LIFT: Byzantine Resilient Hub-Sampling

TL;DR

This paper introduces LIFT, a protocol enhancing the Elevator peer sampling method by using cryptographically secure randomness to resist Byzantine attacks, significantly improving network robustness against malicious nodes.

Contribution

LIFT extends Elevator with cryptographically secure hub selection, providing Byzantine resilience up to 10% malicious nodes, a notable improvement over prior methods.

Findings

Elevator is vulnerable to 2% Byzantine nodes.

LIFT withstands up to 10% Byzantine nodes.

Secure randomness is crucial for Byzantine resilience.

Abstract

Recently, a novel peer sampling protocol, Elevator, was introduced to construct network topologies tailored for emerging decentralized applications such as federated learning and blockchain. Elevator builds hub-based topologies in a fully decentralized manner, randomly selecting hubs among participating nodes. These hubs, acting as central nodes connected to the entire network, can be leveraged to accelerate message dissemination. Simulation results have shown that Elevator converges rapidly (within 3--4 cycles) and exhibits robustness against crash failures and churn. However, its resilience to Byzantine adversaries has not been investigated. In this work, we provide the first evaluation of Elevator under Byzantine adversaries and show that even a small fraction (2%) of Byzantine nodes is sufficient to subvert the network. As a result, we introduce LIFT, a new protocol that extends Elevator by employing a cryptographically secure pseudo-random number generator (PRNG) for hub selection, thereby mitigating Byzantine manipulation. In contrast, LIFT withstands adversarial infiltration and remains robust with up to 10% Byzantine nodes. These results highlight the necessity of secure randomness in decentralized hub formation and position LIFT as a more reliable building block for Byzantine-resilient decentralized systems.