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Terminology
Broadcast channel
A secure broadcast channel in the context of multi-party computation protocols such as FROST has the following properties:
- Consistent. Each participant has the same view of the message sent over the channel.
- Authenticated. Players know that the message was in fact sent by the claimed sender. In practice, this requirement is often fulfilled by a PKI.
- Reliable Delivery. Player i knows that the message it sent was in fact received by the intended participants.
- Unordered. The channel does not guarantee ordering of messages.
Possible deployment options:
- Echo-broadcast (Goldwasser-Lindell)
- Posting commitments to an authenticated centralized server that is trusted to provide a single view to all participants (also known as 'public bulletin board')
Peer to peer channel
Peer-to-peer channels are authenticated, reliable, and unordered, per the
definitions above. Additionally, peer-to-peer channels are confidential; i.e.,
only participants i and j are allowed to know the contents of
a message msg_i,j.
Possible deployment options:
- Mutually authenticated TLS
- Wireguard
Threshold secret sharing
Threshold secret sharing does not require a broadcast channel because the dealer is fully trusted.
Verifiable secret sharing
Verifiable secret sharing requires a broadcast channel because the dealer is not fully trusted: keygen participants verify the VSS commitment which is transmitted over the broadcast channel before accepting the shares distributed from the dealer, to ensure all participants have the same view of the commitment.