Security of the decoy state method for quantum key distribution

TL;DR

This paper provides a formal security proof for the decoy state method in quantum key distribution, addressing vulnerabilities and comparing attack strategies to enhance quantum cryptography security.

Contribution

It offers a rigorous security proof for the decoy state method against all attacks and analyzes different attack strategies in QKD.

Findings

Decoy state method is secure against all possible attacks.

Photon-number splitting and beam splitting attacks are compared.

Polarization and phase coding are shown to be equivalent.

Abstract

Quantum cryptography or, more precisely, quantum key distribution (QKD), is one of the advanced areas in the field of quantum technologies. The confidentiality of keys distributed with the use of QKD protocols is guaranteed by the fundamental laws of quantum mechanics. This paper is devoted to the decoy state method, a countermeasure against vulnerabilities caused by the use of coherent states of light for QKD protocols whose security is proved under the assumption of single-photon states. We give a formal security proof of the decoy state method against all possible attacks. We compare two widely known attacks on multiphoton pulses: photon-number splitting and beam splitting. Finally, we discuss the equivalence of polarization and phase coding.