MuSig2 lets n people, each with their own private key, act as one signer. Together they create one combined Schnorr signature key and, when spending, one 64-byte signature. On-chain, it looks exactly like a single-signer Taproot spend.
How it works
- Key aggregation: everyone's public keys are combined into one aggregate key.
- Round 1: each signer shares two nonce points. This can happen before the message is known.
- Round 2: each signer sends a partial signature. These add up to the final signature.
The catch
It is n-of-n: everyone must sign. Nonces must never be reused, so signing devices must protect their session state carefully. BIP327 is marked Deployed in the BIPs repository.