Attacks against a Simplified Experimentally Feasible Semiquantum Key Distribution Protocol.

Michel Boyer,Rotem Liss,Tal Mor

doi:10.3390/e20070536

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.

Highlights

Quantum key distribution (QKD) protocols allow two parties, Alice and Bob, to share a secret random key that is secure even against the most powerful adversaries
Proving robustness is a step towards proving security; proving the security of Semiquantum key distribution (SQKD) protocols is difficult because those protocols are usually two-way: for example, Alice sends a quantum state to Bob, and Bob performs a specific classical operation and sends the resulting quantum state back to Alice
We have found the simplified Mirror protocol to be completely non-robust; this protocol is an “over-simplified” Mirror protocol

Summary

Introduction

Quantum key distribution (QKD) protocols allow two parties, Alice and Bob, to share a secret random key that is secure even against the most powerful adversaries. The generated states {|0i, |1i} must be indistinguishable from states that Alice reflects towards Bob. Using current photonic technology, Alice’s devices are imperfect, which makes this assumption incorrect and makes possible attacks by the eavesdropper Eve: for example, Eve may send a slightly modified state towards Alice (a “tagging attack”) or may distinguish between the states sent by Alice. Alice’s devices are imperfect, which makes this assumption incorrect and makes possible attacks by the eavesdropper Eve: for example, Eve may send a slightly modified state towards Alice (a “tagging attack”) or may distinguish between the states sent by Alice Full details about those practical attacks are available in [14,15,16].

The Mirror Protocol

Attacks against the Simplified Mirror Protocol

A Full Attack on the Simplified Protocol that Gives Eve Full Information

Discussion