Round-based distributed protocols

The body is round

Goals

• Sans-I/O API. That is, bring your own async libraries, or don't.
• Generic over signer/verifier/signature types, so you can use whatever your blockchain uses.
• Support parallelization where possible, to offload expensive cryptographic operations into spawned tasks (but since it's Sans-I/O, it's up to you to make use of that functionality).
• Provide tools for unit and integration testing of the protocols.
• Support generating malicious behavior proofs with bundled signed messages.
• Support caching messages intended for the next round and then applying them when it starts (since some nodes can finalize a round before others and send out a new batch of messages).

Assumptions

We try to find the balance between supporting the majority of protocols and keeping the API simple. Currently we operate under the following assumptions:

• A protocol consists of several rounds.
• A round generates messages to send out without any additional external input, then waits for messages from other parties. When it receives enough messages, it can be finalized.
• On finalization, a round can return the result, halt with an error, or continue to another round.
• Each round declares a set of parties it sends messages to. Then it can optionally send a direct message to each party in the set, set a regular broadcast to all parties in the set, or send an echo-broadcast to all parties in the set (that is, a broadcast where it is ensured that all parties received the same thing). Any number of these options can be picked.