What protocol does Diffie-Hellman use for key exchange?

The Diffie-Hellman key exchange protocol primarily utilizes mathematical concepts related to prime numbers for securely exchanging cryptographic keys over a public channel. The method relies on the properties of modular exponentiation and the difficulty of certain mathematical problems, such as the discrete logarithm problem, which is computationally hard to solve when prime numbers are involved.

In the protocol, two parties agree on a large prime number and a base (also a primitive root modulo that prime). Each party then selects a secret private key and computes their respective public keys using the large prime and base. They exchange these public keys and, through additional calculations involving their own private key and the received public key, derive the same shared secret key independently.

While various cryptographic processes may use public key cryptography, hash functions, or symmetric key encryption, they do not specifically define the mechanism by which Diffie-Hellman operates for key exchange. The focus on prime numbers helps ensure that the shared secret remains secure from eavesdroppers who only observe the public exchanges. Therefore, the correct answer highlights the foundational role of prime numbers in the Diffie-Hellman protocol for establishing shared keys securely.