The document summarizes the Diffie-Hellman key exchange algorithm. It was the first practical method for public key exchange proposed by Diffie and Hellman in 1976. It allows two parties to establish a shared secret key over an insecure channel. Each party generates a public/private key pair, and the secret key is derived from the exponentiation of each public key with the other party's private key. While it can securely establish a shared key, it is vulnerable to man-in-the-middle attacks without authentication of the participating identities.