Merge pull request #444 from lightning-signer/funding-script

Construct funding redeem script in signer

Author: TheBlueMatt

fuzz/src/chanmon_consistency.rs

@@ -158,6 +158,7 @@ impl KeysInterface for KeyProvider {
 			delayed_payment_base_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, 7, self.node_id]).unwrap(),
 			htlc_base_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, 8, self.node_id]).unwrap(),
 			commitment_seed: [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, 9, self.node_id],
+			remote_funding_pubkey: None,
 		})
 	}
 

fuzz/src/full_stack.rs

@@ -257,6 +257,7 @@ impl KeysInterface for KeyProvider {
 				delayed_payment_base_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, 4, ctr]).unwrap(),
 				htlc_base_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, 5, ctr]).unwrap(),
 				commitment_seed: [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, 6, ctr],
+				remote_funding_pubkey: None,
 			}
 		} else {
 			InMemoryChannelKeys {
@@ -266,6 +267,7 @@ impl KeysInterface for KeyProvider {
 				delayed_payment_base_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, 10, ctr]).unwrap(),
 				htlc_base_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, 11, ctr]).unwrap(),
 				commitment_seed: [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, 12, ctr],
+				remote_funding_pubkey: None,
 			}
 		})
 	}

lightning/src/chain/keysinterface.rs

@@ -24,7 +24,7 @@ use util::logger::Logger;
 use util::ser::Writeable;
 
 use ln::chan_utils;
-use ln::chan_utils::{TxCreationKeys, HTLCOutputInCommitment};
+use ln::chan_utils::{TxCreationKeys, HTLCOutputInCommitment, make_funding_redeemscript};
 use ln::msgs;
 
 use std::sync::Arc;
@@ -142,7 +142,7 @@ pub trait ChannelKeys : Send {
 	/// TODO: Document the things someone using this interface should enforce before signing.
 	/// TODO: Add more input vars to enable better checking (preferably removing commitment_tx and
 	/// making the callee generate it via some util function we expose)!
-	fn sign_remote_commitment<T: secp256k1::Signing>(&self, channel_value_satoshis: u64, channel_funding_redeemscript: &Script, feerate_per_kw: u64, commitment_tx: &Transaction, keys: &TxCreationKeys, htlcs: &[&HTLCOutputInCommitment], to_self_delay: u16, secp_ctx: &Secp256k1<T>) -> Result<(Signature, Vec<Signature>), ()>;
+	fn sign_remote_commitment<T: secp256k1::Signing>(&self, channel_value_satoshis: u64, feerate_per_kw: u64, commitment_tx: &Transaction, keys: &TxCreationKeys, htlcs: &[&HTLCOutputInCommitment], to_self_delay: u16, secp_ctx: &Secp256k1<T>) -> Result<(Signature, Vec<Signature>), ()>;
 
 	/// Create a signature for a (proposed) closing transaction.
 	///
@@ -157,6 +157,12 @@ pub trait ChannelKeys : Send {
 	/// our counterparty may (though likely will not) close the channel on us for violating the
 	/// protocol.
 	fn sign_channel_announcement<T: secp256k1::Signing>(&self, msg: &msgs::UnsignedChannelAnnouncement, secp_ctx: &Secp256k1<T>) -> Result<Signature, ()>;
+
+	/// Set the remote funding key.  This is done immediately on incoming channels
+	/// and as soon as the channel is accepted on outgoing channels.
+	///
+	/// Will be called before any signatures are applied.
+	fn set_remote_funding_pubkey(&mut self, key: &PublicKey);
 }
 
 #[derive(Clone)]
@@ -174,6 +180,8 @@ pub struct InMemoryChannelKeys {
 	pub htlc_base_key: SecretKey,
 	/// Commitment seed
 	pub commitment_seed: [u8; 32],
+	/// Remote funding pubkey
+	pub remote_funding_pubkey: Option<PublicKey>,
 }
 
 impl ChannelKeys for InMemoryChannelKeys {
@@ -184,8 +192,13 @@ impl ChannelKeys for InMemoryChannelKeys {
 	fn htlc_base_key(&self) -> &SecretKey { &self.htlc_base_key }
 	fn commitment_seed(&self) -> &[u8; 32] { &self.commitment_seed }
 
-	fn sign_remote_commitment<T: secp256k1::Signing>(&self, channel_value_satoshis: u64, channel_funding_redeemscript: &Script, feerate_per_kw: u64, commitment_tx: &Transaction, keys: &TxCreationKeys, htlcs: &[&HTLCOutputInCommitment], to_self_delay: u16, secp_ctx: &Secp256k1<T>) -> Result<(Signature, Vec<Signature>), ()> {
+	fn sign_remote_commitment<T: secp256k1::Signing>(&self, channel_value_satoshis: u64, feerate_per_kw: u64, commitment_tx: &Transaction, keys: &TxCreationKeys, htlcs: &[&HTLCOutputInCommitment], to_self_delay: u16, secp_ctx: &Secp256k1<T>) -> Result<(Signature, Vec<Signature>), ()> {
 		if commitment_tx.input.len() != 1 { return Err(()); }
+
+		let funding_pubkey = PublicKey::from_secret_key(secp_ctx, &self.funding_key);
+		let remote_funding_pubkey = self.remote_funding_pubkey.as_ref().expect("must set remote funding key before signing");
+		let channel_funding_redeemscript = make_funding_redeemscript(&funding_pubkey, remote_funding_pubkey);
+
 		let commitment_sighash = hash_to_message!(&bip143::SighashComponents::new(&commitment_tx).sighash_all(&commitment_tx.input[0], &channel_funding_redeemscript, channel_value_satoshis)[..]);
 		let commitment_sig = secp_ctx.sign(&commitment_sighash, &self.funding_key);
 
@@ -222,6 +235,11 @@ impl ChannelKeys for InMemoryChannelKeys {
 		let msghash = hash_to_message!(&Sha256dHash::hash(&msg.encode()[..])[..]);
 		Ok(secp_ctx.sign(&msghash, &self.funding_key))
 	}
+
+	fn set_remote_funding_pubkey(&mut self, key: &PublicKey) {
+		assert!(self.remote_funding_pubkey.is_none(), "Already set remote funding key");
+		self.remote_funding_pubkey = Some(*key);
+	}
 }
 
 impl_writeable!(InMemoryChannelKeys, 0, {
@@ -230,7 +248,8 @@ impl_writeable!(InMemoryChannelKeys, 0, {
 	payment_base_key,
 	delayed_payment_base_key,
 	htlc_base_key,
-	commitment_seed
+	commitment_seed,
+	remote_funding_pubkey
 });
 
 /// Simple KeysInterface implementor that takes a 32-byte seed for use as a BIP 32 extended key
@@ -379,6 +398,7 @@ impl KeysInterface for KeysManager {
 			delayed_payment_base_key,
 			htlc_base_key,
 			commitment_seed,
+			remote_funding_pubkey: None,
 		}
 	}
 

lightning/src/ln/chan_utils.rs

@@ -255,6 +255,22 @@ pub fn get_htlc_redeemscript(htlc: &HTLCOutputInCommitment, keys: &TxCreationKey
 	get_htlc_redeemscript_with_explicit_keys(htlc, &keys.a_htlc_key, &keys.b_htlc_key, &keys.revocation_key)
 }
 
+/// Gets the redeemscript for a funding output from the two funding public keys.
+/// Note that the order of funding public keys does not matter.
+pub fn make_funding_redeemscript(a: &PublicKey, b: &PublicKey) -> Script {
+	let our_funding_key = a.serialize();
+	let their_funding_key = b.serialize();
+
+	let builder = Builder::new().push_opcode(opcodes::all::OP_PUSHNUM_2);
+	if our_funding_key[..] < their_funding_key[..] {
+		builder.push_slice(&our_funding_key)
+			.push_slice(&their_funding_key)
+	} else {
+		builder.push_slice(&their_funding_key)
+			.push_slice(&our_funding_key)
+	}.push_opcode(opcodes::all::OP_PUSHNUM_2).push_opcode(opcodes::all::OP_CHECKMULTISIG).into_script()
+}
+
 /// panics if htlc.transaction_output_index.is_none()!
 pub fn build_htlc_transaction(prev_hash: &Sha256dHash, feerate_per_kw: u64, to_self_delay: u16, htlc: &HTLCOutputInCommitment, a_delayed_payment_key: &PublicKey, revocation_key: &PublicKey) -> Transaction {
 	let mut txins: Vec<TxIn> = Vec::new();

lightning/src/ln/channel.rs

@@ -20,7 +20,7 @@ use ln::msgs;
 use ln::msgs::{DecodeError, OptionalField, DataLossProtect};
 use ln::channelmonitor::ChannelMonitor;
 use ln::channelmanager::{PendingHTLCStatus, HTLCSource, HTLCFailReason, HTLCFailureMsg, PendingForwardHTLCInfo, RAACommitmentOrder, PaymentPreimage, PaymentHash, BREAKDOWN_TIMEOUT, MAX_LOCAL_BREAKDOWN_TIMEOUT};
-use ln::chan_utils::{LocalCommitmentTransaction,TxCreationKeys,HTLCOutputInCommitment,HTLC_SUCCESS_TX_WEIGHT,HTLC_TIMEOUT_TX_WEIGHT};
+use ln::chan_utils::{LocalCommitmentTransaction, TxCreationKeys, HTLCOutputInCommitment, HTLC_SUCCESS_TX_WEIGHT, HTLC_TIMEOUT_TX_WEIGHT, make_funding_redeemscript};
 use ln::chan_utils;
 use chain::chaininterface::{FeeEstimator,ConfirmationTarget};
 use chain::transaction::OutPoint;
@@ -545,7 +545,8 @@ impl<ChanSigner: ChannelKeys> Channel<ChanSigner> {
 	/// Creates a new channel from a remote sides' request for one.
 	/// Assumes chain_hash has already been checked and corresponds with what we expect!
 	pub fn new_from_req(fee_estimator: &FeeEstimator, keys_provider: &Arc<KeysInterface<ChanKeySigner = ChanSigner>>, their_node_id: PublicKey, their_features: InitFeatures, msg: &msgs::OpenChannel, user_id: u64, logger: Arc<Logger>, config: &UserConfig) -> Result<Channel<ChanSigner>, ChannelError> {
-		let chan_keys = keys_provider.get_channel_keys(true);
+		let mut chan_keys = keys_provider.get_channel_keys(true);
+		chan_keys.set_remote_funding_pubkey(&msg.funding_pubkey);
 		let mut local_config = (*config).channel_options.clone();
 
 		if config.own_channel_config.our_to_self_delay < BREAKDOWN_TIMEOUT {
@@ -1111,16 +1112,9 @@ impl<ChanSigner: ChannelKeys> Channel<ChanSigner> {
 	/// pays to get_funding_redeemscript().to_v0_p2wsh()).
 	/// Panics if called before accept_channel/new_from_req
 	pub fn get_funding_redeemscript(&self) -> Script {
-		let builder = Builder::new().push_opcode(opcodes::all::OP_PUSHNUM_2);
-		let our_funding_key = PublicKey::from_secret_key(&self.secp_ctx, self.local_keys.funding_key()).serialize();
-		let their_funding_key = self.their_funding_pubkey.expect("get_funding_redeemscript only allowed after accept_channel").serialize();
-		if our_funding_key[..] < their_funding_key[..] {
-			builder.push_slice(&our_funding_key)
-				.push_slice(&their_funding_key)
-		} else {
-			builder.push_slice(&their_funding_key)
-				.push_slice(&our_funding_key)
-		}.push_opcode(opcodes::all::OP_PUSHNUM_2).push_opcode(opcodes::all::OP_CHECKMULTISIG).into_script()
+		let our_funding_key = PublicKey::from_secret_key(&self.secp_ctx, self.local_keys.funding_key());
+		let their_funding_key = self.their_funding_pubkey.expect("get_funding_redeemscript only allowed after accept_channel");
+		make_funding_redeemscript(&our_funding_key, &their_funding_key)
 	}
 
 	/// Builds the htlc-success or htlc-timeout transaction which spends a given HTLC output
@@ -1407,6 +1401,7 @@ impl<ChanSigner: ChannelKeys> Channel<ChanSigner> {
 		self.channel_monitor.set_basic_channel_info(&msg.htlc_basepoint, &msg.delayed_payment_basepoint, msg.to_self_delay, funding_redeemscript, self.channel_value_satoshis, obscure_factor);
 
 		self.channel_state = ChannelState::OurInitSent as u32 | ChannelState::TheirInitSent as u32;
+		self.local_keys.set_remote_funding_pubkey(&msg.funding_pubkey);
 
 		Ok(())
 	}
@@ -1425,7 +1420,7 @@ impl<ChanSigner: ChannelKeys> Channel<ChanSigner> {
 
 		let remote_keys = self.build_remote_transaction_keys()?;
 		let remote_initial_commitment_tx = self.build_commitment_transaction(self.cur_remote_commitment_transaction_number, &remote_keys, false, false, self.feerate_per_kw).0;
-		let remote_signature = self.local_keys.sign_remote_commitment(self.channel_value_satoshis, &self.get_funding_redeemscript(), self.feerate_per_kw, &remote_initial_commitment_tx, &remote_keys, &Vec::new(), self.our_to_self_delay, &self.secp_ctx)
+		let remote_signature = self.local_keys.sign_remote_commitment(self.channel_value_satoshis, self.feerate_per_kw, &remote_initial_commitment_tx, &remote_keys, &Vec::new(), self.our_to_self_delay, &self.secp_ctx)
 				.map_err(|_| ChannelError::Close("Failed to get signatures for new commitment_signed"))?.0;
 
 		// We sign the "remote" commitment transaction, allowing them to broadcast the tx if they wish.
@@ -2645,6 +2640,7 @@ impl<ChanSigner: ChannelKeys> Channel<ChanSigner> {
 
 		self.channel_state |= ChannelState::LocalShutdownSent as u32;
 		self.channel_update_count += 1;
+
 		Ok((our_shutdown, self.maybe_propose_first_closing_signed(fee_estimator), dropped_outbound_htlcs))
 	}
 
@@ -3151,7 +3147,7 @@ impl<ChanSigner: ChannelKeys> Channel<ChanSigner> {
 	fn get_outbound_funding_created_signature(&mut self) -> Result<(Signature, Transaction), ChannelError> {
 		let remote_keys = self.build_remote_transaction_keys()?;
 		let remote_initial_commitment_tx = self.build_commitment_transaction(self.cur_remote_commitment_transaction_number, &remote_keys, false, false, self.feerate_per_kw).0;
-		Ok((self.local_keys.sign_remote_commitment(self.channel_value_satoshis, &self.get_funding_redeemscript(), self.feerate_per_kw, &remote_initial_commitment_tx, &remote_keys, &Vec::new(), self.our_to_self_delay, &self.secp_ctx)
+		Ok((self.local_keys.sign_remote_commitment(self.channel_value_satoshis, self.feerate_per_kw, &remote_initial_commitment_tx, &remote_keys, &Vec::new(), self.our_to_self_delay, &self.secp_ctx)
 				.map_err(|_| ChannelError::Close("Failed to get signatures for new commitment_signed"))?.0, remote_initial_commitment_tx))
 	}
 
@@ -3459,7 +3455,7 @@ impl<ChanSigner: ChannelKeys> Channel<ChanSigner> {
 				htlcs.push(htlc);
 			}
 
-			let res = self.local_keys.sign_remote_commitment(self.channel_value_satoshis, &self.get_funding_redeemscript(), feerate_per_kw, &remote_commitment_tx.0, &remote_keys, &htlcs, self.our_to_self_delay, &self.secp_ctx)
+			let res = self.local_keys.sign_remote_commitment(self.channel_value_satoshis, feerate_per_kw, &remote_commitment_tx.0, &remote_keys, &htlcs, self.our_to_self_delay, &self.secp_ctx)
 				.map_err(|_| ChannelError::Close("Failed to get signatures for new commitment_signed"))?;
 			signature = res.0;
 			htlc_signatures = res.1;
@@ -4131,6 +4127,7 @@ mod tests {
 			// These aren't set in the test vectors:
 			revocation_base_key: SecretKey::from_slice(&hex::decode("0fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff").unwrap()[..]).unwrap(),
 			commitment_seed: [0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff],
+			remote_funding_pubkey: None,
 		};
 		assert_eq!(PublicKey::from_secret_key(&secp_ctx, chan_keys.funding_key()).serialize()[..],
 				hex::decode("023da092f6980e58d2c037173180e9a465476026ee50f96695963e8efe436f54eb").unwrap()[..]);

lightning/src/util/enforcing_trait_impls.rs

@@ -9,7 +9,7 @@ use bitcoin::blockdata::transaction::Transaction;
 use bitcoin::blockdata::script::Script;
 
 use secp256k1;
-use secp256k1::key::SecretKey;
+use secp256k1::key::{SecretKey, PublicKey};
 use secp256k1::{Secp256k1, Signature};
 
 /// Enforces some rules on ChannelKeys calls. Eventually we will probably want to expose a variant
@@ -35,7 +35,7 @@ impl ChannelKeys for EnforcingChannelKeys {
 	fn htlc_base_key(&self) -> &SecretKey { self.inner.htlc_base_key() }
 	fn commitment_seed(&self) -> &[u8; 32] { self.inner.commitment_seed() }
 
-	fn sign_remote_commitment<T: secp256k1::Signing>(&self, channel_value_satoshis: u64, channel_funding_script: &Script, feerate_per_kw: u64, commitment_tx: &Transaction, keys: &TxCreationKeys, htlcs: &[&HTLCOutputInCommitment], to_self_delay: u16, secp_ctx: &Secp256k1<T>) -> Result<(Signature, Vec<Signature>), ()> {
+	fn sign_remote_commitment<T: secp256k1::Signing>(&self, channel_value_satoshis: u64, feerate_per_kw: u64, commitment_tx: &Transaction, keys: &TxCreationKeys, htlcs: &[&HTLCOutputInCommitment], to_self_delay: u16, secp_ctx: &Secp256k1<T>) -> Result<(Signature, Vec<Signature>), ()> {
 		if commitment_tx.input.len() != 1 { panic!(); }
 		let obscured_commitment_transaction_number = (commitment_tx.lock_time & 0xffffff) as u64 | ((commitment_tx.input[0].sequence as u64 & 0xffffff) << 3*8);
 
@@ -49,7 +49,7 @@ impl ChannelKeys for EnforcingChannelKeys {
 			commitment_data.1 = cmp::max(commitment_number, commitment_data.1)
 		}
 
-		Ok(self.inner.sign_remote_commitment(channel_value_satoshis, channel_funding_script, feerate_per_kw, commitment_tx, keys, htlcs, to_self_delay, secp_ctx).unwrap())
+		Ok(self.inner.sign_remote_commitment(channel_value_satoshis, feerate_per_kw, commitment_tx, keys, htlcs, to_self_delay, secp_ctx).unwrap())
 	}
 
 	fn sign_closing_transaction<T: secp256k1::Signing>(&self, channel_value_satoshis: u64, channel_funding_redeemscript: &Script, closing_tx: &Transaction, secp_ctx: &Secp256k1<T>) -> Result<Signature, ()> {
@@ -59,6 +59,10 @@ impl ChannelKeys for EnforcingChannelKeys {
 	fn sign_channel_announcement<T: secp256k1::Signing>(&self, msg: &msgs::UnsignedChannelAnnouncement, secp_ctx: &Secp256k1<T>) -> Result<Signature, ()> {
 		self.inner.sign_channel_announcement(msg, secp_ctx)
 	}
+
+	fn set_remote_funding_pubkey(&mut self, key: &PublicKey) {
+		self.inner.set_remote_funding_pubkey(key)
+	}
 }
 
 impl_writeable!(EnforcingChannelKeys, 0, {