5. Access Control and Identity Management

5.1 Explain the function and purpose of authentication services

Remote Authentication Dial-In User Service (RADIUS) : It provides centralized administration of dial-up, VPN, and wireless authentication and can be used with EAP and 802.1X.

Terminal Access Controller Access-Control System (TACACS ) : It is remote authentication protocol used more often in UNIX networks. In UNIX, the TACACS service is known as the TACACS daemon. The newer and more commonly used implementation of TACACS is called TACACS+. It is not backward compatible with TACACS. TACACS+, and its predecessor XTACACS, were developed by Cisco. TACACS+ uses inbound port 49. TACACS and XTACACS are not commonly seen anymore. The two common protocols used today are RADIUS and TACACS+.

Kerberos : Kerberos is basically an authentication protocol that uses secret-key cryptography for secure authentication. In Kerberos, all authentication takes place between clients and servers. The name Kerberos comes from Greek mythology; it is the three-headed dog that guarded the entrance to Hades. It was developed by the Massachusetts Institute of Technology, USA

Kerberos require that the time sources are approximately in synchronization (with in 5 minutes) with each other. However, with recent revisions of Kerberos software, this rule has become flexible.

Some of the features of Kerberos authentication system:

Uses client-server based architecture. Kerberos server, referred to as KDC (Key Distribution Ceter) implements the Authentication Service (AS) and the Ticket Granting Service (TGS). The term "application server" generally refers to Kerberized programs that clients communicate with using Kerberos tickets for authentication purpose. For example, the Kerberos telnet daemon (telnetd) is an example of an application server.

When the user wants to talk to a Kerberized service, he uses the TGT to talk to the Ticket Granting Service (TGS, also runs on the KDC). The TGS verifies the user's identity using the TGT and issues a ticket for the desired service.

The TGT ensures that a user doesn't have to enter in their password every time they wish to connect to a Kerberized service. The TGT usually expires after eight hours. If the Ticket Granting Ticket is compromised, an attacker can only masquerade as a user until the ticket expires.

The following are the important properties of Kerberos:

It uses symmetric encryption

Tickets are time stamped

Passwords are not sent over the network

LDAP (Lightweight Directory Access Protocol) : It contains the directory for a network and allows for a single point of user management of that directory.

5.2 Explain the fundamental concepts and best practices related to authentication, authorization and access control

Computer based access controls prescribe not only who or what process may have access to a given resource, but also the type of access that is permitted. These controls may be implemented in the computer system or in external devices. Different types of access control are: