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System Design

The BitVM Bridge is a sophisticated system designed to enable seamless interoperability between Bitcoin and other blockchain ecosystems while maintaining the highest standards of security, decentralization, and user experience. This document provides an in-depth exploration of the system's architecture, components, and operational framework, focusing on how the BitVM Bridge Network (BBN), Finality Chain, and supporting infrastructure work together to facilitate trust-minimized cross-chain transactions.

Overview​

The BitVM Bridge is composed of several interconnected components that together form a robust and efficient system for managing cross-chain operations. At its core, the system relies on the BitVM Bridge Network (BBN) and the BitVM Bridge Backend.

Participants in the BitVM Bridge Network include three distinct types of nodes, each with specialized roles:

  1. Broker Nodes: Provide liquidity and participate in operational processes such as transaction signing and dispute resolution.
  2. Watcher Nodes: Monitor and verify operations, ensuring the integrity of the system by challenging invalid reclaims.
  3. Attester Nodes: Validate and sign transaction graphs, ensuring that all operations adhere to the protocol's specifications.

The Finality Chain, a Proof-of-Stake blockchain currently under development, plays a pivotal role in managing the registration and coordination of these nodes while serving as a bridge between Bitcoin and the broader blockchain ecosystem.

BitVM Bridge Architecture​

The architecture of the BitVM Bridge is built around the BitVM Bridge Network (BBN), which serves as the operational backbone of the system, and the Bridge Backend, which provides an interface layer for end-users and applications. Together, these components ensure that the protocol can handle complex cross-chain interactions while maintaining a user-friendly experience.

BitVM Bridge Network (BBN)​

The BitVM Bridge Network is composed of three types of nodes, each contributing to the protocol's functionality in distinct ways:

1. Broker Nodes​

Broker nodes are the liquidity providers within the BitVM Bridge Network. Their primary role is to support the front-and-reclaim process by providing short-term liquidity for peg-out requests, for which they earn fees. In addition to their liquidity function, broker nodes perform several critical tasks:

  • Attesting: Brokers validate the transaction graph, which defines all possible state transitions for the bridge funds, and sign one or more transactions within the graph. These signatures are sent to the Coordinator module on the Finality Chain.
  • Proving: Brokers execute the Reclaim Check process to generate Reclaim Proofs, which are zero-knowledge proofs that validate the correctness of a reclaim request.
  • Defending: In cases where a reclaim request is challenged, brokers participate in the dispute resolution game to defend the validity of their claims.

2. Attester Nodes​

Attester nodes are responsible for validating and signing the majority of transactions within the transaction graph. Their tasks include:

  • Attesting: Similar to broker nodes, attester nodes validate the transaction graph and provide signatures for most transactions. These signatures are also sent to the Coordinator module on the Finality Chain.
  • Transaction Validation: Attester nodes ensure that all transactions adhere to the Transaction Graph Specification, which defines the structure and rules for transaction execution within the protocol.

3. Watcher Nodes​

Watcher nodes act as the watchdogs of the BitVM Bridge Network, ensuring that all operations are carried out correctly and challenging any invalid claims. Their responsibilities include:

  • Monitoring: Watchers monitor peg-out events and pending reclaim requests on Bitcoin, ensuring that all actions are consistent with the protocol's rules.
  • Verification: Watchers run the Reclaim Checker to independently verify the validity of reclaim requests.
  • Challenging: If a reclaim request is found to be invalid, watchers initiate a challenge and participate in the dispute resolution game to prevent unauthorized fund withdrawals.

Bridge Backend​

The Bridge Backend serves as an interface layer between end-users and the underlying infrastructure of the BitVM Bridge. While it is a centralized service operated by Bitlayer, the backend has no control over the bridge funds, ensuring that the protocol remains trust-minimized. The backend provides the following functionalities:

  • User APIs: These APIs enable users to interact with the protocol, facilitating operations such as peg-in, peg-out, and reclaim requests.
  • Data APIs: These APIs provide data for dashboards and explorers, allowing users to trace transactions, view statistics, and monitor the status of the bridge.

Bridge Frontend​

The frontend layer provides user-facing applications that make the BitVM Bridge accessible and transparent:

  1. Bridge Application: This is the primary interface through which users interact with the protocol, performing operations such as peg-in and peg-out.
  2. Bridge Explorer: The explorer allows users to check the status of their transactions and monitor the overall activity of the bridge.
  3. Bridge Dashboard: The dashboard provides an overview of the bridge's operational status, including metrics and statistics related to its performance.