Realms, Principals, and Instances
Every entity contained within a Kerberos installation, including individual users, computers, and services running on servers, has a principal associated with it. Each principal is associated with a long-term key. This key can be, for example, a password or passphrase. Principals are globally unique names. To accomplish this, the principal is divided into a hierarchical structure.
Every principal starts with a username or service name. The username or service name is then followed by an optional instance. The instance is used in two situations: for service principals (which we’ll discuss later), and in order to create special principals for administrative use. For example, administrators can have two principals: one for day-to-day usage, and another (an “admin” principal) to use only when the administrator needs elevated privileges.
The username and optional instance, taken together, form a unique identity within a given realm . Each Kerberos installation defines an administrative realm of control that is distinct from every other Kerberos installation. Kerberos defines this as the realm name . By convention, the Kerberos realm for a given DNS domain is the domain converted to uppercase. So, for example, Wedgie International, which owns the domain name wedgie.org, would create a Kerberos realm for its users named WEDGIE.ORG.
While it is the convention to make the realm name equivalent to the DNS domain name, it is not necessary to do so. It certainly ...
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