A Novel Proof of Shuffle: Exponentially Secure Cut-and-Choose

Abstract

Shuffling is one of the most important techniques for privacypreserving protocols. Its applications are manifold, including, for example, e-voting, anonymous broadcast, or privacy-preserving machinelearning. For many applications, such as secure e-voting, it is crucial that the correctness of the shuffling operation be (publicly) verifiable. To this end, numerous proofs of shuffle have been proposed in the literature. Several of these proofs are actually employed in the real world. In this work, we propose a generic compiler which can transform any "shuffle-compatible" Σ-protocol (including, among others, Σ-protocols for re-randomization, decryption, or key shifting) into a Σ-protocol for permutations of the underlying relation. The resulting proof of shuffle is black-box, easily implementable, simple to explain, and comes with an acceptable computational overhead over the state-of-the-art. Because we machine-checked our compiler in Coq, the new proof of shuffle is particularly suitable for applications that require a superior level of security assurance (e.g., high-stake elections).

DeVoS: Deniable Yet Verifiable Vote Updating

“…NIZKP of shuffle and of correct decryption. Since there are several ways to instantiate the NIZKP of shuffle 𝜋 Shuffle for ElGamal PKE in the literature (e.g., [30,52]), we will not single out one of them. For the NIZKP of correct decryption, we can choose a standard Schnorr proof [49].…”

Verifiability Experiences in Ontario’s 2022 Online Elections

“…While research on online voting claims that no binding public elections can be considered low-stakes [6,13], elections research frequently defines local elections as such [5,30]. Scholars argue that unlike in high-stakes elections, the financial costs of an online voting system is of particular concern for low-stakes elections [11,16]. Furthermore, in terms of security, "a weaker threat model is [seen as being] suitable" [16].…”