Final answer:
Kerberos primarily serves as an authentication protocol for client/server applications, using secret-key cryptography to securely prove identity over non-secure networks.
Step-by-step explanation:
The primary purpose of Kerberos is B. Authentication. Kerberos is a computer network authentication protocol that works on the basis of tickets which allow nodes communicating over a non-secure network to prove their identity to one another in a secure manner. Its primary goal is to provide strong authentication for client/server applications by using secret-key cryptography. Kerberos also addresses issues of confidentiality and integrity, however, these functions are secondary to its principal aim of ensuring authentication. The system offers a centralized authentication server whose purpose is to authenticate users and services, thus ensuring a trusted third party verifies the credentials of the entities involved in the communication.