Add support for blinded trampoline payments

We add support for trampoline payments to blinded recipients, where
each node of the blinded path is used as trampoline node. This is
particularly useful to include custom TLVs from the payer to the
recipient.

Author: t-bast

eclair-core/src/main/scala/fr/acinq/eclair/payment/PaymentPacket.scala

@@ -59,6 +59,7 @@ object IncomingPaymentPacket {
     def innerPayload: IntermediatePayload.NodeRelay
   }
   case class RelayToTrampolinePacket(add: UpdateAddHtlc, outerPayload: FinalPayload.Standard, innerPayload: IntermediatePayload.NodeRelay.Standard, nextPacket: OnionRoutingPacket) extends NodeRelayPacket
+  case class RelayToBlindedTrampolinePacket(add: UpdateAddHtlc, outerPayload: FinalPayload.Standard, innerPayload: IntermediatePayload.NodeRelay.Blinded, nextPacket: OnionRoutingPacket) extends NodeRelayPacket
   case class RelayToNonTrampolinePacket(add: UpdateAddHtlc, outerPayload: FinalPayload.Standard, innerPayload: IntermediatePayload.NodeRelay.ToNonTrampoline) extends NodeRelayPacket
   case class RelayToBlindedPathsPacket(add: UpdateAddHtlc, outerPayload: FinalPayload.Standard, innerPayload: IntermediatePayload.NodeRelay.ToBlindedPaths) extends NodeRelayPacket
   // @formatter:on
@@ -172,9 +173,14 @@ object IncomingPaymentPacket {
                     val totalAmount = payload.get[OnionPaymentPayloadTlv.AmountToForward].map(_.amount).getOrElse(add.amountMsat)
                     payload.copy(records = payload.records + OnionPaymentPayloadTlv.PaymentData(dummyPaymentSecret, totalAmount))
                 }
-                // NB: when we enable blinded trampoline routes, we will need to check if the outer onion contains a
-                // path key and use it to derive the decryption key for the blinded trampoline onion.
-                decryptOnion(add.paymentHash, privateKey, trampolinePacket).flatMap {
+                // If we are an intermediate trampoline node inside a blinded path, the payer doesn't know our node_id
+                // and has encrypted the trampoline onion to our blinded node_id: in that case, the previous trampoline
+                // node will provide the path key in the outer onion.
+                val trampolineOnionDecryptionKey = payload.get[OnionPaymentPayloadTlv.PathKey].map(_.publicKey) match {
+                  case Some(pathKey) => Sphinx.RouteBlinding.derivePrivateKey(privateKey, pathKey)
+                  case None => privateKey
+                }
+                decryptOnion(add.paymentHash, trampolineOnionDecryptionKey, trampolinePacket).flatMap {
                   case DecodedOnionPacket(innerPayload, Some(next)) =>
                     // We are an intermediate trampoline node.
                     if (innerPayload.get[InvoiceRoutingInfo].isDefined) {
@@ -183,7 +189,8 @@ object IncomingPaymentPacket {
                       // The payer is a wallet using the legacy trampoline feature.
                       validateTrampolineToNonTrampoline(add, outerPayload, innerPayload)
                     } else {
-                      validateNodeRelay(add, outerPayload, innerPayload, next)
+                      // The recipient supports trampoline (and may support blinded payments).
+                      validateNodeRelay(add, privateKey, outerPayload, innerPayload, next)
                     }
                   case DecodedOnionPacket(innerPayload, None) =>
                     if (innerPayload.get[OutgoingBlindedPaths].isDefined) {
@@ -195,8 +202,8 @@ object IncomingPaymentPacket {
                       // They can be reached with the invoice data provided.
                       validateTrampolineToNonTrampoline(add, outerPayload, innerPayload)
                     } else {
-                      // We're the final recipient of this trampoline payment.
-                      validateTrampolineFinalPayload(add, outerPayload, innerPayload)
+                      // We're the final recipient of this trampoline payment (which may be blinded).
+                      validateTrampolineFinalPayload(add, privateKey, outerPayload, innerPayload)
                     }
                 }
               case None =>
@@ -238,31 +245,50 @@ object IncomingPaymentPacket {
     }
   }
 
-  private def validateTrampolineFinalPayload(add: UpdateAddHtlc, outerPayload: TlvStream[OnionPaymentPayloadTlv], innerPayload: TlvStream[OnionPaymentPayloadTlv]): Either[FailureMessage, FinalPacket] = {
-    // The outer payload cannot use route blinding, but the inner payload may (but it's not supported yet).
-    FinalPayload.Standard.validate(outerPayload).left.map(_.failureMessage).flatMap { outerPayload =>
-      FinalPayload.Standard.validate(innerPayload).left.map(_.failureMessage).flatMap {
-        case _ if add.amountMsat < outerPayload.amount => Left(FinalIncorrectHtlcAmount(add.amountMsat))
-        case _ if add.cltvExpiry < outerPayload.expiry => Left(FinalIncorrectCltvExpiry(add.cltvExpiry))
-        case innerPayload if outerPayload.expiry < innerPayload.expiry => Left(FinalIncorrectCltvExpiry(add.cltvExpiry)) // previous trampoline didn't forward the right expiry
-        case innerPayload if outerPayload.totalAmount < innerPayload.amount => Left(FinalIncorrectHtlcAmount(outerPayload.totalAmount)) // previous trampoline didn't forward the right amount
-        case innerPayload =>
-          // We merge contents from the outer and inner payloads.
-          // We must use the inner payload's total amount and payment secret because the payment may be split between multiple trampoline payments (#reckless).
-          val trampolinePacket = outerPayload.records.get[OnionPaymentPayloadTlv.TrampolineOnion].map(_.packet)
-          Right(FinalPacket(add, FinalPayload.Standard.createPayload(outerPayload.amount, innerPayload.totalAmount, innerPayload.expiry, innerPayload.paymentSecret, innerPayload.paymentMetadata, trampolinePacket)))
-      }
+  private def validateTrampolineFinalPayload(add: UpdateAddHtlc, privateKey: PrivateKey, outerPayload: TlvStream[OnionPaymentPayloadTlv], innerPayload: TlvStream[OnionPaymentPayloadTlv]): Either[FailureMessage, FinalPacket] = {
+    // The outer payload cannot use route blinding, but the inner payload may.
+    FinalPayload.Standard.validate(outerPayload).left.map(_.failureMessage).flatMap {
+      case outerPayload if add.amountMsat < outerPayload.amount => Left(FinalIncorrectHtlcAmount(add.amountMsat))
+      case outerPayload if add.cltvExpiry < outerPayload.expiry => Left(FinalIncorrectCltvExpiry(add.cltvExpiry))
+      case outerPayload =>
+        innerPayload.get[OnionPaymentPayloadTlv.EncryptedRecipientData] match {
+          case Some(encrypted) =>
+            decryptEncryptedRecipientData(add, privateKey, outerPayload.records, encrypted.data).flatMap {
+              case DecodedEncryptedRecipientData(blindedPayload, _) => validateBlindedFinalPayload(add, innerPayload, blindedPayload)
+            }
+          case None =>
+            FinalPayload.Standard.validate(innerPayload).left.map(_.failureMessage).flatMap {
+              case innerPayload if outerPayload.expiry < innerPayload.expiry => Left(FinalIncorrectCltvExpiry(add.cltvExpiry)) // previous trampoline didn't forward the right expiry
+              case innerPayload if outerPayload.totalAmount < innerPayload.amount => Left(FinalIncorrectHtlcAmount(outerPayload.totalAmount)) // previous trampoline didn't forward the right amount
+              case innerPayload =>
+                // We merge contents from the outer and inner payloads.
+                // We must use the inner payload's total amount and payment secret because the payment may be split between multiple trampoline payments (#reckless).
+                val trampolinePacket = outerPayload.records.get[OnionPaymentPayloadTlv.TrampolineOnion].map(_.packet)
+                Right(FinalPacket(add, FinalPayload.Standard.createPayload(outerPayload.amount, innerPayload.totalAmount, innerPayload.expiry, innerPayload.paymentSecret, innerPayload.paymentMetadata, trampolinePacket)))
+            }
+        }
     }
   }
 
-  private def validateNodeRelay(add: UpdateAddHtlc, outerPayload: TlvStream[OnionPaymentPayloadTlv], innerPayload: TlvStream[OnionPaymentPayloadTlv], next: OnionRoutingPacket): Either[FailureMessage, RelayToTrampolinePacket] = {
-    // The outer payload cannot use route blinding, but the inner payload may (but it's not supported yet).
-    FinalPayload.Standard.validate(outerPayload).left.map(_.failureMessage).flatMap { outerPayload =>
-      IntermediatePayload.NodeRelay.Standard.validate(innerPayload).left.map(_.failureMessage).flatMap {
-        case _ if add.amountMsat < outerPayload.amount => Left(FinalIncorrectHtlcAmount(add.amountMsat))
-        case _ if add.cltvExpiry != outerPayload.expiry => Left(FinalIncorrectCltvExpiry(add.cltvExpiry))
-        case innerPayload => Right(RelayToTrampolinePacket(add, outerPayload, innerPayload, next))
-      }
+  private def validateNodeRelay(add: UpdateAddHtlc, privateKey: PrivateKey, outerPayload: TlvStream[OnionPaymentPayloadTlv], innerPayload: TlvStream[OnionPaymentPayloadTlv], next: OnionRoutingPacket): Either[FailureMessage, IncomingPaymentPacket] = {
+    // The outer payload cannot use route blinding, but the inner payload may.
+    FinalPayload.Standard.validate(outerPayload).left.map(_.failureMessage).flatMap {
+      case outerPayload if add.amountMsat < outerPayload.amount => Left(FinalIncorrectHtlcAmount(add.amountMsat))
+      case outerPayload if add.cltvExpiry != outerPayload.expiry => Left(FinalIncorrectCltvExpiry(add.cltvExpiry))
+      case outerPayload =>
+        innerPayload.get[OnionPaymentPayloadTlv.EncryptedRecipientData] match {
+          case Some(encrypted) =>
+            // The path key can be found:
+            //  - in the inner payload if we are the introduction node of the blinded path (provided by the payer).
+            //  - in the outer payload if we are an intermediate node in the blinded path (provided by the previous trampoline node).
+            val pathKey_opt = innerPayload.get[OnionPaymentPayloadTlv.PathKey].orElse(outerPayload.records.get[OnionPaymentPayloadTlv.PathKey]).map(_.publicKey)
+            decryptEncryptedRecipientData(add, privateKey, pathKey_opt, encrypted.data).flatMap {
+              case DecodedEncryptedRecipientData(blindedPayload, nextPathKey) =>
+                IntermediatePayload.NodeRelay.Blinded.validate(innerPayload, blindedPayload, nextPathKey).left.map(_.failureMessage).map(innerPayload => RelayToBlindedTrampolinePacket(add, outerPayload, innerPayload, next))
+            }
+          case None =>
+            IntermediatePayload.NodeRelay.Standard.validate(innerPayload).left.map(_.failureMessage).map(innerPayload => RelayToTrampolinePacket(add, outerPayload, innerPayload, next))
+        }
     }
   }
 

eclair-core/src/main/scala/fr/acinq/eclair/payment/relay/NodeRelay.scala

@@ -64,6 +64,7 @@ object NodeRelay {
   private case class WrappedPaymentSent(paymentSent: PaymentSent) extends Command
   private case class WrappedPaymentFailed(paymentFailed: PaymentFailed) extends Command
   private case class WrappedPeerReadyResult(result: PeerReadyNotifier.Result) extends Command
+  private case class WrappedOutgoingNodeId(nodeId_opt: Option[PublicKey]) extends Command
   private case class WrappedResolvedPaths(resolved: Seq[ResolvedPath]) extends Command
   private case class WrappedPeerInfo(remoteFeatures_opt: Option[Features[InitFeature]]) extends Command
   private case class WrappedOnTheFlyFundingResponse(result: Peer.ProposeOnTheFlyFundingResponse) extends Command
@@ -108,6 +109,7 @@ object NodeRelay {
         val incomingPaymentHandler = context.actorOf(MultiPartPaymentFSM.props(nodeParams, paymentHash, totalAmountIn, mppFsmAdapters))
         val nextPacket_opt = nodeRelayPacket match {
           case IncomingPaymentPacket.RelayToTrampolinePacket(_, _, _, nextPacket) => Some(nextPacket)
+          case IncomingPaymentPacket.RelayToBlindedTrampolinePacket(_, _, _, nextPacket) => Some(nextPacket)
           case _: IncomingPaymentPacket.RelayToNonTrampolinePacket => None
           case _: IncomingPaymentPacket.RelayToBlindedPathsPacket => None
         }
@@ -184,6 +186,7 @@ object NodeRelay {
           case nextPayload: IntermediatePayload.NodeRelay.Standard => failures.collectFirst { case RemoteFailure(_, _, e) if e.originNode == nextPayload.outgoingNodeId => e.failureMessage }
           case nextPayload: IntermediatePayload.NodeRelay.ToNonTrampoline => failures.collectFirst { case RemoteFailure(_, _, e) if e.originNode == nextPayload.outgoingNodeId => e.failureMessage }
           // When using blinded paths, we will never get a failure from the final node (for privacy reasons).
+          case _: IntermediatePayload.NodeRelay.Blinded => None
           case _: IntermediatePayload.NodeRelay.ToBlindedPaths => None
         }
         val otherNodeFailure = failures.collectFirst { case RemoteFailure(_, _, e) => e.failureMessage }
@@ -253,6 +256,28 @@ class NodeRelay private(nodeParams: NodeParams,
         val recipient = ClearRecipient(payloadOut.outgoingNodeId, features, payloadOut.amountToForward, payloadOut.outgoingCltv, paymentSecret, nextTrampolineOnion_opt = nextPacket_opt)
         context.log.debug("forwarding payment to the next trampoline node {}", recipient.nodeId)
         attemptWakeUpIfRecipientIsWallet(upstream, recipient, nextPayload, nextPacket_opt)
+      case payloadOut: IntermediatePayload.NodeRelay.Blinded =>
+        // Blinded paths in Bolt 12 invoices may use an scid to reference the next node, if it is one of our peers.
+        // We need to resolve that to a nodeId in order to create a payment onion.
+        payloadOut.outgoing match {
+          case Left(outgoingNodeId) => context.self ! WrappedOutgoingNodeId(Some(outgoingNodeId.publicKey))
+          case Right(outgoingChannelId) => register ! Register.GetNextNodeId(context.messageAdapter[Option[PublicKey]](WrappedOutgoingNodeId), outgoingChannelId)
+        }
+        Behaviors.receiveMessagePartial {
+          rejectExtraHtlcPartialFunction orElse {
+            case WrappedOutgoingNodeId(Some(outgoingNodeId)) =>
+              val outgoingAmount = nextPayload.outgoingAmount(upstream.amountIn)
+              val outgoingExpiry = nextPayload.outgoingExpiry(upstream.expiryIn)
+              val paymentSecret = randomBytes32() // we generate a new secret to protect against probing attacks
+              val recipient = ClearRecipient(outgoingNodeId, Features.empty, outgoingAmount, outgoingExpiry, paymentSecret, nextTrampolineOnion_opt = nextPacket_opt, trampolinePathKey_opt = Some(payloadOut.nextPathKey))
+              context.log.debug("forwarding payment to the next blinded trampoline node {}", recipient.nodeId)
+              attemptWakeUpIfRecipientIsWallet(upstream, recipient, nextPayload, nextPacket_opt)
+            case WrappedOutgoingNodeId(None) =>
+              context.log.warn("rejecting trampoline payment to blinded trampoline: cannot identify next node for scid={}", payloadOut.outgoing)
+              rejectPayment(upstream, Some(UnknownNextPeer()))
+              stopping()
+          }
+        }
       case payloadOut: IntermediatePayload.NodeRelay.ToNonTrampoline =>
         val paymentSecret = payloadOut.paymentSecret
         val features = Features(payloadOut.invoiceFeatures).invoiceFeatures()

eclair-core/src/main/scala/fr/acinq/eclair/payment/send/Recipient.scala

@@ -73,6 +73,8 @@ case class ClearRecipient(nodeId: PublicKey,
                           extraEdges: Seq[ExtraEdge] = Nil,
                           paymentMetadata_opt: Option[ByteVector] = None,
                           nextTrampolineOnion_opt: Option[OnionRoutingPacket] = None,
+                          // Must be provided if the payer is using a blinded trampoline path.
+                          trampolinePathKey_opt: Option[PublicKey] = None,
                           customTlvs: Set[GenericTlv] = Set.empty) extends Recipient {
   // Feature bit used by the legacy trampoline feature.
   private val isLegacyTrampoline = features.unknown.contains(UnknownFeature(149))
@@ -81,8 +83,8 @@ case class ClearRecipient(nodeId: PublicKey,
     ClearRecipient.validateRoute(nodeId, route).map(_ => {
       val finalPayload = nextTrampolineOnion_opt match {
         case Some(trampolinePacket) if isLegacyTrampoline => NodePayload(nodeId, FinalPayload.Standard.createLegacyTrampolinePayload(route.amount, totalAmount, expiry, paymentSecret, trampolinePacket))
-        case Some(trampolinePacket) => NodePayload(nodeId, FinalPayload.Standard.createTrampolinePayload(route.amount, totalAmount, expiry, paymentSecret, trampolinePacket))
-        case None => NodePayload(nodeId, FinalPayload.Standard.createPayload(route.amount, totalAmount, expiry, paymentSecret, paymentMetadata_opt, trampolineOnion_opt = None, customTlvs = customTlvs))
+        case Some(trampolinePacket) => NodePayload(nodeId, FinalPayload.Standard.createTrampolinePayload(route.amount, totalAmount, expiry, paymentSecret, trampolinePacket, trampolinePathKey_opt))
+        case None => NodePayload(nodeId, FinalPayload.Standard.createPayload(route.amount, totalAmount, expiry, paymentSecret, paymentMetadata_opt, trampolineOnion_opt = None, customTlvs))
       }
       Recipient.buildPayloads(PaymentPayloads(route.amount, expiry, Seq(finalPayload), None), route.hops)
     })
@@ -91,7 +93,7 @@ case class ClearRecipient(nodeId: PublicKey,
 
 object ClearRecipient {
   def apply(invoice: Bolt11Invoice, totalAmount: MilliSatoshi, expiry: CltvExpiry, customTlvs: Set[GenericTlv]): ClearRecipient = {
-    ClearRecipient(invoice.nodeId, invoice.features, totalAmount, expiry, invoice.paymentSecret, invoice.extraEdges, invoice.paymentMetadata, None, customTlvs)
+    ClearRecipient(invoice.nodeId, invoice.features, totalAmount, expiry, invoice.paymentSecret, invoice.extraEdges, invoice.paymentMetadata, None, None, customTlvs)
   }
 
   def validateRoute(nodeId: PublicKey, route: Route): Either[OutgoingPaymentError, Route] = {