Paper 2022/382

Witness-Authenticated Key Exchange Revisited: Improved Models, Simpler Constructions, Extensions to Groups

Matteo Campanelli and Rosario Gennaro and Kelsey Melissaris and Luca Nizzardo

Abstract

We revisit the notion of Witness Authenticated Key Exchange ($\mathsf{WAKE}$) where a party can be authenticated through a generic witness to an $\mathsf{NP}$ statement. We point out shortcomings of previous definitions, protocols and security proofs in Ngo et al. (Financial Cryptography 2021) for the (unilaterally-authenticated) two-party case. In order to overcome these limitations we introduce new models and protocols, including the first definition in literature of group witness-authenticated key exchange. We provide simple constructions based on (succinct) signatures of knowledge. Finally, we discuss their concrete performance for several practical applications in highly decentralized networks.