Which authentication protocol is primarily used by Windows systems?

The authentication protocol primarily used by Windows systems is Kerberos. Developed as a part of the MIT project Athena, Kerberos is designed to provide secure authentication over insecure networks. It relies on a system of tickets to allow nodes to prove their identity in a secure manner.

In the context of Windows, starting from Windows 2000, Kerberos has been the default authentication method for Active Directory (AD) environments. When a user logs in to a Windows domain, Kerberos is used to authenticate their identity with the help of a Key Distribution Center (KDC). This method enhances security through mutual authentication, ensuring that both the user and the service they are attempting to access verify each other's identity before a secure session is established.

The strength of Kerberos lies in its use of symmetric key cryptography and its ability to manage secure ticket exchanges, making it robust against unauthorized access and certain types of attacks. In a modern enterprise environment, Kerberos is preferred due to its efficiency and ability to handle multiple authentication requests efficiently.

While RADIUS and TACACS+ are also used for authentication, particularly in network devices, they are more common in network access scenarios rather than in integrated operating systems like Windows. OAuth, on the other hand, primarily provides authorization rather than authentication