Griefing attacks in optimistic rollups occur when a participant deliberately imposes extra cost on others without seeking direct profit. These attacks exploit the challenge-and-punish model that optimistic schemes use: proposers publish compressed state and a challenge window gives watchers time to submit fraud proofs. If watching is under-incentivized or proposer stakes are too small, attackers can force expensive challenges or long delays that harm liveness and user experience.
Economic bonds and slashing
A core deterrent is a stake or bond from proposers and sequencers that is large enough to exceed the expected cost an attacker can impose. When a fraud proof succeeds, part of the slashed bond reimburses the challenger and the remainder penalizes the attacker. Vitalik Buterin at the Ethereum Foundation has emphasized the role of stake-backed fraud proofs in aligning costs and responsibilities so that mounting a griefing campaign is economically irrational. Bond sizing must account for worst-case challenge costs and variable gas markets, because under-sized deposits simply shift costs onto honest users.
Incentivizing watchers and structuring challenge rewards
A second class of defenses pays or protects watchers so they act as public goods providers. Reward structures that reimburse gas and award a bounty for successful disputes turn watchers into compensated verifiers rather than volunteer auditors. Karl Floersch at Optimism has discussed mechanisms that compensate challengers for their work and design challenge bonds to avoid frivolous disputes while keeping honest monitoring profitable. Complementary designs include shortening unnecessary windows for low-risk transactions, adaptive fees that reflect dispute likelihood, and partial fee-burning to reduce rent-seeking.
Both approaches carry trade-offs. Higher bonds and guaranteed bounties raise the operational cost for legitimate sequencers and can centralize proposers toward well-capitalized operators, affecting cultural and territorial access for smaller economies and community-driven sequencers. Conversely, too-light incentives leave custodial services and average users exposed to denial-of-service style griefing that raises transaction latency and gas consumption. Effective designs therefore balance economic disincentives, sustainable rewards for public monitoring, and technical mitigations such as efficient fraud-proof compression and faster verification paths. When calibrated with awareness of differing regional gas economics and community capacities, these incentive designs materially reduce the attractiveness and practical feasibility of griefing attacks in optimistic rollups.