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 a focus of research.

This report explores the current development status of Blockchain consensus protocols, with a focus on the latest advancements in asynchronous Byzantine Fault Tolerance State Machine Replication (BFT SMR) protocols. The fastest current asynchronous protocol is 2-chain VABA, but due to its vulnerabilities, it has failed to achieve its expected latency of 9.5δ. Therefore, sMVBA has become the fastest asynchronous MVBA protocol, with an expected latency of 10δ. The report also proposes two new protocol designs, namely 2PAC (2-Phase Asynchronous Consensus) and ultra-fast pipelined blocks, demonstrating significant improvements in throughput and latency.

Model and Definition

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

Blockchain Consensus

The blockchain consensus protocol aims to ensure that all honest nodes reach an agreement on the state of the blockchain. Specifically, each node continuously receives new transactions and packages them into blocks, ensuring that these blocks achieve consensus among all honest nodes through the consensus protocol. The blockchain consensus protocol needs to meet the following basic requirements:

• Liveness: In an 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 decided Blockchain, the proportion of transactions input by honest nodes must be at least p.

Current Challenges of Asynchronous Consensus Protocols

The fastest asynchronous consensus protocol currently is the 2-chain VABA, with an expected latency of 9.5δ. However, we have found that this protocol has multiple attack vectors that undermine its consistency and liveness. For example, attacks due to a lack of verification authentication, attacks that hinder liveness by exploiting enhancement strategies, and consistency attacks resulting from a relaxed definition of leader authentication. Although the 2-chain VABA introduces some new mechanisms, such as the parallel operation of multiple parallel instances, it still fails to fully address these issues.

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

Based on the analysis of the existing protocol, we propose 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 9.5δ expected latency, with message complexity of O(n²).
• Improved the efficiency of the protocol by eliminating unnecessary interactions and computational overhead.

2PACBIG：

• It is currently the fastest Blockchain Consensus protocol with a message complexity of O(n³).
• The fault-free single MVBA runtime is 4δ, greatly reducing latency.

Ultra-fast Pipeline Block

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

Quantitative Results

Through theoretical analysis and practical testing, the expected delay of 2PAClean in the worst case is 9.5δ, while in the good case (failure-free 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 improves by 80% to 100% compared to the chain-based sMVBA, primarily due to the new design avoiding unnecessary Block discards and computational overhead.

2PACBIG, with a message complexity of O(n³), has a single MVBA execution time of 4δ, which is faster than all existing protocols. Moreover, 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 Evaluation

To validate the performance of the new protocol, we 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 message transmission latency and computational complexity, while 2PACBIG achieved lower latency through parallelization and optimization of the voting process.

With the continuous development of Blockchain technology, the asynchronous BFT Consensus protocol will play an increasingly important role in ensuring security and improving performance. The design of 2PAC and ultra-fast pipelined Blocks demonstrates the future direction of Blockchain Consensus protocols, which is to achieve higher throughput and lower latency by simplifying protocol structures 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 transmission and computational overhead.

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

3. Practical Application: Apply the new protocol to 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 proposes two new protocol designs, namely 2PAC and ultra-fast pipelined Block. 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 outstanding performance in practical tests, offering new ideas for achieving efficient and secure Blockchain Consensus protocols.

Through continuous research and optimization, we have reason to believe that Blockchain technology will play an increasingly important role in the future digital economy, and the new generation of Consensus protocols will provide a solid foundation for the development of this technology.