Abstract: Many people mistakenly assume that Diffie–Hellman is an encryption algorithm, while in fact it is not. It is a key-agreement protocol designed specifically to establish a shared secret between two parties. This shared secret—essentially a large number—can later be used as a key to encrypt subsequent communications using a more efficient symmetric-key cipher such as AES or 3DES. Thus, Diffie–Hellman serves as a critical component in hybrid cryptosystems, where asymmetric cryptography solves the hard problem of key exchange, while the actual data encryption is performed by fast symmetric cryptography.

One of the most important advantages of Diffie–Hellman is its ability to provide perfect forward secrecy (PFS)—a crucial property that ensures past communications remain confidential even if the server’s long-term key is compromised in the future.