Time-shift attack in practical quantum cryptosystems

TL;DR

This paper introduces a novel 'time-shift' attack on quantum key distribution systems that exploits detector efficiency mismatches, potentially allowing eavesdroppers to obtain full key information without detection.

Contribution

The paper presents a new 'time-shift' attack method exploiting detector inefficiencies, expanding understanding of vulnerabilities in practical quantum cryptosystems.

Findings

Eve can shift pulse arrival times to gain full key information

The attack works without introducing errors in the key

Countermeasures against the attack are discussed

Abstract

Recently, a new type of attack, which exploits the efficiency mismatch of two single photon detectors (SPD) in a quantum key distribution (QKD) system, has been proposed. In this paper, we propose another "time-shift" attack that exploits the same imperfection. In our attack, Eve shifts the arrival time of either the signal pulse or the synchronization pulse or both between Alice and Bob. In particular, in a QKD system where Bob employs time-multiplexing technique to detect both bit "0" and bit "1" with the same SPD, Eve, in principle, could acquire full information on the final key without introducing any error. Finally, we discuss some counter measures against our and earlier attacks.