Protocols explains how algorithms and data structures are signify to implement multiple, interoperable versions of programs. Security protocols apply cryptographic methods to perform security-related functions. Authentication protocols are security protocols planned to authenticate entities looking for secure communication.

Kerberos
Kerberos permits nodes to securely verify their individuality during communication over non-secure networks. The protocol possibly implemented via open-source software available through the Massachusetts Institute of Technology (MIT). This widely adopted authentication protocol gives mutual authentication in a client-server model and protects against snoop and replay attacks.

RADIUS
Remote Authentication Dial-In User Service (RADIUS) build by Livingston Enterprises for server authentication within networked computer services. The protocol also accounts for usage of such services.

TACACS+
Terminal Access Controller Access-Control System (TACACS+) is an authentication protocol planned to find out whether remote access servers are authorized to communicate over a network. TACACS+ separates authentication and authorization in a user profile.

TLS/SSL
Transport Layer Security (TLS)/Secure Socket Layer (SSL) gives the capacity to control the ciphers and cryptographic algorithms permitted for connections and authentication.