What is a Threshold Signature Scheme?
A threshold signature scheme (TSS) is a cryptographic protocol where a signing key is split into n shares, and any t (threshold) of those shares can collaboratively produce a valid digital signature — without reconstructing the full key.
WHY IT MATTERS
TSS is the cryptographic foundation of MPC wallets. In a 2-of-3 TSS, the key is split into 3 shares. Any 2 shares can produce a valid signature through an interactive protocol. No single share holder can sign alone, and the complete key is never assembled in one place.
The mathematics behind TSS (often based on Shamir's Secret Sharing and distributed key generation protocols) ensure that even colluding parties below the threshold learn nothing about the key. This provides information-theoretic security for the key material.
TSS produces a standard signature that's indistinguishable from a regular one — unlike multisig, which requires a specialized on-chain contract. This makes TSS compatible with any blockchain and any account type.
HOW POLICYLAYER USES THIS
PolicyLayer can function as a threshold condition in the signing process. Before the TSS signing ceremony completes, PolicyLayer validates the transaction against policies — adding a policy check to the threshold signature flow.