The paper by Dominic Mayers discusses the unconditional security of quantum key distribution (QKD) protocols, focusing on a specific protocol proposed by Bennett and Brassard in 1984. The proof of security considers a practical scenario where the communication channel is noisy and photons may be lost during transmission. Each signal sent into the channel must contain a single photon or a two-dimensional system in the exact state described in the protocol. The detector at the receiving end can be unrestricted, except that the detection must be independent of the basis used to measure the received system. The paper reviews basic notions and principles applicable to any QKD protocol, emphasizing the importance of privacy and the need to ensure that Eve's information about the key is exponentially small in the security parameter \( N \). The security criteria are defined in terms of the Shannon entropy of the key conditional to Eve's view, ensuring that the key is uniformly distributed and that Eve's attack does not influence the distribution of the key. The proof relies on techniques from previous works, including those by Mayers and Salvail, Yao, and Mayers himself. The paper also introduces a fictive test lemma, which provides an upper bound on the probability of certain events related to error detection, and discusses privacy amplification techniques to extract a smaller key from a nonprivate string. The basic model for the analysis of the QKD protocol is described, separating the overall outcome into classical and quantum parts. The classical part is represented by a random tape, while the quantum part is represented by the outcome of measurements on quantum registers. The paper emphasizes the importance of understanding the connection between the classical and quantum parts of the protocol to ensure the security of the key distribution.The paper by Dominic Mayers discusses the unconditional security of quantum key distribution (QKD) protocols, focusing on a specific protocol proposed by Bennett and Brassard in 1984. The proof of security considers a practical scenario where the communication channel is noisy and photons may be lost during transmission. Each signal sent into the channel must contain a single photon or a two-dimensional system in the exact state described in the protocol. The detector at the receiving end can be unrestricted, except that the detection must be independent of the basis used to measure the received system. The paper reviews basic notions and principles applicable to any QKD protocol, emphasizing the importance of privacy and the need to ensure that Eve's information about the key is exponentially small in the security parameter \( N \). The security criteria are defined in terms of the Shannon entropy of the key conditional to Eve's view, ensuring that the key is uniformly distributed and that Eve's attack does not influence the distribution of the key. The proof relies on techniques from previous works, including those by Mayers and Salvail, Yao, and Mayers himself. The paper also introduces a fictive test lemma, which provides an upper bound on the probability of certain events related to error detection, and discusses privacy amplification techniques to extract a smaller key from a nonprivate string. The basic model for the analysis of the QKD protocol is described, separating the overall outcome into classical and quantum parts. The classical part is represented by a random tape, while the quantum part is represented by the outcome of measurements on quantum registers. The paper emphasizes the importance of understanding the connection between the classical and quantum parts of the protocol to ensure the security of the key distribution.