Deterministic Bounds in Committee Selection: Enhancing Decentralization and Scalability in Distributed Ledgers
Grigorii Melnikov, Sebastian Müller, Nikita Polyanskii, Yury Yanovich
TL;DR
The work tackles scalable and decentralized consensus in distributed ledgers by enforcing fixed-size committee selection through cryptographic sortition. It shifts from probabilistic guarantees to deterministic decentralization, introducing four fair algorithms—Stitch, Cumulative Rejection Sampling, Weighted Rejection Sampling, and Representative Electoral College—that provide explicit decentralization bounds tied to initial weights. Through numerical experiments on synthetic Zipf-weighted networks, the authors compare how these methods perform under varying weight distributions and show that Weighted Rejection Sampling and Representative Electoral College offer strong decentralization, with tunable parameters and practical runtimes. The results inform design choices for PoS-based systems, aiming to improve security and efficiency while maintaining proportional representation of participants.
Abstract
Consensus plays a crucial role in distributed ledger systems, impacting both scalability and decentralization. Many blockchain systems use a weighted lottery based on a scarce resource such as a stake, storage, memory, or computing power to select a committee whose members drive the consensus and are responsible for adding new information to the ledger. Therefore, ensuring a robust and fair committee selection process is essential for maintaining security, efficiency, and decentralization. There are two main approaches to randomized committee selection. In one approach, each validator candidate locally checks whether they are elected to the committee and reveals their proof during the consensus phase. In contrast, in the second approach, a sortition algorithm decides a fixed-sized committee that is globally verified. This paper focuses on the latter approach, with cryptographic sortition as a method for fair committee selection that guarantees a constant committee size. Our goal is to develop deterministic guarantees that strengthen decentralization. We introduce novel methods that provide deterministic bounds on the influence of adversaries within the committee, as evidenced by numerical experiments. This approach overcomes the limitations of existing protocols that only offer probabilistic guarantees, often providing large committees that are impractical for many quorum-based applications like atomic broadcast and randomness beacon protocols.