Add get_phantom_scid and get_phantom_route_hints + scid_utils::fake_scid module

See method and module docs for more details

Author: valentinewallace

fuzz/src/full_stack.rs

@@ -390,6 +390,7 @@ pub fn do_test(data: &[u8], logger: &Arc<dyn Logger>) {
 		best_block: BestBlock::from_genesis(network),
 	};
 	let channelmanager = Arc::new(ChannelManager::new(fee_est.clone(), monitor.clone(), broadcast.clone(), Arc::clone(&logger), keys_manager.clone(), config, params));
+	keys_manager.counter.fetch_sub(1, Ordering::AcqRel);
 	let our_id = PublicKey::from_secret_key(&Secp256k1::signing_only(), &keys_manager.get_node_secret(Recipient::Node).unwrap());
 	let network_graph = Arc::new(NetworkGraph::new(genesis_block(network).block_hash()));
 	let net_graph_msg_handler = Arc::new(NetGraphMsgHandler::new(Arc::clone(&network_graph), None, Arc::clone(&logger)));

lightning/src/ln/channelmanager.rs

@@ -52,6 +52,7 @@ use chain::keysinterface::{Sign, KeysInterface, KeysManager, InMemorySigner, Rec
 use util::config::UserConfig;
 use util::events::{EventHandler, EventsProvider, MessageSendEvent, MessageSendEventsProvider, ClosureReason};
 use util::{byte_utils, events};
+use util::scid_utils::fake_scid;
 use util::ser::{BigSize, FixedLengthReader, Readable, ReadableArgs, MaybeReadable, Writeable, Writer};
 use util::logger::{Level, Logger};
 use util::errors::APIError;
@@ -973,6 +974,13 @@ pub struct ChannelManager<Signer: Sign, M: Deref, T: Deref, K: Deref, F: Deref,
 
 	inbound_payment_key: inbound_payment::ExpandedKey,
 
+	/// LDK puts the [fake scids] that it generates into namespaces, to identify the type of an
+	/// incoming payment. To make it harder for a third-party to identify the type of a payment,
+	/// we encrypt the namespace identifier using these bytes.
+	///
+	/// [fake scids]: crate::util::scid_utils::fake_scid
+	fake_scid_rand_bytes: [u8; 32],
+
 	/// Used to track the last value sent in a node_announcement "timestamp" field. We ensure this
 	/// value increases strictly since we don't assume access to a time source.
 	last_node_announcement_serial: AtomicUsize,
@@ -1309,6 +1317,19 @@ pub enum PaymentSendFailure {
 	},
 }
 
+/// Route hints used in constructing invoices for [phantom node payents].
+///
+/// [phantom node payments]: crate::chain::keysinterface::PhantomKeysManager
+pub struct PhantomRouteHints {
+	/// The list of channels to be included in the invoice route hints.
+	pub channels: Vec<ChannelDetails>,
+	/// A fake scid used for representing the phantom node's fake channel in generating the invoice
+	/// route hints.
+	pub phantom_scid: u64,
+	/// The pubkey of the real backing node that would ultimately receive the payment.
+	pub real_node_pubkey: PublicKey,
+}
+
 macro_rules! handle_error {
 	($self: ident, $internal: expr, $counterparty_node_id: expr) => {
 		match $internal {
@@ -1690,6 +1711,7 @@ impl<Signer: Sign, M: Deref, T: Deref, K: Deref, F: Deref, L: Deref> ChannelMana
 			secp_ctx,
 
 			inbound_payment_key: expanded_inbound_key,
+			fake_scid_rand_bytes: keys_manager.get_secure_random_bytes(),
 
 			last_node_announcement_serial: AtomicUsize::new(0),
 			highest_seen_timestamp: AtomicUsize::new(0),
@@ -5089,6 +5111,34 @@ impl<Signer: Sign, M: Deref, T: Deref, K: Deref, F: Deref, L: Deref> ChannelMana
 		inbound_payment::get_payment_preimage(payment_hash, payment_secret, &self.inbound_payment_key)
 	}
 
+	/// Gets a fake short channel id for use in receiving [phantom node payments]. These fake scids
+	/// are used when constructing the phantom invoice's route hints.
+	///
+	/// [phantom node payments]: crate::chain::keysinterface::PhantomKeysManager
+	pub fn get_phantom_scid(&self) -> u64 {
+		let mut channel_state = self.channel_state.lock().unwrap();
+		let best_block = self.best_block.read().unwrap();
+		loop {
+			let scid_candidate = fake_scid::get_phantom_scid(&self.fake_scid_rand_bytes, best_block.height(), &self.genesis_hash, &self.keys_manager);
+			// Ensure the generated scid doesn't conflict with a real channel.
+			match channel_state.short_to_id.entry(scid_candidate) {
+				hash_map::Entry::Occupied(_) => continue,
+				hash_map::Entry::Vacant(_) => return scid_candidate
+			}
+		}
+	}
+
+	/// Gets route hints for use in receiving [phantom node payments].
+	///
+	/// [phantom node payments]: crate::chain::keysinterface::PhantomKeysManager
+	pub fn get_phantom_route_hints(&self) -> PhantomRouteHints {
+		PhantomRouteHints {
+			channels: self.list_usable_channels(),
+			phantom_scid: self.get_phantom_scid(),
+			real_node_pubkey: self.get_our_node_id(),
+		}
+	}
+
 	#[cfg(any(test, feature = "fuzztarget", feature = "_test_utils"))]
 	pub fn get_and_clear_pending_events(&self) -> Vec<events::Event> {
 		let events = core::cell::RefCell::new(Vec::new());
@@ -5819,6 +5869,12 @@ impl_writeable_tlv_based!(ChannelDetails, {
 	(32, is_public, required),
 });
 
+impl_writeable_tlv_based!(PhantomRouteHints, {
+	(2, channels, vec_type),
+	(4, phantom_scid, required),
+	(6, real_node_pubkey, required),
+});
+
 impl_writeable_tlv_based_enum!(PendingHTLCRouting,
 	(0, Forward) => {
 		(0, onion_packet, required),
@@ -6220,7 +6276,8 @@ impl<Signer: Sign, M: Deref, T: Deref, K: Deref, F: Deref, L: Deref> Writeable f
 		write_tlv_fields!(writer, {
 			(1, pending_outbound_payments_no_retry, required),
 			(3, pending_outbound_payments, required),
-			(5, self.our_network_pubkey, required)
+			(5, self.our_network_pubkey, required),
+			(7, self.fake_scid_rand_bytes, required),
 		});
 
 		Ok(())
@@ -6516,11 +6573,16 @@ impl<'a, Signer: Sign, M: Deref, T: Deref, K: Deref, F: Deref, L: Deref>
 		let mut pending_outbound_payments_no_retry: Option<HashMap<PaymentId, HashSet<[u8; 32]>>> = None;
 		let mut pending_outbound_payments = None;
 		let mut received_network_pubkey: Option<PublicKey> = None;
+		let mut fake_scid_rand_bytes: Option<[u8; 32]> = None;
 		read_tlv_fields!(reader, {
 			(1, pending_outbound_payments_no_retry, option),
 			(3, pending_outbound_payments, option),
-			(5, received_network_pubkey, option)
+			(5, received_network_pubkey, option),
+			(7, fake_scid_rand_bytes, option),
 		});
+		if fake_scid_rand_bytes.is_none() {
+			fake_scid_rand_bytes = Some(args.keys_manager.get_secure_random_bytes());
+		}
 
 		if pending_outbound_payments.is_none() && pending_outbound_payments_no_retry.is_none() {
 			pending_outbound_payments = Some(pending_outbound_payments_compat);
@@ -6616,6 +6678,7 @@ impl<'a, Signer: Sign, M: Deref, T: Deref, K: Deref, F: Deref, L: Deref>
 			inbound_payment_key: expanded_inbound_key,
 			pending_inbound_payments: Mutex::new(pending_inbound_payments),
 			pending_outbound_payments: Mutex::new(pending_outbound_payments.unwrap()),
+			fake_scid_rand_bytes: fake_scid_rand_bytes.unwrap(),
 
 			our_network_key,
 			our_network_pubkey,

lightning/src/util/scid_utils.rs

@@ -60,6 +60,176 @@ pub fn scid_from_parts(block: u64, tx_index: u64, vout_index: u64) -> Result<u64
 	Ok((block << 40) | (tx_index << 16) | vout_index)
 }
 
+/// LDK has multiple reasons to generate fake short channel ids:
+/// 1) zero-conf channels that don't have a confirmed channel id yet
+/// 2) phantom node payments, to get an scid for the phantom node's phantom channel
+pub(crate) mod fake_scid {
+	use bitcoin::hash_types::BlockHash;
+	use bitcoin::hashes::hex::FromHex;
+	use chain::keysinterface::{Sign, KeysInterface};
+	use util::chacha20::ChaCha20;
+	use util::scid_utils;
+
+	use core::convert::TryInto;
+	use core::ops::Deref;
+
+	const TEST_SEGWIT_ACTIVATION_HEIGHT: u32 = 0;
+	const MAINNET_SEGWIT_ACTIVATION_HEIGHT: u32 = 481_824;
+	const MAX_TX_INDEX: u32 = 2_500;
+	const MAX_NAMESPACES: u8 = 8; // We allocate 3 bits for the namespace identifier.
+	const NAMESPACE_ID_BITMASK: u8 = 0b111;
+
+	/// Fake scids are divided into namespaces, with each namespace having its own identifier between
+	/// [0..7]. This allows us to identify what namespace a fake scid corresponds to upon HTLC
+	/// receipt, and handle the HTLC accordingly. The namespace identifier is encrypted when encoded
+	/// into the fake scid.
+	#[derive(Copy, Clone)]
+	pub(super) enum Namespace {
+		Phantom,
+		// Coming soon: a variant for the zero-conf scid namespace
+	}
+
+	impl Namespace {
+		/// We generate "realistic-looking" random scids here, meaning the scid's block height is
+		/// between segwit activation and the current best known height, and the tx index and output
+		/// index are also selected from a "reasonable" range. We add this logic because it makes it
+		/// non-obvious at a glance that the scid is fake, e.g. if it appears in invoice route hints.
+		pub(super) fn get_fake_scid<Signer: Sign, K: Deref>(&self, highest_seen_blockheight: u32, genesis_hash: &BlockHash, fake_scid_rand_bytes: &[u8; 32], keys_manager: &K) -> u64
+			where K::Target: KeysInterface<Signer = Signer>,
+		{
+			// Ensure we haven't created a namespace that doesn't fit into the 3 bits we've allocated for
+			// namespaces.
+			assert!((*self as u8) < MAX_NAMESPACES);
+			const BLOCKS_PER_MONTH: u32 = 144 /* blocks per day */ * 30 /* days per month */;
+			let rand_bytes = keys_manager.get_secure_random_bytes();
+
+			let segwit_activation_height = segwit_activation_height(genesis_hash);
+			let mut valid_block_range = if highest_seen_blockheight > segwit_activation_height {
+				highest_seen_blockheight - segwit_activation_height
+			} else {
+				1
+			};
+			// We want to ensure that this fake channel won't conflict with any transactions we haven't
+			// seen yet, in case `highest_seen_blockheight` is updated before we get full information
+			// about transactions confirmed in the given block.
+			if valid_block_range > BLOCKS_PER_MONTH { valid_block_range -= BLOCKS_PER_MONTH; }
+
+			let rand_for_height = u32::from_be_bytes(rand_bytes[..4].try_into().unwrap());
+			let fake_scid_height = segwit_activation_height + rand_for_height % valid_block_range;
+
+			let rand_for_tx_index = u32::from_be_bytes(rand_bytes[4..8].try_into().unwrap());
+			let fake_scid_tx_index = rand_for_tx_index % MAX_TX_INDEX;
+
+			// Put the scid in the given namespace.
+			let fake_scid_vout = self.get_encrypted_vout(fake_scid_height, fake_scid_tx_index, fake_scid_rand_bytes);
+			scid_utils::scid_from_parts(fake_scid_height as u64, fake_scid_tx_index as u64, fake_scid_vout as u64).unwrap()
+		}
+
+		/// We want to ensure that a 3rd party can't identify a payment as belong to a given
+		/// `Namespace`. Therefore, we encrypt it using a random bytes provided by `ChannelManager`.
+		fn get_encrypted_vout(&self, block_height: u32, tx_index: u32, fake_scid_rand_bytes: &[u8; 32]) -> u8 {
+			let mut salt = [0 as u8; 8];
+			let block_height_bytes = block_height.to_be_bytes();
+			salt[0..4].copy_from_slice(&block_height_bytes);
+			let tx_index_bytes = tx_index.to_be_bytes();
+			salt[4..8].copy_from_slice(&tx_index_bytes);
+
+			let mut chacha = ChaCha20::new(fake_scid_rand_bytes, &salt);
+			let mut vout_byte = [*self as u8];
+			chacha.process_in_place(&mut vout_byte);
+			vout_byte[0] & NAMESPACE_ID_BITMASK
+		}
+	}
+
+	pub fn get_phantom_scid<Signer: Sign, K: Deref>(fake_scid_rand_bytes: &[u8; 32], highest_seen_blockheight: u32, genesis_hash: &BlockHash, keys_manager: &K) -> u64
+		where K::Target: KeysInterface<Signer = Signer>,
+	{
+		let namespace = Namespace::Phantom;
+		namespace.get_fake_scid(highest_seen_blockheight, genesis_hash, fake_scid_rand_bytes, keys_manager)
+	}
+
+	fn segwit_activation_height(genesis: &BlockHash) -> u32 {
+		const MAINNET_GENESIS_STR: &'static str = "000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f";
+		if BlockHash::from_hex(MAINNET_GENESIS_STR).unwrap() == *genesis {
+			MAINNET_SEGWIT_ACTIVATION_HEIGHT
+		} else {
+			TEST_SEGWIT_ACTIVATION_HEIGHT
+		}
+	}
+
+	/// Returns whether the given fake scid falls into the given namespace.
+	pub fn is_valid_phantom(fake_scid_rand_bytes: &[u8; 32], scid: u64) -> bool {
+		let block_height = scid_utils::block_from_scid(&scid);
+		let tx_index = scid_utils::tx_index_from_scid(&scid);
+		let namespace = Namespace::Phantom;
+		let valid_vout = namespace.get_encrypted_vout(block_height, tx_index, fake_scid_rand_bytes);
+		valid_vout == scid_utils::vout_from_scid(&scid) as u8
+	}
+
+	#[cfg(test)]
+	mod tests {
+		use bitcoin::blockdata::constants::genesis_block;
+		use bitcoin::network::constants::Network;
+		use util::scid_utils::fake_scid::{is_valid_phantom, MAINNET_SEGWIT_ACTIVATION_HEIGHT, MAX_TX_INDEX, MAX_NAMESPACES, Namespace, NAMESPACE_ID_BITMASK, segwit_activation_height, TEST_SEGWIT_ACTIVATION_HEIGHT};
+		use util::scid_utils;
+		use util::test_utils;
+		use sync::Arc;
+
+		#[test]
+		fn namespace_identifier_is_within_range() {
+			let phantom_namespace = Namespace::Phantom;
+			assert!((phantom_namespace as u8) < MAX_NAMESPACES);
+			assert!((phantom_namespace as u8) <= NAMESPACE_ID_BITMASK);
+		}
+
+		#[test]
+		fn test_segwit_activation_height() {
+			let mainnet_genesis = genesis_block(Network::Bitcoin).header.block_hash();
+			assert_eq!(segwit_activation_height(&mainnet_genesis), MAINNET_SEGWIT_ACTIVATION_HEIGHT);
+
+			let testnet_genesis = genesis_block(Network::Testnet).header.block_hash();
+			assert_eq!(segwit_activation_height(&testnet_genesis), TEST_SEGWIT_ACTIVATION_HEIGHT);
+
+			let signet_genesis = genesis_block(Network::Signet).header.block_hash();
+			assert_eq!(segwit_activation_height(&signet_genesis), TEST_SEGWIT_ACTIVATION_HEIGHT);
+
+			let regtest_genesis = genesis_block(Network::Regtest).header.block_hash();
+			assert_eq!(segwit_activation_height(&regtest_genesis), TEST_SEGWIT_ACTIVATION_HEIGHT);
+		}
+
+		#[test]
+		fn test_is_valid_phantom() {
+			let namespace = Namespace::Phantom;
+			let fake_scid_rand_bytes = [0; 32];
+			let valid_encrypted_vout = namespace.get_encrypted_vout(0, 0, &fake_scid_rand_bytes);
+			let valid_fake_scid = scid_utils::scid_from_parts(0, 0, valid_encrypted_vout as u64).unwrap();
+			assert!(is_valid_phantom(&fake_scid_rand_bytes, valid_fake_scid));
+			let invalid_fake_scid = scid_utils::scid_from_parts(0, 0, 12).unwrap();
+			assert!(!is_valid_phantom(&fake_scid_rand_bytes, invalid_fake_scid));
+		}
+
+		#[test]
+		fn test_get_fake_scid() {
+			let mainnet_genesis = genesis_block(Network::Bitcoin).header.block_hash();
+			let seed = [0; 32];
+			let fake_scid_rand_bytes = [1; 32];
+			let keys_manager = Arc::new(test_utils::TestKeysInterface::new(&seed, Network::Testnet));
+			let namespace = Namespace::Phantom;
+			let fake_scid = namespace.get_fake_scid(500_000, &mainnet_genesis, &fake_scid_rand_bytes, &keys_manager);
+
+			let fake_height = scid_utils::block_from_scid(&fake_scid);
+			assert!(fake_height >= MAINNET_SEGWIT_ACTIVATION_HEIGHT);
+			assert!(fake_height <= 500_000);
+
+			let fake_tx_index = scid_utils::tx_index_from_scid(&fake_scid);
+			assert!(fake_tx_index <= MAX_TX_INDEX);
+
+			let fake_vout = scid_utils::vout_from_scid(&fake_scid);
+			assert!(fake_vout < MAX_NAMESPACES as u16);
+		}
+	}
+}
+
 #[cfg(test)]
 mod tests {
 	use super::*;