Paper 2017/1044

Strain: A Secure Auction for Blockchains

Erik-Oliver Blass and Florian Kerschbaum

Abstract

We present Strain, a new auction protocol running on top of blockchains and guaranteeing bid confidentiality against fully-malicious parties. As our goal is efficiency and low blockchain latency, we abstain from using traditional, highly interactive MPC primitives such as garbled circuits. Instead for Strain, we design a new maliciously-secure two-party comparison mechanism executed between any pair of bids in parallel. Using zero-knowledge proofs, Strain broadcasts the outcome of comparisons on the blockchain in a way such that all parties can verify each outcome. While Strain leaks the order of bids, similar to OPE, its core technique of determining the auction's winner is very efficient and asymptotically optimal, requiring only 2 blockchain blocks latency. Strain also provides typical auction security requirements like non-retractable bids against fully-malicious adversaries. Finally, it protects against adversaries aborting the auction by reversible commitments.