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.

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.

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

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