Innovations in Consensus: An Academic Study of SSV Network

Thank you, Matheus, for your contributions, hands-on testing, and insights into these complex consensus algorithms.

SSV: an Academic Case Study of Consensus

The SSV Network is an interesting use case at the intersection of ETH staking and BFT consensus. As an open-source protocol, the SSV code base is open to testing from anyone. The SSV Network has recently garnered attention in the academic community for its innovative approach to decentralized systems. It was featured as a case study in a research paper presented at the prestigious 21st USENIX Symposium on Networked Systems Design and Implementation (NSDI 2024) in Santa Clara, CA.

This recognition highlights SSV’s position at the forefront of distributed validator technology (DVT) infrastructure. This blog post delves into the study’s findings, exploring if the SSV Network could leverage Alea-BFT to enhance performance and resilience over the current QBFT protocol.

Understanding SSV Network

SSV Network’s unique implementation of DVT enables it to be a permissionless network of nodes. Unlike traditional Ethereum validator node setups, SSV allows an ETH validator to be distributed between multiple nodes in a trustless and fault-tolerant manner. It does this by splitting the private key used for signing duties across multiple machines organized into a “cluster”.

One of the critical pillars of this network is consensus. As part of the node stack, the SSV Node allows a machine to communicate with the other nodes inside the SSV Network. These operator nodes (operators) with different EL/CL clients, locations, and hardware types can then coordinate with each other to securely run validators in a distributed manner with zero coordination.

Consensus in a Nutshell

In a distributed network, consensus guarantees that all nodes agree on the network’s current state, even in the presence of faults or failures. It aims to achieve trustworthy and tamper-resistant transaction records in a decentralized network. The consensus mechanism is the core set of rules followed by nodes, which determine various important characteristics, such as security, scalability, and decentralization.

In the SSV Network, nodes communicate with one another by sending messages, which allows them to reach a consensus on the execution of validator duties. By reaching a consensus and using threshold signing, a cluster can collectively sign duties on behalf of the validator with encrypted keyshares, allowing for a certain amount of nodes to go offline while still being able to produce a valid signature. Therefore, SSV dramatically improves fault tolerance and decentralizes node operations for ETH re/staking applications.

The Study

Researchers from the Instituto Superior Técnico (ULisboa) and INESC-ID conducted a comprehensive study to evaluate the performance of Alea-BFT within the SSV Network. A notable contributor to this study is Matheus Franco, whose exceptional research on SSV Network began as his master’s thesis. Matheus demonstrated great promise, insight, and skill, which led him to become an integral part of the SSV Labs – one of the contributors to the ssv.network DAO.

The study measured the network’s base latency and throughput under various conditions, providing valuable insights into its practical applications. It provided valuable insights into the broader applications of novel consensus protocols within the SSV Network, highlighting the importance of exploring new consensus mechanisms to enhance the performance, resilience, and scalability of decentralized networks.

Key Insights from the Study

Safety and Integrity: The research emphasized the importance of maintaining safety properties such as integrity and total order within the network. Ensuring that each message appears only once and that all correct processes deliver messages in the same order is crucial for network reliability.
Liveness: The study demonstrated the protocol’s ability to guarantee progress and eventual message delivery, even under adverse conditions. This ensures that the network remains functional and responsive under different stressors.
Censorship Resilience: Alea-BFT’s design to prevent Byzantine replicas from delaying consensus termination was a significant focus. Allowing any replica to initiate a consensus process for a client request ensures timely and unbiased message delivery.

Real-World Implementations

Ethereum Distributed Validators

The study focused on implementing Alea-BFT in SSV’s distributed validator network. In this setup, the system progresses in fixed-duration slots (12 seconds each), with validators assigned specific duties such as block proposal and attestation. The base latency was measured by setting the number of duties per slot to one, while throughput was assessed by increasing the number of duties until performance peaked.

Performance Evaluation

The results showed that Alea-BFT, when combined with BLS aggregation and Hash-based message authentication codes (HMACs), achieved similar peak throughput and better latency compared to the existing QBFT-based codebase. This highlights Alea-BFT’s efficient design and how it effectively leverages cryptographic primitives even though it has more message steps than QBFT.

Inter-Replica Latency: The study revealed that Alea-BFT’s performance closely follows QBFT across different inter-replica latencies, with notable advantages in lower latency and higher throughput.
System Size: Alea-BFT demonstrated lower latency and higher throughput in larger group sizes, as defined by Ethereum’s smart contract settings.
Crash Fault Resilience: Alea-BFT proved more resilient to crash faults, quickly recovering and maintaining productivity, unlike QBFT, which experienced slight delays due to leader change protocols.

Tradeoff Analysis — Despite the results of Alea-BFT, research by SSV Labs suggested that the SSV DAO should choose to continue using QBFT in the SSV protocol. Here’s why:

Testing Protocols: QBFT was always tested using BLS, a slower but secure message authentication scheme. Alea-BFT, on the other hand, was tested with various schemes. While Alea-BFT showed better performance with HMAC, it did not outperform QBFT when both used BLS.
Fair Comparison: The comparison between Alea-BFT and QBFT wasn’t entirely fair since QBFT did not benefit from the same performance improvements with HMAC.
Latency and Practicality: With BLS, QBFT demonstrated better latency than Alea-BFT. Given that BLS was the standard scheme used in the SSV Network, this was a crucial factor in the decision.

The study’s gain was recognizing that Alea-BFT performed similarly (just slightly worse) to QBFT when both used BLS. This is significant because QBFT is a partially synchronous protocol, while Alea-BFT is asynchronous. Asynchronous protocols typically offer better resilience but come with a more complex design. This insight helps underline the robustness and suitability of QBFT for the SSV Network’s current needs.

Conclusion

In summary, the academic study highlights the SSV Network’s potential to improve consensus with Alea-BFT. The improved latency, throughput, and fault resilience demonstrated in the study point to a promising future for blockchain technology and decentralized systems. As we look ahead, continued research and development will be crucial in harnessing the SSV Network’s full potential.

Innovations in Consensus: An Academic Study of SSV Network