Hacking on decoy-state quantum key distribution system with partial phase randomization

TL;DR

This paper demonstrates a hybrid measurement attack on decoy-state quantum key distribution systems with partial phase randomization, showing that such systems can be compromised without detection, thus questioning their security assumptions.

Contribution

It introduces a novel hybrid measurement attack exploiting partial phase randomization, revealing vulnerabilities in practical QKD implementations.

Findings

The attack can break entanglement in certain regimes.

Eavesdropper can steal all key information undetected.

Partial phase randomization is insufficient for security.

Abstract

Quantum key distribution (QKD) provides means for unconditional secure key transmission between two distant parties. However, in practical implementations, it suffers from quantum hacking due to device imperfections. Here we propose a hybrid measurement attack, with only linear optics, homodyne detection, and single photon detection, to the widely used vacuum+weak decoy state QKD system when the phase of source is partially randomized. Our analysis shows that, in some parameter regimes, the proposed attack would result in an entanglement breaking channel but still be able to trick the legitimate users to believe they have transmitted secure keys. That is, the eavesdropper is able to steal all the key information without discovered by the users. Thus, our proposal reveals that partial phase randomization is not sufficient to guarantee the security of phase-encoding QKD systems with weak coherent states.