kvantnyckeldistribution

Quantum key distribution (QKD) is a method for two parties to establish a shared secret key using the principles of quantum mechanics. In Swedish, the term kvantnyckeldistribution is commonly used to refer to QKD. The security of QKD relies on fundamental quantum properties, such as the no-cloning theorem and the disturbance of quantum states, which allow the communicating parties to detect any eavesdropping.

Most well-known protocols include BB84, introduced in 1984 by Bennett and Brassard, which encodes key bits on non-orthogonal quantum states; and E91, proposed by Ekert in 1991, which uses entangled photon pairs. Once quantum transmission completes, the parties perform error estimation and privacy amplification over an authenticated classical channel to produce a shorter, secure key.

QKD is typically implemented with photons transmitted through optical fibers or via free-space links, including satellite systems for long distances. Practical deployments face loss, noise, and device imperfections, which can create security vulnerabilities if not properly addressed. This has led to variants like device-independent QKD and measurement-device-independent QKD that aim to reduce assumptions about hardware.

Despite advances, QKD does not replace conventional encryption by itself; it provides a secure key that can be used with symmetric algorithms such as the one-time pad or AES in a quantum-safe configuration. Real-world networks combine QKD with classical infrastructure, and research continues toward larger-scale quantum networks and space-based links, such as demonstrators that have linked ground stations with satellites.

QKD remains primarily in the research and pilot deployment stage, with ongoing work on standardization, interoperability, and cost reduction to enable wider commercial use.