Centralized sequencing is the norm for Arbitrum, Optimism, and Base because it provides low-latency, atomic composability. This creates a single point of failure where a sequencer can censor or reorder transactions.
zk-rollups-the-endgame-for-scaling
Blog
The Future of Censorship Resistance in Ordered Rollups
Ethereum's L1 credibly neutral ordering is being traded for L2 scalability. We dissect how centralized sequencers and encrypted mempools in rollups like Starknet and zkSync Era create new, profitable vectors for censorship.
introduction
THE CORE DILEMMA
Introduction: The Great Trade-Off
Ordered rollups sacrifice censorship resistance for performance, creating a systemic vulnerability.
Censorship resistance is a public good that Ethereum's base layer provides but rollups outsource. The trade-off is explicit: you get cheap, fast transactions but inherit the sequencer's moral and legal framework.
The vulnerability is contractual, not cryptographic. Users have no cryptographic guarantee their transaction will be included. Their only recourse is a slow, expensive L1 force-inclusion mechanism, which defeats the purpose of using an L2.
Evidence: During the OFAC sanctions against Tornado Cash, centralized sequencers complied, demonstrating the protocol-level censorship risk. This is a design flaw, not an implementation bug.
key-trends
ORDERED ROLLUP VULNERABILITY
The Censorship Pressure Matrix
Centralized sequencers in rollups like Arbitrum and Optimism create a single point of failure for transaction ordering, inviting regulatory and MEV-driven censorship.
01
The Problem: The Sequencer Kill Switch
A single entity controls the transaction ordering and inclusion. Under regulatory pressure (e.g., OFAC sanctions), they can be compelled to censor. This is a regulatory single point of failure that undermines the base layer's neutrality.
- Real Risk: Arbitrum and Optimism sequencers could be forced to filter transactions.
- Network Effect: Censorship scales with adoption, threatening $30B+ in bridged value.
- Architectural Flaw: Inherits L1 security for execution, but not for liveness or inclusion.
1
Central Point
$30B+
TVL at Risk
02
The Solution: Decentralized Sequencer Sets
Replace the single sequencer with a permissionless set, like Espresso Systems or Astria, using a consensus mechanism (e.g., HotStuff, Tendermint) for ordering.
- Byzantine Fault Tolerance: Requires 2/3+ honest nodes to guarantee liveness and censorship resistance.
- MEV Resistance: Distributed ordering reduces the power of a single entity to extract value.
- Progressive Decentralization: Path implemented by Arbitrum (via BOLD) and Optimism (via its upcoming protocol).
2/3+
Honest Nodes
<2s
Finality Target
03
The Problem: Enshrined MEV & Order Flow Auctions
Even with decentralized sequencers, validators can collude to reorder transactions for maximal extractable value (MEV). This is a covert form of censorship where users pay hidden costs.
- Cartel Formation: Sequencer sets can form PBS-like (Proposer-Builder Separation) cartels.
- User Harm: Results in worse prices and unpredictable latency for end-users.
- Protocol Capture: The economic incentive to censor/prioritize is baked into the design.
$500M+
Annual MEV
~15%
Price Impact
04
The Solution: Commit-Reveal Schemes & Encrypted Mempools
Hide transaction content until ordering is fixed. Projects like Flashbots SUAVE and Shutter Network use threshold encryption (e.g., ECDKG) to prevent frontrunning.
- Pre-commitment: Sequencers order encrypted blobs, then the key is revealed.
- Strong Guarantee: Makes transaction content unpredictable, neutralizing most MEV.
- Integration Path: Can be layered atop rollups like Base or zkSync.
T-Of-N
Encryption
>90%
MEV Reduction
05
The Problem: L1 Finality as a Censorship Tool
Rollups rely on L1 (e.g., Ethereum) for data availability and dispute resolution. If L1 validators censor a rollup's batch, the entire chain halts. This is a cross-layer contagion risk.
- Ethereum's OFAC Compliance: >50% of Ethereum blocks are currently OFAC-compliant, creating a precedent.
- Data Availability Attack: Censoring the batch on L1 is a denial-of-service attack on the L2.
- Systemic Risk: Turns Ethereum's social consensus into a political battleground for all rollups.
>50%
OFAC Blocks
L1->L2
Contagion
06
The Solution: Multi-Channel Data Availability & Escape Hatches
Mitigate L1 dependency by using alternative DA layers (e.g., Celestia, EigenDA) and implementing forced inclusion protocols.
- DA Redundancy: Post data to 2+ independent layers (Ethereum + Celestia).
- User Sovereignty: Arbitrum's force-include lets users post directly to L1 after a delay, a last-resort bypass.
- Modular Defense: Splits the trust assumption, requiring collusion across multiple systems.
2+
DA Layers
~24h
Force-Include Delay
thesis-statement
THE CENSORSHIP FRONTIER
Core Thesis: Ordering is Sovereignty
The final, non-negotiable layer of censorship resistance for rollups depends on who controls transaction ordering.
Sequencer centralization creates a kill switch. A single entity controlling the transaction ordering for a rollup can front-run, censor, or reorder transactions at will, replicating the exact permissioned control that blockchains were built to eliminate.
Sovereign rollups are the logical endpoint. By posting data to a base layer like Celestia or Ethereum but retaining the right to fork the chain, sovereign rollups like Dymension RollApps make sequencer censorship a temporary nuisance, not a permanent failure.
Shared sequencers are a half-step. Networks like Espresso Systems or Astria decentralize ordering across many rollups, but the fork choice rule remains tied to the L1, creating a political, not technical, censorship guarantee.
Evidence: The Ethereum PBS (Proposer-Builder Separation) model proves that separating block building from proposing is possible, but rollups must adopt a forkable data availability layer to achieve the same sovereign guarantees.
ORDERING LAYER ANALYSIS
Censorship Risk Profile: Major ZK-Rollups
Compares the censorship resistance and liveness guarantees of leading ZK-Rollups based on their sequencer and proposer architectures.
| Feature / Metric | zkSync Era | Starknet | Polygon zkEVM | Linea |
|---|---|---|---|---|
Centralized Sequencer | ||||
Permissioned Proposer Set | ||||
Sequencer Liveness SLA | 99.9% | 99.9% | 99.9% | 99.9% |
Forced Inclusion Time | ~24 hours | ~12 hours | ~24 hours | ~24 hours |
Decentralized Sequencer Roadmap | Q4 2024 | Q4 2024 | Q3 2024 | 2025 |
Proposer Bond Required | N/A | 500K STRK | N/A | N/A |
MEV Auction (MEVA) Support | ||||
Base Layer Finality to L1 | ~1 hour | ~3-5 hours | ~30-45 min | ~4 hours |
deep-dive
THE INCENTIVE SHIFT
From MEV Extraction to Censorship-For-Profit
The economic model of rollup sequencing is evolving from passive MEV capture to active censorship as a service.
Sequencers become censors. A rollup's centralized sequencer holds absolute ordering power, enabling them to filter transactions for profit. This is a direct transition from MEV extraction, where value is captured from order, to censorship-for-profit, where value is captured from exclusion.
The OFAC compliance trap. Protocols like Tornado Cash create a regulatory attack surface. A sequencer complying with sanctions must censor transactions, creating a two-tiered access system that violates blockchain's core neutrality principle. This is not hypothetical; it's the operational reality for any sequencer under US jurisdiction.
Forced decentralization is the only defense. The long-term solution is permissionless proposer-builder separation (PBS). Systems like Espresso, Astria, and Shared Sequencer networks decouple block building from proposing, preventing any single entity from controlling the transaction funnel. This architecture mirrors Ethereum's post-merge roadmap.
Evidence: The 2022 OFAC sanctions demonstrated that centralized infrastructure like Infura and RPC providers will censor. Rollup sequencers with similar central points of failure face identical pressure, making their current neutrality a temporary, not permanent, state.
protocol-spotlight
THE FUTURE OF CENSORSHIP RESISTANCE IN ORDERED ROLLUPS
Architectural Responses & Mitigations
Centralized sequencers create a single point of failure for transaction ordering, threatening the core value proposition of blockchains. These are the emerging counter-strategies.
01
The Problem: Centralized Sequencer as a Censor
A single entity controls transaction ordering, enabling MEV extraction, front-running, and transaction blacklisting. This violates the credible neutrality of the base layer (e.g., Ethereum).\n- Single Point of Failure: Network halts if the sequencer goes down.\n- Regulatory Attack Vector: A legal order can force censorship of specific addresses.
100%
Control
~0s
Censorship Latency
02
The Solution: Decentralized Sequencer Sets (e.g., Espresso, Astria)
Replace the single sequencer with a permissionless set of nodes using consensus (e.g., HotStuff, Tendermint) to order transactions. This distributes trust and makes censorship collusion exponentially harder.\n- Byzantine Fault Tolerance: Requires >1/3 of nodes to be malicious for liveness failure.\n- Interoperability Play: Shared sequencers like Espresso can serve multiple rollups, creating a unified liquidity layer.
1-4s
Finality Time
>33%
Malicious Threshold
03
The Solution: Based Sequencing & L1 Finality
Pioneered by Optimism's Superchain, this model delegates sequencing rights directly to the underlying L1 (Ethereum). Transactions are ordered via L1 block builders, inheriting Ethereum's censorship resistance and decentralization.\n- L1 Alignment: Eliminates separate sequencer governance and token.\n- Force Inclusion: Users can submit transactions directly to an L1 contract if censored, with a ~24h delay.
Ethereum
Security Source
~24h
Force Inclusion Delay
04
The Solution: Proposer-Builder Separation (PBS) for Rollups
Adapt Ethereum's PBS design to the rollup layer. Separate the role of block builder (who orders tx) from proposer (who commits to L1). Builders compete in a marketplace, making sustained censorship economically irrational.\n- MEV Auction: Censorship becomes an opportunity cost.\n- Permissionless Building: Any entity can become a builder, increasing decentralization.
Market
Censorship Cost
Permissionless
Builder Set
05
The Hedge: Intent-Based & SUAVE-Like Architectures
Shift paradigm from transaction broadcasting to intent expression. Users specify a desired outcome (e.g., "swap X for Y at best rate"), and a decentralized solver network competes to fulfill it. This abstracts away the sequencer as the sole orderer.\n- Solver Competition: Breaks sequencer's monopoly on order flow.\n- Native Integration: Protocols like UniswapX and CowSwap are early adopters; SUAVE aims to be a universal intent chain.
Solver Network
Order Flow
Best Execution
User Guarantee
06
The Fallback: Direct L1 Submission & Escape Hatches
A mandatory, protocol-enforced mechanism allowing users to bypass the sequencer entirely. Transactions are sent to a verifier contract on L1, which forces their inclusion in the next rollup batch after a challenge period.\n- Non-Optional: A core part of the protocol, not a social consensus.\n- Critical Safeguard: The ultimate guarantee against total network capture, as seen in designs from Arbitrum and Optimism.
L1 Contract
Escape Hatch
7 Days
Typical Delay
counter-argument
THE ARCHITECTURAL TRADE-OFF
Steelman: Censorship is a Feature, Not a Bug
Ordered rollups can leverage controlled sequencing to create superior user experiences and unlock new design space, re-framing censorship resistance as a variable parameter.
Sequencer control enables UX breakthroughs that permissionless systems cannot match. A centralized sequencer can guarantee instant pre-confirmations, atomic cross-rollup composability, and enforceable MEV protection, as seen in early Arbitrum Stylus testnet behavior.
The trade-off is liveness for performance. Users accept a trusted liveness assumption for faster, cheaper, and more predictable execution. This mirrors the pragmatic choice users make with Coinbase or Binance over fully decentralized exchanges.
Censorship resistance becomes a slidable variable. Protocols like Espresso Systems and Astria are building shared sequencer networks that reintroduce credibly neutral ordering as an opt-in service layer, decoupling it from execution.
Evidence: The market vote is clear. Over 95% of rollup TVL resides on chains with explicit, upgradeable sequencer control, demonstrating that performance guarantees currently outweigh maximalist decentralization for most users and developers.
takeaways
THE CENSORSHIP-RESISTANT STACK
TL;DR for Builders and Investors
Ordered rollups (e.g., OP Stack, Arbitrum Orbit) trade decentralization for performance. This is the emerging toolkit to reclaim it.
01
The Problem: Centralized Sequencer = Single Point of Censorship
A single operator can reorder, delay, or censor transactions, undermining the core value proposition of Ethereum. This is the primary vulnerability in Arbitrum One, Optimism, and most L2s today.
- Risk: Protocol-level blacklisting becomes trivial.
- Reality: ~100% of transactions flow through a centralized sequencer.
~100%
Centralized Tx Flow
1
Failure Point
02
The Solution: Permissionless Proposer-Builder Separation (PBS)
Decouple transaction ordering (proposer) from block building (builder), creating a competitive market. Inspired by Ethereum's PBS, this is the endgame for chains like Espresso Systems and Astria.
- Mechanism: Proposers win the right to order blocks via auction; builders compete on inclusion.
- Outcome: Censorship requires collusion across a dynamic, permissionless set.
N > 1
Competing Builders
Auction-Based
Ordering Rights
03
The Enforcer: Force Inclusion via L1
A last-resort mechanism that allows users to bypass a censoring sequencer by submitting transactions directly to the L1 rollup contract. This is a foundational feature of Arbitrum and Optimism.
- Trade-off: High latency (~24h delay) and cost, but guarantees eventual inclusion.
- Utility: Acts as a credible threat, making censorship economically non-viable.
~24h
Delay
L1 Gas Cost
Execution Price
04
The Market: Intent-Based & SUAVE-Like Systems
Shift from transaction-based to intent-based flows, where users specify what they want, not how. Solvers (like in UniswapX or CowSwap) compete to fulfill it, abstracting away the sequencer. SUAVE aims to be a decentralized block builder for this entire ecosystem.
- Benefit: Censorship resistance emerges from solver competition.
- Future: A specialized mempool and execution network for cross-domain intents.
Solver Competition
Execution Layer
Cross-Domain
SUAVE Vision
05
The Fallback: Decentralized Sequencer Sets
A practical near-term step: replace a single operator with a permissioned set (e.g., Polygon PoS, Celo), then gradually decentralize. Espresso and Astria provide shared sequencing layers for this.
- Threshold: Censorship requires collusion of a majority (e.g., 2/3) of nodes.
- Path: Serves as a stepping stone to full permissionless PBS.
2/3+
Collusion Needed
Shared Layer
Architecture
06
The Investor Lens: Valuation Lies in the Stack
The value accrual shifts from the rollup's token to the critical middleware enabling its censorship resistance. Invest in the sequencer layer (Astria, Espresso), force inclusion mechanisms, and intent infrastructure (SUAVE, UniswapX).
- Thesis: The base layer commoditizes; the anti-censorship stack captures premium.
- Metric: Watch for % of rollups adopting a shared, decentralized sequencer.
Middleware
Value Accrual
Adoption %
Key Metric
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