onion_message: use trampoline nodes for onion messages
What the developer wrote
Authored by f321x
onion_message: use trampoline nodes for onion messages
What changed, and why it matters
This commit changes how Electrum routes private 'onion messages' through the Lightning Network. For users on 'trampoline' payment setups, it now sends messages via a randomly chosen trampoline peer and trusts that peer to forward the message to the final recipient. The change removes some safety checks that previously required an active channel or a known network path, and it uses Python's standard random module to pick the trampoline peer. This could make message delivery less reliable or more predictable, and it shifts trust onto trampoline nodes, but it does not appear to be a direct theft or remote-code-execution vulnerability.
Review whether random.choice is acceptable here or whether secrets.choice should be used for peer selection. Confirm that trampoline peers are expected to relay arbitrary onion messages (Eclair's relay-all policy is noted in a comment). Consider adding a fallback or retry mechanism when the chosen trampoline cannot reach the destination, and re-evaluate removing the is_frozen_for_sending() filter. Treat this as a routine protocol/logic change rather than an urgent security patch unless further review shows exploitable message interception or deanonymization.
Security signals we found
Routing logic now trusts trampoline peers to open direct connections and forward onion messages (relayed trust assumption)
Random trampoline peer selection uses Python's standard random module, which is not cryptographically secure and could be predictable if an attacker can influence process state
Removed the is_frozen_for_sending() filter when building my_sending_channels in non-trampoline path
NoRouteFound now only carries peer_addr in the non-trampoline branch, removing a potential direct-connection fallback for trampoline users
No explicit validation that the chosen trampoline peer is online, connected, or willing to relay onion messages
Evidence from the diff
The patch refactors create_onion_message_route_to in electrum/onion_message.py. In non-trampoline mode it still tries to find a graph path, but it no longer filters out channels frozen for sending and it moves the address fallback inside the non-trampoline branch. In trampoline mode it constructs a two-hop route us -> random trampoline -> destination without verifying that the trampoline can reach the destination, relying on the trampoline to open a direct connection. The random selection uses random.choice on lnwallet.lnpeermgr.peers values filtered by is_trampoline_peer. A minor type-hint change from ‘Network’ to Network is also included.
Changed components
electrum/onion_message.pycreate_onion_message_route_to()OnionMessageManagerInspect captured patch +34 / −21
diff --git a/electrum/onion_message.py b/electrum/onion_message.py
index 1bd7d29..9d802eb 100644
--- a/electrum/onion_message.py
+++ b/electrum/onion_message.py
@@ -27,6 +27,7 @@ import io
import os
import threading
import time
+import random
from typing import TYPE_CHECKING, Optional, Sequence, NamedTuple, Tuple, Union
@@ -151,18 +152,27 @@ def is_onion_message_node(node_id: bytes, node_info: Optional['NodeInfo']) -> bo
def create_onion_message_route_to(lnwallet: 'LNWallet', node_id: bytes) -> Sequence[PathEdge]:
- """Constructs a route to the destination node_id, first by starting with peers with existing channels,
- and if no route found, opening a direct peer connection if node_id is found with an address in
- channel_db."""
- # TODO: is this the proper way to set up my_sending_channels?
- my_active_channels = [
- chan for chan in lnwallet.channels.values() if
- chan.is_active() and not chan.is_frozen_for_sending()]
- my_sending_channels = {chan.short_channel_id: chan for chan in my_active_channels
- if chan.short_channel_id is not None}
- # find route to introduction point over existing channel mesh
- # NOTE: nodes that are in channel_db but are offline are not removed from the set
- if lnwallet.network.path_finder:
+ """
+ Constructs a route for sending an onion message to node_id.
+ With Gossip: Tries to find a route through the graph. If no route can be found, raise NoRouteFound.
+ If a connection address is known for node_id it is added to NoRouteFound for potential direct connection.
+ With Trampoline: Construct a route: us -> random trampoline peer -> node_id.
+ We hope the trampoline peer will open a direct connection to node_id and forward the message.
+ NOTE: Eclair only does this with the relay-policy config set to relay-all!
+ """
+ # destination is existing peer, use direct route
+ if lnwallet.lnpeermgr.get_peer_by_pubkey(node_id):
+ return [PathEdge(short_channel_id=None, start_node=None, end_node=node_id)]
+
+ if not lnwallet.uses_trampoline():
+ # find route to introduction point over existing channel mesh
+ # NOTE: nodes that are in channel_db but are offline are not removed from the set
+ my_active_channels = [chan for chan in lnwallet.channels.values() if chan.is_active()]
+ my_sending_channels = {
+ chan.short_channel_id: chan for chan in my_active_channels
+ if chan.short_channel_id is not None
+ }
+
if path := lnwallet.network.path_finder.find_path_for_payment(
nodeA=lnwallet.node_keypair.pubkey,
nodeB=node_id,
@@ -174,15 +184,18 @@ def create_onion_message_route_to(lnwallet: 'LNWallet', node_id: bytes) -> Seque
peer = lnwallet.lnpeermgr.get_peer_by_pubkey(path[0].end_node)
assert peer, 'first hop not a peer'
return path
-
- # alt: dest is existing peer?
- if lnwallet.lnpeermgr.get_peer_by_pubkey(node_id):
- return [PathEdge(short_channel_id=None, start_node=None, end_node=node_id)]
-
- # if we have an address, pass it.
- if lnwallet.channel_db:
- if peer_addr := lnwallet.channel_db.get_last_good_address(node_id):
+ elif peer_addr := lnwallet.channel_db.get_last_good_address(node_id):
+ # if we have an address, pass it.
raise NoRouteFound('no path found, peer_addr available', peer_address=peer_addr)
+ else:
+ # if we use trampoline just assume the trampoline will open a direct connection to the next_node_id
+ trampoline_peers = [p for p in lnwallet.lnpeermgr.peers.values() if lnwallet.is_trampoline_peer(p.pubkey)]
+ if trampoline_peers:
+ random_trampoline_peer = random.choice(trampoline_peers)
+ return [
+ PathEdge(short_channel_id=None, start_node=None, end_node=random_trampoline_peer.pubkey),
+ PathEdge(short_channel_id=None, start_node=random_trampoline_peer.pubkey, end_node=node_id),
+ ]
raise NoRouteFound('no path found')
@@ -539,7 +552,7 @@ class OnionMessageManager(Logger):
def __init__(self, lnwallet: 'LNWallet'):
Logger.__init__(self)
- self.network = None # type: Optional['Network']
+ self.network = None # type: Optional[Network]
self.taskgroup = None # type: OldTaskGroup
self.lnwallet = lnwallet
self.pending = {} # type: dict[bytes, OnionMessageManager.Request]
Why this scored 25/100
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