Make BlindedMessagePath creation infallible

The LDK codebase in general is comfortable panicking if the entropy source
provided to it is dysfunctional. Up until now we made an exception for blinded
path creation, where we would handle an error that could occur on mul_tweak
that could only occur if the session_priv provided was not actually random.
In comparable cases in onion_utils, we would panic instead.

In upcoming commits, we will be including blinded paths in outbound
revoke_and_ack messages as part of implementing async payments, where it is
difficult to handle failing back an HTLC if blinded path creation fails. Thus
we now have an incentive to make the blinded path creation methods infallible,
so do so here.

Author: valentinewallace

lightning-dns-resolver/src/lib.rs

@@ -239,8 +239,7 @@ mod test {
 				context,
 				&keys,
 				secp_ctx,
-			)
-			.unwrap()])
+			)])
 		}
 	}
 	impl Deref for DirectlyConnectedRouter {
@@ -349,8 +348,7 @@ mod test {
 			query_context,
 			&*payer_keys,
 			&secp_ctx,
-		)
-		.unwrap();
+		);
 		payer.pending_messages.lock().unwrap().push((
 			DNSResolverMessage::DNSSECQuery(msg),
 			MessageSendInstructions::WithSpecifiedReplyPath {

lightning/src/blinded_path/message.rs

@@ -57,23 +57,19 @@ impl BlindedMessagePath {
 	pub fn one_hop<ES: Deref, T: secp256k1::Signing + secp256k1::Verification>(
 		recipient_node_id: PublicKey, local_node_receive_key: ReceiveAuthKey,
 		context: MessageContext, entropy_source: ES, secp_ctx: &Secp256k1<T>,
-	) -> Result<Self, ()>
+	) -> Self
 	where
 		ES::Target: EntropySource,
 	{
 		Self::new(&[], recipient_node_id, local_node_receive_key, context, entropy_source, secp_ctx)
 	}
 
-	/// Create a path for an onion message, to be forwarded along `node_pks`. The last node
-	/// pubkey in `node_pks` will be the destination node.
-	///
-	/// Errors if no hops are provided or if `node_pk`(s) are invalid.
-	//  TODO: make all payloads the same size with padding + add dummy hops
+	/// Create a path for an onion message, to be forwarded along `node_pks`.
 	pub fn new<ES: Deref, T: secp256k1::Signing + secp256k1::Verification>(
 		intermediate_nodes: &[MessageForwardNode], recipient_node_id: PublicKey,
 		local_node_receive_key: ReceiveAuthKey, context: MessageContext, entropy_source: ES,
 		secp_ctx: &Secp256k1<T>,
-	) -> Result<Self, ()>
+	) -> Self
 	where
 		ES::Target: EntropySource,
 	{
@@ -96,7 +92,7 @@ impl BlindedMessagePath {
 		intermediate_nodes: &[MessageForwardNode], recipient_node_id: PublicKey,
 		dummy_hop_count: usize, local_node_receive_key: ReceiveAuthKey, context: MessageContext,
 		entropy_source: ES, secp_ctx: &Secp256k1<T>,
-	) -> Result<Self, ()>
+	) -> Self
 	where
 		ES::Target: EntropySource,
 	{
@@ -107,7 +103,7 @@ impl BlindedMessagePath {
 		let blinding_secret =
 			SecretKey::from_slice(&blinding_secret_bytes[..]).expect("RNG is busted");
 
-		Ok(Self(BlindedPath {
+		Self(BlindedPath {
 			introduction_node,
 			blinding_point: PublicKey::from_secret_key(secp_ctx, &blinding_secret),
 			blinded_hops: blinded_hops(
@@ -118,9 +114,8 @@ impl BlindedMessagePath {
 				context,
 				&blinding_secret,
 				local_node_receive_key,
-			)
-			.map_err(|_| ())?,
-		}))
+			),
+		})
 	}
 
 	/// Attempts to a use a compact representation for the [`IntroductionNode`] by using a directed
@@ -669,7 +664,7 @@ pub(super) fn blinded_hops<T: secp256k1::Signing + secp256k1::Verification>(
 	secp_ctx: &Secp256k1<T>, intermediate_nodes: &[MessageForwardNode],
 	recipient_node_id: PublicKey, dummy_hop_count: usize, context: MessageContext,
 	session_priv: &SecretKey, local_node_receive_key: ReceiveAuthKey,
-) -> Result<Vec<BlindedHop>, secp256k1::Error> {
+) -> Vec<BlindedHop> {
 	let dummy_count = cmp::min(dummy_hop_count, MAX_DUMMY_HOPS_COUNT);
 	let pks = intermediate_nodes
 		.iter()

lightning/src/blinded_path/payment.rs

@@ -116,7 +116,6 @@ impl BlindedPaymentPath {
 	/// Create a blinded path for a payment, to be forwarded along `intermediate_nodes`.
 	///
 	/// Errors if:
-	/// * a provided node id is invalid
 	/// * [`BlindedPayInfo`] calculation results in an integer overflow
 	/// * any unknown features are required in the provided [`ForwardTlvs`]
 	//  TODO: make all payloads the same size with padding + add dummy hops
@@ -151,8 +150,7 @@ impl BlindedPaymentPath {
 					payee_node_id,
 					payee_tlvs,
 					&blinding_secret,
-				)
-				.map_err(|_| ())?,
+				),
 			},
 			payinfo: blinded_payinfo,
 		})
@@ -663,7 +661,7 @@ pub(crate) const PAYMENT_PADDING_ROUND_OFF: usize = 30;
 pub(super) fn blinded_hops<T: secp256k1::Signing + secp256k1::Verification>(
 	secp_ctx: &Secp256k1<T>, intermediate_nodes: &[PaymentForwardNode], payee_node_id: PublicKey,
 	payee_tlvs: ReceiveTlvs, session_priv: &SecretKey,
-) -> Result<Vec<BlindedHop>, secp256k1::Error> {
+) -> Vec<BlindedHop> {
 	let pks = intermediate_nodes
 		.iter()
 		.map(|node| (node.node_id, None))

lightning/src/blinded_path/utils.rs

@@ -51,10 +51,8 @@ macro_rules! build_keys_helper {
 						hmac.input(encrypted_data_ss.as_ref());
 						Hmac::from_engine(hmac).to_byte_array()
 					};
-					pk.mul_tweak(
-						$secp_ctx,
-						&Scalar::from_be_bytes(hop_pk_blinding_factor).unwrap(),
-					)?
+					pk.mul_tweak($secp_ctx, &Scalar::from_be_bytes(hop_pk_blinding_factor).unwrap())
+						.expect("RNG is busted")
 				};
 				let onion_packet_ss = SharedSecret::new(&blinded_hop_pk, &onion_packet_pubkey_priv);
 
@@ -84,9 +82,9 @@ macro_rules! build_keys_helper {
 					Sha256::from_engine(sha).to_byte_array()
 				};
 
-				msg_blinding_point_priv = msg_blinding_point_priv.mul_tweak(
-					&Scalar::from_be_bytes(msg_blinding_point_blinding_factor).unwrap(),
-				)?;
+				msg_blinding_point_priv = msg_blinding_point_priv
+					.mul_tweak(&Scalar::from_be_bytes(msg_blinding_point_blinding_factor).unwrap())
+					.expect("RNG is busted");
 				msg_blinding_point =
 					PublicKey::from_secret_key($secp_ctx, &msg_blinding_point_priv);
 
@@ -96,9 +94,9 @@ macro_rules! build_keys_helper {
 					sha.input(onion_packet_ss.as_ref());
 					Sha256::from_engine(sha).to_byte_array()
 				};
-				onion_packet_pubkey_priv = onion_packet_pubkey_priv.mul_tweak(
-					&Scalar::from_be_bytes(onion_packet_pubkey_blinding_factor).unwrap(),
-				)?;
+				onion_packet_pubkey_priv = onion_packet_pubkey_priv
+					.mul_tweak(&Scalar::from_be_bytes(onion_packet_pubkey_blinding_factor).unwrap())
+					.expect("RNG is busted");
 				onion_packet_pubkey =
 					PublicKey::from_secret_key($secp_ctx, &onion_packet_pubkey_priv);
 			};
@@ -109,8 +107,7 @@ macro_rules! build_keys_helper {
 pub(crate) fn construct_keys_for_onion_message<'a, T, I, F>(
 	secp_ctx: &Secp256k1<T>, unblinded_path: I, destination: Destination, session_priv: &SecretKey,
 	mut callback: F,
-) -> Result<(), secp256k1::Error>
-where
+) where
 	T: secp256k1::Signing + secp256k1::Verification,
 	I: Iterator<Item = PublicKey>,
 	F: FnMut(SharedSecret, PublicKey, [u8; 32], Option<PublicKey>, Option<Vec<u8>>),
@@ -134,13 +131,11 @@ where
 			}
 		},
 	}
-	Ok(())
 }
 
 fn construct_keys_for_blinded_path<'a, T, I, F, H>(
 	secp_ctx: &Secp256k1<T>, unblinded_path: I, session_priv: &SecretKey, mut callback: F,
-) -> Result<(), secp256k1::Error>
-where
+) where
 	T: secp256k1::Signing + secp256k1::Verification,
 	H: Borrow<PublicKey>,
 	I: Iterator<Item = H>,
@@ -151,7 +146,6 @@ where
 	for pk in unblinded_path {
 		build_keys_in_loop!(pk, false, None);
 	}
-	Ok(())
 }
 
 struct PublicKeyWithTlvs<W: Writeable> {
@@ -168,7 +162,7 @@ impl<W: Writeable> Borrow<PublicKey> for PublicKeyWithTlvs<W> {
 
 pub(crate) fn construct_blinded_hops<'a, T, I, W>(
 	secp_ctx: &Secp256k1<T>, unblinded_path: I, session_priv: &SecretKey,
-) -> Result<Vec<BlindedHop>, secp256k1::Error>
+) -> Vec<BlindedHop>
 where
 	T: secp256k1::Signing + secp256k1::Verification,
 	I: Iterator<Item = ((PublicKey, Option<ReceiveAuthKey>), W)>,
@@ -194,8 +188,8 @@ where
 				),
 			});
 		},
-	)?;
-	Ok(blinded_hops)
+	);
+	blinded_hops
 }
 
 /// Encrypt TLV payload to be used as a [`crate::blinded_path::BlindedHop::encrypted_payload`].

lightning/src/ln/blinded_payment_tests.rs

@@ -1552,7 +1552,7 @@ fn route_blinding_spec_test_vector() {
 	];
 	let mut dave_eve_blinded_hops = blinded_path::utils::construct_blinded_hops(
 		&secp_ctx, path.into_iter(), &dave_eve_session_priv,
-	).unwrap();
+	);
 
 	// Concatenate an additional Bob -> Carol blinded path to the Eve -> Dave blinded path.
 	let bob_carol_session_priv = secret_from_hex("0202020202020202020202020202020202020202020202020202020202020202");
@@ -1563,7 +1563,7 @@ fn route_blinding_spec_test_vector() {
 	];
 	let bob_carol_blinded_hops = blinded_path::utils::construct_blinded_hops(
 		&secp_ctx, path.into_iter(), &bob_carol_session_priv,
-	).unwrap();
+	);
 
 	let mut blinded_hops = bob_carol_blinded_hops;
 	blinded_hops.append(&mut dave_eve_blinded_hops);
@@ -2030,7 +2030,7 @@ fn do_test_trampoline_single_hop_receive(success: bool) {
 		let path = [((carol_node_id, None), WithoutLength(&carol_unblinded_tlvs))];
 		blinded_path::utils::construct_blinded_hops(
 			&secp_ctx, path.into_iter(), &carol_alice_trampoline_session_priv,
-		).unwrap()
+		)
 	} else {
 		let payee_tlvs = blinded_path::payment::TrampolineForwardTlvs {
 			next_trampoline: alice_node_id,
@@ -2051,7 +2051,7 @@ fn do_test_trampoline_single_hop_receive(success: bool) {
 		let path = [((carol_node_id, None), WithoutLength(&carol_unblinded_tlvs))];
 		blinded_path::utils::construct_blinded_hops(
 			&secp_ctx, path.into_iter(), &carol_alice_trampoline_session_priv,
-		).unwrap()
+		)
 	};
 
 	let route = Route {
@@ -2255,7 +2255,7 @@ fn test_trampoline_unblinded_receive() {
 	let carol_blinding_point = PublicKey::from_secret_key(&secp_ctx, &carol_alice_trampoline_session_priv);
 	let carol_blinded_hops = blinded_path::utils::construct_blinded_hops(
 		&secp_ctx, path.into_iter(), &carol_alice_trampoline_session_priv,
-	).unwrap();
+	);
 
 	let route = Route {
 		paths: vec![Path {