confium_tc::inprocess — synchronous session driver

Wraps the multi-round session state machine in a single function call so language bindings (Ruby, Python, WASM) and integration tests don’t have to reconstruct the round / message-routing loop on their own side.

Why this exists

Without this module every binding had to copy the same N-session-create + route-messages + drive-rounds boilerplate. The CMP20 and GG18 in-process shims used to be ~200 LOC each, ~90% of which was identical. This module collapses that pattern into one place; scheme-specific shims now only declare their scheme name and how to extract a public key from a share blob.

Public API

use confium_tc::inprocess;

// Drive a registered DKG scheme to completion in-process.
// Returns the per-party share blobs in roster order.
let share_blobs: Vec<Vec<u8>> = inprocess::run_dkg("CMP20-ECDSA-P256", 2, 3)?;

// Drive a registered signing / decapsulation scheme to completion.
// Returns the cryptographic artifact (e.g. 64-byte (r, s) ECDSA sig).
let signature: Vec<u8> = inprocess::run_sign("CMP20-ECDSA-P256-SIGN", &share_blobs[..2], 2, b"msg")?;

How it works

  1. Build N sessions — one per party, all sharing the same PartyList. Parties are in-process (Party::inproc), identified p0 … p\{n-1\}.
  2. Drive rounds — each iteration:
    • Routes the previous round’s outgoing messages to their recipients as the next round’s incoming.
    • Calls Session::round_step on every session.
    • Checks if every session reports is_complete().
  3. Bound at MAX_ROUNDS = 8 — if a scheme hasn’t completed after 8 framework rounds, the driver returns RoundOverflow. Real protocols top out at 4.

When to use this vs confium-tc-coordinator

Use case Driver
Language binding (Ruby, Python, WASM) inprocess
Integration test / unit test inprocess
Local demo / example binary inprocess
Real network deployment coordinator
Cross-datacenter signing ceremony coordinator

The driver is local — no networking. For real distributed deployments use confium-tc-coordinator, which drives the same Session::create

  • round_step API but routes messages over confium-net transports.

Security notes

  • The driver inherits whatever security properties the underlying scheme has. For CMP20 / GG18 the MtA sub-round is a simplified in-clear stub — see each crate’s docs.
  • Parties are identified by string IDs only. The driver does not authenticate peers. Real deployments authenticate via the coordinator’s transport layer.
  • All in-process state (sessions, messages) is dropped on function return. Scalars inside share blobs are zeroized by the scheme-specific Drop impls.

Scheme-specific wrappers

Each threshold crate ships a thin wrapper that names its scheme constants and pulls the joint public key out of the first share:

These wrappers are the recommended entry points for bindings — they return (shares, public_key) directly.