The Answer: authentication. Kerberos is an authentication service. It can use single-factor or multi-factor authentication methods.
The following answers are incorrect:
non-repudiation. Since Kerberos deals primarily with symmetric cryptography, it does not help with non-repudiation. confidentiality. Once the client is authenticated by Kerberos and obtains its session key and ticket, it may use them to assure confidentiality of its communication with a server; however, that is not a Kerberos service as such. authorization. Although Kerberos tickets may include some authorization information, the meaning of the authorization fields is not standardized in the Kerberos specifications, and authorization is not a primary Kerberos service.
The following reference(s) were/was used to create this question:
ISC2 OIG,2007 p. 179-184 Shon Harris AIO v.3 152-155