Fast Byzantine Fault Tolerance (FBFT)

Harmony’s consensus algorithm, Fast Byzantine Fault Tolerance (FBFT), is an innovative adaptation of the Practical Byzantine Fault Tolerance (PBFT) algorithm. FBFT enhances scalability and speed by utilizing Boneh–Lynn–Shacham (BLS) aggregate signatures, which significantly reduce communication overhead, allowing the network to achieve consensus rapidly and efficiently.

In FBFT, the consensus process involves a leader and three phases: announce, prepare, and commit. The leader proposes a new block and broadcasts its hash to validators during the announce phase. Validators then verify the message, sign the block hash, and return their signatures to the leader. The prepare phase concludes once signatures representing over two-thirds of the voting power are collected.

The leader aggregates these signatures into a single BLS aggregate signature and broadcasts it along with the full block to initiate the commit phase. Validators then verify the block and repeat the signing process. Consensus is reached once the commit phase concludes, typically within 2 seconds on the mainnet, demonstrating FBFT’s efficiency.

FBFT’s design includes a synchronous view change protocol to address potential stalls in consensus due to malicious leaders. Unlike PBFT, which relies on a timeout mechanism, Harmony’s view change protocol is based on local clocks and the elapsed time since the last successfully committed block, ensuring robustness and functionality even when nodes experience downtime or desynchronization.

This synchronous view change, combined with the use of BLS aggregate signatures, ensures the liveness of the FBFT consensus and maintains the network’s efficiency and security. The protocol’s design guarantees that as long as a supermajority of honest validators are online, the consensus process remains live and resilient to faults.

Effective Proof-of-Stake (EPoS)

Harmony’s Effective Proof-of-Stake (EPoS) is a novel staking mechanism designed to enhance network security and decentralization. EPoS addresses the limitations of traditional Proof-of-Stake (PoS) systems by introducing features that prevent stake centralization and ensure a fair distribution of rewards among validators.

EPoS allows validators to be elected based on their staked tokens, with the mechanism encouraging validators to run multiple nodes if they possess a large amount of stake, thereby supporting the network’s security and scalability. This system ensures that validators with smaller stakes can still participate effectively in the network, promoting inclusivity and decentralization.

The EPoS mechanism is designed to randomly and evenly distribute stakes across all shards, enhancing the security of each shard and preventing any single shard from being less secure than others. This distribution also mitigates the risk of shard takeovers and enhances the overall resilience of the network.

EPoS incorporates slashing conditions to penalize malicious behavior, such as double-signing, and to penalize elected but unavailable nodes, ensuring that all validators contribute positively to network security and reliability. This approach incentivizes validators to maintain high uptime and adhere to network protocols.

The economic model of EPoS caps annual token issuance and burns all transaction fees, aiming for zero inflation when network usage is high. This model provides validators with a predictable return on their staked tokens, encouraging long-term participation and investment in the network’s health and growth.

Comparison with Other Consensus Mechanisms

Harmony’s FBFT and EPoS consensus mechanisms offer distinct advantages over traditional consensus models like Proof of Work (PoW) and standard PoS. FBFT’s efficiency in reaching consensus, enabled by BLS aggregate signatures, allows for rapid transaction finality and reduced communication overhead, making it significantly faster and more scalable than PBFT and PoW-based systems.

EPoS addresses the centralization concerns associated with traditional PoS mechanisms by ensuring a fair and inclusive validator election process and equitable reward distribution. This system enhances network security and decentralization by preventing stake concentration and promoting validator diversity.

The combination of FBFT and EPoS positions Harmony as a more energy-efficient, scalable, and secure blockchain platform compared to PoW blockchains, which are characterized by high energy consumption and slower transaction finality. Harmony’s consensus mechanisms also offer improvements in terms of inclusivity and fairness over traditional PoS systems, which can favor wealth concentration among validators.

Highlights

• Harmony’s Fast Byzantine Fault Tolerance (FBFT) is an advanced version of PBFT, utilizing BLS aggregate signatures to reduce communication costs and achieve consensus within 2 seconds, enhancing scalability and speed.
• FBFT operates through a leader-based model with announce, prepare, and commit phases, ensuring rapid consensus with a requirement for over two-thirds of validators’ agreement, maintaining network efficiency and security.
• The synchronous view change protocol in FBFT addresses potential stalls due to malicious leaders by relying on local clocks for timekeeping, ensuring the consensus remains live and robust even with node downtime.
• Effective Proof-of-Stake (EPoS) in Harmony introduces a fair staking and validator election mechanism that prevents stake centralization, supports multiple nodes for large stakeholders, and ensures equitable reward distribution.
• EPoS enhances shard security by evenly distributing stakes across all shards and incorporates slashing conditions to penalize malicious behaviors, promoting network reliability and validator accountability.
• Compared to traditional consensus mechanisms like PoW and PoS, Harmony’s FBFT and EPoS offer faster transaction finality, lower energy consumption, greater scalability, and improved security and decentralization, setting a new standard in blockchain consensus models.