Mediated Semi-Quantum Key Distribution with Improved Efficiency

TL;DR

This paper presents a new mediated semi-quantum key distribution protocol that achieves asymptotically perfect efficiency, offering a practical and backward-compatible solution despite reduced noise tolerance.

Contribution

Introduces a novel mediated semi-quantum protocol with perfect asymptotic efficiency and backward compatibility, along with a security proof via reduction to entanglement-based protocols.

Findings

Achieves asymptotically perfect efficiency

Maintains backward compatibility with prior protocols

Provides a security proof through reduction to entanglement-based protocols

Abstract

Mediated semi-quantum key distribution involves the use of two end-users who have very restricted, almost classical, capabilities, who wish to establish a shared secret key using the help of a fully-quantum server who may be adversarial. In this paper, we introduce a new mediated semi-quantum key distribution protocol, extending prior work, which has asymptotically perfect efficiency. Though this comes at the cost of decreased noise tolerance, our protocol is backwards compatible with prior work, so users may easily switch to the old (normally less efficient) protocol if the noise level is high enough to justify it. To prove security, we show an interesting reduction from the mediated semi-quantum scenario to a fully-quantum entanglement based protocol which may be useful when proving the security of other multi-user QKD protocols.