Lightning Network Penalty

The Lightning Network penalty is the enforcement mechanism that punishes a channel party for broadcasting an outdated channel state. If cheating is detected in time, the honest counterparty can claim 100 percent of the cheater's channel balance. The threat works because every superseded state carries a revocation secret that was handed over when the balance was updated.

Why it matters

Off-chain money only works if old states cannot be replayed. Without the penalty, a party could make payments, then publish an earlier state in which it still had the money, effectively reversing its spending. The penalty makes that gamble irrational: the potential loss is the entire channel balance, while the potential gain is only the amount already spent.

The design assumes the honest party is watching the chain. Channel closes are subject to a dispute delay, commonly on the order of 144 blocks or about one day, and users who cannot stay online delegate monitoring to watchtower services.

How it works

Each commitment transaction pays the broadcaster's balance to an output encumbered by a time delay, while the counterparty holds a revocation key for that specific state. If an old commitment appears on-chain, the counterparty uses the revocation key to sweep the delayed output with a so-called justice transaction before the delay expires, taking the cheater's funds as the penalty.