Abstract
Quantum key distribution (QKD) is a cryptographic primitive that allows to exponentially grow a key, initially shared between the end points of a quantum channel–a communications channel over which quantum signals can be transmitted. Its security can be derived from the laws of quantum mechanics, which allow to prove the information‐theoretic security of QKD. In this entry, the process and specific characteristics of QKD are discussed. This includes the meaning of the “absolute security” character that is usually ascribed to QKD, its limitations and practical implementations.