Derive per-channel destination and shutdown scripts for improved on-chain privacy

fuzz/src/chanmon_consistency.rs

@@ -870,7 +870,7 @@ impl SignerProvider for KeyProvider {
 			.into_script())
 	}
 
-	fn get_shutdown_scriptpubkey(&self) -> Result<ShutdownScript, ()> {
+	fn get_shutdown_scriptpubkey(&self, _channel_keys_id: [u8; 32]) -> Result<ShutdownScript, ()> {
 		let secp_ctx = Secp256k1::signing_only();
 		#[rustfmt::skip]
 		let secret_key = SecretKey::from_slice(&[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 3, self.node_secret[31]]).unwrap();

fuzz/src/full_stack.rs

@@ -510,7 +510,7 @@ impl SignerProvider for KeyProvider {
 			.into_script())
 	}
 
-	fn get_shutdown_scriptpubkey(&self) -> Result<ShutdownScript, ()> {
+	fn get_shutdown_scriptpubkey(&self, _channel_keys_id: [u8; 32]) -> Result<ShutdownScript, ()> {
 		let secp_ctx = Secp256k1::signing_only();
 		let secret_key = SecretKey::from_slice(&[
 			0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,

fuzz/src/onion_message.rs

@@ -309,7 +309,7 @@ impl SignerProvider for KeyProvider {
 		unreachable!()
 	}
 
-	fn get_shutdown_scriptpubkey(&self) -> Result<ShutdownScript, ()> {
+	fn get_shutdown_scriptpubkey(&self, _channel_keys_id: [u8; 32]) -> Result<ShutdownScript, ()> {
 		unreachable!()
 	}
 }

lightning/src/ln/async_signer_tests.rs

@@ -1437,8 +1437,9 @@ fn do_test_closing_signed(extra_closing_signed: bool, reconnect: bool) {
 	if extra_closing_signed {
 		let node_1_closing_signed_2_bad = {
 			let mut node_1_closing_signed_2 = node_1_closing_signed.clone();
-			let holder_script = nodes[0].keys_manager.get_shutdown_scriptpubkey().unwrap();
-			let counterparty_script = nodes[1].keys_manager.get_shutdown_scriptpubkey().unwrap();
+			let holder_script = nodes[0].keys_manager.get_shutdown_scriptpubkey([0; 32]).unwrap();
+			let counterparty_script =
+				nodes[1].keys_manager.get_shutdown_scriptpubkey([0; 32]).unwrap();
 			let funding_outpoint = bitcoin::OutPoint { txid: funding_tx.compute_txid(), vout: 0 };
 			let closing_tx_2 = ClosingTransaction::new(
 				50000,

lightning/src/ln/channel.rs

@@ -4085,7 +4085,7 @@ impl<SP: SignerProvider> ChannelContext<SP> {
 
 		let shutdown_scriptpubkey =
 			if config.channel_handshake_config.commit_upfront_shutdown_pubkey {
-				match signer_provider.get_shutdown_scriptpubkey() {
+				match signer_provider.get_shutdown_scriptpubkey(channel_keys_id) {
 					Ok(scriptpubkey) => Some(scriptpubkey),
 					Err(_) => {
 						return Err(ChannelError::close(
@@ -4408,7 +4408,7 @@ impl<SP: SignerProvider> ChannelContext<SP> {
 
 		let shutdown_scriptpubkey =
 			if config.channel_handshake_config.commit_upfront_shutdown_pubkey {
-				match signer_provider.get_shutdown_scriptpubkey() {
+				match signer_provider.get_shutdown_scriptpubkey(channel_keys_id) {
 					Ok(scriptpubkey) => Some(scriptpubkey),
 					Err(_) => {
 						return Err(APIError::ChannelUnavailable {
@@ -11197,14 +11197,15 @@ where
 			Some(_) => false,
 			None => {
 				assert!(send_shutdown);
-				let shutdown_scriptpubkey = match signer_provider.get_shutdown_scriptpubkey() {
-					Ok(scriptpubkey) => scriptpubkey,
-					Err(_) => {
-						return Err(ChannelError::close(
-							"Failed to get shutdown scriptpubkey".to_owned(),
-						))
-					},
-				};
+				let shutdown_scriptpubkey =
+					match signer_provider.get_shutdown_scriptpubkey(self.context.channel_keys_id) {
+						Ok(scriptpubkey) => scriptpubkey,
+						Err(_) => {
+							return Err(ChannelError::close(
+								"Failed to get shutdown scriptpubkey".to_owned(),
+							))
+						},
+					};
 				if !shutdown_scriptpubkey.is_compatible(their_features) {
 					return Err(ChannelError::close(format!(
 						"Provided a scriptpubkey format not accepted by peer: {}",
@@ -14420,7 +14421,9 @@ where
 					Some(script) => script,
 					None => {
 						// otherwise, use the shutdown scriptpubkey provided by the signer
-						match signer_provider.get_shutdown_scriptpubkey() {
+						match signer_provider
+							.get_shutdown_scriptpubkey(self.context.channel_keys_id)
+						{
 							Ok(scriptpubkey) => scriptpubkey,
 							Err(_) => {
 								return Err(APIError::ChannelUnavailable {
@@ -17488,7 +17491,9 @@ mod tests {
 				.into_script())
 		}
 
-		fn get_shutdown_scriptpubkey(&self) -> Result<ShutdownScript, ()> {
+		fn get_shutdown_scriptpubkey(
+			&self, _channel_keys_id: [u8; 32],
+		) -> Result<ShutdownScript, ()> {
 			let secp_ctx = Secp256k1::signing_only();
 			let hex = "0fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff";
 			let channel_close_key =

lightning/src/ln/functional_tests.rs

@@ -74,6 +74,7 @@ use crate::prelude::*;
 use crate::sync::{Arc, Mutex, RwLock};
 use alloc::collections::BTreeSet;
 use bitcoin::hashes::Hash;
+use bitcoin::hex::FromHex;
 use core::iter::repeat;
 use lightning_macros::xtest;
 
@@ -1030,7 +1031,19 @@ fn do_test_forming_justice_tx_from_monitor_updates(broadcast_initial_commitment:
 	// is properly formed and can be broadcasted/confirmed successfully in the event
 	// that a revoked commitment transaction is broadcasted
 	// (Similar to `revoked_output_claim` test but we get the justice tx + broadcast manually)
-	let chanmon_cfgs = create_chanmon_cfgs(2);
+	//
+	// Use legacy (V1) key derivation so that the destination scripts we hand to the watchtower
+	// match the per-node static destination scripts that the channels close to. With per-channel
+	// (V2) derivation each channel uses a distinct destination script which we cannot predict
+	// before the channel is created.
+	let node0_key_id =
+		<[u8; 32]>::from_hex("0000000000000000000000004D49E5DA0000000000000000000000000000002A")
+			.unwrap();
+	let node1_key_id =
+		<[u8; 32]>::from_hex("0000000000000000000000004D49E5DAD000D6201F116BAFD379F1D61DF161B9")
+			.unwrap();
+	let predefined_key_ids = Some(vec![node0_key_id, node1_key_id]);
+	let chanmon_cfgs = create_chanmon_cfgs_with_legacy_keys(2, predefined_key_ids);
 	let destination_script0 = chanmon_cfgs[0].keys_manager.get_destination_script([0; 32]).unwrap();
 	let destination_script1 = chanmon_cfgs[1].keys_manager.get_destination_script([0; 32]).unwrap();
 	let persisters = [

lightning/src/ln/shutdown_tests.rs

@@ -1196,7 +1196,7 @@ fn test_unsupported_anysegwit_shutdown_script() {
 
 	// Check that using an unsupported shutdown script fails and a supported one succeeds.
 	let supported_shutdown_script =
-		chanmon_cfgs[1].keys_manager.get_shutdown_scriptpubkey().unwrap();
+		chanmon_cfgs[1].keys_manager.get_shutdown_scriptpubkey([0; 32]).unwrap();
 	let unsupported_witness_program = WitnessProgram::new(WitnessVersion::V16, &[0, 40]).unwrap();
 	let unsupported_shutdown_script =
 		ShutdownScript::new_witness_program(&unsupported_witness_program).unwrap();