Revisiting Deniability in Quantum Key Exchange via Covert Communication and Entanglement Distillation

TL;DR

This paper explores the concept of deniability in quantum key exchange, proposing a new covert QKE protocol and demonstrating how entanglement distillation can enable information-theoretic deniability.

Contribution

It introduces the notion of coercer-deniable QKE, connects covert communication to deniability, and proposes a simple deniable covert QKE protocol with entanglement distillation techniques.

Findings

DC-QKE protocol is deniable via security reduction

Covert QKE can be used to achieve deniability

Entanglement distillation enables information-theoretic deniability

Abstract

We revisit the notion of deniability in quantum key exchange (QKE), a topic that remains largely unexplored. In the only work on this subject by Donald Beaver, it is argued that QKE is not necessarily deniable due to an eavesdropping attack that limits key equivocation. We provide more insight into the nature of this attack and how it extends to other constructions such as QKE obtained from uncloneable encryption. We then adopt the framework for quantum authenticated key exchange, developed by Mosca et al., and extend it to introduce the notion of coercer-deniable QKE, formalized in terms of the indistinguishability of real and fake coercer views. Next, we apply results from a recent work by Arrazola and Scarani on covert quantum communication to establish a connection between covert QKE and deniability. We propose DC-QKE, a simple deniable covert QKE protocol, and prove its deniability via a reduction to the security of covert QKE. Finally, we consider how entanglement distillation can be used to enable information-theoretically deniable protocols for QKE and tasks beyond key exchange.