This article explores the evolution, current state, and key engineering efforts behind BitVM, along with Bitlayer's significant contributions to the BitVM ecosystem.
Introduction
Bitcoin, the world's most secure and decentralized blockchain, has historically been viewed as limited in programmability compared to platforms like Ethereum. BitVM is changing this narrative by introducing an advanced computational and programmable framework for Bitcoin. At its core, BitVM unlocks the potential for trust-minimized Bitcoin bridging and other applications while preserving Bitcoin's principles of decentralization and security.
The Evolution of BitVM
BitVM represents a transformative step in expanding Bitcoin's capabilities beyond digital currency. Key milestones in BitVM's journey include:
- Initial Proposal: Robin Linus first proposed BitVM as a universal computation solution for Bitcoin.
- Interactive Dichotomy: Robin improved the concept by introducing interactive dichotomy (using RISC-V instructions) to enhance computational efficiency.
- BitVM2: The latest version, BitVM2, eliminates the dichotomy and introduces a permissionless challenge mechanism, creating a robust Bitcoin bridging framework.
Today, the BitVM community largely focuses on BitVM2, which is the version discussed in this article.
The BitVM Alliance
The BitVM Alliance, founded by Robin Linus and Lukas George, aims to accelerate BitVM's development and adoption. This coalition brings together leading projects and teams to push the boundaries of Bitcoin's programmability.
Current State of BitVM
How BitVM Works: A Simplified Explanation
BitVM implements a bridging mechanism that connects Bitcoin to programmable environments, facilitating workflows like asset transfers. The process involves three key steps:
- Peg-in: Users lock BTC in a BitVM smart contract and mint wrapped BTC (YBTC) on the target system.
- Peg-out: Users request withdrawals, with brokers providing liquidity to transfer BTC.
- Claim: Brokers retrieve funds from the BitVM smart contract if no challenges are raised against the request.
The Role of BitVM Smart Contracts
BitVM smart contracts are essentially pre-signed Bitcoin transaction graphs that define rules and workflows for participants. Key features include:
- Pre-signed transactions: These are signed in advance to enforce protocol rules.
- Multi-signature control: Funds are locked in a multi-signature wallet controlled by workflow participants.
Once the transaction graph is published, users can lock BTC into the BitVM contract and mint wrapped BTC, initiating the workflow.
Ensuring Integrity: Dispute Resolution
To validate requests, BitVM employs a dispute resolution protocol:
- Pre-commitment: Brokers pre-commit a Groth16 verifier result, computed offline to ensure request validity.
- Challenge: If challenged, brokers must reveal intermediate values from the verifier computation.
- Verification: Challengers run the verifier offline to detect invalid segments. Fraudulent requests are invalidated via Bitcoin transactions.
Key Engineering Efforts
1. Groth16 Verifier Development
The Groth16 verifier is BitVM's cornerstone, enabling efficient zero-knowledge proof verification on Bitcoin. Achievements include:
Building the verifier:
- Implemented a monolithic Groth16 verifier using Bitcoin Script.
- Developed foundational primitives like BIGINT arithmetic, BLAKE3 hashing, BN254 elliptic curve pairing, and Winternitz signatures.
Optimizations:
- Reduced verifier size from 7.4GB to 1GB using advanced cryptographic techniques.
Chunked verifier:
- Split the verifier into smaller blocks (each <4MB) for on-chain dispute resolution.
2. Protocol Implementation
With the Groth16 verifier in place, the next step was developing a complete transaction graph to connect all components, including:
- Monitoring on-chain events and storing necessary data.
- Building and validating transactions like ASSERT and DISPROVE.
- Managing Connector outputs for reliable on-chain execution.
Current Status
Groth16 Verifier
- Monolithic verifier size reduced to 1GB.
- Chunked verifier consists of fewer than 1,000 blocks, ready for deployment.
Protocol Implementation
- Transaction graph is nearly complete.
Next Steps
- The BitVM Alliance is conducting a comprehensive code audit.
- Plans are underway to demo the first end-to-end BitVM bridge.
Bitlayer's Contributions
Bitlayer has been a primary contributor to BitVM, particularly in:
1. Groth16 Verifier Contributions
Optimizations:
- Developed batch multi-scalar multiplication (MSM) techniques to reduce script size from 7.4GB to 5.6GB.
- Introduced an MSM algorithm using affine coordinates, further shrinking the verifier to 1GB.
Verifier chunking:
- Proposed the first viable chunker implementation, splitting the verifier into logical segments.
- Fine-tuned chunking for optimal size and input/output granularity.
2. Bridging Protocol Contributions
- Developed core components like ASSERT and DISPROVE transactions.
- Plans to contribute additional protocol implementations.
Beyond BitVM: Bitlayer's Innovations
Bitlayer is exploring BitVM's potential beyond Bitcoin bridging:
- BitVM Abstraction: Developing reusable components like BitVM-style smart contracts and fraud proofs.
- Finality Bridge: Launching its own BitVM bridge implementation (testnet live).
- Bitcoin Rollup: A Rollup protocol based on BitVM abstraction, featuring recursive BitVM smart contracts and zkVM.
Recap of Bitlayer's Contributions
- Pioneered Groth16 verifier optimizations, drastically reducing script size.
- Developed the first viable verifier chunker implementation.
- Contributed core components to the BitVM bridging protocol.
- Explored innovative use cases like Bitcoin-native Rollup and zkVM.
👉 Explore BitVM's latest developments
FAQ
What is BitVM?
BitVM is a computational framework enabling programmable functionality on Bitcoin while maintaining its security and decentralization.
How does BitVM enhance Bitcoin?
It introduces trust-minimized bridging and smart contract-like capabilities without altering Bitcoin's core protocol.
What is Bitlayer's role in BitVM?
Bitlayer is a key contributor, optimizing the Groth16 verifier and developing critical protocol components.