MuSig2: A New Scheme for Enhancing Bitcoin Multisignature

Bitcoin users prove they are the transaction sender through digital signatures and specific messages, which is a legitimate operation as the owner of the private key. Digital signatures indicate that the user knows the private key associated with the address, while not exposing key information to the network.

With the development of the Bitcoin network, developers have been working to optimize signing schemes to improve security, efficiency, and privacy. The introduction of Taproot has provided new possibilities for improving signing schemes. Recently, MuSig1 and its upgraded version MuSig2 have gained much attention, as they are a new type of signing scheme aimed at enhancing multisignature transactions.

Multisignature Transaction Introduction

Unlike common single-signature transactions, multisignature transactions require multiple keys to authorize Bitcoin transfers. This method is often used to decentralize the responsibility of Bitcoin ownership and is also used to interact with second-layer solutions such as the Lightning Network or Liquid Network.

The earliest multisignature technology for Bitcoin, "CHECKMULTISIG" OP-code, has lower privacy compared to the MuSig1 scheme, despite having less communication demand. MuSig1 enhances user privacy protection by increasing the steps in the signing process.

Introduction to MuSig1

MuSig1 is a multisignature scheme that allows multiple parties to jointly sign a single message or transaction. It is based on Schnorr signatures and has significant improvements over traditional ECDSA multisignature schemes. MuSig1 supports key aggregation, allowing a group of signers to create a single joint public key and transaction signature. This not only simplifies multisignature transactions but also reduces transaction size, lowers fees, and enhances privacy.

MuSig2: An upgraded version of MuSig1

MuSig2 is an improved version of MuSig1, offering better security, efficiency, and privacy features. It is a two-round multisignature scheme that requires communication between signers only during the two rounds to create a valid signature, significantly reducing the coordination complexity of multi-party signatures.

The Main Differences Between MuSig1 and MuSig2

1. Communication Rounds: MuSig1 requires three rounds of communication, while MuSig2 only needs two, making the signing process faster.

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

Contribution of MuSig2 to Bitcoin

1. Improve efficiency: The two-round communication model simplifies the coordination of multisignature transactions.

2. Enhanced Privacy: Supports key aggregation, making multisignature transactions difficult to distinguish from single-signature transactions on the blockchain.

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

4. Stronger Security: AGM security proof provides a more solid foundation for multisignature transactions.

Applications of MuSig2

1. Shared custody: Safely manage shared funds, such as trust or joint accounts.

2. Cold storage: Create a multisignature cold storage solution to enhance the security of funds.

3. Privacy Protection Wallet: Achieve multisignature transactions that are difficult to distinguish from single-signature transactions.

4. Second Layer Protocol Improvements: Optimize the efficiency and security of second layer solutions such as the Lightning Network and Liquid Network.

Conclusion

MuSig2, as an important advancement in Bitcoin multisignature technology, provides higher security, efficiency, and privacy protection. It has the potential to unlock new application scenarios, enhance existing use cases, and make Bitcoin safer and more user-friendly for global users. With the maturation and widespread application of the technology, MuSig2 is expected to play a key role in shaping the future of Bitcoin and blockchain technology.