Latest Developments and Applications of Blockchain Consensus Protocols

Blockchain technology, as a decentralized distributed ledger technology, ensures the integrity and consistency of data through consensus mechanisms. The consensus mechanism is the core of the blockchain system, and its performance directly affects the scalability and security of the blockchain. Asynchronous Byzantine Fault Tolerance (BFT) consensus mechanisms have unique advantages in dealing with network delays and partial node failures, making them the focus of research.

This report explores the current development status of blockchain consensus protocols, focusing on the latest advancements in Asynchronous Byzantine Fault Tolerant State Machine Replication (BFT SMR) protocols. The fastest asynchronous protocol currently is 2-chain VABA, but due to its vulnerabilities, its expected latency of 9.5δ has not been achieved. Therefore, sMVBA has become the fastest asynchronous MVBA protocol, with an expected latency of 10δ. The report also introduces two new protocol designs, namely 2PAC (2-phase Asynchronous Consensus) and Ultra-Fast Pipelined Blocks, demonstrating significant improvements in throughput and latency.

Models and Definitions

In the asynchronous BFT model, the system consists of n = 3f + 1 processes, where f processes may be maliciously compromised by an adversary. These processes communicate with each other through asynchronous channels, and the message delivery delays are controlled by the adversary. Each process has a pair of public and private keys for signing and verification, ensuring the authenticity and integrity of the messages.

Blockchain Consensus

Blockchain consensus protocols aim to achieve agreement among all honest nodes regarding the state of the blockchain. Specifically, each node continuously receives new transactions and packages them into blocks, ensuring that these blocks reach consensus across all honest nodes through the consensus protocol. Blockchain consensus protocols must meet the following basic requirements:

• Liveness: In infinite execution, there exists an infinitely long decided blockchain.
• Consistency: If there are two decided blockchains, one must be a prefix of the other.
• P-Quality: In a determined blockchain, the proportion of transactions input by honest nodes is at least p.

Challenges of Current Asynchronous Consensus Protocols

The currently fastest asynchronous consensus protocol is 2-chain VABA, with an expected delay of 9.5δ. However, research has found that this protocol has various attack vectors that undermine its consistency and liveness. For example, attacks stemming from a lack of authentication checks, attacks that hinder liveness using elevation strategies, and consistency attacks caused by relaxed definitions of leader authentication, among others. Although 2-chain VABA introduces some new mechanisms, such as running multiple parallel instances, it still fails to completely resolve these issues.

New Protocol Design: 2PAC (2-Phase Asynchronous Consensus)

Based on the analysis of existing protocols, researchers proposed the 2PAC protocol. This protocol significantly improves performance by simplifying and optimizing the consensus process. Specifically, it includes two variants:

2PAClean:

• Achieved +90% throughput and an expected delay of 9.5δ, with a message complexity of O(n²).
• The efficiency of the protocol has been improved by eliminating unnecessary interactions and computational overhead.

2PACBIG:

• It is currently the fastest blockchain consensus protocol with a message complexity of O(n³).
• The faultless single MVBA runtime is 4δ, greatly reducing latency.

Ultra-Fast Pipeline Block

Researchers proposed a new pipelined block design that significantly reduces the latency of pipelined blocks. By introducing a fast path mechanism, under a fair scheduler, the decision time of pipelined blocks is even smaller than that of non-pipelined blocks. This mechanism guarantees the latency of the fast path in all executions and is not affected by the behavior of faulty processes.

Quantitative Results

Through theoretical analysis and practical testing, 2PAClean has an expected delay of 9.5δ in the worst case, while in the good case (no failures and semi-fair scheduler) it is 6δ. In contrast, the expected delay of sMVBA is 10δ, and in the good case it is 6δ. Therefore, 2PAClean reduces the worst-case delay by 0.5δ while maintaining the same good-case delay. Additionally, the throughput of 2PAClean is improved by 80% to 100% compared to the chain-based sMVBA, primarily due to the avoidance of unnecessary block discards and computational overhead in the new design.

2PACBIG, with a message complexity of O(n³), has a single MVBA runtime of 4δ, making it faster than all existing protocols. Additionally, the ultra-fast pipelined block design allows s2PAClean and s2PACBIG to achieve pipelined block decision times of 4δ and 3δ respectively, further enhancing the performance of the protocol.

Calculation Assessment

To verify the performance of the new protocol, researchers conducted extensive computational evaluations. The results showed that 2PAClean and 2PACBIG exhibited excellent performance under various network conditions, particularly in environments with high latency and high failure rates. Specifically, 2PAClean achieved a good balance between messaging delay and computational complexity, while 2PACBIG achieved lower latency through parallelization and optimization of the voting process.

As blockchain technology continues to evolve, asynchronous BFT consensus protocols will play an increasingly important role in ensuring security and enhancing performance. The design of 2PAC and ultra-fast pipelined blocks showcases the future direction of blockchain consensus protocols, which is to achieve higher throughput and lower latency by simplifying the protocol structure and optimizing the consensus process.

Future Research Directions

Future research can further explore the following directions:

1. Protocol Optimization: Further simplify and optimize the protocol structure, reducing unnecessary message passing and computational overhead.

2. Security Analysis: Conduct an in-depth analysis of the new protocol's security under various attack scenarios to ensure its reliability in practical applications.

3. Practical Application: Apply the new protocol in actual blockchain systems to verify its performance in real network environments.

This report provides a detailed analysis of the advantages and disadvantages of current asynchronous blockchain consensus protocols and presents two new protocol designs, namely 2PAC and Ultra-Fast Pipelined Blocks. The new designs show significant advantages in improving throughput and reducing latency, providing important references for the future development of blockchain technology. These new protocols not only demonstrate their superiority theoretically but also showcase excellent performance in practical testing, offering new ideas for achieving efficient and secure blockchain consensus protocols.

Through continuous research and optimization, blockchain technology will play an increasingly important role in the future digital economy, while the new generation of consensus protocols will provide a solid foundation for the development of this technology.