The Diffie–Hellman key agreement is an anonymous, non-authenticated key-agreement protocol. U.S. Patent 4,200,770, from 1977 (now expired) describes the algorithm. It credits Hellman, Diffie, and Merkle as inventors.

DH is one of the earliest, practical examples of public key exchange implemented within the field of cryptography and provides the basis for a variety of authenticated protocols. For example: DH is used to provide perfect forward secrecy in Transport Layer Security's ephemeral modes (referred to as EDH or DHE depending on the cipher suite). The Diffie–Hellman key agreement was followed shortly afterwards by RSA, an implementation of public key cryptography using asymmetric algorithms.