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Security Fundamentals & Crypto · Intermediate

Kerberos

Ticket-based network authentication protocol using a trusted KDC and symmetric cryptography.

Definition

Kerberos (v5, RFC 4120) authenticates users once and issues tickets for access to services, providing single sign-on within a realm. It uses port 88, requires synchronized clocks (default tolerance 5 minutes in Active Directory), and supports mutual authentication. It is the default authentication protocol for Active Directory domains.

Example

After logon, a user's TGT lets them access file shares without re-entering credentials.

Exam tip

Kerberos depends on time sync; clock skew causes authentication failures. The KDC is a single point of failure.

Don't confuse it with

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