Final answer:
The Diffie-Hellman key exchange was the first example of a public key exchange mechanism, utilizing hard mathematical problems to establish a shared secret over an insecure network.
Step-by-step explanation:
The Diffie-Hellman key exchange was the first example of a public key exchange mechanism. The algorithm was published in 1976 by Whitfield Diffie and Martin Hellman and it fundamentally changed the way cryptographic keys are exchanged over an unsecured network, like the Internet. The Diffie-Hellman algorithm allows two parties to establish a shared secret over an insecure channel without having to exchange any secret information beforehand. This shared secret can then be used to encrypt further communications using a symmetric key cipher. The brilliance of the Diffie-Hellman method is that it exploits the difficulty of calculating discrete logarithms in a finite field, which is a hard mathematical problem, to allow secure key exchange. While the Diffie-Hellman key exchange was a major breakthrough in cryptography, it is important to note that it only provides a way to exchange keys and does not by itself provide encryption of messages.