Add support for custom initial fillers

All-zero initial packets should only be used for generating test vectors or other instances that requires deterministic packet generation also according to bolt #4, The packet is initialized with 1300 random bytes derived from a CSPRNG (ChaCha20). The pad key is used to extract additional random bytes from a ChaCha20 stream, using it as a CSPRNG for this purpose. Once the paddingKey has been obtained, ChaCha20 is used with an all zero nonce, to generate 1300 random bytes. Those random bytes are then used as the starting state of the mix-header to be created. See more (https://github.com/lightningnetwork/lightning-rfc/blob/master/04-onion-routing.md#packet-construction)
nblockchain · Jun 11, 2021 · 42876d9 · 42876d9
1 parent b2f17bc
commit 42876d9
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Showing 2 changed files with 18 additions and 5 deletions.
diff --git a/src/DotNetLightning.Core/Crypto/Sphinx.fs b/src/DotNetLightning.Core/Crypto/Sphinx.fs
@@ -194,22 +194,35 @@ module Sphinx =
                               HMAC = nextHmac }
             nextPacket
 
+    module PacketFiller =
+        // DeterministicPacketFiller is a packet filler that generates a deterministic
+        // set of filler bytes by using chacha20 with a key derived from the session
+        // key.
+        let DeterministicPacketFiller (sessionKey: Key) =
+            generateStream(generateKey("pad",sessionKey.ToBytes()), 1300)
+
+        // BlankPacketFiller is a packet filler that doesn't attempt to fill out the
+        // packet at all. It should ONLY be used for generating test vectors or other
+        // instances that required deterministic packet generation.
+        let BlankPacketFiller _=
+            Array.zeroCreate 1300
+
     type PacketAndSecrets = {
         Packet: OnionPacket
         /// Shared secrets (one per node in the route). Known (and needed) only if you're creating the
         /// packet. Empty if you're just forwarding the packet to the next node
         SharedSecrets: (Key * PubKey) list
     }
         with
-            static member Create (sessionKey: Key, pubKeys: PubKey list, payloads: byte[] list, ad: byte[]) =
+            static member Create (sessionKey: Key, pubKeys: PubKey list, payloads: byte[] list, ad: byte[], initialPacketFiller: Key -> byte[]) =
                 let (ephemeralPubKeys, sharedSecrets) = computeEphemeralPublicKeysAndSharedSecrets (sessionKey) (pubKeys)
                 let filler = generateFiller "rho" payloads sharedSecrets
 
                 let lastPacket = makeNextPacket(payloads |> List.last,
                                                 ad,
                                                 ephemeralPubKeys |> List.last,
                                                 (sharedSecrets |> List.last |> fun ss -> ss.ToBytes()),
-                                                OnionPacket.LastPacket,
+                                                {OnionPacket.LastPacket with HopData = initialPacketFiller(sessionKey)},
                                                 Some(filler))
                 let rec loop (hopPayloads: byte[] list, ephKeys: PubKey list, ss: Key list, packet: OnionPacket) =
                     if (hopPayloads.IsEmpty) then

diff --git a/tests/DotNetLightning.Core.Tests/SphinxTests.fs b/tests/DotNetLightning.Core.Tests/SphinxTests.fs
@@ -73,7 +73,7 @@ let bolt4Tests1 =
 
         testCase "Create packet (reference test vector)" <| fun _ ->
             let (onion, _ss) =
-                let p = PacketAndSecrets.Create (sessionKey, pubKeys, payloads, associatedData)
+                let p = PacketAndSecrets.Create (sessionKey, pubKeys, payloads, associatedData, PacketFiller.BlankPacketFiller)
                 (p.Packet, p.SharedSecrets)
             let expectedPacket =
                 "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"
@@ -108,7 +108,7 @@ let bolt4Tests1 =
 
         testCase "last node replies with an error message" <| fun _ ->
             let (onion, ss) =
-                let p = PacketAndSecrets.Create (sessionKey, pubKeys, payloads, associatedData)
+                let p = PacketAndSecrets.Create (sessionKey, pubKeys, payloads, associatedData, PacketFiller.BlankPacketFiller)
                 (p.Packet, p.SharedSecrets)
             let { NextPacket = packet1; SharedSecret = ss0 }: ParsedPacket =
                 Sphinx.parsePacket (privKeys.[0]) (associatedData) (onion.ToBytes())
@@ -166,7 +166,7 @@ let bolt4Tests1 =
 
         testCase "Intermediate node replies with an error message" <| fun _ ->
             let { Packet = packet; SharedSecrets = ss } =
-                Sphinx.PacketAndSecrets.Create(sessionKey, pubKeys, payloads, associatedData)
+                Sphinx.PacketAndSecrets.Create(sessionKey, pubKeys, payloads, associatedData, PacketFiller.BlankPacketFiller)
             let { NextPacket = packet1; SharedSecret = ss0 } =
                 Sphinx.parsePacket(privKeys.[0]) (associatedData) (packet.ToBytes())
                 |> Result.defaultWith(fun _ -> failwith "Fail: bolt4 intrm node replies with err msg defaultClosure0")