Revocation enforcement in signer

We want to make sure that we don't sign revoked transactions.

Given that ChannelKeys are not singletons and revocation enforcement is stateful,
we need to store the revocation state in KeysInterface.

Author: devrandom

lightning/src/ln/functional_tests.rs

@@ -1617,27 +1617,26 @@ fn test_fee_spike_violation_fails_htlc() {
 
 	// 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_secret, local_secret2) = {
+	let (local_revocation_basepoint, local_htlc_basepoint, local_payment_point, local_secret, next_local_point) = {
 		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_keys();
 		let pubkeys = chan_keys.pubkeys();
 		(pubkeys.revocation_basepoint, pubkeys.htlc_basepoint, pubkeys.payment_point,
-		 chan_keys.release_commitment_secret(INITIAL_COMMITMENT_NUMBER), chan_keys.release_commitment_secret(INITIAL_COMMITMENT_NUMBER - 2))
+		 chan_keys.release_commitment_secret(INITIAL_COMMITMENT_NUMBER),
+		 chan_keys.get_per_commitment_point(INITIAL_COMMITMENT_NUMBER - 2, &secp_ctx))
 	};
-	let (remote_delayed_payment_basepoint, remote_htlc_basepoint, remote_payment_point, remote_secret1) = {
+	let (remote_delayed_payment_basepoint, remote_htlc_basepoint, remote_payment_point, remote_point) = {
 		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_keys();
 		let pubkeys = chan_keys.pubkeys();
 		(pubkeys.delayed_payment_basepoint, pubkeys.htlc_basepoint, pubkeys.payment_point,
-		 chan_keys.release_commitment_secret(INITIAL_COMMITMENT_NUMBER - 1))
+		 chan_keys.get_per_commitment_point(INITIAL_COMMITMENT_NUMBER - 1, &secp_ctx))
 	};
 
 	// Assemble the set of keys we can use for signatures for our commitment_signed message.
-	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::derive_new(&secp_ctx, &per_commitment_point, &remote_delayed_payment_basepoint,
+	let commit_tx_keys = chan_utils::TxCreationKeys::derive_new(&secp_ctx, &remote_point, &remote_delayed_payment_basepoint,
 		&remote_htlc_basepoint, &local_revocation_basepoint, &local_htlc_basepoint).unwrap();
 
 	// Build the remote commitment transaction so we can sign it, and then later use the
@@ -1720,10 +1719,11 @@ 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 = 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};
+	let raa_msg = msgs::RevokeAndACK {
+		channel_id: chan.2,
+		per_commitment_secret: local_secret,
+		next_per_commitment_point: next_local_point
+	};
 	nodes[1].node.handle_revoke_and_ack(&nodes[0].node.get_our_node_id(), &raa_msg);
 
 	let events = nodes[1].node.get_and_clear_pending_msg_events();
@@ -4309,7 +4309,6 @@ fn test_no_txn_manager_serialize_deserialize() {
 	let fee_estimator: test_utils::TestFeeEstimator;
 	let persister: test_utils::TestPersister;
 	let new_chain_monitor: test_utils::TestChainMonitor;
-	let keys_manager: test_utils::TestKeysInterface;
 	let nodes_0_deserialized: ChannelManager<EnforcingChannelKeys, &test_utils::TestChainMonitor, &test_utils::TestBroadcaster, &test_utils::TestKeysInterface, &test_utils::TestFeeEstimator, &test_utils::TestLogger>;
 	let mut nodes = create_network(2, &node_cfgs, &node_chanmgrs);
 
@@ -4324,12 +4323,12 @@ fn test_no_txn_manager_serialize_deserialize() {
 	logger = test_utils::TestLogger::new();
 	fee_estimator = test_utils::TestFeeEstimator { sat_per_kw: 253 };
 	persister = test_utils::TestPersister::new();
-	keys_manager = test_utils::TestKeysInterface::new(&nodes[0].node_seed, Network::Testnet);
-	new_chain_monitor = test_utils::TestChainMonitor::new(Some(nodes[0].chain_source), nodes[0].tx_broadcaster.clone(), &logger, &fee_estimator, &persister, &keys_manager);
+	let keys_manager = &chanmon_cfgs[0].keys_manager;
+	new_chain_monitor = test_utils::TestChainMonitor::new(Some(nodes[0].chain_source), nodes[0].tx_broadcaster.clone(), &logger, &fee_estimator, &persister, keys_manager);
 	nodes[0].chain_monitor = &new_chain_monitor;
 	let mut chan_0_monitor_read = &chan_0_monitor_serialized.0[..];
 	let (_, mut chan_0_monitor) = <(BlockHash, ChannelMonitor<EnforcingChannelKeys>)>::read(
-		&mut chan_0_monitor_read, &keys_manager).unwrap();
+		&mut chan_0_monitor_read, keys_manager).unwrap();
 	assert!(chan_0_monitor_read.is_empty());
 
 	let mut nodes_0_read = &nodes_0_serialized[..];
@@ -4339,7 +4338,7 @@ fn test_no_txn_manager_serialize_deserialize() {
 		channel_monitors.insert(chan_0_monitor.get_funding_txo().0, &mut chan_0_monitor);
 		<(BlockHash, ChannelManager<EnforcingChannelKeys, &test_utils::TestChainMonitor, &test_utils::TestBroadcaster, &test_utils::TestKeysInterface, &test_utils::TestFeeEstimator, &test_utils::TestLogger>)>::read(&mut nodes_0_read, ChannelManagerReadArgs {
 			default_config: config,
-			keys_manager: &keys_manager,
+			keys_manager,
 			fee_estimator: &fee_estimator,
 			chain_monitor: nodes[0].chain_monitor,
 			tx_broadcaster: nodes[0].tx_broadcaster.clone(),
@@ -4386,7 +4385,6 @@ fn test_manager_serialize_deserialize_events() {
 	let persister: test_utils::TestPersister;
 	let logger: test_utils::TestLogger;
 	let new_chain_monitor: test_utils::TestChainMonitor;
-	let keys_manager: test_utils::TestKeysInterface;
 	let nodes_0_deserialized: ChannelManager<EnforcingChannelKeys, &test_utils::TestChainMonitor, &test_utils::TestBroadcaster, &test_utils::TestKeysInterface, &test_utils::TestFeeEstimator, &test_utils::TestLogger>;
 	let mut nodes = create_network(2, &node_cfgs, &node_chanmgrs);
 
@@ -4395,8 +4393,8 @@ fn test_manager_serialize_deserialize_events() {
 	let push_msat = 10001;
 	let a_flags = InitFeatures::known();
 	let b_flags = InitFeatures::known();
-	let node_a = nodes.pop().unwrap();
-	let node_b = nodes.pop().unwrap();
+	let node_a = nodes.remove(0);
+	let node_b = nodes.remove(0);
 	node_a.node.create_channel(node_b.node.get_our_node_id(), channel_value, push_msat, 42, None).unwrap();
 	node_b.node.handle_open_channel(&node_a.node.get_our_node_id(), a_flags, &get_event_msg!(node_a, MessageSendEvent::SendOpenChannel, node_b.node.get_our_node_id()));
 	node_a.node.handle_accept_channel(&node_b.node.get_our_node_id(), b_flags, &get_event_msg!(node_b, MessageSendEvent::SendAcceptChannel, node_a.node.get_our_node_id()));
@@ -4434,12 +4432,12 @@ fn test_manager_serialize_deserialize_events() {
 	fee_estimator = test_utils::TestFeeEstimator { sat_per_kw: 253 };
 	logger = test_utils::TestLogger::new();
 	persister = test_utils::TestPersister::new();
-	keys_manager = test_utils::TestKeysInterface::new(&nodes[0].node_seed, Network::Testnet);
-	new_chain_monitor = test_utils::TestChainMonitor::new(Some(nodes[0].chain_source), nodes[0].tx_broadcaster.clone(), &logger, &fee_estimator, &persister, &keys_manager);
+	let keys_manager = &chanmon_cfgs[0].keys_manager;
+	new_chain_monitor = test_utils::TestChainMonitor::new(Some(nodes[0].chain_source), nodes[0].tx_broadcaster.clone(), &logger, &fee_estimator, &persister, keys_manager);
 	nodes[0].chain_monitor = &new_chain_monitor;
 	let mut chan_0_monitor_read = &chan_0_monitor_serialized.0[..];
 	let (_, mut chan_0_monitor) = <(BlockHash, ChannelMonitor<EnforcingChannelKeys>)>::read(
-		&mut chan_0_monitor_read, &keys_manager).unwrap();
+		&mut chan_0_monitor_read, keys_manager).unwrap();
 	assert!(chan_0_monitor_read.is_empty());
 
 	let mut nodes_0_read = &nodes_0_serialized[..];
@@ -4449,7 +4447,7 @@ fn test_manager_serialize_deserialize_events() {
 		channel_monitors.insert(chan_0_monitor.get_funding_txo().0, &mut chan_0_monitor);
 		<(BlockHash, ChannelManager<EnforcingChannelKeys, &test_utils::TestChainMonitor, &test_utils::TestBroadcaster, &test_utils::TestKeysInterface, &test_utils::TestFeeEstimator, &test_utils::TestLogger>)>::read(&mut nodes_0_read, ChannelManagerReadArgs {
 			default_config: config,
-			keys_manager: &keys_manager,
+			keys_manager,
 			fee_estimator: &fee_estimator,
 			chain_monitor: nodes[0].chain_monitor,
 			tx_broadcaster: nodes[0].tx_broadcaster.clone(),
@@ -4510,7 +4508,6 @@ fn test_simple_manager_serialize_deserialize() {
 	let fee_estimator: test_utils::TestFeeEstimator;
 	let persister: test_utils::TestPersister;
 	let new_chain_monitor: test_utils::TestChainMonitor;
-	let keys_manager: &test_utils::TestKeysInterface;
 	let nodes_0_deserialized: ChannelManager<EnforcingChannelKeys, &test_utils::TestChainMonitor, &test_utils::TestBroadcaster, &test_utils::TestKeysInterface, &test_utils::TestFeeEstimator, &test_utils::TestLogger>;
 	let mut nodes = create_network(2, &node_cfgs, &node_chanmgrs);
 	create_announced_chan_between_nodes(&nodes, 0, 1, InitFeatures::known(), InitFeatures::known());
@@ -4527,7 +4524,7 @@ fn test_simple_manager_serialize_deserialize() {
 	logger = test_utils::TestLogger::new();
 	fee_estimator = test_utils::TestFeeEstimator { sat_per_kw: 253 };
 	persister = test_utils::TestPersister::new();
-	keys_manager = &chanmon_cfgs[0].keys_manager;
+	let keys_manager = &chanmon_cfgs[0].keys_manager;
 	new_chain_monitor = test_utils::TestChainMonitor::new(Some(nodes[0].chain_source), nodes[0].tx_broadcaster.clone(), &logger, &fee_estimator, &persister, keys_manager);
 	nodes[0].chain_monitor = &new_chain_monitor;
 	let mut chan_0_monitor_read = &chan_0_monitor_serialized.0[..];
@@ -4572,7 +4569,6 @@ fn test_manager_serialize_deserialize_inconsistent_monitor() {
 	let fee_estimator: test_utils::TestFeeEstimator;
 	let persister: test_utils::TestPersister;
 	let new_chain_monitor: test_utils::TestChainMonitor;
-	let keys_manager: &test_utils::TestKeysInterface;
 	let nodes_0_deserialized: ChannelManager<EnforcingChannelKeys, &test_utils::TestChainMonitor, &test_utils::TestBroadcaster, &test_utils::TestKeysInterface, &test_utils::TestFeeEstimator, &test_utils::TestLogger>;
 	let mut nodes = create_network(4, &node_cfgs, &node_chanmgrs);
 	create_announced_chan_between_nodes(&nodes, 0, 1, InitFeatures::known(), InitFeatures::known());
@@ -4608,7 +4604,7 @@ fn test_manager_serialize_deserialize_inconsistent_monitor() {
 	logger = test_utils::TestLogger::new();
 	fee_estimator = test_utils::TestFeeEstimator { sat_per_kw: 253 };
 	persister = test_utils::TestPersister::new();
-	keys_manager = &chanmon_cfgs[0].keys_manager;
+	let keys_manager = &chanmon_cfgs[0].keys_manager;
 	new_chain_monitor = test_utils::TestChainMonitor::new(Some(nodes[0].chain_source), nodes[0].tx_broadcaster.clone(), &logger, &fee_estimator, &persister, keys_manager);
 	nodes[0].chain_monitor = &new_chain_monitor;
 
@@ -8126,9 +8122,11 @@ fn test_counterparty_raa_skip_no_crash() {
 	let mut guard = nodes[0].node.channel_state.lock().unwrap();
 	let keys = &guard.by_id.get_mut(&channel_id).unwrap().holder_keys;
 	const INITIAL_COMMITMENT_NUMBER: u64 = (1 << 48) - 1;
+	let per_commitment_secret = keys.release_commitment_secret(INITIAL_COMMITMENT_NUMBER);
+	// Must revoke without gaps
+	keys.release_commitment_secret(INITIAL_COMMITMENT_NUMBER - 1);
 	let next_per_commitment_point = PublicKey::from_secret_key(&Secp256k1::new(),
 		&SecretKey::from_slice(&keys.release_commitment_secret(INITIAL_COMMITMENT_NUMBER - 2)).unwrap());
-	let per_commitment_secret = keys.release_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/ln/onchaintx.rs

@@ -962,7 +962,7 @@ impl<ChanSigner: ChannelKeys> OnchainTxHandler<ChanSigner> {
 	pub(crate) fn get_fully_signed_copy_holder_tx(&mut self, funding_redeemscript: &Script) -> Option<Transaction> {
 		if let Some(ref mut holder_commitment) = self.holder_commitment {
 			let holder_commitment = holder_commitment.clone();
-			match self.key_storage.sign_holder_commitment(&holder_commitment, &self.secp_ctx) {
+			match self.key_storage.unsafe_sign_holder_commitment(&holder_commitment, &self.secp_ctx) {
 				Ok(sig) => Some(holder_commitment.add_holder_sig(funding_redeemscript, sig)),
 				Err(_) => return None,
 			}

lightning/src/util/enforcing_trait_impls.rs

@@ -24,19 +24,32 @@ use util::ser::{Writeable, Writer, Readable};
 use std::io::Error;
 use ln::msgs::DecodeError;
 
+/// Initial value for revoked commitment downward counter
+pub const INITIAL_REVOKED_COMMITMENT_NUMBER: u64 = 1 << 48;
+
 /// Enforces some rules on ChannelKeys calls. Eventually we will probably want to expose a variant
 /// of this which would essentially be what you'd want to run on a hardware wallet.
 #[derive(Clone)]
 pub struct EnforcingChannelKeys {
 	pub inner: InMemoryChannelKeys,
-	commitment_number_obscure_and_last: Arc<Mutex<(Option<u64>, u64)>>,
+	pub(crate) revoked_commitment: Arc<Mutex<u64>>,
+	pub(crate) commitment_number_obscure_and_last: Arc<Mutex<(Option<u64>, u64)>>,
 }
 
 impl EnforcingChannelKeys {
 	pub fn new(inner: InMemoryChannelKeys) -> Self {
 		Self {
 			inner,
 			commitment_number_obscure_and_last: Arc::new(Mutex::new((None, 0))),
+			revoked_commitment: Arc::new(Mutex::new(INITIAL_REVOKED_COMMITMENT_NUMBER))
+		}
+	}
+
+	pub fn new_with_revoked(inner: InMemoryChannelKeys, revoked_commitment: Arc<Mutex<u64>>) -> Self {
+		Self {
+			inner,
+			commitment_number_obscure_and_last: Arc::new(Mutex::new((None, 0))),
+			revoked_commitment
 		}
 	}
 }
@@ -62,7 +75,11 @@ impl ChannelKeys for EnforcingChannelKeys {
 	}
 
 	fn release_commitment_secret(&self, idx: u64) -> [u8; 32] {
-		// TODO: enforce the ChannelKeys contract - error here if we already signed this commitment
+		{
+			let mut revoked = self.revoked_commitment.lock().unwrap();
+			assert!(idx == *revoked || idx == *revoked - 1, "can only revoke the current or next unrevoked commitment - trying {}, revoked {}", idx, *revoked);
+			*revoked = idx;
+		}
 		self.inner.release_commitment_secret(idx)
 	}
 
@@ -90,6 +107,20 @@ impl ChannelKeys for EnforcingChannelKeys {
 	fn sign_holder_commitment<T: secp256k1::Signing + secp256k1::Verification>(&self, holder_commitment_tx: &HolderCommitmentTransaction, secp_ctx: &Secp256k1<T>) -> Result<Signature, ()> {
 		// TODO: enforce the ChannelKeys contract - error if this commitment was already revoked
 		// TODO: need the commitment number
+		let revoked = self.revoked_commitment.lock().unwrap();
+		let keys = &holder_commitment_tx.keys;
+		if keys.per_commitment_point != self.inner.get_per_commitment_point(*revoked - 1, secp_ctx) {
+			if keys.per_commitment_point != self.inner.get_per_commitment_point(*revoked - 2, secp_ctx) {
+				if keys.per_commitment_point == self.inner.get_per_commitment_point(*revoked, secp_ctx) {
+					println!("attempted to sign the latest revoked local commitment {}", self.inner.commitment_seed[0]);
+					return Err(())
+				} else {
+					println!("can only sign the next two unrevoked commitment numbers, {} revoked={} point={}",
+					       self.inner.commitment_seed[0], *revoked, keys.per_commitment_point);
+					return Err(())
+				}
+			}
+		}
 		Ok(self.inner.sign_holder_commitment(holder_commitment_tx, secp_ctx).unwrap())
 	}
 
@@ -149,11 +180,12 @@ impl Writeable for EnforcingChannelKeys {
 
 impl Readable for EnforcingChannelKeys {
 	fn read<R: ::std::io::Read>(reader: &mut R) -> Result<Self, DecodeError> {
-		let inner = Readable::read(reader)?;
+		let inner: InMemoryChannelKeys = Readable::read(reader)?;
 		let obscure_and_last = Readable::read(reader)?;
 		Ok(EnforcingChannelKeys {
-			inner: inner,
-			commitment_number_obscure_and_last: Arc::new(Mutex::new(obscure_and_last))
+			inner,
+			commitment_number_obscure_and_last: Arc::new(Mutex::new(obscure_and_last)),
+			revoked_commitment: Arc::new(Mutex::new(INITIAL_REVOKED_COMMITMENT_NUMBER)),
 		})
 	}
 }

lightning/src/util/test_utils.rs

@@ -18,7 +18,7 @@ use chain::keysinterface;
 use ln::features::{ChannelFeatures, InitFeatures};
 use ln::msgs;
 use ln::msgs::OptionalField;
-use util::enforcing_trait_impls::EnforcingChannelKeys;
+use util::enforcing_trait_impls::{EnforcingChannelKeys, INITIAL_REVOKED_COMMITMENT_NUMBER};
 use util::events;
 use util::logger::{Logger, Level, Record};
 use util::ser::{Readable, ReadableArgs, Writer, Writeable};
@@ -35,7 +35,7 @@ use bitcoin::secp256k1::{SecretKey, PublicKey, Secp256k1, Signature};
 use regex;
 
 use std::time::Duration;
-use std::sync::Mutex;
+use std::sync::{Mutex, Arc};
 use std::sync::atomic::{AtomicBool, AtomicUsize, Ordering};
 use std::{cmp, mem};
 use std::collections::{HashMap, HashSet};
@@ -402,6 +402,7 @@ pub struct TestKeysInterface {
 	backing: keysinterface::KeysManager,
 	pub override_session_priv: Mutex<Option<[u8; 32]>>,
 	pub override_channel_id_priv: Mutex<Option<[u8; 32]>>,
+	revoked_commitments: Mutex<HashMap<[u8;32], Arc<Mutex<u64>>>>,
 }
 
 impl keysinterface::KeysInterface for TestKeysInterface {
@@ -411,7 +412,9 @@ impl keysinterface::KeysInterface for TestKeysInterface {
 	fn get_destination_script(&self) -> Script { self.backing.get_destination_script() }
 	fn get_shutdown_pubkey(&self) -> PublicKey { self.backing.get_shutdown_pubkey() }
 	fn get_channel_keys(&self, inbound: bool, channel_value_satoshis: u64) -> EnforcingChannelKeys {
-		EnforcingChannelKeys::new(self.backing.get_channel_keys(inbound, channel_value_satoshis))
+		let keys = self.backing.get_channel_keys(inbound, channel_value_satoshis);
+		let revoked_commitment = self.make_revoked_commitment_cell(keys.commitment_seed);
+		EnforcingChannelKeys::new_with_revoked(keys, revoked_commitment)
 	}
 
 	fn get_secure_random_bytes(&self) -> [u8; 32] {
@@ -429,22 +432,37 @@ impl keysinterface::KeysInterface for TestKeysInterface {
 		self.backing.get_secure_random_bytes()
 	}
 
-	fn read_chan_signer(&self, reader: &[u8]) -> Result<Self::ChanKeySigner, msgs::DecodeError> {
-		EnforcingChannelKeys::read(&mut std::io::Cursor::new(reader))
+	fn read_chan_signer(&self, buffer: &[u8]) -> Result<Self::ChanKeySigner, msgs::DecodeError> {
+		let mut reader = std::io::Cursor::new(buffer);
+
+		let inner: InMemoryChannelKeys = Readable::read(&mut reader)?;
+		let revoked_commitment = self.make_revoked_commitment_cell(inner.commitment_seed);
+
+		let obscure_and_last = Readable::read(&mut reader)?;
+
+		Ok(EnforcingChannelKeys {
+			inner,
+			commitment_number_obscure_and_last: Arc::new(Mutex::new(obscure_and_last)),
+			revoked_commitment,
+		})
 	}
 }
 
+
 impl TestKeysInterface {
 	pub fn new(seed: &[u8; 32], network: Network) -> Self {
 		let now = Duration::from_secs(genesis_block(network).header.time as u64);
 		Self {
 			backing: keysinterface::KeysManager::new(seed, network, now.as_secs(), now.subsec_nanos()),
 			override_session_priv: Mutex::new(None),
 			override_channel_id_priv: Mutex::new(None),
+			revoked_commitments: Mutex::new(HashMap::new()),
 		}
 	}
 	pub fn derive_channel_keys(&self, channel_value_satoshis: u64, user_id_1: u64, user_id_2: u64) -> EnforcingChannelKeys {
-		EnforcingChannelKeys::new(self.backing.derive_channel_keys(channel_value_satoshis, user_id_1, user_id_2))
+		let keys = self.backing.derive_channel_keys(channel_value_satoshis, user_id_1, user_id_2);
+		let revoked_commitment = self.make_revoked_commitment_cell(keys.commitment_seed);
+		EnforcingChannelKeys::new_with_revoked(keys, revoked_commitment)
 	}
 }
 
@@ -486,3 +504,14 @@ impl chain::Filter for TestChainSource {
 		self.watched_outputs.lock().unwrap().insert((*outpoint, script_pubkey.clone()));
 	}
 }
+
+impl TestKeysInterface {
+	fn make_revoked_commitment_cell(&self, commitment_seed: [u8; 32]) -> Arc<Mutex<u64>> {
+		let mut revoked_commitments = self.revoked_commitments.lock().unwrap();
+		if !revoked_commitments.contains_key(&commitment_seed) {
+			revoked_commitments.insert(commitment_seed, Arc::new(Mutex::new(INITIAL_REVOKED_COMMITMENT_NUMBER)));
+		}
+		let cell = revoked_commitments.get(&commitment_seed).unwrap();
+		Arc::clone(cell)
+	}
+}