NTLM / Kerberos Authentication Mechanism
Windows Challenge/Response (NTLM) is the authentication protocol used on networks that include systems running the Windows operating system and on stand-alone systems.
The Kerberos protocol defines how clients interact with a network authentication service. Clients obtain tickets from the Kerberos Key Distribution Center (KDC), and they present these tickets to servers when connections are established. Kerberos tickets represent the client’s network credentials.
Windows authentication uses either Kerberos authentication or NTLM authentication, depending upon the client and server configurations.