Lux Consensus

Lux Network uses a novel family of leaderless consensus protocols that achieve sub-second finality without a designated block proposer. This approach combines the best properties of classical and Nakamoto consensus while avoiding their limitations.

The Snow Protocol Family

Lux consensus is built on the Snow family of protocols, which achieve agreement through repeated random sub-sampling of the network.

How It Works

Query Phase

A node receives a transaction and selects a small random subset of validators (typically k=20) to query.

Response Phase

Each queried validator responds with its current preference for the transaction (accept or reject).

Confidence Accumulation

If a supermajority (alpha threshold, e.g. 14 out of 20) agree, the node increases its confidence in that outcome. This process repeats with new random samples.

Finalization

After sufficient consecutive rounds of supermajority agreement (the beta threshold), the decision is finalized and irreversible.

Protocol Variants

Snowball

Snowball is the core binary consensus protocol. Each node maintains a confidence counter for each preference and flips its preference when the opposing side accumulates more confidence.

Maintains running confidence counters
Flips preference based on accumulated evidence
Probabilistic safety guarantees grow exponentially with rounds

Snowflake

Snowflake is a simplified variant that tracks only consecutive successes rather than cumulative confidence. It is simpler but slightly less robust than Snowball.

Uses a consecutive success counter
Resets counter on any conflicting supermajority
Faster convergence in low-contention scenarios

Avalanche (DAG-based)

The Avalanche protocol extends Snowball to operate over a directed acyclic graph (DAG) of transactions. This is used on the X-Chain for high-throughput asset transfers.

Transactions form a DAG with parent-child dependencies
Confidence flows transitively through the DAG
A parent transaction's acceptance reinforces its children
Enables massive parallelism: non-conflicting transactions finalize concurrently

       ┌────┐     ┌────┐
       │ T1 │     │ T2 │    Independent transactions
       └──┬─┘     └─┬──┘    finalize in parallel
          │         │
       ┌──┴─────────┴──┐
       │      T3        │    T3 depends on T1 and T2
       └───────┬────────┘
               │
       ┌───────┴────────┐
       │      T4        │    DAG grows as transactions arrive
       └────────────────┘

Snowman (Linear Chain)

Snowman adapts the Snow consensus to linear chains where blocks must be totally ordered. This is used on the P-Chain and C-Chain.

Builds a single chain of blocks (not a DAG)
Each block has exactly one parent
Well-suited for smart contract execution where state must be sequential
Preserves the leaderless and rapid finality properties of Snow

Consensus Parameters

Parameter	Description	Typical Value
k (sample size)	Number of validators queried per round	20
alpha (quorum)	Supermajority threshold	14 (70%)
beta (decision threshold)	Consecutive successes to finalize	20
max rounds	Maximum query rounds before timeout	30

Finality

Lux consensus provides probabilistic finality that becomes overwhelming within milliseconds.

Lux achieves finality in under 1 second for most transactions. The probability of reversal decreases exponentially with each round, reaching negligible levels (less than 10^-9) well before the beta threshold.

Finality Comparison

Consensus	Finality Time	Finality Type	Leader Required
Lux (Snow)	< 1 second	Probabilistic (overwhelming)	No
Bitcoin (PoW)	~60 minutes	Probabilistic	Yes (miner)
Ethereum (PoS)	~15 minutes	Economic	Yes (proposer)
Tendermint (BFT)	~6 seconds	Absolute	Yes (proposer)

Chain-Specific Consensus

Each chain in the Lux Primary Network uses the consensus variant best suited to its workload.

Chain	Protocol	Reason
X-Chain	Avalanche (DAG)	High-throughput parallel asset transfers
C-Chain	Snowman (Linear)	Sequential smart contract execution
P-Chain	Snowman (Linear)	Ordered validator set changes and staking

Properties

Liveness

The protocol guarantees progress as long as a sufficient fraction of the network is reachable. There is no single leader whose failure can stall the chain.

Safety

Safety holds as long as the fraction of Byzantine (malicious) nodes remains below the parameterized threshold. With typical parameters, the protocol tolerates up to ~20% Byzantine validators while maintaining safety with overwhelming probability.

Scalability

Because each node only queries a small fixed-size sample per round (not the entire validator set), the per-node communication overhead is O(k) per round regardless of total network size. This allows Lux to scale to thousands of validators without degrading finality speed.

Consensus