Attacks against a Simplified Experimentally Feasible Semiquantum Key Distribution Protocol

TL;DR

This paper demonstrates that a simplified version of a feasible semiquantum key distribution protocol is vulnerable to attacks, highlighting the importance of complexity for ensuring robustness in quantum cryptography.

Contribution

It introduces a simplified SQKD protocol and proves its non-robustness through specific attacks, emphasizing the necessity of complexity for security.

Findings

The simplified Mirror protocol is completely non-robust.

Two specific attacks can compromise the simplified protocol.

Complexity appears essential for robustness in SQKD protocols.

Abstract

A semiquantum key distribution (SQKD) protocol makes it possible for a quantum party and a classical party to generate a secret shared key. However, many existing SQKD protocols are not experimentally feasible in a secure way using current technology. An experimentally feasible SQKD protocol, "classical Alice with a controllable mirror" (the "Mirror protocol"), has recently been presented and proved completely robust, but it is more complicated than other SQKD protocols. Here we prove a simpler variant of the Mirror protocol (the "simplified Mirror protocol") to be completely non-robust by presenting two possible attacks against it. Our results show that the complexity of the Mirror protocol is at least partly necessary for achieving robustness.