What is a critical requirement for the effective operation of Kerberos?

For Kerberos to function effectively, time synchronization is a critical requirement. The Kerberos authentication protocol relies heavily on timestamps to ensure the validity and freshness of the authentication tickets it issues. When a user requests access to a service, Kerberos grants a ticket that includes a timestamp. This timestamp helps prevent replay attacks, where an adversary could otherwise use a valid ticket from a past session.

If the clocks on the client and server systems are not synchronized, the validity period of the ticket may be misaligned, leading to authentication failures. Typically, Kerberos implementations require that system clocks remain within a certain threshold (often five minutes) of each other to function correctly. This requirement emphasizes the importance of accurate timekeeping within the network infrastructure to maintain secure authentication processes.