etckrb5keytab

The etckrb5keytab refers to the Kerberos keytab file commonly found at /etc/krb5.keytab on many Unix-like systems. A keytab is a binary file that stores one or more Kerberos principals and their associated secret keys, enabling services to authenticate to the Kerberos Key Distribution Center (KDC) without requiring human input such as passwords. The file is read by Kerberos libraries when a service starts or authenticates, allowing the service to present a valid credential as its principal.

Contents and format: A keytab contains key entries, each consisting of a principal name, a key version number, an encryption type, and the actual key material. The format is defined by the Kerberos implementation (MIT Kerberos, Heimdal), and the data is typically not human-readable. Different principals can share a single keytab, or multiple keytabs can be used to segregate service identities.

Usage and management: The keytab is populated by administrators when a service is installed or when keys are rotated. Common management tools include ktutil and kadmin (or kadmin.local). Keys are rotated by adding new entries with an incremented key version number (kvno) or by purging old entries when they are no longer needed. Services may use distinct keytabs per host or per service to limit exposure.

Security considerations: Access to /etc/krb5.keytab should be tightly controlled. The file should typically have permissions such as 0600 and be owned by root. Unauthorized access or tampering can enable impersonation of services. Regular auditing, secure backups, and key rotation practices are recommended.

See also: Kerberos, keytab, kvno, ktutil, kadmin.