ChannelKeys - provide to_self_delay alongside the remote channel pubkeys

In the phase 2 signer, we will construct the commitment transaction inside the signer.
In preparation, provide needed channel related data.

Author: devrandom

lightning/src/chain/keysinterface.rs

@@ -69,7 +69,7 @@ pub enum SpendableOutputDescriptor {
 	///
 	/// To derive the remote_revocation_pubkey provided here (which is used in the witness
 	/// script generation), you must pass the remote revocation_basepoint (which appears in the
-	/// call to ChannelKeys::set_remote_channel_pubkeys) and the provided per_commitment point
+	/// call to ChannelKeys::on_accept) and the provided per_commitment point
 	/// to chan_utils::derive_public_revocation_key.
 	///
 	/// The witness script which is hashed and included in the output script_pubkey may be
@@ -223,7 +223,7 @@ pub trait ChannelKeys : Send+Clone {
 	// 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 + secp256k1::Verification>(&self, feerate_per_kw: u32, 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 + secp256k1::Verification>(&self, feerate_per_kw: u32, commitment_tx: &Transaction, keys: &TxCreationKeys, htlcs: &[&HTLCOutputInCommitment], secp_ctx: &Secp256k1<T>) -> Result<(Signature, Vec<Signature>), ()>;
 
 	/// Create a signature for a local commitment transaction. This will only ever be called with
 	/// the same local_commitment_tx (or a copy thereof), though there are currently no guarantees
@@ -254,7 +254,7 @@ pub trait ChannelKeys : Send+Clone {
 	/// (implying they were considered dust at the time the commitment transaction was negotiated),
 	/// a corresponding None should be included in the return value. All other positions in the
 	/// return value must contain a signature.
-	fn sign_local_commitment_htlc_transactions<T: secp256k1::Signing + secp256k1::Verification>(&self, local_commitment_tx: &LocalCommitmentTransaction, local_csv: u16, secp_ctx: &Secp256k1<T>) -> Result<Vec<Option<Signature>>, ()>;
+	fn sign_local_commitment_htlc_transactions<T: secp256k1::Signing + secp256k1::Verification>(&self, local_commitment_tx: &LocalCommitmentTransaction, secp_ctx: &Secp256k1<T>) -> Result<Vec<Option<Signature>>, ()>;
 
 	/// Create a signature for the given input in a transaction spending an HTLC or commitment
 	/// transaction output when our counterparty broadcasts an old state.
@@ -313,11 +313,13 @@ pub trait ChannelKeys : Send+Clone {
 	/// protocol.
 	fn sign_channel_announcement<T: secp256k1::Signing>(&self, msg: &msgs::UnsignedChannelAnnouncement, secp_ctx: &Secp256k1<T>) -> Result<Signature, ()>;
 
-	/// Set the remote channel basepoints.  This is done immediately on incoming channels
-	/// and as soon as the channel is accepted on outgoing channels.
+	/// Set the remote channel basepoints and remote/local to_self_delay.
+	/// This is done immediately on incoming channels and as soon as the channel is accepted on outgoing channels.
+	///
+	/// We bind local_to_safe_delay late here for API convenience.
 	///
 	/// Will be called before any signatures are applied.
-	fn set_remote_channel_pubkeys(&mut self, channel_points: &ChannelPublicKeys);
+	fn on_accept(&mut self, channel_points: &ChannelPublicKeys, remote_to_self_delay: u16, local_to_self_delay: u16);
 }
 
 /// A trait to describe an object which can get user secrets and key material.
@@ -342,6 +344,18 @@ pub trait KeysInterface: Send + Sync {
 	fn get_channel_id(&self) -> [u8; 32];
 }
 
+#[derive(Clone)]
+/// Holds late-bound channel data
+/// This data is available after the remote accepted the channel.
+pub struct AcceptedChannelData {
+	/// Remote public keys and base points
+	pub(crate) remote_channel_pubkeys: ChannelPublicKeys,
+	/// Remote to_self_delay
+	pub(crate) remote_to_self_delay: u16,
+	/// Local to_self_delay
+	pub(crate) local_to_self_delay: u16,
+}
+
 #[derive(Clone)]
 /// A simple implementation of ChannelKeys that just keeps the private keys in memory.
 pub struct InMemoryChannelKeys {
@@ -359,8 +373,8 @@ pub struct InMemoryChannelKeys {
 	pub commitment_seed: [u8; 32],
 	/// Local public keys and basepoints
 	pub(crate) local_channel_pubkeys: ChannelPublicKeys,
-	/// Remote public keys and base points
-	pub(crate) remote_channel_pubkeys: Option<ChannelPublicKeys>,
+	/// Remote public keys and remote/local to_self_delay, populated on channel acceptance
+	pub(crate) accepted_channel_data: Option<AcceptedChannelData>,
 	/// The total value of this channel
 	channel_value_satoshis: u64,
 	/// Key derivation parameters
@@ -392,7 +406,7 @@ impl InMemoryChannelKeys {
 			commitment_seed,
 			channel_value_satoshis,
 			local_channel_pubkeys,
-			remote_channel_pubkeys: None,
+			accepted_channel_data: None,
 			key_derivation_params,
 		}
 	}
@@ -413,7 +427,17 @@ impl InMemoryChannelKeys {
 		}
 	}
 
-	fn remote_pubkeys<'a>(&'a self) -> &'a ChannelPublicKeys { self.remote_channel_pubkeys.as_ref().unwrap() }
+	/// Remote pubkeys
+	/// Will panic if the remote pubkeys were not set with on_accept
+	pub fn remote_pubkeys(&self) -> &ChannelPublicKeys { &self.accepted_channel_data.as_ref().unwrap().remote_channel_pubkeys }
+
+	/// Remote to-self delay, constraining local commitment txs
+	/// Will panic if the remote pubkeys were not set with on_accept
+	pub fn remote_to_self_delay(&self) -> u16 { self.accepted_channel_data.as_ref().unwrap().remote_to_self_delay }
+
+	/// Local to-self delay, constraining remote commitment txs
+	/// Will panic if the remote pubkeys were not set with on_accept
+	pub fn local_to_self_delay(&self) -> u16 { self.accepted_channel_data.as_ref().unwrap().local_to_self_delay }
 }
 
 impl ChannelKeys for InMemoryChannelKeys {
@@ -429,12 +453,12 @@ impl ChannelKeys for InMemoryChannelKeys {
 	fn pubkeys(&self) -> &ChannelPublicKeys { &self.local_channel_pubkeys }
 	fn key_derivation_params(&self) -> (u64, u64) { self.key_derivation_params }
 
-	fn sign_remote_commitment<T: secp256k1::Signing + secp256k1::Verification>(&self, feerate_per_kw: u32, 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 + secp256k1::Verification>(&self, feerate_per_kw: u32, commitment_tx: &Transaction, keys: &TxCreationKeys, htlcs: &[&HTLCOutputInCommitment], 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_channel_pubkeys = self.remote_channel_pubkeys.as_ref().expect("must set remote channel pubkeys before signing");
-		let channel_funding_redeemscript = make_funding_redeemscript(&funding_pubkey, &remote_channel_pubkeys.funding_pubkey);
+		let accepted_data = self.accepted_channel_data.as_ref().expect("must accept before signing");
+		let channel_funding_redeemscript = make_funding_redeemscript(&funding_pubkey, &accepted_data.remote_channel_pubkeys.funding_pubkey);
 
 		let commitment_sighash = hash_to_message!(&bip143::SighashComponents::new(&commitment_tx).sighash_all(&commitment_tx.input[0], &channel_funding_redeemscript, self.channel_value_satoshis)[..]);
 		let commitment_sig = secp_ctx.sign(&commitment_sighash, &self.funding_key);
@@ -444,7 +468,7 @@ impl ChannelKeys for InMemoryChannelKeys {
 		let mut htlc_sigs = Vec::with_capacity(htlcs.len());
 		for ref htlc in htlcs {
 			if let Some(_) = htlc.transaction_output_index {
-				let htlc_tx = chan_utils::build_htlc_transaction(&commitment_txid, feerate_per_kw, to_self_delay, htlc, &keys.a_delayed_payment_key, &keys.revocation_key);
+				let htlc_tx = chan_utils::build_htlc_transaction(&commitment_txid, feerate_per_kw, accepted_data.local_to_self_delay, htlc, &keys.a_delayed_payment_key, &keys.revocation_key);
 				let htlc_redeemscript = chan_utils::get_htlc_redeemscript(&htlc, &keys);
 				let htlc_sighash = hash_to_message!(&bip143::SighashComponents::new(&htlc_tx).sighash_all(&htlc_tx.input[0], &htlc_redeemscript, htlc.amount_msat / 1000)[..]);
 				let our_htlc_key = match chan_utils::derive_private_key(&secp_ctx, &keys.per_commitment_point, &self.htlc_base_key) {
@@ -460,22 +484,23 @@ impl ChannelKeys for InMemoryChannelKeys {
 
 	fn sign_local_commitment<T: secp256k1::Signing + secp256k1::Verification>(&self, local_commitment_tx: &LocalCommitmentTransaction, secp_ctx: &Secp256k1<T>) -> Result<Signature, ()> {
 		let funding_pubkey = PublicKey::from_secret_key(secp_ctx, &self.funding_key);
-		let remote_channel_pubkeys = self.remote_channel_pubkeys.as_ref().expect("must set remote channel pubkeys before signing");
-		let channel_funding_redeemscript = make_funding_redeemscript(&funding_pubkey, &remote_channel_pubkeys.funding_pubkey);
+		let remote_channel_data = self.accepted_channel_data.as_ref().expect("must accept before signing");
+		let channel_funding_redeemscript = make_funding_redeemscript(&funding_pubkey, &remote_channel_data.remote_channel_pubkeys.funding_pubkey);
 
 		Ok(local_commitment_tx.get_local_sig(&self.funding_key, &channel_funding_redeemscript, self.channel_value_satoshis, secp_ctx))
 	}
 
 	#[cfg(test)]
 	fn unsafe_sign_local_commitment<T: secp256k1::Signing + secp256k1::Verification>(&self, local_commitment_tx: &LocalCommitmentTransaction, secp_ctx: &Secp256k1<T>) -> Result<Signature, ()> {
 		let funding_pubkey = PublicKey::from_secret_key(secp_ctx, &self.funding_key);
-		let remote_channel_pubkeys = self.remote_channel_pubkeys.as_ref().expect("must set remote channel pubkeys before signing");
+		let remote_channel_pubkeys = &self.accepted_channel_data.as_ref().expect("must accept before signing").remote_channel_pubkeys;
 		let channel_funding_redeemscript = make_funding_redeemscript(&funding_pubkey, &remote_channel_pubkeys.funding_pubkey);
 
 		Ok(local_commitment_tx.get_local_sig(&self.funding_key, &channel_funding_redeemscript, self.channel_value_satoshis, secp_ctx))
 	}
 
-	fn sign_local_commitment_htlc_transactions<T: secp256k1::Signing + secp256k1::Verification>(&self, local_commitment_tx: &LocalCommitmentTransaction, local_csv: u16, secp_ctx: &Secp256k1<T>) -> Result<Vec<Option<Signature>>, ()> {
+	fn sign_local_commitment_htlc_transactions<T: secp256k1::Signing + secp256k1::Verification>(&self, local_commitment_tx: &LocalCommitmentTransaction, secp_ctx: &Secp256k1<T>) -> Result<Vec<Option<Signature>>, ()> {
+		let local_csv = self.accepted_channel_data.as_ref().unwrap().remote_to_self_delay;
 		local_commitment_tx.get_htlc_sigs(&self.htlc_base_key, local_csv, secp_ctx)
 	}
 
@@ -532,9 +557,9 @@ impl ChannelKeys for InMemoryChannelKeys {
 		if closing_tx.input[0].witness.len() != 0 { return Err(()); }
 		if closing_tx.output.len() > 2 { return Err(()); }
 
-		let remote_channel_pubkeys = self.remote_channel_pubkeys.as_ref().expect("must set remote channel pubkeys before signing");
 		let funding_pubkey = PublicKey::from_secret_key(secp_ctx, &self.funding_key);
-		let channel_funding_redeemscript = make_funding_redeemscript(&funding_pubkey, &remote_channel_pubkeys.funding_pubkey);
+		let remote_channel_data = self.accepted_channel_data.as_ref().expect("must accept before signing");
+		let channel_funding_redeemscript = make_funding_redeemscript(&funding_pubkey, &remote_channel_data.remote_channel_pubkeys.funding_pubkey);
 
 		let sighash = hash_to_message!(&bip143::SighashComponents::new(closing_tx)
 			.sighash_all(&closing_tx.input[0], &channel_funding_redeemscript, self.channel_value_satoshis)[..]);
@@ -546,12 +571,19 @@ impl ChannelKeys for InMemoryChannelKeys {
 		Ok(secp_ctx.sign(&msghash, &self.funding_key))
 	}
 
-	fn set_remote_channel_pubkeys(&mut self, channel_pubkeys: &ChannelPublicKeys) {
-		assert!(self.remote_channel_pubkeys.is_none(), "Already set remote channel pubkeys");
-		self.remote_channel_pubkeys = Some(channel_pubkeys.clone());
+	fn on_accept(&mut self, channel_pubkeys: &ChannelPublicKeys, remote_to_self_delay: u16, local_to_self_delay: u16) {
+		assert!(self.accepted_channel_data.is_none(), "Already accepted");
+		self.accepted_channel_data = Some(AcceptedChannelData {
+			remote_channel_pubkeys: channel_pubkeys.clone(),
+			remote_to_self_delay,
+			local_to_self_delay,
+		});
 	}
 }
 
+impl_writeable!(AcceptedChannelData, 0,
+ { remote_channel_pubkeys, remote_to_self_delay, local_to_self_delay });
+
 impl Writeable for InMemoryChannelKeys {
 	fn write<W: Writer>(&self, writer: &mut W) -> Result<(), Error> {
 		self.funding_key.write(writer)?;
@@ -560,7 +592,7 @@ impl Writeable for InMemoryChannelKeys {
 		self.delayed_payment_base_key.write(writer)?;
 		self.htlc_base_key.write(writer)?;
 		self.commitment_seed.write(writer)?;
-		self.remote_channel_pubkeys.write(writer)?;
+		self.accepted_channel_data.write(writer)?;
 		self.channel_value_satoshis.write(writer)?;
 		self.key_derivation_params.0.write(writer)?;
 		self.key_derivation_params.1.write(writer)?;
@@ -577,7 +609,7 @@ impl Readable for InMemoryChannelKeys {
 		let delayed_payment_base_key = Readable::read(reader)?;
 		let htlc_base_key = Readable::read(reader)?;
 		let commitment_seed = Readable::read(reader)?;
-		let remote_channel_pubkeys = Readable::read(reader)?;
+		let remote_channel_data = Readable::read(reader)?;
 		let channel_value_satoshis = Readable::read(reader)?;
 		let secp_ctx = Secp256k1::signing_only();
 		let local_channel_pubkeys =
@@ -596,7 +628,7 @@ impl Readable for InMemoryChannelKeys {
 			commitment_seed,
 			channel_value_satoshis,
 			local_channel_pubkeys,
-			remote_channel_pubkeys,
+			accepted_channel_data: remote_channel_data,
 			key_derivation_params: (params_1, params_2),
 		})
 	}

lightning/src/ln/channel.rs

@@ -458,6 +458,7 @@ impl<ChanSigner: ChannelKeys> Channel<ChanSigner> {
 	where K::Target: KeysInterface<ChanKeySigner = ChanSigner>,
 	      F::Target: FeeEstimator,
 	{
+		let our_to_self_delay = config.own_channel_config.our_to_self_delay;
 		let chan_keys = keys_provider.get_channel_keys(false, channel_value_satoshis);
 
 		if channel_value_satoshis >= MAX_FUNDING_SATOSHIS {
@@ -467,8 +468,8 @@ impl<ChanSigner: ChannelKeys> Channel<ChanSigner> {
 		if push_msat > channel_value_msat {
 			return Err(APIError::APIMisuseError { err: format!("Push value ({}) was larger than channel_value ({})", push_msat, channel_value_msat) });
 		}
-		if config.own_channel_config.our_to_self_delay < BREAKDOWN_TIMEOUT {
-			return Err(APIError::APIMisuseError {err: format!("Configured with an unreasonable our_to_self_delay ({}) putting user funds at risks", config.own_channel_config.our_to_self_delay)});
+		if our_to_self_delay < BREAKDOWN_TIMEOUT {
+			return Err(APIError::APIMisuseError {err: format!("Configured with an unreasonable our_to_self_delay ({}) putting user funds at risks", our_to_self_delay)});
 		}
 		let background_feerate = fee_estimator.get_est_sat_per_1000_weight(ConfirmationTarget::Background);
 		if Channel::<ChanSigner>::get_remote_channel_reserve_satoshis(channel_value_satoshis) < Channel::<ChanSigner>::derive_our_dust_limit_satoshis(background_feerate) {
@@ -535,7 +536,7 @@ impl<ChanSigner: ChannelKeys> Channel<ChanSigner> {
 			their_htlc_minimum_msat: 0,
 			our_htlc_minimum_msat: if config.own_channel_config.our_htlc_minimum_msat == 0 { 1 } else { config.own_channel_config.our_htlc_minimum_msat },
 			their_to_self_delay: 0,
-			our_to_self_delay: config.own_channel_config.our_to_self_delay,
+			our_to_self_delay,
 			their_max_accepted_htlcs: 0,
 			minimum_depth: 0, // Filled in in accept_channel
 
@@ -582,7 +583,7 @@ impl<ChanSigner: ChannelKeys> Channel<ChanSigner> {
 			delayed_payment_basepoint: msg.delayed_payment_basepoint,
 			htlc_basepoint: msg.htlc_basepoint
 		};
-		chan_keys.set_remote_channel_pubkeys(&their_pubkeys);
+		chan_keys.on_accept(&their_pubkeys, msg.to_self_delay, config.own_channel_config.our_to_self_delay);
 		let mut local_config = (*config).channel_options.clone();
 
 		if config.own_channel_config.our_to_self_delay < BREAKDOWN_TIMEOUT {
@@ -1457,7 +1458,7 @@ impl<ChanSigner: ChannelKeys> Channel<ChanSigner> {
 			htlc_basepoint: msg.htlc_basepoint
 		};
 
-		self.local_keys.set_remote_channel_pubkeys(&their_pubkeys);
+		self.local_keys.on_accept(&their_pubkeys, msg.to_self_delay, self.our_to_self_delay);
 		self.their_pubkeys = Some(their_pubkeys);
 
 		self.their_cur_commitment_point = Some(msg.first_per_commitment_point);
@@ -1483,7 +1484,7 @@ 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, logger).0;
-		let remote_signature = self.local_keys.sign_remote_commitment(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.feerate_per_kw, &remote_initial_commitment_tx, &remote_keys, &Vec::new(), &self.secp_ctx)
 				.map_err(|_| ChannelError::Close("Failed to get signatures for new commitment_signed".to_owned()))?.0;
 
 		// We sign the "remote" commitment transaction, allowing them to broadcast the tx if they wish.
@@ -3512,7 +3513,7 @@ impl<ChanSigner: ChannelKeys> Channel<ChanSigner> {
 	fn get_outbound_funding_created_signature<L: Deref>(&mut self, logger: &L) -> Result<Signature, ChannelError> where L::Target: Logger {
 		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, logger).0;
-		Ok(self.local_keys.sign_remote_commitment(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.feerate_per_kw, &remote_initial_commitment_tx, &remote_keys, &Vec::new(), &self.secp_ctx)
 				.map_err(|_| ChannelError::Close("Failed to get signatures for new commitment_signed".to_owned()))?.0)
 	}
 
@@ -3865,7 +3866,7 @@ impl<ChanSigner: ChannelKeys> Channel<ChanSigner> {
 				htlcs.push(htlc);
 			}
 
-			let res = self.local_keys.sign_remote_commitment(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(feerate_per_kw, &remote_commitment_tx.0, &remote_keys, &htlcs, &self.secp_ctx)
 				.map_err(|_| ChannelError::Close("Failed to get signatures for new commitment_signed".to_owned()))?;
 			signature = res.0;
 			htlc_signatures = res.1;
@@ -4658,7 +4659,7 @@ mod tests {
 			delayed_payment_basepoint: public_from_secret_hex(&secp_ctx, "1552dfba4f6cf29a62a0af13c8d6981d36d0ef8d61ba10fb0fe90da7634d7e13"),
 			htlc_basepoint: public_from_secret_hex(&secp_ctx, "4444444444444444444444444444444444444444444444444444444444444444")
 		};
-		chan_keys.set_remote_channel_pubkeys(&their_pubkeys);
+		chan_keys.on_accept(&their_pubkeys, chan.their_to_self_delay, chan.our_to_self_delay);
 
 		assert_eq!(their_pubkeys.payment_point.serialize()[..],
 		           hex::decode("032c0b7cf95324a07d05398b240174dc0c2be444d96b159aa6c7f7b1e668680991").unwrap()[..]);
@@ -4714,7 +4715,7 @@ mod tests {
 				assert_eq!(serialize(&localtx.add_local_sig(&redeemscript, local_sig))[..],
 						hex::decode($tx_hex).unwrap()[..]);
 
-				let htlc_sigs = chan_keys.sign_local_commitment_htlc_transactions(&localtx, chan.their_to_self_delay, &chan.secp_ctx).unwrap();
+				let htlc_sigs = chan_keys.sign_local_commitment_htlc_transactions(&localtx, &chan.secp_ctx).unwrap();
 				let mut htlc_sig_iter = localtx.per_htlc.iter().zip(htlc_sigs.iter().enumerate());
 
 				$({