Quantum cryptography

Quantum cryptography is the application of quantum information theory to cryptographic security, exploiting the structural constraints of quantum mechanics — the No-Cloning Theorem and the disturbance caused by measurement — to create protocols whose security is information-theoretic rather than computational. Unlike classical cryptography, which depends on the assumed hardness of mathematical problems like factoring or discrete logarithms, quantum cryptography derives its security from the physical laws governing quantum communication. The foundational protocol is BB84, which enables two parties to establish a shared secret key while detecting any eavesdropping attempt through the statistical anomalies it introduces. The field is not merely a faster or smaller version of classical cryptography; it is a different security paradigm, one that trades computational assumptions for physical ones. Yet this trade is not free: the security proofs depend on idealized device models, and the gap between theory and implementation remains a fertile ground for side-channel attacks.