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.

量子密码学或更准确地说是量子密钥分发（QKD），是量子技术领域的先进领域之一。使用 QKD 协议分发的密钥的机密性由量子力学的基本定律保证。本文致力于诱饵状态方法，这是一种针对在单光子状态假设下证明其安全性的 QKD 协议使用光相干状态引起的漏洞的对策。我们针对所有可能的攻击给出了诱饵状态方法的正式安全证明。我们比较了对多光子脉冲的两种广为人知的攻击：光子数分裂和光束分裂。最后，我们讨论极化和相位编码的等效性。