Add user configurable csv delay encumbering channel refund output,

within reasonable lower or upper bound

Add our_to_self_delay in Channel, to cache user config field at
channel construction.

diff --git a/src/ln/channel.rs b/src/ln/channel.rs
index 4afcbefec33c124d817fa3f74af14964a144004c..e838305adbddf472a6e641b01727f8308ff21c7a 100644 (file)
--- a/src/ln/channel.rs
+++ b/src/ln/channel.rs
@@ -317,7 +317,7 @@ pub(super) struct Channel {
        their_htlc_minimum_msat: u64,
        our_htlc_minimum_msat: u64,
        their_to_self_delay: u16,
-       //implied by BREAKDOWN_TIMEOUT: our_to_self_delay: u16,
+       our_to_self_delay: u16,
        #[cfg(test)]
        pub their_max_accepted_htlcs: u16,
        #[cfg(not(test))]
@@ -413,6 +413,9 @@ impl Channel {
                if push_msat > channel_value_satoshis * 1000 {
                        return Err(APIError::APIMisuseError{err: "push value > channel value"});
                }
+               if config.own_channel_config.our_to_self_delay < BREAKDOWN_TIMEOUT {
+                       return Err(APIError::APIMisuseError{err: "Configured with an unreasonable our_to_self_delay putting user funds at risks"});
+               }
 
 
                let background_feerate = fee_estimator.get_est_sat_per_1000_weight(ConfirmationTarget::Background);
@@ -424,7 +427,7 @@ impl Channel {
 
                let secp_ctx = Secp256k1::new();
                let channel_monitor = ChannelMonitor::new(&chan_keys.revocation_base_key, &chan_keys.delayed_payment_base_key,
-                                                         &chan_keys.htlc_base_key, &chan_keys.payment_base_key, &keys_provider.get_shutdown_pubkey(), BREAKDOWN_TIMEOUT,
+                                                         &chan_keys.htlc_base_key, &chan_keys.payment_base_key, &keys_provider.get_shutdown_pubkey(), config.own_channel_config.our_to_self_delay,
                                                          keys_provider.get_destination_script(), logger.clone());
 
                Ok(Channel {
@@ -481,6 +484,7 @@ impl Channel {
                        their_htlc_minimum_msat: 0,
                        our_htlc_minimum_msat: Channel::derive_our_htlc_minimum_msat(feerate),
                        their_to_self_delay: 0,
+                       our_to_self_delay: config.own_channel_config.our_to_self_delay,
                        their_max_accepted_htlcs: 0,
                        minimum_depth: 0, // Filled in in accept_channel
 
@@ -518,6 +522,10 @@ impl Channel {
                let chan_keys = keys_provider.get_channel_keys(true);
                let mut local_config = (*config).channel_options.clone();
 
+               if config.own_channel_config.our_to_self_delay < BREAKDOWN_TIMEOUT {
+                       return Err(ChannelError::Close("Configured with an unreasonable our_to_self_delay putting user funds at risks"));
+               }
+
                // Check sanity of message fields:
                if msg.funding_satoshis >= MAX_FUNDING_SATOSHIS {
                        return Err(ChannelError::Close("funding value > 2^24"));
@@ -539,7 +547,7 @@ impl Channel {
                }
                Channel::check_remote_fee(fee_estimator, msg.feerate_per_kw)?;
 
-               if msg.to_self_delay > MAX_LOCAL_BREAKDOWN_TIMEOUT {
+               if msg.to_self_delay > config.peer_channel_config_limits.their_to_self_delay || msg.to_self_delay > MAX_LOCAL_BREAKDOWN_TIMEOUT {
                        return Err(ChannelError::Close("They wanted our payments to be delayed by a needlessly long period"));
                }
                if msg.max_accepted_htlcs < 1 {
@@ -612,7 +620,7 @@ impl Channel {
 
                let secp_ctx = Secp256k1::new();
                let mut channel_monitor = ChannelMonitor::new(&chan_keys.revocation_base_key, &chan_keys.delayed_payment_base_key,
-                                                             &chan_keys.htlc_base_key, &chan_keys.payment_base_key, &keys_provider.get_shutdown_pubkey(), BREAKDOWN_TIMEOUT,
+                                                             &chan_keys.htlc_base_key, &chan_keys.payment_base_key, &keys_provider.get_shutdown_pubkey(), config.own_channel_config.our_to_self_delay,
                                                              keys_provider.get_destination_script(), logger.clone());
                channel_monitor.set_their_base_keys(&msg.htlc_basepoint, &msg.delayed_payment_basepoint);
                channel_monitor.set_their_to_self_delay(msg.to_self_delay);
@@ -692,6 +700,7 @@ impl Channel {
                        their_htlc_minimum_msat: msg.htlc_minimum_msat,
                        our_htlc_minimum_msat: Channel::derive_our_htlc_minimum_msat(msg.feerate_per_kw as u64),
                        their_to_self_delay: msg.to_self_delay,
+                       our_to_self_delay: config.own_channel_config.our_to_self_delay,
                        their_max_accepted_htlcs: msg.max_accepted_htlcs,
                        minimum_depth: config.own_channel_config.minimum_depth,
 
@@ -927,7 +936,7 @@ impl Channel {
                        log_trace!(self, "   ...including {} output with value {}", if local { "to_local" } else { "to_remote" }, value_to_a);
                        txouts.push((TxOut {
                                script_pubkey: chan_utils::get_revokeable_redeemscript(&keys.revocation_key,
-                                                                                      if local { self.their_to_self_delay } else { BREAKDOWN_TIMEOUT },
+                                                                                      if local { self.their_to_self_delay } else { self.our_to_self_delay },
                                                                                       &keys.a_delayed_payment_key).to_v0_p2wsh(),
                                value: value_to_a as u64
                        }, None));
@@ -1126,7 +1135,7 @@ impl Channel {
        /// @local is used only to convert relevant internal structures which refer to remote vs local
        /// to decide value of outputs and direction of HTLCs.
        fn build_htlc_transaction(&self, prev_hash: &Sha256dHash, htlc: &HTLCOutputInCommitment, local: bool, keys: &TxCreationKeys, feerate_per_kw: u64) -> Transaction {
-               chan_utils::build_htlc_transaction(prev_hash, feerate_per_kw, if local { self.their_to_self_delay } else { BREAKDOWN_TIMEOUT }, htlc, &keys.a_delayed_payment_key, &keys.revocation_key)
+               chan_utils::build_htlc_transaction(prev_hash, feerate_per_kw, if local { self.their_to_self_delay } else { self.our_to_self_delay }, htlc, &keys.a_delayed_payment_key, &keys.revocation_key)
        }
 
        fn create_htlc_tx_signature(&self, tx: &Transaction, htlc: &HTLCOutputInCommitment, keys: &TxCreationKeys) -> Result<(Script, Signature, bool), ChannelError> {
@@ -1380,7 +1389,7 @@ impl Channel {
                if msg.htlc_minimum_msat >= (self.channel_value_satoshis - msg.channel_reserve_satoshis) * 1000 {
                        return Err(ChannelError::Close("Minimum htlc value is full channel value"));
                }
-               if msg.to_self_delay > MAX_LOCAL_BREAKDOWN_TIMEOUT {
+               if msg.to_self_delay > config.peer_channel_config_limits.their_to_self_delay || msg.to_self_delay > MAX_LOCAL_BREAKDOWN_TIMEOUT {
                        return Err(ChannelError::Close("They wanted our payments to be delayed by a needlessly long period"));
                }
                if msg.max_accepted_htlcs < 1 {
@@ -3064,7 +3073,7 @@ impl Channel {
                        channel_reserve_satoshis: Channel::get_our_channel_reserve_satoshis(self.channel_value_satoshis),
                        htlc_minimum_msat: self.our_htlc_minimum_msat,
                        feerate_per_kw: fee_estimator.get_est_sat_per_1000_weight(ConfirmationTarget::Background) as u32,
-                       to_self_delay: BREAKDOWN_TIMEOUT,
+                       to_self_delay: self.our_to_self_delay,
                        max_accepted_htlcs: OUR_MAX_HTLCS,
                        funding_pubkey: PublicKey::from_secret_key(&self.secp_ctx, &self.local_keys.funding_key),
                        revocation_basepoint: PublicKey::from_secret_key(&self.secp_ctx, &self.local_keys.revocation_base_key),
@@ -3097,7 +3106,7 @@ impl Channel {
                        channel_reserve_satoshis: Channel::get_our_channel_reserve_satoshis(self.channel_value_satoshis),
                        htlc_minimum_msat: self.our_htlc_minimum_msat,
                        minimum_depth: self.minimum_depth,
-                       to_self_delay: BREAKDOWN_TIMEOUT,
+                       to_self_delay: self.our_to_self_delay,
                        max_accepted_htlcs: OUR_MAX_HTLCS,
                        funding_pubkey: PublicKey::from_secret_key(&self.secp_ctx, &self.local_keys.funding_key),
                        revocation_basepoint: PublicKey::from_secret_key(&self.secp_ctx, &self.local_keys.revocation_base_key),
@@ -3746,6 +3755,7 @@ impl Writeable for Channel {
                self.their_htlc_minimum_msat.write(writer)?;
                self.our_htlc_minimum_msat.write(writer)?;
                self.their_to_self_delay.write(writer)?;
+               self.our_to_self_delay.write(writer)?;
                self.their_max_accepted_htlcs.write(writer)?;
                self.minimum_depth.write(writer)?;
 
@@ -3907,6 +3917,7 @@ impl<R : ::std::io::Read> ReadableArgs<R, Arc<Logger>> for Channel {
                let their_htlc_minimum_msat = Readable::read(reader)?;
                let our_htlc_minimum_msat = Readable::read(reader)?;
                let their_to_self_delay = Readable::read(reader)?;
+               let our_to_self_delay = Readable::read(reader)?;
                let their_max_accepted_htlcs = Readable::read(reader)?;
                let minimum_depth = Readable::read(reader)?;
 
@@ -3984,6 +3995,7 @@ impl<R : ::std::io::Read> ReadableArgs<R, Arc<Logger>> for Channel {
                        their_htlc_minimum_msat,
                        our_htlc_minimum_msat,
                        their_to_self_delay,
+                       our_to_self_delay,
                        their_max_accepted_htlcs,
                        minimum_depth,
 

diff --git a/src/util/config.rs b/src/util/config.rs
index e1a7e59727cc14d0f6cb9c1ca545b91ead628bae..5b805d45e478ca0ed73392a5cbac91d1561478b4 100644 (file)
--- a/src/util/config.rs
+++ b/src/util/config.rs
@@ -1,6 +1,8 @@
 //! Various user-configurable channel limits and settings which ChannelManager
 //! applies for you.
 
+use ln::channelmanager::{BREAKDOWN_TIMEOUT, MAX_LOCAL_BREAKDOWN_TIMEOUT};
+
 /// Top-level config which holds ChannelHandshakeLimits and ChannelConfig.
 #[derive(Clone, Debug)]
 pub struct UserConfig {
@@ -30,6 +32,18 @@ pub struct ChannelHandshakeConfig {
        /// Applied only for inbound channels (see ChannelHandshakeLimits::max_minimum_depth for the
        /// equivalent limit applied to outbound channels).
        pub minimum_depth: u32,
+       /// Set to the amount of time we require our counterparty to wait to claim their money.
+       ///
+       /// It's one of the main parameter of our security model. We (or one of our watchtowers) MUST
+       /// be online to check for peer having broadcast a revoked transaction to steal our funds
+       /// at least once every our_to_self_delay blocks.
+       /// Default is BREAKDOWN_TIMEOUT, we enforce it as a minimum at channel opening so you can
+       /// tweak config to ask for more security, not less.
+       ///
+       /// Meanwhile, asking for a too high delay, we bother peer to freeze funds for nothing in
+       /// case of an honest unilateral channel close, which implicitly decrease the economic value of
+       /// our channel.
+       pub our_to_self_delay: u16,
 }
 
 impl ChannelHandshakeConfig {
@@ -37,6 +51,7 @@ impl ChannelHandshakeConfig {
        pub fn new() -> ChannelHandshakeConfig {
                ChannelHandshakeConfig {
                        minimum_depth: 6,
+                       our_to_self_delay: BREAKDOWN_TIMEOUT,
                }
        }
 }
@@ -88,6 +103,13 @@ pub struct ChannelHandshakeLimits {
        /// Defaults to true to make the default that no announced channels are possible (which is
        /// appropriate for any nodes which are not online very reliably).
        pub force_announced_channel_preference: bool,
+       /// Set to the amount of time we're willing to wait to claim money back to us.
+       ///
+       /// Not checking this value would be a security issue, as our peer would be able to set it to
+       /// max relative lock-time (a year) and we would "lose" money as it would be locked for a long time.
+       /// Default is MAX_LOCAL_BREAKDOWN_TIMEOUT, which we also enforce as a maximum value
+       /// so you can tweak config to reduce the loss of having useless locked funds (if your peer accepts)
+       pub their_to_self_delay: u16
 }
 
 impl ChannelHandshakeLimits {
@@ -107,6 +129,7 @@ impl ChannelHandshakeLimits {
                        max_dust_limit_satoshis: <u64>::max_value(),
                        max_minimum_depth: 144,
                        force_announced_channel_preference: true,
+                       their_to_self_delay: MAX_LOCAL_BREAKDOWN_TIMEOUT,
                }
        }
 }