MuSig2 is an interactive multisignature protocol 🔐 designed for BIP340 Schnorr signatures. Its formal specification is defined in BIP-327, “MuSig2 for BIP340-compatible Multi-Signatures” 📄. BIP-327 is marked as Deployed and classified as Informational, meaning that it is a published protocol specification that implementations can follow. However, it was not independently activated as a Bitcoin consensus-layer soft fork ₿. Its underlying cryptographic foundation comes from BIP-340, while its application in the Taproot context relies on BIP-341.
The core mechanism of MuSig2 is as follows: the participants first exchange their individual public keys 🔑 and use a key-aggregation algorithm to calculate one aggregate public key. During the signing process ✍️, all participants engage in two rounds of interaction, exchanging nonces and partial signatures. The valid partial signatures are then aggregated into a single Schnorr signature that conforms to the BIP-340 standard.
From the perspective of an on-chain verifier ⛓️, this signature has the same verification format as a Schnorr signature produced by a single signer. Therefore, MuSig2 can implement an n-of-n multisignature scheme, meaning that all participants must take part in the signing process. However, it does not directly implement a traditional m-of-n threshold-signature scheme.
When the aggregate public key is used as a Taproot key-path public key 🌳, the blockchain generally reveals only one 32-byte public key and one 64-byte Schnorr signature. This conceals the actual number of participants while also reducing the amount of transaction data 💸, thereby improving privacy and transaction efficiency.
The core mechanism of MuSig2 is as follows: the participants first exchange their individual public keys 🔑 and use a key-aggregation algorithm to calculate one aggregate public key. During the signing process ✍️, all participants engage in two rounds of interaction, exchanging nonces and partial signatures. The valid partial signatures are then aggregated into a single Schnorr signature that conforms to the BIP-340 standard.
From the perspective of an on-chain verifier ⛓️, this signature has the same verification format as a Schnorr signature produced by a single signer. Therefore, MuSig2 can implement an n-of-n multisignature scheme, meaning that all participants must take part in the signing process. However, it does not directly implement a traditional m-of-n threshold-signature scheme.
When the aggregate public key is used as a Taproot key-path public key 🌳, the blockchain generally reveals only one 32-byte public key and one 64-byte Schnorr signature. This conceals the actual number of participants while also reducing the amount of transaction data 💸, thereby improving privacy and transaction efficiency.