessage
+
+  def verifyMessage(message: ByteVector, recoverableSignature: ByteVector): VerifiedMessage
 }
 
 class EclairImpl(appKit: Kit) extends Eclair {
@@ -393,4 +406,18 @@ class EclairImpl(appKit: Kit) extends Eclair {
     val sendPayment = SendPaymentRequest(amount, paymentHash, recipientNodeId, maxAttempts, externalId = externalId_opt, routeParams = Some(routeParams), userCustomTlvs = keySendTlvRecords)
     (appKit.paymentInitiator ? sendPayment).mapTo[UUID]
   }
+
+  override def signMessage(message: ByteVector): SignedMessage = {
+    val bytesToSign = SignedMessage.signedBytes(message)
+    val (signature, recoveryId) = appKit.nodeParams.keyManager.signDigest(bytesToSign)
+    SignedMessage(appKit.nodeParams.nodeId, message.toBase64, (recoveryId + 31).toByte +: signature)
+  }
+
+  override def verifyMessage(message: ByteVector, recoverableSignature: ByteVector): VerifiedMessage = {
+    val signedBytes = SignedMessage.signedBytes(message)
+    val signature = ByteVector64(recoverableSignature.tail)
+    val recoveryId = recoverableSignature.head.toInt - 31
+    val pubKeyFromSignature = Crypto.recoverPublicKey(signature, signedBytes, recoveryId)
+    VerifiedMessage(true, pubKeyFromSignature)
+  }
 }

eclair-core/src/main/scala/fr/acinq/eclair/crypto/KeyManager.scala

@@ -110,6 +110,19 @@ trait KeyManager {
    *         private key, bitcoinSig is the signature of the channel announcement with our funding private key
    */
   def signChannelAnnouncement(fundingKeyPath: DeterministicWallet.KeyPath, chainHash: ByteVector32, shortChannelId: ShortChannelId, remoteNodeId: PublicKey, remoteFundingKey: PublicKey, features: Features): (ByteVector64, ByteVector64)
+
+  /**
+   * Sign a digest, primarily used to prove ownership of the current node
+   *
+   * When recovering a public key from an ECDSA signature for secp256k1, there are 4 possible matching curve points
+   * that can be found. The recoveryId identifies which of these points is the correct.
+   *
+   * @param digest     SHA256 digest
+   * @param privateKey private key to sign with, default the one from the current node
+   * @return a (signature, recoveryId) pair. signature is a signature of the digest parameter generated with the
+   *         private key given in parameter. recoveryId is the corresponding recoveryId of the signature
+   */
+  def signDigest(digest: ByteVector32, privateKey: PrivateKey = nodeKey.privateKey): (ByteVector64, Int)
 }
 
 object KeyManager {

eclair-core/src/main/scala/fr/acinq/eclair/crypto/LocalKeyManager.scala

@@ -153,4 +153,11 @@ class LocalKeyManager(seed: ByteVector, chainHash: ByteVector32) extends KeyMana
     val localFundingPrivKey = privateKeys.get(fundingKeyPath).privateKey
     Announcements.signChannelAnnouncement(chainHash, shortChannelId, localNodeSecret, remoteNodeId, localFundingPrivKey, remoteFundingKey, features)
   }
-}
+
+  override def signDigest(digest: ByteVector32, privateKey: PrivateKey = nodeKey.privateKey): (ByteVector64, Int) = {
+    val signature = Crypto.sign(digest, privateKey)
+    val (pub1, _) = Crypto.recoverPublicKey(signature, digest)
+    val recoveryId = if (nodeId == pub1) 0 else 1
+    (signature, recoveryId)
+  }
+}

eclair-core/src/test/scala/fr/acinq/eclair/EclairImplSpec.scala

@@ -429,4 +429,61 @@ class EclairImplSpec extends TestKitBaseClass with FixtureAnyFunSuiteLike with I
     assert(expectedPaymentPreimage === ByteVector32(keySendTlv.value))
   }
 
+  test("sign & verify an arbitrary message with the node's private key") { f =>
+    import f._
+
+    val eclair = new EclairImpl(kit)
+
+    val base64Msg = "aGVsbG8sIHdvcmxk" // echo -n 'hello, world' | base64
+    val bytesMsg = ByteVector.fromValidBase64(base64Msg)
+
+    val signedMessage: SignedMessage = eclair.signMessage(bytesMsg)
+    assert(signedMessage.nodeId === kit.nodeParams.nodeId)
+    assert(signedMessage.message === base64Msg)
+
+    val verifiedMessage: VerifiedMessage = eclair.verifyMessage(bytesMsg, signedMessage.signature)
+    assert(verifiedMessage.valid)
+    assert(verifiedMessage.publicKey === kit.nodeParams.nodeId)
+
+    val prefix = ByteVector("Lightning Signed Message:".getBytes)
+    val dhash256 = Crypto.hash256(prefix ++ bytesMsg)
+    val expectedDigest = ByteVector32(hex"cbedbc1542fb139e2e10954f1ff9f82e8a1031cc63260636bbc45a90114552ea")
+    assert(dhash256 === expectedDigest)
+    assert(Crypto.verifySignature(dhash256, ByteVector64(signedMessage.signature.tail), kit.nodeParams.nodeId))
+  }
+
+  test("verify an invalid signature for the given message") { f =>
+    import f._
+
+    val eclair = new EclairImpl(kit)
+
+    val base64Msg = "aGVsbG8sIHdvcmxk" // echo -n 'hello, world' | base64
+    val bytesMsg = ByteVector.fromValidBase64(base64Msg)
+
+    val signedMessage: SignedMessage = eclair.signMessage(bytesMsg)
+    assert(signedMessage.nodeId === kit.nodeParams.nodeId)
+    assert(signedMessage.message === base64Msg)
+
+    val wrongMsg = ByteVector.fromValidBase64(base64Msg.tail)
+    val verifiedMessage: VerifiedMessage = eclair.verifyMessage(wrongMsg, signedMessage.signature)
+    assert(verifiedMessage.valid)
+    assert(verifiedMessage.publicKey !== kit.nodeParams.nodeId)
+  }
+
+  test("ensure that an invalid recoveryId cause the signature verification to fail") { f =>
+    import f._
+
+    val eclair = new EclairImpl(kit)
+
+    val base64Msg = "aGVsbG8sIHdvcmxk" // echo -n 'hello, world' | base64
+    val bytesMsg = ByteVector.fromValidBase64(base64Msg)
+
+    val signedMessage: SignedMessage = eclair.signMessage(bytesMsg)
+    assert(signedMessage.nodeId === kit.nodeParams.nodeId)
+    assert(signedMessage.message === base64Msg)
+
+    val invalidSignature = (if (signedMessage.signature.head.toInt == 31) 32 else 31).toByte +: signedMessage.signature.tail
+    val verifiedMessage: VerifiedMessage = eclair.verifyMessage(bytesMsg, invalidSignature)
+    assert(verifiedMessage.publicKey !== kit.nodeParams.nodeId)
+  }
 }

eclair-core/src/test/scala/fr/acinq/eclair/crypto/LocalKeyManagerSpec.scala

@@ -18,7 +18,7 @@ package fr.acinq.eclair.crypto
 
 import fr.acinq.bitcoin.Crypto.{PrivateKey, PublicKey}
 import fr.acinq.bitcoin.DeterministicWallet.KeyPath
-import fr.acinq.bitcoin.{Block, ByteVector32, DeterministicWallet}
+import fr.acinq.bitcoin.{Block, ByteVector32, Crypto, DeterministicWallet}
 import fr.acinq.eclair.TestConstants
 import fr.acinq.eclair.channel.ChannelVersion
 import org.scalatest.funsuite.AnyFunSuite
@@ -69,7 +69,7 @@ class LocalKeyManagerSpec extends AnyFunSuite {
   }
 
   def makefundingKeyPath(entropy: ByteVector, isFunder: Boolean) = {
-    val items = for(i <- 0 to 7) yield entropy.drop(i * 4).take(4).toInt(signed = false) & 0xFFFFFFFFL
+    val items = for (i <- 0 to 7) yield entropy.drop(i * 4).take(4).toInt(signed = false) & 0xFFFFFFFFL
     val last = DeterministicWallet.hardened(if (isFunder) 1L else 0L)
     KeyPath(items :+ last)
   }
@@ -141,4 +141,15 @@ class LocalKeyManagerSpec extends AnyFunSuite {
     assert(keyManager.htlcPoint(channelKeyPath).publicKey == PrivateKey(hex"b1be27b5232e3bc5d6a261949b4ee68d96fa61f481998d36342e2ad99444cf8a").publicKey)
     assert(keyManager.commitmentSecret(channelKeyPath, 0).value == ShaChain.shaChainFromSeed(ByteVector32.fromValidHex("eeb3bad6808e8bb5f1774581ccf64aa265fef38eca80a1463d6310bb801b3ba7"), 0xFFFFFFFFFFFFL))
   }
+
+  test("generate a signature from a digest") {
+    val seed = hex"deadbeef"
+    val testKeyManager = new LocalKeyManager(seed, Block.RegtestGenesisBlock.hash)
+    val digest = ByteVector32(hex"d7914fe546b684688bb95f4f888a92dfc680603a75f23eb823658031fff766d9") // sha256(sha256("hello"))
+
+    val (signature, recid) = testKeyManager.signDigest(digest)
+    val recoveredPubkey = Crypto.recoverPublicKey(signature, digest, recid)
+    assert(recoveredPubkey === testKeyManager.nodeId)
+    assert(Crypto.verifySignature(digest, signature, testKeyManager.nodeId))
+  }
 }

eclair-node/src/main/scala/fr/acinq/eclair/api/FormParamExtractors.scala

@@ -21,7 +21,7 @@ import java.util.UUID
 import akka.http.scaladsl.unmarshalling.Unmarshaller
 import akka.util.Timeout
 import fr.acinq.bitcoin.Crypto.PublicKey
-import fr.acinq.bitcoin.{ByteVector32, Satoshi}
+import fr.acinq.bitcoin.{ByteVector32, ByteVector64, Satoshi}
 import fr.acinq.eclair.api.JsonSupport._
 import fr.acinq.eclair.io.NodeURI
 import fr.acinq.eclair.payment.PaymentRequest
@@ -59,6 +59,8 @@ object FormParamExtractors {
 
   implicit val millisatoshiUnmarshaller: Unmarshaller[String, MilliSatoshi] = Unmarshaller.strict { str => MilliSatoshi(str.toLong) }
 
+  implicit val base64DataUnmarshaller: Unmarshaller[String, ByteVector] = Unmarshaller.strict { str => ByteVector.fromValidBase64(str) }
+
   private def listUnmarshaller[T](unmarshal: String => T): Unmarshaller[String, List[T]] = Unmarshaller.strict { str =>
     Try(serialization.read[List[String]](str).map(unmarshal))
       .recoverWith(_ => Try(str.split(",").toList.map(unmarshal)))

eclair-node/src/main/scala/fr/acinq/eclair/api/Service.scala

@@ -36,7 +36,7 @@ import fr.acinq.bitcoin.{ByteVector32, Satoshi}
 import fr.acinq.eclair.api.FormParamExtractors._
 import fr.acinq.eclair.io.NodeURI
 import fr.acinq.eclair.payment.{PaymentEvent, PaymentRequest}
-import fr.acinq.eclair.{CltvExpiryDelta, Eclair, MilliSatoshi, randomBytes32}
+import fr.acinq.eclair.{CltvExpiryDelta, Eclair, MilliSatoshi}
 import grizzled.slf4j.Logging
 import scodec.bits.ByteVector
 
@@ -48,6 +48,7 @@ case class ErrorResponse(error: String)
 trait Service extends ExtraDirectives with Logging {
 
   // important! Must NOT import the unmarshaller as it is too generic...see https://github.com/akka/akka-http/issues/541
+
   import JsonSupport.{formats, marshaller, serialization}
 
   def password: String
@@ -226,7 +227,7 @@ trait Service extends ExtraDirectives with Logging {
                         path("sendtonode") {
                           formFields(amountMsatFormParam, nodeIdFormParam, paymentHashFormParam.?, "maxAttempts".as[Int].?, "feeThresholdSat".as[Satoshi].?, "maxFeePct".as[Double].?, "externalId".?, "keysend".as[Boolean].?) {
                             case (amountMsat, nodeId, Some(paymentHash), maxAttempts_opt, feeThresholdSat_opt, maxFeePct_opt, externalId_opt, keySend) =>
-                              keySend match  {
+                              keySend match {
                                 case Some(true) => reject(MalformedFormFieldRejection("paymentHash", "You cannot request a KeySend payment and specify a paymentHash"))
                                 case _ => complete(eclairApi.send(externalId_opt, nodeId, amountMsat, paymentHash, maxAttempts_opt = maxAttempts_opt, feeThresholdSat_opt = feeThresholdSat_opt, maxFeePct_opt = maxFeePct_opt))
                               }
@@ -310,6 +311,16 @@ trait Service extends ExtraDirectives with Logging {
                           formFields("count".as[Int].?, "skip".as[Int].?) { (count_opt, skip_opt) =>
                             complete(eclairApi.onChainTransactions(count_opt.getOrElse(10), skip_opt.getOrElse(0)))
                           }
+                        } ~
+                        path("signmessage") {
+                          formFields("msg".as[ByteVector](base64DataUnmarshaller)) { message =>
+                            complete(eclairApi.signMessage(message))
+                          }
+                        } ~
+                        path("verifymessage") {
+                          formFields("msg".as[ByteVector](base64DataUnmarshaller), "sig".as[ByteVector](binaryDataUnmarshaller)) { (message, signature) =>
+                            complete(eclairApi.verifyMessage(message, signature))
+                          }
                         }
                     } ~ get {
                       path("ws") {