f: blinded tweak calculation

Author: arik-so

lightning/src/ln/onion_utils.rs

@@ -1595,11 +1595,17 @@ where
 			#[cfg(trampoline)]
 			msgs::InboundOnionPayload::TrampolineEntrypoint(hop_data) => {
 				let incoming_trampoline_public_key = hop_data.trampoline_packet.public_key;
+				let trampoline_blinded_node_id_tweak = hop_data.current_path_key.map(|bp| {
+					let blinded_tlvs_ss = node_signer.ecdh(recipient, &bp, None).unwrap().secret_bytes();
+					let mut hmac = HmacEngine::<Sha256>::new(b"blinded_node_id");
+					hmac.input(blinded_tlvs_ss.as_ref());
+					Scalar::from_be_bytes(Hmac::from_engine(hmac).to_byte_array()).unwrap()
+				});
 				let trampoline_shared_secret = node_signer
 					.ecdh(
 						recipient,
 						&incoming_trampoline_public_key,
-						blinded_node_id_tweak.as_ref(),
+						trampoline_blinded_node_id_tweak.as_ref(),
 					)
 					.unwrap()
 					.secret_bytes();