Exploring BitVM Technology Optimization

1. Introduction

As a decentralized, secure, and trusted digital asset, Bitcoin has always faced scalability issues. Its UTXO model leads to a stateless system, making it difficult to execute complex state-dependent computations. This limits the scope for building decentralized applications and complex financial instruments on Bitcoin.

To address the scaling issue, the industry has proposed technologies such as state channels, sidechains, and client validation. However, these solutions have their own limitations. In December 2023, Robin Linus, the head of the ZeroSync project, published a white paper titled “BitVM: Compute Anything On Bitcoin,” which introduced a new solution. The BitVM technology allows for Turing-complete Bitcoin contracts to be implemented without changing the consensus of the Bitcoin network, greatly expanding the potential use cases of Bitcoin.

Although BitVM technology has significant advantages in Bitcoin scalability, it is still in its early stages and has some issues regarding efficiency and security. This article will explore some optimization ideas to further enhance the efficiency and security of BitVM.

2. BitVM Principle

BitVM is positioned as an off-chain contract for Bitcoin, dedicated to promoting Bitcoin’s contract functionality. It enables Bitcoin scripts to have statefulness through Lamport’s one-time signatures and employs a challenge-response model to support higher complexity computational verification. The BitVM system is based on fraud proofs and a challenge-response protocol, but does not require modifications to Bitcoin’s consensus rules.

The key components of BitVM include:

• Circuit Commitment: Provers and verifiers compile the program into a large binary circuit and commit that circuit in the Taproot address.
• Challenge and response: Pre-sign a series of transactions to implement the challenge-response game.
• Ambiguous penalty: If the prover makes an incorrect claim, the verifier may receive the prover’s deposit.

3. BitVM Optimization

Reducing OP Interaction Frequency Based on ZK 3.1

Consider using zero-knowledge proofs to reduce the number of challenges in BitVM and improve efficiency. By transforming the challenge object from the original algorithm F to the verification algorithm Verify, the number of challenge rounds can be reduced and the challenge cycle shortened. In addition, exploring the construction of ZK Fraud Proofs to achieve On-Demand ZK Proofs can further optimize the BitVM system.

3.2 Bitcoin friendly one-time signature

To reduce transaction data and fees, consider using the Winternitz one-time signature as a replacement for the Lamport one-time signature. The Winternitz scheme can significantly reduce the length of signatures and public keys, but it will increase the computational complexity of signing and verification. Using the Winternitz one-time signature with appropriate parameters in BitVM can reduce transaction fees by at least 50%.

3.3 Bitcoin-friendly hash function

It is necessary to study the optimal hash functions for script size and script witness size implemented with Bitcoin scripts to support the Merkle inclusion proof verification function. The BLAKE3 hash function is a potential choice, which can implement its basic operations through Bitcoin scripts. In addition, other hash functions can be explored for implementation in Bitcoin scripts, such as Keccak-256, Grøstl, etc.

3.4 Scriptless Scripts BitVM

Scriptless Scripts can increase the scope and complexity of smart contracts while enhancing privacy and efficiency. By using Schnorr multi-signatures and adapter signatures, logic gate commitments in BitVM circuits can be achieved, saving script space and improving efficiency. This solution can be further improved in the future and Scripless Scripts can be introduced into specific BitVM functional modules.

3.5 Permissionless Multi-Party Challenge

In order to expand the trust model of BitVM and reduce trust assumptions, it is necessary to study permissionless multi-party OP challenge protocols. This will allow anyone to participate in challenges without the need for a pre-approved whitelist. At the same time, issues such as Sybil attacks and delay attacks must also be addressed to ensure the security and efficiency of the system.

4. Conclusion

The exploration of BitVM technology has just begun, and in the future, further research and practical applications will continue in more optimization directions to achieve scalability for Bitcoin and to prosper the Bitcoin ecosystem. Through the aforementioned optimization measures, BitVM is expected to make significant progress in efficiency, security, and functionality, bringing broader application scenarios to the Bitcoin network.