Kerberos u Kerberos was a 3 headed dog

Kerberos u Kerberos was a 3 -headed dog in Greek mythology • Guarded the gates of the dead • Decided who might enter • Talk about strong security!

Kerberos u Three Parties are Present • Kerberos server • Applicant host • Verifier host Kerberos Server Applicant Verifier

Kerberos u Kerberos Server shares a symmetric key with each host • Key shared with the Applicant will be called Key AS (Applicant-Server) • Key shared with verifier will be Key VS Kerberos Server Applicant Key AS Key VS Verifier

Kerberos u Applicant sends message to Kerberos server • Logs in and asks for ticket-granting ticket (TGT) u Authenticates the applicant to the server • Server sends back ticket-granting ticket • TGT allows applicant to request connections TGT RQ Kerberos Server Applicant TGT

Kerberos To connect to the verifier u Applicant asks Kerberos server for credentials to introduce the applicant to the verifier u Request includes the Ticket. Granting Tickets u Kerberos Server Credentials RQ Applicant

Kerberos u Kerberos server sends the credentials • Credential include the session Key AV that applicant and verifier will use for secure communication • Encrypted with Key AS so that interceptors cannot read it Kerberos Server Applicant Credentials= Session Key AV Service Ticket

Kerberos u Kerberos server sends the credentials • Credential also include the Service Ticket, which is encrypted with Key VS; Applicant cannot read or change it Kerberos Server Applicant Credentials= Session Key AV, Service Ticket

Kerberos u Applicant sends the Service Ticket plus a Authenticator to the Verifier • Service ticket contains the symmetric session key (Key AV) • Now both parties have Key AV and so can communicate with confidentiality Applicant Service Ticket (Contains Key AV) + Authenticator Verifier

Kerberos u Applicant sends the Service Ticket plus a Authenticator to the Verifier • Authenticator contains information encrypted with Key AV Guarantees that the service ticket came from the applicant, which alone knows Key AV u Service ticket has a time stamp to prevent replay Service Ticket (Contains Key AV) + Authenticator u

Kerberos u Subsequent communication between the applicant and verifier uses the symmetric session key (Key AV) for confidentiality Applicant Communication Encrypted with Key AV Verifier

Kerberos The Service Ticket can contain more than Key AV u If the applicant is a client and the verifier is a server, service ticket may contain u • Verifier’s user name and password • List of rights to files and directories on the server Verifier

Kerberos Is the basis for security in Microsoft Windows 2000 u Only uses symmetric key encryption for reduced processing cost u