TGTs

TGTs, in the context of computer networks, stands for Ticket Granting Tickets. They are a core component of the Kerberos authentication protocol, designed to enable secure single sign-on by allowing a user to obtain service tickets for multiple network services without re-entering credentials.

A TGT is issued by the Authentication Service (AS) after a user proves their identity to the system. The TGT is encrypted with the secret key of the Ticket Granting Service (TGS) and includes the user’s principal (identity), the user’s realm, a session key for use with the TGS, the ticket’s validity period, and flags such as whether the ticket is renewable or forwardable. The TGT itself does not grant access to services; rather, it proves that the user has already authenticated and can be used to request service tickets from the TGS.

To access a specific network service, the client presents the TGT to the TGS and asks for a service ticket for that service. The TGS validates the TGT, issues a service ticket for the requested service (encrypted with the service’s key), and the client then presents this service ticket to the target service to establish authentication.

Lifetimes and renewal: TGTs have a defined validity window, typically several hours (often around 8–10 hours) and may be renewable. Renewable tickets allow extension of the session without re-entering credentials, up to a configured maximum.

Security considerations: The TGT is sensitive because possession of it can enable the user to obtain service tickets. Protecting endpoints, using secure credentials, and minimizing ticket lifetimes reduce risk. Kerberos deployments are common in environments such as Windows Active Directory and various Unix-like systems.