Security analysis of the time-coding quantum key distribution protocols

TL;DR

This paper analyzes the security of time-coding quantum key distribution protocols using coherent single-photon pulses, demonstrating their potential for secure communication over long distances with practical detectors.

Contribution

It introduces a security framework for time-coding QKD protocols, derives secure key rates, and assesses their performance over fiber links, including countermeasures against photon-number splitting attacks.

Findings

Secure distances over 200 km with superconducting detectors

Secure key rates comparable to BB84 protocol

Decoy states effectively prevent photon-number splitting attacks

Abstract

We report the security analysis of time-coding quantum key distribution protocols. The protocols make use of coherent single-photon pulses. The key is encoded in the photon time-detection. The use of coherent superposition of states allows to detect eavesdropping of the key. We give a mathematical model of a first protocol from which we derive a second, simpler, protocol. We derive the security analysis of both protocols and find that the secure rates can be similar to those obtained with the BB84 protocol. We then calculate the secure distance for those protocols over standard fibre links. When using low-noise superconducting single photon detectors, secure distances over 200 km can be foreseen. Finally, we analyse the consequences of photon-number splitting attacks when faint pulses are used instead of single photon pulses. A decoy states technique can be used to prevent such attacks.