Robust Quantum Public-Key Encryption with Applications to Quantum Key Distribution

TL;DR

This paper introduces a two-message quantum key distribution protocol with everlasting security based on quantum-secure one-way functions, and presents a new quantum public-key encryption scheme relying solely on classical authentication.

Contribution

It proposes the first two-message QKD protocol with everlasting security under minimal assumptions and introduces a novel quantum public-key encryption scheme based on classical authentication.

Findings

Achieves two-message QKD with everlasting security

Constructs quantum public-key encryption relying only on classical authentication

Shows security based on quantum-secure one-way functions

Abstract

Quantum key distribution (QKD) allows Alice and Bob to agree on a shared secret key, while communicating over a public (untrusted) quantum channel. Compared to classical key exchange, it has two main advantages: (i) The key is unconditionally hidden to the eyes of any attacker, and (ii) its security assumes only the existence of authenticated classical channels which, in practice, can be realized using Minicrypt assumptions, such as the existence of digital signatures. On the flip side, QKD protocols typically require multiple rounds of interactions, whereas classical key exchange can be realized with the minimal amount of two messages using public-key encryption. A long-standing open question is whether QKD requires more rounds of interaction than classical key exchange. In this work, we propose a two-message QKD protocol that satisfies everlasting security, assuming only the existence of quantum-secure one-way functions. That is, the shared key is unconditionally hidden, provided computational assumptions hold during the protocol execution. Our result follows from a new construction of quantum public-key encryption (QPKE) whose security, much like its classical counterpart, only relies on authenticated classical channels.