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(also Diffie-Hellman key exchange)

Diffie-Hellman definition

The Diffie-Hellman protocol, frequently called the Diffie-Hellman key exchange, is a robust procedure used to exchange cryptographic keys across an open network safely. The protocol facilitates two entities, each owning a unique public-private key pair, to create a shared secret key even when communicating over an unsecured network.

See also: VPN firewall, firewall, cryptographic key, man-in-the-middle attack

Diffie-Hellman examples

  • Secure communication: Diffie-Hellman is widely used in secure communication protocols, such as HTTPS and SSH, for establishing a secure session between the client and the server.
  • VPN encryption: In VPNs, Diffie-Hellman is used to safely exchange keys between the client and the VPN server, establishing a secure tunnel.

Advantages and disadvantages of Diffie-Hellman


  • Security: Diffie-Hellman allows for the secure exchange of keys over public channels, making it a cornerstone for secure communication on the internet.
  • Privacy: Since the protocol does not expose private keys during the exchange, it maintains the privacy of communication.


  • Computational intensity: The protocol can be computationally heavy, especially with large keys, potentially affecting performance.
  • Susceptible to man-in-the-middle attacks: Without an authentication mechanism, Diffie-Hellman can be vulnerable to attacks where an attacker intercepts and modifies the key exchange.

Using Diffie-Hellman

  • For added security, Diffie-Hellman should be used in conjunction with other protocols that provide authentication.
  • In a VPN, the service should use a strong Diffie-Hellman key to prevent potential breaches.