Introduce test for Padding

Add test to verify blinded message and payment path padding.

Author: shaavan

lightning/src/blinded_path/utils.rs

@@ -258,3 +258,18 @@ impl<T: Writeable> Writeable for BlindedPathWithPadding<T> {
 		self.tlvs.write(writer)
 	}
 }
+
+#[cfg(test)]
+/// Checks if all the packets in the blinded path are properly padded.
+pub fn is_padded(hops: &[BlindedHop], padding_round_off: usize) -> bool {
+	let first_hop = hops.first().expect("BlindedPath must have at least one hop");
+	let first_payload_size = first_hop.encrypted_payload.len();
+
+	// The unencrypted payload data is padded before getting encrypted.
+	// Assuming the first payload is padded properly, get the extra data length.
+	let extra_length = first_payload_size % padding_round_off;
+	hops.iter().all(|hop| {
+		// Check that every packet is padded to the round off length subtracting the extra length.
+		(hop.encrypted_payload.len() - extra_length) % padding_round_off == 0
+	})
+}

lightning/src/ln/blinded_payment_tests.rs

@@ -12,7 +12,8 @@ use bitcoin::secp256k1::{PublicKey, Scalar, Secp256k1, SecretKey, schnorr};
 use bitcoin::secp256k1::ecdh::SharedSecret;
 use bitcoin::secp256k1::ecdsa::{RecoverableSignature, Signature};
 use crate::blinded_path;
-use crate::blinded_path::payment::{BlindedPaymentPath, Bolt12RefundContext, PaymentForwardNode, ForwardTlvs, PaymentConstraints, PaymentContext, PaymentRelay, UnauthenticatedReceiveTlvs};
+use crate::blinded_path::payment::{BlindedPaymentPath, Bolt12RefundContext, ForwardTlvs, PaymentConstraints, PaymentContext, PaymentForwardNode, PaymentRelay, UnauthenticatedReceiveTlvs, PAYMENT_PADDING_ROUND_OFF};
+use crate::blinded_path::utils::is_padded;
 use crate::events::{Event, HTLCDestination, MessageSendEvent, MessageSendEventsProvider, PaymentFailureReason};
 use crate::ln::types::ChannelId;
 use crate::types::payment::{PaymentHash, PaymentSecret};
@@ -1411,6 +1412,42 @@ fn fails_receive_tlvs_authentication() {
 	);
 }
 
+#[test]
+fn blinded_payment_path_padding() {
+	// Make sure that for a blinded payment path, all encrypted payloads are padded to equal lengths.
+	let chanmon_cfgs = create_chanmon_cfgs(5);
+	let node_cfgs = create_node_cfgs(5, &chanmon_cfgs);
+	let node_chanmgrs = create_node_chanmgrs(5, &node_cfgs, &[None, None, None, None, None]);
+	let mut nodes = create_network(5, &node_cfgs, &node_chanmgrs);
+	create_announced_chan_between_nodes_with_value(&nodes, 0, 1, 1_000_000, 0);
+	create_announced_chan_between_nodes_with_value(&nodes, 1, 2, 1_000_000, 0);
+	let chan_upd_2_3 = create_announced_chan_between_nodes_with_value(&nodes, 2, 3, 1_000_000, 0).0.contents;
+	let chan_upd_3_4 = create_announced_chan_between_nodes_with_value(&nodes, 3, 4, 1_000_000, 0).0.contents;
+
+	// Get all our nodes onto the same height so payments don't fail for CLTV violations.
+	connect_blocks(&nodes[0], nodes[4].best_block_info().1 - nodes[0].best_block_info().1);
+	connect_blocks(&nodes[1], nodes[4].best_block_info().1 - nodes[1].best_block_info().1);
+	connect_blocks(&nodes[2], nodes[4].best_block_info().1 - nodes[2].best_block_info().1);
+	assert_eq!(nodes[4].best_block_info().1, nodes[3].best_block_info().1);
+
+	let amt_msat = 5000;
+	let (payment_preimage, payment_hash, payment_secret) = get_payment_preimage_hash(&nodes[4], Some(amt_msat), None);
+
+	let blinded_path = blinded_payment_path(payment_secret, 1, 1_0000_0000,
+		nodes.iter().skip(2).map(|n| n.node.get_our_node_id()).collect(), &[&chan_upd_2_3, &chan_upd_3_4],
+		&chanmon_cfgs[4].keys_manager
+	);
+
+	assert!(is_padded(&blinded_path.blinded_hops(), PAYMENT_PADDING_ROUND_OFF));
+
+	let route_params = RouteParameters::from_payment_params_and_value(PaymentParameters::blinded(vec![blinded_path]), amt_msat);
+
+	nodes[0].node.send_payment(payment_hash, RecipientOnionFields::spontaneous_empty(), PaymentId(payment_hash.0), route_params, Retry::Attempts(0)).unwrap();
+	check_added_monitors(&nodes[0], 1);
+	pass_along_route(&nodes[0], &[&[&nodes[1], &nodes[2], &nodes[3], &nodes[4]]], amt_msat, payment_hash, payment_secret);
+	claim_payment(&nodes[0], &[&nodes[1], &nodes[2], &nodes[3], &nodes[4]], payment_preimage);
+}
+
 fn secret_from_hex(hex: &str) -> SecretKey {
 	SecretKey::from_slice(&<Vec<u8>>::from_hex(hex).unwrap()).unwrap()
 }

lightning/src/onion_message/functional_tests.rs

@@ -10,7 +10,8 @@
 //! Onion message testing and test utilities live here.
 
 use crate::blinded_path::EmptyNodeIdLookUp;
-use crate::blinded_path::message::{AsyncPaymentsContext, BlindedMessagePath, DNSResolverContext, MessageForwardNode, MessageContext, OffersContext};
+use crate::blinded_path::message::{AsyncPaymentsContext, BlindedMessagePath, DNSResolverContext, MessageContext, MessageForwardNode, OffersContext, MESSAGE_PADDING_ROUND_OFF};
+use crate::blinded_path::utils::is_padded;
 use crate::events::{Event, EventsProvider};
 use crate::types::features::{ChannelFeatures, InitFeatures};
 use crate::ln::msgs::{self, DecodeError, OnionMessageHandler};
@@ -563,6 +564,51 @@ fn too_big_packet_error() {
 	assert_eq!(err, SendError::TooBigPacket);
 }
 
+#[test]
+fn test_blinded_path_padding_for_full_length_path() {
+	// Check that for a full blinded path, all encrypted payload are padded to rounded-off length.
+	let nodes = create_nodes(4);
+	let test_msg = TestCustomMessage::Pong;
+
+	let secp_ctx = Secp256k1::new();
+	let intermediate_nodes = [
+		MessageForwardNode { node_id: nodes[1].node_id, short_channel_id: None },
+		MessageForwardNode { node_id: nodes[2].node_id, short_channel_id: None },
+	];
+	// Update the context to create a larger final receive TLVs, ensuring that
+	// the hop sizes vary before padding.
+	let context = MessageContext::Custom(vec![0u8; 42]);
+	let blinded_path = BlindedMessagePath::new(&intermediate_nodes, nodes[3].node_id, context, &*nodes[3].entropy_source, &secp_ctx).unwrap();
+
+	assert!(is_padded(&blinded_path.blinded_hops(), MESSAGE_PADDING_ROUND_OFF));
+
+	let destination = Destination::BlindedPath(blinded_path);
+	let instructions = MessageSendInstructions::WithoutReplyPath { destination };
+
+	nodes[0].messenger.send_onion_message(test_msg, instructions).unwrap();
+	nodes[3].custom_message_handler.expect_message(TestCustomMessage::Pong);
+	pass_along_path(&nodes);
+}
+
+#[test]
+fn test_blinded_path_no_padding_for_compact_path() {
+	// Check that for a compact blinded path, no padding is applied.
+	let nodes = create_nodes(4);
+	let secp_ctx = Secp256k1::new();
+
+	// Include some short_channel_id, so that MessageRouter uses this to create compact blinded paths.
+	let intermediate_nodes = [
+		MessageForwardNode { node_id: nodes[1].node_id, short_channel_id: Some(24) },
+		MessageForwardNode { node_id: nodes[2].node_id, short_channel_id: Some(25) },
+	];
+	// Update the context to create a larger final receive TLVs, ensuring that
+	// the hop sizes vary before padding.
+	let context = MessageContext::Custom(vec![0u8; 42]);
+	let blinded_path = BlindedMessagePath::new(&intermediate_nodes, nodes[3].node_id, context, &*nodes[3].entropy_source, &secp_ctx).unwrap();
+
+	assert!(!is_padded(&blinded_path.blinded_hops(), MESSAGE_PADDING_ROUND_OFF));
+}
+
 #[test]
 fn we_are_intro_node() {
 	// If we are sending straight to a blinded path and we are the introduction node, we need to