Diffie and Hellman are associated with which cryptographic concept?

• A. Symmetric ciphers in hardware.
• B. Hash functions.
• C. Password hashing algorithms.
• D. Public-key cryptography and key exchange.

Answer: (D)

Diffie-Hellman key exchange is about establishing a shared secret for symmetric encryption over an open channel using public-key concepts. In this method, both sides agree on a large prime and a generator, then each side picks a private value and shares a public value derived from it. When each party combines the received public value with their own private value, they arrive at the same shared secret, which an observer cannot compute easily due to the difficulty of the discrete logarithm problem. This shared secret can then be used to seed symmetric encryption for secure communication. Note that while DH enables key agreement, it doesn’t authenticate the parties by itself—authentication (e.g., digital signatures or certificates) is typically added to prevent man-in-the-middle attacks. The other options refer to different cryptographic goals: symmetric ciphers in hardware are about encryption algorithms, hash functions deal with data integrity and digests, and password hashing algorithms are for securely storing credentials, not for exchanging keys.