aitbc/docs/blockchain/4_consensus.md

Consensus Mechanism

Understand AITBC's hybrid Proof-of-Authority/Proof-of-Stake consensus mechanism.

Overview

AITBC uses a hybrid PoA/PoS consensus mechanism with:

• Fixed block time: 2 seconds
• Multi-validator authority set with role-based permissions
• Stake-weighted proposer selection and validator rotation
• Byzantine fault tolerance via PBFT protocol
• Transaction finality on each block

Block Production

Multi-Validator Architecture

AITBC supports multiple validators with distinct roles:

• PROPOSER: Authorized to propose new blocks
• VALIDATOR: Participates in consensus and validates blocks
• STANDBY: Waiting to be promoted to active role

Proposer Selection

Multiple selection strategies are available:

• Round-robin: Validators take turns in fixed order
• Stake-weighted: Higher stake increases selection probability
• Reputation-based: Performance metrics influence selection
• Hybrid: Combines stake and reputation scores (default)

Proposers are selected from active validators with PROPOSER or VALIDATOR roles.

Block Structure

{
  "header": {
    "height": 100,
    "timestamp": "2026-02-13T10:00:00Z",
    "proposer": "ait-devnet-proposer-1",
    "parent_hash": "0xabc123...",
    "state_root": "0xdef456...",
    "tx_root": "0xghi789..."
  },
  "transactions": [...],
  "receipts": [...]
}

Consensus Rules

1. Block Time: 2 seconds minimum
2. Block Size: 1 MB maximum
3. Transactions: 500 maximum per block
4. Fee: Minimum 0 (configurable)
5. Validator Stake: 1000 AITBC minimum
6. Fault Tolerance: Up to 1/3 of validators can be Byzantine (PBFT)

Validator Requirements

Requirement	Value
Stake	1000 AITBC minimum
Uptime	99% minimum
Latency	< 100ms to peers
Reputation	0.7 threshold (for reputation-based rotation)

Byzantine Fault Tolerance (PBFT)

AITBC implements Practical Byzantine Fault Tolerance for safety:

• Pre-prepare phase: Proposer broadcasts block proposal
• Prepare phase: Validators acknowledge proposal
• Commit phase: Validators commit to block execution
• Execute phase: Block is finalized and executed

The system tolerates up to 1/3 faulty validators while maintaining safety and liveness.

Validator Rotation

Validators rotate automatically based on configured strategy:

• Rotation interval: Every 100 blocks (configurable)
• Maximum validators: 10 (configurable)
• Strategies: Round-robin, stake-weighted, reputation-based, or hybrid

Rotation ensures decentralization and prevents single-point failures.

Network Partition Handling

The consensus mechanism detects and handles network partitions:

• Partitioned validators are marked and excluded from consensus
• Consensus requires majority of active validators (not partitioned)
• 5-second cooldown after partition healing before resuming consensus
• Byzantine behavior detection identifies malicious validators

Fork Selection

Longest chain rule applies:

• Validators always extend the longest known chain
• Reorgs occur only on conflicting blocks within the last 10 blocks

Finality

Blocks are considered final after:

• 1 confirmation for normal transactions
• 3 confirmations for high-value transactions

Configuration

Environment Variables

CONSENSUS_MODE=poa                    # Consensus algorithm
PROPOSER_ID=<address>                 # Default proposer (single-validator mode)
ROTATION_INTERVAL=100                 # Blocks between rotations
MAX_VALIDATORS=10                     # Maximum active validators
MIN_STAKE=1000.0                     # Minimum validator stake
REPUTATION_THRESHOLD=0.7              # Minimum reputation for rotation

Single vs Multi-Validator Mode

• Single-validator: Use PROPOSER_ID for simple setup (genesis wallet only)
• Multi-validator: Configure validator set via API or CLI for production

Implementation

The consensus is implemented in:

• apps/blockchain-node/src/aitbc_chain/consensus/multi_validator_poa.py - Core PoA logic
• apps/blockchain-node/src/aitbc_chain/consensus/pbft.py - PBFT protocol
• apps/blockchain-node/src/aitbc_chain/consensus/rotation.py - Validator rotation
• apps/blockchain-node/src/aitbc_chain/consensus/slashing.py - Slashing conditions

Next

• Quick Start — Get started
• Validator Operations - Validator guide
• Networking - P2P networking