Introduce Padding for Blinded Payment Paths

Author: shaavan

lightning/src/blinded_path/payment.rs

@@ -13,7 +13,7 @@ use bitcoin::hashes::hmac::Hmac;
 use bitcoin::hashes::sha256::Hash as Sha256;
 use bitcoin::secp256k1::{self, PublicKey, Secp256k1, SecretKey};
 
-use crate::blinded_path::utils;
+use crate::blinded_path::utils::{self, BlindedPathWithPadding};
 use crate::blinded_path::{BlindedHop, BlindedPath, IntroductionNode, NodeIdLookUp};
 use crate::crypto::streams::ChaChaPolyReadAdapter;
 use crate::io;
@@ -546,6 +546,10 @@ impl Readable for BlindedPaymentTlvs {
 	}
 }
 
+/// Represents the padding round off size (in bytes) that
+/// is used to pad payment bilnded path's [`BlindedHop`]
+pub(crate) const PAYMENT_PADDING_ROUND_OFF: usize = 30;
+
 /// Construct blinded payment hops for the given `intermediate_nodes` and payee info.
 pub(super) fn blinded_hops<T: secp256k1::Signing + secp256k1::Verification>(
 	secp_ctx: &Secp256k1<T>, intermediate_nodes: &[PaymentForwardNode], payee_node_id: PublicKey,
@@ -558,7 +562,9 @@ pub(super) fn blinded_hops<T: secp256k1::Signing + secp256k1::Verification>(
 		.map(|node| BlindedPaymentTlvsRef::Forward(&node.tlvs))
 		.chain(core::iter::once(BlindedPaymentTlvsRef::Receive(&payee_tlvs)));
 
-	let path = pks.zip(tlvs);
+	let path = pks.zip(
+		tlvs.map(|tlv| BlindedPathWithPadding { tlvs: tlv, round_off: PAYMENT_PADDING_ROUND_OFF }),
+	);
 
 	utils::construct_blinded_hops(secp_ctx, path, session_priv)
 }

lightning/src/ln/blinded_payment_tests.rs

@@ -346,7 +346,7 @@ fn do_forward_checks_failure(check: ForwardCheckFail, intro_fails: bool) {
 	let mut route_params = get_blinded_route_parameters(amt_msat, payment_secret, 1, 1_0000_0000,
 		nodes.iter().skip(1).map(|n| n.node.get_our_node_id()).collect(),
 		&[&chan_upd_1_2, &chan_upd_2_3], &chanmon_cfgs[3].keys_manager);
-	route_params.payment_params.max_path_length = 17;
+	route_params.payment_params.max_path_length = 16;
 
 	let route = get_route(&nodes[0], &route_params).unwrap();
 	node_cfgs[0].router.expect_find_route(route_params.clone(), Ok(route.clone()));
@@ -861,6 +861,8 @@ fn do_multi_hop_receiver_fail(check: ReceiveCheckFail) {
 		nodes.iter().skip(1).map(|n| n.node.get_our_node_id()).collect(), &[&chan_upd_1_2],
 		&chanmon_cfgs[2].keys_manager);
 
+	route_params.payment_params.max_path_length = 17;
+
 	let route = if check == ReceiveCheckFail::ProcessPendingHTLCsCheck {
 		let mut route = get_route(&nodes[0], &route_params).unwrap();
 		// Set the final CLTV expiry too low to trigger the failure in process_pending_htlc_forwards.