Knowledge-Coin Fair Exchange

Fair exchange has been studied in computer science for many decades. The problem consists of enabling two participants to exchange digital information in a way which is fair, even when one may be malicious. The goal is to ensure that either all honest participants receive the expected information, or none of them disclose theirs. It has been proven that this cannot be achieved without the involvement of a third party. The challenge, therefore, is to minimize both the cost and the participation of this third party. Furthermore, fair exchange has been shown to imply consensus—another difficult problem in distributed systems. Yet blockchain technology implements consensus on a global scale daily, prompting the question: can we exploit this infrastructure to solve fair exchange? Specifically, smart contracts can serve as third parties in a transparent manner. We focus on a specific scenario in which digital information, characterized by a verifiable description function (e.g., a hash), is exchanged for a digital payment. Two families of protocols exist: those based on zero-knowledge proofs and optimistic protocols. The former requires intensive computation, while the latter involves complex dispute resolution. We propose a new optimistic protocol that advances the state of the art.

Speaker(s): Serge Vaudenay

Serge Vaudenay is a Professor at EPFL, where he leads the Security and Cryptography Laboratory (LASEC). He graduated from the Ecole Normale Supérieure in Paris with a major in mathematics and received his PhD in computer science from University of Paris 7 – Denis Diderot.

Series: Cryptography Talk Series