Specification 22 — Threshold session lifecycle

Overview

A threshold session is the unit of interaction among T-of-N parties producing a single cryptographic output (signature, decryption, etc.).

Session types

Type	Phases	Use case
DKG (Distributed Key Generation)	3 rounds	Initial keypair creation
Signing	2-3 rounds	Produce a signature
Decryption	1-2 rounds	Decrypt a ciphertext
Re-sharing	2-3 rounds	Change committee without changing public key
Refresh	1 round	Proactive share refresh (Herzberg)

State machine

Pending
  ↓ (T commitments received)
CommitmentsCollected
  ↓ (T shares received)
SharesCollected
  ↓ (aggregation)
Completed

Or:

Pending
  ↓ (unlock window expired)
Expired

Message types

Each session involves these messages:

1. SessionInit — created by requester, contains message + quorum ID + threshold
2. Commitment — round 1 output from each signer
3. Share — round 2 output from each signer
4. AggregatedSignature — final output

Every message is signed by the sender’s identity key for non-repudiation.

Identifiable abort

If a party sends an invalid message, the protocol aborts and emits a signed proof of misbehavior:

• Identifies the offending party
• Includes their signed offending message
• Includes the round transcript up to abort

This proof is sufficient for administrative proceedings.

Cross-references

• Coordinator spec: 23 — Async coordinator
• Re-sharing spec: 24 — Share re-sharing
• Implementation: confium-tc/src/session.rs