Partial Signature
In multisig or PSBT workflows, a single participant's signature, awaiting more signatures to finalize spending.
A partial signature is one cosigner's contribution to a multi-party signed transaction. It isn't a complete signature on its own; the transaction is only valid once enough partial signatures combine to meet the script's threshold.
There are two flavors in modern Bitcoin:
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Classical multisig. Each cosigner produces a full ECDSA or Schnorr signature against the same sighash. The script combines M of them on-chain (e.g., 2-of-3 P2WSH or a Taproot script-path leaf). Partial signatures are tracked through the PSBT workflow: each signer adds their signature to the PSBT and passes it on until the threshold is met, then anyone finalizes the transaction.
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Aggregated signatures (MuSig2, FROST). Each cosigner produces a partial signature that's a fragment of a single Schnorr signature. None of them is a valid signature on its own; the protocol combines them into one signature, and one signature is what ends up on-chain. To outside observers it's indistinguishable from single-sig.
The first kind has been Bitcoin standard since P2SH multisig in 2012 and is what most hardware-wallet multisig flows use today. The second is newer (post-Taproot, 2021+) and underpins modern Lightning channels and emerging vault designs where privacy and on-chain footprint matter.
Key takeaways
- Represents one cosigner's authorization in a multisig transaction
- Many partial signatures combine to meet the M-of-N threshold
- Employed in distributed/PSBT setups for secure multi-party approvals