Kerberos = Network Authentication Protocol used by AD environments Provides authentication by issuing tickets to authenticate users and allow them access to the services Tickets are distibuted by KDC (Key Distribution Center), which is typically a Domain Controller (DC) During initial authentication, a TGT (Ticket Granting Ticket) is a ticket asigned to a user by KDC. TGT is later used to authenticate the user to the KDC in order to request a service ticket from TGS (Ticket Granting Service). Service tickets are granted for authentication against services. List of steps / negotiations for Kerberos authentication (of the user with the service): The user requests (AS-REQ) a TGT from the KDC and the KDC verifies and validates the credentials and user information. This request if often done automatically at login. After authenticating the user, the KDC sends an encrypted TGT back to the requester (AS-REP) . The user presents the TGT to the DC and requests a TGS (TGS-REQ) . The TGS is e