Frostr

Frostr is a threshold signing protocol for nostr built on top of FROST (Flexible Round-Optimized Schnorr Threshold signatures). An nsec key is split into shares that live on different devices or services. Any t-of-n quorum of those shares can sign a nostr event together, but a single compromised share does not leak the key. Shares can be rotated and replaced without rotating the underlying identity, which matters on a protocol where your public key is your identity.

Coordination happens over nostr itself. Each share has its own nostr identity and exchanges encrypted DMs with the other shares to produce a signature, so there's no dedicated backend or custodian in the path.

Why fund it?

The default key model on nostr puts one nsec on every device the user touches. A single stolen phone or leaked backup hands over the npub that clients, zaps, and payments are tied to, and there is no clean way to rotate without burning the identity. Threshold signing fixes that: the key is split across devices so no single compromise exposes it, and shares can be rotated without touching the underlying npub. Clients still see the same Schnorr signatures they always have.

OpenSats funded Frostr in the twelfth wave of nostr grants. The work is also a building block for later protocols, for example bitcoin coinjoins and Payjoins coordinated over nostr.

What's next?

The v1 suite is now live across desktop, browser, server, CLI, web, and mobile:

• Bifrost, the core FROST library
• Igloo Desktop for managing shares on a laptop
• Frost2x, a Chrome NIP-07 signer
• Igloo Server, a signer device and personal ephemeral relay with NIP-46 support
• Igloo CLI on npm for scripting
• Igloo Web, a hosted web client
• Igloo Android and Igloo iOS for mobile signing, the latter live on the App Store

With that foundation in place, the core protocol and library have been rewritten as Bifrost v2 in Rust with a WASM build. v2 replaces v1's nonce-extension scheme with nonce pools, reworks the onboarding flow, and adds live peer health monitoring. Over the next quarter the team is landing a v2-native app suite (Igloo PWA, Igloo Chrome, Igloo Home, Igloo Shell, Igloo UI) to replace the v1 clients, after which the v1 protocol can be retired. A written specification is in progress so Frostr can be independently implemented. A packaged Umbrel distribution for Igloo Server is already live, with Start9 packaging next in line.