FROST (Flexible Round-Optimized Schnorr Threshold Signatures) is a threshold signature scheme that allows a group of participants to collaboratively produce valid Schnorr signatures without any single party holding the complete private key.

How It Works

FROST enables T-of-N threshold signing, where T participants out of N total keyholders must cooperate to produce a valid signature. The protocol operates in two rounds:

  1. Commitment Round: Each participant generates and shares cryptographic commitments
  2. Signature Round: Participants combine their partial signatures into a final aggregate signature

The resulting signature is indistinguishable from a standard Schnorr signature, maintaining backward compatibility with existing verification systems.

Key Properties

  • Threshold Security: No single participant can sign alone; T parties must cooperate
  • Round Efficiency: Only two rounds of communication required for signing
  • Forgery Protection: Novel techniques protect against attacks on prior threshold schemes
  • Signature Aggregation: Multiple signatures combine into a single compact signature
  • Privacy: Final signatures reveal nothing about which T participants signed

Use Cases in Nostr

In the context of Nostr, FROST enables:

  • Quorum Governance: Groups can share an nsec through T-of-N schemes, where members can represent themselves or delegate to councils
  • Multi-sig Administration: Community moderation requiring multiple admin signatures
  • Decentralized Key Management: Distributing trust across multiple parties for critical operations

Standardization

FROST was standardized as RFC 9591 in June 2024, titled “The Flexible Round-Optimized Schnorr Threshold (FROST) Protocol for Two-Round Schnorr Signatures.”

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