Quantum Cryptography is defined as

• A. The science of quantum mechanical properties to perform cryptographic functions and tasks.
• B. A VPN protocol
• C. A method of generating random numbers via classical entropy
• D. Using quantum computers to break encryption

Answer: (A)

Quantum cryptography uses the peculiar properties of quantum mechanics to perform cryptographic tasks, notably secure key exchange, by leveraging principles like measurement disturbance and the no-cloning theorem. This means security can be guaranteed by the laws of physics, not just computational assumptions. That’s why the description that frames quantum cryptography as the science of quantum mechanical properties used to perform cryptographic functions and tasks is the best fit. It isn’t a VPN protocol, which is a networking tool for secure channels. It isn’t merely generating random numbers via classical entropy, since the defining feature is using quantum properties to enable cryptographic operations. And it isn’t about using quantum computers to break encryption, which targets defeating cryptographic schemes rather than enabling secure cryptography.