Source: Matthieu Rambaud, Télécom Paris
Adapted by: Anonymous, Bijie.com
Report Summary
This report explores the development status of blockchain consensus protocols, focusing on the latest progress of the asynchronous Byzantine Fault Tolerant State Machine Replication (BFT SMR) protocol. The fastest asynchronous protocol currently is 2-chain VABA, but due to its loopholes, its expected latency of 9.5δ has not been achieved. As a result, sMVBA becomes the fastest asynchronous MVBA protocol currently 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.
As a decentralized distributed ledger technology, blockchain technology ensures the integrity and consistency of data through a consensus mechanism. 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 Tolerant (BFT) consensus mechanism has unique advantages in dealing with network delays and partial node failures, so it has become the focus of research.
Model and Definition
In the asynchronous BFT model, the system consists of n = 3f + 1 processes, of which f processes may be maliciously damaged by the adversary. These processes communicate with each other through asynchronous channels, and the message delivery delay is controlled by the adversary. Each process has a pair of public and private keys for signing and verification to ensure the authenticity and integrity of the message.
Blockchain consensus
The blockchain consensus protocol aims to make all honest nodes agree on the state of the blockchain. Specifically, each node continuously receives new transactions and packages them into blocks, and the consensus protocol ensures that these blocks are agreed upon by all honest nodes. The blockchain consensus protocol needs to meet the following basic requirements:
Liveness: In an infinite execution, there exists an infinitely long chain of determined chains.
Consistency: If there are two determined blockchains, one must be a prefix of the other.
P-Quality: The percentage of transactions entered by honest nodes in the decided blockchain is at least p.
Challenges of Current Asynchronous Consensus Protocols
The fastest asynchronous consensus protocol currently is 2-chain VABA, which has an expected latency of 9.5δ. However, we found that the protocol has multiple attack methods that undermine its consistency and activity. For example, attacks caused by lack of check authentication, attacks that hinder activity using promotion strategies, and consistency attacks caused by relaxing the definition of leader authentication. Although 2-chain VABA introduces some new mechanisms, such as multiple parallel instances running in parallel, these problems have not been completely solved.
New protocol design: 2PAC (2-phase asynchronous consensus)
Based on the analysis of existing protocols, we proposed the 2PAC protocol. The 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 O(n²) message complexity.
The efficiency of the protocol is 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 single MVBA run time without failure is 4δ, which greatly reduces latency.
Ultra-fast pipeline blocks
We propose a new pipeline block design that significantly reduces pipeline block latency. By introducing the fast path mechanism, under the fair scheduler, the decision time of pipeline blocks is even smaller than that of non-pipeline blocks. This mechanism guarantees fast path latency in all executions and is unaffected by the behavior of failed processes.
Quantitative results
Through theoretical analysis and actual testing, 2PAClean has an expected latency of 9.5δ in the worst case and 6δ in the good case (no failures and semi-fair scheduler). In contrast, sMVBA has an expected latency of 10δ and 6δ in the good case. Therefore, 2PAClean reduces the worst-case latency by 0.5δ while maintaining the same good-case latency. In addition, 2PAClean's throughput is improved by 80% to 100% compared to chained sMVBA, mainly due to the avoidance of unnecessary block discards and computational overhead in the new design.
As a protocol with message complexity of O(n³), 2PACBIG has a single MVBA running time of 4δ, which is faster than all existing protocols. In addition, the ultra-fast pipeline block design enables s2PAClean and s2PACBIG to achieve pipeline block decision times of 4δ and 3δ respectively, further improving the performance of the protocol.
Computational evaluation
To verify the performance of the new protocol, we conducted extensive computational evaluations. The results show that 2PAClean and 2PACBIG exhibit excellent performance under various network conditions, especially in high-latency and high-failure environments. Specifically, 2PAClean achieves a good balance between message delivery latency and computational complexity, while 2PACBIG achieves lower latency by parallelizing and optimizing the voting process.
As blockchain technology continues to develop, asynchronous BFT consensus protocols will play an increasingly important role in ensuring security and improving performance. The design of 2PAC and ultra-fast pipeline blocks demonstrates the development direction of future blockchain consensus protocols, which is to achieve higher throughput and lower latency by simplifying the protocol structure and optimizing the consensus process.
Future research can further explore the following directions:
Protocol optimization: further simplify and optimize the protocol structure to reduce unnecessary message passing and computing overhead.
Security analysis: In-depth analysis of the security of the new protocol under various attack scenarios to ensure its reliability in practical applications.
Practical application: Apply the new protocol to the actual blockchain system to verify its performance in the real network environment.
This report analyzes the advantages and disadvantages of current asynchronous blockchain consensus protocols in detail, and proposes two new protocol designs, namely 2PAC and ultra-fast pipeline blocks. The new design shows significant advantages in improving throughput and reducing latency, providing an important reference for future blockchain technology development. These new protocols not only prove their superiority in theory, but also demonstrate excellent performance in actual tests, providing new ideas for realizing efficient and secure blockchain consensus protocols.
Through continuous research and optimization, we have reason to believe that blockchain technology will play a more 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.
