MuSig2: New Developments in Bitcoin Multisignature

Bitcoin users prove the legitimacy of transactions through digital signatures and specific messages, which serve as a means of authentication for the private key owner. Digital signatures are used to indicate that the user is aware of the private key associated with the address, without exposing the actual key to the network.

With the development of the Bitcoin network, the demand for optimizing signature schemes has become increasingly urgent. The introduction of Taproot provides developers with a foundation to build improved signature schemes to enhance security, efficiency, and privacy. MuSig1 and its upgraded version MuSig2 are significant innovations in multisignature transactions.

Bitcoin multisignature transaction overview

Unlike common single-signature transactions, multisignature (multisig) transactions require multiple keys to authorize. This method is often used to distribute the responsibility of Bitcoin ownership and is also applied in interactions with second-layer solutions like the Lightning Network.

Early multisignature technologies such as the "CHECKMULTISIG" OP-code, while requiring less communication, do not offer the same level of privacy as the MuSig1 scheme. MuSig1 enhances user privacy protection by increasing the number of signing steps.

Introduction to MuSig1

MuSig1 is a multisignature scheme that allows multiple parties to jointly sign a single message or transaction. Compared to traditional script-based multisignature, MuSig1 occupies less block space but requires more interaction among participants.

MuSig1 based on Schnorr signatures has significant improvements over traditional ECDSA-based multisignature schemes. It supports key aggregation, allowing a group of signers to create a single combined public key and generate a single signature, simplifying multisignature transactions while reducing transaction costs and enhancing 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 only communication between signers during the two rounds to create a valid signature, reducing the complexity of coordinating multiple signers.

The Main Differences Between MuSig1 and MuSig2

1. Communication Rounds:

   • MuSig1 requires three rounds of communication steps
   • MuSig2 requires only two rounds of communication, making it faster and more convenient.

2. Security Model:

   • MuSig1 relies on the Random Oracle Model (ROM)
   • MuSig2 is based on the algebraic group model (AGM), providing stronger security guarantees.

The Impact of MuSig2 on Bitcoin

1. Improve efficiency: The two-round communication model simplifies multisignature transaction coordination.
2. Enhanced Privacy: Key aggregation makes multisignature transactions difficult to identify on the blockchain.
3. Greater flexibility: Supports more complex signature strategies
4. Enhanced Security: The AGM model provides more reliable security guarantees.

Application Scenarios of MuSig2

1. Shared custody: Secure management of shared funds, such as trusts or joint accounts.
2. Cold Storage: Create a multisignature cold storage solution to add an extra layer of security.
3. Privacy Protection Wallet: Achieve indistinguishable multisignature transactions
4. Layer 2 Protocol Improvements: Optimizing Layer 2 solutions such as the Lightning Network and Liquid Network.

Conclusion

MuSig2, as an important development in the Bitcoin world, offers better security, efficiency, and privacy features compared to MuSig1. It simplifies multisignature transactions and provides stronger security guarantees, with the potential to open up new application scenarios and enhance existing applications. 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.