Merge pull request #2146 from valentinewallace/2023-03-blinded-pathfinding-groundwork

[rust-lightning] / lightning / src / blinded_path / utils.rs

diff --git a/lightning/src/blinded_path/utils.rs b/lightning/src/blinded_path/utils.rs
new file mode 100644 (file)
index 0000000..1993ad9
--- /dev/null
+++ b/lightning/src/blinded_path/utils.rs
@@ -0,0 +1,98 @@
+// This file is Copyright its original authors, visible in version control
+// history.
+//
+// This file is licensed under the Apache License, Version 2.0 <LICENSE-APACHE
+// or http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your option.
+// You may not use this file except in accordance with one or both of these
+// licenses.
+
+//! Onion message utility methods live here.
+
+use bitcoin::hashes::{Hash, HashEngine};
+use bitcoin::hashes::hmac::{Hmac, HmacEngine};
+use bitcoin::hashes::sha256::Hash as Sha256;
+use bitcoin::secp256k1::{self, PublicKey, Secp256k1, SecretKey, Scalar};
+use bitcoin::secp256k1::ecdh::SharedSecret;
+
+use super::BlindedPath;
+use crate::ln::onion_utils;
+use crate::onion_message::Destination;
+
+use crate::prelude::*;
+
+// TODO: DRY with onion_utils::construct_onion_keys_callback
+#[inline]
+pub(crate) fn construct_keys_callback<T: secp256k1::Signing + secp256k1::Verification,
+       FType: FnMut(PublicKey, SharedSecret, PublicKey, [u8; 32], Option<PublicKey>, Option<Vec<u8>>)>(
+       secp_ctx: &Secp256k1<T>, unblinded_path: &[PublicKey], destination: Option<Destination>,
+       session_priv: &SecretKey, mut callback: FType
+) -> Result<(), secp256k1::Error> {
+       let mut msg_blinding_point_priv = session_priv.clone();
+       let mut msg_blinding_point = PublicKey::from_secret_key(secp_ctx, &msg_blinding_point_priv);
+       let mut onion_packet_pubkey_priv = msg_blinding_point_priv.clone();
+       let mut onion_packet_pubkey = msg_blinding_point.clone();
+
+       macro_rules! build_keys {
+               ($pk: expr, $blinded: expr, $encrypted_payload: expr) => {{
+                       let encrypted_data_ss = SharedSecret::new(&$pk, &msg_blinding_point_priv);
+
+                       let blinded_hop_pk = if $blinded { $pk } else {
+                               let hop_pk_blinding_factor = {
+                                       let mut hmac = HmacEngine::<Sha256>::new(b"blinded_node_id");
+                                       hmac.input(encrypted_data_ss.as_ref());
+                                       Hmac::from_engine(hmac).into_inner()
+                               };
+                               $pk.mul_tweak(secp_ctx, &Scalar::from_be_bytes(hop_pk_blinding_factor).unwrap())?
+                       };
+                       let onion_packet_ss = SharedSecret::new(&blinded_hop_pk, &onion_packet_pubkey_priv);
+
+                       let rho = onion_utils::gen_rho_from_shared_secret(encrypted_data_ss.as_ref());
+                       let unblinded_pk_opt = if $blinded { None } else { Some($pk) };
+                       callback(blinded_hop_pk, onion_packet_ss, onion_packet_pubkey, rho, unblinded_pk_opt, $encrypted_payload);
+                       (encrypted_data_ss, onion_packet_ss)
+               }}
+       }
+
+       macro_rules! build_keys_in_loop {
+               ($pk: expr, $blinded: expr, $encrypted_payload: expr) => {
+                       let (encrypted_data_ss, onion_packet_ss) = build_keys!($pk, $blinded, $encrypted_payload);
+
+                       let msg_blinding_point_blinding_factor = {
+                               let mut sha = Sha256::engine();
+                               sha.input(&msg_blinding_point.serialize()[..]);
+                               sha.input(encrypted_data_ss.as_ref());
+                               Sha256::from_engine(sha).into_inner()
+                       };
+
+                       msg_blinding_point_priv = msg_blinding_point_priv.mul_tweak(&Scalar::from_be_bytes(msg_blinding_point_blinding_factor).unwrap())?;
+                       msg_blinding_point = PublicKey::from_secret_key(secp_ctx, &msg_blinding_point_priv);
+
+                       let onion_packet_pubkey_blinding_factor = {
+                               let mut sha = Sha256::engine();
+                               sha.input(&onion_packet_pubkey.serialize()[..]);
+                               sha.input(onion_packet_ss.as_ref());
+                               Sha256::from_engine(sha).into_inner()
+                       };
+                       onion_packet_pubkey_priv = onion_packet_pubkey_priv.mul_tweak(&Scalar::from_be_bytes(onion_packet_pubkey_blinding_factor).unwrap())?;
+                       onion_packet_pubkey = PublicKey::from_secret_key(secp_ctx, &onion_packet_pubkey_priv);
+               };
+       }
+
+       for pk in unblinded_path {
+               build_keys_in_loop!(*pk, false, None);
+       }
+       if let Some(dest) = destination {
+               match dest {
+                       Destination::Node(pk) => {
+                               build_keys!(pk, false, None);
+                       },
+                       Destination::BlindedPath(BlindedPath { blinded_hops, .. }) => {
+                               for hop in blinded_hops {
+                                       build_keys_in_loop!(hop.blinded_node_id, true, Some(hop.encrypted_payload));
+                               }
+                       },
+               }
+       }
+       Ok(())
+}