介绍了密码技术，解释了密码危机的由来。对称密码体制中的密钥分配是维护信息安全的核心问题，自20世纪70年代研发的公钥密码体制存在多种隐患，它们难以保证密钥分配中的绝对安全。论述了量子密钥分配技术的原理及研发进展。

Quantum key distribution (QKD) uses quantum mechanics to guarantee secure communication. It enables two parties to produce a shared random secret key known only to them, which can then be used to encrypt and decrypt messages. The security of encryption that uses quantum key distribution relies on the foundation of quantum mechanics, in contrast to the traditional public key cryptography, which relies on the computational difficulty of certain mathematical functions and cannot provide any mathematical proof as to the actual complexity of reversing the one-way functions used. The history and future development of quantum cryptography are also briefly discussed.