The 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 impacts the scalability and security of the blockchain. Asynchronous Byzantine Fault Tolerance (BFT) consensus mechanism has unique advantages in dealing with network latency and partial node failures, thus becoming the 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 current fastest asynchronous protocol is 2-chain VABA, with an expected delay of 9.5δ. However, due to vulnerabilities, this protocol has failed to achieve its expected performance. Therefore, sMVBA has become the fastest asynchronous MVBA protocol currently, with an expected delay of 10δ. The report also presents 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. These processes communicate with each other through asynchronous channels, and the message transmission delay is uncontrollable. 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. Each node continuously receives new transactions, packages them into blocks, and uses the consensus protocol to ensure that these blocks are agreed upon by all honest nodes. The blockchain consensus protocol needs to 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.

Challenges of the Current Asynchronous Consensus Protocol

The 2-chain VABA protocol, although expected to have a delay of 9.5δ, is subject to various attack methods that compromise its Consensus and liveness. For example, attacks resulting from a lack of verification and authentication, attacks that hinder liveness using enhancement strategies, and consistency attacks due to a relaxed definition of leader authentication, among others. Although the protocol introduces some new mechanisms, such as multiple parallel instances running concurrently, it still fails to fully address 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).
   • 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 runtime is 4δ, significantly reducing latency.

Ultra-Fast Pipeline Block

Researchers 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 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 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 comparison, the expected delay of sMVBA is 10δ, with a good case of 6δ. Therefore, 2PAClean reduces the worst-case delay by 0.5δ while maintaining the same good case delay. Moreover, the throughput of 2PAClean improves 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 a message complexity of O(n³), has a single MVBA runtime of 4δ, making it faster than all existing protocols. Furthermore, 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 verify the performance of the new protocol, researchers conducted extensive computational evaluations. The results showed that 2PAClean and 2PACBIG demonstrated excellent performance under various network conditions, especially in environments with high latency and high failure rates. Specifically, 2PAClean achieved a good balance between message transmission latency and computational complexity, while 2PACBIG realized 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: In-depth analysis of the new protocol's security in 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 a real network environment.

With the continuous development of blockchain technology, 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 the protocol structure and optimizing the consensus process.

These new protocols not only demonstrate their superiority theoretically but also showcase excellent performance in practical tests, providing new ideas for achieving efficient and secure Blockchain Consensus protocols. With continuous research and optimization, 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.