Publicly Verifiable Auctions with Privacy

Online auctions have a steadily growing market size, creating billions of US dollars in sales value every year. To ensure fairness and auditability while preserving the bidder\u27s privacy is the main challenge of an auction scheme. At the same time, utility driven blockchain technology is picking up the pace, offering transparency and data integrity to many applications. In this paper, we present a blockchain-based first price sealed-bid auction scheme. Our scheme offers privacy and public verifiability. It can be built on any public blockchain, which is leveraged to provide transparency, data integrity, and hence auditability. The inability to double spend on a blockchain is used to prevent bid replay attacks. Moreover, our scheme can achieve non-repudiation for both bidders and the auctioneer without revealing the bids and we encapsulate this concept inside the public verification of the auction. We propose to use ElGamal encryption and Bulletproofs to construct an efficient instantiation of our scheme. We also propose to use recursive zkSNARKs to reduce the number of comparison proofs from $N-1$ to $1$, where $N$ is the number of bidders

Fast Contract Signing with Batch Oblivious Transfer

Abstract. Oblivious transfer protocol is a basic building block of various cryptographic constructions. We propose a novel protocol -batch oblivious transfer. It allows efficient computation of multiple instances of oblivious transfer protocols. We apply this protocol to improve the fast simultaneous contract signing protocol, recently proposed i

Efficient Bid Validity Check in ElGamal-Based Sealed-Bid E-Auctions

Bid opening in sealed-bid e-auction is efficient when a homomorphic encryption algorithm is employed to seal the bids and homomorphic bid opening is employed to open the bids. Such e-auction schemes are called homomorphic auctions. However, high efficiency of homomorphic auctions is based on an assumption: the bids are valid (e.g. within a special range). An undetected invalid bid can compromise correctness and fairness of the auction. Unfortunately, in most existing homomorphic auction schemes, proof and verification of validity of the bids is either ignored or too inefficient. Recently, a technique called batched bid validity check [25] is proposed to improve efficiency of proof and verification of bid validity in a special kind of homomorphic auction schemes: secret-sharing-based homomorphic auctions. However, secret-sharing-based homomorphic auction schemes [13, 15, 26, 24] are not a main stream in homomorphic auction schemes as they employ threshold secret sharing techniques to seal the bids. Main stream homomorphic auction schemes employ a homomorphic encryption algorithm with threshold distributed decryption to seal the bids as it is simpler and more efficient than secret sharing. In this paper, an ElGamal-encryption-based homomorphic encryption scheme is proposed. It employs a batched proof and verification of bid validity to achieve high efficiency in bid validity check. Its batch proof and verification technique is more advanced than that in [25], so it is simpler and more efficient than the homomorphic auction scheme in [25]