consensus/examples/quasar_full

Quasar Full Protocol Example

Complete demonstration of the Lux Quasar consensus protocol showing all components working together to achieve sub-second quantum-resistant finality.

What is Quasar?

Quasar is Lux's unified consensus protocol that combines multiple cutting-edge consensus techniques:

1. Fast Probabilistic Consensus (FPC) - Prevents stuck states with dynamic thresholds
2. Wave Protocol - Metastable convergence through repeated sampling
3. Horizon/Flare - DAG-based finality detection
4. Post-Quantum Signatures - Pulsar lattice + BLS fusion

Together, these achieve 2-round quantum finality in <1 second.

Running the Example

cd examples/quasar_full
go run main.go

Running the Tests

# From consensus root
cd ../..
go test ./examples/quasar_full/... -v

# With coverage
go test ./protocol/wave/fpc/... -v -cover
go test ./protocol/flare/... -v -cover
go test ./protocol/horizon/... -v -cover

What The Example Demonstrates

Part 1: FPC Dynamic Thresholds

Shows how FPC uses a PRF (SHA-256) to select different thresholds each round:

• Prevents consensus from getting stuck
• Maintains Byzantine fault tolerance
• Deterministic but varied selection

Example output:

Round  0: α=13/20 (θ=0.650) [█████████████░░░░░░░]
Round  1: α=11/20 (θ=0.550) [███████████░░░░░░░░░]
Round  2: α=15/20 (θ=0.750) [███████████████░░░░░]

Part 2: Wave Consensus & Block Finalization

Demonstrates REAL block finalization:

• Block creation and addition to chain
• Validator vote collection
• Confidence building through repeated sampling
• Final consensus decision

Shows actual timing: typically <100μs for block processing.

Tests all 7 critical Horizon algorithms:

1. IsReachable - DAG connectivity analysis
2. LCA - Lowest Common Ancestor for parallel blocks
3. ComputeSafePrefix - Find finalized vertices
4. ChooseFrontier - Byzantine-tolerant parent selection
5. Antichain - Identify concurrent vertices
6. Horizon - Advance event horizon boundary
7. BeyondHorizon - Check if vertex is immutably finalized

Part 4: Complete Quasar Flow

Visualizes the complete 2-round protocol:

Round 1 (~500ms): Classical BFT

• FPC threshold selection
• Wave repeated sampling
• BLS signature aggregation

Round 2 (~300ms): Quantum Finality

• Horizon finality detection
• Flare certificate verification
• Pulsar post-quantum signatures
• Event horizon advancement

Total: <1 second with quantum resistance

Test Coverage

The test suite includes:

• ✅ FPC threshold selection (determinism + variety)
• ✅ Block finalization (single to multi-validator)
• ✅ Horizon reachability (forward + backward)
• ✅ LCA computation
• ✅ Safe prefix detection
• ✅ Frontier selection with BFT
• ✅ Event horizon advancement
• ✅ Certificate threshold validation
• ✅ Full protocol integration
• ✅ Performance benchmarks

Run go test -v -cover for detailed coverage report.

Key Concepts

Byzantine Fault Tolerance

Quasar ensures safety with f < n/3 Byzantine faults:

• n=20 validators tolerates f=6 faults
• Certificate needs ≥2f+1 = 13 validators
• Safety: Can't have both cert and skip (mutual exclusion)

Metastable Consensus

Wave protocol achieves convergence through:

• Random sampling of k validators
• Check if ≥α prefer this block
• Repeat until β consecutive successes
• FPC varies α to prevent stuck states

DAG Finality

Horizon/Flare detect finality in parallel DAG:

• Certificate: ≥2f+1 validators support vertex
• Skip: ≥2f+1 validators don't support vertex
• Safe Prefix: Vertices that are ancestors of all frontier
• Event Horizon: Immutability boundary (cannot be reverted)

Quantum Resistance

Pulsar provides post-quantum security:

• Lattice-based cryptography (NTRU/ML-KEM family)
• Fused with BLS for 2-round finality
• Resistant to Shor's algorithm (quantum attacks)

Architecture

Quasar Protocol
    │
    ├── Round 1: Classical BFT
    │   ├── FPC (threshold selection)
    │   ├── Wave (metastable convergence)
    │   └── BLS (signature aggregation)
    │
    └── Round 2: Quantum Finality
        ├── Horizon (reachability analysis)
        ├── Flare (certificate verification)
        └── Pulsar (PQ signatures)

Performance

From benchmarks in this example:

• FPC threshold selection: ~100ns per round
• Block finalization: ~30μs
• Horizon algorithms: ~1μs per operation
• Full protocol: <1 second total

Safety Guarantees

✓ Safety: No two conflicting blocks can both finalize
✓ Liveness: Finality in <1s (non-adversarial)
✓ Byzantine Tolerance: Works with f < n/3 faults
✓ Quantum Resistance: Secure against quantum computers

Learn More

• Lux Consensus README
• Quasar Protocol Documentation
• FPC Implementation
• DAG Algorithms

Related Examples

• Simple Consensus - Basic chain consensus
• 01-Simple Bridge - Cross-chain integration
• 02-AI Payment - AI-powered consensus

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Lux Consensus v1.22.0 - Quantum-resistant finality in <1 second