Rename blinding to pathKey (#735)

Rename some variable to align with the spec.

modules/core/src/commonMain/kotlin/fr/acinq/lightning/NodeParams.kt

@@ -262,13 +262,13 @@ data class NodeParams(
      * @return the default offer and the private key that will sign invoices for this offer.
      */
     fun defaultOffer(trampolineNodeId: PublicKey): Pair<OfferTypes.Offer, PrivateKey> {
-        // We generate a deterministic blindingSecret based on:
+        // We generate a deterministic session key based on:
         //  - a custom tag indicating that this is used in the Bolt 12 context
         //  - our trampoline node, which is used as an introduction node for the offer's blinded path
-        //  - our private key, which ensures that nobody else can generate the same blindingSecret
-        val blindingSecret = PrivateKey(Crypto.sha256("bolt 12 default offer".toByteArray(Charsets.UTF_8).byteVector() + trampolineNodeId.value + nodePrivateKey.value).byteVector32())
+        //  - our private key, which ensures that nobody else can generate the same path key secret
+        val sessionKey = PrivateKey(Crypto.sha256("bolt 12 default offer".toByteArray(Charsets.UTF_8).byteVector() + trampolineNodeId.value + nodePrivateKey.value).byteVector32())
         // We don't use our currently activated features, otherwise the offer would change when we add support for new features.
         // If we add a new feature that we would like to use by default, we will need to explicitly create a new offer.
-        return OfferTypes.Offer.createBlindedOffer(amount = null, description = null, this, trampolineNodeId, Features.empty, blindingSecret)
+        return OfferTypes.Offer.createBlindedOffer(amount = null, description = null, this, trampolineNodeId, Features.empty, sessionKey)
     }
 }

modules/core/src/commonMain/kotlin/fr/acinq/lightning/crypto/RouteBlinding.kt

@@ -14,68 +14,68 @@ import fr.acinq.lightning.wire.OnionPaymentPayloadTlv
 object RouteBlinding {
 
     /**
-     * @param nodeId introduction node's id (which cannot be blinded since the sender need to find a route to it).
+     * @param nodeId first node's id (which cannot be blinded since the sender need to find a route to it).
      * @param blindedPublicKey blinded public key, which hides the real public key.
-     * @param blindingEphemeralKey blinding tweak that can be used by the receiving node to derive the private key that matches the blinded public key.
-     * @param encryptedPayload encrypted payload that can be decrypted with the introduction node's private key and the blinding ephemeral key.
+     * @param pathKey blinding tweak that can be used by the receiving node to derive the private key that matches the blinded public key.
+     * @param encryptedPayload encrypted payload that can be decrypted with the introduction node's private key and the path key.
      */
-    data class IntroductionNode(
+    data class FirstHop(
         val nodeId: EncodedNodeId,
         val blindedPublicKey: PublicKey,
-        val blindingEphemeralKey: PublicKey,
+        val pathKey: PublicKey,
         val encryptedPayload: ByteVector
     )
 
     /**
      * @param blindedPublicKey blinded public key, which hides the real public key.
-     * @param encryptedPayload encrypted payload that can be decrypted with the receiving node's private key and the blinding ephemeral key.
+     * @param encryptedPayload encrypted payload that can be decrypted with the receiving node's private key and the path key.
      */
-    data class BlindedNode(val blindedPublicKey: PublicKey, val encryptedPayload: ByteVector)
+    data class BlindedHop(val blindedPublicKey: PublicKey, val encryptedPayload: ByteVector)
 
     /**
-     * @param introductionNodeId the first node, not blinded so that the sender can locate it.
-     * @param blindingKey blinding tweak that can be used by the introduction node to derive the private key that matches the blinded public key.
-     * @param blindedNodes blinded nodes (including the introduction node).
+     * @param firstNodeId the first node, not blinded so that the sender can locate it.
+     * @param firstPathKey blinding tweak that can be used by the introduction node to derive the private key that matches the blinded public key.
+     * @param blindedHops blinded nodes (including the introduction node).
      */
     data class BlindedRoute(
-        val introductionNodeId: EncodedNodeId,
-        val blindingKey: PublicKey,
-        val blindedNodes: List<BlindedNode>
+        val firstNodeId: EncodedNodeId,
+        val firstPathKey: PublicKey,
+        val blindedHops: List<BlindedHop>
     ) {
-        val introductionNode: IntroductionNode = IntroductionNode(
-            introductionNodeId,
-            blindedNodes.first().blindedPublicKey,
-            blindingKey,
-            blindedNodes.first().encryptedPayload
+        val firstHop: FirstHop = FirstHop(
+            firstNodeId,
+            blindedHops.first().blindedPublicKey,
+            firstPathKey,
+            blindedHops.first().encryptedPayload
         )
-        val subsequentNodes: List<BlindedNode> = blindedNodes.drop(1)
-        val blindedNodeIds: List<PublicKey> = blindedNodes.map { it.blindedPublicKey }
-        val encryptedPayloads: List<ByteVector> = blindedNodes.map { it.encryptedPayload }
+        val subsequentHops: List<BlindedHop> = blindedHops.drop(1)
+        val blindedNodeIds: List<PublicKey> = blindedHops.map { it.blindedPublicKey }
+        val encryptedPayloads: List<ByteVector> = blindedHops.map { it.encryptedPayload }
     }
 
     /**
      * @param route blinded route.
-     * @param lastBlinding blinding point for the last node, which can be used to derive the blinded private key.
+     * @param lastPathKey path key for the last node, which can be used to derive the blinded private key.
      */
-    data class BlindedRouteDetails(val route: BlindedRoute, val lastBlinding: PublicKey) {
+    data class BlindedRouteDetails(val route: BlindedRoute, val lastPathKey: PublicKey) {
         /** @param nodeKey private key associated with our non-blinded node_id. */
-        fun blindedPrivateKey(nodeKey: PrivateKey): PrivateKey = derivePrivateKey(nodeKey, lastBlinding)
+        fun blindedPrivateKey(nodeKey: PrivateKey): PrivateKey = derivePrivateKey(nodeKey, lastPathKey)
     }
 
     /**
      * Blind the provided route and encrypt intermediate nodes' payloads.
      *
-     * @param sessionKey this node's session key.
+     * @param sessionKey session key of the blinded path, the corresponding public key will be the first path key.
      * @param publicKeys public keys of each node on the route, starting from the introduction point.
      * @param payloads payloads that should be encrypted for each node on the route.
      * @return a blinded route.
      */
     fun create(sessionKey: PrivateKey, publicKeys: List<PublicKey>, payloads: List<ByteVector>): BlindedRouteDetails {
         require(publicKeys.size == payloads.size) { "a payload must be provided for each node in the blinded path" }
         var e = sessionKey
-        val (blindedHops, blindingKeys) = publicKeys.zip(payloads).map { pair ->
+        val (blindedHops, pathKeys) = publicKeys.zip(payloads).map { pair ->
             val (publicKey, payload) = pair
-            val blindingKey = e.publicKey()
+            val pathKey = e.publicKey()
             val sharedSecret = Sphinx.computeSharedSecret(publicKey, e)
             val blindedPublicKey = Sphinx.blind(publicKey, Sphinx.generateKey("blinded_node_id", sharedSecret))
             val rho = Sphinx.generateKey("rho", sharedSecret)
@@ -85,38 +85,38 @@ object RouteBlinding {
                 payload.toByteArray(),
                 byteArrayOf()
             )
-            e *= PrivateKey(Crypto.sha256(blindingKey.value.toByteArray() + sharedSecret.toByteArray()))
-            Pair(BlindedNode(blindedPublicKey, ByteVector(encryptedPayload + mac)), blindingKey)
+            e *= PrivateKey(Crypto.sha256(pathKey.value.toByteArray() + sharedSecret.toByteArray()))
+            Pair(BlindedHop(blindedPublicKey, ByteVector(encryptedPayload + mac)), pathKey)
         }.unzip()
-        return BlindedRouteDetails(BlindedRoute(EncodedNodeId(publicKeys.first()), blindingKeys.first(), blindedHops), blindingKeys.last())
+        return BlindedRouteDetails(BlindedRoute(EncodedNodeId(publicKeys.first()), pathKeys.first(), blindedHops), pathKeys.last())
     }
 
     /**
      * Compute the blinded private key that must be used to decrypt an incoming blinded onion.
      *
      * @param privateKey this node's private key.
-     * @param blindingEphemeralKey unblinding ephemeral key.
+     * @param pathKey unblinding ephemeral key.
      * @return this node's blinded private key.
      */
-    fun derivePrivateKey(privateKey: PrivateKey, blindingEphemeralKey: PublicKey): PrivateKey {
-        val sharedSecret = Sphinx.computeSharedSecret(blindingEphemeralKey, privateKey)
+    fun derivePrivateKey(privateKey: PrivateKey, pathKey: PublicKey): PrivateKey {
+        val sharedSecret = Sphinx.computeSharedSecret(pathKey, privateKey)
         return privateKey * PrivateKey(Sphinx.generateKey("blinded_node_id", sharedSecret))
     }
 
     /**
      * Decrypt the encrypted payload (usually found in the onion) that contains instructions to locate the next node.
      *
      * @param privateKey this node's private key.
-     * @param blindingEphemeralKey unblinding ephemeral key.
+     * @param pathKey unblinding ephemeral key.
      * @param encryptedPayload encrypted payload for this node.
      * @return a tuple (decrypted payload, unblinding ephemeral key for the next node)
      */
     fun decryptPayload(
         privateKey: PrivateKey,
-        blindingEphemeralKey: PublicKey,
+        pathKey: PublicKey,
         encryptedPayload: ByteVector
     ): Either<InvalidTlvPayload, Pair<ByteVector, PublicKey>> {
-        val sharedSecret = Sphinx.computeSharedSecret(blindingEphemeralKey, privateKey)
+        val sharedSecret = Sphinx.computeSharedSecret(pathKey, privateKey)
         val rho = Sphinx.generateKey("rho", sharedSecret)
         return try {
             val decrypted = ChaCha20Poly1305.decrypt(
@@ -126,8 +126,8 @@ object RouteBlinding {
                 byteArrayOf(),
                 encryptedPayload.takeRight(16).toByteArray()
             )
-            val nextBlindingEphemeralKey = Sphinx.blind(blindingEphemeralKey, Sphinx.computeBlindingFactor(blindingEphemeralKey, sharedSecret))
-            Either.Right(Pair(ByteVector(decrypted), nextBlindingEphemeralKey))
+            val nextPathKey = Sphinx.blind(pathKey, Sphinx.computeBlindingFactor(pathKey, sharedSecret))
+            Either.Right(Pair(ByteVector(decrypted), nextPathKey))
         } catch (_: Throwable) {
             Either.Left(CannotDecodeTlv(OnionPaymentPayloadTlv.EncryptedRecipientData.tag))
         }

modules/core/src/commonMain/kotlin/fr/acinq/lightning/json/JsonSerializers.kt

@@ -49,7 +49,7 @@
     JsonSerializers.FundingSignedSerializer::class,
     JsonSerializers.UpdateAddHtlcSerializer::class,
     JsonSerializers.UpdateAddHtlcTlvSerializer::class,
-    JsonSerializers.UpdateAddHtlcTlvBlindingSerializer::class,
+    JsonSerializers.UpdateAddHtlcTlvPathKeySerializer::class,
     JsonSerializers.UpdateFulfillHtlcSerializer::class,
     JsonSerializers.UpdateFailHtlcSerializer::class,
     JsonSerializers.UpdateFailMalformedHtlcSerializer::class,
@@ -98,7 +98,7 @@
     JsonSerializers.Bolt11UnknownTagSerializer::class,
     JsonSerializers.Bolt11InvalidTagSerializer::class,
     JsonSerializers.EncodedNodeIdSerializer::class,
-    JsonSerializers.BlindedNodeSerializer::class,
+    JsonSerializers.BlindedHopSerializer::class,
     JsonSerializers.BlindedRouteSerializer::class,
 )
 @file:UseContextualSerialization(
@@ -209,7 +209,7 @@ object JsonSerializers {
                 subclass(CommitSigTlv.Batch::class, CommitSigTlvBatchSerializer)
                 subclass(ShutdownTlv.ChannelData::class, ShutdownTlvChannelDataSerializer)
                 subclass(ClosingSignedTlv.FeeRange::class, ClosingSignedTlvFeeRangeSerializer)
-                subclass(UpdateAddHtlcTlv.Blinding::class, UpdateAddHtlcTlvBlindingSerializer)
+                subclass(UpdateAddHtlcTlv.PathKey::class, UpdateAddHtlcTlvPathKeySerializer)
             }
             // TODO The following declarations are required because serializers for [TransactionWithInputInfo]
             //  depend themselves on @Contextual serializers. Once we get rid of v2/v3 serialization and we
@@ -476,8 +476,8 @@ object JsonSerializers {
     @Serializer(forClass = EncryptedChannelData::class)
     object EncryptedChannelDataSerializer
 
-    @Serializer(forClass = UpdateAddHtlcTlv.Blinding::class)
-    object UpdateAddHtlcTlvBlindingSerializer
+    @Serializer(forClass = UpdateAddHtlcTlv.PathKey::class)
+    object UpdateAddHtlcTlvPathKeySerializer
 
     @Serializer(forClass = UpdateAddHtlcTlv::class)
     object UpdateAddHtlcTlvSerializer
@@ -649,8 +649,8 @@ object JsonSerializers {
         delegateSerializer = EncodedNodeIdSurrogate.serializer()
     )
 
-    @Serializer(forClass = RouteBlinding.BlindedNode::class)
-    object BlindedNodeSerializer
+    @Serializer(forClass = RouteBlinding.BlindedHop::class)
+    object BlindedHopSerializer
 
     @Serializer(forClass = RouteBlinding.BlindedRoute::class)
     object BlindedRouteSerializer