Tyche: Collateral-Free Coalition-Resistant Multiparty Lotteries with Arbitrary Payouts

TL;DR

Tyche introduces efficient, collateral-free multiparty lottery protocols that are resistant to aborts and coalitions, utilizing blockchain for transparency without relying on external randomness or collateral.

Contribution

The paper presents novel protocols for multiparty lotteries that are secure, fair, privacy-preserving, and do not depend on third-party randomness or collateral, with practical blockchain implementation.

Findings

Protocols are secure and fair against aborts and coalitions.

Implementation on Sui blockchain shows low transaction fees.

Protocols can support millions of participants.

Abstract

We propose Tyche, a family of protocols for performing practically (as well as asymptotically) efficient multiparty lotteries, resistant against aborts and majority coalitions. Our protocols are based on a commit-and-reveal approach, requiring only a collision-resistant hash function. All our protocols use a blockchain as a public bulletin board and for buy-in collection and payout settlement. Importantly though, they do not rely on it or any other third party for providing randomness. Also, participants are not required to post any collateral beyond their buy-in. Any honest participant can eventually settle the lottery, and dishonest behavior never reduces the winning probability of any honest participant. Further, we adapt all three protocols into anonymous lotteries, where (under certain conditions) the winner is unlinkable to any particular participant. We show that our protocols are secure, fair, and some preserve the participants' privacy. Finally, we evaluate the performance of our protocols, particularly in terms of transaction fees, by implementing them on the Sui blockchain. There we see that per user transaction fees are reasonably low and our protocols could potentially support millions of participants.