Quantum cryptography, with its key technology, quantum key distribution (QKD), can unconditionally achieve secure data communication in the sense that encrypted data can never be cracked by any computation attacks, including with large-scale quantum computers. Quantum cryptography is one of the quantum information technologies and has technically matured for deployment in real uses. This chapter describes the basic principles of QKD, a QKD network, and their applications. We discuss the current QKD network architecture and how to integrate it with other modern security technologies to develop a total security solution that is useful in our society.
