onion_utils: add next_hop_packet_pubkey method

[rust-lightning] / lightning / src / ln / onion_utils.rs

diff --git a/lightning/src/ln/onion_utils.rs b/lightning/src/ln/onion_utils.rs
index 1df374d7e007b8784d7235c0a216fea4679d408e..b223a344dbe204aafcd511c5efc2d4e035cf1ba9 100644 (file)
--- a/lightning/src/ln/onion_utils.rs
+++ b/lightning/src/ln/onion_utils.rs
@@ -74,6 +74,17 @@ pub(super) fn gen_ammag_from_shared_secret(shared_secret: &[u8]) -> [u8; 32] {
        Hmac::from_engine(hmac).into_inner()
 }
 
+pub(super) fn next_hop_packet_pubkey<T: secp256k1::Signing + secp256k1::Verification>(secp_ctx: &Secp256k1<T>, mut packet_pubkey: PublicKey, packet_shared_secret: &[u8; 32]) -> Result<PublicKey, secp256k1::Error> {
+       let blinding_factor = {
+               let mut sha = Sha256::engine();
+               sha.input(&packet_pubkey.serialize()[..]);
+               sha.input(packet_shared_secret);
+               Sha256::from_engine(sha).into_inner()
+       };
+
+       packet_pubkey.mul_assign(secp_ctx, &blinding_factor[..]).map(|_| packet_pubkey)
+}
+
 // can only fail if an intermediary hop has an invalid public key or session_priv is invalid
 #[inline]
 pub(super) fn construct_onion_keys_callback<T: secp256k1::Signing, FType: FnMut(SharedSecret, [u8; 32], PublicKey, &RouteHop, usize)> (secp_ctx: &Secp256k1<T>, path: &Vec<RouteHop>, session_priv: &SecretKey, mut callback: FType) -> Result<(), secp256k1::Error> {