Paper 2023/031 Original: eprint.iacr.org/2023/031 ↗

Sassafras: Efficient Batch Single Leader Election

Abstract

In a single secret leader election (SSLE), a set of participants elect exactly one leader, who remains anonymous until they announce themselves by providing a proof. SSLE protocols are used in proof-of-stake blockchains to elect the leader who publishes the next block. Anonymity of the leader is an important security property, as the leader makes for an attractive target and may be subject to denial-of-service (DOS) attacks. In this work, we propose a novel single leader election protocol, called Sassafras. We depart from the common approach of shuffling for constructing SSLE and instead employ a ring verifiable random function, which hides the identity of the leader within a ring of participants. Moreover, Sassafras is designed for batch leader elections, in which a single leader is selected for several elections at once. This allows the rate of leader election to match the rate of block production, an often-sought property not met by most SSLE protocols in the literature. We characterize single leader election with batching in the form of an ideal functionality in the Universal Composability (UC) framework and prove that Sassafras realizes this functionality. Sassafras is secure against an adaptive adversary, while achieving a slightly relaxed notion of anonymity for leaders. Sassafras features exceptionally low communication and computational complexity, outperforming other SSLE protocols by an order of magnitude or more.