Merge pull request #10532 from spesmilo/variable_trampoline_onions

trampoline: allow trampoline onion packets of arbitrary size

electrum/lnonion.py

@@ -47,7 +47,6 @@ if TYPE_CHECKING:
 
 
 HOPS_DATA_SIZE = 1300      # also sometimes called routingInfoSize in bolt-04
-TRAMPOLINE_HOPS_DATA_SIZE = 400
 PER_HOP_HMAC_SIZE = 32
 ONION_MESSAGE_LARGE_SIZE = 32768
 
@@ -134,7 +133,6 @@ class OnionPacket:
 
     def __post_init__(self):
         assert len(self.public_key) == 33
-        assert len(self.hops_data) in [HOPS_DATA_SIZE, TRAMPOLINE_HOPS_DATA_SIZE, ONION_MESSAGE_LARGE_SIZE]
         assert len(self.hmac) == PER_HOP_HMAC_SIZE
         if not ecc.ECPubkey.is_pubkey_bytes(self.public_key):
             raise InvalidOnionPubkey()
@@ -144,14 +142,10 @@ class OnionPacket:
         ret += self.public_key
         ret += self.hops_data
         ret += self.hmac
-        if len(ret) - 66 not in [HOPS_DATA_SIZE, TRAMPOLINE_HOPS_DATA_SIZE, ONION_MESSAGE_LARGE_SIZE]:
-            raise Exception('unexpected length {}'.format(len(ret)))
         return ret
 
     @classmethod
     def from_bytes(cls, b: bytes) -> 'OnionPacket':
-        if len(b) - 66 not in [HOPS_DATA_SIZE, TRAMPOLINE_HOPS_DATA_SIZE, ONION_MESSAGE_LARGE_SIZE]:
-            raise Exception('unexpected length {}'.format(len(b)))
         return OnionPacket(
             public_key=b[1:34],
             hops_data=b[34:-32],
@@ -217,7 +211,7 @@ def new_onion_packet(
         # FIXME: serializing here and again below. cache bytes in OnionHopsDataSingle? _raw_bytes_payload?
         payload_size += PER_HOP_HMAC_SIZE + len(hops_data[i].to_bytes())
     if trampoline:
-        data_size = TRAMPOLINE_HOPS_DATA_SIZE
+        data_size = payload_size
     elif onion_message:
         if payload_size <= HOPS_DATA_SIZE:
             data_size = HOPS_DATA_SIZE
@@ -446,7 +440,7 @@ def process_onion_packet(
         raise InvalidOnionMac()
     # peel an onion layer off
     rho_key = get_bolt04_onion_key(b'rho', shared_secret)
-    data_size = TRAMPOLINE_HOPS_DATA_SIZE if is_trampoline else HOPS_DATA_SIZE
+    data_size = len(onion_packet.hops_data) if is_trampoline else HOPS_DATA_SIZE
     if is_onion_message and len(onion_packet.hops_data) > HOPS_DATA_SIZE:
         data_size = ONION_MESSAGE_LARGE_SIZE
     stream_bytes = generate_cipher_stream(rho_key, 2 * data_size)
@@ -459,15 +453,8 @@ def process_onion_packet(
     if trampoline_onion_packet:
         if is_trampoline:
             raise Exception("found nested trampoline inside trampoline")
-        top_version = trampoline_onion_packet.get('version')
-        top_public_key = trampoline_onion_packet.get('public_key')
-        top_hops_data = trampoline_onion_packet.get('hops_data')
-        top_hops_data_fd = io.BytesIO(top_hops_data)
-        top_hmac = trampoline_onion_packet.get('hmac')
-        trampoline_onion_packet = OnionPacket(
-            public_key=top_public_key,
-            hops_data=top_hops_data_fd.read(TRAMPOLINE_HOPS_DATA_SIZE),
-            hmac=top_hmac)
+        trampoline_onion_packet = trampoline_onion_packet['trampoline_onion_packet']
+        trampoline_onion_packet = OnionPacket.from_bytes(trampoline_onion_packet)
     # calc next ephemeral key
     blinding_factor = sha256(onion_packet.public_key + shared_secret)
     blinding_factor_int = int.from_bytes(blinding_factor, byteorder="big")

electrum/lnwire/onion_wire.csv

@@ -22,10 +22,7 @@ tlvdata,payload,outgoing_node_id,outgoing_node_id,byte,33
 tlvtype,payload,invoice_routing_info,66099
 tlvdata,payload,invoice_routing_info,invoice_routing_info,byte,...
 tlvtype,payload,trampoline_onion_packet,66100
-tlvdata,payload,trampoline_onion_packet,version,byte,1
-tlvdata,payload,trampoline_onion_packet,public_key,byte,33
-tlvdata,payload,trampoline_onion_packet,hops_data,byte,400
-tlvdata,payload,trampoline_onion_packet,hmac,byte,32
+tlvdata,payload,trampoline_onion_packet,trampoline_onion_packet,byte,...
 tlvtype,encrypted_data_tlv,padding,1
 tlvdata,encrypted_data_tlv,padding,padding,byte,...
 tlvtype,encrypted_data_tlv,short_channel_id,2

electrum/lnworker.py

@@ -4093,10 +4093,7 @@ class LNWallet(Logger):
             self.logger.info(f'adding trampoline onion to final payload')
             trampoline_payload = dict(hops_data[-1].payload)
             trampoline_payload["trampoline_onion_packet"] = {
-                "version": trampoline_onion.version,
-                "public_key": trampoline_onion.public_key,
-                "hops_data": trampoline_onion.hops_data,
-                "hmac": trampoline_onion.hmac
+                "trampoline_onion_packet": trampoline_onion.to_bytes()
             }
             hops_data[-1] = dataclasses.replace(hops_data[-1], payload=trampoline_payload)
             if t_hops_data := trampoline_onion._debug_hops_data:  # None if trampoline-forwarding

electrum/trampoline.py

@@ -7,7 +7,7 @@ from types import MappingProxyType
 
 from .lnutil import LnFeatures, PaymentFeeBudget, FeeBudgetExceeded
 from .lnonion import (
-    calc_hops_data_for_payment, new_onion_packet, OnionPacket, TRAMPOLINE_HOPS_DATA_SIZE, PER_HOP_HMAC_SIZE
+    calc_hops_data_for_payment, new_onion_packet, OnionPacket, PER_HOP_HMAC_SIZE
 )
 from .lnrouter import TrampolineEdge, is_route_within_budget, LNPaymentTRoute
 from .lnutil import NoPathFound
@@ -40,6 +40,8 @@ TRAMPOLINE_NODES_SIGNET = {
 
 _TRAMPOLINE_NODES_UNITTESTS = {}  # used in unit tests
 
+TRAMPOLINE_HOPS_MAX_DATA_SIZE = 500
+
 
 def hardcoded_trampoline_nodes() -> Mapping[str, LNPeerAddr]:
     if _TRAMPOLINE_NODES_UNITTESTS:
@@ -332,7 +334,7 @@ def create_trampoline_onion(
         payload = dict(hops_data[index].payload)
         # try different r_tag order on each attempt
         invoice_routing_info = random_shuffled_copy(route[index].invoice_routing_info)
-        remaining_payload_space = TRAMPOLINE_HOPS_DATA_SIZE \
+        remaining_payload_space = TRAMPOLINE_HOPS_MAX_DATA_SIZE \
                                   - sum(len(hop.to_bytes()) + PER_HOP_HMAC_SIZE for hop in hops_data)
         routing_info_to_use = []
         for encoded_r_tag in invoice_routing_info:

tests/test_lnpeer.py

@@ -2742,10 +2742,7 @@ class TestPeerForwarding(TestPeer):
                 assert len(hops_data) == 1
                 new_payload = dict(hops_data[0].payload)
                 new_payload['trampoline_onion_packet'] = {
-                    "version": modified_trampoline_onion.version,
-                    "public_key": modified_trampoline_onion.public_key,
-                    "hops_data": modified_trampoline_onion.hops_data,
-                    "hmac": modified_trampoline_onion.hmac,
+                    "trampoline_onion_packet": modified_trampoline_onion.to_bytes()
                 }
                 hops_data[0] = dataclasses.replace(hops_data[0], payload=MappingProxyType(new_payload))
                 modified_trampoline_onion = None