Discussion on BitVM Technology Principles and Optimization Solutions

1. Introduction

Bitcoin, as a decentralized digital asset, holds significant value, but it has limitations in terms of scalability. The UTXO model of Bitcoin lacks the ability to perform complex computations, which restricts its application scenarios. To address the scalability issue, various technical solutions have been proposed in the industry, such as state channels, sidechains, and client validation, but they all have varying degrees of security or functionality issues.

Recently, the BitVM solution proposed by the ZeroSync project has attracted widespread attention. BitVM allows for the implementation of Turing-complete contract functionality without altering Bitcoin's consensus, greatly expanding Bitcoin's application potential. However, BitVM is still in its early stages and there is room for optimization in terms of efficiency and security. This article will explore the working principle of BitVM and suggest some possible optimization directions.

2. BitVM Principle

BitVM is an off-chain contract solution designed to enhance the contract functionality of Bitcoin. It achieves stateful Bitcoin scripts through Lamport one-time signatures and utilizes Taproot and challenge-response mechanisms to support the validation of complex computations.

The main components of BitVM include:

• Circuit Commitment: Compile the program into a binary circuit and commit it in the Taproot address.

• Challenge and Response: Achieve the challenge-response game by pre-signing a series of transactions, which can be executed off-chain or on-chain.

• Penalty mechanism: If the prover provides an incorrect statement, the verifier may receive their deposit as a penalty.

3. BitVM Optimization Plan

Reducing OP interaction times based on ZK 3.1

Consider introducing zero-knowledge proof technology, changing the challenge objects from the original algorithm to the verification algorithm, thereby reducing the number of challenge rounds and shortening the challenge cycle. This method can be combined with fraud proof to construct ZK Fraud Proof, achieving an on-demand generation mode for ZK proofs.

3.2 Bitcoin-friendly one-time signature

You can explore using the Winternitz one-time signature scheme as a substitute for Lamport signatures to reduce the length of signatures and public keys, thereby decreasing transaction data and fees. Specifically, you can consider using the parameter combination of d=15, v=160, f=ripemd160(x) to implement Winternitz signatures.

3.3 Bitcoin-friendly hash function

BLAKE3 and other hash functions can be implemented based on the existing Bitcoin scripts. BLAKE3 has good performance and is suitable for Merkle inclusion proof verification in BitVM. In the future, other Bitcoin-friendly hash function implementations can also be explored.

3.4 Scriptless Scripts BitVM

By leveraging Scriptless Scripts technology, BitVM's logic gate commitments can be implemented using Schnorr multi-signatures and adapter signatures, saving script space and improving efficiency. This method still requires further optimization to reduce interaction demands.

3.5 Permissionless Multi-party Challenge

It is possible to study the extension of BitVM to a permissionless multi-party challenge model, in order to achieve smaller trust assumptions. This requires addressing issues such as Sybil attacks and delay attacks, and relevant research findings can be referenced to design solutions suitable for the characteristics of Bitcoin.

4. Conclusion

BitVM provides a new approach for Bitcoin scaling, but there is still significant room for optimization. In the future, it is necessary to conduct in-depth exploration in terms of efficiency, security, and decentralization to fully leverage Bitcoin's potential and promote ecological prosperity.