Randomize initial onion packet data.

This avoids at least the trivial hop count discovery attack, though
other obvious ones remain and are slightly harder to avoid.

See lightning/bolts#697

Author: TheBlueMatt

lightning/src/chain/keysinterface.rs

@@ -77,8 +77,8 @@ pub trait KeysInterface: Send + Sync {
 	/// Get a new set of ChannelKeys for per-channel secrets. These MUST be unique even if you
 	/// restarted with some stale data!
 	fn get_channel_keys(&self, inbound: bool) -> ChannelKeys;
-	/// Get a secret for construting an onion packet
-	fn get_session_key(&self) -> SecretKey;
+	/// Get a secret and PRNG seed for construting an onion packet
+	fn get_onion_rand(&self) -> (SecretKey, [u8; 32]);
 	/// Get a unique temporary channel id. Channels will be referred to by this until the funding
 	/// transaction is created, at which point they will use the outpoint in the funding
 	/// transaction.
@@ -258,13 +258,20 @@ impl KeysInterface for KeysManager {
 		}
 	}
 
-	fn get_session_key(&self) -> SecretKey {
+	fn get_onion_rand(&self) -> (SecretKey, [u8; 32]) {
 		let mut sha = self.unique_start.clone();
 
 		let child_ix = self.session_child_index.fetch_add(1, Ordering::AcqRel);
 		let child_privkey = self.session_master_key.ckd_priv(&self.secp_ctx, ChildNumber::from_hardened_idx(child_ix as u32).expect("key space exhausted")).expect("Your RNG is busted");
 		sha.input(&child_privkey.private_key.key[..]);
-		SecretKey::from_slice(&Sha256::from_engine(sha).into_inner()).expect("Your RNG is busted")
+
+		let mut rng_seed = sha.clone();
+		// Not exactly the most ideal construction, but the second value will get fed into
+		// ChaCha so it is another step harder to break.
+		rng_seed.input(b"RNG Seed Salt");
+		sha.input(b"Session Key Salt");
+		(SecretKey::from_slice(&Sha256::from_engine(sha).into_inner()).expect("Your RNG is busted"),
+		Sha256::from_engine(rng_seed).into_inner())
 	}
 
 	fn get_channel_id(&self) -> [u8; 32] {

lightning/src/ln/channel.rs

@@ -4157,7 +4157,7 @@ mod tests {
 		}
 
 		fn get_channel_keys(&self, _inbound: bool) -> ChannelKeys { self.chan_keys.clone() }
-		fn get_session_key(&self) -> SecretKey { panic!(); }
+		fn get_onion_rand(&self) -> (SecretKey, [u8; 32]) { panic!(); }
 		fn get_channel_id(&self) -> [u8; 32] { [0; 32] }
 	}
 

lightning/src/ln/channelmanager.rs

@@ -1082,14 +1082,14 @@ impl<'a> ChannelManager<'a> {
 			}
 		}
 
-		let session_priv = self.keys_manager.get_session_key();
+		let (session_priv, prng_seed) = self.keys_manager.get_onion_rand();
 
 		let cur_height = self.latest_block_height.load(Ordering::Acquire) as u32 + 1;
 
 		let onion_keys = secp_call!(onion_utils::construct_onion_keys(&self.secp_ctx, &route, &session_priv),
 				APIError::RouteError{err: "Pubkey along hop was maliciously selected"});
 		let (onion_payloads, htlc_msat, htlc_cltv) = onion_utils::build_onion_payloads(&route, cur_height)?;
-		let onion_packet = onion_utils::construct_onion_packet(onion_payloads, onion_keys, &payment_hash);
+		let onion_packet = onion_utils::construct_onion_packet(onion_payloads, onion_keys, prng_seed, &payment_hash);
 
 		let _ = self.total_consistency_lock.read().unwrap();
 

lightning/src/ln/functional_tests.rs

@@ -1435,7 +1435,7 @@ fn do_channel_reserve_test(test_recv: bool) {
 		let cur_height = nodes[0].node.latest_block_height.load(Ordering::Acquire) as u32 + 1;
 		let onion_keys = onion_utils::construct_onion_keys(&secp_ctx, &route, &session_priv).unwrap();
 		let (onion_payloads, htlc_msat, htlc_cltv) = onion_utils::build_onion_payloads(&route, cur_height).unwrap();
-		let onion_packet = onion_utils::construct_onion_packet(onion_payloads, onion_keys, &our_payment_hash);
+		let onion_packet = onion_utils::construct_onion_packet(onion_payloads, onion_keys, [0; 32], &our_payment_hash);
 		let msg = msgs::UpdateAddHTLC {
 			channel_id: chan_1.2,
 			htlc_id,
@@ -4815,7 +4815,7 @@ fn test_onion_failure() {
 		let onion_keys = onion_utils::construct_onion_keys(&Secp256k1::new(), &route, &session_priv).unwrap();
 		let (mut onion_payloads, _htlc_msat, _htlc_cltv) = onion_utils::build_onion_payloads(&route, cur_height).unwrap();
 		onion_payloads[0].realm = 3;
-		msg.onion_routing_packet = onion_utils::construct_onion_packet(onion_payloads, onion_keys, &payment_hash);
+		msg.onion_routing_packet = onion_utils::construct_onion_packet(onion_payloads, onion_keys, [0; 32], &payment_hash);
 	}, ||{}, true, Some(PERM|1), Some(msgs::HTLCFailChannelUpdate::ChannelClosed{short_channel_id: channels[1].0.contents.short_channel_id, is_permanent: true}));//XXX incremented channels idx here
 
 	// final node failure
@@ -4825,7 +4825,7 @@ fn test_onion_failure() {
 		let onion_keys = onion_utils::construct_onion_keys(&Secp256k1::new(), &route, &session_priv).unwrap();
 		let (mut onion_payloads, _htlc_msat, _htlc_cltv) = onion_utils::build_onion_payloads(&route, cur_height).unwrap();
 		onion_payloads[1].realm = 3;
-		msg.onion_routing_packet = onion_utils::construct_onion_packet(onion_payloads, onion_keys, &payment_hash);
+		msg.onion_routing_packet = onion_utils::construct_onion_packet(onion_payloads, onion_keys, [0; 32], &payment_hash);
 	}, ||{}, false, Some(PERM|1), Some(msgs::HTLCFailChannelUpdate::ChannelClosed{short_channel_id: channels[1].0.contents.short_channel_id, is_permanent: true}));
 
 	// the following three with run_onion_failure_test_with_fail_intercept() test only the origin node
@@ -5003,7 +5003,7 @@ fn test_onion_failure() {
 		route.hops[1].cltv_expiry_delta += CLTV_FAR_FAR_AWAY + route.hops[0].cltv_expiry_delta + 1;
 		let onion_keys = onion_utils::construct_onion_keys(&Secp256k1::new(), &route, &session_priv).unwrap();
 		let (onion_payloads, _, htlc_cltv) = onion_utils::build_onion_payloads(&route, height).unwrap();
-		let onion_packet = onion_utils::construct_onion_packet(onion_payloads, onion_keys, &payment_hash);
+		let onion_packet = onion_utils::construct_onion_packet(onion_payloads, onion_keys, [0; 32], &payment_hash);
 		msg.cltv_expiry = htlc_cltv;
 		msg.onion_routing_packet = onion_packet;
 	}, ||{}, true, Some(21), None);
@@ -5253,7 +5253,7 @@ fn test_update_add_htlc_bolt2_receiver_check_max_htlc_limit() {
 	let cur_height = nodes[0].node.latest_block_height.load(Ordering::Acquire) as u32 + 1;
 	let onion_keys = onion_utils::construct_onion_keys(&Secp256k1::signing_only(), &route, &session_priv).unwrap();
 	let (onion_payloads, _htlc_msat, htlc_cltv) = onion_utils::build_onion_payloads(&route, cur_height).unwrap();
-	let onion_packet = onion_utils::construct_onion_packet(onion_payloads, onion_keys, &our_payment_hash);
+	let onion_packet = onion_utils::construct_onion_packet(onion_payloads, onion_keys, [0; 32], &our_payment_hash);
 
 	let mut msg = msgs::UpdateAddHTLC {
 		channel_id: chan.2,

lightning/src/ln/onion_utils.rs

@@ -161,11 +161,19 @@ fn xor_bufs(dst: &mut[u8], src: &[u8]) {
 	}
 }
 
+
 const ZERO:[u8; 21*65] = [0; 21*65];
-pub(super) fn construct_onion_packet(mut payloads: Vec<msgs::OnionHopData>, onion_keys: Vec<OnionKeys>, associated_data: &PaymentHash) -> msgs::OnionPacket {
+pub(super) fn construct_onion_packet(payloads: Vec<msgs::OnionHopData>, onion_keys: Vec<OnionKeys>, prng_seed: [u8; 32], associated_data: &PaymentHash) -> msgs::OnionPacket {
 	let mut buf = Vec::with_capacity(21*65);
 	buf.resize(21*65, 0);
 
+	let mut chacha = ChaCha20::new(&prng_seed, &[0; 8]);
+	chacha.process(&[0; 21*65], &mut buf);
+
+	construct_onion_packet_with_init_noise(payloads, onion_keys, buf, associated_data)
+}
+
+fn construct_onion_packet_with_init_noise(mut payloads: Vec<msgs::OnionHopData>, onion_keys: Vec<OnionKeys>, mut buf: Vec<u8>, associated_data: &PaymentHash) -> msgs::OnionPacket {
 	let filler = {
 		let iters = payloads.len() - 1;
 		let end_len = iters * 65;
@@ -547,7 +555,9 @@ mod tests {
 			},
 		);
 
-		let packet = super::construct_onion_packet(payloads, onion_keys, &PaymentHash([0x42; 32]));
+		let mut buf = Vec::with_capacity(21*65);
+		buf.resize(21*65, 0);
+		let packet = super::construct_onion_packet_with_init_noise(payloads, onion_keys, buf, &PaymentHash([0x42; 32]));
 		// Just check the final packet encoding, as it includes all the per-hop vectors in it
 		// anyway...
 		assert_eq!(packet.encode(), hex::decode("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").unwrap());

lightning/src/util/chacha20.rs

@@ -224,6 +224,7 @@ mod real_chacha {
 			self.offset = 0;
 		}
 
+		#[inline] // Useful cause input may be 0s on stack that should be optimized out
 		pub fn process(&mut self, input: &[u8], output: &mut [u8]) {
 			assert!(input.len() == output.len());
 			let len = input.len();

lightning/src/util/test_utils.rs

@@ -226,10 +226,10 @@ impl keysinterface::KeysInterface for TestKeysInterface {
 	fn get_shutdown_pubkey(&self) -> PublicKey { self.backing.get_shutdown_pubkey() }
 	fn get_channel_keys(&self, inbound: bool) -> keysinterface::ChannelKeys { self.backing.get_channel_keys(inbound) }
 
-	fn get_session_key(&self) -> SecretKey {
+	fn get_onion_rand(&self) -> (SecretKey, [u8; 32]) {
 		match *self.override_session_priv.lock().unwrap() {
-			Some(key) => key.clone(),
-			None => self.backing.get_session_key()
+			Some(key) => (key.clone(), [0; 32]),
+			None => self.backing.get_onion_rand()
 		}
 	}