Research on Blockchain Consensus Protocols: Latest Developments and Applications of Asynchronous BFT

Overview

This article explores the current state of development of blockchain consensus protocols, focusing on the latest advancements in Asynchronous Byzantine Fault Tolerant State Machine Replication (BFT SMR) protocols. Currently, sMVBA is the fastest asynchronous MVBA protocol, with an expected delay of 10δ. The article also introduces two new protocol designs: 2PAC (2-Phase Asynchronous Consensus) and Ultra-Fast Pipelined Blocks, which show significant improvements in throughput and latency.

Background

Blockchain technology is a decentralized distributed ledger technology that 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. The Asynchronous Byzantine Fault Tolerance (BFT) consensus mechanism has unique advantages in dealing with network delays and partial node failures, making it a focus of research.

Model and Definition

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

Blockchain Consensus Requirements

The blockchain consensus protocol must meet the following basic requirements:

1. Activity: In infinite execution, there exists an infinitely long decided Blockchain.
2. Consistency: If there are two decided blockchains, one must be a prefix of the other.
3. P Quality: In the determined Blockchain, the proportion of transactions input by honest nodes must be at least p.

Current Challenges of Asynchronous Consensus Protocols

Although the 2-chain VABA protocol was once considered the fastest asynchronous Consensus protocol, with an expected latency of 9.5δ, research has found that the protocol is vulnerable to various attack methods that undermine its consistency and liveness. These issues include attacks resulting from a lack of verification authentication, attacks that hinder liveness by exploiting elevation strategies, and consistency attacks caused by relaxing the definition of leader authentication.

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

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

1. 2PAClean:

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

2. 2PACBIG：

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

Super Fast Pipeline Block

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

Performance Evaluation

Through theoretical analysis and practical testing, the expected delay of 2PAClean in the worst case is 9.5δ, while in the good case (no faults and semi-fair scheduler) it is 6δ. In contrast, the expected delay of sMVBA is 10δ, with 6δ in the good case. 2PAClean reduces the worst-case delay by 0.5δ while maintaining the same good-case delay. Moreover, the throughput of 2PAClean improved by 80% to 100% compared to the chain-based sMVBA.

2PACBIG, as a protocol with a message complexity of O(n³), has a single MVBA runtime of 4δ, which is faster than all existing protocols. 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 Result

Extensive computational evaluations show that 2PAClean and 2PACBIG perform excellently under various network conditions, especially in environments with high latency and high failure rates. 2PAClean achieves a good balance between message transmission delay and computational complexity, while 2PACBIG realizes lower latency through parallelization and optimization of the voting process.

Future Research 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 to actual blockchain systems to verify its performance in real network environments.

Conclusion

This research 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 blocks. These new designs demonstrate significant advantages in increasing throughput and reducing latency, providing important references for the future development of Blockchain technology. Through continuous research and optimization, Blockchain technology is expected to 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.