StealthDust: Secret Quorums for Faster Fractional Spending
Maxence Perion, Sara Tucci-Piergiovanni, Rida Bazzi
TL;DR
This work tackles the Fractional Spending Problem in fully asynchronous, Byzantine environments by introducing Secret Quorums and instantiating them with ring verifiable random functions (rVRF) to protect quorum composition against rushing adaptive adversaries. Building on $(k_1,k_2)$-quorum systems, the authors present StealthDust, a protocol that reduces payment latency from five to three communication steps and lowers settlement complexity from $O(n^3)$ to $O(n^2)$. Key contributions include the Secret Quorums abstraction with unpredictability, anonymity, and verifiability guarantees, the practical realization via rVRF and ring signatures, and an efficient fractional-spending protocol that preserves safety and liveness without full consensus. The approach enables parallel validation of multiple fractional payments across shared funds while maintaining privacy and robustness, offering a scalable alternative for decentralized asset transfer in adversarial settings.
Abstract
With the goal of building a decentralized and fully parallel payment system, we address the Fractional Spending Problem using (k1, k2)-quorum systems - both introduced by Bazzi and Tucci-Piergiovanni (PODC 2024). Fractional spending enables payments without immediate validation of an entire quorum, as necessary in classical approaches. Multiple spending from a same fund can occur concurrently, with final settlement involving previously contacted quorums. To tolerate a rushing-adaptive adversary, the composition of these quorums must stay hidden until settlement succeeds. We propose a new abstraction called secret quorums - of independent interest - that fulfill this property and implement it through ring verifiable random functions. We then propose a new protocol called StealthDust, where secret quorums allow to reduce payment latency from five to three communications steps and improve settlment message complexity from O(n^3) to O(n^2) compared to the original protocol.