Quantum cryptography uses principles of quantum mechanics, such as the no-cloning theorem and measurement disturbance, to perform cryptographic tasks whose security rests on physical law rather than computational hardness. Its best-known application, quantum key distribution, lets two parties establish a shared secret with detectable eavesdropping. It is distinct from post-quantum cryptography, which is classical algorithms resistant to quantum attack.
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- QKD protocols such as BB84 detect interception because measuring a quantum state perturbs it. Practical deployment requires specialised photonic hardware, trusted nodes or quantum repeaters over distance, and integration with classical authentication. It complements rather than replaces classical and post-quantum schemes used for bulk encryption and integrity.