Diffie-Hellman

Although Diffie–Hellman key exchange itself is a non-authenticated key-agreement protocol, it provides the basis for a variety of authenticated protocols, and is used to provide forward secrecy in Transport Layer Security's ephemeral modes (referred to as EDH or DHE depending on the cipher suite). Forward secrecy results from the use of ephemeral keys: the private keys are discarded once key agreement is complete, making them safe from later compromise. Ephemeral keys are practical because it is computationally cheap to create public-private key pairs suitable for use with Diffie-Hellman exchange.