Latest Developments and Applications of Blockchain Consensus Protocols

Report Summary

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 was originally 2-chain VABA, but due to vulnerabilities, its expected latency of 9.5δ was not achieved. As a result, sMVBA has become the fastest asynchronous MVBA protocol, with an expected latency of 10δ. The report also presents two new protocol designs, namely 2PAC (2-phase Asynchronous Consensus) and Ultra-Fast Pipelined Blocks, which demonstrate significant improvements in throughput and latency.

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 mechanism has unique advantages in dealing with network delays and partial node failures, thus becoming the 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 transmission delay is controlled by the adversary. Each process has a pair of public and private keys for signing and verification, ensuring the authenticity and integrity of 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 reach consensus among all honest nodes through the consensus protocol. 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 finalized blockchains, one must be a prefix of the other.
3. P Quality: In the decided Blockchain, the proportion of transactions input by honest nodes is at least p.

Challenges of Current Asynchronous Consensus Protocols

The current fastest asynchronous Consensus protocol was originally the 2-chain VABA, with an expected latency of 9.5δ. However, research has found that this protocol has various attack vectors that undermine its consistency and liveness. For example, attacks resulting from the lack of authentication checks, attacks that hinder liveness by exploiting promotion strategies, and consistency attacks resulting from the relaxation of leader authentication definitions, among others. Although the 2-chain VABA introduced some new mechanisms, such as running multiple parallel instances in parallel, it still has not fully resolved these issues.

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

Based on the analysis of existing protocols, the study 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 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 fault-free single MVBA runtime is 4δ, significantly reducing latency.

Super Fast Pipeline Block

The research proposes a new pipelined block design that significantly reduces the latency of pipelined blocks. By introducing a fast path mechanism, the decision time for pipelined blocks is even smaller than that for non-pipelined blocks under a fair scheduler. 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 failures and semi-fair scheduler) 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 attributed to avoiding unnecessary Block discards and computational overhead in the new design.

2PACBIG, as a protocol with message complexity 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 Assessment

To validate the performance of the new protocol, extensive computational evaluations were conducted. The results showed that 2PAClean and 2PACBIG demonstrated excellent performance under various network conditions, particularly in high latency and high failure rate 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 development direction of Blockchain Consensus protocols, which is to achieve 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 new protocol's security under various attack scenarios to ensure its reliability in practical applications.
3. Practical Application: Apply the new protocol to real blockchain systems to verify its performance in a real network environment.

This report provides a detailed analysis of the advantages and disadvantages of the current asynchronous Blockchain Consensus protocol, and proposes two new protocol designs: 2PAC and ultra-fast pipelined Block. The new designs demonstrate significant advantages in increasing throughput and reducing latency, providing important references for the future development of Blockchain technology. These new protocols not only prove their superiority theoretically but also showcase exceptional performance in practical testing, offering new ideas for achieving efficient and secure Blockchain Consensus protocols.

Through continuous research and optimization, Blockchain technology is expected to 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.