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 at the core of blockchain systems, 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 latency and partial node failures, making them a 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 delay of 9.5δ has not been achieved. Therefore, sMVBA has become the fastest asynchronous MVBA protocol, with an expected delay 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 delay.

Models and Definitions

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

• Activity: In infinite execution, there exists an infinitely long decided Blockchain.
• Consistency: If there are two determined Blockchains, one of them must be a prefix of the other.
• 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

The fastest asynchronous consensus protocol currently is 2-chain VABA, with an expected latency of 9.5δ. However, this protocol has various attack vectors that compromise its consistency and liveness. For instance, attacks due to a lack of verification and authentication, attacks that hinder liveness by exploiting elevation strategies, and consistency attacks caused by loosening the definition of leader authentication, among others. Although 2-chain VABA introduces some new mechanisms, such as multiple parallel instances running in parallel, it still fails to fully address these issues.

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 over 90% throughput and an expected delay of 9.5δ, with message complexity of O(n²).
   • The efficiency of the protocol has been improved 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 runtime is 4δ, greatly reducing latency.

Ultra-fast Pipeline Block

Researchers have 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 ensures that the latency of the fast path is guaranteed in all executions and is not affected by the behavior of faulty 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 (no faults and semi-fair scheduling) 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, mainly 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, which is faster than all existing protocols. In addition, 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, 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 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 development direction of blockchain consensus protocols, namely achieving 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 messaging and computational overhead.
2. Security Analysis: In-depth analysis of the security of the new protocol in 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.

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.