Pay To Win: Cheap, Crowdfundable, Cross-chain Algorithmic Incentive Manipulation Attacks on PoW Cryptocurrencies Aljosha Judmayer1;2, Nicholas Stifter1;2, Alexei Zamyatin3, Itay Tsabary4, Ittay Eyal4, Peter Gaˇzi5, Sarah Meiklejohn6, and Edgar Weippl2 1 SBA Research fajudmayer,
[email protected] 2 Uni Wien
[email protected] 3 Imperial College London
[email protected] 4 Technion and IC3
[email protected],
[email protected] 5 IOHK
[email protected] 6 University College London
[email protected] eprint from 2021-03-01 for SoK see https://eprint.iacr.org/2020/1614 Abstract. In this paper we extend the attack landscape of bribing at- tacks on cryptocurrencies by presenting a new method, which we call Pay-To-Win (P2W). To the best of our knowledge, it is the first approach capable of facilitating double-spend collusion across different blockchains. Moreover, our technique can also be used to specifically incentivize trans- action exclusion or (re)ordering. For our construction we rely on smart contracts to render the payment and receipt of bribes trustless for the briber as well as the bribee. Attacks using our approach are operated and financed out-of-band i.e., on a funding cryptocurrency, while the conse- quences are induced in a different target cryptocurrency. Hereby, the main requirement is that smart contracts on the funding cryptocurrency are able to verify consensus rules of the target. For a concrete instanti- ation of our P2W method, we choose Bitcoin as a target and Ethereum as a funding cryptocurrency. Our P2W method is designed in a way that reimburses collaborators even in the case of an unsuccessful attack.