The paper by Hoi-Kwong Lo and H. F. Chau addresses the long-standing issue of unconditional security in Quantum Key Distribution (QKD) over long distances. They demonstrate that, given fault-tolerant quantum computers, QKD can be made unconditionally secure even over realistic noisy channels. The proof is achieved by reducing the problem to a noiseless quantum scheme and then to a classical scheme, where classical probability theory can be applied. The authors introduce a new QKD protocol involving fault-tolerant sharing and purification of EPR pairs, which requires quantum computers. They show that the error syndrome does not provide useful information for an eavesdropper, and they develop a quantum verification scheme based on random hashing to distinguish singlets from triplets. This scheme is efficient and secure against all possible attacks, including joint attacks. The paper also discusses the practical implementation of the protocol and its potential applications, emphasizing the importance of quantum repeaters and fault-tolerant quantum computation in achieving secure QKD over long distances.The paper by Hoi-Kwong Lo and H. F. Chau addresses the long-standing issue of unconditional security in Quantum Key Distribution (QKD) over long distances. They demonstrate that, given fault-tolerant quantum computers, QKD can be made unconditionally secure even over realistic noisy channels. The proof is achieved by reducing the problem to a noiseless quantum scheme and then to a classical scheme, where classical probability theory can be applied. The authors introduce a new QKD protocol involving fault-tolerant sharing and purification of EPR pairs, which requires quantum computers. They show that the error syndrome does not provide useful information for an eavesdropper, and they develop a quantum verification scheme based on random hashing to distinguish singlets from triplets. This scheme is efficient and secure against all possible attacks, including joint attacks. The paper also discusses the practical implementation of the protocol and its potential applications, emphasizing the importance of quantum repeaters and fault-tolerant quantum computation in achieving secure QKD over long distances.