Auditing for True Transaction Ordering Independence

Sequencers can reorg their own chain to censor or reorder transactions after they appear final to users, exploiting the ~7-day challenge window. This breaks atomic composability for cross-chain intents.

• Attack Vector: Reorg to invalidate a profitable bridging transaction.
• Impact: Undermines trust in Arbitrum, Optimism fast finality.
• Audit Focus: Prove sequencer commits are immutable and externally verifiable.

Formalize the separation of block building from proposing at the protocol level, as seen with Ethereum's ePBS roadmap. This removes the trusted intermediary role from the sequencer.

• Mechanism: Builders compete on block content; validators only choose the header.
• Outcome: Transaction ordering becomes a verifiable, auction-based output.
• Ecosystem Shift: Forces Flashbots, bloXroute to compete on pure builder efficiency.

Abstracting transaction construction shifts the attack surface from ordering to solver competition and cross-domain fulfillment. Systems like UniswapX and CoW Swap rely on solvers, not user txns.

• New Risk: Solver collusion or malicious fulfillment paths.
• Audit Imperative: Verify fulfillment proofs and solver economic security.
• Key Entity: SUAVE aims to be a decentralized mempool and solver network for this paradigm.

If proposers can predict or influence transaction ordering pre-execution, independence is broken. This creates systemic risk where consensus security is gamed for extractable value.\n- Attack Vector: Proposer-Builder collusion to front-run or censor based on execution outcome.\n- Impact: Undermines liveness and fairness guarantees, centralizing power around a few entities.

Execution that depends on rapidly changing global state (e.g., oracle updates, NFT mints) can create race conditions. A malicious proposer can exploit timing to guarantee a favorable outcome.\n- Attack Vector: Withholding blocks or manipulating network gossip to control which state version executors see.\n- Impact: Breaks the atomic broadcast assumption, allowing for time-bandit attacks similar to those seen in DeFi.

Even with a clean-slate spec, the concrete implementation of the executor network (e.g., using Geth, Erigon) can leak ordering signals. Batch processing, caching behavior, and mempool gossip logic are subtle side-channels.\n- Audit Focus: Must analyze the executor client's I/O patterns and network stack for any deterministic timing or data leaks back to the consensus layer.\n- Real Example: The shift from eth_sendRawTransaction to eth_sendRawTransactionConditional in proposer-builder separation.

Independence fails if the economic rewards for consensus and execution are not properly isolated. A single token staked in both systems creates a correlated failure point.\n- Problem: Slashing conditions or rewards in one layer that are contingent on outcomes in the other.\n- Solution Audit: Verify cryptoeconomic models are fully decoupled, requiring separate stake and separate yield curves, as theorized in EigenLayer-style restaking critiques.

Many 'independent' ordering layers (e.g., Espresso, Astria) rely on a primary L1 (Ethereum) for finality or dispute resolution. This creates a liveness bottleneck and re-introduces L1 MEV dynamics during challenges.\n- Risk: The system degrades to the security of the slowest, most centralized component in its fallback path.\n- Audit Check: Map the happy path vs. failure path latency and validator sets. True independence requires a decentralized fallback.

If the execution layer must pull data (blobs, transactions) from the consensus layer's data availability (DA) solution, the timing and availability of that data becomes a covert communication channel.\n- Attack: A malicious consensus proposer can selectively withhold or delay data to influence execution outcomes.\n- Mitigation: Requires enshrined DA with guaranteed, time-bound delivery, as seen in Celestia and EigenDA designs, plus cryptographic attestations.