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Kerberos Components in Windows 2000

Windows 2000 implements the KDC as a domain service. It uses Active Directory as its account database and gets additional information about security principals from the Global Catalog

As in other implementations of the Kerberos protocol, the KDC is a single process that provides two services.

Authentication Service    The authentication service issues TGTs that are good for admission to the ticket-granting service in its domain. Before network clients can get tickets for services, they must obtain a TGT from the authentication service in the user's account domain.

Ticket-Granting Service    The ticket-granting service issues tickets that are good for admission to other services in its own domain or for admission to the ticket-granting service of a trusted domain. When clients want access to a service, they must contact the ticket-granting service in the service's account domain, present a TGT, and ask for a session ticket. If the client does not have a TGT for admission to the ticket-granting service in the other domain, it must obtain one through the referral process that begins at the ticket-granting service in the user's account domain and ends at the ticket-granting service in the service's account domain.

The KDC is located on every domain controller, as is the Active Directory service. Both services are started automatically by the domain controller's Local Security Authority (LSA) and run in the process space of the LSA. Neither service can be stopped. Windows 2000 ensures availability of these services by allowing each domain to have several domain controllers, all peers. Any domain controller can accept authentication requests and ticket-granting requests addressed to the domain's KDC.

The security principal name used by the KDC in all Windows 2000 domains is krbtgt , as specified by RFC 1510. An account for this security principal is created automatically when a new Windows 2000 domain is created. The account cannot be deleted, nor can the account name be changed. A password is assigned to the KDC's account automatically; this password, like the passwords assigned to domain trust accounts, is changed on a regular schedule. The password for the KDC's account is used to derive a secret key for encrypting and decrypting the TGTs that the KDC issues. The password for a domain trust account is used to derive a Kerberos inter-realm key for encrypting and decrypting referral tickets.

All instances of the KDC in a domain use the domain account for the security principal krbtgt. Clients address messages to a domain's KDC by including both the service's principal name (krbtgt) and the name of the domain. Both items of information are also used in tickets to identify the issuing authority.

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