ChannelKeys provides individual commitment secrets

lightning/src/chain/keysinterface.rs

@@ -195,8 +195,9 @@ impl Readable for SpendableOutputDescriptor {
 // TODO: We should remove Clone by instead requesting a new ChannelKeys copy when we create
 // ChannelMonitors instead of expecting to clone the one out of the Channel into the monitors.
 pub trait ChannelKeys : Send+Clone {
-	/// Gets the commitment seed
-	fn commitment_seed(&self) -> &[u8; 32];
+	/// Gets the commitment seed for a specific commitment number
+	/// Note that the commitment number starts at (1 << 48) - 1 and counts backwards
+	fn commitment_secret(&self, idx: u64) -> [u8; 32];
 	/// Gets the local channel public keys and basepoints
 	fn pubkeys(&self) -> &ChannelPublicKeys;
 	/// Gets arbitrary identifiers describing the set of keys which are provided back to you in
@@ -404,7 +405,10 @@ impl InMemoryChannelKeys {
 }
 
 impl ChannelKeys for InMemoryChannelKeys {
-	fn commitment_seed(&self) -> &[u8; 32] { &self.commitment_seed }
+	fn commitment_secret(&self, idx: u64) -> [u8; 32] {
+		chan_utils::build_commitment_secret(&self.commitment_seed, idx)
+	}
+
 	fn pubkeys(&self) -> &ChannelPublicKeys { &self.local_channel_pubkeys }
 	fn key_derivation_params(&self) -> (u64, u64) { self.key_derivation_params }
 

lightning/src/ln/chan_utils.rs

@@ -52,7 +52,8 @@ impl HTLCType {
 // Various functions for key derivation and transaction creation for use within channels. Primarily
 // used in Channel and ChannelMonitor.
 
-pub(super) fn build_commitment_secret(commitment_seed: &[u8; 32], idx: u64) -> [u8; 32] {
+/// Build the commitment secret from the seed and the commitment number
+pub fn build_commitment_secret(commitment_seed: &[u8; 32], idx: u64) -> [u8; 32] {
 	let mut res: [u8; 32] = commitment_seed.clone();
 	for i in 0..48 {
 		let bitpos = 47 - i;

lightning/src/ln/channel.rs

@@ -783,7 +783,7 @@ impl<ChanSigner: ChannelKeys> Channel<ChanSigner> {
 	// Utilities to derive keys:
 
 	fn build_local_commitment_secret(&self, idx: u64) -> SecretKey {
-		let res = chan_utils::build_commitment_secret(self.local_keys.commitment_seed(), idx);
+		let res = self.local_keys.commitment_secret(idx);
 		SecretKey::from_slice(&res).unwrap()
 	}
 
@@ -2021,7 +2021,7 @@ impl<ChanSigner: ChannelKeys> Channel<ChanSigner> {
 		}
 
 		let next_per_commitment_point = PublicKey::from_secret_key(&self.secp_ctx, &self.build_local_commitment_secret(self.cur_local_commitment_transaction_number - 1));
-		let per_commitment_secret = chan_utils::build_commitment_secret(self.local_keys.commitment_seed(), self.cur_local_commitment_transaction_number + 1);
+		let per_commitment_secret = self.local_keys.commitment_secret(self.cur_local_commitment_transaction_number + 1);
 
 		// Update state now that we've passed all the can-fail calls...
 		let mut need_our_commitment = false;
@@ -2660,7 +2660,7 @@ impl<ChanSigner: ChannelKeys> Channel<ChanSigner> {
 
 	fn get_last_revoke_and_ack(&self) -> msgs::RevokeAndACK {
 		let next_per_commitment_point = PublicKey::from_secret_key(&self.secp_ctx, &self.build_local_commitment_secret(self.cur_local_commitment_transaction_number));
-		let per_commitment_secret = chan_utils::build_commitment_secret(self.local_keys.commitment_seed(), self.cur_local_commitment_transaction_number + 2);
+		let per_commitment_secret = self.local_keys.commitment_secret(self.cur_local_commitment_transaction_number + 2);
 		msgs::RevokeAndACK {
 			channel_id: self.channel_id,
 			per_commitment_secret,
@@ -2743,7 +2743,7 @@ impl<ChanSigner: ChannelKeys> Channel<ChanSigner> {
 		if msg.next_remote_commitment_number > 0 {
 			match msg.data_loss_protect {
 				OptionalField::Present(ref data_loss) => {
-					if chan_utils::build_commitment_secret(self.local_keys.commitment_seed(), INITIAL_COMMITMENT_NUMBER - msg.next_remote_commitment_number + 1) != data_loss.your_last_per_commitment_secret {
+					if self.local_keys.commitment_secret(INITIAL_COMMITMENT_NUMBER - msg.next_remote_commitment_number + 1) != data_loss.your_last_per_commitment_secret {
 						return Err(ChannelError::Close("Peer sent a garbage channel_reestablish with secret key not matching the commitment height provided"));
 					}
 					if msg.next_remote_commitment_number > INITIAL_COMMITMENT_NUMBER - self.cur_local_commitment_transaction_number {

lightning/src/ln/functional_tests.rs

@@ -1599,29 +1599,29 @@ fn test_fee_spike_violation_fails_htlc() {
 
 	let feerate_per_kw = get_feerate!(nodes[0], chan.2);
 
+	const INITIAL_COMMITMENT_NUMBER: u64 = (1 << 48) - 1;
+
 	// Get the EnforcingChannelKeys for each channel, which will be used to (1) get the keys
 	// needed to sign the new commitment tx and (2) sign the new commitment tx.
-	let (local_revocation_basepoint, local_htlc_basepoint, local_payment_point, local_chan_commitment_seed) = {
+	let (local_revocation_basepoint, local_htlc_basepoint, local_payment_point, local_secret, local_secret2) = {
 		let chan_lock = nodes[0].node.channel_state.lock().unwrap();
 		let local_chan = chan_lock.by_id.get(&chan.2).unwrap();
 		let chan_keys = local_chan.get_local_keys();
 		let pubkeys = chan_keys.pubkeys();
-		(pubkeys.revocation_basepoint, pubkeys.htlc_basepoint, pubkeys.payment_point, *chan_keys.commitment_seed())
+		(pubkeys.revocation_basepoint, pubkeys.htlc_basepoint, pubkeys.payment_point,
+		 chan_keys.commitment_secret(INITIAL_COMMITMENT_NUMBER), chan_keys.commitment_secret(INITIAL_COMMITMENT_NUMBER - 2))
 	};
-	let (remote_delayed_payment_basepoint, remote_htlc_basepoint, remote_payment_point, remote_chan_commitment_seed) = {
+	let (remote_delayed_payment_basepoint, remote_htlc_basepoint, remote_payment_point, remote_secret1) = {
 		let chan_lock = nodes[1].node.channel_state.lock().unwrap();
 		let remote_chan = chan_lock.by_id.get(&chan.2).unwrap();
 		let chan_keys = remote_chan.get_local_keys();
 		let pubkeys = chan_keys.pubkeys();
-		(pubkeys.delayed_payment_basepoint, pubkeys.htlc_basepoint, pubkeys.payment_point, *chan_keys.commitment_seed())
+		(pubkeys.delayed_payment_basepoint, pubkeys.htlc_basepoint, pubkeys.payment_point,
+		 chan_keys.commitment_secret(INITIAL_COMMITMENT_NUMBER - 1))
 	};
 
 	// Assemble the set of keys we can use for signatures for our commitment_signed message.
-	const INITIAL_COMMITMENT_NUMBER: u64 = (1 << 48) - 1;
-	let commitment_secret = {
-		let res = chan_utils::build_commitment_secret(&remote_chan_commitment_seed, INITIAL_COMMITMENT_NUMBER - 1);
-		SecretKey::from_slice(&res).unwrap()
-	};
+	let commitment_secret = SecretKey::from_slice(&remote_secret1).unwrap();
 	let per_commitment_point = PublicKey::from_secret_key(&secp_ctx, &commitment_secret);
 	let commit_tx_keys = chan_utils::TxCreationKeys::new(&secp_ctx, &per_commitment_point, &remote_delayed_payment_basepoint,
 		&remote_htlc_basepoint, &local_revocation_basepoint, &local_htlc_basepoint).unwrap();
@@ -1706,8 +1706,8 @@ fn test_fee_spike_violation_fails_htlc() {
 	let _ = nodes[1].node.get_and_clear_pending_msg_events();
 
 	// Send the RAA to nodes[1].
-	let per_commitment_secret = chan_utils::build_commitment_secret(&local_chan_commitment_seed, INITIAL_COMMITMENT_NUMBER);
-	let next_secret = SecretKey::from_slice(&chan_utils::build_commitment_secret(&local_chan_commitment_seed, INITIAL_COMMITMENT_NUMBER - 2)).unwrap();
+	let per_commitment_secret = local_secret;
+	let next_secret = SecretKey::from_slice(&local_secret2).unwrap();
 	let next_per_commitment_point = PublicKey::from_secret_key(&secp_ctx, &next_secret);
 	let raa_msg = msgs::RevokeAndACK{ channel_id: chan.2, per_commitment_secret, next_per_commitment_point};
 	nodes[1].node.handle_revoke_and_ack(&nodes[0].node.get_our_node_id(), &raa_msg);
@@ -8125,11 +8125,12 @@ fn test_counterparty_raa_skip_no_crash() {
 	let nodes = create_network(2, &node_cfgs, &node_chanmgrs);
 	let channel_id = create_announced_chan_between_nodes(&nodes, 0, 1, InitFeatures::known(), InitFeatures::known()).2;
 
-	let commitment_seed = nodes[0].node.channel_state.lock().unwrap().by_id.get_mut(&channel_id).unwrap().local_keys.commitment_seed().clone();
+	let mut guard = nodes[0].node.channel_state.lock().unwrap();
+	let local_keys = &guard.by_id.get_mut(&channel_id).unwrap().local_keys;
 	const INITIAL_COMMITMENT_NUMBER: u64 = (1 << 48) - 1;
 	let next_per_commitment_point = PublicKey::from_secret_key(&Secp256k1::new(),
-		&SecretKey::from_slice(&chan_utils::build_commitment_secret(&commitment_seed, INITIAL_COMMITMENT_NUMBER - 2)).unwrap());
-	let per_commitment_secret = chan_utils::build_commitment_secret(&commitment_seed, INITIAL_COMMITMENT_NUMBER);
+		&SecretKey::from_slice(&local_keys.commitment_secret(INITIAL_COMMITMENT_NUMBER - 2)).unwrap());
+	let per_commitment_secret = local_keys.commitment_secret(INITIAL_COMMITMENT_NUMBER);
 
 	nodes[1].node.handle_revoke_and_ack(&nodes[0].node.get_our_node_id(),
 		&msgs::RevokeAndACK { channel_id, per_commitment_secret, next_per_commitment_point });

lightning/src/util/enforcing_trait_impls.rs

@@ -48,7 +48,7 @@ impl EnforcingChannelKeys {
 }
 
 impl ChannelKeys for EnforcingChannelKeys {
-	fn commitment_seed(&self) -> &[u8; 32] { self.inner.commitment_seed() }
+	fn commitment_secret(&self, idx: u64) -> [u8; 32] { self.inner.commitment_secret(idx) }
 	fn pubkeys(&self) -> &ChannelPublicKeys { self.inner.pubkeys() }
 	fn key_derivation_params(&self) -> (u64, u64) { self.inner.key_derivation_params() }