What is the process of establishing a shared secret between parties over an insecure channel called?

• A. Digital signature
• B. Hash function
• C. Public key cryptography
• D. Key exchange

Answer: (D)

Key exchange is the process of establishing a shared secret between parties over an insecure channel. The goal is that both sides derive the same secret even though an eavesdropper can listen to everything exchanged. A classic example is Diffie-Hellman, where each party contributes private values and exchanges computed data; from those, both sides arrive at the same secret without ever transmitting the secret itself. That shared secret can then be used as a symmetric key to encrypt subsequent communications.

Digital signatures are about authentication and integrity, not agreeing on a secret. A hash function is a one-way mapping used for integrity or data comparison, not for deriving a shared key. Public key cryptography is the broader framework of asymmetric techniques, which can enable key exchange but doesn’t itself describe the act of establishing a shared secret over an insecure channel.