Blockchain-based Practical Multi-agent Secure Comparison and its Application in Auctions

AI applications find widespread use in a variety of domains. For further acceptance, mostly when multiple agents interact with the system, we must aim to preserve the privacy of participants information in such applications. Towards this, the Yao’s Millionaires’ problem (YMP), i.e., to determine the richer among two millionaires’ privately, finds relevance. This work presents a novel, practical, and verifiable solution to YMP, namely, Secure Comparison Protocol (SCP). We show that SCP achieves this comparison in a constant number of rounds, without using encryption and not requiring the participants’ continuous involvement. SCP uses semi-trusted third parties - which we refer to as privacy accountants - for the comparison, who do not learn any information about the values. That is, the probability of information leak is negligible in the problem size. In SCP, we also leverage the Ethereum network for pseudo-anonymous communication, unlike computationally expensive secure channels such as Tor. We present a Secure Truthful cOmbinatorial aUction Protocol (STOUP) for single-minded bidders to demonstrate SCP’s significance. We show that STOUP, unlike previous works, preserves the privacies relevant to an auction even from the auctioneer. We demonstrate the practicality of STOUP through simulations.