Quantum cryptography beyond key distribution: Theory and experiment

Owing to its fundamental principles, quantum theory holds the promise to enhance the security of modern cryptography, from message encryption to anonymous communication, digital signatures, online banking, leader election, one-time passwords, and delegated computation. While quantum key distribution (QKD) has already enabled secure key exchange over hundreds of kilometers, a myriad of other quantum-cryptographic primitives are being developed to secure future applications against quantum adversaries. This review surveys the theoretical and experimental developments in quantum cryptography beyond QKD over the decades, along with advances in secure quantum computation. It provides an intuitive classification of the main quantum primitives and their security levels, summarizes their possibilities and limits, and discusses their implementation with current photonic technology. Cryptography not only involves the sending of secret messages but also encompasses many protocols and procedures that provide privacy and security in the networked world. Likewise, quantum resources have the potential to enhance cryptography in ways that go beyond the well-known example of quantum key distribution. This review offers a classification of the main crypto primitives that are available quantum mechanically. It explains the security that they offer, including the sometimes significant limitations on their theoretical capabilities. Implementations using current photonic techniques are discussed.