Two parties on an untrusted network each generate a private value, exchange derived public values, and both arrive at the same shared secret without the secret itself ever crossing the wire. Which algorithm does this describe?

Why C is correct

Diffie-Hellman is a key agreement algorithm that lets two parties derive a shared secret from exchanged public values, forming the basis of modern TLS key exchange. AES-GCM encrypts data with an already shared key, SHA-256 produces digests, and RSA signing proves authenticity.