The Walther Group published a new paper in Reviews of Modern Physics

02.01.2026

Quantum cryptography beyond key distribution: Theory and experiment

Abstract

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.

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dversarial settings for two-party quantum primitives. a) Honest protocol: Alice generates a quantum state ρ using her source S and an encoding unitary UA. Bob applies a unitary UB and performs a measurement with a detection device D, possibly followed by some classical post-processing CP P b) Protocol with a dishonest Alice: she can replace ρ with another state σ, possibly living in a larger Hilbert space c) Protocol with a dishonest Bob: he can perform any CPTD map on the state ρ he receives.