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The OP Stack implementation uses Rollup-Boost to connect an external sidecar assertion validation components with the L2 sequencer through a bridge proxy.

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Architecture Diagram

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System Components

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Sequencer

  • op-node: The main orchestrator node in the OP Stack, responsible for sequencing transactions and maintaining consensus with the execution layer.
  • op-geth/op-reth: The execution layer clients (Geth or Reth) that process and execute transactions, providing the EVM environment for the rollup.

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Credible Layer (Sidecar)

  • Block Builder: The component of the network that simulates transactions and runs assertions before transaction finalization to ensure they don’t violate defined conditions.
  • op-reth: The execution layer client within the Credible Layer that processes transactions and maintains state.
  • pcl CLI: Command-line interface for developers to write, test, and submit assertions to the system.
  • dApp: The web application interface to register, manage, and view assertions and projects.
  • Assertion DA: The Assertion Data Availability layer, which stores assertion bytecode and serves it to both end-users and the Assertion Enforcer for execution.

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Rollup-Boost

  • Proxy: Acts as a bridge between the block builder and the sequencer, enabling integration without requiring changes to the sequencer code. It handles new block requests and fallback validation.

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Component Interactions

  • The Credible Layer op-reth pulls state and transactions from the Sequencer op-geth/op-reth.
  • The Credible Layer op-reth provides best transactions to the Block Builder.
  • The Block Builder enforces assertions and produces credible blocks, which are requested by Rollup-Boost.
  • Rollup-Boost requests credible blocks from both the Block Builder and the Sequencer op-node.
  • The Assertion DA serves assertion bytecode to the Block Builder, ensuring up-to-date enforcement.
  • The pcl CLI and Credible dApp provide interfaces for assertion submission and management.

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Transaction Flow

Transaction Flow The diagram above illustrates transaction flow through the OP Stack implementation. The top section shows the complete deployment: users submit transactions that flow through OP-Talos (block builder) → Rollup-Boost → OP Stack Sequencer → Network. Malicious transactions are identified and removed before reaching the sequencer. The bottom section zooms into assertion execution - this process is consistent across all Credible Layer implementations, not just OP Stack. The transaction and State 1 (pre-state) flow into the EVM for simulation, producing State 2 (post-state). PhEVM then validates these states against registered assertions, returning valid/invalid.

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Key Technologies

  • OP-Talos: Implementation of rbuilder as the Assertion Enforcer. rbuilder is Flashbots’ open-source block builder, which we’ve adapted to include assertion validation logic for the OP Stack.
  • Rollup-Boost: Developed by Flashbots, Rollup-Boost is a proxy architecture that enables external block builders to integrate with rollup sequencers. It integrates OP-Talos with the Sequencer without requiring code changes to the Sequencer, allowing for modular and non-invasive assertion enforcement.

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Integration Benefits

This solution provides several advantages for OP Stack networks:
  1. Non-invasive: No modifications required to the sequencer code
  2. Modular: Assertion validation runs as a separate, upgradable component
  3. Performant: Parallel assertion execution doesn’t impact sequencer performance
  4. Flexible: Easy to enable/disable assertion enforcement
For more details on the general architecture and other implementations, see the Architecture Overview.