The Real Trust Model of Rollups

A single, centralized sequencer is a single point of failure and censorship. The real risk is a cartel forming among a small set of permissioned sequencers, replicating the miner extractable value (MEV) problems of Ethereum but with less decentralization.

• Censorship Risk: A malicious or compliant sequencer can reorder or exclude transactions.
• Economic Centralization: Profits from MEV and fees concentrate, disincentivizing decentralization.
• Liveness Failure: If the primary sequencer goes offline, the chain halts unless a decentralized fallback mechanism is active.

If the rollup's data is not published and verifiably available, the chain becomes an insecure sidechain. Users and bridges cannot reconstruct state or prove fraud.

• Ethereum Blob Capacity: Congestion or high costs can force sequencers to skip posting data, breaking safety guarantees.
• Alt-DA Compromises: Using Celestia, EigenDA, or other systems trades Ethereum's security for new trust assumptions and potential liveness issues.
• Withdrawal Proofs Impossible: Without the data, a user's Merkle proof for withdrawing funds cannot be constructed.

Most rollups use a multi-signature wallet to control the upgradeable proxy contract that defines their core logic. This is the ultimate admin key.

• Code is Not Law: A super-majority of signers can change any rule, steal funds, or censor users instantly.
• Social Attack Vector: Targets regulatory pressure, key compromise, or insider collusion.
• Misleading "Decentralization": Teams often postpone removing this key, creating systemic risk across a portfolio of chains like Optimism's Superchain or Arbitrum's Orbit.

Validity proofs are cryptographic gold, but the prover infrastructure generating them is a complex, centralized software system. A critical bug is catastrophic.

• Soundness Bug: A single proving error could validate an invalid state transition, corrupting the chain irreversibly.
• Liveness vs. Safety: If the prover fails, the chain stops (liveness failure). If it produces a faulty proof, the chain is corrupted (safety failure).
• Verifier Dependency: The on-chain verifier contract is only as good as the circuit it's verifying; a bug there is an unpatchable protocol flaw.

Canonical bridges are slow and limited by challenge periods. Third-party bridges like LayerZero, Stargate, and Across provide UX but introduce new risks.

• Liquidity Fragility: A bridge's TVL is not capital at rest; it's a hot wallet managed by a multisig or DAO. A hack or bank run can drain it.
• Wrapped Asset Depeg: If the bridge's canonical mint/burn mechanism fails, wrapped assets (e.g., wETH on L2) can depeg from their underlying value.
• Cross-Chain Messaging Risk: Bridges are the most hacked infrastructure in crypto, with over $2.5B stolen, creating a systemic contagion vector.

Rollups derive finality from Ethereum. If Ethereum reorganizes, so does the rollup. This breaks assumptions for fast bridge operators and exchanges.

• Deep Reorg Risk: Although rare, a deep Ethereum reorg could reverse L2 transactions considered final by services, leading to double-spends.
• Settlement Latency: The "soft confirmation" period before an L2 block is cemented on L1 creates a window where value is in flight and vulnerable.
• Forced Inclusion Reliance: Users must wait for the L1 challenge period or use a forced inclusion transaction, which fails if the sequencer censors them.

The sequencer is a centralized, permissioned actor that orders your transactions. Its failure or censorship is a liveness attack on your rollup.\n- Key Benefit 1: High throughput and low latency (~500ms inclusion).\n- Key Benefit 2: MEV extraction is a primary revenue stream, creating misaligned incentives.

If the sequencer fails, users rely on publishing transaction data to a Data Availability layer (Ethereum, Celestia, EigenDA) to force-include transactions. This is your escape hatch.\n- Key Benefit 1: Defines the minimum trust model—you only need one honest actor to monitor and force inclusion.\n- Key Benefit 2: DA cost is the dominant variable in your transaction fee.

A single prover (e.g., a zkEVM) creates a cryptographic proof of correct state transition. You must trust its code is bug-free. Multi-prover/optimistic systems (like Arbitrum's BOLD) introduce a fraud-proof challenge period, trading finality time for potentially stronger security.\n- Key Benefit 1: zk-Rollups offer ~10 minute cryptographic finality.\n- Key Benefit 2: Optimistic Rollups have a 7-day challenge window but simpler, battle-tested VM design.

Almost all rollups use upgradeable contracts controlled by a multi-sig. This council can change any rule of the system, including sequencer logic, proof verifiers, and fee mechanisms.\n- Key Benefit 1: Allows for rapid protocol iteration and bug fixes.\n- Key Benefit 2: Represents a sovereign risk—the multi-sig can rug the entire chain.

The canonical bridge is secured by the rollup's smart contracts on L1. Third-party bridges (like LayerZero, Across) introduce their own validator sets and trust models. Your asset's security is the weakest link in this bridge chain.\n- Key Benefit 1: Canonical bridges inherit L1 security but have slow withdrawals (~7 days for Optimistic).\n- Key Benefit 2: Fast bridges provide liquidity but add validator trust and are frequent exploit targets.

Projects like Espresso, Astria, and Shared Sequencer from the OP Stack aim to decentralize the sequencer role and enable atomic cross-rollup composability. This moves trust from a single entity to a cryptoeconomic network.\n- Key Benefit 1: Mitigates the centralized sequencer risk for individual rollups.\n- Key Benefit 2: Enables native, trust-minimized composability between rollups, unlocking new DeFi primitives.