MuSig2: The Innovation of Bitcoin Multisignature

Bitcoin users prove the legitimacy of transactions through digital signatures and specific messages, which is the right of the private key holder. Digital signatures indicate that the user knows the private key associated with the address without exposing the key itself to the network.

With the development of the Bitcoin network, the demand for optimizing signature schemes has been increasing. The introduction of Taproot provides developers with the opportunity to build improved signature schemes to enhance security, efficiency, and privacy. Among them, MuSig1 and its improved version MuSig2 are new signature schemes designed to enhance multisignature transactions.

Multisignature Transaction Overview

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

The early multisignature technology "CHECKMULTISIG" OP-code of Bitcoin had less communication requirements, but its privacy was not as good as the MuSig1 scheme. MuSig1 improved user privacy by adding steps to 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-based multisignature schemes. MuSig1 achieves key aggregation, enabling a group of signers to create a single combined public key and generate a single signature, simplifying multisignature transactions while reducing transaction size, lowering fees, and enhancing privacy.

MuSig2: Advanced Multisignature

MuSig2 is an upgraded version of MuSig1, offering better security, efficiency, and privacy features. As a two-round multisignature scheme, MuSig2 requires only communication between the signers in 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 steps, while MuSig2 only needs two.

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.

The Impact of MuSig2 on Bitcoin

The introduction of MuSig2 will bring multiple improvements to Bitcoin:

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

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

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

4. Enhanced Security: The security proof under AGM provides a more solid foundation for multisignature transactions.

Applications of MuSig2

MuSig2 is particularly useful in scenarios where enhanced security, privacy, and efficiency are required:

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

2. Cold Storage: Create a multisignature cold storage solution to decentralize fund access.

3. Privacy Protection Wallet: Achieves multisignature transactions that are indistinguishable from single signature transactions.

4. Second Layer Protocol Optimization: Used for second layer protocols such as the Lightning Network, protecting off-chain transactions and improving efficiency.

5. Liquid Network Improvements: Optimize the anchoring mechanism and simplify the bridge management of federation members.

Conclusion

MuSig2, as an important advancement in Bitcoin multisignature technology, has significant improvements in security, efficiency, and privacy. It has the potential to unlock new application scenarios and enhance existing applications, making 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.