The Key Distribution Center (KDC) is the central trusted third party in Kerberos that issues all types of tickets. The KDC consists of two components: the Authentication Server (AS) which issues the initial Ticket Granting Ticket (TGT), and the Ticket Granting Server (TGS) which issues service tickets (session tickets) for specific resources. When a user needs to access a service, the KDC validates their TGT and issues a session ticket that grants access to that service. The Security Identifier (SID) is a Windows security concept unrelated to Kerberos ticket issuance.