Hybrid Consensus: Fast Off-Chain, Final On-Chain

Pure on-chain consensus is too expensive and too slow. Pure off-chain consensus lacks finality guarantees. Arbiter uses a hybrid architecture—fast off-chain operations with on-chain finality.

The Trade-off

On-chain operations are:

• Slow: Block time delays (2-12 seconds on Base)
• Expensive: Gas costs for every operation
• Final: Immutable, permanent, authoritative

Off-chain operations are:

• Fast: Instant, no block time delays
• Cheap: No gas costs
• Not final: Can be disputed, not authoritative

Arbiter combines both: fast off-chain for operations, on-chain for finality.

Off-Chain Operations

Fast, cheap operations happen off-chain:

• Heartbeat messages: Leaders prove liveness to followers
• Vote collection: Agents vote on proposals
• Leader negotiation: Elections happen off-chain
• Lock contention: Lock requests and releases

These use EIP-712 typed signatures. Every message is cryptographically signed and can be verified on-chain if disputes arise.

On-Chain Finality

Critical state is recorded on-chain:

• Leadership proofs: Term numbers and leader addresses
• Fencing tokens: Globally monotonic counter registry
• Stake deposits: Economic security for Sybil resistance
• Final vote outcomes: Permanent record of decisions

On-chain state is authoritative. If there's a dispute, on-chain state resolves it.

EIP-712 Typed Signatures

Off-chain messages use EIP-712 typed signatures:

typescript
// Sign a vote message
const voteMessage = {
  proposalId: 'prop_123',
  vote: 'yes',
  term: 5,
  timestamp: Date.now(),
};

const signature = await signer._signTypedData(
  {
    name: 'Arbiter',
    version: '1',
    chainId: 8453, // Base
  },
  {
    Vote: [
      { name: 'proposalId', type: 'string' },
      { name: 'vote', type: 'string' },
      { name: 'term', type: 'uint256' },
      { name: 'timestamp', type: 'uint256' },
    ],
  },
  voteMessage
);

These signatures can be verified on-chain if disputes arise. Similar to optimistic rollups: most work happens off-chain, but disputes settle on-chain.

Example: Leader Election

Off-chain: Agents negotiate, vote, elect leader (fast, cheap)

On-chain: Leadership proof recorded with term number (slow, expensive, final)

If network partitions cause two agents to both think they're leader, on-chain term number is authoritative. The agent with the lower term must step down.

Why This Matters

Hybrid architecture enables:

• Fast operations: Most consensus happens off-chain
• Final guarantees: Critical state is on-chain
• Cost efficiency: Only finality operations pay gas
• Dispute resolution: On-chain state resolves conflicts

Without hybrid architecture, consensus is either too slow (pure on-chain) or too insecure (pure off-chain). With it, Arbiter provides both speed and security.

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Part of the EchoRift infrastructure series. Learn more about Arbiter.