| Principal | The term principal refers to every entity within a Kerberos database. Users, computers, and services are all assigned principals for Kerberos authentication. Every principal must be unique within the Kerberos database and is defined by its distinguished name. A principal can be a user principal name (UPN) or a service principal name (SPN). <br></br> A principal name has three parts: <ul><li>**Primary** - The primary part can be a user or a service such as the NFS service. It can also be the special service "host," which signifies that this service principal is set up to provide multiple various network services.</li><li>**Instance** - This part is optional in the case of a user. A user can have more than one principal, but each principal must be unique in the KDC. For example, Fred might have a principal that is for everyday use (
[email protected]) and a principal that allows privileged use such as a sysadmin account (
[email protected]). The instance is required for service principals and designates the fully qualified domain name (FQDN) of the host that provides the service.</li><li>**Realm** - A Kerberos realm is the set of Kerberos principals that are registered within a Kerberos server. By convention, the realm name is usually the same as the DNS name, but it's converted to uppercase letters. Uppercase letters aren't obligatory, but the convention provides easy distinction between the DNS name and the realm name.</li></ul> <!-- image --> |
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