Final answer:
Quantum cryptography uses the principles of quantum mechanics and the properties of photons for secure key exchange over an insecure channel, distinct from classical methods like RSA, Diffie-Hellman, and AES.
Step-by-step explanation:
The correct answer to the question is a) Quantum cryptography. Quantum cryptography is a method for secure key exchange that leverages the principles of quantum mechanics. Specifically, it uses the properties of photons to guarantee secure communication. It relies on the fact that, in quantum mechanics, the act of measuring a quantum system in general disturbs the system. This feature is used in quantum key distribution (QKD) where any attempt to eavesdrop on the key will inevitably leave detectable traces.
Unlike classical methods such as RSA encryption, Diffie-Hellman key exchange, and AES encryption, which are based on the difficulty of solving certain mathematical problems, quantum cryptography is considered to be secure against any future advancements in computing power, including quantum computing.