Polysig

Polysig is a library for single-party and multisig use cases for ECDSA, Schnorr and Ed25519 signature schemes.

We refer to single-party implementations as signers and multisig as protocols; all of the multisig protocols are threshold signature schemes. Supported protocols are FROST and CGGMP21.

Protocols communicate via an end-to-end encrypted relay server using the noise protocol and websockets for the transport layer or if you already have a transport you can use the driver crate directly.

The library includes bindings for Webassembly to be used in the browser and for Nodejs; for multisig protocols the client implementation uses web-sys for webassembly and tokio-tungstenite for other platforms.

Other feature flags are full to enable all features or all protocols and signers.

Meeting Rooms

For protocols to be executed the participants need to exchange public key information. To facilitate this we provide the meeting-server which allows for meeting rooms to be created and all participants to be notified once all public keys are available. The client library provides high-level functions for creating and joining rooms; these functions are also exposed in the bindings.

The meeting-server is intentionally distinct from the relay-server so the relay server has no knowledge of the public key exchange.

There are two identifiers for meeting rooms the MeetingId and a UserId for each participant. The UserId is a 32-byte identifier which is typically generated using a hash (such as SHA256) of some unique information. The information could be the participant's email address or other unique identifier.

The creator of the meeting room submits all the user identifiers (including their own) and the server will assign slots and return a MeetingId.

The meeting room creator then needs to share the MeetingId and each participant's assigned UserId with each of the participants; typically this would be done in the form of a URL.

All participants must then join the meeting room using their assigned slot (usually via a URL link) and publish their public keys to the server. Each participant must share both the public_key which is the public key for the noise protocol and the verifying_key which is used to verify authenticity when exchanging protocol round messages.

Once all participants have joined the room the server will send a broadcast notification including all the participant identifiers and public keys.

Now the participants are ready to begin create and join a session context.

Session Context

After exchanging public keys via a meeting room it's required to create a session context on the relay server for protocol execution. If you are using the high-level functions in polysig-client then sessions are automatically created and destroyed.

A session context groups participants in a protocol so that we can ensure only participants with access to the session identifier are communicating and also so that peers can negotiate their noise protocol encrypted channels. We distinguish between an initiator that starts a session and a participant who registers their connection in a session. The initiator is responsible for closing a session once the protocol completes; if a session is not closed, perhaps due to a network error the server will eventually delete the session once it has expired.

The session initiator creates a session by sending all the noise transport public keys (including their own) to the server and then each participant submits their noise transport public key to the server to register as a participant in the session. Once all participants have registered their public keys then the server will send a SessionReady event, once the SessionReady event has been received each party attempts to create the encrypted peer to peer channel. Once all the peers are connected on secure channels a SessionActive event is emitted and then the protocol can begin execution.

Documentation

• protocol Message types and encoding
• driver Signers and protocol drivers
• client Websocket client library
• meeting-server Websocket meeting room server library
• relay-server Websocket relay server library
• cli Command line interface for the server

See BUILD for information on installing, building and testing the source.

License

The server code is licensed under AGPL-3.0 and the client code is licensed as either MIT or Apache-2.0 except when the cggmp feature is enabled which triggers the AGPL-3.0 license via the synedrion library.