Quantum cryptography in optical fiber networks

Quantum cryptography exploits the fundamental properties of quantum complementarity to allow two remote parties to generate a shared random bit sequence that is provably secret. Users can safely use their shared bit sequence as a key for subsequent encrypted communications. In conventional complexity-based approaches to security, privacy depends on the supposed difficulty of solving certain classes of mathematical problem. In contrast, quantum key distribution (QKD), as it is more correctly called, provides a new paradigm for the protection of sensitive information in which security is based on fundamental physical laws. The current status of QKD is reviewed and examples of several fiber-based systems that have been built and tested are provided.