MuSig2: New Advances in Bitcoin Multisignature Technology

Bitcoin users prove themselves as the legitimate initiators of transactions through digital signatures and specific messages, without exposing their private keys. As the network evolves, Bitcoin signature schemes are continuously being optimized to adapt to different use cases.

The launch of Taproot provides developers with the opportunity to create more secure, efficient, and private signing solutions. MuSig1 and its improved version MuSig2 are representative examples aimed at enhancing the performance of multisignature transactions.

Multisignature Transaction Introduction

Unlike common single-signature transactions, multisignature transactions require multiple keys to authorize. This method is typically used to decentralize Bitcoin ownership responsibility or to interact with layer two network solutions.

The early multisignature technology "CHECKMULTISIG" had lower communication requirements, but its privacy was not as good as MuSig1. MuSig1 improved user privacy by adding signature steps, but it also increased complexity.

MuSig1 Overview

MuSig1 is a multisignature scheme based on Schnorr signatures, which has significant improvements compared to traditional ECDSA schemes. It supports key aggregation, allowing multiple signers to create a single combined public key and transaction signature. This not only simplifies multisignature transactions but also reduces transaction size, lowers fees, and enhances privacy.

Innovation of MuSig2

MuSig2 is an upgraded version of MuSig1, proposed by researchers in November 2020. As a two-round multisignature scheme, MuSig2 only requires communication between the signers in two rounds to complete a valid signature, significantly reducing the complexity of multi-party coordination.

Key Differences Between MuSig1 and MuSig2

1. Communication Rounds: MuSig1 requires three rounds of communication, while MuSig2 only requires two rounds, improving efficiency.

2. Security Model: MuSig1 is based on the random oracle model (ROM), while MuSig2 adopts the algebraic group model (AGM), providing stronger security guarantees.

The Advantages of MuSig2 for Bitcoin

1. Efficiency Improvement: The two-round communication model simplifies the coordination process of multisignature transactions.

2. Privacy Enhancement: Supports key aggregation, allowing multisignature transactions to perform on-chain indistinguishably from single-signature transactions.

3. Increased flexibility: Supports more complex signing strategies, such as threshold signatures and hierarchical key structures.

4. Enhanced Security: The AGM security model provides a stronger foundation for multisignature transactions.

Application Scenarios of MuSig2

1. Joint custody: Multiple parties securely manage shared funds, reducing single point of failure risks.

2. Cold Storage: Create a multisignature cold storage solution to enhance fund security.

3. Privacy-focused wallet: Achieving privacy protection through multisignature transactions.

4. Layer 2 Protocol Optimization: Used for Layer 2 solutions such as the Lightning Network, enhancing the security and efficiency of off-chain transactions.

5. Sidechain Applications: Optimize the anchoring mechanism of sidechains like the Liquid Network and simplify the management of cross-chain bridges by federation members.

Conclusion

MuSig2, as an important advancement in the Bitcoin ecosystem, has significant improvements in security, efficiency, and privacy. It not only simplifies multisignature transactions but also opens up possibilities for new application scenarios. With the maturation and widespread adoption of the technology, MuSig2 is expected to play a key role in shaping the future of Bitcoin and blockchain technology.