1. What is qBFT?
qBFT (Quorum Byzantine Fault Tolerance) is a blockchain consensus mechanism belonging to the Byzantine Fault Tolerance (BFT) family, designed for networks with a defined and identity-verified set of validator nodes. In qBFT, validators take turns proposing new blocks and participating in confirmation voting. A block is only accepted when it reaches the minimum consensus threshold, typically two-thirds or more of all validators.
Thanks to its quorum-based voting mechanism, qBFT delivers instant finality, meaning confirmed transactions cannot be reversed once a block is recorded on the blockchain. According to Hyperledger Besu documentation, qBFT is one of the recommended consensus mechanisms for permissioned blockchains, achieving high performance, low latency, and Byzantine fault tolerance without the energy consumption of public blockchain consensus mechanisms.
2. Byzantine Fault Tolerance: the foundation of qBFT
To understand qBFT, it is first necessary to understand Byzantine Fault Tolerance (BFT), the ability of a distributed system to maintain correct consensus even when some nodes encounter errors, are attacked, or deliberately send false information. This concept originates from the Byzantine Generals Problem, a classic computer science problem about achieving consensus in an environment that is not fully trustworthy.
According to BFT theory, a network can continue to operate safely as long as the number of dishonest or faulty nodes does not exceed one third of the total nodes participating in consensus. This is the foundation of algorithms such as PBFT and qBFT, enabling blockchains to maintain data integrity and Byzantine fault resistance. Inheriting this principle, qBFT allows NDAChain to continue operating stably even when some validators encounter failures or behave incorrectly.
3. How does qBFT work?
qBFT operates through consensus rounds, in which validators coordinate to validate transactions and create new blocks. Each consensus round on a qBFT blockchain typically proceeds through the following steps:
Proposer selection: A validator is designated in rotation as the proposer for the current round.
Block proposal (Pre-Prepare): The proposer creates a new block containing valid transactions and sends it to all validators in the network.
Validation and voting (Prepare): Validators check the validity of the block and send confirmation messages if the block meets the consensus rules.
Block commitment (Commit): When the number of consensus votes reaches the minimum threshold, typically more than two-thirds of all validators, the block is approved.
Transaction finality: The block is recorded on the blockchain with instant finality, and cannot be reversed or replaced by another branch.
If the proposer encounters an error or fails to respond, the Round Change mechanism automatically selects a new proposer to continue the consensus process. As a result, qBFT maintains network continuity and ensures stable operation even when some validators experience failures.
4. Instant finality: qBFT's standout advantage
One of the most important advantages of qBFT (Quorum Byzantine Fault Tolerance) is its ability to achieve instant finality. Unlike blockchains using Proof of Work (PoW), where transactions must wait for multiple block confirmations to reduce the risk of reversal, qBFT considers a transaction final as soon as the block is approved by validators and recorded on the blockchain.
🔑 Read more: Proof of Work (PoW): What it is and why national blockchain doesn't use it
qBFT's instant finality delivers several important benefits:
No temporary forks: The blockchain maintains a single chain, with no competing branches appearing as on many public networks.
Near-instant transaction confirmation: Users and systems can trust the result immediately after a block is confirmed.
Suited to real-time services: Meets the requirements of digital identity, data verification, traceability, and transactions requiring fast response.
Legal certainty assurance: Data once confirmed cannot be reversed, creating a reliable foundation for public services and national data infrastructure.
Instant finality is one of the key reasons qBFT has become a suitable choice for enterprise blockchains and national blockchains like NDAChain.
5. PoA-qBFT: NDAChain combines Proof of Authority and qBFT
NDAChain operates on the PoA-qBFT (Proof of Authority - Quorum Byzantine Fault Tolerance) mechanism, combining the strengths of Proof of Authority (PoA) and qBFT to build a national blockchain platform that delivers both high performance and guaranteed transparency and accountability.
🔑 Read more: Proof of Authority (PoA): The consensus mechanism powering national blockchain
In this model:
Proof of Authority (PoA) determines who has the right to participate in transaction validation and network operation. Validator nodes are licensed organizations with verified identities and clearly defined legal accountability.
qBFT determines how validators reach consensus through the block proposal mechanism, threshold-based voting, and transaction confirmation with instant finality.
NDAChain is currently developing 49 public-private validators, comprising state management agencies, data organizations, and major enterprises in the digital ecosystem. Thanks to the PoA-qBFT mechanism, the network achieves performance of 1,200–3,600 TPS, a block creation time of approximately 2 seconds, and low confirmation latency, meeting the requirements of digital identity, data verification, traceability, and national-scale digital services.
🔑 Read more:Vietnam’s National Blockchain Platform Surpasses 5 Million Verified Transactions
The combination of PoA's legal authority and qBFT's Byzantine fault tolerance allows NDAChain to build a digital trust layer suited to national data infrastructure, where performance, data sovereignty, and auditability are all core requirements.
6. Why is qBFT suited to national blockchain?
qBFT is considered one of the most suitable consensus mechanisms for national blockchain, thanks to its ability to balance performance, security, and governance. This is also why many data infrastructure and permissioned blockchain platforms choose qBFT as their consensus foundation.
Outstanding advantages of qBFT include:
High performance: The voting-based consensus mechanism enables transactions to achieve instant finality, supports high TPS, and meets the large volume of public services, digital identity, and data verification demands.
Suited to permissioned networks: qBFT is designed for blockchains with a pre-defined validator set, fitting the national blockchain and licensed data infrastructure model.
Byzantine fault tolerance: The network maintains secure operation even when some validators encounter failures or behave outside the rules.
Energy efficiency: No mining activity or computational power competition as in Proof of Work (PoW) is required, reducing operational costs and aligning with sustainable development objectives.
🔑 Read more: Why is Vietnam building a national blockchain platform?
However, qBFT is not designed for public blockchain networks with thousands of anonymous validators. Instead, this mechanism performs best in systems with a clearly governed validator count, where simultaneous requirements for performance, auditability, and legal accountability apply, precisely the characteristics of a national blockchain like NDAChain.
7. qBFT and NDAChain's digital trust foundation
qBFT is the core consensus mechanism that enables NDAChain to operate at high speed, stability, and reliability at national scale. When combined with Proof of Authority (PoA), qBFT creates a consensus model where validators with verified identities and legal accountability collectively reach agreement with near-instant finality. As a result, transactions are confirmed quickly, irreversibly, and with transparent verifiability.
🔑 Read more: What makes NDAChain - Vietnam's national blockchain special?
For systems such as digital identity, data verification, traceability, and public services, these are foundational requirements. For this reason, PoA-qBFT is not merely a technical choice, it is the digital trust infrastructure layer that enables NDAChain to meet the requirements of performance, security, and data sovereignty in the digital era.
Frequently asked questions about qBFT (QBFT)
What is qBFT?
qBFT (QBFT, Quorum Byzantine Fault Tolerance) is a consensus mechanism belonging to the Byzantine Fault Tolerance family, optimized for networks with a defined validator set. Validators take turns proposing blocks, and a block is accepted when more than two-thirds of all validators agree. qBFT delivers instant finality, once a block is confirmed, it cannot be reversed.
How does qBFT work?
qBFT operates in rounds: a validator is selected as proposer in rotation; the proposer creates a block and sends it to all validators (Pre-Prepare); validators check and agree (Prepare); when more than two-thirds agree, the block is committed (Commit); and the block is added to the chain with instant finality. If the proposer fails, the round-change mechanism selects a new proposer.
How does qBFT differ from Proof of Work?
qBFT delivers instant finality, a committed block is final and irreversible while PoW only provides probabilistic finality after multiple block confirmations. qBFT requires no mining, so it is energy-efficient and achieves high TPS, whereas PoW is energy-intensive and slow. qBFT suits networks with a defined validator set; PoW suits open anonymous networks.
What is NDAChain's PoA-qBFT?
PoA-qBFT is a combination of Proof of Authority and qBFT. PoA determines who may serve as a validator, licensed organizations with verified identities and legal accountability. qBFT determines how validators reach consensus through rotating proposals and threshold-based voting, achieving instant finality. NDAChain uses PoA-qBFT with 49 public-private validators, achieving 1,200–3,600 TPS.
Why is qBFT suited to national blockchain?
qBFT is suited because it delivers instant finality and achieves high TPS without mining; it is designed for networks with a defined validator set, fitting the permissioned model; it tolerates Byzantine faults from up to approximately one-third of validators, ensuring reliability; and it is energy-efficient. These characteristics align with the requirements of a licensed national infrastructure like NDAChain.
