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 latency and partial node failures, making them a key focus of research.

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

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 are agreed upon by 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 decided Blockchains, one must be a prefix of the other.
• P Quality: In a decided Blockchain, the proportion of transactions input by honest nodes is at least p.

Challenges of the Current Asynchronous Consensus Protocol

The currently fastest asynchronous Consensus protocol is 2-chain VABA, with an expected delay of 9.5δ. However, this protocol has various attack vectors that undermine its consistency and liveness. For example, attacks resulting from a lack of verification and authentication, attacks that hinder liveness through elevation strategies, and consistency attacks due to a relaxed definition of leader authentication. Despite 2-chain VABA introducing some new mechanisms, such as multiple parallel instances running concurrently, it still has not fully resolved these issues.

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

Based on the analysis of existing protocols, 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 a 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 can be 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, the expected latency of 2PAClean in the worst case is 9.5δ, while in the good case (no failures and semi-fair scheduler) it is 6δ. In contrast, the expected latency of sMVBA is 10δ, and in the good case, it is 6δ. Therefore, 2PAClean reduces the worst-case latency by 0.5δ while maintaining the same good case latency. 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, as a protocol with message complexity of O(n³), has a single MVBA runtime of 4δ, which is 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 protocol's performance.

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, especially in high-latency and high-failure environments. Specifically, 2PAClean achieved a good balance between message transmission delay and computational complexity, while 2PACBIG realized 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 passing and computational overhead.
2. Security Analysis: 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 Blocks. The new designs demonstrate significant advantages in improving throughput and reducing latency, providing important references for the future development of Blockchain technology. These new protocols not only theoretically prove their superiority but also showcase excellent performance in practical tests, 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.