Improved Eavesdropping Detection in Quantum Key Distribution

TL;DR

This paper introduces a novel QKD protocol that distinguishes between system and eavesdropping errors, enabling secure key distribution over longer distances even with higher error rates by analyzing correlated error patterns.

Contribution

A new QKD protocol that detects eavesdropping by identifying error origins through alternative photon encoding and error correlation analysis.

Findings

Enhanced eavesdropping detection capability

Allows longer communication distances in QKD systems

Supports higher system error rates without compromising security

Abstract

Employing the fundamental laws of quantum physics, Quantum Key Distribution (QKD) promises the unconditionally secure distribution of cryptographic keys. However, in practical realisations, a QKD protocol is only secure, when the quantum bit error rate introduced by an eavesdropper unavoidably exceeds the system error rate. This condition guarantees that an eavesdropper cannot disguise his presence by simply replacing the original transmission line with a less faulty one. Unfortunately, this condition also limits the possible distance between the communicating parties, Alice and Bob, to a few hundred kilometers. To overcome this problem, we design a QKD protocol which allows Alice and Bob to distinguish system errors from eavesdropping errors. If they are able to identify the origin of their errors, they can detect eavesdropping even when the system error rate exceeds the eavesdropping error rate. To achieve this, the proposed protocol employs an alternative encoding of information in two-dimensional photon states. Errors manifest themselves as quantum bit and as index transmission errors with a distinct correlation between them in case of intercept-resend eavesdropping. As a result, Alice and Bob can tolerate lower eavesdropping and higher system error rates without compromising their privacy.