midnight-consensus

Midnight Consensus

The Midnight Network uses a modified Substrate consensus stack: AURA for block production and GRANDPA for finality. Both are extended for Midnight as a Cardano Partnerchain.

Architecture overview

flowchart TB
  subgraph Selection["Validator selection"]
    SPO["Cardano SPO stake delegation"]
    Perm["Optional permissioned validators"]
    VS["Custom validator set function"]
    SPO --> VS
    Perm --> VS
  end

subgraph Production["Block production — AURA"] VS --> Slots["Round-robin slots + session keys"] Slots --> Block["New block proposed"] end

subgraph Finality["Finality — GRANDPA"] Block --> Votes["Validator votes on chain"] Votes --> Final["Provable finality"] end

---

## Validator selection

Unlike standard Substrate chains, Midnight uses a **custom validator set selection function** that:

- Accounts for **stake delegation from Cardano Stake Pool Operators (SPOs)**, letting existing Cardano validators participate in Midnight consensus.
- Supports **optional permissioned validators** for hybrid public/private network deployments.

| Model | Role |
|-------|------|
| SPO delegation | Bridges Cardano stake into Partnerchain validator eligibility |
| Permissioned set | Adds known operators for regulated or consortium networks |
| Custom selection | Combines both into the active session validator set |

---

## AURA: Block production

**AURA (Authority Round)** is a proof-of-authority (PoA) algorithm that determines which validator produces each block.

- Validators take turns in **round-robin** order.
- Scheduling uses **predefined slots** and **session keys**.
- Properties: simple, fast, deterministic — suited to high-throughput chains with known validator sets.

AURA is **not Midnight-specific**; it originated in OpenEthereum. See the [Polkadot protocol glossary — AURA](https://wiki.polkadot.network/docs/glossary#authority-round-aura).

```mermaid
sequenceDiagram
  participant V1 as Validator 1
  participant V2 as Validator 2
  participant V3 as Validator 3
  participant Chain as Chain

  Note over V1,V3: Slot N — Validator 1's turn
  V1->>Chain: Produce block N
  Note over V1,V3: Slot N+1 — Validator 2's turn
  V2->>Chain: Produce block N+1
  Note over V1,V3: Slot N+2 — Validator 3's turn
  V3->>Chain: Produce block N+2

Signing: Block authorship messages in AURA are signed with sr25519 (see the Cryptography skill).

---

GRANDPA: Finality

GRANDPA (GHOST-based Recursive ANcestor Deriving Prefix Agreement) provides asynchronous, provable finality.

• Operates independently of block production.
• Validators vote on chains; blocks finalize when they receive sufficient support.
• General-purpose Polkadot component — formal specification and Polkadot glossary.

flowchart LR
  A["Blocks produced (AURA)"] --> B["GRANDPA voters observe chain"]
  B --> C{"≥ threshold support?"}
  C -->|Yes| D["Block finalized — irreversible"]
  C -->|No| E["Remains unfinalized / fork possible"]

Signing: GRANDPA finality messages use Ed25519.

---

How AURA and GRANDPA work together

Layer	Responsibility	Midnight extension
AURA	Who builds the next block	Standard PoA over Partnerchain validator set
GRANDPA	Which blocks are final	Standard async finality gadget
Validator set	Who may participate	SPO delegation + optional permissioned operators

Key insight: Block production can continue while GRANDPA finalizes earlier blocks asynchronously — throughput and safety are decoupled.

---

Related skills

• midnight-cryptography/ — signature schemes used by AURA and GRANDPA
• midnight-onchain-logic/ — runtime pallets (pallet-aura, pallet-grandpa, session management)
• midnight-p2p-networking/ — how validators discover and communicate