합의 알고리즘 [완료] (??? / Jace)

Overview of the QBFT Consensus Protocol Mechanism

The Quorum Byzantine Fault Tolerance (QBFT) consensus mechanism is a variant of Byzantine Fault Tolerant algorithms, designed for enterprise blockchain platforms that demand high performance, security, and immediate finality. This document outlines the core structure and functioning of QBFT, maintaining the original technical description while adding contextual insights for better understanding.

Byzantine Fault Tolerance (BFT)

QBFT is based on the Byzantine fault tolerance principle, which allows the blockchain network to tolerate up to one-third of its participants behaving maliciously or failing. This fault tolerance property ensures that the network can continue to operate correctly and reach consensus even in the presence of Byzantine faults.

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Note: This means that in a network with 10 validators, up to 3 may behave incorrectly without compromising the safety or liveness of the protocol.

Validator Nodes

In QBFT, the blockchain network consists of a set of validator nodes that participate in the consensus process. These validator nodes are typically selected based on their reputation, identity, or stake in the network.

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Validator selection mechanisms may vary depending on network architecture — they can be fixed, rotated periodically, or selected dynamically through staking or governance mechanisms.

Round-Based Consensus

QBFT operates on a round-based consensus mechanism, where each round consists of a series of steps performed by validator nodes to propose, validate, and agree on a new block of transactions.

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Key Insight: Each round ensures steady progress of the blockchain. In case of failure or timeout, the protocol can switch to the next round with a new proposer.

Proposal Phase

During the proposal phase of each round, a designated validator node proposes a new block of transactions to be added to the blockchain. The proposed block includes a cryptographic hash of the previous block, a timestamp, and a set of transactions.

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Clarification: The designated proposer is typically chosen in a round-robin or deterministic way, ensuring fair participation among validators.

Validation Phase

In the validation phase, validator nodes validate the proposed block by verifying its cryptographic signature, checking the correctness of the transactions, and ensuring that the proposed block follows the consensus rules of the network.

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Validator Role: Validators must reject blocks that are malformed or violate protocol rules, ensuring only valid blocks are committed.

Agreement Phase

Once a supermajority (two-thirds or more) of validator nodes have validated the proposed block, the network reaches an agreement to add the block to the blockchain. This agreement is achieved through a voting process, where validator nodes broadcast their votes to other nodes in the network.

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Consensus Rule: Broadcasting votes ensures all honest nodes are aware of the decision, and supports deterministic agreement without relying on probabilistic finality.

Commitment Phase

In the commitment phase, validator nodes commit to the agreed-upon block by appending it to their local copies of the blockchain. Once a block is committed by a supermajority of validator nodes, it becomes part of the canonical blockchain and is considered immutable.

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Finalization: At this point, the block is irrevocably part of the chain, and cannot be removed or altered unless by network-level intervention (which typically isn't possible in a BFT model).

Finality

QBFT provides fast finality, meaning that once a block is committed by a supermajority of validator nodes, it is considered finalized and cannot be reversed. This property ensures that transactions are confirmed quickly and with a high degree of certainty.

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Enterprise Advantage: Finality in QBFT is immediate and deterministic, unlike probabilistic models (e.g., PoW) that require multiple confirmations to ensure irreversibility.

Resilience to Byzantine Faults

QBFT is resilient to Byzantine faults, meaning that the network can continue to operate correctly even if up to one-third of validator nodes behave maliciously or fail. This resilience is achieved through a combination of cryptographic techniques, consensus rules, and redundancy mechanisms.

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Security Model: This level of fault tolerance makes QBFT suitable for mission-critical applications where trust minimization and data integrity are essential.

Performance and Scalability

QBFT is designed to provide high throughput and low latency, making it suitable for applications requiring fast transaction processing and responsiveness. The protocol's efficiency allows it to scale to support a large number of validator nodes and transactions per second.

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Scalability Note: While QBFT performs best in permissioned environments, careful tuning (e.g., block size, timeout settings) can support horizontal scaling for larger validator sets.